Nitric oxide facilitates N-methyl-D-aspartate-induced burst firing in dopamine neurons from rat midbrain slices

Dopamine (DA) neurons in the ventral tegmental area and substantia nigra pars compacta were induced to fire in bursts with application of N-methyl-D- aspartate (NMDA, 20 μM) and apamin (100 nM) while recording intracellularly in the rat brain slice. L-Arginine (300 μM), a substrate for nitric oxide (NO) production, increased both the number of spikes per burst and the magnitude of interburst hyperpolarizations. Nitric oxide synthase inhibitors N-nitro-L-arginine methyl ester (L-NAME, 100 μM), N-nitro-L-arginine, and 7- nitroindazole inhibited NMDA-induced burst firing by reducing the number of spikes per burst. Moreover, L-arginine (100 μM) reversed the inhibition of burst firing produced by L-NAME. These findings suggest that NO facilitates NMDA-induced burst firing in DA neurons.