Subclassification of histamine receports, H3-receptor subtypes? Localization of H3 receptors in the brain

Publisher Summary Histamine is released in the brain from neurons projecting in a diffuse manner to widely divergent cerebral areas and arising from the tuberomammillary nucleus of the posterior hypothalamus. It affects target cells via the activation of three receptor subtypes that are termed H 1 , H 2 , and H 3 . Understanding the roles of a central neurotransmitter requires the identification of the neuronal populations expressing its various receptor subtypes. Detailed mappings of H 1 , H 2 and H 3 receptors have been established in the rodent brain. Recently, the cloning of H 1 and H 2 -receptor subtypes has allowed to further study via in situ hybridization the phenotype of neurons expressing these receptors. The H 3 receptor has been evidenced as an autoreceptor. Its cloning is still awaited and should clarify its molecular pharmacology, the putative existence of H 3 subtypes, and the phenotype of neurons expressing its gene transcripts.