Entorhinal lesions result in shrinkage of the outer molecular layer of rat dentate gyrus leading subsequently to an apparent increase of glutamate decarboxylase and cytochrome oxidase activities.

In intact dentate gyrus, glutamate decarboxylase immunoreactivity (GAD) and cytochrome oxidase activity (CyO) showed different distributions patterns. Entorhinal lesions caused increases of GAD and CyO in the outer molecular layer (OML) of the ipsilateral side. Submicroscopical localization of these enzymes did not change, except for CyO labeling more astrocytic mitochondria. The increase in numerical density of GAD puncta correlated quantitatively with shrinkage of OML, whereas in the whole molecular layer the number of GAD puncta remained unchanged. Hence, the localized increase of enzyme activities and lysosomes is apparently related to shrinkage of OML, but does not indicate plasticity of GABAergic neurons.