Effects of preoptic, lateral hypothalamic, or dopamine-depleting lesions on behavioral thermoregulation in rats exposed to the cold.

Results of a study with male albino Sprague-Dawley rats indicate that Ss which received medial preoptic/anterior hypothalamic lesions showed impaired physiological thermoregulation in the cold but continued to barpress to activate a heat lamp. After lateral hypothalamic lesions or 6-hydroxydopamine-induced destruction of central dopaminergic neurons, physiological mechansims for body temperature maintenance were unaffected, but performance of the operant task was impaired. In contrast to this difference, Ss from each of the 3 groups constructed nests from tissue paper that were similar in size to one another. These nests generally were much smaller than those of control Ss. The present findings, together with previous observations of behavioral thermoregulation in rats with comparable lesions, are interpreted in terms of the reinforcement obtained by each behavior and the deficits in detecting those reinforcements that may result from each type of brain damage. (47 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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)     

Circadian rhythms and partial recovery of regulatory drinking in rats after lateral hypothalamic lesions.

Eight sighted male albino rats that had recovered spontaneous ingestive behavior after lesions of the lateral hypothalamus were challenged with acute injections of hypertonic NaCl administered at different times during the day-night cycle. Nine intact controls were also studied. Following these injections, drinking was observed only during the nighttime. After morning injections Ss frequently waited until nightfall before drinking, whereas Ss injected at night showed much shorter delays in the behavioral response; a similar nocturnal predominance of drinking was seen after food deprivation and in the ad-lib situation. Studies in 6 blind lesioned Ss suggest that these effects were due to an endogenous circadian rhythm. (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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)     

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)     

Acute homeostatic imbalances reinstate sensorimotor dysfunctions in rats with lateral hypothalamic lesions.

It has previously been demonstrated that rats recovered from aphagia and adipsia after large bilateral electrolytic lesions of the lateral hypothalamic (LH) area do not show the normal feeding response to 2-deoxyglucose or drinking response to polyethylene glycol. The present work found that such homeostatic imbalances reinstate the profound sensorimotor impairments that are seen in the immediate postoperative period but abate in parallel with the gradual recovery of ingestive behaviors. Administration of alpha methyltyrosine or spiroperidol produced sensory and motor dysfunctions in male albino Sprague-Dawley rats with LH lesions that were similar to those observed after 2-deoxyglucose. Results suggest that the residual feeding and drinking deficits of Ss with LH lesions after apparent recovery of function do not reflect specific loss of putative gluco- and volume-regulatory contributions to ingestive behavior. Instead, they indicate continued impairments in nonspecific activational components of motivation that normally are mediated, in part, by central dopaminergic neurons. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of lateral hypothalamic lesions and vagotomy on meal patterns in rats.

Studied meal patterns with liquid diets in 4 female Carworth CFE albino rats with lateral hypothalamic (LH) lesions and in 4 Ss with sham lesions, both before and after vagotomy. LH Ss reduced total intake following lesions but showed no differences from controls after vagotomy on measures of total daily intake, mean meal size, and frequency of feeding. Identical frequency distributions of meal sizes and intermeal interval durations were found in LH and control Ss after vagotomy. However, although sham-lesioned Ss showed significant positive correlations between meal size and subsequent intermeal-interval durations in all phases of the experiment, the LH Ss showed no such correlation following vagotomy. Thus, indices of microregulatory controls may be more sensitive in indicating feeding deficits. (25 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Female-enhanced aggression in male rats: Effects of genital anesthesia, castration, or preoptic lesions.

Male rats that had cohabited with ovariectomized females for 2 weeks became more aggressive toward male intruders after a novel estrous female had been placed in their home cages for a period of 4 hr on the previous day. No increase in aggression was seen in males exposed to anestrous females. Genital anesthesia did not attenuate the female-enhanced aggression effect. By contrast, no enhancement of aggression was observed in long-term castrated males after 24 hr of exposure to estrous females. Rats with bilateral electrolytic lesions in the medial preoptic area showed a normal female-enhanced aggression effect. The observations that exposure to females facilitates aggression in males subjected to genital anesthesia and in males with preoptic lesions raise the possibility that copulatory cues are not always required for the effect. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dissociation between learning and remembering in rats with lesions in the lateral hypothalamus.

10 female Sprague-Dawley albino rats which had recovered regulatory feeding after lesions in the lateral hypothalamus (LH) were tested for retention of a taste aversion acquired prior to the lesions. All 10 Ss retained the aversion. 2 of these Ss provided evidence that preoperative memory can be lost following lesions but subsequently recovers. The same 10 recovered LH-lesioned Ss were exposed to a taste-aversion training procedure identical to that used prior to the lesion, but with novel flavors. 7 of the 10 failed to acquire the new taste aversion. 3 additional Ss served as unoperated controls. It is concluded that rats with lateral hypothalamic damage are thus capable of remembering previously learned taste aversions but unable to learn new ones. (17 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Temperature regulation and salivation following preoptic lesions in the rat.

Investigated whether the preoptic's thermoregulatory deficit might be a reflection of a general salivary deficit. 3 experiments were conducted with adult female Sherman albino rats. Results show that Ss with preoptic lesions quickly become hyperthermic under extreme heat stress. They do not salivate in response to heat as intact Ss do and thus cannot employ this animal's most effective means of evaporative heat loss, saliva spreading. However, if salivation is pharmacologically stimulated, lesioned Ss are able to resist hyperthermia by spreading the saliva. Further, given access to a lever which they can press in order to obtain exogenous coolant from a shower bath, Ss with lesions press more frequently with the higher, more stressful, ambient temperatures than with the more moderate ones, hence maintaining normothermia. Data suggest that rats with preoptic lesions do not lack the capacity for thermoregulation, but only an essential physiological tool, saliva. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Gustatory detection thresholds after parabrachial nuclei lesions in rats.

Rats with either electrolytic (Experiment 1) or excitotoxic lesions (Experiment 2) that had been electrophysiologically centered in the gustatory zone of the parabrachial nuclei (PBN) were tested for sucrose and NaCl taste detection thresholds in a conditioned avoidance task. With 1 exception, all of these rats had previously shown severe deficits in acquiring an LiCl-based conditioned taste aversion (CTA) to sucrose, NaCl, or alanine. The rats with excitotoxic lesions also had failed to express a depletion-induced sodium appetite. Despite the uniformity of these deficits, the rats with lesions exhibited varied performance in the detectability task. Roughly ? of the rats did not perform competently, ? had elevated thresholds, and ? showed no or only marginal impairments in taste detectability. These findings demonstrate that the elimination of CTA following PBN lesions is not necessarily linked to an impairment in taste signal detection. Thus, PBN-induced deficits on 1 taste-related task do not entirely correspond with impairments on another. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Persistence of runway performance after septal lesions in rats.

Assigned 32 male Wistar albino rats to groups receiving bilateral septal lesions or control operations. Septal lesions prevented the partial reinforcement extinction effect after 48 acquisition trials. Septal Ss showed increased resistance to extinction following continuous reinforcement but decreased resistance to extinction following partial reinforcement. Analysis of the acquisition data indicated that the lesions retarded the development of approach-avoidance conflicts associated with reward and nonreward. In a 2nd study, 16 septal and 16 control Ss received 96 acquisition trials. Extended training allowed the development of conflict responses under partial reinforcement, and the Ss with lesions were indistinguishable from controls during extinction. Following continuous reinforcement, septal lesions produced slower extinction of response. It is concluded that the lesions interfered with the development of feedback from frustration, approach-avoidance conflicts, and frustration tolerance. (21 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Weight regulation with palatable food and liquids in rats with lateral hypothalamic lesions.

Maintained 25 female Carworth CFE albino rats with 4- or 7-sec 1-ma bilateral lesions of the lateral hypothalamus (LH) for 87 days on a high-fat diet and a sequence of fluids (water, 6% sucrose, and 1 or .2% saccharin). Lesioned Ss reached a greater weight than 9 sham-lesioned Ss offered the same diet and fluids, and maintained greater weight regardless of the fluid offered. These data do not support the hypothesis that LH lesions lower the set point for weight. Rather, the finickiness of LH Ss results in smaller intake of unpalatable foods and water which, in turn, results in stablization of weight below that of controls. If sufficiently hydrated, LH Ss eat greater quantities of highly palatable foods than do controls, resulting in greater body weight. (24 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of medial preoptic lesions on sexual behavior of female rats is determined by test situation.

Examined the sexual behavior of 47 female Long-Evans rats with bilateral lesions in the medial preoptic area (MPOA) and 27 Long-Evans sham-operated Ss (controls) in 2 testing conditions. In the 1st condition, in which the S could not leave the vicinity of males (no-exit test), lordosis quotients (LQs) were elevated in relation to baseline levels for MPOA Ss. In the 2nd condition, in which the female could control her proximity to males (exit test), MPOA LQs were not different from control levels, and experimental Ss permitted fewer copulatory contacts, exhibited less frequent solicitational behavior, and spent less time with males than the controls did. These findings suggest that the higher LQs seen in no-exit tests as a result of MPOA damage are not due to a lesion-induced potentiation in the Ss' preference to engage in sexual contacts with males. (27 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sham feeding in rats after ventromedial hypothalamic lesions and vagotomy.

Two studies examined sham feeding in female Sprague-Dawley rats with ventromedial hypothalamic (VMH) lesions with or without abdominal vagotomy. In Exp I, intact Ss consumed more than twice as much sweet milk during 1-hr tests of sham feeding as they did when feeding normally. Ss with VMH lesions showed exaggerated sham feeding, which was elevated almost four-fold over their already high normal feeding baseline. In Exp II, vagotomy substantially reduced sham feeding in Ss with VMH lesions. After vagotomy, VMH Ss sham fed half as much as nonvagotomized VMH Ss. Vagotomy did not, however, reduce sham feeding to control levels. Results are consistent with the hypothesis that VMH hyperphagia arise from exaggeration of orosensory responsiveness, which is, in part, a consequence of perturbed vagal function. (40 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual sampling after lesions of the superior colliculus in rats.

In 2 experiments with 20 male black-hooded rats, Ss with bilateral lesions of the superior colliculus showed significantly poorer relearning of a horizontal/vertical stripe discrimination than control Ss. In Exp I, all Ss showed disruption of performance when a stimulus–response (S–R) separation was introduced by raising the stimuli above the site of responding. However, colliculectomized Ss were much more disturbed by the S–R separation than were control Ss. In Exp II, all Ss showed lower performance levels when conflicting patterns were introduced into the upper portion of the stimulus doors, but this time Ss with collicular lesions were less disturbed than controls. It is suggested (a) that when the stimulus and response sites are discontinuous, rats must make an appropriate orienting response to effectively sample the visual stimuli and (b) that lesions of the superior colliculus alter performance by interfering with this orienting behavior. The impairment in relearning is attributed to the absence of preoperative overtraining on the discrimination task. (24 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The substrate for brain-stimulation reward in the lateral preoptic area: III. Connections to the lateral hypothalamic area.

Double-pulse tests were used to estimate the refractory periods and anatomical linkage of the reward-relevant fibers that course between the lateral preoptic and lateral hypothalamic areas. In the 1st study, pairs of conditioning and test pulses were delivered to each site, and the interval between pulses varied; recovery from refractoriness was similar at both sites, with the curves generally rising from 0.6 to 2.0 ms. In the 2nd study, the pairs of pulses were delivered to both sites. Six of 7 rats showed evidence of axonal collision, with estimates of conduction velocity that ranged from 0.48 to 8.95 m/s across rats. These results suggest that a wide spectrum of fiber types characterizes the reward-relevant axons that course uninterruptedly between these 2 regions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sex-related differences in cortical function after medial frontal lesions in rats.

The effects of sex on the performance of 4 spatial mazes (Morris water task, landmark task, radial arm maze, and egocentric radial arm maze) were studied in male and female rats given medial frontal lesions. Operated rats from both sexes were impaired at all of the tasks, but the frontal males were much less impaired than frontal females on the Morris task and the radial arm maze, both of which require animals to use multiple visual-spatial cues for their successful solution. Males also performed better on the egocentric maze. In contrast, frontal females performed better than frontal males at the landmark task, which is best solved by using a single spatial cue. The only sex difference in unoperated rats was a small advantage for females on the egocentric task. The sex differences may reflect an underlying difference in cortical organization or a differential response to cortical lesion in males and females. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of lateral hypothalamic lesions on placentophagia in virgin, primiparous, and multiparous rats.

Produced lesions of the lateral hypothalamus (LH) in 25 pregnant and 25 nonpregnant Sprague-Dawley rats through chronically implanted electrodes to investigate the effect of LH damage on placentophagia. Other variables investigated were prior parturitional experience and stimulus properties of the placenta. Lesions were produced under either anesthesia 24 hr prior to parturition in pregnant Ss and 24 hr prior to placenta presentation in nonpregnant Ss. Lesions produced aphagia to a liquid diet. Pregnancy was not a significant variable in the initiation of placentophagia, but prior parturitional experience was critical. Virgin and primiparous Ss did not exhibit placentophagia following LH damage, but multiparous Ss would eat placenta whenever the opportunity arose, independently of LH damage and pregnancy. (18 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Self-stimulation of preoptic and lateral hypothalamus during behavioral thermoregulation in the albino rat.

Explored self-stimulating behavior in 5 male albino rats under ambient temperatures of 2, 12, 25, and 35.C while radiant-heat reinforcement was concurrently available. Preoptic self-stimulation was accompanied by hypothermia even at neutral temperatures, and in the cold, preoptic self-stimulation behavior was maintained alternating with the use of the heat-lamp lever. Conversely, self-stimulation of the lateral hypothalamus produced hyperthermia at neutral temperatures. In the cold, lateral hypothalamic self-stimulation was suppressed, although maintained sufficiently to preserve normal body temperatures without use of the heat lamp. High-temperature stress suppressed both preoptic and lateral hypothalamic self-stimulation. The interpretation suggests that electrical stimulation of the preoptic area signals a pseudowarmth state which results in activation of heat-loss mechanisms. (15 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)