DEVELOPMENTAL-CHANGES IN THE DISTRIBUTION OF GAMMA-AMINOBUTYRIC ACID-IMMUNOREACTIVE NEURONS IN THE EMBRYONIC CHICK LUMBOSACRAL SPINAL-CORD

The development of gamma-aminobutyric acid (GABA)-immunoreactive neuro ns was investigated in the embryonic and posthatch chick lumbosacral s pinal cord by using pre- and postembedding immunostaining with an anti -GABA antiserum. The first GABA-immunoreactive cells were detected in the ventral one-half of the spinal cord dorsal to the lateral motor co lumn at E4. GABAergic neurons in this location sharply increased in nu mber and, with the exception of the lateral motor column, appeared thr oughout the entire extent of the ventral one-half of the spinal gray m atter by E6. Thereafter, GABA-immunoreactive neurons extended from ven tral to dorsal regions. Stained perikarya first appeared at E8 and the n progressively accumulated in the dorsal horn, white immunoreactive n eurons gradually declined in the ventral horn. The general pattern of GABA immunoreactivity characteristic of mature animals had been achiev ed by E12 and was only slightly altered afterwards. In the dorsal horn , most of the stained neurons were observed in laminae I-III, both at the upper (LS 1-3) and at the lower (LS 5-7) segments of the lumbosacr al spinal cord. In the ventral horn, the upper and lower lumbosacral s egments showed marked differences in the distribution of stained perik arya. GABAergic neurons were scattered in a relatively large region do rsomedial to the lateral motor column at the level of the upper lumbos acral segments, whereas they were confined to the dorsalmost region of lamina VII at the lower segments. The early expression of GABA immuno reactivity may indicate a trophic and synaptogenetic role for GABA in early phases of spinal cord development. The localization of GABAergic neurons in the ventral horn and their distribution along the rostroca udal axis of the lumbosacral spinal cord coincide well with previous p hysiological findings, suggesting that some of these GABAergic neurons may be involved in neural circuits underlying alternating rhythmic mo tor activity of the embryonic chick spinal cord. (C) 1994 Wiley-Liss, Inc.