Abstracts - Association for Chemoreception Sciences

#P278 POSTER SESSION VI:
PERIPHERAL AND CENTRAL TASTE;
PERIPHERAL OLFACTION
NaCl- induced c-fos expression in the nucleus of the solitary
tract of mice that lack P2X receptor subunits necessary for
taste transmission
Jennifer M Stratford, Thomas E Finger
Rocky Mtn Taste & Smell Center, Neurosci Prog, Univ Colo
Denver Anschutz Medical Campus Aurora, CO, USA
The gustatory nerves of mice that lack P2X2 and P2X3 receptor
subunits (P2X dbl KO) are unresponsive to all taste stimulus
qualities (Finger et al., 2005). Surprisingly, P2X dbl KO mice have
residual behavioral responses to concentrated taste solutions,
which may reflect non-gustatory or post-ingestive information
presumably intact in P2X dbl KO mice. We previously measured
brain activation in response to consumption of 150 mM
monosodium glutamate (MSG), using the immediate early gene
c-fos, in the nuc. of the solitary tract (nTS) - the primary central
taste and viscerosensory nucleus. We found significantly less
c-fos-like immunoreactivity (cFLI) in rostral (gustatory) levels of
the nTS of P2X dbl KO animals as compared to WT controls.
In contrast, cFLI did not differ between WT and P2X dbl KO
mice in caudal (viscerosensory) nTS levels. However, MSG has a
sodium component in addition to its primary glutamate
component. Thus, the current study measured NaCl-induced
c-fos activation. P2X dbl KO and WT mice were placed on 22 h
water restriction 3 days prior to stimulation. On stimulation day,
mice consumed water or 150 mM sodium chloride (NaCl) for 30
min. Following taste stimulation, mice were left undisturbed for
approximately 60 min, perfused transcardially with buffered
paraformaldehyde and then their brains were removed and
processed for cFLI. For each genotype, the number of NaClinduced
c-fos-positive cells in the nTS was compared to the
number induced by intake of water, yielding a measure of NaCldependent
cell labeling. NaCl stimulation elicited little NaCldependent
cFLI in either WT or P2X dbl KO animals, which did
not differ between the two groups, and was not different from
water- induced cFLI. Thus, MSG- induced nTS cFLI is
attributable solely to the glutamate component of
MSG. Acknowledgements: NIH and 3ARP grants to T.E.F.
#P279 POSTER SESSION VI:
PERIPHERAL AND CENTRAL TASTE;
PERIPHERAL OLFACTION
Overexpression of BDNF in the Lingual Epithelium Alters
Terminal Field Organization in the Mouse NTS
Chengsan Sun, David L. Hill
Department of Psychology, University of Virginia Charlottesville,
VA, USA
Brain Derived Neurotrophic Factor (BDNF) is expressed within
gustatory epithelia and is required for gustatory neurons to locate
and innervate their correct target during development. Genetic
deletion of the bdnf gene and the BDNF receptor gene, trkB,
results in a 50% loss of geniculate ganglion neurons and a
significant loss of taste buds. Interestingly, when BDNF is
overexpressed (BDNF-OE) throughout the lingual epithelium,
chorda tympani fibers are misdirected and innervate inappropriate
locations in the tongue (non-taste papillae), leading to a severe
loss of taste buds. The remaining taste buds are hyper-innervated
because of increased numbers of innervating neurons, but not
because of increased branching. We sought here to examine the
effects of BDNF-OE on central gustatory organization by
fluorescently labeling the chorda tympani, greater superficial
petrosal (GSP), and glossopharyngeal (IX) nerves in adult BDNF-
OE mice and examine their terminal field organization in the
nucleus of the solitary tract (NTS). The chorda tympani nerve
terminal field volume was approximately 2X greater than in
controls, with the greatest expansion in the dorsal zone of the
NTS. The volumes of the other two nerves were similar to
controls. Furthermore, the overlapping terminal fields that
included the chorda tympani nerve were significantly larger than
in controls, whereas the overlapping terminal field that did not
contain the chorda tympani (GSP with IX) was unaffected. To
extend these findings, we found that the chorda tympani nerve in
BDNF-OE mice was functional and responded to a variety of
taste stimuli and, unexpectedly, the number of geniculate ganglion
cells that comprise the chorda tympani nerve was not different
from controls. Acknowledgements: NIH grant R01 DC00407
#P280 POSTER SESSION VI:
PERIPHERAL AND CENTRAL TASTE;
PERIPHERAL OLFACTION
Development of intrinsic properties of rostral nucleus of
solitary tract (rNST) neurons in embryonic and postnatal rats
Takeshi Suwabe, Catherine E. Krull, Charlotte M. Mistretta,
Robert M. Bradley
Department of Biologic & Materials Sciences, School of Dentistry,
University of Michigan Ann Arbor, MI, USA
The rNST, the first relay in the central taste pathway, must be
functional at birth to guide feeding. However, few details are
available on maturational changes that take place in intrinsic
physiological properties of embryonic rNST neurons during
development. We have characterized the action potential (AP)
discharge characteristics and subthreshold membrane currents in
rNST neurons at gestational days (E) 14, 16, 18 and 20 and
postnatal days 1-2, 6-8, 14 and 19-21. The rNST was identified in
trans-illuminated brainstem slices as lying medial to the solitary
tract. Neural recordings were made with whole-cell patch-clamp.
In response to depolarizing current injections, almost all neurons
tested (135 of 141 neurons) generated APs. Only 4 embryonic and
2 postnatal neurons did not generate an AP in response to
depolarization. APs were largely suppressed by superfusing 1 mM
tetrodotoxin (TTX) over the slices, but in a few neurons at E14
the AP was not significantly diminished by TTX. In all E14
neurons, depolarization elicited only a single AP whereas in older
embryos 75% of neurons responded with a single AP. In contrast,
73% of postnatal neurons generated five or more repetitive APs
when depolarized (on average, trains of 18 APs). About 80% of
neurons had a hyperpolarization-activated, transient outward
potassium current (IKA) across all age groups. The proportion of
neurons with large amplitude IKA currents (> 200 pA) significantly
increased in the postnatal period. The decay time of the IKA
current in embryonic neurons (mean = 26 msec, n = 27) was
significantly faster than the decay time in postnatal neurons
(67 msec, n = 48; Mann-Whitney U test, p