Loss of GABAergic neurons in medial septum after fimbria-fornix transection.

Neurons in the medial septum of the rat brain undergo retrograde degeneration after transection of their projection to the hippocampal formation, the fimbria-fornix. This cell death has been characterized for both Nissl-stained neurons and acetylcholinesterase-stained neurons. The major cell type in the medial septum is GABAergic, and many of these GABAergic neurons project to the hippocampal formation. Because the fimbria-fornix transection causes more neuronal death than can be accounted for by the loss of cholinergic neurons, we have sought to determine if the GABAergic neurons undergo a cell death similar to that reported for the cholinergic neurons. We report here that GABAergic neurons are indeed lost after the transection but the time course is considerably slower than that for the cholinergic neurons.