Fetal noradrenergic transplants into amine-depleted basal forebrain nuclei restore drinking to angiotensin

6-Hydroxydopamine-induced catecholamine denervations in the organum vasculosum of the lamina terminalis and the median preoptic nucleus attenuate drinking responses to systemic angiotensin II (ANG II) injections. Transplanting catecholamines in these nuclei using fetal noradrenergic (NE) cell suspension restores ANG II-elicited thirst. These results emphasize the functional importance of NE neuronal systems in nuclei of the anteroventral third ventricle (AV3V) in mediating ANG II-induced drinking behaviors.

Aortic baroreceptor deafferentation diminishes saline-induced drinking in rats

The effect of bilateral surgical deafferentation of the baroreceptors in the aortic arch and carotid sinus on experimentally induced water intake was investigated in rats. Drinking was induced by subcutaneous administration of one of the following agents: hypertonic saline, polyethylene glycol, isoproterenol and angiotensin II, or by 18 h of water deprivation. Hypertonic saline-induced drinking was significantly attenuated after bilateral denervation of either the aortic arch plus the carotid sinus or the aortic arch alone. However, this diminished response disappeared when hypertonic saline was given in subsequent tests. The initial drinking deficit following hypertonic saline was independent of the time elapsed since the animals had undergone surgery. All other thirst challenges tested resulted in water intake that was not statistically different from sham-operated control groups. It is concluded that aortic baroreceptor deafferentation initially results in a diminished drinking response following hypertonic saline, possibly due to interruption of afferent information originating in osmosensitive areas in the aortic arch. A role of arterial baroreceptors in the regulation of non-osmotically induced water intake is not supported by the present data.

Long-term effects of lesions of the tissue surrounding the preoptic recess on paraventricular nuclei in rats

In this investigation we have observed the effects of withholding water for 5 days, the effects of long-term (5 weeks) lesions of the tissue surrounding the preoptic recess in the anteroventral third ventricle (AV3V region), and the interaction of the effects of long-term AV3V lesions and water deprivation on paraventricular nuclei. The purpose of these observations was to see if recovery of the antidiuretic response after AV3V lesions is associated with recovery of fine structural responses in these neurosecretory cells. Paraventricular neurosecretory cells of rats deprived of water for 5 days were hypertrophied in controls and in rats with AV3V lesions. Areas of cell bodies and their nuclei were increased, as were the number of Golgi stacks and electron dense (immature) neurosecretory granules. A greater percentage of nucleoli were adjacent to the nuclear envelope. Paraventricular neurons of rats with AV3V lesions also had fine structural changes characteristic of increased secretory activity, even in animals with free access to drinking water. The areas of cells and their nucleoli in coronal sections, and the number of Golgi stacks and electron-dense neurosecretory granules per cell were significantly increased in both treatment groups with AV3V lesions. There was a greater increase in the numbers of Golgi stacks and immature neurosecretory granules tended to be more numerous in water-deprived lesioned rats than in water-deprived controls. We suggest that recovery of body fluid balance in rats with chronic AV3V lesions involves enhanced secretory activity of neurosecretory cells in paraventricular nuclei, possibly stimulated via undamaged descending connections from the subfornical organ and by ascending pathways activated by cardiovascular volume receptors.

Changes in magnocellular-neurohypophyseal vasopressin following anteroventral third-ventricle (AV3V) lesions

Lesions of the brain region surrounding the anteroventral third ventricle (AV3V) have been shown to result in adipsia without a corresponding antidiuretic response or rise in plasma vasopressin levels. Electron microscopic examination of the supraoptic nucleus and neural lobe of the pituitary has shown that large stores of neurosecretory material build up in the neurohypophysis. In the present study, the increased neurosecretory material was characterized by immunocytochemistry. Vasopressin immunoreactivity was examined and compared between adipsic rats with AV3V lesions, water-deprived rats, and normal rats. Two days after surgery, sham-lesioned, water-deprived rats displayed decreased vasopressin immunostaining density compared to normal controls, and adipsic AV3V-lesioned rats displayed increased vasopressin immunoreactivity throughout the magnocellular-hypophyseal system. These results indicate that AV3V lesions interrupt neural inputs that stimulate the magnocellular system to release vasopressin in response to normal humoral stimuli.

The periventricular anteroventral third ventricle (AV3V): its relationship with the subfornical organ and neural systems involved in maintaining body fluid homeostasis

The periventricular tissue surrounding the anteroventral third ventricle (AV3V) is critically involved in the maintenance of normal body fluid balance and distribution. The present review examines the anatomical, neurochemical, and functional relationship of the AV3V with neural systems subserving body fluid homeostasis. In particular, the nature of AV3V afferents from the subfornical organ (SFO) and from brainstem noradrenergic cell groups is discussed. A model is presented proposing that specific structures within the AV3V, particularly along the ventral lamina terminalis, function to integrate information derived from blood-borne angiotensin II (via the SFO) with input arising from vascular pressure/volume receptors. The resultant of this integration is important for the generation of a normal component of thirst (i.e., drinking) associated with extracellular dehydration.

Regional depletion of central nervous system catecholamines: effects on blood pressure and drinking behavior

The purpose of the present study was to identify which catecholamine-containing neurons (norepinephrine (NE) or dopamine (DA)) and which central nervous system (CNS) region(s) innervated by them might participate in the pressor and drinking responses produced by central drug stimulation. Forebrain NE was reduced in rats by injecting 4 micrograms of 6-hydroxydopamine (6-OHDA) into the ascending noradrenergic bundles. Spinal cord NE was depleted by intracisternal injection of 50 micrograms 6-OHDA. Depletion of forebrain DA was produced by bilateral injection of 4 micrograms 6-OHDA into the substantia nigra of desipramine-pretreated rats. Pressor responses to various doses of angiotensin II (AII), carbachol or hyperosmolar NaCl injected into the lateral ventricles (LVT); and drinking responses to LVT AII and carbachol were examined. Injection of 6-OHDA into the noradrenergic bundles reduced telencephalic and hypothalamic NE by more than 80% without significantly affecting brain DA or spinal cord NE. Intracisternal 6-OHDA depleted spinal cord NE by 80% and forebrain NE by 20-25% without reducing brain DA. Injection of 6-OHDA into the substantia nigra reduced telencephalic DA by 86% and NE by 29% without significantly affecting NE in other CNS regions. Substantia nigra 6-OHDA injected animals evidenced attenuated drinking to both LVT AII and carbachol. Pressor responses to LVT AII, carbachol and hypertonic saline were largely unaffected. Almost complete depletion of brain and/or spinal cord NE failed to alter centrally mediated drinking or pressor responses. These data indicate that the integrity of brain DA neurons is required for the behavioral but not hypertensive responses produced by central drug stimulation.

Lesions of the tissue surrounding the preoptic recess (AV3V region) affect neurosecretory cells in the paraventricular nuclei in the rat

Lesions of the tissue surrounding the preoptic recess (AV3V region) have severe effects on body fluid homeostasis; these include acute adipsia and failure of the antidiuretic response. Because neurosecretory cells in supraoptic nuclei comprise the major source of antidiuretic hormone (ADH) in this species, we have previously observed the fine structure of supraoptic nuclei in rats with AV3V lesions. Paraventricular nuclei are the other major source of ADH in rats. Therefore, in this investigation we compared the fine structure of paraventricular nuclei in rats which had received AV3V lesions 3 days earlier with that of control rats which had received sham lesions and either had drinking water available or had water withheld for 3 days. Degenerating axons and axon terminals were present in paraventricular nuclei of lesioned rats. The degenerating terminals were in axodendritic and less often in axosomatic synapses. Morphometric evaluation revealed that neurosecretory cells did respond to the dehydrated state of the adipsic-lesioned animals, but the response was significantly attenuated compared to that which occurred in sham-lesioned rats deprived of water for 3 days. It appears that AV3V lesions damage afferent connections and impair the response of neurosecretory cells to dehydration in paraventricular as well as supraoptic nuclei. However, in paraventricular nuclei the response is not completely prevented by AV3V lesions during the adipsic period as was observed in supraoptic nuclei. The presence of a response in paraventricular nuclei may be at least partially stimulated by reduced body fluid volume. Information from volume receptors would be carried from the medulla to paraventricular nuclei by ascending pathways which are not affected by AV3V lesions.

Demonstration of regional blood-brain barrier permeability in human brain

The brain of a 78-year-old woman with argyria was examined at autopsy. Silver nitrate deposition was observed in circumventricular organs (CVO) and in the paraventricular and supraoptic nuclei of the hypothalamus. These findings parallel animal experiments of other investigators and are the best demonstration so far of regional absence of the blood-brain barrier in humans. These observations demonstrate similarities between humans and other mammals of CVO anatomy, permeability to blood-borne agents, and perhaps neural connections between CVOs and magnocellular nuclei.

Sympathetic nervous system mediation of acute cardiovascular actions of gamma 2-melanocyte-stimulating hormone

Peptides of the pro-opiocortin class produce pronounced cardiovascular and natriuretic actions. We have investigated the acute cardiovascular effects of one of the most potent members of this class, gamma 2-melanocyte stimulating hormone (gamma 2-MSH), in rats. Pressor actions of gamma 2-MSH administered systemically were eliminated by ganglionic blockade with chlorisondamine. Peripheral cholinergic blockade failed to affect either the pressor or cardioaccelerator responses to gamma 2-MSH. Administration of gamma 2-MSH (2.0-10.0 micrograms) produced vasoconstriction primarily in the mesenteric and hindlimb vascular beds, while the renal bed showed little response. Infusions of phenylephrine produced pressor responses similar to those found with gamma 2-MSH, which were accompanied by a decrease in heart rate and vasoconstriction in the mesenteric and renal vascular beds. Hemodynamic changes produced by gamma 2-MSH and phenylephrine were blocked or attenuated by alpha 1-adrenergic receptor blockade with prazosin. Direct injection of gamma 2-MSH into the renal artery produced an acute renal vasoconstriction that was not attenuated by alpha 1-adrenergic or ganglionic blockade. These findings and the results of previous publications are consistent with the hypothesis that gamma 2-MSH may produce a centrally mediated activation of the sympathetic nervous system, have direct vasoconstriction actions on the renal vasculature, and inhibit baroreceptor function to produce an increase in blood pressure without an accompanying bradycardia.

Interactions of vasopressin with the area postrema in arterial baroreflex function in conscious rabbits

This study compares the effect of arginine-vasopressin with phenylephrine on arterial pressure, heart rate, and renal sympathetic nerve activity in conscious rabbits with and without functional arterial baroreflexes and in rabbits with lesions of the area postrema. In intact rabbits, progressive infusions of arginine-vasopressin result in large decreases in renal sympathetic nerve activity and heart rate for a given increase in blood pressure as compared to progressive infusions of phenylephrine. In sinoaortic-denervated rabbits, the responses of arterial pressure on heart rate and renal sympathetic nerve activity to both arginine-vasopressin and phenylephrine are markedly attenuated, indicating the necessity for afferent baroreceptor activity in this response. This observation indicates that arginine-vasopressin is acting centrally to enhance the baroreflex. A central site of action of circulating vasopressin may be the area postrema, since it is the only circumventricular organ in the hindbrain. Lesioning the region of the area postrema resulted in a normalization of the responses evoked with arginine-vasopressin and phenylephrine. There was no difference in the phenylephrine responses of arterial pressure on renal sympathetic nerve activity or heart rate in area postrema-lesioned animals, compared to control rabbits. Therefore, we conclude that the area postrema or its surrounding tissue is either a site of action of circulating arginine-vasopressin or contains fibers of passage from another site where arginine-vasopressin acts to enhance baroreflex activity.

Systemic angiotensin II, blood pressure and supraoptic neuronal activity

Recordings of SON single unit activity and systemic arterial blood pressure (B.P.) were taken from 10 rats while systemic infusions of angiotensin II (AII), 1-1000 ng/kg body weight/min in 7 steps, or phenylephrine, 1-100 ng in 3 steps were administered. The relationship between AII concentrations and neuronal activity was biphasic. Within the physiological range (1 ng to 100 ng) AII excited single units in a dose dependent manner, but it had little effect on B.P. At higher concentrations, B.P. rose and neuronal activity was decreased. Phenylephrine, however, did not excite neuronal activity. With increasing phenylephrine concentrations, B.P. rose and neuronal activity slowed. We conclude that increased B.P. may dampen the SON neuronal output by baroreceptor inhibition. Under physiological conditions, therefore, AII may serve to reinforce tonic vasopressin release while inhibiting vasopressin release at pressor doses. This further suggests a role for plasma AII as an important link of the renal-hypothalamic-hormonal feedback loop.

Influence of neonatal handling on blood pressure, locomotor activity, and preweanling heart rate in spontaneously hypertensive and Wistar Kyoto rats

This experiment tested the hypothesis that increased stimulation early in development would (a) alter developmental changes in heart rate and behavioral reactivity and (b) affect the level at which blood pressure was regulated in adulthood. For this purpose, the effects of daily handling and maternal separation (3 min per day) on both behavioral and cardiovascular measures were examined in spontaneously hypertensive (SHR) and normotensive control Wistar Kyoto (WKY) rats. Prior to weaning, elevated heart rates in pups handled during the first postnatal week were most pronounced among 4-week-old prehypertensive SHR pups. Early handling affected behavior observed during open-field testing similarly in young adult rats of the SHR and WKY strains (e.g., increased locomotor activity on the first day of testing). In female rats of the WKY strain, early handling resulted in a lower baseline blood pressure; the blood pressure of SHR rats was not affected by increased stimulation in infancy. Examination of longitudinal data yielded no support for a direct association between behavioral reactivity or preweanling heart rate and high blood pressure. These findings demonstrate the influence of both early environmental conditions and genetic factors on maturation within the cardiovascular system and suggest that genetic models of pathological conditions may provide a productive means of examining environmentally shaped aspects of individual differences in physiological regulation.

The role of vasopressin and the sympathetic nervous system in the cardiovascular response to vagal cold block in the conscious dog

This study examined the role of arginine vasopressin in the pressor response to vagal cold block and evaluated a possible interaction between vasopressin and the sympathetic nervous system during vagal block in conscious dogs with (carotid sinus intact) and without (sinoaortic denervated) functional arterial baroreflexes. In both carotid sinus intact and sinoaortic denervated dogs, elimination of the arginine vasopressin pressor system by the specific vasopressin antagonist d(CH2)5Tyr(Me)AVP did not alter the response to vagal block, as evaluated by changes in arterial pressure. Subsequent removal of the sympathetic nervous system by ganglionic blockade abolished the response to vagal block. When ganglionic blockade was induced in the absence of the vasopressin antagonist, the pressor response to vagal block was reduced by only 60%. Arginine vasopressin antagonist after ganglionic blockade reduced the response to vagal block by an amount equivalent to 45% of the original increase in pressure. The effects of blockade of either vasopressin or the sympathetic nervous system on the pressor response to vagal block were significantly greater when the other system had previously been eliminated. Data suggest that both arginine vasopressin and the sympathetic nervous system contribute to the pressor response to vagal block. One interpretation of these results is that vasopressin also interacts centrally to inhibit sympathetic outflow and thus modulates the hemodynamic manifestation of interruption of vagal afferents.

Alterations in cerebrospinal fluid sodium and osmolality in rats during one-kidney, one-wrap renal hypertension

Measurements of plasma and cerebrospinal fluid (CSF) sodium and osmolality were made throughout the course of one-kidney, one-wrap Grollman renal hypertension. Although the plasma sodium and osmolality did not rise after 28 days, CSF sodium and osmolality was increased significantly at 3 days postwrap. As a result, the CSF to plasma ratio for both sodium and osmolality was significantly elevated during the initial postwrap period. These observations suggest that an increase in CSF sodium may provide an initiating stimulus for an elevated arterial pressure in one-kidney, one-wrap renal hypertension.

Fluid regulation, body weight and drinking responses following hypothalamic knife cuts

Electrolytic ablation of the periventricular tissue surrounding the anteroventral third ventricle (AV3V) alters fluid and electrolyte regulation. In addition, these lesions produce neural degeneration in the supraoptic nucleus (SON) and neural lobe, which suggests a neural pathway from the AV3V region to the SON. To determine if pathways in this brain area may mediate some of the effects which follow AV3V periventricular ablation, food and water ingestion, urine volume, and body weight, as well as drinking responses to a number of dipsogenic challenges were determined following placement of small knife cuts between the level of the organum vasculosum lamina terminalis (OVLT) and the SON. Metabolism measurements were taken daily for 7 days following either knife cuts or control operations, and again 4 weeks after surgery. Drinking responses following subcutaneous injections of angiotensin II, water deprivation, and cellular dehydration were determined at least 2 weeks after surgery. Rats with knife cuts exhibited an increase in water ingestion and urine volume, an enhanced water consumption following water deprivation and acute cellular dehydration, and did not gain weight at the same rate as control operated rats. The hyperdipsia following cellular dehydration was abolished by bilateral nephrectomy. These data indicate that a neural pathway coursing through this brain region is critical for fluid regulation and maintenance of body weight.

The effects of transverse cuts caudal to the preoptic recess on the hypothalamo-neurohypophyseal neurosecretory system

Electrolytic lesions of tissue surrounding the preoptic recess (AV3V region) appear to cause loss of stimulatory input to the supraoptic nuclei from angiotensin receptors and osmoreceptors. To investigate the pathways affected by AV3V lesions, we observed the ultrastructural effects of coronal cuts in a plane caudal to the organum vasculosum lamina terminalis upon supraoptic nuclei and neural lobes of rats. Like AV3V lesions, these cuts caused degeneration of axons and terminals in the supraoptic nuclei. Degenerating terminals lay in axodendritic synapses and in axosomatic synapses on neurosecretory cells. Unlike AV3V lesions, the cuts did not result in an appearance of decreased secretory activity in the supraoptic nuclei or decreased release of hormone from the neural lobe. On the contrary, terminals in the neural lobe tended to be depleted of neurosecretory material, and glial cell processes tended to be withdrawn from the secretory interface at the basal lamina surrounding fenestrated capillaries; both are changes which have been associated with enhanced hormone release. We suggest that inhibitory input to the supraoptic nuclei is lost as a result of these cuts.

Long term effects on the supraoptic nuclei and neural lobe produced by ablation of the tissue surrounding the preoptic recess (AV3V)

In previous investigations, lesions of the AV3V region surrounding the preoptic recess in the rat caused acute loss of the antidiuretic response to severe dehydration. Ultrastructural study of the supraoptic nuclei and neural lobes following several days of adipsia revealed a lack of response in neurosecretory cell bodies, which would normally show hypertrophy, and engorgement of axon terminals in the neural lobe with unreleased hormone, which would normally be depleted. When rats with such lesions were sustained through the acute phase, they regained their ability to concentrate their urine maximally in response to water deprivation, but their antidiuretic responses to angiotensin II or centrally injected hypertonic saline were still impaired. In this study we compared the fine structure of supraoptic nuclei and neural lobes of rats with AV3V lesions and rats with sham lesions after a recovery period of 5 weeks. We also compared responses to 5 days of water deprivation in lesioned and sham lesioned rats. Neurosecretory cell bodies in lesioned rats were smaller and contained fewer neurosecretory granulated vesicles, and axon terminals in the neural lobe contained more neurosecretory granulated vesicles compared to controls. In addition, the basal lamina surrounding fenestrated capillaries was covered to a greater degree by pituicyte processes in neural lobes of lesioned rats. Lesioned rats deprived of water for 5 days had changes in supraoptic nuclei and neural lobes which in general were qualitatively similar to those of controls. However, AV3V lesions blocked the increase in neurosecretory granulated vesicles in cell bodies in supraoptic nuclei and significantly inhibited depletion of neurosecretory granulated vesicles from axon terminals in the neural lobe of water deprived rats. We conclude that after 5 weeks of recovery the neurosecretory system had regained its ability to respond to dehydration, but the response was chronically affected by AV3V lesions.

Vasomotor projections from the anteroventral third ventricle (AV3V) region

The anteroventral third ventricle (AV3V) region is necessary for the development of a variety of models of experimental hypertension. Neuroanatomic studies have identified descending projections from this region to the mesencephalic central gray and tegmentum. This study was done to identify functionally the projections involved in cardiovascular regulation from the AV3V region to the mesencephalon. Regional hemodynamic responses to electrical stimulation of the AV3V region were compared with responses to stimulation of the rostral central gray, and these responses were compared before and after ablation of mesencephalic tissue. Stimulation of the AV3V region elicited hindquarter, vasodilation and renal and mesenteric vasoconstriction associated with a depressor response and bradycardia. These responses were partially dependent on adrenal catecholamines since adrenalectomy reduced hindquarter, mesenteric, and depressor responses. Regional hemodynamic responses to central gray stimulation were qualitatively similar and also demonstrated a partial dependence on adrenal catecholamines. After electrolyte ablation of central gray tissue, significant reductions in hindquarter, mesenteric, and depressor responses to AV3V stimulation were observed. These observations suggest that a cardiovascular control system important for the development of several models of hypertension may be dependent on neuronal projections from the rostral medial hypothalamus through the mesencephalic central gray.

Development of autonomic control of heart rate in genetically hypertensive and normotensive rats

The present study describes developmental changes in autonomic controls of heart rate in a strain of rats genetically predisposed to hypertension (spontaneously hypertensive rats or SHR) and in a normotensive strain of rats (Wistar-Kyoto rats or WKY). Rat pups were tested at 4, 8, 12, and 16 days to determine heart rate changes after selective pharmacological treatments. Specifically, freely moving pups were treated with selective beta-adrenergic and muscarinic receptor blockers (i.e., atenolol and atropine methylnitrate), using procedures designed to produce minimal pain or discomfort. The results indicated that by 4 days of age there is a substantial sympathetic acceleratory influence on heart rate. Comparison of inferred autonomic control of the heart in prehypertensive SHR and normotensive WKY pups suggested exaggeration of this early sympathetic influence among SHR pups. After 2 wk of age, however, equivalent autonomic control of heart rate was seen in SHR and WKY rats, with the higher basal heart rate of SHR rats being mediated by an increased intrinsic heart rate (i.e., heart rate after combined blockade). These findings suggest that enhanced sympathetic nervous system activity may be an early expression of the genetic predisposition to develop hypertension.

Anteroventral hypothalamus and hemorrhagic shock: cardiovascular and neuroendocrine responses

The anteroventral third ventricle (AV3V) region was shown to be a site of central integration of sympathetic pressor pathways and central pressor and vasopressin (VP) release by angiotensin II (ANG II). Since the AV3V area seems to have an important role in the regulation of the three major pressor systems, we investigated the role of the AV3V in cardiovascular recovery after hemorrhage, a known stimulus for sympathetic, ANG II, and VP release. Conscious AV3V-lesioned (n = 19) and sham-operated rats (n = 14) underwent bleeding (40% of blood volume) through an arterial line. Mean blood pressure, heart rate, and plasma ANG II, VP, and catecholamines were monitored over 24 h. The exact site of lesion was determined by microscopic examination. The mean blood pressure and heart rate of both groups of rats were not different before or after hemorrhage. Plasma catecholamines, ANG II, and VP responses were also the same as were hematocrit and water consumption 24 h after the bleeding. Despite the lack of difference between control and lesioned animals with regard to cardiovascular, humoral, and neuroendocrine responses to hypovolemia, the AV3V-lesioned rats had a significantly higher early mortality rate. These data indicate that the AV3V may be an important region in recuperation and survival after hemorrhagic shock, but through mechanisms unrelated to activation of VP, renin-ANG II, or the sympathetic nervous system.

Genetic and environmental influences on developing autonomic control of heart rate

Individual differences in cardiovascular regulation result from a dynamic interaction between genetically programmed developmental processes and extrinsic (environmental) conditions. The alterations in autonomic functioning previously identified among pups of the spontaneously hypertensive rat (SHR) strain suggest a genetic influence on autonomic development. In the present studies, an early stimulation procedure previously shown to reduce the behavioral and endocrine responsiveness of rodents in adulthood was demonstrated to alter both neural control of heart rate and regional brain catecholamine levels during the preweaning period. Pups from litters of SHR and Wistar-Kyoto (WKY) rats were handled daily during the first postnatal week. Selective pharmacological blockade with atenolol and atropine methylnitrate was used to identify autonomic controls of heart rate at 16 and 28 days of age. Combined blockade was used to estimate intrinsic heart rate. In both SHR and WKY, early handling was associated with elevated basal heart rate, elevated intrinsic heart rate, and decreased sympathetic tone. Parasympathetic influence on heart rate was elevated by early handling in WKY and decreased by handling in SHR. In addition, an increase in dorsal cortical norepinephrine concentration was produced by early handling in both strains. These data suggest that early environmental conditions can interact with the genetic predisposition for elevated blood pressure and may play a potentially important role in organizing the neural controls of cardiovascular regulation.

Identification of brainstem projections mediating hemodynamic responses to stimulation of the anteroventral third ventricle (AV3V) region

The anteroventral third ventricle (AV3V) region is necessary for the development of several models of experimental hypertension in rats. Electrical stimulation of the AV3V region produces hindlimb vasodilation, mesenteric and renal vasoconstriction and bradycardia resulting in a depressor response. The effect of selective ablation of diencephalic and mesencephalic sites upon responses to AV3V stimulation was employed earlier to functionally identify descending tracts from the AV3V region through the ventromedial hypothalamus and rostral central gray. This study was performed in a similar manner to identify more caudal projections from the AV3V region to the level of pons and medulla. The vasodilator response to AV3V stimulation was dependent upon sites in and around the nucleus tractus solitarius, although the region receiving primary baroreceptor afferent input was not part of this projection. Visceral vasoconstrictor tracts were less clearly defined suggesting that these projections traverse diffusely through the ventrolateral tegmentum. These data suggest that a topographical differentiation of descending vasomotor tracts from the AV3V region exists in the brainstem of the rat.

The subfornical organ and the integration of multiple factors in thirst

Rats with lesions centered on the ventral stalk of the subfornical organ (SFO) were used to characterize the participation of this structure in the control of drinking. It is concluded that the SFO does indeed play some minor role in the mediation of drinking following intraventricular injections of angiotensin. Further, it is shown that lesions of the SFO, but not lesions of the adjacent septal-hippocampal tissue, attenuate osmotic thirst elicited by two doses of hypertonic saline. Diminished drinking responses following water deprivation, and normal feeding responses following food deprivation, underscore the importance of the SFO for drinking behavior in general, and an expanded role for the SFO in fluid regulation is suggested. However, some incidental observations suggest that the SFO is less than an equal partner with structures in the AV3V region in the overall control of water balance.

Effect of subfornical organ ablation on the development of renal hypertension

Both the AV3V and the SFO have been shown to mediate dipsogenic and pressor responses to angiotensin. Neuroanatomical projections from the SFO to structures in the AV3V region have been associated with angiotensin effects. Since it has been shown that ablation of the AV3V region attenuates the development of experimental renal hypertension in rats, the effect of ablation of the SFO on the development of renal hypertension was examined. One kidney renal hypertension was produced by placing a figure of eight silk wrap around one kidney and removing the contralateral kidney. Rats with SFO lesions developed hypertension to a similar extent as rats with a sham lesion procedure. This study demonstrates that unlike the AV3V region the SFO is not critical for the development of non-renin dependent renal hypertension.