Responses Of Interneurons Research Articles

λ-cyhalothrin induced sex-specific inflammation, glia activation and GABAergic interneuron disruption in the hippocampus of rats

BackgroundGlia mediated neuroinflammation and degeneration of inhibitory GABAergic interneurons are some of the hall marks of pyrethroid neurotoxicity. Here we investigated the sex specific responses of inflammatory cytokines, microglia, astrocyte and parvalbumin positive inhibitory GABAergic interneurons to λ-cyhalothrin (LCT) exposures in rats.MethodsEqual numbers of male and female rats were given oral corn oil, 2 mg/kg.bw and 4 mg/kg.bw of LCT for fourteen days. They were euthanized on day 15, brains were excised and hippocampus (n = 5/group) isolated for interleukin 1 beta (IL-1β) and tumor necrotic factor alpha (TNF-α) analysis. The remaining brains (n = 3/group) were processed for Ionized calcium binding adaptor molecule 1 (Iba1), glial fibrillary acidic protein (GFAP) and parvalbumin (PV) distribution in the hippocampus. All quantitative data was subjected to one way analysis of variance (ANOVA).ResultsLCT caused sex and dose dependent increase in IL-1β and TNF-α concentrations, distribution of microglia (Iba1+) and astrocytes (GFAP+), and reduction of PV + GABAergic interneurons. These effects were greater in males compared to females, and dose-dependent in both sexes.ConclusionLCT specifically induced inflammation and disrupted GABAergic interneurons’ integrities via activation of microglia and reactive astrogliosis and such effects are dose-dependent and sexually dimorphic.

Cortical responses to conflicting binocular stimuli in mouse primary visual cortex.

Binocular vision requires that the brain integrate information coming from each eye. These images are combined (fused) to generate a meaningful composite image. Differences between images, within a range, provide useful information about depth (stereopsis). Interocular disparities that are not effectively combined result in diplopia and rivalry. The neural mechanisms underlying these binocular interactions remain poorly understood. Using a combination of visually evoked potential (VEP) recordings, unit recordings, and 2-photon calcium imaging in the binocular region of mouse primary visual cortex (bV1), we probed the neural mechanisms underlying the processing of two distinct forms of disparate binocular signals. Using a dichoptic display, introduction of a spatial interocular phase disparity in grating stimuli reduced VEP magnitude through decreased neuronal firing in the early phase of the response (40-80 ms after stimulus onset, corresponding to the VEP negativity). Introduction of an interocular orientation disparity also decreased VEP magnitude, but this difference was driven by an increase in firing in the late portion of the visual response (100-200 ms after stimulus onset, corresponding to the VEP positivity). This increase in activity was observed for both regular-spiking (putative excitatory) and fast-spiking (putative parvalbumin-positive inhibitory) units. By contrast, visually evoked calcium responses of somatostatin-positive interneurons decreased with introduction of the interocular orientation disparity. Based on these results, we propose that interocular phase differences largely suppress bV1 responses via feedforward thalamocortical interactions, whereas interocular orientation differences prolong visually evoked activity in bV1 through somatostatin-positive interneuron-mediated disinhibition.

Fxr1 Deletion from Cortical Parvalbumin Interneurons Modifies Their Excitatory Synaptic Responses.

Fragile X autosomal homolog 1 (FXR1), a member of the fragile X messenger riboprotein 1 family, has been linked to psychiatric disorders including autism and schizophrenia. Parvalbumin (PV) interneurons play critical roles in cortical processing and have been implicated in FXR1-linked mental illnesses. Targeted deletion of FXR1 from PV interneurons in mice has been shown to alter cortical excitability and elicit schizophrenia-like behavior. This indicates that FXR1 regulates behaviorally relevant electrophysiological functions in PV interneurons. We therefore expressed a genetically encoded hybrid voltage sensor in PV interneurons and used voltage imaging in slices of mouse somatosensory cortex to assess the impact of targeted FXR1 deletion. These experiments showed that PV interneurons lacking FXR1 had excitatory synaptic potentials with larger amplitudes and shorter latencies compared with wild type. Synaptic potential rise-times, decay-times, and half-widths were also impacted to degrees that varied between cortical layer and synaptic input. Thus, FXR1 modulates the responsiveness of PV interneurons to excitatory synaptic inputs. This will enable FXR1 to control cortical processing in subtle ways, with the potential to influence behavior and contribute to psychiatric dysfunction.

Dynamic responses of striatal cholinergic interneurons control behavioral flexibility.

Striatal cholinergic interneurons (CINs) are key to regulating behavioral flexibility, involving both extinguishing learned actions and adopting new ones. However, the mechanisms driving these processes remain elusive. In this study, we initially demonstrate that chronic alcohol consumption disrupts the burst-pause dynamics of CINs and impairs behavioral flexibility. We next aimed to elucidate the mechanisms by which CIN dynamics control behavioral flexibility. We found that extinction learning enhances acetylcholine (ACh) release and that mimicking this enhancement through optogenetic induction of CIN burst firing accelerates the extinction process. In addition, we demonstrate that disrupting CIN pauses via continuous optogenetic stimulation reversibly impairs the updating of goal-directed behaviors. Overall, we demonstrate that CIN burst firing, which increases ACh release, promotes extinction learning, aiding the extinguishment of learned behaviors. Conversely, CIN firing pauses, which lead to ACh dips, are crucial for reversal learning, facilitating the adaptation of new actions. These findings shed light on how CIN dynamics regulate behavioral flexibility.

Response of parvalbumin interneurons and perineuronal nets in rat medial prefrontal cortex and lateral amygdala to stressor controllability

Behavioral control over a stressor limits the impact of the stressor being experienced and produces enduring changes that reduce the effects of future stressors. In rats, these stress-buffering effects of control (escapable stress, ES) require activation of the medial prefrontal cortex (mPFC) and prevent the typical amygdala-dependent behavioral outcomes of uncontrollable stress (inescapable stress, IS). Parvalbumin (PV) interneurons regulate output of excitatory neurons, and most mPFC PV neurons are surrounded by perineuronal nets (PNNs), which regulate firing. We exposed male rats to a single session of ES, IS, or no stress and measured c-Fos expression within PV/PNN-containing cells in mPFC subregions (prelimbic, PL; infralimbic, IL) and in the lateral amygdala. We also measured the number and intensity of PNNs. Within PL and IL PV/PNN cells, both ES and IS increased c-Fos intensity in PV/PNN, non-PV, and non-PNN cells. Within the IL, only ES increased the number of c-Fos-expressing PV/PNN-labeled cells. In the lateral amygdala, only ES increased c-Fos intensity within PV cells and PV/PNN cells. Thus, PV neurons in the IL and lateral amygdala may represent an important substrate by which behavioral control buffers against the amygdala-dependent behavioral outcomes typically observed after uncontrollable stress.

Sensation is Dispensable for the Maturation of the Vestibulo-ocular Reflex.

Vertebrates stabilize gaze using a neural circuit that transforms sensed instability into compensatory counter-rotation of the eyes. Sensory feedback tunes this vestibulo-ocular reflex throughout life. Gaze stabilization matures progressively, either due to similar tuning, or to a slowly developing circuit component. Here we studied the functional development of vestibulo-ocular reflex circuit components in the larval zebrafish, with and without sensation. Blind fish stabilize gaze normally, and neural responses to body tilts mature before behavior. Instead, synapses between motor neurons and the eye muscles mature with a timecourse similar to behavioral maturation. Larvae without vestibular sensory experience, but whose neuromuscular junction was mature, had a strong vestibulo-ocular reflex. Development of the neuromuscular junction, and not sensory experience, determines the rate of maturation of an ancient behavior.

Suppression of Hippocampal Neurogenesis and Oligodendrocyte Maturation Similar to Developmental Hypothyroidism by Maternal Exposure of Rats to Ammonium Perchlorate, a Gunpowder Raw Material and Known Environmental Contaminant.

The environmental contaminant perchlorate raises concern for hypothyroidism-related brain disorders in children. This study investigated the effects of developmental perchlorate exposure on hippocampal neurogenesis and oligodendrocyte (OL) development. Pregnant Sprague-Dawley rats were administered with ammonium perchlorate (AP) in drinking water at concentrations of 0 (control), 300, and 1000 ppm from gestation day 6 until weaning [postnatal day (PND) 21]. On PND 21, offspring displayed decreased serum triiodothyronine and thyroxine concentrations at 1000 ppm and thyroid follicular epithelial cell hyperplasia at ≥300 ppm (accompanying increased proliferation activity at 1000 ppm). Hippocampal neurogenesis indicated suppressed proliferation of neurogenic cells at ≥300 ppm, causing decreases in type-1 neural stem cells (NSCs) and type-2a neural progenitor cells. In addition, an increase of SST+ GABAergic interneurons and decreasing trend for ARC+ granule cells were observed at 1000 ppm. CNPase+ mature OLs were decreased in number in the dentate gyrus hilus at ≥300 ppm. At PND 77, thyroid changes had disappeared; however, the decrease of type-1 NSCs and increase of SST+ interneurons persisted, CCK+ interneurons were increased, and white matter tissue area was decreased at 1000 ppm. Obtained results suggest an induction of hypothyroidism causing suppressed hippocampal neurogenesis (targeting early neurogenic processes and decreased synaptic plasticity of granule cells involving ameliorative interneuron responses) and suppressed OL maturation during the weaning period. In adulthood, suppression of neurogenesis continued, and white matter hypoplasia was evident. Observed brain changes were similar to those caused by developmental hypothyroidism, suggesting that AP-induced developmental neurotoxicity was due to hypothyroidism.

Loss-of-function of GNAL dystonia gene impairs striatal dopamine receptors-mediated adenylyl cyclase/ cyclic AMP signaling pathway

Loss-of-function mutations in the GNAL gene are responsible for DYT-GNAL dystonia. However, how GNAL mutations contribute to synaptic dysfunction is still unclear. The GNAL gene encodes the Gαolf protein, an isoform of stimulatory Gαs enriched in the striatum, with a key role in the regulation of cAMP signaling.Here, we used a combined biochemical and electrophysiological approach to study GPCR-mediated AC-cAMP cascade in the striatum of the heterozygous GNAL (GNAL+/−) rat model. We first analyzed adenosine type 2 (A2AR), and dopamine type 1 (D1R) receptors, which are directly coupled to Gαolf, and observed that the total levels of A2AR were increased, whereas D1R level was unaltered in GNAL+/− rats. In addition, the striatal isoform of adenylyl cyclase (AC5) was reduced, despite unaltered basal cAMP levels. Notably, the protein expression level of dopamine type 2 receptor (D2R), that inhibits the AC5-cAMP signaling pathway, was also reduced, similar to what observed in different DYT-TOR1A dystonia models. Accordingly, in the GNAL+/− rat striatum we found altered levels of the D2R regulatory proteins, RGS9–2, spinophilin, Gβ5 and β-arrestin2, suggesting a downregulation of D2R signaling cascade. Additionally, by analyzing the responses of striatal cholinergic interneurons to D2R activation, we found that the receptor-mediated inhibitory effect is significantly attenuated in GNAL+/− interneurons. Altogether, our findings demonstrate a profound alteration in the A2AR/D2R-AC-cAMP cascade in the striatum of the rat DYT-GNAL dystonia model, and provide a plausible explanation for our previous findings on the loss of dopamine D2R-dependent corticostriatal long-term depression.

An open platform for visual stimulation of insects.

To study how the nervous system processes visual information, experimenters must record neural activity while delivering visual stimuli in a controlled fashion. In animals with a nearly panoramic field of view, such as flies, precise stimulation of the entire visual field is challenging. We describe a projector-based device for stimulation of the insect visual system under a microscope. The device is based on a bowl-shaped screen that provides a wide and nearly distortion-free field of view. It is compact, cheap, easy to assemble, and easy to operate using the included open-source software for stimulus generation. We validate the virtual reality system technically and demonstrate its capabilities in a series of experiments at two levels: the cellular, by measuring the membrane potential responses of visual interneurons; and the organismal, by recording optomotor and fixation behavior of Drosophila melanogaster in tethered flight. Our experiments reveal the importance of stimulating the visual system of an insect with a wide field of view, and we provide a simple solution to do so.

Inter and intralaminar excitation of parvalbumin interneurons in mouse barrel cortex.

Parvalbumin (PV) interneurons are inhibitory fast-spiking cells with essential roles in directing the flow of information through cortical circuits. These neurons set the balance between excitation and inhibition and control rhythmic activity. PV interneurons differ between cortical layers in their morphology, circuitry, and function, but how their electrophysiological properties vary has received little attention. Here we investigate responses of PV interneurons in different layers of primary somatosensory barrel cortex (BC) to different excitatory inputs. With the genetically-encoded hybrid voltage sensor, hVOS, we recorded voltage changes in many L2/3 and L4 PV interneurons simultaneously, with stimulation applied to either L2/3 or L4. A semi-automated procedure was developed to identify small regions of interest corresponding to single responsive PV interneurons. Amplitude, half-width, and rise-time were greater for PV interneurons residing in L2/3 compared to L4. Stimulation in L2/3 elicited responses in both L2/3 and L4 with longer latency compared to stimulation in L4. These differences in latency between layers could influence their windows for temporal integration. Thus, PV interneurons in different cortical layers of BC respond in a layer specific and input specific manner, and these differences have potential roles in cortical computations.

Effect of applied electric fields on supralinear dendritic integration of interneuron

Evidences show that electric fields (EFs) induced by the magnetic stimulation could modulates brain activities by regulating the excitability of GABAergic interneuron. However, it is still unclear how and why the EF-induced polarization affects the interneuron response as the interneuron receives NMDA synaptic inputs. Considering the key role of NMDA receptor-mediated supralinear dendritic integration in neuronal computations, we suppose that the applied EFs could functionally modulate interneurons’ response via regulating dendritic integration. At first, we build a simplified multi-dendritic circuit model with inhomogeneous extracellular potentials, which characterizes the relationship among EF-induced spatial polarizations, dendritic integration, and somatic output. By performing model-based singular perturbation analysis, it is found that the equilibrium point of fast subsystem can be used to asymptotically depict the subthreshold input–output (sI/O) relationship of dendritic integration. It predicted that EF-induced strong depolarizations on the distal dendrites reduce the dendritic saturation output by reducing driving force of synaptic input, and it shifts the steep change of sI/O curve left by reducing stimulation threshold of triggering NMDA spike. Also, the EF modulation prefers the global dendritic integration with asymmetric scatter distribution of NMDA synapses. Furthermore, we identify the respective contribution of EF-regulated dendritic integration and EF-induced somatic polarization to an action potential generation and find that they have an antagonistic effect on AP generation due to the varied NMDA spike threshold under EF stimulation.

Differences in responses of premotor interneurons to serotonin and 5-hydroxytryptophan, a precursor for serotonin synthesis, in naive and trained snails

This study investigated the responses of premotor interneurons LPa3 and RPa3 of the snails to applications of serotonin and 5-hydroxytryptophan (5-HTP), a precursor for serotonin synthesis, as ingredients of the broth that bathes the central nervous system of naive snails and snails after the formation of long-term sensitization. Measurements of the electrical characteristics have shown that a membrane potential of interneurons LPa3 and RPa3 in naive snails was significantly depolarized (3.7 mV) in the presence of serotonin, while the threshold potential was increased (unsupported hypothesis). The similar pattern was observed in the presence of 5-hydroxytryptophan: true depolarization to 3.1 mV occurred in interneurons until reaching the unreliable rise in the threshold potential inducing an action potential. It was found that application of serotonin causes a significant decrease in the membrane potential of interneurons LPa3 and RPa3 of trained snails (depolarization to 4.6 mV) and the unreliable increase in the threshold potential of premotor interneurons (0.9 mV). In contrast, application of 5-hydroxytryptophan causes an unreliable increase (2.5 mV) of the membrane potential and also an unreliable increase (0.8 mV) in the threshold potential.

Differences in Responses of Premotor Interneurons to Serotonin and the Precursor of Its Synthesis 5-Hydroxytryptophan in Naive and Sensitized Snails

Differences in Responses of Premotor Interneurons to Serotonin and the Precursor of Its Synthesis 5-Hydroxytryptophan in Naive and Sensitized Snails

Marco Capogna, a pioneering neuroscientist and true European

Marco Capogna, a pioneering neuroscientist and true European

Changes in operation of postural networks in rabbits with postural functions recovered after lateral hemisection of the spinal cord.

Acute lateral hemisection of the spinal cord (LHS) severely impairs postural functions, which recover over time. Here, to reveal changes in the operation of postural networks underlying the recovery, male rabbits with recovered postural functions after LHS at T12 (R-rabbits) were used. After decerebration, we characterized the responses of individual spinal interneurons from L5 along with hindlimb EMG responses to stimulation causing postural limb reflexes (PLRs) that substantially contribute to postural corrections in intact animals. The data were compared with those obtained in our previous studies of rabbits with the intact spinal cord and rabbits after acute LHS. Although, in R-rabbits, the EMG responses to postural disturbances both ipsilateral and contralateral to the LHS (ipsi-LHS and co-LHS) were only slightly distorted, PLRs on the co-LHS side (unaffected by acute LHS) were distorted substantially and PLRs on the ipsi-LHS side (abolished by acute LHS) were close to control. Thus, in R-rabbits, plastic changes develop in postural networks both affected and unaffected by acute LHS. PLRs on the ipsi-LHS side recover mainly as a result of changes at brainstem-cerebellum-spinal levels, whereas the forebrain is substantially involved in the generation of PLRs on the co-LHS side. We found that, in areas of grey matter in which the activity of spinal neurons of the postural network was significantly decreased after acute LHS, it recovered to the control level, whereas, in areas unaffected by acute LHS, it was significantly changed. These changes underlie the recovery and distortion of PLRs on the ipsi-LHS and co-LHS sides, respectively. KEY POINTS: After lateral hemisection of the spinal cord (LHS), postural functions recover over time. The underlying changes in the operation of postural networks are unknown. We compared the responses of individual spinal neurons and hindlimb muscles to stimulation causing postural limb reflexes (PLRs) in recovered LHS-rabbits with those obtained in rabbits with the intact spinal cord and rabbits after acute LHS. We demonstrated that changes underlying the recovery of postural functions take place not only in postural networks that are severely impaired, but also in those that are almost unaffected by acute LHS. PLRs on the LHS side recover mainly as a result of changes at brainstem-cerebellum-spinal levels, whereas the forebrain is substantially involved in the generation of PLRs contralateral to the LHS.

Disinhibitory circuit mediated by connections from vasoactive intestinal polypeptide to somatostatin interneurons underlies the paradoxical decrease in spike synchrony with increased border ownership selective neuron firing rate.

The activity of border ownership selective (BOS) neurons in intermediate-level visual areas indicates which side of a contour owns a border relative to its classical receptive field and provides a fundamental component of figure-ground segregation. A physiological study reported that selective attention facilitates the activity of BOS neurons with a consistent border ownership preference, defined as two neurons tuned to respond to the same visual object. However, spike synchrony between this pair is significantly suppressed by selective attention. These neurophysiological findings are derived from a biologically-plausible microcircuit model consisting of spiking neurons including two subtypes of inhibitory interneurons, somatostatin (SOM) and vasoactive intestinal polypeptide (VIP) interneurons, and excitatory BOS model neurons. In our proposed model, BOS neurons and SOM interneurons cooperate and interact with each other. VIP interneurons not only suppress SOM interneuron responses but also are activated by feedback signals mediating selective attention, which leads to disinhibition of BOS neurons when they are directing selective attention toward an object. Our results suggest that disinhibition arising from the synaptic connections from VIP to SOM interneurons plays a critical role in attentional modulation of neurons in intermediate-level visual areas.

Different modes of stimuli delivery elicit changes in glutamate driven, experience-dependent interneuron response in C. elegans

Memory-related neuronal responses are often elicited by sensory stimuli that recapitulate previous experience. Despite the importance of this sensory input processing, its underlying mechanisms remain poorly understood. Caenorhabditis elegans chemotax towards salt concentrations experienced in the presence of food. The amphid sensory neurons ASE-left and ASE-right respond to increases and decreases of ambient salt concentration in opposite manners. AIA, AIB and AIY interneurons are post-synaptic to the ASE pair and are thought to be involved in the processing of salt information transmitted from ASE. However, it remains elusive how the responses of these interneurons are regulated by stimulus patterns. Here we show that AIY interneurons display an experience-dependent response to gradual salt concentration changes but not to abrupt stepwise concentration changes. Animals with AIY intact (but AIA and AIB ablated) chemotax towards low salt concentrations similarly to wild-type animals after cultivation with low salt. ASE neurons transmit salt information about the environment through glutamatergic signaling, directing the activity of the interneurons AIY that promote movement towards favorable conditions.

Unitary synaptic responses of parvalbumin interneurons evoked by excitatory neurons in the mouse barrel cortex.

The mammalian cortex integrates and processes information to transform sensory inputs into perceptions and motor outputs. These operations are performed by networks of excitatory and inhibitory neurons distributed through the cortical layers. Parvalbumin interneurons (PVIs) are the most abundant type of inhibitory cortical neuron. With axons projecting within and between layers, PVIs supply feedforward and feedback inhibition to control and modulate circuit function. Distinct populations of excitatory neurons recruit different PVI populations, but the specializations of these synapses are poorly understood. Here, we targeted a genetically encoded hybrid voltage sensor to PVIs and used fluorescence imaging in mouse somatosensory cortex slices to record their voltage changes. Stimulating a single visually identified excitatory neuron with small-tipped theta-glass electrodes depolarized multiple PVIs, and a common threshold suggested that stimulation elicited unitary synaptic potentials in response to a single excitatory neuron. Excitatory neurons depolarized PVIs in multiple layers, with the most residing in the layer of the stimulated neuron. Spiny stellate cells depolarized PVIs more strongly than pyramidal cells by up to 77%, suggesting a greater role for stellate cells in recruiting PVI inhibition and controlling cortical computations. Response half-width also varied between different excitatory inputs. These results demonstrate functional differences between excitatory synapses on PVIs.

Spherical harmonics based model of electric field effects on neocortical neurons

Abstract Transcranial electrical stimulation (tES) techniques generate electric fields in the brain whose effects on single neurons can be approximated from the cable equation as a membrane potential perturbation that is proportional to the membrane length constant (lambda). This is referred to as the lambda-E model and is a simple mechanistic approach that assumes that the membrane perturbation can be modeled as the dot product of a vector parallel to the orthodromic direction of cortical neurons with the electric field, multiplied by lambda. We propose a more general way to represent the model of the membrane perturbation as a function of the magnitude and angular orientation of the E-field, using a spherical harmonics expansion that can capture the dependence of the perturbation on electric field direction. In this representation, the lambda-E model corresponds to the first-order degree (l=1) term of the expansion. This approach can represent the three-dimensional response of a specific cell part, obtained experimentally. Here we employ it using synthetic data from realistic neocortical cell models in a DC field in the tDCS regime, fitting the coefficients for the membrane responses. We use realistic reconstructions of the somatosensory cortex from the Blue Brain Project to simulate the response of different pyramidal cells and interneurons to electric fields of 1 V/m as a function of the orientation of the field with respect to the cell using the NEURON simulation environment. We report membrane perturbation values comparable to those in the literature, extend it to different cell types, and provide the spherical harmonic coefficient profile for each neuron. Finally, we provide an azimuth-independent version of the model providing an averaged response that only depends on the electric field vector and the cortical surface. We believe this method can improve the accuracy and detail of real life simulation-based stimulation. Keywords: Electric field coupling, Multicompartment models, tES, NEURON

Neural Recruitment During Conventional, Burst, and 10-kHz Spinal Cord Stimulation for Pain

Spinal cord stimulation (SCS) is a popular neurostimulation therapy for severe chronic pain. To improve stimulation efficacy, multiple modes are now used clinically, including conventional, burst, and 10-kHz SCS. Clinical observations have produced speculation that these modes target different neural elements and/or work via distinct mechanisms of action. However, in humans, these hypotheses cannot be conclusively answered via experimental methods. Therefore, we utilized computational modeling to assess the response of primary afferents, interneurons, and projection neurons to conventional, burst, and 10-kHz SCS. We found that local cell thresholds were always higher than afferent thresholds, arguing against direct recruitment of these local cells. Furthermore, although we observed relative threshold differences between conventional, burst, and 10-kHz SCS, the recruitment order was the same. Finally, contrary to previous reports, axon collateralization produced complex changes in activation thresholds of primary afferents. These results motivate future work to contextualize clinical observations across SCS paradigms. PerspectiveThis article presents the first computational modeling study to investigate neural recruitment during conventional, burst, and 10-kilohertz spinal cord stimulation for chronic pain within a single modeling framework. The results provide insight into these treatments’ unknown mechanisms of action and offer context to interpreting clinical observations.