Amplitude Of Afterhyperpolarization Research Articles

Aging-associated weakening of the action potential in fast-spiking interneurons in the human neocortex

Aging is associated with the slowdown of neuronal processing and cognitive performance in the brain; however, the exact cellular mechanisms behind this deterioration in humans are poorly elucidated. Recordings in human acute brain slices prepared from tissue resected during brain surgery enable the investigation of neuronal changes with age. Although neocortical fast-spiking cells are widely implicated in neuronal network activities underlying cognitive processes, they are vulnerable to neurodegeneration. Herein, we analyzed the electrical properties of 147 fast-spiking interneurons in neocortex samples resected in brain surgery from 106 patients aged 11–84 years. By studying the electrophysiological features of action potentials and passive membrane properties, we report that action potential overshoot significantly decreases and spike half-width increases with age. Moreover, the action potential maximum-rise speed (but not the repolarization speed or the afterhyperpolarization amplitude) significantly changed with age, suggesting a particular weakening of the sodium channel current generated in the soma. Cell passive membrane properties measured as the input resistance, membrane time constant, and cell capacitance remained unaffected by senescence. Thus, we conclude that the action potential in fast-spiking interneurons shows a significant weakening in the human neocortex with age. This may contribute to the deterioration of cortical functions by aging.

Enhancement of neuronal excitability in the medial prefrontal cortex following prenatal morphine exposure

The clinical use and abuse of opioids during human pregnancy have been widely reported. Several studies have demonstrated that opioids cross the placenta in rats during late gestation, and prenatal morphine exposure has been shown to have negative outcomes in cognitive function. The medial prefrontal cortex (mPFC) is believed to play a crucial role in cognitive processes, motivation, and emotion, integrating neural information from several brain areas and sending converted information to other structures. Dysfunctions in this area have been observed in numerous psychiatric and neurological disorders, including addiction. This current study aimed to compare the electrophysiological properties of mPFC neurons in rat offspring prenatally exposed to morphine. Pregnant rats were injected with morphine or saline twice a day from gestational days 11–18. Whole-cell patch-clamp recordings were performed in male offspring on postnatal days 14–18. All recordings were obtained in current-clamp configuration from mPFC pyramidal neurons to assess their electrophysiological properties. The results revealed that prenatal exposure to morphine shifted the resting membrane potential (RMP) to less negative voltages and increased input resistance and duration of action potentials. However, the amplitude, rise slope, and afterhyperpolarization (AHP) amplitude of the first elicited action potentials were significantly decreased in rats prenatally exposed to morphine. Moreover, the sag voltage ratio was significantly decreased in the prenatal morphine group. Our results suggest that the changes observed in the electrophysiological properties of mPFC neurons indicate an elevation in neuronal excitability following prenatal exposure to morphine.

Benzydamine plays a role in limiting inflammatory pain induced by neuronal sensitization.

Benzydamine is an active pharmaceutical compound used in the oral care pharmaceutical preparation as NSAID. Beside from its anti-inflammatory action, benzydamine local application effectively reliefs pain showing analgesic and anaesthetic properties. Benzydamine mechanism of action has been characterized on inflammatory cell types and mediators highlighting its capacity to inhibit pro-inflammatory mediator's synthesis and release. On the other hand, the role of benzydamine as neuronal excitability modulator has not been yet fully explored. Thus, we studied benzydamine's effect over primary culture DRG nociceptors excitability and after acute and chronic inflammatory sensitization, as a model to evaluate nociceptor response. Benzydamine demonstrated to effectively inhibit neuronal basal excitability reducing its firing frequency and increasing rheobase and afterhyperpolarization amplitude. Its effect was time and dose-dependent. At higher doses, benzydamine induced changes in action potential wavelength, decreasing its height and slightly increasing its duration. Moreover, the compound reduced neuronal acute and chronic inflammatory sensitization. It inhibited neuronal excitability mediated either by an inflammatory cocktail, acidic pH or high external KCl. Notably, higher potency was evidenced under inflammatory sensitized conditions. This effect could be explained either by modulation of inflammatory and/or neuronal sensitizing signalling cascades or by direct modulation of proalgesic and action potential firing initiating ion channels. Apparently, the compound inhibited Nav1.8 channel but had no effect over Kv7.2, Kv7.3, TRPV1 and TRPA1. In conclusion, the obtained results strengthen the analgesic and anti-inflammatory effect of benzydamine, highlighting its mode of action on local pain and inflammatory signalling.

Isoliquiritigenin modulates the activity of LTS and non-LTS cells in the ventrolateral preoptic area via GABAA receptors

ObjectiveIsoliquiritigenin (ILTG) is a chalcone compound that exhibits hypnotic effects via gamma-aminobutyric acid type A (GABAA) receptors. The ventrolateral preoptic area (VLPO) is a sleep-promoting center that contains a large number of GABA-releasing cells. There are two cell types in the VLPO: one generates a low-threshold spike (LTS), whereas the other lacks an LTS (non-LTS). MethodWhole-cell patch-clamp technology was used to detect the firing and currents of LTS and non-LTS cells in the VLPO. ResultsBath administration of ILTG (10 μM) increased the firing rate of VLPO LTS cells, reversed by flumazenil (5 μM), a GABAA benzodiazepine site antagonist. However, the firing rate of VLPO non-LTS cells was inhibited by ILTG (10 μM), also reversed by flumazenil (5 μM). No differences were detected regarding resting membrane potential (RMP) amplitude, spike threshold, afterhyperpolarization (AHP) amplitude, or action potential duration (APD50) after ILTG (10 μM) perfusion in VLPO LTS cells. RMP amplitude was more hyperpolarized and spike threshold was higher after ILTG (10 μM) application in VLPO non-LTS cells. In addition, ILTG significantly reduced the frequency of miniature inhibitory postsynaptic currents (mIPSCs) in VLPO LTS cells. ILTG significantly increased the amplitude of mIPSCs in VLPO non-LTS cells. ConclusionsThis study revealed that ILTG suppresses presynaptic GABA release on VLPO LTS cells, thereby increasing their excitability. ILTG enhances postsynaptic GABAA receptor function on VLPO non-LTS cells, thereby decreasing their excitability. These results suggest that ILTG may produce hypnotic effects by modulating the GABAergic synaptic transmission properties of these two cell types.

The Na<sup>+</sup>/K<sup>+</sup>-ATPase Inhibitor Ouabain Has Different Effects on the Electrophysiological Properties of Excitatory and Inhibitory Neurons in the Entorhinal Cortex E

Na+/K+-ATPase maintains the neuron’s resting potential and the transmembrane gradient of K+ and Na+ cations, thus regulating ion transport and cellular volume. Mutations in Na+/K+-ATPase genes that impair its function can cause significant impairments in the nervous system function, including the development of epilepsy, if not lethal. Different forms of Na+/K+-ATPase are expressed in various classes of neurons and exhibit different characteristics. Thus, the impaired function of Na+/K+-ATPase may differentially affect the functioning of inhibitory and excitatory neurons. This study aims to determine the effects of the Na+/K+-ATPase antagonist ouabain on the electrophysiological characteristics of pyramidal cells and fast-spiking interneurons, as well as its impact on synaptic transmission. The results indicate that exposure to 5 µM ouabain results in depolarization of the resting membrane potential by 5 mV, as well as decreased amplitude and increased duration of the action potential of pyramidal neurons. Furthermore, ouabain caused a decrease in the amplitude of afterhyperpolarization in fast-spiking i-nterneurons. Moreover, both types of neurons exhibited a decrease in the threshold of action potential generation and the current at which depolarization block occurs. The addition of ouabain did not alter other electrophysiological characteristics of neurons. Furthermore, ouabain rapidly attenuates GABAergic transmission without affecting e-xcitatory synaptic transmission. These new findings on the effects of ouabain on excitatory pyramidal neurons and inhibitory interneurons contribute to the understanding of the mechanism underlying changes in the balance of excitation and inhibition in neural networks under Na+/K+-ATPase function impairment.

Roles of nucleus accumbens shell small-conductance calcium-activated potassium channels in the conditioned fear freezing

BackgroundPosttraumatic stress disorder (PTSD), a psychiatric disorder caused by stressful events, is characterized by long-lasting fear memory. The nucleus accumbens shell (NAcS) is a key brain region that regulates fear-associated behavior. Small-conductance calcium-activated potassium channels (SK channels) play a key role in regulating the excitability of NAcS medium spiny neurons (MSNs) but their mechanisms of action in fear freezing are unclear. MethodWe established an animal model of traumatic memory using conditioned fear freezing paradigm, and investigated the alterations in SK channels of NAc MSNs subsequent to fear conditioning in mice. We then utilized an adeno-associated virus (AAV) transfection system to overexpress the SK3 subunit and explore the function of the NAcS MSNs SK3 channel in conditioned fear freezing. ResultsFear conditioning activated NAcS MSNs with enhanced excitability and reduced the SK channel-mediated medium after-hyperpolarization (mAHP) amplitude. The expression of NAcS SK3 were also reduced time-dependently. The overexpression of NAcS SK3 impaired conditioned fear consolidation without affecting conditioned fear expression, and blocked fear conditioning-induced alterations in NAcS MSNs excitability and mAHP amplitude. Additionally, the amplitudes of mEPSC, AMPAR/NMDAR ratio, and membrane surface GluA1/A2 expression in NAcS MSNs was increased by fear conditioning and returned to normal levels upon SK3 overexpression, indicating that fear conditioning-induced decrease of SK3 expression caused postsynaptic excitation by facilitating AMPAR transmission to the membrane. ConclusionThese findings show that the NAcS MSNs SK3 channel plays a critical role in conditioned fear consolidation and that it may influence PTSD pathogenesis, making it a potential therapeutic target against PTSD.

Pharmacologic antagonism of CB1 receptors improves electrophysiological alterations in Purkinje cells exposed to 3-AP

IntroductionAlthough ataxia is associated with cerebellar dysfunction, little is known about the effects of 3-AP exposure on Purkinje cell electrophysiological properties. Here, we evaluated these parameters in cerebellar vermis brain slices.MethodsPurkinje cells were exposed to artificial cerebrospinal fluid (aCSF) (control) or to 1 mM 3-acetylpyridine (3-AP) in the recording chamber. The effects of a cannabinoid agonist (WIN; 7.5 nmol) and a cannabinoid antagonist (AM; 20 nmol) were evaluated under both conditions.ResultsExposure to 3-AP induced dramatic changes in cellular excitability that likely would affect Purkinje cell output. In whole-cell current clamp recordings, 3-AP-exposed Purkinje cells demonstrated a significantly higher frequency of action potentials, a larger afterhyperpolarization (AHP), and a larger rebound of action potentials. In addition, 3-AP caused a significant decrease in the interspike interval (ISI), half-width, and first spike latency. Remarkably, the action potential frequency, AHP amplitude, rebound, ISI, action potential halfwidth, and first spike latency were no longer different from controls in 3-AP cells treated with AM. Sag percentage, on the other hand, showed no significant difference under any treatment condition, indicating that cannabinoids' actions on 3-AP-mediated Purkinje cell changes may not include effects on neuronal excitability through changes of Ih.ConclusionsThese data show that cannabinoid antagonists reduce the excitability of Purkinje cells following exposure to 3-AP and suggest their potential as therapeutics in cerebellar dysfunctions.

Patch clamp study of benzydamine effect over neuronal excitability on inflammation sensitized rat nociceptors.

Benzydamine (BZ) is an active principle with local anti-inflammatory effect and analgesic properties widely used in oral affections. BZ mechanism of action has been deeply characterized on inflammatory cell types and mediators, highlighting its capacity to inhibit pro-inflammatory mediator's synthesis and release. Nevertheless, its pharmacological action as analgesic has been slightly explored, even more in inflammatory condition, and a more precise understanding of its action at single cell level is needed. To better understand BZ effect on isolated nociceptors, single cell neuronal activity was studied by patch clamp after acute or chronic inflammatory sensitization. Consequently, DRG nociceptors were challenged either by 5-minutes or 24-hours incubation with an inflammatory soup (IS - containing histamine, serotonin, ATP and PGE2), or BZ, or simultaneously with IS and BZ. BZ acute application demonstrated a decrease in action potential firing frequency supported also by rheobase increase and afterhyperpolarization (AHP) amplitude increase. Acute BZ application simultaneously with IS, limited neuronal sensitization contrary to the effect observed after IS application alone, which increased twice the action potential firing frequency. Moreover, chronic incubation of BZ tended to protect neurons against inflammatory sensitization. These results reinforce a previous MEA study, demonstrating a reduction of neuronal excitability elicited by inflammatory mediators after BZ use.As a conclusion we hypothesize that the observed decrease in firing frequency and rheobase increase could be related to the direct inhibition of Nav 1.8 and 1.9 channels, while the changes in AHP could relate with HCN or Kv7 channels modulation. An action via proalgesic channels like ASIC or TRP, sensitized by the inflammatory environment, cannot be excluded. Overall results reinforce the analgesic and anti-inflammatory effect of benzydamine, supporting the complementary action of the compound on local pain signalling and inflammatory conditions.

Diabetes mellitus differently affects electrical membrane properties of vagal afferent neurons of rats.

To study whether diabetes mellitus (DM) would cause electrophysiological alterations in nodose ganglion (NG) neurons, we used patch clamp and intracellular recording for voltage and current clamp configuration, respectively, on cell bodies of NG from rats with DM. Intracellular microelectrodes recording, according to the waveform of the first derivative of the action potential, revealed three neuronal groups (A0 , Ainf , and Cinf ), which were differently affected. Diabetes only depolarized the resting potential of A0 (from -55 to -44 mV) and Cinf (from -49 to -45 mV) somas. In Ainf neurons, diabetes increased action potential and the after-hyperpolarization durations (from 1.9 and 18 to 2.3 and 32 ms, respectively) and reduced dV/dtdesc (from -63 to -52 V s-1 ). Diabetes reduced the action potential amplitude while increasing the after-hyperpolarization amplitude of Cinf neurons (from 83 and -14 mV to 75 and -16 mV, respectively). Using whole cell patch clamp recording, we observed that diabetes produced an increase in peak amplitude of sodium current density (from -68 to -176 pA pF-1 ) and displacement of steady-state inactivation to more negative values of transmembrane potential only in a group of neurons from diabetic animals (DB2). In the other group (DB1), diabetes did not change this parameter (-58 pA pF-1 ). This change in sodium current did not cause an increase in membrane excitability, probably explainable by the alterations in sodium current kinetics, which are also induced by diabetes. Our data demonstrate that diabetes differently affects membrane properties of different nodose neuron subpopulations, which likely have pathophysiological implications for diabetes mellitus.

Further Studies on the Role of BTBD9 in the Cerebellum, Sleep-like Behaviors and the Restless Legs Syndrome

Genetic analyses have linked BTBD9 to restless legs syndrome (RLS) and sleep regulation. Btbd9 knockout mice show RLS-like motor restlessness. Previously, we found hyperactivity of cerebellar Purkinje cells (PCs) in Btbd9 knockout mice, which may contribute to the motor restlessness observed. However, underlying mechanisms for PC hyperactivity in Btbd9 knockout mice are unknown. Here, we used dissociated PC recording, brain slice recording and western blot to address this question. Our dissociated recording shows that knockout PCs had increased TEA-sensitive, Ca2+-dependent K+ currents. Applying antagonist to large conductance Ca2+-activated K+ (BK) channels further isolated the increased current as BK current. Consistently, we found increased amplitude of afterhyperpolarization and elevated BK protein levels in the knockout mice. Dissociated recording also shows a decrease in TEA-insensitive, Ca2+-dependent K+ currents. The result is consistent with reduced amplitude of tail currents, mainly composed of small conductance Ca2+-activated K+ (SK) currents, in slice recording. Our results suggest that BK and SK channels may be responsible for the hyperactivity of knockout PCs. Recently, BTBD9 protein was shown to associate with SYNGAP1 protein. We found a decreased cerebellar level of SYNGAP1 in Btbd9 knockout mice. However, Syngap1 heterozygous knockout mice showed nocturnal, instead of diurnal, motor restlessness. Our results suggest that SYNGAP1 deficiency may not contribute directly to the RLS-like motor restlessness observed in Btbd9 knockout mice. Finally, we found that PC-specific Btbd9 knockout mice exhibited deficits in motor coordination and balance similar to Btbd9 knockout mice, suggesting that the motor effect of BTBD9 in PCs is cell-autonomous.

Spike Afterhyperpolarizations Govern Persistent Firing Dynamics in Rat Neocortical and Hippocampal Pyramidal Cells.

Persistent firing is commonly reported in both cortical and subcortical neurons under a variety of behavioral conditions. Yet the mechanisms responsible for persistent activity are only partially resolved with support for both intrinsic and synaptic circuit-based mechanisms. Little also is known about physiological factors that enable epochs of persistent firing to continue beyond brief pauses and then spontaneously terminate. In the present study, we used intracellular recordings in rat (both sexes) neocortical and hippocampal brain slices to assess the ionic mechanisms underlying persistent firing dynamics. Previously, we showed that blockade of ether-á-go-go-related gene (ERG) potassium channels abolished intrinsic persistent firing in the presence of low concentrations of muscarinic receptor agonists and following optogenetic activation of cholinergic axons. Here we show the slow dynamics of ERG conductance changes allows persistent firing to outlast the triggering stimulus and even to initiate discharges following ∼7 s poststimulus firing pauses. We find that persistent firing dynamics is regulated by the interaction between ERG conductance and spike afterhyperpolarizations (AHPs). Increasing the amplitude of spike AHPs using either SK channel activators or a closed-loop reactive feedback system allows persistent discharges to spontaneously terminate in both neocortical neurons and hippocampal CA1 pyramidal cells. The interplay between ERG and the potassium channels that mediate spike AHPs grades the duration of persistent firing, providing a novel, generalizable mechanism to explain self-terminating persistent firing modes observed behaving animals.SIGNIFICANCE STATEMENT Many classes of neurons generate prolonged spiking responses to transient stimuli. These discharges often outlast the stimulus by seconds to minutes in some in vitro models of persistent firing. While recent work has identified key synaptic and intrinsic components that enable persistent spiking responses, less is known about mechanisms that can terminate and regulate the dynamics of these responses. The present study identified the spike afterhyperpolarizations as a potent mechanism that regulates the duration of persistent firing. We found that amplifying spike afterpotentials converted bistable persistent firing into self-terminating discharges. Varying the spike AHP amplitude grades the duration of persistent discharges, generating in vitro responses that mimic firing modes associated with neurons associated with short-term memory function.

The potassium channel auxiliary subunit Kvβ2 (Kcnab2) regulates Kv1 channels and dopamine neuron firing.

Ion channel complexes typically consist of both pore-forming subunits and auxiliary subunits that do not directly conduct current but can regulate trafficking or alter channel properties. Isolating the role of these auxiliary subunits in neurons has proved difficult due to a lack of specific pharmacological agents and the potential for developmental compensation in constitutive knockout models. Here, we use cell-type-specific viral-mediated CRISPR/Cas9 mutagenesis to target the potassium channel auxiliary subunit Kvβ2 (Kcnab2) in dopamine neurons in the adult mouse brain. We find that mutagenesis of Kcnab2 reduces surface expression of Kv1.2, the primary Kv1 pore-forming subunit expressed in dopamine neurons, and shifts the voltage dependence of inactivation of potassium channel currents toward more hyperpolarized potentials. Loss of Kcnab2 broadens the action potential waveform in spontaneously firing dopamine neurons recorded in slice, reduces the afterhyperpolarization amplitude, and increases spike timing irregularity and excitability, all of which is consistent with a reduction in potassium channel current. Similar effects were observed with mutagenesis of the pore-forming subunit Kv1.2 (Kcna2). These results identify Kv1 currents as important contributors to dopamine neuron firing and demonstrate a role for Kvβ2 subunits in regulating the trafficking and gating properties of these ion channels. Furthermore, they demonstrate the utility of CRISPR-mediated mutagenesis in the study of previously difficult to isolate ion channel subunits.NEW & NOTEWORTHY Here, we utilize CRISPR/Cas9-mediated mutagenesis in dopamine neurons in mice to target the gene encoding Kvβ2, an auxiliary subunit that forms a part of Kv1 channel complexes. We find that the absence of Kvβ2 alters action potential properties by reducing surface expression of pore-forming subunits and shifting the voltage dependence of channel inactivation. This work establishes a new function for Kvβ2 subunits and Kv1 complexes in regulating dopamine neuron activity.

Enhanced firing of locus coeruleus neurons and SK channel dysfunction are conserved in distinct models of prodromal Parkinson\u2019s disease

Parkinson’s disease (PD) is clinically defined by the presence of the cardinal motor symptoms, which are associated with a loss of dopaminergic nigrostriatal neurons in the substantia nigra pars compacta (SNpc). While SNpc neurons serve as the prototypical cell-type to study cellular vulnerability in PD, there is an unmet need to extent our efforts to other neurons at risk. The noradrenergic locus coeruleus (LC) represents one of the first brain structures affected in Parkinson’s disease (PD) and plays not only a crucial role for the evolving non-motor symptomatology, but it is also believed to contribute to disease progression by efferent noradrenergic deficiency. Therefore, we sought to characterize the electrophysiological properties of LC neurons in two distinct PD models: (1) in an in vivo mouse model of focal α-synuclein overexpression; and (2) in an in vitro rotenone-induced PD model. Despite the fundamental differences of these two PD models, α-synuclein overexpression as well as rotenone exposure led to an accelerated autonomous pacemaker frequency of LC neurons, accompanied by severe alterations of the afterhyperpolarization amplitude. On the mechanistic side, we suggest that Ca2+-activated K+ (SK) channels are mediators of the increased LC neuronal excitability, as pharmacological activation of these channels is sufficient to prevent increased LC pacemaking and subsequent neuronal loss in the LC following in vitro rotenone exposure. These findings suggest a role of SK channels in PD by linking α-synuclein- and rotenone-induced changes in LC firing rate to SK channel dysfunction.

The Effect of Valproate Sodium on the Electrical Activity of Helix aspersa F1 Neurons in a Pentylenetetrazole-Induced Epileptic Model Using an Intracellular Recording System

Background: Epilepsy is a chronic central nervous system disorder with a high prevalence in modern society. Despite using common anticonvulsant drugs, its control is not adequately achieved. Animal models for seizures play the leading role in advancing our understanding of the cellular mechanisms of epilepsy. The present study was an attempt to elucidate the electrophysiological mechanism of the effect of sodium valproate on the cellular model of epilepsy. Understanding the cellular mechanisms of this drug may help clarify the pharmacological screening of other drugs. Methods: The intracellular recording was made from F1 cells of garden Helix aspersa in the presence of Ringer solution. Following the extracellular application of valproate sodium at a concentration of 10 mM after and before the use of (25mM) epileptogenic agent (pentylenetetrazol (PTZ)), we evaluated its effect on paroxysmal depolarization shift (PDS) and electrophysiological characteristics. Results: These results showed that valproate sodium could reduce neuronal excitability. It could significantly hyperpolarize rest action potential by decreasing the frequency of firing rate and increasing the amplitude of afterhyperpolarization (AHP) and can prevent depolarization of rest action potential by PTZ. Conclusions: The results suggested that valproate sodium could reduce the PTZ-induced hyperexcitation by hyperpolarization of resting membrane potential (RMP), a reduction in AHP amplitude, and firing the frequency.

Hepatic Acyl CoA Oxidase1 Inhibition Modifies Brain Lipids and Electrical Properties of Dentate Gyrus.

Peroxisomes are essential organelles in lipid metabolism. They contain enzymes for β-oxidation of very long-chain fatty acids (VLCFA) that cannot be broken down in mitochondria. Reduced expression in hepatic acyl-CoA oxidase 1 (ACOX1), a peroxisome β-oxidation enzyme, followed by modification of the brain fatty acid profile has been observed in aged rodents. These studies have suggested a potential role for peroxisome β-oxidation in brain aging. This study was designed to examine the effect of hepatic ACOX1 inhibition on brain fatty acid composition and neuronal cell activities of young rats (200-250 g). A specific ACOX1 inhibitor, 10, 12- tricosadiynoic acid (TDYA), 100 μg/kg (in olive oil) was administered by daily gavage for 25 days in male Wistar rats. The brain fatty acid composition and electrophysiological properties of dentate gyrus granule cells were determined using gas chromatography and whole-cell patch-clamp, respectively. A significant increase in C20, C22, C18:1, C20:1, and a decrease of C18, C24, C20:3n6, and C22:6n3 were found in 10, 12- tricosadiynoic acid (TDYA) treated rats compared to the control group. The results showed that ACOX1 inhibition changes fatty acid composition similar to old rats. ACOX1 inhibition caused hyperpolarization of resting membrane potential, and also reduction of input resistance, action potential duration, and spike firing. Moreover, ACOX1 inhibition increased rheobase current and afterhyperpolarization amplitude in granule cells. The results indicated that systemic inhibition of ACOX1 causes hypo-excitability of neuronal cells. These results provide new evidence on the involvement of peroxisome function and hepatic ACOX1 activity in brain fatty acid profile and the electrophysiological properties of dentate gyrus cells.

Secondhand Smoke Decreased Excitability and Altered Action Potential Characteristics of Cardiac Vagal Neurons in Mice.

Background: Secondhand smoke (SHS), a major indoor pollutant, is a significant risk factor for cardiovascular morbidity and mortality including arrhythmias and sudden cardiac death. Exposure to SHS can produce autonomic imbalance, as evidenced by reduced heart rate variability (HRV)—a clinical metric of cardiac vagal regulation. Currently, the mechanisms through which SHS changes the vagal preganglionic neuronal inputs to the heart to produce this remains unknown.Objectives: To characterize the effect of SHS on both the excitability and action potential (AP) characteristics of anatomically identified cardiac vagal neurons (CVNs) in the nucleus ambiguus and examine whether SHS alters small conductance calcium-activated potassium (SK) channel activity of these CVNs.Methods: Adult male mice were exposed to four weeks of filtered air or SHS (3 mg/m3) 6 h/day, 5 day/week. Using patch-clamp recordings on identified CVNs in brainstem slices, we determined neuronal excitability and AP characteristics with depolarizing step- and ramp-current injections.Results: Four weeks of SHS exposure reduced spiking responses to depolarizing current injections and increased AP voltage threshold in CVNs. Perfusion with apamin (20 nM) magnified these SHS-induced effects, suggesting reduced SK channel activity may serve to minimize the SHS-induced decreases in CVNs excitability. Medium afterhyperpolarization (a measurement of SK channel activity) was smaller in the SHS group, further supporting a lower SK channel activity. AP amplitude, rise rate, fast afterhyperpolarization amplitude (a measurement of voltage-gated channel activity), and decay rate were higher in the SHS group at membrane voltages more positive to 0 mV, suggesting altered inactivation properties of voltage-dependent channels underlying APs.Discussion: SHS exposure reduced neuronal excitability of CVNs with compensatory attenuation of SK channel activity and altered AP characteristics. Neuroplasticity of CVNs could blunt regulatory cardiac vagal signaling and contribute to the cardiovascular consequences associated with SHS exposure, including reduced HRV.

Sex differences in the Role of Basolateral Amygdala Projections to the Bed Nucleus of the Stria Terminalis in Anticipatory Anxiety

Sustained anxiety in the absence of a threat can lead to pathological manifestations like post traumatic stress disorder (PTSD) and anxiety disorders. Recent data suggest that the bed nucleus of the stria terminalis (BST) is implicated in the shift from a phasic to sustained anxiety state, but the specific mechanisms by which this occurs remains unknown. We developed a model for sustained fear conditioning to a long duration cue (8 min) paired with intermittent foot shocks in order to better understand the neurocircuitry of anticipatory anxiety. Sex differences in the prevalence of anxiety disorders exist and a secondary goal of this work was to examine if sex differences exist in anticipatory anxiety during prolonged cues and the circuitry that contributes to this behavior. One of the major inputs to the BST activated during sustained fear learning is the basolateral amygdala (BLA), which also differs in activity between sexes. To determine a role for BLA projecting BST neurons (BLA-BST) in this sustained anxiety paradigm, we examined DREADD-induced suppression of the BLA-BST pathway during prolonged cued fear conditioning in both male and female rats. In males, inhibition of BLA-BST during extinction hastened the extinction of freezing compared to male controls, but had no effect on freezing behavior in females. Inhibition of BLA-BST did not alter exploration of the central area in the open field task, a test of general anxiety-like behavior, in either sex. Since the BLA-BST pathway also mediates social anxiety-like behavior in humans and animals, we assessed potential sex differences in social interaction (SI) following suppression of this pathway. Inhibition of the BLA-BST pathway increased SI time and reduced the latency to interact in male, but not female rats. Together, these results suggest that the BLA-BST projection does not modulate generalized anxiety-like behavior, but is specific to anticipatory anxiety induced by prolonged cued fear or an unpredictable social environment and differs between sexes. To examine potential sex differences in BLA-BST neurons, we implemented in vivo and in vitro electrophysiological approaches to determine the activity of these neurons. While spontaneous general BLA neuronal activity was augmented in females compared to males, sex differences were noted in the activity of BLA-BST projections. In males, the BLA-BST projection neurons were more active and excitable which coincided with a smaller after hyperpolarization (AHP) amplitude compared to other non-BST-projecting BLA neurons whereas in females, BLA-BST neurons were less excitable and had larger AHP amplitudes compared to non-BST-projecting BLA neurons. These physiological data support our behavioral experiment findings in which increased activity of BLA-BST neurons mediates anticipatory anxiety-like behavior in males, but not females. These novel findings suggest BLA-BST neurons contribute to anticipatory anxiety in male rats, but not females. Moreover, these sex differences in neurocircuitry may explain the sex disparity in anxiety disorders.

Formalin-induced inflammatory pain increases excitability in locus coeruleus neurons

Chronic pain is recognized as an important problem in communities. The locus coeruleus (LC) with extensive ascending and descending projections has a critical role in modulating pain. Some studies indicate how the locus coeruleus-noradrenaline system can remain more active after nociceptive stimulation. In the present study, we examined whether formalin-induced inflammatory pain may affect the electrophysiological properties of LC neurons after 24 h. Inflammatory pain was induced by a subcutaneous injection of 2% formalin (10 μL) into the hind paw of 2–3 week-old male Wistar rats. After 24 h, horizontal slices of brain stem containing the locus coeruleus were prepared and whole-cell patch-clamp recordings were carried out on LC neurons.Findings revealed that LC neurons from formalin injected rats had a significant enhancement in firing rate, half-width and instantaneous frequency of action potentials, but their resting membrane potential, input resistance and afterhyperpolarization amplitude almost remained unchanged. In addition, action potential peak amplitude, maximum rise slope, maximum decay slope, first spike latency and rheobase current significantly decreased in LC neurons obtained from formalin-treated rats. Here, for the first time, we demonstrate that inflammatory pain after 24 h induces hyperexcitability in LC neurons, which in turn may result in changes in noradrenaline release and pain processing.

Topographical Organization of M-Current on Dorsal and Median Raphe Serotonergic Neurons.

Dorsal and median raphe nuclei (DR and MR, respectively) are members of the reticular activating system and play important role in the regulation of the sleep-wakefulness cycle, movement, and affective states. M-current is a voltage-gated potassium current under the control of neuromodulatory mechanisms setting neuronal excitability. Our goal was to determine the proportion of DR and MR serotonergic neurons possessing M-current and whether they are organized topographically. Electrophysiological parameters of raphe serotonergic neurons influenced by this current were also investigated. We performed slice electrophysiology on genetically identified serotonergic neurons. Neurons with M-current are located rostrally in the DR and dorsally in the MR. M-current determines firing rate, afterhyperpolarization amplitude, and adaptation index (AI) of these neurons, but does not affect input resistance, action potential width, and high threshold oscillations.These findings indicate that M-current has a strong impact on firing properties of certain serotonergic neuronal subpopulations and it might serve as an effective contributor to cholinergic and local serotonergic neuromodulatory actions.

Membrane excitabilities in neonatal rat mesencephalic trigeminal neurons under dietary zinc deficiency.

The present study aimed to evaluate the effects of zinc deprivation on the properties of membrane and spike-discharge features of mesencephalic trigeminal neurons (MTNs), which are important sensory neurons for oral-motor reflexes and rhythmical jaw movements. Neonatal Sprague Dawley rats (P10-12) were distributed equally into a normal diet group and a zinc-deficient diet (ZD) group. Whole cell patch-clamp recordings were obtained from MTNs from coronal brain slices. Passive membrane properties showed a modest depolarized membrane potential and decreased cell capacitance in the ZD group. Zinc deprivation decreased the minimal current amplitude, which induced an action potential and increased the amplitude of afterhyperpolarization following the action potential. Negligible changes were observed for other action potential properties. A decreased burst duration was observed, accompanied by hastened spike frequency adaptation in the burst discharge. There was no difference in the resonant properties at both the subthreshold depolarized potential and hyperpolarized membrane potential between the control and ZD groups. These results suggests that neither the persistent sodium conductance nor slow inwardly rectifying conductance were altered; however, there appeared to be an increase in Ca2+-dependent K+ conductance in zincdeficient MTNs.