857 lines
29 KiB
Markdown
857 lines
29 KiB
Markdown
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## The chemical senses
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* Chemical Senses
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* Olfaction
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* Taste
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* Trigeminal chemosensory
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* Irritant system
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Note:
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phylogenetically oldest sense.
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not considered very important in humans compared to other senses, but think about the fantastically strong emotional memories tied to smells— the olfactory system when robustly stimulated can have much influence over the formation of olfactory tied memories through its direct connectivity to the limbic and memory systems of the brain. We’ll learn a bit about this connectivity later.
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Mucus membranes of eyes face mouth
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---
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## Olfaction
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* The olfactory system detects airborne molecules called odorants.
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* Provides information about food, self, others, animals, plants, etc.
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* Influence feeding behaviors, social interactions, and even reproduction.
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* Processes information about the identity, concentration, and quality of a wide range of chemical stimuli.
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Note:
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---
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## The route of olfaction
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<div style="font-size:0.8em;">
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<div></div>
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* Starts in the nose, odorants bind to specific receptors found in the olfactory epithelium
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* Olfactory epithelium projects to neurons in the ipsilateral olfactory bulb, which in turn sends projections contra and ipsi to the piriform cortex in the temporal lobe and other forebrain structures
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* Piriform cortex is only 3-layered (sometimes called the archicortex), and is considered phylogenetically older than the neocortex
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* Unique among senses in that it does not include a thalamic relay between primary receptors and the cerebral cortex
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* Piriform cortex relays information via the thalamus to the associational cortex to initiate motor, visceral, and emotional reactions to olfactory stimuli
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</div>
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Note:
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---
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## Human olfactory bulb
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<figure><img src="figs/Neuroscience5e-Fig-15.02-2R_a10bacf.jpg" height="400px"><figcaption>Neuroscience 5e Fig. 15.2</figcaption></figure>
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Note:
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<!-- ## Rodent brain -->
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---
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## The flow of olfactory information
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<div><img src="figs/nobelprize-org-2004-OR_7541302.png" height="400px"><figcaption>[nobelprize.org, 2004](http://www.nobelprize.org/nobel_prizes/medicine/laureates/2004/press.html)</figcaption></div>
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Note:
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---
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## Organization of the human olfactory system
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<figure><img src="figs/Neuroscience5e-Fig-15.01-1R_9fc2539.jpg" height="400px"><figcaption>Neuroscience 5e Fig. 15.1</figcaption></figure>
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Note:
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---
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## Olfactory perception
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* Is not as acute in humans as in a number of other animals
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* Less acute in humans because of a smaller variety of functional olfactory receptor proteins, less receptor neuron density, and also a lesser amount of relative cortex used to process information
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* Mice have ~1000 olfactory receptor genes, humans several hundred
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Note:
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---
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## Fun olfaction factoids
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* Odors can be detected at very low concentrations (bell peppers 0.01 nM)
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* Small changes in molecular structure can change perception
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* Anosmics are people who cannot smell specific odors. 1/100 people cannot smell skunk, 1/10 hydrogen cyanide
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Note:
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---
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## Human odor detection thresholds
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<div>
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<div></div>
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Compound | Odor threshold in air (parts per billion)
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--- | ---
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methanol | 141,000
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acetone | 15,000
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formaldehyde | 870
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menthol | 40
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T-butyl mercaptan | 0.3
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<figcaption>Devol et al., 1990</figcaption>
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</div>
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Note:
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rats 8-50 times more sensitive to odors than humans
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dogs 300-10000 times more sensitive
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humans have 10 million ORNs, dogs have 1 billion
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butyl mercaptan: similar to major constituent of defensive spray in skunk
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tert-butyl mercaptan: natural gas additive
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---
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## Combinatorial coding
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* Distributed code for face representation
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* Color coding by S, M, L cones
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* Language is combinatorial
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* 26 letters gives many different words
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Note:
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alphabet
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: a set of letters or symbols in a fixed order, used to represent the basic sounds of a language
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: the basic elements in a system that combine to form complex entities
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---
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## The vomeronasal organ
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* Many species have a specialized structure that recognizes species-specific odorants called pheromones that play important roles in innate social, reproductive, and parenting behaviors
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* The vomeronasal organ (VNO) projects to the accessory olfactory bulb, which in turn projects to the hypothalamus
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* The VNO is absent or not very prominent in primates (including humans) and there is debate as to whether humans detect pheromones
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* In animals a lesion in the main olfactory projection leaves reproductive behaviors intact, however lesions of the VNO projection severely compromises sexual selection and dominance hierarchies
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Note:
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rudimentary VNO found in 8% of adults. And VNO projects to special region of ob called accessory olfactory bulb which is also largely absent in primates.
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mating, aggression behaviors etc
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loss of sex discrimination and male male aggression in mice without TRP2
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TRP2/TRPC2: Transient receptor potential cation channel, subfamily C, member 2. Not expressed in humans
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Stowers, L.; Holy, T. E.; Meister, M.; Dulac, C.; Koentges, G. (2002). "Loss of sex discrimination and male-male aggression in mice deficient for TRP2". Science 295 (5559): 1493–1500. Bibcode:2002Sci...295.1493S. doi:10.1126/science.1069259.
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[http://science.sciencemag.org/content/295/5559/1493.full-text.pdf+html](http://science.sciencemag.org/content/295/5559/1493.full-text.pdf+html)
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---
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## Pheromones and the VNO
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<figure><img src="figs/Neuroscience5e-Box-15B-0_ac55b96.jpg" height="400px"><figcaption>Neuroscience 5e Box 15B</figcaption></figure>
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Note:
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---
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## Mouse pheromones
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Record from a neuron in the AOB, pink area is when mouse is sniffing at face. Yellow are is when sniffing genitals.
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<div><img src="figs/image1_9b348ce.png" height="400px"><figcaption>[Lou and Katz Science 2003](http://www.sciencemag.org/cgi/content/full/299/5610/1196/DC1)</figcaption></div>
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Note:
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---
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## Human pheromones?
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* Female rodents (mice) grouped together synchronize their estrous cycle upon exposure to pheromones in male mouse urine (‘Whitten effect’). This depends on pheromone receptors and VNO—>AOB connectivity.
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* VNO is vestigial in humans: VRs and TRPC2 are pseudogenes
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* Myth: women who live in close proximity synchronize their menstrual cycle (the ‘McClintock effect’, after McClintock, Nature 1971). The current scientific evidence for this effect in human is not strong.
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* However there’s some evidence for odorants working as pheromone-like molecules to influence behaviors (attraction, fear) mediated by the main olfactory system
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Note:
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Human pheromones??
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vestigial. VNO anatomy is non-functional in human.
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myth of mcclintock effect. statistical issues with these studies, no one has reported human estrous cycle synchrony over more than 6-9 months as indeed the original study was on college women at wellsey over the period of one academic calendar year. Windshield wiper, coupled oscillator analogy. Just out of phase.
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But other animals…
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And olfactory cues that aren’t necessarily odorless certainly can affect our behavior and pheromone like molecules may act through our olfactory system
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[from: http://www.sciencedirect.com/science/article/pii/S2090123211000397](http://www.sciencedirect.com/science/article/pii/S2090123211000397)
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mother-child interactions at birth
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[from http://www.ncbi.nlm.nih.gov/books/NBK55967/](http://www.ncbi.nlm.nih.gov/books/NBK55967/)
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> Different works have shown that odor-cued memories are more emotional than memories triggered by visual or verbal cues
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from one website:
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Pheromones are naturally occurring odorless substances the fertile body excretes externally, conveying an airborne signal that provides information to, and triggers responses from, the opposite sex of the same species.
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oxford dictionary doesn’t include the word ‘odorless’.
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wikipedia: A pheromone (from Ancient Greek φέρω phero "to bear" and hormone, from Ancient Greek ὁρμή "impetus") is a secreted or excreted chemical factor that triggers a social response in members of the same species.
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>the adult human VNO, in different studies, has been reviewed as non-functional as it contains few neurons and has no sensory function where no cells were shown to express olfactory marker protein, have synaptic contacts or have evidence for a nerve connecting to/from the VNO
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VNO is vestigial in humans: VRs and TrpC2 are pseudogenes
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myth: women who live in close proximity synchronize their menstrual cycle (the McClintock effect, McClintock, Nature 1971)
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However there’s some evidence for pheromone like molecules and behaviors (attraction, fear) mediated by the main olfactory system
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whitten effect: exposure of grouped female mice to phermones in male mouse urine synchronizes their estrous cycle. The pheromones in male urine are dependent on male sex hormones like testosterone.
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[from http://www.informatics.jax.org/silver/chapters/4-3.shtml](http://www.informatics.jax.org/silver/chapters/4-3.shtml)
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>The normal estrus cycle of a laboratory mouse is 4-6 days in length
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vandenburgh effect: early estrous cycle induction in prepubertal female mice exposed to urine from dominant male
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lee-boot effect: suppression or prolongation of estrous cycle in female mice (and other rodents) when mice housed in groups and isolated from other males
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bruce effect: female mouse pregnancy termination from exposure to scent of unfamiliar male
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[http://www.ncbi.nlm.nih.gov/pubmed/22087345](http://www.ncbi.nlm.nih.gov/pubmed/22087345)
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>Latent toxoplasmosis, a lifelong infection with the protozoan Toxoplasma gondii, has cumulative effects on the behaviour of hosts, including humans. The most impressive effect of toxoplasmosis is the "fatal attraction phenomenon," the conversion of innate fear of cat odour into attraction to cat odour in infected rodents.
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phylogenetic distance human, mouse, rat:
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[from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC524408/ 2003](http://www.ncbi.nlm.nih.gov/pmc/articles/PMC524408/)
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>human and rodents diverged ∼75 million years ago, whereas mouse and rat diverged ∼12-24 million years ago[Waterston et al. 2002; Rat Sequencing Project Consortium 2004]
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-human has equal genetic distance from both rodents
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-human has been evolving from human/rodent common ancestor at slower rearrangement rate and thus has a more ancestral genome
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>Rat Closer to Human?
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>rearrangement differences between the two rodents suggest that, except for the small inversions, overall, the rat genome might have a structure on a large scale closer to the human genome than the mouse genome.
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>lacking the extra interchromosomal changes of mouse (Table 3), many rat fragments are closer to human.
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>In terms of chromosome morphology (and possibly the genome size as well), rat is also between mouse and human.
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[from https://www.genome.gov/11511308 2012](https://www.genome.gov/11511308)
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Humans have 23 pairs of chromosomes, while rats have 21 and mice have 20.
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>all three organisms to be related to each other by about 280 large regions of sequence similarity - called "syntenic blocks" - distributed in varying patterns across the organisms' chromosomes.
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> 50 chromosomal rearrangements occurred in each of the rodent lines after divergence from their common ancestor
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>number of chromosomal rearrangements, as well as other types of genome changes, was found to be much lower in the primate lineage, indicating that evolutionary change has occurred at a faster rate in rodents than in primates.
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---
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## Olfactory receptors
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* Discovered by Linda Buck and Richard Axel. Shared nobel prize in 2004
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* They found that olfactory receptors comprise a large GPCR gene family (~1000 olfactory receptors)
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* Each olfactory neuron expresses a single olfactory receptor (even inactivates one copy of each allele)
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* Each receptor can bind to multiple odorants
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* Each neuron that expresses a given receptor targets to the same glomeruli in the olfactory bulb
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Note:
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Linda Buck and Richard Axel "for their discoveries of odorant receptors and the organization of the olfactory system"
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---
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## Olfactory receptors
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<figure><img src="figs/Neuroscience5e-Fig-15.09-1R_copy_3521e8e.jpg" height="400px"><figcaption>Neuroscience 5e Fig. 15.9</figcaption></figure>
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---
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## Olfactory receptors
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<figure><img src="figs/Neuroscience5e-Fig-15.09-2R_copy_fde3d57.jpg" height="400px"><figcaption>Neuroscience 5e Fig. 15.9</figcaption></figure>
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Note:
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red arrows indicate intron locations of splice sites in other animals. Mammalian genes for ORs lack introns.
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largest single known gene family in all mammals. Representing 3-5% of genome. Perhaps 60% of these 950 OR genes are not transcribed in humans and chimps rendering them pseudogenes, vs 15-20% in mice and dogs.
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pseudogene
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: sequence of DNA containing a promoter and transcription initiation site, but due to sequence changes the DNA cannot be transcribed into a stable mRNA or the transcript cannot be translated into a protein.
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---
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## Anatomy of the olfactory epithelium
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<figure><img src="figs/Neuroscience5e-Fig-15.07-1R_79a296a.jpg" height="400px"><figcaption>Neuroscience 5e Fig. 15.7</figcaption></figure>
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Note:
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---
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## ORN receptor potentials generated in cilia
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<figure><img src="figs/Neuroscience5e-Fig-15.08-0_2a03d42.jpg" height="400px"><figcaption>Neuroscience 5e Fig. 15.8</figcaption></figure>
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Note:
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---
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## ORNs are continuously generated from basal cells
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* Turnover of 6-8 weeks in rodents
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* Susceptible to pollutants, allergens...
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* Source of neural stem cells
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<figure><img src="figs/Neuroscience5e-Fig-15.07-3R_copy_d15b3aa.jpg" height="200px"><figcaption>Neuroscience 5e Fig. 15.7</figcaption></figure>
|
|||
|
|
|
|||
|
|
|
|||
|
|
Note:
|
|||
|
|
|
|||
|
|
basal cells and progeny in labeled in red
|
|||
|
|
|
|||
|
|
blue is all cell nuclei
|
|||
|
|
|
|||
|
|
green for OMP at right
|
|||
|
|
|
|||
|
|
---
|
|||
|
|
|
|||
|
|
## Olfactory receptor signal transduction
|
|||
|
|
|
|||
|
|
* Binding of odorant to receptor activates a Gα (Called G-olf) that in turn activates adenylyl cyclase
|
|||
|
|
* cAMP gates a Na+/Ca2+ cation channel. Calcium rushes in and activates a Cl- channel. Chloride normally high in-low out in olfactory neurons and thus Cl- leaving also depolarizes cell
|
|||
|
|
|
|||
|
|
Note:
|
|||
|
|
|
|||
|
|
|
|||
|
|
|
|||
|
|
---
|
|||
|
|
|
|||
|
|
## Olfactory receptor signal transduction
|
|||
|
|
|
|||
|
|
<figure><img src="figs/Neuroscience5e-Fig-15.11-1R_a07ccab.jpg" height="400px"><figcaption>Neuroscience 5e Fig. 15.11</figcaption></figure>
|
|||
|
|
|
|||
|
|
|
|||
|
|
Note:
|
|||
|
|
|
|||
|
|
How would you desensitize odorant pathway? PDE, Ca-Cam blocks cAMP channel
|
|||
|
|
|
|||
|
|
Adaptation comes from calmodulin binding up the Ca2+ and closing
|
|||
|
|
|
|||
|
|
Cl- channels and also from being pumped out.
|
|||
|
|
|
|||
|
|
---
|
|||
|
|
|
|||
|
|
## Molecules critical to odorant signal transduction
|
|||
|
|
|
|||
|
|
<figure><img src="figs/Neuroscience5e-Fig-15.11-2R_ecf5538.jpg" height="400px"><figcaption>Neuroscience 5e Fig. 15.11</figcaption></figure>
|
|||
|
|
|
|||
|
|
|
|||
|
|
Note:
|
|||
|
|
|
|||
|
|
Minty odor
|
|||
|
|
|
|||
|
|
EOG electroolfactorogram
|
|||
|
|
|
|||
|
|
---
|
|||
|
|
|
|||
|
|
## A single olfactory receptor can be activated by single or groups of stimuli
|
|||
|
|
|
|||
|
|
<figure><img src="figs/Neuroscience5e-Fig-15.12-0_4019559.jpg" height="400px"><figcaption>Neuroscience 5e Fig. 15.12</figcaption></figure>
|
|||
|
|
|
|||
|
|
|
|||
|
|
Note:
|
|||
|
|
|
|||
|
|
Eucholipyol, banana oil
|
|||
|
|
|
|||
|
|
But there is also broad OSN tuning--
|
|||
|
|
|
|||
|
|
* Primary olfactory sensory neurons are broadly tuned to odorants
|
|||
|
|
* Sicard and Holley (1984) Brain Research 292:283
|
|||
|
|
|
|||
|
|
Eucalyptol is cineole
|
|||
|
|
|
|||
|
|
Camphor is the smell of turpintine. Aromatic
|
|||
|
|
|
|||
|
|
---
|
|||
|
|
|
|||
|
|
## Dogs smell better than humans
|
|||
|
|
|
|||
|
|
<figure><img src="figs/Neuroscience5e-Fig-15.02-1R_copy_cf5395a.jpg" height="200px"><figcaption>Neuroscience 5e Fig. 15.2</figcaption></figure>
|
|||
|
|
|
|||
|
|
<figure><img src="figs/Neuroscience5e-Fig-15.03-0_copy_398483b.jpg" height="200px"><figcaption>Neuroscience 5e Fig. 15.3</figcaption></figure>
|
|||
|
|
|
|||
|
|
Note:
|
|||
|
|
|
|||
|
|
---
|
|||
|
|
|
|||
|
|
## Olfactory system summary video
|
|||
|
|
|
|||
|
|
<div><video height=400px controls src="figs/Animation15-01TheOlfactorySystem.mp4"></video><figcaption>Neuroscience 5e Animation 15.1</figcaption></div>
|
|||
|
|
|
|||
|
|
|
|||
|
|
Note:
|
|||
|
|
|
|||
|
|
|
|||
|
|
---
|
|||
|
|
|
|||
|
|
## The olfactory bulb
|
|||
|
|
|
|||
|
|
* A small structure above the nasal passages
|
|||
|
|
* Site where sensory information is collected and gets sorted
|
|||
|
|
* Sensory neurons project to glomeruli
|
|||
|
|
* Olfactory receptor neurons synapse onto the dendrites of mitral cells which then project to the cerebral cortex
|
|||
|
|
|
|||
|
|
Note:
|
|||
|
|
|
|||
|
|
ORNs that carry same olfactory receptors converge upon same glomeruli (Mombaerts et al Cell 1996)
|
|||
|
|
|
|||
|
|
---
|
|||
|
|
|
|||
|
|
## Olfactory receptors are localized into discreet areas
|
|||
|
|
|
|||
|
|
<div><img src="figs/image3_7693919.jpg" height="200px"><figcaption></figcaption></div>
|
|||
|
|
|
|||
|
|
<figure><figcaption class="big">olfactory cilia, all ORNs, I7 ORNs, M71 ORNs</figcaption><img src="figs/Neuroscience5e-Fig-15.10-0_copy_3bcd339.jpg" height="200px"><figcaption>Neuroscience Fig. 15.10</figcaption></figure>
|
|||
|
|
|
|||
|
|
|
|||
|
|
Note:
|
|||
|
|
|
|||
|
|
omp (green all ORNs). Adenylyl cyclase II (red) limited to olfactory cilia
|
|||
|
|
|
|||
|
|
all ORNs
|
|||
|
|
|
|||
|
|
I7 ORNs
|
|||
|
|
|
|||
|
|
M71 ORNs
|
|||
|
|
|
|||
|
|
|
|||
|
|
---
|
|||
|
|
|
|||
|
|
## Localization preserved in the olfactory bulb
|
|||
|
|
|
|||
|
|
<div><img src="figs/image4_e4638ef.jpg" height="400px"><figcaption></figcaption></div>
|
|||
|
|
|
|||
|
|
Note:
|
|||
|
|
|
|||
|
|
|
|||
|
|
* fig from luo principals of neurobiology?
|
|||
|
|
|
|||
|
|
|
|||
|
|
---
|
|||
|
|
|
|||
|
|
## Subtle changes in a molecules structure can be detected by different receptors
|
|||
|
|
|
|||
|
|
* Johnson, Woo, Hingco, Pham and Leon (1999) J. Comp. Neurol. 409:529
|
|||
|
|
* n-amyl acetate, (control)
|
|||
|
|
* Acetic acid, (2)COOH
|
|||
|
|
* Propanoic acid, (3)COOH
|
|||
|
|
* Butanoic acid, (4)COOH
|
|||
|
|
* Pentanoic acid, (5)COOH
|
|||
|
|
* Hexanoic acid, (6)COOH
|
|||
|
|
|
|||
|
|
|
|||
|
|
|
|||
|
|
Note:
|
|||
|
|
|
|||
|
|
|
|||
|
|
* acid series of similar structures
|
|||
|
|
* 2-deoxyglucose activation patterns in the rat olfactory bulb in response to an aliphatic acid series
|
|||
|
|
* Johnson, Woo, Hingco, Pham and Leon (1999) J. Comp. Neurol. 409:529
|
|||
|
|
|
|||
|
|
---
|
|||
|
|
|
|||
|
|
## Neurons of olfactory bulb
|
|||
|
|
|
|||
|
|
* Mitral cell, dendrites to a single glomerulus and axon to brain
|
|||
|
|
* Tufted cell contacts multiple glomeruli
|
|||
|
|
* Interneurons (PG) also participate in processing (inhibition)
|
|||
|
|
* Bulb also gets info from the cortex
|
|||
|
|
|
|||
|
|
<figure><figcaption class="big">Mitral Cell, MC. Tufted Cell, TC. Granule cell, GC. Periglomerular Cell, PG.</figcaption><img src="figs/olfactorybulbwiring_43ed7c4_copy_ab80a23.jpg" height="200px"><figcaption></figcaption></figure>
|
|||
|
|
|
|||
|
|
|
|||
|
|
Note:
|
|||
|
|
|
|||
|
|
* fig origin unknown. No find through image search
|
|||
|
|
|
|||
|
|
---
|
|||
|
|
|
|||
|
|
## Neurons of olfactory bulb
|
|||
|
|
|
|||
|
|
<div><figcaption class="big">Periglomerular cells</figcaption><img src="figs/periglomerular_04f528f.png" height="400px"><figcaption>J. Ackman 2003</figcaption></div>
|
|||
|
|
|
|||
|
|
Note:
|
|||
|
|
|
|||
|
|
|
|||
|
|
---
|
|||
|
|
|
|||
|
|
## Olfactory pathways
|
|||
|
|
|
|||
|
|
* OB axons go to piriform (olfactory) cortex, amygdala (fear), entorhinal cortex (hippocampus, memory)
|
|||
|
|
* VNO axons go directly to amygdala (fear)
|
|||
|
|
|
|||
|
|
<figure><img src="figs/olfactorypathways_dfe0730_copy_d011baa.jpg" height="300px"><figcaption></figcaption></figure>
|
|||
|
|
|
|||
|
|
|
|||
|
|
Note:
|
|||
|
|
|
|||
|
|
* fig origin unknown. No find through image search
|
|||
|
|
|
|||
|
|
---
|
|||
|
|
|
|||
|
|
## Organization of the human olfactory system
|
|||
|
|
|
|||
|
|
* piriform ctx and OFC: conscious odor perception, multimodal association
|
|||
|
|
* olfactory tubercle: reward, motivation
|
|||
|
|
* amygdala, hypothalamus: fear, aggression, feeding, reproduction
|
|||
|
|
* entorhinal ctx, hippocampal formation: memory
|
|||
|
|
|
|||
|
|
<div><img src="figs/Neuroscience5e-Fig-15.01-3R_3252af3.jpg" height="200px"><figcaption>Neuroscience 5e Fig. 15.1</figcaption></div>
|
|||
|
|
<div><img src="figs/Neuroscience5e-Fig-15.01-2R_8ff6462.jpg" height="200px"><figcaption>Neuroscience 5e Fig. 15.1</figcaption></div>
|
|||
|
|
|
|||
|
|
|
|||
|
|
Note:
|
|||
|
|
|
|||
|
|
piriform ctx and OFC: conscious odor perception, multimodal association
|
|||
|
|
|
|||
|
|
olfactory tubercle: reward, motivation
|
|||
|
|
|
|||
|
|
amygdala, hypothalamus: fear, aggression, feeding, reproduction
|
|||
|
|
|
|||
|
|
entorhinal ctx, hippocampal formation: memory
|
|||
|
|
|
|||
|
|
---
|
|||
|
|
|
|||
|
|
## Taste (gustation)
|
|||
|
|
|
|||
|
|
* Used to determine whether food should be ingested (together with smell, touch, and pain).
|
|||
|
|
* Provides information about the identity, concentration, and pleasant or unpleasant quality of a substance.
|
|||
|
|
* Works together with the GI system to get it ready to receive food (saliva and swallowing) or reject food (regurgitation).
|
|||
|
|
* Information of texture and temperature of things in mouth processed by somatic sensory system receptors.
|
|||
|
|
* Contains both peripheral receptors and central processing.
|
|||
|
|
|
|||
|
|
Note:
|
|||
|
|
|
|||
|
|
|
|||
|
|
---
|
|||
|
|
|
|||
|
|
## The gustatory system
|
|||
|
|
|
|||
|
|
<figure><img src="figs/Neuroscience5e-Fig-15.17-1R_0025e07.jpg" height="400px"><figcaption></figcaption></figure>
|
|||
|
|
|
|||
|
|
Note:
|
|||
|
|
|
|||
|
|
|
|||
|
|
These afferent fibers all end in the nucleus of the solitary tract (NST) in the medulla. From there the information flows mainly to the thalamus and then to the gustatory cortex.
|
|||
|
|
|
|||
|
|
pathways
|
|||
|
|
|
|||
|
|
* afferents from tongue and epiglottis to gustatory nucleus (in medulla next to 4th ventricle, part of solitary nuclear complex) and then to VPM
|
|||
|
|
* from taste bud to solitary nuclear complex and then to VPM
|
|||
|
|
* Solitary nuclear complext to nucleus ambiguous to salivary glands
|
|||
|
|
* Other somatosensory to parabrachial nuclei
|
|||
|
|
|
|||
|
|
---
|
|||
|
|
|
|||
|
|
## Cortical projections of gustatory pathway
|
|||
|
|
|
|||
|
|
<figure><img src="figs/gustatorycentralpathways_2d4c5ae_copy_2f00775.jpg" height="400px"><figcaption></figcaption></figure>
|
|||
|
|
|
|||
|
|
|
|||
|
|
Note:
|
|||
|
|
|
|||
|
|
* fig origin unknown.
|
|||
|
|
|
|||
|
|
From the VPM projections reach the gustatory cortex: anterior insular cortex and frontal operculum.
|
|||
|
|
|
|||
|
|
Information derived from different areas of the tongue is spatially segregated in the n. of the solitary tract, the thalamus, and the cortex. (Still true?)
|
|||
|
|
|
|||
|
|
---
|
|||
|
|
|
|||
|
|
## Gustatory cortex
|
|||
|
|
|
|||
|
|
* Primary somatosensorycortex (Postcentral gyrus)
|
|||
|
|
* Gustatory Cortex (frontal operculum andanterior insular cortex)
|
|||
|
|
* Fronto-parietal operculum
|
|||
|
|
* Lateral sulcus
|
|||
|
|
* Insular cortex
|
|||
|
|
|
|||
|
|
|
|||
|
|
<div><img src="figs/gustatorycortex_52762a1_copy_ffa872c.jpg" height="100px"><figcaption></figcaption></div>
|
|||
|
|
<div><img src="figs/gustatorycortexscheme_0fbbbe3_copy_d0e2238.jpg" height="100px"><figcaption></figcaption></div>
|
|||
|
|
|
|||
|
|
|
|||
|
|
Note:
|
|||
|
|
|
|||
|
|
* fig origin unknown.
|
|||
|
|
|
|||
|
|
Note that the gustatory cortex is very close to the tongue area on the somatosensory cortex!
|
|||
|
|
|
|||
|
|
---
|
|||
|
|
|
|||
|
|
## Organization of the gustatory system
|
|||
|
|
|
|||
|
|
<figure><img src="figs/Neuroscience5e-Fig-15.17-2R_c37e52e.jpg" height="400px"><figcaption>Neuroscience 5e Fig. 15.17</figcaption></figure>
|
|||
|
|
|
|||
|
|
Note:
|
|||
|
|
|
|||
|
|
---
|
|||
|
|
|
|||
|
|
## Taste perception
|
|||
|
|
|
|||
|
|
* Most tastes are hydrophilic molecules solubilized in saliva
|
|||
|
|
* Tastants include salts, amino acids, sugars, acids, plant alkaloids
|
|||
|
|
* quantity of substance also perceived, the higher the concentration the more intensity the taste
|
|||
|
|
* Tastants act in the millimolar range, except for bitter things (strychnine 0.1 µM)
|
|||
|
|
* The tongue is not strictly regionalized by taste although some areas are more sensitive than others
|
|||
|
|
|
|||
|
|
Note:
|
|||
|
|
|
|||
|
|
---
|
|||
|
|
|
|||
|
|
## 5 basic tastes
|
|||
|
|
|
|||
|
|
* Sweet (sucrose, aspartame, glycine, etc.)
|
|||
|
|
* Sour (H+)
|
|||
|
|
* Salty (Na+, some other salts)
|
|||
|
|
* Umami (savory, glutamates)
|
|||
|
|
* Bitter (alkaloids)
|
|||
|
|
|
|||
|
|
<figure><img src="figs/five-tastes_copy_93d5298.jpg" height="100px"><figcaption></figcaption></figure>
|
|||
|
|
|
|||
|
|
Note:
|
|||
|
|
|
|||
|
|
* fig origin unknown. No find through image search
|
|||
|
|
|
|||
|
|
|
|||
|
|
---
|
|||
|
|
|
|||
|
|
## The organization of the taste system
|
|||
|
|
|
|||
|
|
* Taste receptors are organized in taste buds
|
|||
|
|
* Taste buds contain between 30-100 taste cells
|
|||
|
|
* 75% of all taste buds are found in papillae
|
|||
|
|
* 3-types: fungiform (25%, localized in anterior tongue), circumvallate (50%, rear of tongue) and foliate (25%, posterolateral edge)
|
|||
|
|
* There is great variability in the human population with respect to the number of taste buds
|
|||
|
|
|
|||
|
|
Note:
|
|||
|
|
|
|||
|
|
---
|
|||
|
|
|
|||
|
|
## Tongue anatomy
|
|||
|
|
|
|||
|
|
<figure><img src="figs/Neuroscience5e-Fig-15.18-1R_495eb15.jpg" height="400px"><figcaption>Neuroscience 5e Fig. 15.18</figcaption></figure>
|
|||
|
|
|
|||
|
|
Note:
|
|||
|
|
|
|||
|
|
Types of papillae:
|
|||
|
|
|
|||
|
|
Circumvallatepapillae
|
|||
|
|
|
|||
|
|
Foliatepapillae
|
|||
|
|
|
|||
|
|
Fungiformpapillae
|
|||
|
|
|
|||
|
|
---
|
|||
|
|
|
|||
|
|
## Structure of a taste bud
|
|||
|
|
|
|||
|
|
<figure><img src="figs/Neuroscience5e-Fig-15.18-2R_ae72520.jpg" height="400px"><figcaption>Neuroscience 5e Fig. 15.18</figcaption></figure>
|
|||
|
|
|
|||
|
|
Note:
|
|||
|
|
|
|||
|
|
|
|||
|
|
---
|
|||
|
|
|
|||
|
|
## Tastes
|
|||
|
|
|
|||
|
|
<figure><img src="figs/Neuroscience5e-Fig-15.19-0_41ee554.jpg" height="400px"><figcaption>Neuroscience 5e Fig. 15.19</figcaption></figure>
|
|||
|
|
|
|||
|
|
|
|||
|
|
Note:
|
|||
|
|
|
|||
|
|
|
|||
|
|
Composite fMRI image showing different locations of activation in insular cortex to each of these tastes.
|
|||
|
|
|
|||
|
|
---
|
|||
|
|
|
|||
|
|
## Taste receptors
|
|||
|
|
|
|||
|
|
* 5 distinct classes of taste receptors
|
|||
|
|
* Salty and sour generally transduced by ions (Na+ or H+) that open channels
|
|||
|
|
* This depolarizes neuron, that then leads to opening of voltage gated Na+ channels
|
|||
|
|
* This depolarizes neuron more and leads to opening of voltage gated Ca2+ channels
|
|||
|
|
* Leads to the release of serotonin
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Note:
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---
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## Transduction mechanisms in a generic taste cell
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<figure><img src="figs/Neuroscience5e-Fig-15.20-0_505080d.jpg" height="300px"><figcaption>Neuroscience 5e Fig. 15.20</figcaption></figure>
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Note:
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---
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## Taste receptors
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* Sweet and Unami receptors are GPCRs that share a subunit called T1R3
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* T1R3 is paired with T1R2 for sweet and T1R1 for amino acids
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* T1R1 and T1R2 are expressed in non-overlapping neurons
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* T1R2/3 activation leads to activation of PLC, increases IP3 and opens Ca2+channels (TRPM5). Ca2+ channel opening depolarizes cell
|
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* Bitter taste receptors (T2R) have 30 subtypes. Multiple members are expressed in same neurons but not in same neurons as the others. These use a specific Gα called gustucin
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Note:
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---
|
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## Taste receptors
|
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<figure><img src="figs/Neuroscience5e-Fig-15.21-0_copy_3a88321.jpg" height="400px"><figcaption>Neuroscience 5e Fig. 15.21</figcaption></figure>
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Note:
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---
|
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## Taste coding specificity and segregated representation
|
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|
<figure><img src="figs/Neuroscience5e-Fig-15.22-0_copy_8088d1f.jpg" height="400px"><figcaption>Neuroscience 5e Fig. 15.22</figcaption></figure>
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Note:
|
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sweet a.a. and bitter receptors are expressed in diff subsets of taste cells.
|
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gene from the TRPM5 channel is inactivated in ko mice and behavioral responses measured with taste preference test. Mouse gets two drinking spouts (one with water and one with tastant and relative frequency of licking is measured).
|
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|
pleasant tastes (sugar and umami), incr concentration gives incr response. For bitter there is decr response.
|
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|
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|
KO the PLCB2 (phospholipase) and responses are eliminated to sweet, umami, and bitter but rescuing expression only in T2R expressing cells recovers just the bitter taste response to wildtype levels.
|
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|
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|
|
* Sour receptor is expressed in every taste bud but isn’t in the same neurons as other receptors
|
|||
|
|
* An experiment to show that T1R2 is a sweet receptor and PKD2L1 is a sour receptor
|
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|
|
* Taste pathways remain segregated in the cortex (Zuker lab imaging?)
|
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|
|||
|
|
---
|
|||
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|
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|
|
## Putting the bitter receptor into sweet receptor neurons will cause mice to be attracted to bitter!
|
|||
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|
|||
|
|
<div><img src="figs/image16_190e843.png" height="300px"><figcaption>Based on Fig. 5 from Zhang et al., Cell 2003</figcaption></div>
|
|||
|
|
|
|||
|
|
Note:
|
|||
|
|
|
|||
|
|
Based on/adapted from Fig. 5 from Zhang et al., Cell 2003
|
|||
|
|
|
|||
|
|
[http://www.sciencedirect.com/science/article/pii/S0092867403000710](http://www.sciencedirect.com/science/article/pii/S0092867403000710)
|
|||
|
|
|
|||
|
|
And the Zuker lab has recently silenced specific brain areas for bitter and sweet in mouse to alter perceptive sense of these tastes:
|
|||
|
|
|
|||
|
|
[http://newsroom.cumc.columbia.edu/blog/2015/11/18/scientists-turn-tastes-on-and-off-by-activating-and-silencing-clusters-of-brain-cells/](http://newsroom.cumc.columbia.edu/blog/2015/11/18/scientists-turn-tastes-on-and-off-by-activating-and-silencing-clusters-of-brain-cells/)
|
|||
|
|
|
|||
|
|
Peng et al, Nature 2015
|
|||
|
|
|
|||
|
|
[http://www.nature.com/nature/journal/vaop/ncurrent/pdf/nature15763.pdf](http://www.nature.com/nature/journal/vaop/ncurrent/pdf/nature15763.pdf)
|
|||
|
|
|
|||
|
|
---
|
|||
|
|
|
|||
|
|
## Stimulation of the ‘bitter’ taste cortex is sufficient to make a mouse pucker
|
|||
|
|
|
|||
|
|
<div><img src="figs/ScreenShot2016-02-22at4.43.22PM_712d13b.png" height="400px"><figcaption>[Video 1 from Peng et al., Nature 2015](http://www.nature.com/nature/journal/vaop/ncurrent/fig_tab/nature15763_SV1.html)</figcaption></div>
|
|||
|
|
|
|||
|
|
Note:
|
|||
|
|
|
|||
|
|
Based on/adapted from Fig. 5 from Zhang et al., Cell 2003
|
|||
|
|
|
|||
|
|
[http://www.sciencedirect.com/science/article/pii/S0092867403000710](http://www.sciencedirect.com/science/article/pii/S0092867403000710)
|
|||
|
|
|
|||
|
|
And the Zuker lab has recently silenced specific brain areas for bitter and sweet in mouse to alter perceptive sense of these tastes:
|
|||
|
|
|
|||
|
|
[http://newsroom.cumc.columbia.edu/blog/2015/11/18/scientists-turn-tastes-on-and-off-by-activating-and-silencing-clusters-of-brain-cells/](http://newsroom.cumc.columbia.edu/blog/2015/11/18/scientists-turn-tastes-on-and-off-by-activating-and-silencing-clusters-of-brain-cells/)
|
|||
|
|
|
|||
|
|
Peng et al, Nature 2015
|
|||
|
|
|
|||
|
|
[http://www.nature.com/nature/journal/vaop/ncurrent/pdf/nature15763.pdf](http://www.nature.com/nature/journal/vaop/ncurrent/pdf/nature15763.pdf)
|
|||
|
|
|
|||
|
|
Bradbury J (2004) Taste Perception: Cracking the Code. PLoS Biol 2(3): e64. [doi:10.1371/journal.pbio.0020064](http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.0020064)
|
|||
|
|
|
|||
|
|
---
|
|||
|
|
|
|||
|
|
## The physiology of flavor perception
|
|||
|
|
|
|||
|
|
* Responses from taste and smell are first combined in the orbital frontal cortex (OFC)
|
|||
|
|
* OFC also receives input from the primary somatosensory cortex and the inferotemporal cortex in the visual what pathway
|
|||
|
|
* Bimodal neurons in this area respond to taste and smell as well as taste and vision
|
|||
|
|
* Firing of these neurons is also affected by the level of hunger of the animal for a specific food
|
|||
|
|
|
|||
|
|
<figure><img src="figs/MRI_jba1-OFC_copy_8a13a73.jpg" height="100px"><figcaption></figcaption></figure>
|
|||
|
|
|
|||
|
|
Note:
|
|||
|
|
|
|||
|
|
|
|||
|
|
|
|||
|
|
---
|
|||
|
|
|
|||
|
|
## Multimodal integration in orbitofrontal cortex
|
|||
|
|
|
|||
|
|
<figure><img src="figs/orbitofrontal-cortex-pathways_4393768.png" height="400px"><figcaption></figcaption></figure>
|
|||
|
|
|
|||
|
|
Note:
|
|||
|
|
|
|||
|
|
The orbital frontal cortex (OFC) receives inputs from vision, olfaction, and touch, as shown. It is the first area where signals from the taste and smell systems meet. (info based on E. T. Rolls (2000). The orbitofrontal cortex and reward. Cerebral Cortex, 10, 284-294, Fig. 2.)
|
|||
|
|
|
|||
|
|
---
|
|||
|
|
|