Activation of the caspase cascade underlies the rat trigeminal primary neuronal apoptosis induced by neonatal capsaicin administration.
The systemic administration of capsaicin is known to cause a massive loss of sensory primary neurons in newborn rats. Here we examined the trigeminal ganglion neurons immunohistochemically for the possible induction of activated forms of caspases-9 and -3 following a subcutaneous injection of capsaicin in newborn rats. The DNA fragmentation signal was labeled by a TUNEL method. TUNEL-positive neurons were rare (< 0.5%) at 24 h after injection of the vehicle without capsaicin. After the capsaicin injection, TUNEL-positive neurons began to increase by 12 h, reached a peak at 24 h (11.4%), and returned to the control level by 120 h. Vehicle control levels of caspase- 9-immunoreactive (ir) and caspase-3-ir neurons were low (< 0.5%). Neonatal capsaicin administration induced caspase-9-immunoreactivity (ir) and -3-ir. The temporal distributions of caspase-9-ir and caspase-3-ir neurons were similar to those of TUNEL-positive neurons with peak expressions at 24 h of 13.2 and 11.1%, respectively. A double-stain analysis at 24 h post-injection indicated 72% of TUNEL-positive neurons were caspase-9-ir, and 70% caspase-3-ir. Conversely, 78 and 68% of caspase-9-ir and caspase-3-ir neurons, respectively, were TUNEL-positive. Comparison of two adjacent sections immunostained for the two different antigens revealed the co-expression of the two caspases. These results suggest that neonatal capsaicin triggers the caspase cascade and, thereby, induces trigeminal primary neuronal apoptosis.
Jin
Hai Wei
HW
Department of Oral Function and Anatomy, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Japan.
Ichikawa
Hiroyuki
H
Nomura
Kayo
K
Mukae
Kazuo
K
Terayama
Ryuji
R
Yamaai
Tomoichiro
T
Sugimoto
Tomosada
T
D000818:Animals; D000831:Animals, Newborn; D017209:Apoptosis / Q000187:drug effects*; D002211:Capsaicin / Q000008:administration & dosage*; D053148:Caspase 3 / Q000378:metabolism*; D053453:Caspase 9 / Q000378:metabolism*; D053938:DNA Fragmentation / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D005260:Female; D020287:In Situ Nick-End Labeling; D007279:Injections, Subcutaneous; D008297:Male; D009474:Neurons / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012668:Trigeminal Ganglion / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology*
D053148:Caspase 3; D053453:Caspase 9; D002211:Capsaicin