The risk of seizures is 10-fold higher in patients with Alzheimer's disease than the general population, yet the mechanisms underlying this susceptibility and the effects of these seizures are poorly ...understood. To elucidate the proposed bidirectional relationship between Alzheimer's disease and seizures, we studied human brain samples (n = 34) from patients with Alzheimer's disease and found that those with a history of seizures (n = 14) had increased amyloid-β and tau pathology, with upregulation of the mechanistic target of rapamycin (mTOR) pathway, compared with patients without a known history of seizures (n = 20). To establish whether seizures accelerate the progression of Alzheimer's disease, we induced chronic hyperexcitability in the five times familial Alzheimer's disease mouse model by kindling with the chemoconvulsant pentylenetetrazol and observed that the mouse model exhibited more severe seizures than the wild-type. Furthermore, kindled seizures exacerbated later cognitive impairment, Alzheimer's disease neuropathology and mTOR complex 1 activation. Finally, we demonstrated that the administration of the mTOR inhibitor rapamycin following kindled seizures rescued enhanced remote and long-term memory deficits associated with earlier kindling and prevented seizure-induced increases in Alzheimer's disease neuropathology. These data demonstrated an important link between chronic hyperexcitability and progressive Alzheimer's disease pathology and suggest a mechanism whereby rapamycin may serve as an adjunct therapy to attenuate progression of the disease.
Approximately half of people infected with HIV (PWH) exhibit HIV-associated neuropathology (neuroHIV), even when receiving combined antiretroviral therapy. Opiate use is widespread in PWH and ...exacerbates neuroHIV. While neurons themselves are not infected, they incur sublethal damage and GABAergic disruption is selectively vulnerable to viral and inflammatory factors released by infected/affected glia. Here, we demonstrate diminished K+-Cl− cotransporter 2 (KCC2) levels in primary human neurons after exposure to HIV-1 or HIV-1 proteins ± morphine. Resulting disruption of GABAAR-mediated hyperpolarization/inhibition was shown using genetically-encoded voltage (Archon1) and calcium (GCaMP6f) indicators. The HIV proteins Tat (acting through NMDA receptors) and R5-gp120 (acting via CCR5) but not X4-tropic gp120 (acting via CXCR4), and morphine (acting through μ-opioid receptors) all induced KCC2 loss. We demonstrate that modifying KCC2 levels or function, or antagonizing NMDAR, CCR5 or MOR rescues KCC2 and GABAAR-mediated hyperpolarization/inhibition in HIV, Tat, or gp120 ± morphine-exposed neurons. Using an inducible, Tat-transgenic mouse neuroHIV model, we found that chronic exposure to Tat also reduces KCC2. Our results identify KCC2 as a novel therapeutic target for ameliorating the pathobiology of neuroHIV, including PWH exposed to opiates.
•HIV-1 proteins, infective HIV, and morphine reduce KCC2 levels in primary human neurons.•Viral factors reduced KCC2 via NMDAR and CCR5; morphine acted via μ-opioid receptors.•The loss of KCC2 dysregulated GABAAR-mediated hyperpolarization and inhibition.•KCC2 and neuronal dysfunction were rescued by manipulating KCC2 or upstream pathways.•HIV-Tat expression in vivo diminished KCC2 levels in the striatum.
Early-life seizures (ELSs) can cause permanent cognitive deficits and network hyperexcitability, but it is unclear whether ELSs induce persistent changes in specific neuronal populations and whether ...these changes can be targeted to mitigate network dysfunction. We used the targeted recombination of activated populations (TRAP) approach to genetically label neurons activated by kainate-induced ELSs in immature mice. The ELS-TRAPed neurons were mainly found in hippocampal CA1, remained uniquely susceptible to reactivation by later-life seizures, and displayed sustained enhancement in α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor-mediated (AMPAR-mediated) excitatory synaptic transmission and inward rectification. ELS-TRAPed neurons, but not non-TRAPed surrounding neurons, exhibited enduring decreases in Gria2 mRNA, responsible for encoding the GluA2 subunit of the AMPARs. This was paralleled by decreased synaptic GluA2 protein expression and heightened phosphorylated GluA2 at Ser880 in dendrites, indicative of GluA2 internalization. Consistent with increased GluA2-lacking AMPARs, ELS-TRAPed neurons showed premature silent synapse depletion, impaired long-term potentiation, and impaired long-term depression. In vivo postseizure treatment with IEM-1460, an inhibitor of GluA2-lacking AMPARs, markedly mitigated ELS-induced changes in TRAPed neurons. These findings show that enduring modifications of AMPARs occur in a subpopulation of ELS-activated neurons, contributing to synaptic dysplasticity and network hyperexcitability, but are reversible with early IEM-1460 intervention.
Approximately 22% of Alzheimer's disease (AD) patients suffer from seizures, and the co-occurrence of seizures and epileptiform activity exacerbates AD pathology and related cognitive deficits, ...suggesting that seizures may be a targetable component of AD progression. Given that alterations in neuronal excitatory:inhibitory (E:I) balance occur in epilepsy, we hypothesized that decreased markers of inhibition relative to those of excitation would be present in AD patients. We similarly hypothesized that in 5XFAD mice, the E:I imbalance would progress from an early stage (prodromal) to later symptomatic stages and be further exacerbated by pentylenetetrazol (PTZ) kindling. Post-mortem AD temporal cortical tissues from patients with or without seizure history were examined for changes in several markers of E:I balance, including levels of the inhibitory GABAA receptor, the sodium potassium chloride cotransporter 1 (NKCC1) and potassium chloride cotransporter 2 (KCC2) and the excitatory NMDA and AMPA type glutamate receptors. We performed patch-clamp electrophysiological recordings from CA1 neurons in hippocampal slices and examined the same markers of E:I balance in prodromal 5XFAD mice. We next examined 5XFAD mice at chronic stages, after PTZ or control protocols, and in response to chronic mTORC1 inhibitor rapamycin, administered following kindled seizures, for markers of E:I balance. We found that AD patients with comorbid seizures had worsened cognitive and functional scores and decreased GABAA receptor subunit expression, as well as increased NKCC1/KCC2 ratios, indicative of depolarizing GABA responses. Patch clamp recordings of prodromal 5XFAD CA1 neurons showed increased intrinsic excitability, along with decreased GABAergic inhibitory transmission and altered glutamatergic neurotransmission, indicating that E:I imbalance may occur in early disease stages. Furthermore, seizure induction in prodromal 5XFAD mice led to later dysregulation of NKCC1/KCC2 and a reduction in GluA2 AMPA glutamate receptor subunit expression, indicative of depolarizing GABA receptors and calcium permeable AMPA receptors. Finally, we found that chronic treatment with the mTORC1 inhibitor, rapamycin, at doses we have previously shown to attenuate seizure-induced amyloid-β pathology and cognitive deficits, could also reverse elevations of the NKCC1/KCC2 ratio in these mice. Our data demonstrate novel mechanisms of interaction between AD and epilepsy and indicate that targeting E:I balance, potentially with US Food and Drug Administration-approved mTOR inhibitors, hold therapeutic promise for AD patients with a seizure history.
Despite marked regional differences in HIV susceptibility within the CNS, there has been surprisingly little exploration into the differential vulnerability among neuron types and the circuits they ...underlie. The dorsal striatum is especially susceptible, harboring high viral loads and displaying marked neuropathology, with motor impairment a frequent manifestation of chronic infection. However, little is known about the response of individual striatal neuron types to HIV or how this disrupts function. Therefore, we investigated the morphological and electrophysiological effects of HIV-1
-activator of transcription (Tat) in dopamine subtype 1 (D1) and dopamine subtype 2 (D2) receptor-expressing striatal medium spiny neurons (MSNs) by breeding transgenic Tat-expressing mice to
-tdTomato- or
-eGFP-reporter mice. An additional goal was to examine neuronal vulnerability early during the degenerative process to gain insight into key events underlying the neuropathogenesis. In D2 MSNs, exposure to HIV-1 Tat reduced dendritic spine density significantly, increased dendritic damage (characterized by swellings/varicosities), and dysregulated neuronal excitability (decreased firing at 200-300 pA and increased firing rates at 450 pA), whereas insignificant morphologic and electrophysiological consequences were observed in Tat-exposed D1 MSNs. These changes were concomitant with an increased anxiety-like behavioral profile (lower latencies to enter a dark chamber in a light-dark transition task, a greater frequency of light-dark transitions, and reduced rearing time in an open field), whereas locomotor behavior was unaffected by 2 weeks of Tat induction. Our findings suggest that D2 MSNs and a specific subset of neural circuits within the dorsal striatum are preferentially vulnerable to HIV-1.
Despite combination antiretroviral therapy (cART), neurocognitive disorders afflict 30-50% of HIV-infected individuals and synaptodendritic injury remains evident in specific brain regions such as the dorsal striatum. A possible explanation for the sustained neuronal injury is that the neurotoxic HIV-1 regulatory protein
-activator of transcription (Tat) continues to be expressed in virally suppressed patients on cART. Using inducible Tat-expressing transgenic mice, we found that dopamine subtype 2 (D2) receptor-expressing medium spiny neurons (MSNs) are selectively vulnerable to Tat exposure compared with D1 receptor-expressing MSNs. This includes Tat-induced reductions in D2 MSN dendritic spine density, increased dendritic damage, and disruptions in neuronal excitability, which coincide with elevated anxiety-like behavior. These data suggest that D2 MSNs and specific circuits within the basal ganglia are preferentially vulnerable to HIV-1.
To improve understanding of uni- versus multidirectional movement, seasonal dynamics, and the role of body size in tropical and sub-tropical nursery habitat, we conducted a 4 yr study on 1917 tagged ...juvenile common snook Centropomus undecimalis in 4 mangrove creeks. We detected 86% of individuals marked with autonomous passive integrated transponder (PIT) tag antennae. Marked fish were divided into 2 size classes (SC) for analysis: SC1 (approximately age-0) and SC2 (approximately age-1). A higher percentage of SC2 than SC1 snook migrated, SC2 made longer movements, and the 10 d probability of migration was 2.4-fold higher in SC2 than SC1. For both size classes, migration probabilities varied seasonally, with lowest rates in the coldest months. Furthermore, migration events during fall and winter tended to be temporary movements, while migration in spring and summer was more often permanent. Increased catch proportion of late-stage SC1 and early-stage SC2 individuals outside the creeks in spring/summer temporally aligns with increased permanent migration, suggesting a large-scale seasonal movement away from the study creeks. During this potential seasonal transition to alternative habitats, increased mortality at the end of the first year, as implied by proportionally fewer SC1 than SC2 individuals returning to the creeks in the following year, may act as an early population bottleneck. Alternatively, some individuals may lack fidelity and instead move to habitat not studied here. This work suggests that movement from nursery habitat can be bidirectional, size dependent, and seasonally dependent, and that the studied habitat functions as part of a habitat mosaic.
People infected with HIV (PWH) are highly susceptible to striatal and hippocampal damage. Motor and memory impairments are common among these patients, likely as behavioral manifestations of damage ...to these brain regions. GABAergic dysfunction from HIV infection and viral proteins such as transactivator of transcription (Tat) have been well documented. We recently demonstrated that the neuron specific Cl− extruder, K+ Cl− cotransporter 2 (KCC2), is diminished after exposure to HIV proteins, including Tat, resulting in disrupted GABAAR-mediated hyperpolarization and inhibition. Here, we utilized doxycycline (DOX)-inducible, GFAP-driven HIV-1 Tat transgenic mice to further explore this phenomenon. After two weeks of Tat expression, we found no changes in hippocampal KCC2 levels, but a significant decrease in the striatum that was associated with hyperlocomotion in the open field assay. We were able to restore KCC2 activity and baseline locomotion with the KCC2 enhancer, CLP290. Additionally, we found that CLP290, whose mechanism of action has yet to be described, acts to restore phosphorylation of serine 940 resulting in increased KCC2 membrane localization. We also examined neuronal subpopulation contributions to the noted effects and found significant differences. Dopamine D2 receptor-expressing medium spiny neurons (MSNs) were selectively vulnerable to Tat-induced KCC2 loss, with no changes observed in dopamine D1 receptor-expressing MSNs. These results suggest that disinhibition/diminished hyperpolarization of dopamine D2 receptor-expressing MSNs can manifest as increased locomotion in this context. They further suggest that KCC2 activity might be a therapeutic target to alleviate motor disturbances related to HIV.
To better understand habitat use through ontogeny, this paper synthesizes 7 yr of biologging research on the adult and juvenile life stages of an estuarine-dependent fish, the common snookCentropomus ...undecimalisin Charlotte Harbor, Florida, USA. During 3 yr of telemetry research in a putative nursery habitat (mangrove creeks), we resighted 85.4% of 1924 juvenile snook marked after, and 13.5% of 2191 juveniles marked prior to, deployment of a telemetry array. During 4 yr of research in spawning habitat (barrier island beaches), we used seine nets and recaptured 5.63% of 3304 marked adult snook. After analyzing these concurrent data sets, we found significant intra- and interannual site fidelity patterns in both life stages, while documenting movement between juvenile and adult spawning habitats. Additionally, this tag-based approach allowed an investigation of the relative effects of a severe cold event, which reduced apparent survival by 22.6 to 38.3% for juveniles and 97.8 to 98.5% for adults. This work presents data within and between life stages that are critical to understanding processes affecting ontogenetic habitat use and connectivity and underscores the importance of incorporating withinstage fidelity and emigration in studies on ontogeny.
We studied how emigration and seasonal dynamics affect apparent survival estimates in a nursery habitat, thereby altering habitat valuation. During a 3 yr study, we marked 1917 juvenile common snook ...Centropomus undecimalis and resighted 85.7% with a telemetry array in 4 mangrove creeks. We grouped individuals by size class, marking year, and creek, and estimated survival (ϕ) using the Barker joint-data model. Using telemetry data, we estimated seasonal emigration probabilities and simulated the effect of emigration on ϕ estimates. We found a minimal effect of emigration on ϕ estimates, the magnitude of which may be explained by emigration underestimates due to telemetry coverage or high resighting rates reducing bias. We found seasonal and size-based variation in ϕ estimates. Our approach allowed survival estimation during a severe thermal-disturbance event that reduced survival in 2 creeks and may have had its impact mitigated in a third creek by an anthropogenic habitat alteration serving as a thermal refuge. Significant fine-scale spatial segregation of size classes likely acted to reduce intercohort cannibalism, thereby maintaining the high survival rates. We recommend caution when estimating apparent survival, since the lack of estimated survival bias was likely due to our extensive telemetry data, which buffered against the effects of emigration. We conclude that temporal variability in juvenile habitat use and survival requires seasonal classification of nursery habitat value, the consideration of multi-habitat nursery mosaics, and an exploration of the role of predation on habitat use.
About half the people infected with human immunodeficiency virus (HIV) have neurocognitive deficits that often include memory impairment and hippocampal deficits, which can be exacerbated by opioid ...abuse. To explore the effects of opioids and HIV on hippocampal CA1 pyramidal neuron structure and function, we induced HIV-1 transactivator of transcription (Tat) expression in transgenic mice for 14 d and co-administered time-release morphine or vehicle subcutaneous implants during the final 5 d (days 9-14) to establish steady-state morphine levels. Morphine was withheld from some
slices during recordings to begin to assess the initial pharmacokinetic consequences of opioid withdrawal. Tat expression reduced hippocampal CA1 pyramidal neuronal excitability at lower stimulating currents. Pyramidal cell firing rates were unaffected by continuous morphine exposure. Behaviorally, exposure to Tat or high dosages of morphine impaired spatial memory Exposure to Tat and steady-state levels of morphine appeared to have largely independent effects on pyramidal neuron structure and function, a response that is distinct from other vulnerable brain regions such as the striatum. By contrast, acutely withholding morphine (from morphine-tolerant
slices) revealed unique and selective neuroadaptive shifts in CA1 pyramidal neuronal excitability and dendritic plasticity, including some interactions with Tat. Collectively, the results show that opioid-HIV interactions in hippocampal area CA1 are more nuanced than previously assumed, and appear to vary depending on the outcome assessed and on the pharmacokinetics of morphine exposure.
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