ONTOGENIC DIFFERENCES IN THE EFFECTS OF EEDQ ON DOPAMINE-MEDIATED BEHAVIORS

Previous results suggest that 17-day-old rat pups may have substantial reserves of both D1 and D2 receptors. To assess this possibility, the behavioral effects of a nonselective dopamine (DA) agonist, R-propyln orapomorphine (NPA), were measured in 11- and 17-day-old rat pups prev iously treated with the irreversible DA receptor antagonist N-ethoxyca rbonyl-2-ethoxy- 1,2-dihydroquinoline (EEDQ). Rat pups were treated wi th EEDQ (7.5 mg/kg) either alone or in combination with the D1 and D2 antagonists, SCH 23390 (1.0 mg/kg) and sulpiride (100 mg/kg), respecti vely. (The SCH 23390 and sulpiride were used to protect dopamine recep tors from EEDQ-induced inactivation.) NPA's effects on stereotyped sni ffing and locomotor activity were then assessed 1, 2, and 4 days after EEDQ pretreatment. Results showed that NPA (0.01, 0. 1, 1.0, or 5.0 m g/kg) produced a dose-dependent increase in the stereotyped sniffing o f both aged rats. Unexpectedly, however, EEDQ did not disrupt the NPA- induced stereotyped sniffing of either the 11- or 17-day-old rat pups. Thus a behavior (i.e., stereotyped sniffing) that requires the activa tion of a large complement of DA receptors was not sensitive to the re ceptor-depleting actions of EEDQ. Moreover, the behaviors of 11-day-ol d rats, which have fewer DA receptors than older pups or adults, were also not susceptible to the effects of EEDQ. When taken together, thes e results suggest that EEDQ's inability to block the agonist-induced b ehaviors of preweanling rat pups cannot be explained by ontogenetic ch anges in DA receptor reserves.