Effects of dopamine on spontaneous activity generated by isolated spinal cord in 16- to 20-day-old chick embryos

Abstract

The effects were investigated of applying L-DOPA, dopamine (DA), and noradrenaline (NA) on spontaneous activity (cyclic fluctuations in electrotonic dorsal and ventral root (DR and VR) potentials generated by a section of spinal cord isolated from 16 to 20-day-old chick embryos. A low concentration of L-DOPA (30–150 µm) intensified operation of the spinal generator, giving rise to above-threshold rhythm (i.e., spike activity in the DR and the VR). At a high concentration, L-DOPA produced inhibition of generator operation, although spontaneous activity did intensify during subsequent washout of the substance, with the onset of above-threshold rhythm. Both DA and NA failed to affect spontaneous activity in the VR and the DR at a concentration to 50 µM but a concentration of 100 µM produced inhibition. Application of 20 µM 2-amino-5-phosphonovaleric acid blocked the reinforced spontaneous activity produced by low L-DOPA concentrations. Activity generated by the neuronal network of the isolated dorsal horn rose under the effects of low L-DOPA concentrations; rhythmic activity was observed neither before nor after applying this substance in isolated ventral horn. Findings obtained would point to the occurrence of a direct (i.e., non-catecholamine dependent) excitatory influence of L-DOPA on the neuronal network of the chick embryo dorsal horn.