Neurodegenerative effects of recombinant HIV-1 Tat(1-86) are associated with inhibition of microtubule formation and oxidative stress-related reductions in microtubule-associated protein-2(a,b).

The human immunodeficiency virus 1 (HIV-1) protein Trans-activator of Transcription (Tat) is a nuclear regulatory protein that may contribute to the development of HIV-1 associated dementia by disrupting the neuronal cytoskeleton. The present studies examined effects of recombinant Tat(1-86; 1-100 nM) on microtubule-associated protein (MAP)-dependent and MAP-independent microtubule formation ex vivo and oxidative neuronal injury in rat organotypic hippocampal explants. Acute exposure to Tat(1-86) (≥1 nM) markedly reduced MAP-dependent and -independent microtubule formation ex vivo, as did vincristine sulfate (0.1-10 µM). Cytotoxicity, as measured by propidium iodide uptake, was observed in granule cells of the DG with exposure to 100 nM Tat(1-86) for 24 or 72 h, while significant reductions in MAP-2 immunoreactivity were observed in granule cells and pyramidal cells of the CA1 and CA3 regions at each timepoint. These effects were prevented by co-exposure to the soluble vitamin E analog Trolox (500 µM). Thus, effects of Tat(1-86) on the neuronal viability may be associated with direct interactions with microtubules and generation of oxidative stress.

Potentiation of N-methyl-D-aspartate receptor-mediated neuronal injury during methamphetamine withdrawal in vitro requires co-activation of IP3 receptors.

Recent findings suggest that methamphetamine (METH) functions acutely to inhibit N-methyl-d-aspartate (NMDA) receptor function. Protracted withdrawal from METH exposure may increase the sensitivity of NMDA receptors to agonist exposure, promoting neuronal excitability. However, the relevance of METH effects on NMDA receptor activity with regard to neuronal viability has not been fully studied. The present studies examined the effects of protracted METH exposure (6 or 7 days; 1.0-100 microM) and withdrawal (1 or 7 days) on NMDA receptor-dependent neurotoxicity, determined with use of the non-vital fluorescent marker propidium iodide, in organotypic slice cultures of male and female rats. Prolonged exposure to METH (100 microM) produced only modest toxicity in the granule cell layer of the dentate gyrus. Withdrawal from METH exposure (1 or 7 days) did not produce overt neuronal injury in any region of slice cultures. Exposure to NMDA (5 microM) produced marked neurotoxicity in the CA1 pyramidal cell layer. Neither co-exposure to METH nor 1 day of METH withdrawal in combination with NMDA exposure altered NMDA-induced neurotoxicity. In contrast, protracted withdrawal from METH exposure (7 days) was associated with a marked (approximately 400%) increase in NMDA-induced neurotoxicity in CA1 region pyramidal cells. This potentiation of neurotoxicity was prevented by co-exposure to the selective NMDA receptor antagonist 5-2-amino-5-phosphonovaleric acid (20 microM) and was markedly attenuated by co-exposure of slices to xestospongin C (1 microM), an antagonist of IP(3) receptors. The results of the present studies suggest that long-term METH withdrawal functionally sensitizes the NMDA receptor to agonist exposure and requires the co-activation of NMDA and IP(3) receptors.

Sex differences in the neurotoxic effects of adenosine A1 receptor antagonism during ethanol withdrawal: reversal with an A1 receptor agonist or an NMDA receptor antagonist.

BACKGROUND: Neuronal adaptations that occur during chronic ethanol (EtOH) exposure have been observed to sensitize the brain to excitotoxic insult during withdrawal. The adenosine receptor system warrants further examination in this regard, as recent evidence has implicated adenosine receptor involvement in the behavioral effects of both EtOH exposure and withdrawal. METHODS: The current studies examined effects of adenosine A(1) receptor manipulation on neuronal injury in EtOH-naive and EtOH-withdrawn male and female rat hippocampal slice cultures. EtOH-naive and EtOH pretreated (43.1 to 26.9 mM from days 5 to 15 DIV) cultures were exposed to the A(1) receptor agonist 2-Chloro-N(6)-cyclopentyladenosine (CCPA; 10 nM), the A(1) receptor antagonist 8-Cyclopentyl-1,3-dipropylxanthine (DPCPX;10 nM), or the N-methyl-D-aspartate (NMDA) receptor antagonist D,L,-2-amino-5-phosphovalerate (APV; 20 microM) at 15 days in vitro (DIV). Cytotoxicity was measured in the primary neuronal layers of the dentate gyrus, CA3 and CA1 hippocampal regions by quantification of propidium iodide (PI) fluorescence after 24 hours. Immunohistochemical analysis of A(1) receptor abundance was conducted in EtOH-naive and EtOH pretreated slice cultures at 15 DIV. RESULTS: Twenty-four hour exposure to DPCPX in EtOH-naive slice cultures did not produced neurotoxicity in any region of slice cultures. Though withdrawal from 10 day EtOH exposure produced no toxicity in either male or female slice cultures, exposure to DPCPX during 24 hours of EtOH withdrawal produced a marked increase in PI uptake in all hippocampal culture subregions in female cultures (to approximately 160% of control values). A significant effect for sex was observed in the CA1 region such that toxicity in females cultures exposed to the A(1) antagonist during withdrawal was greater than that observed in male cultures. These effects of DPCPX in EtOH withdrawn female and male slices were prevented by co-exposure to either the A(1) agonist CCPA or the NMDA receptor antagonist APV for 24 hours. No differences in the abundance of A(1) receptors were observed in male and female EtOH-naive or EtOH pretreated cultures. CONCLUSIONS: The current findings suggest that the female hippocampus possesses an innate sensitivity to effects of EtOH exposure and withdrawal on neuronal excitability that is independent of hormonal influences. Further, this sex difference is not related to effects of EtOH exposure on A(1) receptor abundance, but likely reflects increased NMDA receptor-mediated signaling downstream of A(1) inhibition in females.