In vivo binding of [3H]nimodipine in rat brain after transient forebrain ischemia

Contribution of downregulation of L-type calcium currents to delayed neuronal death in rat hippocampus after global cerebral ischemia and reperfusion

Transient forebrain ischemia induces delayed, selective neuronal death in the CA1 region of the hippocampus. The underlying molecular mechanisms are as yet unclear, but it is known that activation of L-type Ca2+ channels specifically increases the expression of a group of genes required for neuronal survival. Accordingly, we examined temporal changes in L-type calcium-channel activity in CA1 and CA3 pyramidal neurons of rat hippocampus after transient forebrain ischemia by patch-clamp techniques. In vulnerable CA1 neurons, L-type Ca2+-channel activity was persistently downregulated after ischemic insult, whereas in invulnerable CA3 neurons, no change occurred. Downregulation of L-type calcium channels was partially caused by oxidation modulation in postischemic channels. Furthermore, L-type but neither N-type nor P/Q-type Ca2+-channel antagonists alone significantly inhibited the survival of cultured hippocampal neurons. In contrast, specific L-type calcium-channel agonist remarkably reduced neuronal cell death and restored the inhibited channels induced by nitric oxide donor. More importantly, L-type calcium-channel agonist applied after reoxygenation or reperfusion significantly decreased neuronal injury in in vitro oxygen-glucose deprivation ischemic model and in animals subjected to forebrain ischemia-reperfusion. Together, the present results suggest that ischemia-induced inhibition of L-type calcium currents may give rise to delayed death of neurons in the CA1 region, possibly via oxidation mechanisms. Our findings may lead to a new perspective on neuronal death after ischemic insult and suggest that a novel therapeutic approach, activation of L-type calcium channels, could be tested at late stages of reperfusion for stroke treatment.

In vivo receptor binding of benidipine and amlodipine in mesenteric arteries and other tissues of spontaneously hypertensive rats

The present study was undertaken to characterize the in vivo 1,4-dihydropyridine (DHP) receptor binding of long-acting 1,4-DHP calcium channel antagonists in the mesenteric artery and other tissues of SHR. In vivo specific binding of (+)-[3H]PN 200-110 in the SHR mesenteric artery was significantly (36.6-49.7 %) reduced 1-8 h after oral administration of benidipine (1.84 micromol/kg). A greater reduction in (+)-[3H]PN 200-110 binding in the mesenteric artery was observed at a higher dose (5.53 micromol/kg) of this drug. This dose of benidipine also reduced significantly the in vivo specific (+)-[3H]PN 200-110 binding in the aorta but not in the myocardium and cerebral cortex. Following oral administration of amlodipine (17.6 micromol/kg), a significant (51.7-94.2 %) reduction in (+)-[3H]PN 200-110 binding was seen at 1-18 h in the mesenteric artery and at 1-12 h in the aorta. Only a slight reduction in myocardial and cerebral cortical (+)-[3H]PN 200-110 binding was seen following amlodipine administration. In contrast, oral administration of nifedipine (28.9 micromol/kg) reduced markedly in vivo (+)-[3H]PN 200-110 binding in all the tissues of SHR at 1-6 h, and the degree and time-course of the reduction did not differ significantly among the tissues. The area under the curve (AUC) for the receptor occupancy vs time was calculated from the reduction rate (%) of in vivo specific (+)-[3H]PN 200-110 binding. The ratios of the AUCmesenteric artery to AUCaorta or AUCmesenteric artery to AUCmyocardium after oral administration of benidipine and amlodipine were greater than the corresponding value for nifedipine. The degree and time-course of arterial receptor occupancy by benidipine and amlodipine agreed well with those of their hypotensive effects in the conscious SHR. In conclusion, the present study demonstrates that benidipine and amlodipine may occupy, in a more selective and sustained manner, 1,4-DHP receptors in arterial tissues than in other tissues of SHR, and thus, such receptor binding specificity may be responsible for the long-lasting hypotensive effects of these drugs.

Immediate-early gene expression in the brain of the thiamine-deficient rat

Pyrithiamine-induced thiamine deficiency (PTD) in the rat is associated with neuronal loss in the thalamus and inferior colliculus. Recently, we were able to demonstrate the occurrence of apoptosis in the thalamus of these animals. Given that immediate-early genes (IEGs) participate in signal transduction pathways that mediate programmed cell death, the present study utilized in situ hybridization and immunohistochemistry to examine the expression of four IEGs (c-fos, c-jun, fos-B, and NGFI-A) during the progression of PTD. Elevated c-fos mRNA levels were initially observed in the posterior medial thalamus on d 12 of the deficiency. At the acute symptomatic stage (characterized by a loss of righting reflex on d 16-17), the posterior-medial thalamus exhibited increased mRNA for all genes examined, whereas the inferior colliculus demonstrated mRNA induction for c-fos, c-jun, and NGFI-A. Immunohistochemical analysis revealed that elevations of IEG mRNA associated with the acute symptomatic stage were consistently translated into protein in the thalamus. In contrast, whereas elevated Fos- and Jun-like immunoreactivity were detected in the inferior colliculus at this stage, NGFI-A-like immunoreactivity declined significantly below basal levels, suggesting a translational block. These results are consistent with our recent findings of apoptotic cell death, and indicate that differential patterns of IEG expression occur in the thalamus and inferior colliculus during PTD, which may contribute to the pathogenesis of this disorder.

In vivo uptake of [3H]nimodipine into brain during cortical spreading depression

We report autoradiographic measurements of the in vivo uptake of [3H]nimodipine during the nonischemic depolarization of cortical spreading depression (CSD) in rat brain. [3H]Nimodipine uptake in brain was determined regionally in rats undergoing CSD (n = 8) and was significantly increased in cortex (14 +/- 7%) and hippocampus (10 +/- 6%) on the stimulated side relative to the contralateral hemisphere when compared with the same measurements in a control group (n = 8). A similar measurement using the physiologically inert radiotracer [14C]iodoantipyrine to control for potential effects of CSD on radioligand distribution showed a minimal increase (2.4 +/- 0.7%) of radiotracer uptake in cortex after CSD. This increase was significantly less than that observed in the [3H]nimodipine uptake studies. We hypothesize that increased in vivo [3H]nimodipine uptake in CSD identifies regions of depolarization and thus infers activation of the L-type voltage sensitive calcium channels.

Transient forebrain ischemia protects against subsequent focal cerebral ischemia without changing cerebral perfusion

BACKGROUND AND PURPOSE

The possibility that the brain may be preconditioned to be more tolerant of ischemia is an important concept with important clinical implications. Exploring the concept offers the possibility of advancing our understanding of protective molecular responses in the brain. This article compares two preconditioning methods and explores the role that changes in regional cerebral blood flow (rCBF) may play in conferring ischemic protection.

METHODS

Temporary occlusion of the middle cerebral artery (MCA) using the thread model was preceded 4 days earlier by short-lasting focal or global ischemia or by sham surgery. rCBF was measured in the frontoparietal region of the ischemic hemisphere during all focal ischemia episodes. Four days after the second ischemic exposure, animals were killed, and the size of infarction was determined.

RESULTS

rCBF was significantly higher in the frontoparietal region during MCA occlusion when it was preceded by prior focal ischemia (36.8 +/- 7.6 mL x 100 g-1 at 30 minutes) compared with controls (24.7 +/- 4.0 mL x 100 g-1.min-1, P = .0008). Despite this, there was no significant difference in the resulting infarct volume. In contrast, when MCA occlusion was preceded by global ischemia, infarct volume was significantly reduced (68.1 +/- 30.9 mm3 in the controls versus 22.9 +/- 22.1 mm3 in the preconditioned group, P = .002) without significant change in rCBF.

CONCLUSIONS

Protection from ischemic injury requires specific conditions of prior exposure to ischemia. Improved perfusion would not seem to be a sufficient or necessary accompaniment to providing neuroprotection.

A selective N-type Ca(2+)-channel blocker prevents CA1 injury 24 h following severe forebrain ischemia and reduces infarction following focal ischemia

SNX-111 (NEUREX Corporation, Menlo Park, CA, U.S.A.) an omega-conopeptide, was tested for cytoprotection following normothermic ischemia using both a four-vessel occlusion model of severe forebrain ischemia and a model of transient middle cerebral artery occlusion focal ischemia. Adult male Wistar rats were subjected to 10 min of forebrain ischemia followed by 7 days of reperfusion. A single dose of SNX-111 (5 mg/kg) was injected intravenously following delays of either 6 or 24 h after reperfusion. For 11 rats treated with saline, there was 78 +/- 13% CA1 neuronal injury (mean +/- SD); for 11 given SNX-111 delayed by 6 h, injury was reduced to 35 +/- 30% (p < 0.01); and remarkably, treatment delayed by 24 h (n = 10), still resulted in protection, with only 50 +/- 29% injury (p < 0.05). Adult male spontaneously hypertensive rats had transient occlusion of the right middle cerebral artery of 1.5- or 2-h duration followed by 22.5 or 22 h of reperfusion, respectively. Rats were randomly assigned to receive either saline or SNX-111 (5 mg/kg i.v.), with treatment starting immediately after reperfusion (1.5-h ischemic group) or at 1 h following the onset of ischemia (2-h ischemic group). In the 1.5-h ischemic group, saline-treated animals sustained 138 +/- 32 mm3 of neocortical infarction (n = 9), and SNX-111 treatment resulted in an infarct reduction to 76 +/- 25 mm3 (n = 9; p < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium-mediated mechanisms of ischemic injury and protection

Our understanding of calcium's role in cerebral ischemia continues to evolve from the initial recognition that it may be harmful to the ischemic cell. A multitude of experiments have supported the hypothesis that excessive influx of calcium into the cell under ischemic conditions is a major mechanism of cell injury and death. Pharmacological intervention to restore cellular calcium homeostasis is protective in many models of cell anoxia. Principle routes of calcium entry are the voltage-sensitive (VSCC) and N-methyl-D-aspartate linked receptor operated (ROCC) calcium channels. Regional variations in channel densities have been described and it is now known that these classes of channels are located in different regions of the neurons. Activation of both channel types has been identified in in vivo models of cerebral ischemia. Although the ROCC is predominant in number, the VSCC appears to activate at higher cerebral blood flow values suggesting that it is an earlier conduit for calcium than the glutamate-driven ROCC. Intracellular calcium is well recognized as a second messenger system and there is increasing appreciation that it induces immediate early genes (IEG). Since IEGs function as transcriptional regulating factors, the differential expression of specific target genes may be of importance for determining death or survival of the ischemic tissue.