Synaptic Enlargement Research Articles

Relapse-Associated Transient Synaptic Potentiation Requires Integrin-Mediated Activation of Focal Adhesion Kinase and Cofilin in D1-Expressing Neurons.

Relapse to drug use can be initiated by drug-associated cues. The intensity of cue-induced drug seeking in rodent models correlates with the induction of transient synaptic potentiation (t-SP) at glutamatergic synapses in the nucleus accumbens core (NAcore). Matrix metalloproteinases (MMPs) are inducible endopeptidases that degrade extracellular matrix (ECM) proteins, and reveal tripeptide Arginine-Glycine-Aspartate (RGD) domains that bind and signal through integrins. Integrins are heterodimeric receptors composed of αβ subunits, and a primary signaling kinase is focal adhesion kinase (FAK). We previously showed that MMP activation is necessary for and potentiates cued reinstatement of cocaine seeking, and MMP-induced catalysis stimulates β3-integrins to induce t-SP. Here, we determined whether β3-integrin signaling through FAK and cofilin (actin depolymerization factor) is necessary to promote synaptic growth during t-SP. Using a small molecule inhibitor to prevent FAK activation, we blocked cued-induced cocaine reinstatement and increased spine head diameter (dh). Immunohistochemistry on NAcore labeled spines with ChR2-EYFP virus, showed increased immunoreactivity of phosphorylation of FAK (p-FAK) and p-cofilin in dendrites of reinstated animals compared with extinguished and yoked saline, and the p-FAK and cofilin depended on β3-integrin signaling. Next, male and female transgenic rats were used to selectively label D1 or D2 neurons with ChR2-mCherry. We found that p-FAK was increased during drug seeking in both D1 and D2-medium spiny neurons (MSNs), but increased p-cofilin was observed only in D1-MSNs. These data indicate that β3-integrin, FAK and cofilin constitute a signaling pathway downstream of MMP activation that is involved in promoting the transient synaptic enlargement in D1-MSNs induced during reinstated cocaine by drug-paired cues.SIGNIFICANCE STATEMENT Drug-associated cues precipitate relapse, which is correlated with transient synaptic enlargement in the accumbens core. We showed that cocaine cue-induced synaptic enlargement depends on matrix metalloprotease signaling in the extracellular matrix (ECM) through β3-integrin to activate focal adhesion kinase (FAK) and phosphorylate the actin binding protein cofilin. The nucleus accumbens core (NAcore) contains two predominate neuronal subtypes selectively expressing either D1-dopamine or D2-dopamine receptors. We used transgenic rats to study each cell type and found that cue-induced signaling through cofilin phosphorylation occurred only in D1-expressing neurons. Thus, cocaine-paired cues initiate cocaine reinstatement and synaptic enlargement through a signaling cascade selectively in D1-expressing neurons requiring ECM stimulation of β3-integrin-mediated phosphorylation of FAK (p-FAK) and cofilin.

Activity Dependent and Independent Determinants of Synaptic Size Diversity.

The extraordinary diversity of excitatory synapse sizes is commonly attributed to activity-dependent processes that drive synaptic growth and diminution. Recent studies also point to activity-independent size fluctuations, possibly driven by innate synaptic molecule dynamics, as important generators of size diversity. To examine the contributions of activity-dependent and independent processes to excitatory synapse size diversity, we studied glutamatergic synapse size dynamics and diversification in cultured rat cortical neurons (both sexes), silenced from plating. We found that in networks with no history of activity whatsoever, synaptic size diversity was no less extensive than that observed in spontaneously active networks. Synapses in silenced networks were larger, size distributions were broader, yet these were rightward-skewed and similar in shape when scaled by mean synaptic size. Silencing reduced the magnitude of size fluctuations and weakened constraints on size distributions, yet these were sufficient to explain synaptic size diversity in silenced networks. Model-based exploration followed by experimental testing indicated that silencing-associated changes in innate molecular dynamics and fluctuation characteristics might negatively impact synaptic persistence, resulting in reduced synaptic numbers. This, in turn, would increase synaptic molecule availability, promote synaptic enlargement, and ultimately alter fluctuation characteristics. These findings suggest that activity-independent size fluctuations are sufficient to fully diversify glutamatergic synaptic sizes, with activity-dependent processes primarily setting the scale rather than the shape of size distributions. Moreover, they point to reciprocal relationships between synaptic size fluctuations, size distributions, and synaptic numbers mediated by the innate dynamics of synaptic molecules as they move in, out, and between synapses.SIGNIFICANCE STATEMENT Sizes of glutamatergic synapses vary tremendously, even when formed on the same neuron. This diversity is commonly thought to reflect the outcome of activity-dependent forms of synaptic plasticity, yet activity-independent processes might also play some part. Here we show that in neurons with no history of activity whatsoever, synaptic sizes are no less diverse. We show that this diversity is the product of activity-independent size fluctuations, which are sufficient to generate a full repertoire of synaptic sizes at correct proportions. By combining modeling and experimentation we expose reciprocal relationships between size fluctuations, synaptic sizes and synaptic counts, and show how these phenomena might be connected through the dynamics of synaptic molecules as they move in, out, and between synapses.

Le cophénotype sympathique efférent des fibres autonomes angiotensinergiques dans le cœur humain

AimThe autonomic innervation of the heart consists of sympathetic and parasympathetic nerve fibres, and fibres of the intrinsic ganglionated plexus with noradrenaline and acytylcholine as principal neurotransmitters. The fibres co-release neuropeptides to modulate intracardiac neurotransmission by specific presynaptic and postsynaptic receptors. The coexpression of angiotensin II in sympathetic fibres of the human heart and its role are not known so far. MethodsAutopsy specimens of human hearts were studied (n=3; ventricles). Using immunocytological methods, cryostat sections were stained by a murine monoclonal antibody (4B3) directed against angiotensin II and co-stained by polyclonal antibodies against tyrosine hydroxylase, a catecholaminergic marker. Visualisation of the antibodies was by confocal light microscopy or laser scanning microscopy. ResultsAngiotensin II-positive autonomic fibres with and without a catecholaminergic cophenotype (hydroxylase-positive) were found in all parts of the human ventricles. In the epicardium, the fibres were grouped in larger bundles of up to 100 and more fibres. They followed the preformed anatomic septa and epicardial vessels towards the myocardium and endocardium where the bundles dissolved and the individual fibres spread between myocytes and within the endocardium. Generally, angiotensinergic fibres showed no synaptic enlargements or only a few if they were also catecholaminergic. The exclusively catechalominergic fibres were characterised by multiple beaded synapses. ConclusionThe autonomic innervation of the human heart contains angiotensinergic fibres with a sympathetic efferent phenotype and exclusively angiotensinergic fibers representing probably afferents. Angiotensinergic neurotransmission may modulate intracardiac sympathetic and parasympathetic activity and thereby influence cardiac and circulatory function.

Synaptic Targeting of PSD-Zip45 (Homer 1c) and Its Involvement in the Synaptic Accumulation of F-actin

PSD-Zip45/Homer1c, which contains an enabled/VASP homology 1 (EVH1) domain and leucine zipper motifs, is a postsynaptic density (PSD) scaffold protein that interacts with metabotropic glutamate receptors and the shank family. We studied the molecular mechanism underlying the synaptic targeting of PSD-Zip45 in cultured hippocampal neurons. The EVH1 domain and the extreme C-terminal leucine zipper motif were molecular determinants for its synaptic targeting. The overexpression of the mutant of the EVH1 domain or deletion of the extreme C-terminal leucine zipper motif markedly suppressed the synaptic localization of endogenous shank but not PSD-95 or GKAP. In contrast, an overexpressed GKAP mutant lacking shank binding activity had no effect on the synaptic localization of shank. Actin depolymerization by latrunculin A reduced the synaptic localization of PSD-Zip45, shank, and F-actin but not of PSD-95 or GKAP. Overexpression of PSD-Zip45 enhanced the accumulation of synaptic F-actin. Additionally, overexpression of PSD-Zip45 and an isoform of shank induced synaptic enlargement in association with the further accumulation of synaptic F-actin. The EVH1 domain and extreme C-terminal leucine zipper motif of PSD-Zip45 were also critical for these events. Thus, these data suggest that the PSD-Zip45-shank and PSD-95-GKAP complexes form different synaptic compartments, and PSD-Zip45 alone or PSD-Zip45-shank is involved in the synaptic accumulation of F-actin.

Aberrancies in signal transduction and cell cycle related events in Alzheimer's disease.

Neurodegeneration in Alzheimer's disease (AD) is associated with the appearance of dystrophic neuronal growth profiles that most likely reflects an aberrant attempt of neuronal repair. This process of neuronal reorganisation, which eventually goes awry and becomes a disease itself, might be initiated physiologically as a response to neuronal injuries. Minor neuronal damage due to a variety of life events or genetic pertubations that are usually compensated in the normal adult brain by adaptation and repair might thus be amplified and accumulated, thereby resulting in a progressive neurodegeneration. The present paper summarizes recent evidence supporting the hypothesis that a primary impairment of intracellular signal transduction that is mediated by a hierarchy of phosphorylation signals and associated with a aborted attempt of neurons to re-enter the cell-cycle is a key element in the pathomechanism of AD. These changes might result in malfunction of neuronal adaptation and repair and eventually lead to neuronal death. During the process of aging as well as in chronic neurodegenerative disorders such as Alzheimer's disease (AD), the continuous but rather slow action of pathogenetic factors might give room for the activation of compensatory mechanisms, serving to regain a neuronal population much of its synaptic connectivity in the presence of cell loss. An upregulation in the capacity to synthesize and store neurotransmitters (Lapchak et al., 1991), an increased expression of trophic factors (Hellweg et al., 1990; Arendt et al., 1995a,b), as well as regenerative sprouting (Fritschy and Grzanna, 1992), synaptic enlargement (Scheff et al., 1990; Lippa et al., 1992), and neosynaptogenesis (Ramirez and Ulfhake, 1992) have been described among other processes.

Comparison of first degree relatives and spouses of people with chronic tension headache

The extraordinary diversity of excitatory synapse sizes is commonly attributed to activity-dependent processes that drive synaptic growth and diminution. Recent studies also point to activity-independent size fluctuations, possibly driven by...

Homeostasis of Synaptic Transmission inDrosophilawith Genetically Altered Nerve Terminal Morphology

We present a new test of the hypothesis that synaptic strength is directly related to nerve terminal morphology through analysis of synaptic transmission at Drosophila neuromuscular junctions with a genetically reduced number of nerve terminal varicosities. Synaptic transmission would decrease in target cells with fewer varicosities if there is a relationship between the number of varicosities and the strength of synaptic transmission. Animals that have an extreme hypomorphic allele of the gene for the cell adhesion molecule Fasciclin II possess fewer synapse-bearing nerve terminal varicosities; nevertheless, synaptic strength is maintained at a normal level for the muscle cell as a whole. Fewer failures of neurotransmitter release and larger excitatory junction potentials from individual varicosities, as well as more frequent spontaneous release and larger quantal units, provide evidence for enhancement of transmitter release from varicosities in the mutant. Ultrastructural analysis reveals that mutant nerve terminals have bigger synapses with more active zones per synapse, indicating that synaptic enlargement and an accompanying increase in synaptic complexity provide for more transmitter release at mutant varicosities. These results show that morphological parameters of transmitting nerve terminals can be adjusted to functionally compensate for genetic perturbations, thereby maintaining optimal synaptic transmission.

Quantitative analysis of central terminal projections of visceral and somatic unmyelinated (C) primary afferent fibers in the guinea pig.

In guinea pigs, intracellular labeling of the dorsal root ganglion (DRG) cells with Phaseolus vulgaris-leucoagglutinin (PHA-L) was used to demonstrate the central projections of somatic and visceral afferent C-fibers. The terminations of the afferent fibers were analyzed qualitatively and quantitatively with the aid of camera lucida drawings. Terminal branches of C-fibers of both somatic and visceral origin were, in general, distributed in accord with the organization of the neuropil in lamina of the spinal cord. Terminal boutons arranged from longitudinally coursing fibers were distributed in lamina I, while boutons in lamina II were scattered in an apparent random fashion. The synaptic enlargements were counted in gray matter of the spinal dorsal horn and measured on each terminal branch of a fiber. All synaptic boutons (over one thousand) of somatic fibers were found in the superficial dorsal horn (laminae I and II). More than 60% of the synaptic enlargements of the visceral afferents also were localized superficially (lamina I and adjacent dorsal funiculus) while 10-20% of the visceral enlargements appeared in deeper layers of the spinal cord. Boutons of somatic C-fibers were larger than those of visceral origin. Quantitative data of the unmyelinated afferent fibers are discussed in the context of the sensory functions of myelinated afferent fibers.

Alzheimer's disease and aging: Effects on perforant pathway perikarya and synapses

The hippocampal perforant pathway originates in the entorhinal cortex (ERC) and terminates in the outer molecular layer of the dentate gyrus (DG). To compare the effects of normal aging and Alzheimer's disease (AD) on the elements of the perforant pathway, we compared relative perikaryal numbers (determined by counting cell bodies and estimating volumes) in layer II of the ERC with synaptic quantities (estimated from immunoreactivity for the synaptic terminal protein synapsin I and DG volume) in the molecular layer of the DG. The brains of 5 young and 9 elderly cognitively normal individuals, and of 9 AD patients were studied. In normal aging we found a significant age-related decline in perikaryal numbers in the ERC without demonstrable synaptic loss in the DG. In AD there was marked and equivalent, (or proportional) reduction in both ERC perikaryal numbers and DG synapses. These data suggest that in normal aging remaining neurons may continue to support a full array of synapses, perhaps due to mechanisms such as axonal sprouting, synaptic enlargement, or synaptic ingrowth. In AD, however, the accelerated neuronal loss may overwhelm such compensatory mechanisms or alternatively, independent synaptic and perikaryal losses may occur.

Reorganization of primary afferent nerve terminals in the spinal dorsal horn of the primate caudal to anterolateral chordotomy.

A primate model has been used to explore the possibility that anterolateral chordotomy may produce intraspinal sprouting or rearrangement of primary afferent nerve terminations that could account for delayed postoperative recovery of sensory function. Monkeys were trained to limit the duration of an electrical stimulus, and the vigor and frequency of their escape responses were used to differentiate painful from nonpainful levels of stimulation. Behavioral testing after chordotomy revealed: 1) contralateral hypalgesia in all animals, with sensory recovery in half of the group, and 2) bilateral decreases in reflexive force in all animals, with reflex recovery in the majority of monkeys. At the terminal experiment, dorsal rootlets caudal to the spinal lesion were labeled bilaterally with HRP, and the distribution of labeled synaptic complexes was determined within the dorsal horn. When compared to controls, animals undergoing chordotomy showed a loss of terminals in the superficial dorsal horn and an increase of synaptic enlargements in deeper layers. These effects were bilateral, but were most pronounced on the side contralateral to chordotomy. Animals with diffuse spinal lesions showed a completely different change in the distribution of primary afferent terminals. Animals with sensory recovery demonstrated a more normal terminal distribution pattern than persistently hypalgesic monkeys, but there was considerable variability in the data, and analysis by different statistical tests yielded varying results.

On the vegetative network of guinea pig thoracic spinal cord.

A dense AChE-positive network was visualized by light microscopy in the thoracic spinal cord of grown-up guinea pigs of both sexes (bodyweight 250-300 g). This network connects in a horizontal and vertical direction the preganglionic sympathetic nuclei (n. intermediolateralis pars principalis (ILp), n. intermediolateralis pars funicularis (ILf), n intercalatus spinals (IC), n. intercalatus pars paraependymalis (ICpe), (Petras and Cummings, 1972) all along the thoracic spinal cord. In addition to AChE activity, the bundles of fibers of this network also show a strong formaldehyde-induced NA fluorescence. Electron microscopy demonstrated granular vesicles in the cytoplasm of ILp cells. The surface of the ILp and IC neurons is almost entirely covered with synaptic bottons which have clear and granulated synaptic vesicles. The bundles of fibers consists of parallel myelin-free axones and dendrites. On their cource the axones form varicosities. In the varicosities and in the synaptic enlargements there are also clear and granulated (40-100 nm) vesicles. The probable origin of the vegetative network fibers of guinea pig thoracic spinal cord is discussed.

The distribution of recurrent Purkinje collateral synapses in the mouse cerebellar cortex: an electron microscopic study.

AbstractMyelinated fibers found in the lower molecular layer of the mouse cerebellum form synaptic enlargements of a uniform morphological appearance. Similar synapses have been observed to come from myelinated fibers in the upper granularlower Purkinje cell layer. Both have been interpreted as Purkinje collateral boutons. The study of the distribution of Purkinje collateral synapses revealed that one third formed the supraganglionic plexus in the lower molecular layer and two thirds formed an infraganglionic plexus in the lower Purkinje upper granular zone. In the molecular layer, basket cell somata and dendrites received the gratest number of Purkinje collaterals, while Purkinje dendrites and branchlets received relatively few. In the infraganglionic plexus, the Purkinje collaterals terminated on “very low basket” cells and upon a dense dendritic “thicket” belived to be contributed largely by basket cells.

Distribution of gangliosides, glycoprotein-NANA and acetylcholinesterase in axonal and synaptosomal fractions of cat cerebellum.

Mild homogenization of the cat cerebellum and centrifugation of the resultant particulate matter yielded a crude mitochondrial fraction which was further fractionated by sucrose-density gradient centrifugation. The fractions obtained were examined under the electron microscope. Fraction P2A contained large numbers of myelin fragments. Fraction P2B was enriched in segments of unmyelinated axons. Fraction P2C was enriched in axons with their synaptic enlargements. Fractions P2D and P2E were composed predominately of free mitochondria, although axonal segments with bulbar enlargements corresponding to synaptosomes were also seen. Fractions enriched in axons were characterized by a high concentration of gangliosides and acetylcholinesterase (per mg protein). Fractions that contain axons with synaptic enlargements were similarly enriched in these constituents. Glycoprotein-NANA was rather widely distributed, but the concentration of glycoprotein-NANA, per mg protein, was somewhat higher in those fractions that contain axons with attached synaptic enlargements. The distribution of gangliosides and glycoproteins differed so that the ratio of glycoprotein-NANA to ganglioside-NANA increased with increasing particle size or density.