title: Tolerance to morphine microinjections in the periaqueductal gray (PAG) induces tolerance to systemic, but not intrathecal morphine.
abstract: The acquisition and retention of tolerance to the antinociceptive effect of supraspinal morphine on the tail withdrawal reflex was assessed in rats implanted with unilateral cannulae in the periaqueductal gray (PAG). Development of tolerance to daily microinjections of morphine was indicated by the return of the tail flick response within 4 days, followed by the recovery of analgesic sensitivity one week later. After tolerance had developed, the effect of an acute systemic (1.5-4.5 mg/kg) or intrathecal (5-15 micrograms) morphine injection was determined. 'Cross-tolerance' was observed between systemic and supraspinal morphine but not between intrathecal and supraspinal morphine. The data indicate that tolerance to chronic intracerebral morphine produces the same behavioral consequences as tolerance to systemic morphine.
authors: Department of Pharmacology, University of Illinois College of Medicine, Chicago 60612.
authors: J A
authors: JA
authors: Siuciak
authors: C
authors: C
authors: Advokat
mesh_terms: D000818:Animals; D004305:Dose-Response Relationship, Drug; D004361:Drug Tolerance; D007278:Injections, Spinal; D008297:Male; D008845:Microinjections; D009020:Morphine / Q000008:administration & dosage* / Q000494:pharmacology; D010146:Pain / Q000503:physiopathology; D010487:Periaqueductal Gray / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D012684:Sensory Thresholds / Q000187:drug effects; D013997:Time Factors
chemical_list: D009020:Morphine