PLASTICITY IN FAST SYNAPTIC INHIBITION OF ADULT OXYTOCIN NEURONS CAUSED BY SWITCH IN GABA(A) RECEPTOR SUBUNIT EXPRESSION

We found that magnocellular oxytocin neurons in adult female rats exhi bit an endogenous GABA(A) receptor subunit switch around parturition: a decrease in alpha 1:alpha 2 subunit mRNA ratio correlated with a dec rease in allopregnanolone potentiation and increase in decay time cons tant of the GABA(A) receptor-mediated IPSCs in these cells. The causal relationship between changes in alpha 1:alpha 2 mRNA ratio and the io n channel kinetics was confirmed using in vitro antisense deletion. Fu rther, GABA(A) receptors exhibited a tonic inhibitory influence upon o xytocin release in vivo, and allopregnanolone helped to restrain oxyto cin neuron in vitro firing only before parturition, when the alpha 1:a lpha 2 subunit mRNA ratio was still high. Such observations provide ev idence for the physiological significance of GABA(A) receptor subunit heterogeneity and plasticity in the adult brain.