Widespread and Heterologous Effects of L-DOPA on Monoaminergic Tissue Metabolism in Newborn Rats Expressing Air-Stepping

L-DOPA triggers a dose-dependent increase in locomotor activity in newborn rats suspended in the air (air-stepping). Here, we report the effects of L-DOPA injection on the tissue level of monoamines and metabolites in different regions of the central nervous system (CNS) of postnatal day 5 pups. We also established correlations between some of our neurochemical measurements and basic locomotor parameters. L-DOPA (25-100 mg/kg) enhanced its tissue levels in the spinal cord, cortex, striatum, and brainstem regions. It induced a strong increase in the levels of the L-DOPA, dopamine, and their metabolites but had low effects on noradrenaline and serotonin across CNS regions. Of note, we also detected the tyramine derivative octopamine in the spinal cord. The inter-regional pattern of correlations between monoamine content showed an almost full metabolic connectivity for dopamine only when all L-DOPA conditions were pooled, and it revealed restricted connectivity for noradrenaline and serotonin in the spinal cord and the mesencephalic locomotor region. Locomotor parameters (quadrupedal locomotion and step numbers) correlated with the levels of L-DOPA and DA in restricted CNS regions at variance with noradrenaline and serotonin. Altogether, our data extend the idea that the neurochemical effect of L-DOPA is widespread and heterogeneous in the CNS, with prominent biochemical changes notably present in the spinal cord and M1 cortex, to the newborn rat.