Reproductive Experience Modifies the Dopaminergic System of Postpartum Estrous Rats: Changes in the Sensitivity to the Behavioural Effects of SCH- 23390 and in its Receptors Binding

Rationale: Postpartum estrous (PPE) rats are both maternal and sexually motivated and prefer pups to males. However, this preference is stronger in females with previous reproductive experience than in primiparous rats, which suggests that experienced females have a stronger maternal motivation. Dopaminergic neurotransmission in the Nucleus Accumbens (NAcc) and the medial Preoptic Area (mPOA), particularly that acting on D1-like receptors, has been implicated in controlling maternal motivation. Objective: To determine whether the dopaminergic system differs between primiparous and multiparous PPE rats. Methods: Two approaches were employed: 1) to determine the effect of the systemic administration of the D1-like receptors antagonist SCH-23390 (at doses of 0.0, 0.025, and 0.05 mg/kg) on maternal behavior and locomotion, and 2) to determine D1- and D2-like receptors binding in the NAcc, dorsal striatum, medial prefrontal cortex, and mPOA of primiparous and multiparous PPE rats. Results: SCH-23390 reduced the active components of maternal behavior and locomotor activity in PPE rats, with slightly greater effects in multiparous females. Multiparous rats also exhibited greater binding to the D-1-like receptors antagonist [H ³ ]-SCH-23390 in NAcc and dorsal striatum, as well as reduced binding to the D2-like receptors antagonist [H ³ ]-nemonapride in the NAcc shell when compared to primiparous females. Conclusions: These findings indicate that prior reproductive experience alters D1-like receptor function during PPE, which could account for the motivational differences observed between experienced and inexperienced PPE rats.