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British Journal of Pharmacology Dec 19901. The alpha 2-adrenoceptors on cell bodies of submucosal neurones, on presynaptic cholinergic nerve terminals innervating submucosal neurones, and on presynaptic...
1. The alpha 2-adrenoceptors on cell bodies of submucosal neurones, on presynaptic cholinergic nerve terminals innervating submucosal neurones, and on presynaptic sympathetic fibres innervating submucosal arterioles were characterized in functional studies by use of subtype selective ligands. 2. Both membrane hyperpolarization and presynaptic inhibition of nicotinic excitatory synaptic potentials (e.p.s.ps) produced by UK 14304 were similarly antagonized by idazoxan, yohimbine. SKF 104078, WB 4101 and ARC-239. Antagonism was competitive and dissociation equilibrium constants were the same for both effects. 3. Vasoconstriction of submucosal arterioles in response to stimulation of the sympathetic nerves (20 Hz for 2 s) was inhibited by UK 14304 and clonidine: concentrations producing half-maximum responses were 6 nm and 10 nM respectively. Idazoxan, yohimbine, WB 4101 and SKF 104078 antagonized this action, with dissociation constants similar to those for antagonism of the postsynaptic membrane hyperpolarization and presynaptic inhibition of nicotinic e.p.s.ps. 4. Oxymetazoline was a partial agonist when membrane hyperpolarization or presynaptic inhibition of nicotinic e.p.s.ps were measured but a full agonist when presynaptic inhibition of sympathetically-mediated arteriolar vasoconstriction was measured. As an agonist, oxymetazoline produced half maximum responses at 80-120 nM; the dissociation constant for oxymetazoline as an antagonist was 130 nM. 5. Neither prazosin nor chlorpromazine (up to 30 microM) altered any of the three responses to alpha 2-adrenoceptor agonists. 6. It is concluded that alpha 2-adrenoceptors present on submucosal neuronal cell bodies, on presynaptic cholinergic nerve terminals and on presynaptic sympathetic nerve terminals are the alpha 2A subtype. However, functional characterization of this subtype differs from that provided by ligand binding studies.
Topics: Acetylcholine; Adrenergic alpha-Agonists; Animals; Guinea Pigs; In Vitro Techniques; Intestinal Mucosa; Membrane Potentials; Neurons; Neurotransmitter Agents; Oxymetazoline; Receptors, Adrenergic, alpha; Receptors, Nicotinic; Sympathetic Nervous System; Synapses; Vasoconstriction
PubMed: 1982232
DOI: 10.1111/j.1476-5381.1990.tb14182.x -
Neuroscience 2004Recent data indicate that most "silent" synapses in the hippocampus are "presynaptically silent" due to low transmitter release rather than "postsynaptically silent" due...
Recent data indicate that most "silent" synapses in the hippocampus are "presynaptically silent" due to low transmitter release rather than "postsynaptically silent" due to "latent" receptors of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid type (AMPARs). That synapses bearing only N-methyl-d-aspartate (NMDAR) receptors do exist is suggested by the decreased number of transmission failures during postsynaptic depolarisation and by the presence of NMDA-mediated excitatory postsynaptic currents (EPSCs) in synapses silent at rest. We tested whether these effects could be due to potentiated transmitter release at depolarised postsynaptic potentials rather than removal of Mg(2+) block from NMDARs. Using whole-cell recordings of minimal EPSCs from CA1 and CA3 neurones of hippocampal slices we confirmed decreased incidence of failures at +40 mV as compared with -60 mV. This effect was associated with a gradual increase of EPSC amplitude after switching to +40 mV and with a decrease of paired-pulse facilitation. In initially silent synapses, potentiation of pharmacologically isolated AMPAR-mediated EPSCs was still observed at +40 mV and this persisted after stepping back to -60 mV. All above effects were blocked when the cell was dialysed with the Ca(2+) chelator BAPTA (20 mM). These observations are difficult to reconcile with the "latent AMPAR" hypothesis and suggest an alternative explanation, namely that the reduction in failure rates at positive potentials is due to potentiation of transmitter release following Ca(2+) influx through NMDARs. Our results suggest that silent synapses can be mainly "presynaptically" rather than "postsynaptically silent" and thus increased transmitter release rather than insertion of AMPARs is a major mechanism of early long-term potentiation maintenance.
Topics: Animals; Calcium; Excitatory Postsynaptic Potentials; Hippocampus; Membrane Potentials; Rats; Rats, Wistar; Receptors, AMPA; Receptors, N-Methyl-D-Aspartate; Synapses; Synaptic Transmission
PubMed: 15145072
DOI: 10.1016/j.neuroscience.2004.03.026 -
Journal of Psychopharmacology (Oxford,... Feb 2019Three different α-adrenoceptor (α-AR) subtypes have been described. The α-AR and α-AR subtypes are highly expressed in the human prefrontal cortex, where they...
BACKGROUND
Three different α-adrenoceptor (α-AR) subtypes have been described. The α-AR and α-AR subtypes are highly expressed in the human prefrontal cortex, where they modulate neurotransmission. However, due to the lack of subtype-selective ligands, the physiological relevance of both subtypes has not been fully resolved.
AIMS
In this context, the aim of the present study was to characterize the protein expression of both α-AR subtypes, in different synaptic fractions of postmortem human prefrontal cortex.
METHODS
A subcellular fractionation of the samples was performed and the protein expression of α- and α-ARs was measured in presynaptic membranes and postsynaptic density fractions by Western blot.
RESULTS
The results revealed that the α-AR subtype is mainly located postsynaptically (95±3%) whereas the remaining 5±3% is in the presynapse. Conversely, the α-AR subtype showed a similar distribution between pre- and postsynaptic membranes, with a slightly higher percentage present in the presynapse (60±2% vs. 40±2%).
CONCLUSIONS
These findings could explain some contradictory effects reported for α-AR agonists and antagonists in the human prefrontal cortex. Furthermore, the present data could contribute to elucidating the therapeutic potential of selectively targeting α- or α-AR subtypes.
Topics: Adult; Animals; Autopsy; CHO Cells; Cricetulus; Female; Humans; Male; Middle Aged; Post-Synaptic Density; Prefrontal Cortex; Presynaptic Terminals; Receptors, Adrenergic, alpha-2
PubMed: 30255728
DOI: 10.1177/0269881118798612 -
The Journal of Physiology Oct 19931. Intracellular recordings were made from submucosal neurones in guinea-pig ileum. In some animals, the extrinsic (sympathetic) nerves to the submucosal plexus were...
1. Intracellular recordings were made from submucosal neurones in guinea-pig ileum. In some animals, the extrinsic (sympathetic) nerves to the submucosal plexus were severed 5-7 days previously. The actions of somatostatin and somatostatin analogues on membrane potential, membrane current and inhibitory postsynaptic potentials (IPSPs) were examined. 2. Somatostatin, somatostatin(1-28), [D-Trp8]somatostatin and the somatostatin analogue CGP 23996 all produced equivalent maximum hyperpolarizations or outward currents; half-maximal concentrations (EC50 values) were 9-11 nM. The somatostatin analogue MK 678 had an EC50 of 0.9 nM. Extrinsic sympathectomy did not alter concentration-response relations for somatostatin or its analogues. 3. Somatostatin (> 100 nM) produced hyperpolarization or outward current that declined almost completely during superfusion for 2-4 min; decline of the somatostatin current was exponential with a time constant of 30 s in the presence of 2 microM somatostatin. Desensitization was not altered by extrinsic denervation. 4. Recovery from desensitization was rapid and followed the time course of agonist wash-out. Forskolin, phorbol esters, dithiothreitol, hydrogen peroxide, concanavalin A, or reducing temperature from 35 to 29 degrees C did not alter the time course, degree of, or recovery from desensitization. 5. The somatostatin-induced desensitization was of the homologous type; no cross-desensitization to opiate or alpha 2-adrenoceptor agonists (which activate the same potassium conductance) occurred. 6. Somatostatin desensitization did not alter the adrenergic IPSP seen in sympathetically innervated preparations but abolished the non-adrenergic IPSP recorded from normal preparations and from preparations in which the extrinsic sympathetic nerve supply had been surgically removed. 7. The selective blockade of the non-adrenergic IPSP by the homologous-type somatostatin desensitization characterized in the present study provides strong support for the hypothesis that somatostatin is the neurotransmitter underlying the non-adrenergic IPSP in both normal and extrinsically denervated submucosal neurones.
Topics: Animals; Autonomic Denervation; Electrophysiology; Guinea Pigs; Ileum; In Vitro Techniques; Intestinal Mucosa; Membrane Potentials; Microelectrodes; Muscle Contraction; Muscle, Smooth; Neurons; Receptors, Adrenergic, alpha-2; Receptors, Opioid; Somatostatin; Sympathetic Nervous System
PubMed: 7905923
DOI: 10.1113/jphysiol.1993.sp019878 -
American Journal of Physiology.... Nov 2006In the gastrointestinal tract, CFTR, in conjunction with one or several members of the SLC26 anion exchanger family, mediates electrogenic Cl- and HCO3- secretion.... (Review)
Review
In the gastrointestinal tract, CFTR, in conjunction with one or several members of the SLC26 anion exchanger family, mediates electrogenic Cl- and HCO3- secretion. Na+/H+ exchanger isoform NHE3, on the other hand, coupled to one or several of the SLC26 isoforms, mediates electroneutral NaCl absorption. The agonist-induced activation of anion secretion and inhibition of salt absorption causes secretory diarrhea. Current dogma sees the formation of a multiprotein complex of transport proteins, postsynaptic density-95/discs large/zonula occludens-1 (PDZ) adapter proteins, anchoring proteins, the cytoskeleton, and the involved protein kinases as one crucial step in the regulation of these transport processes. Data obtained in heterologous expression studies suggest an important role of these PDZ adapter proteins in trafficking, endocytic recycling, and membrane retention of the respective transmembrane proteins. This article reviews recent advances in our understanding of the role of the PDZ adapter proteins NHERF, E3KARP, PDZK1, IKEPP (NHERF-1 to NHERF-4), CAL, and Shank-2 that bind to CFTR, NHE3, and the intestinal SLC26 members in the regulation of intestinal fluid transport. Current concepts are mostly derived from heterologous expression studies and studies on their role in organ physiology are still in infancy. Recently, however, PDZ adapter protein-deficient mice and organ-specific cell lines have become available, and the first results suggest a more cell-type and possibly signal-specific role of these adapter proteins. This opens the potential for drug development targeted to PDZ domain interactions, which is, in theory, one of the most efficient antidiarrheal strategies.
Topics: Animals; Biological Transport, Active; Carrier Proteins; Humans; Intestinal Mucosa; Intestines; Ions; LIM Domain Proteins; Mice; Mice, Knockout; Microfilament Proteins; Protein Binding
PubMed: 16798722
DOI: 10.1152/ajpgi.00135.2006 -
Science Progress 2024Proton concentration can change within the cleft during synaptic activity due to vesicular release and Ca extrusion from cellular compartments. These changes within the...
Proton concentration can change within the cleft during synaptic activity due to vesicular release and Ca extrusion from cellular compartments. These changes within the synaptic cleft can impact neural activity by proton-dependent modulation of ion channel function. The pH transient differs in magnitude and direction between synapses, requiring different synapse types to be measured to generate a complete understanding of this mechanism and its impacts on physiology. With a focus on the mouse neuromuscular junction (NMJ), the recently published "Postsynaptic Calcium Extrusion at the Mouse Neuromuscular Junction Alkalinizes the Synaptic Cleft" measured synaptic cleft pH at a cholinergic synapse and found a biphasic pH transient. The study demonstrated that the changes in proton concentration found were due to postsynaptic signaling when measuring pH at the muscle membrane, despite the expectation of a presynaptic contribution. This result suggests a diffusional barrier within the NMJ isolates pH transients to presynaptic versus postsynaptic compartments. Generating a Donnan equilibrium that impacts protons, evidence suggests the basal lamina may be a key regulator of pH at the NMJ. Exploring synaptic pH, proton regulating factors, and downstream pH transient effects at presynaptic versus postsynaptic membranes may lead to new insight for a variety of diseases.
Topics: Animals; Mice; Basement Membrane; Protons; Neuromuscular Junction; Hydrogen-Ion Concentration; Signal Transduction
PubMed: 38196184
DOI: 10.1177/00368504231225066 -
The Journal of Cell Biology Jun 1972
Topics: Animals; Axons; Basement Membrane; Cell Membrane; Guinea Pigs; Iris; Microscopy, Electron; Muscle, Smooth; Neuromuscular Junction; Schwann Cells; Synapses; Synaptic Vesicles
PubMed: 5028264
DOI: 10.1083/jcb.53.3.849 -
Journal of Neurophysiology Aug 19941. In anesthetized, atropine-treated cats we measured the acetylcholine (ACh) release into the venous effluent of the superior cervical ganglion (SCG) and the...
1. In anesthetized, atropine-treated cats we measured the acetylcholine (ACh) release into the venous effluent of the superior cervical ganglion (SCG) and the nictitating membrane (NM) contraction evoked by a 2-Hz, 20-s test train to the ipsilateral cervical sympathetic trunk (CST). We also measured NM contraction produced by injection of ACh (50 micrograms) or 1,1-dimethyl-4-phenylpiperazinium (DMPP, 5 micrograms) into the arterial supply of the ipsilateral SCG. 2. After a 10- to 30-s, 40-Hz conditioning train to CST these responses were all potentiated. The potentiation of the NM response evoked by the test train or by the exogenous agonists was long lasting (90% decay in 64 +/- 10 min, mean +/- SE, for the train-evoked response; 42 +/- 9 min for the response to injected ACh; 61 +/- 18 min for the response to injected DMPP), whereas the potentiation of the ACh release lasted only for 9 min. 3. On the assumption that ACh and DMPP injected into the ganglionic arterial supply acted postsynaptically, these data suggest that the main mechanism of the long-term potentiation (LTP) of nicotinic transmission in SCG is an increase in postsynaptic responsiveness. Because the response to KCl (250 micrograms) injected into the ganglionic arterial supply was not potentiated after the conditioning train, a posttrain increase in excitability of the postsynaptic membrane is not likely to be the cause of the postsynaptic increased responsiveness to ACh and DMPP.(ABSTRACT TRUNCATED AT 250 WORDS)
Topics: Acetylcholine; Adrenergic Fibers; Animals; Blinking; Cats; Female; Long-Term Potentiation; Male; Receptors, Nicotinic; Superior Cervical Ganglion; Synapses; Synaptic Transmission
PubMed: 7983537
DOI: 10.1152/jn.1994.72.2.819 -
The Journal of Pharmacology and... Apr 1981The effect of trifluoperazine (TFP) on neuromuscular transmission was investigated on chick biventer cervicis and frog cutaneous pectoris and sartorius nerve-muscles. In...
The effect of trifluoperazine (TFP) on neuromuscular transmission was investigated on chick biventer cervicis and frog cutaneous pectoris and sartorius nerve-muscles. In the chick, TFP inhibited indirectly elicited twitches in a frequency-dependent manner. Inhibition was much more rapid at higher frequencies of stimulation. Directly elicited twitches, KCl contracture and action potentials of desheathed frog sciatic nerve and sartorius muscles were unaffected by TFP, suggesting an action of TFP on neuromuscular transmission. TFP depressed end plate potential amplitude and miniature end plate potential (MEPP) amplitude without affecting MEPP frequency. When MEPP frequency was increased by high Na+ Ringer, depression of MEPP amplitude was much more rapid. Similarly, at high frequencies of stimulation (100 Hz), TFP rapidly depressed end plate currents. TFP inhibited contractures induced by bath-applied acetylcholine (ACh); depressed ACh potentials produced by iontophoretically applied ACh; decreased ionic current and time constant of decay of end-plate currents of transected muscle; and inhibited [alpha-125I]bungarotoxin binding to ACh receptor. These data suggest that TFP acts postsynaptically in a frequency-dependent manner to inhibit neuromuscular transmission. Based on recent evidence that TFP is a potent antagonist of calmodulin and that calmodulin is localized mainly to postsynaptic regions, we postulate that the postsynaptic inhibitory actions of TFP may be mediated through antagonism of calmodulin, which in turn may regulate ACh receptor function.
Topics: Acetylcholine; Animals; Anura; Calmodulin; Chickens; Electric Stimulation; In Vitro Techniques; Membrane Potentials; Muscle Contraction; Neuromuscular Junction; Synaptic Transmission; Trifluoperazine
PubMed: 6259329
DOI: No ID Found -
Experimental Physiology May 2017Although patch pipettes were initially designed to record extracellularly the elementary current events from muscle and neuron membranes, the whole-cell and loose... (Review)
Review
Although patch pipettes were initially designed to record extracellularly the elementary current events from muscle and neuron membranes, the whole-cell and loose cell-attached recording configurations proved to be useful tools for examination of signalling within and between nerve cells. In this Paton Prize Lecture, I will initially summarize work on electrical signalling within single neurons, describing communication between the dendritic compartments, soma and nerve terminals via forward- and backward-propagating action potentials. The newly discovered dendritic excitability endows neurons with the capacity for coincidence detection of spatially separated subthreshold inputs. When these are occurring during a time window of tens of milliseconds, this information is broadcast to other cells by the initiation of bursts of action potentials (AP bursts). The occurrence of AP bursts critically impacts signalling between neurons that are controlled by target-cell-specific transmitter release mechanisms at downstream synapses even in different terminals of the same neuron. This can, in turn, induce mechanisms that underly synaptic plasticity when AP bursts occur within a short time window, both presynaptically in terminals and postsynaptically in dendrites. A fundamental question that arises from these findings is: 'what are the possible functions of active dendritic excitability with respect to network dynamics in the intact cortex of behaving animals?' To answer this question, I highlight in this review the functional and anatomical architectures of an average cortical column in the vibrissal (whisker) field of the somatosensory cortex (vS1), with an emphasis on the functions of layer 5 thick-tufted cells (L5tt) embedded in this structure. Sensory-evoked synaptic and action potential responses of these major cortical output neurons are compared with responses in the afferent pathway, viz. the neurons in primary somatosensory thalamus and in one of their efferent targets, the secondary somatosensory thalamus. Coincidence-detection mechanisms appear to be implemented in vivo as judged from the occurrence of AP bursts. Three-dimensional reconstructions of anatomical projections suggest that inputs of several combinations of thalamocortical projections and intra- and transcolumnar connections, specifically those from infragranular layers, could trigger active dendritic mechanisms that generate AP bursts. Finally, recordings from target cells of a column reveal the importance of AP bursts for signal transfer to these cells. The observations lead to the hypothesis that in vS1 cortex, the sensory afferent sensory code is transformed, at least in part, from a rate to an interval (burst) code that broadcasts the occurrence of whisker touch to different targets of L5tt cells. In addition, the occurrence of pre- and postsynaptic AP bursts may, in the long run, alter touch representation in cortex.
Topics: Action Potentials; Afferent Pathways; Animals; Dendrites; Excitatory Postsynaptic Potentials; Neurons; Somatosensory Cortex; Synapses; Synaptic Transmission
PubMed: 28139019
DOI: 10.1113/EP085776