The effect of morphine on some electrophysiological parameters of paragigantocellularis and locus coeruleus nuclei interconnections

Abstract

As one of the most important diffused brain modulatory systems, the nucleus locus coeruleus (LC) receives most of its afferents from the nucleus paragigantocellularis (PGi) and plays a major role in the control of drug dependence and some emotional and exciting states. For detailed investigation of the effect of morphine on relationship between these two brain stem nuclei, the activity of the rat (Sprague-Dawley) LC neurons was examined after being dependent on morphine in comparison with independent group. The activity of the nucleus LC neurons with and without the activity of nucleus PGi neurons was recorded using extracellular single unit recording technique. Lidocaine microinjection (1 ml, in 1-2 min, 2.5%) was used for inactivation of PGi. The PSTH (Peri-Stimulus Time Histogram) of the neuronal activity showed a decrease in neuronal firing rate of LC by 85.8±1.7% in morphine-dependent group (from 2.95 spike/sec to 0.64 spike/sec, n = 4) and by 48.3±4.3% (from 3.5 spike/sec to 1.94 spike/sec, n = 6) for independent one. The difference was significant (P