Role of preoperative experience on reaction to quinine taste in hypothalamic hyperphagic rats.

In a study with female Holtzman albino rats, the commonly reported overreactivity to quinine-adulterated water in hyperphagic rats was observed only in those Ss which had no preoperative adaptation to quinine-adulterated water. Those Ss with preoperative adaptation to quinine-adulterated water drank as much as control Ss. Findings suggest that reactivity to taste in hyperphagic rats is dependent on training and testing conditions rather than motivational deficit. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of preoperative training on food-motivated behavior of hypothalamic hyperphagic rats.

Conducted an experiment in which 35 female Holtzman albino rats with lesions in the ventromedial hypothalamic area performed significantly more poorly than 18 normal controls on a food-motivated task. This result was obtained, however, only if Ss were not preoperatively trained on the task. Ss trained preoperatively did not show any deficit and their performance was comparable to that of normal Ss. Findings suggest that the performance of hypothalamic hyperphagic rats on appetitively motivated tasks is a function of training and testing conditions rather than lower food motivation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Thiamin deprivation in ventromedial hypothalamic hyperphagic rats: Anorexia, specificity of food aversion, and a dietary consideration.

In 3 studies, the anorexic consequence of thiamine deprivation was investigated in ventromedial hypothalamic (VMH) hyperphagic CD male rats under either high-fat or low-fat (HF and LF, respectively) thiamine-free diet conditions. The LF diet maintained feeding significantly longer in thiamine-deprived VMH Ss than in intact Ss, whereas the HF diet sustained feeding in thiamine-deficient intact Ss and accelerated anorexia onset in vitamin-B1-deprived VMH Ss. This effect was noted under both ad lib and pair-feeding conditions. Thiamine-deprived VMH Ss subjected to weight control developed anorexia sooner than intact Ss regardless of the diet employed. The VMH Ss fed an HF diet failed to resume feeding after thiamine readministration, which is interpreted as a permanent aversion to this diet. The relation between dietary intake and conditioned taste aversion is discussed with reference to the VMH and intact rats. (28 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Food motivation and body weight levels in hypothalamic hyperphagic rats: A dual lipostat model of hunger and appetite.

Compared the food and water motivations of 26 normal and 29 hyperphagic female Carworth CFE rats using barpressing performance on continuous reinforcement, VI, and fixed-ratio schedules. Under conditions of food or water deprivation, hyperphagic Ss displayed normal barpressing rates for food or water when their body weights were limited to preoperative or control levels but subnormal barpressing rates when they were tested at obese body-weight levels. Under nondeprived conditions, dynamic hyperphagic Ss barpressed more than controls for a palatable milk diet, while obese hyperphagic Ss worked at control levels for this diet. The findings suggest a dual lipostat model of hunger and appetite to explain feeding and body weight regulations in normal and hypothalamic hyperphagic animals. (62 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Active regulation to be lean by rats with ventromedial hypothalamic lesions.

52 adult female Long-Evans rats with electrolytic or radio-frequency thermocoagulatory lesions of the ventromedial hypothalamus (VMH) lived on pellet fragments or powdered chow containing as much as 1.2% quinine sulfate or lived in Skinner boxes with 45-mg pellets delivered contingent on FRs of leverpressing up to FR 128. Body weights maintained by VMH Ss were determined by the percentage of quinine in or the contingency of reinforcement of the food on which they lived. Even when Ss lived on highly adulterated or response-contingent food and were lean, they ate more of that food when the ambient temperature was reduced and less of that food during several weeks of forced feeding of eggnog. Weight maintenance in the cold and caloric compensation during forced feeding were as precise for VMH Ss eating highly adulterated chow or Noyes pellets contingent on high FRs as for VMH Ss eating laboratory chow ad lib, even though the former Ss at the time maintained weights no greater than intact Ss and the latter Ss were grossly obese. Regulation in the cold or during forced feeding was only a little less precise for Ss with lesions than for intact Ss. It may be as characteristic of VMH Ss that they eat to become lean and remain lean as that they eat to be obese. (36 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)     

Consumption of a high dietary dose of monosodium glutamate fails to affect extracellular glutamate levels in the hypothalamic arcuate nucleus of adult rats

We examined the effects of systemic or oral ad libitum monosodium glutamate (MSG) administration on glutamate levels in plasma, and on glutamate release from the arcuate nucleus of the hypothalamus (estimated using brain microdialysis). Systemic MSG administration (0.25, 0.5, 1 or 2 g/kg, i.p.) to adult rats caused dose-dependent increases in glutamate levels within arcuate nucleus dialysates. These levels increased during the initial 20 min after systemic MSG administration, and peaked during the second 20-min interval (maximally to 116 +/- 7%, 146 +/- 15%, 790 +/- 191% and 1230 +/- 676% of basal values, respectively). Plasma glutamate levels, measured simultaneously, were increased maximally during the initial 20 min after MSG administration. These increases were 10-, 13-, 76- and 163-fold after doses of 0.25, 0.5, 1 and 2 g/kg, i.p., respectively. In feeding experiments, consumption of 2.3 g/kg of MSG by previously-trained rats during an 1-h period increased plasma glutamate levels to 352 +/- 61% of basal values 140 min after the start of the feeding period. No changes were observed in glutamate levels of arcuate nucleus dialysates. These findings may explain why ad libitum dietary consumption of MSG apparently lacks neurotoxic potential.     

Failure of recovered lateral hypothalamic rats to learn specific food aversions.

Assigned 16 female Sprague-Dawley albino rats to either a group receiving lesions of the lateral hypothalamus, a group receiving lesions of the ventromedial nuclei of the hypothalamus, or a control group. After lesioned Ss recovered the ability to feed voluntarily, Ss were exposed to a procedure in which intake of a preferred diet was followed by LiCl poisoning. Whereas unoperated controls decreased subsequent intake of this diet and showed an aversion to it on a later preference test, most lesioned Ss showed little or no sign of having learned to avoid the poison-paired food. There was evidence, however, that the ability of brain-damaged Ss to learn this avoidance recovers over time. In Exp. II, intake of another preferred diet was accompanied by shock to the tongue. Again, lesioned Ss, unlike unoperated controls, appeared unable to associate ingestion of the diet with its aversive consequences. (35 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Adrenocortical response to hypertonic saline in rats with lateral hypothalamic lesions.

Used plasma corticosterone levels to assess the response to stress induced by ip injections of hypertonic saline in 27 male albino Harlan-Sprague rats with lateral hypothalamic (LH) or sham lesions. Ss with LH lesions displayed a corticosterone response equal to that of normal Ss under basal conditions, after control injections of isotonic saline, and 20 min after injection of hypertonic saline (1.5 M, 1.0 ml/100 g of body weight). The corticosterone response of Ss with LH lesions, however, was significantly less than that of normal Ss 90 min after injection of hypertonic saline when no water was available. With access to water, normal Ss displayed substantial drinking (14.5 ml/90 min), which resulted in a reduction in plasma corticosterone concentrations to a level observed after a control injection of isotonic saline, but the little water ingested by Ss with LH lesions (2.5 ml) had no effect on the pituitary-adrenal system. It is concluded that the failure of Ss with LH lesions to drink following a hydrational challenge is not the result of an exaggerated response to stress. (17 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The FIS protein fails to block the binding of DnaA protein to oriC, the Escherichia coli chromosomal origin

The Escherichia coli chromosomal origin contains several bindings sites for factor for inversion stimulation (FIS), a protein originally identified to be required for DNA inversion by the Hin and Gin recombinases. The primary FIS binding site is close to two central DnaA boxes that are bound by DnaA protein to initiate chromosomal replication. Because of the close proximity of this FIS site to the two DnaA boxes, we performed in situ footprinting with 1, 10-phenanthroline-copper of complexes formed with FIS and DnaA protein that were separated by native gel electrophoresis. These studies show that the binding of FIS to the primary FIS site did not block the binding of DnaA protein to DnaA boxes R2 and R3. Also, FIS appeared to be bound more stably to oriC than DnaA protein, as deduced by its reduced rate of dissociation from a restriction fragment containing oriC . Under conditions in which FIS was stably bound to the primary FIS site, it did not inhibit oriC plasmid replication in reconstituted replication systems. Inhibition, observed only at high levels of FIS, was due to absorption by FIS binding of the negative superhelicity of the oriC plasmid that is essential for the initiation process.     

Adrenal axis activation by chronic social stress fails to inhibit gonadal function in male rats

Stress in males via the hypothalamic-pituitary-adrenal (HPA) axis may set into motion varied physiological alterations, including dysfunction of the hypothalamic-pituitary-gonadal (HPG) axis. However, the influence of the HPA on the HPG axis may not always be inhibitory. Presence or absence of stimuli of sexual significance that typically activates the HPG axis may alter the influence of the adrenal axis on gonadal axes. In this project, we used male rats and chronic social stimulation that included brief or extended periods with female rats to examine HPA-HPG axes interactions. In experiment 1, we used intact males and a 'chronic social stress' paradigm developed in our previous research that induces social instability by daily changing the membership of group-housed males with females. Thymus weight was reduced and corticosterone levels were marginally increased by chronic social stress, indicating a HPA axis hyperactivity. The HPG axis was also activated as shown by the increased weight of the androgen-sensitive sex structures. These results indicate that when these two axes are stimulated together, neither interferes with nor suppresses activities of the other. Implants of corticosterone pellets to adrenalectomized animals that maintained constant, high corticosterone levels failed to reverse the gonadal hyperactivity induced by sexual stimulation. In a second experiment, we studied the influence of different intensity of sexual stimulations on HPA-HPG axes interactions. Increased corticosterone levels and adrenal weight, indicating a HPA hyperactivity, failed to inhibit HPG hyperactivity as measured by the increased sexual organs weight, whatever the sexual intensity of the stimulation. This work demonstrates that the gonadal axis is freed from suppression when sexual stimulation occurs together with stress. The general conclusion is that the nature of complex social settings is important in determining interactions between the two neuroendocrine axes.     

Medial hypothalamic involvement in maternal aggression of rats.

Extensive electrolytic lesions of the medial hypothalamus, or more restricted ones in its ventral division, decreased maternal aggression in rats operated upon on postpartum Days 2 and 3 and tested with female intruders 4 days later. Maternal aggression was attenuated also in mothers receiving intrahypothalamic infusions with ibotenic acid or parasagittal knife cuts along the lateral border of the ventromedial hypothalamic nucleus; in addition, the females with ibotenate lesions or knife cuts showed impaired lordosis behavior. None of the hypothalamic interventions were associated with deficits in pup retrieval. Lactation was impaired in groups with hypothalamic electrocoagulations but not in mothers with ibotenate lesions or knife cuts. The results suggest that the ventromedial hypothalamus and its lateral connections participate in control of maternal aggression. (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 lateral hypothalamic lesions on food intake of rats during exposure to cold.

Two experiments investigated the feeding behavior of 41 male Sprague-Dawley rats with lateral hypothalamic (LH) lesions and 13 Ss with chemical lesions of central dopaminergic neurons. LH damage impaired both physiological and behavioral responses of Ss during exposure to a 5°C environment. The LH-lesioned Ss usually did not conserve heat in the cold as well as did controls (n?=?13), nor did they always increase their caloric intake to meet their energy needs. However, when given sucrose solution to drink instead of water, LH-lesioned Ss increased their ingestion of chow in response to cold exposure. It is likely that the elevated consumption of palatable fluid served to relieve dehydration and thereby removed its constraints on eating, thus permitting hyperphagia to occur. In contrast to these results, Ss with large dopamine-depleting brain lesions, produced by intraventricular 6-hydroxydopamine treatments, always increased food intake when exposed to cold stress and demonstrated no apparent problems in peripheral vasoconstriction. Thus, it is unlikely that striatal dopamine depletions account for either the impaired feeding response or the inadequate heat conservation of rats with lateral hypothalamic lesions during cold stress. (33 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

First-order projections activated by stimulation of hypothalamic sites eliciting attack and flight in rats.

–2–4C-deoxyglucose autoradiographs of attack rats were compared densitometrically with those of control rats whose electrodes were located nearby and elicited nonaggressive behaviors like those that accompanied the attack. Most closely associated with attack was the path from the ventromedial hypothalamus through the ventral supraoptic commissural pathway to the peripeduncular area, subparafascicular nucleus, zone incerta, and cuneiform area. Moderately correlated with attack were 4 visual areas: the dorsal and ventral lateral geniculate nuclei, pretectal area, and superior colliculus. Activity in the periaqueductal gray was unrelated to attack ipsilaterally and only weakly related contralaterally. In an orthogonal analysis, upward-oriented flight thresholds were significantly correlated with medial activation extending anteriorly to the lateral septal nucleus, dorsally to the thalamic paraventricular-parataenial region, and posteriorly to the periaqueductal gray. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of ventromedial hypothalamic lesions on hunger-motivated behavior in rats.

Previous studies show that lesions of the ventromedial hypothalamus (VMH) paradoxically increase food intake and decrease hunger motivation in the rat. In a series of experiments designed to examine this paradox, independent groups of VMH-lesioned, female hooded rats (N = 48) were tested on a VI schedule or were run in a straight alley to a food reward. Rate of food ingestion was also measured for all Ss. Performance of the VMH and control groups was compared at identical deprivation conditions defined in terms of preoperative base-line weights (80, 90, 100, and 110%). All test measures showed a significantly higher level of performance for VMH-lesioned Ss at the least severe deprivation conditions. Results suggest that the previously reported VMH paradox originated, in part, from inappropriate testing procedures and between-group comparisons. (20 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Failure to obtain sex differences in development of obesity following ventromedial hypothalamic lesions in rats.

Gave 24 male and 24 female albino Charles River rats either a high-fat or a ground-food diet following ventromedial hypothalamic or sham lesions. After 63 days on 1 diet, diets were reversed for 27 days. Over 63 days (a) lesioned Ss of both sexes showed a significant increase in weight over their controls, (b) Ss on high fat gained more weight than those on ground food, and (c) there was no difference between the sexes in weight gain. When diets were reversed, lesioned Ss now on ground food maintained about the same weight as before reversal, while Ss switched to the high-fat diet rapidly increased their body weight to a point near that of Ss originally on the high-fat diet. Data indicate that there is no sex difference in weight gain following ventromedial lesions. It is suggested that previously reported differences result from (a) insufficient periods of observation, (b) offering unpalatable diets, or (c) the use of random-bred strains which increases variability of animal size and lesion placement. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Comparison of behavioral deficits caused by lesions in septal and ventromedial hypothalamic areas of female rats.

41 female Holtzman rats with lesions in ventromedial hypothalamic (VMH) area and 37 Ss with lesions in septal area were compared with 30 normal Ss for passive-avoidance performance (Exp I), reversal learning (Exp II), and spontaneous alternation (Exp III). Lesions in both septal and VMH areas produced a deficit in passive-avoidance performance, a greater number of errors in reversal learning, and reduced spontaneous alternation in a -maze. The qualitatively similar behavioral deficits produced by septal and VMH lesions suggests that at least part of the functions of both of these areas may overlap in a single system. An attempt was made to identify such a functional system, and an explanation for the behavioral deficits produced by VMH damage was offered. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)