Short-term potentiation of GABAergic synaptic inputs to vasopressin and oxytocin neurones.

The magnocellular vasopressin (VP) and oxytocin (OT) neurones undergo long-term synaptic plasticity to accommodate prolonged hormone demand. By contrast, rapidly induced,transient synaptic plasticity in response to brief stimuli could enable the activation of magnocellular neurones in response to acute challenges. Here, we report a robust short-term potentiation of asynchronous GABAergic synaptic inputs (STP(GABA)) to VP and OT neurones of the hypothalamic supraoptic nucleus elicited by repetitive extracellular electrical stimulation.The STP(GABA) required extracellular Ca2+, but did not require activation of glutamate, VP or OT receptors or nitric oxide synthesis. Presynaptic action potential generation was necessary for the induction, but not the maintenance, of STP(GABA). The STP(GABA) led to a minutes-long GABA(A)receptor-dependent increase in spike frequency in VP neurones, but not in OT neurones,consistent with an excitatory function of GABA in only VP neurones and with the generation of prolonged bursts of action potentials in VP neurones. Therefore, this short-term plasticity of GABAergic synaptic inputs is likely to play very different roles in the regulation of OT and VP neurones and their distinct patterns of physiological activation.