We previously demonstrated that the lentivirus lytic peptide 1 (LLP-1) corresponding to the carboxyl terminus of HIV-1 gp41 induced cell death in human neuronal cells. Present study was conducted to further elucidate the pathogenic mechanisms involved in HIV-1 gp41-induced neurodegeneration in AIDS patients with cognitive deficits. The effect of LLP-1 on activation of calpain-1, a calcium-activated cysteine protease, which has been implicated in neuronal degeneration and death, was monitored by the proteolysis of spectrin in rat organotypic hippocampal slice cultures. Protease specific spectrin breakdown products revealed that LLP-1 generated ${sim}150/145-kDa$ fragments characteristic of calpain-1 activation in hippocampus undergoing cell death as evidenced by LDH release. This spectrin cleavage pattern was further confirmed by in vitro calpain-1 proteolysis. Futhermore, ca1pectin and MDL28170, inhibitors of calpain activity, blocked ca1pain-1-mediated spectrin cleavage. Spectrin cleavage likely occurred in the absence of overt synaptic loss, as suggested by the preserved levels of synaptophysin. Among pharmacological agents tested, apocynin, NADPH oxidase inhibitor, ameliorated the LLP-1-induced spectrin. Given the role of spectrin essential for synapse stabilization, LLP-1-induced spectrin cleavage as occurs with the activation of calpain-1 may be an important effector in LLP-1-mediated cell injury in hippocampus, which is primarily linked to cognitive dysfunction.