Adrenergic regulation of GABA release from presynaptic terminals in rat cerebral cortex

Abstract

The α1-adrenoceptor agonist phenylephrine and the β-adrenoceptor agonist isoproterenol have opposite effects on evoked EPSPs (eEPSPs) in the cerebral cortex. The suppressive effects of phenylephrine on eEPSPs are mediated by modulation of postsynaptic glutamate receptors, whereas enhancement of eEPSPs by isoproterenol is due to facilitation of glutamate release from presynaptic terminals. The present study used whole-cell patch-clamp recordings from layer V pyramidal neurons in visuocortical slice preparations to assess the effects of phenylephrine and isoproterenol on the release probability of γ-aminobutyric acid (GABA). The present study recorded evoked inhibitory postsynaptic potentials (eIPSCs) by repetitive electrical stimulation (duration, 100 μs; 10 stimuli at 33 Hz) and miniature IPSCs (mIPSCs). The effects of phenylephrine (100 μM) depended on the amplitude of eIPSCs: phenylephrine decreased the paired-pulse ratios (PPRs) of eIPSCs with smaller amplitudes (