DEVELOPMENT OF IMMUNOREACTIVITY FOR CALCITONIN GENE-RELATED PEPTIDE, SUBSTANCE-P AND GLUTAMATE IN PRIMARY SENSORY NEURONS, AND FOR SEROTONIN IN THE SPINAL-CORD OF FETAL SHEEP

In this study we have described the ontogeny of immunoreactivity for c alcitonin gene-related peptide, substance P and glutamate in primary s ensory neurons, and for serotonin in the sacral spinal cord, of fetal sheep (n = 37) from 56 to 140 days of gestation (term = 146 days). A f ew fine, varicose fibres immunoreactive for calcitonin gene-related pe ptide were present in Lissauer's tract, the dorsolateral funiculus and in laminae I and V in the dorsal horn of the spinal cord at 56-61 day s of gestation. At this age, two groups of intensely staining immunore active cells were present in the motoneuron pool in laminae VIII and I X in the ventral horn of the spinal cord. By 77 days, immunoreactive f ibres were also present in laminae II and X. With advancing gestationa l age, an increase in the intensity of staining was observed throughou t the cord to term, with the exception of laminae VIII and IX, where a decrease was seen. Intense staining of cells in the motoneuron pool w as evident until c. 128 days, after which time staining became very fa int. Fine fibres immunoreactive for substance P were present in Lissau er's tract and lamina I of the spinal cord at 56 61 days of gestation. They were also present throughout laminae IV-VI and X as well as thro ughout the entire ventral horn. Immunoreactive fibres in lamina II wer e evident by 77 days. The staining increased in density but remained s imilar in distribution with increasing gestational age to term in the dorsal horn, but decreased markedly in the ventral horn. Cells immunor eactive for substance P were evident from 56 days. particularly on the border of laminae II and III, until late in gestation. Ultrastructura l studies showed that axon terminals immunoreactive for calcitonin gen e-related peptide and for substance P were present in lamina I by 61 d ays. Immunoreactivity for glutamate was evident at 83 days in dorsal r oot fibres and also in lamina I and II, where it was more prominent in cells than in fibres. At all ages examined, the dorsal horn stained m ore intensely than the ventral horn. Immunoreactivity for glutamate an d neuropeptides appeared in the cells and fibres of dorsal root gangli a at 97 100 days. In the skin, immunoreactivity for calcitonin gene-re lated peptide and substance P was present at 85 days, some time after its appearance in the cord. Fibres immunoreactive for serotonin appear ed in lamina I, at the neck of the dorsal horn and in the ventral horn at 83 days of gestation. Few immunoreactive fibres were seen at any s tage during gestation in laminae II and III. Staining increased in lam inae IV X during gestation, but there was eventually a slight decrease in the ventral horn prior to term. These studies have shown that neur ochemicals thought to be involved in the transmission and modification of somatosenory information in the spinal cord are present in fetal s heep from early in gestation, with neuropeptides appearing before glut amate and serotonin.