Morphine tolerance and dependence in the nucleus paragigantocellularis: single unit recording study in vivo.
In this study, a single unit activity was recorded in the nucleus paragigantocellularis (PGi), located in the rostral ventrolateral medulla of anesthetized, morphine-dependent rats. The spontaneous activity of PGi neurons was significantly decreased by administration of morphine (10 mg/kg; i.p.) in sham-operated, control and morphine-dependent rats. However, in PGi neurons of morphine-dependent rats, the firing rate decreased significantly less than those of sham-operated and control ones. There was also significant enhancement of spontaneous activity of PGi neurons for 30 min following administration of naloxone (2 mg/kg; s.c.) in morphine-dependent rats as an opiate withdrawal-induced activation of PGi neurons. The results indicated the occurrence of morphine tolerance and dependence in the PGi and/or elsewhere which appeared in PGi unit activity. The findings are consistent with the hypothesis that during morphine withdrawal, there is an increase in unit activity of the PGi afferents to the nucleus locus coeruleus (LC) or an increased release of excitatory transmitter from their nerve terminals in the LC.
Haghparast
A
A
Department of Physiology, School of Medical Sciences, Tarbiat Modarres University, PO Box 14155-4838, Tehran, Iran. haghpara@net1cs.modares.ac.ir
Semnanian
S
S
Fathollahi
Y
Y
D000200:Action Potentials / Q000187:drug effects; D000704:Analysis of Variance; D000818:Animals; D004361:Drug Tolerance; D008297:Male; D008526:Medulla Oblongata / Q000187:drug effects*; D009021:Morphine Dependence; D009270:Naloxone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains
D009292:Narcotic Antagonists; D009270:Naloxone