Mice lacking alpha-synuclein display functional deficits in the nigrostriatal dopamine system

alpha-Synuclein (alpha-Syn) is a 14 kDa protein of unknown function that has been implicated in the pathophysiology of Parkinson's disease (PD). Here, we show that alpha-Syn-/- mice are viable and fertile, exhibit intact brain architecture, and possess a normal complement of dopaminergic cell bodies, fibers, and synapses. Nigrostriatal terminals of alpha-Syn-/- mice display a standard pattern of dopamine (DA) discharge and reuptake in response to simple electrical stimulation. However, they exhibit an increased release with paired stimuli that can be mimicked by elevated Ca2+. Concurrent with the altered DA release, alpha-Syn-/- mice display a reduction in striatal DA and an attenuation of DA-dependent locomotor response to amphetamine. These findings support the hypothesis that alpha-Syn is an essential presynaptic, activity-dependent negative regulator of DA neurotransmission.

Distribution of orexin neurons in the adult rat brain

Orexin (ORX)-A and -B are recently identified neuropeptides, which are specifically localized in neurons within and around the lateral hypothalamic area (LHA) and dorsomedial hypothalamic nucleus (DMH), the regions classically implicated in feeding behavior. Here, we report a further study of the distribution of ORX-containing neurons in the adult rat brain to provide a general overview of the ORX neuronal system. Immunohistochemical study using anti-ORX antiserum showed ORX-immunoreactive (ir) neurons specifically localized within the hypothalamus, including the perifornical nucleus, LHA, DMH, and posterior hypothalamic area. ORX-ir axons and their varicose terminals showed a widespread distribution throughout the adult rat brain. ORX-ir nerve terminals were observed throughout the hypothalamus, including the arcuate nucleus and paraventricular hypothalamic nucleus, regions implicated in the regulation of feeding behavior. We also observed strong staining of ORX-ir varicose terminals in areas outside the hypothalamus, including the cerebral cortex, medial groups of the thalamus, circumventricular organs (subfornical organ and area postrema), limbic system (hippocampus, amygdala, and indusium griseum), and brain stem (locus coeruleus and raphe nuclei). These results indicate that the ORX system provides a link between the hypothalamus and other brain regions, and that ORX-containing LHA and DMH neurons play important roles in integrating the complex physiology underlying feeding behavior.

Nicotine enhancement of fast excitatory synaptic transmission in CNS by presynaptic receptors

The behavioral and cognitive effects of nicotine suggest that nicotinic acetylcholine receptors (nAChRs) participate in central nervous system (CNS) function. Although nAChR subunit messenger RNA (mRNA) and nicotine binding sites are common in the brain, there is little evidence for synapses mediated by nAChRs in the CNS. To test whether, CNS nAChRs might modify rather than mediate transmission, the regulation of excitatory synaptic transmission by these receptors was examined. Nanomolar concentrations of nicotine enhanced both glutamatergic and cholinergic synaptic transmission by activation of presynaptic nAChRs that increased presynaptic [Ca2]i. Pharmacological and subunit deletion experiments reveal that these presynaptic nAChRs include the alpha 7 subunit. These findings reveal that CNS nAChRs enhance fast excitatory transmission, providing a likely mechanism for the complex behavioral effects of nicotine.

Defective neuromuscular synaptogenesis in agrin-deficient mutant mice

During neuromuscular synapse formation, motor axons induce clustering of acetylcholine receptors (AChRs) in the muscle fiber membrane. The protein agrin, originally isolated from the basal lamina of the synaptic cleft, is synthesized and secreted by motoneurons and triggers formation of AChR clusters on cultured myotubes. We show here postsynaptic AChR aggregates are markedly reduced in number, size, and density in muscles of agrin-deficient mutant mice. These results support the hypothesis that agrin is a critical organizer of postsynaptic differentiation does occur in the mutant, suggesting the existence of a second-nerve-derived synaptic organizing signal. In addition, we show that intramuscular nerve branching and presynaptic differentiation are abnormal in the mutant, phenotypes which may reflect either a distinct effect of agrin or impaired retrograde signaling from a defective postsynaptic apparatus.

G protein-coupled inwardly rectifying K+ channels (GIRKs) mediate postsynaptic but not presynaptic transmitter actions in hippocampal neurons

To study the role of G protein-coupled, inwardly rectifying K+ (GIRK) channels in mediating neurotransmitter actions in hippocampal neurons, we have examined slices from transgenic mice lacking the GIRK2 gene. The outward currents evoked by agonists for GABA(B) receptors, 5HT1A receptors, and adenosine A1 receptors were essentially absent in mutant mice, while the inward current evoked by muscarinic receptor activation was unaltered. In contrast, the presynaptic inhibitory action of a number of presynaptic receptors on excitatory and inhibitory terminals was unaltered in mutant mice. These included GABA(B), adenosine, muscarinic, metabotropic glutamate, and NPY receptors on excitatory synapses and GABA(B) and opioid receptors on inhibitory synapses. These findings suggest that a number of G protein-coupled receptors activate the same class of postsynaptic K+ channel, which contains GIRK2. In addition, the GIRK2 channels play no role in the inhibition mediated by presynaptic G protein-coupled receptors, suggesting that the same receptor can couple to different effector systems according to its subcellular location in the neuron.

Presynaptic alpha-synuclein aggregates, not Lewy bodies, cause neurodegeneration in dementia with Lewy bodies

Lewy bodies, the pathological hallmark of dementia with Lewy bodies (DLB), are large juxtanuclear inclusions of aggregated alpha-synuclein. However, the small number of cortical Lewy bodies relative to the total neuron count does not correlate with the extent of cognitive impairment. In contrast to dopaminergic neurons in Parkinson's disease, nerve cell loss is usually less prevalent in the cortex of DLB, suggesting a different mechanism of neurodegeneration. Because antibodies used for immunodetection per se do not generally differentiate the aggregated from the physiological and monomeric isoform of alpha-synuclein, we developed the paraffin-embedded tissue (PET) blot and the protein aggregate filtration (PAF) assay for the sensitive and selective detection of alpha-synuclein aggregates in tissue slides and brain homogenates, respectively. In contrast to common immunohistochemistry, the PET blot detected an enormous number of small alpha-synuclein aggregates, which, in contrast to the few Lewy bodies, may explain the cognitive impairment in DLB. Using the PAF assay, we demonstrate that the absolute majority of alpha-synuclein aggregates are located at presynaptic terminals, suggesting a severe pathological impact on synaptic function. Indeed, parallel to the massive presynaptic accumulation of alpha-synuclein aggregates, we observed significant synaptic pathology with almost complete loss of dendritic spines at the postsynaptic area. Our results provide strong evidence for a novel concept of neurodegeneration for DLB in which synaptic dysfunction is caused by presynaptic accumulation of alpha-synuclein aggregates. This concept may also be valid for Parkinson's disease.

Combinatorial and chemotopic odorant coding in the zebrafish olfactory bulb visualized by optical imaging

Odors are thought to be represented by a distributed code across the glomerular modules in the olfactory bulb (OB). Here, we optically imaged presynaptic activity in glomerular modules of the zebrafish OB induced by a class of natural odorants (amino acids [AAs]) after labeling of primary afferents with a calcium-sensitive dye. AAs induce complex combinatorial patterns of active glomerular modules that are unique for different stimuli and concentrations. Quantitative analysis shows that defined molecular features of stimuli are correlated with activity in spatially confined groups of glomerular modules. These results provide direct evidence that identity and concentration of odorants are encoded by glomerular activity patterns and reveal a coarse chemotopic organization of the array of glomerular modules.

Cannabinoids inhibit hippocampal GABAergic transmission and network oscillations

Using a new antibody developed against the C-terminus of the cannabinoid receptor (CB1), the immunostaining in the hippocampus revealed additional axon terminals relative to the pattern reported previously with an N-terminus antibody. Due to a greater sensitivity of this antibody, a large proportion of boutons in the dendritic layers displaying symmetrical (GABAergic) synapses were also strongly immunoreactive for CB1 receptors, as were axon terminals of perisomatic inhibitory cells containing cholecystokinin. Asymmetrical (glutamatergic) synapses, however, were always negative for CB1. To investigate the effect of presynaptic CB1 receptor activation on hippocampal inhibition, we recorded inhibitory postsynaptic currents (IPSCs) from principal cells. Bath application of CB1 receptor agonists (WIN55,212-2 and CP55,940) suppressed IPSCs evoked by local electrical stimulation, which could be prevented or reversed by the CB1 receptor antagonist SR141716A. Action potential-driven IPSCs, evoked by pharmacological stimulation of a subset of interneurons, were also decreased by CB1 receptor activation. We also examined the effects of CB1 receptor agonists on Ca2+-independent miniature IPSCs (mIPSC). Both agonists were without significant effect on the frequency or amplitude of mIPSCs. Synchronous gamma oscillations induced by kainic acid in the CA3 region of hippocampal slices were reversibly reduced in amplitude by the CB1 receptor agonist CP 55,940, which is consistent with an action on IPSCs. We used CB1-/- knock-out mice to confirm the specificity of the antibody and of the agonist (WIN55,212-2) action. We conclude that activation of presynaptic CB1 receptors decreases Ca2+-dependent GABA release, and thereby reduces the power of hippocampal network oscillations.

The expression of vesicular glutamate transporters VGLUT1 and VGLUT2 in neurochemically defined axonal populations in the rat spinal cord with emphasis on the dorsal horn

Two vesicular glutamate transporters, VGLUT1 and VGLUT2, have recently been identified, and it has been reported that they are expressed by largely nonoverlapping populations of glutamatergic neurons in the brain. We have used immunocytochemistry with antibodies against both transporters, together with markers for various populations of spinal neurons, in an attempt to identify glutamatergic interneurons in the dorsal horn of the mid-lumbar spinal cord of the rat. The great majority (94-100%) of nonprimary axonal boutons that contained somatostatin, substance P or neurotensin, as well as 85% of those that contained enkephalin, were VGLUT2-immunoreactive, which suggests that most dorsal horn neurons that synthesize these peptides are glutamatergic. In support of this, we found that most somatostatin- and enkephalin-containing boutons (including somatostatin-immunoreactive boutons that lacked calcitonin gene-related peptide and were therefore probably derived from local interneurons) formed synapses at which AMPA receptors were present. We also investigated VGLUT expression in central terminals of primary afferents. Myelinated afferents were identified with cholera toxin B subunit; most of those in lamina I were VGLUT2-immunoreactive, whereas all those in deeper laminae were VGLUT1-immunoreactive, and some (in laminae III-VI) appeared to contain both transporters. However, peptidergic primary afferents that contained substance P or somatostatin (most of which are unmyelinated), as well as nonpeptidergic C fibres (identified with Bandeiraea simplicifolia isolectin B4) showed low levels of VGLUT2-immunoreactivity, or were not immunoreactive with either VGLUT antibody. As all primary afferents are thought to be glutamatergic, this raises the possibility that unmyelinated afferents, most of which are nociceptors, express a different vesicular glutamate transporter.

The presynaptic particle web: ultrastructure, composition, dissolution, and reconstitution

We report the purification of a presynaptic "particle web" consisting of approximately 50 nm pyramidally shaped particles interconnected by approximately 100 nm spaced fibrils. This is the "presynaptic grid" described in early EM studies. It is completely soluble above pH 8, but reconstitutes after dialysis against pH 6. Interestingly, reconstituted particles orient and bind PSDs asymmetrically. Mass spectrometry of purified web components reveals major proteins involved in the exocytosis of synaptic vesicles and in membrane retrieval. Our data support the idea that the CNS synaptic junction is organized by transmembrane adhesion molecules interlinked in the synaptic cleft, connected via their intracytoplasmic domains to the presynaptic web on one side and to the postsynaptic density on the other. The CNS synaptic junction may therefore be conceptualized as a complicated macromolecular scaffold that isostatically bridges two closely aligned plasma membranes.

The postsynaptic density at glutamatergic synapses

The postsynaptic density (PSD) is a tiny, amorphous structure located beneath the postsynaptic membrane of synapses in the CNS. Until recently, the molecular composition and function of the PSD were mostly matters of speculation. With the advent of powerful new microchemical tools and molecular-genetic methods, three new classes of proteins have been identified in the PSD at glutamatergic synapses: the PSD-95 family, the NR2B subunit of the NMDA-type glutamate receptor, and densin-180. The PSD-95 family is involved in clustering of NMDA receptors. NR2B is phosphorylated by Ca2(+)-calmodulin-dependent protein kinase type II, a prominent constituent of the PSD. Densin-180 might represent a new class of synaptic adhesion molecule. Study of these molecules is beginning to reveal the functional significance of the PSD.

Paralysis and early death in cysteine string protein mutants of Drosophila

Multimeric complexes of synaptic vesicle and terminal membrane proteins are important components of the neurotransmitter release mechanism. The csp gene of Drosophila encodes proteins homologous to synaptic vesicle proteins in Torpedo. Monoclonal antibodies demonstrate different distributions of isoforms at distinct subsets of terminals. Deletion of the csp gene in Drosophila causes a temperature-sensitive block of synaptic transmission, followed by paralysis and premature death.

Some forms of cAMP-mediated long-lasting potentiation are associated with release of BDNF and nuclear translocation of phospho-MAP kinase

Long-lasting forms of synaptic plasticity like the late phase of LTP (L-LTP) typically require an elevation of cAMP, the recruitment of the cAMP-dependent protein kinase (PKA), and ultimately the activation of transcription and translation; some forms also require brain-derived neurotrophic factor (BDNF). Both cAMP and BDNF can activate mitogen-activated protein kinase (MAPK/ERK), which also plays a role in LTP. However, little is known about the mechanisms whereby cAMP, BDNF, and MAPK interact. We find that increases in cAMP can rapidly activate the BDNF receptor TrkB and induce BDNF-dependent long-lasting potentiation at the Schaffer collateral-CA1 synapse in hippocampus. Surprisingly, in these BDNF-dependent forms of potentiation, which are also MAPK dependent, TrkB activation is not critical for the activation of MAPK but instead appears to modulate the subcellular distribution and nuclear translocation of the activated MAPK.

Orbitomedial prefrontal cortical projections to distinct longitudinal columns of the periaqueductal gray in the rat

We utilised retrograde and anterograde tracing procedures to study the origin and termination of prefrontal cortical (PFC) projections to the periaqueductal gray (PAG) in the rat. A previous study, in the primate, had demonstrated that distinct subgroups of PFC areas project to specific PAG columns. Retrograde tracing experiments revealed that projections to dorsolateral (dlPAG) and ventrolateral (vlPAG) periaqueductal gray columns arose from medial PFC, specifically prelimbic, infralimbic, and anterior cingulate cortices. Injections made in the vlPAG also labeled cells in medial, ventral, and dorsolateral orbital cortex and dorsal and posterior agranular insular cortex. Other orbital and insular regions, including lateral and ventrolateral orbital, ventral agranular insular, and dysgranular and granular insular cortex did not give rise to appreciable projections to the PAG. Anterograde tracing experiments revealed that the projections to different PAG columns arose from specific PFC areas. Projections from the caudodorsal medial PFC (caudal prelimbic and anterior cingulate cortices) terminated predominantly in dlPAG, whereas projections from the rostroventral medial PFC (rostral prelimbic cortex) innervated predominantly the vlPAG. As well, consistent with the retrograde data, projections arising from select orbital and agranular insular cortical areas terminated selectively in the vlPAG. The results indicate: (1) that rat orbital and medial PFC possesses an organisation broadly similar to that of the primate; and (2) that subdivisions within the rat orbital and medial PFC can be recognised on the basis of projections to distinct PAG columns.

Precise localization of alpha7 nicotinic acetylcholine receptors on glutamatergic axon terminals in the rat ventral tegmental area

Alpha7 neuronal nicotinic acetylcholine receptors (nAChRs) constitute one of the predominant nAChR subtypes in the mammalian brain. Within the ventral tegmental area (VTA), nicotine application, paired with postsynaptic stimulation, contributes to a form of long-term potentiation, an effect attributed to presynaptic alpha7 nAChRs on glutamatergic afferents (Mansvelder and McGehee, 2000). The aim of this study was to examine the precise subcellular distribution of alpha7 nAChRs in the adult rat VTA to establish whether these receptors are indeed present on glutamatergic axon terminals and to determine their relationship with cholinergic afferents. The spatial relationship between alpha7 nAChRs, labeled using the alpha7 nAChR-specific antagonist alpha-bungarotoxin, and the local neurochemical environment was investigated by the application of multiple labeling strategies with antibodies against tyrosine hydroxylase, vesicular glutamate transporters (VGluTs), vesicular acetylcholine transporter, and glial fibrillary acidic protein. alpha7 nAChRs were localized at both somatodendritic and presynaptic loci within the VTA: on subpopulations of dopaminergic and nondopaminergic neurons and glutamatergic and nonglutamatergic terminals. There was no detectable alpha7 nAChR expression within astrocytes in the VTA. Most alpha7 nAChRs were cytoplasmic (82%), and the remainder were associated with the plasma membrane. Most presynaptic receptors (75%) were on glutamatergic axon terminals, with similar levels of alpha-bungarotoxin binding present on both VGluT1- and VGluT2-immunoreactive boutons. Both preembedding and postembedding electron microscopy revealed that presynaptic alpha7 nAChRs are often located at extrasynaptic (27%) and perisynaptic (61%) loci. alpha7 nAChRs were not associated with cholinergic synapses, consistent with their activation by a paracrine mode of acetylcholine or choline delivery.

Unitary assembly of presynaptic active zones from Piccolo-Bassoon transport vesicles

Recent studies indicate that active zones (AZs)-sites of neurotransmitter release-may be assembled from preassembled AZ precursor vesicles inserted into the presynaptic plasma membrane. Here we report that one putative AZ precursor vesicle of CNS synapses-the Piccolo-Bassoon transport vesicle (PTV)-carries a comprehensive set of AZ proteins genetically and functionally coupled to synaptic vesicle exocytosis. Time-lapse imaging reveals that PTVs are highly mobile, consistent with a role in intracellular transport. Quantitative analysis reveals that the Bassoon, Piccolo, and RIM content of individual PTVs is, on average, half of that of individual presynaptic boutons and shows that the synaptic content of these molecules can be quantitatively accounted for by incorporation of integer numbers (typically two to three) of PTVs into presynaptic membranes. These findings suggest that AZs are assembled from unitary amounts of AZ material carried on PTVs.

Reduced striatal dopamine transporters in idiopathic rapid eye movement sleep behaviour disorder. Comparison with Parkinson's disease and controls

Rapid eye movement (REM) sleep behaviour disorder (RBD) is characterized by complex behaviour during REM sleep. The aetiology of this disorder is still unknown, but a recent study showed an association between RBD and Parkinson's disease. We therefore studied striatal postsynaptic dopamine D2 receptor density with [123I](S)-2-hydroxy-3-iodo-6-methoxy-(1-ethyl-2-pyrrolidinylmethyl ) benzamide ([123I]IBZM) and the striatal presynaptic dopamine transporter with (N)-(3-iodopropene-2-yl)-2beta-carbomethoxy-3beta-(4-chlorop henyl) tropane ([123I]IPT) using single-photon emission computed tomography (SPECT) in patients with idiopathic RBD. We compared the [123I]IPT-SPECT results of five patients with polysomnographically confirmed idiopathic RBD with the [123I]IPT-SPECTs of seven age- and sex-matched controls without a history of sleep disorders, and of 14 patients with Parkinson's disease (Hoehn and Yahr stage I). All RBD patients had significantly reduced striatal [123I]IPT binding compared with the controls (RBD: right, 2.94 +/- 0.32, left, 3.03 +/- 0.41; controls: right, 4.41 +/- 0.17, left, 4.34 +/- 0.21; P = 0.003), but significantly higher striatal [123I]IPT binding compared with the striatum contralateral to the symptomatic body side of the Parkinson's disease patients (Parkinson's disease: ipsilateral, 3.17 +/- 0.36, P = 0.298; contralateral, 2.51 +/- 0.31, P = 0.019). Uptake of [123I]IBZM was not significantly different in the RBD group compared with the controls. This study demonstrates that [123I]IPT-SPECT is a useful diagnostic tool in RBD and that reduced striatal dopamine transporters may be a pathophysiological mechanism of idiopathic RBD. (Results are given as mean +/- standard deviation.)

Rapid activity-dependent modifications in synaptic structure and function require bidirectional Wnt signaling

Activity-dependent modifications in synapse structure play a key role in synaptic development and plasticity, but the signaling mechanisms involved are poorly understood. We demonstrate that glutamatergic Drosophila neuromuscular junctions undergo rapid changes in synaptic structure and function in response to patterned stimulation. These changes, which depend on transcription and translation, include formation of motile presynaptic filopodia, elaboration of undifferentiated varicosities, and potentiation of spontaneous release frequency. Experiments indicate that a bidirectional Wnt/Wg signaling pathway underlies these changes. Evoked activity induces Wnt1/Wg release from synaptic boutons, which stimulates both a postsynaptic DFz2 nuclear import pathway as well as a presynaptic pathway involving GSK-3beta/Shaggy. Our findings suggest that bidirectional Wg signaling operates downstream of synaptic activity to induce modifications in synaptic structure and function. We propose that activation of the postsynaptic Wg pathway is required for the assembly of the postsynaptic apparatus, while activation of the presynaptic Wg pathway regulates cytoskeletal dynamics.

Piccolo, a presynaptic zinc finger protein structurally related to bassoon

Piccolo is a novel component of the presynaptic cytoskeletal matrix (PCM) assembled at the active zone of neurotransmitter release. Analysis of its primary structure reveals that Piccolo is a multidomain zinc finger protein structurally related to Bassoon, another PCM protein. Both proteins were found to be shared components of glutamatergic and GABAergic CNS synapses but not of the cholinergic neuromuscular junction. The Piccolo zinc fingers were found to interact with the dual prenylated rab3A and VAMP2/Synaptobrevin II receptor PRA1. We show that PRA1 is a synaptic vesicle-associated protein that is colocalized with Piccolo in nerve terminals of hippocampal primary neurons. These data suggest that Piccolo plays a role in the trafficking of synaptic vesicles (SVs) at the active zone.

Presynaptic nicotinic modulation of dopamine release in the three ascending pathways studied by in vivo microdialysis: comparison of naive and chronic nicotine-treated rats

The modulation of dopamine release by presynaptic nicotinic receptors in vitro is well established, but the significance of this effect in vivo is unclear. We have characterised the effect of nicotine, locally applied via a microdialysis probe, on dopamine release from the terminal regions of three ascending dopaminergic pathways in conscious, freely moving rats. Nicotine caused a dose-dependent increase in dopamine release in the striatum, the nucleus accumbens, and, to a lesser extent, the frontal cortex. Metabolite levels were unaltered by any concentration of nicotine. Prior administration of mecamylamine via the probe abolished the nicotine-evoked increase in dopamine release, confirming the mediation of nicotinic receptors. The dose dependence of mecamylamine-sensitive, nicotine-evoked dopamine release was similar in all three brain regions. However, 10(-5) M tetrodotoxin totally blocked nicotine-stimulated dopamine release in the striatum and the accumbens but not the cortex. Daily subcutaneous injections of nicotine (0.4 mg kg-1 for 7 days) increased the response to a subsequent local application of nicotine in the striatum, and a similar trend was found in the other brain areas. The same daily dose of nicotine given as a continuous infusion had no effect, whereas infusion of 4 mg kg-1 day-1 increased the response to a subsequent nicotine challenge. The localisation and regulation of nicotinic receptors in the terminal fields of dopaminergic pathways are discussed.

Two distinct pools of synaptic vesicles in single presynaptic boutons in a temperature-sensitive Drosophila mutant, shibire

In a temperature-sensitive Drosophila mutant, shibire, synaptic vesicles are completely depleted in nerve terminals after stimulation at 34 degrees C, but upon returning to 22 degrees C, endocytosis resumes. In this study, synaptic vesicles in the boutons of nerve terminals at the mutant neuromuscular junction were loaded with a fluorescent dye, FM1-43, during vesicle reformation at 22 degrees C after complete depletion at 34 degrees C. We found two distinct pools of synaptic vesicles, namely an exo/endo cycling pool, located in the periphery of the bouton, and a reserve pool, located in its center. Cytochalasin D treatment eliminated the reserve pool and reduced synaptic transmission evoked by high frequency stimulation. Thus, the reserve pool may play a crucial role for sustaining high frequency synaptic transmission.

The physiological role of α-synuclein and its relationship to Parkinson's Disease

The protein α-synuclein has a central role in the pathogenesis of Parkinson's disease (PD). In this review, we discuss recent results concerning its primary function, which appears to be on cell membranes. The pre-synaptic location of synuclein has suggested a role in neurotransmitter release and it apparently associates with synaptic vesicles because of their high curvature. Indeed, synuclein over-expression inhibits synaptic vesicle exocytosis. However, loss of synuclein has not yet been shown to have a major effect on synaptic transmission. Consistent with work showing that synuclein can promote as well as sense membrane curvature, recent analysis of synuclein triple knockout mice now shows that synuclein accelerates dilation of the exocytic fusion pore. This form of regulation affects primarily the release of slowly discharged lumenal cargo such as neural peptides, but presumably also contributes to maintenance of the release site. This article is part of the Special Issue "Synuclein".

Role of Drosophila alpha-adaptin in presynaptic vesicle recycling

Rapid flow of information in the nervous system involves presynaptic vesicle recycling by clathrin-mediated endocytosis, an event triggered by the alpha-adaptin-containing AP2 complex. We identified a Drosophila alpha-adaptin expressed in the garland cells, imaginal discs, and the CNS. Here we show its role in presynaptic vesicle recycling. In presynaptic terminals, alpha-adaptin defines a network-like membrane structure to which the GTPase dynamin is recruited. alpha-adaptin is necessary for the formation of clathrin-coated pits and participates in the dynamin-dependent release of coated vesicles from the membrane surface. Our results suggest an alpha-adaptin-dependent control of the vesicle cycle that maintains the balance between the amount of vesicle- and surface-associated membranes.

Identification and localization of an actin-binding motif that is unique to the epsilon isoform of protein kinase C and participates in the regulation of synaptic function

Individual isoforms of the protein kinase C (PKC) family of kinases may have assumed distinct responsibilities for the control of complex and diverse cellular functions. In this study, we show that an isoform specific interaction between PKC epsilon and filamentous actin may serve as a necessary prelude to the enhancement of glutamate exocytosis from nerve terminals. Using a combination of cosedimentation, overlay, and direct binding assays, we demonstrate that filamentous actin is a principal anchoring protein for PKC epsilon within intact nerve endings. The unusual stability and direct nature of this physical interaction indicate that actin filaments represent a new class of PKC-binding protein. The binding of PKC epsilon to actin required that the kinase be activated, presumably to expose a cryptic binding site that we have identified and shown to be located between the first and second cysteine-rich regions within the regulatory domain of only this individual isoform of PKC. Arachidonic acid (AA) synergistically interacted with diacylglycerol to stimulate actin binding to PKC epsilon. Once established, this protein-protein interaction securely anchored PKC epsilon to the cytoskeletal matrix while also serving as a chaperone that maintained the kinase in a catalytically active conformation. Thus, actin appears to be a bifunctional anchoring protein that is specific for the PKC epsilon isoform. The assembly of this isoform-specific signaling complex appears to play a primary role in the PKC-dependent facilitation of glutamate exocytosis.

Reciprocal alterations in pre- and postsynaptic inhibitory markers at chandelier cell inputs to pyramidal neurons in schizophrenia

In the prefrontal cortex of subjects with schizophrenia, markers of the synthesis and re-uptake of GABA appear to be selectively altered in a subset of interneurons that includes chandelier cells. Determining the effect of these disturbances in presynaptic GABA markers on inhibitory signaling requires knowledge of the status of GABA(A) receptors at the postsynaptic targets of chandelier cells, the axon initial segments (AIS) of pyramidal neurons. Because the alpha(2) subunit of the GABA(A) receptor is preferentially localized at pyramidal neuron AIS, we quantified alpha(2) subunit immunoreactive AIS in tissue sections containing prefrontal cortex area 46 from 14 matched triads of subjects with schizophrenia, subjects with major depression and control subjects. Systematic, random sampling revealed that the mean number of alpha(2)-labeled AIS per mm(2) in subjects with schizophrenia was significantly (P = 0.007) increased by 113% compared to control subjects and non-significantly increased compared to subjects with major depression. Furthermore, within subjects with schizophrenia, the density of alpha(2)-labeled AIS was negatively correlated (r = -0.49, P = 0.038) with the density of chandelier axon terminals immunoreactive for the GABA membrane transporter. These data suggest that GABA(A) receptors are up-regulated at pyramidal neuron AIS in response to deficient GABA neuro-transmission at chandelier axon terminals in schizophrenia. Thus, disturbances in inhibition at the chandelier neuron-pyramidal neuron synapse may be a critical component of prefrontal cortical dysfunction in schizophrenia.