Dynamics of Neuromuscular Transmission Reproduced by Calcium-Dependent and Reversible Serial Transitions in the Vesicle Fusion Complex.

Neuromuscular transmission, from spontaneous release to facilitation and depression, was accurately reproduced by a mechanistic kinetic model of sequential maturation transitions in the molecular fusion complex. The model incorporates three predictions. First, calcium-dependent forward transitions take vesicles from docked to preprimed to primed states, followed by fusion.

The Thermodynamically Expensive Contribution of Three Calcium Sources to Somatic Release of Serotonin.

The soma, dendrites and axon of neurons may display calcium-dependent release of transmitters and peptides. Such release is named extrasynaptic for occurring in absence of synaptic structures. This review describes the cooperative actions of three calcium sources on somatic exocytosis.

Extrasynaptic Communication.

Streams of action potentials or long depolarizations evoke a massive exocytosis of transmitters and peptides from the surface of dendrites, axons and cell bodies of different neuron types. Such mode of exocytosis is known as extrasynaptic for occurring without utilization of synaptic structures. Most transmitters and all peptides can be released extrasynaptically.

Transcriptional profiling of identified neurons in leech.

Background: While leeches in the genus Hirudo have long been models for neurobiology, the molecular underpinnings of nervous system structure and function in this group remain largely unknown. To begin to bridge this gap, we performed RNASeq on pools of identified neurons of the central nervous system (CNS): sensory T (touch), P (pressure) and N (nociception) neurons; neurosecretory Retzius cells; and ganglia from which these four cell types had been removed.

Results: Bioinformatic analyses identified 3565 putative genes whose expression differed significantly among the samples.

A tale of two leeches: Toward the understanding of the evolution and development of behavioral neural circuits.

In the animal kingdom, behavioral traits encompass a broad spectrum of biological phenotypes that have critical roles in adaptive evolution, but an EvoDevo approach has not been broadly used to study behavior evolution. Here, we propose that, by integrating two leech model systems, each of which has already attained some success in its respective field, it is possible to take on behavioral traits with an EvoDevo approach. We first identify the developmental changes that may theoretically lead to behavioral evolution and explain why an EvoDevo study of behavior is challenging.

Fluorescence of serotonin in the visible spectrum upon multiphotonic photoconversion.

The vital molecule serotonin modulates the functioning of the nervous system. The chemical characteristics of serotonin provide multiple advantages for its study in living or fixed tissue. Serotonin has the capacity to emit fluorescence directly and indirectly through chemical intermediates in response to mono- and multiphoton excitation.

Thermodynamic Efficiency of Somatic Exocytosis of Serotonin.

Through somatic exocytosis neurons liberate immense amounts of transmitter molecules that modulate the functioning of the nervous system. A stream of action potentials triggers an ATP-dependent transport of transmitter-containing vesicles to the plasma membrane, that ends with a large-scale exocytosis. It is commonly assumed that biological processes use metabolic energy with a high thermodynamic efficiency, meaning that most energy generates work with minor dissipation.

Extrasynaptic Neurotransmission Mediated by Exocytosis and Diffusive Release of Transmitter Substances.

This review article deals with the mechanisms of extrasynaptic release of transmitter substances, namely the release from the soma, axon and dendrites in the absence of postsynaptic counterparts. Extrasynaptic release occurs by exocytosis or diffusion. Spillover from the synaptic cleft also contributes to extrasynaptic neurotransmission.

Corrigendum: On the Basis of Synaptic Integration Constancy during Growth of a Neuronal Circuit.

[This corrects the article on p. 198 in vol. 10, PMID: 27587998.

Octopamine cyclic release and its modulation of visual sensitivity in crayfish.

The biogenic amine octopamine (OA) modulates invertebrate behavior by changing neuronal responses from sensory inputs to motor outputs. However, the OA modulation of visual sensitivity and its possible coupling to diurnal cycles remains unexplored. Here we studied the diurnal variations in the OA levels in the hemolymph of the crayfish Procambarus clarkii, its release from the structures in the eyestalk and its modulation of the retinal light sensitivity.

On the Basis of Synaptic Integration Constancy during Growth of a Neuronal Circuit.

We studied how a neuronal circuit composed of two neuron types connected by chemical and electrical synapses maintains constant its integrative capacities as neurons grow. For this we combined electrophysiological experiments with mathematical modeling in pairs of electrically-coupled Retzius neurons from postnatal to adult leeches. The electrically-coupled dendrites of both Retzius neurons receive a common chemical input, which produces excitatory postsynaptic potentials (EPSPs) with varying amplitudes.

Serotonin release from the neuronal cell body and its long-lasting effects on the nervous system.

Serotonin, a modulator of multiple functions in the nervous system, is released predominantly extrasynaptically from neuronal cell bodies, axons and dendrites. This paper describes how serotonin is released from cell bodies of Retzius neurons in the central nervous system (CNS) of the leech, and how it affects neighbouring glia and neurons. The large Retzius neurons contain serotonin packed in electrodense vesicles.

Release of chemical transmitters from cell bodies and dendrites of nerve cells.

Papers in this issue concern extrasynaptic transmission, namely release of signalling molecules by exocytosis or diffusion from neuronal cell bodies, dendrites, axons and glia. Problems discussed concern the molecules, their secretion and importance for normal function and disease. Molecules secreted extrasynaptically include transmitters, peptides, hormones and nitric oxide.

Exocytosis of serotonin from the neuronal soma is sustained by a serotonin and calcium-dependent feedback loop.

The soma of many neurons releases large amounts of transmitter molecules through an exocytosis process that continues for hundreds of seconds after the end of the triggering stimulus. Transmitters released in this way modulate the activity of neurons, glia and blood vessels over vast volumes of the nervous system. Here we studied how somatic exocytosis is maintained for such long periods in the absence of electrical stimulation and transmembrane Ca(2+) entry.

Biophysics of active vesicle transport, an intermediate step that couples excitation and exocytosis of serotonin in the neuronal soma.

Transmitter exocytosis from the neuronal soma is evoked by brief trains of high frequency electrical activity and continues for several minutes. Here we studied how active vesicle transport towards the plasma membrane contributes to this slow phenomenon in serotonergic leech Retzius neurons, by combining electron microscopy, the kinetics of exocytosis obtained from FM1-43 dye fluorescence as vesicles fuse with the plasma membrane, and a diffusion equation incorporating the forces of local confinement and molecular motors. Electron micrographs of neurons at rest or after stimulation with 1 Hz trains showed cytoplasmic clusters of dense core vesicles at 1.

Extrasynaptic exocytosis and its mechanisms: a source of molecules mediating volume transmission in the nervous system.

We review the evidence of exocytosis from extrasynaptic sites in the soma, dendrites, and axonal varicosities of central and peripheral neurons of vertebrates and invertebrates, with emphasis on somatic exocytosis, and how it contributes to signaling in the nervous system. The finding of secretory vesicles in extrasynaptic sites of neurons, the presence of signaling molecules (namely transmitters or peptides) in the extracellular space outside synaptic clefts, and the mismatch between exocytosis sites and the location of receptors for these molecules in neurons and glial cells, have long suggested that in addition to synaptic communication, transmitters are released, and act extrasynaptically. The catalog of these molecules includes low molecular weight transmitters such as monoamines, acetylcholine, glutamate, gama-aminobutiric acid (GABA), adenosine-5-triphosphate (ATP), and a list of peptides including substance P, brain-derived neurotrophic factor (BDNF), and oxytocin.

Cycling of dense core vesicles involved in somatic exocytosis of serotonin by leech neurons.

We studied the cycling of dense core vesicles producing somatic exocytosis of serotonin. Our experiments were made using electron microscopy and vesicle staining with fluorescent dye FM1-43 in Retzius neurons of the leech, which secrete serotonin from clusters of dense core vesicles in a frequency-dependent manner. Electron micrographs of neurons at rest or after 1 Hz stimulation showed two pools of dense core vesicles.

Regulation of synaptic vesicle docking by different classes of macromolecules in active zone material.

The docking of synaptic vesicles at active zones on the presynaptic plasma membrane of axon terminals is essential for their fusion with the membrane and exocytosis of their neurotransmitter to mediate synaptic impulse transmission. Dense networks of macromolecules, called active zone material, (AZM) are attached to the presynaptic membrane next to docked vesicles. Electron tomography has shown that some AZM macromolecules are connected to docked vesicles, leading to the suggestion that AZM is somehow involved in the docking process.

NeuronGrowth, a software for automatic quantification of neurite and filopodial dynamics from time-lapse sequences of digital images.

We developed NeuronGrowth, a software for the automatic quantification of extension and retraction of neurites and filopodia, from time-lapse sequences of two-dimensional digital micrographs. NeuronGrowth requires a semiautomatic characterization of individual neurites in a reference frame, which is then used for automatic tracking and measurement of every neurite over the whole image sequence. Modules for sequence alignment, background subtraction, flat field correction, light normalization, and cropping have been integrated to improve the quality of the analysis.

Real-time measurements of synaptic autoinhibition produced by serotonin release in cultured leech neurons.

We studied autoinhibition produced immediately after synaptic serotonin (5-HT) release in identified leech Retzius neurons, cultured singly or forming synapses onto pressure-sensitive neurons. Cultured Retzius neurons are isopotential, thus allowing accurate recordings of synaptic events using intracellular microelectrodes. The effects of autoinhibition on distant neuropilar presynaptic endings were predicted from model simulations.

A method for semiautomatic tracing and morphological measuring of neurite outgrowth from DIC sequences.

We present a method for semi-automatic tracing and measuring of neurite outgrowth from time-lapse sequences of digital Nomarski micrographs. The algorithm is based on neurite ridge extraction and characterization from a single frame, followed by an automatic neurite tracking and measurement along the image sequence. Our method was tested with two sequences one containing 29 and other with 77 frames taken at intervals of 2 min.

Synaptic and extrasynaptic secretion of serotonin.

Serotonin is a major modulator of behavior in vertebrates and invertebrates and deficiencies in the serotonergic system account for several behavioral disorders in humans. The small numbers of serotonergic central neurons of vertebrates and invertebrates produce their effects by use of two modes of secretion: from synaptic terminals, acting locally in "hard wired" circuits, and from extrasynaptic axonal and somatodendritic release sites in the absence of postsynaptic targets, producing paracrine effects. In this paper, we review the evidence of synaptic and extrasynaptic release of serotonin and the mechanisms underlying each secretion mode by combining evidence from vertebrates and invertebrates.

Calcium-induced calcium release contributes to somatic secretion of serotonin in leech Retzius neurons.

We analyzed the contribution of calcium (Ca2+)-induced Ca2+ release to somatic secretion in serotonergic Retzius neurons of the leech. Somatic secretion was studied by the incorporation of fluorescent dye FM1-43 upon electrical stimulation with trains of 10 impulses and by electron microscopy. Quantification of secretion with FM1-43 was made in cultured neurons to improve optical resolution.

Synaptic integration in electrically coupled neurons.

Interactions among chemical and electrical synapses regulate the patterns of electrical activity of vertebrate and invertebrate neurons. In this investigation we studied how electrical coupling influences the integration of excitatory postsynaptic potentials (EPSPs). Pairs of Retzius neurons of the leech are coupled by a nonrectifying electrical synapse by which chemically induced synaptic currents flow from one neuron to the other.