Evaluation the effects of intracereboventricular injection of riluzole and minocycline on chronic morphine- induced tolernce to the analgesic effect and apoptosis in CNs of rat

Abstract

Long-term exposure to opiates induces tolerance to the analgesic effect. The neurobiological mechanism of this phenomenon is not completely clear. It has been indicated that neuronal apoptotic process is in association with the development of morphine tolerance. In the present study we tried to investigate the effect of intracerebroventricular (icv) administration of minocycline (a tetracycline derivative) and riluzole (an anti-glutamatergic agent) on morphine-induced tolerance and apoptosis in rat’s central nervous system. Different groups of rats received either morphine (ip) and drugs vehicle (icv) or morphine and different doses of minocycline or riluzole (icv) once per day. Nociception was assessed using a hot plate apparatus. The terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) method was used to analyze apoptosis. The anti-apoptotic factors, Bcl-2 and HSP70 and the pro-apoptotic element caspase-3 were evaluated by immunoblotting. The results showed that central administration of minocycline and riluzole delayed morphine-induced tolerance. Additionally results indicated that minocycline attenuated the number of apoptotic cells in both the cerebral cortex and lumbar spinal cord. Immunoblotting findings showed that the amounts of anti-apoptotic agents (Bcl-2 and HSP70) were greater in the minocycline treated groups than in the controls in both regions. However, minocycline did not change the level of caspase-3 at the doses used with morphine. Furthermore the results showed that intracerebroventricular administration

of riluzole attenuated morphine tolerance and number of TUNEL positive cells in both the cerebral cortex and lumbar spinal cord. The amount of anti-apoptotic agents (Bcl-2 and HSP70) was greater in the treatment groups than controls in both regions. Additionally, riluzole significantly decreased the caspase-3 content of the cerebral cortex. In conclusion, we found that intracerebroventricular administration of minocycline or riluzole attenuated the morphine induced tolerance and apoptosis in the cerebral cortex and lumbar spinal cord of rat.