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#P175
POSTER SESSION V:
TRIGEMINAL SYSTEM; BEHAVIOR
AND PSYCHOPHYSICS; ODORANT
RECEPTORS & OLFACTION PERIPHERY
Activation of the trigeminal system by different odorants
Matthias Luebbert
1,2
, Jessica Kyereme
1
, Markus Rothermel
3
,
Klaus Peter Hoffmann
1
, Hanns Hatt
1
1
Ruhr Universitaet Bochum Bochum, Germany,
2
Ruhr University
Research School Bochum, Germany,
3
The Brain Institute,
University of Utah Salt Lake City, UT, USA
Mammalian nasal chemosensation is predominantly mediated via
the olfactory (OS) and the trigeminal system (TS). The TS is
provided by the trigeminal nerve, representing a cranial analog of
the dorsal root ganglia. Somata of trigeminal neurons are localized
within the two trigeminal ganglia (TG) at the base of the skull.
Since the OS and the TS are closely linked together, most odorants
are detected by both systems. Interestingly, anosmics can still
discriminate between different groups of odorants. Until today,
the underlying mechanisms of this phenomenon remain elusive.
In order to search for stimulus-specific spatio-temporal dynamics
of neuronal activity within the TG of narcotized adult male wistar
rats, we used voltage-sensitive-dyes to monitor neuronal activity
upon nasal stimulation with different volatile substances. Most of
these substances induced the strongest activity within
posteromedial areas of the ganglion. Additionally, we observed the
shortest onset latencies in these regions. The intensity of the
monitored signals appeared to be highly dependent on the stimulus
used and the concentrations used. Interestingly, the monitored
activity seemed to spread from these posteromedial regions to more
anterior and lateral parts of the ganglion. Here, the somata of
neurons innervating other facial regions are localized. These
findings might point on a cross-excitation between different cells
within the TG (e.g. neuron-neuron, or neuron-glia). The existence
of a cross-excitation between cells within the TG has been
previously assumed, based on data obtained from cultured
trigeminal neurons or TG-slices. Our data indicate for the first
time that this cross-excitation might appear not only
in vitro
but
also
in vivo
.
#P176
POSTER SESSION V:
TRIGEMINAL SYSTEM; BEHAVIOR
AND PSYCHOPHYSICS; ODORANT
RECEPTORS & OLFACTION PERIPHERY
Gustatory modulation of the responses of trigeminal
subnucleus caudalis (Vc) neurons to noxious stimulation
of the tongue in rats
Yves Boucher
1
, Mirela Iodi Carstens
2
, Earl Carstens
2
1
UFR odontologie Universite Diderot Paris France,
2
NPB, UC Davis Davis, CA, USA
Psychophysical evidence supports interactions between the taste
and trigeminal systems in man. Tastants attenuate irritation elicited
by oral application of capsaicin in adults, and anesthesia of the
chorda tympani (CT) enhances the oral burning sensation elicited
by capsaicin. Our aim was to test the hypothesis that CT activation
suppresses responses of Vc neurons to noxious oral stimuli. Single-
unit recordings were made from neurons in superficial lamina of
dorsomedial Vc in pentobarbital-anesthetized rats. We recorded
responses to noxious electrical (0.5ms pulse trains, 15 V), chemical
(pentanoic acid, 200 µM) and thermal (55°C water) stimulation of
the tongue. Each electrical or pentanoic acid stimulus was
immediately preceded by 30 sec superfusion of the tongue with
either water (control) or tastant (either 0.3 M sucrose, 0.1M NaCl,
0.05 M glutamate [potassium salt], 0.01M citric acid, or 0.001M
quinine, or a mixture of all tastants). Electrically- and chemically-
evoked responses preceded by water or tastant were compared
(Wilcoxon). The effect of heat was tested by comparing Vc
neuronal responses to water vs. tastant, both heated to 55°C.
Electrically-evoked responses were significantly reduced when
preceded by the tastant mixture (p=0.012) or by individual
application of NaCl or glutamate (p<0.05 for both). Sucrose, citric
acid and quinine had no effect. Similarly, pentanoic acid-evoked
responses were significantly attenuated when preceded by
application of NaCl and glutamate (p<0.05 for all). There was no
difference between Vc responses to heated water vs. tastants.
Thus, certain tastants (i.e., NaCl and glutamate) selectively inhibit
responses of Vc neurons to electrical and chemonociceptive tongue
stimuli, via peripheral and/or central interactions currently under
investigation. Acknowledgements: National Institutes of Health
grants [DE013685 and ARO57194]
#P177
POSTER SESSION V:
TRIGEMINAL SYSTEM; BEHAVIOR
AND PSYCHOPHYSICS; ODORANT
RECEPTORS & OLFACTION PERIPHERY
Eugenol and carvacrol increase lingual heat responses in
trigeminal subnucleus caudalis (Vc) neurons and activate
capsaicin-sensitive trigeminal ganglion neurons in rats
Amanda H Klein, Christopher L Joe, Auva Davoodi,
Kenichi Takechi, Mirela Iodi Carstens, Earl Carstens
University of California Davis/Neurobiology Physiology and
Behavior Davis, CA, USA
Eugenol and carvacrol from clove and oregano, respectively, are
agonists of TRPV3 which is implicated in innocuous warmth and
possibly heat pain transduction. TRPV3 agonists induce oral
irritation that rapidly desensitizes, accompanied by a short-lasting
heat hyperalgesia in humans. We investigated the responses of
Vc neurons with lingual receptive fields in the rat. Eugenol (1%)
directly activated 9/20 (45%) units and carvacrol (1%) directly
activated 13/19 (68%) of heat-sensitive units. Eugenol increased
neuron responses to noxious heat by almost 70%. Carvacrol
increased noxious heat-evoked responses by 37%. Of 78 Vc
units tested, 42% responded to 1% menthol, 47% to 10%
cinnamaldehyde, and 75% to lingual application of 0.01%
capsaicin. We also presently investigated if trigeminal primary
afferent neurons responded to eugenol or carvacrol and other TRP
channel agonists. Using ratiometric calcium fluorometry with
Fura2-AM, we found that 200 µM eugenol and 100 µM carvacrol
activated 20-30% of cultured trigeminal ganglion (TG) neurons but
only activated 7-20% of dorsal root ganglion (DRG) neurons. TG
and DRG neurons also responded to bath application of 250 µM
menthol (TRPM8,~25%), 100 µM mustard oil (TRPA1,13-38%)
and 1 µM capsaicin (TRPV1,52-62%) with large overlapping
populations. The largest overlapping populations were those
responding to eugenol and capsaicin (70, 76%) or carvacrol and
capsaicin, (85, 93% for TG and DRG cells, respectively). This
overlap provides a basis for a potential peripheral site of TRPV3
agonist modulation ofTRPV1-mediated noxious heat sensitivity of
trigeminal afferents. Peripheral sensitization may account for the
enhancement of Vc heat-evoked responses, and human heat
hyperalgesia, by TRPV3 agonists although central sensitization
cannot be ruled out. Acknowledgements: NIH DE013685 and
AR057194
86 | AChemS Abstracts 2012
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