115 research outputs found
Loss of neuronal integrity during progressive HIV-1 infection of humanized mice.
Neuronal damage induced by ongoing human immunodeficiency virus type 1 (HIV-1) infection was investigated in humanized NOD/scid-IL-2Rγ(c)(null) mice transplanted at birth with human CD34-positive hematopoietic stem cells. Mice infected at 5 months of age and followed for up to 15 weeks maintained significant plasma viral loads and showed reduced numbers of CD4(+) T-cells. Prospective serial proton magnetic resonance spectroscopy tests showed selective reductions in cortical N-acetyl aspartate in infected animals. Diffusion tensor imaging revealed structural changes in cortical gray matter. Postmortem immunofluorescence brain tissue examinations for neuronal and glial markers, captured by multispectral imaging microscopy and quantified by morphometric and fluorescence emission, showed regional reduction of neuronal soma and synaptic architectures. This was evidenced by loss of microtubule-associated protein 2, synaptophysin, and neurofilament antigens. This study is the first, to our knowledge, demonstrating lost neuronal integrity after HIV-1 infection in humanized mice. As such, the model permits studies of the relationships between ongoing viral replication and virus-associated neurodegeneration
Two-photon NADH imaging exposes boundaries of oxygen diffusion in cortical vascular supply regions
Oxygen transport imposes a possible constraint on the brain's ability to sustain variable metabolic demands, but oxygen diffusion in the cerebral cortex has not yet been observed directly. We show that concurrent two-photon fluorescence imaging of endogenous nicotinamide adenine dinucleotide (NADH) and the cortical microcirculation exposes well-defined boundaries of tissue oxygen diffusion in the mouse cortex. The NADH fluorescence increases rapidly over a narrow, very low pO2 range with a p50 of 3.4±0.6 mm Hg, thereby establishing a nearly binary reporter of significant, metabolically limiting hypoxia. The transient cortical tissue boundaries of NADH fluorescence exhibit remarkably delineated geometrical patterns, which define the limits of tissue oxygen diffusion from the cortical microcirculation and bear a striking resemblance to the ideal Krogh tissue cylinder. The visualization of microvessels and their regional contribution to oxygen delivery establishes penetrating arterioles as major oxygen sources in addition to the capillary network and confirms the existence of cortical oxygen fields with steep microregional oxygen gradients. Thus, two-photon NADH imaging can be applied to expose vascular supply regions and to localize functionally relevant microregional cortical hypoxia with micrometer spatial resolution
The mixed lineage kinase-3 inhibitor URMC-099 improves therapeutic outcomes for long-acting antiretroviral therapy.
During studies to extend the half-life of crystalline nanoformulated antiretroviral therapy (nanoART) the mixed lineage kinase-3 inhibitor URMC-099, developed as an adjunctive neuroprotective agent was shown to facilitate antiviral responses. Long-acting ritonavir-boosted atazanavir (nanoATV/r) nanoformulations co-administered with URMC-099 reduced viral load and the numbers of HIV-1 infected CD4+ T-cells in lymphoid tissues more than either drug alone in infected humanized NOD/SCID/IL2Rγc-/- mice. The drug effects were associated with sustained ART depots. Proteomics analyses demonstrated that the antiretroviral responses were linked to affected phagolysosomal storage pathways leading to sequestration of nanoATV/r in Rab-associated recycling and late endosomes; sites associated with viral maturation. URMC-099 administered with nanoATV induced a dose-dependent reduction in HIV-1p24 and reverse transcriptase activity. This drug combination offers a unique chemical marriage for cell-based viral clearance. From the Clinical Editor: Although successful in combating HIV-1 infection, the next improvement in antiretroviral therapy (nanoART) would be to devise long acting therapy, such as intra-cellular depots. In this report, the authors described the use of nanoformulated antiretroviral therapy given together with the mixed lineage kinase-3 inhibitor URMC-099, and showed that this combination not only prolonged drug half-life, but also had better efficacy. The findings are hoped to be translated into the clinical setting in the future
Allotransplanted Neurons Used to Repair Peripheral Nerve Injury Do Not Elicit Overt Immunogenicity
A major problem hindering the development of autograft alternatives for repairing peripheral nerve injuries is immunogenicity. We have previously shown successful regeneration in transected rat sciatic nerves using conduits filled with allogeneic dorsal root ganglion (DRG) cells without any immunosuppression. In this study, we re-examined the immunogenicity of our DRG neuron implanted conduits as a potential strategy to overcome transplant rejection. A biodegradable NeuraGen® tube was infused with pure DRG neurons or Schwann cells cultured from a rat strain differing from the host rats and used to repair 8 mm gaps in the sciatic nerve. We observed enhanced regeneration with allogeneic cells compared to empty conduits 16 weeks post-surgery, but morphological analyses suggest recovery comparable to the healthy nerves was not achieved. The degree of regeneration was indistinguishable between DRG and Schwann cell allografts although immunogenicity assessments revealed substantially increased presence of Interferon gamma (IFN-γ) in Schwann cell allografts compared to the DRG allografts by two weeks post-surgery. Macrophage infiltration of the regenerated nerve graft in the DRG group 16 weeks post-surgery was below the level of the empty conduit (0.56 fold change from NG; p<0.05) while the Schwann cell group revealed significantly higher counts (1.29 fold change from NG; p<0.001). Major histocompatibility complex I (MHC I) molecules were present in significantly increased levels in the DRG and Schwann cell allograft groups compared to the hollow NG conduit and the Sham healthy nerve. Our results confirmed previous studies that have reported Schwann cells as being immunogenic, likely due to MHC I expression. Nerve gap injuries are difficult to repair; our data suggest that DRG neurons are superior medium to implant inside conduit tubes due to reduced immunogenicity and represent a potential treatment strategy that could be preferable to the current gold standard of autologous nerve transplant
Neuronal Assembly Detection and Cell Membership Specification by Principal Component Analysis
In 1949, Donald Hebb postulated that assemblies of synchronously activated neurons are the elementary units of information processing in the brain. Despite being one of the most influential theories in neuroscience, Hebb's cell assembly hypothesis only started to become testable in the past two decades due to technological advances. However, while the technology for the simultaneous recording of large neuronal populations undergoes fast development, there is still a paucity of analytical methods that can properly detect and track the activity of cell assemblies. Here we describe a principal component-based method that is able to (1) identify all cell assemblies present in the neuronal population investigated, (2) determine the number of neurons involved in ensemble activity, (3) specify the precise identity of the neurons pertaining to each cell assembly, and (4) unravel the time course of the individual activity of multiple assemblies. Application of the method to multielectrode recordings of awake and behaving rats revealed that assemblies detected in the cerebral cortex and hippocampus typically contain overlapping neurons. The results indicate that the PCA method presented here is able to properly detect, track and specify neuronal assemblies, irrespective of overlapping membership
Dual coding with STDP in a spiking recurrent neural network model of the hippocampus.
The firing rate of single neurons in the mammalian hippocampus has been demonstrated to encode for a range of spatial and non-spatial stimuli. It has also been demonstrated that phase of firing, with respect to the theta oscillation that dominates the hippocampal EEG during stereotype learning behaviour, correlates with an animal's spatial location. These findings have led to the hypothesis that the hippocampus operates using a dual (rate and temporal) coding system. To investigate the phenomenon of dual coding in the hippocampus, we examine a spiking recurrent network model with theta coded neural dynamics and an STDP rule that mediates rate-coded Hebbian learning when pre- and post-synaptic firing is stochastic. We demonstrate that this plasticity rule can generate both symmetric and asymmetric connections between neurons that fire at concurrent or successive theta phase, respectively, and subsequently produce both pattern completion and sequence prediction from partial cues. This unifies previously disparate auto- and hetero-associative network models of hippocampal function and provides them with a firmer basis in modern neurobiology. Furthermore, the encoding and reactivation of activity in mutually exciting Hebbian cell assemblies demonstrated here is believed to represent a fundamental mechanism of cognitive processing in the brain
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A randomized, double-blind, placebo-controlled trial of deprenyl and thioctic acid in human immunodeficiency virus-associated cognitive impairment
Cognitive impairment is a frequent manifestation of advanced human immunodeficiency virus (HIV) infection. The response to antiretroviral medication is often partial and poorly sustained. Recent studies suggest that free radical production within the CNS and neuronal apoptosis may play important roles in the pathogenesis of HIV dementia. We conducted a randomized double-blind, placebo-controlled trial using a parallel group, 2× 2 factorial design evaluating deprenyl, a monoamine oxidase B inhibitor and putative anti-apoptotic agent, and thioctic acid, an antioxidant, in 36 patients with HIV-associated cognitive impairment. Both deprenyl and thioctic acid were well tolerated with few adverse events. Deprenyl recipients showed significant improvement on tests of verbal memory compared with patients not taking deprenyl. Thioctic acid treatment did not improve cognitive function. These results suggest that deprenyl treatment is associated with cognitive improvement in subjects with mild HIV-associated cognitive impairment, whereas thioctic acid has no benefit. A larger efficacy trial is needed to assess the long-term effect of deprenyl on cognitive performance in patients with HIV infection.
Human immunodeficiency virus type 1 (HIV-1)-associated dementia complex(HIV dementia) occurs in 15 to 20% of acquired immunodeficiency syndrome(AIDS) patients and is characterized by cognitive impairment, motor dysfunction, and behavioral changes.1-5 The cognitive impairment includes mental slowing, forgetfulness, and poor concentration. Motor symptoms include loss of fine motor control, clumsiness, unsteady gait, and tremor. Behavioral changes include apathy, lethargy, and depression.2,3,6 HIV dementia is usually a rapidly progressive disorder with a mean survival of about 6 months,2 although recently, patients with slower progression or a stable course have been identified.7 HIV-1-associated minor cognitive motor disorder, a milder syndrome, is estimated to occur in 25% of patients with symptomatic HIV infection.8
Few available antiretroviral agents have been studied for the treatment of HIV dementia. Open label studies with zidovudine (ZDV) in demented patients showed improvements in clinical functioning, neuropsychological performance, and neuroimaging studies.9 ZDV, in a placebo-controlled blinded study, also improved neuropsychological function in AIDS or AIDS-related complex patients without dementia.10 The only placebo-controlled trial of ZDV in HIV dementia demonstrated the greatest neurocognitive improvement only with very high dosages (i.e., 2,000 mg/day).11 Unfortunately, the response to ZDV treatment may be short-lived or associated with intolerable side effects and therefore often unsatisfactory. There is very limited information about the therapeutic effects of other antiretroviral medications (e.g., dideoxynucleosides)12 or protease inhibitors.
Neurotoxins from HIV-infected activated macrophages or microglia interacting with astrocytes may play a central pathogenetic role in HIV dementia.13,14 Putative neurotoxins include cytokines (tumor necrosis factor alpha [TNF-α]) and oxygen radicals.2,15 Both TNF-α and hydroxyl free radicals may stimulate apoptosis (programmed cell death), and apoptotic neurons have been demonstrated in the cerebral cortex and basal ganglia of both children and adults with HIV encephalitis.16,17
We hypothesized that these indirect mechanisms of neuronal injury could be modified by deprenyl and thioctic acid to improve or even prevent HIV-associated cognitive impairment. Deprenyl, a selective monoamine oxidase type B inhibitor, at very low dosages in in vitro and in vivo systems has a trophic effect on injured neurons.18-21 Thioctic acid is a naturally occurring enzymatic cofactor for pyruvate dehydrogenase and alpha oxoglutarate dehydrogenase and scavenges harmful hydroxyl radicals and other reactive oxygen species.22,23
We conducted a randomized, double-blind, placebo-controlled clinical trial of deprenyl and thioctic acid to assess their safety and tolerability and to assess their impact on HIV-associated cognitive impairment in HIV seropositive (HIV+) patients
Persistently active neurons in human medial frontal and medial temporal lobe support working memory
Persistent neural activity is a putative mechanism for the maintenance of working memories. Persistent activity relies on the activity of a distributed network of areas, but the differential contribution of each area remains unclear. We recorded single neurons in the human medial frontal cortex and medial temporal lobe while subjects held up to three items in memory. We found persistently active neurons in both areas. Persistent activity of hippocampal and amygdala neurons was stimulus-specific, formed stable attractors and was predictive of memory content. Medial frontal cortex persistent activity, on the other hand, was modulated by memory load and task set but was not stimulus-specific. Trial-by-trial variability in persistent activity in both areas was related to memory strength, because it predicted the speed and accuracy by which stimuli were remembered. This work reveals, in humans, direct evidence for a distributed network of persistently active neurons supporting working memory maintenance
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