Extracellular Field Recordings Research Articles

Dopamine D1 Receptors Activation Rescues Hippocampal Synaptic Plasticity and Cognitive Impairments in the MK-801 Neonatal Schizophrenia Model.

Schizophrenia is a disorder with a higher cognitive decline in early adulthood, causing impaired retention of episodic memories. However, the physiological and behavioral functions that underlie cognitive deficits with a potential mechanism to ameliorate and improve cognitive performance are unknown. In this study, we used the MK-801 neurodevelopmental schizophrenia-like model. Rats were divided into two groups: one received MK-801, and the other received saline for five consecutive days (7- 11 postnatal days, PND). We evaluated synaptic plasticity late-LTP and spatial memory consolidation in early adolescence and young adulthood using extracellular field recordings in acute hippocampal slices and the Barnes maze task. Next, we examined D1 receptor (D1R) activation as a mechanism to ameliorate cognitive impairments. Our results suggest that MK-801 neonatal treatment induces impairment in late-LTP expression and deficits in spatial memory retrieval in early adolescence that is maintained until young adulthood. Furthermore, we found that activation of dopamine D1R ameliorates the impairments and promotes a robust expression of late-LTP and an improved performance in the Barnes maze task, suggesting a novel and potential therapeutic role in treating cognitive impairments in schizophrenia.

Cannabidiol Exerts Anticonvulsant Effects Alone and in Combination with Δ9-THC through the 5-HT1A Receptor in the Neocortex of Mice.

Cannabinoids have shown potential in drug-resistant epilepsy treatment; however, we lack knowledge on which cannabinoid(s) to use, dosing, and their pharmacological targets. This study investigated (i) the anticonvulsant effect of Cannabidiol (CBD) alone and (ii) in combination with Delta-9 Tetrahydrocannabinol (Δ9-THC), as well as (iii) the serotonin (5-HT)1A receptor's role in CBD's mechanism of action. Seizure activity, induced by 4-aminopyridine, was measured by extracellular field recordings in cortex layer 2/3 of mouse brain slices. The anticonvulsant effect of 10, 30, and 100 µM CBD alone and combined with Δ9-THC was evaluated. To examine CBD's mechanism of action, slices were pre-treated with a 5-HT1A receptor antagonist before CBD's effect was evaluated. An amount of ≥30 µM CBD alone exerted significant anticonvulsant effects while 10 µM CBD did not. However, 10 µM CBD combined with low-dose Δ9-THC (20:3 ratio) displayed significantly greater anticonvulsant effects than either phytocannabinoid alone. Furthermore, blocking 5-HT1A receptors before CBD application significantly abolished CBD's effects. Thus, our results demonstrate the efficacy of low-dose CBD and Δ9-THC combined and that CBD exerts its effects, at least in part, through 5-HT1A receptors. These results could address drug-resistance while providing insight into CBD's mechanism of action, laying the groundwork for further testing of cannabinoids as anticonvulsants.

FUS and surfactant-based nanocarriers: A combined strategy for nose to brain drug delivery

Brain drug delivery is hampered by the presence of the blood brain barrier and nanocarriers, administered by intranasal route, could represent an alternative and efficient strategy to improve drug localization in the Central Nervous System (CNS). The aim of this work is to design and characterize non-ionic surfactant vesicles (NSVs) and perfluorocarbon gas non-ionic surfactant based nanobubbles (VNBs) suitable for Nose to Brain Delivery (N2B). In particular, Pluronic F127, Span 85 and cholesterol have been employed to prepare NSVs and VNBs. Both systems have been characterized in terms of (a) hydrodynamic diameter, ζ-potential and morphology (b) vesicle bilayer feature (anisotropy), (c) physical-chemical stability and (d) fluorescent model probe release capability. VNBs have been also studied in terms of gas entrapment and acoustic efficiency. In addition, in order to understand optimal ultrasound (US) parameters to obtain in vitro stable cavitation, the acoustic pressure effect on VNBs fluorescent probes release kinetics was evaluated. The obtained results suggest that NSVs and VNBs show a hydrodynamic diameter suitable for N2B delivery. Moreover, in this study, we develop a new kind of protocol to evaluate an in vitro US characterization of VNBs and our data suggest a stable and controlled probe release, encouraging the possibility to deliver VNBs in mixture with NSVs loaded neuroprotective drugs for brain delivery coupled to US obtaining stable cavitation. In this context, extracellular field recordings in specific area of hippocampus (CA1-CA3) have been carried out in order to assure that empty NSVs do not affect synaptic plasticity in the form of long-term potentiation, a molecular mechanism which underlies learning and memory.

Estradiol receptors inhibit long-term potentiation in the dorsomedial striatum.

Estradiol, a female sex hormone and the predominant form of estrogen, has diverse effects throughout the brain including in learning and memory. Estradiol modulates several types of learning that depend on the dorsomedial striatum (DMS), a subregion of the basal ganglia involved in goal-directed learning, cued action-selection, and motor skills. A cellular basis of learning is synaptic plasticity, and the presence of extranuclear estradiol receptors ERα, ERβ, and G protein-coupled estrogen receptor (GPER) throughout the DMS suggests that estradiol may influence rapid cellular actions including those involved in plasticity. To test whether estradiol affects synaptic plasticity in the DMS, corticostriatal long-term potentiation (LTP) was induced using theta-burst stimulation in ex vivo brain slices from intact male and female C57BL/6 mice. Extracellular field recordings showed that female mice in the diestrus stage of the estrous cycle exhibited LTP similar to male mice, while female mice in estrus did not exhibit LTP. Furthermore, antagonists of ERα or GPER rescued LTP in estrus females and agonists of ERα or GPER reduced LTP in diestrus females. In males, activating ERα but not GPER reduced LTP. These results uncover an inhibitory action of estradiol receptors on cellular learning in the DMS and suggest a cellular mechanism underlying the impairment in certain types of DMS-based learning observed in the presence of high estradiol. Due to the dorsal striatum's role in drug addiction, these findings may provide a mechanism underlying an estradiol-mediated progression from goal-directed to habitual drug use.Significance StatementThis study examined the role of the female reproductive cycle and female sex hormones in synaptic plasticity, a cellular process that underlies learning behavior, in a brain region involved in goal-directed learning. Synaptic plasticity was similar between male mice and female mice in the low estradiol phase of the cycle. In contrast, female mice in a high estradiol phase of the cycle did not exhibit synaptic plasticity. The effect of estradiol was mediated by two of the three estradiol receptors found in the brain. The results have implications for the role of the female reproductive cycle in the development of drug addiction, which involves a progression from goal-directed learning to habit-based learning as drug use switches from recreational to compulsive.

Kcna1a mutant zebrafish model episodic ataxia type 1 (EA1) with epilepsy and response to first-line therapy carbamazepine.

KCNA1 mutations are associated with a rare neurological movement disorder known as episodic ataxia type 1 (EA1), and epilepsy is a common comorbidity. Current medications provide only partial relief for ataxia and/or seizures, making new drugs needed. Here, we characterized zebrafish kcna1a-/- as a model of EA1 with epilepsy and compared the efficacy of the first-line therapy carbamazepine in kcna1a-/- zebrafish to Kcna1-/- rodents. CRISPR/Cas9 mutagenesis was used to introduce a mutation in the sixth transmembrane segment of the zebrafish Kcna1 protein. Behavioral and electrophysiological assays were performed on kcna1a-/- larvae to assess ataxia- and epilepsy-related phenotypes. Real-time quantitative polymerase chain reaction (qPCR) was conducted to measure mRNA levels of brain hyperexcitability markers in kcna1a-/- larvae, followed by bioenergetics profiling to evaluate metabolic function. Drug efficacies were tested using behavioral and electrophysiological assessments, as well as seizure frequency in kcna1a-/- zebrafish and Kcna1-/- mice, respectively. Zebrafish kcna1a-/- larvae showed uncoordinated movements and locomotor deficits, along with scoliosis and increased mortality. The mutants also exhibited impaired startle responses when exposed to light-dark flashes and acoustic stimulation as well as hyperexcitability as measured by extracellular field recordings and upregulated fosab transcripts. Neural vglut2a and gad1b transcript levels were disrupted in kcna1a-/- larvae, indicative of a neuronal excitatory/inhibitory imbalance, as well as a significant reduction in cellular respiration in kcna1a-/- , consistent with dysregulation of neurometabolism. Notably, carbamazepine suppressed the impaired startle response and brain hyperexcitability in kcna1a-/- zebrafish but had no effect on the seizure frequency in Kcna1-/- mice, suggesting that this EA1 zebrafish model might better translate to humans than rodents. We conclude that zebrafish kcna1a-/- show ataxia and epilepsy-related phenotypes and are responsive to carbamazepine treatment, consistent with EA1 patients. These findings suggest that kcna1-/- zebrafish are a useful model for drug screening as well as studying the underlying disease biology.

Abstract WP240: TRPM2 Channel Deletion In Neurons Reduces Injury Following Ischemic Stroke And Improves Post-stroke Cognitive Function

Background: Emerging evidence implicates post-stroke cognitive impairment as a major contributor to long-term disability. Therefore, optimal therapeutic targets reduce acute ischemic injury and enhance post-stroke brain function. Strong data demonstrates that a novel TRPM2 channel antagonist (tat-M2NX) provides neuroprotection and improves synaptic function, thereby reducing post-stroke cognitive impairment (PSCI). Hypothesis: Knockout of neuron-specific TRPM2 channel expression reduces infarct volume and enhances functional recovery following MCAO Methods: Transient MCAO (60 min) was performed on adult (8-10 week) male and female TRPM2 neuron-specific KO (TRPM2fl/fl, CaMKII Cre) and TRPM2 floxed controls (TRPM2fl/fl)Hemispheric infarct volume analyzed from MRI (T2) images 3 days post-injury by a blinded investigator. Extracellular field recordings of CA1 neurons were performed in acute hippocampal slices prepared 7 days after recovery from MCAO to analyze synaptic placticity (LTP). Results: We observed that neuronal-specific TRPM2 channel knockout reduces acute ischemic injury (infarct volume) in male animals, while having minimal effect on female mice. Consistent with the hypothesis that neuronal TRPM2 channels contribute to ischemia-induced synaptic dysfunction, recordings obtained in brain slices from neuronal TRPM2 channel KO mice (TRPM2fl/fl-CaMKII CRE) mice 7 days after recovery from 60 min MCAo exhibited intact hippocampal plasticity compared to control TRPM2fl/fl mice not expressing CRE. Male sham control mice exhibit robust LTP of 163±10.4% (n=3) compared to 115±5.6% (n=4) in TRPM2fl/fl mice after MCAO. Neuronal KO exhibited 175±9.8% (n=2). Similarly, female mice had control LTP of 170±6.8% (n=4) compared to 125±6.8% (n=3) in TRPM2fl/fl mice after MCAO. Neuronal KO exhibited 208±7.8% (n=5, p<0.05 ANOVA compared to TRPM2fl/fl MCAO). Conclusion: Our data highlight that TRPM2 channels expressed in neurons contribute to both acute injury following transient ischemic stroke and subacute/chronic functional recovery.

Calcineurin activation and scaffolding in Aß‐induced synaptic dysfunction

AbstractBackgroundCalcineurin (CaN) is a protein phosphatase that is essential for synaptic long‐term depression (LTD) through its regulation of AMPA‐type glutamate receptors (AMPAR). AMPAR regulation by CaN is critically mediated by the postsynaptic scaffold protein A‐kinase anchoring protein 150 (AKAP150), which localizes a pool of CaN to the postsynaptic membrane. Our lab has generated knockin mice carrying a mutant version of AKAP150 lacking its CaN‐binding site, the PxIxIT motif; AKAP150ΔPIX (PIX). LTD does not occur in these mice, underscoring the importance of the synaptic pool of CaN for normal synaptic function and plasticity. Pharmacological inhibition of calcineurin prevents diverse manifestations of Aβ‐mediated synaptotoxicity, including long‐term potentiation (LTP) blockade, synapse loss, and impaired learning and memory in AD mouse models. However, the importance of synaptically‐localized calcineurin in Aβ synaptotoxicity is unknown.MethodTo test our novel hypothesis that Aβ synaptotoxicity requires spatial positioning of CaN at the synapse via AKAP150 anchoring, we used our innovative AKAP150ΔPIX (PIX) knock‐in mouse model. Primary hippocampal neuronal cultures and acute hippocampal slices from WT and PIX mice were treated with various doses of Aβ oligomers and assayed for Aβ’s effect on dendritic spine density, quantal calcium transients through NMDA receptors (both in culture), and LTP through extracellular field recordings (in slices). Additionally, utilizing the 5xFAD AD mouse model, we generated PIX/5xFAD mice to test long‐term behavioral (via radial arm water maze and contextual fear conditioning tasks) and electrophysiological effects (through field recordings) of the PIX mutation on the 5xFAD phenotype in 6‐month‐old animals.ResultThe PIX mutation protects against acute Aβ‐mediated synaptic loss, decreased Ca2+ entry through NMDA receptors, and LTP deficits. Long‐term, the PIX mutation rescues contextual fear conditioning memory, but not radial arm water maze performance or chronic LTP deficits of 5xFAD mice.ConclusionSynaptically‐localized calcineurin is necessary for early Aβ‐mediated synaptic deficits. Long‐term Aβ exposure engages mechanisms beyond its AKAP‐anchored calcineurin pathway.

Environmental enrichment and social isolation modulate inhibitory transmission and plasticity in hippocampal area CA2.

Environmental factors are well-accepted to play a complex and interdependent role with genetic factors in learning and memory. The goal of this study was to examine how environmental conditions altered synaptic plasticity in hippocampal area CA2. To do this, we housed adult mice for 3 weeks in an enriched environment (EE) consisting of a larger cage with running wheel, and regularly changed toys, tunnels and treats. We then performed whole-cell or extracellular field recordings in hippocampal area CA2 and compared the synaptic plasticity from EE-housed mice with slices from littermate controls housed in standard environment (SE). We found that the inhibitory transmission recruited by CA3 input stimulation in CA2 was significantly less plastic in EE conditions as compared to SE following an electrical tetanus. We demonstrate that delta-opioid receptor (DOR) mediated plasticity is reduced in EE conditions by direct application of DOR agonist. We show that in EE conditions the overall levels of GABA transmission is reduced in CA2 cells by analyzing inhibition of ErbB4 receptor, spontaneous inhibitory currents and paired-pulse ratio. Furthermore, we report that the effect of EE of synaptic plasticity can be rapidly reversed by social isolation. These results demonstrate how the neurons in hippocampal area CA2 are sensitive to environment and may lead to promising therapeutic targets.

Lack of APLP1 leads to subtle alterations in neuronal morphology but does not affect learning and memory.

The amyloid precursor protein APP plays a crucial role in Alzheimer pathogenesis. Its physiological functions, however, are only beginning to be unraveled. APP belongs to a small gene family, including besides APP the closely related amyloid precursor-like proteins APLP1 and APLP2, that all constitute synaptic adhesion proteins. While APP and APLP2 are ubiquitously expressed, APLP1 is specific for the nervous system. Previous genetic studies, including combined knockouts of several family members, pointed towards a unique role for APLP1, as only APP/APLP1 double knockouts were viable. We now examined brain and neuronal morphology in APLP1 single knockout (KO) animals, that have to date not been studied in detail. Here, we report that APLP1-KO mice show normal spine density in hippocampal CA1 pyramidal cells and subtle alterations in dendritic complexity. Extracellular field recordings revealed normal basal synaptic transmission and no alterations in synaptic plasticity (LTP). Further, behavioral studies revealed in APLP1-KO mice a small deficit in motor function and reduced diurnal locomotor activity, while learning and memory were not affected by the loss of APLP1. In summary, our study indicates that APP family members serve both distinct and overlapping functions that need to be considered for therapeutic treatments of Alzheimer's disease.

Differences in hippocampal plasticity and memory outcomes in anterior versus posterior cerebellar stroke

Neurological symptoms following cerebellar stroke can range from motor to cognitive-affective impairments. Topographic imaging studies from patients with lesions confined to the cerebellum have shown evidence linking anterior cerebellar lobules with motor function and posterior lobules with cognitive function. Damage to the cerebellum can disrupt functional connectivity in cerebellar stroke patients, as it is highly interconnected with forebrain motor and cognitive areas. The hippocampus plays a key role in memory acquisition, a cognitive domain that is negatively impacted by posterior cerebellar stroke, and there is increasing evidence that the cerebellum can affect hippocampal function in health and disease. To study these topographical dissociations, we developed a mouse photo-thrombosis model to produce unilateral strokes in anterior (lobules III-V) or posterior (lobules VI-VIII) cerebellar cortex to examine hippocampal plasticity and behavior. Histological and MRI data demonstrate reproducible injury that is confined to the targeted lobules. We then measured hippocampal long-term potentiation (LTP) ex-vivo with extracellular field recording experiments in acute brain slices obtained from mice 7 days post-cerebellar stroke. Interestingly, we found that a unilateral posterior stroke resulted in a contralateral hippocampal impairment, matching the cerebellothalamic pathway trajectory, while LTP was intact in both hippocampi of mice with anterior strokes. We also assessed motor coordination and memory function at 7 days post-stroke using a balance beam, contextual and delay fear conditioning (CFC and DFC), and novel object recognition (NOR) tasks. Mice with anterior strokes showed lack of coordination evaluated as an increased number of missteps, while mice with posterior strokes did not. Mice with anterior or posterior cerebellar strokes demonstrated similar freezing behavior to shams in CFC and DFC, while only posterior stroke mice displayed a reduced discrimination index in the NOR task. These data suggest that a unilateral LTP impairment observed in mice with posterior strokes produces a mild memory impairment. Our results demonstrate that our model recapitulates aspects of clinical lesion-symptom mapping, with anterior cerebellar strokes producing impaired motor coordination and posterior cerebellar strokes producing an object-recognition memory impairment. Further studies are warranted to interrogate other motor and cognitive-affective behaviors and brain region specific alterations following focal cerebellar stroke. The novel model presented herein will allow for future preclinical translational studies to improve neurological deficits after cerebellar stroke.

Strong Gamma Frequency Oscillations in the Adolescent Prefrontal Cortex.

Working memory ability continues to mature into adulthood in humans and nonhuman primates. At the single-neuron level, adolescent development is characterized by increased prefrontal firing rate in the delay period, but less is known about how coordinated activity between neurons is altered. Local field potentials (LFPs) provide a window into the computations conducted by the local network. To address the effects of adolescent development on LFP activity, three male rhesus monkeys were trained to perform an oculomotor delayed response task and tested at both the adolescent and adult stages. Simultaneous single-unit and LFP signals were recorded from areas 8a and 46 of the dorsolateral prefrontal cortex. In both the cue and delay period, power relative to baseline in the gamma frequency range (32-128 Hz) was higher in the adolescent than the adult stage. The changes between developmental stages could not be accounted for by differences in performance and were observed in more posterior as well as more anterior recording sites. In the adult stage, high-firing neurons were also more likely to reside at sites with strong gamma power increase from baseline. For both stages, the gamma power increase in the delay was selective for sites with neuron-encoding stimulus information in their spiking. Our results establish gamma power decrease to be a feature of prefrontal cortical maturation.SIGNIFICANCE STATEMENT Gamma-frequency oscillations in extracellular field recordings (e.g., local field potential or EEG) are a marker of normal interactions between excitatory and inhibitory neurons in neural circuits. Abnormally low gamma power during working memory is seen in conditions such as schizophrenia. We sought to examine whether the immature prefrontal cortex similarly exhibits lower power in the gamma-frequency range during working memory, in a nonhuman primate model of adolescence. Contrary to this expectation, the adolescent PFC exhibited stronger gamma power during the maintenance of working memory. Our findings reveal an unknown developmental maturation trajectory of gamma-band oscillations, propose a refinement of information encoding during PFC maturation, and raise the possibility that schizophrenia represents an excessive state of prefrontal maturation.

Abstract TMP115: Increased Expression Of Cd38 In Activated Astrocytes Contributes To Impaired Synaptic Plasticity Following Middle Cerebral Artery Occlusion

Introduction: Emerging evidence has implicated post-stroke cognitive impairment (PSCI) as a major contributor to long-term disability following acute ischemic stroke. While the hippocampus is shown to contribute to PSCI, the exact mechanisms underlying PSCI have yet to be elucidated. Interestingly, a preclinical model of large artery stroke (middle cerebral artery occlusion; MCAO) causes hippocampal dysfunction, despite direct ischemic insult to brain regions distant from the hippocampus, suggesting the injury causes perturbations in neural circuits. Thus, we utilize electrophysiological recordings of hippocampal LTP as an indicator of network health following ischemia. We hypothesize activated astrocytes in the hippocampus following MCAO increase expression of the ectoenzyme, CD38, which signals to neurons to impair plasticity. Methods: Extracellular field recordings of CA1 neurons were performed in acute hippocampal slices prepared 30 days after recovery from MCAO in adult (8-12 week) mice. Immunohistochemistry was performed to assess hippocampal CD38 expression and astrogliosis. Acute slices were treated with CD38 inhibitors (78c & apigenin) to assess plasticity. Results: Recordings obtained in brain slices 30 days after MCAO exhibited a significant reduction in LTP; 161±9%, n=6 in sham compared to 115±4%, n=7 30 days after MCAO, in both ipsilateral and contralateral hippocampi. Immunohistochemical (IHC) staining indicates CD38 levels are increased and colocalize with activated astrocyte marker, GFAP, 30 days following MCAO. Bath application of CD38 inhibitors, 78c (vehicle n=6, 4.0±8.5% vs. 100nM 78c n=6, 78.3±15.8%; p<0.05) and apigenin (vehicle n=7, 23.9±7% vs. 10μM apigenin n=7, 65.5±2.5%; p<0.05), restored LTP in MCAO brain slices 30 days following injury. Conclusion: These data indicate that MCAO provides a reproducible model of post-stroke memory dysfunction (PSCI) and that remote astrogliosis in the uninjured hippocampus may contribute to altered neuronal function (plasticity). Our data implicates increased levels of CD38 impair plasticity following stroke. Therefore, reducing CD38 activity at chronic timepoints following ischemia may represent a novel strategy to treat the symptoms of PSCI.

Abstract WP248: Extended Therapeutic Window Of A Novel Peptide Inhibitor Of Trpm2 Channels On Memory Following Focal Cerebral Ischemia

Adult stroke is the a leading cause of mortality and morbidity, with significant sequelae including memory deficits. Despite intense research, no pharmacological interventions are currently available to improve cognitive outcome following ischemic stroke (MCAO). Studies suggest that the non-selective transient receptor potential M2 (TRPM2) channels may contribute to brain injury, specifically in males. This study used electrophysiology and neurobehavior to investigate whether TRPM2 could restore cognitive impairments 30 days after MCAO. To assess the functional role of TRPM2 channels, our novel TRPM2 channel antagonist tat-M2NX was administered intravenously 29 days following MCAO, with contextual fear conditioning performed to measure memory function in mice on day 31. Sham operated mice exhibited intact spatial memory, as indicated by high an increase in freezing behavior (65.44% ± 4.167, N=6) whereas) whereas MCAO mice treated with tat-Scr treated reduced freezing behavior (36.7%, ± 24.4 N=7). . Administration of tatM2NX resulted in improved memory function (72.26% ± 10.98 n=9) compared to tatSCR-treated mice. To assess the effect of MCAO on hippocampal long-term potentiation (LTP), a well-accepted model of learning and memory, extracellular field recordings of CA1 neurons were performed in acute hippocampal slices prepared 31 days after MCAO. Under control conditions, a physiological theta burst stimulation (40 pulses, 100Hz) resulted in LTP that increased the slope of fEPSP to 70.8%, n=5 of baseline MCAO injured mice had impaired LTP (121.1%, n=5). However, mice treated with tat-M2NX on day 30 and recorded on day 31 preserved LTP (185.4, n=5), consistent with improved memory function above. This study suggests that TRPM2 channels contribute to the functional memory impairment seen after MAO at delayed timepoints. Therefore, targeting TRPM2 channel activity may be a potential therapeutic approach to improve long-term functional outcome following MCAO.

Feasibility of cerium-doped LSO particles as a scintillator for x-ray induced optogenetics

Objective. Non-invasive light delivery into the brain is needed for in vivo optogenetics to avoid physical damage. An innovative strategy could employ x-ray activation of radioluminescent particles (RLPs) to emit localized light. However, modulation of neuronal or synaptic function by x-ray induced radioluminescence from RLPs has not yet been demonstrated. Approach. Molecular and electrophysiological approaches were used to determine if x-ray dependent radioluminescence emitted from RLPs can activate light sensitive proteins. RLPs composed of cerium doped lutetium oxyorthosilicate (LSO:Ce), an inorganic scintillator that emits blue light, were used as they are biocompatible with neuronal function and synaptic transmission. Main results. We show that 30 min of x-ray exposure at a rate of 0.042 Gy s−1 caused no change in the strength of basal glutamatergic transmission during extracellular field recordings in mouse hippocampal slices. Additionally, long-term potentiation, a robust measure of synaptic integrity, was induced after x-ray exposure and expressed at a magnitude not different from control conditions (absence of x-rays). We found that x-ray stimulation of RLPs elevated cAMP levels in HEK293T cells expressing OptoXR, a chimeric opsin receptor that combines the extracellular light-sensitive domain of rhodopsin with an intracellular second messenger signaling cascade. This demonstrates that x-ray radioluminescence from LSO:Ce particles can activate OptoXR. Next, we tested whether x-ray activation of the RLPs can enhance synaptic activity in whole-cell recordings from hippocampal neurons expressing channelrhodopsin-2, both in cell culture and acute hippocampal slices. Importantly, x-ray radioluminescence caused an increase in the frequency of spontaneous excitatory postsynaptic currents in both systems, indicating activation of channelrhodopsin-2 and excitation of neurons. Significance. Together, our results show that x-ray activation of LSO:Ce particles can heighten cellular and synaptic function. The combination of LSO:Ce inorganic scintillators and x-rays is therefore a viable method for optogenetics as an alternative to more invasive light delivery methods.

Abstract P733: Astroglial Activation Following Stroke Contributes to Impaired Synaptic Plasticity Through Increased Cd38-trpm2 Channel Signaling

Introduction: Post-stroke cognitive impairment (PSCI) is a major contributor to long-term disability following acute ischemic stroke. Learning and memory deficits are a common feature of PSCI and alterations in hippocampal function are a likely contributor. Interestingly, common experimental stroke models (middle cerebral artery occlusion; MCAO) cause hippocampal dysfunction, despite no direct ischemic insult to the hippocampus, suggesting perturbations in neural circuits. Thus, we utilize electrophysiological recordings of hippocampal plasticity in combination with neurobehavioral assessments of memory function. Hypothesis: Activated astrocytes in the hippocampus following MCAO increase expression of the surface enzyme CD38, which signals to neurons to impair plasticity. Methods: Extracellular field recordings of CA1 neurons were performed in acute hippocampal slices prepared 30 days after recovery from transient MCAO (60 min) in adult (6-8 week) mice. A behavioral fear conditioning paradigm (CFC) was used to evaluate contextual memory. Immunohistochemistry was performed to assess CD38 expression and slices were treated with CD38 inhibitors (78c) to assess plasticity. Results: Recordings obtained in brain slices 30 days after MCAO exhibited loss of hippocampal LTP; 134±6%, n=4 in sham and 107±12%, n=4 30 days after MCAO. Memory function, measured using CFC, was consistent with our LTP findings. MCAO decreased freezing behavior, indicating lack of memory (65±7% in sham mice (n=6) and 37±7% in MCAO mice, n=7). Immunohistochemical data indicates increased CD38 expression in activated astrocytes following MCAO in the hippocampus. Treatment of hippocampal slices with 78c, a potent CD38 inhibitor, after MCAO rescues LTP impairment. Finally, no additive increase in LTP when 78c is co-administered with a TRPM2 channel inhibitor was observed. Conclusion: These data indicate that MCAO is a reproducible model of post-stroke memory dysfunction (PSCI) and remote astrogliosis in the uninjured hippocampus may contribute to altered neuronal function (plasticity). Our data implicates increased levels of CD38 as an upstream activator of neuronal TRPM2 channel in the hippocampus following stroke, resulting in impaired synaptic plasticity.

Abstract P765: Therapeutic Approaches to Reduce Post-Stroke Cognitive Impairment

Introduction: Cognitive impairments and memory loss are common after stroke, with an emerging awareness of a high risk of conversion to post-stroke dementia. It is increasingly clear that in addition to neuronal injury following cerebral ischemia, impaired functional networks contribute to long-term functional deficits. Synaptic plasticity (LTP) is the leading cellular model of learning and memory. Thus, we utilize electrophysiological recordings of hippocampal LTP as an indicator of network health following ischemia in combination with neurobehavioral assessments of memory function. Hypothesis: Focal ischemic stroke increases soluble amyloid beta (Aβ) in the hippocampus, causing impaired plasticity and memory function. Methods: Extracellular field recordings of CA1 neurons were performed in acute hippocampal slices prepared 30 days after recovery from transient MCAO (45 min) in adult (6-8 week) mice. A behavioral fear conditioning paradigm (CFC) was used to evaluate memory. ELISA assay was used to quantify soluble Aβ42 from the hippocampus. Slices were treated with Aβ42 oligomers with and without our newly developed peptide inhibitor of TRPM2, termed tatM2NX. Results: Recordings from brain slices 30 days after MCAO showed near complete loss of LTP; 161±9%, n=6 in sham compared to 115±4%, n=7 30 days after MCAO in the hippocampus. MCAO decreased freezing behavior, indicating lack of memory (65±7% in sham mice (n=6) and 37±7% in MCAO mice, n=7). We observed a 48% increase in Aβ42 in the hippocampus 30 days after MCAo. We observed that addition of Aβ42 oligomers (500 nM) impaired LTP. This impaired LTP was prevented with co-application of the TRPM2 channel inhibitor tatM2NX. Consistent with a role of TRPM2 channels in post-stroke cognitive impairment, MCAO mice treated with tatM2NX (20 mg/kg iv injection 24 hr before testing) on day 29 post MCA demonstrated increasing freezing to 72±5% (n=9). Conclusion: Our data implicates increased levels of soluble Aβ42 in the hippocampus following stroke, resulting in activation of TRPM2 channels and impaired synaptic plasticity. Therefore, reducing soluble Aβ42 and/or inhibition of TRPM2 channels at chronic time points following ischemia may represent a novel strategy to improve functional recovery following stroke.

Dexpramipexole Enhances K+ Currents and Inhibits Cell Excitability in the Rat Hippocampus In Vitro.

Dexpramipexole (DEX) has been described as the first-in-class F1Fo ATP synthase activator able to boost mitochondrial bioenergetics and provide neuroprotection in experimental models of ischemic brain injury. Although DEX failed in a phase III trial in patients with amyotrophic lateral sclerosis, it showed favorable safety and tolerability profiles. Recently, DEX emerged as a Nav1.8 Na+ channel and transient outward K+ (IA) conductance blocker, revealing therefore an unexpected, pleiotypic pharmacodynamic profile. In this study, we performed electrophysiological experiments in vitro aimed to better characterize the impact of DEX on voltage-dependent currents and synaptic transmission in the hippocampus. By means of patch-clamp recordings on isolated hippocampal neurons, we found that DEX increases outward K+ currents evoked by a voltage ramp protocol. This effect is prevented by the non-selective voltage-dependent K+ channel (Kv) blocker TEA and by the selective small-conductance Ca2+-activated K+ (SK) channel blocker apamin. In keeping with this, extracellular field recordings from rat hippocampal slices also demonstrated that the compound inhibits synaptic transmission and CA1 neuron excitability. Overall, these data further our understanding on the pharmacodynamics of DEX and disclose an additional mechanism that could underlie its neuroprotective properties. Also, they identify DEX as a lead to develop new modulators of K+ conductances.

Abstract TP111: TRPM2 is a Therapeutic Target for Reversal of Stroke-Induced Dementia-Like Symptoms

Introduction: Cognitive impairments and memory loss are common after stroke, with an emerging awareness of a high risk of conversion to post-stroke dementia. It is increasingly clear that in addition to neuronal injury following cerebral ischemia, impaired functional networks contribute to long-term functional deficits. Synaptic plasticity (long term potentiation; LTP) is the leading cellular model of learning and memory. Thus, we utilize electrophysiological recordings of hippocampal LTP as an indicator of network health following ischemia in combination with neurobehavioral assessments of memory function. TRPM2 channels are oxidative stress sensitive ion channels that have been implicated in ischemic injury. Hypothesis: Inhibition of TRPM2 channels reverse stroke-induced cognitive deficits. Methods: Extracellular field recordings of CA1 neurons were performed in acute hippocampal slices prepared 30 days after recovery from transient MCAO (45 min) in adult (6-8 week) mice. A behavioral fear conditioning paradigm was used to evaluate contextual memory 30 days after MCAO. Slices or mice were treated with our newly developed peptide inhibitor of TRPM2, termed tatM2NX. Results: Recordings obtained in brain slices 30 days after MCAO exhibited near complete loss of LTP; 161±9%, n=6 in sham compared to 115±4%, n=7 30 days after MCAO in the ipsilateral hippocampus. Similar deficit in LTP observed in the contralateral hippocampus. Remarkably, iv injection of 20 mg/kg tatM2NX on day 29 after MCAO reversed MCAO-induced loss of LTP when recorded on day 30, recovering to 175±9% (n=3). Memory function, measured using contextual fear conditioning, was consistent with our LTP findings. MCAO decreased freezing behavior, indicating lack of memory (62±5% in sham mice (n=5) and 24±3% in MCAO mice, n=4). This was reversed in MCAO mice given tatM2NX (20 mg/kg iv injection 24 hr before testing) on day 29 post MCAO, increasing freezing to 73±12% (n=3). Conclusion: These data indicate that our new TRPM2 channel inhibitor, tatM2NX, restores synaptic plasticity and memory function after experimental stroke. Therefore, inhibition of TRPM2 channels at chronic timepoints following ischemia may represent a novel strategy to improve functional recovery following stroke.

Syntaxin-3 is dispensable for basal neurotransmission and synaptic plasticity in postsynaptic hippocampal CA1 neurons

Recent evidence suggests that SNARE fusion machinery play critical roles in postsynaptic neurotransmitter receptor trafficking, which is essential for synaptic plasticity. However, the key SNAREs involved remain highly controversial; syntaxin-3 and syntaxin-4 are leading candidates for the syntaxin isoform underlying postsynaptic plasticity. In a previous study, we showed that pyramidal-neuron specific conditional knockout (cKO) of syntaxin-4 significantly reduces basal transmission, synaptic plasticity and impairs postsynaptic receptor trafficking. However, this does not exclude a role for syntaxin-3 in such processes. Here, we generated and analyzed syntaxin-3 cKO mice. Extracellular field recordings in hippocampal slices showed that syntaxin-3 cKO did not exhibit significant changes in CA1 basal neurotransmission or in paired-pulse ratios. Importantly, there were no observed differences during LTP in comparison to control mice. Syntaxin-3 cKO mice performed similarly as the controls in spatial and contextual learning tasks. Consistent with the minimal effects of syntaxin-3 cKO, syntaxin-3 mRNA level was very low in hippocampal and cortex pyramidal neurons, but strongly expressed in the corpus callosum and caudate axon fibers. Together, our data suggest that syntaxin-3 is dispensable for hippocampal basal neurotransmission and synaptic plasticity, and further supports the notion that syntaxin-4 is the major isoform mediating these processes.

Investigating Long-term Synaptic Plasticity in Interlamellar Hippocampus CA1 by Electrophysiological Field Recording.

The study of synaptic plasticity in the hippocampus has focused on the use of the CA3-CA1 lamellar network. Less attention has been given to the longitudinal interlamellar CA1-CA1 network. Recently however, an associational connection between CA1-CA1 pyramidal neurons has been shown. Therefore, there is the need to investigate whether the longitudinal interlamellar CA1-CA1 network of the hippocampus supports synaptic plasticity. We designed a protocol to investigate the presence or absence of long-term synaptic plasticity in the interlamellar hippocampal CA1 network using electrophysiological field recordings both in vivo and in vitro. For in vivo extracellular field recordings, the recording and stimulation electrodes were placed in a septal-temporal axis of the dorsal hippocampus at a longitudinal angle, to evoke field excitatory postsynaptic potentials. For in vitro extracellular field recordings, hippocampal longitudinal slices were cut parallel to the septal-temporal plane. Recording and stimulation electrodes were placed in the stratum oriens (S.O) and the stratum radiatum (S.R) of the hippocampus along the longitudinal axis. This enabled us to investigate the directional and layer specificity of evoked excitatory postsynaptic potentials. Already established protocols were used to induce long-term potentiation (LTP) and long-term depression (LTD) both in vivo and in vitro. Our results demonstrated that the longitudinal interlamellar CA1 network supports N-methyl-D-aspartate (NMDA) receptor-dependent long-term potentiation (LTP) with no directional or layer specificity. The interlamellar network, however, in contrast to the transverse lamellar network, did not present with any significant long-term depression (LTD).