Reciprocal cross-sensitization between cocaine and RU 24969 in male and female preweanling rats.

Neuronal adaptations involving dopaminergic, glutamatergic, and serotonergic neurotransmitter systems are responsible for behavioral sensitization. Because of common underlying mechanisms, cross-sensitization between compounds of different drug classes can be observed. The purpose of the present study was to determine whether a one- or four-day pretreatment regimen of RU 24969 (a 5-HT1A/1B receptor agonist) would reciprocally cross-sensitize with cocaine or methamphetamine in male and female preweanling rats. Rats were pretreated with RU 24969 (0 or 5 mg/kg) for 4 days (PD 17-20) and then challenged with cocaine (10 or 20 mg/kg) or methamphetamine (1 or 2 mg/kg) on PD 22. Reciprocal cross-sensitization was also assessed (i.e., rats were pretreated with psychostimulants and tested with RU 24969). In a follow-up experiment, the ability of RU 24969 and cocaine to reciprocally cross-sensitize was assessed using a one-day pretreatment regimen. Reciprocal cross-sensitization between cocaine and RU 24969 was evident in preweanling rats, whereas methamphetamine and RU 24969 did not cross-sensitize. When a one-trial pretreatment regimen was used, cross-sensitization was only detected when rats were pretreated with RU 24969 and tested with cocaine, but not the reverse. In sum, the present results show that the nonselective 5-HT1A/1B receptor agonist RU 24969 cross-sensitizes with cocaine, but not methamphetamine, in preweanling rats. This dichotomy may be a function of cocaine having a greater affinity for the serotonin transporter than methamphetamine.