The reinforcing actions of a serotonin-3 receptor agonist within the ventral tegmental area: evidence for subregional and genetic differences and involvement of dopamine neurons.

Studies from our laboratory indicated that local perfusion of the ventral tegmental area (VTA) with a serotonin-3 (5-HT(3)) receptor agonist increased dopamine (DA) neuronal activity and that the self-infusion of ethanol (EtOH) and cocaine into the posterior VTA could be inhibited with coadministration of a 5-HT(3) receptor antagonist. The study tested the hypothesis that activating 5-HT(3) receptors within the VTA produces reinforcing effects. The study also examined whether there were differences between Wistar rats and a line of rats selectively bred for high alcohol consumption with regard to the self-infusion of a 5-HT(3) receptor agonist within the VTA. Adult female alcohol-preferring (P) and Wistar rats were allowed to self-infuse the 5-HT(3) receptor agonist 1-(m-chlorophenyl)-biguanide (CPBG) into the posterior or anterior VTA. Furthermore, experiments examined the effects of coinfusion of the 5-HT(3) antagonist ICS 205,930 (ICS), and the DA D(2,3) agonist quinpirole on the self-infusion of CPBG. Both Wistar and P rats readily self-administered CPBG into the posterior, but not anterior, VTA. P rats self-infused lower concentrations of CPBG (0.10 microM) than did Wistar rats (1.0 microM). Coinfusion of either ICS or quinpirole reduced CPBG self-infusion into the posterior VTA. The results of this study suggest that activation of 5-HT(3) receptors within the posterior VTA produces reinforcing effects and that these reinforcing effects are mediated through activation of DA neurons. Furthermore, the data suggest that selective breeding for alcohol-preference results in the posterior VTA being more sensitive to the reinforcing effects of CPBG.

Longitudinal assessment of immune response and viral characteristics in HIV-infected patients with prolonged CD4(+)/viral load discordance.

Although suppression of HIV-1 RNA below the limit of detection is associated with optimal outcomes, many patients can maintain or increase their CD4(+) count for prolonged time periods in the presence of persistent low-level viremia. We followed seven patients with prolonged (>5 years) discordant CD4(+)/viral load (VL) responses on protease inhibitor (PI)-based highly active antiretroviral therapy (HAART) prospectively for 1 year to assess evolution of immune function, viral phenotype, replication capacity (RC), and resistance profile. Immune function was assessed by qualitative and quantitative measurement of cellular activation (CD38(+)HLA-DR(+) and CD38 antibodies bound per cell), and the interferon (IFN)-() ELISpot assay. Presence of syncytium-inducing (SI) or nonsyncytium-inducing (NSI) viral strains was determined by MT-2 cell culture. RC was measured by a modified rapid recombinant virus assay. The resistance profile was characterized by both genotypic and phenotypic analysis. Over the year of follow-up, IFN-() production to gag persisted, responses to other HIV antigens increased, and markers of cellular activation did not change. NSI virus predominated. The genotypic (GSS) and phenotypic (PSS) susceptibility scores remained stable. Evolution of RC was variable over the year of follow-up, but the RC of viruses remained well below that of wild-type clinical isolates. Thus, CD4(+)/VL discordance can be maintained for periods exceeding 5 years in some patients receiving PI-based HAART without significant evolution of HIV resistance.

Prolonged CD4+ cell/virus load discordance during treatment with protease inhibitor-based highly active antiretroviral therapy: immune response and viral control.

Mechanisms that underly discordant CD4+ cell/virus load (VL) responses in patients who receive highly active antiretroviral therapy (HAART) were studied in 30 human immunodeficiency virus (HIV)-positive patients, in 3 groups. Discordant responders maintained CD4+ cell levels >200/mm(3) with stable or increasing trend, despite sustained VLs of 500-5000 copies/mL, for >2 years. Treatment-success patients had CD4+ cell counts >200/mm(3) with stable or increasing trend and VLs <50 copies/mL, for >2 years. Treatment-failure patients initially responded to HAART, followed by decreasing CD4+ cell counts and increasing VLs. Interferon-gamma production to gag and noncytolytic CD8+ cell suppressive activity were greater in discordant responders. Cellular activation was greatest in patients with treatment failure. All discordant responders had non-syncytium-inducing (CCR5-tropic) viruses. Viruses from discordant responders and from patients with treatment failure had extensive resistance mutations; discordant responders had significantly lower viral replication capacities. These findings suggest that discordant responses may be related to enhanced HIV-directed immune responses, diminished cellular activation, decreased viral replication capacity, and preservation of non-syncytium-inducing virus strains.