Yihui Cui

Polymodal activation of the endocannabinoid system in the extended amygdala

The reason why neurons synthesize more than one endocannabinoid (eCB) and how this is involved in the regulation of synaptic plasticity in a single neuron is not known. We found that 2-arachidonoylglycerol (2-AG) and anandamide mediate different forms of plasticity in the extended amygdala of rats. Dendritic L-type Ca2+ channels and the subsequent release of 2-AG acting on presynaptic CB1 receptors triggered retrograde short-term depression. Long-term depression was mediated by postsynaptic mGluR5-dependent release of anandamide acting on postsynaptic TRPV1 receptors. In contrast, 2-AG/CB1R-mediated retrograde signaling mediated both forms of plasticity in the striatum. These data illustrate how the eCB system can function as a polymodal signal integrator to allow the diversification of synaptic plasticity in a single neuron.

Activation of Extracellular Signal-Regulated Kinase in the Anterior Cingulate Cortex Contributes to the Induction and Expression of Affective Pain

The anterior cingulate cortex (ACC) is implicated in the affective response to noxious stimuli. However, little is known about the molecular mechanisms involved. The present study demonstrated that extracellular signal-regulated kinase (ERK) activation in the ACC plays a crucial role in pain-related negative emotion. Intraplantar formalin injection produced a transient ERK activation in laminae V-VI and a persistent ERK activation in laminae II-III of the rostral ACC (rACC) bilaterally. Using formalin-induced conditioned place avoidance (F-CPA) in rats, which is believed to reflect the pain-related negative emotion, we found that blockade of ERK activation in the rACC with MEK inhibitors prevented the induction of F-CPA. Interestingly, this blockade did not affect formalin-induced two-phase spontaneous nociceptive responses and CPA acquisition induced by electric foot-shock or U69,593, an innocuous aversive agent. Upstream, NMDA receptor, adenylyl cyclase (AC) and phosphokinase A (PKA) activators activated ERK in rACC slices. Consistently, intra-rACC microinjection of AC or PKA inhibitors prevented F-CPA induction. Downstream, phosphorylation of cAMP response element binding protein (CREB) was induced in the rACC by formalin injection and by NMDA, AC and PKA activators in brain slices, which was suppressed by MEK inhibitors. Furthermore, ERK also contributed to the expression of pain-related negative emotion. Thus, when rats were re-exposed to the conditioning context for retrieval of pain experience, ERK and CREB were reactivated in the rACC, and inhibiting ERK activation blocked the expression of F-CPA. All together, our results demonstrate that ERK activation in the rACC is required for the induction and expression of pain-related negative affect.

Distinct coincidence detectors govern the corticostriatal spike timing-dependent plasticity

Corticostriatal projections constitute the main input to the basal ganglia, an ensemble of interconnected subcortical nuclei involved in procedural learning. Thus, long‐term plasticity at corticostriatal synapses would provide a basic mechanism for the function of basal ganglia in learning and memory. We had previously reported the existence of a corticostriatal anti‐Hebbian spike timing‐dependent plasticity (STDP) at synapses onto striatal output neurons, the medium‐sized spiny neurons. Here, we show that the blockade of GABAergic transmission reversed the time dependence of corticostriatal STDP. We explored the receptors and signalling mechanisms involved in the corticostriatal STDP. Although classical models for STDP propose NMDA receptors as the unique coincidence detector, the involvement of multiple coincidence detectors has also been demonstrated. Here, we show that corticostriatal STDP depends on distinct coincidence detectors. Specifically, long‐term potentiation is dependent on NMDA receptor activation, while long‐term depression requires distinct coincidence detectors: the phospholipase Cβ (PLCβ) and the inositol‐trisphosphate receptor (IP3R)‐gated calcium stores. Furthermore, we found that PLCβ activation is controlled by group‐I metabotropic glutamate receptors, type‐1 muscarinic receptors and voltage‐sensitive calcium channel activities. Activation of PLCβ and IP3Rs leads to robust retrograde endocannabinoid signalling mediated by 2‐arachidonoyl‐glycerol and cannabinoid CB1 receptors. Interestingly, the same coincidence detectors govern the corticostriatal anti‐Hebbian STDP and the Hebbian STDP reported at cortical synapses. Therefore, LTP and LTD induced by STDP at corticostriatal synapses are mediated by independent signalling mechanisms, each one being controlled by distinct coincidence detectors.

Forebrain NR2B Overexpression Facilitating the Prefrontal Cortex Long-Term Potentiation and Enhancing Working Memory Function in Mice

Prefrontal cortex plays an important role in working memory, attention regulation and behavioral inhibition. Its functions are associated with NMDA receptors. However, there is little information regarding the roles of NMDA receptor NR2B subunit in prefrontal cortical synaptic plasticity and prefrontal cortex-related working memory. Whether the up-regulation of NR2B subunit influences prefrontal cortical synaptic plasticity and working memory is not yet clear. In the present study, we measured prefrontal cortical synaptic plasticity and working memory function in NR2B overexpressing transgenic mice. In vitro electrophysiological data showed that overexpression of NR2B specifically in the forebrain region resulted in enhancement of prefrontal cortical long-term potentiation (LTP) but did not alter long-term depression (LTD). The enhanced LTP was completely abolished by a NR2B subunit selective antagonist, Ro25-6981, indicating that overexpression of NR2B subunit is responsible for enhanced LTP. In addition, NR2B transgenic mice exhibited better performance in a set of working memory paradigms including delay no-match-to-place T-maze, working memory version of water maze and odor span task. Our study provides evidence that NR2B subunit of NMDA receptor in prefrontal cortex is critical for prefrontal cortex LTP and prefrontal cortex-related working memory.

The Effects of NMDA Subunit Composition on Calcium Influx and Spike Timing-Dependent Plasticity in Striatal Medium Spiny Neurons

Calcium through NMDA receptors (NMDARs) is necessary for the long-term potentiation (LTP) of synaptic strength; however, NMDARs differ in several properties that can influence the amount of calcium influx into the spine. These properties, such as sensitivity to magnesium block and conductance decay kinetics, change the receptors response to spike timing dependent plasticity (STDP) protocols, and thereby shape synaptic integration and information processing. This study investigates the role of GluN2 subunit differences on spine calcium concentration during several STDP protocols in a model of a striatal medium spiny projection neuron (MSPN). The multi-compartment, multi-channel model exhibits firing frequency, spike width, and latency to first spike similar to current clamp data from mouse dorsal striatum MSPN. We find that NMDAR-mediated calcium is dependent on GluN2 subunit type, action potential timing, duration of somatic depolarization, and number of action potentials. Furthermore, the model demonstrates that in MSPNs, GluN2A and GluN2B control which STDP intervals allow for substantial calcium elevation in spines. The model predicts that blocking GluN2B subunits would modulate the range of intervals that cause long term potentiation. We confirmed this prediction experimentally, demonstrating that blocking GluN2B in the striatum, narrows the range of STDP intervals that cause long term potentiation. This ability of the GluN2 subunit to modulate the shape of the STDP curve could underlie the role that GluN2 subunits play in learning and development.

Ketamine blocks bursting in the lateral habenula to rapidly relieve depression

The N-methyl-d-aspartate receptor (NMDAR) antagonist ketamine has attracted enormous interest in mental health research owing to its rapid antidepressant actions, but its mechanism of action has remained elusive. Here we show that blockade of NMDAR-dependent bursting activity in the ‘anti-reward center’, the lateral habenula (LHb), mediates the rapid antidepressant actions of ketamine in rat and mouse models of depression. LHb neurons show a significant increase in burst activity and theta-band synchronization in depressive-like animals, which is reversed by ketamine. Burst-evoking photostimulation of LHb drives behavioural despair and anhedonia. Pharmacology and modelling experiments reveal that LHb bursting requires both NMDARs and low-voltage-sensitive T-type calcium channels (T-VSCCs). Furthermore, local blockade of NMDAR or T-VSCCs in the LHb is sufficient to induce rapid antidepressant effects. Our results suggest a simple model whereby ketamine quickly elevates mood by blocking NMDAR-dependent bursting activity of LHb neurons to disinhibit downstream monoaminergic reward centres, and provide a framework for developing new rapid-acting antidepressants.

Endocannabinoids mediate bidirectional striatal spike‐timing‐dependent plasticity

Although learning can arise from few or even a single trial, synaptic plasticity is commonly assessed under prolonged activation. Here, we explored the existence of rapid responsiveness of synaptic plasticity at corticostriatal synapses in a major synaptic learning rule, spike‐timing‐dependent plasticity (STDP). We found that spike‐timing‐dependent depression (tLTD) progressively disappears when the number of paired stimulations (below 50 pairings) is decreased whereas spike‐timing‐dependent potentiation (tLTP) displays a biphasic profile: tLTP is observed for 75–100 pairings, is absent for 25–50 pairings and re‐emerges for 5–10 pairings. This tLTP induced by low numbers of pairings (5–10) depends on activation of the endocannabinoid system, type‐1 cannabinoid receptor and the transient receptor potential vanilloid type‐1. Endocannabinoid‐tLTP may represent a physiological mechanism operating during the rapid learning of new associative memories and behavioural rules characterizing the flexible behaviour of mammals or during the initial stages of habit learning.

Astroglial Kir4.1 in the lateral habenula drives neuronal bursts in depression

Enhanced bursting activity of neurons in the lateral habenula (LHb) is essential in driving depression-like behaviours, but the cause of this increase has been unknown. Here, using a high-throughput quantitative proteomic screen, we show that an astroglial potassium channel (Kir4.1) is upregulated in the LHb in rat models of depression. Kir4.1 in the LHb shows a distinct pattern of expression on astrocytic membrane processes that wrap tightly around the neuronal soma. Electrophysiology and modelling data show that the level of Kir4.1 on astrocytes tightly regulates the degree of membrane hyperpolarization and the amount of bursting activity of LHb neurons. Astrocyte-specific gain and loss of Kir4.1 in the LHb bidirectionally regulates neuronal bursting and depression-like symptoms. Together, these results show that a glia–neuron interaction at the perisomatic space of LHb is involved in setting the neuronal firing mode in models of a major psychiatric disease. Kir4.1 in the LHb might have potential as a target for treating clinical depression.

Activation of extracellular signal-regulated kinase in the anterior cingulate cortex contributes to the induction of long-term potentiation in rats.

ObjectiveTo explore the role of the extracellular signal-regulated kinase (ERK)/cAMP response element binding protein (CREB) pathway in the induction of long-term potentiation (LTP) in the anterior cingulate cortex (ACC) that may be implicated in pain-related negative emotion.MethodsLTP of field potential was recorded in ACC slice and the expressions of phospho-ERK (pERK) and phospho-CREB (pCREB) were examined using immunohistochemistry method.ResultsLTP could be induced stably in ACC slice by high frequency stimulation (2-train, 100 Hz, 1 s), while APv (an antagonist of NMDA receptor) could block the induction of LTP in the ACC, indicating that LTP in this experiment was NMDA receptor-dependent. Bath application of PD98059 (50 μmol/L), a selective MEK inhibitor, at 30 min before tetanic stimulation could completely block the induction of LTP. Moreover, the protein level of pERK in the ACC was transiently increased after LTP induction, starting at 5 min and returning to basal at 1 h after tetanic stimulation. The protein level of pCREB was also increased after LTP induction. The up-regulation in pERK and pCREB expressions could be blocked by pretreatment of PD98059. Double immunostaining showed that after LTP induction, most pERK was co-localized with pCREB.ConclusionNMDA receptor and ERK-CREB pathway are necessary for the induction of LTP in rat ACC and may play important roles in pain emotion.摘要目的探讨细胞外信号激酶(ERK)/cAMP 反应原件蛋白 (CREB) 信号通路对大鼠前扣带皮层神经元长时程增强(LTP) 诱导的影响。方法采用离体脑片场电位记录方法观察ERK激酶抑制剂对大鼠前扣带皮层 (ACC) LTP诱导的影响, 采用免疫组织化学方法观察ACC脑片在强直刺激后不同时间点磷酸化ERK (pERK)和磷酸化CREB (pCREB)的表达情况。结果在大鼠ACC脑薄片上, 高频刺激 (2-train, 100 Hz, 1 s) 能诱导出稳定的场电位 (fEPSP) 长时程增强。 预先给予NMDA 受体竞争性拮抗剂APv (50 µmol/L)可完全阻断LTP 的产生, 提示本实验中ACC 神经元LTP是NMDA受体依赖性的。 灌流液中预先给予MEK抑制剂PD98059 (50 µmol/L)能完全阻断LTP 的产生。 取高频刺激后不同时间点的脑片进行免疫组化检测, 结果显示, 高频刺激后 5 min 时, pERK 表达显著升高, 在10 min 达到最高峰, 1 h 后回复到基础表达水平。 同样, 高频刺激后ACC 脑片中pCREB 的表达也显著增加。 预先灌流液中给予MEK抑制剂PD98059能够阻断高频刺激引起的pERK和pCREB表达上调。 免疫双标结果显示几乎所有的pERK都能与pCREB共定位于同一个神经细胞。结论大鼠前扣带皮层中NMDA受体和ERK/CREB信号通路是长时程增强诱导所必需的。To explore the role of the extracellular signal-regulated kinase (ERK)/cAMP response element binding protein (CREB) pathway in the induction of long-term potentiation (LTP) in the anterior cingulate cortex (ACC) that may be implicated in pain-related negative emotion. LTP of field potential was recorded in ACC slice and the expressions of phospho-ERK (pERK) and phospho-CREB (pCREB) were examined using immunohistochemistry method. LTP could be induced stably in ACC slice by high frequency stimulation (2-train, 100 Hz, 1 s), while APv (an antagonist of NMDA receptor) could block the induction of LTP in the ACC, indicating that LTP in this experiment was NMDA receptor-dependent. Bath application of PD98059 (50 μmol/L), a selective MEK inhibitor, at 30 min before tetanic stimulation could completely block the induction of LTP. Moreover, the protein level of pERK in the ACC was transiently increased after LTP induction, starting at 5 min and returning to basal at 1 h after tetanic stimulation. The protein level of pCREB was also increased after LTP induction. The up-regulation in pERK and pCREB expressions could be blocked by pretreatment of PD98059. Double immunostaining showed that after LTP induction, most pERK was co-localized with pCREB. NMDA receptor and ERK-CREB pathway are necessary for the induction of LTP in rat ACC and may play important roles in pain emotion. 探讨细胞外信号激酶(ERK)/cAMP 反应原件蛋白 (CREB) 信号通路对大鼠前扣带皮层神经元长时程增强(LTP) 诱导的影响。 采用离体脑片场电位记录方法观察ERK激酶抑制剂对大鼠前扣带皮层 (ACC) LTP诱导的影响, 采用免疫组织化学方法观察ACC脑片在强直刺激后不同时间点磷酸化ERK (pERK)和磷酸化CREB (pCREB)的表达情况。 在大鼠ACC脑薄片上, 高频刺激 (2-train, 100 Hz, 1 s) 能诱导出稳定的场电位 (fEPSP) 长时程增强。 预先给予NMDA 受体竞争性拮抗剂APv (50 µmol/L)可完全阻断LTP 的产生, 提示本实验中ACC 神经元LTP是NMDA受体依赖性的。 灌流液中预先给予MEK抑制剂PD98059 (50 µmol/L)能完全阻断LTP 的产生。 取高频刺激后不同时间点的脑片进行免疫组化检测, 结果显示, 高频刺激后 5 min 时, pERK 表达显著升高, 在10 min 达到最高峰, 1 h 后回复到基础表达水平。 同样, 高频刺激后ACC 脑片中pCREB 的表达也显著增加。 预先灌流液中给予MEK抑制剂PD98059能够阻断高频刺激引起的pERK和pCREB表达上调。 免疫双标结果显示几乎所有的pERK都能与pCREB共定位于同一个神经细胞。 大鼠前扣带皮层中NMDA受体和ERK/CREB信号通路是长时程增强诱导所必需的。

A concurrent excitation and inhibition of dopaminergic subpopulations in response to nicotine

Midbrain dopamine (DA) neurons are key players in motivation and reward processing. Increased DA release is thought to be central in the initiation of drug addiction. Whereas dopamine neurons are generally considered to be activated by drugs such as nicotine, we report here that nicotine not only induces excitation of ventral tegmental area (VTA) DA cells but also induces inhibition of a subset of VTA DA neurons that are anatomically segregated in the medial part of the VTA. These opposite responses do not correlate with the inhibition and excitation induced by noxious stimuli. We show that this inhibition requires D2 receptor (D2-R) activation, suggesting that a dopaminergic release is involved in the mechanism. Our findings suggest a principle of concurrent excitation and inhibition of VTA DA cells in response to nicotine. It promotes unexplored roles for DA release in addiction contrasting with the classical views of reinforcement and motivation, and give rise to a new interpretation of the mode of operation of the reward system.