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Proceedings. Biological Sciences Nov 2022In the conventional model of serotonin neurotransmission, serotonin released by neurons in the midbrain raphe nuclei exerts its actions on forebrain neurons by... (Review)
Review
In the conventional model of serotonin neurotransmission, serotonin released by neurons in the midbrain raphe nuclei exerts its actions on forebrain neurons by interacting with a large family of post-synaptic receptors. The actions of serotonin are terminated by active transport of serotonin back into the releasing neuron, which is mediated by the serotonin reuptake transporter (SERT). Because SERT is expressed pre-synaptically and is widely thought to be the only serotonin transporter in the forebrain, the conventional model does not include serotonin transport into post-synaptic neurons. However, a large body of evidence accumulating since the 1970s has shown that serotonin, despite having a positive charge, can cross cell membranes through a diffusion-like process. Multiple low-affinity, high-capacity, sodium-independent transporters, widely expressed in the brain, allow the carrier-mediated diffusion of serotonin into forebrain neurons. The amount of serotonin crossing cell membranes through this mechanism under physiological conditions is considerable. Most prominent textbooks fail to include this alternative method of serotonin uptake in the brain, and even most neuroscientists are unaware of it. This failure has limited our understanding of a key regulator of serotonergic neurotransmission, impeded research on the potential intracellular actions of serotonin in post-synaptic neurons and glial cells, and may have impeded our understanding of the mechanism by which antidepressant medications reduce depressive symptoms.
Topics: Serotonin; Serotonin Plasma Membrane Transport Proteins; Neurons; Cell Membrane; Brain
PubMed: 36321487
DOI: 10.1098/rspb.2022.1565 -
Cell Reports Apr 2012An increase in the number of AMPA-type glutamate receptors (AMPARs) is critical for long-term potentiation (LTP), synaptic plasticity regarded as a basal mechanism of...
An increase in the number of AMPA-type glutamate receptors (AMPARs) is critical for long-term potentiation (LTP), synaptic plasticity regarded as a basal mechanism of learning and memory. However, when and how each type of AMPAR reaches the postsynaptic membrane remain unclear. We have developed experimental methods to form postsynaptic-like membrane (PSLM) on a glass surface to precisely visualize the location and movement of receptors. We observed fluorescence-labeled AMPAR subunits (GluA1-3) around PSLM with total internal reflection fluorescence microscopy. The increases of GluA1, 2, and 3 in PSLM showed different time courses after LTP induction. GluA1 increased first, and was exocytosed to the periphery of PSLM soon after LTP induction. GluA2 and GluA3 initially decreased, and then increased. Exocytosis of GluA2 and GluA3 occurred primarily in non-PSLM, and later than exocytosis of GluA1. Thus, GluA1-3 appear to increase in the postsynaptic membrane through distinct pathways during LTP.
Topics: Animals; Exocytosis; HEK293 Cells; Hippocampus; Humans; Long-Term Potentiation; Membranes, Artificial; Neuronal Plasticity; Protein Subunits; Rats; Receptors, AMPA
PubMed: 22832222
DOI: 10.1016/j.celrep.2012.02.004 -
Pain Aug 2013Current concepts of memory storage are largely based on Hebbian-type synaptic long-term potentiation induced by concurrent activity of pre- and postsynaptic neurons....
Current concepts of memory storage are largely based on Hebbian-type synaptic long-term potentiation induced by concurrent activity of pre- and postsynaptic neurons. Little is known about non-Hebbian synaptic plasticity, which, if present in nociceptive pathways, could resolve a number of unexplained findings. We performed whole-cell patch-clamp recordings in rat spinal cord slices and found that a rise in postsynaptic [Ca(2+)]i due to postsynaptic depolarization was sufficient to induce synaptic long-term potentiation (LTP) in the absence of any presynaptic conditioning stimulation. LTP induction could be prevented by postsynaptic application of the Ca(2+) chelator BAPTA (1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid), the L-type voltage-gated calcium channel (VGCC) antagonist nifedipine, and by postsynaptic application of the NMDA receptor antagonist MK801. This indicates that synaptic potentiation was induced postsynaptically by Ca(2+) entry likely via L-type voltage-gated Ca(2+) channels (VGCC) and via NMDA receptor channels. The paired pulse ratio and the coefficient of variation remained unchanged in neurons expressing LTP, suggesting that this form of synaptic potentiation was not only induced, but also expressed postsynaptically. Postsynaptic depolarization had no influence on firing patterns, action potential shape, or neuronal excitability. An increase in [Ca(2+)]i in spinal lamina I neurons induces a non-Hebbian form of synaptic plasticity in spinal nociceptive pathways without affecting neuronal active and passive membrane properties.
Topics: Animals; Animals, Newborn; Calcium; Calcium Channel Blockers; Dizocilpine Maleate; Electric Stimulation; Excitatory Amino Acid Antagonists; In Vitro Techniques; Long-Term Potentiation; Male; Nerve Fibers, Unmyelinated; Neurons; Nifedipine; Patch-Clamp Techniques; Rats; Rats, Sprague-Dawley; Ryanodine; Spinal Cord; Synapses
PubMed: 23707311
DOI: 10.1016/j.pain.2013.04.011 -
Proceedings of the National Academy of... Apr 1982A cytochemical probe for cholesterol, the polyene antibiotic filipin, was applied to aldehyde-fixed samples of the electric organ of Torpedo marmorata to identify...
A cytochemical probe for cholesterol, the polyene antibiotic filipin, was applied to aldehyde-fixed samples of the electric organ of Torpedo marmorata to identify filipin-binding sites in the various membrane components of the organ and, hence, the probable cholesterol content at these levels. In both thin-sectioned and freeze-fractured samples, filipin-cholesterol complexes appeared numerous and homogeneously distributed on the Schwann cell plasma membrane. On the presynaptic membrane, filipin-cholesterol complexes occurred in patches alternating with unlabeled membrane segments. The postsynaptic, acetylcholine receptor-rich plasma membrane of the electroplax showed no or few filipin-cholesterol complexes in the flat region and upper part of the invaginations (both areas characterized by a lattice of small intramembrane particles); however, the membrane of the bottom part of the postsynaptic invaginations contained several complexes. The ventral, noninnervated plasma membrane of the electroplax showed a moderate, homogeneous filipin labeling. These data suggest that the distribution of cholesterol among membranes of the electroplax is not homogeneous and that the acetylcholine receptor-rich region of the postsynaptic membrane (as characterized by the lattice of small intramembrane particles) may contain little cholesterol.
Topics: Animals; Cell Membrane; Cholesterol; Electric Organ; Female; Filipin; Freeze Fracturing; Microscopy, Electron; Synapses; Torpedo
PubMed: 6953416
DOI: 10.1073/pnas.79.8.2598 -
The EMBO Journal Jul 2013Remodelling neuronal connections by synaptic activity requires membrane trafficking. We present evidence for a signalling pathway by which synaptic activity and its...
Remodelling neuronal connections by synaptic activity requires membrane trafficking. We present evidence for a signalling pathway by which synaptic activity and its consequent Ca(2+) influx activate the small GTPase Ral and thereby recruit exocyst proteins to postsynaptic zones. In accord with the ability of the exocyst to direct delivery of post-Golgi vesicles, constitutively active Ral expressed in Drosophila muscle causes the exocyst to be concentrated in the region surrounding synaptic boutons and consequently enlarges the membrane folds of the postsynaptic plasma membrane (the subsynaptic reticulum, SSR). SSR growth requires Ral and the exocyst component Sec5 and Ral-induced enlargement of these membrane folds does not occur in sec5(-/-) muscles. Chronic changes in synaptic activity influence the plastic growth of this membrane in a manner consistent with activity-dependent activation of Ral. Thus, Ral regulation of the exocyst represents a control point for postsynaptic plasticity. This pathway may also function in mammals as expression of activated RalA in hippocampal neurons increases dendritic spine density in an exocyst-dependent manner and increases Sec5 in spines.
Topics: Animals; Animals, Genetically Modified; Calcium Signaling; Dendritic Spines; Drosophila Proteins; Drosophila melanogaster; Exocytosis; Genes, Insect; Membrane Proteins; Monomeric GTP-Binding Proteins; Mutant Proteins; Neuromuscular Junction; Neurons; Protein Transport; Rats; Signal Transduction; Synaptic Membranes; ral GTP-Binding Proteins
PubMed: 23812009
DOI: 10.1038/emboj.2013.147 -
The Journal of Physiology Jun 2002Presynaptic and postsynaptic membrane activities during experimental metabolic inhibition were analysed in mechanically dissociated rat hippocampal neurons using...
Presynaptic and postsynaptic membrane activities during experimental metabolic inhibition were analysed in mechanically dissociated rat hippocampal neurons using nystatin-perforated and conventional whole-cell patch clamp recordings. NaCN, an inhibitor of mitochondrial ATP synthesis, induced an outward current across the postsynaptic soma membrane. This current was blocked by tolbutamide, a sulfonylurea, which blocks ATP-sensitive K+ (KATP) channels. The presynaptic effect of metabolic inhibitors such as NaCN, NaN3, or glucose-free solution was to increase the frequency of GABAergic miniature inhibitory postsynaptic currents (mIPSCs). Tolbutamide had no effect on this increase in mIPSC frequency induced by metabolic inhibition. Diazoxide, a KATP channel opener, evoked a similar somatic outward current in a dose-dependent manner. In addition, diazoxide decreased the frequency of mIPSCs in a dose-dependent fashion. Both these pre- and postsynaptic effects of diazoxide were reversed by tolbutamide, suggesting the existence of KATP channels on both pre- and postsynaptic membranes. These results confirm the presence of KATP channels on both the pre- and postsynaptic membranes but indicate that the channels have significantly different sensitivities to metabolic inhibition.
Topics: ATP-Binding Cassette Transporters; Algorithms; Animals; Antimetabolites; Electric Stimulation; Electrophysiology; Excitatory Postsynaptic Potentials; Hippocampus; KATP Channels; Male; Membrane Potentials; Neurons; Patch-Clamp Techniques; Potassium Channels; Potassium Channels, Inwardly Rectifying; Rats; Rats, Wistar; Receptors, GABA-A; Receptors, Presynaptic; Sodium Cyanide; Synapses; gamma-Aminobutyric Acid
PubMed: 12042355
DOI: 10.1113/jphysiol.2002.018267 -
Kidney International Apr 1999Neuronal nitric oxide synthase (nNOS) is expressed in skeletal muscle beneath the sarcolemma associated with dystrophin complex. In brain, nNOS is anchored to synaptic...
BACKGROUND
Neuronal nitric oxide synthase (nNOS) is expressed in skeletal muscle beneath the sarcolemma associated with dystrophin complex. In brain, nNOS is anchored to synaptic membranes by specific postsynaptic density proteins (PSD)-95 and PSD-93. We have investigated the cellular and subcellular localization of these PSD proteins in the kidney and their relationship to nNOS and the cell membrane.
METHODS
Kidneys from male Sprague-Dawley rats were processed for light and electron microscopic immunohistochemistry with polyclonal antibodies against PSD and nNOS proteins.
RESULTS
Western blot analysis of rat kidney revealed a specific band for PSD-93 at the molecular weight of 103 kDa. Immunostaining for PSD-93 was located in the thick ascending limb of the loop of Henle, macula densa cells, distal convoluted tubules, cortical collecting ducts, outer and inner medullary collecting duct, glomerular epithelium, and Bowman's capsule. A pre-embedding electron microscopic immunoperoxidase procedure localized PSD-93 to the basolateral membrane of these tubular cells. Using different sized immunogold particles, a portion of nNOS in the macula densa colocalized with PSD-93 adjacent to cytoplasmic vesicles and the basolateral membrane. In contrast, PSD-95 protein was detected only weakly in the cortex by Western blot. Immunostaining for PSD-95 was located only faintly in the apical membrane of the thick ascending limb, macula densa, distal convoluted tubule and cortical collecting duct cells.
CONCLUSION
PSD-93 is the predominant PSD expressed in the rat kidney. It is located primarily in the basolateral membranes of distal nephron and colocalizes with a pool of nNOS in cytoplasmic vesicles and basolateral membranes of macula densa cells.
Topics: Animals; Disks Large Homolog 4 Protein; Immunohistochemistry; Intracellular Signaling Peptides and Proteins; Kidney; Male; Membrane Proteins; Microscopy, Immunoelectron; Nerve Tissue Proteins; Nitric Oxide Synthase; Nitric Oxide Synthase Type I; Protein Isoforms; Rats; Rats, Sprague-Dawley; Tissue Distribution
PubMed: 10201003
DOI: 10.1046/j.1523-1755.1999.00392.x -
Proceedings of the National Academy of... Nov 1980Neostriatal tissue from rat brain was examined in ribbons of serial sections, using tissue from subjects in which the synaptic marker 5-hydroxydopamine had been injected...
Neostriatal tissue from rat brain was examined in ribbons of serial sections, using tissue from subjects in which the synaptic marker 5-hydroxydopamine had been injected into the lateral ventricle. A total of 440 synaptic terminals, identified by the presence of a population of vesicles, was studied, including those labeled by 5-hydroxydopamine and all those unlabeled in the surrounding neuropil. Three categories of synaptic profiles innervating neostriatal dendrites could be discerned. One category contained small rounded or slightly pleomorphic vesicles and consisted of a sample of 375 endings, 53 of which exhibited light to heavy label inside the synaptic vesicles. All of these, labeled and unlabeled, showed evidence of membrane specializations and other conventional criteria of synaptic contact, mostly in the form of asymmetric synaptic contacts with the heads of dendritic spines. A second category of 40 terminals, 3 of which were lightly labeled, contained large rounded or slightly pleomorphic vesicles and made predominantly symmetric contacts with the shafts of dendritic spines or spine-free portions of dendritic membrane. None of these synaptic endings appeared to lack synaptic contact with postsynaptic targets in the neostriatum. A third category of 25 terminals, 3 of which were labeled, contained small flattened vesicles, and these endings also invariably made synaptic contact, mostly onto spine-free dendritic membrane, and were characterized by symmetric membrane thickenings at the point of apposition. Our evidence supports the view that dopaminergic and other synaptic terminals in the rat caudate-putamen make synaptic contact with postsynaptic targets in the neostriatum and, at least in the adult, do not exist in appreciable numbers in the form of terminals that are not apposed to membranes of postsynaptic targets in the neostriatum.
Topics: Animals; Axons; Corpus Striatum; Hydroxydopamines; Male; Microscopy, Electron; Rats; Synapses; Synaptic Vesicles
PubMed: 6935693
DOI: 10.1073/pnas.77.11.6926 -
The Journal of Neuroscience : the... Jun 2010GABA(A) receptors (GABA(A)-Rs) play a significant role in mediating fast synaptic inhibition and it is the main inhibitory receptor in the CNS. The role of Wnt signaling...
GABA(A) receptors (GABA(A)-Rs) play a significant role in mediating fast synaptic inhibition and it is the main inhibitory receptor in the CNS. The role of Wnt signaling in coordinating synapse structure and function in the mature CNS is poorly understood. In previous studies we found that Wnt ligands can modulate excitatory synapses through remodeling both presynaptic and postsynaptic regions. In this current study we provide evidence for the effect of Wnt-5a on postsynaptic GABA(A)-Rs. We observed that Wnt-5a induces surface expression and maintenance of this receptor in the neuronal membrane. The evoked IPSC recordings in rat hippocampal slice indicate that Wnt-5a can regulates postsynaptically the hippocampal inhibitory synapses. We found also that Wnt-5a: (a) induces the insertion and clustering of GABA(A)-Rs in the membrane; (b) increases the amplitude of GABA-currents due exclusively to postsynaptic mechanisms; (c) does not affect the endocytic process, but increases the receptor recycling. Finally, all these effects on the GABA(A)-Rs are mediated by the activation of calcium/calmodulin-dependent kinase II (CaMKII). Therefore, we postulate that Wnt-5a, by activation of CaMKII, induces the recycling of functional GABA(A)-Rs on the mature hippocampal neurons.
Topics: Analysis of Variance; Animals; Calcium-Calmodulin-Dependent Protein Kinase Type 2; Cell Membrane; Cells, Cultured; Electrophysiology; Endocytosis; Enzyme-Linked Immunosorbent Assay; Hippocampus; Inhibitory Postsynaptic Potentials; Miniature Postsynaptic Potentials; Neural Inhibition; Neurons; Presynaptic Terminals; Rats; Rats, Wistar; Receptors, GABA-A; Signal Transduction; Statistics, Nonparametric; Synapses; Wnt Proteins; Wnt-5a Protein
PubMed: 20573888
DOI: 10.1523/JNEUROSCI.5736-09.2010 -
Proceedings of the National Academy of... Jul 1974In various skeletal muscles, the mean density of acetylcholine receptors in the muscle postsynaptic membrane is constant at about 8700 per mum(2), even though the...
In various skeletal muscles, the mean density of acetylcholine receptors in the muscle postsynaptic membrane is constant at about 8700 per mum(2), even though the overall size of an endplate ranged from 400 mum(2) to 1300 mum(2) in these muscles. This measurement was by electron microscope autoradiography of alpha-[(3)H]bungarotoxin binding sites; only one-half of these, however, appear to be true active centers of the acetylcholine receptor. The highest density of these receptors is on the juxtaneuronal regions of the postsynaptic membrane, and their density in the depths of the fold is less than one quarter of that at the tips. A maximum sensitivity to externally applied acetylcholine, about 3000-5000 mV/nC, is found in diverse types of endplates when truly focal recording is achieved. This acetylcholine sensitivity appears to be determined by the local density of receptors in the membrane, and not by their total number at the endplate. A quantal efficiency term is also disclosed. The maximal sensitivity per molecule obtainable by microiontophoresis of acetylcholine is 5-10% of that operative when a quantum reacts. When acetylcholine is released from a vesicle, in contrast to its application from outside, geometric factors are more favorable. Consideration of the local packing density, acetylcholine molecule numbers, and the current flow when one quantum of acetylcholine interacts at the membrane suggests that one, or possibly two, activated receptor active centers are linked to one open gate of the ionic conductance modulator.
Topics: Acetylcholine; Animals; Autoradiography; Binding Sites; Bungarotoxins; Chickens; Chiroptera; Electrophysiology; Iontophoresis; Male; Mice; Microscopy, Electron; Neuromuscular Junction; Rana pipiens; Receptors, Cholinergic; Synaptic Membranes; Tritium
PubMed: 4546945
DOI: 10.1073/pnas.71.7.2818