bluuebunny/crossref_metadata_2025 huggingface dataset:
Purification of Synaptic Ribbons, Structural Components of the Photoreceptor Active Zone Complex
Authors: Schmitz Frank , Bechmann Martin , Drenckhahn Detlev
Published: April 2018

Synaptic ribbons are plasma membrane-associated structural elements in photoreceptor synaptic terminals. They seem to act as high capacity “docking sites” of synaptic vesicles that provide the fusion sites of the photoreceptor synapse (“active zones”), with a large supply of immobilized synaptic vesicles rapidly available for exocytosis. Synaptic ribbons are regarded as a specialized type of presynaptic densities found in virtually all synapses. The molecular composition of presynaptic densities and synaptic ribbons is unknown. The aim of this study was the isolation of synaptic ribbons from photoreceptor synapses. For this purpose, we first isolated a membrane fraction from the bovine retina that was strongly enriched in photoreceptor synapses. From this fraction, a Triton X-100-resistant subfraction was purified that consisted mainly of synaptic ribbons and their disassembly products. The high enrichment of synaptic ribbons was verified by electron microscopy and immunolabeling using an antibody that specifically binds to synaptic ribbons. SDS-PAGE analysis of this synaptic ribbon fraction displayed several major polypeptide bands migrating at ∼240, 60, 55, 43, and 30 kDa. The purification procedure described here is a first promising step toward the identification of the yet unknown constituents of synaptic ribbons from photoreceptor synapses and possibly also of presynaptic densities from other synapses.
Genetic and Environmental Control of Variation in Retinal Ganglion Cell Number in Mice
Authors: Williams Robert W. , Strom Richelle C. , Rice Dennis S. , Goldowitz Dan
Published: April 2018

How much of the remarkable variation in neuron number within a species is generated by genetic differences, and how much is generated by environmental factors? We address this problem for a single population of neurons in the mouse CNS. Retinal ganglion cells of inbred and outbred strains, wild species and subspecies, andF1hybrids were studied using an unbiased electron microscopic method with known technical reliability.

Ganglion cell numbers among diverse types of mice are highly variable, ranging from 32,000 to 87,000. The distribution of all cases (n = 252) is close to normal, with a mean of 58,500 and an SD of 7800. Genetic factors are most important in controlling this variation; 76% of the variance is heritable and up to 90% is attributable to genetic factors in a broad sense.

Strain averages have an unanticipated bimodal distribution, with distinct peaks at 55,500 and 63,500 cells. Three pairs of closely related strains have ganglion cell populations that differ by >20% (10,000 cells). These findings indicate that different alleles at one or two genes have major effects on normal variation in ganglion cell number.

Nongenetic factors are still appreciable and account for a coefficient of variation that averages ∼3.6% within inbred strains and isogenicF1hybrids. Age- and sex-related differences in neuron number are negligible. Variation within isogenic strains appears to be generated mainly by developmental noise.
Cloning and Characterization of Postsynaptic Density 93, a Nitric Oxide Synthase Interacting Protein
Authors: Brenman Jay E. , Christopherson Karen S. , Craven Sarah E. , McGee Aaron W. , Bredt David S.
Published: April 2018

Nitric oxide (NO) formation in brain is regulated by the calcium/calmodulin dependence of neuronal NO synthase (nNOS). Calcium influx through NMDA-type glutamate receptors is efficiently coupled to nNOS activity, whereas many other intracellular calcium pathways are poorly coupled. To elucidate possible mechanisms responsible for this coupling, we performed yeast two-hybrid screening to identify proteins that interact with nNOS. Two nNOS interacting proteins were identified: the postsynaptic density proteins PSD-93 and PSD-95. Here, we report the cloning and characterization of PSD-93. PSD-93 is expressed in discrete neuronal populations as well as in specific non-neuronal cells, and it exhibits complex molecular diversity attributable to tissue-specific alternative splicing. PSD-93, like PSD-95, binds to nNOS and to the NMDA receptor 2B. PSD-93, however, is unique among PSD-95/SAP-90 family members in its expression in Purkinje neuron cell bodies and dendrites. We also demonstrate that the PDZ domain at the N terminus of nNOS is required, but it is not sufficient for interaction with PSD-93/95. Given that PSD-93 and PSD-95 each contain multiple potential binding sites for nNOS and the NMDA receptor, complexes involving oligomers of PSD-93/95 may help account for the functional as well as the physical coupling of nNOS to NMDA receptors.
Differential Reinforcing Effects of Cocaine and GBR-12909: Biochemical Evidence for Divergent Neuroadaptive Changes in the Mesolimbic Dopaminergic System
Authors: Tella Srihari R. , Ladenheim Bruce , Andrews Anne M. , Goldberg Steven R. , Cadet Jean Lud
Published: April 2018

The dopamine (DA) transporter is thought to be the primary mediator of reinforcing effects of cocaine. In the present study, an intravenous drug self-administration procedure,in vitroautoradiography, and HPLC methods were used to investigate possible differences in reinforcing and neuroadaptive responses to cocaine versus GBR-12909, a selective inhibitor of the DA transporter with a postulated therapeutic use in cocaine abuse. Drug-naive rats readily acquired and subsequently maintained cocaine self-administration behavior during 2 hr daily sessions over a prolonged period. In contrast, although GBR-12909 was initially self-administered, both cocaine-naive and cocaine-trained rats failed to maintain self-administration behavior for GBR-12909 over prolonged periods of time. After self-administration responding decreased with GBR-12909, rats showed a delay of 6.6 ± 1.3 sessions in reacquiring consistent cocaine self-administration. Moreover, when GBR-12909 was again substituted for cocaine, they failed to self-administer GBR-12909, even during the initial days of testing. In contrast, after extinction of self-administration responding by water substitution, rats readily self-administered both cocaine and GBR-12909. Cocaine self-administration upregulated DA transporters, whereas water-substituted cocaine withdrawal upregulated both DA transporters and D1 receptors. Unlike cocaine, GBR-12909 self-administration by itself altered neither DA transporters nor D1 or D2 receptors. Nevertheless, substitution of GBR-12909 for cocaine reversed the cocaine-induced upregulation of DA transporters and reduced DA and dihydroxyphenylacetic acid levels in the mesolimbic system. These data suggest that cocaine and GBR-12909 differentially affect dopaminergic systems and also cause different reinforcing and neuroadaptive effects. GBR-12909-like compounds may be useful pharmacotherapeutic agents for cocaine addiction. Upregulation of DA transporters and D1 receptors might play important roles in the neuroadaptive cascade that leads to cocaine addiction and withdrawal.
Intrinsic Injury Signals Enhance Growth, Survival, and Excitability ofAplysiaNeurons
Authors: Ambron Richard T. , Zhang Xiao-Ping , Gunstream John D. , Povelones Michael , Walters Edgar T.
Published: April 2018

Neurons undergo extensive changes in growth and electrophysiological properties in response to axon injury. Efforts to understand the molecular mechanisms that initiate these changes have focused almost exclusively on the role of extrinsic signals, primarily neurotrophic factors released from target and glial cells. The objective of the present investigation was to determine whether the response to axonal injury also involves intrinsic axoplasmic signals.Aplysianeurons were removed from their ganglia and placedin vitroon a substratum permissive for growth, but in the absence of glia and soluble growth factors. Under these conditions, neurites emerged and grew for ∼4 d. Once growth had ceased, the neurites were transected. In all, 46 of 50 cells regenerated, either by resorbing the remaining neurites and elaborating a new neuritic arbor or by merely replacing the neurites that had been severed. Cut cells also exhibited enhanced excitability and, paradoxically, prolonged survival, when compared with uninjured neurons. These findings indicate that axons contain intrinsic molecular signals that are directly activated by injury to trigger changes underlying regeneration and compensatory plasticity.
Differential Distribution of Functional Receptors for Neuromodulators Evoking Short-Term Heterosynaptic Plasticity inAplysiaSensory Neurons
Authors: Sun Zhong-Yi , Kauderer Beth , Schacher Samuel
Published: April 2018

Synaptic transmission and excitability inAplysiasensory neurons (SNs) are bidirectionally modulated by 5-HT and FMRFamide. To explore the regional distribution of different functional receptors that modulate SN properties, we examined changes in synaptic efficacy and excitability with brief focal applications of the neuromodulators to different regions of SNs that have established connections with motor cell L7 in culture. Short-term changes in synaptic efficacy were evoked only when 5-HT or FMRFamide was applied to regions with SN varicosities along the surface of L7 axons. Applications to adjacent SN neurites with few varicosities in contact with L7 axons failed to evoke a significant change in synaptic efficacy. The distribution of functional receptors mediating changes in excitability differed for 5-HT and FMRFamide. Whereas excitability increases were evoked only when 5-HT was applied to SN cell bodies, excitability decreases in SNs were evoked only when FMRFamide was applied to regions along the L7 axon with SN varicosities. Without the target cell, cell bodies of SNs expressed both 5-HT and FMRFamide receptors that modulate excitability. These results indicate that functional G-protein-coupled receptors for two neuromodulators are distributed differentially along the surface of a presynaptic neuron that forms chemical connectionsin vitro. This differential distribution of receptors on the presynaptic neuron is regulated by a target and does not require the physical presence of neurons that release the neuromodulators.
Reduction of Lower Motor Neuron Degeneration inwobblerMice byN-Acetyl-l-Cysteine
Authors: Henderson Jeffrey T. , Javaheri Mohammed , Kopko Susan , Roder John C.
Published: April 2018

The murine mutantwobbleris a model of lower motoneuron degeneration with associated skeletal muscle atrophy. This mutation most closely resembles Werdnig–Hofmann disease in humans and shares some of the clinical features of amyotrophic lateral sclerosis (ALS). It has been suggested that reactive oxygen species (ROS) may play a role in the pathogenesis of disorders such as ALS. To examine the relationship between ROS and neural degeneration, we have studied the effects of agents such asN-acetyl-l-cysteine (NAC), which reduce free radical damage. Litters ofwobblermice were given a 1% solution of the glutathione precursor NAC in their drinking water for a period of 9 weeks. Functional and neuroanatomical examination of these animals revealed thatwobblermice treated with NAC exhibited (1) a significant reduction in motor neuron loss and elevated glutathione peroxidase levels within the cervical spinal cord, (2) increased axon caliber in the medial facial nerve, (3) increased muscle mass and muscle fiber area in the triceps and flexor carpi ulnaris muscles, and (4) increased functional efficiency of the forelimbs, as compared with untreatedwobblerlittermates. These data suggest that reactive oxygen species may be involved in the degeneration of motor neurons inwobblermice and demonstrate that oral administration of NAC effectively reduces the degree of motor degeneration inwobblermice. This treatment thus may be applicable in the treatment of other lower motor neuropathies.
The Expression Pattern of the Transcription Factor Phox2 Delineates Synaptic Pathways of the Autonomic Nervous System
Authors: Tiveron Marie-Catherine , Hirsch Marie-Rose , Brunet Jean-François
Published: April 2018

Many transcription factors, and most prominently among them, homeodomain proteins, are expressed in specific groups of cells in the developing nervous system in patterns that suggest their involvement in neural fate determination. How various aspects of neural identity are controlled by such transcription factors, or sets of them, is still mostly unknown. It has been shown previously that Phox2 is such a homeodomain protein, expressed exclusively in differentiated groups of neurons or their precursors, and that its expression correlated with that of the noradrenaline synthesis enzyme dopamine-β-hydroxylase. Here we confirm this striking correlation at the single-cell level with the use of an anti-Phox2 antibody. Moreover, we uncover a second, nonmutually exclusive correlative clue to the Phox2 expression pattern: a high proportion of Phox2-expressing cells are involved in, or located in areas involved in, synaptic circuits, i.e., that of the medullary control reflexes of autonomic functions. This suggests that Phox2 could be involved in the establishment of these circuits.
A Population of Supramammillary Area Calretinin Neurons Terminating on Medial Septal Area Cholinergic and Lateral Septal Area Calbindin-Containing Cells Are Aspartate/Glutamatergic
Authors: Leranth Csaba , Kiss Jozsef
Published: April 2018

The excitatory amino acid, aspartate/glutamate content of septal complex calretinin (CR)-, choline acetyltransferase plus substance P-, and Leu-enkephalin (Leu-enk)-containing extrinsic afferents was examined. Experiments were carried out using the transmitter-specific [3H]-d-aspartate retrograde tracer technique in combination with immunostaining for CR, choline acetyltransferase, and Leu-enk. The extrinsic and intrinsic CR innervation of the same brain areas were elucidated on control rats and on animals in which the septum was surgically separated from its ventral afferents. Correlated light and electron microscopic double-immunostaining experiments were used to determine the synaptic connections between CR axon terminals and lateral septal area calbindin (CB)- and medial septal area choline acetyltransferase-immunoreactive neurons. Furthermore, to determine the synaptic power of supramammilloseptal aspartate/glutamatergic neurons on the septal complex, semiquantitative analyses were performed in the supramammillary area on retrogradely (1) [3H]-d-aspartate-radiolabeled and (2) HRP-labeled material.

The results demonstrated that a population of the extrinsic CR axons originating in the supramammillary area are aspartate/glutamatergic. These fibers forming asymmetric synaptic contacts terminate on both CB and cholinergic neurons. Intraseptal CR neurons, which establish symmetric synapses, innervate only lateral septal area neurons, including the CB-containing cells. These observations, together with other published data, raise the possibility of a hippocampus–lateral septal (GABAergic CB-containing neurons)–supramammillary area (aspartate/glutamatergic cells)–medial septal (cholinergic neurons)–hippocampus signal loop, which might be involved in the generation and regulation of hippocampal theta rhythm activity.
Cellular Mechanisms of the Augmenting Response: Short-Term Plasticity in a Thalamocortical Pathway
Authors: Castro-Alamancos Manuel A. , Connors Barry W.
Published: April 2018

Some thalamocortical pathways display an “augmenting response” when stimuli are delivered at frequencies between 7 and 14 Hz. Cortical responses to the first three stimuli of a series increase progressively in amplitude and are relatively stable thereafter. We have investigated the cellular mechanisms of the augmenting response using extracellular and intracellular recordingsin vivoand in slices of the sensorimotor neocortex of the rat.

Single stimuli to the ventrolateral (VL) nucleus of the thalamus generate EPSPs followed by feedforward IPSPs that hyperpolarize cells in layer V. A long-latency depolarization interrupts the IPSP with a peak at ∼200 msec. A second VL stimulus delivered during the hyperpolarization and before the peak of the long-latency depolarization yields an augmenting response. The shortest latency for augmenting responses occurs in cells of layer V, and they appear in dendrites and somata recorded in upper layers ∼5 msec later. Recordingsin vitroshow that some layer V cells have hyperpolarization-activated and deinactivated conductances that may serve to increase their excitability after IPSPs. Alsoin vitro, cells from layer V, but not from layer III, generated augmenting responses at the same stimulation frequencies that were effectivein vivo. Control experiments indicated that neither paired-pulse depression of IPSPs nor presynaptically mediated facilitation can account for the augmenting response. Active dendritic conductances contribute to the spread of augmenting responses into upper layers by way of back-propagating fast spikes, which attenuate with repetition, and long-lasting spikes, which enhance in parallel with the augmenting response. In conclusion, we propose that the initiation of augmenting responses depends on an interaction between inhibition, intrinsic membrane properties, and synaptic interconnections of layer V pyramidal neurons.
Synaptic Interactions between Primate Precentral Cortex Neurons Revealed by Spike-Triggered Averaging of Intracellular Membrane PotentialsIn Vivo
Authors: Matsumura Michikazu , Chen Dao-fen , Sawaguchi Toshiyuki , Kubota Kisou , Fetz Eberhard E.
Published: April 2018

To document synaptic interactions between neurons in the precentral cortex of macaque monkeys, we recordedin vivothe intracellular (IC) membrane potentials of cortical neurons simultaneously with extracellular (EC) action potentials of neighboring cells. The synaptic potentials correlated with EC spikes were obtained by spike-triggered averages (STA) of the IC membrane potentials for 373 cell pairs recorded in anesthetized and awake behaving monkeys. Sixty-three STAs (17%) showed excitatory postsynaptic potentials (EPSPs), beginning after the trigger spike. Pure EPSPs had onset latencies of 0.9 ± 0.7 msec (mean ± SD) and amplitudes of 226 ± 130 μV. Sixteen STAs (4%) showed postspike inhibitory postsynaptic potentials (IPSPs), with onset latencies of 0.4 ± 0.4 msec and amplitudes of −274 ± 188 μV. The most common waveform, observed in 82% of the STAs with features, was a broad depolarization straddling the trigger spikes, reflecting synchronized synaptic input to both IC and EC neurons. These average synchronous excitation potentials (ASEPs) began 14.3 ± 6.6 msec before the trigger spike and had amplitudes of 1064 ± 867 μV. Twenty-three STAs (6%) showed an average synchronous inhibitory potential (ASIP): a hyperpolarization beginning before the trigger spike and reflecting IPSPs produced by a group of local inhibitory cells synchronized with the trigger cell. ASIPs had an onset latency of −5.5 ± 2.7 msec and amplitude of −589 ± 502 μV. Combinations of synchronous and postspike potentials were also observed. Successive recordings provided examples of convergent and divergent connections between EC and IC cells. Neuron pairs with depolarizing postsynaptic potentials (PSPs) in the STA yielded peaks in the cross-correlograms of the IC and EC action potentials; the peak area was proportional to the amplitude of the PSP. These data suggest that a significantly larger proportion of cortical neurons interact through synchronous activity than through simple serial interactions; moreover, synchronous excitation affected more widely separated cell pairs than EPSPs and IPSPs, which were seen most often among the closest cells.
Actions of the ORL1Receptor Ligand Nociceptin on Membrane Properties of Rat Periaqueductal Gray NeuronsIn Vitro
Authors: Vaughan Christopher W. , Ingram Susan L. , Christie MacDonald J.
Published: April 2018

The actions of the endogenous ORL1-receptor ligand nociceptin on the membrane properties and synaptic currents in rat periaqueductal gray (PAG) neurons were examined by the use of whole-cell patch-clamp recording in brain slices. Nociceptin produced an outward current in all neurons tested, with an EC50of 39 ± 7 nm. The outward current was unaffected by naloxone. Outward currents reversed polarity at −110 ± 3 mV in 2.5 mmextracellular potassium, and the reversal potential increased when the extracellular potassium concentration was raised (slope = 66.3 mV/log[K+]omm). Thus, the nociceptin-induced outward current was attributable to an increased K+conductance. Nociceptin inhibited evoked fast GABAergic (IPSCs) and glutamatergic (EPSCs) postsynaptic currents and increased paired-pulse facilitation in a subpopulation of PAG neurons. Nociceptin inhibited evoked IPSCs and EPSCs in ∼50% of neurons throughout the PAG, except in the ventrolateral PAG, where nociceptin inhibited evoked IPSCs in most neurons. Nociceptin decreased the frequency of spontaneous miniature postsynaptic currents (mIPSCs and mEPSCs) in a subpopulation of PAG neurons but had no effect on their amplitude distributions. Thus, nociceptin had a presynaptic inhibitory effect on transmitter release. These findings suggest that nociceptin, via its pre- and postsynaptic actions, has the potential to modulate the analgesic, behavioral, and autonomic functions of the PAG.
Cell Surface Amyloid β-Protein Precursor Colocalizes with β1 Integrins at Substrate Contact Sites in Neural Cells
Authors: Yamazaki Tsuneo , Koo Edward H. , Selkoe Dennis J.
Published: April 2018

Amyloid β-protein (Aβ), the principal constituent of the senile plaques seen in Alzheimer’s disease (AD), is derived by proteolysis from the β-amyloid precursor protein (βPP). The distribution and trafficking of cell surface βPP are of particular interest because some of these molecules are direct precursors of secreted Aβ and because the localization of βPP at the cell surface may be related directly to its physiological functions. Recently, we reported that, in cultured hippocampal neurons, cell surface βPP is preferentially expressed on axons in a striking discontinuous pattern. In this study, we describe the colocalization of cell surface βPP and integrins in primary cultured cells. In rat hippocampal neurons, cell surface βPP was colocalized selectively with α1β1 and α5β1 integrin heterodimers at these characteristic segmental locations. In rat cortical astrocytes, both cell surface βPP and β1 integrin were located at the cell periphery in the “spreading” stage shortly after plating. In “flattened” astrocytes cultured for several days, βPP was found in punctate deposits called point contacts. In these sites, βPP was colocalized with α1β1, but not with α5β1 integrin heterodimers, the latter of which were situated at focal contact sites. In both neurons and astrocytes examined after shearing, clathrin and α-adaptin were colocalized with βPP on the surface that directly contacts the substratum. These results are consistent with the putative role of βPP in cell adhesion and suggests that βPP either interacts with selected integrins or shares similar cellular machinery to promote cell adhesion.
Neuropathology of Degenerative Cell Death inCaenorhabditis elegans
Authors: Hall David H. , Gu Guoqiang , Garcı́a-Añoveros Jaime , Gong Lei , Chalfie Martin , Driscoll Monica
Published: April 2018

InCaenorhabditis elegansnecrosis-like neuronal death is induced by gain-of-function (gf) mutations in two genes,mec-4anddeg-1, that encode proteins similar to subunits of the vertebrate amiloride-sensitive epithelial Na+channel. We have determined the progress of cellular pathology in dying neurons via light and electron microscopy. The first detectable abnormality is an infolding of the plasma membrane and the production of small electron-dense whorls. Later, cytoplasmic vacuoles and larger membranous whorls form, and the cell swells. More slowly, chromatin aggregates and the nucleus invaginates. Mitochondria and Golgi are not dramatically affected until the final stages of cell death when organelles, and sometimes the cells themselves, lyse. Certain cells, including some muscle cells indeg-1animals, express the abnormal gene products and display a few membrane abnormalities but do not die. These cells either express the mutant genes at lower levels, lack other proteins needed to form inappropriately functioning channels, or are better able to compensate for the toxic effects of the channels. Overall, the ultrastructural changes in these deaths suggest that enhanced membrane cycling precedes vacuolation and cell swelling. The pathology ofmec-4(gf)anddeg-1(gf)cells shares features with that of genetic disorders with alterations in channel subunits, such as hypokalemic periodic paralysis in humans and theweavermouse, and with degenerative conditions, e.g., acute excitotoxic death. The initial pathology in all of these conditions may reflect attempts by affected cells to compensate for abnormal membrane proteins or functions.
Cloning, Characterization, and Expression of a G-Protein-Coupled Receptor fromLymnaea stagnalisand Identification of a Leucokinin-Like Peptide, PSFHSWSamide, as Its Endogenous Ligand
Authors: Cox Kingsley J. A. , Tensen Cornelis P. , Van der Schors Roel C. , Li Ka Wan , van Heerikhuizen Harm , Vreugdenhil Erno , Geraerts Wijnand P. M. , Burke Julian F.
Published: April 2018

Neuropeptides are known to be important signaling molecules in several neural systems of the pond snailLymnaea stagnalis. Although the functions of these peptides have been studied in many neurons, the nature of the postsynaptic signal transduction is mainly unknown. The cloning and characterization of neuropeptide receptors inLymnaeathus would be very valuable in further elucidating peptidergic pathways. Indirect evidence suggests that these neuropeptides operate via G-protein-coupled mechanisms indicating the presence of G-protein-coupled receptors as the initial postsynaptic targets. Here we describe the cloning of a neuropeptide receptor fromLymnaeaand the isolation of an endogenous ligand. This peptide, PSFHSWSamide, belongs to the leucokinin family of peptides, and, thus, thisLymnaeareceptor is the first example of a leucokinin-like neuropeptide receptor, representing a new subfamily of G-protein-coupled neuropeptide receptors.
Occurrence and Biosynthesis of Endogenous Cannabinoid Precursor,N-Arachidonoyl Phosphatidylethanolamine, in Rat Brain
Authors: Cadas Hugues , di Tomaso Emmanuelle , Piomelli Daniele
Published: April 2018

It has been suggested that anandamide (N-arachidonoylethanolamine), an endogenous cannabinoid substance, may be produced through Ca2+-stimulated hydrolysis of the phosphatidylethanolamine (PE) derivativeN-arachidonoyl PE. The presence ofN-arachidonoyl PE in adult brain tissue and the enzyme pathways that underlie its biosynthesis are, however, still undetermined. We report here that rat brain tissue contains both anandamide (11 ± 7 pmol/gm wet tissue) andN-arachidonoyl PE (22 ± 16 pmol/gm), as assessed by gas chromatography/mass spectrometry. We describe aN-acyltransferase activity in brain that catalyzes the biosynthesis ofN-arachidonoyl PE by transferring an arachidonate group from thesn-1 carbon of phospholipids to the amino group of PE. We also show thatsn-1 arachidonoyl phospholipids are present in brain, where they constitute ∼0.5% of total phospholipids.N-acyltransferase activity is Ca2+dependent and is enriched in brain and testis. Within the brain,N-acyltransferase activity is highest in brainstem; intermediate in cortex, striatum, hippocampus, medulla, and cerebellum; and lowest in thalamus, hypothalamus, and olfactory bulb. Pharmacological inhibition ofN-acyltransferase activity in primary cultures of cortical neurons prevents Ca2+-stimulatedN-arachidonoyl PE biosynthesis. Our results demonstrate, therefore, that rat brain tissue contains the complement of enzymatic activity and lipid substrates necessary for the biosynthesis of the anandamide precursorN-arachidonoyl PE. They also suggest that biosynthesis ofN-arachidonoyl PE and formation of anandamide are tightly coupled processes, which may concomitantly be stimulated by elevations in intracellular Ca2+occurring during neural activity.
Modulation of the Cloned Skeletal Muscle L-Type Ca2+Channel by Anchored cAMP-Dependent Protein Kinase
Authors: Johnson Barry D. , Brousal Jeffrey P. , Peterson Blaise Z. , Gallombardo Peter A. , Hockerman Gregory H. , Lai Yvonne , Scheuer Todd , Catterall William A.
Published: April 2018

Ca2+influx through skeletal muscle Ca2+channels and the force of contraction are increased in response to β-adrenergic stimulation and high-frequency electrical stimulation. These effects are thought to be mediated by cAMP-dependent phosphorylation of the skeletal muscle Ca2+channel. Modulation of the cloned skeletal muscle Ca2+channel by cAMP-dependent phosphorylation and by depolarizing prepulses was reconstituted by transient expression in tsA-201 cells and compared to modulation of the native skeletal muscle Ca2+channel as expressed in mouse 129CB3 skeletal muscle cells. The heterologously expressed Ca2+channel consisting of α1, α2δ, and β subunits gave currents that were similar in time course, current density, and dihydropyridine sensitivity to the native Ca2+channel. cAMP-dependent protein kinase (PKA) stimulation by Sp-5,6-DCl-cBIMPS (cBIMPS) increased currents through both native and expressed channels two- to fourfold. Tail currents after depolarizations to potentials between −20 and +80 mV increased in amplitude and decayed more slowly as either the duration or potential of the depolarization was increased. The time- and voltage-dependent slowing of channel deactivation required the activity of PKA, because it was enhanced by cBIMPS and reduced or eliminated by the peptide PKA inhibitor PKI (5–24) amide. This voltage-dependent modulation of the cloned skeletal muscle Ca2+channel by PKA also required anchoring of PKA by A-Kinase Anchoring Proteins because it was blocked by peptide Ht 31, which disrupts such anchoring. The results show that the skeletal muscle Ca2+channel expressed in heterologous cells is modulated by PKA at rest and during depolarization and that this modulation requires anchored protein kinase, as it does in native skeletal muscle cells.
Arg-Gly-Asp-Ser-Selective Adhesion and the Stabilization of Long-Term Potentiation: Pharmacological Studies and the Characterization of a Candidate Matrix Receptor
Authors: Bahr Ben A. , Staubli Ursula , Xiao Peng , Chun Daniel , Ji Zhan-Xin , Esteban Everard T. , Lynch Gary
Published: April 2018

Peptides known to block the extracellular interactions of adhesion receptors belonging to a subclass of the integrin family were tested for their effects on the stabilization of long-term potentiation (LTP) in hippocampal slices. Theta burst stimulation delivered after infusions of Gly-Ala-Val-Ser-Thr-Ala (GAVSTA) resulted in a potentiation effect that decayed steadily over a period of 40 min; LTP elicited in the presence of inactive control peptides remained stable over this time period. GAVSTA had no detectible influence on baseline responses, induction processes, or the initial degree of potentiation. Infusions of integrin antagonistsafterapplication of theta bursts also resulted in the occurrence of a decremental form of LTP. Affinity chromatography was then used in an effort to identify targets of the structurally dissimilar integrin blockers that disrupt LTP stabilization. Both integrin antagonists Gly-Arg-Gly-Asp-Ser-Pro and GAVSTA eluted a major species of 55 kDa (synaptegrin-1) from GRGDSP-affinity columns that had been loaded with solubilized synaptic membranes; lesser concentrations of three polypeptides of ∼20, 27, and 30 kDa were also collected. Synaptegrin-1 was labeled by antibodies to the RGDS-binding integrin α5β1. In addition, the synaptegrin, as well as the 27 kDa, protein was found to copurify with pre- and postsynaptic markers during the isolation of forebrain synaptosomes. These results indicate that a matrix recognition event occurring several minutes after induction of LTP is a necessary step in the stabilization of potentiated synapses; they also identify an integrin-like matrix receptor of 55 kDa that may contribute to this event.
Experience-Dependent Developmental Plasticity in the Optic Lobe ofDrosophila melanogaster
Authors: Barth Martin , Hirsch Helmut V. B. , Meinertzhagen Ian A. , Heisenberg Martin
Published: April 2018

Early experience can affect nervous system development in both vertebrate and invertebrate animals. We have now demonstrated that visual stimulation modifies the size of the optic lobes in the laboratory fruitflyDrosophila melanogaster. Monocular deprivation (painting over one eye) decreases the aggregate volume of the lamina, medulla, and lobula plate by up to 6%. The laminae of control flies kept in complete darkness showed a more robust volume difference that could be as much as 30%. An electron microscopy study revealed that the changes in the lamina are largely attributable to an increase in the terminals of the photoreceptor cell axons. The volume of the lamina increases during the first 24 hr after emergence, and it grows more in the light than in darkness. When flies are kept in the dark for the first 12 hr of their adult life and are then brought back to light for the next 3.5 days, the lamina is almost as small as in flies raised for 4 d in constant darkness. Twelve hour dark shifts at a later time are less effective. This finding suggests a critical period for lamina development during day 1 of the adult. The lamina depends on visual stimulation to maintain its size during the first 5 d after emergence. Dark-rearing for 1 d or more at any stage during that period decreases its volume to the level of flies raised in constant darkness. A lamina that is once reduced in size seems not to recover.
Bitter Taste Transduction of Denatonium in the MudpuppyNecturus maculosus
Authors: Ogura Tatsuya , Mackay-Sim Alan , Kinnamon Sue C.
Published: April 2018

Bitter substances are a structurally diverse group of compounds that appear to act via several transduction mechanisms. The bitter-tasting denatonium ion has been proposed to act via two different G-protein-regulated pathways, one involving inositol 1,4,5-trisphosphate and raised intracellular calcium levels, the other involving phosphodiesterase and membrane depolarization via a cyclic nucleotide-suppressible cation channel. The aim of the present study was to examine these transduction mechanisms in taste cells of the mudpuppyNecturus maculosusby calcium-imaging and whole-cell recording. Denatonium benzoate increased intracellular calcium levels and induced an outward current independently of extracellular calcium. The denatonium-induced increase in intracellular calcium was inhibited by U73122, an inhibitor of phospholipase C, and by thapsigargin, an inhibitor of calcium transport into intracellular stores. The denatonium-induced outward current was blocked by GDP-β-S, a blocker of G-protein activation. Neither resting nor denatonium-induced intracellular calcium levels were affected by inhibition of phosphodiesterase (with IBMX) or adenylate cyclase (with SQ22536) or by raising intracellular cyclic nucleotides directly (with cell permeant analogs). Our results support the hypothesis that denatonium is transduced via a G-protein cascade involving phospholipase C, inositol 1,4,5-trisphosphate, and raised intracellular calcium levels. Our results do not support the hypothesis that denatonium is transduced via phosphodiesterase and cAMP.
Aberrant Expression of Mitotic Cdc2/Cyclin B1 Kinase in Degenerating Neurons of Alzheimer’s Disease Brain
Authors: Vincent Inez , Jicha Gregory , Rosado Michelle , Dickson Dennis W.
Published: April 2018

We have shown previously that M-phase phospho-epitopes accumulate in neuronal tau proteins incorporated into the hallmark neurofibrillary tangles (NFT) of Alzheimer’s disease (AD). In M phase, the epitopes are produced by cdc2/cyclin B1 kinase by a highly conserved mechanism believed to be quiescent in terminally differentiated neurons of adult brain. To determine whether an M-phase mechanism is possible in AD neurons, we first investigated the presence of cdc2 and cyclin B1 in AD. Both proteins were enriched in neurons with NFT and in neurons susceptible to NFT. An antibody specific for catalytically active cdc2 stained numerous NFT-containing neurons in AD but did not react with normal neurons. Double-labeling studies showed that active cdc2 and cyclin B1 coexist in AD neurons and co-localize with AD-specific mitotic phospho-epitopes. Mitotic kinase purified from AD and normal brain, using the yeast p13suc1 protein as affinity ligand, showed higher histone H1 phosphorylation activity in AD. Accordingly, the levels of cdc2 and cyclin B1 in p13suc1 fractions from AD were higher than normal. Consistent with a physiological relationship between NFT and mitotic kinase, NFT proteins co-purified with and became phosphorylated by the p13suc1-bound kinasein vitro. Furthermore, cdc2/cyclin B1 is the only one of several proline-directed kinases that created the TG/MC mitotic phospho-epitopes in recombinant tauin vitro. These findings suggest that aberrantly reexpressed cdc2/cyclin B1 in NFT-bearing neurons in AD brain contributes to the generation of M-phase phospho-epitopes in NFT.
Dynamic Control of Location-Specific Information in Tactile Cutaneous Reflexes from the Foot during Human Walking
Authors: Van Wezel Bart M. H. , Ottenhoff Frans A. M. , Duysens Jacques
Published: April 2018

The purpose of the present study was to determine whether tactile cutaneous reflexes from the skin of the foot contain location-specific information during human walking. Muscular responses to non-nociceptive electrical stimulation of the sural, posterior tibial, and superficial peroneal nerves, each supplying a different skin area of the foot, were studied in both legs during walking on a treadmill. For all three nerves the major responses in all muscles were observed at a similar latency of ∼80–85 msec. In the ipsilateral leg these reflex responses and their phase-dependent modulation were highly nerve-specific. During most of the stance phase, for example, the peroneal and tibial nerves generally evoked small responses in the biceps femoris muscle. In contrast, during late swing large facilitations generally occurred for the peroneal nerve, whereas suppressions were observed for the tibial nerve. In the contralateral leg the reflex responses for the three nerves were less distinct, although some nerve specificity was observed for individual subjects. It is concluded that non-nociceptive stimulation of the sural, posterior tibial, and superficial peroneal nerves each evokes distinct reflex responses, indicating the presence of location-specific information from the skin of the foot in cutaneous reflexes during human walking. It will be argued that differentially controlled reflex pathways can account for the differences in the phase-dependent reflex modulation patterns of the three nerves, which points to the dynamic control of this information during the course of a step cycle.
Passive and Active Membrane Properties Contribute to the Temporal Filtering Properties of Midbrain NeuronsIn Vivo
Authors: Fortune Eric S. , Rose Gary J.
Published: April 2018

This study examined the contributions of passive and active membrane properties to the temporal selectivities of electrosensory neuronsin vivo. The intracellular responses to time-varying (2–30 Hz) electrosensory stimulation and current injection of 27 neurons in the midbrain of the weakly electric fishEigenmanniawere recorded. Each neuron was filled with biocytin to reveal its anatomy.

Neurons were divided into two biophysically distinct groups based on their frequency-dependent responses to sinusoidal current injection over the range 2–30 Hz. Fourteen neurons showed low-pass filtering, with a maximum decline in the amplitude of voltage responses of >2.6 dB (X= 4.30 dB,s= 1.10 dB) to sinusoidal current injection. These neurons also showed low-pass filtering of electrosensory information but with larger maximum declines in postsynaptic potential amplitude (X= 9.53 dB,s= 3.34 dB;n= 10). These neurons had broad dendritic arbors and relatively spiny dendrites. Five neurons showed all-pass filtering, having maximum decline in the amplitude of voltage responses of <2.0 dB (X= 1.16 dB,s= 0.61 dB). For electrosensory stimuli, however, these neurons showed low-, band-, or high-pass filtering. These neurons had small dendritic arbors and few or no spines.

Voltage-dependent “active” conductances were revealed in eight neurons by using several levels of current clamp. In four of these neurons, the duration of the voltage-dependent conductances decreased in concert with the period of the electrosensory stimulus, whereas in the other four neurons the duration of the voltage-dependent conductances was relatively short (<30 msec) and nearly constant across sensory stimulation frequencies. These conductances enhanced the temporal filtering properties of neurons.
Hippocampal Tissue Transplants Reverse Lesion-Induced Spatial Memory Deficits in Zebra Finches (Taeniopygia guttata)
Authors: Patel Sanjay N. , Clayton Nicky S. , Krebs John R.
Published: April 2018

The avian hippocampal formation (Hf) plays an important role in spatial memory for food storing. Here we examined the effects of excitotoxic lesions of the Hf and subsequent neural transplantation on a one-trial associative memory task in zebra finches. The results showed (1) that small ibotenic acid lesions of the dorsal Hf of zebra finches produced significant spatial memory impairments compared with controls, sham-lesioned birds, and prelesion performance; and (2) that Hf-lesioned birds given transplants of embryonic hippocampal (H) tissue, but not those given transplants of embryonic anterior telencephalon (AT) tissue, showed a significant reversal of the performance deficits on the spatial memory task. Lesioned-only birds and lesioned birds given H or AT transplants that did not survive did not show behavioral improvement. Sham-lesioned and untreated control birds maintained good performance throughout the experiment. The H and AT transplants were found to be growing partially within the Hf and partially within the underlying ventricle. The transplants appeared healthy and contained neurons with beaded and unbeaded fibers (shown by immunohistochemistry with antibodies to parvalbumin, substance P, and a 200 kDa neurofilament protein). Blood vessels and erythrocytes were also present within the transplants. The results show that neural transplants can survive within the bird brain and that small lesions of the Hf produce significant spatial memory deficits that can only be reversed by surviving homologous H transplants, and not by heterologous telencephalon transplants.
Molecular and Physiological Diversity of Cortical Nonpyramidal Cells
Authors: Cauli Bruno , Audinat Etienne , Lambolez Bertrand , Angulo Maria Cecilia , Ropert Nicole , Tsuzuki Keisuke , Hestrin Shaul , Rossier Jean
Published: April 2018

The physiological and molecular features of nonpyramidal cells were investigated in acute slices of sensory-motor cortex using whole-cell recordings combined with single-cell RT-PCR to detect simultaneously the mRNAs of three calcium binding proteins (calbindin D28k, parvalbumin, and calretinin) and four neuropeptides (neuropeptide Y, vasoactive intestinal polypeptide, somatostatin, and cholecystokinin). In the 97 neurons analyzed, all expressed mRNAs of at least one calcium binding protein, and the majority (n= 73) contained mRNAs of at least one neuropeptide. Three groups of nonpyramidal cells were defined according to their firing pattern. (1) Fast spiking cells (n= 34) displayed tonic discharges of fast action potentials with no accommodation. They expressed parvalbumin (n= 30) and/or calbindin (n= 19) mRNAs, and half of them also contained transcripts of at least one of the four neuropeptides. (2) Regular spiking nonpyramidal cells (n= 48) displayed a firing behavior characterized by a marked accommodation and presented a large diversity of expression patterns of the seven biochemical markers. (3) Finally, a small population of vertically oriented bipolar cells, termed irregular spiking cells (n= 15), fired bursts of action potentials at an irregular frequency. They consistently co-expressed calretinin and vasoactive intestinal polypeptide. Additional investigations of these cells showed that they also co-expressed glutamic acid decarboxylase and choline acetyl transferase. Our results indicate that neocortical nonpyramidal neurons display a large diversity in their firing properties and biochemical patterns of co-expression and that both characteristics could be correlated to define discrete subpopulations.
Development of Vasoactive Intestinal Peptide mRNA Rhythm in the Rat Suprachiasmatic Nucleus
Authors: Ban Yuriko , Shigeyoshi Yasufumi , Okamura Hitoshi
Published: April 2018

Development of the daily rhythm of vasoactive intestinal peptide (VIP) mRNA in the rat suprachiasmatic nucleus (SCN), a main locus of circadian oscillation, was investigated byin situhybridization. The phenotypic expression of VIP neurons occurred in two developmental stages in the ventrolateral portion of the SCN (VLSCN): the first was found before birth in the rostral part, and the second occurred in the main part between postnatal day (P) 10 and P20. The latter period coincided with the time that the massive VIP-efferent fibers project to the subparaventricular zone. In the adult and P20, the VIP mRNA signals of the SCN showed a clear diurnal rhythm with a trough in the light phase and a peak in the dark phase under light/dark (LD) conditions, but under constant dark (DD) conditions, no VIP mRNA fluctuations were observed. At P10, however, it was found that SCN VIP mRNA showed a peak at the transition from night to day and a trough at early dark period in LD conditions, in sharp contrast to the night peak in the adult rhythm. In DD conditions, a light-phase peak and a dark-phase trough were also observed at P10, contrasting the arrhythmic feature at adult stage. The present findings suggest that daily VIP rhythm was first generated in the early developed clock-controlled rostral SCN neurons, and later regulated by light-dependent main VLSCN neurons.
The Relationship between Curvature and Velocity in Two-Dimensional Smooth Pursuit Eye Movements
Authors: de’Sperati Claudio , Viviani Paolo
Published: April 2018

Curvature and tangential velocity of voluntary hand movements are constrained by an empirical relation known as the Two-Thirds Power Law. It has been argued that the law reflects the working of central control mechanisms, but it is not known whether these mechanisms are specific to the hand or shared also by other types of movement. Three experiments tested whether the power law applies to the smooth pursuit movements of the eye, which are controlled by distinct neural motor structures and a peculiar set of muscles. The first experiment showed that smooth pursuit of elliptic targets with various curvature–velocity relationships was most accurate when targets were compatible with the Two-Thirds Power Law. Tracking errors in all other cases reflected the fact that, irrespective of target kinematics, eye movements tended to comply with the law. Using only compatible targets, the second experiment demonstrated that kinematics per se cannot account for the pattern of pursuit errors. The third experiment showed that two-dimensional performance cannot be fully predicted on the basis of the performance observed when the horizontal and vertical components of the targets used in the first condition were tracked separately. We conclude that the Two-Thirds Power Law, in its various manifestations, reflects neural mechanisms common to otherwise distinct control modules.