DEVELOPMENT OF SPECIFIC POPULATIONS OF INTERNEURONS IN THE VENTRAL HORN OF THE EMBRYONIC CHICK LUMBOSACRAL SPINAL-CORD

The development, morphological and neurochemical properties of specifi c populations of interneurons were investigated in the ventral horn of the embryonic and mature chick lumbosacral spinal cord by using pre- and post-embedding immunocytochemical as well as anterograde axonal tr acing techniques. We have identified and traced the morphological matu ration of the following cell groups: (1) Neurons immunoreactive for ca lbindin-D 28k (CaB), a calcium-binding protein that has been reported to be a marker of certain subsets of excitatory spinal neurons. We hav e distinguished and traced the maturation of three CaB-immunoreactive cell groups in the ventral horn; (2) Neurons immunoreactive for GABA a nd glycine, the two putative inhibitory amino acid neurotransmitters i n the spinal cord; (3) Neurons within the nucleus marginalis, a cell g roup located in the ventrolateral aspect of the white matter in close proximity to the lateral motor column. The characteristic features of the development of these neurons are discussed and correlated with pre vious neuroanatomical and physiological studies concerning motor funct ions in the developing chick spinal cord.