Recent epidemiological literatures reported that NO(2) is a potential risk factor of
ischemic stroke in polluted area. Meanwhile, our previous in vivo study found that NO(2) could delay the recovery of nerve function after
stroke, implying a possible risk of
vascular dementia (VaD) with NO(2) inhalation, which is often a common cognitive complication resulting from
stroke. However, the effect and detailed mechanisms have not been fully elucidated. In the present study, synaptic mechanisms, the foundation of neuronal function and viability, were investigated in both model rats of
ischemic stroke and healthy rats after NO(2) exposure. Transmission electron microscope (TEM) observation showed that 5 mg m(-3) NO(2) exposure not only exacerbated the ultrastructural impairment of synapses in
stroke model rats, but also induced neuronal damage in healthy rats. Meantime, we found that the expression of
synaptophysin (SYP) and
postsynaptic density protein 95 (PSD-95), two structural markers of synapses in
ischemic stroke model were inhibited by NO(2) inhalation; and so it was with the key
proteins mediating long-term potentiation (LTP), the major form of synaptic plasticity. On the contrary, NO(2) inhalation induced the expression of nearly all these
proteins in healthy rats in a concentration-dependent manner. Our results implied that NO(2) exposure could increase the risk of VaD through inducing excitotoxicity in healthy rats but weakening synaptic plasticity directly in
stroke model rats.