Bilateral kainic acid lesions in the rat hilus induce non-linear additive mossy fiber neoinnervation

Abstract

Kainic acid (KA) lesions of the rat hilus model hippocampal sclerosis and temporal lobe epilepsy. Unilateral hilar cell loss denervates the associational afferents normally projecting to the inner molecular layer (IML) granule cell dendrites, followed by ipsilateral mossy fiber (MF) sprouting. Hilar neurons also project through the hippocampal commissure to the contralateral IML. This study compared densities of IML MF sprouting following unilateral versus bilateral low dose KA lesions, using Neo-Timm stain 30 days later. Unilateral KA (0.4 μg) caused only dense ipsilateral MF sprouting. Bilateral lesions with lower doses of KA (0.1 with 0.2 or 0.3 μg) induced dense bilateral MF sprouting. However, the same low doses of KA injected unilaterally did not induce significant sprouting ipsilaterally or contralaterally. These data show that denervations of both associational and commissural afferents to the same IML dendritic zones of granule cells induce non-linear, additive bilateral MF neoinnervations.