Ghrelin-containing neurons in the olfactory bulb send collateralized projections into medial amygdaloid and arcuate hypothalamic nuclei: neuroanatomical study
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Ghrelin, a gastrointestinal hormone, is a modulator of the sense of smell. The main source of ghrelin in the central nervous system has been mainly observed in specific populations of hypothalamic neurons. An increasing number of studies have reported ghrelin synthesis and its effect on neurons outside the hypothalamus. Ghrelin and its receptors are expressed in the olfactory bulbs and in other centres of the brain, such as the amygdala, for processing olfactory signals, pyramidal neurons of the cerebral cortex and the dorsal vagal complex of the medulla oblongata. It is known that ghrelin is involved in cognitive mechanisms and eating behaviours, in fact, its expression increases in anticipation of food intake. In order to identify the existence of centrifugal direct afferents from the main olfactory bulb to the medial amygdala and the hypothalamus arcuate nucleus, in this work we used two retrograde tracers, Dil and Fluoro Gold, and immunohistochemical procedure to visualize positive ghrelin neurons. Our paper provides neuroanatomic support for the ghrelin modulation of smell. Our results show that ghrelin neuron projections from mitral cells of bulbs can transmit olfactory information via branching connections to the amygdala and the hypothalamus. This pathway could play an important role in regulating feeding behaviour in response to odours.
KeywordsGhrelin Olfactory bulbs Retrograde tracers Immunohistochemistry Feeding behaviour Rat
This research was supported by Ministero Istruzione, Università e Ricerca (MIUR). We wish to thank the Scientific Bureau of the University of Catania for language support.
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Conflict of interest
All authors declare that they have no conflicts of interest.
All applicable international, national, and institutional guidelines for the care and use of animals were followed.
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