H3 receptor modulation of neuroendocrine responses to histamine and stress

Abstract

Publisher Summary This chapter discusses H 3 receptor modulation of neuroendocrine responses to histamine and stress. The neurotransmitter histamine (HA) exerts several functions in the hypothalamus including an involvement in the neuroendocrine regulation of pituitary hormone secretion. HA has no effect directly at the level of the pituitary gland, but influences the secretion of anterior pituitary hormones either by an exerted, for example, in the paraventricular nucleus (PVN) on other central transmitters or hypothalamic regulating factors, which subsequently regulate the release of anterior pituitary hormones. In addition, HA acts on the supraoptic nucleus (SON) in the hypothalamus where the posterior pituitary hormones are synthesized, and thereby exerts a direct effect on the release of the posterior pituitary hormones. Immunohistochemical studies have revealed that the histaminergic neurons, which originate in the tuberomammillary nuclei of the posterior hypothalamus, densely innervate most of the hypothalamic areas involved in the neuroendocrine control of pituitary hormone secretion. To clarify the role of HA in hormone regulation most studies have used central administration of HA either alone or in combination with the blockade of postsynaptic H 1 and H 2 receptors or the administration of compounds that affect HA synthesis or metabolism. Autoradiographic studies have revealed that H 3 receptors are located in most areas of the brain with the highest content in the basal ganglia and the cortex. H 3 receptors are distributed with moderate density in the hypothalamus where the highest density of histaminergic nerve fibers are found and have been demonstrated in the anterior, medial, and posterior hypothalamus.