Co-localization of NK1-receptor mRNA with glutamate immunopositivity in cat hypothalamic neurons by the combination of in situ hybridization and immunohistochemistry

Abstract

Previous studies had demonstrated that, in the cat, aggression is mediated by glutamatergic neurons in the anterior medial hypothalamus which project to the periaqueductal gray. Additionally, NK1 receptor activation in the medial hypothalamus plays a role in the regulation of aggressive behavior by the medial amygdala. In the present study, in situ hybridization and immunohistochemistry were combined in order to provide neurochemical characterization of medial hypothalamic neurons containing NK1-receptor mRNA. In order to identify NK1 receptors in cat brain, a 650-bp fragment of the cat NK1 cDNA was cloned. This fragment was used to synthesize a riboprobe for in situ hybridization. Partial DNA sequence analysis of the fragment indicated a 90% homology with human cDNA. In situ hybridization revealed the presence of NK1-receptor mRNA in cat hypothalamic neurons. Tissue used to localize NK1 receptors was also processed for glutamate immunopositivity. The results demonstrated that NK1-receptor mRNA is present in glutamate-immunopositive neurons in the anterior medial hypothalamus of cat, thus reinforcing the hypothesis that NK1 receptors play an important role in this neural circuit.