Fig. 2: Effect of ChABC PNN digestion 1 week before HLS on synaptic changes.

A Focused ion beam-scanning electron microscopy (FIB-SEM) of synapses in the CA1 dendritic tree area before, immediately and 24 h after HLS pre-synapses are green, dendrites yellow. At the initial euthermic condition, the ChABC treated CA1 area showed an increased number of synapses. Immediately after HLS in control and ChABC groups a drop-in number of synapses was observed. After 24 h rewarming period both groups recovered synapses to the euthermic level (Illustration A1, detail A2). B–E Effects of HLS on excitatory and inhibitory synapses on parvalbumin⁺ interneurons. Collocation of presynaptic terminals (vGAT (B, D)/vGLUT (C, E)) and postsynaptic densities (Gephyrin (B, D)/PSD95 (C, E)) were evaluated on single neuron confocal Z-stack series (under Airyscan super-resolution mode) and newly appearing co-locations per slice were counted. Both excitatory and inhibitory synapses decreased after HLS with recovery at 24 h. The impact of the PNN integrity was significant, with a robust increase of excitatory synapses on PV⁺ neurones in comparison with intact PNNs. F–I Long-term impact of integrity of PNNs was observed at the end of behavioral study. HLS has shown increase in inhibitory synapses (F, H) and decrease in excitatory synapses on parvalbumin⁺ interneurons. This long-term impact of PNN integrity was significant, decreasing the inhibitory synapses and increasing excitatory ones. Illustrative images of measured samples are shown. Significance *p < 0.05, **p < 0.01, ***p < 0.001. Statistics Table S2. (A n = 66 sections per group/time point; B–I n = 2–3 neurons per group/time point (av. ratio from Z-stack planes images)). Statistical color coding: Between different time points the asterisk color coding indicates in which group the statistical significance was found. Within the single time points, the asterisk color coding indicates to which group the statistically significant difference was detected.