Increased responsiveness of mesolimbic and mesostriatal dopamine neurons to cocaine following repeated administration of a selective kappa-opioid receptor agonist.
Previous data have shown that the repeated administration of kappa-opioid receptor agonists attenuates the acute behavioral effects of cocaine. The site and mechanism by which kappa-agonists interact with this psychostimulant, however, are unknown. Accordingly, the present microdialysis study characterized the effects of prior, repeated administration of the selective kappa-opioid receptor agonist U69593 on basal and cocaine-evoked DA levels within the nucleus accumbens (NAC) and caudate putamen (CPU). The influence of U69593 treatment on the locomotor-activating effects of an acute cocaine challenge was also assessed. Rats received once daily injections of U69593 (0.16-0.32 mg/kg/day) or vehicle (1.0 ml/kg/day) for 3 days. The behavioral and neurochemical effects produced by an acute cocaine challenge (20 mg/kg i.p.) were assessed 2 days following treatment cessation. Administration of cocaine to control animals increased locomotor activity. This effect was attenuated in animals which had previously received U69593 (0.32 mg/kg/day x 3 days). Prior administration of U69593 failed to modify basal DA levels in either the NAC or CPU. Thus, 2 days following the cessation of U69593 treatment, dialysate DA levels did not differ from that of controls. Administration of cocaine to vehicle-treated animals increased dialysate levels of DA in both brain regions. However, in animals previously exposed to U69593 (0.32 mg/kg/day x 3 days), a significant enhancement in the response of DA neurons to cocaine was seen. These data demonstrate that prior, repeated administration of a selective kappa-opioid receptor agonist attenuates the locomotor-activating effects of cocaine and increases cocaine-evoked DA overflow in terminal projection areas of mesostriatal and mesolimbic DA neurons. These findings indicate that the behavioral interactions of kappa-agonists with cocaine observed in this and previous studies cannot be attributed to a presynaptic inhibition of DA release. Rather, they suggest that postsynaptic or non-DA mechanisms mediate the interaction of these agents with cocaine.
Integrative Neuroscience Unit, Behavioral Neuroscience Branch, National Institute of Health, National Institute on Drug Abuse, Baltimore, Maryland 21224, USA.
C A
CA
Heidbreder
S
S
Schenk
B
B
Partridge
T S
TS
Shippenberg
D000700:Analgesics / Q000494:pharmacology; D000704:Analysis of Variance; D000818:Animals; D044482:Benzeneacetamides; D002421:Caudate Nucleus / Q000187:drug effects / Q000378:metabolism*; D003042:Cocaine / Q000494:pharmacology*; D004298:Dopamine / Q000378:metabolism*; D004347:Drug Interactions; D007700:Kinetics; D008032:Limbic System / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D017551:Microdialysis; D009043:Motor Activity / Q000187:drug effects; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D009714:Nucleus Accumbens / Q000187:drug effects / Q000378:metabolism*; D011699:Putamen / Q000187:drug effects / Q000378:metabolism*; D011759:Pyrrolidines / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017473:Receptors, Opioid, kappa / Q000819:agonists*; D013997:Time Factors
D000700:Analgesics; D044482:Benzeneacetamides; D011759:Pyrrolidines; D017473:Receptors, Opioid, kappa; D003042:Cocaine; C045444:U 69593; D004298:Dopamine