(1/239) Disinfection of upper gastrointestinal fibreoptic endoscopy equipment: an evaluation of a cetrimide chlorhexidine solution and glutaraldehyde.
There is little information available on the bacteriological contamination of upper gastrointestinal fibreoptic endoscopes during routine use and the effects of 'disinfecting solutions'. A bacteriological evaluation was therefore made of cleaning an endoscope and its ancillary equipment with (1) water, (2) an aqueous solution of 1% cetrimide with 0.1% chlorhexidine, and (3) activated aqueous 2% glutaraldehyde. All equipment, but particularly the endoscope itself, was found to be heavily contaminated after use with a wide variety of organisms of which 53% were Gram positive. Cleaning the endoscope and ancillary equipment with water and the cetrimide/chlorhexidine solution alone or in combination was inadequate to produce disinfection but immersion in glutaraldehyde for two minutes consistently produced sterile cultures with our sampling technique. A rapid and simple method for disinfection of endoscopic equipment is therefore recommended and we think this is especially suitable for busy endoscopy units. (+info)
(2/239) Spermine and arcaine block and permeate N-methyl-D-aspartate receptor channels.
Polyamines such as spermine are thought to be endogenous regulators of NMDA (N-methyl-D-aspartate)-type glutamate receptors. Polyamine block of NMDA receptors was studied in excised outside-out patches from rat hippocampal neurons and Xenopus oocytes expressing recombinant receptors. Extracellular spermine and arcaine reduced NMDA single-channel conductance in a voltage-dependent manner, with partial relief of block evident at large inside negative membrane potentials. Reducing extracellular Na+ concentration increased the apparent affinities for spermine and arcaine, indicating strong interaction between spermine and permeant ions. Internal spermine also blocked NMDA channels in a voltage-dependent manner, with relief of block evident at large inside positive potentials. The Woodhull model of channel block by an impermeant ion adequately described the actions of external spermine from -60 to +60 mV, but failed for more negative potentials. Eyring rate theory for a permeable blocker with two barriers and one binding site adequately described the voltage-dependent block and relief from block by both external and internal spermine over the range of -120 to +60 mV. These findings indicate that polyamines block and permeate neuronal NMDA receptor channels from the extracellular and intracellular sides, although sensitivity to internal spermine is probably too low to be physiologically relevant. (+info)
(3/239) Human retina contains polyamine sensitive [3H]-ifenprodil binding sites: implications for neuroprotection?
AIMS: This study characterised the pharmacology of [3H]-ifenprodil binding to the polyamine binding sites (PBS) on the N-methyl-D-aspartate (NMDA) receptor channel complex on human retinas. These data were correlated with the known neuroprotective effects of ifenprodil and eliprodil. METHODS: Specific binding of [3H]-ifenprodil (under sigma site blockade) was investigated using human retinal homogenates and radioligand binding techniques. Scatchard and competition analyses were utilised to define the pharmacology of the [3H]-ifenprodil binding sites. RESULTS: Specific binding of [3H]-ifenprodil comprised 73% (SEM 3%) of total and reflected interaction with two affinity sites (Kds = 0.39 and 4.3 microM) of different densities (Bmax = 14.4 and 105 pmol/mg protein) (n = 5). The rank order of affinity of compounds competing for [3H]-ifenprodil binding to the high affinity PBS was: ifenprodil > eliprodil > arcaine > spermine > diaminodecane > spermidine > putrescine >> MK-801 (n = 3-7). However, [3H]-ifenprodil binding was minimally inhibited by glutamate, NMDA, and kainate. CONCLUSION: These studies have shown, for the first time, the presence of specific [3H]-ifenprodil binding sites in the human retina with pharmacological characteristics of PBS associated with the NMDA receptor ionophore complex. The neuroprotective effects of eliprodil and ifenprodil may, in part, be mediated via these [3H]-ifenprodil labelled sites. (+info)
(4/239) Modulation of afferent-evoked neurotransmission by 5-HT3 receptors in young rat dorsal horn neurones in vitro: a putative mechanism of 5-HT3 induced anti-nociception.
1. The in vitro hemisected spinal cord from young rat was used to investigate the mechanism of serotoninergic modulation of primary afferent-mediated synaptic transmission in the dorsal horn through activation of the 5-HT3 receptor. 2. Dorsal root-evoked excitatory post-synaptic potentials (DR-EPSPs) were recorded intracellularly from dorsal horn neurones. Extracellular recordings of the population primary afferent depolarization (PAD) and the dorsal root-evoked dorsal root reflex (DR-DRR) were made from segmental dorsal roots. 3. 5-Hydroxytryptamine (5-HT) and the selective 5-HT3 receptor agonist 1-(m-chloro-phenyl)-biguanide hydrochloride (m-ChPB) (10 and 50 microM) induced statistically significant reductions of the DR-EPSP amplitude (P<0.001) and duration (P<0.001) in the majority of dorsal horn neurones. The 5-HT3 receptor selective antagonists 3-Tropanyl-indole-3-carboxylate hydrochloride (Tropisetron, 10 microM) and N-(1-Azabicyclo[2.2.2]oct-3-yl)-6-chloro-4-methyl-3-oxo-3,4-dihydro-2H-1 ,4-benzoxazine-8-carboxamide (Y-25130, 10 microM) abolished m-ChPB-induced DR-EPSP attenuation and partially blocked the 5-HT effect. 4. m-ChPB (50 microM)-induced DR-EPSP amplitude and duration attenuation was retained in the presence of the GABA(A) receptor antagonist bicuculline (30 microM), the GABA(B) receptor antagonist saclofen (50 microM) and the opioid receptor antagonist naloxone (50 microM). 5. Both 5-HT and m-ChPB (10 and 50 microM) induced a PAD but the mean peak amplitude of 5-HT-induced PAD was significantly greater than PAD to m-ChPB (98.6+/-12 microV compared to 51.8+/-10 V for 50 microM of agonist, respectively). Tropisetron partially reduced 5-HT-induced PAD and abolished m-ChPB-induced PAD. 5-HT, but not m-ChPB, significantly (P<0.001) reduced the peak amplitude of the DR-DRR and this action of 5-HT was unaffected by Tropisetron or Y-25130. 6. These data provide experimental evidence for a putative cellular mechanism at the level of the dorsal horn for anti-nociceptive effects of 5-HT3 receptor activation. This 5-HT3-mediated modulation of sensory afferent transmission was evidently independent of inhibitory GABA- or opioid-dependent interneuronal pathways. The extent to which the 5-HT3 receptor could be involved in the operation of endogenous analgesia and sensory modulation by descending monoamine bulbo-spinal pathways is discussed. (+info)
(5/239) Effects of various serotonin agonists, antagonists, and uptake inhibitors on the discriminative stimulus effects of methamphetamine in rats.
Neurochemical studies indicate that methamphetamine increases central serotonin (5-HT) levels more markedly than other psychomotor stimulants such as amphetamine or cocaine. In the present study, we investigated 5-HT involvement in the discriminative stimulus effects of methamphetamine. In Sprague-Dawley rats trained to discriminate 1.0 mg/kg methamphetamine i.p. from saline under a fixed-ratio schedule of food presentation, the effects of selected 5-HT agonists, antagonists, and uptake inhibitors were tested. Fluoxetine (1.8-18.0 mg/kg) and clomipramine (3.0-18.0 mg/kg), selective serotonin uptake inhibitors, did not produce any methamphetamine-like discriminative stimulus effects when administered alone, but fluoxetine (5.6 mg/kg), unlike clomipramine (5.6 mg/kg), significantly shifted the methamphetamine dose-response curve to the left. Both 8-hydroxy-2-dipropylaminotetralin (0.03-0.56 mg/kg), a full agonist, and buspirone (1.0-10.0 mg/kg), a partial agonist at 5-HT(1A) receptors, partially generalized to the training dose of methamphetamine but only at high doses that decreased response rate. This generalization was antagonized by the coadministration of the 5-HT(1A) antagonist WAY-100635 (1.0 mg/kg). WAY-100635 (1.0 mg/kg) also partially reversed the leftward shift of the methamphetamine dose-response curve produced by fluoxetine. (+/-)-1-(2, 5-Dimethoxy-4-iodophenyl)-2-aminopropane (0.3 mg/kg), a 5-HT(2A/2C) agonist, shifted the methamphetamine dose-response curve to the left, and this leftward shift was antagonized by the coadministration of ketanserin (3.0 mg/kg), a 5-HT(2A/2C) antagonist. Ketanserin (3.0 mg/kg) also produced a shift to the right in the methamphetamine dose-response curve and completely reversed the leftward shift in the methamphetamine dose-response curve produced by fluoxetine. In contrast, tropisetron (1.0 mg/kg), a 5-HT(3) antagonist, produced a shift to the left of the methamphetamine dose-response curve, and this effect of tropisetron was antagonized by the coadministration of m-chlorophenyl-biguanide (1.8 mg/kg), a 5-HT(3) agonist. The present data suggest that the 5-HT system plays a modulatory role in the discriminative stimulus effects of methamphetamine. These effects appear to be mediated through 5-HT release and blockade of reuptake and subsequent activation of 5-HT(2A/2C) receptors, with limited involvement of other 5-HT receptor subtypes. (+info)
(6/239) The pharmacological and functional characteristics of the serotonin 5-HT(3A) receptor are specifically modified by a 5-HT(3B) receptor subunit.
While homomers containing 5-HT(3A) subunits form functional ligand-gated serotonin (5-HT) receptors in heterologous expression systems (Jackson, M. B., and Yakel, J. L. (1995) Annu. Rev. Physiol. 57, 447-468; Lambert, J. J., Peters, J. A., and Hope, A. G. (1995) in Ligand-Voltage-Gated Ion Channels (North, R., ed) pp. 177-211, CRC Press, Inc., Boca Raton, FL), it has been proposed that native receptors may exist as heteromers (Fletcher, S., and Barnes, N. M. (1998) Trends Pharmacol. Sci. 19, 212-215). We report the cloning of a subunit 5-HT(3B) with approximately 44% amino acid identity to 5-HT(3A) that specifically modified 5-HT(3A) receptor kinetics, voltage dependence, and pharmacology. Co-expression of 5-HT(3B) with 5-HT(3A) modified the duration of 5-HT(3) receptor agonist-induced responses, linearized the current-voltage relationship, increased agonist and antagonist affinity, and reduced cooperativity between subunits. Reverse transcriptase-polymerase chain reaction in situ hybridization revealed co-localization of both 5-HT(3B) and 5-HT(3A) in a population of neurons in the amygdala, telencephalon, and entorhinal cortex. Furthermore, 5-HT(3A) and 5-HT(3B) mRNAs were expressed in spleen and intestine. Our data suggest that 5-HT(3B) might contribute to tissue-specific functional changes in 5-HT(3)-mediated signaling and/or modulation. (+info)
(7/239) Pulmonary oedema produced by scorpion venom augments a phenyldiguanide-induced reflex response in anaesthetized rats.
1. The involvement of pulmonary oedema produced by scorpion venom in augmenting a phenyldiguanide (PDG)-induced reflex response was evaluated in urethane-anaesthetized rats. 2. PDG-induced bradycardiac, hypotensive and apnoeic responses, expressed as time-response area, exhibited similarities before or after venom treatment. Hence, the time-response area of bradycardia was taken as a reflex parameter. Pulmonary oedema was determined by physical evaporation and histological methods. 3. Exposure to Indian red scorpion (Buthus tamulus, BT; i.v.) venom for 30 min increased the pulmonary water content (P < 0.05; Student's t test) and augmented the PDG-induced bradycardiac reflex response by more than 2 times (P < 0.001). The increase of pulmonary water content was maximal with 100 microg kg-1 of venom and the augmentation was maximal with 10 microg kg-1. In a separate series of experiments, the venom (100 microg kg-1)-induced pulmonary oedema was confirmed by histological and physical methods. In this group also, the venom augmented the reflex to the same magnitude. 4. Pulmonary oedema (physical and histological) and augmentation of the bradycardiac reflex response after BT venom (100 microg kg-1; i.v.) were absent in animals pretreated with aprotinin, a kallikrein-kinin inhibitor (6000 KIU; i. v.). 5. Ondansetron (10 microg kg-1; i.v.), a 5-HT3 receptor antagonist, failed to block the venom-induced pulmonary oedema (physical and histological) but blocked the venom-induced augmentation of the reflex. 6. The results of this study indicate that the venom-induced augmentation of the PDG reflex is associated with pulmonary oedema involving kinins utilizing 5-HT3 receptors. (+info)
(8/239) The role of tryptophan residues in the 5-Hydroxytryptamine(3) receptor ligand binding domain.
Aromatic amino acids are important components of the ligand binding site in the Cys loop family of ligand-gated ion channels. To examine the role of tryptophan residues in the ligand binding domain of the 5-hydroxytryptamine(3) (5-HT(3)) receptor, we used site-directed mutagenesis to change each of the eight N-terminal tryptophan residues in the 5-HT(3A) receptor subunit to tyrosine or serine. The mutants were expressed as homomeric 5-HT(3A) receptors in HEK293 cells and analyzed with radioligand binding, electrophysiology, and immunocytochemistry. Mutation of Trp(90), Trp(183), and Trp(195) to tyrosine resulted in functional receptors, although with increased EC(50) values (2-92-fold) to 5-HT(3) receptor agonists. Changing these residues to serine either ablated function (Trp(90) and Trp(183)) or resulted in a further increase in EC(50) (Trp(195)). Mutation of residue Trp(60) had no effect on ligand binding or receptor function, whereas mutation of Trp(95), Trp(102), Trp(121), and Trp(214) ablated ligand binding and receptor function, and all but one of the receptors containing these mutations were not expressed at the plasma membrane. We propose that Trp(90), Trp(183), and Trp(195) are intimately involved in ligand binding, whereas Trp(95), Trp(102), Trp(121), and Trp(214) have a critical role in receptor structure or assembly. (+info)