A surface antigen delineating a subset of neurons in the primary somatosensory cortex of the mouse

Synapsins are a family of proteins associated with synaptic vesicles that are widely used as markers of synaptic terminals. We decided to investigate synapsin I expression in the mouse primary somatosensory cortex (SI). Immunostaining experiments using a polyclonal antibody against C-terminal domain of synapsin Ia/b (anti-SynI-C) showed an unusual pattern in the SI cortex compared to other regions of the neocortex. The staining delineated the cells located in barrel hollows. The immunoreactive product was located on the perikarya and proximal dendrites of gabaergic neurons found in layer IV and VI of the SI cortex. Other anti-synapsin antibodies did not reveal this pattern within the SI cortex, although in the hippocampus all antibodies examined produced a similar pattern of immunostaining. Deglycosylation of sections resulted in complete loss of immunodecoration on the cell perikarya. We suggest that the anti-SynI-C recognizes a saccharide surface epitope, possibly an element of perineuronal nets that is specific for the primary somatosensory cortex.