[ effect of reversible anesthesia of nucleus paragigantocellularis [PGi] on local EEG amplitude of locus coeruleus [LC] nucleus during opiate-withdrawal in rats]

ABSTRACT

Since several evidences exist that the nucleus paragigantocellularis [PGi], located in the rostral ventrolateral medulla, is one of the major afferent to the nucleus locus coeruleus [LC], in this study the effect of reversible anesthesia of PGi nucleus with 4% lidocaine [0.5microl/rat] on local EEG amplitude of LC and behavioral signs of morphine-induced witdrawal was investigated. The local EEG amplitude of LC nucleus was significantly decreased by administration of lidocaine in control and morphine-dependent rats. Also, in LC nucleus of morphine-dependent rats, the amplitude and behavioral signs increased significantly following administration of naloxone [10mg/kg; s.c.]. In addition, microinjection of lidocaine into the PGi before administration of naloxone reversed the local EEG amplitude of LC to the amount of controls and decreased the behavioral signs of withdrawal syndrome, significantly. There was no significant change in the amplitude in morphine-dependent rat after chronic exposure to morphine than before. These results indicated that during withdrawal syndrome, activation of LC neurons and behavioral signs of it likely arise from PGi nucleus and are mediated by LC neurons. In addition, no changes in the amplitude of LC and/ or elsewhere were appeared in LC activity. The findings are consistent with the hypothesis that during morphine withdrawal, there is an increased in unit activity of the PGi afferents to the LC or an increased release of excitatory transmitter from their terminals in the LC