Effect of ischaemia and reperfusion on the extra- and intracellular distribution of glutamate, glutamine, aspartate and GABA in the rat hippocampus, with a note on the effect of the sodium channel blocker BW1003C87

Abstract

The redistribution of neurotransmitter amino acids resulting from 20 min of ischaemia was studied in the rat hippocampus by quantitative, electron microscopic immunocytochemistry and by in vivo microdialysis. Changes in the distribution of glutamate, glutamine, aspartate and GABA in various cell compartments of CA1 were analysed immediately after ischaemia or after 60 min of reperfusion, by incubating ultrathin sections with antisera raised against protein glutaraldehyde conjugates of the respective amino acids and subsequently with a secondary antibody coupled to colloidal gold particles. Transverse microdialysis probes coupled with HPLC and implanted in the same animals were used to determine the extracellular concentration of amino acids in the left hippocampus and to apply a drug (BW1003C87) believed to modify the extracellular release of amino acids induced by ischaemia. Forebrain ischaemia was induced by temporary occlusion of the common carotid arteries in rats with permanently occluded vertebral arteries. The extracellular concentrations of glutamate, aspartate and GABA increased markedly during ischaemia, but returned rapidly to normal during reperfusion. BW1003C87 (250 microM, in the dialysis fluid) did not modify the increase in extracellular concentration of amino acids during ischaemia. Glutamate-like immunoreactivity was reduced in pyramidal cell somata both immediately after ischaemia and after 60 min of reperfusion. This reduction appeared to be somewhat less pronounced for cells in the left hemisphere (perfused with BW1003C87) than in the contralateral hemisphere. Ischaemia caused no consistent changes in terminals. The ratio between the intracellular levels of glutamate and glutamine was assessed by double-labelling immunocytochemistry, using two different gold particle sizes. The glutamate-glutamine ratio in glial cells was greatly increased after ischaemia, but recovered to a normal level within 1 h of reperfusion. Aspartate-like immunoreactivity was substantially reduced in pyramidal cell somata both immediately and 60 min after ischaemia, while profiles that were immunopositive for GABA in control brains showed increased GABA immunolabelling. These results suggest that postsynaptic neuronal elements as well as glial cells contribute to the extracellular overflow of excitatory amino acids during an ischaemic event: post-synaptic elements by leaking or releasing glutamate and aspartate, and glial cells by losing their ability to convert glutamate to glutamine effectively.(ABSTRACT TRUNCATED AT 400 WORDS)

Glutamate release by an Na+ load and oxidative stress in nerve terminals: relevance to ischemia/reperfusion

“…In vivo studies showed a recovery of glutamate release to the baseline during reperfusion (Torp et al 1993); however, in other studies a transient further increase in the release of glutamate was found in the initial phase (Taguchi et al 1996;Caragine et al 1998) or after hours of reperfusion (Matsumoto et al 1996;Yang et al 2001). In addition, in vivo neuroprotection exerted by NMDA and non-NMDA receptor antagonists, even when added after the initiation of a transient ischemia (Park et al 1988;Sheardown et al 1990;Nellgard and Wieloch 1992) suggested that glutamate neurotransmission could also be important after the ischemic attack, during reperfusion (see also Nishizawa 2001).…”

Sequential Release of GABA by Exocytosis and Reversed Uptake Leads to Neuronal Swelling in Simulated Ischemia of Hippocampal Slices

“…The increase in [GABA] i is primarily in neuronal terminals, rather than glia (Torp et al, 1993;Madl and Royer, 2000), so the rise of [GABA] i produced by these mechanisms will preferentially promote the reversal of the neuronal GAT-1.…”

Changes in Localization of Amino Acids in the Detached Cat Retina

“…Additionally, the impairment of the cell membrane due to metabolic disruption may be related to the increase in the amino acids. There is a signifi cant increase in the extracellular concentration of glutamate, aspartate and GABA immediately after ischemia [24,31] . If ischemia makes the cell membrane of the photoreceptor more permeable, glutamate and aspartate may freely penetrate the membrane followed by the increase in the intracellular concentration of glutamate and aspartate.…”

“…The previous studies reported that the intracellular concentration of glutamate, aspartate and glutamine decrease in neural cells and glutamate uptake is disrupted following brain ischemia [3,24] . The present results in retinal detachment are in contrast to the previous results in brain tissue.…”