Organization of projections from the dorsomedial nucleus of the hypothalamus: A PHA-L study in the rat

Abstract

The axonal projections of the dorsomedial nucleus of the hypothalamus were investigated by using Phaseolous vulgaris-leucoagglutinin. The main conclusion of this work is that these projections are largely intrahypothalamic, with smaller components directed toward the brainstem and telencephalon. Although the intrahypothalamic pathways are very complex and intermix at various levels, we conclude that dorsomedial nucleus outputs follow three distinct ascending pathways: periventricular, coursing through the hypothalamic periventricular zone; ventral, traveling beneath the medial zone; and lateral, ascending in medial parts of the lateral hypothalamic area. Within the hypothalamus, the most densely innervated areas are the paraventricular nucleus, other dorsal regions of the periventricular zone, the preoptic suprachiasmatic nucleus, and the parastrial nucleus. Other significant terminal fields include the median preoptic, anteroventral periventricular, lateral part of the medial preoptic, and anteroventral preoptic nuclei; and the retrochiasmatic (including perisuprachiasmatic) area. Descending projections follow two pathways that also converge at various levels: a dorsal pathway in the midbrain periventricular system travels through, and primarily innervates, the periaqueductal and pontine gray, and a ventral pathway extends through ventromedial regions of the brainstem. Although sparse, fibers in the later pathway can be traced as far caudally as the nucleus of the solitary tract. The results are discussed relative to the pathways and properties of nearby hypothalamic medial zone nuclei. Dorsomedial nucleus projections are similar to certain other nuclei (e.g., anteroventral periventricular and parastrial) with predominantly intrahypothalamic projections, and different from those arising in the medial zone nuclei (medial preoptic, anterior hypothalamic, ventromedial, and mammillary.

Identification and characterization of a gonadotropin-inhibitory system in the brains of mammals

“…The DMH projects extensively to neuroendocrine and preautonomic hypothalamic regions, and to a lesser extent to extrahypothalamic sites (24). The DMH, along with five other preoptic nuclei, forms a complex interconnected network that plays a role in coordinating neuroendocrine, autonomic, and somatic responses to external stimuli, sensory feedback, and cognitive͞ motivational input (25).…”

α-Melanocyte-Stimulating Hormone Is Contained in Nerve Terminals Innervating Thyrotropin-Releasing Hormone-Synthesizing Neurons in the Hypothalamic Paraventricular Nucleus and Prevents Fasting-Induced Suppression of Prothyrotropin-Releasing Hormone Gene Expression

“…The anatomical selectivity of ␣-MSH-containing axon terminals for pro-TRH neurons in the periventricular parvocellular subdivision of the PVN and the generalized effect of ␣-MSH to increase pro-TRH gene expression in hypophysiotropic pro-TRH neurons, including medial parvocellular neurons, raise the possibility that ␣-MSH may exert both direct and indirect effects on parvocellular neurons in the PVN. Along these lines, the hypothalamic dorsomedial nucleus (DMN) has well established projections to the parvocellular PVN (Ter Horst and Luiten, 1987;Thompson et al, 1996) and contains a subpopulation of neurons that are activated by the systemic administration of leptin (Elmquist et al, 1998). In addition, the DMN is one of the main targets for both ␣-MSH-and AGRP-IR fibers (Jacobowitz and O'Donohue, 1978;Broberger et al, 1998), the latter originating exclusively from the arcuate nucleus (Broberger et al, 1998;Legradi and Lechan, 1999).…”

Distribution and regulation of galanin receptor 1 messenger RNA in the forebrain of wild type and galanin-transgenic mice

“…The hypothalamic regions where both male and female GALTGs expressed elevated levels of GALR1 compared with WT (PeN, DMN and VMN) are known to be centers of neuroendocrine integration (Bernardis and Bellinger, 1998;Rohner-Jeanrenaud, 1995;Simerly, 1998). Cells in these nuclei are richly endowed with receptors for both neuropeptides and sex steroids, and neurons in these regions send and receive projections to and from other hypothalamic areas (Gu and Simerly, 1997;Luiten and Room, 1980;Thompson et al, 1996). If galanin signaling in these nuclei were important for maintaining proper neuroendocrine function, then mitigating the impact of galanin overexpression by altering galanin receptor expression would be beneficial as an adaptive mechanism to limit potentially harmful swings in the secretion of this neuropeptide.…”