Modulation of in vivo GABA-evoked responses by nitric oxide-active compounds in the globus pallidus of rat

Nitric oxide (NO) is a gaseous molecule acting as a messenger in both the peripheral and the central nervous systems. NO affects synaptic activity by modulating neurotransmitter release and/or receptor function. We previously observed that NO-active compounds modify the bioelectric activity of basal ganglia (BG) units. In this study, we applied microiontophoresis to extracellular in vivo recordings to investigate the effect of NO-active compounds on GABA-evoked responses in the globus pallidus (GP) of anesthetized rats. The changes induced by NO-active drugs on the GABA-induced inhibition were used as indicators of NO modulation. The response to GABA release was tested on recorded GP neurons before and during the administration of S-nitroso-glutathione (SNOG, a NO donor) and/or Nω-nitro-l-arginine methyl ester (l-NAME), an inhibitor of nitric oxide synthase (NOS); furthermore, SNOG and l-NAME were tested at different ejection currents in order to highlight the possibility of a current-dependent effect in the nitrergic modulation of GABA transmission. In general, during SNOG ejection the magnitude of GABA-evoked responses was reduced, whereas the administration of l-NAME produced the opposite effect. The results suggest that NO-active drugs modulate the response of GP neurons to GABA transmission; the effects induced by SNOG and l-NAME were strictly related to the ejection currents. Then, the modulation of GABAergic transmission by NO could represent a mechanism to finely regulate the GP neurons activity with important consequences on the overall BG function.