Ghrelin-containing neurons in the olfactory bulb send collateralized projections into medial amygdaloid and arcuate hypothalamic nuclei: neuroanatomical study
- 272 Downloads
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.
Compliance with ethical standards
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.
- Bader A, Klein B, Breer H, Strotmann J (2012) Connectivity from OR37 expressing olfactory sensory neurons to distinct cell types in the hypothalamus. Front Neural Circuits 16:6–84Google Scholar
- Cádiz-Moretti B, Abellán-Álvaro M, Pardo-Bellver C, Martínez-García F, Lanuza E (2016) Afferent and efferent connections of the cortex-amygdala transition zone in mice. Front Neuroanat 23:10–125Google Scholar
- Carlini VP, Varas MM, Cragnolini AB, Schiöth HB, Scimonelli TN, de Barioglio SR (2004) Differential role of the hippocampus, amygdala, and dorsal raphe nucleus in regulating feeding, memory, and anxiety-like behavioral responses to ghrelin. Biochem Biophys Res Commun 313:635–641CrossRefPubMedGoogle Scholar
- Gascuel J, Lemoine A, Rigault C, Datiche F, Benani A, Penicaud L, Lopez-Mascaraque L (2012) Hypothalamus-olfactory system crosstalk: orexin A immunostaining in mice. Front Neuroanat 8:6–44Google Scholar
- Paxinos G, Watson C (1998) The rat brain in stereotaxic coordinates. Academic Press, SydneyGoogle Scholar
- Savigner A, Duchamp-Viret P, Grosmaitre X, Chaput M, Garcia S, Ma M, Palouzier-Paulignan B (2009) Modulation of spontaneous and odorant-evoked activity of rat olfactory sensory neurons by two anorectic peptides, insulin and leptin. J Neurophysiol 101:2898–2906CrossRefPubMedPubMedCentralGoogle Scholar
- Tong J, Mannea E, Aime P, Pfluger PT, Yi C, Castaneda TR, Davis HW, Ren X, Pixley S, Benoit S, Julliard K, Woods SC, Horvath TL, Sleeman MM, D’Alessio D, Obici S, Frank R, Tschöp MH (2011) Ghrelin enhances olfactory sensitivity and exploratory sniffing in rodents and humans. J Neurosci 31(15):5841–5846CrossRefPubMedPubMedCentralGoogle Scholar