Regional expression of the histamine H-2 receptor in adult and developing rat brain

Histamine H-2 receptor expression was studied in adult and developing rat b rain. Northern blot and in situ hybridizations indicated that histamine H-2 receptor messenger RNA expression is widespread and not limited to neurons in the adult rat brain. Prominent H-2 receptor expression in the adult bra in was seen in the dentate gyrus, hippocampal subfields CA1-CA3, piriform c ortex and in some diencephalic nuclei, e.g. in the suprachiasmatic nucleus and the red nucleus. Most of the adult brain nuclei displayed a very low H- 2 receptor expression. Histamine H-2 receptor was also expressed during dev elopment in widespread areas of the central nervous system, coinciding with the transient production of histamine in the raphe neurons at embryonic da y 15. From embryonic days 16 and 17 until birth, histamine H-2 receptor exp ression in the cortical plate coincided with the development and sprouting of histaminergic fibers into the cerebral cortex. The widespread and diffuse expression of histamine H-2 receptors in the adu lt rat brain suggests that the H-2 receptor modulates the excitability of n euron and astrocyte functions in many brain areas rather than mediating tar geted cell-to-cell signals. During development, histamine Hz receptor expre ssion is seen in several target areas for the histaminergic fibers. This co uld indicate that histamine, through the H-2 receptor, regulates fetal deve lopment of the brain. (C) 2001 IBRO. Published by Elsevier Science Ltd. All rights reserved.