Extracellular Neuronal Recordings Research Articles

Amitriptyline and duloxetine attenuate activities of superficial dorsal horn neurons in a rat reserpine-induced fibromyalgia model

Fibromyalgia (FM) is an intractable disease with a chief complaint of chronic widespread pain. Amitriptyline (AMI) and duloxetine (DLX), which are antidepressant drugs, have been reported to ameliorate pain in patients with FM and pain-related behaviors in several rodent models of FM. However, the mechanisms of action of AMI and DLX are not yet fully understood. Here, we examined the effects of these drugs on the responsiveness of superficial dorsal horn (SDH) neurons in the spinal cord, using a rat FM model developed by injecting a biogenic amine depleter (reserpine). Extracellular recordings of SDH neurons in vivo demonstrated that bath application of AMI and DLX at concentrations of 0.1–1.0 mM on the dorsal surface of the spinal cord markedly suppressed spontaneous discharge and von Frey filament-evoked mechanical firing in SDH neurons. The suppression induced by the drugs was noted in a concentration-dependent manner and the suppressive effects resolved after washing the spinal cord surface. These results show that SDH neurons are the site of action for AMI and DLX in a rat reserpine-induced FM model. Spinal mechanisms may underlie the therapeutic effects of these drugs in patients with FM.

From Finite Element Simulations to Equivalent Circuit Models of Extracellular Neuronal Recording Systems Based on Planar and Mushroom Electrodes.

define a new methodology to build multi-compartment lumped-elements equivalent circuit models for neuron/electrode systems. the equivalent circuit topology is derived by careful scrutiny of accurate and validated multiphysics finite-elements method (FEM) simulations that couple ion transport in the intra- and extracellular fluids, activation of the neuron membrane ion channels, and signal acquisition by the electronic readout. robust and accurate circuit models are systematically derived, suited to represent the dynamics of the sensed extracellular signals over a wide range of geometrical/physical parameters (neuron and electrode sizes, electrolytic cleft thicknesses, readout input impedance, non-uniform ion channel distributions). FEM simulations point out phenomena that escape an accurate description by equivalent circuits; notably: steric effects in the thin electrolytic cleft and the impact of extracellular ion transport on the reversal potentials of the Hodgkin-Huxley neuron model. our multi-compartment equivalent circuits match accurately the FEM simulations. They unveil the existence of an optimum number of compartments for accurate circuit simulation. FEM simulations suggest that while steric effects are in most instances negligible, the extracellular ion transport affects the reversal potentials and consequently the recorded signal if the electrolytic cleft becomes thinner than approximately 100 nm. the proposed methodology and circuit models improve upon the existing area and point contact models. The coupling between the extracellular concentrations and reversal potential highlighted by FEM simulations emerges as a challenge for future developments in lumped-element modeling of the neuron/sensor interface.

Quantitative and qualitative sex difference in habenula-induced inhibition of midbrain dopamine neurons in the rat.

Clinically relevant sex differences have been noted in a number of affective, behavioral, cognitive, and neurological health disorders. Midbrain dopamine neurons are implicated in several of these same disorders and consequently are under investigation for their potential role in the manifestation of these sex differences. The lateral habenula exerts significant inhibitory control over dopamine neuronal firing, yet little is known about sex differences in this particular neurocircuit. We performed in vivo, single unit, extracellular recordings of dopamine neurons in female and male anesthetized rats in response to single pulse stimulation of the lateral habenula. In addition, we assessed baseline firing properties of lateral habenula neurons and, by immunochemical means, assessed the distribution of estrogen receptor alpha cells in the lateral habenula. Habenula-induced inhibition of dopamine neuronal firing is reduced in female rats relative to male rats. In addition, male rats had a higher prevalence of rebound excitation. Furthermore, the firing pattern of lateral habenula neurons was less variable in female rats, and female rats had a higher density of estrogen receptor alpha positive cells in the lateral habenula. We found that the dopamine neuronal response to habenular stimulation is both qualitatively and quantitatively different in female and male rats. These novel findings together with reports in the contemporary literature lead us to posit that the sex difference in dopamine inhibition seen here relate to differential firing properties of lateral habenula neurons resulting from the presence of sex hormones. Further work is needed to test this hypothesis, which may have implications for understanding the etiology of several mental health disorders including depression, schizophrenia, and addiction.

Advanced Biomimetic Nanostructured Microelectrode Arrays for Enhanced Extracellular Recordings of Enteric Neurons

AbstractMicroelectrode surfaces covered with nanostructures derived from components of extracellular matrix, such as collagen fibers, have shown immense beneficial effects in promoting neuronal growth and cellular signaling. Synthetic nanostructures mimicking the features of biological nanostructures with durable conductive materials could promote the cell adhesion on microelectrode surfaces by providing topographical cues and simultaneously improve the charge transfer properties by reducing its global impedance. Therefore, an advanced nanostructuring method mimicking the structural and organizational features of natural collagen fibers onto metallic microelectrode surfaces has been presented here, which is adapted from previous technological achievements of the group and is based on nanoimprint lithography and gold electroplating. Surface characterization methods reveal an increase in surface area between 20% and 68% on the microelectrodes fabricated with two different nanostructure heights. Impedance spectroscopy measurements reveal reduction in impedance magnitude (at 1 kHz) between 22% and 41%, depending upon the nanostructure height and density on the microelectrode, which should subsequently modulate its charge transfer properties for biosensing application. Cell adhesion analysis performed with seal impedance measurements reveals a tighter coupling of enteric neurons on the nanostructured microelectrodes. Finally, extracellular recordings from enteric neurons exhibit a significant improvement in spike detection properties of the nanostructured microelectrodes.

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.

Motor cortico-nigral and cortico-entopeduncular information transmission and its modulation by buspirone in control and after dopaminergic denervation.

Cortical information is transferred to the substantia nigra pars reticulata (SNr) and the entopeduncular nucleus (EP), the output structures of the basal ganglia (BG), through three different pathways: the hyperdirect trans-subthalamic and the direct and indirect trans-striatal pathways. The nigrostriatal dopamine (DA) and the activation of 5-HT1A receptors, distributed all along the BG, may modulate cortical information transmission. We aimed to investigate the effect of buspirone (5-HT1A receptor partial agonist) and WAY-100635 (5-HT1A receptor antagonist) on cortico-nigral and cortico-entopeduncular transmission in normal and DA loss conditions. Herein, simultaneous electrical stimulation of the motor cortex and single-unit extracellular recordings of SNr or EP neurons were conducted in urethane-anesthetized sham and 6-hydroxydopamine (6-OHDA)-lesioned rats before and after drug administrations. Motor cortex stimulation evoked monophasic, biphasic, or triphasic responses, combination of an early excitation, an inhibition, and a late excitation in both the SNr and EP, while an altered pattern of evoked response was observed in the SNr after 6-OHDA lesion. Systemic buspirone potentiated the direct cortico-SNr and cortico-EP transmission in sham animals since increased duration of the inhibitory response was observed. In DA denervated animals, buspirone administration enhanced early excitation amplitude in the cortico-SNr transmission. In both cases, the observed effects were mediated via a 5-HT1A-dependent mechanism as WAY-100635 administration blocked buspirone’s effect. These findings suggest that in control condition, buspirone potentiates direct pathway transmission and DA loss modulates responses related to the hyperdirect pathway. Overall, the results may contribute to understanding the role of 5-HT1A receptors and DA in motor cortico-BG circuitry functionality.

Dopamine D2-Subtype Receptors Outside the Blood-Brain Barrier Mediate Enhancement of Mesolimbic Dopamine Release and Conditioned Place Preference by Intravenous Dopamine.

Dopamine (DA) is a cell-signaling molecule that does not readily cross the blood-brain barrier. Despite this, peripherally administered DA enhances DA levels in the nucleus accumbens and alters DA-related behaviors. This study was designed to investigate whether DA subtype-2 receptors are involved in the enhancement of nucleus accumbens (NAc) DA levels elicited by intravenous DA administration. This was accomplished by using microdialysis in the NAc and extracellular single unit recordings of putative DA neurons in the ventral tegmental area (VTA). Additionally, the reinforcing properties of intravenous DA were investigated using a place conditioning paradigm and the effects of intravenous DA on ultrasonic vocalizations were assessed. Following administration of intravenous dopamine, the firing rate of putative DA neurons in the VTA displayed a biphasic response and DA levels in the nucleus accumbens were enhanced. Pretreatment with domperidone, a peripheral-only DA D2 receptor (D2R) antagonist, reduced intravenous DA mediated increases in VTA DA neuron activity and NAc DA levels. Pretreatment with phentolamine, a peripheral α-adrenergic receptor antagonist, did not alter the effects of IV DA on mesolimbic DA neurotransmission. These results provide evidence for peripheral D2R mediation of the effects of intravenous DA on mesolimbic DA signaling.

Characterization of electrically conductive, printable ink based on alginate hydrogel and graphene nanoplatelets

In recent years, there has been an increasing interest in electrically conductive hydrogels for a wide range of biomedical applications, like tissue engineering or biosensors. In this study, we present a cost-effective conductive hydrogel based on alginate and graphene nanoplatelets for extrusion-based bioprinters. The hydrogel is prepared under ambient conditions avoiding high temperatures detrimental for cell culture environments. Investigation of the hydrogel revealed a conductivity of up to 7.5 S/cm, depending on the ratio of platelets. Furthermore, in vitro tests with human embyronic kidney cells - as an example cell type - showed good adhesion of the cells to the surface of the conductive hydrogel. Electrochemical measurements revealed a low electrode impedance which is desirable for the extracellular recording, but also low electrode capacitance, which is unfavorable for electrical stimulation purposes. Therefore, future experiments with the graphene nanoplatelets-based hydrogels will focus on electrodes for biosensors and extracellular recordings of neurons or cardiac myocytes.

Kv1.1 channels inhibition in the rat motor cortex recapitulates seizures associated with anti-LGI1 encephalitis.

Autoimmune encephalitis associated with antibodies directed against the leucine-rich glioma inactivated 1 (LGI1) protein is responsible for specific tonic-dystonic motor seizures. Although dysfunctions in neuronal excitability have been associated with anti-LGI1 autoantibodies, their relation to seizures remain inconclusive. We developed a new in vivo experimental rat model to determine whether inhibition of Kv1.1 channels by dentrotoxin-K (DTX) in the primary motor cortex (M1) could recapitulate the human seizures and to elucidate their subtending cortical mechanisms. Comparing electro-clinical features of DTX-induced seizures in rats with those recorded from a cohort of anti-LGI1 encephalitis patients revealed striking similarities in their electroencephalographic (EEG) signature, frequency of recurrence and semiology. By combining multi-site extracellular and intracellular recordings of M1 pyramidal neurons in DTX rats, we demonstrated that the blockade of Kv1.1 channels induced a sequence of changes in neuronal excitability and synaptic activity, leading to massive suprathreshold membrane depolarizations underlying the paroxysmal EEG activity. Our results suggest the central role of Kv1.1 channels disruption in the emergence of anti-LGI1-associated seizures and suggest that this new rodent model could serve future investigations on ictogenesis in autoimmune encephalitis.

Two Types of Auditory Spatial Receptive Fields in Different Parts of the Chicken's Midbrain.

The optic tectum (OT) is an avian midbrain structure involved in the integration of visual and auditory stimuli. Studies in the barn owl, an auditory specialist, have shown that spatial auditory information is topographically represented in the OT. Little is known about how auditory space is represented in the midbrain of birds with generalist hearing, i.e., most of avian species lacking peripheral adaptations such as facial ruffs or asymmetric ears. Thus, we conducted in vivo extracellular recordings of single neurons in the OT and in the external portion of the formatio reticularis lateralis (FRLx), a brain structure located between the inferior colliculus (IC) and the OT, in anaesthetized chickens of either sex. We found that most of the auditory spatial receptive fields (aSRFs) were spatially confined both in azimuth and elevation, divided into two main classes: round aSRFs, mainly present in the OT, and annular aSRFs, with a ring-like shape around the interaural axis, mainly present in the FRLx. Our data further indicate that interaural time difference (ITD) and interaural level difference (ILD) play a role in the formation of both aSRF classes. These results suggest that, unlike mammals and owls which have a congruent representation of visual and auditory space in the OT, generalist birds separate the computation of auditory space in two different midbrain structures. We hypothesize that the FRLx-annular aSRFs define the distance of a sound source from the axis of the lateral visual fovea, whereas the OT-round aSRFs are involved in multimodal integration of the stimulus around the lateral fovea.SIGNIFICANCE STATEMENT Previous studies implied that auditory spatial receptive fields (aSRFs) in the midbrain of generalist birds are only confined along azimuth. Interestingly, we found SRFs s in the chicken to be confined along both azimuth and elevation. Moreover, the auditory receptive fields are arranged in a concentric manner around the overlapping interaural and visual axes. These data suggest that in generalist birds, which mainly rely on vision, the auditory system mainly serves to align auditory stimuli with the visual axis, while auditory specialized birds like the barn owl compute sound sources more precisely and integrate sound positions in the multimodal space map of the optic tectum (OT).

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.

Hippocampal α5-GABAA Receptors Modulate Dopamine Neuron Activity in the Rat Ventral Tegmental Area

BackgroundAberrant dopamine neuron activity is attributable to hyperactivity in hippocampal subfields driving a pathological increase in dopamine neuron activity, which is positively correlated with psychosis in humans. Evidence indicates that hippocampal hyperactivity is due to loss of intrinsic GABAergic (gamma-aminobutyric acidergic) inhibition. We have previously demonstrated that hippocampal GABAergic neurotransmission can be modulated by targeting α5-GABAA receptors, which are preferentially expressed in hippocampal regions. Positive and negative allosteric modulators of α5-GABAA receptors (α5-PAMs and α5-NAMs) elicit effects on hippocampal-dependent behaviors. We posited that the selective manipulation of hippocampal inhibition, using α5-PAMs or α5-NAMs, would modulate dopamine activity in control rats. Further, α5-PAMs would reverse aberrant dopamine neuron activity in a rodent model with schizophrenia-related pathophysiologies (methylazoxymethanol acetate [MAM] model). MethodsWe performed in vivo extracellular recordings of ventral tegmental area dopamine neurons in anesthetized rats to compare the effects of two novel, selective α5-PAMs (GL-II-73, MP-III-022), a nonselective α-PAM (midazolam), and two selective α5-NAMs (L-655,708, TB 21007) in control and MAM-treated male Sprague Dawley rats (n = 5–9). ResultsSystemic or intracranial administration of selective α5-GABAA receptor modulators regulated dopamine activity. Specifically, both α5-NAMs increased dopamine neuron activity in control rats, whereas GL-II-73, MP-III-022, and L-655,708 attenuated aberrant dopamine neuron activity in MAM-treated rats, an effect mediated by the ventral hippocampus. ConclusionsThis study demonstrated that α5-GABAA receptor modulation can regulate dopamine neuron activity under control or abnormal activity, providing additional evidence that α5-PAMs and α5-NAMs may have therapeutic applications in psychosis and other psychiatric diseases where aberrant hippocampal activity is present.

Activity and Coupling to Hippocampal Oscillations of Median Raphe GABAergic Cells in Awake Mice.

Ascending serotonergic/glutamatergic projection from the median raphe region (MRR) to the hippocampal formation regulates both encoding and consolidation of memory and the oscillations associated with them. The firing of various types of MRR neurons exhibits rhythmic modulation coupled to hippocampal oscillatory activity. A possible intermediary between rhythm-generating forebrain regions and entrained ascending modulation may be the GABAergic circuit in the MRR, known to be targeted by a diverse array of top-down inputs. However, the activity of inhibitory MRR neurons in an awake animal is still largely unexplored. In this study, we utilized whole cell patch-clamp, single cell, and multichannel extracellular recordings of GABAergic and non-GABAergic MRR neurons in awake, head-fixed mice. First, we have demonstrated that glutamatergic and serotonergic neurons receive both transient, phasic, and sustained tonic inhibition. Then, we observed substantial heterogeneity of GABAergic firing patterns but a marked modulation of activity by brain states and fine timescale coupling of spiking to theta and ripple oscillations. We also uncovered a correlation between the preferred theta phase and the direction of activity change during ripples, suggesting the segregation of inhibitory neurons into functional groups. Finally, we could detect complementary alteration of non-GABAergic neurons’ ripple-coupled activity. Our findings support the assumption that the local inhibitory circuit in the MRR may synchronize ascending serotonergic/glutamatergic modulation with hippocampal activity on a subsecond timescale.

Prenatal Androgen Treatment Does Not Alter the Firing Activity of Hypothalamic Arcuate Kisspeptin Neurons in Female Mice

Neuroendocrine control of reproduction is disrupted in many individuals with polycystic ovary syndrome (PCOS), who present with increased luteinizing hormone (LH), and presumably gonadotropin-releasing hormone (GnRH), release frequency, and high androgen levels. Prenatal androgenization (PNA) recapitulates these phenotypes in primates and rodents. Female offspring of mice injected with dihydrotestosterone (DHT) on gestational days 16–18 exhibit disrupted estrous cyclicity, increased LH and testosterone, and increased GnRH neuron firing rate as adults. PNA also alters the developmental trajectory of GnRH neuron firing rates, markedly blunting the prepubertal peak in firing that occurs in three-week (3wk)-old controls. GnRH neurons do not express detectable androgen receptors and are thus probably not the direct target of DHT. Rather, PNA likely alters GnRH neuronal activity by modulating upstream neurons, such as hypothalamic arcuate neurons co-expressing kisspeptin, neurokinin B (gene Tac2), and dynorphin, also known as KNDy neurons. We hypothesized PNA treatment changes firing rates of KNDy neurons in a similar age-dependent manner as GnRH neurons. We conducted targeted extracellular recordings (0.5–2 h) of Tac2-identified KNDy neurons from control and PNA mice at 3wks of age and in adulthood. About half of neurons were quiescent (<0.005 Hz). Long-term firing rates of active cells varied, suggestive of episodic activity, but were not different among groups. Short-term burst firing was also similar. We thus reject the hypothesis that PNA alters the firing rate of KNDy neurons. This does not preclude altered neurosecretory output of KNDy neurons, involvement of other neuronal populations, or in vivo networks as critical drivers of altered GnRH firing rates in PNA mice.

Hypergravity-induced malfunction was moderated by the regulation of NMDA receptors in the vestibular nucleus

Gravity alteration is one of the critical environmental factors in the space, causing various abnormal behaviors related with the malfunctioned vestibular system. Due to the high plastic responses in the central vestibular system, the behavioral failures were resolved in a short period of time (in approx. 72 h). However, the plastic neurotransmission underlying the functional recovery is still elusive. To understand the neurotransmitter-induced plasticity under hypergravity, the extracellular single neuronal recording and the immunohistochemistry were conducted in the vestibular nucleus (VN). The animals were grouped as control, 24-h, 72-h, and 15-day exposing to 4G-hypergravity, and each group had two subgroups based on the origins of neuronal responses, such as canal and otolith. The averaged firing rates in VN showed no significant difference in the subgroups (canal-related: p > 0.105, otolith-related: p > 0.138). Meanwhile, the number of NMDAr was significantly changed by the exposing duration to hypergravity. The NMDAr decreased in 24 h (p = 1.048 × 10–9), and it was retrieved in 72 h and 15 days (p < 4.245 × 10–5). Apparently, the reduction and the retrieval in the number of NMDAr were synchronized with the generation and recovery of the abnormal behaviors. Thus, the plasticity to resolve the hypergravity-induced malfunctional behaviors was conducted by regulating the number of NMDAr.

Changes to the activity and sensitivity of nerves innervating subchondral bone contribute to pain in late-stage osteoarthritis.

Although it is clear that osteoarthritis (OA) pain involves activation and/or sensitization of nociceptors that innervate knee joint articular tissues, much less is known about the role of the innervation of surrounding bone. In this study, we used monoiodoacetate (MIA)-induced OA in male rats to test the idea that pain in OA is driven by differential contributions from nerves that innervate knee joint articular tissues vs the surrounding bone. The time-course of pain behavior was assayed using the advanced dynamic weight-bearing device, and histopathology was examined using haematoxylin and eosin histology. Extracellular electrophysiological recordings of knee joint and bone afferent neurons were made early (day 3) and late (day 28) in the pathogenesis of MIA-induced OA. We observed significant changes in the function of knee joint afferent neurons, but not bone afferent neurons, at day 3 when there was histological evidence of inflammation in the joint capsule, but no damage to the articular cartilage or subchondral bone. Changes in the function of bone afferent neurons were only observed at day 28, when there was histological evidence of damage to the articular cartilage and subchondral bone. Our findings suggest that pain early in MIA-induced OA involves activation and sensitization of nerves that innervate the joint capsule but not the underlying subchondral bone, and that pain in late MIA-induced OA involves the additional recruitment of nerves that innervate the subchondral bone. Thus, nerves that innervate bone should be considered important targets for development of mechanism-based therapies to treat pain in late OA.

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.

Activity of Posterior Lateral Line Afferent Neurons during Swimming in Zebrafish.

Sensory systems gather cues essential for directing behavior, but animals must decipher what information is biologically relevant. Locomotion generates reafferent cues that animals must disentangle from relevant sensory cues of the surrounding environment. For example, when a fish swims, flow generated from body undulations is detected by the mechanoreceptive neuromasts, comprising hair cells, that compose the lateral line system. The hair cells then transmit fluid motion information from the sensor to the brain via the sensory afferent neurons. Concurrently, corollary discharge of the motor command is relayed to hair cells to prevent sensory overload. Accounting for the inhibitory effect of predictive motor signals during locomotion is, therefore, critical when evaluating the sensitivity of the lateral line system. We have developed an in vivo electrophysiological approach to simultaneously monitor posterior lateral line afferent neuron and ventral motor root activity in zebrafish larvae (4-7 days post fertilization) that can last for several hours. Extracellular recordings of afferent neurons are achieved using the loose patch clamp technique, which can detect activity from single or multiple neurons. Ventral root recordings are performed through the skin with glass electrodes to detect motor neuron activity. Our experimental protocol provides the potential to monitor endogenous or evoked changes in sensory input across motor behaviors in an intact, behaving vertebrate.