Structural and functional consequences in the amygdala of leptin-deficient mice.

On the one hand, the emotional state can influence food intake and on the other hand, hunger can have an impact on the emotional state. Leptin, which is encoded by the ob gene, is involved in the energy homeostasis and plays a role in development of obesity. Mice deficient for leptin (ob/ob) are obese and display several behavioral alterations. It has been shown that ob/ob mice display striking changes in neuronal plasticity within the limbic system, e.g., hippocampal formation. We focus on alterations in ob/ob mice that can be related to alter processing in another part of the limbic system, the amygdala. ob/ob mice have a higher food consumption than age-matched controls, which might have an impact on the emotional state of these mice. Since the amygdala is involved in emotional processing, we analyze whether ob/ob mice display alterations in plasticity at the electrophysiological and structural level. No changes were seen in dendritic spine densities in the basolateral and lateral (LA) nucleus of the amygdala. Interestingly and in contrast to the hippocampus (Porter et al. 2013), long-term potentiation in the LA was increased in ob/ob mice. Our results indicate that amygdalar and hippocampal synaptic plasticity are regulated in different ways by leptin deficiency in accordance with the different functions of these limbic structures in stress and anxiety.

Priming of LTP in amygdala and hippocampus by prior paired pulse facilitation paradigm in mice lacking brain serotonin.

This study focuses on analyzing long-term potentiation (LTP) changes in the lateral nucleus of the amygdala (LA) and in the CA1 region of the hippocampus in slices derived from mice deficient in tryptophan hydroxylase 2 (TPH2-/- ), the rate-limiting enzyme for 5-HT synthesis in the brain. We found a reduced LTP in both brain structures in TPH2-/- mice. However, we found no changes in the magnitude of LTP in TPH2-/- mice compared to wildtype mice when it was preceded by a paired pulse protocol. Whereas the magnitude of long-term depression (LTD) did not differ between wildtype and TPH2-/- mice, priming synapses by LTD-induction facilitated subsequent CA1-LTP in wildtype mice to a greater extent than in TPH2-/- mice. In the LA we found no differences between the genotypes in this protocol of metaplasticity. These data show that, unlike exogenous 5-HT application, lack of 5-HT in the brain impairs cellular mechanisms responsible for induction of LTP. It is supposed that suppression of LTP observed in TPH2-/- mice might be compensated by mechanisms of metaplasticity induced by paired pulse stimulation or low frequency stimulation before the induction of LTP.

Glutamate receptor GluA1 subunit is implicated in capsaicin induced modulation of amygdala LTP but not LTD.

Capsaicin has been shown to modulate synaptic plasticity in various brain regions including the amygdala. Whereas in the lateral amygdala the modulatory effect of capsaicin on long-term potentiation (LA-LTP) is mediated by TRPV1 channels, we have recently shown that capsaicin-induced enhancement of long term depression (LA-LTD) is mediated by TRPM1 receptors. However, the underlying mechanism by which capsaicin modulates synaptic plasticity is poorly understood. In the present study, we investigate the modulatory effect of capsaicin on synaptic plasticity in mice lacking the AMPAR subunit GluA1. Capsaicin reduced the magnitude of LA-LTP in slices derived from wild-type mice as previously described, whereas this capsaicin-induced suppression was absent in GluA1-deficient mice. In contrast, neither LA-LTD nor the capsaicin-mediated enhancement of LA-LTD was changed in GluA1 knockout mice. Our data indicate that capsaicin-induced modulation of LA-LTP via TRPV1 involves GluA1-containing AMPARs whereas capsaicin-induced modulation of LA-LTD via TRPM1 is independent of the expression of the AMPAR GluA1 subunit.

A novel form of capsaicin-modified amygdala LTD mediated by TRPM1.

Recently we have shown that capsaicin attenuates the strength of LTP in the lateral amygdala (LA) and demonstrated that this effect is mediated by the transient receptor potential (TRP) channel TRPV1. Here we further show that capsaicin, which is thought to act primarily through TRPV1, modifies long term depression (LTD) in the LA. Yet the application of various TRPV1 antagonists does not reverse this effect and it remains in TRPV1-deficient mice. In addition, voltage gated calcium channels, nitric oxide and CB1 receptors are not involved. Using pharmacology and TRPM1-/- mice, our electrophysiological data indicate that capsaicin-induced activation of TRPM1 channels contribute to the induction of LA-LTD. Whereas LA-LTD in general depends on the acitvation of NMDA receptors- and group II metabotropic glutamate receptors (mGluR), the modifying effect of capsaicin on LA-LTD via TRPM1 appears to be specifically mediated by group I mGluRs and in interaction with another member of the TRP family, TRPC5. Additionally, intact GABAergic transmission is required for the capsaicin-effect to take place. This is the first documentation that beside their function in the retina TRPM1 proteins are expressed in the brain and have a functional relevance in modifying synaptic plasticity.

Early adenosine release contributes to hypoxia-induced disruption of stimulus-induced sharp wave-ripple complexes in rat hippocampal area CA3.

We investigated the effects of hypoxia on sharp wave-ripple complex (SPW-R) activity and recurrent epileptiform discharges in rat hippocampal slices, and the mechanisms underlying block of this activity. Oxygen levels were measured using Clark-style oxygen sensor microelectrodes. In contrast to recurrent epileptiform discharges, oxygen consumption was negligible during SPW-R activity. These network activities were reversibly blocked when oxygen levels were reduced to 20% or less for 3 min. The prolongation of hypoxic periods to 6 min caused reversible block of SPW-Rs during 20% oxygen and irreversible block when 0% oxygen (anoxia) was applied. In contrast, recurrent epileptiform discharges were more resistant to prolonged anoxia and almost fully recovered after 6 min of anoxia. SPW-Rs were unaffected by the application of 1-butyl-3-(4-methylphenylsulfonyl) urea, a blocker of KATP channels, but they were blocked by activation of adenosine A1 receptors. In support of a modulatory function of adenosine, the amplitude and incidence of SPW-Rs were increased during application of the A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX). Interestingly, hypoxia decreased the frequency of miniature excitatory post-synaptic currents in CA3 pyramidal cells, an effect that was converted into increased frequency by the adenosine A1 agonist DPCPX. In addition, DPCPX also delayed the onset of hypoxia-mediated block of SPW-Rs. Our data suggest that early adenosine release during hypoxia induces a decrease in pre-synaptic glutamate release and that both might contribute to transient block of SPW-Rs during hypoxia/anoxia in area CA3.

ERK activation causes epilepsy by stimulating NMDA receptor activity.

The ERK MAPK signalling pathway is a highly conserved kinase cascade linking transmembrane receptors to downstream effector mechanisms. To investigate the function of ERK in neurons, a constitutively active form of MEK1 (caMEK1) was conditionally expressed in the murine brain, which resulted in ERK activation and caused spontaneous epileptic seizures. ERK activation stimulated phosphorylation of eukaryotic translation initiation factor 4E (eIF4E) and augmented NMDA receptor 2B (NR2B) protein levels. Pharmacological inhibition of NR2B function impaired synaptic facilitation in area cornus ammonicus region 3 (CA3) in acute hippocampal slices derived from caMEK1-expressing mice and abrogated epilepsy in vivo. In addition, expression of caMEK1 caused phosphorylation of the transcription factor, cAMP response element-binding protein (CREB) and increased transcription of ephrinB2. EphrinB2 overexpression resulted in increased NR2B tyrosine phosphorylation, which was essential for caMEK1-induced epilepsy in vivo, since conditional inactivation of ephrinB2 greatly reduced seizure frequency in caMEK1 transgenic mice. Therefore, our study identifies a mechanism of epileptogenesis that links MAP kinase to Eph/Ephrin and NMDA receptor signalling.

Lithium acts as a potentiator of AMPAR currents in hippocampal CA1 cells by selectively increasing channel open probability.

Recent evidence suggests that lithium, which is used in the treatment of bipolar disorders, may act by influencing AMPAR properties at central glutamatergic synapses. While it is clear that lithium potentiates recombinant AMPAR responses in a subunit specific way, the origin of this potentiation is not known. We examined the effects of lithium on native AMPAR channels in CA1 pyramidal cells in hippocampal slices where AMPARs are expected to be associated with auxiliary subunits. We found that lithium produced a selective increase in single-channel open probability (P(open)), with little effect on single-channel conductance or burst length. From the present and previous finding it is likely that lithium causes a reduction in the time to recovery from desensitization, resulting in the observed increase in P(open). This would be consistent with the view that lithium acts like certain other allosteric AMPAR modulators to reduce the time spent in the desensitized state, but differs from those that act by slowing dissociation of glutamate.

Both NR2A and NR2B subunits of the NMDA receptor are critical for long-term potentiation and long-term depression in the lateral amygdala of horizontal slices of adult mice.

The lateral nucleus of the amygdala (LA) is implicated in emotional and social behaviors. We recently showed that in horizontal brain slices, activation of NMDA receptors (NMDARs) is a requirement for persistent synaptic alterations in the LA, such as long-term potentiation (LTP) and long-term depression (LTD). In the LA, NR2A- and NR2B-type NMDRs coexist in synapses of LA projection neurons. We assessed the contribution of the two NMDAR subtypes to LA-LTP and LA-LTD in adult mouse brain slices by different induction protocols and by different inputs to LA neurons in the presence of different NMDAR subunit antagonists. In general, our results indicate that both NR2A and NR2B subunits are required for the formation of LA-LTP and LA-LTD. The abolishment or reduction of plasticity changes by these compounds could be due to the reduction in calcium influx via NMDARs. We also show, to our knowledge for the first time, that paired-pulse (40-msec interstimulus interval), low-frequency stimulation of external capsule fibers causes stable LTD. Rather than resulting from exclusive roles of the NMDAR subtypes, the synaptic plasticity response in the amygdala appears to be directed by the pattern of synaptic activation and the used inputs, which recruit the major NMDAR subtypes to variable extents.

Physical Performance and Quality of Life after Ankle Fusion. / Körperliche Leistungsfähigkeit und Lebensqualität nach Arthrodese des oberen Sprunggelenks.

INTRODUCTION: Ankle fusion is still considered as an established therapy for end-stage ankle osteoarthritis. To determine exact description of postoperative functioning, it is necessary to consult a variety of functional scores and quality of life questionnaires. METHODS/PATIENTS: 34 patients with 34 ankle fusions were investigated on average 5.9 years postoperatively by functional tests and health-related quality of life questionnaires (AOFAS hindfoot score [AOFAS: American Orthopaedic Foot/Ankle Society], Foot Function Index [FFI], Lower Extremity Functional Scale [LEFS], Lower Extremity Activity Scale [LEAS], Visual Analogue Scale Foot/Ankle Surgery [VAS FA], Short Form 36 [SF-36], EuroQol 5D [EQ-5D]). RESULTS: After ankle fusion: the majority of cases gain pain reduction, but residual symptoms may persist; the maximum walking distance (subjectively more than objectively) will be extended; rarely walking without any aids can be achieved; in most cases, the gait pattern is only slightly changed; the re-entry into working life is often possible; climbing stairs without any restrictions is not always possible; the psychological situation will be equalized with that of healthy people. CONCLUSION: The results of the study confirm the success rates of ankle fusions in the majority of cases. Well defined limitations and residual symptoms can be named on the basis of the available data.

Expression of glutamate receptor subunits in human cancers.

Emerging evidence suggests a role for glutamate and its receptors in the biology of cancer. This study was designed to systematically analyze the expression of ionotropic and metabotropic glutamate receptor subunits in various human cancer cell lines, compare expression levels to those in human brain tissue and, using electrophysiological techniques, explore whether cancer cells respond to glutamate receptor agonists and antagonists. Expression analysis of glutamate receptor subunits NR1-NR3B, GluR1-GluR7, KA1, KA2 and mGluR1-mGluR8 was performed by means of RT-PCR in human rhabdomyosarcoma/medulloblastoma (TE671), neuroblastoma (SK-NA-S), thyroid carcinoma (FTC 238), lung carcinoma (SK-LU-1), astrocytoma (MOGGCCM), multiple myeloma (RPMI 8226), glioma (U87-MG and U343), lung carcinoma (A549), colon adenocarcinoma (HT 29), T cell leukemia cells (Jurkat E6.1), breast carcinoma (T47D) and colon adenocarcinoma (LS180). Analysis revealed that all glutamate receptor subunits were differentially expressed in the tumor cell lines. For the majority of tumors, expression levels of NR2B, GluR4, GluR6 and KA2 were lower compared to human brain tissue. Confocal imaging revealed that selected glutamate receptor subunit proteins were expressed in tumor cells. By means of patch-clamp analysis, it was shown that A549 and TE671 cells depolarized in response to application of glutamate agonists and that this effect was reversed by glutamate receptor antagonists. This study reveals that glutamate receptor subunits are differentially expressed in human tumor cell lines at the mRNA and the protein level, and that their expression is associated with the formation of functional channels. The potential role of glutamate receptor antagonists in cancer therapy is a feasible goal to be explored in clinical trials.

A pathway-specific function for different AMPA receptor subunits in amygdala long-term potentiation and fear conditioning.

The AMPA receptor subunit glutamate receptor 1 (GluR1 or GluR-A) contributes to amygdala-dependent emotional learning. It remains unclear, however, to what extent different amygdala pathways depend on GluR1, or other AMPA receptor subunits, for proper synaptic transmission and plasticity, and whether GluR1-dependent long-term potentiation (LTP) is necessary for auditory and contextual fear conditioning. Here, we dissected the role of GluR1 and GluR3 (GluR-C) subunits in AMPA receptor-dependent amygdala LTP and fear conditioning using knock-out mice (GluR1-/- and GluR3-/-). We found that, whereas LTP at thalamic inputs to lateral amygdala (LA) projection neurons and at glutamatergic synapses in the basal amygdala was completely absent in GluR1-/- mice, both GluR1 and GluR3 contributed to LTP in the cortico-LA pathway. Because both auditory and contextual fear conditioning were selectively impaired in GluR1-/- but not GluR3-/- mice, we conclude that GluR1-dependent synaptic plasticity is the dominant form of LTP underlying the acquisition of auditory and contextual fear conditioning, and that plasticity in distinct amygdala pathways differentially contributes to aversive conditioning.

Delayed anoxic depolarizations in hippocampal neurons of mice lacking the excitatory amino acid carrier 1.

Hypoxia leads to a rapid increase in vesicular release of glutamate. In addition, hypoxic glutamate release might be caused by reversed operation of neuronal glutamate transporters. An increase in extracellular glutamate concentration might be an important factor in generating anoxic depolarizations (AD) and subsequent neuronal damage. To study the AD and the vesicular release in hippocampal slices from CD1 wild-type mice and mice in which the neuronal glutamate transporter excitatory amino acid carrier 1 (EAAC1) had been knocked out, the authors performed recordings of field potentials and patch clamp recordings of CA1 pyramidal cells. Latency to anoxic depolarizations was enhanced in EAAC1-/- mice, whereas the hypoxia-induced increase in miniature excitatory postsynaptic current frequency occurred with similarly short latencies and to a similar extent in control and mutated animals. Additional block of glial glutamate uptake with TBOA (dl-threo-beta-benzyloxyaspartate), a nontransportable and potent inhibitor, dramatically reduced the latency to onset of AD and abolished the difference between wild-type mice and EAAC1-/- mice. The authors conclude that the neuronal glutamate transporter greatly influences the latency to generation of AD. Because ADs are not prevented in EAAC1-deficient mice, vesicular release mechanisms also seem to be involved. They become prominent when glial glutamate transport is blocked.

Glutamate transporters and metabotropic receptors regulate excitatory neurotransmission in the medial entorhinal cortex of the rat.

In layer III of the medial entorhinal cortex (mEC), a region that is especially prone to cell damage in Alzheimer's disease, schizophrenia and epilepsy, effects of blocking glutamate uptake on excitatory synaptic transmission were studied. Two competitive glutamate transporter antagonists, TBOA and tPDC, reduced the amplitude of pharmacologically isolated AMPAR and NMDAR mediated EPSPs/EPSCs without changing the time course of the events. This effect was mimicked by tACPD, an agonist of groups I and II metabotropic glutamate receptors (mGluRs). The competitive groups I and II mGluR antagonist MCPG blocked the depression of the EPSC amplitude induced by tACPD and also prevented the effect of either TBOA or tPDC. Furthermore, EGLU, which selectively antagonizes group II mGluRs, blocked the effect of tPDC and LY3414965, a specific group I mGluR antagonist, abolished the reduction of amplitude caused by TBOA. Additionally, application of TBOA increased the paired-pulse index, suggesting a presynaptic mechanism for the depression of EPSP/EPSC amplitude. The present data suggest that glutamate transporters and group I/II mGluRs regulate excitatory synaptic transmission in the mEC. Presynaptic mGluRs may limit excessive glutamate accumulation if uptake becomes compromised.

Capsaicin-induced changes in LTP in the lateral amygdala are mediated by TRPV1.

The transient receptor potential vanilloid type 1 (TRPV1) channel is a well recognized polymodal signal detector that is activated by painful stimuli such as capsaicin. Here, we show that TRPV1 is expressed in the lateral nucleus of the amygdala (LA). Despite the fact that the central amygdala displays the highest neuronal density, the highest density of TRPV1 labeled neurons was found within the nuclei of the basolateral complex of the amygdala. Capsaicin specifically changed the magnitude of long-term potentiation (LTP) in the LA in brain slices of mice depending on the anesthetic (ether, isoflurane) used before euthanasia. After ether anesthesia, capsaicin had a suppressive effect on LA-LTP both in patch clamp and in extracellular recordings. The capsaicin-induced reduction of LTP was completely blocked by the nitric oxide synthase (NOS) inhibitor L-NAME and was absent in neuronal NOS as well as in TRPV1 deficient mice. The specific antagonist of cannabinoid receptor type 1 (CB1), AM 251, was also able to reduce the inhibitory effect of capsaicin on LA-LTP, suggesting that stimulation of TRPV1 provokes the generation of anandamide in the brain which seems to inhibit NO synthesis. After isoflurane anesthesia before euthanasia capsaicin caused a TRPV1-mediated increase in the magnitude of LA-LTP. Therefore, our results also indicate that the appropriate choice of the anesthetics used is an important consideration when brain plasticity and the action of endovanilloids will be evaluated. In summary, our results demonstrate that TRPV1 may be involved in the amygdala control of learning mechanisms.

Influence of agonist concentration on AMPA and kainate channels in CA1 pyramidal cells in rat hippocampal slices.

We have determined the functional properties of single AMPA receptor (AMPAR) and kainate receptor channels present in CA1 cells in hippocampal slices, to shed light on the relationship between single-channel behaviour and synaptic currents in these cells. To derive basic properties of AMPA and kainate channels activated by their excitatory transmitter, we examined outside-out patches exposed to glutamate. The kainate agonist SYM 2081, was used to confirm the presence of kainate receptors. Channels activated by glutamate or SYM 2081 exhibited conductance levels of 2-20 pS. Properties of single channels depended on the glutamate or AMPA concentration used. We observed a marked increase in mean channel conductance (gamma) from gamma = 6.9, to 11.2 pS, when glutamate was increased from 10 mum to 10 mm. The kinetic behaviour of AMPAR channels was also influenced by agonist concentration, with an increase in 'bursty' events at higher concentrations. In contrast, kainate channels were characterized by brief openings without bursts. Consistent with the view that 'bursty' events arose from AMPARs, these openings decreased in the presence of the AMPAR blocker GYKI 53655. Furthermore, our experiments revealed a concentration-dependent increase in the number of conductance states during an individual AMPAR opening; AMPAR channels displayed up to four distinct levels. Our results are consistent with the view that the AMPAR channel conductance depends on the number of transmitter molecules bound in CA1 cells. We consider the implications of these findings for the change in EPSC properties during long-term potentiation (LTP).

Kindling enhances kainate receptor-mediated depression of GABAergic inhibition in rat granule cells.

Several lines of evidence indicate a substantial contribution of kainate receptors to temporal lobe seizures. The activation of kainate receptors located on hippocampal inhibitory interneurons was shown to reduce GABA release. A reduced GABA release secondary to kainate receptor activation could contribute to an enhanced seizure susceptibility. As the dentate gyrus serves a pivotal gating function in the spread of limbic seizures, we tested the role of kainate receptors in the regulation of GABA release in the dentate gyrus of control and kindled animals. Application of glutamate (100 micro m) in the presence of the NMDA receptor antagonist d-APV and the AMPA receptor antagonist, SYM 2206 caused a slight depression of evoked monosynaptic inhibitory postsynaptic currents (IPSCs) in control, but a substantial decrease in kindled dentate granule cells. The observation that kainate receptor activation altered paired-pulse depression and reduced the frequency of TTX-insensitive miniature IPSCs without affecting their amplitude is consistent with a presynaptic action on the inhibitory terminal to reduce GABA release. In kindled preparations, neither glutamate (100 micro m) nor kainate (10 micro m) applied in a concentration known to depolarize hippocampal interneurons led to an increase of the TTX-sensitive spontaneous IPSC frequency nor to changes of the postsynaptic membrane properties. Consistently, the inhibitory effect on evoked IPSCs was not affected by the presence of the GABAB receptor antagonist, CGP55845A, thus excluding a depression by an enhanced release of GABA acting on presynaptic GABAB receptors. The enhanced inhibition of GABA release following presynaptic kainate receptor activation favours a use-dependent hyperexcitability in the epileptic dentate gyrus.