Environmental enrichment and social isolation differentially shape catecholaminergic development after early...

Methamphetamine exposure during early postnatal development can disrupt the maturation of catecholaminergic neurotransmitter systems, which play a critical role in cognitive and emotional functions. Increasing evidence suggests that environmental conditions during development may substantially modify these neurochemical effects. The present study investigated how early-life methamphetamine exposure interacts with environmental factors to influence catecholaminergic development during adolescence. Male Wistar rats were exposed to methamphetamine during postnatal days 1-12 either directly by pup injections or indirectly through maternal administration during lactation. Animals were subsequently reared under different environmental conditions consisting of standard housing or enriched environment during the preweaning period, followed by either group housing or social isolation after weaning. Dopamine and noradrenaline concentrations were measured in the hippocampus and striatum during early, mid, and late adolescence. Environmental enrichment markedly increased dopamine and noradrenaline levels in the striatum and, to a lesser extent, in the hippocampus, particularly during early and mid-adolescence. In contrast, postweaning social isolation tended to produce opposite effects and was associated with increased noradrenergic activation in the hippocampus during mid-adolescence. Methamphetamine exposure produced more modest neurochemical alterations, with direct exposure inducing clearer changes than indirect exposure. However, many of these drug-related effects were strongly modulated by environmental conditions. These findings demonstrate that environmental context plays a major role in shaping catecholaminergic maturation during adolescence and may either buffer or exacerbate neurochemical consequences of early-life psychostimulant exposure.