Species-specific expression of parvalbumin in the entorhinal cortex of the Mongolian gerbil: dependence on local activity but not extrinsic afferents.

Mongolian gerbils are genetically predisposed to develop epileptic seizures in limbic structures. A species-specific property of the Mongolian gerbil is the expression of the calcium-binding protein parvalbumin in the perforant path where it is predominantly concentrated in nerve terminals. To test the hypothesis that this atypical expression of parvalbumin is induced by seizure-correlated hyperactivity in the entorhinohippocampal loop, we investigated whether it is dependent on extrinsic afferents to the entorhinal cortex. We cultivated organotypic slice cultures of neonate gerbil entorhinal cortex, isolated from all regions it is normally connected with in vivo. In these cultures, parvalbumin-expressing neurons demonstrated their characteristic features like in vivo. Blockade of spontaneous local activity with the sodium-channel blocker tetrodotoxin, however, considerably reduced the number of parvalbumin-expressing neurons in culture. These results indicate that spontaneous local activity, but not activity mediated by extrinsic afferents, is an essential factor for the expression of parvalbumin in the entorhinal cortex of the Mongolian gerbil.