Hypothalamus hypothalamic neurons

The intermediate length systems include the tuberoinfundibular system, which projects from the arcuate and periventricular nuclei into the intermediate lobe of the pituitary and the median eminence. This system is responsible for the regulation of such hormones as prolactin. The inter hypothalamic neurons send projections to the dorsal and posterior hypothalamus, the lateral septal nuclei and the medullary periventricular group, which are linked to the dorsal motor nucleus of the vagus such projections may play a role in the effects of dopamine on the autonomic nervous system. 

Oxytocin (Pitocin, Syntocinon) is a cyclic 8-amino acid peptide that is synthesized in the paraventricular nucleus of the hypothalamus and transported within hypothalamic neurons (in association with neurophysin) to the posterior pituitary for storage. Its mechanism of action involves the direct stimulation of oxytocin receptors found on the myometrial cells. Oxytocin circulates unbound in the plasma, where it has a half-Ufe of approximately 15 minutes. It is primarily inactivated in the kidneys and liver. 

The hypothalamus is a small region of the brain in the ventral aspect of the diencephalon. In the adult human, it is about 2.5 cm in length and weighs about 4 g. Ventromedi-ally, it surrounds the third ventricle and is continuous with the infundibular stalk of the pituitary (hypophysis). This cone-shaped region of the hypothalamus, the median eminence, consists mainly of axonal fibers from hypothalamic neurons, which either terminate in the median eminence or continue down into the posterior lobe of the pituitary, and it is perfused by a capillary network (primary plexus) derived from the carotid arteries. Blood from the primary plexus is transported by portal vessels (hypophyseal portal vessels) to another capillary network (secondary plexus) in the anterior lobe of the pituitary (adenohypophysis) (Figure 31-1). 

The hypothalamus contains a high density of nerve cell bodies clustered into nuclei or areas. Neurons in each of these nuclei tend to send their axons to the same regions in the form of traets. These nuclei innervate the median eminence, other hypothalamic nuclei, the posterior pituitary, and various structures in the extrahy-pothalamic central nervous system. All of the hypothalamic neurons are presumably monoaminergic (i.e., they... 

There are direct olfactory projections to the hypothalamus from neurons in the deepest layers of PC that terminate most heavily in the lateral hypothalamic area. Other components of PC project to medial and anterior parts of the hypothalamus and to the thalamus (Benjamin et al., 1982 Price and Slotnick, 1983). 

The presence of endocannabinoids has been shown in the hypothalamus (Herkenham 1995) and in the anterior pituitary (Gonzales 1999). The central cannabinoid receptor (CBi receptor) is also present is these structures. The hypothalamus contains fewer cannabinoid binding sites than other areas of the CNS. Nevertheless the effects caused by the activation of CBi receptors in the hypothalamus are important, maybe because the receptors are more or less concentrated within specific hypothalamic nuclei-areas (Fig. 2). CBi receptors seem to be located on intrinsic hypothalamic neurons rather than on neurons with cell bodies located outside the hypothalamus, since hypothalamic deafferentation is not followed by any reduction in the number of cannabinoid receptor binding sites within this brain area (Romero 1998). 

When the localization of the LRF was determined by this method, activity was also localized to a basal zone of the hypothalamus but extended over a wider area. Activity was found as far rostrally as the optic chiasm and persisted as far caudally as the point of separation of the pituitary stalk from the hypothalamus. Thus neurons which synthesize LRF are still found rostral to the median eminence and arcuate nucleus in the hypothalamic region which would contain the suprachiasmatic and anterior hypothalamic nuclei. 

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