bluuebunny/crossref_metadata_2025 huggingface dataset:
Reduction of Calcium Currents by Lambert–Eaton Syndrome Sera: Motoneurons Are Preferentially Affected, and L-Type Currents Are Spared
Authors: Garcı́a Kelly D. , Beam Kurt G.
Published: April 2018

Previous work has demonstrated that Lambert–Eaton syndrome (LES) antibodies reduce calcium currents in non-neuronal cells and sensory neurons and reduce the amplitude of extracellularly recorded currents at mouse motor nerve terminals. We compared effects of LES sera on whole-cell currents of cultured nerve and muscle. LES sera more strongly reduced calcium currents in motoneurons than in sensory neurons. Motoneuronal potassium currents were unaffected. The sera minimally affected calcium currents in skeletal and cardiac muscle. In motoneurons, both low voltage-activated (LVA) and high voltage-activated (HVA) components of calcium current were decreased, demonstrating that the sera targeted more than one calcium channel type. The HVA current remaining in LES-treated motoneurons was little affected by micromolar ω-conotoxin MVIIC but was reduced >70% by micromolar nimodipine. This pharmacological profile contrasts with untreated cells and suggests that LES sera primarily spare L-type currents in motoneurons.
Site Specificity of Short-Term and Long-Term Habituation in the Tail-Elicited Siphon Withdrawal Reflex ofAplysia
Authors: Stopfer Mark , Chen Xinghai , Tai Yu-Tzu , Huang Gloria S. , Carew Thomas J.
Published: April 2018

The study of habituation in animals with relatively simple nervous systems has contributed significantly to the understanding of mechanisms underlying learning and memory. Using the tail-elicited siphon withdrawal reflex ofAplysia, which is mediated in part by bilaterally symmetrical clusters of tail sensory neurons, we found that both short-term and long-term habituation can be restricted laterally, such that habituation produced by stimulation of one side of the tail does not generalize to the other side. Further experiments in this preparation revealed that long-term, laterally restricted habituation is sensitive to the temporal pattern with which stimuli are presented. We also determined that both short-term and long-term habituation can take place in a reduced behavioral preparation, and that short-term habituation can be restricted within relatively small stimulation sites located on the same side of the tail. These results provide insights into the cellular organization of habituation, and they provide a useful preparation for a cellular analysis of this basic form of learning.
Heterosynaptic Facilitation of Tail Sensory Neuron Synaptic Transmission during Habituation in Tail-Induced Tail and Siphon Withdrawal Reflexes ofAplysia
Authors: Stopfer Mark , Carew Thomas J.
Published: April 2018

In cellular studies of habituation, such as in the gill and siphon withdrawal reflex to tactile stimulation of the siphon ofAplysia, a mechanism that has emerged as an explanation for response decrement during habituation is homosynaptic depression at sensory neurons mediating the behavioral response. We have examined the contribution of homosynaptic depression to habituation in sensory neurons that contribute to two reflex behaviors inAplysia, tail withdrawal and siphon withdrawal, both elicited by threshold-level tail stimulation. In a companion paper (this issue), we reported that repeated tail stimulation, identical to that producing habituation in siphon withdrawal in freely moving animals, also produces habituation in reduced preparations. In this paper, we extend these behavioral findings by showing that in reduced preparations, identical tail stimulation also produces habituation of the tail withdrawal reflex. In addition, our cellular experiments show that (1) identified sensory and motor neurons in both reflex systems respond to identical repeated tail stimulation; in sensory neurons it produces a progressive decrease in spike number and increase in spike latency, and in motor neurons it produces progressive decrement in complex EPSPs and spike output. (2) Homosynaptic depression of the tail sensory neuron to tail motor neuron synapse does occur when the sensory neurons are activated repetitively by intracellular current. (3) Homosynaptic depression at this synapse does not occur when the sensory neurons are activated repetitively by threshold-level tail stimuli that elicit the behavioral reflex and cause habituation; rather, the sensory neurons exhibit significant heterosynaptic facilitation. Thus, in these reflexes, habituation is not accompanied by homosynaptic depression at the sensory neurons, suggesting that the plasticity underlying habituation occurs primarily at interneuronal sites.
Activation of Intrinsic and Synaptic Currents in Leech Heart Interneurons by Realistic Waveforms
Authors: Olsen Øystein H. , Calabrese Ronald L.
Published: April 2018

Leech heart interneurons were voltage-clamped with realistic waveforms to investigate the currents underlying the oscillation in the cells. By estimating the leak current parameters in regions in which there was little contamination by voltage-gated currents, it was possible to measure the Ca2+current, the persistent Na+current,IP, and the hyperpolarization-activated inward current,Ih.

The experiments verified a prediction of a computer model of HN cells that the shape of the typical waveform was such that the low-threshold Ca2+currents were partially inactivated during a slow up-ramp to a plateau potential. A step within the same range of the membrane potential as the realistic waveform produced >4 times as much Ca2+current. In two-cell voltage-clamp experiments, the step produced 20 times more graded inhibition than the normal presynaptic waveform. When the presynaptic heart interneuron oscillated with spikes, the graded inhibition was larger. The difference may arise from integration of a slowly decaying component of the spike-mediated inhibition.

The persistent Na+current had a very low threshold. During the most hyperpolarized phase of the waveform,IPdeactivated to 50% of its maximum conductance. A substantial part ofIP, therefore, was effectively contributing to the leak current in the HN cells.

The h-current increased for waveforms that had longer periods, whereas increasing the h-current in the model reduced the period. The h-current thus provides negative feedback to perturbations that alter the period of the oscillation.
The α1ECalcium Channel Exhibits Permeation Properties Similar to Low-Voltage-Activated Calcium Channels
Authors: Bourinet Emmanuel , Zamponi Gerald W. , Stea Anthony , Soong Tuck W. , Lewis Bertram A. , Jones Lisa P. , Yue David T. , Snutch Terry P.
Published: April 2018

The physiological and pharmacological properties of the α1Ecalcium (Ca) channel subtype do not exactly match any of the established categories described for native neuronal Ca currents. Many of the key diagnostic features used to assign cloned Ca channels to their native counterparts, however, are dependent on a number of factors, including cellular environment, β subunit coexpression, and modulation by second messengers and G-proteins. Here, by examining the intrinsic pore characteristics of a family of transiently expressed neuronal Ca channels, we demonstrate that the permeation properties of α1Eclosely resemble those described for a subset of low-threshold Ca channels. The α1A(P-/Q-type), α1B(N-type), and α1C(L-type) high-threshold Ca channels all exhibit larger whole-cell currents with barium (Ba) as the charge carrier as compared with Ca or strontium (Sr). In contrast, macroscopic α1Ecurrents are largest in Sr, followed by Ca and then Ba. The unique permeation properties of α1Eare maintained at the single-channel level, are independent of the nature of the expression system, and are not affected by coexpression of α2and β subunits. Overall, the permeation characteristics of α1Eare distinct from those described for R-type currents and share some similarities with native low-threshold Ca channels.
Precision of Reinnervation and Synaptic Remodeling Observed in Neuromuscular Junctions of Living Frogs
Authors: Astrow Stephanie H. , Pitaevski Vladimir , Herrera Albert A.
Published: April 2018

Repeatedin vivoobservations were used to study regenerated nerve terminals in neuromuscular junctions of the adult frogRana pipiens. Sartorius junctions in living animals were stained with the fluorescent vital dye RH414 and viewed with video fluorescence microscopy. Each junction was observed in the intact muscle and then again 7, 10, and 13 weeks after nerve crush. At 13 weeks, junctions were determined to be mono- or polyneuronally innervated using intracellular recording. Between 7 and 13 weeks, most identified junctions were reinnervated less precisely and completely than described previously. Although some of the original synaptic gutters were reoccupied by regenerated terminal branches, other gutters were only partially occupied, and many appeared abandoned. Junctions showing precise recapitulation of original terminal arborizations comprised a small number of the total examined, as did those where reinnervation was very imprecise. Striking differences in the precision of reinnervation were found within the muscle such that distal terminals regenerated more precisely and completely than did proximal terminals. Terminals in reinnervated muscles were more dynamic than terminals in unoperated muscles over equivalent times. In singly innervated junctions, terminal growth was favored over regression. In doubly innervated junctions, regressive events were more common. Imprecise reinnervation is explained in terms of multisite innervation of muscle fibers and the activity dependence of synaptic stability. We hypothesize that when axons reinnervate the second or third junctions on a fiber, they do so less precisely, because the activity restored by reinnervation of the first junction renders later sites less attractive or less stable.
Melanocortin Antagonists Define Two Distinct Pathways of Cardiovascular Control by α- and γ-Melanocyte-Stimulating Hormones
Authors: Li Si-Jia , Varga Károly , Archer Phillip , Hruby Victor J. , Sharma Shubh D. , Kesterson Robert A. , Cone Roger D. , Kunos George
Published: April 2018

Melanocortin peptides and at least two subtypes of melanocortin receptors (MC3-R and MC4-R) are present in brain regions involved in cardiovascular regulation. In urethane-anesthetized rats, unilateral microinjection of α-melanocyte-stimulating hormone (MSH) into the medullary dorsal–vagal complex (DVC) causes dose-dependent (125–250 pmol) hypotension and bradycardia, whereas γ-MSH is less effective. The effects of α-MSH are inhibited by microinjection to the same site of the novel MC4-R/MC3-R antagonist SHU9119 (2–100 pmol) but not naloxone (270 pmol), whereas the similar effects of intra-DVC injection of β-endorphin (1 pmol) are inhibited by naloxone and not by SHU9119. Hypotensive and bradycardic responses to electrical stimulation of the arcuate nucleus also are inhibited by ipsilateral intra-DVC microinjection of SHU9119. γ-MSH and ACTH(4–10), but not α-MSH, elicit dose-dependent (0.1–12.5 nmol) pressor and tachycardic effects, which are much more pronounced after intracarotid than after intravenous administration. The effects of γ-MSH (1.25 nmol) are not inhibited by the intracarotid injection of SHU9119 (1.25–12.5 nmol) or the novel MC3-R antagonist SHU9005 (1.25–12.5 nmol). We conclude that the hypotension and bradycardia elicited by the release of α-MSH from arcuate neurons is mediated by neural melanocortin receptors (MC4-R/MC3-R) located in the DVC, whereas the similar effects of β-endorphin, a peptide derived from the same precursor, are mediated by opiate receptors at the same site. In contrast, neither MC3-R nor MC4-R is involved in the centrally mediated pressor and tachycardic actions of γ-MSH, which, likely, are mediated by an as yet unidentified receptor.
Behavioral and Neurochemical Recovery from Partial 6-Hydroxydopamine Lesions of the Substantia Nigra Is Blocked by Daily Treatment with Glutamate Receptor Antagonists MK-801 and CPP
Authors: Emmi Adriana , Rajabi Heshmat , Stewart Jane
Published: April 2018

To determine whether glutamate plays a role in the recovery from lesions of the substantia nigra, measures of behavioral functioning and extracellular levels of striatal dopamine (DA) were made after partial unilateral 6-OHDA lesions in adult male rats. In experiments 1 and 2, animals were treated on days 1–8 after lesioning with the noncompetitive NMDA receptor antagonist dizocilpine maleate (MK-801; 0.25 mg/kg, i.p.) or saline, and in experiment 3 with the competitive antagonist 3-[(±)-2-carboxypiperazin-4-yl]-propyl-1-phosphonic acid (CPP; 1.0 mg/kg, i.p.) or saline. In experiment 1, behavior was assessed 3 and 8 d after lesioning before daily drug treatment; on days 9 and 10, basal extracellular DA and metabolites were measured in both striata using microdialysis. In experiments 2 and 3, behavior was assessed on days 3 and 15 and microdialysis on days 16 and 17, 8–9 d post-termination of drug treatments. On day 3, all animals turned ipsilateral to the lesion. On days 8 or 15, saline-treated animals showed no behavioral asymmetries, whereas MK-801- and CPP-treated animals turned ipsilaterally. In antagonist-treated animals, basal levels of extracellular DA were lower on the lesioned side whether measured 9–10 or 16–17 d after lesioning, whereas in saline-treated animals DA levels on the two sides did not differ. These results suggest that glutamate plays a role in the development of compensatory changes in the DA neurons that accompany behavioral recovery from partial lesions of nigrostriatal DA system.
Neurotoxic Lesions of Basolateral, But Not Central, Amygdala Interfere with Pavlovian Second-Order Conditioning and Reinforcer Devaluation Effects
Authors: Hatfield Tammy , Han Jung-Soo , Conley Michael , Gallagher Michela , Holland Peter
Published: April 2018

Considerable evidence suggests that various discrete nuclei within the amygdala complex are critically involved in the assignment of emotional significance or value to events through associative learning. Much of this evidence comes from aversive conditioning procedures. For example, lesions of either basolateral amygdala (ABL) or the central nucleus (CN) interfere with the acquisition or expression of conditioned fear. The present study examined the effects of selective neurotoxic lesions of either ABL or CN on the acquisition of positive incentive value by a conditioned stimulus (CS) with two appetitive Pavlovian conditioning procedures. In second-order conditioning experiments, rats first received light–food pairings intended to endow the light with reinforcing power. The acquired reinforcing power of the light was then measured by examining its ability to serve as a reinforcer for second-order conditioning of a tone when tone–light pairings were given in the absence of food. Acquisition of second-order conditioning was impaired in rats with ABL lesions but not in rats with CN lesions. In reinforcer devaluation procedures, conditioned responding of rats with ABL lesions was insensitive to postconditioning changes in the value of the reinforcer, whereas rats with CN lesions, like normal rats, were able to spontaneously adjust their CRs to the current value of the reinforcer. The results of both test procedures indicate that ABL, but not CN, is part of a system involved in CSs’ acquisition of positive incentive value. Together with evidence that identifies a role for CN in certain changes in attentional processing of CSs in conditioning, these results suggest that separate amygdala subsystems contribute to a variety of processes inherent in associative learning.
Allergic Inflammation in Isolated Vagal Sensory Ganglia Unmasks Silent NK-2 Tachykinin Receptors
Authors: Weinreich Daniel , Moore Kimberly A. , Taylor Glen E.
Published: April 2018

Neuroplastic changes in vagal afferents inflicted by allergic inflammation were examined in nodose ganglia (NG) removed from guinea pigs immunized to chick ovalbumin. In control NG neurons, substance P (SP; 0.1–10 μm) produces no discernable changes in membrane electrophysiological properties or [Ca2+]i. After exposing NG from immunized animals to the sensitizing antigenin vitro, 83% of the neurons were depolarized by 100 nmSP. SP also produces an inward current, an increase in membrane conductance, and an elevation of [Ca2+]i. Buffering [Ca2+]iwith BAPTA blocked the [Ca2+]irise and the SP depolarization, indicating that internal stores of Ca2+are required. When protein synthesis was inhibited >96% (as determined by [3H] leucine incorporation), antigen challenge still unmasked SP responses. The SP response was maximal 30 min after antigen challenge, and it was evident for at least 8 hr in intact ganglia and for 3.5 d in isolated neurons. [β-Ala8]Neurokinin A ([β-Ala8]NKA; 10 nm), an NK-2 selective agonist, mimicked SP; selective NK-1 and NK-3 agonists were ineffective. The EC50values for SP and [β-Ala8]NKA membrane currents were 78 and 33 nm, respectively. Additionally, SR48968, an NK-2 receptor antagonist, blocked these responses. Thus, antigen challenge appears to unmask an NK-2 tachykinin receptor. These data further support the hypothesis that inflammatory mediators released during immediate hypersensitivity (allergic) reactions can produce profound effects on the excitability of sensory nerves. Unmasked NK-2 receptors may serve an excitatory autoreceptor function, provide a pathway for paracrine signaling between NG neurons, and contribute to ectopic sensory nerve activity.
Active Polysomes Are Present in the Large Presynaptic Endings of the Synaptosomal Fraction from Squid Brain
Authors: Crispino M. , Kaplan B. B. , Martin R. , Alvarez J. , Chun J. T. , Benech J. C. , Giuditta A.
Published: April 2018

Previous data have suggested that the large nerve terminals present in the synaptosomal fraction from squid optic lobe are capable of protein synthesis (Crispino et al., 1993a,b). We have further examined this issue by comparing the translation products of synaptosomal and microsomal polysomes. Both preparations programmed an active process of translation, which was completely abolished by their previous treatment with EDTA. After immunoabsorption of the newly synthesized neurofilament (NF) proteins, the labeling ratio of the 60 and 70 kDa NF proteins was found to differ, in agreement with comparable differences obtained with intact synaptosomes. These observations indicate that the set of mRNAs translated by synaptosomes differs from that translated by nerve cell bodies. Hence, because NF proteins are neuron-specific, they support the view that the active synaptosomal polysomes are mostly localized in the large nerve terminals that represent the most abundant neuronal component of the fraction. This hypothesis was confirmed (1) by electron spectroscopic data demonstrating the presence of ribosomes and polysomes within the large nerve endings of the synaptosomal fraction, as well as in the carrot-like nerve endings of the retinal photoreceptors that constitute the only large terminals in the optic lobe, and (2) by light and high resolution autoradiography of synaptosomal samples incubated with [3H]leucine, showing that most labeled proteins are associated with the large nerve endings. This response was abolished by cycloheximide. Taken together, the data provide the first unequivocal demonstration that presynaptic nerve terminals are capable of protein synthesis.
Aggregated Amyloid-β Protein Induces Cortical Neuronal Apoptosis and Concomitant “Apoptotic” Pattern of Gene Induction
Authors: Estus Steven , Tucker H. Michael , van Rooyen Corlia , Wright Sarah , Brigham Elizabeth F. , Wogulis Mark , Rydel Russell E.
Published: April 2018

To gain a molecular understanding of neuronal responses to amyloid-β peptide (Aβ), we have analyzed the effects of Aβ treatment on neuronal gene expressionin vitroby quantitative reverse transcription-PCR andin situhybridization. Treatment of cultured rat cortical neurons with Aβ1–40results in a widespread apoptotic neuronal death. Associated with death is an induction of several members of the immediate early gene family. Specifically, we (1) report the time-dependent and robust induction ofc-jun,junB,c-fos, andfosB, as well astransin, which is induced by c-Jun/c-Fos heterodimers and encodes an extracellular matrix protease; these gene inductions appear to be selective because other Jun and Fos family members, i.e.,junDandfra-1, are induced only marginally; (2) show that thec-juninduction is widespread, whereasc-fosexpression is restricted to a subset of neurons, typically those with condensed chromatin, which is a hallmark of apoptosis; (3) correlate gene induction and neuronal death by showing that each has a similar dose–response to Aβ; and (4) demonstrate that both cell death and immediate early gene induction are dependent on Aβ aggregation state. This overall gene expression pattern during this “physiologically inappropriate” apoptotic stimulus is markedly similar to the pattern we previously identified after a “physiologically appropriate” stimulus, i.e., the NGF deprivation-induced death of sympathetic neurons. Hence, the parallels identified here further our understanding of the genetic alterations that may lead neurons to apoptosis in response to markedly different insults.
Mosaics of Islet-1-Expressing Amacrine Cells Assembled by Short-Range Cellular Interactions
Authors: Galli-Resta Lucia , Resta Giovanni , Tan Seong-Seng , Reese Benjamin E.
Published: April 2018

The nervous system has a modular architecture with neurons of the same type commonly organized in nonrandom arrays or mosaics. Modularity is essential to parallel processing of sensory information and has provided a key element for brain evolution, but we still know very little of the way neuronal mosaics form during development. Here we have identified the immature elements of two retinal mosaics, the choline acetyltransferase (ChAT) amacrine cells, by their early expression of the homeodomain protein Islet-1, and we show that spatial ordering is an intrinsic property of the two Islet-1 mosaics, dynamically maintained while new elements are inserted into the mosaics. Migrating Islet-1 cells do not show this spatial ordering, indicating that they must move tangentially as they enter the mosaic, under the action of local mechanisms. Clonal territory analysis in X-inactivation transgenic mice confirms the lateral displacement of ChAT amacrine cells away from their clonal columns of origin, and mathematical models show how short-range cellular interactions can guide the assemblage of these mosaics via a simple biological rule.
In VitroSynaptogenesis between the Somata of IdentifiedLymnaeaNeurons Requires Protein Synthesis But Not Extrinsic Growth Factors or Substrate Adhesion Molecules
Authors: Feng Zhong-Ping , Klumperman Judith , Lukowiak Ken , Syed Naweed I.
Published: April 2018

Nerve growth factors, substrate and cell adhesion molecules, and protein synthesis are considered necessary for most developmental programs, including cell proliferation, migration, differentiation, axogenesis, pathfinding, and synaptic plasticity. Their direct involvement in synapse formation, however, has not yet been fully determined. The neurite outgrowth that precedes synaptogenesis is contingent on protein synthesis, the availability of externally supplied growth factors, and substrate adhesion molecules. It is therefore difficult to ascertain whether these factors are also needed for synapse formation. To examine this issue directly we reconstructed synapses between the cell somata of identifiedLymnaeaneurons. We show that when paired in the presence of brain conditioned medium (CM), mutual inhibitory chemical synapses between neurons right pedal dorsal 1 (RPeD1) and visceral dorsal 4 (VD4) formed in a soma–soma configuration (86%;n= 50). These synapses were reliable and target cell specific and were similar to those seen in the intact brain. To test whether synapse formation between RPeD1 and VD4 requiredde novoprotein synthesis, the cells were paired in the presence of anisomycin (a nonspecific protein synthesis blocker). Chronic anisomycin treatment (18 hr) after cell pairing completely blocked synaptogenesis between RPeD1 and VD4 (n= 24); however, it did not affect neuronal excitability or responsiveness to exogenously applied transmitters (n= 7), nor did chronic anisomycin treatment affect synaptic transmission between pairs of cells that had formed synapses (n= 5). To test the growth and substrate dependence of synapse formation, RPeD1 and VD4 were paired in the absence of CM [defined medium; (n= 22)] on either plain plastic culture dishes (n= 10) or glass coverslips (n= 10). Neither CM nor any exogenous substrate was required for synapse formation. In summary, our data provide direct evidence that synaptogenesis in this system requires specific, cell contact-induced,de novoprotein synthesis but does not depend on extrinsic growth factors or substrate adhesion molecules.
Organization of Corticostriatal and Corticoamygdalar Projections Arising from the Anterior Inferotemporal Area TE of the Macaque Monkey: APhaseolus vulgarisLeucoagglutinin Study
Authors: Cheng K. , Saleem K. S. , Tanaka K.
Published: April 2018

Corticostriatal and corticoamygdalar projections arising from area TE of the macaque monkey were studied by focal injections of the anterograde tracerPhaseolus vulgarisleucoagglutinin into the dorsolateral and ventromedial subdivisions of the anterior TE (TEad and TEav, respectively). This approach yielded several new results. First, the global distributions of labeled terminals revealed that both TEad and TEav projected to the ventrocaudal striatum, including the tail of the caudate nucleus and the adjacent ventral putamen, and the dorsolateral aspect of the deep amygdaloid nuclei. TEav also projected to the medial basal nucleus of the amygdala and the ventral striatum. Second, the reconstructed single axons (n= 18) demonstrated that some axons originating from TEav or TEad projected simultaneously to the ventrocaudal striatum and the dorsolateral aspect of the deep amygdaloid nuclei by giving off collaterals. TEav axons projected to the medial basal nucleus of the amygdala also had collaterals projecting to the perirhinal cortex or area TG. And third, it was revealed that the axons originating from a focal TEav or TEad projected to a restricted territory (3.4–3.6 mm rostrocaudally) in the ventrocaudal striatum with four to six dispersed, rostrocaudally elongated, rod-like modules. Individual axons with multiple arbors innervated many of these modules. These findings add the evidence that the anterior part of TE is anatomically heterogeneous and suggest that the deep amygdaloid nuclei may be functionally dissociated, with the dorsolateral aspect more closely related to the ventrocaudal striatum and the medial basal nucleus more closely related to the perirhinal cortex.
A Quantitative Description of Short-Term Plasticity at Excitatory Synapses in Layer 2/3 of Rat Primary Visual Cortex
Authors: Varela Juan A. , Sen Kamal , Gibson Jay , Fost Joshua , Abbott L. F. , Nelson Sacha B.
Published: April 2018

Cortical synapses exhibit several forms of short-term plasticity, but the contribution of this plasticity to visual response dynamics is unknown. In part, this is because the simple patterns of stimulation used to probe plasticityin vitrodo not correspond to patterns of activity that occurin vivo. We have developed a method of quantitatively characterizing short-term plasticity at cortical synapses that permits prediction of responses to arbitrary patterns of stimulation. Synaptic responses were recorded intracellularly as EPSCs and extracellularly as local field potentials in layer 2/3 of rat primary visual cortical slices during stimulation of layer 4 with trains of electrical stimuli containing random mixtures of frequencies. Responses exhibited complex dynamics that were well described by a simple three-component model consisting of facilitation and two forms of depression, a stronger form that decayed exponentially with a time constant of several hundred milliseconds and a weaker, but more persistent, form that decayed with a time constant of several seconds. Parameters obtained from fits to one train were used to predict accurately responses to other random and constant frequency trains. Control experiments revealed that depression was not caused by a decrease in the effectiveness of extracellular stimulation or by a buildup of inhibition. Pharmacological manipulations of transmitter release and postsynaptic sensitivity suggested that both forms of depression are mediated presynaptically. These results indicate that firing evoked by visual stimuli is likely to cause significant depression at cortical synapses. Hence synaptic depression may be an important determinant of the temporal features of visual cortical responses.
Identification of a Sex-Specific Quantitative Trait Locus Mediating Nonopioid Stress-Induced Analgesia in Female Mice
Authors: Mogil Jeffrey S. , Richards Susan P. , O’Toole Laurie A. , Helms Melinda L. , Mitchell Steve R. , Kest Benjamin , Belknap John K.
Published: April 2018

It is increasingly appreciated that the sexes differ in their perception of noxious stimuli and in their responsivity to exogenous and endogenous analgesic manipulations. We previously reported the existence of qualitative sex differences in the neurochemical mediation of nonopioid (i.e., naloxone-insensitive) stress-induced analgesia (SIA) produced by forced swims and suggested that female mice possess a sex-specific SIA mechanism. This female-specific system is now known to be estrogen-dependent, to be ontogenetically organized, and to vary with reproductive status; however, its neurochemical identity remains obscure. In an attempt to identify candidate genes underlying SIA in both sexes, we performed a two-phase quantitative trait locus (QTL) mapping experiment using the BXD/Ty recombinant inbred (RI) set derived from DBA/2J (D2) and C57BL/6J (B6) inbred mouse strains and (B6xD2)F2hybrid mice derived from these same progenitors. All mice were subjected to 3 min forced swims in 15°C water; nociceptive sensitivity on the 54°C hot-plate assay was assessed immediately before and 2 min after cessation of the swim. We report the localization of a QTL statistically associated with SIA magnitude [p= 0.00000012; logarithm of the odds (LOD) = 6.1] in female mice only. This female-specific QTL, which we nameFsia1, is located on chromosome 8 at 52–84 cM from the centromere and accounts for 17–26% of the overall trait variance in this sex. The present data provide further evidence of the existence of a female-specific SIA mechanism and highlight the important role of both genetic background and gender in the inhibition of pain.
The Photovoltage of Macaque Cone Photoreceptors: Adaptation, Noise, and Kinetics
Authors: Schneeweis David M. , Schnapf Julie L.
Published: April 2018

Whole-cell voltage and current recordings were obtained from red and green cone photoreceptors in isolated retina from macaque monkey. It was demonstrated previously that the cone photovoltage is generated from two sources, phototransduction current in the cone outer segment and photocurrent from neighboring rods. Rod signals are likely transmitted to cones across the gap junctions between rods and cones. In this study, the “pure” cone and rod components of the response were extracted with rod-adapting backgrounds or by subtracting the responses to flashes of different wavelength equated in their excitation of either rods or cones. For dim flashes, the pure cone component was similar in waveform to the cone outer segment current, and the rod component was similar to the photovoltage measured directly in rods. With bright flashes, the high frequencies of the rod signal were filtered out by the rod/cone network. The two components of the cone photovoltage adapted separately to background illumination. The amplitude of the rod component was halved by backgrounds eliciting ∼100 photoisomerizations sec−1per rod; the cone component was halved by backgrounds of 8700 photoisomerizations sec−1per cone. Coupling between rods and cones was not modulated by either dim backgrounds or dopamine. Voltage noise in dark-adapted cones was dominated by elementary events other than photopigment isomerizations. The dark noise was equivalent in magnitude to a steady light eliciting ∼3800 photoisomerizations sec−1per cone, a value significantly higher than the psychophysical estimates of cone “dark light.”
Uptake of Precursor and Synthesis of Transmitter in a Histaminergic Photoreceptor
Authors: Morgan Jennifer R. , Gebhardt Kelley A. , Stuart Ann E.
Published: April 2018

As a first step in understanding how the supply of the neurotransmitter histamine is maintained in a photoreceptor, we followed the uptake and metabolism of the immediate precursor of histamine, histidine. [3H]Histidine taken up into photoreceptors and glia was detected using autoradiography, and synthesis of [3H]histamine from [3H]histidine was assayed with thin-layer chromatography. Photoreceptors from barnacles were pulsed (15 min) with [3H]histidine (0.2–200 μm), then maintained in normal saline for up to 24 hr. Autoradiography showed that photoreceptor somata, axons, and presynaptic arbors were labeled, but only weakly, like (nonhistaminergic) ganglion cells. Label instead was concentrated over surrounding glia. Stimulating preparations with light did not increase photoreceptor labeling. Grain counts from photoreceptor axons showed uptake of [3H]histidine into these neurons by a Na+-dependent mechanism with aKmof ∼50 μm. Over 24 hr only 1% of the [3H]histidine taken up by preparations was converted to [3H]histamine either in the dark or in the light. Injections of [3H]histidine directly into photoreceptors established that synthesis takes place within the photoreceptors and confirmed that stimulation with light did not measurably affect the rate of conversion of [3H]histidine to [3H]histamine. These results suggest thatde novosynthesis of transmitter is unlikely to be as important as its reuptake in maintaining neurotransmitter supply in these photoreceptor terminals. In support of this conclusion, photoreceptors accumulated more label when transmitter release was stimulated with high K+and histamine uptake was antagonized with chlorpromazine.
BEN/SC1/DM-GRASP Expression during Neuromuscular Development: a Cell Adhesion Molecule Regulated by Innervation
Authors: Fournier-Thibault C. , Pourquié O. , Rouaud T. , Le Douarin N. M.
Published: April 2018

BEN/SC1/DM-GRASP is a cell adhesion molecule belonging to the Ig superfamily that is transiently expressed during avian embryogenesis in a variety of cell types, including the motoneurons of the spinal cord. We have investigated the pattern of BEN expression during neuromuscular development of the chick. We show that both motoneurons and their target myoblasts express BEN during early embryonic development and that the protein becomes restricted at neuromuscular contacts as soon as postsynaptic acetylcholine receptor clusters are observed in muscle fibers. Muscle cells grownin vitroexpress and maintain BEN expression even when they fuse and give rise to mature myotubes. When embryos are deprived of innervation by neural tube ablation, BEN expression is observed in muscle fibers, whereas, in control, the protein is already restricted at neuromuscular synaptic sites. These results demonstrate that all myogenic cells intrinsically express BEN and maintain the protein in the absence of innervation.

Conversely, when neurons are added to myogenic cultures, BEN is rapidly downregulated in muscle cells, demonstrating that innervation controls the restricted pattern of BEN expression seen in innervated muscles. After nerve section in postnatal muscles, BEN protein becomes again widely spread over muscle fibers. When denervated muscles are allowed to be reinnervated, the protein is reexpressed in regenerating motor axons, and reinnervation of synaptic sites leads to the concentration of BEN at neuromuscular junctions.

Our results suggest that BEN cell adhesion molecule acts both in the formation of neuromuscular contacts during development and in the events leading to muscle reinnervation.
Gonadal Steroids Promote Glial Differentiation and Alter Neuronal Morphology in the Developing Hypothalamus in a Regionally Specific Manner
Authors: Mong Jessica A. , Glaser Edmund , McCarthy Margaret M.
Published: April 2018

One of the more striking sexual dimorphisms in the adult brain is the synaptic patterning in some hypothalamic nuclei. In the arcuate nucleus (ARC) males have twice the number of axosomatic and one-half the number of axodendritic spine synapses as females. The opposite pattern is observed in the immediately adjacent ventromedial nucleus (VMN). In both cases, early exposure to testosterone dictates adult dimorphism, but the exact timing, mechanism, and site of steroid action remain unknown. Astrocytes also exhibit sexual dimorphisms, and their role in mediating neuronal morphology is becoming increasingly evident. Using Golgi-Cox impregnation to examine neuronal morphology and glial fibrillary acidic protein immunoreactivity (GFAP-IR) to characterize astrocytic morphology, we compared structural differences in dendrites and astrocytes from the ARC and VMN in postnatal day 2 rat pups from four hormonally different groups. Consistent with previous observations, testosterone exposure induced a rapid and dramatic stellation response in ARC astrocytes. Coincident with this change in astrocytic morphology was a 37% reduction in the density of dendritic spines on ARC neurons. In contrast, astrocytes in the VMN were poorly differentiated and did not respond to testosterone exposure, nor were there any changes in neuronal dendrite spine density. However, VMN neurons exposed to testosterone had almost double the number of branches compared with that in controls. These data suggest that the degree of maturation and the differentiation of hypothalamic astrocytesin vivoare correlated with the ability of neurons to sprout branches or spines in response to steroid hormones and may underlie regionally specific differences in synaptic patterning.
Optokinetic and Vestibular Stimulation Determines the Spatial Orientation of Negative Optokinetic Afternystagmus in the Rabbit
Authors: Pettorossi Vito E. , Errico Pierangelo , Ferraresi Aldo , Barmack Neal H.
Published: April 2018

Prolonged binocular optokinetic stimulation (OKS) in the rabbit induces a high-velocity negative optokinetic afternystagmus (OKAN II) that persists for several hours. We have taken advantage of this uniform nystagmus to study how changes in static head orientation in the pitch plane might influence the orientation of the nystagmus. After horizontal OKS, the rotation axis of the OKAN II remained almost constant in space as it was kept aligned with the gravity vector when the head was pitched by as much as 80° up and 35° down. Moreover, during reorientation, slow-phase eye velocity decreased according to the head pitch angle.

Thereafter, we analyzed the space orientation of OKAN II after optokinetic stimulation during which the head and/or the OKS were pitched upward and downward. The rotation axis of OKAN II did not remain aligned with an earth vertical axis nor a head vertical axis, but it tended to be aligned with that of the OKS respace. The slow-phase eye velocity of OKAN II was also affected by the head pitch angle during OKS, because maximal OKAN II velocity occurred at the same head pitch angle as that during optokinetic stimulation.

We suggest that OKAN II is coded in gravity-centered rather than in head-centered coordinates, but that this coordinate system may be influenced by optokinetic and vestibular stimulation. Moreover, the velocity attenuation of OKAN II seems to depend on the mismatch between the space-centered nystagmus rotation axis orientation and that of the “remembered” head-centered optokinetic pathway activated by OKS.
Rapid Induction of Functional and Morphological Continuity between Severed Ends of Mammalian or Earthworm Myelinated Axons
Authors: Lore April B. , Hubbell Jeffery A. , Bobb David S. , Ballinger Martis L. , Loftin Keisha L. , Smith Jeffory W. , Smyers Mark E. , Garcia Habacuc D. , Bittner George D.
Published: April 2018

The inability to rapidly restore the loss of function that results from severance (cutting or crushing) of PNS and CNS axons is a severe clinical problem. As a novel strategy to help alleviate this problem, we have developedin vitroprocedures using Ca2+-free solutions of polyethylene glycol (PEG solutions), which within minutes induce functional and morphological continuity (PEG-induced fusion) between the cut or crushed ends of myelinated sciatic or spinal axons in rats. Using a PEG-based hydrogel that binds to connective tissue to provide mechanical strength at the lesion site and is nontoxic to nerve tissues in earthworms and mammals, we have also developedin vivoprocedures that permanently maintain earthworm myelinated medial giant axons whose functional and morphological integrity has been restored by PEG-induced fusion after axonal severance. In all thesein vitroorin vivoprocedures, the success of PEG-induced fusion of sciatic or spinal axons and myelinated medial giant axons is measured by the restored conduction of action potentials through the lesion site, the presence of intact axonal profiles in electron micrographs taken at the lesion site, and/or the intra-axonal diffusion of fluorescent dyes across the lesion site. These and other data suggest that the application of polymeric fusiogens (such as our PEG solutions), possibly combined with a tissue adherent (such as our PEG hydrogels), could lead toin vivotreatments that rapidly and permanently repair cut or crushed axons in the PNS and CNS of adult mammals, including humans.
A Test of the Cytosolic Apolipoprotein E Hypothesis Fails to Detect the Escape of Apolipoprotein E from the Endocytic Pathway into the Cytosol and Shows that Direct Expression of Apolipoprotein E in the Cytosol is Cytotoxic
Authors: DeMattos Ronald B. , Thorngate Fayanne E. , Williams David L.
Published: April 2018

Genetic evidence indicates that apolipoprotein E4 (apoE4) is a risk factor for the development of Alzheimer’s disease. A controversial hypothesis proposes that apoE, a typical secretory protein, accesses the neuronal cytosol in which apoE3, but not apoE4, protects tau from hyperphosphorylation. However, no conclusive evidence for the presence of apoE in the cytosolic compartment has been presented. We designed a novel assay to test whether apoE can access the cytosol via escape from the endocytic pathway by incorporating a nuclear localization signal (NLS) into apoE. Control experiments demonstrated that apoE plus NLS (apoE+NLS) is chaperoned to the nucleus if it reaches the cytosolic compartment. When exogenous apoE+NLS was endocytosed by neuronal cells, no nuclear apoE was detected, indicating that apoE remains within the endocytic pathway and does not escape into the cytosol. Furthermore, we show that direct cytosolic expression of apoE is cytotoxic. These data argue that effects of apoE on the neuronal cytoskeleton and on neurite outgrowth are not mediated via cytosolic interactions but rather by actions originating at the cell surface.
A Critical Role of the Nitric Oxide/cGMP Pathway in Corticostriatal Long-Term Depression
Authors: Calabresi Paolo , Gubellini Paolo , Centonze Diego , Sancesario Giuseppe , Morello Maria , Giorgi Mauro , Pisani Antonio , Bernardi Giorgio
Published: April 2018

High-frequency stimulation (HFS) of corticostriatal glutamatergic fibers induces long-term depression (LTD) of excitatory synaptic potentials recorded from striatal spiny neurons. This form of LTD can be mimicked by zaprinast, a selective inhibitor of cGMP phosphodiesterases (PDEs). Biochemical analysis shows that most of the striatal cGMP PDE activity is calmodulin-dependent and inhibited by zaprinast. The zaprinast-induced LTD occludes further depression by tetanic stimulation and vice versa. Both forms of synaptic plasticity are blocked by intracellular 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), a selective inhibitor of soluble guanylyl cyclase, indicating that an increased cGMP production in the spiny neuron is a key step. Accordingly, intracellular cGMP, activating protein kinase G (PKG), also induces LTD. Nitric oxide synthase (NOS) inhibitorsN(G)-nitro-l-arginine methyl ester hydrochloride (L-NAME) and 7-nitroindazole monosodium salt (7-NINA) block LTD induced by either HFS or zaprinast, but not that induced by cGMP. LTD is also induced by the NO donorsS-nitroso-N-acetylpenicillamine (SNAP) and hydroxylamine. SNAP-induced LTD occludes further depression by HFS or zaprinast, and it is blocked by intracellular ODQ but not by L-NAME. Intracellular application of PKG inhibitors blocks LTD induced by HFS, zaprinast, and SNAP. Electron microscopy immunocytochemistry shows the presence of NOS-positive terminals of striatal interneurons forming synaptic contacts with dendrites of spiny neurons. These findings represent the first demonstration that the NO/cGMP pathway exerts a feed-forward control on the corticostriatal synaptic plasticity.
Reorganization of Cholinergic Terminals in the Cerebral Cortex and Hippocampus in Transgenic Mice Carrying Mutated Presenilin-1 and Amyloid Precursor Protein Transgenes
Authors: Wong Tak Pan , Debeir Thomas , Duff Karen , Cuello A. Claudio
Published: April 2018

Cholinergic deficits are one of the most consistent neuropathological landmarks in Alzheimer’s disease (AD). We have examined transgenic mouse models (PS1M146L, APPK670N,M671L) and a doubly transgenic line (APPK670N,M671L+ PS1M146L) that overexpress mutated AD-related genes [presenilin-1 (PS1) and the amyloid precursor protein (APP)] to investigate the effect of AD-related gene overexpression and/or amyloidosis on cholinergic parameters.

The size of the basal forebrain cholinergic neurons and the pattern of cholinergic synapses in the hippocampus and cerebral cortex were revealed by immunohistochemical staining for choline acetyltransferase and the vesicular acetylcholine transporter, respectively. At the time point studied (8 months), no apparent changes in either the size or density of cholinergic synapses were found in the PS1M146Lmutant relative to the nontransgenic controls. However, the APPK670N,M671Lmutant showed a significant elevation in the density of cholinergic synapses in the frontal and parietal cortices. Most importantly, the double mutant (APPK670N,M671L+ PS1M146L), which had extensive amyloidosis, demonstrated a prominent diminution in the density of cholinergic synapses in the frontal cortex and a reduction in the size of these synapses in the frontal cortex and hippocampus. Nonetheless, no significant changes in the size of basal forebrain cholinergic neurons were observed in these three mutants. This study shows a novel role of APP and a synergistic effect of APP and PS1 that correlates with amyloid load on the reorganization of the cholinergic network in the cerebral cortex and hippocampus at the time point studied.