Givaudan-Roure Lecture - Association for Chemoreception Sciences

85 Poster [ ] Gustatory Processing
CHEMICAL AND THERMAL RESPONSES OF GUSTATORY
NEURONS IN THE GENICULATE GANGLION
Breza J.M. 1, Curtis K. 1, Contreras R.J. 1 1Department of Psychology and
Program in Neuroscience, Florida State University, Tallahassee, FL
We examined chemical and thermal responses of gustatory neurons
(N=18) in the geniculate ganglion using extracellular single-cell
electrophysiology. Cells were categorized by responses to lingual
stimulation with the 4 classic tastants: NaCl (100mM), QHCl (20mM),
sucrose (500mM), and citric acid (10mM) at a baseline temperature of
25°C. Responses to temperature change of 1°C/s/15s (±15°C) also
were measured. Finally, responses to the 4 tastants were evaluated after
adaptation to 40°C and to 10°C. We recorded from 1 Na-specialist
(5.6%), 1 QHCl-best (5.6%), 2 acid-best (11.1%) and 14 Na-generalists
(77.8%). Temperature change affected firing in only 3/18 cells (16.7%)
and only when cooled from 40° to 25°C. Specifically, 2 Na-generalists
increased firing by 1.1spikes/s (sps) during cooling and the QHCl-best
cell increased by 2.9sps. After 3-5min adaptation to 10°C, responses to
all chemical stimuli decreased in all cells, with the responses to the best
stimulus reduced by 2.5±0.3sps. The most robust decrease in activity
occurred in the QHCl-best cell (-4.9sps); acid best cells decreased firing
by -3.9sps. In contrast, after 3-5min adaptation to 40°C, responses
increased to the best stimulus in 10/16 cells tested (62.5%): 2/2 acidbest
(+1.9sps) and 8/13 Na-generalists (+2.0±0.4sps). Responses
decreased or were not affected in the remaining 6 cells: 5/13 Nageneralists
(-0.8±0.5sps) and the QHCl-best cell (-1.5sps). Thus,
temperature differentially affects responses of geniculate ganglion
neurons to taste stimuli. Supported by NIH Grant DC 04875.
86 Poster [ ] Gustatory Processing
FEEDING RELATED PEPTIDES: INVOLVEMENT WITH THE
GUSTATORY SYSTEM IN THE BRAIN OF GOLDFISH
(CARASSIUS AURATUS)
Huesa G. 1, Finger T. 2 1University of Colorado Health Sciences Center,
Denver, CO; 2Cell and Developmental Biology, University of Colorado
Health Sciences Center, Denver, CO
Melanin Concentrating Hormone (MCH) and Hypocretins (Hcrt) -
also called orexins-, are peptidergic neurotransmitters expressed
primarily in neurons located in the lateral hypothalamus. This region is
known to have a critical role in control of feeding and these peptides
actively participate in the modulation (stimulation) of food intake. To
test whether these orexigenic peptidergic systems are involved in the
gustatory information processing we examined their distribution in
gustatory nuclei of the CNS of goldfish. For this purpose we employed
immunocytochemical techniques using polyclonal antisera directed
against MCH or Hcrt2. The reaction was developed with
diaminobenzidine to enhance the intensity of the labeling. The
distribution of these two peptides was similar to those described in
mammals, with cell bodies in the hypothalamic region and fibers
projecting rostrally and caudally. Hcrt2 immunoreactive fibers are
located mainly in preoptic areas, hypothalamus, a few mesencephalic
regions and the dorsal horn in the spinal cord, but are scarce in taste
related brainstem nuclei. In contrast, MCH fibers were present in many
encephalic regions including the vagal gustatory lobe. These MCH
fibers occur mainly in layer IV of the sensory zone of the vagal lobe,
where many primary gustatory afferents terminate. In addition,
occasional MCH fibers could be observed crossing the sensory zone, in
layer IX and also in fiber and motor layers. These results support the
concept that MCH but not Hypocretins may act as a central modulator
of gustatory processing in goldfish. Supported by NIDCD Grant:
DC00147
22
87 Poster [ ] Gustatory Processing
EXPRESSION OF NEUROTRANSMITTER RECEPTORS
WITHIN THE NUCLEUS OF THE SOLITARY TRACT OF THE
HAMSTER
Ye M.K. 1, Rubrum A.M. 1, Christy R.C. 1, Smith D.V. 1 1Anatomy &
Neurobiology, University of Tennessee Health Science Center,
Memphis, TN
The nucleus of the solitary tract (NST) processes taste information
from the periphery that is modulated by descending projections from
several areas of the forebrain. Glutamate receptors (GluR) mediate
peripheral excitation of all taste-responsive NST neurons: Both
AMPA/kainate and NMDA antagonists block driven activity. Subsets
of these neurons are excited by microinjection of substance P and
inhibited by local infusion of γ-aminobutyric acid (GABA) or metenkephalin.
To further delineate the neural circuitry involved in these
modulatory effects, we are examining the expression of a number of
neurotransmitter receptors in the NST. Serial coronal or horizontal 50-
µm sections through the hamster brainstem were processed for
immunoreactivity to antibodies directed against µ- and δ-opioid
receptors, glutamate receptor subtypes GluR-1, -3 and -4 (AMPA) and
GluR-6 (kainate), the tachykinin receptor NK1, and the GABAA receptor. A given brain was processed using the ABC method for one
of these eight antibodies. Cells within the gustatory region of the NST
expressed GluR-1, -3, -4 or –6, the NK1, or the GABA receptor.
A
Afferent fibers of the VIIth and IXth nerves entering the solitary tract
expressed the µ-opioid receptor, whereas the δ-opioid receptor was seen
in cells of the NST, including the gustatory zone. This pattern of
expression would suggest a substrate for both pre- and postsynaptic
inhibition of gustatory neurons. Further work will examine receptor
expression in physiologically characterized NST neurons. Supported
by NIDCD DC000066 to DVS.
88 Poster [ ] Gustatory Processing
PAIRED PULSE FACILITATION AND DEPRESSION
OBSERVED IN TASTE CELLS IN THE RAT NUCLEUS OF
THE SOLITARY TRACT FOLLOWING
GLOSSOPHARYNGEAL NERVE STIMULATION
Hallock R. 1, Di Lorenzo P. 1 1Psychology, State University of New York
at Binghamton, Binghamton, NY
Evoked responses from paired pulse stimulation of the
glossopharyngeal (GP) nerve was studied in taste responsive cells in the
nucleus of the solitary tract (NTS) of anesthetized rats. Adult male rats
were anesthetized with urethane (1.4 g/kg) and Nembutal (25 mg/kg)
and prepared for unilateral electrical stimulation of the lingual branch
of the GP nerve and for electrophysiological recording from the
ipsilateral NTS. Once a taste-responsive cell was isolated, responses to
taste stimuli (0.1 M NaCl, 0.5 M sucrose, 0.01 M quinine HCl, 0.01 M
HCl) and electrical stimulation of the GP nerve were recorded. Up to
100 Pairs of pulses were delivered to the GP nerve at various interpulse
intervals and responses from cells were recorded. For each cell, the
threshold for stimulation of the nerve that evoked a response was
determined and a slightly higher current level was used for subsequent
stimulation. Electrical pulses were .2 ms in duration and the maximum
current level was 1.5 mA. Thus far, both paired pulse facilitation and
depression have been demonstrated in taste cells in the NTS in response
to stimulation of the GP. Much like paired pulse depression that has
been previously demonstrated with stimulation of the chorda tympani
nerve, paired pulse facilitation and depression in the GP may be
mechanisms by which cells integrate incoming information, modify the
responses of other cells, or enable the system to increase contrast
among taste stimuli.
Supported by NIDCD grant 1-RO1-DC005219 to PMD.