Page 28 - ACHEMS 2012 PROGRAM

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28 | AChemS Abstracts 2012
signals appear to be modulated differently by brain states.
These observations suggest a mechanism that modifies odor
representation at the glomerular input. Acknowledgements:
NIDCD008003 Stowers Institute
Feedback Control of Circuits and Codes in the Olfactory Bulb
Foivos Markopoulos, Dan Rokni, Allison Provost,
Venkatesh Murthy
Department of Molecular & Cellular Biology and Center for
Brain Science, Harvard University Cambridge, MA, USA
The formation of sensory percepts in our brain is often described as
a feed-forward process that involves serial transformation of
sensory stimuli into neural activity. Yet our everyday experience
clearly shows that higher brain areas can actively modulate how
sensory information is processed even in the earliest stages.
In the mammalian olfactory system, the first stages of synaptic
processing are in the olfactory bulb, which receives massive
feedback projections from the cortex as well as midbrain
neuromodulatory regions. In this talk, I will present our studies on
the circuitry of these feedback projections as well as their influence
on odor coding. First, I will present data on how on serotonergic
innervation from the raphe nucleus influences odor-evoked
responses in vivo, both at the level of input to and the output of the
olfactory bulb. Then, I aim to discuss recent work on identifying
the functional targets of feedback inputs from the anterior olfactory
nucleus to the olfactory bulb, done in slices using optogenetic
methods. Finally, I will describe the consequences of this
centrifugal feedback on odor evoked responses in the
olfactory bulb.
Neural & molecular mechanisms of taste reception,
transmission & modulation: A sweet (taste) story that began
with simple Mendel’s law
Yuzo Ninomiya
Kyushu University
Gustatory system plays the important role in maintaining
homeostasis in animals. If animals lack nutrients essential for their
survival, such as carbohydrates, minerals and essential amino acids,
they may be able to find these insufficient nutrients using taste
cues. However, for a long time it has been unknown how these taste
cues are detected and transmitted to the brain and how they are
modulated by homeostasis. When I started taste research in 1970’s,
there was the lack of understanding of the taste coding system from
signal detection in taste cells to transmission to taste nerves.
My collaborators and I studied the taste coding using combined
techniques in physiology, molecular biology and genetics. In my
lecture, results of these studies will be illustrated by our research
on reception, transmission and modulation of sweet taste.
These studies began with identification of a Mendelian genetic
locus (dpa) responsible for sweet taste, which was mapped to the
mouse chromosome 4, and which subsequently led to the finding
of the Sac locus encoding the T1R3 sweet/umami receptor
component. Using our recently developed techniques for recording
of taste-evoked activity and analyses of gene expression in the
same taste cells, we have shown that T1R3 and its heterodimeric
partner, T1R2, determine taste selectivity of sweet responsive
cells. Using this approach, we also demonstrated the role of
action potentials and a hemichannel, pannexin 1, in ATP release
by taste cells.
Our earlier genetic studies have shown that the db locus is involved
in inhibitory modulation of sweet taste by leptin. These studies
led to our recent discovery of other sweet taste modulators,
endocannabinoids (EDs), which enhance sweet taste responses,
i.e., have an effect opposite to the action of leptin. Leptin and EDs
are known as anorexigenic (reducing food intake) and orexigenic
(stimulating food intake) mediators, respectively, that act via their
receptors in the hypothalamus and limbic forebrain. Reciprocal
regulation of peripheral sweet taste sensitivity by leptin and
EDs may contribute to their opposing actions on food intake
and thereby sweet taste cue plays an important role in regulating
energy homeostasis.
Abstracts are printed as submitted by the author(s)