Cell death of primary afferent nerve cells in neonatal mice treated with capsaicin.

Capsaicin (50 mg kg-1) or vehicle (control) was injected into 2-day-old mice, and apoptotic cell death of the lumbar dorsal root ganglion (DRG) cells was examined using in situ terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick end labeling (TUNEL) method at 5, 24, 48 and 72 h after treatment. Apoptotic cells were counted per section under a fluorescent microscope. The mean number of apoptotic cells showed a significant increase in the capsaicin-treated DRG at 24 h, but the number was at most 1-2 per section. Thus, many previous findings of an approximate 70-80% loss of the small primary afferent neurons induced by capsaicin could not be explained by apoptosis alone. Moreover, according to the morphological changes, it appeared that capsaicin preferentially induced necrosis rather than apoptosis, at least in mice.