Frequency Of Postsynaptic Currents Research Articles

Ca2+ binding to synapsin I regulates resting Ca2+ and recovery from synaptic depression in nerve terminals

Synapsin I (SynI) is a synaptic vesicle (SV)-associated phosphoprotein that modulates neurotransmission by controlling SV trafficking. The SynI C-domain contains a highly conserved ATP binding site mediating SynI oligomerization and SV clustering and an adjacent main Ca2+ binding site, whose physiological role is unexplored. Molecular dynamics simulations revealed that the E373K point mutation irreversibly deletes Ca2+ binding to SynI, still allowing ATP binding, but inducing a destabilization of the SynI oligomerization interface. Here, we analyzed the effects of this mutation on neurotransmitter release and short-term plasticity in excitatory and inhibitory synapses from primary hippocampal neurons. Patch-clamp recordings showed an increase in the frequency of miniature excitatory postsynaptic currents (EPSCs) that was totally occluded by exogenous Ca2+ chelators and associated with a constitutive increase in resting terminal Ca2+ concentrations. Evoked EPSC amplitude was also reduced, due to a decreased readily releasable pool (RRP) size. Moreover, in both excitatory and inhibitory synapses, we observed a marked impaired recovery from synaptic depression, associated with impaired RRP refilling and depletion of the recycling pool of SVs. Our study identifies SynI as a novel Ca2+ buffer in excitatory terminals. Blocking Ca2+ binding to SynI results in higher constitutive Ca2+ levels that increase the probability of spontaneous release and disperse SVs. This causes a decreased size of the RRP and an impaired recovery from depression due to the failure of SV reclustering after sustained high-frequency stimulation. The results indicate a physiological role of Ca2+ binding to SynI in the regulation of SV clustering and trafficking in nerve terminals.

Restraint Stress and Repeated Corticosterone Administration Differentially Affect Neuronal Excitability, Synaptic Transmission and 5-HT7 Receptor Reactivity in the Dorsal Raphe Nucleus of Young Adult Male Rats.

Exogenous corticosterone administration reduces GABAergic transmission and impairs its 5-HT7 receptor-dependent modulation in the rat dorsal raphe nucleus (DRN), but it is largely unknown how neuronal functions of the DRN are affected by repeated physical and psychological stress. This study compared the effects of repeated restraint stress and corticosterone injections on DRN neuronal excitability, spontaneous synaptic transmission, and its 5-HT7 receptor-dependent modulation. Male Wistar rats received corticosterone injections for 7 or 14 days or were restrained for 10 min twice daily for 3 days. Repeated restraint stress and repeated corticosterone administration evoked similar changes in performance in the forced swim test. They increased the frequency of spontaneous excitatory postsynaptic currents (sEPSCs) recorded from DRN neurons. In contrast to the treatment with corticosterone, restraint stress-induced changes in sEPSC kinetics and decreased intrinsic excitability of DRN neurons did not modify inhibitory transmission. Repeated injections of the 5-HT7 receptor antagonist SB 269970 ameliorated the effects of restraint on excitability and sEPSC frequency but did not restore the altered kinetics of sEPSCs. Thus, repeated restraint stress and repeated corticosterone administration differ in consequences for the intrinsic excitability of DRN projection neurons and their excitatory and inhibitory synaptic inputs. Effects of repeated restraint stress on DRN neurons can be partially abrogated by blocking the 5-HT7 receptor.

Differential Levels of Tryptophan-Kynurenine Pathway Metabolites in the Hippocampus, Anterior Temporal Lobe, and Neocortex in an Animal Model of Temporal Lobe Epilepsy.

Glutamate-receptor-mediated hyperexcitability contributes to seizure generation in temporal lobe epilepsy (TLE). Tryptophan-kynurenine pathway (TKP) metabolites regulate glutamate receptor activity under physiological conditions. This study was designed to investigate alterations in the levels of TKP metabolites and the differential regulation of glutamatergic activity by TKP metabolites in the hippocampus, anterior temporal lobe (ATL), and neocortex samples of a lithium-pilocarpine rat model of TLE. We observed that levels of tryptophan were reduced in the hippocampus and ATL samples but unaltered in the neocortex samples. The levels of kynurenic acid were reduced in the hippocampus samples and unaltered in the ATL and neocortex samples of the TLE rats. The levels of kynurenine were unaltered in all three regions of the TLE rats. The magnitude of reduction in these metabolites in all regions was unaltered in the TLE rats. The frequency and amplitude of spontaneous excitatory postsynaptic currents were enhanced in hippocampus ATL samples but not in the neocortex samples of the TLE rats. The exogenous application of kynurenic acid inhibited glutamatergic activity in the slice preparations of all these regions in both the control and the TLE rats. However, the magnitude of reduction in the frequency of kynurenic acid was higher in the hippocampus (18.44 ± 2.6% in control vs. 30.02 ± 1.5 in TLE rats) and ATL (16.31 ± 0.91% in control vs. 29.82 ± 3.08% in TLE rats) samples of the TLE rats. These findings suggest the differential regulation of glutamatergic activity by TKP metabolites in the hippocampus, ATL, and neocortex of TLE rats.

Chronic, episodic nicotine exposure alters GABAergic synaptic transmission to hypoglossal motor neurons and genioglossus muscle function at a critical developmental age.

Regulation of GABAergic signaling through nicotinic acetylcholine receptor (nAChR) activation is critical for neuronal development. Here, we test the hypothesis that chronic episodic developmental nicotine exposure (eDNE) disrupts GABAergic signaling, leading to dysfunction of hypoglossal motor neurons (XIIMNs), which innervate the tongue muscles. We studied control and eDNE pups at two developmentally vulnerable age ranges: postnatal days (P)1-5 and P10-12. The amplitude and frequency of spontaneous and miniature inhibitory postsynaptic currents (sIPSCs, mIPSCs) at baseline were not altered by eDNE at either age. In contrast, eDNE increased GABAAR-α1 receptor expression on XIIMNs and, in the older group, the postsynaptic response to muscimol (GABAA receptor agonist). Activation of nAChRs with exogenous nicotine increased the frequency of GABAergic sIPSCs in control and eDNE neurons at P1-5. By P10-12, acute nicotine increased sIPSC frequency in eDNE but not control neurons. In vivo experiments showed that the breathing-related activation of tongue muscles, which are innervated by XIIMNs, is reduced at P10-12. This effect was partially mitigated by subcutaneous muscimol, but only in the eDNE pups. Taken together, these data indicate that eDNE alters GABAergic transmission to XIIMNs at a critical developmental age, and this is expressed as reduced breathing-related drive to XIIMNs in vivo.NEW & NOTEWORTHY Here, we provide a thorough assessment of the effects of nicotine exposure on GABAergic synaptic transmission, from the cellular to the systems level. This work makes significant advances in our understanding of the impact of nicotine exposure during development on GABAergic neurotransmission within the respiratory network and the potential role this plays in the excitatory/inhibitory imbalance that is thought to be an important mechanism underlying neonatal breathing disorders, including sudden infant death syndrome.

Sex differences in the medial prefrontal cortical glutamate system

BackgroundDysregulation in the prefrontal cortex underlies a variety of psychiatric illnesses, including substance use disorder, depression, and anxiety. Despite the established sex differences in prevalence and presentation of these illnesses, the neural mechanisms driving these differences are largely unexplored. Here, we investigate potential sex differences in glutamatergic transmission within the medial prefrontal cortex (mPFC). The goal of these experiments was to determine if there are baseline sex differences in transmission within this region that may underlie sex differences in diseases that involve dysregulation in the prefrontal cortex.MethodsAdult male and female C57Bl/6J mice were used for all experiments. Mice were killed and bilateral tissue samples were taken from the medial prefrontal cortex for western blotting. Both synaptosomal and total GluA1 and GluA2 levels were measured. In a second set of experiments, mice were killed and ex vivo slice electrophysiology was performed on prepared tissue from the medial prefrontal cortex. Spontaneous excitatory postsynaptic currents and rectification indices were measured.ResultsFemales exhibit higher levels of synaptosomal GluA1 and GluA2 in the mPFC compared to males. Despite similar trends, no statistically significant differences are seen in total levels of GluA1 and GluA2. Females also exhibit both a higher amplitude and higher frequency of spontaneous excitatory postsynaptic currents and greater inward rectification in the mPFC compared to males.ConclusionsOverall, we conclude that there are sex differences in glutamatergic transmission in the mPFC. Our data suggest that females have higher levels of glutamatergic transmission in this region. This provides evidence that the development of sex-specific pharmacotherapies for various psychiatric diseases is important to create more effective treatments.

Glycolysis regulates neuronal excitability via lactate receptor, HCA1R.

Repetitively firing neurons during seizures accelerate glycolysis to meet energy demand, which leads to the accumulation of extracellular glycolytic by-product lactate. Here, we demonstrate that lactate rapidly modulates neuronal excitability in times of metabolic stress via the hydroxycarboxylic acid receptor type 1 (HCA1R) to modify seizure activity. The extracellular lactate concentration, measured by a biosensor, rose quickly during brief and prolonged seizures. In two epilepsy models, mice lacking HCA1R (lactate receptor) were more susceptible to developing seizures. Moreover, HCA1R deficient (knockout) mice developed longer and more severe seizures than wild-type littermates. Lactate perfusion decreased tonic and phasic activity of CA1 pyramidal neurons in genetically encoded calcium indicator 7 imaging experiments. HCA1R agonist 3-chloro-5-hydroxybenzoic acid (3CL-HBA) reduced the activity of CA1 neurons in HCA1R WT but not in knockout mice. In patch-clamp recordings, both lactate and 3CL-HBA hyperpolarized CA1 pyramidal neurons. HCA1R activation reduced the spontaneous excitatory postsynaptic current frequency and altered the paired-pulse ratio of evoked excitatory postsynaptic currents in HCA1R wild-type but not in knockout mice, suggesting it diminished presynaptic release of excitatory neurotransmitters. Overall, our studies demonstrate that excessive neuronal activity accelerates glycolysis to generate lactate, which translocates to the extracellular space to slow neuronal firing and inhibit excitatory transmission via HCA1R. These studies may identify novel anticonvulsant target and seizure termination mechanisms.

Dissociable effects of oxycodone on behavior, calcium transient activity, and excitability of dorsolateral striatal neurons.

Opioids are the most common medications for moderate to severe pain. Unfortunately, they also have addictive properties that have precipitated opioid misuse and the opioid epidemic. In the present study, we examined the effects of acute administration of oxycodone, a μ-opioid receptor (MOR) agonist, on Ca2+ transient activity of medium-sized spiny neurons (MSNs) in freely moving animals. Ca2+ imaging of MSNs in dopamine D1-Cre mice (expressing Cre predominantly in the direct pathway) or adenosine A2A-Cre mice (expressing Cre predominantly in the indirect pathway) was obtained with the aid of miniaturized microscopes (Miniscopes) and a genetically encoded Cre-dependent Ca2+ indicator (GCaMP6f). Systemic injections of oxycodone (3 mg/kg) increased locomotor activity yet, paradoxically, reduced concomitantly the number of active MSNs. The frequency of Ca2+ transients was significantly reduced in MSNs from A2A-Cre mice but not in those from D1-Cre mice. For comparative purposes, a separate group of mice was injected with a non-Cre dependent Ca2+ indicator in the cerebral cortex and the effects of the opioid also were tested. In contrast to MSNs, the frequency of Ca2+ transients in cortical pyramidal neurons was significantly increased by oxycodone administration. Additional electrophysiological studies in brain slices confirmed generalized inhibitory effects of oxycodone on MSNs, including membrane hyperpolarization, reduced excitability, and decreased frequency of spontaneous excitatory and inhibitory postsynaptic currents. These results demonstrate a dissociation between locomotion and striatal MSN activity after acute administration of oxycodone.

α2δ-1 protein drives opioid-induced conditioned reward and synaptic NMDA receptor hyperactivity in the nucleus accumbens.

Glutamate NMDA receptors (NMDARs) in the nucleus accumbens (NAc) are critically involved in drug dependence and reward. α2δ-1 is a newly discovered NMDAR-interacting protein that promotes synaptic trafficking of NMDARs independently of its conventional role as a calcium channel subunit. However, it remains unclear how repeated opioid exposure affects synaptic NMDAR activity and α2δ-1-NMDAR interaction in the NAc. In this study, whole-cell patch-clamp recordings showed that repeated treatment with morphine in mice markedly increased the NMDAR-mediated frequency of miniature excitatory postsynaptic currents (mEPSCs) and amplitude of puff NMDAR currents in medium spiny neurons in the NAc core region. Morphine treatment significantly increased the physical interaction of α2δ-1 with GluN1 and their synaptic trafficking in the NAc. In Cacna2d1 knockout mice, repeated treatment with morphine failed to increase the frequency of mEPSCs and amplitude of puff NMDAR currents in the NAc core. Furthermore, inhibition of α2δ-1 with gabapentin or disruption of the α2δ-1-NMDAR interaction with the α2δ-1 C terminus-interfering peptide blocked the morphine-elevated frequency of mEPSCs and amplitude of puff NMDAR currents in the NAc core. Correspondingly, systemically administered gabapentin, Cacna2d1 ablation, or microinjection of the α2δ-1 C terminus-interfering peptide into the NAc core attenuated morphine-induced conditioned place preference and locomotor sensitization. Our study reveals that repeated opioid exposure strengthens presynaptic and postsynaptic NMDAR activity in the NAc via α2δ-1. The α2δ-1-bound NMDARs in the NAc have a key function in the rewarding effect of opioids and could be targeted for treating opioid use disorder and addiction.

WNK3 kinase maintains neuronal excitability by reducing inwardly rectifying K+ conductance in layer V pyramidal neurons of mouse medial prefrontal cortex.

The with-no-lysine (WNK) family of serine-threonine kinases and its downstream kinases of STE20/SPS1-related proline/alanine-rich kinase (SPAK) and oxidative stress-responsive kinase-1 (OSR1) may regulate intracellular Cl− homeostasis through phosphorylation of cation-Cl− co-transporters. WNK3 is expressed in fetal and postnatal brains, and its expression level increases during development. Its roles in neurons, however, remain uncertain. Using WNK3 knockout (KO) mice, we investigated the role of WNK3 in the regulation of the intracellular Cl− concentration ([Cl−]i) and the excitability of layer V pyramidal neurons in the medial prefrontal cortex (mPFC). Gramicidin-perforated patch-clamp recordings in neurons from acute slice preparation at the postnatal day 21 indicated a significantly depolarized reversal potential for GABAA receptor-mediated currents by 6 mV, corresponding to the higher [Cl−]i level by ~4 mM in KO mice than in wild-type littermates. However, phosphorylation levels of SPAK and OSR1 and those of neuronal Na+-K+-2Cl− co-transporter NKCC1 and K+-Cl− co-transporter KCC2 did not significantly differ between KO and wild-type mice. Meanwhile, the resting membrane potential of neurons was more hyperpolarized by 7 mV, and the minimum stimulus current necessary for firing induction was increased in KO mice. These were due to an increased inwardly rectifying K+ (IRK) conductance, mediated by classical inwardly rectifying (Kir) channels, in KO neurons. The introduction of an active form of WNK3 into the recording neurons reversed these changes. The potential role of KCC2 function in the observed changes of KO neurons was investigated by applying a selective KCC2 activator, CLP290. This reversed the enhanced IRK conductance in KO neurons, indicating that both WNK3 and KCC2 are intimately linked in the regulation of resting K+ conductance. Evaluation of synaptic properties revealed that the frequency of miniature excitatory postsynaptic currents (mEPSCs) was reduced, whereas that of inhibitory currents (mIPSCs) was slightly increased in KO neurons. Together, the impact of these developmental changes on the membrane and synaptic properties was manifested as behavioral deficits in pre-pulse inhibition, a measure of sensorimotor gating involving multiple brain regions including the mPFC, in KO mice. Thus, the basal function of WNK3 would be the maintenance and/or development of both intrinsic and synaptic excitabilities.

Early-life social stress induces permanent alterations in plasticity and perineuronal nets in the mouse anterior cingulate cortex.

Child maltreatment disrupts trajectories of brain development, but the underlying pathways are unclear. Stressful stimuli in early life interfere with maturation of local inhibitory circuitry and deposition of perineuronal nets (PNNs), specialized extracellular matrix structures involved in the closure of critical periods of development. Alterations in cortical PNN and parvalbumin (PV) following early-life stress (ELS) have been detected in human and animal studies. Aberrations in the anterior cingulate cortex (ACC) are the most consistent neuroimaging findings in maltreated people, but the molecular mechanisms linking ELS with ACC dysfunctions are unknown. Here, we employed a mouse model of early social threat to test whether ELS experienced in a sensitive period for ACC maturation could induce long-term aberrations of PNN and PV development in the ACC, with consequences on plasticity and ACC-dependent behavior. We found that ELS increased PNN but not PV expression in the ACC of young adult mice. This was associated with reduced frequency of inhibitory postsynaptic currents and long-term potentiation impairments and expression of intense object phobia. Our findings provide information on the long-term effects of ELS on ACC functionality and PNN formation and present evidence for a novel neurobiological pathway underlying the impact of early adversity on the brain.

Prenatal cyanuric acid exposure disrupts cognitive flexibility and mGluR1-mediated hippocampal long-term depression in male rats

Cyanuric acid is one of the most widely used classes of industrial chemicals and is now well known as food adulterant and contaminant in pet food and infant formula. Previously, it was reported that animals prenatally exposed to cyanuric acid showed neurotoxic effects that impaired memory consolidating and suppressed long-term potentiation (LTP) in the hippocampus. However, it is not clear if prenatal exposure to cyanuric acid induces deficits in reversal learning and long-term depression (LTD), which is required for the developmental reorganization of synaptic circuits and updating learned behaviors. Here, pregnant rats were i.p. injected with cyanuric acid (20 mg/kg) during the whole of gestation, and male offspring were selected to examine the levels of hippocampal mGluR1 and mGluR2/3 in young adulthood. The LTD at the Schaffer collateral-CA1 pathway was induced by low-frequency stimulation (LFS) and recorded. Reversal learning and hippocampus-dependent learning strategy were tested in Morris-water maze (MWM) and T-maze tasks, respectively. To further confirm the potential mechanism, selective agonists of mGluR1 and mGluR2/3 and antagonists of mGluR were intra-hippocampal infused before behavioral and neuronal recording. We found the levels of alkaline phosphatase were markedly increased in the maternal placenta and fetal brain following prenatal exposure. The expression of mGluR1 but not mGluR2/3 was significantly decreased and mGluR1-mediated LTD was selectively weakened. Prenatal cyanuric acid impaired reversal learning ability, without changing place learning strategy. The mGluR1 agonist could effectively enhance LFS-induced LTD and mitigate reversal learning deficits. Meanwhile, the reductions in the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPAR)-mediated spontaneous excitatory postsynaptic currents (sEPSCs) amplitude and frequency of cyanuric acid offspring were simultaneously alleviated by mGluR1 agonist infusions. Therefore, the results indicate the cognitive and synaptic impairments induced by prenatal cyanuric acid exposure are attributed to the disruption of the hippocampal mGluR1 signaling. Our findings provided the first evidence for the deteriorated effects of cyanuric acid on synaptic depression and advanced cognitive performance.

Combined alcohol and cannabinoid exposure leads to synergistic toxicity by affecting cerebellar Purkinje cells.

Combined use of cannabis and alcohol results in greater psychoactive toxicity than either substance alone, but the underlying central mechanisms behind this worsened outcome remain unclear. Here we show that the synergistic effect of Δ9-tetrahydrocannabinol (THC) and ethanol on motor incoordination in mice is achieved by activating presynaptic type 1 cannabinoid receptors (CB1R) and potentiating extrasynaptic glycine receptors (GlyR) within cerebellar Purkinje cells (PCs). The combination of ethanol and THC significantly reduces miniature excitatory postsynaptic current frequency in a CB1R-dependent manner, while increasing the extrasynaptic GlyR-mediated chronic chloride current, both leading to decreased PC activity. Ethanol enhances THC actions by boosting the blood-brain-barrier permeability of THC and enriching THC in the cell membrane. Di-desoxy-THC, a designed compound that specifically disrupts THC-GlyR interaction without affecting the basic functions of CB1R and GlyR, is able to restore PC function and motor coordination in mice. Our findings provide potential therapeutic strategies for overcoming the synergistic toxicity caused by combining cannabis and alcohol use.

Anti-stress Effect of Octopus Cephalotocin in Rats.

Cephalotocin is a bioactivity-regulating peptide expressed in octopus (Octopus vulgaris). The peptide sequence of cephalotocin is very similar to the peptide sequence of mammalian vasopressin, and cephalotocin has been proposed to mainly activate arginine vasopressin 1b receptor (Avpr1b) in the brain. However, the effects of cephalotocin on mammalian behavior have not been studied. In the current study, cephalotocin significantly reduced both the frequency and amplitude of spontaneous excitatory postsynaptic currents (sEPSCs) recorded from not only cultured neuronal cells from postnatal Sprague–Dawley (SD) rats but also hippocampal slices from 4-week-old male C57BL/6 mice. Intraperitoneal (IP) injection did not affect the open field behaviors of C57BL/6 mice. Cephalotocin was directly infused into the hippocampus because the normalized Avpr1b staining intensity divided by the DAPI staining intensity indicated that Avpr1b expression tended to be high in the hippocampus. A hippocampal infusion of 1 mg/kg cephalotocin via an implanted cannula exerted an anti-stress effect, significantly reducing the immobility time in the tail suspension test (TST). The present results provide evidence that the effects of cephalotocin on the activity of hippocampal neurons are related to ameliorating stress, suggesting that cephalotocin may be developed as an anti-stress biomodulator that functions by affecting the brain.

Role of 5-HT2A Receptor in Modulating Glutamatergic Activity in the Ventrolateral Orbital Cortex: Implication in Trigeminal Neuralgia

5-HT2A receptors (5-HT2ARs) are widely expressed in the central nervous system, including in the ventrolateral orbital cortex (VLO). The VLO is an important cortical component for pain processing. Brain 5-HT2ARs are implicated in both pro- and anti- nociceptive functions. However, the roles of 5-HT2ARs in the VLO in trigeminal neuralgia and neuronal synaptic function remain to be understood. We used chronic constriction injury of infraorbital nerve (IoN-CCI) model and shRNA mediated gene knockdown in mice to investigate the role of 5-HT2ARs in the VLO in trigeminal neuralgia. We found that knockdown of 5-HT2ARs in the VLO aggravated spontaneous pain and mechanical allodynia in mice after IoN-CCI. At the synaptic level, decreasing 5-HT2AR expression by shRNA or inhibition of 5-HT2AR activity by its antagonist ketanserin decreased the frequency and amplitude of spontaneous excitatory postsynaptic currents (sEPSCs) of the neurons in the VLO, whereas 5-HT2AR partial agonist 2,5-Dimethoxy-4-iodoamphetamine (DOI) enhanced sEPSCs of the neurons in the VLO. In summary, 5-HT2ARs in the VLO modulate the trigeminal pain by regulating neuronal glutamatergic activity.

5-HT3 Receptors in Rat Dorsal Root Ganglion Neurons: Ca2+ Entry and Modulation of Neurotransmitter Release.

Rat dorsal root ganglion (DRG) neurons express 5-hydroxytryptamine receptors (5-HT3Rs). To elucidate their physiological role in the modulation of sensory signaling, we aimed to quantify their functional expression in newborn and adult rat DRG neurons, as well as their ability to modulate the Ca2+-dependent neurotransmitter release, by means of electrophysiological techniques combined with fluorescence-based Ca2+ imaging. The selective 5-HT3R agonist mCPBG (10 μM) elicited whole-cell currents in 92.5% of adult DRG neurons with a significantly higher density current than in responding newborn cells (52.2%), suggesting an increasing serotoninergic modulation on primary afferent cells during development. Briefly, 5-HT3Rs expressed by adult DRG neurons are permeable to Ca2+ ions, with a measured fractional Ca2+ current (i.e., the percentage of total current carried by Ca2+ ions, Pf) of 1.0%, similar to the value measured for the human heteromeric 5-HT3A/B receptor (Pf = 1.1%), but lower than that of the human homomeric 5-HT3A receptor (Pf = 3.5%). mCPBG applied to co-cultures of newborn DRG and spinal neurons significantly increased the miniature excitatory postsynaptic currents (mEPSCs) frequency in a subset of recorded spinal neurons, even in the presence of Cd2+, a voltage-activated Ca2+ channel blocker. Considered together, our findings indicate that the Ca2+ influx through heteromeric 5-HT3Rs is sufficient to increase the spontaneous neurotransmitter release from DRG to spinal neurons.

A Deficiency of the Psychiatric Risk Gene DLG2/PSD-93 Causes Excitatory Synaptic Deficits in the Dorsolateral Striatum.

Genetic variations resulting in the loss of function of the discs large homologs (DLG2)/postsynaptic density protein-93 (PSD-93) gene have been implicated in the increased risk for schizophrenia, intellectual disability, and autism spectrum disorders (ASDs). Previously, we have reported that mice lacking exon 14 of the Dlg2 gene (Dlg2–/– mice) display autistic-like behaviors, including social deficits and increased repetitive behaviors, as well as suppressed spontaneous excitatory postsynaptic currents in the striatum. However, the neural substrate underpinning such aberrant synaptic network activity remains unclear. Here, we found that the corticostriatal synaptic transmission was significantly impaired in Dlg2–/– mice, which did not seem attributed to defects in presynaptic releases of cortical neurons, but to the reduced number of functional synapses in the striatum, as manifested in the suppressed frequency of miniature excitatory postsynaptic currents in spiny projection neurons (SPNs). Using transmission electron microscopy, we found that both the density of postsynaptic densities and the fraction of perforated synapses were significantly decreased in the Dlg2–/– dorsolateral striatum. The density of dendritic spines was significantly reduced in striatal SPNs, but notably, not in the cortical pyramidal neurons of Dlg2–/– mice. Furthermore, a DLG2/PSD-93 deficiency resulted in the compensatory increases of DLG4/PSD-95 and decreases in the expression of TrkA in the striatum, but not particularly in the cortex. These results suggest that striatal dysfunction might play a role in the pathology of psychiatric disorders that are associated with a disruption of the Dlg2 gene.

Effects of 3-methylmethcathinone on conditioned place preference and anxiety-like behavior: Comparison with methamphetamine.

3-Methylmethcathinone (3-MMC), a drug belonging to synthetic cathinones family, raised public attention due to its harmful health effects and abuse potential. Although it has similar properties to other cathinone derivatives, the behavioral effects of 3-MMC remain largely unknown. In the present research, we evaluated the rewarding effect of 3-MMC using conditioned place preference (CPP) paradigm and its effect on anxiety-like behavior using elevated plus maze (EPM) and compared with methamphetamine (METH). Then, we performed a whole-brain c-Fos mapping to identify the specific brain regions in response to 3-MMC exposure and explored the changes of synaptic transmission in nucleus accumbens (NAc) using patch-clamp recording after chronic 3-MMC and METH exposure. 3-MMC induced CPP at higher doses of 3 or 10 mg/kg in rats and acute exposure of 3 mg/kg 3-MMC to rats produced anxiolytic-like effect, while anxiety-like behavior was increased after 7 days of injection with 3-MMC. Whole-brain immunostaining revealed increased c-Fos expression in anterior cingulate cortex (ACC), NAc and ventral tegmental area (VTA) after chronic 3-MMC injection compared with saline, which was similar to METH. Especially, 3-MMC induced more neural activation of VTA compared with METH. Finally, we found that amplitude of spontaneous inhibitory postsynaptic currents (sIPSCs) in NAc was decreased after chronic 3-MMC injection, while frequency of sIPSCs and spontaneous excitatory postsynaptic currents (sEPSCs) were not affected. Taken together, our results revealed the addictive potential of 3-MMC and its effect on anxiety-like behavior, which warn the risks of 3-MMC abuse and justify the control of synthetic cathinones. And 3-MMC selectively inhibit inhibitory but not excitatory transmission onto neurons in NAc, which may contribute to its effects.

Increased GABA transmission to GnRH neurons after intrahippocampal kainic acid injection in mice is sex-specific and associated with estrous cycle disruption

Patients with epilepsy develop reproductive endocrine comorbidities at a rate higher than that of the general population. Clinical studies have identified disrupted luteinizing hormone (LH) release patterns in patients of both sexes, suggesting potential epilepsy-associated changes in hypothalamic gonadotropin-releasing hormone (GnRH) neuron function. In previous work, we found that GnRH neuron firing is increased in diestrous females and males in the intrahippocampal kainic acid (IHKA) mouse model of temporal lobe epilepsy. Notably, GABAA receptor activation is depolarizing in adult GnRH neurons. Therefore, here we tested the hypothesis that increased GnRH neuron firing in IHKA mice is associated with increased GABAergic drive to GnRH neurons. When ionotropic glutamate receptors (iGluRs) were blocked to isolate GABAergic postsynaptic currents (PSCs), no differences in PSC frequency were seen between GnRH neurons from control and IHKA diestrous females. In the absence of iGluR blockade, however, GABA PSC frequency was increased in GnRH neurons from IHKA females with disrupted estrous cycles, but not saline-injected controls nor IHKA females without estrous cycle disruption. GABA PSC amplitude was also increased in IHKA females with disrupted estrous cycles. These findings suggest the presence of an iGluR-dependent increase in feed-forward GABAergic transmission to GnRH neurons specific to IHKA females with comorbid cycle disruption. In males, GABA PSC frequency and amplitude were unchanged but PSC duration was reduced. Together, these findings suggest that increased GABA transmission helps drive elevated firing in IHKA females on diestrus and indicate the presence of a sex-specific hypothalamic mechanism underlying reproductive endocrine dysfunction in IHKA mice.

Hippocampal Inhibitory Synapsis Deficits Induced by α5-Containing GABAA Receptors Mediate Chronic Neuropathic Pain-Related Cognitive Impairment.

Chronic neuropathic pain often leads to cognitive impairment, but the exact mechanism remains unclear. Gamma-aminobutyric acid A receptors (GABAARs) are the major inhibitory receptors in the brain, of which the α5-containing GABAARs (GABAARs-α5) are implicated in a range of neuropsychiatric disorders with cognitive deficits. However, whether GABAARs-α5 are involved in chronic neuropathic pain-related cognitive impairment remains unknown. In this study, the rats with chronic neuropathic pain induced by right sciatic nerve ligation injury (SNI) exhibited cognitive impairment with declined spontaneous alternation in Y-maze test and discrimination index in novel object recognition test. The GABAARs-α5 expressing on parvalbumin and somatostatin interneurons increased remarkably in hippocampus, resulting in decreased mean frequency of spontaneous inhibitory postsynaptic currents in hippocampal pyramidal neurons. Significantly, antagonizing the GABAARs-α5 by L655708 rescued weakened inhibitory synaptic transmission and cognitive impairment induced by chronic neuropathic pain. Taken together, these data suggest that the GABAARs-α5 play a crucial role in chronic neuropathic pain-induced cognitive impairment by weakening inhibitory synaptic transmission, which may provide insights into the pharmacologic treatment of chronic neuropathic pain-related cognitive impairment.

Plasticity of neuronal excitability and synaptic balance in the anterior nucleus of paraventricular thalamus after nerve injury

The anterior nucleus of the paraventricular thalamus (aPVT) integrates various synaptic inputs and conveys information to the downstream brain regions for arousal and pain regulation. Recent studies have indicated that the PVT plays a crucial role in the regulation of chronic pain, but the plasticity mechanism of neuronal excitability and synaptic inputs for aPVT neurons in neuropathic pain remains unclear. Here, we report that spinal nerve ligation (SNL) significantly increased the neuronal excitability and reset the excitatory/inhibitory (E/I) synaptic inputs ratio of aPVT neurons in mice. SNL significantly increased the membrane input resistance, firing frequency, and the half-width of action potential. Additionally, SNL enlarged the area of afterdepolarization and prolonged the rebound low-threshold spike following a hyperpolarized current injection. Further results indicate that an inwardly rectifying current density was decreased in SNL animals. SNL also decreased the amplitude, but not the frequency of spontaneous excitatory postsynaptic currents (sEPSCs), nor the amplitude or frequency of spontaneous inhibitory postsynaptic currents (sIPSCs) of aPVT neurons. Moreover, SNL disrupted the E/I synaptic ratio, caused a decrease in weighted tau and half-width of averaged sIPSCs, but did not change these physiological properties of averaged sEPSCs. Finally, pharmacological activation of the GABAA receptor at aPVT could effective relieve SNL-induced mechanical allodynia in mice. These results reveal the plasticity of intrinsic neuronal excitability and E/I synaptic balance in the aPVT neurons after nerve injury and it may play an important role in the development of pain sensitization.