Paraventricular nucleus

Two AT-II receptors, AT and AT2 are known and show wide distribution (27). The AT receptor has been cloned and predominates ia regions iavolved ia the regulation of blood pressure and water and sodium retention, eg, the aorta, Hver, adrenal cortex, and ia the CNS ia the paraventricular nucleus, area postrema, and nucleus of the soHtary tract. AT2 receptors are found primarily ia the adrenal medulla, utems, and ia the brain ia the locus coeruleus and the medial geniculate nucleus. AT receptors are GCPRs inhibiting adenylate cyclase activity and stimulating phosphoHpases C, A2, and D. AT2 receptors use phosphotyrosiae phosphatase as a transduction system. 

Apelin receptor and pqrtides are co-expressed in two nuclei of the hypothalamus, the supraopticus and paraventricular nucleus which play a major role in... 

Lesions of the lateral hypothalamic area (LHA) cause anorexia, whereas ablation of the paraventricular nucleus (PVN) cause a hyperphagic obesity syndrome. Consistent with these results, LHA neurons express the orexigenic neuropeptides MCH and orexin. PVN neurons produce several neuropeptides that are anorex-igenic when administered directly into the brain (CRH, TRH, oxytocin), in addition to their better known roles as endocrine regulators. LHA and PVN receive rich inputs from axons of NPY/AgRP and aMSH/CART-producing neurons in the arcuate nucleus. 

The paraventricular nucleus in the hypothalamus is located adjacent to the third ventricle and has been identified as a satiety center. Neurons in the paraventricular nucleus produce neuropeptides which inhibit feeding when injected into the brain (thyrotropinreleasing hormone (TRH), corticotropin-releasing hormone (CRH), oxytocin). 

Parasympathetic Nervous System Parasympatholytics Parasympathomimetics Parathyroid Hormone Paraventricular Nucleus Parkin... 

To our knowledge no smdies have examined the effects of nitrites on GABA neuro transmission. However, when NO, the major mediator of the peripheral effects of nitrites, was administered within the paraventricular nucleus, it caused an increase in GABA concentrations (Horn et al. 1994). 

Horn T, Smith PM, McLaughlin BE, et al Nitric oxide actions in paraventricular nucleus cardiovascular and neurochemical implications. Am J Physiol 266 R306— R313,1994... 

Many brain areas are innervated by neurons projecting from both the locus coeruleus and the lateral tegmental system but there are exceptions (Fig. 8.3). The frontal cortex, hippocampus and olfactory bulb seem to be innervated entirely by neurons with cell bodies in the locus coeruleus whereas most hypothalamic nuclei are innervated almost exclusively by neurons projecting from the lateral tegmental system. The paraventricular nucleus (and possibly the suprachiasmatic nucleus, also) is an exception and receives an innervation from both systems. 

Thaiamus Hypothaiamus (paraventricular nucleus) Amygdala Septum... 

Obviously, regulation of food intake depends on many neurotransmitters and hormones but this final section will outline the role played by central 5-HT transmission in this process. It had been the belief for some time that increased 5-HT transmission in the brain reduces food intake (Blundell 1977) and this certainly explains the satiety in rats that follows infusion of 5-HT into the paraventricular nucleus (PVN) of the hypothalamus. However, recent studies using microdialysis have found that 5-HT efflux in the lateral hypothalamus is itself increased by food intake, suggesting the existence of a feedback control system. In fact, because the increase in 5-HT efflux is greater in genetically obese rats than in their lean counterparts, it has been proposed that there is a deficiency in the 5-HT inhibition of food intake in obesity. 

FIGURE 41-1. Hypothalamic-pituitary-thyroid axis. Thyrotropinreleasing hormone (TRH) is synthesized in the neurons within the paraventricular nucleus of the hypothalamus. TRH is released into the hypothalamic-pituitary portal circulation and carried to the pituitary, where it activates the pituitary to synthesize and release thyrotropin (TSH). TSH activates the thyroid to stimulate the synthesis and secretion of thyroxine (T4) and triiodothyronine (T3). T4 and T3 inhibit TRH and TSH secretion, closing the feedback loop. 

Huang, H., Ghosh, P. van den Pol, A. N. (2006). Prefrontal cortex-projecting glutamatergic thalamic paraventricular nucleus excited by hypocretin a feedforward circuit that may enhance cognitive arousal. J. Neurophysiol. 95, 1656-68. 

Kalsbeek, A., Garidou, M. L., Palm, I. F. et al. (2000). Melatonin sees the light blocking GABA-ergic transmission in the paraventricular nucleus induces daytime secretion of melatonin. Eur. J. Neurosci. 12, 3146-54. 

LH), paraventricular nucleus (PVN), ARC, dorsomedial hypothalamic nucleus (DMH), anteroventral preoptic nucleus, anterior hypothalamic area, suprachias-matic nucleus (SCN), anterolateral hypothalamic nucleus, and the tuberomam-millary nucleus (TMN) (Guan et al. 1997 Mitchell et al. 2001). In rats, hypothalamic ghrelin content displays diurnal rhythmicity and increases in response to sleep deprivation and feeding restriction (Bodosi et al. 2004). 

Figure 11.2 Increases in wakefulness after intracerebroventricular (ICV) or intrahypothalamic administration of ghrelin, neuropeptide Y (NPY), and orexin-A in the first hour of the light period in rats. LH, lateral hypothalamus MPA, medial preoptic area PVN, paraventricular nucleus asterisks denote significant differences from baseline. Orexin data are extracted from Vogel et at, J. Neuroscience Methods, 2002, 118 89-96.

The sites in brain where these drugs, and presumably 5-HT as well, act to cause such effects remain to be identified. The paraventricular nucleus (PVN) of the hypothalamus may be an important site, although some data indicate that actions on the PVN maybe sufficient but not necessary to reduce caloric intake. In addition to brain mechanisms, 5-HT may also act through peripheral mechanisms to produce satiety. 

With respect to in vivo noradrenaline release, several studies report increases in response to nicotine challenge after chronic administration, consistent with a sensitised response. Sharp and co-workers demonstrated that rats self-administering nicotine in an unlimited access paradigm exhibited markedly increased levels of endogenous noradrenaline in the hypothalamic paraventricular nucleus (Fu et al. 2001) and amygdala (Fu et al. 2003). Also, in rats that received a daily nicotine injection (0.4mgkg ) for 5 days, noradrenaline release in the ventral hippocampus was enhanced in response to a subsequent nicotine challenge (Benwell and Balfour 1997). 

Fagen ZM, Mitchum R, Vezina P, McGehee DS (2007) Enhanced nicotinic receptor function and drug abuse vulnerability. J Neurosci 27 8771-8778 Fu Y, Malta SG, Brower VG, Sharp BM (2001) Norepinephrine secretion in the hypothalamic paraventricular nucleus of rats during unlimited access to self-administered nicotine an in vivo microdialysis study. J Neurosci 21 8979-8989... 

Lu J, Zhang YH, Chou TC et al 2001 Contrasting effects of ibotenate lesions of the paraventricular nucleus and subparaventricular zone on sleep-wake cycle and temperature regulation. J Neurosci 21 4864-4874... 

GC, in turn, exert a very sensitive negative feedback on the HPA system at the level of the paraventricular nucleus of the hypothalamus (PVN) and the anterior pituitary, and also at the level of the hippocampus, which projects to the bed nucleus of the stria terminalis, the latter which sends off projections to the PVN. In concert with other components of the stress hormone system, the action of corticosterone displays two modes of operation (for review see De Kloet et al. 1998). In the first proactive mode, GC maintain basal activity of the HPA system and control the sensitivity or threshold of the system s response to stress. GC promote coordination of circadian events, such as the... 

---