Possible release of nitric oxide from cholinergic axons in the thalamus by stimulation of the rat laterodorsal tegmental nucleus as measured with voltammetry

Abstract

By means of the differential direct current voltammetry technique with carbon fiber electrodes in urethane-anesthetized rats, we monitored nitric oxide (NO) concentrations in the thalamus in the basal condition and following electrical stimulation of the laterodorsal tegmental nucleus (LDT), whose neurons have the strongest activity of NADPH-diaphorase, or NO synthase, together with acetylcholine. NO levels, measured as the height of the peak at +970–1000 mV in the voltammetry (NO was soon oxidized in vivo to be detected at the voltage of this peak, so that NO levels in this report are, in the strict sense, levels of the oxidized metabolites reflecting very possibly those of NO in physiological conditions; see Section 2, Methods), increased just after repetitive stimulation of the LDT. Stimulation of the surrounding areas or the cerebellum produced virtually no change in NO levels. An intravenous injection of l-nitroarginine methyl ester reduced the basal level of NO, but stimulation of the LDT still increased NO levels, which may be due to very strong activity of NO synthase in the LDT neurons. These results are consistent with the notion that NO can be released from axons of the LDT neurons by their excitation.