Effect of cerebral ischemia on synaptosomal uptake and release of 3H-5-hydroxytryptamine in adult and young Mongolian gerbils

Transient focal ischemia affects the cAMP second messenger system and coupled dopamine D1 and 5-HT1A receptors in the living monkey brain: a positron emission tomography study using microdialysis

Using positron emission tomography (PET) and microdialysis, the present study showed that neuronal damages after transient focal ischemia was partly induced by hyperactivation of the cyclic adenosine 3',5'-monophosphate (cAMP) second messenger system through modulations of dopamine D, and serotonin 5-HT1A receptors in the living brains of cynomolgus monkeys. Occlusion of the right middle cerebral artery for 3 hours suppressed CBF in the striatum, and reperfusion induced hyperperfusion in the neocortex and striatum of the occluded side. Six hours after reperfusion, the activity of the cAMP second messenger system assayed with [11C]rolipram was significantly facilitated in the neocortex and striatum where CBF was lowered more than 40% of normal during occlusion ("ischemic" area). Seven days later, impaired dopamine D1 and 5-HT1A receptor binding, measured with [11C]SCH23390 and [carbonyl-11C]WAY-100635, respectively, was observed in the ischemic area. Microdialysis analysis revealed that the striatal dopamine level provided a transient and marked increased during occlusion and after reperfusion, whereas the cortical serotonin level transiently increased only after reperfusion, and was at an undetectable level thereafter. Administration of rolipram (0.1 and 1 mg/kg, intravenously) during occlusion facilitated reduction of dopamine D1 binding, whereas rolipram administration 6 hours after reperfusion induced a further decrease in 5-HT1A receptor binding. These results suggest that the activation of cAMP second messenger system modulated by dopamine D1 and 5-HT1A receptors could be involved in the neuronal degeneration after transient cerebral ischemic insult.

Chronic methamphetamine administration inhibits cerebral ischemia-induced hyperactivity in Mongolian gerbils

The effect of single and chronic methamphetamine (MAP) administration on ischemia-induced hyperactivity was investigated and the mechanism of ischemia-induced hyperactivity was discussed. Ischemia-induced hyperactivity was recognized 3 h after ischemia. However, ischemia-induced hyperactivity at 1 day after ischemia was inhibited when MAP, in a dose of 10 mg/kg, was administered for 7 days and withdrawn for 7 days. It was reported that MAP treatment caused an irreversible decrease in the number of dopamine (DA) uptake sites. In addition to this, monoamine oxidase and the uptake of DA into the nerve terminals are disturbed by cerebral ischemia. Therefore, a lot of DA release happened during and immediately after ischemia, and a marked down-regulation of DA receptor occurred 24 h after ischemia in MAP-injected group. It is conceivable that the DA receptor, especially the presynaptic DA uptake site, is related to the occurrence of ischemia-induced hyperactivity. Further studies appear to be necessary to clarify acceptor susceptibility when neurotransmitters are normalized after transient ischemia.

Alteration of dopamine transport and dopamine D(2) receptor binding in the brain induced by early and late consequences of global ischaemia caused by cardiac arrest in the rat

This study was designed to determine the effects of global cerebral ischaemia caused by temporary cardiac arrest and the early and late consequences of this ischaemia on dopamine transport and dopamine D(2) receptor binding in rat brain. The effects of 10 min of global ischaemia were measured immediately and after 1 h and 7 days post-resuscitation. A decrease of dopamine uptake in the rats by synaptosomes was noted immediately following global ischaemia and 1 h after resuscitation. However, at 7 days post-resuscitation, the dopamine uptake returned to control values. Reversibility of the changes in the synaptosomal dopamine uptake is undoubtedly a favourable sign. Global ischaemia and reperfusion after 1 h or 7 days did not show altered rates of dopamine release but did affect the dopamine D(2) receptor. An observed increase of receptor affinity may be an adaptive response to the reduction in binding capacity. The reduction of visible D(2) receptor binding sites in the early post-resuscitation phase, which was extended to the period of 7 days after resuscitation without recovery, is probably associated with neuronal necrotic damage.

Differential expression of HSC73 and HSP72 mRNA and proteins between young and adult gerbils after transient cerebral ischemia: relation to neuronal vulnerability

This study presents a quantitative comparison of the time courses and regional distribution of both constitutive HSC73 and inducible HSP72 mRNA expression and their respective encoded proteins between young (3-week-old) and adult (3-month-old) gerbil hippocampus after transient global ischemia. The constitutive expression of HSC73 mRNA and protein in the hippocampus of the young sham-operated gerbils was significantly higher than in the adults. The HSC73 mRNA expression after ischemia in the CA1 layer of young gerbils was greater than in adult gerbils. HSC73 immunoreactivity was not significantly changed after ischemia-reperfusion in adult hippocampus, whereas it decreased in young gerbils. Ischemia-reperfusion led to induction of HSP72 mRNA expression throughout the hippocampus of both young and adult gerbils. HSP72 mRNA induction was more intense and sustained in the CA1 subfield of young gerbils; this was associated with a marked induction of HSP72 proteins and neuronal survival. The transient expression of HSP72 mRNA in the CA1 layer of adult gerbils was not associated with a subsequent synthesis of HSP72 protein but was linked to neuronal loss. Expression of HSP72 mRNA was shifted to an earlier period of reflow in CA3 and dentate gyrus (DG) subfields of young animals. These findings suggest that the induction of both HSP72 mRNA and proteins in the CA1 pyramidal neurons of young gerbils, as well as the higher constitutive expression of HSC73, may partially contribute to higher neuronal resistance of young animals to transient cerebral ischemia.

Cerebral ischemia in young and adult gerbils: effects on cholinergic metabolism

The effect of transient cerebral ischemia on cholinergic metabolism was investigated in adult and young gerbils subjected to bilateral carotid artery occlusion (15 min) alone or with release. Ischemia decreased brain acetylcholine (ACh) and increased choline (Ch) levels, affecting the young to a lesser degree than the adult gerbils. Blood recirculation induced a rapid early restoration of brain ACh levels in young animals, whereas a tremendous rebound of ACh was observed in the adults. After 2 h of reflow, Ch levels normalized in the adult brain, whereas a decreased choline level was seen in the young brain. This is the first study demonstrating an age-dependent susceptibility of cholinergic neurotransmission to cerebral ischemia.

The relationship between cerebral ischemic edema and monoamines: revisited

The association of changes in the metabolic pathway of monoamines (dopamine and 5-hydroxytryptamine) with mitochondrial enzymatic systems which are involved in the production and removal of free radicals formed during dopamine metabolism and formation of edema was investigated in bilateral brain ischemia in gerbils. The results suggest that the involvement of DA-derived free radicals in brain edema is unlikely in early reflow, because disbalance between H2O2-producing reactions of DA-metabolism, and mitochondrial antioxidative capacity does not occur prior to 1 hour reflow after 15 min bilateral ischemia in gerbils. However, the findings of this study reinforce the participation of 5-HT in the formation of ischemic brain edema.

Acute noise stress reduces [3H]5-hydroxytryptamine uptake in rat brain synaptosomes: protective effects of buspirone and tianeptine

Acute noise stress decreased [3H]5-hydroxytryptamine ([3H]5-HT) uptake in synaptosomes from rat hypothalamus, hippocampus and cerebral cortex. The decrease was due to the maximum rate of [3H]5-HT uptake, which peaked 30 min after stress and partly returned to resting values within 4 h, with no changes in affinity (Km values). No changes in [3H]paroxetine binding and basal [3H]5-HT release were found in stressed rats. Tianeptine, given at the dose of 10 mg/kg 1 h before stress, counteracted the noise-induced decrease of 5-HT uptake, since it increased [3H]5-HT uptake in both resting and stressed animals, but did not prevent the rise in plasma corticosterone of stressed rats. Buspirone pretreatment had no effect on [3H]5-HT uptake in resting rats but prevented the noise-induced decrease in [3H]-HT uptake. Diazepam did not modify either the basal or the noise-induced reduction in [3H]5-HT uptake. The evidence that treatments reducing extrasynaptic 5-HT, by increasing its reuptake (tianeptine) or reducing its release (buspirone) in innervated regions are able to modify the stress-induced decrease in 5-HT uptake, further confirms the importance of serotonin in the mechanisms mediating neurochemical responses to stress.

Effects of cerebral ischemia on regional dopamine release and D1 and D2 receptors

To expand on the nature of regional cerebral vulnerability to ischemia, the release of dopamine (DA) and dopaminergic (D1 and D2) receptors were investigated in Mongolian gerbils subjected to bilateral carotid artery occlusion (15 min) alone or with reflow (1-2 h). Extracellular cortical and striatal content of DA and its metabolites was measured by microdialysis using HPLC with electrochemical detection. The kinetic properties of D1 and/or D2 receptor binding sites were determined in cortical and striatal membranes with the use of radiolabeled ligands (125I-SCH23982 and [3H]YM-09151-2, respectively). The ischemic release of DA from the striatum was greater (400-fold over preischemic level) than that from the cortex (12-fold over preischemic content). The affinity for the D1-receptor ligand was lower (KD = 1.248 +/- 0.047 nM) after ischemia than that for sham controls (KD = 0.928 +/- 0.032 nM, p < 0.001). The number of binding sites for D2 receptors decreased in striatum (Bmax = 428 +/- 18.4 fmol/mg of protein) after ischemia compared with sham controls (Bmax = 510 +/- 25.2 fmol/mg of protein, p < 0.05). D1 or D2 binding sites were not changed either in the ischemic cortex or postischemic striatum and cortex. The findings strongly suggest that the ischemic release of DA from striatum is associated with early transient changes in D1- and D2-mediated DA neurotransmission.