Nitric oxide modulates respiratory-related neural activity in the isolated brainstem of the bullfrog

The effects of nitric oxide (NO) on respiratory-related neural activity were investigated using the isolated brainstem preparation from bullfrogs ( Rana catesbeiana). Addition of the NO donor, sodium nitroprusside (SNP), or the amino acid precursor for NO synthesis, l-arginine ( l-Arg), produced significant increases in respiratory-related burst frequency. Inhibition of nitric oxide synthase (NOS) with N ω -nitro- l-arginine ( l-NA), a non-selective NOS inhibitor, 7-nitro indazole (7-NI), reversibly abolished burst activity. These results suggest that production of NO, probably via neuronal NOS (nNOS), provides a facilitatory input to the respiratory central pattern generator (CPG) in the amphibian brainstem. Endogenous production of NO may be a necessary inter- or intracellular messenger for neurotransmission and/or neuromodulation of central respiratory drive to motor effecters in the bullfrog.