TRANSPLANTATION OF EMBRYONIC NORADRENERGIC NEURONS IN 2 MODELS OF ADULT-RAT SPINAL-CORD INJURY - ULTRASTRUCTURAL IMMUNOCYTOCHEMICAL STUDY

The synaptic connections established by grafted noradrenergic (NA) neu rons into the lesioned adult rat spinal cord were analysed using immun ocytochemistry at the electron microscopic level. An embryonic cell su spension of the locus coeruleus region from E-13 rat embryos was trans planted into the spinal cord following either: (1) spinal cord transec tion or (2), partial selective denervation by B-hydroxy dopamine (6-OH DA). One month after grafting, the NA-neurons established, in the two models, an innervation pattern similar to that found in the intact sp inal cord. In both models, the transplanted NA-immunoreactive neurons formed extensive synaptic contacts with dendrites, spines and perikary a. The proportion of axodendritic and axospinous contacts was inverse in the two models. The first model thus reproduced more closely the no rmal synaptic pattern prefering dendritic targets, which could corresp ond to a better integration of the graft. In the second model, a parti ally NA-denervated spinal cord, there existed a competition between re sidual intrinsic and grafted neuron-derived fibres, which presumably a ffects synaptogenesis. In conclusion, the present study illustrate the complexity of cell interations conducting to the formation of a speci fic circuitry. Recognition phenomenon are likely modulated by space co nstraints, which ultimately shape-up the geometry of synaptic contacts .