Sigma Receptor Activation Reduces Infarct Size at 24 Hours After Permanent Middle Cerebral Artery Occlusion in Rats

Abstract

The only available treatment for embolic stroke is recombinant tissue plasminogen activator, which must be administered within three hours of stroke onset. We examined the effects of 1,3-di-o-tolyguanidine (DTG), a high affinity sigma receptor agonist, as a potential treatment for decreasing infarct area at delayed time points. Rats were subjected to permanent embolic middle cerebral artery occlusion (MCAO) and allowed to recover before receiving subcutaneous injections of 15 mg/kg of DTG at 24, 48, and 72 hours. At 96 hours the rats were euthanized, and brains harvested and sectioned. Infarct areas were quantified at the level of the cortical/striatal and cortical/hippocampal regions in control (MCAO-only) and DTG treated animals using a marker for neurodegeneration, Fluoro-Jade. DTG treatment significantly reduced infarct area in both cortical/striatal and cortical/hippocampal regions by >80%, relative to control rats. These findings were confirmed by immunohistochemical experiments using the neuronal marker, mouse anti-neuronal nuclei monoclonal antibody (NeuN), which showed that application of DTG significantly increased the number of viable neurons in these regions. Furthermore, DTG blocked the inflammatory response evoked by MCAO, as indicated by decreases in the number of reactive astrocytes and activated microglia/macrophages detected by immunostaining for glial fibrillary acidic protein (GFAP) and binding of isolectin IB4, respectively. Thus, our results demonstrate that the sigma receptor-selective agonist, DTG, can enhance neuronal survival when administered 24 hr after an ischemic stroke. In addition, the efficacy of sigma receptors for stroke treatment at delayed time points is likely the result of combined neuroprotective and anti-inflammatory properties of these receptors.

Pro-Inflammatory Interferon Gamma Signaling is Directly Associated with Stroke Induced Neurodegeneration

“…The laser doppler probe was inserted into the guide screw, and the tip of the probe was placed against the surface of the brain. Rats that did not show ≥ 60% reduction in perfusion during MCAO were excluded from this study (Ajmo et al 2006; Ajmo et al 2008; Hall et al 2009). Sham operated rats had the guide screw and laser doppler probe placed and blood flow was monitored to ensure that there was not a drop in cerebral blood flow during the sham procedure.…”

“…MCAO surgery was performed using the intraluminal method originally described by Longa et al (Longa et al 1989) and previously reported (Ajmo et al 2006; Ajmo et al 2008; Hall et al 2009). Briefly, rats were anesthetized with 5% isoflurane and maintained on 2–3%.…”

The spleen contributes to stroke induced neurodegeneration through interferon gamma signaling

“…The probe was inserted into the guide screw, and the tip of the probe was placed against the pial surface of the brain. Rats that did not show ≥60% reduction in perfusion during MCAO were excluded from the study (Ajmo et al 2006; Ajmo et al 2008; Hall et al 2009a)…”

Sigma receptors as potential therapeutic targets for neuroprotection

“…Sigma receptor ligands have displayed neuroprotective effects against excitotoxic mechanisms in retinal ganglion cells, primary neuronal cultures, and ischemic stroke models (DeCoster et al, 1995; Dun et al, 2007; Shen et al, 2008). Of note, the sigma receptor agonist DTG (1,3-di-o-tolylguanidine) has been shown to enhance neuronal survival when administered 24 h after ischemic stroke in rats (Ajmo et al, 2006). The possible mechanisms whereby sigma receptor ligands have the potential to mitigate excitotoxicity include: i) attenuating the release of glutamate (Lobner and Lipton, 1990), ii) reducing the level of activation or expression of NMDA receptors (Zhang et al, 2011), iii) altering intracellular calcium levels (Monnet, 2005), and iv) decreasing reactive species (see below).…”