EFFECTS OF NMDA AND ITS ANTAGONISTS ON VENTRAL HORN CHOLINERGIC NEURONS IN ORGANOTYPIC ROLLER TUBE SPINAL-CORD CULTURES

Neurotoxic effects of excitatory amino acid (EAA) receptor agonist N-m ethyl-D-aspartic acid (NMDA) and its antagonists on ventral horn choli nergic neurons were studied in organotypic rollertube cultures of spin al cord (OTC-SCs) using biochemical assays of choline acetyltransferas e (ChAT) and acetylcholinesterase (AChE) activity, and AChE histochemi stry. NMDA exposure decreased ChAT and AChE activity by 83% and 66%, r espectively. Cultures treated with NMDA also showed a marked loss of A ChE staining in both dorsal and ventral horns and a significant, dose- dependent decrease in the number of ventral horn AChE-positive neurons (VHANs). NMDA treatment primarily resulted in the loss of small VHANs (<300 mu m(2)). VHANs with a size and distribution typical of alpha-m otoneurons were relatively well preserved. The effects of NMDA on OTC- SCs appeared to be independent of the age of the cultures. The NMDA an tagonist DL-APS completely prevented the NMDA-induced loss of ChAT act ivity, but only attenuated the effect of NMDA on AChE activity. The an tagonists DL-APS, D-APS and MK-801, used alone, caused significant los s and/or shrinkage of VHANs. These effects appeared to be distinct fro m the NMDA mediated toxicity. The results indicate that NMDA and its a ntagonists exert powerful toxic effects on ventral horn cholinergic ne urons. The large cholinergic alpha-motoneurons, however, appear to be relatively immune to these toxic effects.