AXOTOMY-INDUCED ALTERATIONS IN THE RED NUCLEUS REVEALED BY MONOCLONAL-ANTIBODY, PY, FOLLOWING A LOW THORACIC SPINAL-CORD LESION IN THE ADULT-RAT

The monoclonal antibody Py was previously developed as a tool for the identification of subpopulations of hippocampal neurons. Here, the dif ferential distribution of Py immunoreactivity in the mid-brain is desc ribed showing that Py also serves as a useful marker for other populat ions of neurons. Medium to strong immunoreactivity was observed in the cell body and dendrites of neurons of the oculomotor nucleus, superio r colliculus and substantia gelatinosa reticulata. However, particular ly intense Py-immunoreactivity was identified in the magnocellular neu rons in the caudal pole of the red nucleus. Unilateral transection of the rubrospinal tract at Th9-10 induced a marked reduction of Py immun oreactivity in the ventrolateral territory of the caudal pole of the a xotomised red nucleus. A small but statistically significant reduction of Py-immunoreactivity was first seen at 7 days after surgery and a m aximal loss of immunoreactivity (reduced to 66% of control levels) was observed by 21 days after surgery. Immunoreactivity in the axotomised red nucleus was reduced for the duration of the experiment but at the longer survival times studied (3 and 6 months) a small degree of reco very of staining was observed in small-medium diameter atrophic neuron s. These results indicate that monoclonal antibody Py, may be a useful novel and sensitive tool for investigating the cell body reaction of particular populations of axotomised CNS neurons following spinal cord injury.