A variety of G protein coupled receptors (GPCRs) are expressed in the presynaptic terminals of central and peripheral synapses and play regulatory roles in transmitter release. The patch-clamp whole-cell recording technique, applied to the calyx of Held presynaptic terminal in brainstem slices of rodents, has made it possible to directly examine intracellular mechanisms underlying the GPCR-mediated presynaptic inhibition. At the calyx of Held, bath-application of agonists for GPCRs such as GABAB receptors, group III metabotropic glutamate receptors (mGluRs), adenosine A1 receptors, or adrenaline alpha2 receptors, attenuate evoked transmitter release via inhibiting voltage-activated Ca2+ currents without affecting voltage-activated K+ currents or inwardly rectifying K+ currents. Furthermore, inhibition of voltage-activated Ca2+ currents fully explains the magnitude of GPCR-mediated presynaptic inhibition, indicating no essential involvement of exocytotic mechanisms in the downstream of Ca2+ influx. Direct loadings of G protein beta gamma subunit (G beta gamma) into the calyceal terminal mimic and occlude the inhibitory effect of a GPCR agonist on presynaptic Ca2+ currents (IpCa), suggesting that G beta gammamediates presynaptic inhibition by GPCRs. Among presynaptic GPCRs glutamate and adenosine autoreceptors play regulatory roles in transmitter release during early postnatal period when the release probability (p) is high, but these functions are lost concomitantly with a decrease in p during postnatal development.
Adenosine ; Autoreceptors ; Brain Stem ; Epinephrine ; Glutamic Acid ; GTP-Binding Proteins* ; Patch-Clamp Techniques ; Presynaptic Terminals ; Receptor, Adenosine A1 ; Receptors, G-Protein-Coupled* ; Receptors, Metabotropic Glutamate ; Rodentia ; Synapses

Migraine and anxiety disorders are frequently co-morbid with balance disorders. Potential mechanisms for migrainous vertigo include sites of action of 5-HT (serotonin) 1B and 1D receptor agonists such as rizatriptan, which attenuate motion sickness in migraineurs. Selective serotonin reuptake inhibitors (SSRIs) are also known to be efficacious in the treatment of vertigo. Relative distribution of the 5-HT receptor subtypes and their functional roles in the vestibular nuclei and inner ear is still unknown. Using 5-HT1A, 1B, AND 1D receptors-specific antibody, we have demonstrated a differential distribution of these receptor subtypes within the rat vestibular nuclei and inner ear. For 5-HT receptor subtypes expression in the vestibular and auditory periphery, most ganglion cells in the vestibular ganglion showed immunoreactivity for 5-HT1A, 5-HT1B and 5-HT1D receptors. In addition, 5-HT1B and 1D receptors immunopositive reactivities were associated with endothelial cells of small blood vessels in the vestibular ganglion and nerve, endothelial cells in both the spiral ligament deep to the spiral prominence and stria vascularis and endothelial cells on blood vessels along the margins of the spiral ganglion. For 5-HT receptor subtypes expression in the vestibular nuclei (VN), the 5-HT1A, 1B and 1D receptors were expressed differentially in the VN. Fine varicose axons in the periventricular plexus showed intense 5-HT1A receptor expression in the medial VN (MVN) and extended into the superior VN (SVN). By contrast, 5-HT1B receptors were not expressed the ventricular plexus axons. Rather, 5-HT1B and 1D receptors immunopositive cell bodies and neuronal processes were dense in rostral MVN, dorsal SVN, lateral VN (LVN) and ventral aspect of nucleus prepositus hypoglossi (NPH). In the present study, inner ear and vestibular nuclei showed distinct distributions of 5- HT1A, 1B and 1D receptors expressions that are parallel to their distribution in peripheral and central nociceptive pathways. These differentially distributed 5-HT receptor subtypes are potential targets to explain the efficacy of SSRIs and triptans in treating migraine and migrainous vertigo.
Animals ; Anxiety Disorders ; Axons ; Blood Vessels ; Ear, Inner ; Endothelial Cells ; Ganglion Cysts ; Migraine Disorders ; Motion Sickness ; Neurons ; Rats ; Receptor, Serotonin, 5-HT1A ; Receptor, Serotonin, 5-HT1B ; Receptor, Serotonin, 5-HT1D ; Serotonin ; Serotonin Uptake Inhibitors ; Spiral Ganglion ; Spiral Ligament of Cochlea ; Stria Vascularis ; Triazoles ; Tryptamines ; Vertigo ; Vestibular Nuclei

Background: This study was designed to determine whether presynaptic receptor blockade could be differentiated from postsynaptic receptor blockade by examining the effect of increasing frequencies of indirect stimulation on partial twitch depression in vitro rat phrenic nerve hemidiaphragm preparations. Methods: After isolating rat phrenic nerve hemidiaphragm preparation, T200/T1 ratio (twitch height of the 200th stimuli divided by that of the 1st stimuli) at frequencies of 0.2, 0.5, 1.0, and 2.0 Hz using a drug concentration which provided approximately 20% twitch depression at 0.1 Hz was calculated. To compare T200/T1 ratios with TOF ratios, 2.0 Hz TOF response was measured immediately after 200th stimuli at either frequency of stimulation. Results: Hexamethonium caused a marked decrease in T200/T1 ratio at 0.5~2.0 Hz of stimulation, whereas alpha-bungarotoxin caused no change in T200/T1 ratios at up to 2.0 Hz of stimulation. The T200/T1 ratios produced by d-tubocurarine, vecuronium, mivacurium, and rocuronium located intermediate between alpha-bungarotoxin and hexamethonium, however significant differences among four drugs were found at 2.0 Hz. The propensity for decrease in T200/T1 ratios at 2.0 Hz might differ from this study: hexamethonium >d-tubocurarine >rocuronium >mivacurium = vecuronium >alpha-bungarotoxin. T200/T1 ratios at 2.0 Hz were not different from TOF ratios. Conclusions: When the observed effects in this study were provided with result of alpha-bungarotoxin acting predominantly at postsynaptic receptors and hexamethonium acting predominantly at presynaptic receptors, the effects of nondepolarizing muscle relaxants at each binding site could be differentiated by examining the T200/T1 ratios at 2.0 Hz.
Animals ; Binding Sites ; Bungarotoxins ; Depression* ; Hexamethonium ; Phrenic Nerve* ; Rats* ; Receptors, Presynaptic ; Tubocurarine ; Vecuronium Bromide

BACKGROUND: This study was performed to evaluate the presynaptic effects of depolarizing neuromuscular blocking drugs by using slow and fast frequencies of indirect stimulation on partial twitch depression in vitro. METHODS: A rat phrenic nerve hemidiaphragm was dissected and was mounted in an organ bath containing an oxygenated Krebs solution. The phrenic nerve was stimulated supramaximally and the twitch response (0.1 Hz) was stabilized for at least 30 minutes. T200/T1 ratio (twitch height of the 200th stimuli divided by that of the first stimuli) at frequencies of 0.2, 0.5, 1.0, and 2.0 Hz using a drug concentration which provided approximately 20% twitch depression at 0.1 Hz was calculated. To compare T200/T1 ratios with TOF ratios, a 2.0 Hz TOF response was measured immediately after the 200th stimuli at either frequency of stimulation. RESULTS: T200/T1 ratios produced by succinylcholine (SCC) and decamethonium (C10) were located between alpha-bungarotoxin (ABX) and hexamethonium (C6), however, significant differences among the four drugs were found at 2.0 Hz. The propensity for a decrease in T200/T1 ratios at 2.0 Hz might differ from this study: C6 > C10 > SCC > ABX. T200/T1 ratios at 2.0 Hz were not different from TOF ratios. CONCLUSIONS: It is concluded that small doses of C10 have a greater presynaptic activity than that of SCC, when the observed effects in this study were compared with the result of ABX acting predominantly at postsynaptic receptors and C6 acting predominantly at presynaptic receptors.
Animals ; Baths ; Bungarotoxins ; Depression ; Hexamethonium ; Neuromuscular Blockade* ; Neuromuscular Blocking Agents* ; Oxygen ; Phrenic Nerve ; Rats ; Receptors, Presynaptic ; Succinylcholine

BACKGROUND: The train of four (TOF) stimulation is valuable to study pharmacodynamics associated with the interaction between muscle relaxants and receptors in the neuromuscular junction. TOF fade expresses presynaptic effect diminished output of transmitters. The aim of this study was to examine differences in presynaptic effects of different relaxants by measuring the TOF ratio during the onset and offset of block. METHODS: Eighty four healthy adult patients of ASA grades I or II were included in the study. The muscle relaxants studied were vecuronium (0.08 mg/kg), atracurium (0.5 mg/kg), mivacurium (0.15 mg/kg), rocuronium (0.6 mg/kg) and succinylcholine (1.0 mg/kg, 0.1 mg/kg, 0.2 mg/kg, 0.4 mg/kg). The TOF ratios were measured at approximate height of first response in the TOF (T1) of 75, 50 and 25% during onset and offset. Especially its ratios were measured at first depress of T1 during onset and its corresponding T1 during offset following administration of subclinical doses of succinylcholine. RESULTS: In the non-depolarizing muscle relaxants, TOF fade is more evident during offset than onset (p<0.05). The extent of fade varies between muscle relaxants. The greatest TOF fade has been shown in rocuronium during onset. In the succinylcholine, the TOF fade is apparent during onset and related to doses given (p<0.05). However the significant TOF fade is not seen during offset. CONCLUSIONS: All muscle relaxants, including both depolarizing and nondepolarizing agent, have predominantly postsynaptic and presynaptic effects. Furthermore, the fact that moderate TOF fade after subclinical doses of succinylcholine occurred obviously during onset of block is possibly indicating a greater presynaptic receptor blocking action.
Adult ; Atracurium ; Humans ; Neuromuscular Blockade* ; Neuromuscular Blocking Agents* ; Neuromuscular Junction ; Neuromuscular Nondepolarizing Agents ; Receptors, Presynaptic ; Succinylcholine ; Vecuronium Bromide

Neuromuscular blockade plays an important role in the safe management of patient airways, surgical field improvement, and respiratory care. Rapid-sequence induction of anesthesia is indispensable to emergency surgery and obstetric anesthesia, and its purpose is to obtain a stable airway, adequate depth of anesthesia, and appropriate respiration within a short period of time without causing irritation or damage to the patient. There has been a continued search for new neuromuscular blocking drugs (NMBDs) with a rapid onset of action. Factors that affect the onset time include the potency of the NMBDs, the rate of NMBDs reaching the effect site, the onset time by dose control, metabolism and elimination of NMBDs, buffered diffusion to the effect site, nicotinic acetylcholine receptor subunit affinity, drugs that affect acetylcholine (ACh) production and release at the neuromuscular junction, drugs that inhibit plasma cholinesterase, presynaptic receptors responsible for ACh release at the neuromuscular junction, anesthetics or drugs that affect muscle contractility, site and methods for monitoring neuromuscular function, individual variability, and coexisting disease. NMBDs with rapid onset without major adverse events are expected in the next few years, and the development of lower potency NMBDs will continue. Anesthesiologists should be aware of the use of NMBDs in the management of anesthesia. The choice of NMBD and determination of the appropriate dosage to modulate neuromuscular blockade characteristics such as onset time and duration of neuromuscular blockade should be considered along with factors that affect the effects of the NMBDs. In this review, we discuss the factors that affect the onset time of NMBDs.
Acetylcholine ; Anesthesia ; Anesthesia, Obstetrical ; Anesthetics ; Cholinesterases ; Diffusion ; Drug Interactions ; Emergencies ; Humans ; Metabolism ; Neuromuscular Blockade* ; Neuromuscular Blocking Agents* ; Neuromuscular Junction ; Neuromuscular Monitoring ; Pharmacokinetics ; Plasma ; Receptors, Nicotinic ; Receptors, Presynaptic ; Respiration

OBJECTIVES: Recently, polymorphisms of several serotonin genes have been suggested to be associated with suicide, but the results are still unclear. We examined whether the T102C polymorphisms of the serotonin 2A receptor gene and the G861C polymorphisms of the serotonin 1B receptor gene were associated with suicidal behavior using drug intoxication. METHODS: The subjects were 52 patients who visited emergency room with suicidal behaviors. Fifty controls were selected from healthy volunteers matched for sex and age to the suicide subjects. The polymorphisms were analyzed with TaqMan(R) assay using primers based on previous studies. RESULTS: The T102C polymorphism of the serotonin 2A receptor gene showed no significant difference between the suicidal attempters and controls in both genotype and allele frequency analyses(p=0.179 and p=0.422, respectively). There was no statistically significant difference between the suicidal attempters and the controls in the G861C polymorphism of the serotonin 1B receptor gene and any significant effect of the genotype distributions or the allele frequencies was not observed(p=0.092 and p=0.987, respectively). CONCLUSION: These findings suggest that the T102C polymorphism in serotonin 2A receptor gene and the G861C polymorphism in serotonin 1B receptor gene are not related to the susceptibility to suicide attempts using drugs. To clarify the genetic influences of the serotonergic system on suicidal behavior, the polymorphisms of other candidate genes in the serotonergic system should be studied with larger numbers of subjects.
Emergency Service, Hospital ; Gene Frequency ; Genotype ; Healthy Volunteers ; Humans ; Receptor, Serotonin, 5-HT1B ; Receptor, Serotonin, 5-HT2A ; Serotonin* ; Suicide

BACKGREOUND: The speed of action of nondepolarizing muscle relaxants might be correlated with the drug potency and the receptor-plasma concentration gradient. However, because of dissociation constants (KDs) being masked by plasma concentration following systemic administration, we investigated the degrees C of train-of-four (TOF) fade at various stages of the measured first twitch height of TOF (T1) during recovery related to potency of various muscle relaxants using isolated forearm technique. METHODS: Thirty two volunteers of the conscious healthy adults who were not receiving any medication which might have influence neuromuscular transmission were involved in this study. The electrodes were applied over the ulnar nerve at the wrist and supramaximal transcutaneous single twitch stimulation (0.1 Hz) delivered by a peripheral nerve stimulator (Innervator, Fisher & Paykel, New Zealand) using a 0.2 ms square wave pulses was applied. The twitch response of the thumb adductor was measured mechanomyographically using a 2 kg Load Cell strain gauge (Model No. 505H, RS Components Ltd., UK) with a thumb piece modification. Following a 5 min. period of stabilization, forearm pneumatic tourniquet was inflated to 300 mmHg in order to occlude the systemic circulation. The equipotent dose (ED95 0.1) of various muscle relaxants diluted in 20 ml of saline was injected into a vein on the dorsal hand respectively: rocuronium 30 microgram/kg, atracurium 25 microgram/kg, mivacurium 8 microgram/kg and vecuronium 4 microgram/kg. Eight volunteers received each dose. The forearm tourniquet was released at 3 min after drugs given. The neuromuscular block was allowed to recovery spontaneously, and at 25, 50, 75 and 100% recovery of control twitch height, TOF stimulation (2 Hz for 2 s) was administered in order to compare TOF ratios between musle relaxants. RESULTS: In the aminosteroid compounds, the TOF ratios of rocuronium were greater than those of vecuronium at all of the assessment points during recovery. In the benzylisoquinolium compounds, the TOF ratios of atracurium were greater than those of mivacurium at 25 and 50% recovery of control twitch height. CONCLUSION: The degree of TOF fade during recovery is related to drug potency at presynaptic receptors separated from the effects of plasma drug concentration.
Adult ; Atracurium ; Electrodes ; Forearm* ; Hand ; Humans ; Masks ; Neuromuscular Blockade* ; Peripheral Nerves ; Plasma ; Receptors, Presynaptic ; Thumb ; Tourniquets ; Ulnar Nerve ; Vecuronium Bromide ; Veins ; Volunteers ; Wrist

Late-phase long-term potentiation (L-LTP) plays a very important role in the maintenance of long-term memory in hippocampus. However, studies have shown that L-LTP can be reversed by subsequent neuronal activity. The aim of the present study is to investigate whether the presynaptic mechanism and the change of AMPARs expressions are involved in the reversal of L-LTP in hippocampal CA1 area. Standard extracellular recording technique was used to record the potential change in the stratum radiatum of CA1 area of adult rat hippocampal slices. Two hours after LTP induction, which was induced by high-frequency stimulation (HFS), two episodes of high-intensity paired-pulse low-frequency stimulation (HI-PP-LFS) were delivered to induce L-LTP reversal. Paired-pulse ratios (PPR) were obtained before LTP induction, 2 h after LTP induction and 30 min after LTP reversal. On the other hand, immunofluorescence histochemistry was used to detect AMPARs expressions before and after L-LTP reversal. The results showed that, after 2 h of induction, L-LTP was partially reversed by two episodes of HI-PP-LFS, and the percentage of depotentiation was 61.79%+/-14.51%. PPR obtained before and after LTP induction, and as well that after LTP reversal, are all more than 1, showing paired-pulse facilitation (PPF). Multiple comparison indicated PPR before LTP induction was the greatest one, and PPR after LTP induction was the smallest. In addition, no significant difference was observed in the intensity of AMPAR/GluR2 immunoreactivity in CA1 area among control group, LTP group and LTP reversal group. These results suggest that the presynaptic mechanism is involved in both the maintenance and reversal of L-LTP and there is no change in AMPAR/GluR2 expression before and after the reversal of L-LTP.
Animals ; CA1 Region, Hippocampal ; metabolism ; physiology ; Electric Stimulation ; Long-Term Potentiation ; physiology ; Male ; Presynaptic Terminals ; physiology ; Rats ; Rats, Sprague-Dawley ; Receptors, AMPA ; metabolism

Primary afferents sensitive to capsaicin and noxious heat express vanilloid receptor 1(VR1) in both their peripheral and central fibers and terminals. We used multiple immunofluorescence and confocal microscopy to characterize their pattern of termination in rat spinal cord, colocalization of neurochemical markers of primary afferents and other presynaptic receptors. VR1-positive unmyelinated fibers mainly terminate in lamina I, where they co-stain for CGRP, and to a limited extent for SP, and in lamina II, especially its medial half, where they co-stain for IB4. VR1 positive thin myelinated fibers terminate in lamina I and co-stain for the neurochemical tracer CTB, injected in the sciatic nerve. As revealed by simultaneous staining for the synaptic marker synaptophysin, VR1-positive terminals are abundant in lamina I and sparse in lamina II. In L6-S1 spinal cord, VR1-positive fibers and terminals were abundant in Lissauer's tract, lamina I-V, medial collateral path to lamina X, and lateral collateral path to sacral parasympathetic nucleus. Most of VR1 positive fibers in Lissuer's tract and LCP are colocalized with SP. In conclusion, it is suggested that VR1 positive fibers in spinal cord are both peptidergic and non-peptidergic, IB4 positive fibers, mediating both somatic and visceral sensations, and that peptidergic VR1 positive fibers are mainly related with visceral sense.
Animals ; Capsaicin ; Fluorescent Antibody Technique ; Ganglia, Spinal ; Hot Temperature ; Microscopy, Confocal ; Myelin Sheath ; Negotiating ; Rats* ; Receptors, Presynaptic ; Sciatic Nerve ; Sensation ; Spinal Cord ; Synaptophysin