Hypothalamus Posterior area

The result of this anatomical characteristic of endothelial cells in the CNS is an increased resistance to water-soluble and ionized drugs entering the brain, and cerebrospinal fluid (CSF), from capillary blood. However, in a few areas of the brain the barrier is absent. These areas include the lateral nuclei of the hypothalamus, the area postrema of the fourth ventricle, the pineal body, and the posterior lobe of the hypophysis. Highly lipophilic compounds can cross the barrier. Tranquilizers such as diazepam and its analogs are known to gain access rapidly to the CSF with a half-life (tm) entry time of less than 1 minute. 

The location of the thyrotropic center within the anterior hypothalamus varies depending upon the animal. In dog and hamster, the anterior portion. of the median eminence must be in the injured area to inhibit TSH secretion. In guinea pigs, the lesion must include the paraventricular nuclei, and in rat it must include regions of anterior hypothalamus posterior and ventral to the paraventricular nuclei. 

Although mast cells and basophils probably account for >90% of stored histamine in the body, histamine is also present in platelets, enterochromaffin-like cells, endothelial cells, and neurons. Histamine can act as a neurotransmitter in the brain. Histaminergic nerves have their cell bodies within a very small area of the brain (the magnocellular nuclei of the posterior hypothalamus) but have axons in most areas of the forebrain. There is also evidence for axons projecting into the spinal (Fig. 1) cord. Finally, there is evidence that histamine synthesis can be induced in tissues undergoing rapid tissue growth and repair. In certain neonatal tissues (e.g. liver), the rate of synthesis of this unstored diffusable histamine (termed nascent histamine) is profound and may point to a role for histamine is cell proliferation. 

Figure 2.1 Schematic of the rat brain (sagittal section) showing the approximate location of important brain structures controlling wakefulness and REM sleep. Abbreviations AH, anterior hypothalamus BF, basal forebrain DL pons, dorsolateral pons (rapid eye movement sleep control area) M-RA, Magoun/Rhines inhibitory area in the ventral medulla PH, posterior hypothalamus.

Ferraro, L., Antonelh, T., TanganeUr, S. et al. (1999). The vigilance promoting drug modafinil increases extracellular glutamate levels in the medial preoptic area and the posterior hypothalamus of the conscious rat prevention by local GABAA receptor blockade. Neuropsychopharmacology 20, 346-56. 

Hypothalamus medial and lateral preoptic areas anterior, lateral, and posterior hypothalamic areas dorsomedial and ventromedial nuclei tuberomammillary nucleus medial and lateral preoptic areas, lateral hypothalamic area, dorsomedial nucleus, complex of mammillary bodies... 

Fig. 35.1 Simplified diagram of chemosensory circuit in amygdala. Vomeronasal input via accessory olfactory bulb (VNO/ AOB) is analyzed in anterior and posterior medial amygdala (MeA, MeP). MeP appears to be inhibited by intercalated nucleus (ICNc) for heterospecific and artificial stimuli. MOE/ MOB Main olfactory epithelium/Main olfactory bulb. ACN Anterior Cortical Nucleus. PC Piriform Cortex. BLA Basolateral amygdala. ICNr rostral part of medial intercalated nucleus. ICNc caudal part of ICN. MPOA Medial Preoptic Area. VMH Ventro-medial hypothalamus...

The neurotransmitter histamine (HA) exerts several functions in the hypothalamus [1-2] including an involvement in the neuroendocrine regulation of pituitary hormone secretion [3]. HA has no effect directly at the level of the pituitary gland, but influences the secretion of anterior pituitary hormones either by an exerted e.g. 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 [4-5]. Within the last two decades the effect of HA on pituitary hormone secretion have been explored in several studies and it has been... 

Autoradiographic studies have revealed that H3 receptors are located in most areas of the brain with the highest content in the basal ganglia and the cortex [9]. H3 receptors are distributed with moderate density in the hypothalamus, where the highest density of histaminergic nerve fibers are found [4-5], and were demonstrated in the anterior, medial and posterior hypothalamus [8]. However, their localization in hypothalamic areas primarily involved in the regulation of pituitary hormone secretion were not studied in detail. In the pituitary gland the H3 receptors were scarce. 

Structures implicated in the production of wakefulness and/or cortical arousal include the ventral medullary reticular formation, oral pontine reticular formation, midbrain reticular formation, posterior hypothalamus, subthalamus, certain areas of the basal forebrain, and the cortical mantle. None of these brain areas are individually necessary for the production or maintenance of wakefulness or arousal. Normal or near-normal wakefulness-arousal results when lesions are produced gradually or when sufficient time is allowed for recovery. 

There is evidence that the histaminergic tract that passes from the posterior hypothalamus to the cortex via the thalamus is inhibited by a GABAergic pathway. It is now known that H3 receptors act as autoreceptors on histaminergic neurons and that agonists of H3 receptors augment slow-wave sleep. In addition, histamine can increase cortical arousal by enhancing excitatory cholinergic neurons from the basal forebrain and also inhibits the hypothalamic pre-optic area which normally promotes sleep. With respect to the control of the circadian rhythm, histamine has... 

Other structures in this area make up the limbic system which is directly linked to the olfactory system. Areas called the septal nuclei and amygdala contain regions often called the pleasure centres, with the hippocampus concerned with motivational memory. Projections from the cerebral cortex connect with the thalamus, hypothalamus and posterior pituitary gland. The network of connections between all these different areas of the brain is highly complex. The role of the limbic system is significant in autonomic (involuntary or non-conscious) reactions that are implicated with emotional responses including fear, rage and motivation. 

Fig. 1. Location of dopaminergic perikarya (Au-A15) are depicted schematically on frontal sections (B-F) through the diencephalon of the rat. Section A is a sagittal view of the rat brain depicting the rostrocaudal location of frontal sections B-F. Abbreviations AH, anterior hypothalamus ARC, arcuate nucleus BST, bed nucleus of the stria terminalis f, fornix ic, internal capsule inf, infundibulum me, median eminence mt, mamillothalamic tract OC, optic chiasm ot, optic tract PH, posterior hypothalamus PIT, pituitary gland PeV, periventricular nucleus PVN, paraventricular nucleus RCH, retrochiasmatic area SON, supraoptic nucleus VMN, ventromedial nucleus ZI, zona incerta.

Urinary excretion of water is regulated by ADH /vasopressin, produced in the hypothalamus and released from the posterior pituitary gland. ADH acts on the distal nephron to make this area water-permeable and to allow reabsorption of water. In the absence of ADH the distal nephron is impermeable to water and dilute urine is produced. 

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... 

Schematic diagram of the gustatory pathway in rodents. Taste receptor cells are innervated by one of three cranial nerves (VII, IX, or X), which project topographically into the rostral portion of nucleus of the solitary tract (NST). Cells within the NST send projections into the reticular formation (RF), through which connections are made to oral motor nuclei V, VII, and XII and the nucleus ambiguous (NA). Ascending fibers connect to the parabrachial nuclei (PbN) of the pons, from which two parallel pathways emerge. One pathway carries taste information to the insular cortex (IC) via the ventral posterior medial nucleus, parvicellularis (VPMpc), of the thalamus. The other pathway projects into areas of the limbic forebrain involved in food and water regulation, reinforcement, reward, and stress, including the lateral hypothalamus (LH), the central nucleus ofthe amygdala (CeA), and the bed nucleus of the stria terminalis (BST). These areas and the IC are interconnected and send descending projections back to both the PbN and NST...

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