Some observations on the preference deficits produced by lateral preoptic lesions in the rat.

Conducted 4 experiments with a total of 20 female albino Sherman rats which show that, following water deprivation, Ss with lateral preoptic (LPO) damage lost the normal preference for glucose solutions. Food deprivation reinstated the preference. This dependency was specific to sweet-tasting fluids, and the deficit persisted even when thirst was alleviated prior to the preference test. Such Ss would drink sweet solutions in response to intravascular fluid depletion, but they were deficient in response to sweet solutions under nondeprived conditions. This last finding in particular suggests that hunger and palatibility, as determinants of the response to sweet solutions, may be dissociated by LPO damage. (18 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Forebrain lesions differentially affect drinking elicited by dipsogenic challenges and injections of muscimol into the median raphe nucleus.

Injections of muscimol into the median raphe nucleus (MR) elicit intense drinking in normally hydrated rats. To determine whether this response is dependent on forebrain systems mediating other aspects of water intake, the authors examined the effects of lesions of the subfornical organ (SFO), median preoptic nucleus (MnPO), lateral preoptic area (LPO), or lateral hypothalamus (LH) on the drinking. Lesions of the SFO or LH attenuated muscimol-elicited drinking, whereas lesions of the MnPO or LPO increased water intake after the treatment. All of the lesion groups showed a deficit in drinking to injections of polyethylene glycol and at least one of the doses of hypertonic saline. Only the SFO- and LH-lesioned groups showed a suppression of drinking to systemic injections of angiotensin II, suggesting that the drinking elicited by intra-MR injections of muscimol may involve changes in the central circuits mediating angiotensin-induced drinking. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cessation of drinking following intracranial injections of angiotensin in the rat.

Injection of angiotensin amide into the preoptic area is known to elicit drinking in rats that are in water balance. 2 experiments were conducted with a total of 15 male hooded rats. When Ss were injected with 10 ng. angiotensin and access to water was delayed for varying times, the dipsogenic effect of angiotensin lasted for 60-90 min. When access to water was not delayed, Ss stopped drinking after 8.5 min., indicating that the ingestion of water is satiating. When Ss were offered isotonic saline, they stopped drinking 11 min. after injection, indicating that satiation or inhibition of angiotensin-induced thirst can also occur when there are no osmotic changes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects on homeostasis of intraventricular injections of 6-hydroxydopamine in rats.

Data from a series of experiments with male albino Sprague-Dawley rats show that intraventricular injections of 6-hydroxydopamine after pretreatment with desmethylimipramine and pargyline, or pargyline alone, produced severe depletions of brain dopamine. Like Ss with lateral hypothalamic damage, these Ss became aphagic and adipsic, showed prolonged periods of anorexia before they again accepted dry chow and water, maintained relatively low body weights, no longer increased food intakes after injection of 2-deoxy-dextroglucose, and delayed drinking to thirst stimuli. However, unlike recovered laterals, they did not have marked impairments of feeding efficiency, learned taste aversions, or thermoregulation during heat stress. Results suggest that brain catecholamines play an important role in some regulatory processes, but that lateral hypothalamic lesions may not be tantamount to destruction of the dopamine-containing neurons of the nigrostriatal pathway. (4? p ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differential effects of septal, preoptic, and habenula ablations on thirst-motivated behaviors in rats.

Two experiments used a total of 59 male Sprague-Dawley rats. Bilateral septal lesions dramatically enhanced barpressing rates generated under progressive ratio schedules of reinforcement. This increased barpressing was dependent on deprivation level but independent of the type of deprivation (i.e., food or water). Equivalent effects on barpressing were observed in Ss with bilateral medial forebrain bundle lesions at the level of the lateral preoptic area. Septal lesions, medial forebrain bundle lesions, and habenula lesions did not result in a hyperreactivity to bitter quinine solutions. Hyperreactivity to quinine was observed only in Ss with medial preoptic lesions. This medial preoptic lesion also impaired operant responding for water on a progressive ratio schedule of reinforcement. It is suggested that the medial preoptic lesion produced a deficit in thirst-motivated behavior. (16 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Increased ipsilateral expression of Fos following lateral hypothalamic self-stimulation

Immunohistochemical labeling of Fos protein was used to visualize neurons activated by rewarding stimulation of the lateral hypothalamic level of the medial forebrain bundle (MFB). Following training and stabilization of performance, seven rats were allowed to self-stimulate for 1 h prior to anesthesia and perfusion. Brains were then processed for immunohistochemistry. Two control subjects were trained and tested in an identical manner except that the stimulator was disconnected during the final 1 h test. Among the structures showing a greater density of labeled neurons on the stimulated side of the brains of the experimental subjects were the septum, lateral preoptic area (LPO), medial preoptic area, bed nucleus of the stria terminalis, substantia innominata (SI), and the lateral hypothalamus (LH). Several of these structures, the LPO, SI, and LH, have been implicated in MFB self-stimulation by the results of psychophysical, electrophysiological, and lesion studies.     

Impaired drinking responses of rats with lesions of the subfornical organ.

Electrolytic lesions of the subfornical organ (SFO) in rats are known to abolish their drinking response to iv infusion of angiotensin II (AII). Such lesions also attenuate drinking after 20% polyethylene glycol solution (PEG) is given sc, which suggests that AII may play an important role in mediating thirst during hypovolemia. However, the 3 present studies show that male albino Sprague-Dawley rats (N?=?57) with SFO lesions drank normal amounts when larger plasma volume deficits were caused by 30% PEG treatment. Ss did not drink in response to relatively low doses of hypertonic saline but drank normal amounts when given larger doses. Results suggest that the SFO is involved in a control system for thirst and that after damage to it, greater stimulation than usual may be required for drinking to be initiated. From this perspective, drinking would be expected following either suprathreshold stimulation or drug-induced lowering of the activation threshold in these animals, as was observed, with the loss of putative AII receptors in the SFO also contributing to their particularly severe deficits in thirst induced by AII. (37 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Anteroventral third ventricle site of action for angiotensin induced thirst

The central site of action for angiotensin induced thirst was investigated in rats. Subfornical organ lesions resulted in a temporary abolition of drinking induced by lateral preoptic or lateral ventricle microinjections of angiotensin but drinking to anteroventral third ventricle microinjections of angiotensin (or carbachol) was unaffected. Drinking to elevated systemic levels of angiotensin was attenuated but not abolished by subfornical organ lesions. When spread of injected angiotensin via cerebrospinal fluid circulation was controlled by placing plugs at selected locations in the ventricles, drinking was elicited only when intracranial microinjections of angiotensin gained access to anteroventral third ventricle. It was concluded that subfornical organ is not the exclusive dipsogenic receptor for angiotensin, rather angiotensin exerts at least part of its dipsogenic effect by spread through the ventricular system to receptors in the vicinity of the anteroventral third ventricle.     

Osmosensitive neurons in the rat's preoptic area: Medial-lateral comparison.

Conducted an experiment with 17 Charles River Long-Evans hooded rats in which, for the 1st time, brain-recording data were brought to bear directly on the question of a critical osmosensitive zone in the lateral preoptic area as specifically delimited in the rat by E. M. Blass and A. N. Epstein (see record 1972-02252-001) and in the rabbit by J. W. Peck and D. Novin (see record 1971-07490-001). The present data clearly show that this critical zone in the lateral preoptic area of the rat contains cells that are osmosensitive. Simultaneous recording from cell populations (a) inside the critical zone and (b) in a zone medial to it showed that the net acceleratory response to challenge for the former was much greater than it was for the latter. Findings constitute new evidence for the critical importance of the lateral preoptic area in cellular dehydration thirst. (47 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Drinking by rats after lateral hypothalamic lesions: A new look at the lateral hypothalamic syndrome.

Rats that have recovered from aphagia and adipsia following lateral hypothalamic lesions are believed to be incapable of experiencing thirst and drink water simply to facilitate the consumption of dry food. However, the present results from adult Sprague-Dawley albino rats indicate that these Ss will drink in response to dehydration of the intracellular or intravascular fluid compartments and to hyperangiotensinemia, if testing continues beyond a few hours. Comparable effects also were obtained in Ss with mesencephalic brain damage, which appeared to destroy portions of the substantia nigra and the ascending nigrostriatal dopaminergic projections. These findings, when placed in the context of a recent neurochemical model for recovery of function, suggest a new interpretation of the lateral hypothalamic syndrome. (2 p ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Diminished salt appetite in spontaneously hypertensive rats following local administration of the angiotensin II antagonist saralasin in the median preoptic area

Previous studies have suggested that angiotensin (ANG) synthesis, receptor activation, or both, in the median preoptic nucleus (MnPO) are responsible for initiating ANG-related salt appetite in normotensive rats. The present study was designed to test whether treatment with saralasin (Sar), an ANG II antagonist, in the MnPO area causes changes in saline (0.3 M NaCl solution) and water intakes in the spontaneously hypertensive rat (SHR), which is known to show greater salt appetite compared to normotensive Wistar-Kyoto (WKY) rats. Treatment with Sar in the MnPO area produced significantly attenuated saline intake, but had no effect on water intake. The results may support the importance of the ANG system in the MnPO area for salt appetite, and suggest that a disorder in the system may cause abnormal salt intake in SHR.     

Axon-sparing lesions of the preoptic region and substantia innominata disrupt maternal behavior in rats.

In this study we investigated the effects of axon-sparing lesions of the preoptic region on the maternal behavior of postpartum rats. The lesions were produced with the excitotoxic amino acid N-methyl-{d},{l}-aspartic acid (NMA). The first experiment determined that bilateral injections of NMA into the medial preoptic area (MPOA) of fully maternal lactating rats disrupted maternal behavior. In a second experiment, bilateral injections of NMA into the lateral preoptic area and adjoining substantia innominata (LP/SI region) also disrupted maternal behavior. A third experiment, employing horseradish peroxidase histochemistry, provided anatomical evidence that NMA destroys neuronal cell bodies while sparing fibers of passage. These findings were discussed with respect to the view that an MPOA-to-LP/SI-to-ventral tegmental area circuit underlies maternal behavior in the rat. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Subfornical organ participates in salt appetite.

The effects of subfornical organ (SFO) lesions on salt and water intakes after sodium depletion were studied. Water and salt intakes were measured over 45 hr during a regimen that combined furosemide diuresis and access to low-sodium diet. Water was solely available for 23 hr after diuresis, and water and 0.3 M NaCl solution were available in choice for the next 22 hr. After diuresis, rats with SFO lesions drank significantly less water in 2 hr than controls but achieved equivalent water and sodium balances before salt access 20 hr later. After salt access, rats with SFO lesions drank significantly less saline and water in 2 hr than controls but had similar saline and water intakes over the next 20 hr. Thus, SFO lesions blunted acutely, but not chronically, saline and water intakes to sodium depletion, and the blunted intakes are not explainable by hydrational status. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of sequential preoptic and mammillary lesions on male rat sexual behavior.

Observed the sexual behavior of 52 male Sprague-Dawley rats prior to and following bilateral medial preoptic, unilateral medial preoptic, bilateral posterior preoptic, bilateral mammillary, and sham lesions. Bilateral medial preoptic lesions and mammillary lesions were made either simultaneously or sequentially within the same Ss in separate groups. Mammillary lesions had no effect on sexual behavior. Complete destruction of the medial preoptic area made prior to, simultaneous with, and following mammillary lesions completely abolished mating behavior. Partial destruction of the medial preoptic area increased mount and intromission latencies and slightly increased ejaculation latency. Results suggest that since there was no change in the postejaculatory-refractory interval, the medial preoptic area mediates sexual arousal but apparently is not involved in a copulatory-ejaculatory mechanism. (32 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of unilateral hypothalamic manipulations on the sexual behaviors of rats.

Four experiments that assessed the contributions of each side of the hypothalamus to the control of sexual behavior found the following: (1) Exposing the left, but not the right, ventromedial nucleus to estrogen neonatally defeminized sexual behavior in female rats. This asymmetry did not reverse as sexual differentiation progressed. (2) Unilateral cuts lateral to the medial preoptic area disrupted mounting in females that had mounted regularly before surgery, when given testosterone. The deficits were greater when the cuts were on the left side, but a third of the females with unilateral cuts showed severe deficits regardless of the side. (3) Comparable cuts did not impair masculine sexual behavior in gonadally intact males. In fact, left-side cuts seemed to accelerate copulation in males. (4) Unilateral lesions of the ventromedial nucleus disrupted lordosis in female rats in an essentially all-or-none fashion. This effect did not vary with side. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of lesions in the basolateral amygdala on fluid intake in the rat.

Conducted 6 experiments with 33 rats with bilateral lesions in the lateral amygdaloid region and 22 intact controls. Drinking response to hypertonic saline, a cellular thirst stimulus, and to isoproterenol, probably an extracellular thirst stimulus, was normal in lesioned Ss. The overnight water intake of the lesioned Ss was a little higher than normal. However, the lesioned Ss showed a major impairment in learning to avoid ingesting a poisonous solution of LiCl when they were thirsty and an increased preference of 25% sucrose in a 2-bottle sucrose-water test. It is concluded that the basolateral region of the amygdala is involved in the effects of previous experience on drinking and not primarily in the cellular or extracellular controls of drinking. (25 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Motivational and neuroanatomical specificity of hypodipsia for aversive solutions produced by medial preoptic injury to the rat.

In an experiment with a total of 28 Sprague-Dawley rats, bilateral medial preoptic lesions dramatically lowered the rejection threshold for quinine-adulterated water but not for food in 24-hr forced-choice tests. The detection threshold for quinine in a 2-bottle choice test, however, was unaffected by the medial preoptic lesion. Bilateral septal and lateral preoptic lesions had no effect on any quinine adulteration tests. The enhanced rejection of quinine-adulterated water in a forced-choice test by medial-preoptic-damaged Ss was also observed after 24 hrs of water deprivation. The plasma osmolality of medial preoptic Ss was significantly elevated above controls after 24 hrs of water deprivation. Findings suggest that a medial preoptic lesion produces a deficit in thirst-motivated behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Studies on the role of the preoptic area in the control of reproductive function in the rat

The present study was designed to determine the effects of bilateral lesions restricted to the medial preoptic area on reproductive function in rats. Adult female rats were placed in a stereotaxic instrument, and bilateral lesions were made in the medial preoptic area of the diencephalon using an anodic current and platinum or stainless steel electrodes. Both types of lesions produced identical effects. Most animals with lesions restricted to the medial preoptic area showed repeated periods of pseudopregnancy for the duration of their lives. Ova were detected in the oviducts on the day of estrus between pseudopregnancies, and deciduomata could be produced by uterine traumatization during pseudopregnancy. Daily administration of lergotrile mesylate, a dopamine agonist, for about two weeks, to the pseudopregnant rats with lesions resulted in the appearance of normal 4 or 5-day estrous cycles. These results suggest that the medial preoptic area may not be necessary for ovulation in the rat, and that the normal function of the preoptic area in the control of reproductive cyclicity may be mediated via dopaminergic neurons. In agreement with earlier studies, we found that lesions that extended into the anterior hypothalamus resulted in constant estrus.     

Thirst and sodium appetite after colloid treatment in rats with septal lesions.

Previous experiments in which angiotensin II (AII) and mineralocorticoids were administered to rats have suggested that these hormones play a natural role in mediating thirst and sodium appetite. This hypothesis was examined by making use of 20 male Sprague-Dawley rats with septal lesions, which have an apparent sensitivity to the central effects of AII, and by studying their behavioral response to sc treatment with 5 ml of a 30% polyethylene glycol solution, which produces hypovolemia and thereby stimulates the secretions of renin and aldosterone. The induced thirst and sodium appetite both were markedly enhanced in the brain-damaged Ss. However, water intake was not increased when the hypovolemia was moderate, and sodium appetite was augmented only when Ss had been sodium deprived, a procedure known to potentiate aldosterone secretion. Findings support suggestions that while AII normally contributes little to thirst, it may help to mediate sodium appetite in rats when aldosterone is abundant. The 2 drives were not elicited uniformly; those Ss that drank the most water after colloid treatment consumed the least saline. While septal lesions may sensitize the rat's brain to the sodium-appetite-eliciting effects of AII as well as to its dipsogenic effects, sodium appetite may emerge only if the induced thirst is not too pronounced. (16 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Water and NaCl intake after furosemide treatment in sheep (Ovis aires).

Iv infusions of the natriuretic drug furosemide in sheep led to the excretion of large quantities of hypotonic urine. Ss consumed more water than was needed simply to restore osmotic equilibrium. The stimulus for the additional intake was presumably hypovolemia resulting from the loss of sodium in urine. Despite the natriuresis, in only 2 of the 15 experiments did sheep drink significant amounts of .5 M NaCl solution during the first 10 hrs after the onset of furosemide treatment, and hemoconcentration and arterial hypotension were evident during this time. By 24 hrs, however, the saline consumption in all but 3 experiments had increased and compensated adequately (together with the water intakes) for the furosemide-induced loss of sodium-rich fluid in urine. Results provide evidence that following acute hypovolemia in sheep, as in rats, the onset of sodium appetite is delayed relative to the appearance of thirst. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)