Tyrosine pretreatment alleviates suppression of schedule-controlled responding produced by corticotropin releasing factor (CRF) in rats

Disruption of performance observed when animals are exposed to physical Stressors which deplete brain catecholamines can be alleviated by pretreatment with the catecholamine precursor tyrosine. Central administration of the stress hormone corticotropin releasing factor (CRF) has been shown to affect a variety of behaviors and also to potently increase the release of central catecholamines. Since CRF-induced disruption of behavior may involve CRF-induced depletion of brain catecholamines, the present study examined whether tyrosine would alleviate suppression of schedule-controlled responding in rats resulting from ICV administration of CRF. Administration of CRF (1.0 μg-10 μg) produced dose-dependent suppression of response rate and total number of earned reinforcers in rats responding on a multiple fixed-interval 60 s/fixed-ratio 20 schedule for food reinforcement. Pretreatment with 200 mg/kg tyrosine (IP) administered with ICV saline decreased response rate but did not lower total reinforcers, whereas 400 mg/kg of tyrosine decreased both. Injection of 400 mg/kg tyrosine reduced, but did not completely restore, CRF-induced suppression of behavior. The 200 mg/kg tyrosine dose was less effective in alleviating CRF-induced suppression of performance. These data indicate that pretreatment with the catecholamine precursor tyrosine can partially ameliorate performance decrements resulting from CRF administration.