The aim of this study was to test whether environmental enrichment alters the status and responsiveness of pituitary-adrenocortical and sympathetic-adrenomedullary hormones in rats. Previous studies have shown that rats kept in an enriched environment differ from those kept in standard cages in dendritic branching, synaptogenesis, memory function, emotionality and behaviour. In male Wistar rats kept in an enriched environment for 40 days, we studied basal concentrations of hormones, endocrine responses to 5-HT(1A) challenge and responsiveness and adaptation to repeated handling. Environmental enrichment consisted of large plexiglass cages with 10 rats per cage, which contained variety of objects exchanged three times a week. Rats kept in this enriched environment had higher resting plasma concentrations of corticosterone, larger adrenals and increased corticosterone release to buspirone challenge compared to controls. Lower adrenocorticotropic hormone, corticosterone and adrenaline responses to handling were noticed in rats kept in an enriched environment. Exposure to repeated handling led to a more rapid extinction of corticosterone responses in rats kept in an enriched environment. Thus, environmental enrichment leads to pronounced changes in neuroendocrine regulation, including larger adrenals and increased adrenocortical function, which are so far considered to be indication of chronic stress.

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The present work was aimed at verifying the following hypotheses: (a) lamotrigine, a drug used to treat mood disorders, affects regulation of stress hormone release in humans, and (b) non-verbal behavior during mental stress situations (public speech) is related to hormonal responses. To achieve these aims, we performed a controlled, double-blind study investigating hormonal responses and non-verbal behavior during public speech in healthy subjects with placebo or lamotrigine (300 mg per os) pretreatment. The stress procedure was performed in 19 young healthy males 5 h following drug or placebo administration. Data were obtained from cardiovascular monitoring, blood and saliva samples, as well as the video-recorded speech. Pre-stress hormone levels were not affected by lamotrigine treatment. Lamotrigine significantly inhibited diastolic blood pressure, growth hormone and cortisol increases during psychosocial stress. In contrast, it potentiated plasma renin activity and aldosterone responses. Non-verbal behavior analysis revealed a correlation between catecholamines and submissive or flight behavior in controls, while between catecholamines and displacement behavior following lamotrigine administration. In conclusion, effects of lamotrigine on hormone release might be of value for its mood-stabilizing action used in the treatment of bipolar disorder. The data are in support of a stimulatory role of glutamate in the control of cortisol and growth hormone release during psychosocial stress in humans; however, further studies using more selective drugs are needed to prove this suggestion. The effects on plasma renin activity and aldosterone release observed seem to be related to other actions of lamotrigine.

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Neuroendocrine activation during stress is affected by many factors contributing to the variability of the stress response. The present study was aimed at evaluating long-term changes in hypothalamo-pituitary-adrenocortical (HPA) axis function and in hedonic behavior in adult offspring prenatally stressed by maternal food restriction, with attention on possible gender differences. Adult offspring were blood sampled via a tail artery cannula. Prenatally stressed females had significantly higher adrenal weights compared to males. Plasma ACTH levels, which rose in response to acute stress induced by handling, were significantly higher in females compared to those in males. A similar pattern was found in plasma corticosterone. The rise in ACTH levels was more pronounced in prenatally stressed rats though the rise in corticosterone failed to be modified. Corticotropin releasing hormone (CRH) and proopiomelanocortin mRNA levels in the hypothalamic paraventricular nucleus and anterior pituitary, respectively, were found to be unchanged. The present experiments failed to reveal a decrease in hedonic behavior in prenatally stressed rats. In contrast, in male offspring a tendency to a higher sucrose preference was observed. These data together with observed changes in hormone and CRH mRNA levels indicate that the gestational stress used did not result in a depression-like state in adult offspring.

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Physical activities such as long-distance running can form a habit and might be related to drug-induced addictive behaviors. We investigated possible modulations of N-methyl-D-aspartate (NMDA) receptor subunits during voluntary wheel running in brain regions implicated in reward and addiction. It was observed that Lewis rats progressively increased their amount of daily running, reaching maximum levels of 4-6 km/day. After 3 weeks of running, mRNA levels coding for NR2A and NR2B subunits were increased in the ventral tegmental area, while only NR2A mRNA levels were found to be elevated in the frontal cortex. Long-term wheel running was also associated with increased binding of specific NMDA receptor antagonist [3H]CGP39653 in the frontal cortex. Moreover, pharmacological inhibition of glutamate release by repeated administration of phenytoin (20 mg/kg IP for 21 days) significantly suppressed daily running. These results suggest that glutamatergic neurotransmission might be related to neurobiological mechanisms underlying the compulsive character of voluntary wheel running.