Alpha-selenoconotoxins, a new class of potent alpha(7) neuronal nicotinic receptor antagonists

Disulfide bonds are important structural motifs that play an essential role in maintaining the conformational stability of many bioactive peptides. Of particular importance are the conotoxins, which selectively target a wide range of ion channels that are implicated in numerous disease states. Despite the enormous potential of conotoxins as therapeutics, their multiple disulfide bond frameworks are inherently unstable under reducing conditions. Reduction or scrambling by thiol-containing molecules such as glutathione or serum albumin in intracellular or extracellular environments such as blood plasma can decrease their effectiveness as drugs. To address this issue, we describe a new class of selenoconotoxins where cysteine residues are replaced by selenocysteine to form isosteric and non-reducible diselenide bonds. Three isoforms of alpha-conotoxin ImI were synthesized by t-butoxycarbonyl chemistry with systematic replacement of one([ Sec(2,8)] ImI or [Sec(3,12)] ImI), or both([Sec(2,3,8,12)] ImI) disulfide bonds with a diselenide bond. Each analogue demonstrated remarkable stability to reduction or scrambling under a range of chemical and biological reducing conditions. Three-dimensional structural characterization by NMR and CD spectroscopy indicates conformational preferences that are very similar to those of native ImI, suggesting fully isomorphic structures. Additionally, full bioactivity was retained at the alpha(7) nicotinic acetylcholine receptor, with each seleno-analogue exhibiting a dose-response curve that overlaps with wild-type ImI, thus further supporting an isomorphic structure. These results demonstrate that selenoconotoxins can be used as highly stable scaffolds for the design of new drugs.

Functional interconnectivity between the globus pallidus and the subthalamic nucleus in the mouse brain slice

In accordance with its central role in basal ganglia circuitry, changes in the rate of action potential firing and pattern of activity in the globus pallidus (GP)-subthalamic nucleus (STN) network are apparent in movement disorders. In this study we have developed a mouse brain slice preparation that maintains the functional connectivity between the GP and STN in order to assess its role in shaping and modulating bursting activity promoted by pharmacological manipulations. Fibre-tract tracing studies indicated that a parasagittal slice cut 20 deg to the midline best preserved connectivity between the GP and the STN. IPSCs and EPSCs elicited by electrical stimulation confirmed connectivity from GP to STN in 44/59 slices and from STN to GP in 22/33 slices, respectively. In control slices, 74/76 (97%) of STN cells fired tonically at a rate of 10.3 ± 1.3 Hz. This rate and pattern of single spiking activity was unaffected by bath application of the GABAA antagonist picrotoxin (50 μM, n = 9) or the glutamate receptor antagonist (6-cyano-7-nitroquinoxaline-2, 3-dione (CNQX) 10 μM, n = 8). Bursting activity in STN neurones could be induced pharmacologically by application of NMDA alone (20 μM, 3/18 cells, 17%) but was more robust if NMDA was applied in conjunction with apamin (20-100 nM, 34/77 cells, 44%). Once again, neither picrotoxin (50 μM, n = 5) nor CNQX (10 μM, n = 5) had any effect on the frequency or pattern of the STN neurone activity while paired STN and GP recordings of tonic and bursting activity show no evidence of coherent activity. Thus, in a mouse brain slice preparation where functional GP-STN connectivity is preserved, no regenerative synaptically mediated activity indicative of a dynamic network is evident, either in the resting state or when neuronal bursting in both the GP and STN is generated by application of NMDA/apamin. This difference from the brain in Parkinson's disease may be attributed either to insufficient preservation of cortico-striato-pallidal or cortico-subthalamic circuitry, and/or an essential requirement for adaptive changes resulting from dopamine depletion for the expression of network activity within this tissue complex. © The Physiological Society 2005.

Effect of dopamine on synchronous neuronal oscillations in the globus pallidus-subthalamic nucleus network

Changes in the pattern of activity of neurones within the basal ganglia are relevant in the pathophysiology and symptoms of Parkinson’s disease. The globus pallidus (GP) – subthalamic nucleus (STN) network has been proposed to form a pacemaker driving regenerative synchronous bursting activity. In order to test whether this activity can be sustained in vitro a 20o parasagittal slice of mouse midbrain was developed which preserved functional connectivity between the STN and GP. Mouse STN and GP cells were characterised electrophysiologically by the presence or absence of a voltage sag in response to hyperpolarising current steps indicative of Ih and the presence of rebound depolarisations. The presence of evoked and spontaneous post-synaptic GABA and glutamatergic currents indicated functional connectivity between the STN and GP. In control slices, STN cells fired action potentials at a regular rate, activity which was unaffected by bath application of the GABAA receptor antagonist picrotoxin (50 μM) or the glutamate receptor antagonist CNQX (10 μM). Paired extracellular recordings of STN cells showed uncorrelated firing. Oscillatory burst activity was induced pharmacologically using the glutamate receptor agonist, NMDA (20 μM), in combination with the potassium channel blocker apamin (50 -100 nM). The burst activity was unaffected by bath application of picrotoxin or CNQX while paired STN recordings showed uncorrelated activity indicating that the activity is not produced by the neuronal network. Thus, no regenerative activity is evident in this mouse brain preparation, either in control slices or when bursting is pharmacologically induced, suggesting the requirement of other afferent inputs that are not present in the slice. Using single-unit extracellular recording, dopamine (30 μM) produced an excitation of STN cells. This excitation was independent of synaptic transmission and was mimicked by both the Dl-like receptor agonist SKF38393 (10 μM) and the D2-like receptor agonist quinpirole (10 μM). However, the excitation was partially reduced by the D1-like antagonist SCH23390 (2 μM) but not by the D2-like antagonists sulpiride (10 μM) and eticlopride (10 μM). Using whole-recordings, dopamine was shown to induce membrane depolarisation. This depolarisation was caused either by a D1-like receptor mediated increase in a conductance which reversed at -34 mV, consistent with a non-specific cation conductance, or a D2-like receptor mediated decrease in conductance which reversed around -100 mV, consistent with a potassium conductance. Bath application of dopamine altered the pattern of the burst-firing produced by NMDA an apamin towards a more regular pattern. This effect was associated with a decrease in amplitude and ll1crease in frequency of TTX-resistant plateau potentials which underlie the burst activity.

Novel peptide antagonists of adrenomedullin and calcitonin gene-related peptide receptors:identification, pharmacological characterization, and interactions with position 74 in receptor activity-modifying protein 1/3

Human adrenomedullin (AM) is a 52-amino acid peptide belonging to the calcitonin peptide family, which also includes calcitonin gene-related peptide (CGRP) and AM2. The two AM receptors, AM(1) and AM(2), are calcitonin receptor-like receptor (CL)/receptor activity-modifying protein (RAMP) (RAMP2 and RAMP3, respectively) heterodimers. CGRP receptors comprise CL/RAMP1. The only human AM receptor antagonist (AM(22-52)) is a truncated form of AM; it has low affinity and is only weakly selective for AM(1) over AM(2) receptors. To develop novel AM receptor antagonists, we explored the importance of different regions of AM in interactions with AM(1), AM(2), and CGRP receptors. AM(22-52) was the framework for generating further AM fragments (AM(26-52) and AM(30-52)), novel AM/alphaCGRP chimeras (C1-C5 and C9), and AM/AM(2) chimeras (C6-C8). cAMP assays were used to screen the antagonists at all receptors to determine their affinity and selectivity. Circular dichroism spectroscopy was used to investigate the secondary structures of AM and its related peptides. The data indicate that the structures of AM, AM2, and alphaCGRP differ from one another. Our chimeric approach enabled the identification of two nonselective high-affinity antagonists of AM(1), AM(2), and CGRP receptors (C2 and C6), one high-affinity antagonist of AM(2) receptors (C7), and a weak antagonist selective for the CGRP receptor (C5). By use of receptor mutagenesis, we also determined that the C-terminal nine amino acids of AM seem to be responsible for its interaction with Glu74 of RAMP3. We provide new information on the structure-activity relationship of AM, alphaCGRP, and AM2 and how AM interacts with CGRP and AM(2) receptors.

Investigating G protein signalling bias at the glucagon-like peptide-1 receptor in yeast

Background and Purpose The glucagon-like peptide 1 (GLP-1) receptor performs an important role in glycaemic control, stimulating the release of insulin. It is an attractive target for treating type 2 diabetes. Recently, several reports of adverse side effects following prolonged use of GLP-1 receptor therapies have emerged: most likely due to an incomplete understanding of signalling complexities. Experimental Approach We describe the expression of the GLP-1 receptor in a panel of modified yeast strains that couple receptor activation to cell growth via single Gα/yeast chimeras. This assay enables the study of individual ligand-receptor G protein coupling preferences and the quantification of the effect of GLP-1 receptor ligands on G protein selectivity. Key Results The GLP-1 receptor functionally coupled to the chimeras representing the human Gαs, Gαi and Gαq subunits. Calculation of the dissociation constant for a receptor antagonist, exendin-3 revealed no significant difference between the two systems. We obtained previously unobserved differences in G protein signalling bias for clinically relevant therapeutic agents, liraglutide and exenatide; the latter displaying significant bias for the Gαi pathway. We extended the use of the system to investigate small-molecule allosteric compounds and the closely related glucagon receptor. Conclusions and Implications These results provide a better understanding of the molecular events involved in GLP-1 receptor pleiotropic signalling and establish the yeast platform as a robust tool to screen for more selective, efficacious compounds acting at this important class of receptors in the future. © 2014 The Authors. British Journal of Pharmacology published by John Wiley & Sons Ltd on behalf of The British Pharmacological Society.

EP4 prostanoid receptor-mediated vasodilatation of human middle cerebral arteries

1 Dilatation of the cerebral vasculature is recognised to be involved in the pathophysiology of migraine. Furthermore, elevated levels of prostaglandin E2 (PGE2) occur in the blood, plasma and saliva of migraineurs during an attack, suggestive of a contributory role. In the present study, we have characterised the prostanoid receptors involved in the relaxation and contraction of human middle cerebral arteries in vitro. 2 In the presence of indomethacin (3μM) and the TP receptor antagonist GR32191 (1 μM), PGE2 was found to relax phenylephrine precontracted cerebral arterial rings in a concentration-dependent manner (mean pEC50 8.0 ± 0.1, n = 5). 3 Establishment of a rank order of potency using the EP4 > EP2 agonist 11-deoxy PGE1, and the EP2 > EP4 agonist PGE1-OH (mean pEC 50 of 7.6 ± 0.1 (n = 6) and 6.4 ± 0.1 (n = 4), respectively), suggested the presence of functional EP4 receptors. Furthermore, the selective EP2 receptor agonist butaprost at concentrations < 1 μM failed to relax the tissues. 4 Blockade of EP 4 receptors with the EP4 receptor antagonists AH23848 and EP4A caused significant rightward displacements in PGE2 concentration-response curves, exhibiting pA2 and pKB values of 5.7 ± 0.1, n = 3, and 8.4, n = 3, respectively. 5 The IP receptor agonists iloprost and cicaprost relaxed phenylephrine precontracted cerebral arterial rings (mean pEC50 values 8.3 ± 0.1 (n = 4) and 8.1 ± 0.1 (n = 9), respectively). In contrast, the DP and FP receptor agonists PGD2 and PGFα2 failed to cause appreciable relaxation or contraction at concentrations of up to 30 μM. In the absence of phenylephrine contraction and GR32191, the TP receptor agonist U46619 caused concentration-dependent contraction of cerebral artery (mean pEC50 7.4 ± 0.3, n = 3). 6 These data demonstrate the presence of prostanoid EP4 receptors mediating PGE2 vasodilatation of human middle cerebral artery. IP receptors mediating relaxation and TP receptors mediating contraction were also functionally demonstrated.

O antagonismo do receptor de serotonina do tipo 7 da substância cinzenta periaquedutal dorsal reduz a ansiedade experimental basal, mas não aquela gerada pela retirada do etanol em ratos

Ethanol-dependent individuals who reduce or discontinue its use may present Alcohol Withdrawal Syndrome, which is characterized by unpleasant signs and symptoms, such as anxiety, that may trigger relapses. Ethanol, a psychotropic drug, is able to promote behavioral and neurophysiological changes, acting on different neurotransmitter systems, including the serotonergic, which has also been directly associated with aversive states, including anxiety. This study aimed to investigate the participation of type 7 serotonin receptor (5-HT7) of the dorsal periaqueductal gray (DPAG) on basal experimental anxiety and that caused by ethanol withdrawal. For this, 75-100 days old Wistar rats were subjected to two experiments. On the first one, animals underwent stereotactic surgery for implantation of guide cannulas used for administration of the drug directly into the DPAG. After seven days, the animals received doses of 2.5; 5 and 10 nmols of type 7 receptor antagonist SB269970 (SB) or vehicle intra-DPAG and, ten minutes after, they were exposed to elevated plus maze (EPM). In the following day, the animals were submitted to the same treatment and tested in the open field (OF). In the second experiment, animals received increasing concentrations (2%, 4%, 6%) of ethanol as the only source of liquid diet or water (control group), both with free access to chow. Seventy two hours and ninety six hours after the ethanol withdrawal, animals received SB (2.5 and 5.0 nmols) intraDPAG ten minutes before the test in the LCE and OF, respectively. In experiment 1, the dose of antagonist 10 nmols was able of reversing the anxiety generated by EPM. In the experiment 2, ineffective SB doses on the LCE (2.5 and 5.0 nmol) were not able to reverse the anxiety caused by the ethanol withdrawal in the EPM, although the dose of 2.5 nmols of SB has reversed its hipolocomotor effect in this test. This result suggests that the 5-HT7 receptor is involved in the modulation of the basal experimental anxiety in rats, but not in the anxiety caused by ethanol withdrawal in the DPAG.

Sinalização endógena do sistema Nociceptina/Orfanina FQ - receptor NOP: envolvimento na modulação da depressão experimental induzida por lipopolissacarídeo

During the last decades, it has been established that there is a relationship between major depression and activation of immune system. Nociceptin/orphanin FQ (N/OFQ) is the natural ligand of a Gi-protein coupled receptor named NOP, both compose the peptidergic system wich is involved in the regulation of mood states and inflammatory responses. Considering these actions, the present thesis aimed to investigate the consequences of blocking NOP signaling in lipopolysaccharide (LPS)-induced sickness and depressive-like behaviors in mice. Systemic administration of LPS doses, that do not cause sepsis in mice, induce changes in their behaviors related with activity of pro-inflammatory cytokines tumor necrosis factor-α (TNF-α) and interleukins 6 (IL-6) and 1β (IL-1 β). At the time points of 2 to 6 h and 24 h after intraperitoneal injection, mice treated with LPS displayed, respectively, sickness and depressive-like behaviors. In the present work the administration of LPS 0.8 mg/kg (ip) significantly induced sickness signs in Swiss and CD-1 mice, such as weight loss, transient reduction in rectal temperature and decrease of food and water intake. Moreover at 24 h after LPS injection these same mice strains displayed significantly increased immobility time on the tail suspension test (TST) when compared with control mice, this alteration was not related with possible locomotion impairments as verified on the open field test. Treatment with Nortriptyline 30 mg/kg (ip, 60 min prior the TST) reduced the immobility time of control and LPS-treated mice and was used as standard antidepressant. The NOP receptor antagonist SB-612111 (10 mg/kg, ip), 30 min prior LPS, did not modify LPS-induced sickness signs and depressive-like behavior. However, when injected 24 h after LPS treatment, SB-612111 (ip, 30 min prior the TST) as well as the peptidergic NOP receptor antagonist UFP-101 (10 nmol/2μL, icv, 5 min prior the TST) significantly reversed the toxin effects. The protocol of LPS-induced depressive-like states was also tested in NOP receptor knockout mice (NOP(-/-)) and their respective wild types (NOP(+/+)). LPS evoked transient rectal temperature reduction in NOP(-/-) mice and loss of body weight, food and water intake reduction in both NOP(+/+) and NOP(-/-) mice. The consumption of water was significantly different due to the genotype. LPS injection induced transient changes in pro-inflammatory cytokines. At 6 h after LPS injection, serum levels of TNF-α were significantly increased in NOP(+/+) and NOP(-/-) mice, as the IL-6 levels were significantly increased just in NOP(+/+) serum. At 24 h after LPS treatment the pro-inflammatory cytokines had returned to the baseline levels in both genotypes. LPS treatment elicited depressive-like effects in NOP(+/+) but not in NOP(-/-) mice. The data obtained during the execution of this doctoral thesis reveal that pharmacological and genetic blockade of NOP signaling does not affect LPS evoked sickness signs while reversing depressive-like behavior. In conclusion, these results highlight the involvement of the peptidergic system N/OFQ - NOP receptor in the modulation of behaviors related to mood and activation of the immune system.

Efeitos in vivo e in vitro de agonistas parciais do receptor NOP: implicações para o tratamento da ansiedade, depressão e mania

Introduction: This study aimed to investigate the effects of the two peptide NOP partial agonists (UFP-113 and [F/G]N/OFQ(1-13)NH2) and the non peptide NOP partial agonist (AT-090) in the mouse emotional behavior as well as in the intracellular transduction pathways following the receptor binding. Methods: Male Swiss or CD-1 mice were used in this study together with NOP(+/+) and NOP(-/-) mice. The elevated plus maze (EPM) was used to evaluate the effects of compounds on anxiety-like behaviors. Diazepam and the NOP agonists, N/OFQ and Ro 65-6570, were used as positive controls in the EPM. NOP(+/+) and NOP(-/-) mice were used to evaluate the selectivity of those compounds that induced anxiolytic-like behaviors. The forced swim test (FST) was used to evaluate the effects of compounds on depressive-like behaviors. Nortriptyline and the NOP antagonists, UFP-101 and SB-612111, were used as positive controls in the FST. The effects of N/OFQ, UFP-101, SB-612111, UFP-113, [F/G]N/OFQ(1-13)NH2, and AT-090 were assessed in the methylphenidate-induced hyperlocomotion (MIH) test; in this assay valproate was used as positive control. The G protein and β-arrestin 2 transduction pathways of NOP receptor agonists (N/OFQ and Ro 65-6570), antagonist (UFP-101), and partial agonists (UFP-113, [F/G]N/OFQ(1-13)NH2, and AT-090) were also evaluated using an innovative assay that measures a bioluminescence resonance energy transfer process. For this, cell lines permanently co-expressing the NOP receptor coupled to luciferase (energy donor), and green fluorescent protein (energy acceptor) coupled to one of the effector proteins (G protein or β-arrestin 2) were used. Results: Diazepam (1 mg/kg), N/OFQ (1 nmol), Ro 65-6570 (0.1 mg/kg), and AT-090 (0.01 mg/kg) induced anxiolytic-like effect in mice in the EPM. The effects of Ro 65-6570 and AT-090 were selective to NOP receptor. UFP-113 (0.01-1 nmol) and [F/G]N/OFQ(1-13)NH2 (0.1-3 nmol) were inactive in the EPM. In the FST, nortriptyline (30 mg/kg), UFP-101 (10 nmol), SB-612111 (10 mg/kg), UFP-113 (0.01 and 0.1 nmol), and [F/G]N/OFQ(1-13)NH2 (0.3 and 1 nmol) induced antidepressant-like effects, while AT-090 (0.001-0.1 mg/kg) was inactive in this assay. The effects of UFP-113 and [F/G]N/OFQ(1-13)NH2 were selective to NOP receptor. Valproate (400 mg/kg) counteracted methylphenidate (MPH, 10 mg/kg)-induced hyperlocomotion in mice in the open field. N/OFQ (1 nmol), UFP-113 (0.01-0.1 nmol), and [F/G]N/OFQ(1-13)NH2 (1 nmol) were also able to reduce the MPH-induced hyperlocomotion, without changing the locomotor activity per se. The effect of UFP-113 was selective to NOP receptor. The UFP-101 (10 nmol), SB-612111 (10 mg/kg), and AT-090 (0.001-0.03 mg/kg) did not change the hyperlocomotor effect of methylphenidate. In vitro, N/OFQ and Ro 65-6570 behaved as NOP full agonists for G-protein and β-arrestin 2 pathways. AT-090 behaved as NOP receptor partial agonist for both transduction pathways, while UFP-113 and [F/G]N/OFQ(1-13)NH2 behaved as partial agonists and antagonists of NOP receptor for NOP/G protein and NOP/β-arrestin 2, respectively. UFP-101 behaved as NOP receptor antagonist for both transduction pathways. Conclusion: NOP ligands producing same effects on NOP/G protein interaction (partial agonism), but with opposite effects on β-arrestin 2 recruitment (partial agonism vs antagonism), can promote different in vivo effects on anxiety and mood as it was observed in the behavioral tests. This work corroborates the potential of NOP receptor as an innovative pharmacological target for the treatment of emotional disorders.

Efeitos in vivo e in vitro de agonistas parciais do receptor NOP: implicações para o tratamento da ansiedade, depressão e mania

Introduction: This study aimed to investigate the effects of the two peptide NOP partial agonists (UFP-113 and [F/G]N/OFQ(1-13)NH2) and the non peptide NOP partial agonist (AT-090) in the mouse emotional behavior as well as in the intracellular transduction pathways following the receptor binding. Methods: Male Swiss or CD-1 mice were used in this study together with NOP(+/+) and NOP(-/-) mice. The elevated plus maze (EPM) was used to evaluate the effects of compounds on anxiety-like behaviors. Diazepam and the NOP agonists, N/OFQ and Ro 65-6570, were used as positive controls in the EPM. NOP(+/+) and NOP(-/-) mice were used to evaluate the selectivity of those compounds that induced anxiolytic-like behaviors. The forced swim test (FST) was used to evaluate the effects of compounds on depressive-like behaviors. Nortriptyline and the NOP antagonists, UFP-101 and SB-612111, were used as positive controls in the FST. The effects of N/OFQ, UFP-101, SB-612111, UFP-113, [F/G]N/OFQ(1-13)NH2, and AT-090 were assessed in the methylphenidate-induced hyperlocomotion (MIH) test; in this assay valproate was used as positive control. The G protein and β-arrestin 2 transduction pathways of NOP receptor agonists (N/OFQ and Ro 65-6570), antagonist (UFP-101), and partial agonists (UFP-113, [F/G]N/OFQ(1-13)NH2, and AT-090) were also evaluated using an innovative assay that measures a bioluminescence resonance energy transfer process. For this, cell lines permanently co-expressing the NOP receptor coupled to luciferase (energy donor), and green fluorescent protein (energy acceptor) coupled to one of the effector proteins (G protein or β-arrestin 2) were used. Results: Diazepam (1 mg/kg), N/OFQ (1 nmol), Ro 65-6570 (0.1 mg/kg), and AT-090 (0.01 mg/kg) induced anxiolytic-like effect in mice in the EPM. The effects of Ro 65-6570 and AT-090 were selective to NOP receptor. UFP-113 (0.01-1 nmol) and [F/G]N/OFQ(1-13)NH2 (0.1-3 nmol) were inactive in the EPM. In the FST, nortriptyline (30 mg/kg), UFP-101 (10 nmol), SB-612111 (10 mg/kg), UFP-113 (0.01 and 0.1 nmol), and [F/G]N/OFQ(1-13)NH2 (0.3 and 1 nmol) induced antidepressant-like effects, while AT-090 (0.001-0.1 mg/kg) was inactive in this assay. The effects of UFP-113 and [F/G]N/OFQ(1-13)NH2 were selective to NOP receptor. Valproate (400 mg/kg) counteracted methylphenidate (MPH, 10 mg/kg)-induced hyperlocomotion in mice in the open field. N/OFQ (1 nmol), UFP-113 (0.01-0.1 nmol), and [F/G]N/OFQ(1-13)NH2 (1 nmol) were also able to reduce the MPH-induced hyperlocomotion, without changing the locomotor activity per se. The effect of UFP-113 was selective to NOP receptor. The UFP-101 (10 nmol), SB-612111 (10 mg/kg), and AT-090 (0.001-0.03 mg/kg) did not change the hyperlocomotor effect of methylphenidate. In vitro, N/OFQ and Ro 65-6570 behaved as NOP full agonists for G-protein and β-arrestin 2 pathways. AT-090 behaved as NOP receptor partial agonist for both transduction pathways, while UFP-113 and [F/G]N/OFQ(1-13)NH2 behaved as partial agonists and antagonists of NOP receptor for NOP/G protein and NOP/β-arrestin 2, respectively. UFP-101 behaved as NOP receptor antagonist for both transduction pathways. Conclusion: NOP ligands producing same effects on NOP/G protein interaction (partial agonism), but with opposite effects on β-arrestin 2 recruitment (partial agonism vs antagonism), can promote different in vivo effects on anxiety and mood as it was observed in the behavioral tests. This work corroborates the potential of NOP receptor as an innovative pharmacological target for the treatment of emotional disorders.

Effect of Melatonin and Analogues on Corneal Wound Healing: Involvement of Mt2 Melatonin Receptor

Purpose: We have investigated the effect of melatonin and its analogues on rabbit corneal epithelial wound healing. Methods: New Zealand rabbits were anaesthetised and wounds were made by placing Whatman paper discs soaked in n-heptanol on the cornea. Melatonin and analogues (all 10 nmol) were instilled. Wound diameter was measured every 2 hours by means of fluorescein application with a Topcon SL-8Z slit lamp. Melatonin antagonists (all 10 nmol) were applied 2 hours before the application of the n-heptanol-soaked disc and then every 6 hours together with melatonin. To confirm the presence of MT2 receptors in corneal epithelial cells immunohistochemistry, Western blot and RT-PCR assays in native tissue and in rabbit corneal epithelial cells were performed. The tear components were extracted then processed by HPLC to quantify melatonin in tears. Results: Migration assays revealed that melatonin and particularly the treatment with the MT2 agonist IIK7, accelerated the rate of healing (p < 0.001). The application of the non-selective melatonin receptor antagonist luzindole and the MT2 antagonist DH97 (but not prazosin), prevented the effect of melatonin on wound healing (both p < 0.001). Immunohistochemistry, Western blot and RT-PCR assays showed the presence of MT2 melatonin receptor in corneal epithelial cells. In addition, we have identified melatonin in tears and determined its daily variations. Conclusions: These data suggest that MT2 receptors are implicated in the effect of melatonin on corneal wound healing regulating migration rate. This suggests the potential use of melatonin and its analogues to enhance epithelial wound healing in ocular surface disease.

Muscle Hyperalgesia Induced By Peripheral P2x3 Receptors Is Modulated By Inflammatory Mediators.

ATP, via activation of P2X3 receptors, has been highlighted as a key target in inflammatory hyperalgesia. Therefore, the aim of this study was to confirm whether the activation of P2X3 receptors in the gastrocnemius muscle of rats induces mechanical muscle hyperalgesia and, if so, to analyze the involvement of the classical inflammatory mediators (bradykinin, prostaglandins, sympathetic amines, pro-inflammatory cytokines and neutrophil migration) in this response. Intramuscular administration of the non-selective P2X3 receptor agonist α,β-meATP in the gastrocnemius muscle of rats induced mechanical muscle hyperalgesia, which, in turn, was prevented by the selective P2X3 and P2X2/3 receptors antagonist A-317491, the selective bradykinin B1-receptor antagonist Des-Arg9-[Leu8]-BK (DALBK), the cyclooxygenase inhibitor indomethacin, the β1- or β2-adrenoceptor antagonist atenolol and ICI 118,551, respectively. Also, the nonspecific selectin inhibitor fucoidan. α,β-meATP induced increases in the local concentration of the pro-inflammatory cytokines tumor necrosis factor-α (TNF-α) and interleukin 1β (IL-1β), which were reduced by bradykinin antagonist. Finally, α,β-meATP also induced neutrophil migration. Together, these findings suggest that α,β-meATP induced mechanical hyperalgesia in the gastrocnemius muscle of rats via activation of peripheral P2X3 receptors, which involves bradykinin, prostaglandins, sympathetic amines, pro-inflammatory cytokines release and neutrophil migration. It is also indicated that bradykinin is the key modulator of the mechanical muscle hyperalgesia induced by P2X3 receptors. Therefore, we suggest that P2X3 receptors are important targets to control muscle inflammatory pain.

Stress-induced neuroinflammation: mechanisms and new pharmacological targets

Stress is triggered by numerous unexpected environmental, social or pathological stimuli occurring during the life of animals, including humans, which determine changes in all of their systems. Although acute stress is essential for survival, chronic, long-lasting stress can be detrimental. In this review, we present data supporting the hypothesis that stress-related events are characterized by modifications of oxidative/nitrosative pathways in the brain in response to the activation of inflammatory mediators. Recent findings indicate a key role for nitric oxide (NO) and an excess of pro-oxidants in various brain areas as responsible for both neuronal functional impairment and structural damage. Similarly, cyclooxygenase-2 (COX-2), another known source of oxidants, may account for stress-induced brain damage. Interestingly, some of the COX-2-derived mediators, such as the prostaglandin 15d-PGJ2 and its peroxisome proliferator-activated nuclear receptor PPARγ, are activated in the brain in response to stress, constituting a possible endogenous anti-inflammatory mechanism of defense against excessive inflammation. The stress-induced activation of both biochemical pathways depends on the activation of the N-methyl-D-aspartate (NMDA) glutamate receptor and on the activation of the transcription factor nuclear factor kappa B (NFκB). In the case of inducible NO synthase (iNOS), release of the cytokine TNF-α also accounts for its expression. Different pharmacological strategies directed towards different sites in iNOS or COX-2 pathways have been shown to be neuroprotective in stress-induced brain damage: NMDA receptor blockers, inhibitors of TNF-α activation and release, inhibitors of NFκB, specific inhibitors of iNOS and COX-2 activities and PPARγ agonists. This article reviews recent contributions to this area addressing possible new pharmacological targets for the treatment of stress-induced neuropsychiatric disorders.

Alstonine as an Antipsychotic: Effects on Brain Amines and Metabolic Changes

Managing schizophrenia has never been a trivial matter. Furthermore, while classical antipsychotics induce extrapyramidal side effects and hyperprolactinaemia, atypical antipsychotics lead to diabetes, hyperlipidaemia, and weight gain. Moreover, even with newer drugs, a sizable proportion of patients do not show significant improvement. Alstonine is an indole alkaloid identified as the major component of a plant-based remedy used in Nigeria to treat the mentally ill. Alstonine presents a clear antipsychotic profile in rodents, apparently with differential effects in distinct dopaminergic pathways. The aim of this study was to complement the antipsychotic profile of alstonine, verifying its effects on brain amines in mouse frontal cortex and striatum. Additionally, we examined if alstonine induces some hormonal and metabolic changes common to antipsychotics. HPLC data reveal that alstonine increases serotonergic transmission and increases intraneuronal dopamine catabolism. In relation to possible side effects, preliminary data suggest that alstonine does not affect prolactin levels, does not induce gains in body weight, but prevents the expected fasting-induced decrease in glucose levels. Overall, this study reinforces the proposal that alstonine is a potential innovative antipsychotic, and that a comprehensive understanding of its neurochemical basis may open new avenues to developing newer antipsychotic medications.

Ethanol-induced vasoconstriction is mediated via redox-sensitive cyclo-oxygenase-dependent mechanisms

The present study investigated the role of ROS (reactive oxygen species) and COX (cyclooxygenase) in ethanol-induced contraction and elevation of [Ca(2+)](i) (intracellular [Ca(2+)]). Vascular reactivity experiments, using standard muscle bath procedures, showed that ethanol (1-800 mmol/l) induced contraction in endothelium-intact (EC(50): 306 +/- 34 mmol/l) and endothelium-denuded (EC(50): 180 +/- 40 mmol/l) rat aortic rings. Endothelial removal enhanced ethanol-induced contraction. Preincubation of intact rings with L-NAME [N(G)-nitro-L-arginine methyl ester; non-selective NOS (NO synthase) inhibitor, 100 mu mol/l], 7-nitroindazole [selective nNOS (neuronal NOS) inhibitor, 100 mu mol/l], oxyhaemoglobin (NO scavenger, 10 mu mol/l) and ODQ (selective inhibitor of guanylate cyclase enzyme, 1 mu mol/l) increased ethanol-induced contraction. Tiron [O(2)(-) (superoxide anion) scavenger, 1 mmol/l] and catalase (H(2)O(2) scavenger, 300 units/ml) reduced ethanol-induced contraction to a similar extent in both endothelium-intact and denuded rings. Similarly, indomethacin (non-selective COX inhibitor, 10 mu mol/l), SC560 (selective COX- I inhibitor, 1 mu mol/l), AH6809 [PGF(2 alpha) (prostaglandin F(2 alpha))] receptor antagonist, 10 mu mol/l] or SQ29584 [PGH(2)(prostaglandin H(2))/TXA(2) (thromboxane A(2)) receptor antagonist, 3 mu mol/l] inhibited ethanol-induced contraction in aortic rings with and without intact endothelium. In cultured aortic VSMCs (vascular smooth muscle cells), ethanol stimulated generation of O(2)(-) and H(2)O(2). Ethanol induced a transient increase in [Ca(2+)](i), which was significantly inhibited in VSMCs pre-exposed to tiron or indomethacin. Our data suggest that ethanol induces vasoconstriction via redox-sensitive and COX-dependent pathways, probably through direct effects on ROS production and Ca(2+) signalling. These findings identify putative molecular mechanisms whereby ethanol, at high concentrations, influences vascular reactivity. Whether similar phenomena occur in vivo at lower concentrations of ethanol remains unclear.