Effects of single and group housing conditions and alterations in social and physical contexts on amphetamine-induced behavioral sensitization in rats

Environmental Enrichment Components Required to Reduce Methamphetamine-Induced Behavioral Sensitization in Mice: Examination of Behaviors and Neural Substrates

Environmental enrichment (EE) involves the presentation of various sensory, physical, social, and cognitive stimuli in order to alter neural activity in specific brain areas, which can ameliorate methamphetamine (MAMPH)-induced behavioral sensitization and comorbid anxiety symptoms. No previous studies have comprehensively examined which EE components are critical for effectively reducing MAMPH-induced behavioral sensitization and anxiety. This study examined different housing conditions, including standard housing (SH, No EE), standard EE (STEE), physical EE (PEE), cognitive EE (CEE), and social EE (SEE). In the beginning, mice were randomly assigned to the different combinations of housing conditions and injections, consisting of No EE/Saline, No EE/MAMPH, STEE/MAMPH, PEE/MAMPH, CEE/MAMPH, and SEE/MAMPH groups. Then, the mice received intraperitoneal injections of 1 mg/kg MAMPH or normal saline daily for 7 days, followed by a final injection of 0.5 mg/kg MAMPH or normal saline. After behavioral tests, all mice were examined for c-Fos immunohistochemical staining. The results showed that MAMPH induced behavioral sensitization as measured by distance traveled. MAMPH appeared to induce lowered anxiety responses and severe hyperactivity. All EE conditions did not affect MAMPH-induced lowered anxiety behaviors. STEE was likely more effective for reducing MAMPH-induced behavioral sensitization than PEE, CEE, and SEE. The c-Fos expression analysis showed that the medial prefrontal cortex (i.e., cingulate cortex 1 (Cg1), prelimbic cortex (PrL), and infralimbic cortex (IL)), nucleus accumbens (NAc), basolateral amygdala (BLA), ventral tegmental area (VTA), caudate-putamen (CPu), and hippocampus (i.e., CA1, CA3, and dentate gyrus (DG)) contributed to MAMPH-induced behavioral sensitization. The Cg1, IL, NAc, BLA, VTA, CPu, CA3, and DG also mediated STEE reductions in MAMPH-induced behavioral sensitization. This study indicates that all components of EE are crucial for ameliorating MAMPH-induced behavioral sensitization, as no individual EE component was able to effectively reduce MAMPH-induced behavioral sensitization. The present findings provide insight into the development of non-pharmacological interventions for reducing MAMPH-induced behavioral sensitization.

Roles of nucleus accumbens shell and core in footshock-induced stress altering behavioral sensitization by methamphetamine in acquisition and testing: Running head: stress, nucleus accumbens, and behavioral sensitization

How the subregions of the nucleus accumbens (NAc) shell and core and stress are involved in behavioral sensitization induced by psychostimulants remains unclear. The present study manipulated methamphetamine (MAMPH) injections, lesions of the NAc shell or core, and footshock-treatment-induced stress to address this issue. The present data showed that during the acquisition phase, MAMPH injections, lesions of the NAc shell, and footshock treatments induced hyperactivity for the NAc shell. For the NAc core, MAMPH injections induced hyperactivity; however, lesions of the NAc core did not affect locomotor activity. Footshock treatments disrupted hyperactivity of behavioral sensitization. During the testing phase, MAMPH injections, lesions of the NAc shell, and footshock-treatment-induced stress facilitated hyperactivity for the NAc shell. For the NAc core, MAMPH injections and footshock-treatment-induced stress increased hyperactivity. However, the lesion of the NAc core did not affect locomotor activity. In conclusion, MAMPH injections and footshock-treatment-induced stress play an excitatory role for the NAc shell in acquisition and testing. For the NAc core, footshock-treatment-induced stress plays an inhibitory role in acquisition but an excitatory role in testing. The NAc core was not involved in MAMPH-induced behavioral sensitization in acquisition and testing. The NAc shell plays an inhibitory role in acquisition and testing phases. The present data might provide some insights for drug addiction. The results should be discussed further.

CNS Safety Screening Under ICH S7A Guidelines Requires Observations of Multiple Behavioral Units to Assess Motor Function

In the adoption of behavior as a critical end point in safety pharmacology and neurotoxicity screening, federal regulatory agencies have shifted the predominating scientific perspective from pharmacology back to the experimental analysis of behavior (psychology). Nowhere is this more evident than in tier I safety assessment of the central nervous system (CNS). The CNS and peripheral nervous system have multiple behavioral units of general activity. A complete picture of the motor control neural pathways cannot be measured by any one single approach. The CNS safety protocols under International Council for Harmonization of Technical Requirements for Pharmaceuticals for Human Use S7A are required to be conducted in accordance with Good Laboratory Practices by trained technical staff. The CNS safety assessments necessitate the inclusion of a thorough and detailed behavioral analysis of home cage activity, the response to handling, and transportation to and observations within an open-field apparatus with ancillary measures of basal muscle tone, muscle strength, and tremor in a functional observation battery, as well as quantitative measurements of 3-dimensional activity in an automated photobeam arena. Cost-cutting initiatives or a radical application of the "reduce use" principle of the 3 Rs only jeopardize the spirit, intent, and predictive validity of tier I safety testing assays dictated by current drug safety guidelines.

Sex differences in morphine-induced behavioral sensitization and social behaviors in ICR mice

Gender and genetic strain are two prominent variants that influence drug abuse. Although certain sex-related behavioral responses have been previously characterized in ICR mice, little is known about the effects of sex on morphine-induced behavioral responses in this outbred strain. Therefore, in this study, we investigated the sex differences of morphine-induced locomotion, anxiety-like and social behaviors in ICR mice. After morphine or saline exposure for four consecutive days (twice daily), increased locomotion, more time spent in the central area, as well as attenuated rearing and self-grooming behaviors were found in morphine-treated females in an open field; no differences were found in locomotion and the time spent in the central area between male and female controls. When interacting with the same-sex individuals, female controls were engaged in more social investigation, following, body contacting and self-grooming behaviors than controls; morphine exposure reduced contacting and self-grooming behaviors in females; in contrast, these effects were not found in males. These results indicate that female ICR mice are more prosocial and are more susceptible to morphine exposure than males.

Amphetamine sensitization and cross-sensitization with acute restraint stress: impact of prenatal alcohol exposure in male and female rats

RATIONALE

Individuals with fetal alcohol spectrum disorder (FASD) are at increased risk for substance use disorders (SUD). In typically developing individuals, susceptibility to SUD is associated with alterations in dopamine and hypothalamic-pituitary-adrenal (HPA) systems, and their interactions. Prenatal alcohol exposure (PAE) alters dopamine and HPA systems, yet effects of PAE on dopamine-HPA interactions are unknown. Amphetamine-stress cross-sensitization paradigms were utilized to investigate sensitivity of dopamine and stress (HPA) systems, and their interactions following PAE.

METHODS

Adult Sprague-Dawley offspring from PAE, pair-fed, and ad libitum-fed control groups were assigned to amphetamine-(1-2 mg/kg) or saline-treated conditions, with injections every other day for 15 days. Fourteen days later, all animals received an amphetamine challenge (1 mg/kg) and 5 days later, hormones were measured under basal or acute stress conditions. Amphetamine sensitization (augmented locomotion, days 1-29) and cross-sensitization with acute restraint stress (increased stress hormones, day 34) were assessed.

RESULTS

PAE rats exhibited a lower threshold for amphetamine sensitization compared to controls, suggesting enhanced sensitivity of dopaminergic systems to stimulant-induced changes. Cross-sensitization between amphetamine (dopamine) and stress (HPA hormone) systems was evident in PAE, but not in control rats. PAE males exhibited increased dopamine receptor expression (medial prefrontal cortex (mPFC)) compared to controls.

CONCLUSIONS

PAE alters induction and expression of sensitization/cross-sensitization, as reflected in locomotor, neural, and endocrine changes, in a manner consistent with increased sensitivity of dopamine and stress systems. These results provide insight into possible mechanisms that could underlie increased prevalence of SUD, as well as the impact of widely prescribed stimulant medications among adolescents with FASD.

Differences in cocaine-induced place preference persistence, locomotion and social behaviors between C57BL/6J and BALB/cJ mice

C57BL/6J and BALB/cJ mice display significant differences in sociability and response to drugs, but the phenotypic variability of their susceptibility to cocaine is still not well known. In this study, the differences between these two mice strains in the persistence of cocaine-induced conditioned place preference (CPP), as well as the locomotion and social behaviors after the 24-hour withdrawal from a four-day cocaine (20 mg/kg/day) administration were investigated. The results showed that the cocaine-induced CPP persisted over two weeks in C57BL/6J mice, while it diminished within one week among BALB/cJ mice. After 24-hours of cocaine withdrawal, high levels of locomotion as well as low levels of social interaction and aggressive behavior were found in C57BL/6J mice, but no significant changes were found in BALB/cJ mice, indicating that cocaine-induced CPP persistence, locomotion and social behavior are not consistent between these two strains, and that overall C57BL/6J mice are more susceptible to cocaine than BALB/cJ mice at the tested doses.

Concurrent choice for social interaction and amphetamine using conditioned place preference in rats: effects of age and housing condition

BACKGROUND

Social interaction can serve as a natural reward that attenuates drug reward in rats; however, it is unknown if age or housing conditions alter the choice between social interaction and drug.

METHODS

Individually- and pair-housed adolescent and adult male rats were tested using conditioned place preference (CPP) in separate experiments in which: (1) social interaction was conditioned against no social interaction; (2) amphetamine (AMPH; 1mg/kg, s.c.) was conditioned against saline; or (3) social interaction was conditioned against AMPH.

RESULTS

Social interaction CPP was obtained only in individually-housed adolescents, whereas AMPH CPP was obtained in both individually-housed adolescents and adults; however, the effect of AMPH was not statistically significant in pair-housed adults. When allowed to choose concurrently between compartments paired with either social interaction or AMPH, individually-housed adolescents preferred the compartment paired with social interaction, whereas pair-housed adolescents preferred the compartment paired with AMPH. Regardless of housing condition, adults showed a similar preference for the compartments paired with either social interaction or AMPH.

CONCLUSIONS

Although some caution is needed in interpreting cross-experiment comparisons, the overall results suggest that individually-housed adolescents were most sensitive to the rewarding effect of social interaction, and this hypersensitivity to social reward effectively competed with AMPH reward.

Effect of early life housing manipulation on baseline and drug-induced behavioural responses on neurochemistry in the male rat

Employing environmental enrichment (EE) provides continual sources of dynamic interaction for animals. Though an established discipline in behavioural science, the consequences of EE on behavioural pharmacological tests have not been extensively examined. The purpose of this study was to examine the consequences of EE (or isolation housing) on a range of behavioural pharmacological tests and brain monoamine and brain-derived neurotrophic factor (BDNF) expression in the rat. Male rats were randomly assigned to IC (isolation), SC (standard group-housed) or EE conditions. IC and SC animals were housed singly or in groups of four in standard cages, whilst the EE group were housed in groups of four in larger cages enriched with a variety of wooden, cardboard and plastic objects. After 5weeks of housing, its impact on the effects of diazepam (DZP) in the elevated plus maze (EPM); desipramine (DMI) in the forced swim test (FST) and amphetamine (AMP) effects on homecage activity were assessed. Post-mortem monoamine and BDNF levels were analysed using HPLC and ELISA. EE rats displayed reduced activity in the OFT, however no other differences were found in baseline behaviours. DMI reduced immobility time in the FST, but only for rats housed in IC, while AMP effects were somewhat greater for socially-housed animals than those in IC. There were no housing effects on monoamine or BDNF levels in discreet brain regions. The results suggest that post-weaning enrichment had no significant effect on baseline behaviours or monoamine and BDNF levels, thus it is suitable to implement as a commonplace husbandry practice, however, caution must be taken when investigating responsiveness to psychotropic drugs.