Search PubMed⌕ Search

Biomedical subjects

C W Vaughan

Publications and source records attributed to C W Vaughan.

At least 19 recordsLinked to original sources
PubMed2006

muO-conotoxin MrVIB selectively blocks Nav1.8 sensory neuron specific sodium channels and chronic pain behavior without motor deficits.

The tetrodotoxin-resistant voltage-gated sodium channel (VGSC) Na(v)1.8 is expressed predominantly by damage-sensing primary afferent nerves and is important for the development and maintenance of persistent pain states. Here we demonstrate that muO-conotoxin MrVIB from Conus marmoreus displays substantial selectivity for Na(v)1.8 and inhibits pain behavior in models of persistent pain. In rat sensory neurons, submicromolar concentrations of MrVIB blocked tetrodotoxin-resistant current characteristic of Na(v)1.8 but not Na(v)1.9 or tetrodotoxin-sensitive VGSC currents. MrVIB blocked human Na(v)1.8 expressed in Xenopus oocytes with selectivity at least 10-fold greater than other VGSCs. In neuropathic and chronic inflammatory pain models, allodynia and hyperalgesia were both reduced by intrathecal infusion of MrVIB (0.03-3 nmol), whereas motor side effects occurred only at 30-fold higher doses. In contrast, the nonselective VGSC blocker lignocaine displayed no selectivity for allodynia and hyperalgesia versus motor side effects. The actions of MrVIB reveal that VGSC antagonists displaying selectivity toward Na(v)1.8 can alleviate chronic pain behavior with a greater therapeutic index than nonselective antagonists.

Animals↗
PubMed2005

Retrograde signalling by endocannabinoids.

The cannabinoid neurotransmitter system comprises cannabinoid G protein-coupled membrane receptors (CB1 and CB2), endogenous cannabinoids (endocannabinoids), as well as mechanisms for their synthesis, membrane transport and metabolism. Within the brain the marijuana constituent delta9-tetrahydrocannabinol (THC) produces its pharmacological actions by acting on cannabinoid CB1 receptors. THC modulates neuronal excitability by inhibiting synaptic transmission via presynaptic CB1-mediated mechanisms. More recently, it has been established that physiological stimulation of neurons can induce the synthesis of endocannabinoids, which also modulate synaptic transmission via cannabinoid CB1 and other receptor systems. These endogenously synthesised endocannabinoids appear to act as retrograde signalling agents, reducing synaptic inputs onto the stimulated neuron in a highly selective and restricted manner. In this review we describe the cellular mechanisms underlying retrograde endocannabinoid signalling.

Animals↗
PubMed2004

Antidepressant-like effects of the nociceptin/orphanin FQ receptor antagonist UFP-101: new evidence from rats and mice.

Receptor antagonist and knockout studies have demonstrated that blockade of signalling via nociceptin/orphanin FQ (N/OFQ) and its receptor (NOP) has antidepressant-like effects in mice submitted to the forced swimming test (FST). The aim of the present study was to explore further the antidepressant-like properties of the NOP antagonist UFP-101 in different species (mouse and rat) and using different assays [FST and tail suspension test (TST)], and to investigate the mechanism(s) involved in its actions.UFP-101 (10 nmol i.c.v.) reduced immobility time of Swiss mice in the TST (mean+/-SEM) from 179+/-11 to 111+/-10 s. N/OFQ (1 nmol i.c.v.) was without effect per se, but fully prevented the effect of UFP-101. The spontaneous immobility time of NOP(-/-) CD1-C57BL/6J-129 mice in the TST was much lower than that of wild-type (NOP(+/+)) littermates (75+/-11 vs. 144+/-17 s) or of Swiss mice. UFP-101 (10 nmol i.c.v.) decreased immobility time (-65%) and increased climbing time (71%) in rats submitted to the FST. In rat brain slices, N/OFQ (100 nM) triggered robust K(+)-dependent hyperpolarizing currents in locus coeruleus and dorsal raphe neurons. UFP-101 (3 microM) fully prevented N/OFQ-induced currents, but was inactive per se. Fluoxetine, desipramine (both 30 mg/kg i.p.) and UFP-101 (10 nmol i.c.v.) reduced immobility time of mice in the FST. The serotonin synthesis inhibitor p-chlorophenylalanine methylester (PCPA, 4 x 100 mg/kg per day i.p.) prevented the antidepressant-like effects of fluoxetine and UFP-101 (but not desipramine), whereas N-(2-chloroethyl)- N-ethyl-2-bromobenzylamine (DSP-4, neurotoxic for noradrenergic neurons; 50 mg/kg i.p., 7 days beforehand), suppressed only the effect of desipramine. Neither pretreatment affected spontaneous immobility time per se.Thus, UFP-101 exhibits pronounced antidepressant-like effects in different species and animal models, possibly by preventing the inhibitory effects of endogenous N/OFQ on brain monoaminergic (in particular serotonergic) neurotransmission. Participation of the N/OFQ-NOP receptor system in mood modulation sets new potential targets for antidepressant drug development.

Animals↗
PubMed2003

The actions of anandamide on rat superficial medullary dorsal horn neurons in vitro.

Whole-cell patch-clamp recordings were made from neurons in the trigeminal nucleus caudalis and trigeminal ganglion, in vitro, to investigate the cellular actions of the endogenous cannabinoid, anandamide. Anandamide has been shown to act through both the cannabinoid receptor 1 (CB1) and the vanilloid receptor 1 (VR1). Anandamide (30 microM) caused a 54 % increase in the rate of miniature excitatory post-synaptic currents (mEPSCs), without affecting their amplitude. The effect of anandamide was blocked by the VR1 antagonist capsazepine (20 microM), but not by the CB1-specific antagonist AM251 (3 microM). Application of the VR1 receptor agonist capsaicin (300 nM) caused a 4200 % increase in the mEPSC rate. In dissociated trigeminal ganglion neurons, both anandamide and capsaicin caused an outward current in neurons that were voltage clamped at +40 mV. The maximal outward current produced by anandamide (EC50, 10 microM) was 45 % of that produced by capsaicin (10 microM). Co-application of the VR1 antagonist capsazepine (30 microM) completely reversed the effects of both capsaicin and anandamide. The anandamide transport inhibitor, AM404 (30 microM) caused a 40 % increase in mEPSC rate in the slice preparation and an outward current in dissociated neurons. The latter current was reversed by the VR1 antagonist iodoresiniferatoxin (1 microM). The fatty acid amide hydrolase (FAAH) inhibitors phenylmethylsulfonyl fluoride (PMSF) (20 microM) and OL53 (1 microM) did not enhance the effect of anandamide in either the slice or dissociated neuron preparations. These results suggest that within the superficial medullary dorsal horn, anandamide (30 microM) acts presynaptically to enhance the release of glutamate via activation of the VR1 receptor.

Amidohydrolases↗
PubMed2001

Cannabinoid actions on rat superficial medullary dorsal horn neurons in vitro.

1. This study examined the cellular actions of cannabinoids on neurons in the substantia gelatinosa of the spinal trigeminal nucleus pars caudalis, using whole-cell and perforated patch recording in brain slices. 2. The cannabinoid agonist WIN55,212-2 (3 microM) decreased the amplitude of both GABAergic and glycinergic electrically evoked inhibitory postsynaptic currents (IPSCs) by 35 and 41 %, respectively. This inhibition was completely reversed by the CB(1) receptor-selective antagonist N-piperidino-5-(4-chlorophenyl)-l-(2,4-dichlorophenyl)-4-methyl-3-pyrazole-carboxamide) (SR141716A, 3 microM). WIN55,212-2 also produced relative facilitation of the second evoked IPSC to paired stimuli. 3. WIN55,212-2 decreased the rate of both GABAergic and glycinergic miniature IPSCs by 44 and 34 %, respectively, without changing their amplitude distributions or kinetics. 4. WIN55,212-2 did not affect the amplitude of electrically evoked non-NMDA glutamatergic excitatory postsynaptic currents (EPSCs). 5. WIN55,212-2 produced no postsynaptic membrane current and had no significant effect on membrane conductance over a range of membrane potentials (-60 to -130 mV). 6. These results suggest that, within the superficial medullary dorsal horn, cannabinoids presynaptically inhibit GABAergic and glycinergic neurotransmission. At the cellular level, the analgesic action of cannabinoids on these medullary dorsal horn neurons therefore differs from that of mu-opioids, which have both pre- and postsynaptic actions.

Animals↗
PubMed2001

Actions of nociceptin/orphanin FQ and other prepronociceptin products on rat rostral ventromedial medulla neurons in vitro.

1. Whole-cell patch clamp recordings were made from rat rostral ventromedial medulla (RVM) neurons in vitro to investigate the cellular actions of the opioid-like receptor ORL1 (NOP), ligand nociceptin/orphanin FQ and other putative prepronociceptin products. 2. Primary and secondary RVM neurons were identified as responding to the kappa-opioid receptor agonist U-69593 (300 nM to 1 microM) and the mu- and delta-opioid receptor agonist met-enkephalin (10 microM), respectively. Both primary and secondary RVM neurons responded to nociceptin (3 nM to 1 microM) with an outward current that reversed polarity at -115 mV in brain slices and with inhibition of Ca(2+) channel currents in acutely isolated cells. 3. The putative ORL1 antagonist J-113397 (1 microM) produced no change in membrane current and abolished the outward current produced by nociceptin (100 nM). In contrast, Phe(1)psi(CH(2)-NH)Gly(2)]-nociceptin-(1-13)NH(2) (300 nM to 1 microM) alone produced an outward current and partially reduced the outward current produced by nociceptin (300 nM) when co-applied. 4. In brain slices nociceptin (300 nM) reduced the amplitude of evoked GABA(A) receptor-mediated inhibitory postsynaptic currents (IPSCs) but not non-NMDA receptor-mediated excitatory postsynaptic currents (EPSCs). 5. Met-enkephalin (10 microM), but not nociceptin (300 nM), reduced the rate of spontaneous miniature IPSCs in normal external potassium solution (K(+) 2.5 mM). In high external potassium (K(+) 17.5 mM), nociceptin reduced the rate of miniature IPSCs in the presence (Ca(2+) 2.4 mM, Mg(2+) 1.2 mM) but not in the absence of external calcium (Ca(2+) 0 mM, Mg(2+) 10 mM, Cd(2+) 10 microM). Nociceptin and met-enkephalin had no effect on the amplitude of miniature IPSCs. 6. The putative nociceptin precursor products nocistatin (rat prepronociceptin(125-132)) and rat prepronociceptin(154-181) had no effect on membrane currents, evoked IPSCs and evoked EPSCs. 7. These results indicate that nociceptin acts via the ORL1 receptor to directly inhibit both primary and secondary RVM neurons by activating a potassium conductance and by inhibiting calcium conductances. In addition, nociceptin inhibits GABA release within the RVM via a presynaptic Ca(2+)-dependent mechanism. Thus, nociceptin has the potential to exert both disinhibitory and inhibitory effects on neuronal action potential firing within the RVM.

Animals↗
PubMed2000

Changes in the distribution of synaptic potentials from bulbospinal neurones following axotomy in cat thoracic spinal cord.

1. Plasticity in functional connections of expiratory bulbospinal neurones was investigated by measurement of terminal potentials (TPs) and focal synaptic potentials (FSPs), recorded with spike-triggered averaging in the thoracic spinal cord of anaesthetized, paralysed cats. These measurements were made in normal cats and in those which had previously been subjected to spinal cord lesions that transected the axons of the bulbospinal neurones in the segment below that under investigation, either about 2 weeks or about 16 weeks previously. 2. In both groups of operated animals bulbospinal neurones with firing properties and conduction velocities similar to normal were present. The extracellular recordings that were averaged to reveal TPs and FSPs were made on two standard grids, each consisting of eight sites spaced 0.25 mm apart on two electrode tracks. One grid was positioned at a rostral and one at a caudal location within one segment (T7-T9). 3. Tn the normal animals TPs and FSPs were larger and/or more common at rostral sites than at caudal sites, by a factor of about 1.7. In both 2 week and 16 week animals, TPs and FSPs were observed, both showing normal tine courses and latencies. At rostral sites in 2 week and 16 week animals the amplitudes and/or the frequency of occurrence of TPs and FSPs were similar to normal, as was the case fir caudal sites in the 2 week animals. However, at caudal sites in the 16 week animals the FSPs were mole common and/or significantly larger than normal, with the increase particularly marked on the lateral track, being equivalent to a factor of about 2. A corresponding increase in the amplitude and/or frequency of occurrence of TPs at caudal lateral sites was also seen, but was not significant. 4. The results are interpreted as evidence for short-range sprouting of the bulbospinal axons and the formation by them of new connections in the caudal parts of the segments concerned.

Animals↗
PubMed2000

Cellular actions of opioids and other analgesics: implications for synergism in pain relief.

1. mu-Opioid receptor agonists mediate their central analgesic effects by actions on neurons within brain regions such as the mid-brain periaqueductal grey (PAG). Within the PAG, mu-opioid receptor-mediated analgesia results from inhibition of GABAergic influences on output projection neurons. We have established that mu-opioid receptor activation in the PAG causes a presynaptic inhibition of GABA release that is mediated by activation of a voltage-dependent K+ channel via 12-lipoxygenase (LOX) metabolites of arachidonic acid. 2. At a cellular level, mu-opioid agonists have also been shown to open inwardly rectifying K+ channels, close voltage-gated Ca2+ channels and presynaptically inhibit glutamatergic synaptic transmission in the PAG. 3. The mu-opioid receptor-mediated presynaptic inhibition of GABAergic transmission was abolished by phospholipase A2 inhibitors and non-specific LOX and specific 12-LOX inhibitors. Cyclo-oxygenase (COX) and specific 5-LOX inhibitors did not reduce the inhibitory effects of mu-opioid agonists. 4. The opioid actions on GABAergic transmission were mimicked by arachidonic acid and 12-LOX metabolites, but not 5-LOX metabolites. The efficacy of mu-opioids was enhanced synergistically by treatment of PAG neurons with inhibitors of the other major enzymes responsible for arachidonic acid metabolism, COX and 5-LOX. 5. These results explain a previously described analgesic action of COX inhibitors in the central nervous system that was both independent of prostanoid release and inhibited by opioid receptor antagonists and they also explain the synergistic interaction of opioids with COX inhibitors. These findings also suggest new avenues for the development of centrally active analgesic agents involving combinations of lowered doses of opioids and specific 5-LOX inhibitors.

Analgesics↗
PubMed2000

An analgesic role for cannabinoids.

Cannabinoids have significant analgesic properties in animal models, particularly for chronic pain states, but there are few human studies. An endogenous cannabinoid system, with specific receptors and transmitters, has recently been discovered. This discovery has led pharmacologists to explore the potential of synthetic cannabinoids to selectively target chronic pain disorders without producing the side effects associated with cannabis. Well-controlled clinical trials on cannabinoids, and cannabinoid delivery systems, are now required.

Animals↗
PubMed2000

Actions of cannabinoids on membrane properties and synaptic transmission in rat periaqueductal gray neurons in vitro.

The midbrain periaqueductal gray (PAG) is a major site of cannabinoid-mediated analgesia in the central nervous system. In the present study, we examined the actions of cannabinoids on rat PAG neurons in vitro. In brain slices, superfusion of the cannabinoid receptor agonist WIN55,212-2 inhibited electrically evoked inhibitory and excitatory postsynaptic currents in all PAG neurons. The endogenous cannabinoid anandamide inhibited evoked inhibitory postsynaptic currents in the presence of the anandamide transport inhibitor AM404, but not in its absence. The stable anandamide analog R1-methanandamide also inhibited evoked inhibitory postsynaptic currents. WIN55,212-2 reduced the rate of spontaneous miniature inhibitory postsynaptic currents in normal and Ca(2+)-free solutions, but had no effect on their amplitude distributions or kinetics. The WIN55,212-2-induced decrease in miniature inhibitory postsynaptic current rate was concentration dependent (EC(50) = 520 nM). The effects of cannabinoids were reversed by the CB(1) receptor antagonist SR141716. WIN55,212-2 produced no change in membrane current or conductance in PAG neurons in brain slices and had no effect on Ca(2+)-channel currents in acutely isolated PAG neurons. These findings suggest that cannabinoids act via CB(1) receptors to inhibit GABAergic and glutamatergic synaptic transmission in rat PAG, although the efficacy of endogenous cannabinoids is likely to be limited by uptake and breakdown. Like mu-opioids, cannabinoids act to reduce the probability of transmitter release from presynaptic terminals via a Ca(2+)-independent mechanism. In contrast to mu-opioids, cannabinoids have no direct postsynaptic actions on PAG neurons. Thus, cannabinoids and mu-opioids are likely to produce analgesia within PAG in part by different mechanisms.

Animals↗
PubMed1999

Inhibition by adenosine receptor agonists of synaptic transmission in rat periaqueductal grey neurons.

1. The actions of selective adenosine A1 and A2 receptor agonists were examined on synaptic currents in periaqueductal grey (PAG) neurons using patch-clamp recordings in brain slices. 2. The A1 receptor agonist 2-chloro-N-cyclopentyladenosine (CCPA), but not the A2 agonist, 2-p-(2-carboxyethyl)phenethylamino-5'-N-ethylcarboxamidoadenosine (CGS21680), inhibited both electrically evoked inhibitory (eIPSCs) and excitatory (eEPSCs) postsynaptic currents. The actions of CCPA were reversed by the A1 receptor antagonist 8-cyclopentyl-1, 3-dipropylxanthine (DPCPX). 3. In the absence or presence of forskolin, DPCPX had no effect on eIPSCs, suggesting that concentrations of tonically released adenosine are not sufficient to inhibit synaptic transmission in the PAG. 4. CCPA decreased the frequency of spontaneous miniature action potential-independent IPSCs (mIPSCs) but had no effect on their amplitude distributions. Inhibition persisted in nominally Ca2+-free, high Mg2+ solutions and in 4-aminopyridine. 5. The CCPA-induced decrease in mIPSC frequency was partially blocked by the non-selective protein kinase inhibitor staurosporine, the specific protein kinase A inhibitor 8-para-chlorophenylthioadenosine-3',5'-cyclic monophosphorothioate (Rp-8-CPT-cAMPS), and by 8-bromoadenosine cyclic 3',5' monophosphate (8-Br-cAMP). 6. These results suggest that A1 adenosine receptor agonists inhibit both GABAergic and glutamatergic synaptic transmission in the PAG. Inhibition of GABAergic transmission is mediated by presynaptic mechanisms that partly involve protein kinase A.

Action Potentials↗
PubMed1999

Opioids, NSAIDs and 5-lipoxygenase inhibitors act synergistically in brain via arachidonic acid metabolism.

We have established that mu-opioid receptor activation causes a presynaptic inhibition of neurotransmitter release that is mediated by 12-lipoxygenase metabolites of arachidonic acid in midbrain neurons [1]. We further demonstrated that the efficacy of opioids was enhanced synergistically by treatment of brain neurons with inhibitors of the other major enzymes responsible for arachidonic acid metabolism; cyclooxygenase (COX-1) and 5-lipoxygenase. These findings explain a mechanism of analgesic action of NSAIDs in the central nervous system that is both independent of prostanoid release and inhibited by opioid antagonists, as well as the synergistic interaction of opioids with NSAIDs. These findings also suggest new avenues for development of centrally active medications involving combinations of lowered doses of opioids and specific 5-lipoxygenase inhibitors.

Analgesics, Opioid↗
PubMed1999

Cannabinoid receptor activation inhibits GABAergic neurotransmission in rostral ventromedial medulla neurons in vitro.

1. The rostral ventromedial medulla (RVM) is thought to play a crucial role in the antinociceptive actions of cannabinoids. This study examined the actions of the cannabinoid receptor agonist, WIN55,212-2, on membrane properties and GABAergic synaptic transmission in RVM neurons using whole cell patch clamp recordings in brain slices. 2. WIN55,212-2 (3 microM) had no effect on membrane K+ conductance of primary or secondary RVM neurons. Primary neurons responded to the kappa-opioid receptor agonist U69,593 (300 nM - 1 microM). Secondary neurons responded to the mu,delta-opioid receptor agonist met-enkephalin (10 microM). 3. WIN55,212-2 reduced the amplitude of electrically evoked (GABAergic) inhibitory postsynaptic currents (IPSCs) in all neurons (58%, pEC50=6.2+/-0.1). The inhibition was reversed by the CB1 receptor selective antagonist, SR141716 (3 microM). WIN55,212-2 also produced relative facilitation of the second IPSC to paired evoked IPSCs. 4. WIN55,212-2 and met-enkephalin reduced the rate of spontaneous miniature IPSCs in all cells (44 and 53%), but had no effect on their amplitude distributions or kinetics. 5. These results suggest that the antinociceptive actions of cannabinoids within RVM are primarily due to presynaptic inhibition of GABAergic neurotransmission. The neuronal substrates of cannabinoid actions in RVM therefore differ from those of opioids, which have both pre- and postsynaptic inhibitory actions.

Analgesics↗
PubMed1999

Nociceptin, Phe(1)psi-nociceptin(1 - 13), nocistatin and prepronociceptin(154 - 181) effects on calcium channel currents and a potassium current in rat locus coeruleus in vitro.

1. The actions of the neuropeptide nociceptin, the putative nociceptin receptor antagonist [Phe1psi(CH(2)-NH)Gly(2)]-nociceptin-(1 - 13)NH(2) (Phe(1)psi-nociceptin(1 - 13)) and the putative nociceptin precursor products nocistatin (rat prepronociceptin(125 - 132)) and rat prepronociceptin(154 - 181) were examined on membrane properties of rat locus coeruleus (LC) neurons using whole cell patch clamp techniques. 2. Nociceptin inhibited I(Ba) in all LC neurons, (pD(2) of 8.9, maximum inhibition 50%). The inhibition of I(Ba) by nociceptin was associated with slowing of the activation of I(Ba) and could be significantly reversed by a strong depolarizing prepulse. Phe(1)psi-nociceptin(1 - 13) also inhibited I(Ba) in LC neurons (notional pD(2) of 7.6, maximum inhibition 18%). Application of Phe(1)psi-nociceptin(1 - 13) (1 microM) significantly occluded the subsequent effects of a co-application of nociceptin (3 nM) on I(Ba). 3. As previously reported for nociceptin, Phe(1)psi-nociceptin(1 - 13) caused an outward current in LC neurons voltage clamped at -60 mV (pD(2) of 7.1, maximum current 50% of that of methionine enkephalin, 10 microM). The Phe(1)psi-nociceptin(1 - 13) induced current reversed polarity at -112 mV and exhibited pronounced inward rectification. Phe(1)psi-nociceptin(1 - 13) (1 microM) reversibly inhibited the current caused by nociceptin (300 nM) by 30%. 4. Neither nocistatin nor rat prepronociceptin(154 - 181) inhibited I(Ba) in LC neurons, or prevented the subsequent inhibition by nociceptin. Neither nocistatin or prepronociceptin(154 - 181) affected the membrane properties of LC neurons. 5. This study demonstrates that nociceptin modulates somatic I(Ba) in rat LC neurons. The putative ORL1 antagonist Phe(1)psi-nociceptin(1 - 13) exhibited partial agonist activity at inhibiting I(Ba) and opening K(+) channels in LC. Other putative nociceptin precursor products were without effect on LC cells.

Animals↗
PubMed1998

Enhanced opioid efficacy in opioid dependence is caused by an altered signal transduction pathway.

Chronic morphine administration induces adaptations in neurons resulting in opioid tolerance and dependence. Functional studies have implicated a role for the periaqueductal gray area (PAG) in the expression of many signs of opioid withdrawal, but the cellular mechanisms are not fully understood. This study describes an increased efficacy, rather than tolerance, of opioid agonists at mu-receptors on GABAergic (but not glutamatergic) nerve terminals in PAG after chronic morphine treatment. Opioid withdrawal enhanced the amplitudes of electrically evoked inhibitory synaptic currents mediated by GABAA receptors and increased the frequency of spontaneous miniature GABAergic synaptic currents. These effects were not blocked by 4-aminopyridine or dendrotoxin, although both Kv channel blockers abolish acute opioid presynaptic inhibition of GABA release in PAG. Instead, the withdrawal-induced increases were blocked by protein kinase A inhibitors and occluded by metabolically stable cAMP analogs, which do not prevent acute opioid actions. These findings indicate that opioid dependence induces efficacious coupling of mu-receptors to presynaptic inhibition in GABAergic nerve terminals via adenylyl cyclase- and protein kinase A-dependent processes in PAG. The potential role of these adaptations in expression of withdrawal behavior was supported by inhibition of enhanced GABAergic synaptic transmission by the alpha2 adrenoceptor agonist clonidine. These findings provide a cellular mechanism that is consistent with other studies demonstrating attenuated opioid withdrawal behavior after injections of protein kinase A inhibitors into PAG and suggest a general mechanism whereby opioid withdrawal may enhance synaptic neurotransmission.

4-Aminopyridine↗