Effect of acute intraperitoneal injection of Methamphetamine on the level of pain and changes in the expression of specific genes in the lumbar spinal cord of male rats

Methamphetamine is known as a nerve stimulant and addictive substance.Prerequisite for methamphetamine-induced behaviors is the effect of the drug on the relevant genes and proteins mentioned in the previous studies. Here, we made an attempt to examine the effect of intraperitoneal injection of this drug on the expression of specific genes AKT, GSK3b, BDNF, and CREB in the lumbar spinal cord. 

 In the current experimental study, we examined the effect of five days of intraperitoneal injection of methamphetamine and its withdrawal on increasing the reaction time of the tail in response to the shock of burning light and shook and alterations in the expression of specific genes in comparison with the sequence relevant primers in the lumbar spinal cord of four experimental groups (each including 7 male rats). For data analysis, one-way ANOVA was run in SPSS.

Intraperitoneal injection of 10 mg/kg methamphetamine over a five-day period, by increasing the reaction time of the animal's tail to the shock of burning light from 3.17 to 6.8.8 seconds, induced analgesia (P-<0.01) and increased the expression of Protein kinase B (AKT) and cAMP response element-binding protein (CREB) genes in the lumbar spinal cord of male rats (P <0.05 and P<0.01, respectively), whereas it did not significantly alter the expression of Glycogen synthase kinase3 (GSK3b) and Brain-Derived Neurotrophic Factor (BDNF) genes in this region (P =0.2 and P=1, respectively). Also, deprivation of methamphetamine in the drug deprivation group, by reducing the tail reaction time from 6.88 seconds to 3.9 seconds, reduced the analgesic effect of the drug (P <0.01), but the expression of the mentioned genes in this group did not change significantly as compared with the methamphetamine group.

It seems that the intraperitoneal injection of methamphetamine dose over a short period of time has only a beneficial analgesic effect and its minimal effect on changes in gene expression is not sufficient to be interpreted as drug abuse and induce addiction.