The neurological manifestations of HIV-1 affect between one and two- thirds of adults patients with AIDS. Included in these complications are a form of dementia producing cognitive, motor, and possible visual dysfunction in the absences of viral infection of neurons, in the absence of opportunistic superinfections, and in the absence of HIV-associated malignancies of the CNS. Recent progress has been made in the laboratory investigation of the basis for this form of dementia (termed the AIDS dementia complex, or more recently, HIV-associated motor/cognitive complex). Evidence from a variety of laboratories around the world suggests that at least part of the neuronal loss observed in the brains of patients with AIDS may be related to a final common pathway invoking excessive stimulation of excitatory amino acid receptors such as the N- methyl-D-aspartate (NMDA)subtype of these receptors. These findings are in the mainstream of current neuroscience research which has found that several acute and degenerative neurologic disorders, ranging from stroke to trauma and epilepsy to Huntington's disease, may have a similar basis for neuronal injury. In the face of overstimulation of excitatory amino acid receptors, ion channels permit excessive influx of calcium ions and consequent nerve cell injury. Although the exact mechanism for neuronal injury by calcium overload is still a matter of intense investigation and current debate, many laboratories have found that limiting the influx of calcium ions under these conditions can protect neurons form injury. For example, laboratory investigation using in vitro and in vivo animal models has suggested that blockade of ion channels permeable to calcium ions may prevent nerve cell damage engendered by HIV-infected macrophages or macrophages stimulated by the HIV-1 coat protein, gp120. At least two types of ion channels contribute to this form of injury, L-type voltage- dependent calcium channels and NMDA receptor-coupled channels. For this reason, clinically-tolerated antagonists of these channels are proposed to be studied in conjunction with the best available anti-retroviral therapy, i.e. zidovudine (ZDV) or nucleosides such as dideoxyinosine (ddI). A second study will be used an adjunctive therapy to these anti- retroviral another well-known drug, memantine, which has recently been recognized to be a potent NMDA open-channel blocker capable of attenuating neuronal injury associated with exposure to gp120 by the P.I.'s laboratory.
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