Allostatic gene regulation of inhibitory synaptic factors in the rat ventral hippocampus in a juvenile/adult stress model of psychopathology

Early life stress is an important vulnerability factor for the development of anxiety disorders, depression and late-onset cognitive decline. Recently, we demonstrated that juvenile stress (JS) lastingly enhanced long-term potentiation via reduction of steady-state glutamine synthetase mRNA expression and the associated dysregulation of the astrocytic glutamate-glutamine cycle in the rat ventral CA1. We now investigated the regulation of steady-state mRNA expression of neuronal gene products that determine GABAergic and glutamatergic neurotransmission in layers of the ventral and dorsal CA1 after JS. We further studied their interaction with stress in young adult age (AS) to address their putative role in psychopathology development. Strikingly, mRNA levels of the glutamic acid decarboxylase (GAD) isoforms GAD65 and of the GABA-A receptor α2 (Gabra2) were increased after single JS or AS, but not after combined JS/AS stress experience. In fact, JS/AS resulted in layer-specific reduction of Gabra2 and also of Gabra1 mRNA levels in the ventral CA1. Furthermore, GAD65 and Gabra2 mRNAs were correlated with glutamatergic AMPA and NMDA receptor subunit mRNAs after single JS and AS, but not after combined JS/AS. Together, these data indicate a loss of allostatic regulation of steady-state mRNA levels of key GABAergic components that may result in a dysregulation of excitation/ inhibition balance in the ventral CA1 upon dual stress exposure. Finally, individual differences in local glucocorticoid receptor mRNA expression may contribute to this regulation.