Evidence for a neuroinflammatory mechanism in delayed effects of early life adversity in rats: relationship to cortical NMDA receptor expression.

Postnatal maternal separation in rats causes a reduction of GABAergic parvalbumin-containing interneurons in the prefrontal cortex that first occurs in adolescence. This parvalbumin loss can be prevented by pre-adolescent treatment with a non-steroidal anti-inflammatory drug that also protects against excitotoxicity. Therefore, the neuropsychiatric disorders associated with early life adversity and interneuron dysfunction may involve neuroinflammatory processes and/or aberrant glutamatergic activity. Here, we aimed to determine whether delayed parvalbumin loss after maternal separation was due to inflammatory activity, and whether central administration of the anti-inflammatory cytokine interleukin (IL)-10 could protect against such loss. We also investigated the effects of maternal separation and IL-10 treatment on cortical NMDA receptor expression. Male rat pups were isolated for 4h/day between postnatal days 2-20. IL-10 was administered intracerebroventricularly through an indwelling cannula between P30 and 38. Adolescent prefrontal cortices were analyzed using Western blotting and immunohistochemistry for parvalbumin and NMDA NR2A subunit expression. We demonstrate that central IL-10 administration during pre-adolescence protects maternally separated animals from parvalbumin loss in adolescence. Linear regression analyses revealed that increased circulating levels of the pro-inflammatory cytokines IL-1β and IL-6 predicted lowered parvalbumin levels in maternally separated adolescents. Maternal separation also increases cortical expression of the NR2A NMDA receptor subunit in adolescence, which is prevented by IL-10 treatment. These data suggest that inflammatory damage to parvalbumin interneurons may occur via aberrant glutamatergic activity in the prefrontal cortex. Our findings provide a novel interactive mechanism between inflammation and neural dysfunction that helps explain deleterious effects of early life adversity on prefrontal cortex interneurons.