Role of HCN channels in the functions of basal ganglia and Parkinson's disease.

Parkinson's disease (PD) is a motor disorder resulting from dopaminergic neuron degeneration in the substantia nigra caused by age, genetics, and environment. The disease severely impacts a patient's quality of life and can even be life-threatening. The hyperpolarization-activated cyclic nucleotide-gated (HCN) channel is a member of the HCN1-4 gene family and is widely expressed in basal ganglia nuclei. The hyperpolarization-activated current mediated by the HCN channel has a distinct impact on neuronal excitability and rhythmic activity associated with PD pathogenesis, as it affects the firing activity, including both firing rate and firing pattern, of neurons in the basal ganglia nuclei. This review aims to comprehensively understand the characteristics of HCN channels by summarizing their regulatory role in neuronal firing activity of the basal ganglia nuclei. Furthermore, the distribution and characteristics of HCN channels in each nucleus of the basal ganglia group and their effect on PD symptoms through modulating neuronal electrical activity are discussed. Since the roles of the substantia nigra pars compacta and reticulata, as well as globus pallidus externus and internus, are distinct in the basal ganglia circuit, they are individually described. Lastly, this investigation briefly highlights that the HCN channel expressed on microglia plays a role in the pathological process of PD by affecting the neuroinflammatory response.

Histamine signaling in the bed nucleus of the stria terminalis modulates stress-induced anxiety.

BACKGROUND: Anxiety disorder is one of the most prevalent psychiatric disorders. Intriguingly, dysfunction of the central histaminergic system, which is recognized as a general regulator for whole-brain activity, may result in anxiety, suggesting an involvement of the central histaminergic signaling in the modulation of anxiety. However, the neural mechanisms involved have not been fully identified. METHODS: Here, we examined the effect of histaminergic signaling in the bed nucleus of the stria terminalis (BNST) on anxiety-like behaviors both in normal and acute restraint stressed male rats by using anterograde tracing, immunofluorescence, qPCR, neuropharmacology, molecular manipulation and behavioral tests. RESULTS: We found that histaminergic neurons in the hypothalamus send direct projections to the BNST, which forms a part of the circuitry involved in stress and anxiety. Infusion of histamine into the BNST produced anxiogenic effect. Moreover, histamine H1 and H2 receptors are expressed and distributed in the BNST neurons. Blockade of histamine H1 or H2 receptors in the BNST did not affect anxiety-like behaviors in normal rats, but ameliorated anxiogenic effect induced by acute restraint stress. Furthermore, knockdown of H1 or H2 receptors in the BNST induced anxiolytic effect in acute restraint stressed rats, which confirmed the pharmacological results. LIMITATIONS: A single dose of histamine receptor antagonist was used. CONCLUSIONS: Together, these findings demonstrate a novel mechanism for the central histaminergic system in the regulation of anxiety, and suggest that inhibition of histamine receptors may be a useful strategy for treating anxiety disorder.

Ameliorating parkinsonian motor dysfunction by targeting histamine receptors in entopeduncular nucleus-thalamus circuitry.

In Parkinson's disease (PD), reduced dopamine levels in the basal ganglia have been associated with altered neuronal firing and motor dysfunction. It remains unclear whether the altered firing rate or pattern of basal ganglia neurons leads to parkinsonism-associated motor dysfunction. In the present study, we show that increased histaminergic innervation of the entopeduncular nucleus (EPN) in the mouse model of PD leads to activation of EPN parvalbumin (PV) neurons projecting to the thalamic motor nucleus via hyperpolarization-activated cyclic nucleotide-gated (HCN) channels coupled to postsynaptic H2R. Simultaneously, this effect is negatively regulated by presynaptic H3R activation in subthalamic nucleus (STN) glutamatergic neurons projecting to the EPN. Notably, the activation of both types of receptors ameliorates parkinsonism-associated motor dysfunction. Pharmacological activation of H2R or genetic upregulation of HCN2 in EPNPV neurons, which reduce neuronal burst firing, ameliorates parkinsonism-associated motor dysfunction independent of changes in the neuronal firing rate. In addition, optogenetic inhibition of EPNPV neurons and pharmacological activation or genetic upregulation of H3R in EPN-projecting STNGlu neurons ameliorate parkinsonism-associated motor dysfunction by reducing the firing rate rather than altering the firing pattern of EPNPV neurons. Thus, although a reduced firing rate and more regular firing pattern of EPNPV neurons correlate with amelioration in parkinsonism-associated motor dysfunction, the firing pattern appears to be more critical in this context. These results also confirm that targeting H2R and its downstream HCN2 channel in EPNPV neurons and H3R in EPN-projecting STNGlu neurons may represent potential therapeutic strategies for the clinical treatment of parkinsonism-associated motor dysfunction.

Receptor and Ionic Mechanism of Histamine on Mouse Dorsolateral Striatal Neurons.

The dorsolateral striatum (DLS) is the critical neural substrate that plays a role in motor control and motor learning. Our past study revealed a direct histaminergic projection from the tuberomammillary nucleus (TMN) of the hypothalamus to the rat striatum. However, the afferent of histaminergic fibers in the mouse DLS, the effect of histamine on DLS neurons, and the underlying receptor and ionic mechanisms remain unclear. Here, we demonstrated a direct histaminergic innervation from the TMN in the mouse DLS, and histamine excited both the direct-pathway spiny projection neurons (d-SPNs) and the indirect-pathway spiny projection neurons (i-SPNs) of DLS via activation of postsynaptic H1R and H2R, albeit activation of presynaptic H3R suppressed neuronal activity by inhibiting glutamatergic synaptic transmission on d-SPNs and i-SPNs in DLS. Moreover, sodium-calcium exchanger 3 (NCX3), potassium-leak channels linked to H1R, and hyperpolarization-activated cyclic nucleotide-gated channel 2 (HCN2) coupled to H2R co-mediated the excitatory effect induced by histamine on d-SPNs and i-SPNs in DLS. These results demonstrated the pre- and postsynaptic receptors and their downstream multiple ionic mechanisms underlying the inhibitory and excitatory effects of histamine on d-SPNs and i-SPNs in DLS, suggesting a potential modulatory effect of the central histaminergic system on the DLS as well as its related motor control and motor learning.

Histamine bidirectionally regulates the intrinsic excitability of parvalbumin-positive neurons in the lateral globus pallidus and promotes motor behaviour.

BACKGROUND AND PURPOSE: Parvalbumin (PV)-positive neurons are a type of neuron in the lateral globus pallidus (LGP) which plays an important role in motor control. The present study investigated the effect of histamine on LGPPV neurons and motor behaviour. EXPERIMENTAL APPROACH: Histamine levels in LGP as well as its histaminergic innervation were determined through brain stimulation, microdialysis, anterograde tracing and immunostaining. Mechanisms of histamine action were detected by immunostaining, single-cell qPCR, whole-cell patch-clamp recording, optogenetic stimulation and CRISPR/Cas9 gene-editing techniques. The effect of histamine on motor behaviour was detected by animal behavioural tests. KEY RESULTS: A direct histaminergic innervation in LGP from the tuberomammillary nucleus (TMN) and a histamine-induced increase in the intrinsic excitability of LGPPV neurons were determined by pharmacological blockade or by genetic knockout of the histamine H1 receptor (H1 R)-coupled TWIK-related potassium channel-1 (TREK-1) and the small-conductance calcium-activated potassium channel (SK3), as well as by activation or overexpression of the histamine H2 receptor (H2 R)-coupled hyperpolarization-activated cyclic nucleotide-gated channel (HCN2). Histamine negatively regulated the STN → LGPGlu transmission in LGPPV neurons via the histamine H3 receptor (H3 R), whereas blockage or knockout of H3 R increased the intrinsic excitability of LGPPV neurons. CONCLUSIONS AND IMPLICATIONS: Our results indicated that the endogenous histaminergic innervation in the LGP can bidirectionally promote motor control by increasing the intrinsic excitability of LGPPV neurons through postsynaptic H1 R and H2 R, albeit its action was negatively regulated by the presynaptic H3 R, thereby suggesting possible role of histamine in motor deficits manifested in Parkinson's disease (PD).

Targeting presynaptic H3 heteroreceptor in nucleus accumbens to improve anxiety and obsessive-compulsive-like behaviors.

Anxiety commonly co-occurs with obsessive-compulsive disorder (OCD). Both of them are closely related to stress. However, the shared neurobiological substrates and therapeutic targets remain unclear. Here we report an amelioration of both anxiety and OCD via the histamine presynaptic H3 heteroreceptor on glutamatergic afferent terminals from the prelimbic prefrontal cortex (PrL) to the nucleus accumbens (NAc) core, a vital node in the limbic loop. The NAc core receives direct hypothalamic histaminergic projections, and optogenetic activation of hypothalamic NAc core histaminergic afferents selectively suppresses glutamatergic rather than GABAergic synaptic transmission in the NAc core via the H3 receptor and thus produces an anxiolytic effect and improves anxiety- and obsessive-compulsive-like behaviors induced by restraint stress. Although the H3 receptor is expressed in glutamatergic afferent terminals from the PrL, basolateral amygdala (BLA), and ventral hippocampus (vHipp), rather than the thalamus, only the PrL- and not BLA- and vHipp-NAc core glutamatergic pathways among the glutamatergic afferent inputs to the NAc core is responsible for co-occurrence of anxiety- and obsessive-compulsive-like behaviors. Furthermore, activation of the H3 receptor ameliorates anxiety and obsessive-compulsive-like behaviors induced by optogenetic excitation of the PrL-NAc glutamatergic afferents. These results demonstrate a common mechanism regulating anxiety- and obsessive-compulsive-like behaviors and provide insight into the clinical treatment strategy for OCD with comorbid anxiety by targeting the histamine H3 receptor in the NAc core.

Facilitation of spinal α-motoneuron excitability by histamine and the underlying ionic mechanisms.

Spinal α-motoneurons directly innervate skeletal muscles and function as the final common path for movement and behavior. The processes that determine the excitability of motoneurons are critical for the execution of motor behavior. In fact, it has been noted that spinal motoneurons receive various neuromodulatory inputs, especially monoaminergic one. However, the roles of histamine and hypothalamic histaminergic innervation on spinal motoneurons and the underlying ionic mechanisms are still largely unknown. In the present study, by using the method of intracellular recording on rat spinal slices, we found that activation of either H1 or H2 receptor potentiated repetitive firing behavior and increased the excitability of spinal α-motoneurons. Both of blockage of K+ channels and activation of Na+-Ca2+ exchangers were involved in the H1 receptor-mediated excitation on spinal motoneurons, whereas the hyperpolarization-activated cyclic nucleotide-gated (HCN) channels were responsible for the H2 receptor-mediated excitation. The results suggest that, through switching functional status of ion channels and exchangers coupled to histamine receptors, histamine effectively biases the excitability of the spinal α-motoneurons. In this way, the hypothalamospinal histaminergic innervation may directly modulate final motor outputs and actively regulate spinal motor reflexes and motor execution.

Ionic Mechanisms Underlying the Excitatory Effect of Orexin on Rat Subthalamic Nucleus Neurons.

Central orexinergic system deficiency results in cataplexy, a motor deficit characterized with a sudden loss of muscle tone, highlighting a direct modulatory role of orexin in motor control. However, the neural mechanisms underlying the regulation of orexin on motor function are still largely unknown. The subthalamic nucleus (STN), the only excitatory structure of the basal ganglia, holds a key position in the basal ganglia circuitry and motor control. Previous study has revealed a wide distribution of orexinergic fibers as well as orexin receptors in the basal ganglia including the STN. Therefore, in the present study, by using whole-cell patch clamp recording and immunostaining techniques, the direct effect of orexin on the STN neurons in brain slices, especially the underlying receptor and ionic mechanisms, were investigated. Our results show that orexin-A elicits an excitatory effect on STN neurons in rats. Tetrodotoxin (TTX) does not block the orexin-induced excitation on STN neurons, suggesting a direct postsynaptic action of the neuropeptide. The orexin-A-induced inward current on STN neurons is mediated by the activation of both OX1 and OX2 receptors. Immunofluorescence result shows that OX1 and OX2 receptors are co-expressed and co-localized in STN neurons. Furthermore, Na+-Ca2+ exchangers (NCXs) and inward rectifier K+ channels co-mediate the excitatory effect of orexin-A on STN neurons. These results demonstrate a dual receptor in conjunction with the downstream ionic mechanisms underlying the excitatory action of orexin on STN neurons, suggesting a potential modulation of the central orexinergic system on basal ganglia circuitry as well as its related motor control and motor diseases.

Regularizing firing patterns of rat subthalamic neurons ameliorates parkinsonian motor deficits.

The subthalamic nucleus (STN) is an effective therapeutic target for deep brain stimulation (DBS) for Parkinson's disease (PD), and histamine levels are elevated in the basal ganglia in PD patients. However, the effect of endogenous histaminergic modulation on STN neuronal activities and the neuronal mechanism underlying STN-DBS are unknown. Here, we report that STN neuronal firing patterns are more crucial than firing rates for motor control. Histamine excited STN neurons, but paradoxically ameliorated parkinsonian motor deficits, which we attributed to regularizing firing patterns of STN neurons via the hyperpolarization-activated cyclic nucleotide-gated channel 2 (HCN2) channel coupled to the H2 receptor. Intriguingly, DBS increased histamine release in the STN and regularized STN neuronal firing patterns under parkinsonian conditions. HCN2 contributed to the DBS-induced regularization of neuronal firing patterns, suppression of excessive ß oscillations, and alleviation of motor deficits in PD. The results reveal an indispensable role for regularizing STN neuronal firing patterns in amelioration of parkinsonian motor dysfunction and a functional compensation for histamine in parkinsonian basal ganglia circuitry. The findings provide insights into mechanisms of STN-DBS as well as potential therapeutic targets and STN-DBS strategies for PD.

Histamine Excites Striatal Dopamine D1 and D2 Receptor-Expressing Neurons via Postsynaptic H1 and H2 Receptors.

The central histaminergic nervous system, originating from the tuberomammillary nucleus (TMN) of the hypothalamus, widely innervates almost the whole brain, including the basal ganglia. Intriguingly, the histaminergic system is altered in parkinsonian patients. Yet, little is known about the effect and mechanisms of histamine on different types of neurons in the basal ganglia circuitry. Here, by using anterograde tracing, immunostaining, patch clamp recording, and single-cell qPCR techniques, we investigate the histaminergic afferents in the striatum, the major input structure of the basal ganglia, as well as the effect of histamine on the striatal GABAergic medium spiny projection neurons (MSNs). We report a direct histaminergic projection from the hypothalamic TMN to the striatum in rats. Furthermore, histamine exerts a strong postsynaptic excitatory effect on both dopamine D1 and D2 receptor-expressing MSNs. The concentration-response curves and the EC50 values for histamine on these two types of MSNs are similar. In addition, dopamine D1 and D2 receptor-expressing MSNs co-express histamine H1 and H2 receptor mRNAs. Both histamine H1 and H2 receptors are co-localized on dopamine D1 and D2 receptor-expressing MSNs and co-mediate the histamine-induced excitation on the two types of neurons. These results suggest that the histaminergic afferent inputs in the striatum may modulate both dopamine D1 and D2 receptor-expressing MSNs by activation of postsynaptic histamine H1 and H2 receptors and thus serve as an important extrastriatal modulator for biasing the direct and indirect pathways to actively regulate functions of the basal ganglia and participate in the pathogenesis and pathophysiology of basal ganglia diseases.

[Subthalamic nucleus: from circuits, functions to a deep brain stimulation target for the treatment of Parkinson's disease].

The subthalamic nucleus (STN) is the only excitatory glutamatergic nucleus in the basal ganglia circuitry. It not only is a key node in the classical indirect pathway, but also forms the "hyperdirect" pathway directly connecting the cortex, and even is implicated as a pacemaker for activity of whole basal ganglia. Due to the key position of STN in the basal ganglia circuitry, the STN is an optimal target for deep brain stimulation (DBS) in the neurosurgical treatment of Parkinson's disease (PD). However, the therapeutic mechanisms underlying the amelioration of parkinsonian motor dysfunctions induced by DBS on STN remain enigmatic. This paper reviews recent progresses in the studies on the input-output configurations and functions of STN in the basal ganglia circuitry, and summarizes the hypotheses for mechanisms of DBS for the treatment of motor dysfunctions in PD. Studying on the DBS mechanisms will not only help to develop strategies for treatment of PD, but also contribute to the understanding of functions of the basal ganglia circuitry.

Role of Corticotropin-Releasing Factor in Cerebellar Motor Control and Ataxia.

Cerebellar ataxia, characterized by motor incoordination, postural instability, and gait abnormality [1-3], greatly affects daily activities and quality of life. Although accumulating genetic and non-genetic etiological factors have been revealed [4-7], effective therapies for cerebellar ataxia are still lacking. Intriguingly, corticotropin-releasing factor (CRF), a peptide hormone and neurotransmitter [8, 9], is considered a putative neurotransmitter in the olivo-cerebellar system [10-14]. Notably, decreased levels of CRF in the inferior olive (IO), the sole origin of cerebellar climbing fibers, have been reported in patients with spinocerebellar degeneration or olivopontocerebellar atrophy [15, 16], yet little is known about the exact role of CRF in cerebellar motor coordination and ataxia. Here we report that deficiency of CRF in the olivo-cerebellar system induces ataxia-like motor abnormalities. CRFergic neurons in the IO project directly to the cerebellar nuclei, the ultimate integration and output node of the cerebellum, and CRF selectively excites glutamatergic projection neurons rather than GABAergic neurons in the cerebellar interpositus nucleus (IN) via two CRF receptors, CRFR1 and CRFR2, and their downstream inward rectifier K+ channel and/or hyperpolarization-activated cyclic nucleotide-gated (HCN) channel. Furthermore, CRF promotes cerebellar motor coordination and rescues ataxic motor deficits. The findings define a previously unknown role for CRF in the olivo-cerebellar system in the control of gait, posture, and motor coordination, and provide new insight into the etiology, pathophysiology, and treatment strategy of cerebellar ataxia.

Orexin Directly Enhances the Excitability of Globus Pallidus Internus Neurons in Rat by Co-activating OX1 and OX2 Receptors.

Orexin, released from the hypothalamus, has been implicated in various basic non-somatic functions including feeding, the sleep-wakefulness cycle, emotion, and cognition. However, the role of orexin in somatic motor control is still little known. Here, using whole-cell patch clamp recording and immunostaining, we investigated the effect and the underlying receptor mechanism of orexin-A on neurons in the globus pallidus internus (GPi), a critical structure in the basal ganglia and an effective target for deep brain stimulation therapy. Our results showed that orexin-A induced direct postsynaptic excitation of GPi neurons in a concentration-dependent manner. The orexin-A-induced excitation was mediated via co-activation of both OX1 and OX2 receptors. Furthermore, the immunostaining results showed that OX1 and OX2 receptors were co-localized in the same GPi neurons. These results suggest that the central orexinergic system actively modulates the motor functions of the basal ganglia via direct innervation on GPi neurons and presumably participates in somatic-non-somatic integration.

Medial cerebellar nucleus projects to feeding-related neurons in the ventromedial hypothalamic nucleus in rats.

The cerebellum, a hindbrain motor center, also participates in regulating nonsomatic visceral activities such as feeding control. However, the underlying neural mechanism is largely unknown. Here, we investigate whether the cerebellar medial nucleus (MN), one of the final outputs of the cerebellum, could directly project to and modulate the feeding-related neurons in the ventromedial hypothalamic nucleus (VMN), which has been traditionally implicated in feeding behavior, energy balance, and body weight regulation. The retrograde tracing results show that both GABAergic and glutamatergic projection neurons in the cerebellar MN send direct projections to the VMN. Electrical stimulation of cerebellar MN elicits an inhibitory, excitatory or biphasic response of VMN neurons. Interestingly, the VMN neurons modulated by cerebellar MN afferents not only receive phasic and tonic inputs from the gastric vagal nerves, but also are sensitive to peripheral glycemia and ghrelin signals. Moreover, a summation of inputs from the cerebellar MN and gastric vagal afferents occurs on single glycemia/ghrelin-sensitive neurons in the VMN, and the immunostaining result show that the axons from the cerebellar MN and the projections from the nucleus tractus solitarius, which conveys the gastric vagal inputs to hypothalamus, converge on single VMN glycemia/ghrelin-sensitive neurons. These results demonstrate that the somatic information forwarded by the cerebellar MN, together with the feeding signals from periphery, converge onto single VMN neurons, suggesting that a somatic-visceral integration related to feeding may occur in the VMN and the cerebellum may actively participate in the feeding regulation through the direct cerebellar MN-VMN projections.

Excitatory effect of norepinephrine on neurons in the inferior vestibular nucleus and the underlying receptor mechanism.

The central noradrenergic system, originating mainly from the locus coeruleus in the brainstem, plays an important role in many physiological functions, including arousal and attention, learning and memory, anxiety, and nociception. However, little is known about the roles of norepinephrine (NE) in somatic motor control. Therefore, using extracellular recordings on rat brainstem slices and quantitative real-time RT-PCR, we investigate the effect and mechanisms of NE on neuronal activity in the inferior vestibular nucleus (IVN), the largest nucleus in the vestibular nuclear complex, which holds an important position in integration of information signals controlling body posture. Here, we report that NE elicits an excitatory response on IVN neurons in a concentration-dependent manner. Activation of α1 - and ß2 -adrenergic receptors (ARs) induces an increase in firing rate of IVN neurons, whereas activation of α2 -ARs evokes a decrease in firing rate of IVN neurons. Therefore, the excitation induced by NE on IVN neurons is a summation of the excitatory components mediated by coactivation of α1 - and ß2 -ARs and the inhibitory component induced by α2 -ARs. Accordingly, α1 -, α2 -, and ß2 -AR mRNAs are expressed in the IVN. Although ß1 -AR mRNAs are also detected, they are not involved in the direct electrophysiological effect of NE on IVN neurons. All these results demonstrate that NE directly regulates the activity of IVN neurons via α1 -, α2 -, and ß2 -ARs and suggest that the central noradrenergic system may actively participate in IVN-mediated vestibular reflexes and postural control. © 2016 Wiley Periodicals, Inc.

Corticotropin releasing factor excites neurons of posterior hypothalamic nucleus to produce tachycardia in rats.

Corticotropin releasing factor (CRF), a peptide hormone involved in the stress response, holds a key position in cardiovascular regulation. Here, we report that the central effect of CRF on cardiovascular activities is mediated by the posterior hypothalamic nucleus (PH), an important structure responsible for stress-induced cardiovascular changes. Our present results demonstrate that CRF directly excites PH neurons via two CRF receptors, CRFR1 and CRFR2, and consequently increases heart rate (HR) rather than the mean arterial pressure (MAP) and renal sympathetic nerve activity (RSNA). Bilateral vagotomy does not influence the tachycardia response to microinjection of CRF into the PH, while ß adrenergic receptor antagonist propranolol almost totally abolishes the tachycardia. Furthermore, microinjecting CRF into the PH primarily increases neuronal activity of the rostral ventrolateral medulla (RVLM) and rostral ventromedial medulla (RVMM), but does not influence that of the dorsal motor nucleus of the vagus nerve (DMNV). These findings suggest that the PH is a critical target for central CRF system in regulation of cardiac activity and the PH-RVLM/RVMM-cardiac sympathetic nerve pathways, rather than PH-DMNV-vagus pathway, may contribute to the CRF-induced tachycardia.

Selective Modulation of Histaminergic Inputs on Projection Neurons of Cerebellum Rapidly Promotes Motor Coordination via HCN Channels.

Insights into function of central histaminergic system, a general modulator originating from the hypothalamus for whole brain activity, in motor control are critical for understanding the mechanism underlying somatic-nonsomatic integration. Here, we show a novel selective role of histamine in the cerebellar nuclei, the final integrative center and output of the cerebellum. Histamine depolarizes projection neurons but not interneurons in the cerebellar nuclei via the hyperpolarization-activated cyclic nucleotide-gated (HCN) channels coupled to histamine H2 receptors, which are exclusively expressed on glutamatergic and glycinergic projection neurons. Furthermore, blockage of HCN channels to block endogenous histaminergic afferent inputs in the cerebellar nuclei significantly attenuates motor balance and coordination. Therefore, through directly and quickly modulation on projection neurons but not interneurons in the cerebellar nuclei, central histaminergic system may act as a critical biasing force to not only promptly regulate ongoing movement but also realize a rapid integration of somatic and nonsomatic response.

Interleukin-6 reduces NMDAR-mediated cytosolic Ca²âº overload and neuronal death via JAK/CaN signaling.

Cytosolic Ca(2+) overload induced by N-methyl-D-aspartate (NMDA) is one of the major causes for neuronal cell death during cerebral ischemic insult and neurodegenerative disorders. Previously, we have reported that the cytokine interleukin-6 (IL-6) reduces NMDA-induced cytosolic Ca(2+) overload by inhibiting both L-type voltage-gated calcium channel (L-VGCC) activity and intracellular Ca(2+) store release in cultured cerebellar granule neurons (CGNs). Here we aimed to show that NMDA-gated receptor channels (i.e., NMDA receptors, NMDARs) are an inhibitory target of IL-6 via a mediation of calcineurin (CaN) signaling. As expected, IL-6 decreased NMDAR-mediated cytosolic Ca(2+) overload and inward current in cultured CGNs. The NMDAR subunits, NR1, NR2A, NR2B and NR2C, were expressed in CGNs. Blocking either of NR2A, NR2B and NR2C with respective antagonist reduced NMDA-induced extracellular Ca(2+) influx and neuronal death. Importantly, the reduced percentages in extracellular Ca(2+) influx and neuronal death by either NR2B or NR2C antagonist were weaker in the presence of IL-6 than in the absence of IL-6, while the reduced percentage by NR2A antagonist was not significantly different between the presence and the absence of IL-6. AG490, an inhibitor of Janus kinase (JAK), abolished IL-6 protection against extracellular Ca(2+) influx, mitochondrial membrane depolarization, neuronal death, and CaN activity impairment induced by NMDA. The CaN inhibitor FK506 reduced these IL-6 neuroprotective properties. Collectively, these results suggest that IL-6 exerts neuroprotection by inhibiting activities of the NMDAR subunits NR2B and NR2C (but not NR2A) via the intermediation of JAK/CaN signaling.

Orexin excites rat inferior vestibular nuclear neurons via co-activation of OX1 and OX 2 receptors.

Orexin deficiency results in cataplexy, a motor deficit characterized by sudden loss of muscle tone, strongly indicating an active role of central orexinergic system in motor control. However, effects of orexin on neurons in central motor structures are still largely unknown. Our previous studies have revealed that orexin excites neurons in the cerebellar nuclei and lateral vestibular nucleus, two important subcortical motor centers for control of muscle tone. Here, we report that both orexin-A and orexin-B depolarizes and increases the firing rate of neurons in the inferior vestibular nucleus (IVN), the largest nucleus in the vestibular nuclear complex and holding an important position in integration of information signals in the control of body posture. TTX does not block orexin-induced excitation on IVN neurons, suggesting a direct postsynaptic action of the neuropeptide. Furthermore, bath application of orexin induces an inward current on IVN neurons in a concentration-dependent manner. SB334867 and TCS-OX2-29, specific OX1 and OX2 receptor antagonists, blocked the excitatory effect of orexin, and [Ala(11), D-Leu(15)]-orexin B, a selective OX2 receptor agonist, mimics the orexin-induced inward current on IVN neurons. qPCR and immunofluorescence results show that both OX1 and OX2 receptor mRNAs and proteins are expressed and localized in the rat IVN. These results demonstrate that orexin excites the IVN neurons by co-activation of both OX1 and OX2 receptors, suggesting that via the direct modulation on the IVN, the central orexinergic system may actively participate in the central vestibular-mediated postural and motor control.

5-HT2A receptor-mediated excitation on cerebellar fastigial nucleus neurons and promotion of motor behaviors in rats.

It has long been known that serotonergic afferent inputs are the third largest afferent population in the cerebellum after mossy fibers and climbing fibers. However, the role of serotonergic inputs in cerebellar-mediated motor behaviors is still largely unknown. Here, we show that only 5-HT2A receptors among the 5-HT2 receptor subfamily are expressed and localized in the rat cerebellar fastigial nucleus (FN), one of the ultimate outputs of the spinocerebellum precisely regulating trunk and limb movements. Remarkably, selective activation of 5-HT2A receptors evokes a postsynaptic excitatory effect on FN neurons in a concentration-dependent manner in vitro, which is in accord with the 5-HT-elicited excitation on the same tested neurons. Furthermore, selective 5-HT2A receptor antagonist M100907 concentration-dependently blocks the excitatory effects of 5-HT and TCB-2, a 5-HT2A receptor agonist, on FN neurons. Consequently, microinjection of 5-HT into bilateral FNs significantly promotes rat motor performances on accelerating rota-rod and balance beam and narrows stride width rather than stride length in locomotion gait. All these motor behavioral effects are highly consistent with those of selective activation of 5-HT2A receptors in FNs, and blockage of the component of 5-HT2A receptor-mediated endogenous serotonergic inputs in FNs markedly attenuates these motor performances. All these results demonstrate that postsynaptic 5-HT2A receptors greatly contribute to the 5-HT-mediated excitatory effect on cerebellar FN neurons and promotion of the FN-related motor behaviors, suggesting that serotonergic afferent inputs may actively participate in cerebellar motor control through their direct modulation on the final output of the spinocerebellum.