Inhibitory Interneurons Research Articles

Fast-Spike Interneurons in Visual Cortical Layer 5: Heterogeneous Response Properties Are Related to Thalamocortical Connectivity.

Layer 4 (L4) of rabbit V1 contains fast-spike GABAergic interneurons (suspected inhibitory interneurons, SINs) that receive potent synaptic input from the LGN and generate fast, local feedforward inhibition. These cells display receptive fields with overlapping ON/OFF subregions, nonlinear spatial summation, very broad orientation/directional tuning, and high spontaneous and visually driven firing rates. Fast-spike interneurons are also found in Layer 5 (L5), which receives a much sparser input from the LGN, but the response properties and thalamocortical connectivity of L5 SINs are relatively unstudied. Here, we study L5 SINs in awake rabbits (both sexes) and compare their response properties with previously studied SINs of L4. We also assess thalamocortical connectivity of L5 SINs, examining cross-correlation of retinotopically aligned LGN-SIN spike trains and L5 SIN responses to electrical stimulation of the LGN. These analyses confirmed that many L5 SINs, like L4 SINs, receive a strong, fast monosynaptic drive from the LGN. Moreover, these LGN-connected L5 SINs had response properties similar to those of L4 SINs and were predominantly found in the upper half of L5. In contrast, L5 SINs with longer synaptic latencies to LGN stimulation displayed (1) sharper orientation tuning, (2) longer visual response latencies, (3) lower spontaneous and (4) visually driven firing rates, and (5) were found in the deeper half of L5. We suggest that the long-latency synaptic responses in such L5 SINs reflect a multisynaptic intracortical pathway that generates a different constellation of response properties than seen in L5 SINs that are driven directly by LGN input.

Experience-dependent reorganization of inhibitory neuron synaptic connectivity.

Organisms continually tune their perceptual systems to the features they encounter in their environment 1-3 . We have studied how ongoing experience reorganizes the synaptic connectivity of neurons in the olfactory (piriform) cortex of the mouse. We developed an approach to measure synaptic connectivity in vivo , training a deep convolutional network to reliably identify monosynaptic connections from the spike-time cross-correlograms of 4.4 million single-unit pairs. This revealed that excitatory piriform neurons with similar odor tuning are more likely to be connected. We asked whether experience enhances this like-to-like connectivity but found that it was unaffected by odor exposure. Experience did, however, alter the logic of interneuron connectivity. Following repeated encounters with a set of odorants, inhibitory neurons that responded differentially to these stimuli exhibited a high degree of both incoming and outgoing synaptic connections within the cortical network. This reorganization depended only on the odor tuning of the inhibitory interneuron and not on the tuning of its pre- or postsynaptic partners. A computational model of this reorganized connectivity predicts that it increases the dimensionality of the entire network's responses to familiar stimuli, thereby enhancing their discriminability. We confirmed that this network-level property is present in physiological measurements, which showed increased dimensionality and separability of the evoked responses to familiar versus novel odorants. Thus, a simple, non-Hebbian reorganization of interneuron connectivity may selectively enhance an organism's discrimination of the features of its environment.

Molecular hallmarks of excitatory and inhibitory neuronal resilience and resistance to Alzheimer's disease.

A significant proportion of individuals maintain healthy cognitive function despite having extensive Alzheimer's disease (AD) pathology, known as cognitive resilience. Understanding the molecular mechanisms that protect these individuals can identify therapeutic targets for AD dementia. This study aims to define molecular and cellular signatures of cognitive resilience, protection and resistance, by integrating genetics, bulk RNA, and single-nucleus RNA sequencing data across multiple brain regions from AD, resilient, and control individuals. We analyzed data from the Religious Order Study and the Rush Memory and Aging Project (ROSMAP), including bulk (n=631) and multi-regional single nucleus (n=48) RNA sequencing. Subjects were categorized into AD, resilient, and control based on β-amyloid and tau pathology, and cognitive status. We identified and prioritized protected cell populations using whole genome sequencing-derived genetic variants, transcriptomic profiling, and cellular composition distribution. Transcriptomic results, supported by GWAS-derived polygenic risk scores, place cognitive resilience as an intermediate state in the AD continuum. Tissue-level analysis revealed 43 genes enriched in nucleic acid metabolism and signaling that were differentially expressed between AD and resilience. Only GFAP (upregulated) and KLF4 (downregulated) showed differential expression in resilience compared to controls. Cellular resilience involved reorganization of protein folding and degradation pathways, with downregulation of Hsp90 and selective upregulation of Hsp40, Hsp70, and Hsp110 families in excitatory neurons. Excitatory neuronal subpopulations in the entorhinal cortex (ATP8B1+ and MEF2Chigh) exhibited unique resilience signaling through neurotrophin (modulated by LINGO1) and angiopoietin (ANGPT2/TEK) pathways. We identified MEF2C, ATP8B1, and RELN as key markers of resilient excitatory neuronal populations, characterized by selective vulnerability in AD. Protective rare variant enrichment highlighted vulnerable populations, including somatostatin (SST) inhibitory interneurons, validated through immunofluorescence showing co-expression of rare variant associated RBFOX1 and KIF26B in SST+ neurons in the dorsolateral prefrontal cortex. The maintenance of excitatory-inhibitory balance emerges as a key characteristic of resilience. We identified molecular and cellular hallmarks of cognitive resilience, an intermediate state in the AD continuum. Resilience mechanisms include preservation of neuronal function, maintenance of excitatory/inhibitory balance, and activation of protective signaling pathways. Specific excitatory neuronal populations appear to play a central role in mediating cognitive resilience, while a subset of vulnerable SST interneurons likely provide compensation against AD-associated dysregulation. This study offers a framework to leverage natural protective mechanisms to mitigate neurodegeneration and preserve cognition in AD.

Mechanisms for dysregulation of excitatory-inhibitory balance underlying allodynia in dorsal horn neural subcircuits.

Chronic pain is a wide-spread condition that is debilitating and expensive to manage, costing the United States alone around $600 billion in 2010. In a common symptom of chronic pain called allodynia, non-painful stimuli produce painful responses with highly variable presentations across individuals. While the specific mechanisms remain unclear, allodynia is hypothesized to be caused by the dysregulation of excitatory-inhibitory (E-I) balance in pain-processing neural circuitry in the dorsal horn of the spinal cord. In this work, we analyze biophysically-motivated subcircuit structures that represent common motifs in neural circuits in laminae I-II of the dorsal horn. These circuits are hypothesized to be part of the neural pathways that mediate two different types of allodynia: static and dynamic. We use neural firing rate models to describe the activity of populations of excitatory and inhibitory interneurons within each subcircuit. By accounting for experimentally-observed responses under healthy conditions, we specify model parameters defining populations of subcircuits that yield typical behavior under normal conditions. Then, we implement a sensitivity analysis approach to identify the mechanisms most likely to cause allodynia-producing dysregulation of the subcircuit's E-I signaling. We find that disruption of E-I balance generally occurs either due to downregulation of inhibitory signaling so that excitatory neurons are "released" from inhibitory control, or due to upregulation of excitatory neuron responses so that excitatory neurons "escape" their inhibitory control. Which of these mechanisms is most likely to occur, the subcircuit components involved in the mechanism, and the proportion of subcircuits exhibiting the mechanism can vary depending on the subcircuit structure. These results suggest specific hypotheses about diverse mechanisms that may be most likely responsible for allodynia, thus offering predictions for the high interindividual variability observed in allodynia and identifying targets for further experimental studies on the underlying mechanisms of this chronic pain symptom.

Spike frequency adaptation in primate lateral prefrontal cortex neurons results from interplay between intrinsic properties and circuit dynamics.

Cortical neurons in brain slices display intrinsic spike frequency adaptation (I-SFA) to constant current inputs, while extracellular recordings show extrinsic SFA (E-SFA) during sustained visual stimulation. Inferring how I-SFA contributes to E-SFA during behavior is challenging due to the isolated nature of slice recordings. To address this, we recorded macaque lateral prefrontal cortex (LPFC) neurons invivo during a visually guided saccade task and invitro in brain slices. Broad-spiking (BS) putative pyramidal cells and narrow-spiking (NS) putative inhibitory interneurons exhibit both E-SFA and I-SFA. Developing a data-driven hybrid circuit model comprising NS model neurons receiving BS input reveals that NS model neurons exhibit longer SFA than observed invivo; however, adding feedforward inhibition corrects this in a manner dependent on I-SFA. Identification of this circuit motif shaping E-SFA in LPFC highlights the roles of both intrinsic and network mechanisms in neural activity underlying behavior.

Capacitance Measurements of Exocytosis From AII Amacrine Cells in Retinal Slices.

During neuronal synaptic transmission, theexocytotic release of neurotransmitters from synaptic vesicles in the presynaptic neuron evokes a change in conductance for one or more types of ligand-gated ion channels in the postsynaptic neuron. The standard method of investigation uses electrophysiological recordings of the postsynaptic response. However, electrophysiological recordings can directly quantify the presynaptic release of neurotransmitters with high temporal resolution by measuring the membrane capacitance before and after exocytosis, as fusion of the membrane of presynaptic vesicles with the plasma membrane increases the total capacitance. While the standard technique for capacitance measurement assumes that the presynaptic cell is unbranched and can be represented as a simple resistance-capacitance (RC) circuit, neuronal exocytosis typically occurs at a distance from the soma. Even in such cases, however, it can be possible to detect a depolarization-evoked increase in capacitance. Here, we provide a detailed, step-by-step protocol that describes how "Sine + DC" (direct current) capacitance measurements can quantify the exocytotic release of neurotransmitters from AII amacrine cells in rat retinal slices. The AII is an important inhibitory interneuron of the mammalian retina that plays an important role in integrating rod and cone pathway signals. AII amacrines release glycine from their presynaptic dendrites, and capacitance measurements have been important for understanding the release properties of these dendrites. When the goal is to directly quantify the presynaptic release, there is currently no other competing method available. This protocol includes procedures for measuring depolarization-evoked exocytosis, using both standard square-wave pulses, arbitrary stimulus waveforms, and synaptic input. Key features • Quantification of exocytosis with the Sine + DC technique for visually targeted AII amacrines in retinal slices, using voltage-clamp and whole-cell patch-clamp recording. • Because exocytosis occurs away from the somatic recording electrode, the sine wave frequency must be lower than for the standard Sine + DC technique. • Because AII amacrines are electrically coupled, the sine wave frequency must be sufficiently high to avoid interference from other cells in the electrically coupled network. • The protocol includes procedures for measuring depolarization-evoked exocytosis using standard square-wave pulses, stimulation with arbitrary and prerecorded stimulus waveforms, and activation of synaptic inputs.

Inhibition of prefrontal cortex parvalbumin interneurons mitigates behavioral and physiological sequelae of chronic stress in male mice

Chronic stress leads to hypofunction of the medial prefrontal cortex (mPFC), mechanisms of which remain to be determined. Enhanced activation of GABAergic of parvalbumin (PV) expressing interneurons (INs) is thought to play a role in stress-induced prefrontal inhibition. In this study, we tested whether chemogenetic inhibition of mPFC PV INs after chronic stress can rescue chronic stress-related behavioral and physiological phenotypes. Mice underwent 2 weeks of chronic variable stress (CVS) followed by a battery of behavioral tests known to be affected by chronic stress exposure, e.g. an open field (OF), novel object recognition (NOR), tail suspension test (TST), sucrose preference test (SPT), and light dark (LD) box. Inhibitory DREADDs were actuated by 3 mg/kg CNO administered 30 min prior to each behavioral test. CVS caused hyperactivity in the OF, reduced sucrose preference in the SPT (indicative of enhanced anhedonia), and increased anxiety-like behavior in the LD box. Inhibition of PV IN after stress mitigated these effects. In addition, CVS also resulted in reduced thymus weight and body weight loss, which were also mitigated by PV IN inhibition. Our results indicate that chronic stress leads to plastic changes in PV INs that may be mitigated by chemogenetic inhibition. Our findings implicate cortical GABAergic INs as a therapeutic target in stress-related diseases.

Molecular and cellular targets of GABAergic anesthetics in the mesopontine tegmentum that enable pain-free surgery.

The mesopontine tegmental anesthesia area (MPTA) is a focal brainstem locus which, when exposed to GABAergic agents, induces brain-state transitioning from wakefulness to unconsciousness. Correspondingly, MPTA lesions render animals relatively insensitive to GABAergic anesthetics delivered systemically. Using chemogenetics, we recently identified a neuronal subpopulation within the MPTA whose excitation induces this same pro-anesthetic effect. However, very few of these "effector-neurons" express synaptic γ2-containing GABAA receptor isoforms and none express extrasynaptic δ-subunit containing receptors, suggesting that they are not the direct cellular target of GABAergic agents. Here we used pharmacological tools in rats to define the molecular target(s) of GABAergics in the MPTA. GABA microinjected into the MPTA at nanomolar concentrations, selective for GABAAδ-Rs, proved to be pro-anesthetic as was blocking GABA reuptake. Likewise, low-concentration gaboxadol/THIP, also selective for GABAAδ-Rs, was effective, whereas benzodiazepines and zolpidem, which selectively target GABAAγ2-Rs, were not. The GABAergic anesthetics pentobarbital and propofol proved pro-anesthetic when applied to the MPTA at the low concentrations present in the brain after systemic dosing. Glycinergic agonists which are inhibitory, but infective on GABAAδ-Rs, and other non-GABAergic agonists tested, were at most only marginally effective. We conclude that GABAAδ-Rs are the primary molecular target of GABAergic anesthetics in the MPTA. Immunolabeling revealed that this GABAA-R isoform is expressed exclusively by a distinct subpopulation of MPTA "δ-cells" that reside in close apposition to effector neurons. This suggests that during wakefulness, δ-cells serve as inhibitory interneurons which, when silenced by GABAergic agents, disinhibit (excite) the effector-neurons, triggering transition to unconsciousness.

GlyT2-positive interneurons regulate timing and variability of information transfer in a cerebellar-behavioural loop.

GlyT2-positive interneurons, Golgi and Lugaro cells, reside in the input layer of the cerebellar cortex in a key position to influence information processing. Here, we examine the contribution of GlyT2-positive interneurons to network dynamics in Crus 1 of mouse lateral cerebellar cortex during free whisking. We recorded neuronal population activity using NeuroPixels probes before and after chemogenetic downregulation of GlyT2-positive interneurons in male and female mice. Under resting conditions, cerebellar population activity reliably encoded whisker movements. Reductions in the activity of GlyT2-positive cells produced mild increases in neural activity which did not significantly impair these sensorimotor representations. However, reduced Golgi and Lugaro cell inhibition did increase the temporal alignment of local population network activity at the initiation of movement. These network alterations had variable impacts on behaviour, producing both increases and decreases in whisking velocity. Our results suggest that inhibition mediated by GlyT2-positive interneurons primarily governs the temporal patterning of population activity, which in turn is required to support downstream cerebellar dynamics and behavioural coordination.Significance statement The cerebellum has a simple and conserved structure which has tantalised neurobiologists wishing to understand its function. Here we look at the role of granule cell layer inhibitory interneurons, Golgi and Lugaro cells, in the cerebellar cortex. We selectively turned down the activity of these cells in the awake cerebellum to characterise their influence on network activity and behaviour. We show that downregulation of Golgi and Lugaro cells has very little influence on sensorimotor representations in the cerebellum (i.e., what is represented), but instead modulates the timing of cortical population activity (i.e., when information is represented). Our results indicate that inhibitory interneurons in the granule cell layer are necessary to appropriately pace changes in cerebellar activity to match ongoing behaviour.

Imaging distinct neuronal populations with a dual channel miniscope

Miniature fluorescence microscopes (miniscopes) are one of the most powerful and versatile tools for recording large scale neural activity in freely moving rodents with single cell resolution. Recent advances in the design of genetically encoded calcium indicators (GECIs) allow to target distinct neuronal populations with non-overlapping emission spectral profiles. However, conventional miniscopes are limited to a single excitation, single focal plane imaging, which does not allow to compensate for chromatic aberration and image from two spectrally distinct calcium indicators. In this paper we present an open-source dual channel miniscope capable of simultaneous imaging of genetically or functionally distinct neuronal populations. Chromatic aberrations are corrected using an electrowetting lens (EWL), which allows fast focal plane change between frames. To demonstrate the capabilities of the dual channel miniscope, we labeled layer specific excitatory neurons or inhibitory interneurons in the medial prefrontal cortex (mPFC) with a red fluorescence protein, and simultaneously imaged neural activity of distinct neuronal populations of freely moving mice via a green GECI.

Cortical dynamics in hand/forelimb S1 and M1 evoked by brief photostimulation of the mouse's hand.

Spiking activity along synaptic circuits linking primary somatosensory (S1) and motor (M1) areas is fundamental for sensorimotor integration in cortex. Circuits along the ascending somatosensory pathway through mouse hand/forelimb S1 and M1 were recently described in detail (Yamawaki et al., 2021). Here, we characterize the peripherally evoked spiking dynamics in these two cortical areas in the same system. Brief (5 ms) optogenetic photostimulation of the hand generated short (~25 ms) barrages of activity first in S1 (onset latency 15 ms) then M1 (10 ms later). The estimated propagation speed was 20-fold faster from hand to S1 than from S1 to M1. Response amplitudes in M1 were strongly attenuated to approximately a third of those in S1. Responses were typically triphasic, with suppression and rebound following the initial peak. Parvalbumin (PV) inhibitory interneurons were involved in each phase, accounting for three-quarters of the initial spikes generated in S1, and their selective photostimulation sufficed to evoke suppression and rebound in both S1 and M1. Partial silencing of S1 by PV activation during hand stimulation reduced the M1 sensory responses. These results provide quantitative measures of spiking dynamics of cortical activity along the hand/forelimb-related transcortical loop; demonstrate a prominent and mechanistic role for PV neurons in each phase of the response; and, support a conceptual model in which somatosensory signals reach S1 via high-speed subcortical circuits to generate characteristic barrages of cortical activity, then reach M1 via densely polysynaptic corticocortical circuits to generate a similar but delayed and attenuated profile of activity.

Differential behavioral engagement of inhibitory interneuron subtypes in the zebra finch brain.

Inhibitory interneurons are highly heterogeneous circuit elements often characterized by cell biological properties, but how these factors relate to specific roles underlying complex behavior remains poorly understood. Using chronic silicon probe recordings, we demonstrate that distinct interneuron groups perform different inhibitory roles within HVC, a song production circuit in the zebra finch forebrain. To link these functional subtypes to molecular identity, we performed two-photon targeted electrophysiological recordings of HVC interneurons followed by post hoc immunohistochemistry of subtype-specific markers. We find that parvalbumin-expressing interneurons are highly modulated by sensory input and likely mediate auditory gating, whereas a more heterogeneous set of somatostatin-expressing interneurons can strongly regulate activity based on arousal. Using this strategy, we uncover important cell-type-specific network functions in the context of an ethologically relevant motor skill.

Social and nonsocial environmental loss have differential effects on ventral hippocampus-dependent behavior and inhibitory synaptic markers in adult male mice.

In humans, psychological loss, whether social or nonsocial, can lead to clinical depression, anxiety disorders, and social memory impairments. Researchers have modeled combined social and nonsocial loss in rodents by transitioning them from social, enriched environments (EE) to individual housing, affecting behaviors related to avoidance, stress coping, and cognitive function. However, it remains unclear if these effects are driven by social or nonsocial loss. We examined the effects of nonsocial loss by housing adult male mice in EE before moving them to standard cages, where they were pair-housed, and compared this to mice experiencing complete social loss. Continuous EE reduced social investigation time while leaving social memory intact, also decreasing avoidance behavior. Nonsocial loss restored social investigation and avoidance behavior to control levels, while social loss impaired social memory and increased avoidance. In rodents, social memory and avoidance require ventral hippocampus (vHIP) neuronal oscillations, which involve parvalbumin-positive (PV+) inhibitory interneurons. We found decreased vHIP PV intensity in the social loss group, with no differences in the nonsocial loss group. Most PV+ cells are surrounded by perineuronal nets (PNNs) concentrating GABAA receptors in their lattice-like holes. Social loss decreased GABAA-δ expression, a subunit associated with extrasynaptic receptors, across PNN+ soma and in PNN holes, while nonsocial loss reduced gephyrin in these regions. These findings suggest social and nonsocial losses differentially affect vHIP function and behavior, with social loss having a more pronounced impact through mechanisms involving PV+ interneurons, PNN structure, and neurotransmitter receptor expression.

Therapeutic dose prediction of α5-GABA receptor modulation from simulated EEG of depression severity.

Treatment for major depressive disorder (depression) often has partial efficacy and a large portion of patients are treatment resistant. Recent studies implicate reduced somatostatin (SST) interneuron inhibition in depression, and new pharmacology boosting this inhibition via positive allosteric modulators of α5-GABAA receptors (α5-PAM) offers a promising effective treatment. However, testing the effect of α5-PAM on human brain activity is limited, meriting the use of detailed simulations. We utilized our previous detailed computational models of human depression microcircuits with reduced SST interneuron inhibition and α5-PAM effects, to simulate EEG of individual microcircuits across depression severity and α5-PAM doses. We developed machine learning models that predicted optimal dose from EEG with high accuracy and recovered microcircuit activity and EEG. This study provides dose prediction models for α5-PAM administration based on EEG biomarkers of depression severity. Given limitations in doing the above in the living human brain, the results and tools we developed will facilitate translation of α5-PAM treatment to clinical use.

Prenatal THC exposure drives sex-specific alterations in spatial memory and hippocampal excitatory/inhibitory balance in adolescent rats

The interaction between the main psychotropic ingredient of Cannabis, Δ⁹- tetrahydrocannabinol (THC), with the endogenous cannabinoid system (ECS) is a critical and underrated issue that deserves utmost attention. The ECS, indeed, contributes to the formation and regulation of excitatory and inhibitory (E/I) neuronal networks that in the hippocampus underly spatial memory. This study explored sex-specific consequences of prenatal exposure to THC in hippocampus-dependent memory and the underlying cellular and molecular contributors of synaptic plasticity and E/I homeostasis. Sprague Dawley dams were exposed to THC (2 mg/kg) or vehicle, from gestational day 5–20. The adolescent progeny of both sexes was tested for: spatial memory retrieval and flexibility in the Barnes Maze; mRNA expression of relevant players of hippocampal synaptic plasticity; density of cholecystokinin-positive basket cells (CCK+BCs) – a major subtype of hippocampal inhibitory interneurons; mRNA expression of the excitatory and inhibitory synaptic proteins neuroligins (Nlgns), as a proxy of synaptic efficiency. Our results show a sex-specific disruption in spatial memory retrieval and flexibility, a male-specific decrease in CCK+BCs density and increase in the expression of markers of neuroplasticity, and consistent changes in the expression of Nlgn-1 and 3 isoforms. Despite a delay in memory retrieval, flexibility of memory was spared in prenatally-THC-exposed female offspring as well as most of the markers of neuroplasticity; a sex-specific increase in CCK+BCs density, and a consistent expression of Nlgn-3 was observed. The current results highlight a major vulnerability to prenatal exposure to THC on memory processing in the male progeny, and sex-specific alterations in the E/I balance and synaptic plasticity.

Postsynaptic dopamine D3 receptors selectively modulate μ-opioid receptor-expressing GABAergic inputs onto CA1 pyramidal cells in the rat ventral hippocampus.

Although the actions of dopamine throughout the brain are clearly linked to motivation and cognition, the specific role(s) of dopamine in the CA1 subfield of the ventral hippocampus (vH) is unresolved. Prior preclinical studies suggest that dopamine D3 receptors (D3Rs) expressed on CA1 pyramidal cells exhibit a unique capacity to modulate mechanisms of long-term synaptic plasticity, but less is known about how interneuronal inputs modulate these cells. We hypothesized that inputs from μ-opioid receptor (MOR)-expressing inhibitory interneurons selectively modulate the activity of postsynaptic D3Rs expressed on CA1 principal cells to shape neurotransmission in the rat vH. We used the whole cell voltage-clamp technique to test this hypothesis by measuring evoked inhibitory postsynaptic currents (eIPSCs) from CA1 principal cells in vH slices or GABAA currents from acutely dissociated vH neurons. The eIPSC response recorded from CA1 neurons in vH slices was inhibited by either the MOR agonist DAMGO or the D3R agonist PD128907, but pretreatment with DAMGO occluded any further inhibition by PD128907. GABAA currents measured in acutely dissociated vH CA1 neurons were inhibited by D3R activation via PD128907, consistent with postsynaptic localization of D3 receptors. Kinetic alterations induced by the neuromodulatory agonists are consistent with selective targeting of postsynaptic D3Rs expressed on CA1 principal cells by MOR-expressing GABAergic inputs. Our findings suggest that postsynaptic D3R-mediated modulation of MOR-expressing GABAergic inputs is a site at which dopaminergic and opioidergic activity may contribute to disinhibition of vH excitatory neurotransmission and, thus, influence critical physiological processes such as synaptic plasticity and network oscillations.NEW & NOTEWORTHY We report that the activity of an inhibitory synapse on CA1 pyramidal cells in the rat ventral hippocampus is shaped by heterogeneous neuromodulators. Specifically, postsynaptic dopamine D3 receptors on ventral hippocampal CA1 pyramidal neurons are selectively targeted by an inhibitory input from µ-opioid receptor-expressing GABAergic terminals.

Spinal V1 inhibitory interneuron clades differ in birthdate, projections to motoneurons, and heterogeneity.

Spinal cord interneurons play critical roles shaping motor output, but their precise identity and connectivity remain unclear. Focusing on the V1 interneuron cardinal class we defined four major V1 subsets in the mouse according to neurogenesis, genetic lineage-tracing, synaptic output to motoneurons, and synaptic inputs from muscle afferents. Sequential neurogenesis delineates different V1 subsets: two early born (Renshaw and Pou6f2) and two late born (Foxp2 and Sp8). Early born Renshaw cells and late born Foxp2-V1 interneurons are tightly coupled to motoneurons, while early born Pou6f2-V1 and late born Sp8-V1 interneurons are not, indicating that timing of neurogenesis does not correlate with motoneuron targeting. V1 clades also differ in cell numbers and diversity. Lineage labeling shows that the Foxp2-V1 clade contains over half of all V1 interneurons, provides the largest inhibitory input to motoneuron cell bodies, and includes subgroups that differ in birthdate, location, and proprioceptive input. Notably, one Foxp2-V1 subgroup, defined by postnatal Otp expression, is positioned near the LMC and receives substantial input from proprioceptors, consistent with an involvement in reciprocal inhibitory pathways. Combined tracing of ankle flexor sensory afferents and interneurons monosynaptically connected to ankle extensors confirmed placement of Foxp2-V1 interneurons in reciprocal inhibitory pathways. Our results validate previously proposed V1 clades as unique functional subtypes that differ in circuit placement, with Foxp2-V1 cells forming the most heterogeneous subgroup. We discuss how V1 organizational diversity enables understanding of their roles in motor control, with implications for their diverse ontogenetic and phylogenetic origins.

Spinal V1 inhibitory interneuron clades differ in birthdate, projections to motoneurons, and heterogeneity

Spinal V1 inhibitory interneuron clades differ in birthdate, projections to motoneurons, and heterogeneity

Elevated vesicular Zn2+ in dorsal root ganglion neurons expressing the transporter TMEM163 causes age-associated itchy skin in mice.

The prevalent itching condition associated with aging, historically referred to as senile pruritus, diminishes quality of life. Despite its impact, effective treatments remain elusive, largely due to an incomplete understanding of its pathological cause. In this study, we reveal a subset of dorsal root ganglion neurons enriched with Zn2+ that express the vesicular Zn2+ transporter TMEM163. These neurons form direct synapses with and modulate the activity of spinal NPY+ inhibitory interneurons. In aged mice, both the expression of TMEM163 and the concentration of vesicular Zn2+ within the central terminals of TMEM163+ primary afferents show marked elevation. Importantly, the excessive release of vesicular Zn2+ significantly dampens the activity of NPY+ neurons, triggering the disinhibition of itch-transmitting neural circuits and resulting in chronic itch. Intriguingly, chelating Zn2+ within the spinal dorsal horn effectively relieves itch in aged mice. Our study thus unveils a novel molecular mechanism underlying senile pruritus.

Hypoxia increases intracellular calcium in glutamate-activated horizontal cells of goldfish retina via mitochondrial KATP channels and intracellular stores

Central neurons of the common goldfish (Carassius auratus) are exceptional in their capacity to survive Ca2+-induced excitotoxicity and cell death during hypoxia. Horizontal cells (HCs) are inhibitory interneurons of the retina that are tonically depolarized by the neurotransmitter, glutamate, yet preserve intracellular Ca2+ homeostasis. In HCs isolated from goldfish, and in the absence of glutamatergic input, intracellular Ca2+ concentration ([Ca2+]i) is protected from prolonged exposure to hypoxia by mitochondrial ATP-dependent K+ (mKATP) channel activity. In the present study, we investigated the effects of hypoxia upon [Ca2+]i in isolated HCs during tonic activation by glutamate to better predict the effects of hypoxia in the active retina. Dynamic changes in [Ca2+]i were measured using the ratiometric Ca2+ indicator, Fura-2. Application of 100 μM glutamate during hypoxia (PO2 = 25 mmHg) produced a 1.3-fold greater rise in [Ca2+]i compared to the same glutamate stimulus during normoxia. The hypoxia-dependent increase in [Ca2+]i was abolished by application of 5-hydroxydecanoic acid, which renders mKATP channels inactive. Extracellular Ca2+ did not contribute to the elevated [Ca2+]i observed during hypoxia, as the effect persisted in Ca2+-free solution and during application of verapamil, an L-type Ca2+ channel blocker. By contrast, inhibition of the mitochondrial Ca2+ uniporter or ryanodine receptors (with ruthenium red or ryanodine, respectively) abolished the hypoxia-dependent rise in [Ca2+]i. This study reports an mKATP-dependent rise in [Ca2+]i during hypoxia in HCs activated by glutamate, and suggests roles for the mitochondria and intracellular Ca2+ stores in regulating this mechanism.