Electrophysiology of the Fetal Spinal Cord II. Interaction among peripheral inputs and recurrent inhibition

Interactions of peripheral inputs to the motoneuron of the kitten fetus as young as 3 weeks prenatal were studied by reflex discharge from the ventral root as well as by recording from single motoneurons. Facilitation was found between two synergists in fetuses I to 2 weeks before birth. Intracellular recording showed that the facilitation could be explained by summation of excitatory postsynaptic potentials. Inhibition was found between antagonists in the fetuses 2 to 3 weeks before birth and was accompanied by inhibitory postsynaptic potentials. Recurrent inhibition was very powerful in the fetal spinal cord as shown by large motoneuron hyperpolarization by antidromic stimulation. Cells presumed to be "Renshaw cells" and which responded to both orthoand antidromic stimulation with repetitive firing were shown in the 2 weeks prenatal fetus. These results lead to the conclusion that there is considerable effective synaptic connection of afferent collaterals already established by the later stage of intrauterine life and that this may be achieved independently of external stimuli. I N T R O D U C T I O N Malcolm (1953 and 1955) was the first to record the ventral root (VR) reflex in the neonatal kitten and to observe interaction of various peripheral inputs. In his series of papers, Skoglund (1960 a, b, c) concluded that: (a) inhibition is present in the newborn kitten and (b) facilitation appears considerably later than inhibition. His conclusions were partly supported by Arutyunyan (1961) and Wilson (1962). No attempt has been made to study changes in synaptic organization