¹Cerebral Vascular Disease Research Center, Department of Neurology, Leonard M. Miller School of Medicine, University of Miami, Miami, Florida, USA

Correspondence: Dr RA DeFazio, Department of Neurology, D4-5, University of Miami Miller School of Medicine, 1501 NW 9th Ave, PO Box 016960, Miami, FL 33101, USA. E-mail: rdefazio@med.miami.edu

Received 3 July 2008; Revised 10 September 2008; Accepted 4 October 2008; Published online 29 October 2008.

Abstract

Delayed neuroprotection against ischemic challenges is conferred by both ischemic preconditioning (IPC) and preconditioning by activation of the -isoform of protein kinase C (PKC-PC). In vivo, ischemic preconditioning enhances GABA release and ameliorates glutamate release during lethal cerebral ischemia. We tested the hypothesis that IPC and PKC-PC confer neuroprotection by GABA synapses in rat organotypic hippocampal slices. Ischemic preconditioning or PKC-PC was induced with 15 mins oxygen-glucose deprivation (OGD) or RACK, a selective PKC activator; and test ischemia consisted of 40 mins OGD. At the time of peak neuroprotection (48 h after preconditioning), we recorded GABA_A receptor-mediated miniature postsynaptic currents (GABA mPSCs) in vulnerable CA1 pyramidal neurons using whole-cell voltage clamp techniques. The frequency and amplitude of GABA mPSCs significantly increased 48 h after IPC. In contrast, PKC-PC enhanced only the amplitude of GABA mPSCs with no effect on frequency. We next asked if neuroprotection depended on these changes in GABA synapses. Weak antagonism of the GABA_A receptor with bicuculline (100 nmol/L) decreased the amplitude of GABA mPSCs by 20.96.1%. When applied during test ischemia, 100 nmol/L bicuculline abolished neuroprotection conferred by either IPC or PKC-PC. We conclude that neuroprotection conferred by preconditioning depends on functional modifications of GABA synapses.