Maternal restraint stress delays maturation of cation-chloride cotransporters and GABAA receptor subunits in the hippocampus of rat pups at puberty.

The GABAergic synapse undergoes structural and functional maturation during early brain development. Maternal stress alters GABAergic synapses in the pup's brain that are associated with the pathophysiology of neuropsychiatric disorders in adults; however, the mechanism for this is still unclear. In this study, we examined the effects of maternal restraint stress on the development of Cation-Chloride Cotransporters (CCCs) and the GABAA receptor α1 and α5 subunits in the hippocampus of rat pups at different postnatal ages. Our results demonstrate that maternal restraint stress induces a transient but significant increase in the level of NKCC1 (Sodium-Potassium Chloride Cotransporter 1) only at P14, followed by a brief, yet significant increase in the level of KCC2 (Potassium-Chloride Cotransporter 2) at P21, which then decreases from P28 until P40. Thus, maternal stress alters NKCC1 and KCC2 ratio in the hippocampus of rat pups, especially during P14 to P28. Maternal restraint stress also caused biphasic changes in the level of GABAA receptor subunits in the pup's hippocampus. GABAA receptor α1 subunit gradually increased at P14 then decreased thereafter. On the contrary, GABAA receptor α5 subunit showed a transient decrease followed by a long-term increase from P21 until P40. Altogether, our study suggested that the maternal restraint stress might delay maturation of the GABAergic system by altering the expression of NKCC1, KCC2 and GABAA receptor α1 and α5 subunits in the hippocampus of rat pups. These changes demonstrate the dysregulation of inhibitory neurotransmission during early life, which may underlie the pathogenesis of psychiatric diseases at adolescence.