Vestibular Testing-New Physiological Results for the Optimization of Clinical VEMP Stimuli.

Both auditory and vestibular primary afferent neurons can be activated by sound and vibration. This review relates the differences between them to the different receptor/synaptic mechanisms of the two systems, as shown by indicators of peripheral function-cochlear and vestibular compound action potentials (cCAPs and vCAPs)-to click stimulation as recorded in animal studies. Sound- and vibration-sensitive type 1 receptors at the striola of the utricular macula are enveloped by the unique calyx afferent ending, which has three modes of synaptic transmission. Glutamate is the transmitter for both cochlear and vestibular primary afferents; however, blocking glutamate transmission has very little effect on vCAPs but greatly reduces cCAPs. We suggest that the ultrafast non-quantal synaptic mechanism called resistive coupling is the cause of the short latency vestibular afferent responses and related results-failure of transmitter blockade, masking, and temporal precision. This "ultrafast" non-quantal transmission is effectively electrical coupling that is dependent on the membrane potentials of the calyx and the type 1 receptor. The major clinical implication is that decreasing stimulus rise time increases vCAP response, corresponding to the increased VEMP response in human subjects. Short rise times are optimal in human clinical VEMP testing, whereas long rise times are mandatory for audiometric threshold testing.

Two types of GLR channels cooperate differently in light and dark growth of Arabidopsis seedlings.

BACKGROUND: GLutamate Receptor-like (GLR) channels are multimeric, ionotropic, ligand-gated plant transmembrane receptors. They are homologous to mammalian glutamate receptors, iGLuRs, which are critical to neuronal function. GLRs have been reported several times to play a role in photomorphogenesis. However, to date, no study has looked at the mechanism of their involvement in this process. Here we focused on examining the impact of GLRs on the regulation of early seedling growth in blue light, red light, and in the dark. RESULTS: Wild type and six photoreceptor mutant seedlings were grown on media supplemented with known iGLuR/GLR channel antagonists: MK-801, which non-competitively blocks NMDA channels in mammalian cells, and CNQX, known for competitive blocking of AMPA channels in mammalian cells. The lengths of hypocotyls and roots were measured in seedlings of phyA, phyB, phot1, phot2, cry1, and cry2 mutants after 7 days of in vitro culture. Changes in growth parameters, both in light and in darkness upon application of chemical antagonists, show that both types of GLR channels, NMDA-like and AMPA-like, are involved in the regulation of seedling growth irrespective of light conditions. Analysis of seedling growth of photoreceptor mutants indicates that the channels are influenced by signaling from phot1, phot2, and cry1. To extend our analysis, we also evaluated the elicitation of a calcium wave, which is likely to be partially driven by GLRs, in Arabidopsis seedlings. The changes in cellobiose-induced calcium waves observed after applying GLR inhibitors suggest that both types of channels likely cooperate in shaping Arabidopsis seedling growth and development. CONCLUSIONS: Our work provides the first experimental evidence that two types of GLR channels function in plants: NMDA-like and AMPA-like. We also demonstrate that the channels are involved in seedling growth and development, at least partially through modulation of calcium signaling, but they are unlikely to play a major role in photomorphogenesis.

Alteration of Lateral Habenula Function Prevents the Proper Exploration of a Novel Environment.

The lateral habenula (LHb) is an epithalamic brain region viewed as a converging hub, integrating information from a large connectome and then projecting to few critical midbrain monoaminergic systems. Numerous studies have explored the roles of the LHb, notably in aversion and avoidance. An important recurring finding when manipulating the LHb is the induction of anxiety-related behaviours. However, its exact role in such behaviours remains poorly understood. In the present study, we used two pharmacological approaches altering LHb activity, intra-LHb infusion of either the GABA-A receptor agonist, Muscimol, or the glutamatergic AMPA receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and exposed rats to three consecutive open field (OF) sessions. We found that both pharmacological treatments prevented rats to explore the centre of the OF, considered as the most anxiogenic part of the apparatus, across the three OF sessions. In addition, during the first, but not the two consecutive sessions, both treatments prevented a thorough exploration of the OF. Altogether, these results confirm the crucial role played by the LHb in anxiety-related behaviours and further suggest its implication in the exploration of new anxiogenic environments.

The effect of CNQX on self-administration: present in nicotine, absent in methamphetamine model.

Objective: Addiction is a chronic disease with limited pharmacological options for intervention. Focusing on reducing glutamate levels in the brain seems to be a promising strategy in addiction treatment research. Our research aimed to evaluate the effects of CNQX, an antagonist that targets AMPA and kainate glutamatergic receptors while also exhibiting affinity for the NMDA receptor, especially by modulating its glycine site. We conducted this assessment on the self-administration of nicotine and methamphetamine via intravenous (IV) administration in rats. Methods: An operant IV self-administration model was used in male Wistar rats. When animals maintained a stable intake of nicotine or methamphetamine, we administered a single injection of CNQX (in the dose of 3 or 6 mg/kg IV) to evaluate its effect on drug intake. Subsequently, the rats were forced to abstain by staying in their home cages for 2 weeks. The period of abstinence was followed by a context-induced relapse-like session before which animals were pretreated with the injection of CNQX (3 or 6 mg/kg IV) to evaluate its effect on drug seeking. Results: CNQX significantly reduced nicotine intake during the maintenance phase, but no effect was revealed on nicotine seeking after forced abstinence. CNQX did not affect methamphetamine taking or seeking. Conclusion: The effect of reducing nicotine taking but not seeking could be explained by different involvement of glutamatergic receptors in various stages of nicotine dependence.

Effects of dibenzylbutyrolactone lignans arctigenin and trachelogenin on the motility of isolated rat ileum.

Dibenzylbutyrolactone-type lignans are phenolic compounds of medical importance. The purpose of the study was to determine the effects of two such lignans, arctigenin and trachelogenin on the motility of isolated rat ileum and obtain indications on their mechanism of action. They were isolated from Arctium lappa and Cirsium arvense, respectively, which have been used traditionally to treat gastrointestinal disorders. 1-1.5 cm long segments of distal ileum were obtained from adult male Wistar rats. The intestinal segments were suspended vertically in a well-aerated organ-bath according to Magnus mounting method. The intestinal motility was monitored for 30 min before treatment to obtain the baseline, followed by treatment with 1 µM, 10 µM, 20 µM and 40 µM concentrations of arctigenin and 0.5 µM, 1 µM, 10 µM and 20 µM of trachelogenin concentrations. The amplitude, tone, and period of spontaneous contractions were measured after 15 and 30 min of treatment. To investigate their mechanism of action, cholinergic, glutamatergic, adrenergic antagonists and compounds inhibiting nitric oxide synthase and L-type calcium channels were also tested. Arctigenin and trachelogenin decreased the frequency of contractions in a dose-dependent manner. At the concentration of 20 µM and 40 µM of trachelogenin and arctigenin, respectively, there was a marked alteration in spontaneous contraction pattern with an observable increase in the period time. This activity was comparable to 0.5 µM nifedipine (L-type calcium channel blocker) treatment. Our results demonstrate relaxant effect of arctigenin and trachelogenin on the ileum motility that may be mediated by L-type calcium ion channel blockade.

Glutamate receptor antagonist suppresses the activation of nesfatin-1 neurons following refeeding or glucose administration.

BACKGROUND: Nesfatin-1 is a newly identified satiety peptide that has regulatory effects on food intake and glucose metabolism, and is located in the hypothalamic nuclei, including the supraoptic nucleus (SON). In this study, we have investigated the hypothesis that nesfatin-1 neurons are activated by refeeding and intraperitoneal glucose injection and that the glutamatergic system has regulatory influences on nesfatin-1 neurons in the SON. MATERIALS AND METHODS: The first set of experiments analysed activation of nesfatin-1 neurons after refeeding as a physiological stimulus and the effectiveness of the glutamatergic system on this physiological stimulation. The subjects were randomly divided into three groups: fasting group, refeeding group and antagonist (CNQX + refeeding) group. The second set of experiments analysed activation of nesfatin-1 neurons by glucose injection as a metabolic stimulus and the effectiveness of the glutamatergic system on this metabolic stimulation. The subjects were randomly divided into three groups: saline group, glucose group and antagonist (CNQX + glucose) group. RESULTS: Refeeding significantly increased the number of activated nesfatin-1 neurons by approximately 66%, and intraperitoneal glucose injection activated these neurons by about 55%, compared to the fasting and saline controls. The injections of glutamate antagonist (CNQX) greatly decreased the number of activated nesfatin-1 neurons. CONCLUSIONS: This study suggested that nesfatin-1 neurons were activated by peripheral and/or metabolic signals and that this effect was mediated through the glutamatergic system.

dCA1-NAc shell glutamatergic projection mediates context-induced memory recall of morphine.

Opioid relapse is generally caused by the recurrence of context-induced memory reinstatement of reward. However, the internal mechanisms that facilitate and modify these processes remain unknown. One of the key regions of the reward is the nucleus accumbens (NAc) which receives glutamatergic projections from the dorsal hippocampus CA1 (dCA1). It is not yet known whether the dCA1 projection to the NAc shell regulates the context-induced memory recall of morphine. Here, we used a common model of addiction-related behavior conditioned place preference paradigm, combined with immunofluorescence, chemogenetics, optogenetics, and electrophysiology techniques to characterize the projection of the dCA1 to the NAc shell, in context-induced relapse memory to morphine. We found that glutamatergic neurons of the dCA1 and gamma aminobutyric acidergic (GABA) neurons of the NAc shell are the key brain areas and neurons involved in the context-induced reinstatement of morphine memory. The dCA1-NAc shell glutamatergic input pathway and the excitatory synaptic transmission of the dCA1-NAc shell were enhanced via the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) when mice were re-exposed to environmental cues previously associated with drug intake. Furthermore, chemogenetic and optogenetic inactivation of the dCA1-NAc shell pathway decreased the recurrence of long- and short-term morphine-paired context memory in mice. These results provided evidence that the dCA1-NAc shell glutamatergic projections mediated the context-induced memory recall of morphine.

Cannabidiol inhibits febrile seizure by modulating AMPA receptor kinetics through its interaction with the N-terminal domain of GluA1/GluA2.

Cannabidiol (CBD) is a major phytocannabinoid in Cannabis sativa. CBD is being increasingly reported as a clinical treatment for neurological diseases. Febrile seizure is one of the most common diseases in children with limited therapeutic options. We investigated possible therapeutic effects of CBD on febrile seizures and the underlying mechanism. Use of a hyperthermia-induced seizures model revealed that CBD significantly prolonged seizure latency and reduced the severity of thermally-induced seizures. Hippocampal neuronal excitability was significantly decreased by CBD. Further, CBD significantly reduced the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) mediated evoked excitatory postsynaptic currents (eEPSCs) and the amplitude and frequency of miniature EPSCs (mEPSCs). Furthermore, CBD significantly accelerated deactivation in GluA1 and GluA2 subunits. Interestingly, CBD slowed receptor recovery from desensitization of GluA1, but not GluA2. These effects on kinetics were even more prominent when AMPAR was co-expressed with γ-8, the high expression isoform 8 of transmembrane AMPAR regulated protein (TARPγ8) in the hippocampus. The inhibitory effects of CBD on AMPAR depended on its interaction with the distal N-terminal domain of GluA1/GluA2. CBD inhibited AMPAR activity and reduced hippocampal neuronal excitability, thereby improving the symptoms of febrile seizure in mice. The putative binding site of CBD in the N-terminal domain of GluA1/GluA2 may be a drug target for allosteric gating modulation of AMPAR.

Contribution of the ventrolateral thalamus to the locomotion-related activity of motor cortex.

The activity of motor cortex is necessary for accurate stepping on a complex terrain. How this activity is generated remains unclear. The goal of this study was to clarify the contribution of signals from the ventrolateral thalamus (VL) to formation of locomotion-related activity of motor cortex during vision-independent and vision-dependent locomotion. In two cats, we recorded the activity of neurons in layer V of motor cortex as cats walked on a flat surface and a horizontal ladder. We reversibly inactivated ~10% of the VL unilaterally with the glutamatergic transmission antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and analyzed how this affected the activity of motor cortex neurons. We examined neuronal subpopulations with somatosensory receptive fields on different segments of the forelimb and pyramidal tract projecting neurons (PTNs). We found that the VL contribution to the locomotion-related activity of motor cortex is very powerful and has both excitatory and inhibitory components. The magnitudes of both the excitatory and inhibitory contributions fluctuate over the step cycle and depend on locomotion task. On a flat surface, the VL contributes more excitation to the shoulder- and elbow-related neurons than the wrist/paw-related cells. The VL excites the shoulder-related group the most during the transition from stance to swing phase, while most intensively exciting the elbow-related group during the transition from swing to stance. The VL contributes more excitation for the fast- than slow-conducting PTNs. Upon transition to vision-dependent locomotion on the ladder, the VL contribution increases more for the wrist/paw-related neurons and slow-conducting PTNs.NEW & NOTEWORTHY How the activity of motor cortex is generated and the roles that different inputs to motor cortex play in formation of response properties of motor cortex neurons during movements remain unclear. This is the first study to characterize the contribution of the input from the ventrolateral thalamus (VL), the main subcortical input to motor cortex, to the activity of motor cortex neurons during vision-independent and vision-dependent locomotion.

Prenatal exposure to nicotine disrupts synaptic network formation by inhibiting spontaneous correlated wave activity.

Correlated spontaneous activity propagating over a wide region of the central nervous system is expressed during a specific period of embryonic development. We previously demonstrated using an optical imaging technique with a voltage-sensitive dye that this wave-like activity, which we referred to as the depolarization wave, is fundamentally involved in the early process of synaptic network formation. We found that the in ovo application of bicuculline/strychnine or d-tubocurarine, which blocked the neurotransmitters mediating the wave, significantly reduced functional synaptic expression in the brainstem sensory nucleus. This result, particularly for d-tubocurarine, an antagonist of nicotinic acetylcholine receptors, suggested that prenatal nicotine exposure associated with maternal smoking affects the development of neural circuit formation by interfering with the correlated wave. In the present study, we tested this hypothesis by examining the effects of nicotine on the correlated activity and assessing the chronic action of nicotine in ovo on functional synaptic expression along the vagal sensory pathway. In ovo observations of chick embryo behavior and electrical recording using in vitro preparations showed that the application of nicotine transiently increased embryonic movements and electrical bursts associated with the wave, but subsequently inhibited these activities, suggesting that the dominant action of the drug was to inhibit the wave. Optical imaging with the voltage-sensitive dye showed that the chronic exposure to nicotine in ovo markedly reduced functional synaptic expression in the higher-order sensory nucleus of the vagus nerve, the parabrachial nucleus. The results suggest that prenatal nicotine exposure disrupts the initial formation of the neural circuitry by inhibiting correlated spontaneous wave activity.

Resveratrol derivative excited postsynaptic potentiation specifically via PKCß-NMDA receptor mediation.

Several decades have passed since resveratrol (RSV) was first identified in red wine. Researchers have reported the pleiotropic anti-oxidant, anti-inflammatory, anti-cancer, anti-aging, and neuronal protective effects of resveratrol and its glycosylated derivative. However, few studies have distinguished the minute differences in the properties between resveratrol and its glycosylated derivative in terms of synaptic plasticity. As an abundant natural product of glycosylated resveratrol, the derivative 2,3,4',5-tetrahydroxystilbene-2-O-ß-d-glucoside (TSG) has been determined to be a better option for long-term potentiation (LTP) in the hippocampus under physiological and pathological conditions than resveratrol. TSG, as well as its parent molecule RSV, could elicit early-LTP and recover fast excitatory postsynaptic potentials (EPSPs) in the hippocampus. Using various modalities, including pre- and post-whole-cell patch clamping techniques in the calyx of Held, pharmacological inhibition of the N-methyl-d-aspartic acid receptor (NMDAr) and the α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid receptor (AMPAr) as well as protein kinase C (PKC) activation, we demonstrated that TSG, unlike RSV, could merely promote NMDA-mediated EPSC via PKCß cascade. Our results provide new knowledge that glycosylation of resveratrol could significantly improve its specificity in promoting sole NMDAr mediation of EPSPs, in addition to improving solubility and resistance against oxidation in vivo. These observations could contribute to further exploration of pharmaceutical evaluation of glycosylated stilbene in the future.

Two distinct electrophysiological mechanisms underlie extensive depolarization elicited by 2,4 diaminobutyric acid in leech Retzius neurons.

Recent studies suggest that 2,4-DABA, a neurotoxic excitatory amino acid present in virtually all environments, but predominantly in aquatic ecosystems may be a risk factor for development of neurodegenerative diseases in animals and humans. Despite its neurotoxicity and potential environmental importance, mechanisms underlying the excitatory and putative excitotoxic action of 2,4-DABA in neurons are still unexplored. We previously reported on extensive two-stage membrane depolarization and functional disturbances in leech Retzius neurons induced by 2,4-DABA. Current study presents the first detailed look into the electrophysiological processes leading to this depolarization. Intracellular recordings were performed on Retzius neurons of the leech Haemopis sanguisuga using glass microelectrodes and input membrane resistance (IMR) was measured by injecting hyperpolarizing current pulses through these electrodes. Results show that the excitatory effect 2,4-DABA elicits on neurons' membrane potential is dependent on sodium ions. Depolarizing effect of 5·10-3 mol/L 2,4-DABA in sodium-free solution was significantly diminished by 91% reducing it to 3.26 ±â€¯0.62 mV and its two-stage nature was abrogated. In addition to being sodium-dependent, the depolarization of membrane potential induced by this amino acid is coupled with an increase of membrane permeability, as 2,4-DABA decreases IMR by 8.27 ±â€¯1.47 MΩ (67.60%). Since present results highlight the role of sodium ions, we investigated the role of two putative sodium-dependent mechanisms in 2,4-DABA-induced excitatory effect - activation of ionotropic glutamate receptors and the electrogenic transporter for neutral amino acids. Excitatory effect of 5·10-3 mol/L 2,4-DABA was partially blocked by 10-5 mol/L 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) a non-NMDA receptor antagonist as the first stage of membrane depolarization was significantly reduced by 2.59 ±â€¯0.98 mV (40%), whilst second stage remained unaltered. Moreover, involvement of the sodium-dependent transport system for neutral amino acids was investigated by equimolar co-application of 5·10-3 mol/L 2,4-DABA and L-alanine, a competitive inhibitor of this transporter. Although L-alanine exhibited no effect on the first stage of membrane depolarization elicited by 2,4-DABA, it substantially reduced the second stage (the overall membrane depolarization) from 39.63 ±â€¯2.22 mV to 16.28 ±â€¯2.58 mV, by 58.92%. We therefore propose that the electrophysiological effect of 2,4-DABA on Retzius neurons is mediated by two distinct mechanisms, i.e. by activation of ionotropic glutamate receptor that initiates the first stage of membrane depolarization followed by the stimulation of an electrogenic sodium-dependent neutral amino acid transporter, leading to additional influx of positive charge into the cell and the second stage of depolarization.

Functional strengthening through synaptic scaling upon connectivity disruption in neuronal cultures.

An elusive phenomenon in network neuroscience is the extent of neuronal activity remodeling upon damage. Here, we investigate the action of gradual synaptic blockade on the effective connectivity in cortical networks in vitro. We use two neuronal cultures configurations-one formed by about 130 neuronal aggregates and another one formed by about 600 individual neurons-and monitor their spontaneous activity upon progressive weakening of excitatory connectivity. We report that the effective connectivity in all cultures exhibits a first phase of transient strengthening followed by a second phase of steady deterioration. We quantify these phases by measuring GEFF, the global efficiency in processing network information. We term hyperefficiency the sudden strengthening of GEFF upon network deterioration, which increases by 20-50% depending on culture type. Relying on numerical simulations we reveal the role of synaptic scaling, an activity-dependent mechanism for synaptic plasticity, in counteracting the perturbative action, neatly reproducing the observed hyperefficiency. Our results demonstrate the importance of synaptic scaling as resilience mechanism.

Involvement of glutamate receptors of the paragigantocellularis lateralis nucleus in the pain modulatory effect of 17ß-estradiol in male rats.

The pain modulatory role of the paragigantocellularis lateralis nucleus (LPGi) and the 17ß-estradiol has thoroughly been probed. This study investigates the contribution of ionotropic glutamate receptors in pain modulatory effect of intra-LPGi injection of 17ß-estradiol. For this purpose, the LPGi nucleus cannulation was performed and drugs were injected into this nucleus, 15 min prior to the formalin test. The duration of formalin-induced flexing and licking behaviors was recorded for 60 min immediately after formalin injection. The results showed that the flexing behavior is significantly decreased by intra-LPGi injection of 0.8 µmol 17ß-estradiol duringboth phases of formalin test (P < 0.001). However, 17ß-estradiol attenuated the licking duration only in the second phase (P < 0.001). Interestingly, NMDA and AMPA/kainate receptor antagonists (AP5 and CNQX, respectively) significantly counteracted the analgesic effect of intra-LPGi injection of 17ß-estradiol in both phases of the formalin test (P < 0.001). Consequently, the revealing results showed that the analgesic effect of intra-LPGi injection of 17ß-estradiol on acute inflammatory pain might be mediated via the activation of ionotropic glutamate receptors.

Voltage-sensitive dye recording of glossopharyngeal nerve-related synaptic networks in the embryonic mouse brainstem.

The glossopharyngeal nerve (N.IX) transfers motor and sensory information related to visceral and somatic functions, such as salivary secretion, gustation and the control of blood pressure. N.IX-related neural circuits are indispensable for these essential functions. Compared with the strenuous analysis of morphogenesis, we are only just starting to elucidate the functiogenesis of these neural circuits during ontogenesis. In the present study, we applied voltage-sensitive dye recording to the embryonic mouse brainstem, and examined the functional development of the N.IX-related neural circuits. First, we optically identified the motor nucleus (the inferior salivatory nucleus (ISN)) and the first-order sensory nucleus (the nucleus of the tractus solitarius (NTS)). We also succeeded in recording optical responses in the second/higher-order sensory nuclei via the NTS, including the parabrachial nucleus. Second, we pursued neuronal excitability and the onset of synaptic function in the N.IX-related nuclei. The neurons in the ISN were excitable at least at E11, and functional synaptic transmission in the NTS was first expressed at E12. In the second/higher-order sensory nuclei, synaptic function emerged at around E12-13. Third, by mapping optical responses to N.IX and vagus nerve (N.X) stimulation, we showed that the distribution patterns of neural activity in the NTS were different between the N.IX and the N.X from the early stage of ontogenesis. We discuss N.IX-related neural circuit formation in the brainstem, in comparison with our previous results obtained from chick and rat embryos.

Electrical stimulation mPFC affects morphine addiction by changing glutamate concentration in the ventral tegmental area.

Morphine addiction is known as a serious social problem. Medial prefrontal cortex (mPFC) and ventral tegmental area (VTA) are two important sites of the brain that contribute to this type of addiction, and a complicated relation exists in between. In addition, neurotransmitters like glutamate and γ--Amino Butyric Acid (GABA) play an important role in the formation of these relations. Thus, the present study was undertaken to investigate these relations by evaluating the level of associated changes in the indicated neurotransmitters in the VTA, using HPLC method. This was performed after electrical stimulation and inducing lesion of mPFC and through microinjections of N-Methyl-D-Aspartate (NMDA) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonists, respectively AP5 and CNQX, into the VTA of addicted rats. Our results showed that intra-peritoneal (i.p.) administration of morphine in 9 days in the morphine group, and also electrical stimulation (100 µA) of mPFC, receiving (i.p.) morphine, caused an increase in the glutamate release in the VTA, compared to the control group, but the increase of glutamate levels in the VTA in the morphine-stimulation group was not significant, compared to the morphine group. Moreover, GABA release into this area was decreasing in morphine and morphine- stimulation groups, compared to the control group. Our findings also showed that electrical lesion (0.4 mA) of mPFC, and also microinjection of glutamate antagonists into the VTA, receiving (i.p.) morphine in rats, caused a decrease of glutamate in the VTA. Therefore, it could be concluded that the relation between mPFC and VTA is highly effective in the formation of reward system.

The Role of the Rodent Insula in Anxiety.

The human insula has been consistently reported to be overactivated in all anxiety disorders, activation which has been suggested to be proportional to the level of anxiety and shown to decrease with effective anxiolytic treatment. Nonetheless, studies evaluating the direct role of the insula in anxiety are lacking. Here, we set out to investigate the role of the rodent insula in anxiety by either inactivating different insular regions via microinjections of glutamatergic AMPA receptor antagonist CNQX or activating them by microinjection of GABA receptor antagonist bicuculline in rats, before measuring anxiety-like behavior using the elevated plus maze. Inactivation of caudal and medial insular regions induced anxiogenic effects, while their activation induced anxiolytic effects. In contrast, inactivation of more rostral areas induced anxiolytic effects and their activation, anxiogenic effects. These results suggest that the insula in the rat has a role in the modulation of anxiety-like behavior in rats, showing regional differences; rostral regions have an anxiogenic role, while medial and caudal regions have an anxiolytic role, with a transition area around bregma +0.5. The present study suggests that the insula has a direct role in anxiety.

Mechanisms of N-oleoyldopamine activation of central histaminergic neurons.

Histaminergic (HA) neurons located in the tuberomamillary nucleus (TMN) of the posterior hypothalamus fire exclusively during waking and support many physiological functions. We investigated the role of the endovanilloid N-oleoyldopamine (OLDA) in TMN, where dopamine synthesis and its conjugation with oleic acid likely occur. We show that several known targets of OLDA including TRPV1 and cannabinoid receptors are expressed in HA neurons. In contrast to capsaicin, which failed to increase firing of HA neurons in TRPV1 knockout mice (TRPVI KO), OLDA was still able to induce excitation. This excitation was not sensitive to the blockade of cannabinoid receptors 1 and 2 and could result from OLDA interaction with GPR119, as the ligand of GPR119, oleoylethanolamide (OEA), also increased the firing of HA neurons. However, we ruled out this possibility as OEA- (but not OLDA-) excitation was abolished by the PPAR (peroxisome proliferator activated receptor) alpha antagonist MK886. The dopamine uptake blocker nomifensine blanked OLDA-excitation and dopamine receptor antagonists abolished the OLDA action in TRPV1 KO mice. Therefore OLDA excites HA neurons through multiple targets suggesting a central role of the histaminergic system in the behavioral stimulation seen after systemic OLDA application.

Inhibition of non-NMDA ionotropic glutamate receptors delays the retinal degeneration in rd10 mouse.

Retinitis pigmentosa (RP) is a hereditary blinding disease characterized by neurodegeneration of photoreceptors. Retinal ganglion cells (RGCs) in animal models of RP exhibit an abnormally high spontaneous activity that interferes with signal processing. Blocking AMPA/Kainate receptors by bath application of CNQX decreases the spontaneous firing, suggesting that inhibiting these receptors in vivo may help maintain the function of inner retinal neurons in rd10 mice experiencing photoreceptor degeneration. To test this, rd10 mice were i.p. injected with CNQX or GYKI 52466 (an AMPA receptor antagonist) for 1-2 weeks, and examined for their retinal morphology (by immunocytochemistry), function (by MEA recordings) and visual behaviors (using a black/white box). Our data show that iGluRs were up-regulated in the inner plexiform layer (IPL) of rd10 retinas. Application of CNQX at low doses both in vitro and in vivo, attenuated the abnormal spontaneous spiking in RGCs, and increased the light-evoked response of ON RGCs, whereas GYKI 52466 had little effect. CNQX application also improved the behavioral performance. Interestingly, in vivo administration of CNQX delayed photoreceptor degeneration, evidenced by the increased cell number and restored structure. CNQX also improved the structure of bipolar cells. Together, we demonstrated that during photoreceptor degeneration, blockade of the non-NMDA iGluRs decelerates the progression of RGCs dysfunction, possibly by dual mechanisms including slowing photoreceptor degeneration and modulating signal processing within the IPL. Accordingly, this strategy may effectively extend the time window for treating RP.

Role of AMPA glutamate receptors in the conditioned rewarding effects of MDMA in mice.

Currently, there is not an effective treatment for 3,4-methylenedioxymethamphetamine (MDMA) dependence but pharmacotherapies targeting glutamate neurotransmission are a promising strategy. Previously, we showed that blockade of glutamate NMDA and AMPA receptors impairs the conditioned rewarding effects of MDMA and cocaine, respectively. In this study we evaluated the role of AMPA receptors in the rewarding effects of MDMA in mice using the conditioned place preference (CPP) paradigm. Mice were conditioned with MDMA (1.25 mg/kg) 60 min after the treatment with saline or different doses (0.25, 1 and 5 mg/kg) of the AMPA/kainate receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). Mice conditioned with MDMA acquired CPP while those treated with any dose of CNQX + MDMA did not. These results supported the involvement of the glutamatergic system in the rewarding properties of MDMA, and suggest that AMPA receptor blockade could be a new therapeutic option for the treatment of those individuals that develop MDMA dependence.