Ethanol influences on the chick embryo spinal cord motor system. II. Effects of neuromuscular blockade and period of exposure.

The study described below was performed as a continuation of a previous study in which we found reduced motoneuron number in lumbar spinal cord of the chick embryo following chronic ethanol administration from embryonic day 4 (E4) to E11. We sought to determine whether this reduction was due to primary ethanol toxicity or to enhancement of naturally occurring cell death (NOCD) and to determine whether administration of ethanol at a later period of development could also reduce motoneuron number. Earlier studies have shown that curare suspends NOCD in the chick embryo. By administering both ethanol and curare to these embryos from E4 to E11 and examining the lumbar spinal cord on E12, we determined that ethanol was directly toxic to motoneurons and reduced motoneuron number in the absence of NOCD. By administering ethanol from E10 to E15 and examining the lumbar spinal cord on E16, we determined that ethanol can reduce motoneuron number without altering spinal cord length during more than one stage of chick embryo development, and that ethanol toxicity is not dependent on NOCD. In addition, we demonstrated that ethanol does not affect the neurotrophic content of chick muscle when it is administered from E10 to E15.