Immunohistochemical Study of Distribution of GAD and GABA in the Entorhinal Cortex after Spreading Depression in Juvenile Rats

Spreading depression (SD), discovered by Leao in 1944, is a pathophysiological depolarization wave that propagates slowly in the brain (3 mm/min) and causes dramatic ionic and hemodynamic changes. SD appears to act through several mechanisms and receptors, which have not completely understood. Here, we studied the effect of inhibitory system in animal model of SD using immunohistochemistry technique.
After implanting recording electrodes and cannula over the brain, repetitive SD was induced by KCl injection (2 M) in juvenile rats for four consecutive weeks. Then all rats’ brains removed. The mean number of dark neurons in the entorhinal cortex (EC) were determined using toluidine blue staining. To identify the prevalence and distribution of GABAA subunit receptors as well as glutamic acid decarboxylase (GAD), the GABA biosynthetic enzyme, immunohistochemistry technique was performed.
The mean number of SD induced was statistically increased during four weeks of experiments. The mean number of dark neurons in EC was significantly increased in SD group compared to sham rats. Furthermore, expression of GAD 65 in EC significantly increased in SD group compared to sham group. However, both GABA-A&alpha and GABA-A&beta subunit receptors didn’t significantly change in that region after SD.
These data suggest that SD is able to damage the neuronal cells in neural tissues in juvenile rats and parallelly lead to enhancement of GAD 65 in the central nervous system.