Tumor suppressor down-regulated in renal cell carcinoma 1 (DRR1) is a stress-induced actin bundling factor that modulates synaptic efficacy and cognition.

Stress has been identified as a major causal factor for many mental disorders. However, our knowledge about the chain of molecular and cellular events translating stress experience into altered behavior is still rather scant. Here, we have characterized a murine ortholog of the putative tumor suppressor gene DRR1 as a unique stress-induced protein in brain. It binds to actin, promotes bundling and stabilization of actin filaments, and impacts on actin-dependent neurite outgrowth. Endogenous DRR1 localizes to some, but not all, synapses, with preference for the presynaptic region. Hippocampal virus-mediated enhancement of DRR1 expression reduced spine density, diminished the probability of synaptic glutamate release, and altered cognitive performance. DRR1 emerges as a protein to link stress with actin dynamics, which in addition is able to act on synaptic function and cognition.

Topical review on the abuse and misuse potential of tramadol and tilidine in Germany.

BACKGROUND: Tramadol and tilidine (in combination with naloxone) are used as weak opioid analgesics in Germany. Tramadol is not scheduled in the German Narcotic Drugs Act. Tilidine is scheduled, whereas Tilidine in fixed combinations with naloxone is exempt from some of the provisions of the Narcotic Drugs Act. Recent reports on misuse of both substances led to an evaluation of their potential for misuse, abuse, and dependency by the expert advisory committee established by the German Federal Government, resident at the Federal Institute for Drugs and Medical Devices. METHODS: A subcommittee formulated key questions and identified available data sources for each of these questions. Additional information was solicited where necessary, including a survey among a panel of pharmacists, a survey in an addiction clinic, analysis of prescription patterns, and information from the boards of pharmacists of the federal states and the Federal Bureau of Criminal Investigation. RESULTS: Analgesic efficiency in the treatment of acute and chronic pain has been proven for both tramadol and tilidine/naloxone. For tramadol, high evidence has been confirmed in systematic reviews, and tramadol is listed in national and international guidelines on acute and chronic pain management. Animal and human studies found a low potential for misuse, abuse, and dependency for both substances. Information from 2 tramadol safety databases allowed calculation of the incidence of abuse or dependency as 0.21 and 0.12 cases per million defined daily dosages (DDDs), with lower incidences in recent years. For tilidine/naloxone, the incidence was calculated as 0.43 cases per million DDDs for oral solution and 0.18 for slow-release tablets. In an online survey among German pharmacies as well as in the reports from state pharmacy boards, fraud attempts were repeated more frequently with tilidine/naloxone than with tramadol in the last 2 years. The Federal Bureau of Criminal Investigations reported prescription fraud only with tilidine/naloxone and predominantly in the region of Berlin. Dependency on tramadol or tilidine/naloxone is reported only rarely from addiction counseling centers. One third of the patients surveyed in an addiction clinic reported experiences with tramadol or tilidine/naloxone, but mostly with duration of less than 4 weeks and with a medical prescription based on a reasonable indication. Also, occasional illegal use of opioid analgesics as a substitute of heroin was reported. An evaluation of pooled data from statutory health insurance companies found 2.5% of persons receiving at least 1 prescription of tramadol or the combination of tilidine and naloxone in 2009 (1.6% with tramadol and 1.0% with tilidine/naloxone). High usage with more than 180 DDDs per year was found in 8.6% of patients treated with tramadol and 17.2% of patients with tilidine/naloxone. CONCLUSIONS: In conclusion, the subcommittee of the expert advisory committee found a low potential for misuse, abuse, and dependency for tramadol, and a low prevalence in clinical practice. Considerable less information is available for the combination of tilidine and naloxone. However, the cumulation of evidence indicated a higher risk of misuse, abuse, and dependency for tilidine/naloxone solution, but not for slow-release tablets.

Chronic Pain and the Endocannabinoid System: Smart Lipids - A Novel Therapeutic Option?

The development of a high-end cannabinoid-based therapy is the result of intense translational research, aiming to convert recent discoveries in the laboratory into better treatments for patients. Novel compounds and new regimes for drug treatment are emerging. Given that previously unreported signaling mechanisms for cannabinoids have been uncovered, clinical studies detailing their high therapeutic potential are mandatory. The advent of novel genomic, optogenetic, and viral tracing and imaging techniques will help to further detail therapeutically relevant functional and structural features. An evolutionarily highly conserved group of neuromodulatory lipids, their receptors, and anabolic and catabolic enzymes are involved in a remarkable variety of physiological and pathological processes and has been termed the endocannabinoid system (ECS). A large body of data has emerged in recent years, pointing to a crucial role of this system in the regulation of the behavioral domains of acquired fear, anxiety, and stress-coping. Besides neurons, also glia cells and components of the immune system can differentially fine-tune patterns of neuronal activity. Dysregulation of ECS signaling can lead to a lowering of stress resilience and increased incidence of psychiatric disorders. Chronic pain may be understood as a disease process evoked by fear-conditioned nociceptive input and appears as the dark side of neuronal plasticity. By taking a toll on every part of your life, this abnormal persistent memory of an aversive state can be more damaging than its initial experience. All strategies for the treatment of chronic pain conditions must consider stress-related comorbid conditions since cognitive factors such as beliefs, expectations, and prior experience (memory of pain) are key modulators of the perception of pain. The anxiolytic and anti-stress effects of medical cannabinoids can substantially modulate the efficacy and tolerability of therapeutic interventions and will help to pave the way to a successful multimodal therapy. Why some individuals are more susceptible to the effects of stress remains to be uncovered. The development of personalized prevention or treatment strategies for anxiety and depression related to chronic pain must also consider gender differences. An emotional basis of chronic pain opens a new horizon of opportunities for developing treatment strategies beyond the repeated sole use of acutely acting analgesics. A phase I trial to determine the pharmacokinetics, psychotropic effects, and safety profile of a novel nanoparticle-based cannabinoid spray for oromucosal delivery highlights a remarkable innovation in galenic technology and urges clinical studies further detailing the huge therapeutic potential of medical cannabis (Lorenzl et al.; this issue).

Neurogenic inflammation as a novel treatment target for chronic pain syndromes.

Chronic pain syndrome is a heterogeneous group of diseases characterized by several pathological mechanisms. One in five adults in Europe may experience chronic pain. In addition to the individual burden, chronic pain has a significant societal impact because of work and school absences, loss of work, early retirement, and high social and healthcare costs. Several anti-inflammatory treatments are available for patients with inflammatory or autoimmune diseases to control their symptoms, including pain. However, patients with degenerative chronic pain conditions, some with 10-fold or more elevated incidence relative to these manageable diseases, have few long-term pharmacological treatment options, limited mainly to non-steroidal anti-inflammatory drugs or opioids. For this review, we performed multiple PubMed searches using keywords such as "pain," "neurogenic inflammation," "NGF," "substance P," "nociception," "BDNF," "inflammation," "CGRP," "osteoarthritis," and "migraine." Many treatments, most with limited scientific evidence of efficacy, are available for the management of chronic pain through a trial-and-error approach. Although basic science and pre-clinical pain research have elucidated many biomolecular mechanisms of pain and identified promising novel targets, little of this work has translated into better clinical management of these conditions. This state-of-the-art review summarizes concepts of chronic pain syndromes and describes potential novel treatment strategies.

The Rab5 guanylate exchange factor Rin1 regulates endocytosis of the EphA4 receptor in mature excitatory neurons.

Ephrin signaling through Eph receptor tyrosine kinases regulates important morphogenetic events during development and synaptic plasticity in the adult brain. Although Eph-ephrin endocytosis is required for repulsive axon guidance, its role in postnatal brain and synaptic plasticity is unknown. Here, we show that Rin1, a postnatal brain-specific Rab5-GEF, is coexpressed with EphA4 in excitatory neurons and interacts with EphA4 in synaptosomal fractions. The interaction of Rin1 and EphA4 requires Rin1's SH2 domain, consistent with the view that Rin1 targets tyrosine phosphorylated receptors to Rab5 compartments. We find that Rin1 mediates EphA4 endocytosis in postnatal amygdala neurons after engagement of EphA4 with its cognate ligand ephrinB3. Rin1 was shown to suppress synaptic plasticity in the amygdala, a forebrain structure important for fear learning, possibly by internalizing synaptic receptors. We find that the EphA4 receptor is required for synaptic plasticity in the amygdala, raising the possibility that an underlying mechanism of Rin1 function in amygdala is to down-regulate EphA4 signaling by promoting its endocytosis.

Differential effects of visually induced analgesia and attention depending on the pain stimulation site.

BACKGROUND: The term 'visually induced analgesia' describes a reduced pain perception induced by watching the painful body part as opposed to watching a neutral object. In chronic back pain patients, experimental pain, movement-induced pain and habitual pain can be reduced with visual feedback. Visual feedback can also enhance the effects of both massage treatment and manual therapy. The impact of somatosensory attentional processes remains unclear. METHODS: In the current study, participants received painful electrical stimuli to their thumb and back while being presented with either a real-time video of their thumb or back (factor feedback). In addition, using an oddball paradigm, they had to count the number of deviant stimuli, applied to either their back or thumb (factor attention) and rate the pain intensity. RESULTS: We found a significant main effect for attention with decreased pain ratings during attention. There was no main effect for visual feedback and no significant interaction between visual feedback and attention. Post-hoc tests revealed that the lowest pain intensity ratings were achieved during visual feedback of the back/ thumb and counting at the back/ thumb. CONCLUSION: These data suggest that the modulation of perceived acute pain by visually induced analgesia may be influenced by a simultaneous somatosensory attention task. SIGNIFICANCE: Somatosensory attention reduced experimental pain intensity in the thumb and back in the presence of both congruent and incongruent visual feedback. We found no significant visual feedback effect on the complex interplay between visual feedback and somatosensory attention.

The endocannabinoid system controls key epileptogenic circuits in the hippocampus.

Balanced control of neuronal activity is central in maintaining function and viability of neuronal circuits. The endocannabinoid system tightly controls neuronal excitability. Here, we show that endocannabinoids directly target hippocampal glutamatergic neurons to provide protection against acute epileptiform seizures in mice. Functional CB1 cannabinoid receptors are present on glutamatergic terminals of the hippocampal formation, colocalizing with vesicular glutamate transporter 1 (VGluT1). Conditional deletion of the CB1 gene either in cortical glutamatergic neurons or in forebrain GABAergic neurons, as well as virally induced deletion of the CB1 gene in the hippocampus, demonstrate that the presence of CB1 receptors in glutamatergic hippocampal neurons is both necessary and sufficient to provide substantial endogenous protection against kainic acid (KA)-induced seizures. The direct endocannabinoid-mediated control of hippocampal glutamatergic neurotransmission may constitute a promising therapeutic target for the treatment of disorders associated with excessive excitatory neuronal activity.

Isoflurane anaesthesia reversibly improves cognitive function and long-term potentiation (LTP) via an up-regulation in NMDA receptor 2B subunit expression.

Postoperative cognitive dysfunction (POCD) is a decline in cognitive performance after a surgery performed under anaesthesia. The exact roles of surgery and/or anaesthesia for facilitating POCD are unclear. This study investigates the effects of isoflurane anaesthesia on cognitive performance and cellular mechanisms involved in learning and memory function. Male C57BL6/J mice (age: 4-5 months) were anaesthetized with isoflurane in oxygen/air (FiO(2)=0.5) for 2h, non-anaesthetized mice served as controls. After 24h, neurocognitive function, in vitro long-term potentiation (LTP), or protein expression were evaluated. In a visuospatial test, anaesthetized mice showed better cognitive performance as they learned faster compared to controls. In hippocampal slices of anaesthetized mice, in vitro LTP was enhanced as reflected in an increased extracellular field potential (fEPSP) slope after 1h to 210.2+/-17% (control: 156.8+/-7.2%; n=14; p<0.05). NR2B subunits of the NMDA receptors were selectively up-regulated in hippocampal neurones after anaesthesia. Blocking these receptors either with the NR2B selective antagonists ifenprodil or RO25-6981 (R-(R,S)-alpha-(4-hydroxyphenyl)-beta-methyl-4-(phenylmethyl)-1-piperidine propranol), prevents the anaesthesia-induced improvement in cognitive function as well as enhancement of in vitro LTP. The anaesthesia-mediated effects on NR2B subunits were fully reversed to control levels seven days after anaesthesia. The present data suggests that isoflurane anaesthesia induces a hippocampus-specific elevation of NR2B subunit composition, enhances LTP in CA1 neurones, and produces hippocampal-dependent cognitive improvement.

Activation of CB1 specifically located on GABAergic interneurons inhibits LTD in the lateral amygdala.

Previously, we found that in the lateral amygdala (LA) of the mouse, WIN55,212-2 decreases both glutamatergic and GABAergic synaptic transmission via activation of the cannabinoid receptor type 1 (CB1), yet produces an overall reduction of neuronal excitability. This suggests that the effects on excitatory transmission override those on inhibitory transmission. Here we show that CB1 activation by WIN55,212-2 and Delta(9)-THC inhibits long-term depression (LTD) of basal synaptic transmission in the LA, induced by low-frequency stimulation (LFS; 900 pulses/1 Hz). The CB1 agonist WIN55,212-2 blocked LTD via G(i/o) proteins, activation of inwardly rectifying K+ channels (K(ir)s), inhibition of the adenylate cyclase-protein kinase A (PKA) pathway, and PKA-dependent inhibition of voltage-gated N-type Ca2+ channels (N-type VGCCs). Interestingly, WIN55,212-2 effects on LTD were abolished in CB1 knock-out mice (CB1-KO), and in conditional mutants lacking CB1 expression only in GABAergic interneurons, but were still present in mutants lacking CB1 in principal forebrain neurons. LTD induction per se was unaffected by the CB1 antagonist SR141716A and was normally expressed in CB1-KO as well as in both conditional CB1 mutants. Our data demonstrate that activation of CB1 specifically located on GABAergic interneurons inhibits LTD in the LA. These findings suggest that CB1 expressed on either glutamatergic or GABAergic neurons play a differential role in the control of synaptic transmission and plasticity.

Reduced anxiety, conditioned fear, and hippocampal long-term potentiation in transient receptor potential vanilloid type 1 receptor-deficient mice.

The transient receptor potential vanilloid type 1 channel (TRPV1) (formerly called vanilloid receptor VR1) is known for its key role of functions in sensory nerves such as perception of inflammatory and thermal pain. Much less is known about the physiological significance of the TRPV1 expression in the brain. Here we demonstrate that TRPV1 knock-out mice (TRPV1-KO) show less anxiety-related behavior in the light-dark test and in the elevated plus maze than their wild-type littermates with no differences in locomotion. Furthermore, TRPV1-KO mice showed less freezing to a tone after auditory fear conditioning and stress sensitization. This reduction of conditioned and sensitized fear could not be explained by alterations in nociception. Also, tone perception per se was unaffected, as revealed by determination of auditory thresholds through auditory brainstem responses and distortion-product otoacoustic emissions. TRPV1-KO showed also less contextual fear if assessed 1 d or 1 month after strong conditioning protocols. These impairments in hippocampus-dependent learning were mirrored by a decrease in long-term potentiation in the Schaffer collateral-commissural pathway to CA1 hippocampal neurons. Our data provide first evidence for fear-promoting effects of TRPV1 with respect to both innate and conditioned fear and for a decisive role of this receptor in synaptic plasticity.

Xenon reduces N-methyl-D-aspartate and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor-mediated synaptic transmission in the amygdala.

BACKGROUND: The neuronal and molecular targets of the inhalational general anesthetic xenon are a matter of debate. The current knowledge is largely based on studies using neurons in culture or heterologous expression systems. In the current study, the authors evaluated for the first time the effect of xenon on synaptic transmission in the basolateral amygdala in an in vitro brain slice preparation of the mouse. METHODS: A patch clamp technique was used to evaluate the effects of xenon on N-methyl-d-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor-mediated excitatory postsynaptic currents (EPSCs), as well as on gamma-aminobutyric acid type A receptor-mediated inhibitory postsynaptic currents. The currents were either evoked upon electrical stimulation (NMDA-eEPSCs, AMPA-eEPSCs) or upon focal, laser-guided photolysis of caged l-glutamate (p-NMDA-Cs, p-AMPA-Cs). In addition, the authors investigated the effects of xenon on miniature EPSCs. RESULTS: Xenon reversibly reduced basal synaptic transmission but had no effect on gamma-aminobutyric acid type A receptor-mediated inhibitory synaptic transmission. Xenon concentration-dependently diminished NMDA-eEPSCs and p-NMDA-Cs to the same amount. Likewise, xenon-induced reduction of AMPA-eEPSCs and p-AMPA-Cs did not differ. Xenon did not affect the frequency of miniature EPSCs but reduced their amplitude. CONCLUSIONS: In the current study, xenon considerably depressed NMDA and AMPA receptor-mediated synaptic transmission in the basolateral amygdala without affecting inhibitory synaptic transmission. The results provide evidence that the effects of xenon on NMDA- and AMPA-EPSCs are primarily mediated via postsynaptic mechanisms.

Cannabinoid receptor type 1 located on presynaptic terminals of principal neurons in the forebrain controls glutamatergic synaptic transmission.

It is widely accepted that cannabinoids regulate GABA release by activation of cannabinoid receptor type 1 (CB1). Results obtained from a variety of brain regions consistently indicate that cannabinoid agonists can also reduce glutamatergic synaptic transmission. However, there are still conflicting data concerning the role of CB1 in cannabinoid-induced inhibition of glutamatergic transmission in cortical areas. Here, we provide direct evidence that activation of CB1 on terminals of principal neurons controls excitatory synaptic responses in the forebrain. In slices of the basolateral amygdala, the CA1 region of the hippocampus, and the primary somatosensory cortex of wild-type mice, application of the CB1 agonist (R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphthalenylmethanone (WIN55,212-2; WIN) (5 mum) reduced evoked excitatory postsynaptic responses. In contrast, in slices obtained from conditional mouse mutants lacking CB1 in all principal forebrain neurons but not in GABAergic interneurons (CB1(f/f;CaMKIIalphaCre)), WIN no longer affected glutamatergic synaptic transmission in any of the brain regions tested. Compatible with a presynaptic mechanism, WIN did not change the sensitivity to focally uncaged l-glutamate. WIN reduced glutamatergic responses in slices obtained from mice lacking CB1 exclusively in GABAergic neurons (CB1(f/f;Dlx5/6-Cre)), thus excluding the involvement of CB1 expressed on GABAergic neurons in this effect of the drug. The present data strongly indicate that excitatory synaptic transmission in forebrain areas is directly modulated by CB1 expressed on presynaptic axon terminals originating from glutamatergic neurons.

Nitrous oxide (N2O) pre- and postsynaptically attenuates NMDA receptor-mediated neurotransmission in the amygdala.

The gaseous anaesthetic N(2)O displays analgesic, anxiolytic, and amnesic properties and has addictive psychedelic effects. N(2)O can further act as a neuroprotective agent, but may also become neurotoxic under certain conditions. Here, we employed whole-cell patch-clamp techniques in acute brain slices, and electrical afferent and infrared-guided laser stimulation to examine how N(2)O (65%) can affect NMDA receptor (NMDAR)-mediated synaptic transmission to principal neurons (PNs) of the adult murine basolateral amygdala (BLA). The BLA plays a critical role in anaesthetic-induced amnesia, the formation of aversive memories, as well as in fear and addictive behaviour. We evoked NMDAR-mediated excitatory postsynaptic currents (NMDAR-EPSCs) in PNs of the BLA (BLA-PNs). We found these currents to be markedly decreased by N(2)O via pre- and postsynaptic actions: Without changing their kinetics and open probability, N(2)O impeded the voltage-dependent channel opening of NMDARs in BLA-PNs and diminished their unitary conductance as estimated by non-stationary fluctuation analysis. In addition, our data speak in favour of a N(2)O-produced reduction in the probability of glutamate release at the synapses generating the NMDAR-EPSCs. It is conceivable that these effects not only contribute to anaesthesia and anxiolysis, but also have bearings on learning and memory as well as excitotoxicity in the amygdala.

Corticotropin-releasing factor (CRF) receptor type 1-dependent modulation of synaptic plasticity.

CRF receptor type (CRHR) 1 exerts neuroregulatory control on associative learning processes such as fear and anxiety like behaviour. Using hippocampal slices, we investigated the neuronal excitability in mice lacking CRHR1 (Crhr1(-/-)). Compared to wild-type mice, long-term potentiation (LTP) elicited by 100 pulses at 100Hz was not different. Unexpectedly, at lower frequencies (1, 5 or 10Hz), the resulting synaptic changes in CA1 neurons of Crhr1(-/-) were systematically shifted towards long-term depression (LTD). Furthermore, testing paired-pulse paradigm revealed a GABA receptor-dependent decrease of paired-pulse ratio in Crhr1(-/-). It might be assumed that a lack of CRHR1 induce developmental changes which resulted in altered GABAergic activity, producing attenuated synaptic potentiation after repetitive stimulation and thus favouring LTD in principal neurons. Since CRHR1 are located in GABAergic somata, axons and boutons the activity of these receptor types rather might contribute to the development of the neuronal ability for plasticity like processes on the level of NMDAR subunit composition and GABAergic activity.

Infrared-guided laser stimulation as a tool for elucidating the synaptic site of expression of long-term synaptic plasticity.

Long-term potentiation is a synaptic mechanism thought to be involved in learning and memory. Long-term depression (LTD), an activity-dependent decrease in synaptic efficacy, may be an equally important mechanism that permits neural networks to store information more effectively. Two forms of LTD have been identified in the mammalian central nervous system, which are induced by the synaptic activation of N-methyl-D: -aspartate (NMDA) and metabotropic glutamate (mGlu) receptors, respectively. Whereas the expression mechanisms of NMDA receptor-dependent LTD have been demonstrated to be postsynaptic, those of mGlu receptor-dependent LTD have not been clearly identified. In order to address this issue, a variety of different electrophysiological methods have been used. A very elegant way to realize this experimental approach is provided by the development of photolytic application of glutamate, which allows the temporally and spatially highly specific activation of any neuron or any part of the neuron. By means of simultaneous application of electrical and photolytic stimulation techniques, it has been demonstrated that mGlu receptor-induced LTD is compatible with a presynaptic mechanism of expression.

Pain, opioids, and sleep: implications for restless legs syndrome treatment.

Opioid receptor agonists are known to relieve restless legs syndrome (RLS) symptoms, including both sensory and motor events, as well as improving sleep. The mechanisms of action of opioids in RLS are still a matter of speculation. The mechanisms by which endogenous opioids contribute to the pathophysiology of this polygenetic disorder, in which there are a number of variants, including developmental factors, remains unknown. A summary of the cellular mode of action of morphine and its (partial) antagonist naloxone via α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors and the involvement of dendritic spine activation is described. By targeting pain and its consequences, opioids are the first-line treatment in many diseases and conditions with both acute and chronic pain and have thus been used in both acute and chronic pain conditions over the last 40 years. Addiction, dependence, and tolerability of opioids show a wide variability interindividually, as the response to opioids is influenced by a complex combination of genetic, molecular, and phenotypic factors. Although several trials have now addressed opioid treatment in RLS, hyperalgesia as a complication of long-term opioid treatment, or opioid-opioid interaction have not received much attention so far. Therapeutic opioids may act not only on opioid receptors but also via histamine or N-methyl-d-aspartate (NMDA) receptors. In patients with RLS, one of the few studies investigating opioid bindings found that possible brain regions involved in the severity of RLS symptoms are similar to those known to be involved in chronic pain, such as the medial pain system (medial thalamus, amygdala, caudate nucleus, anterior cingulate gyrus, insular cortex, and orbitofrontal cortex). The results of this diprenorphine positron emission tomography study suggested that the more severe the RLS, the greater the release of endogenous opioids. Since 1993, when the first small controlled study was performed with oxycodone in RLS, opioids have been considered an efficacious off-label therapy in patients with severe RLS. A recent trial has proved the efficacy of a combination of prolonged release oxycodone/naloxone in patients with severe RLS as second-line therapy, with a mean dosage of 10/5 mg twice daily (mean difference of International Restless Legs Syndrome Study Group Rating Scale (IRLS) score between groups at 12 weeks: 8.15), and has now been licensed as the first opioid therapy in Europe. The current results from both short- and long-term trials and studies with opioids encourage optimism in alleviating RLS symptoms in patients with severe RLS, or possibly during or after augmentation.

Antidepressants and antipsychotic drugs colocalize with 5-HT3 receptors in raft-like domains.

Despite different chemical structure and pharmacodynamic signaling pathways, a variety of antidepressants and antipsychotics inhibit ion fluxes through 5-HT3 receptors in a noncompetitive manner with the exception of the known competitive antagonists mirtazapine and clozapine. To further investigate the mechanisms underlying the noncompetitive inhibition of the serotonin-evoked cation current, we quantified the concentrations of different types of antidepressants and antipsychotics in fractions of sucrose flotation gradients isolated from HEK293 (human embryonic kidney 293) cells stably transfected with the 5-HT3A receptor and of N1E-115 neuroblastoma cells in relation to the localization of the 5-HT3 receptor protein within the cell membrane. Western blots revealed a localization of the 5-HT3 receptor protein exclusively in the low buoyant density (LBD) fractions compatible with a localization within raft-like domains. Also, the antidepressants desipramine, fluoxetine, and reboxetine and the antipsychotics fluphenazine, haloperidol, and clozapine were markedly enriched in LBD fractions, whereas no accumulation occurs for mirtazapine, carbamazepine, moclobemide, and risperidone. The concentrations of psychopharmacological drugs within LBD fractions was strongly associated with their inhibitory potency against serotonin-induced cation currents. The noncompetitive antagonism of antidepressants at the 5-HT3 receptor was not conferred by an enhancement of receptor internalization as shown by immunofluorescence studies, assessment of receptor density in clathrin-coated vesicles, and electrophysiological recordings after coexpression of a dominant-negative mutant of dynamin I, which inhibits receptor internalization. In conclusion, enrichment of antidepressants and antipsychotics in raft-like domains within the cell membrane appears to be crucial for their antagonistic effects at ligand-gated ion channels such as 5-HT3 receptors.

Corrigendum: Local Optogenetic Induction of Fast (20-40 Hz) Pyramidal-Interneuron Network Oscillations in the In Vitro and In Vivo CA1 Hippocampus: Modulation by CRF and Enforcement of Perirhinal Theta Activity.

[This corrects the article on p. 108 in vol. 10, PMID: 27199662.].

Local Optogenetic Induction of Fast (20-40 Hz) Pyramidal-Interneuron Network Oscillations in the In Vitro and In Vivo CA1 Hippocampus: Modulation by CRF and Enforcement of Perirhinal Theta Activity.

The neurophysiological processes that can cause theta-to-gamma frequency range (4-80 Hz) network oscillations in the rhinal cortical-hippocampal system and the potential connectivity-based interactions of such forebrain rhythms are a topic of intensive investigation. Here, using selective Channelrhodopsin-2 (ChR2) expression in mouse forebrain glutamatergic cells, we were able to locally, temporally precisely, and reliably induce fast (20-40 Hz) field potential oscillations in hippocampal area CA1 in vitro (at 25°C) and in vivo (i.e., slightly anesthetized NEX-Cre-ChR2 mice). As revealed by pharmacological analyses and patch-clamp recordings from pyramidal cells and GABAergic interneurons in vitro, these light-triggered oscillations can exclusively arise from sustained suprathreshold depolarization (~200 ms or longer) and feedback inhibition of CA1 pyramidal neurons, as being mandatory for prototypic pyramidal-interneuron network (P-I) oscillations. Consistently, the oscillations comprised rhythmically occurring population spikes (generated by pyramidal cells) and their frequency increased with increasing spectral power. We further demonstrate that the optogenetically driven CA1 oscillations, which remain stable over repeated evocations, are impaired by the stress hormone corticotropin-releasing factor (CRF, 125 nM) in vitro and, even more remarkably, found that they are accompanied by concurrent states of enforced theta activity in the memory-associated perirhinal cortex (PrC) in vivo. The latter phenomenon most likely derives from neurotransmission via a known, but poorly studied excitatory CA1→PrC pathway. Collectively, our data provide evidence for the existence of a prototypic (CRF-sensitive) P-I gamma rhythm generator in area CA1 and suggest that CA1 P-I oscillations can rapidly up-regulate theta activity strength in hippocampus-innervated rhinal networks, at least in the PrC.

Neocortical long-term potentiation and long-term depression: site of expression investigated by infrared-guided laser stimulation.

The synaptic site of expression of long-term potentiation (LTP) and long-term depression (LTD) is still a matter of debate. To address the question of presynaptic versus postsynaptic expression of neocortical LTP and LTD in a direct approach, we measured the glutamate sensitivity of apical dendrites of layer 5 pyramidal neurons during LTP and LTD. We used infrared-guided laser stimulation to release glutamate from its "caged" form with high spatial and temporal resolution. Responses to photolytically released glutamate and synaptically evoked EPSPs were recorded with patch-clamp pipettes from the neuronal somata. LTP and LTD could be induced by electrical stimulation at the same synapses in succession. The NMDA receptor-dependent LTD was accompanied by a decrease in the dendritic glutamate sensitivity, suggesting a postsynaptic expression of neocortical LTD. In contrast, LTP was never accompanied by a change in the dendritic glutamate sensitivity. A possible explanation for this finding is a presynaptic expression of neocortical LTP. Another set of experiments corroborated these results: Photolytic application of glutamate with a frequency of 5 Hz caused a long-lasting Ca2+ and NMDA receptor-dependent decrease in the dendritic glutamate sensitivity. In contrast, LTP of dendritic glutamate sensitivity was never induced by photostimulation, despite several experimental modifications to prevent washout of the induction mechanism and to induce a stronger postsynaptic Ca2+ influx. In conclusion, our findings provide strong evidence for a postsynaptic expression of neocortical LTD and favor a primarily presynaptic locus of neocortical LTP.