A hunger hormone that attenuates conditioned fear?: investigating the role of ghrelin receptor signaling in the acquisition and consolidation of fear memory
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Ghrelin has been established as a hunger hormone because of its role in weight regulation and appetite stimulation. However, recent studies have uncovered a role for ghrelin in the modulation of negative emotional states like fear, anxiety and depression. The unusually high constitutive activity of the ghrelin receptor, growth hormone secretagogue receptor type 1a (GHSR1a) and its extensive ability to dimerize with other neuromodulatory receptors highlights the complexity of ghrelin receptor signaling. This led us to examine one of the essential constituents of this signaling mechanism. We exogenously administered GHSR1a into the basolateral complex of the amygdala (BLA), a region known to regulate negative emotional states. The Pavlovian fear conditioning paradigm was used to observe and compare the fear response of rats injected with GHSR1a and GFP to the fear response in rats injected with GFP alone. Our analyses revealed a significant attenuation of aversive memory recall in rats injected with GHSR1a and GFP, which suggests that increased ghrelin receptor signaling due to an overexpression of GHSR1a in the BLA impairs the consolidation and retrieval of conditioned fear memory. While other constituents of the ghrelin signaling mechanism remain to be investigated, our study provides an initial step in establishing ghrelin as a novel biomarker for stress-induced fear disorders.