Apoptotic cascade of neurons in the subcortical sensory relay nuclei following the neonatal infraorbital nerve transection

A terminal transferase-mediated dUTP nick end labeling (TUNEL) method was u tilized for detection of neuronal death in the subcortical relay nuclei of the trigeminosensory system following the infraorbital nerve transection in newborn rats. At 18-24 h after injury, numerous TUNEL-positive profiles we re found within the ventroposteromedial thalamic nucleus (VPM) contralatera l to the injury, whereas the VPM on the ipsilateral side and of the age-mat ched normal control contained only a few profiles per section. Electron mic roscopy revealed that the TUNEL-positive profiles were apoptotic neurons. T he ventral part of thr ipsilateral brainstem sensory trigeminal nuclear com plex (the nucleus principalis, and the subnuclei oralis and interpolaris) e xhibited statistically significant 65-70% increase in number of apoptotic n eurons compared to the contralateral side. Taken together with our previous study [T. Sugimoto, C. Xiao, H. Ichikawa, Neonatal primary neuronal death induced by capsaicin and axotomy involves an apoptotic mechanism, Brain Res . 807 (1998) 147-154], the present results demonstrated a cascade of apopto sis in the primary, secondary and tertiary order sensory neurons along the neuroaxis. (C) 1999 Elsevier Science B.V. All rights reserved.