Effects of apomorphine on ventilation in the neonate rat.

Systemic administration of apomorphine (APO) to anesthetized adult rats can influence breathing pattern, and several studies suggest that dopaminergic pathways are involved. To evaluate whether ventilatory responses to APO were already present in the neonate rat, animals between 3 and 9 days of age, with sectioned vagal and sympathetic trunks, were tested. Results showed that subcutaneously administered APO (1 mg/kg) decreased breathing frequency and increased tidal volume. In addition, an instability in inspiratory off-switching was sometimes obtained. Effects on breathing with APO were antagonized by the dopaminergic blocking agent, haloperidol (2 mg/kg). Except for changes in inspiratory off-switching, these results in neonate rats are qualitatively comparable to effects obtained with APO in similarly prepared adult animals.