Givaudan-Roure Lecture - Association for Chemoreception Sciences

69 Slide [ ] Trigeminal Chemoreception
FATTY ACIDS INHIBIT DELAYED RECTIFYING K
CHANNELS IN ISOLATED TRIGEMINAL NEURONS.
Gilbertson T.A. 1, Klein J.T. 1, Farmer-George M. 1, Hansen D.R. 1, Simon
S.A. 2 1Biology & Center for Integrated BioSystems, Utah State
University, Logan, UT; 2Anesthesiology, Duke University, Durham, NC
Chemosensory cues for fat have been shown to be mediated by fatty
acids (FA) acting directly on subtypes of delayed rectifying K (DRK)
channels in taste receptor cells (TRCs). Since it is generally believed
that texture is important for oral fat recognition and that texture
perception is mediated, at least in part, by trigeminal (TG) innervation,
we have examined the effects of fatty acids (0.1-10 µM) on isolated rat
TG neurons using whole-cell patch clamp recording. TG ganglia were
removed and individual TG neurons were isolated by enzymatic
methods and placed into culture for 24-72 h. Patch recordings were
made before, during and after application of a variety of fatty acids
including saturated (SFA), monounsaturated (MUFA) and
polyunsaturated (PUFA) forms. Similar to our results in TRCs, PUFAs
caused a reversible, time-dependent inhibition of DRK channels in TG
neurons, consistent with an open-channel block leading to cell
activation. In contrast to fungiform TRCs, which respond specifically to
PUFAs, TG neurons were much less specific and responded to a variety
of fatty acid types, including some MUFA and SFA, in a similar
fashion. Thus, FA effects on DRK channels may not only mediate the
taste of fat, but may also contribute to the perception of its textural
properties via activation of oral TG fibers. Currently, we are using
quantitative PCR to compare the expression of DRK channels in TG
neurons with TRCs to determine the source of the FA specificity
differences. Supported by NIH DK59611(TAG), DC01065 (SAS).
70 Symposium [ ] Receptors: Choosing Genes, Targeting
Axons, Detecting Chemicals
PERCEPTION OF CHEMICAL CUES AND NAVIGATION IN C.
ELEGANS
Bargmann C.I. 1 1Anatomy, University of California, San Francisco,
San Francisco, CA
Behavior arises from the interplay between the environment and
intrinsic properties of neurons and neural circuits. To understand how
the genetics and development of the nervous system contribute to
specific behaviors, we are studying olfactory system in the nematode C.
elegans. C. elegans senses hundreds of different compounds,
discriminates between them, and generates different behaviors in
response to different odors. It is possible to define the specific neurons
that generate these behaviors, since the C. elegans nervous system
consists of just 302 neurons that have reproducible functions,
morphologies and synaptic connections. Previous studies have
generated an understanding of the methods by which animals detect and
respond to a single sensory stimulus. In C. elegans, odors are detected
by over 1000 G protein-coupled odorant receptors. Individual olfactory
neurons express multiple receptor genes, allowing a few cells to detect
many odors. A given sensory neuron is primarily dedicated to a single
behavioral task, such as attraction or repulsion. We are now asking how
animals navigate through complex sensory environments using multiple
odors or sensory inputs. For these studies, we have focused on complex
natural stimuli that should be present in the soil environment, such as
different bacterial foods, natural physical stimuli, and other animals
(social groups). C. elegans shows unexpected sophistication in its
behavior when it faces ecologically relevant challenges like pathogenic
bacteria or metabolic stress. Using the wiring diagram, we are
identifying the circuits for navigation behavior and asking how sensory
inputs regulate those circuits.
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71 Symposium [ ] Receptors: Choosing Genes, Targeting
Axons, Detecting Chemicals
THE BIOLOGY OF SWEET, BITTER AND UMAMI TASTE
Zuker C.S. 1 1Section of Neurobiology, University of California, San
Diego, La Jolla, CA
72 Symposium [ ] Receptors: Choosing Genes, Targeting
Axons, Detecting Chemicals
INTERNAL REPRESENTATIONS OF THE OLFACTORY
WORLD
Wang J. 1, Wong A.M. 2, Axel R. 3 1Neurobiology and Behavior,
Columbia University, New York, NY; 2Department of Biochemistry and
Molecular Biophysics, Columbia University, New YOrk, NY;
3Biochemistry and Molecular Biophysics, Columbia University, New
York, NY
Olfactory perception requires the recognition of a vast repertoire of
odorants in the periphery and central neural mechanisms that allow the
discrimination of odors. The organization of the peripheral olfactory
system appears remarkably similar in fruit flies and mammals. The
convergence of like axons into discrete glomerular structures provides
an anatomic map in the antennal lobe. How does the anatomic map
translate into a functional map? We have developed a sensitive imaging
system in the Drosophila brain that couples two-photon microscopy
with the specific expression of the calcium-sensitive fluorescent
protein, G-CaMP, to examine neural activity. At natural odor
concentrations, each odor elicits a distinct and sparse pattern of activity
that is conserved in different flies. We have combined Ca2+ imaging
with electrical recordings to demonstrate the faithful propagation of the
glomerular map by projection neurons that innervate the protocerebrum.
The quality of an odor may therefore be reflected by defined spatial
patterns of activity, first in the antennal lobe and ultimately in higher
olfactory centers. We have identified a spatially invariant sensory map
in the fly protocerebrum that is divergent and no longer exhibits the
insular segregation of like axons observed in the antennal lobe. This
organization provides the opportunity for the integration of multiple
glomerular inputs by hierarchical cell assemblies in the protocerebrum.