An early increase in somatostatin mRNA expression in the frontal cortex of rhesus monkeys infected with simian immunodeficiency virus

Prefrontal dopaminergic and enkephalinergic synaptic accommodation in HIV-associated neurocognitive disorders and encephalitis

Changes in synapse structure occur in frontal neocortex with HIV encephalitis (HIVE) and may contribute to HIV-associated neurocognitive disorders (HAND). A postmortem survey was conducted to determine if mRNAs involved in synaptic transmission are perturbed in dorsolateral prefrontal cortex (DLPFC) in subjects with HIVE or HAND. Expression of the opioid neurotransmitter preproenkephalin mRNA (PENK) was significantly decreased in a sampling of 446 brain specimens from HIV-1 infected people compared to 67 HIV negative subjects. Decreased DLPFC PENK was most evident in subjects with HIVE and/or increased expression of interferon regulatory factor 1 mRNA (IRF1). Type 2 dopamine receptor mRNA (DRD2L) was decreased significantly, but not in the same set of subjects with PENK dysregulation. DRD2L downregulation occurred primarily in the subjects without HIVE or neurocognitive impairment. Subjects with neurocognitive impairment often failed to significantly downregulate DRD2L and had abnormally high IRF1 expression. Conclusion: Dysregulation of synaptic preproenkephalin and DRD2L in frontal neocortex can occur with and without neurocognitive impairment in HIV-infected people. Downregulation of DRD2L in the prefrontal cortex was associated with more favorable neuropsychological and neuropathological outcomes; the failure to downregulate DRD2L was significantly less favorable. PENK downregulation was related neuropathologically to HIVE, but was not related to neuropsychological outcome independently. Emulating endogenous synaptic plasticity pharmacodynamically could enhance synaptic accommodation and improve neuropsychological and neuropathological outcomes in HIV/AIDS.

Lentiviral infection of rhesus macaques causes long-term injury to cortical and hippocampal projections of prostaglandin-expressing cholinergic basal forebrain neurons

The simian immunodeficiency virus (SIV) macaque model resembles human immunodeficiency virus-acquired immunodeficiency syndrome (AIDS) and associated brain dysfunction. Altered expression of synaptic markers and transmitters in neuro-AIDS has been reported, but limited data exist for the cholinergic system and lipid mediators such as prostaglandins. Here, we analyzed cholinergic basal forebrain neurons with their telencephalic projections and the rate-limiting enzymes for prostaglandin synthesis, cyclooxygenase isotypes 1 and 2 (COX1 and COX2) in the brains of SIV-infected macaques with or without encephalitis and antiretroviral therapy and uninfected controls.Cyclooxygenase isotype 1, but not COX2, was coexpressed with markers of cholinergic phenotype, that is, choline acetyltransferase and vesicular acetylcholine transporter (VAChT), in basal forebrain neurons of monkey, as well as human, brain. Cyclooxygenase isotype 1 was decreased in basal forebrain neurons in macaques with AIDS versus uninfected and asymptomatic SIV-infected macaques. The VAChT-positive fiber density was reduced in frontal, parietal, and hippocampal-entorhinal cortex. Although brain SIV burden and associated COX1- and COX2-positive mononuclear and endothelial inflammatory reactions were mostly reversed in AIDS-diseased macaques that received 6-chloro-2',3'-dideoxyguanosine treatment, decreased VAChT-positive terminal density and reduced cholinergic COX1 expression were not. Thus, COX1 expression is a feature of primate cholinergic basal forebrain neurons; it may be functionally important and a critical biomarker of cholinergic dysregulation accompanying lentiviral encephalopathy. These results further imply that insufficiently prompt initiation of antiretroviral therapy in lentiviral infection may lead to neurostructurally unremarkable but neurochemically prominent irreversible brain damage.

Alterations in somatostatin mRNA expression in the dorsolateral prefrontal cortex of subjects with schizophrenia or schizoaffective disorder

Alterations in the inhibitory circuitry of the dorsolateral prefrontal cortex (DLPFC) in schizophrenia include reduced expression of the messenger RNA (mRNA) for somatostatin (SST), a neuropeptide present in a subpopulation of gamma-aminobutyric acid (GABA) neurons. However, neither the cellular substrate nor the causal mechanisms for decreased SST mRNA levels in schizophrenia are known. We used in situ hybridization to quantify the compartmental, laminar, and cellular levels of SST mRNA expression in the DLPFC of 23 pairs of schizophrenia or schizoaffective disorder and control subjects. We also explored potential causal mechanisms by utilizing similar methods to analyze SST mRNA expression in 2 animal models. The expression of SST mRNA was significantly decreased in layers 2-superficial 6 of subjects with schizophrenia, but not in layer 1, deep 6 or the white matter. At the cellular level, both the density of cortical SST mRNA-positive neurons and the expression of SST mRNA per neuron were reduced in the subjects with schizophrenia. These alterations were not due to potential confounds and appeared to be a downstream consequence of impaired neurotrophin signaling through the trkB receptor. These findings support the hypothesis that a marked reduction in SST mRNA expression in a subset of GABA neurons contributes to DLPFC dysfunction in schizophrenia.

Colocalization of somatostatin receptor subtypes (SSTR1-5) with somatostatin, NADPH-diaphorase (NADPH-d), and tyrosine hydroxylase in the rat hypothalamus

The hypothalamus is a major site of somatostatin (SST) production and action. SST is synthesized in several hypothalamic nuclei and involved in a variety of functions. Using SST receptor (SSTR)-specific antibodies, we localized SSTR subtypes in the rat hypothalamus. In addition, we also demonstrated SSTRs colocalization with SST, NADPH-diaphorase (NADPH-d), and tyrosine hydroxylase (TH). SSTR1 is strongly localized in neurons in all major hypothalamic nuclei as well as in nerve fibers in the zona externa of the median eminence and the ependyma of the third ventricle. SSTR2 is also well expressed in most regions but with a relatively lower abundance in comparison to SSTR1. In contrast, SSTR3 is localized primarily in the paraventricular nucleus, dorsomedial hypothalamic nucleus, arcuate nucleus, and median eminence. SSTR4-like immunoreactivity is mainly confined to the arcuate nucleus, ventromedial hypothalamic nucleus, median eminence, and ependymal cells of third ventricle, with the rare SSTR4-positive neuron in the paraventricular nucleus. SSTR5 is the least expressed subtype occurring only in few cells in the inner layer of the median eminence. Overall, SSTR1 is the predominant subtype, followed by SSTR2, 4, 3, and 5. Combined immunofluorescence, immunocytochemistry, and histochemistry were used to demonstrate SSTRs colocalization with SST, TH, and NADPH-d. SSTRs colocalization with SST, TH, and NADPH-d displays in a region and receptor specificity. Colocalization of SST and NADPH-d with SSTRs in hypothalamic regions was similar, suggesting that SST and NADPH-d producing cells are same. In contrast, TH was selectively coexpressed with SSTRs in the hypothalamus in a receptor-specific manner. Taken together, these data suggest that SSTRs may interact with NADPH-d and TH to exert a physiological role in concert within the hypothalamus.

Fractalkine expression in the rhesus monkey brain during lentivirus infection and its control by 6-chloro-2',3'-dideoxyguanosine

Existing data concerning the role of the delta-chemokine fractalkine (CX3CL1) and its receptor (CX3CR1) in lentivirus-induced encephalitis are limited and controversial. We explored, by quantitative in situ hybridization and immunohistochemistry, the cell-specific changes of CX3CL1 and CX3CR1 in rhesus macaque brain during simian immunodeficiency virus (SIV) infection and antiretroviral treatment. Neuronal expression of CX3CL1 was significantly reduced in cortex and striatum of AIDS-diseased monkeys as compared with uninfected and asymptomatic SIV-infected monkeys. CX3CL1 mRNA was increased in some endothelial cells and newly induced in astrocytes and macrophages focally in areas of SIV burden and inflammatory infiltrates. In most CX3CL1-positive astrocytes and macrophages, the transcription factor NF-kappaB was translocated to the nucleus. CX3CR1 was upregulated in scattered, nodule, and giant cell-forming microglia/macrophages and mononuclear infiltrates close to CX3CL1-induced cells in the brain. Treatment of AIDS monkeys with the central nervous system-permeant 6-chloro-2',3'-dideoxyguanosine fully reversed SIV burden, productive inflammation, nuclear NF-kappaB translocation as well as focal induction of CX3CL1 in astrocytes and macrophages and downregulation in neurons. In contrast, diffuse CX3CR1-positive microgliosis and GFAP-positive astrogliosis were partially reversed by 6-chloro-2',3'-dideoxyguanosine. Thus, focally induced CX3CL1 may be a target for therapeutic intervention to limit ongoing inflammatory infiltration into brain in lentivirus infection.

Brain virus burden and indoleamine-2,3-dioxygenase expression during lentiviral infection of rhesus monkey are concomitantly lowered by 6-chloro-2',3'-dideoxyguanosine

Increased kynurenine pathway metabolism has been implicated in the aetiology of lentiviral encephalopathy. Indoleamine-2,3-dioxygenase (IDO) initiates the increased production of kynurenine pathway metabolites like quinolinic acid (QUIN). QUIN itself is elevated in AIDS-diseased monkey and human brain parenchyma and cerebrospinal fluid at levels excitotoxic for neurons in vitro. This study investigates the cellular origin of IDO biosynthesis in the brain of rhesus monkeys infected with simian immunodeficiency virus (SIV) and explores the effects of CNS-permeant antiretroviral treatment. IDO transcript and protein were absent from the brain of non-infected and SIV-infected asymptomatic monkeys. IDO biosynthesis was induced in the brain of monkeys exhibiting AIDS. Nodule and multinucleated giant cell-forming macrophages were the main sources of IDO synthesis. Treatment with the lipophilic 6-chloro-2',3'-dideoxyguanosine suppressed IDO expression in the brain of AIDS-diseased monkeys. The effectiveness of this treatment was confirmed by the reduction of virus burden and SIV-induced perivascular infiltrates, mononuclear nodules and multinucleated giant cells. Our data demonstrate that brain IDO biosynthesis is induced in a subset of monocyte-derived cells, depends on viral burden and is susceptible to antiretroviral treatment. Thus, IDO induction is associated with reversible overt inflammatory events localized to areas of active viral replication in the SIV-infected brain.

Impaired performance on a rhesus monkey neuropsychological testing battery following simian immunodeficiency virus infection

Infection with simian immunodeficiency virus (SIV) in macaques provides an excellent model of AIDS including HIV-induced central nervous system (CNS) pathology and cognitive/behavioral impairment. Recently a behavioral test battery has been developed for macaques based on the CANTAB human neuropsychological testing battery. As with human neuropsychological batteries, different tasks are thought to involve different neural substrates, and therefore performance profiles may assess function in particular brain regions. Ten rhesus monkeys were infected with SIV after being trained on two or more of the battery tasks addressing memory (delayed nonmatching to sample, DNMS), spatial working memory (using a self-ordered spatial search task, SOSS), motivation (progressive-ratio, PR), reaction time (RT), and/or fine motor skills (bimanual motor skill, BMS). Performance was compared to that of 9 uninfected monkeys. Overall, some aspect of performance was impaired in all 10 monkeys following infection. Consistent with results in human AIDS patients, individual performance was impaired most often on battery tasks thought to be sensitive to frontostriatal dopaminergic functioning such as SOSS, RT, and BMS. These results further demonstrate the similarity of behavioral impairment produced by SIV and HIV on homologous behavioral tests, and establish the utility of the testing battery for further investigations into the CNS mechanisms of the reported behavioral changes.

Parasite manipulation of the proximate mechanisms that mediate social behavior in vertebrates

Paul MacLean was instrumental in establishing the brain regions that mediate the expression of social behaviors in vertebrates. Pathogens can exploit these central mechanisms to alter host social behaviors, including aggressive, reproductive, and parental behaviors. Although some behavioral changes after infection are mediated by the host (e.g., sickness behaviors), other behavioral modifications are mediated by the pathogen to facilitate transmission. The goal of this review is to provide examples of parasite-mediated changes in social behavior and to illustrate that parasites affect host behavior by infecting neurons, causing central nervous system (CNS) inflammation, and altering neurotransmitter and hormonal communication. Secondarily, a comparative approach will be used to demonstrate that the effects of parasites on social behavior are retained across several classes of vertebrates possibly because parasites affect the phylogenetically primitive structures of the limbic system and related neurochemical systems.

Brain somatostatin receptors are up-regulated in somatostatin-deficient mice

The peptide somatostatin (SST) is widely synthesized in the brain and periphery and acts through a family of five receptors (SSTR1-5) to exert numerous effects. A gene product related to SST, cortistatin (CST), also interacts with SSTR1-5. Here we have investigated the regulation of SSTR1-5 and of CST in SST knockout (SSTKO) mice. The five SSTRs were quantitated individually by subtype-selective binding analysis, by immunocytochemistry, and by mRNA measurement and showed, in the brain of SSTKO mice, up-regulation of subtypes 1, 2, 4, and 5, and down-regulation of SSTR3. Peripheral tissues displayed both subtype- and tissue-specific changes in SSTR1-5 mRNA levels of expression. Lack of SST did not up-regulate normal CST expression in brain nor did it induce its expression in the periphery. SST-like immunoreactivity, however, was induced in the proximal midgut in SSTKO animals, suggesting intestinal expression of a novel SST-like gene.

Evidence for a synergistic effect of the HIV-1 envelope protein gp120 and brain-derived neurotrophic factor (BDNF) leading to enhanced expression of somatostatin neurons in aggregate cultures derived from the human fetal cortex

Changes in the expression of somatostatin (SRIF) have been observed in the brains of HIV encephalitis. Since gp120 is thought to play a major role in AIDS-associated abnormalities in the brain, we addressed the question: Does gp120 alter the functional expression of human fetal SRIF neurons in culture and if so, is this effect fetal-age dependent? Aggregate cultures, obtained from cortices of nine fetuses (14.9-20.7 weeks), were exposed for 7 days to BDNF or BDNF+gp120; BDNF induced production of SRIF during the subsequent 24-48 h was assessed. Similar effects of BDNF and gp120 were observed in the 9 brain-cultures. A 7-day exposure to BDNF alone led to a significant increase in SRIF production (p=0.014), whereas exposure to gp120 alone did not. Co-exposure to BDNF and gp120 led to an increase in BDNF-induced SRIF production which was significantly greater than that after BDNF alone (p=0.006). These effects were BDNF- and gp120-dose dependent and they were not accompanied by changes in DNA content of the aggregates nor in lactate dehydrogenase activity in the medium; indicating that gp120 did not lead to a major loss of cell integrity. These results are consistent with a synergistic effect of BDNF and gp120 leading to enhanced functional expression of the signalling pathway(s) mediating BDNF induction of SRIF production; an effect expressed by fetal brains throughout the 2nd trimester of gestation. Thus, this culture system can serve as a model to study the mechanism(s) underlying the early interactions between gp120 BDNF in the developing human brain.

Simian immunodeficiency virus: a model for neuroAIDS

In addition to its profound effects on the immune system, HIV also infects the CNS and can cause abnormalities in infected individuals ranging from mild cognitive and motor disorders to frank dementia. We have been actively investigating the molecular and cellular mechanisms underlying the CNS manifestations of lentivirus infection through the comparative evaluation of brain pathophysiology under a number of parallel interrelated strategies. Here we describe our ongoing studies with the SIV/rhesus macaque system. We have applied an interdisciplinary multistep approach, utilizing viral, immunological, pathological, behavioral, and electrophysiological techniques to assess disease and study CNS dysfunction induced by SIV. The profile of the infection and the host response, and the resulting cognitive, motor, and neurophysiological abnormalities in SIV-infected monkeys, recapitulates many aspects of the functional impairments associated with HIV-induced CNS disease in humans. Consequently, the SIV model is ideal for examining the mechanisms underlying these functional abnormalities and for testing potential therapeutic agents.

Transforming growth factor-beta1 in adult human microglia and its stimulated production by interleukin-1

Ameboid microglia express human immunodeficiency virus 1 (HIV-1) more frequently than do ramified microglia. These two microglial subtypes might also differ in the frequency with which they express transforming growth factor-beta1 (TGF-beta1), a cytokine that regulates HIV-1 expression in monocytes. Results described here show that ameboid and ramified microglia express TGF-beta1. In brain tissues from HIV-1-infected individuals as compared with seronegative controls, ameboid rather than ramified microglia more frequently expressed TGF-beta1. Ameboid microglia, isolated and cultured from postmortem adult human brain more frequently expressed TGF-beta1 in presence of interleukin-1(IL-1), a cytokine that is elevated in brains of HIV-1-infected individuals when compared with seronegative controls. The stimulation of TGF-beta1 by IL-1 was dose and time dependent, occurring with ameboid microglia isolated from either frontal cortex or globus pallidus but not midbrain pons. Ameboid microglia are similar to the RCA-1-positive cells that form clusters, called microglial nodules, in the brain of HIV-1-infected individuals. Pathologic conditions, such as disseminated microglial nodules, are associated with HIV-1 encephalitis, direct infection of the brain, and moderate to severe neurologic impairment. TGF-beta1 expression in ameboid microglia may play a role in HIV-1 neuropathogenesis.