Changes in autonomic control of heart associated with classical appetitive conditioning in rats.

The aim of this study was to examine the changes in autonomic control of the heart associated with classical appetitive conditioning in rats. We trained rats to learn that a movement into a test chamber was followed by delivery of reward (contextual conditioning) and performed power spectral analysis of heart rate variability from electrocardiograms recorded using the telemetry system. We investigated the sympathovagal balance of autonomic regulation of the heart in response to not only the conditioned stimulus (the movement into the test chamber), but also the unconditioned stimulus (reward), and compared the results of these two kinds of emotional states; it might be considered that "the reward-expecting state" is evoked by the conditioned stimulus and "the reward-receiving state" is evoked by the unconditioned stimulus in rats. The reward-expecting state resulted in a significant increase in both low frequency (LF) power and high frequency (HF) power with no change in heart rate (HR) and LF/HF ratio, indicating that both sympathetic and parasympathetic activity increased with no change in sympathovagal balance. The reward-receiving state resulted in a significant increase in HR and a significant decrease in LF power, HF power, and LF/HF ratio, indicating that both sympathetic and parasympathetic activity decreased with predominance in the parasympathetic activity. These results suggest that the method performed in our present study might be useful for distinguishing between two different emotional states evoked by classical appetitive conditioning in rats.     

Macaque Cardiac Physiology Is Sensitive to the Valence of Passively Viewed Sensory Stimuli

Autonomic nervous system activity is an important component of affective experience. We demonstrate in the rhesus monkey that both the sympathetic and parasympathetic branches of the autonomic nervous system respond differentially to the affective valence of passively viewed video stimuli. We recorded cardiac impedance and an electrocardiogram while adult macaques watched a series of 300 30-second videos that varied in their affective content. We found that sympathetic activity (as measured by cardiac pre-ejection period) increased and parasympathetic activity (as measured by respiratory sinus arrhythmia) decreased as video content changes from positive to negative. These findings parallel the relationship between autonomic nervous system responsivity and valence of stimuli in humans. Given the relationship between human cardiac physiology and affective processing, these findings suggest that macaque cardiac physiology may be an index of affect in nonverbal animals.     

The socially enriched environment in early age alters the exploratory activity and ability for learning in rats

The effects of socially enriched environment on exploration activity in early age and avoidance learning in adult rats were studied. Rats reared in enriched environment were housed with mother and three young rats before weaning. Control rats were housed with mother only. An increase in exporation activity in the open-field test and modified plus-maze was observed in the socially reared rats. The capability for two-way avoidance conditioning was significantly improved in adult socially reared rats.     

Cooperative social coordination and aggression in male laboratory rats: effects of housing and testosterone

A cooperative behavior, coordinated shuttling by pairs of laboratory rats in a rectangular chamber, can be influenced strongly by an interaction between housing and sex. Males and females learn readily when housed together socially, but individual housing ("isolation") causes severe deficits selectively in males. The aim of the present study was to examine the role of testosterone in the differential effects of housing on cooperation learning. Males of a Sprague-Dawley derived strain were housed socially or individually and treated daily in one of three ways (six groups, n = 6 per group): (1) castrated, injected with oil vehicle (without testosterone); (2) castrated, injected with 500 micrograms testosterone propionate (exogenous TP); and (3) sham operated, injected with oil (intact, endogenous testosterone). Socially housed pairs learned readily in all treatment groups, using strategies of coordination in which stereotyped contact or aggressive interactions were interpolated. Individual housing was associated with a deficit, but only in the TP-treated and intact groups in which some pairs either did not learn or performed poorly. The deficit was associated with violent fighting and extreme and stable differentiation into dominants and subordinates, the latter exhibiting prolonged freezing. Oil-treated castrates, when housed individually, were unimpaired and actually surpassed their socially housed counterparts on some measures. Their success was associated with an increase only in low-level aggression. The housing-hormone interaction in male rats suggests that testosterone influences the capacity to develop cooperative behavior by modulating both aggression and its consequences for the relationship between partners. The use of social interaction models, including cooperation, for the study of behavior-hormone interactions was also discussed.     

Baroreflex dysfunction in rats submitted to protein restriction

Earlier studies from the authors' laboratory showed that malnourishment induces alterations in the cardiovascular homeostasis increasing the basal mean arterial pressure and heart rate. In this study, the authors evaluated whether the sympathetic and parasympathetic efferent activities contribute to changes in the cardiovascular homeostasis through altered modulation of the arterial baroreflex of malnourished rats. After weaning, male Fischer rats were given 15% (Normal Protein--NP) or 6% (Low Protein--LP) protein diet for 35 d. The baroreflex gain and latency were evaluated before and after selective autonomic blockades in control and malnourished rats. It was observed that malnourishment affected the baroreflex gain in response to activation and deactivation of the arterial baroreflex. Moreover, malnourished rats showed increased baroreflex latency as compared to that of control rats. Regarding the autonomic efferent activity directed to the heart, the data showed increased sympathetic and decreased parasympathetic efferent activities in malnourished rats, and such alterations could be related to the observed changes in the arterial baroreflex gain as well as in the basal mean arterial pressure and heart rate.     

Effects of pre-weaning housing in a multi-suckling system on performance and carbohydrate absorption of relatively light and heavy piglets around weaning

The low feed intake and stress associated with abrupt weaning in conventional pig farming often result in poor post-weaning performance, which is related to impaired intestinal function. We investigated effects of housing conditions before weaning on performance around weaning of relatively light and heavy piglets. Before weaning, piglets were housed either with five sows and their litters in a multi-suckling (MS) system or in pens with individually housed sows in farrowing crates (FC). After weaning at 4 weeks of age (day 0), 16 groups of four piglets (two light and two heavy litter-mates) were housed under equal conditions in enriched pens. Mannitol (day −5 and day 5) and galactose (day 5) were orally administered as markers for gastrointestinal carbohydrate absorption, and after 20 min a blood sample was taken (sugar absorption test). In addition, BW, feed intake and faecal consistency as an indicator for diarrhoea, were assessed frequently during 2 weeks post-weaning. Pre-weaning housing, weight class and their interaction did not affect post-weaning faecal consistency scores. Weight gain over 2 weeks did not differ between pre-weaning housing treatments, but MS piglets gained more (0.67±0.12 kg) than FC piglets (0.39±0.16 kg) between days 2 and 5 post-weaning, P=0.02), particularly in the ‘heavy’ weight class (interaction, P=0.04), whereas feed intake was similar for both treatments. This indicates a better utilisation of the ingested feed of the MS piglets compared with the FC piglets in the early post-weaning period. Pre-weaning mannitol concentrations were unaffected by pre-weaning housing, weight class and their interaction. On day 5 post-weaning, however, MS piglets had a lower plasma concentration of mannitol (320 v. 592 nmol/ml, SEM=132, P=0.04) and galactose (91 v. 157 nmol/ml, SEM=20, P=0.04) than FC piglets, regardless of weight class. In conclusion, MS and FC piglets differed in aspects of post-weaning gastrointestinal carbohydrate absorption and in weight gain between days 2 and 5 after weaning, but pre-weaning housing did not affect feed intake, weight gain and measures of faecal consistency over the first 2 weeks after weaning.     

Perinatal and juvenile social environments interact to shape cognitive behaviour and neural phenotype in prairie voles

Social environments experienced at different developmental stages profoundly shape adult behavioural and neural phenotypes, and may have important interactive effects. We asked if social experience before and after weaning influenced adult social cognition in male prairie voles. Animals were raised either with or without fathers and then either housed singly or in sibling pairs. Males that were socially deprived before (fatherless) and after (singly housed) weaning did not demonstrate social recognition or dissociate spatial from social information. We also examined oxytocin and vasopressin receptors (OTR and V1aR) in areas of the forebrain associated with social behaviour and memory. Pre- and post-wean experience differentially altered receptor expression in several structures. Of note, OTR in the lateral septum—an area in which oxytocin inhibits social recognition—was greatest in animals that did not clearly demonstrate social recognition. The combination of absentee fathers on V1aR in the retrosplenial cortex and single housing on OTR in the septohippocampal nucleus produced a unique phenotype previously found to be associated with poor reproductive success in nature. We demonstrate that interactive effects of early life experiences throughout development have tremendous influence over brain–behaviour phenotype and can buffer potentially negative outcomes due to social deprivation.     

Influence of housing conditions from weaning to adulthood on the ventilatory, thermoregulatory, and endocrine responses to hypoxia of adult female rats

Housing conditions affect animal physiology. We previously showed that the hypoxic ventilatory and thermoregulatory responses to hypoxia of adult male rats housed in triads during the juvenile period (postnatal day 21 to adulthood) were significantly reduced compared with animals housed in pairs. Because sex hormones influence development and responsiveness to environmental stressors, this study investigated the impact of housing on the respiratory and thermoregulatory physiology of female rats. Since neonatal stress attenuates the hypoxic ventilatory response (HVR) of female rats at adulthood, experiments were performed both on "control" (undisturbed) animals and rats subjected to neonatal maternal separation (NMS; 3 h/day, postnatal days 3-12). At adulthood, ventilatory activity was measured by whole body plethysmography under normoxic and hypoxic conditions [fraction of inspired oxygen (Fi(O(2))) = 0.12; 20 min]. The ventilatory and body temperature responses to hypoxia of female rats raised in triads were reduced compared with rats housed in pairs. Housing female rats in triads did not affect basal or hypoxic plasma corticosterone levels but did increase levels of estradiol significantly. We conclude that modest changes in housing conditions (pairs vs. triads) from weaning to adulthood does influence basic homeostatic functions such as temperature and respiratory regulation. Triad housing can reverse the manifestations of respiratory instability at adulthood induced by stressful neonatal treatments. This should raise awareness of the benefits of increasing social interactions in clinical settings but also caution researchers of the potential impact of such subtle changes on experimental protocols and interpretation of results.     

Age-related changes in the innervation of the prostate gland

The adult prostate gland grows and develops under hormonal control while its physiological functions are controlled by the autonomic nervous system. The prostate gland receives sympathetic input via the hypogastric nerve and parasympathetic input via the pelvic nerve. In addition, the hypogastric and pelvic nerves also provide sensory inputs to the gland. This review provides a summary of the innervation of the adult prostate gland and describes the changes which occur with age and disease. Growth and development of the prostate gland is age dependent as is the occurrence of both benign prostate disease and prostate cancer. In parallel, the activity and influence of both the sympathetic and parasympathetic nervous system changes with age. The influence of the sympathetic nervous system on benign prostatic hyperplasia is well documented and this review considers the possibility of a link between changes in autonomic innervation and prostate cancer progression.     

Interaction between pre-weaning undernutrition and post-weaning environmental enrichment on somatic development and behaviour in male and female rats

Male and female rats were undernourished from birth to 30 days by restricting access to the lactating mother, and then fed ad libitum. At weaning, underfed and normally suckled controls were permanently housed either in pairs in standard cages or in groups of 10 in 1 m³ cages containing ladders, ropes etc. Severe undernutrition during suckling followed by 4 months of refeeding, produced some changes in sexual behaviour in adult males (increased ejaculation frequency) but had no effect on behaviour in open field, dark preference or passive avoidance. Differential post-weaning environment produced significant differences in behaviour, irrespective of previous feeding conditions. Enriched animals were more active and exploratory. Females differed from males in the same direction as enriched from standard, and were more responsive to social and housing conditions.     

Noninvasive cardiac psychophysiology as a tool for translational science with marmosets

The importance of marmosets for comparative and translational science has grown in recent years because of their relatively rapid development, birth cohorts of twins, family social structure, and genetic tractability. Despite this, they remain understudied in investigations of affective processes. In this methodological note, we establish the validity of using noninvasive commercially available equipment to record cardiac physiology and compute indices of autonomic nervous system activity—a major component of affective processes. Specifically, we recorded electrocardiogram and impedance cardiogram, from which we derived heart rate, respiration rate, measures of high‐frequency heart rate variability (indices of parasympathetic autonomic nervous system activity), and ventricular contractility (an index of sympathetic autonomic nervous system activity). Our methods produced physiologically plausible data, and further, animals with increased heart rates during testing were also more reactive to isolation from their social partner and presentation of novel objects, though no relationship was observed between reactivity and specific indices of parasympathetic or sympathetic nervous system activity.     

Autonomic involvement in the permanent metabolic programming of hyperinsulinemia in the high-carbohydrate rat model

Exposure to a high-carbohydrate (HC) milk formula during the suckling period results in permanent metabolic programming of hyperinsulinemia in HC rats. Previous studies have shown that hyperinsulinemia in HC rats involves a programmed hyperresponsiveness to glucose. However, the immediate onset and persistence of enhanced insulin secretion throughout life suggests a role for numerous factors that control insulin secretion. Present in vivo and in vitro studies have shown a role for altered autonomic activity, including increased parasympathetic and decreased sympathetic activities, in the maintenance of hyperinsulinemia in 100-day-old HC rats. HC rats were shown to be more sensitive to cholinergic-induced potentiation of glucose-stimulated insulin secretion (GSIS) in response to acetylcholine and showed increased sensitivity to blockade of cholinergic-induced insulin secretion by the muscarinic-type 3 receptor-specific antagonist 4-diphenylacetoxy-N-methylpiperidine. In addition, HC rats were less sensitive to adrenergic-induced inhibition of insulin secretion by oxymetazoline, whereas treatment with yohimbine resulted in increased GSIS. Furthermore, HC rats showed greater reductions in plasma insulin levels after vagotomy, as well as an attenuation of yohimbine-induced potentiation of GSIS, suggesting that yohimbine-mediated changes are mediated by parasympathetic activity. Changes in autonomic regulation of GSIS are supported by increased mRNA levels of the parasympathetic signaling molecules muscarinic-type 3 receptor, phospholipase Cbeta1, and protein kinase C-alpha and decreased levels of alpha(2a)-adrenergic receptors in islets from adult HC rats. In conclusion, metabolic programming of hyperinsulinemia throughout adulthood of HC rats involves changes in autonomic activity in response to the HC dietary intervention in the suckling period.     

Early exposure to a high-fat diet has more drastic consequences on metabolism compared with exposure during adulthood in rats

The aim of this study was determine whether the introduction of a high-fat diet during the peripubertal phase induces significant changes in body weight control, glucose homeostasis and the parasympathetic tonus compared with the administration of this diet to adult rats. High-fat diet was offered to male Wistar rats at weaning or during adulthood. A group of rats received high-fat diet for 60 days, from weaning to 81-day-old (HF81) or from 60 to 120-day-old (HF120), whereas 2 other groups received a normal-fat diet (i. e., NF81 and NF120). We analyzed adiposity, glucose homeostasis, insulin sensitivity, and vagal nerve activity. High-fat diet increased the accumulation of adipose tissue in all of the rats, but the difference was greater in the rats that were fed the high-fat diet since weaning (p<0.001). The HF rats showed glucose intolerance with high levels of insulin secretion during the glucose tolerance test (p<0.01). Rats that were fed the high-fat diet presented severe insulin resistance, indicated by a low K itt (p<0.01). Interestingly, the HF81 rats exhibited greater insulin resistance compared with the HF120 rats (p<0.05). The recordings of vagus nerve activity showed that the HF rats had higher parasympathetic activity than the NF rats irrespective of age (p<0.01). Our results show that a high-fat diet offered to rats just after weaning or in adulthood both cause impairment of glycemic homeostasis and imbalance in parasympathetic activity. Importantly, the consumption of high-fat diet immediately after weaning has more drastic consequences compared with the consumption of the same diet during adulthood.     

Postweaning environmental and social factors influencing the onset and expression of agonistic behavior in Norway rats

Two studies were conducted to determine the importance of the postweaning environment and social milieu in regulating the expression of intraspecific aggression in Norway rats. In Experiment 1, male rats were housed either individually or in pairs at 21 days of age. In addition, one-half of the singly housed and paired animals were given experiences with intruders during maturation. At 85 days of age, all animals were given a brief intruder test and then removed from their postweaning environment and provided individually with homecages for a two week period until tested for aggression toward intruders. Results of intruder tests given during maturation indicated agonistic exchanges appeared earlier and more frequently in cages housing a single resident than cages with cohabiting males. However, agonistic exchanges between singly reared residents and intruders had detrimental consequences in adulthood especially under long-term combat situations. That is, although individually reared animals, with early fighting experiences, were capable of initiating intraspecific aggression, such individuals were unable to defend their homecage over a long period of time as evidenced by the high number of wounds and tendency to lose body weight during adult fighting.In Experiment 2, male Norway rats were reared in pairs from 21 days of age and identified as dominant or subordinate on the basis of intracolony social interactions shown during maturation. At 80 days of age, animals were paired with individually reared males in an unfamiliar cage for a 20 day period and examined for agonistic behavior toward intruders at 100 days of age. Group-reared subordinate males exhibited defensive behavior during confrontations with individually reared animals and incurred more wounds and lost more body weight than their cohabiting partner. In addition, subordinate males showed significantly fewer offensive postures toward intruders than individually reared cohabitants. In contrast, group-reared dominant animals did not differ from individually reared males in display of agonistic patterns, in number of wounds, and body weight changes during the period of cohabitation. These findings demonstrate that early rearing factors have pronounced effects on agonistic behavior. Animals experiencing defeat during development are more likely to lose agonistic confrontations in unfamiliar territory than either animals dominant in their early social interactions or animals without the experience of winning or losing agonistic encounters. These results have implications for the understanding of agonistic behavior and predicting outcomes of animal contests, and reveal important differences in agonistic experiences among animals reared in groups.     

Effects of early weaning and housing conditions on the development of stereotypies in farmed mink

Female mink pups were weaned at 6, 8 or 10 weeks of age and subjected to two different housing conditions. They were either kept together with a single male sibling in traditional mink cages (30x45x90 cm) or housed socially with all litter-mates in an alternative system consisting of three adjoining traditional cages (90x45x90 cm). All cages were supplied with nest boxes. At 5 months of age, the siblings were removed leaving the females socially isolated in the two different cage systems. Females' stereotypies were quantified by repeated scanning observations under the social housing conditions immediately before removal of the siblings, and again at the age of 7 and 9 months, when the animals had stayed solitary in the two systems for 2 and 4 months. Solitary females showed significantly more stereotypies than females under social housing conditions in both cage systems. Stereotypies were more frequent in the smaller traditional cages. Stereotypies declined from 7 to 9 months of age among solitary animals in traditional cages but not in alternative cages. Early-weaned solitary females in traditional cages showed more stereotypies than later-weaned animals, but only when measured at the age of 7 months. It is suggested that early weaning, individual housing and small cages promote the development of stereotypies in farmed mink. The influence of early weaning on stereotypies seems to decline with age, while effects related to individual housing and small cages appear to be more persistent.     

Higher heart rate of laboratory mice housed individually vs in pairs

Many studies have shown that housing mice individually over a long period significantly alters their physiology, but in most cases measurement has required human interference and restraint for sampling. Using a radio-telemetry system with implantable transmitters, we recorded heart rate (HR), motor activity (ACT) and body temperature (BT) of freely moving male mice (NMRI) housed either individually or in pairs with an ovarectomized female. Data for each parameter were collected at 5 min intervals for two consecutive 24 h periods. Even after several weeks of habituation to the social conditions, HR was increased in mice housed individually compared with mice housed in pairs, although their measured ACT did not differ. Additionally, BT tended to be reduced in individually-housed mice. When the data were analysed according to different ACT levels, HR was increased in individually-housed mice during phases of low and high, but not intermediate, motor activity. Furthermore, individually-housed mice had more, but shorter, resting bouts, indicating disruption of the normal circadian sleep pattern. Enhanced HR in individually-housed mice does not necessarily indicate stress, but might be an important physiological indicator of discomfort. The fact that individual housing alters basic physiological parameters in laboratory mice highlights the need to control for housing-dependent variation, especially in experiments that are sensitive to changes in these parameters.     

Altered stress responsiveness and hypothalamic‐pituitary‐adrenal axis function in male rat offspring of socially isolated parents

Social isolation in male rats at weaning results in reduced basal levels of the neuroactive steroid 3α,5α‐tetrahydroprogesterone (3α,5α‐TH PROG) in the brain and plasma as well as increased anxiety‐like behavior. We now show that socially isolated female rats also manifest a reduced basal cerebrocortical concentration of 3α,5α‐TH PROG as well as an anxiety‐like profile in the elevated plus‐maze and Vogel conflict tests compared with group‐housed controls. In contrast, despite the fact that they were raised under normal conditions, adult male offspring of male and female rats subjected to social isolation before mating exhibited an increased basal cerebrocortical level of 3α,5α‐TH PROG but no difference in emotional reactivity compared with the offspring of group‐housed parents. These animals also showed an increased basal activity of the hypothalamic‐pituitary‐adrenal axis as well as reduced abundance of corticotropin‐releasing factor in the hypothalamus and of corticotropin‐releasing factor receptor type 1 in the pituitary. Moreover, negative feedback regulation of hypothalamic‐pituitary‐adrenal axis activity by glucocorticoid was enhanced in association with up‐regulation of glucocorticoid receptor expression in the hippocampus. There was also attenuation of corticosterone release induced by foot‐shock stress in the offspring of socially isolated parents. The increase in the brain concentration of 3α,5α‐TH PROG induced by acute stress was also blunted in these animals. Our results thus show that a stressful experience before mating can influence neuroendocrine signaling in the next generation.     

Genetic selection on a behavioural fear trait is associated with changes in heart rate variability in quail

This study investigated whether genetic selection on a divergent behavioural trait of fearfulness (tonic immobility duration) was related to changes in the nervous control of the heart. Quail selected for either long or short tonic immobility (LTI or STI, respectively) duration was compared with an unselected control line (CTI). The autonomic control of the heart was assessed by heart rate variability analysis and pharmacological blockades. Quail were surgically fitted with a telemetric device. Heart rate before injection did not differ between the three lines. The vagal-sympathetic effect (VSE) at rest differed significantly from 1 in CTI and STI quail, suggesting that parasympathetic activity was dominant. In LTI quail, VSE did not differ from 1, suggesting a balance between parasympathetic and sympathetic activities. The intrinsic heart rate reached after the successive injections of propranolol and atropine did not differ between lines and was higher than the heart rate at rest in STI, which was in line with results of VSE at rest. After atropine injection, the sympathetic activity indicated by the low-frequency power was lower in CTI than in the two selected quail. After propranolol injection, the parasympathetic activity indicated by the root of the mean squares of successive differences and the high-frequency power was higher in STI than in CTI and LTI quail. Selection on tonic immobility duration thus appears to be associated with changes in the sympathovagal control of the heart, which may influence behavioural responses to stressful situations.     

Metabolic Consequences and Vulnerability to Diet-Induced Obesity in Male Mice under Chronic Social Stress

Social and psychological factors interact with genetic predisposition and dietary habit in determining obesity. However, relatively few pre-clinical studies address the role of psychosocial factors in metabolic disorders. Previous studies from our laboratory demonstrated in male mice: 1) opposite status-dependent effect on body weight gain under chronic psychosocial stress; 2) a reduction in body weight in individually housed (Ind) male mice. In the present study these observations were extended to provide a comprehensive characterization of the metabolic consequences of chronic psychosocial stress and individual housing in adult CD-1 male mice. Results confirmed that in mice fed standard diet, dominant (Dom) and Ind had a negative energy balance while subordinate (Sub) had a positive energy balance. Locomotor activity was depressed in Sub and enhanced in Dom. Hyperphagia emerged for Dom and Sub and hypophagia for Ind. Dom also showed a consistent decrease of visceral fat pads weight as well as increased norepinephrine concentration and smaller adipocytes diameter in the perigonadal fat pad. On the contrary, under high fat diet Sub and, surprisingly, Ind showed higher while Dom showed lower vulnerability to obesity associated with hyperphagia. In conclusion, we demonstrated that social status under chronic stress and individual housing deeply affect mice metabolic functions in different, sometime opposite, directions. Food intake, the hedonic response to palatable food as well as the locomotor activity and the sympathetic activation within the adipose fat pads all represent causal factors explaining the different metabolic alterations observed. Overall this study demonstrates that pre-clinical animal models offer a suitable tool for the investigation of the metabolic consequences of chronic stress exposure and associated psychopathologies.     

Heterosexual housing increases the retention of courtship behavior following castration and elevates metabolic capacity in limbic brain nuclei in male whiptail lizards,Cnemidophorus inornatus

In male vertebrates the display of courtship behavior depends on the presence of testicular androgens. However, social experiences in adulthood can alter the hormonal dependence of courtship behavior in a variety of species, and we have previously proposed that these behavioral changes are linked to changes in neural metabolic capacity (cytochrome oxidase activity). Here we investigated the effects of prior social experience (housing with females vs housing in isolation) on the retention of courtship behavior following gonadectomy and on cytochrome oxidase (CO) activity in male little striped whiptail lizards, Cnemidophorus inornatus. In Experiment 1, we found that males that were previously housed with females (HWF males) continued to display courtship behavior longer after castration than males previously housed in isolation (ISOLATE males). This is similar to the behavioral plasticity found in rodents and cats. On the other hand, courtship behavior while gonadally intact was indistinguishable between HWF and ISOLATE males. Because all males were housed individually following castration, the difference is due to different social experiences prior to castration. In Experiment 2, we found that gonadally intact HWF males had significantly elevated CO activity in the preoptic area, amygdala, and anterior and ventromedial hypothalamic areas relative to intact ISOLATE males. No significant differences in metabolism were found in the lateral septum, lateral hypothalamus, and habenula or in hindlimb muscle, suggesting that the increase in metabolism is specific to brain nuclei involved in courtship behavior. Altogether, this demonstrates that elevations in metabolic capacity correlate with experience-dependent increases in robustness to castration.