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The Neural Link between Novel
Olfactory Signals and Locomotion
and Réjean Dubuc3,4
1Department of Biological Sciences,
University of Windsor, Windsor, Ontario.
2Great Lakes Institute for Environmental
Research, University of Windsor, Windsor, Ontario.
3Groupe de Recherche
en Activité Physique Adaptée (GRAPA), Département des
Sciences de l’Activité Physique, Université
du Québec à Montréal, Montréal, Québec.
4Groupe de Recherche
sur le Système Nerveux
Central (GRSNC), Département de Neurosciences, Université de Montréal,
lamprey life cycle is heavily dependent on chemoreception, as feeding,
migratory, and reproductive behaviors are driven by
chemical cues. Under previous GLFC funding, we characterized a specific neural
pathway linking olfactory and motor brain centers in lampreys. It extends from
the medial part of the olfactory bulb (OB) to the mesencephalic locomotor region,
with a single relay in the posterior tuberculum .
Modulatory mechanisms acting on this pathway may account for the variability of
lampreys’ behavioral responses to olfactory inputs .
During the granting period, we focused our investigation on responses of
olfactory sensory neurons (OSNs), olfactory bulb (olfactory integration) and reticulospinal neurons (motor control) to semiochemicals including pheromones and combinations of
these compounds. The newly discovered phermone DKPES
and its combination with the well-characterized 3kPZS were of particular
interest for our study. However, we also tested PZS, PSDS, PAMS-24, compound
971, compound 973, as well as the two polyamines spermine and spermidine. Using electrophysiological and
imaging techniques we showed that DKPES alone could
activate the olfacto-motor circuitry all the way down
to the reticulospinal system. However, the most
potent responses were seen when it was combined with
3kPZS. Calcium imaging of the olfactory epithelium further showed that lamprey
OSNs were narrowly-tuned and responded only to one
odorant. OSNs responding to a particular odorant were intermingled with OSNs
responding to other odorants. This is consistent with results from in situ
experiments that showed that chemosensory receptors 6425.OR and 3721.TAAR are
expressed in OSNs widely distributed in the main olfactory epithelium (i.e. we
did not observe any segregation in their distribution). A series of
electrophysiological and neuroanatomical experiments showed that olfactory inputs are processed by two parallel neural pathways from
these sensory neurons to brainstem locomotor centers. These two pathways
are strongly modulated by GABA, 5-HT, and Dopamine. Moreover, we found that
olfactory bulb responses to pheromones are modulated
by hormonal changes. Taken together, our results show that olfactomotor
responses can be potentiated by using mixtures ofolfactory-stimulating compounds but also by using
neuromodulators acting on the pathways we have identified.