Sensitive Nicotinic Receptors Research Articles

Caenorhabditis elegans muscle Cys-loop receptors as novel targets of terpenoids with potential anthelmintic activity.

The anthelmintic treatment of nematode infections remains the pillar of worm control in both human and veterinary medicine. Since control is threatened by the appearance of drug resistant nematodes, there is a need to develop novel compounds, among which phytochemicals constitute potential anthelmintic agents. Caenorhabditis elegans has been pivotal in anthelmintic drug discovery and in revealing mechanisms of drug action and resistance. By using C. elegans, we here revealed the anthelmintic actions of three plant terpenoids -thymol, carvacrol and eugenol- at the behavioral level. Terpenoids produce a rapid paralysis of worms with a potency rank order carvacrol > thymol > eugenol. In addition to their paralyzing activity, they also inhibit egg hatching, which would, in turn, lead to a broader anthelmintic spectrum of activity. To identify drug targets, we performed an in vivo screening of selected strains carrying mutations in receptors involved in worm locomotion for determining resistance to the paralyzing effect of terpenoids. The assays revealed that two Cys-loop receptors with key roles in worm locomotion -Levamisole sensitive nicotinic receptor (L-AChR) and GABA(A) (UNC-49) receptor- are involved in the paralyzing effects of terpenoids. To decipher the mechanism by which terpenoids affect these receptors, we performed electrophysiological studies using a primary culture of C. elegans L1 muscle cells. Whole cell recordings from L1 cells demonstrated that terpenoids decrease macroscopic responses of L-AChR and UNC-49 receptor to their endogenous agonists, thus acting as inhibitors. Single-channel recordings from L-AChR revealed that terpenoids decrease the frequency of opening events, probably by acting as negative allosteric modulators. The fact that terpenoids act at different receptors may have important advantages regarding efficacy and development of resistance. Thus, our findings give support to the use of terpenoids as either an alternative or a complementary anthelmintic strategy to overcome the ever-increasing resistance of parasites to classical anthelmintic drugs.

Neuromuscular Nicotinic Receptors Mediate Bladder Contractions Following Bladder Reinnervation with Somatic to Autonomic Nerve Transfer after Decentralization by Spinal Root Transection

We investigated whether the reinnervated neuronal pathway mediates contraction via the same neurotransmitter and receptor mechanisms as the original pathway. After decentralizing the bladder by transecting the sacral roots in dogs we performed peripheral nerve transfer, including bilateral genitofemoral to pelvic nerve transfer and unilateral left femoral nerve to bilateral pelvic nerve transfer. Reinnervation was assessed 7.5 months postoperatively by monitoring bladder pressure during electrical stimulation of the transferred nerves, spinal ventral roots and spinal cord. Of the 17 dogs with genitofemoral to pelvic nerve transfer 14 (82%) demonstrated functional bladder reinnervation as evidenced by increased bladder pressure during stimulation of the transferred genitofemoral nerve, or L3 or L4 spinal ventral roots. Lumbar spinal cord stimulation caused increased bladder pressure in 9 of 10 dogs (90%) with unilateral left femoral nerve to bilateral pelvic nerve transfer. Succinylcholine virtually eliminated the bladder pressure increases induced by electrical stimulation of the transferred somatic nerves or of the lumbar spinal segments that contribute axons to these donor nerves. In unoperated or sham operated controls succinylcholine had no effect on nerve evoked bladder pressure increases but it substantially decreased the urethral and anal sphincter pressure induced by stimulating the lumbosacral spinal cord or the S2-S3 spinal ventral roots. The reinnervated detrusor muscles of dogs with genitofemoral to pelvic nerve transfer and unilateral left femoral nerve to bilateral pelvic nerve transfer also showed increased α1 nicotinic receptor subunit immunoreactivity in punctate dots on detrusor muscle fascicles and in neuronal cell bodies. This staining was not observed in controls. Succinylcholine sensitive nicotinic receptors, which normally mediate only skeletal muscle neuromuscular junction neurotransmission, appeared in the new neuronal pathway after genitofemoral to pelvic and unilateral femoral nerve to bilateral pelvic nerve transfer. This suggests end organ neuroplasticity after reinnervation by somatic motor axons.

290 THE SKELETAL NEUROMUSCULAR JUNCTION NICOTINIC RECEPTOR ANTAGONIST SUCCINYL CHOLINE BLOCKS BLADDER CONTRACTIONS INDUCED BY FUNCTIONAL ELECTRICAL STIMULATION OF A NEW NEURONAL PATHWAY CREATED BY REINNERVATION WITH GENITOFEMORAL TO PELVIC NERVE TRANSFER

You have accessJournal of UrologyBladder and Urethra: Anatomy, Physiology and Pharmacology (I)1 Apr 2013290 THE SKELETAL NEUROMUSCULAR JUNCTION NICOTINIC RECEPTOR ANTAGONIST SUCCINYL CHOLINE BLOCKS BLADDER CONTRACTIONS INDUCED BY FUNCTIONAL ELECTRICAL STIMULATION OF A NEW NEURONAL PATHWAY CREATED BY REINNERVATION WITH GENITOFEMORAL TO PELVIC NERVE TRANSFER Michael Ruggieri, Sandra Gomez, Alan Braverman, Vicky Massicotte, and Mary Barbe Michael RuggieriMichael Ruggieri Philadelphia, PA More articles by this author , Sandra GomezSandra Gomez Philadelphia, PA More articles by this author , Alan BravermanAlan Braverman Philadelphia, PA More articles by this author , Vicky MassicotteVicky Massicotte Philadelphia, PA More articles by this author , and Mary BarbeMary Barbe Philadelphia, PA More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2013.02.1674AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES Following bladder denervation by transection of sacral spinal cord roots, genitofemoral nerve (GFN) transfer to vesical branches of pelvic nerve (PN) reinnervates the canine bladder because functional electrical stimulation of the transferred GFN induces bladder contraction. The new pathway reinnervates both intramural bladder ganglia as well as detrusor smooth muscle cells directly which are not normally innervated by parasympathetic spinal cord neurons. This study investigates whether the reinnervated neuronal pathway mediates contraction by the same neurotransmitter and receptor mechanisms as the original pathway. METHODS After bladder, urethral sphincter and anal sphincter denervation in 4 female canines, GFN were transferred bilaterally to PN and implanted with nerve cuff electrodes interfaced with radiofrequency micro-stimulators (RFMS). The effect of GFN stimulation on bladder pressure was determined before and after neuromuscular blockade with succinyl choline (SC) 3-6 months after reinnervation. The effects of SC on bladder contractions induced by intraoperative electrical stimulation of sacral spinal nerve roots was determined in 1 normal control and by stimulation of vesical branches of the pelvic nerve in 3 sham operated controls. RESULTS RFMS functional electrical stimulation of the GFN induced bladder contractions in 7 of 8 transferred nerves causing pressure increases of 11.2±4.1 cm H2O that were completely blocked with succinyl choline. Stimulation of the sacral nerve roots in the normal control induced bladder, urethral sphincter and anal sphincter pressure. The urethral and anal sphincter pressures were completely blocked with succinyl choline but the bladder pressure increases induced by sacral root stimulation in the normal control or pelvic nerve stimulation in the sham operate controls were not affected (13.5±3.3 vs 11.4±3.1 cm H2O). CONCLUSIONS This study demonstrates plasticity in the nicotinic receptors involved in nerve evoked bladder contractions induced by bladder reinnervation. GF to PN transfer results in the emergence of succinyl choline sensitive nicotinic receptors in this pathway that normally mediate cholinergic contractions at the neuromuscular junction of skeletal but not smooth muscle. These new nicotinic receptors may mediate contractions of the reinnervated bladder at the intramural ganglia cells or the newly reinnervated smooth muscle cells. © 2013 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 189Issue 4SApril 2013Page: e118 Advertisement Copyright & Permissions© 2013 by American Urological Association Education and Research, Inc.MetricsAuthor Information Michael Ruggieri Philadelphia, PA More articles by this author Sandra Gomez Philadelphia, PA More articles by this author Alan Braverman Philadelphia, PA More articles by this author Vicky Massicotte Philadelphia, PA More articles by this author Mary Barbe Philadelphia, PA More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

Nicotine exposure refines visual map topography through an NMDA receptor‐mediated pathway

The precise mapping of one surface onto another is fundamental to visual system organization and depends upon adequate stimulation of postsynaptic targets to stabilize correctly placed synapses. As exogenous nicotine alters neuronal activity, we investigated whether it would affect the visual map created by retinal ganglion cell terminals in the frog optic tectum. Chronic exposure of the tectum to nicotine decreased the retinal area from which cells project to a given tectal site. This map refinement was also produced by exposure to either the alpha-bungarotoxin sensitive nicotinic receptor agonist, anatoxin-a or the alpha-bungarotoxin-insensitive nicotinic receptor agonist epiboxidine. Immunocytochemical studies using mAb306 and mAb22 demonstrated that alpha-bungarotoxin-sensitive and -insensitive nicotinic receptors, respectively, occupied different tectal sites. Choline acetyltransferase immunoreactivity overlapped with mAb306, but not mAb22, staining. The developing optic tectum was more sensitive to nicotine than the adult tectum and nicotine induced both map refinements and map disruptions in a concentration-dependent manner. Blockade of the N-methyl-D-aspartate (NMDA) receptor with D(-)-2-amino-5-phosphonopentanoic acid (D-APV) prevented nicotine from refining the map in the adult tectum. Exposure to the use-dependent NMDA antagonist MK801 alone had no effect on retinotectal topography but in combination with either NMDA or nicotine it disrupted the map. Exposure to NMDA alone produced refinement. We conclude that the map refinement induced by chronic nicotine treatment has as its basis an increase in the level of NMDA receptor activity. The data are consistent with a model whereby map topography can be bidirectionally affected by either increasing or decreasing NMDA receptor activity.

Prenatal nicotine exposure alters the nicotinic receptor subtypes that modulate excitation of parasympathetic cardiac neurons in the nucleus ambiguus from primarily α3β2 and/or α6βX to α3β4

Nicotinic receptors play an essential role in central cardiorespiratory function, however, the types of nicotinic receptors responsible for activating cardiac vagal neurons in the nucleus ambiguus that control heart rate are unknown. This study tests whether α-conotoxin MII and α-conotoxin AuIB sensitive nicotinic receptors are involved in augmentation of glutamatergic neurotransmission and changes in holding current in cardiac vagal neurons, and whether exposure to nicotine in the prenatal period alters these responses. The nicotinic agonist cytisine significantly increased the holding current and amplitude of glutamatergic mEPSCs. In unexposed animals α-conotoxin MII (100 nM) significantly reduced the increase in mEPSC amplitude and change in holding current evoked by cytisine. However, in animals prenatally exposed to nicotine, α-conotoxin MII blunted but did not block the increase in mEPSC amplitude but blocked the increase in holding current evoked by cytisine. In unexposed animals, α-conotoxin AuIB (10 μM) blocked the cytisine evoked increase in mEPSC amplitude and inhibited but did not abolish the increase in holding current. In contrast, in animals exposed to nicotine, α-conotoxin AuIB blunted the increase in mEPSC amplitude, and completely abolished the cytisine evoked increase in holding current. These data demonstrate that the prenatal nicotine exposure alters the nicotinic receptors involved in excitation of cardiac vagal neurons.

Rigidified acetylcholine mimics: conformational requirements for binding to neuronal nicotinic receptors.

Rigidified derivatives have been designed and synthesized assuming the g+t conformer of acetylcholine (N-C-C-O=+60 degrees, C-C-O-C=180 degrees ) as active conformation for binding to cytisine sensitive neuronal nicotinic receptors. The SAR of the compounds evaluated, along with those of more flexible analogues, support the g+t conformer hypothesis and highlight the stringent steric limitation of this nicotinic receptor sub-type. Compound 3e has low microM affinity for cytisine sensitive nicotinic receptor binding sites while being selective with regard to the alpha-bungarotoxin sensitive subclass. We also report few compounds with microM affinity for the alpha-bungarotoxin sensitive subclass.

Activation and inhibition of native neuronal alpha-bungarotoxin-sensitive nicotinic ACh receptors

Tuberomammillary histamine neurons (TM) of the posterior hypothalamus exclusively express alpha-bungarotoxin (αBgt) sensitive nicotinic receptors, providing a unique model system for studying physiological properties of native α7-like receptors. Here the properties of αBgt-sensitive receptors were investigated using the patch-clamp technique and rapid application of acetylcholine (ACh) or the α7-selective agonists, 3-(4-hydroxy,2-methoxybenzylidene)anabaseine (4OH-GTS-21), and choline. Alpha-Bgt-sensitive receptor responses to rapid application of high agonist concentrations were characterized by a transient current which rapidly decayed in a voltage-independent concentration-dependent manner to a relatively sustained slow current. Upon agonist removal, current persisted for several milliseconds (or longer) and increased above the level of the slow current (rebound). Lower agonist concentrations did not produce a rebound. Our analysis suggests that the current rebound represents a recovery phase from a low potency inhibition. This inhibition was voltage-dependent for ACh and choline but voltage-independent for 4OH-GTS-21. A slow form of desensitization was present which was relatively agonist-independent and was faster than the rate of 4OH-GTS-21 unbinding. Kinetic analysis revealed that the concentration dependence of the transient response amplitudes was compromised by solution exchange; net charge measurements over the late response phases were chosen as an alternative measure of concentration/response function. Our data suggest that low agonist concentrations can evoke a prolonged or tonic-like receptor activation. Functioning in this modality, receptors would regulate calcium homeostasis over a narrow, but therapeutically important, range of intracellular calcium concentrations. This could then provide the basis for cytoprotective effects of 4OH-GTS-21 and other nicotinic agonists, mediating trophic and neuromodulatory functions.