Stereologic estimation of hippocampal GluR2/3- and calretinin-immunoreactive hilar neurons (presumptive mossy cells) in two mouse models of temporal lobe epilepsy

Abstract

Summary Purpose: Hippocampal mossy cells receive dense innervation from dentate granule cells and, in turn, mossy cells innervate both granule cells and interneurons. Mossy cell loss is thought to trigger granule cell mossy fiber sprouting, which may affect granule cell excitability. The aim of this study was to quantify mossy cell loss in two animal models of temporal lobe epilepsy, and determine whether there exists a relationship between mossy cell loss, mossy fiber sprouting, and granule cell dispersion. Methods: Representative hippocampal sections from p35 knockout mice and mice with unilateral intrahippocampal kainate injection were immunolabeled for GluR2/3, two subunits of the amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionate (AMPA) receptor and calretinin to identify mossy cells. Mossy fibers were immunostained against synaptoporin. Key Findings: p35 Knockout mice showed no hilar cell death, but moderate mossy fiber sprouting and granule cell dispersion. In the kainate‐injected hippocampus, there was an 80% and 85% reduction of GluR2/3‐ and GluR2/3/calretinin‐positive hilar neurons, respectively, and dense mossy fiber sprouting and significant granule cell dispersion. In the contralateral hippocampus there was a 52% loss of GluR2/3‐, but only a 20% loss of GluR2/3‐calretinin‐immunoreactive presumptive mossy cells, and granule cell dispersion; no mossy fiber sprouting was observed. Significance: These results indicate a probable lack of causality between mossy cell death and mossy fiber sprouting.

Dentate gyrus mossy cells control spontaneous convulsive seizures and spatial memory

“…We found that MC excitation in the ipsilateral hemisphere also prevented seizure generalization (Fig. 3, C and D), despite the greater degree of hippocampal sclerosis ipsilaterally, where we observed a 77% MC loss compared with a 55% MC loss contralaterally, consistent with previous studies (9) (fig. S15).…”

“…We first tested how MC activity affects spontaneous electrographic, nonconvulsive seizures in a well-established model of TLE with kainic acid (KA) injected unilaterally into the left dorsal hippocampus (8, 9). We used a closed-loop seizure detection and intervention method in chronically epileptic mice (10) to deliver a 15-s light pulse at the onset of 50% of detected seizures (Fig.…”

“…3, C and D). Because DG microcircuit alterations are different in the hemispheres ipsilateral and contralateral to the KA injection site (8, 9), we also targeted MCs ipsilateral to the KA injection site. We found that MC excitation in the ipsilateral hemisphere also prevented seizure generalization (Fig.…”

Cognitive Deficits and Disruption of Neurogenesis in a Mouse Model of Apolipoprotein E4 Domain Interaction

“…The total number of cells counted was multiplied by 68.6 (1/12 for sections analyzed; 1 ⁄ 4 counting area and 70/100 tissue shrink factor (29). In all cases optimum sampling was achieved as the coefficient of error (CE) is lower than the coefficient of variation (30). The doublecortin-positive cells were categorized into the mitotic and post mitotic types as previously described by Plümpe et al (31).…”

Immunohistochemical investigations of the neuronal changes induced by chronic recurrent seizures in a pilocarpine rodent model of temporal lobe epilepsy

“…Our findings on the MCs of the CFLP strain are in sharp contrast with the general and widely accepted concept that the MCs are highly vulnerable to glutamate-mediated seizures. SE induced by convulsants such as PILO (Silva and Mello 2000) and kainate (Volz et al 2011) led to a loss of MCs. However, in two other mouse strains (Balb/c and NMRI) lacking documented common ancestors (Beck et al 2000) with the CFLP strain, we also found dramatic and different reductions in the density of the MCs after PILO treatment (Dobó et al 2015).…”