Olfaction, Neuropeptides and Behaviour Flashcards
How are pheromones detected?
Via the vomeronasal organ in the nasal septum. VNO sensory neurons project to ACCESSORY OB and from there to the AMYGDALA and HYPOTHALAMUS via the OF tract
What are the 3 principle cell types in the olfactory epithelium? What are their key features?
Olfactory receptor neurons:
- Bipolar shape
- Dendrite with cilia hairs coming off
- Site of OF transduction
- Penetrate the CNS
Basal cells:
- Like a stem cell, is the source of new receptor cells
- Needed as nasal epithelium are turned over every 4-6 weeks
Supporting cells:
- Act like glia, physically supporting receptor cells
- Provide protective mucus with antimicrobial and odorant binding properties
How is odour detection transduced (molecularly)? (Jones and Reed)
- GPCR in the OF epithelium called Golf
- Causes increase in intracellular cAMP
- Opens calcium channels (depolarises the cell) and chloride channels (sustains activation)
What did Buck and Axel DO?
- They identified a large GPCR gene family of ~1000members, and that they were expressed in the nasal epithelium- potential odorant receptors
- Axel studied catfish
- Used an in situ hybridisation to analyse receptor expression in the catfish olfactory epithelium
- They found that each individual receptor gene is expressed in sensory neurons within a given spatial zone (i.e., in specific areas)
- Axel essentially took the G[olf] promoter made it express Tau-LacZ, a protein that produces axonal beta-Galactosidase that can be visualised by a colorimetric assay (dyed blue)
- They visualised the innovation of the OB by neurons from the OF epithelium
What is allelic exclusion?
Receptor neurons only expressing one type of receptor protein
Why did Axel use Tau-LacZ rather than just LacZ?
Tau allows LacZ to innovate neurons
Receptor neurons expressing one type of receptor project to a small number of (USUALLY 1) glomeruli, even when they are spatially separated.
With what cells do receptor neurons synapse with in glomeruli
Mitral cells
How is a spatial map of olfaction maintained when cells turn over every 3-4 weeks? (Wang et al)
- Inducing death of neurons expressing one type of receptor
- When reintroduced, these neurons innovated the SAME PLACE and SAME GLOMERULUS of the OB
- They found projections from the OFE found the rough area on the OB but the receptor on the surface was required to establish specific connectivity
- Each glomerulus responds only to the chemicals that activate a specific receptor
- Swapped M1 and P2 receptors genes - neurons went to completely different places (not where the other receptor goes. So dependent on environment, not just receptor)
What is the idea behind population coding of smells? What was used to study this and why?
What was studied?
- Drosophila as 80 receptor genes
- Sensory receptors project to one glomerulus
- Used Ca2+ reporters to map glomerular activation
Findings:
- You get grades of coding from different glomeruli from a single odour
- Smells are made up of composite odours that interact with multiple receptor types
- Ratios of glomeruli activation determine the smell perceived
What is the nuance of spatial coding in olfaction?
- Glomeruli that detect chemically similar odours are grouped closer together
What are trace amine odours?
- Small family of GPCRs coupled to Golf
- More related to biogenic amine receptors than OF receptors
What are the 2 types of TAAR and what are their functions?
TAAR4:
- Sensitive to 2-Phenylethylamine
- Which is in carnivore urine, lions, tigers, jaguars have 1000 fold this
- Related to avoidance evolution
TAAR5:
- Sensitive to trimethylamine
- Sexually dimorphic, males have large amounts in urine which is attractive to females
- Positive attractive quality is fully mediated by TAAR5
What is the formula for the perfect social signal?
cheap to transmit, cheap to receive, discreet, selective, long-range, long-lasting, easy identification
What is chemosensation
- Traditionally a sense of smell detects volatile compounds for identification of substances that may be beneficial of harmful
- Male selection in sexual reproduction
- Essential impetus for evolution
What is the Proust effect
Smell can be used to recall memories better than other senses
What is the definition of a pheromone?
Any chemical signal conveying information between members of the same species (usually eliciting a particular behavioural or physiological change)
What are common uses of pheromones and what are the two types?
- Health, mate choice, incest avoidance, sexual maturation, aggression (locusts) territory marking (dogs), dominance (wolves)
Two types:
- Releaser pheromones: Immediate effect
- Primer pheromones: Long term, e.g., puberty
What is bombykol
- First isolated pheromone
- Discovered by Germans studying silkworm moths
- Sense organs were on the antennae of moths
What are 2 examples of releaser pheromones?
Alarm pheromones:
- Some species release when attacked by predator to warn same species
- aggregation of locusts
Trail making:
- Leaf-cutter ants lay pheromones to mark the trail to a food source
The VNO projects to the accessory OB. Where is this information then relayed?
Amygdala and Hypothalamus
Due to anatomical connections, organism may not be conscious of effects
Not detailed, but what does cranial nerve 0 do?
- Structure of the accessory nasal system
- Secretes gonadotrophin releasing hormone which effects reproductive endocrinology
Match the Effect to the Description:
a) Pregnant mice exposed to novel male spontaneously abort, followed by mating with novel mouse
b) Re-mating with arrival of new potential mate
c) These female mice will eventually become anoestrous in the absence of males. If a male is introduced, the females will start to cycle synchronously within 3 days. Females cycling together have higher chance of offspring survival
d) Female mice housed together in small groups in the absence of males exhibit prolonged dioestrous that is maintained by progesterone secretion from the corpora lutea
e) Female rodent pups undergo puberty earlier if males are present than if males are absent, isolated female mice go through puberty later than when raised with other females due to pheromones
- Lee-Boot effect
- Whitten effect
- Vandenburgh effect
- Bruce effect
- Coolidge effect
a) Bruce effect
b) Coolidge effect
c) Whitten effect
d) Lee-Boot effect
e) Vandenburgh effect
What is the major histocompatibility complex (MHC), and why is it?
- MHC genes code for special protein markers that attach to a cell and help recognition of intruders
- Different MHCs recognise different intruders
- Advantageous for mother to select a mate with different MHCs
- Evolutionary drive
Most of the studies have studied animal pheromones.
What evidence is there for/against human pheromones?
FOR:
- Dogs can detect bladder cancer from human urine due to alterations in odorants caused by MHC changes in oncotic cells
- Androgen-based volatile steroids have MHC constituents
- Hypothesised that humans are able to detect pheromones via the MAIN olfactory system rather than the accessory OF system
- PET scan of brain found that we do respond to pheromones in a sexually dimorphic manner
- Synchrony of menstrual cycles among women thought to be due to pheromones
AGAINST:
- Humans do have a VNO but is thought to be non-functional
- VNO signal and receptor genes are pseudogenes in humans