Journal of Neuroscience, Vol 7, 621-628, Copyright © 1987 by Society for Neuroscience
Spinal cholinergic neurons and the expression of morphine withdrawal symptoms in the rat
DC Marshall and JJ Buccafusco
Behavioral and autonomic signs of the morphine withdrawal syndrome were
measured in dependent rats injected with the opiate antagonist naloxone.
The purpose of this study was to determine whether spinal cholinergic
pathways play a role in the expression of spinally mediated withdrawal
symptoms. Intrathecal (i.t.) administration of 1 microgram carbachol or 5
micrograms neostigmine resulted in increases in mean arterial pressure
(MAP) of 32 and 45 mm Hg, respectively, in conscious, freely moving rats.
The pressor response to carbachol began almost immediately after injection,
but that to neostigmine was delayed in onset. Both responses were
completely abolished following i.v. injection of 2 mg/kg atropine. However,
in spinal-transected (C-1), ventilated rats, i.t. injection of carbachol or
neostigmine resulted in only small, transient increases in MAP.
Intraarterial (i.a.) injection of 0.5 mg/kg naloxone to morphine-dependent
rats resulted in an immediate increase in MAP (to 33 mm Hg) that lasted at
least 1 hr. This was accompanied by classical behavioral signs of
withdrawal. Pretreatment of dependent rats with i.t. injection of atropine
or hemicholinium-3 (HC-3) significantly reduced the pressor and several
behavioral responses elicited by naloxone. In contrast, when morphine-
dependent, spinal-transected rats were pretreated with i.t. injection of
cholinergic antagonists, i.a. injection of naloxone resulted in an enhanced
MAP response. Finally, in intact dependent rats, i.t. injection of naloxone
(6 micrograms) produced a 14 mm Hg increase in MAP that was significantly
augmented (21 mm Hg) following i.t. pretreatment with HC-3.(ABSTRACT
TRUNCATED AT 250 WORDS)