Nature, recent
Presented by Guisheng
5 classes of taste receptors
- for umami, sweet, bitter, sodium and sour and carbonation
- each taste bud contains different cell types containing different receptors
- tongue map is wrong — each tastebud has all cell types. – classic example of error in textbooks, not based on science. See wikipedia — testing individual regions of the tongue this doesn’t hold up.
- maybe an organized pattern in cortex — there are spatial regions of the brain that respond.
salt
- exceptional in switch from craving to aversive — we like a little bit but not too much
- low salt activates ENaC receptors, strictly attractive. High salt aversive pathway?
- Find molecule (AITC) which inhibits the high salt response (and the bitter response). Propose high salt aversion may be mediated by ‘bitter’ responsive cells. AITC — active component of mustard/wasabi, believed to be specific activator of TRP1A (‘pain receptor’)
- Immunofluorescently label bitter cells, calcium imaging shows bitter cells respond to high salt.
- Other components critical to the bitter signalling pathway are involved and necessary for the AITC sensitivity but not essential for the neural response to high salt. –> must be additional pathway. Also see knockouts still aversive to high salt.
- other pathway response requires sour aversive response. Double mutant (sour and bitter required components) no longer show neural aversive response to high salt.
- express and aversive responsive receptor in sweet cell get a favorable response to same ligand. Cell type determines response.
- Are the mice no longer high salt aversive in the double mutant? – yes. KCl become unresponsive to higher and higher levels. NaCl, the more the better, whereas wildtype have peak.