Distribution of calbindin- and parvalbumin-positive interneurons in controls and FCD cases from the temporal or frontal lobe. (a-h) Representative sections of calbindin (a-d) and parvalbumin immunostainings (e-h) in control cortex (a,e), FCD IIIa (b,f), FCD IIa temporal (c,g) and FCD IIa, frontal (d,h). Scale bars: 200 μm (a-d); 250 μm (e-h). (a) Control. A dense ribbon of calbindin-positive neurons can be observed at the level of layer II. (b) FCD IIIa. Calbindin-positive neurons are similarly distributed when compared to control. (c) FCD IIa, temporal. Density of calbindin-positive neurons appears reduced in layer II. (d) FCD IIa, frontal. Reduction of calbindin-positive neurons, individual cells show a dysmorphic appearance. (e) Control. Parvalbumin-positive cells and a dense axonal plexus are concentrated at layer IV, but are also seen in layer III and V. (f) FCD IIIa. In this patient the axonal plexus is smaller and cell numbers are reduced, especially in layer III. (g) FCD IIa, temporal. Note the rudimentary and discontinuous axonal plexus in layer IV, but an accumulation of parvalbumin-positive cells in layer II. (h) FCD IIa, frontal. Parvalbumin-positive neurons appear more numerous and are widely distributed over the layers II-IV. (i,j). Densities of calbindin- (i) and parvalbumin-positive (layer IV) neurons (j) in controls and FCD cases. (i) Densities of calbindin-positive cells were significantly reduced in FCD FCx when compared to AHS groups (control + AHS, p < 0.05, FCD IIIa, p < 0.01. One-way ANOVA with Tukey’s post-test). (j) Densities of parvalbumin-positive cells were significantly reduced in FCD IIIa when compared to controls (p < 0.05). All other FCD groups did not differ significantly. (k,l) Quantification of calbindin and parvalbumin mRNA expression does not show significant differences between controls or FCD cases.