Facilitation of efficient search of an unbaited radial-arm maze in rats by D1, but not D2, dopamine receptors.

Dopamine (DA) agonists facilitate and antagonists inhibit conditioned preparatory behaviors in rats. We provide added evidence that increased D1 receptor activation facilitates unconditioned preparatory behavior as well, this time in the form of efficient search of an unbaited radial-arm maze. Administration of 0.1, but not 1.0, mg/kg sc SKF81297, a full D1 agonist, increased the number of novel arms chosen in the first eight arms entered. Treatment 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 following a test day with a 1.0 mg/kg dose. The 0.1-mg/kg amphetamine-induced facilitation was blocked by coinjection of 0.005 mg/kg SCH23390, a D1 antagonist. Treatment with quinpirole, a D2 agonist, or eticlopride, a D2 antagonist, decreased amount of maze search, but did not affect efficiency. Collectively, our results support the possibility there is a general facilitatory effect of D1 activation on unconditioned preparatory behavior.