Differential effects of environmental enrichment and isolation housing on the hormonal and neurochemical responses to stress in the prefrontal cortex of the adult rat: relationship to working and emotional memories.

The present study was designed to investigate the modulation of the stress responses by the environmental conditions and its putative neurobiological mechanisms. For that an integrative study on the effects of environmental enrichment and isolation housing on (1) the corticosterone, dopamine and acetylcholine responses to acute restraint stress in the prefrontal cortex (PFC) of the awake rat; (2) the mRNA levels of glucocorticoid receptors (GRs) in the PFC, and (3) the behavioral responses to stress, related to the PFC (habituation to a novel environment, spatial-working memory and inhibitory avoidance response) was performed. Male Wistar rats were maintained from 3 to 6 months of age in two different conditions: enriched (EC) or impoverished (IC). Animals were stereotaxically implanted with bilateral guide cannulae in the PFC to perform microdialysis experiments to evaluate the concentrations of corticosterone, dopamine and acetylcholine. EC animals showed lower increases of corticosterone and dopamine but not of acetylcholine than IC animals in the PFC in response to acute restraint stress (20 min). In the PFC, GR mRNA levels showed a trend towards an enhancement in EC animals. EC reduced the days to learn the spatial working memory task (radial-water maze). Spatial working memory, however, was not different between groups in either basal or stress conditions. Inhibitory avoidance response was reduced in EC rats. The changes produced by EC in the neurochemical, neuroendocrine and behavioral parameters evaluated suggest that EC rats could show a better coping during an acute stress challenge.