Evidence for a Neurotoxic Role of Nitric Oxide Synthase on Sertonin Neurons

Abstract

Abstract: : Purpose: Substituted amphetamines such as p–chloroamphetamine (PCA) cause selective destruction of serotonin axons in rats, by unknown mechanisms. Since some serotonin neurones also express neuronal nitric oxide synthase (nNOS), which has been implicated in neurotoxicity, the present study was undertaken to determine whether NOS expressing serotonin neurones are selectively vulnerable to MDMA or PCA. Methods: Using double–labelling immunocytochemistry and double in situ hybridisation for nNOS and the serotonin transporter (SERT), it was confirmed that about two thirds of serotonergic cell bodies in the dorsal raphé nucleus expressed nNOS, however few if any SERT immunoreactive axons in striatum expressed nNOS at detectable levels. MDMA (30mg/kg) or PCA (2 x 10 mg/kg) was administered to Sprague–Dawley rats, and seven days after drug administration there were modest decreases in the levels of SERT protein in frontal cortex, and striatum using Western blotting, even though axonal loss could be clearly seen by immunostaining. PCA or MDMA administration did not alter the level of nNOS in striatum or frontal cortex, determined by Western blotting. Results: Analysis of serotonin neuronal cell bodies seven days after PCA treatment, revealed a net down–regulation of SERT mRNA levels, and a profound change in expression of nNOS, with 33% of SERT mRNA positive cells containing nNOS mRNA, compared to 65% in control animals. Conclusions: These results support the hypothesis that serotonin neurones which express nNOS are most vulnerable to substituted amphetamine toxicity, supporting the concept that the selective vulnerability of serotonin neurones has a molecular basis.

Keywords: nitric oxide • neurotransmitters/neurotransmitter systems • drug toxicity/drug effects