Repetitive HBOT affects CD40 expression after CSI. ((a) and (b)) In control cortical sections CD40 is expressed on neuron-like cells. (c) CSI increased CD40 immunoreactivity in the perilesioned cortex. ((c) inset) High magnification photomicrograph depicts a typical neutrophil with round morphology and multiple nuclei (left up corner of inset), while the enlarged cell in the right corner of inset is probably activated microglia. (d) CD40-positive dark-stained pyknotic neurons, transected axonal processes (denoted with arrows), nerve fiber varicosities (arrow head), and blood vessels (asterisk) were abundantly present in perilesioned area. ((e) and (f)) 10 days of HBOT significantly reduced CD40 immunoreactivity in the injured cortex. Rectangles indicate where the high magnification images are taken from. Scale bar = 50 μm.