NEUROTOXIC LESION OF OCULOMOTOR NEURONS - EVIDENCE FOR REARRANGEMENT OF AXON TERMINALS OF SURVIVING AFFERENT NEURONS

The fate of abducens internuclear neurons was studied after the loss o f their target medial rectus motoneurons of the oculomotor nucleus in adult cats. Target motoneurons were killed by injecting ricin, a toxic lectin, into the medial rectus muscle of the eye. The entire populati on of abducens internuclear neurons survived the loss of target for a long time (1 year), although they exhibited an initial critical period after target loss characterized by a marked reduction of afferent syn aptic transmission. One month later, the normal parameters of synaptic transmission resumed. In contrast, the density of axonal terminals of abducens internuclear neurons in the oculomotor nucleus progressively decreased during the year following target loss. Evidence is presente d for the reinnervation of a new neuronal target within the oculomotor nucleus that might support both the long-term survival and the recove ry of physiological characteristics in the abducens internuclear neuro ns. (C) 1994 Intox Press, Inc.