Pre-administration of low-dose methamphetamine enhances movement and neural activity after high-dose methamphetamine administration in the striatum.

Methamphetamine (METH) is a powerful stimulant drug of abuse, with potent addictive and neurotoxic properties. In this study, the effects of low-dose METH administration prior to high-dose METH administration on movement and neural activity in rats were examined. Rats were administered low-dose (1 mg/kg/day) METH or saline for 5 consecutive days (m5 and s5, respectively), followed by high-dose (10 mg/kg) METH on day 6 (m5M and s5M, respectively). An accelerometer was used to evaluate the frequency of movement when rats were placed in a cage for 30 min. The expression of c-fos, a neuronal activity marker, in the striatum was analyzed using immunohistochemistry. Striatal protein expression of neuronal markers, including vesicular glutamate transporter 2 (VGLUT2), glutamate decarboxylase 67 (GAD67), tyrosine hydroxylase (TH), tryptophan hydroxylase 2 (TPH2), and the glial marker, glial fibrillary acidic protein (GFAP), was analyzed by western blot. Accelerometer counts and the numbers of c-fos-positive cells in the striatum were significantly higher in the m5M than in the s5, m5, and s5M groups. The expression levels of VGLUT2 and GAD67, but not those of TH, TPH2, or GFAP, were significantly higher in the m5M than in the s5M group. These results suggest that pre-administration of low-dose METH prior to high-dose METH administration in rats may alter excitatory and inhibitory neurons in the striatum, thereby affecting movement and neural activity in rats.