GABAA receptors facilitate spontaneous glutamate release in rat periaqueductal gray neurons

The functional role of presynaptic γ-aminobutyric acid (GABA)A receptors in excitatory glutamatergic transmission was examined in rat periaqueductal gray neurons recorded using a conventional whole-cell patch clamp technique. Muscimol, a GABAA receptor agonist, significantly increased the frequency of spontaneous excitatory postsynaptic currents without affecting their amplitude, and this effect was completely blocked by the selective GABAA receptor antagonist. The muscimol-induced facilitation of spontaneous excitatory postsynaptic current frequency disappeared either in the presence of tetrodotoxin or Cd. The results suggest that the activation of presynaptic GABAA receptors directly depolarizes glutamatergic terminals resulting in the facilitation of spontaneous glutamate release, and that presynaptic GABAA receptors play an important role in the regulation of various physiological functions mediated by the periaqueductal gray.