Fig. 1.

Dopamine reduces locomotor rhythm frequency and increases rhythm stability. A: ventral root neurogram recordings from an isolated spinal cord of a neonatal mouse. Bi and Bii: bath application of dopamine alone (50 μM) evokes low-frequency rhythmic bursting activity in ventral root pairs that does not resemble a locomotor pattern. When dopamine is applied during a preexisting fictive locomotor rhythm evoked by 5-hydroxytryptamine (5-HT, 10 μM) and N-methyl-d(l)-aspartic acid (NMA, 5 μM) (Ci) it reduces the frequency of the rhythm (Cii, Ei, Fi) and increases the stability of the rhythm indicated by an increase in power (Cii, Eii, Fii). D: spectrogram depicts a cross-wavelet analysis of a locomotor rhythm recorded from left and right L₂ ventral root neurograms evoked by 5-HT and NMA in the first 600 s with subsequent addition of dopamine for up to 20 min after addition of dopamine. Rhythm frequency is displayed on the y-axis and rhythm power displayed as warm or cool colors, with warmer colors representing higher power. Line and bar graphs depict the average normalized frequency and power of the locomotor rhythm (±SE) from neurograms recorded in the left and right L₂ and L₅ and ipsilateral L₂-L₅ bursting activity. Bar graphs depict normalized data averaged over 10-min time intervals during respective drug conditions. *P < 0.05; **P < 0.01; ***P < 0.001.