[D(1)-dopamine receptor is involved in the modulation of the respiratory rhythmical discharge activity in the medulla oblongata slice preparation of neonatal rats in vitro.].

To explore the role of D(1)-dopamine receptor in the modulation of basic respiratory rhythm, neonatal (0-3 d) Sprague-Dawley rats of either sex were used. The medulla oblongata slice was prepared and the surgical procedure was performed in the modified Kreb's solution (MKS) with continuous ventilating 95% O2 and 5% CO2 and ended in 3 min. A 600-700 mum single transverse slice containing the hypoglossal nerve roots and some parts of the ventral respiratory group was cut. The preparation was quickly transferred to a recording chamber and continuously perfused with oxygen-saturated MKS at a rate of 4-6 mL/min at 27-29 degrees C. Ten medulla oblongata slice preparations were randomly divided into two groups. In group I, the preparations were perfused with perfusion solution containing D(1)-dopamine receptor specific agonist cis-(+/-)-1-(Aminomethyl)-3,4-dihydro-3-phenyl-1H-2-Benzopyran-5,6-Diolhy-drochlo-ride (A68930, 5 mumol/L) for 10 min first; after washing out, the preparations were then perfused with perfusion solution containing D(1)-dopamine receptor specific antagonist R(+)-7-Chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride (SCH-23390, 2 mumol/L) for 10 min. In group II, after perfusion with A68930 for 10 min, the preparations were perfused with additional A68930 + SCH-23390 for 10 min. Respiratory rhythmical discharge activity (RRDA) of the rootlets of hypoglossal nerve was recorded by suction electrodes. The results showed that A68930 shortened the respiratory cycle (RC) and expiratory time (TE) with an increase in the integral amplitude (IA). However, SCH-23390 significantly prolonged RC and TE, and decreased IA with a decrease in inspiratory time (TI). Moreover, the effect of A68930 on the respiratory rhythm was partially reversed by additional application of A68930 + SCH-23390. These results indicate that D(1)-dopamine receptor is possibly involved in the modulation of the RRDA in the isolated neonatal rat brainstem slice.