Neurocognitive disorders seen in HIV disease

Persistent EcoHIV infection induces nigral degeneration in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-intoxicated mice

The widespread use of antiretroviral therapy for treatment of human immunodeficiency virus (HIV) infections has dramatically improved the quality and duration of life for HIV-positive individuals. Despite this success, HIV persists for the life of an infected person in tissue reservoirs including the nervous system. Thus, whether HIV exacerbates age-related brain disorders such as Parkinson's disease (PD) is of concern. In support of this idea, HIV infection can be associated with motor and gait abnormalities that parallel late-stage manifestations of PD including dopaminergic neuronal loss. With these findings in hand, we investigated whether viral infection could affect nigrostriatal degeneration or exacerbate chemically induced nigral degeneration. We now demonstrate an additive effect of EcoHIV on dopaminergic neuronal loss and neuroinflammation induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine intoxication. HIV-1-infected humanized mice failed to recapitulate these EcoHIV results suggesting species-specific neural signaling. The results demonstrate a previously undefined EcoHIV-associated neurodegenerative response that may be used to model pathobiological aspects of PD.

Effects of the HIV-1 viral protein TAT on central neurotransmission: role of group I metabotropic glutamate receptors

Human immunodeficiency virus 1 (HIV-1)-associated dementia (HAD) represents a common complication of HIV-1 infection. Antiretroviral therapy has diminished its incidence, but it is insufficient to eradicate the problem. HAD depends on the presence of the virus in central nervous system (CNS), but the molecular mechanisms involved are not completely understood. It is widely accepted that proteins shed by the virus, such as the envelope glycoprotein gp120 and the nonstructural viral protein Tat, may themselves cause alterations to CNS. By one side, viral proteins are toxic to neurons because of their ability (1) to act as excitotoxins and (2) to evoke the release of endogenous neurotoxins and/or proinflammatory cytokines. By the other side, evidences are emerging that viral components can alter neuronal functions either by modifying the release of neurotransmitters or by influencing the functions of classical receptors controlling central neurotransmission. We here review some results concerning the effects of Tat on cholinergic and noradrenergic neurotransmission in human and rat cortex. The protein can induce the release of acetylcholine from both human and rat cortical cholinergic nerve terminals in a specie-specific manner. In human cholinergic terminals, Tat-mediated releasing effect depends on activation of receptors belonging to I group of metabotropic glutamate receptors (mGluRs), while in rat terminals Tat-induced effect involves the activation of a so far unknown receptor. The protein, unable on its own to release noradrenaline from human and rat cortical noradrenergic nerve endings, potentiates the release of amine induced by presynaptic NMDA receptors. Also in this case, Tat effect involves activation of a receptor belonging to the group I mGluRs, in particular of the mGluR1 subtype. The finding that group I mGluRs may represent a preferential target of the protein in CNS may be relevant to the proposal of new therapeutic approaches for the cure of HAD.

The human immunodeficiency virus type-1 transcription factor Tat produces elevations in intracellular Ca2+ that require function of an N-methyl-d-aspartate receptor polyamine-sensitive site

Human immunodeficiency virus type-1 (HIV-1) infection is commonly associated with neuronal loss, as well as, cognitive and motor deficits collectively termed HIV-1-associated dementia (HAD). Function of the HIV-1 transcription factor Tat, activation of N-methyl-D-aspartate (NMDA)-type glutamate receptors, and subsequent rapid rises in free intracellular Ca2+ have been implicated in the development of this neurological disorder. However, the role of specific NMDA receptor modulatory sites in mediating effects of Tat has not been examined. The present studies examined the ability of two variants of Tat protein (1-100 nM), Tat 1-72 and Tat 1-86, to produce rapid rises in intracellular Ca2+ in organotypic slice cultures of rat hippocampus. Further, these studies evaluated the role of an NMDA receptor polyamine-sensitive site in mediating Tat-induced elevations in intracellular Ca2+. Brief exposure (10 min) to each variant of Tat protein (>1 nM) markedly increased levels of intracellular Ca2+ in each region of the hippocampus to as much as 145% of controls. In contrast, exposure of cultures to a deletion mutant of Tat protein devoid of amino acids 31-61 (Tat Delta31-61) did not produce changes in intracellular Ca2+ levels. Most significantly, exposure to the NMDA receptor antagonist dizocilpine (MK801 20 microM) and the polyamine site antagonist arcaine (10 microM) significantly attenuated increases in intracellular Ca2+ levels when co-administered with either the Tat 1-72 or Tat 1-86 amino acid variant of Tat. Thus, exposure of the hippocampus to Tat produces increases in intracellular Ca2+ levels that require function of an NMDA receptor polyamine-sensitive site and this may well contribute to the neurotoxic effects of HIV-1 infection. Polyamine-sensitive portions of this receptor may then represent novel therapeutic targets in the pharmacologic treatment of HAD-related neurotoxicity.

The medical, personal, and social causes of uncertainty in HIV illness

Uncertainty is an important part of the illness experience. Mishel elaborated a theory of uncertainty in acute illness and later expanded the framework to account for uncertainty in chronic illness. Researchers subsequently have investigated the causes and outcomes associated with the uncertainty in illness experience across a variety of medical conditions. The current study applies and extends Mishel's model within the context of HIV illness-related uncertainty. In this qualitative study, focus group methods were used to examine the nature of illness uncertainty experienced by persons living with HIV or AIDS. Findings confirm Mishel's contention that the causes of uncertainty extend beyond those of medical diagnosis, treatment, and recovery to personal and social aspects of daily life. Identified sources of uncertainty may have important mental health and quality of life implications.

Relationships between cognition and structural neuroimaging findings in adults with human immunodeficiency virus type-1

Infection of the central nervous system with human immunodeficiency virus type-1 (HIV) is associated with cognitive impairments that range from mild cognitive and motor difficulties to dementia. Structural neuroimaging abnormalities are also common in HIV-infected patients both with and without cognitive disturbances. The most common abnormalities include high signal intensities in the white matter and atrophy. Research over the past 12 years has helped define the relationship between these neuroimaging abnormalities and the manifestation of cognitive disturbance in HIV. In the present paper, we provide a synopsis of these studies and report the current state of the literature. Our review revealed that atrophy of the caudate nucleus is most consistently associated with cognitive impairment in HIV. The current literature does not support a strong relationship between cortical atrophy or white matter abnormalities and cognitive dysfunction in this population, though methodological issues may have influenced the results. Suggestions for study design and new research directions are provided.