GABA Synapses Mediate Neuroprotection after Ischemic and εPKC Preconditioning in Rat Hippocampal Slice Cultures

Abstract

Delayed neuroprotection against ischemic challenges is conferred by both ischemic preconditioning (IPC) and preconditioning by activation of the e-isoform of protein kinase C (ePKC-PC). In vivo, ischemic preconditioning enhances GABA release and ameliorates glutamate release during lethal cerebral ischemia. We tested the hypothesis that IPC and ePKC-PC confer neuroprotection by GABA synapses in rat organotypic hippocampal slices. Ischemic preconditioning or ePKC-PC was induced with 15 mins oxygen-glucose deprivation (OGD) or weRACK, a selective ePKC 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, ePKC-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 20.9 ± 6.1%. When applied during test ischemia, 100 nmol/L bicuculline abolished neuroprotection conferred by either IPC or ePKC-PC. We conclude that neuroprotection conferred by preconditioning depends on functional modifications of GABA synapses.

Activation of Epsilon Protein Kinase C-Mediated Anti-Apoptosis Is Involved in Rapid Tolerance Induced by Electroacupuncture Pretreatment Through Cannabinoid Receptor Type 1

“…33 The role for PKC in cerebral tolerance has been verified using various in vitro models in which PKC was activated after a preconditioning stimulus, such as application of ischemia or adenosine or NMDA, and was required for preconditioning-induced protection. 12,15,20,34 Similar to these studies in vitro, using an in vivo animal model PKC isoformspecific membrane translocation and protein expression in brain regions in intact mice with hypoxic preconditioning was investigated. Those results demonstrated that the development of cerebral hypoxic preconditioning was accompanied by an obvious increase in membrane translocation of PKC in the cortex and hippocampus, but no significant changes were noted in the membrane translocation of other PKC isoforms or in the whole protein expression of all 11 PKC isoforms, suggesting that activation of PKC might be involved in the development of cerebral hypoxic preconditioning of mice.…”

“…8 -11 Interestingly, among the different PKC isozymes, multiple studies have now demonstrated that epsilon PKC (PKC) was a key player in the induction of ischemic tolerance in various models of preconditioning. [12][13][14][15] Furthermore, a recent study reported that PKC confers acute tolerance to cerebral ischemic/reperfusion injury. 10 Based on these findings, the present study was undertaken to test the hypothesis that an activation of PKC was involved in EA pretreatment-induced neuroprotection via CB1 receptors in rat model of transient focal cerebral ischemia.…”

Effects of GABAA receptor blockade on regional cerebral blood flow and blood–brain barrier disruption in focal cerebral ischemia

“…Previous studies already showed that GABA A receptor agonists such as muscimol, barbiturates and volatile anesthetic agents were effective in neuroprotection in some models of cerebral ischemia [19,29,35]. It is possible that the characteristics of GABA A receptors in modulating rCBF and BBB in cerebral ischemia could have contributed to the neuroprotection reported by other animal studies.…”

“…In vivo, however, they could act differently because of interactions with neurons, neurotransmitters, and other chemicals present. Most of the GABA agonists have been known to decrease cerebral metabolism and rCBF, and provide some type of neuroprotection in in vivo and in vitro studies [6,[27][28][29]. Neurotransmitters may also alter cerebral capillary diameter by affecting pericytes in the microvasculature [30].…”

Global Cerebral Ischemia: Synaptic and Cognitive Dysfunction

“…εPKC preconditioning increases the average amplitude of GABA-related inhibitory post-synaptic events [159], maintains ion homeostasis during ischemia by inhibiting Na + /K + -ATPase and voltage gated Na + channels [160], improves cerebral blood flow [161], and phosphorylates the mitochondrial K + ATP channel [162]. The plethora of responses that are produced from εPKC activation indicates the necessity for a preconditioning agent to have numerous targets for neuroprotection or IPC mimetic.…”