Paradoxical effects of kappa-opioid stimulation on the locomotor activity and Fos immunoreactivity of the preweanling rat: role of dopamine receptors.
The kappa-opioid agonist U-50,488 increases the locomotor activity of preweanling rats. The authors attempted to determine whether this effect was modulated by dopamine (DA) system functioning. Surprisingly, U-50,488's locomotor activating effects were attenuated by both the DA receptor antagonist flupenthixol and the DA receptor agonist R(-)-propylnorapomorphine (NPA). In order to determine those brain areas stimulated by U-50,488, Fos immunoreactivity was assessed in 17- and 80-day-old rats. U-50,488 not only enhanced the locomotor activity of the younger rats, but it also enhanced Fos expression in various brain areas, including the nucleus accumbens and medial striatum. NPA blocked U-50,488-induced Fos expression in the latter region. When considered together, these results indicate that U-50,488 does not increase locomotion by stimulating a DA mechanism. Instead, either agonizing or antagonizing DA receptors is sufficient to disrupt U-50,488's locomotor activating effects in the preweanling rat.
Duke
M A
MA
Department of Psychology, California State University, San Bernardino 92407, USA.
Meier
T L
TL
Bolanos
C A
CA
Crawford
C A
CA
McDougall
S A
SA
D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer / Q000494:pharmacology; D018712:Analgesics, Non-Narcotic / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D001921:Brain / Q000187:drug effects / Q000502:physiology*; D001931:Brain Mapping; D005260:Female; D015870:Gene Expression / Q000187:drug effects; D007124:Immunoenzyme Techniques; D008297:Male; D009043:Motor Activity / Q000187:drug effects / Q000502:physiology*; D016760:Proto-Oncogene Proteins c-fos / Q000235:genetics*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011954:Receptors, Dopamine / Q000187:drug effects / Q000502:physiology*; D017473:Receptors, Opioid, kappa / Q000187:drug effects / Q000502:physiology*; D013239:Stereotyped Behavior / Q000187:drug effects / Q000502:physiology
D018712:Analgesics, Non-Narcotic; D016760:Proto-Oncogene Proteins c-fos; D011954:Receptors, Dopamine; D017473:Receptors, Opioid, kappa; D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer