Administration of a Sigma Receptor Agonist Delays MCAO-Induced Neurodegeneration and White Matter Injury.

Many pharmacological treatments for stroke have afforded protection in rodent models but failed to show efficacy in clinical trials. This discrepancy may be due to the lack of long-term functional studies. Previously, delayed administration of the sigma receptor agonist 1,3-di-o-tolylguanidine (DTG) reduced infarct volume after middle cerebral artery occlusion (MCAO) in rats. The present study was conducted to determine whether the protective effects of DTG lead to improvements in behavioral functioning. Rats were subjected to MCAO and administered 7.5, 1.5, or 0.75 mg/kg DTG beginning 24 h post-surgery. Histological outcomes (96 h, 2 weeks, and 5 weeks) were compared with performance on a series of behavioral tests (2 and 4 weeks). Fluoro-Jade staining and immunohistochemistry were used to assess infarct volume and immune cell recruitment. All doses significantly reduced infarct volume and perturbation of striatal white matter tracts at 96 h. These reductions were associated with decreased numbers of CD11b-positive amoeboid microglia/macrophages. Despite short-term efficacy, DTG failed to improve behavioral outcomes or reduce infarct volumes after 96 h. While DTG may prove beneficial as a short-term therapy, these data highlight the importance of long-term functional recovery when evaluating novel therapies to treat stroke.

Blockade of adrenoreceptors inhibits the splenic response to stroke.

Recent studies have highlighted the involvement of the peripheral immune system in delayed cellular degeneration after stroke. In the permanent middle cerebral artery occlusion (MCAO) model of stroke, the spleen decreases in size. This reduction occurs through the release of splenic immune cells. Systemic treatment with human umbilical cord blood cells (HUCBC) 24 h post-stroke blocks the reduction in spleen size while significantly reducing infarct volume. Splenectomy 2 weeks prior to MCAO also reduces infarct volume, further demonstrating the detrimental role of this organ in stroke-induced neurodegeneration. Activation of the sympathetic nervous system after MCAO results in elevated catecholamine levels both at the level of the spleen, through direct splenic innervation, and throughout the systemic circulation upon release from the adrenal medulla. These catecholamines bind to splenic alpha and beta adrenoreceptors. This study examines whether catecholamines regulate the splenic response to stroke. Male Sprague-Dawley rats either underwent splenic denervation 2 weeks prior to MCAO or received injections of carvedilol, a pan adrenergic receptor blocker, prazosin, an alpha1 receptor blocker, or propranolol, a beta receptor blocker. Denervation was confirmed by reduced splenic expression of tyrosine hydroxylase. Denervation prior to MCAO did not alter infarct volume or spleen size. Propranolol treatment also had no effects on these outcomes. Treatment with either prazosin or carvedilol prevented the reduction in spleen size, yet only carvedilol significantly reduced infarct volume (p < 0.05). These results demonstrate that circulating blood borne catecholamines regulate the splenic response to stroke through the activation of both alpha and beta adrenergic receptors.