PMID- 9929638
OWN - NLM
STAT- MEDLINE
DCOM- 19990224
LR  - 20190616
IS  - 0077-8923 (Print)
IS  - 0077-8923 (Linking)
VI  - 855
DP  - 1998 Nov 30
TI  - Excitatory and inhibitory modulation of taste responses in the hamster brainstem.
PG  - 450-6
AB  - The rostral portion of the nucleus of the solitary tract (NST) contains 
      second-order gustatory neurons, sends projections to the parabrachial complex and 
      brainstem reticular formation, and receives descending projections from several 
      nuclei of the ascending gustatory pathway. Electrophysiological responses of NST 
      neurons can be modulated by several factors, including blood glucose and insulin 
      levels and taste aversion conditioning. We are using extracellular 
      electrophysiological recording in vivo, combined with local microinjection of 
      neurotransmitter agonists and antagonists, to study the mechanisms by which taste 
      responses of cells in the hamster NST can be modulated. Afferent fibers of the 
      chorda tympani (CT) nerve make excitatory synaptic contact with NST neurons; this 
      excitation is probably mediated by the excitatory amino acid glutamate. 
      Microinjection of kynurenic acid, a nonspecific glutamate receptor antagonist, 
      into the NST completely and reversibly blocks afferent input from the CT nerve, 
      produced by either anodal electrical or chemical stimulation of the anterior 
      tongue. The non-NMDA ((RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic 
      acid (AMPA)/kainate) receptor antagonist 6-cyano-7-nitroquinoxaline-2, 3-dione 
      (CNQX) also completely blocks gustatory input to these cells, whereas the 
      N-methyl-D-aspartate (NMDA) antagonist DL-2-amino-5-phosphonovalerate (APV) 
      produces only a small effect. There are many gamma-aminobutyric acid 
      (GABA)-containing neurons within the NST and taste-responsive NST cells are 
      maintained under a tonic GABAergic inhibition. Microinjection of the GABAA 
      receptor antagonist bicuculline methiodide increases the taste responsiveness of 
      NST neurons, whereas application of GABA inhibits taste responses in these cells. 
      Preliminary data show that GABAergic inhibition can be produced by stimulation of 
      the gustatory cortex. There are both intrinsic substance P (SP)-containing 
      neurons and extrinsic SP-immunoreactive fibers in the rostral NST. Microinjection 
      of SP into the NST enhances the responses of many NST cells to gustatory 
      stimulation; NaCl-best neurons are preferentially excited by SP.
FAU - Smith, D V
AU  - Smith DV
AD  - Department of Anatomy & Neurobiology, University of Maryland School of Medicine, 
      Baltimore 21201-1509, USA. dvsmith@umaryland.edu
FAU - Li, C S
AU  - Li CS
FAU - Davis, B J
AU  - Davis BJ
LA  - eng
GR  - DC00066/DC/NIDCD NIH HHS/United States
GR  - DC00207/DC/NIDCD NIH HHS/United States
PT  - Journal Article
PT  - Research Support, U.S. Gov't, P.H.S.
PT  - Review
PL  - United States
TA  - Ann N Y Acad Sci
JT  - Annals of the New York Academy of Sciences
JID - 7506858
RN  - 0 (Neurotransmitter Agents)
SB  - IM
MH  - Animals
MH  - Brain Stem/*physiology
MH  - Cricetinae
MH  - Electrophysiology
MH  - Neurotransmitter Agents/agonists/antagonists & inhibitors/physiology
MH  - Taste/*physiology
RF  - 29
EDAT- 1999/02/04 00:00
MHDA- 1999/02/04 00:01
CRDT- 1999/02/04 00:00
PHST- 1999/02/04 00:00 [pubmed]
PHST- 1999/02/04 00:01 [medline]
PHST- 1999/02/04 00:00 [entrez]
AID - 10.1111/j.1749-6632.1998.tb10605.x [doi]
PST - ppublish
SO  - Ann N Y Acad Sci. 1998 Nov 30;855:450-6. doi: 10.1111/j.1749-6632.1998.tb10605.x.