PSY391S March 8, 10, 2006 John Yeomans Chemical Senses PSY391S March 8, 10, 2006 John Yeomans

Taste Sensation Salt: Na+ ions Sour: H+ ions block K+ channels Sweet: Sugars activate 2 types of G-coupled receptors. Bitter: Many G-coupled receptors for proteins. Umami: Glutamate receptors for “good taste”, G- coupled. Saliva important for dissolving tastants. Cranial nerves VII and IX: Sensation and salivation.

Taste Buds in Tongue

Olfaction Many G-coupled receptors in olfactory epithelium responding to airborne odorants. Most mammals have G-coupled receptors in vomeronasal organ (ventral nasal cavity). For pheromones (chemical detection of individuals of same species). Access to VNO via tongue and palate, and via wet nose. These are mainly lost in adult humans.

Vomeronasal Organ in Mice Needed for detecting males vs. females and for conspecifics (family vs. intruder). Mate with all if TRP2 receptor knocked out. Attack intruder males if VNO and TRP2 receptors are working. Projections to accessory olfactory bulb and medial amygdala.

Olfactory Inputs Axel and Buck

Olfactory Receptor Genes Located on cilia of receptor cells in olfactory epithelium. 1/cell in most cells. About 400 genes expressed in humans, over 1200 in mice. ~3-5% of genome. Each synaptic zone (glomerulus) receives input from receptors of one type. Each mitral cell receives input from one glomerulus, and project to brain via CN I. Suggests that olfactory coding is mainly by labelled lines of hundreds of types.

TRP Channels

Olfactory tubercle Entorhinal cortex

Segregation of Projections in Brain