[The action of L-DOPA on the spontaneous activity generated by the isolated spinal cord of 16- to 20-day-old chick embryos].

Abstract

Effect of bath application of L-DOPA, dopamine (DA), noradrenaline (NA) on the spontaneous activity--cyclical oscillations of electrotonic potentials in dorsal and ventral roots (DR and VR, respectively) generated by isolated spinal cord of 16-20-day-old chick embryo was studied. L-DOPA in low concentration (30-150 mumol/l) activated spinal generator: suprathreshold rhythms appeared (i.e., spike activity in DR and VR). High concentration (200-1000 mumol/l) of L-DOPA depressed generator activity, but in the course of washing of the spinal cord spontaneous activity was enhanced and suprathreshold rhythms appeared. DA and NA (50 mumol/l) did not influence the activity but in concentration 100 mumol/l they depressed spontaneous activity in DR and VR. Bath application of 2-amino-5-phosphonovaleric acid (20 mumol/l) blocked activity induced by small concentration of L-DOPA. Activity generated by the neuronal network of the isolated dorsal horn was intensified after bath-application of L-DOPA in small concentration. Rhythmic activity in the isolated ventral horn did not appear after bath-application of L-DOPA. It is concluded that excitatory action of L-DOPA on the neuronal network of dorsal horn chick embryo was direct (i.e., did not depend on catecholamines).