Facilitation of efficient search of an unbaited radial-arm maze in rats byD1, but not D2, dopamine receptors

Dopamine (DA) agonists facilitate and antagonists inhibit conditioned prepa ratory behaviors in rats. We provide added evidence that increased D1 recep tor activation facilitates unconditioned preparatory behavior as well, this time in the form of efficient search of an unbaited radial-arm maze. Admin istration of 0.1, but not 1.0, mg/kg sc SKF81297, a full D1 agonist, increa sed the number of novel arms chosen in the first eight arms entered. Treatm ent with 0.1 mg/kg SC D-amphetamine, an indirect DA agonist, also increased search efficiency when given on the first test day but not when given foll owing a test day with a 1.0 mg/kg dose. The 0.1-mg/kg amphetamine-induced f acilitation was blocked by coinjection of 0.005 mg/kg SCH23390, a D1 antago nist. Treatment with quinpirole, a D2 agonist, or eticlopride, a D2 antagon ist, decreased amount of maze search, but did not affect efficiency. Collec tively, our results support the possibility there is a general facilitatory effect of D1 activation on unconditioned preparatory behavior. (C) 2001 El sevier Science Inc. All rights reserved.