Further studies of the effects of intranigral morphine on behavioral responses to noxious stimuli.
Bilateral intranigral microinjection of morphine produces dose-related and naloxone reversible analgesic-like effects on the hot-plate and tail-flick tests. The main objectives of the present studies were to further characterize the analgesic-like effects of intranigral morphine, to determine whether these effects were related to a general impairment of sensory or motor function, and to assess their anatomical specificity. The principal findings are: (1) intranigral morphine (10 micrograms) suppresses pain-related behavior without altering responses to a variety of non-noxious auditory, visual, and somatic stimuli, and without producing motor impairment; (2) movement of injector needles approximately 1 mm rostral, dorsal, or medial to the active nigral site significantly reduces the analgesic-like effect of morphine on the tail-flick test; and (3) electrolytic lesions confined to the nigra significantly reduced the analgesic-like effect of morphine on the hot-plate test. It is concluded that the analgesic-like effects of intranigral morphine are mediated by the substantia nigra and that these effects are specifically related to pain.
Baumeister
A A
AA
Department of Psychology, Louisiana State University, Baton Rouge 70803.
Nagy
M
M
Hebert
G
G
Hawkins
M F
MF
Vaughn
A
A
Chatellier
M O
MO
D000818:Animals; D005557:Formaldehyde; D008297:Male; D008636:Mesencephalon / Q000187:drug effects; D008845:Microinjections; D009020:Morphine / Q000494:pharmacology*; D010146:Pain / Q000503:physiopathology*; D010487:Periaqueductal Gray / Q000187:drug effects; D011597:Psychomotor Performance / Q000187:drug effects*; D051381:Rats; D011919:Rats, Inbred Strains; D012154:Reticular Formation / Q000187:drug effects; D013378:Substantia Nigra / Q000187:drug effects* / Q000473:pathology / Q000502:physiology*; D013681:Tegmentum Mesencephali / Q000187:drug effects
D005557:Formaldehyde; D009020:Morphine