Alteration of aminergic neurotransmitter release after two consecutive transient global ischaemias: an in vivo microdialysis study in rat.

This study was designed to evaluate the effects of two consecutive ischaemias on extracellular monoaminergic neurotransmitter concentrations. The data on the neuroamine changes induced by the second ischaemia could be used to assess the delay in aminergic neurotransmission subsequent to the primary injury. Dopamine (DA), serotonin (5HT) and their metabolites, homovanillic acid (HVA), dihydroxyphenyl-acetic acid (DOPAC) and 5-hydroxyindolacetic acid (5-HIAA) were measured in vivo through striatal microdialysis of awake rats, using HPLC and electrochemical detection. Pulsinelli and Brierley's four-vessel occlusion model was used to induce a 20-minute global transient ischaemia in the forebrain. Two experimental groups were formed: the second ischaemic period was induced 3 h after the first one in group I (n = 5) and after 24 h in group II (n = 5). Dramatic increases in DA (150 times the baseline level) and 5HT (10 times the baseline level) were recorded during the first ischaemia, consistent with literature data. Metabolites of DA and 5HT (HVA and 5HIAA) decreased significantly. Baseline values were restored after 40 min of reperfusion. There was no significant difference between the effects of the first and second ischaemias on neurotransmitter release in group I. In group II, the second ischaemia did not significantly alter the baseline aminergic neurotransmitter content, although all the clinical signs of global ischaemia were present (in particular the loss of righting reflex). These original data could be explained by delayed impairment of release mechanisms, rather than by exhaustion of the releasable pools of these neurotransmitters one day after the first ischaemia.