C-TERMINALS ON MOTONEURONS - ELECTRON-MICROSCOPE LOCALIZATION OF CHOLINERGIC MARKERS IN ADULT-RATS AND ANTIBODY-INDUCED DEPLETION IN NEONATES

C-terminals on motoneurons are defined as those accompanied by charact eristic postsynaptic specializations termed subsurface cisterns. We ha ve previously shown, by light microscope immunolabelling methods, that subsurface cisterns occur regularly beneath choline acetyltransferase - and acetylcholinesterase-containing boutons on motoneurons. In the p resent study, the cholinergic nature of C-terminals suggested by these results was further investigated by immunohistochemistry and electron microscopy in adult rats and in neonates treated with a murine monocl onal acetylcholinesterase antibody which was previously shown to cause immunological lesions of central cholinergic systems. In both the fac ial nucleus and lumbar segment of spinal cord of adult rats, C-termina ls were seen intensely immunostained for the cholinergic markers choli ne acetyltransferase and acetylcholinesterase. Immunolabelled terminal s made contact with either neuronal somata or large calibre dendrites, which were positive for the cholinergic markers, and exhibited club-s haped or thin elongated morphologies suggestive of terminal or ell pas sant type synaptic interactions. The close relationship found between cholinergic markers and immunolabelled subsurface cisterns in adults w as maintained on motoneurons of eight-day-old rats. While subcutaneous treatment of newborn rat with acetylcholinesterase antibody appeared to have no effect on the distribution of immunopositive subsurface cis terns in motoneurons when examined on postnatal day 8, the density of labelling for the two cholinergic markers around these neurons was red uced. Areas of neuropil immediately surrounding motoneurons in treated animals often showed signs of extensive swelling and deterioration in dicative of a lesion event, and these motoneurons frequently displayed subsurface cisterns unapposed to C-terminals. These results support o ur earlier conclusion, based on light microscope investigation, that t he majority if not all C-terminals are cholinergic in the areas invest igated and demonstrate the potential utility of immunolesion methods i n the study of C-terminal function.