The effects of opioids in the periaqueductal grey region of rat brain on hind-limb muscle tone.
A mechanical apparatus was used to measure hind limb resistance to flexion in rats injected with opioid peptides in the brain periaqueductal grey region (PAG). (D-Ala2, D-Leu5) enkephalin (delta agonist) and dynorphin1-8 and ethylketocyclazocine (kappa agonists) had no effects on hind limb tone. The mu agonist (D-Ala2, MePhe4, Gly-ol5) enkephalin induced limb rigidity when injected into the PAG. beta-Endorphin caused a dose-related limb rigidity that persisted for up to 2h. beta-Endorphin rigidity was prevented by pretreatment of rats with the serotonin depletor 5,7-dihydroxytryptamine. It is concluded that mu receptors and serotonin mechanisms in the PAG can mediate opiate rigidity.
P S
PS
Widdowson
E C
EC
Griffiths
P
P
Slater
D000818:Animals; D004745:Enkephalins / Q000494:pharmacology; D006614:Hindlimb; D007700:Kinetics; D008297:Male; D009129:Muscle Tonus / Q000187:drug effects*; D009294:Narcotics / Q000494:pharmacology*; D010487:Periaqueductal Gray / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D013329:Structure-Activity Relationship
D004745:Enkephalins; D009294:Narcotics