Summary: Researchers report an inhibitory circuit which releases GABA into the olfactory bulb modulates behavioral responses to odors in lampreys.
Source: University of Montreal.
In all animals, including humans, smell – the oldest of the five senses – plays a predominant role in many behaviors essential for survival and reproduction. It has been known since ancient times that animals react to odours.
Yet researchers are just beginning to elucidate the neural pathways and mechanisms responsible for odour-induced behavior. A first step was made by showing the existence of a neural pathway connecting the olfactory and motor centers of the brain in invertebrates with the worm C. elegans and in vertebrates with the lamprey, a primitive, eel-like fish native to the Atlantic Ocean.
In a new study published in PLoS Biology, scientists at Université de Montréal, in Quebec, and the University of Windsor, in Ontario, show that an inhibitory circuit that releases the neurotransmitter GABA into the olfactory bulb strongly modulates behavioural responses to odours in lampreys. The study of these modulatory mechanisms allowed the researchers to discover a new pathway linking together olfactory and motor centers in the brain.
This discovery demonstrates that odourscan activate locomotor centers via two distinct brain pathways,” said lead author Gheylen Daghfous, a researcher in the laboratory of UdeM neuroscience associate professor Réjean Dubuc, also a professor at Université du Québec à Montréal. “This work shed snew light on the evolution of the olfactory systems in vertebrates.”
He added: “It is well-known that animals are attracted to odors, whether it be a dog tracking its prey or a shark attracted to blood. On the other hand, we are only beginning to understand how the brain uses odors to produce behavior. Our study revealed a new brain highway dedicated to transmitting smell information to the regions controlling movements.”
Funded by the Great Lakes Fishery Commission (GLFC), with the Canadian Institutes of Health Research (CIHR) and the Natural Sciences Research Council of Canada (NSERC), the study is the result of a long-standing collaboration between Dubuc and Windsor’s Barbara Zielinski.
“Our purpose was to identify the neural circuitry linking olfaction to locomotion in lampreys,” a parasitic type of fish that attach themselves to other fish and suck their blood, leaving a gaping wound, said Dubuc. “Lampreys invaded the Great Lakes decades ago and have decimated large populations of fish, with major commercial impact. The GLFC is looking for new means to control lamprey populations, and attracting them using olfactory stimuli is one such avenue.”
Funding: Great Lakes Fishery Commission (GLFC), Canadian Institutes of Health Research (CIHR), Natural Sciences Research Council of Canada (NSERC) funded this study.
Source: Jeff Heinrich – University of Montreal
Publisher: Organized by NeuroscienceNews.com.
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Original Research: Open access research for “GABAergic modulation of olfactomotor transmission in lampreys” by Gheylen Daghfous, François Auclair, Felix Clotten, Jean-Luc Létourneau, Elias Atallah, Jean-Patrick Millette, Dominique Derjean, Richard Robitaille, Barbara S. Zielinski, and Réjean Dubuc in PLOS Biology. Published October 4 2018.
GABAergic modulation of olfactomotor transmission in lampreys
Odor-guided behaviors, including homing, predator avoidance, or food and mate searching, are ubiquitous in animals. It is only recently that the neural substrate underlying olfactomotor behaviors in vertebrates was uncovered in lampreys. It consists of a neural pathway extending from the medial part of the olfactory bulb (medOB) to locomotor control centers in the brainstem via a single relay in the caudal diencephalon. This hardwired olfactomotor pathway is present throughout life and may be responsible for the olfactory-induced motor behaviors seen at all life stages. We investigated modulatory mechanisms acting on this pathway by conducting anatomical (tract tracing and immunohistochemistry) and physiological (intracellular recordings and calcium imaging) experiments on lamprey brain preparations. We show that the GABAergic circuitry of the olfactory bulb (OB) acts as a gatekeeper of this hardwired sensorimotor pathway. We also demonstrate the presence of a novel olfactomotor pathway that originates in the non-medOB and consists of a projection to the lateral pallium (LPal) that, in turn, projects to the caudal diencephalon and to the mesencephalic locomotor region (MLR). Our results indicate that olfactory inputs can induce behavioral responses by activating brain locomotor centers via two distinct pathways that are strongly modulated by GABA in the OB. The existence of segregated olfactory subsystems in lampreys suggests that the organization of the olfactory system in functional clusters may be a common ancestral trait of vertebrates.