Gradual development of the ventral funiculus input to lumbar motoneurons in the neonatal rat

The in vitro brainstem-spinal cord preparation of newborn rats (0 to six-da ys-old) was used to investigate the development of pathways descending vent rally from the brainstem, which are important for the control of posture an d locomotion. The ventral funiculus of the spinal cord was stimulated at th e cervical (C1) level. Responses were recorded at the lumbar level from eit her motoneurons or ventral roots using intracellular microelectrodes or suc tion electrodes, respectively. Responses consisted of a pure excitation las ting 15 ms, followed by mixed excitatory/inhibitory responses. The inhibiti on was, at least partly, mediated by glycine. Excitatory amino acid transmi ssion appears to be responsible for the excitation. The characteristics of the ventral funiculus-evoked postsynaptic potentials and ventral root poten tials changed significantly with age. Their latency decreased whereas the s lope and the area, measured over the first 15 ms, increased. The increase o f the ventral funiculus input to motoneurons was slightly more pronounced t han that of the monosynaptic dorsal root-evoked potentials from day 0 to da y 4. These data suggest a gradual arrival of ventral descending axons in the lum bar enlargement which may be responsible for the gradual acquisition of pos tural control that takes place during the first days after birth. This is a prerequisite for the development of the adult pattern of quadrupedal locom otion, with elevated hunk. (C) 1999 IBRO. Published by Elsevier Science Ltd .