Abstract
Argyrophilic dark neurons (DNs) reflect an early histopathological state of neuronal damage in various brain insults. In the present study, we examined the fate of DNs following two kinds of brain insults: an injection of ibotenic acid (IA) into the hippocampus and a stressful swimming exercise (SWIM). Wistar rats were unilaterally injected IA into the hippocampus CA1 or were made to swim in a pool for 3 h. Argyrophil III (DNs)-, activated caspase-3 immuno-, TUNEL- and H-E-, stainings and ultrastractural examinations were done after these insults. IA injection; typical DNs were densely detected around the injection site at 1-3 h after injection, and argyrophilic only in soma with pycnotic nucleus at 12-24 h. Caspase-3 activation was detected 3 h to 3 d, TUNEL positive cells were detected at 3-7 d after, and the decrease in cell number was detected. SWIM; no typical DNs, but "brown" neurons, were detected in the hippocampus, striatum, amygdala, cortex etc (most frequently in CA1 pyramidal cell layer) up to 3 days. A light activation of caspase-3 was detected but no TUNEL positive cells. EM study revealed that, after IA injection, silver particles aggregated diffusely in dendrites and cytoplasm. After SWIM, silver particles distributed mainly on mitochondria. These data suggest that DNs reflect a various degree of neuronal damages. [Jpn J Physiol 54 Suppl:S251 (2004)]
