Nitric Oxide Linked to mGluR5 Upregulates BDNF Synthesis by Activating MMP2 in the Caudate and Putamen after Challenge Exposure to Nicotine in Rats

Nitric oxide (NO) linked to glutamate receptors in the caudate and putamen (CPu) regulates neuroadaptation after drug exposure. Matrix-metalloproteinase (MMP), a Ca(2+)-dependent zinc-containing endopeptidase, increases mature brain-derived neurotrophic factor (BDNF) synthesis after drug exposure in the brain. The present study determined that NO synthesis linked to metabotropic glutamate receptor subtype 5 (mGluR5) stimulation after challenge exposure to nicotine activates MMP, which upregulates BDNF synthesis in the CPu. Subcutaneous injection of challenge nicotine (1.0 mg/kg) after repeated injections of nicotine (1.0 mg/kg/day) for 14 days and 7 days of nicotine withdrawal increased MMP2 activity and BDNF expression in the CPu of rats. These increases were prevented by the bilateral intra-CPu infusion of the mGluR5 antagonist, MPEP (0.1 nmol/side), the IP(3) receptor antagonist, xestospongin C (0.004 nmol/side) or the neuronal nitric oxide synthase (nNOS) and NO inhibitor, Nω-propyl (0.1 nmol/side) prior to the challenge nicotine. Furthermore, bilateral intra-CPu infusion of the MMP2 inhibitor, OA-Hy (1 nmol/side) prevented the challenge nicotine-induced increase in the expression of BDNF. These findings suggest that elevation of NO synthesis linked to mGluR5 potentiates BDNF synthesis via activation of MMP2 after challenge exposure to nicotine in the CPu of rats.