Isolation Housing Research Articles

Behavioral and neurochemical effects of anpirtoline and citalopram in isolated and group housed mice

1. Acute effects of serotonergic drugs acting via different mechanisms were investigated by a social interaction test and subsequent determination of serotonin and dopamine metabolisms in mice housed in groups or isolated for 6 weeks. 2. A resident / intruder test was performed with anpirtoline (5-HT 1B receptor agonist in rodents; 1 mg/kg), citalopram (SSRI; 0.5 mg/kg) and saline treatment before animals were decapitated and different brain regions were frozen for subsequent HPLC-analyses. 3. Behavioral investigations indicated a strong increase of aggressive behavior after 6 weeks of isolation housing. Acute citalopram treatment did not influence behavioral parameters of isolated and group housed mice. In contrast, anpirtoline antagonized isolation induced aggressive behavioral components in a specific manner. 4. Analysis of dopamine and serotonin metabolism revealed that citalopram treatment did not affect dopamine metabolism, but reduced serotonin metabolism in the striatum, hippocampus, cortex and midbrain independent of housing conditions. 5. In contrast, anpirtoline treatment increased dopamine metabolism in cortex, striatum and midbrain as well as influenced serotonin metabolism in a structure- and state-specific manner. Whereas anpirtoline decreased serotonin metabolism in the cortex, the midbrain and the hippocampus independent of housing conditions, in the striatum anpirtoline abolished the isolation induced decrease of serotonin metabolism. 6. These results indicate that anpirtoline might induce antiaggressive effects via postsynaptic receptor- and structure- specific activation of serotonergic but also dopaminergic processes, whereas structure independent increase of synaptic serotonin via citalopram was ineffective to reverse aggressivity in isolated mice.

Genetic–environment analysis of sensitivity and acute tolerance to ethanol in mice

The purpose of this study was to characterize initial sensitivity (IS), acute functional tolerance (AFT), and rate of tolerance development to ethanol in lines of mice selected for aggression mice as well as to investigate the impact of isolate housing on these phenotypes. The results showed that for IS, there were no differences among treatment groups. For acute tolerance and rate of tolerance development, a Line×Sex×Housing interaction was present, with the response to housing being more pronounced in the low aggressive line than the high aggressive line, and the females being more affected than the males. Correlational analysis showed low to moderate associations between rate of tolerance development and IS, as well as between rate of tolerance and AFT. Housing condition significantly influenced female expression of ethanol phenotypes as compared to males. The line of the subject also influenced the magnitude of expression of these phenotypes. These findings suggest that environmental and genetic influences interact to influence acute tolerance and rate of tolerance development.

Tickling induces reward in adolescent rats

In adolescent rats, 50-kHz vocalizations are most evident during tickling and rough-and-tumble play. The following experiments evaluated whether 50-kHz vocalizations reflect positive social affect by determining (1) if tickling is a rewarding event, (2) if social or isolate housing conditions differentially influence the response (since housing condition has been found to effect the reward magnitude of social encounters), and (3) if drugs that work on μ-opiate receptors, which has been hypothesized to control positive social affect, modulate tickling. Tickling was positively reinforcing as demonstrated by elevated operant behavior, conditioned place preference, and approach measures. A significant negative correlation between vocalization rate and approach latency measures was found. Social housing reduced tickle-induced vocalizations and approach speeds compared to isolate housing. Naloxone (1 mg/kg) increased vocalization in the socially housed rats and decreased it in isolated Subjects (Ss). These findings suggest that tickling can be used to induce positive social affect in rodents, and that it is modulated by endogenous opioids.

Long term modulation of the HPA axis by the hippocampus. Behavioral, biochemical and immunological endpoints in rats exposed to chronic mild stress.

Mature rats were given lesions of the hippocampus (HIPPO), subiculum (SUBIC) or fimbria-fornix (FIFO) and then received the mild chronic stressors of food deprivation and isolation housing for ten months prior to testing. Group differences in circadian activity were investigated along with locomotion elicited by amphetamine (AMP 1.0-2.0 mg/kg i.p.) alone, and following the corticosterone (CORT) synthesis inhibitor, metyrapone (MET 10.0-25.0 mg/kg i.p.). Basal levels of plasma CORT, (ng/ml), plasma glucose (GLUC, mmol/l), thymic and splenic wet weights were subsequently determined along with complete blood counts (CBC). In comparison to age matched, unoperated controls, selective SUBIC lesions altered the circadian periodicity of locomotion, while rats with FIFO lesions were spontaneously hyperactive. Both HIPPO and FIFO animals showed significantly higher levels of amphetamine-induced locomotion. In all groups metyrapone significantly enhanced locomotion elicited by amphetamine, probably due to a pharmacokinetic interaction between these drugs. In comparison to controls, animals in the HIPPO group showed significant reductions in plasma glucose levels, decreased thymic wet weights and reductions in lymphocyte numbers, indicating lesion-related immuno-suppression. These findings highlight a functional difference among the effects of these specific hippocampal lesions on neural regulation of the HPA axis, under conditions of chronic mild stress, suggesting that the modulatory influence of the hippocampus on the stress axis is dependent on the neuroanatomical location and total extent of cell loss within this structure. They further suggest that the heightened response to amphetamine occurs independently of any lesion-induced changes in modulation of the HPA axis.

D 3 and D 2 dopamine receptor agonists differentially modulate isolation-induced social-emotional reactivity in mice

Following isolation housing, mice typically exhibit heightened emotional reactivity to mild social stimulation. Aggression, social avoidance and a variety of defensive behaviors that differ in terms of motor activation (e.g. freezing, escape) can be observed depending on strain. Previous studies suggested that D 2-like dopamine (DA) receptors play an important, albeit strain specific, role in the mediation of particular forms of defensive behavior. D 3 receptors are subtypes of D 2-like receptors that are highly expressed in limbic areas of the brain and, therefore, they have been hypothesized to mediate emotional behavior. This study examined the effects of the putative D 3 receptor agonists 7-OH-DPAT and PD128907 on social-emotional behavior in isolated C57BL/6J and A/J mice. These effects were compared with those of the selective D 2 receptor agonist PNU91356A. All three DA agonists increased non-locomotor forms of defensive behavior (e.g. freezing, upright defensive posture). These effects were observed at low doses in C57BL/6J and at higher doses in A/J mice. Only the D 3 receptor agonists were effective in increasing locomotor forms of defensive behavior (i.e. escape, jump) at higher doses. These effects were more pronounced in C57BL/6J mice than A/J mice. The increases in stationary and locomotor defensive behavior were accompanied by marked reduction in social investigation in both the strains. Aggressive behavior was also abolished in the aggressive C57BL/6J strain. These results support previous findings and suggest that DA agonists potentiate defensive behavior and/or social fearfulness. They also suggest that D 3 and D 2 DA receptors differentially modulate the expression of social-emotional reactivity and indicate the importance of strain in examining the effects of DA ligands on emotional behavior.

Differential effects of social isolation upon body weight, food consumption, and responsiveness to novel and social environment in bombesin receptor subtype-3 (BRS-3) deficient mice

The effects of social isolation on body weight gain, food consumption, and responsiveness to novel and social environment were assessed in an animal model for obesity, bombesin receptor subtype-3 (BRS-3) deficient mice. In Experiment 1, body weight gain and food consumption of group- and isolation-housed wild-type and BRS-3-deficient mice were compared. In wild-type mice, group-housed animals showed greater mean body weight gain and food consumption than did the isolation-housed cohort in the early stage of the experiment, whereas in BRS-3-deficient mice, the isolation-housed mice showed greater body weight gain and food consumption than the group-housed cohort by prolonged isolation housing. In Experiment 2, isolation-housed wild-type mice exhibited increased stereotypic and vertical movements relative to group-housed subjects in a novel environment, but this effect was not observed in BRS-3-deficient mice. In Experiment 3, when social response was assessed in animals housed in isolation, BRS-3-deficient mice exhibited lower social responses than did wild-type mice. We conclude that BRS-3-deficient mice and wild-type mice are differentially affected by social isolation. These results suggest that BRS-3 expression in the CNS may affect the neural mechanisms that regulate isolation effects in wild-type animals.

D1 dopamine receptor mediation of social and nonsocial emotional reactivity in mice: effects of housing and strain difference in motor activity.

The study examined the effects of isolation housing and the role of D1 dopamine receptors on isolation-induced social and nonsocial (acoustic startle) reactivity in mice high (C57BL/6) and low (A) in motor activity. Isolation housing had no effect on acoustic startle but increased strain-specific forms of social reactivity. The D1 agonist dihydrexidine (DHX) increased acoustic startle in isolated mice of both strains, but this effect was more pronounced in C57BL/6 mice. In this strain, DHX and the D1 agonist SKF-81297 increased locomotor forms of social reactivity (e.g., escape, jump), whereas the D1 antagonist SCH-23390 increased stationary reactivity (e.g., freezing). In A mice, DHX and SKF-81297 increased and decreased stationary reactivity, respectively, whereas SCH-23390 had no effect on these behaviors. Administration of SKF-81297 after pretreatment with SCH-23390 or the D2 antagonist sulpiride confirmed the importance of D1 receptors in mediating specific forms of social reactivity in C57BL/6 mice. These results suggest an important relationship between social reactivity and motor activity and an important, albeit strain-dependent, role for D1 receptors in mediating specific emotional behaviors.

Effects of a short period of isolation in adulthood on the aggressive behavior of dominant and subordinate male mice

Male ddY mice were used to investigate the effect of a short period of isolation in adulthood on aggressive behavior. The relationship between the dominance status previous to isolation and the effect of isolation was investigated. The mice were kept in isolation for 3 weeks from 9 weeks of age, during which intruder tests were conducted once a week. They the went through an encounter test, in which the mice encountered dominant or subordinate mice in a neutral space. The number of the formerly-dominant isolated mice that attacked the intruder mice decreased at first and then increased. The latency to attack also lengthened at first and then shortened. Seven former-dominants continued to show aggression throughout the intruder The number of the formerly-subordinate isolated mice that attacked the intruder mice increased linearly. But 3 former-subordinates did not show aggression through the entire experiment. After 3 weeks isolation, the number of mice that showed aggression and the amount of aggression did not differ between the former-dominants and subordinatcs. Isolation housing was concluded to differentially affect the dominant and subordinate mice during the 3 weeks of isolation. It was also concluded to differentially affect the mice of absolute dominance and relative dominance differentially. The aggressive behavior of the isolated mice appears to occur independently of site.

Psychosocial stress, catecholamines, and essential fatty acid metabolism in rats.

To examine the effects of psychosocial stress and the "stress hormone," epinephrine, on essential fatty acid metabolism in rats, two studies were conducted. In the first, the effects of four weeks of (i) social isolation and (ii) group housing (control) on liver microsomal delta 6 and delta 5 n-6 desaturase activity were studied in group-reared male normotensive (Wistar Kyoto) and spontaneously hypertensive (SHR) rats (n = 5/group). The second study examined the effects of acute ip epinephrine (0.0, 1.0, 2.0, and 4.0 mg/kg) 6 hr prior to and following an ig dose (4 g/kg) of safflower oil (rich in 18:2n-6, LA) on plasma and liver LA, 20:4n-6 (AA), and LA/AA ratios in adult essential fatty acid deficient Sprague-Dawley rats (n = 6/group). In the first experiment, isolation stress significantly inhibited the activity of delta 6 (P < 0.05) and delta 5 (P < 0.01) desaturase in the normotensive rats and of delta 5 desaturase in the SHR (P < 0.05). In the second study, epinephrine increased plasma and liver LA at doses 1.0 and 2.0 mg/kg in most of the fractions examined, and suppressed AA levels. The response of the LA/AA ratio to epinephrine varied between tissues and among lipid fractions, but increased this ratio at the moderate doses (2.0-4.0 mg/kg) of epinephrine in most cases. These data suggest that psychosocial stressors are capable of inhibiting the rate limiting steps of essential fatty acid metabolism and that this response is more pronounced in the SHR than in the Wistar Kyoto. They also suggest that epinephrine is capable of altering the in vivo metabolism of essential fatty acids in the rat.

Effects of Isolation Housing and Timing of Drug Administration on Theophylline Kinetics in Mice.

ICR mice were grouped according to 1) housing environment: individual (I) or aggregated (A) and 2) timing of drug administration: midlight (L) or middark (D), i.e. I-L, I-D, A-L, A-D groups. Theophylline was orally administered at midlight or middark. The results showed that both social environment and timing of drug administration exerted significant influence on the pharmacokinetics of theophylline. These data may suggest the importance of considering many non-drug factors in toxicological studies with experimental animals.

Effects of Isolation Housing and Timing of Drug Administration on Theophylline Kinetics in Mice

ICR mice were grouped according to 1) housing environment: individual (I) or aggregated (A) and 2) timing of drug administration: midlight (L) or middark (D), i.e. I-L, I-D, A-L, A-D groups. Theophylline was orally administered at midlight or middark. The results showed that both social environment and timing of drug administration exerted significant influence on the pharmacokinetics of theophylline. These data may suggest the importance of considering many non-drug factors in toxicological studies with experimental animals.

Differential effects of an early housing manipulation on cocaine-induced activity and self-administration in laboratory rats

Several reports in the literature suggested that environmental influences which are reflected in the social housing conditions of the rat may play a role in the expression of individual differences in drug self-administration. The present experiments were performed in order to further examine the effects of early housing manipulations, as reflected by grouped or isolation housing, on cocaine-induced behavioral responding. The first study examined the effects of this manipulation on the locomotor stimulant properties of cocaine. The results suggested that grouped housing produced a significantly greater increase in cocaine-induced locomotion than was observed in animals housed in isolation. Experiment 2 examined the effects of housing manipulations on the self-administration of cocaine under a continuous reinforcement schedule. Differences in the rate of cocaine self-administration were only observed at the lowest dose tested. Responding at all other doses was equivalent, including the optimal dose for both groups, suggesting that the housing manipulations failed to affect the reinforcing efficacy of cocaine. The present investigation suggests that, while the early housing manipulation produced a differential sensitivity in rats to the stimulant properties of cocaine, the same manipulation failed to alter the sensitivity of rats to the reinforcing properties of cocaine as assessed through self-administration.

Social context and reaction to separation in peer-reared pigtail macaques: Some preliminary observations

The social environment affects both behavioral and physiological responses to separation from the mother. Less information is available on the impact of the social environment on the response to separation in peer-reared infant monkeys. This study reports the responses of peer-reared pigtail macaque infants to repeated separations, and the impact of social versus isolation housing during the separation. The responses of two pairs of monkeys were studied during four three-day separations. One of each pair was housed in isolation during the separation, and the other was with another pair of peers, with whom they had been living for one month prior to the separation. The isolation-housed peer responded to the separation with behavioral agitation, but no depression. The socially-housed peer's behavior did not differ from baseline during the separation. During successive reunions, all the separated monkeys, regardless of housing condition, exhibited declining levels of behaviors related to maintaining proximity to their attachment figure. Although the number of subjects is small, the results suggest that the presence of social support, in the form of a familiar peer, can ameliorate the response to separation, and that with repeated separations the responses of the monkeys changes significantly.

Age-dependent effects of isolation housing on the self-administration of ethanol in laboratory rats

Studies of the influence of housing conditions on ethanol self-administration have been inconsistent, with findings that isolation housing increases, decreases or produces no effects on ethanol intake. One possible explanation for these discrepant findings is that the effects of housing are dependent on the age at which the manipulation is performed. In the present experiment rats were housed from weaning or from age 65 days in either an isolated or grouped condition. After 12 weeks, they were tested for the voluntary oral self-administration of ethanol. Although all rats consumed comparable quantities of ethanol when lower concentrations were available, the rats isolated from weaning consumed significantly greater amounts of more concentrated ethanol than their group-housed counterparts. In contrast, there was no difference in ethanol consumption between isolated and grouped rats when they were differentially housed at maturity. These data suggest that an important determinant of ethanol intake in rats is related to environmental factors and that the influence of these factors is age-dependent.

A developmental-genetic analysis of aggressive behavior in mice. II. Cross-sex inheritance.

Differences in aggression produced by selective breeding for differential aggressiveness among male mice are also inherited by females: the expression of these differences in female mice depends on the conditions of assessment. In the standard opponents tests after isolation housing, consistent line differentiation was clear in males to the S 8 generation, but no aggressive behavior occurred at all in female tests. In contrast, in postpartum tests and in repeated intruder trials over the life span of group-reared animals, females from the line of high-aggressive males were more aggressive than females from the line of low-aggressive males. These findings indicate that the genetic pathways that mediate aggressive behavior in male and female mice are not entirely independent.

Female Aggression in Albino ICR Mice: Development, Social Experience, and the Effects of Selective Breeding

Social experience has been shown to mask or eliminate heritable effects on aggressive behavior in male mice. This work assesses the impact of social experience in females from lines of mice selectively bred for differential male aggressiveness. These results confirm the earlier report of cross-sex similarity in aggressive behavior after selection directed only at male behaviors ( Hood &amp; Cairns, 1 988 ). Repeated test experience increased aggressive behavior of S6 females. In addition, a genetic-developmental interaction was found, with enhanced aggressiveness in mature vs. young high-aggressive line females. Repeated test experience in 4 daily trials with mature S15 females obscured the clear line differences in attack frequency obtained on the first trial. In particular, a few highly aggressive individuals emerged among the group-reared low-aggressive line females. Isolation housing did not alter female aggressiveness. These findings are discussed in regard to conceptions of genetic-experiential-developmental interactions, and the role of female social behavior in microevolutionary processes.

Isolation housing decreases the effectiveness of morphine in the conditioned taste aversion paradigm.

Male Long Evans rats were obtained at 21 days of age and were housed in either an aggregated (four per double cage) or isolated (one per single cage) condition for 6 weeks. They were then placed on a fluid deprivation schedule that allowed them access to fluids for 20 min daily. This schedule was maintained for the remainder of the experiment. Following habituation, sensitivity to morphine-induced conditioned taste aversion (CTA) was compared in the differentially housed rats. On the 1st day and every 5 days thereafter the rats were presented with a 0.1% solution of sodium saccharin for the 20-min drinking period, followed immediately by an injection of morphine (0, 2.5, 5.0, 10.0, or 20.0 mg/kg). On intervening days they received water as the fluid. No drugs were given on these days. There was no difference in baseline saccharin consumption as a function of housing condition. In comparison with the isolated rats, the grouped animals were more sensitive to the CTA-inducing properties of low doses of morphine. These data strengthen the already existing evidence for the influence of the early housing environment on drug sensitivity and provide additional support for the conclusion that variability in response to a number of drugs of abuse can be reduced by environmental means. Possible mechanisms for the differences between isolation and aggregation housed rats are discussed.

Aggression, defeat and opioid activation in mice: Influences of social factors, size and territory

The aggressive components and opioid-mediated behavioral consequences of various types of intraspecific agonistic interactions between individual male mice were examined. The size of the animals, their previous social history (group or isolation housing) and territory on which the encounter took place were varied to yield 26 different ‘resident-intruder’ paradigms. In these agonistic encounters the latency to first attack, number of bites and time to defeat, as well as the number of attack bouts present varied according to the ‘resident-intruder’ paradigm employed. The behavioral consequences of aggression and defeat, including analgesia, increased activity and augmented feeding were determined from the subordinate mice in 5 representative agonistic interactions. These behavioral responses, which had been previously shown to be mediated by endogenous opioid systems also varied according to the ‘resident-intruder’ paradigm employed. When both mice were group-housed, there was no agonistic behavior, regardless of the size of the mice or the testing arena. In isolated animals the defeat posture was only observed in 1 of the 19 paradigms. It is suggested that various ‘resident-intruder’ pairings and agonistic interactions can provide a reliable and useful means of examining differential naturalistic stress-induced endogenous opioid activation.

The golden-mantled ground squirrel (Spermophilus lateralis) as a model for the effects of environmental enrichment in solitary animals.

It has been proposed that the brain effects induced by laboratory environmental enrichment may be a product of the social stimulation inherent in the standard enriched environment. This experiment was conducted in order to study the suitability of the golden-mantled ground squirrel Spermophilus lateralis (a solitary-living species) for studies attempting to dissociate social factors from other effects in brain and behavioral effects of environmental enrichment. Juvenile Spermophilus lateralis, born in the laboratory of mothers wild-caught while pregnant, were assigned singly to individual enriched conditions (I-EC) or impoverished (IC) conditions at 55-62 days (an age at which wild individuals would disperse from the natal burrow and live alone). After 30 days, the subjects were videotaped in two 10-min opportunities for exploration; following this, they were sacrificed and their brains dissected. Multiple indications of isolation stress were observed, including unusual difficulty in handling, stereotyped pacing behavior, and escape behaviors in the exploration arena. Comparisons between I-EC and IC showed no differences in whole-brain weight or weights of several brain regions. These results indicate that S. lateralis is not suitable for this type of study; in addition, this species' reported nonsociality is questioned, based on these subjects' reactions to isolation housing and field observations of social interactions in this species.

Effects of Long-term Isolation Housing on Pentobarbital-induced Sleep in Mice(From the viewpoint of interaction between housing condition and testing condition)

Effects of Long-term Isolation Housing on Pentobarbital-induced Sleep in Mice(From the viewpoint of interaction between housing condition and testing condition)