bluuebunny/crossref_metadata_2025 huggingface dataset:
Amyloid Fibrils Activate Tyrosine Kinase-Dependent Signaling and Superoxide Production in Microglia
Authors: McDonald Douglas R. , Brunden Kurt R. , Landreth Gary E.
Published: April 2018

Alzheimer’s disease (AD) is a devastating neurological disorder characterized by loss of cognitive skills and progressive dementia. The pathological hallmark of AD is the presence of numerous senile plaques throughout the hippocampus and cerebral cortex associated with degenerating axons, neurofibrillary tangles, and gliosis. The core of the senile plaque primarily is composed of the 39–43 amino acid β-amyloid peptide (Aβ), which forms fibrils of β-pleated sheets. Although considerable genetic evidence implicates Aβ in the pathogenesis of AD, a direct causal link remains to be established.

Senile plaques are foci of local inflammatory processes, as evidenced by the presence of numerous activated microglia and acute phase proteins. Aβ has been shown to elicit inflammatory responses in microglia; however, the intracellular events mediating these effects are largely unknown. We report that exposure of microglia and THP1 monocytes to fibrillar Aβ led to time- and dose-dependent increases in protein tyrosine phosphorylation of a population of proteins similar to that elicited by classical immune stimuli such as immune complexes. The tyrosine kinases Lyn, Syk, and FAK were activated on exposure of microglia and THP1 monocytes to Aβ, resulting in the tyrosine kinase-dependent generation of superoxide radicals. The present data support a role for oxidative damage in the pathogenesis of AD, provide an important mechanistic link between Aβ and the generation of reactive oxygen intermediates, and identify molecular targets for therapeutic intervention in AD.
Rapid Exocytosis in Single Chromaffin Cells Recorded from Mouse Adrenal Slices
Authors: Moser Tobias , Neher Erwin
Published: April 2018

We report here that brief depolarizations such as action potentials trigger exocytosis in thin mouse adrenal slices. The secretory rates obtained in membrane capacitance recordings from chromaffin cells in slices are faster than those observed in isolated cells. Fast exocytosis in slices is attributable to the rapid release of a small pool of vesicles. The pool recovers from depletion with a time constant of 10 sec. Recruitment of the rapidly released vesicles is strongly hindered by the fast Ca2+chelator BAPTA and much less by the slower chelator EGTA. We suggest that these vesicles are located in close proximity to Ca2+channels. Spatial coupling of Ca2+entry and exocytosis may be sensitive to cell isolation and culture.
The Secretion of Classical and Peptide Cotransmitters from a Single Presynaptic Neuron Involves a Synaptobrevin-Like Molecule
Authors: Whim Matthew D. , Niemann Heiner , Kaczmarek Leonard K.
Published: April 2018

It is not yet understood how the molecular mechanisms controlling the release of neuropeptides differ from those controlling the release of classical transmitters, mainly because there are few peptidergic synapses in which the environment at the presynaptic release sites can be manipulated. UsingAplysia californicaneuron B2, which synthesizes both peptide and classical transmitters, we have established two synaptic types. When B2 is cocultured with a sensory neuron, a peptidergic synapse is formed. In contrast, when B2 is cocultured with neuron B6, a classical synapse is formed. In contrast to a common assumption, single action potentials can release both types of transmitters. The secretion of peptide and classical transmitters by B2 is inhibited by the presynaptic injection of tetanus toxin, but not by an inactive mutant. Thus a synaptobrevin-like molecule is involved in the secretion of these two types of transmitters.
Adenosine Release Mediates Cyanide-Induced Suppression of CA1 Neuronal Activity
Authors: Zhu Ping Jun , Krnjević Kresimir
Published: April 2018

The rapid suppression of CNS function produced by cyanide (CN) was studied by field, intracellular, and whole-cell recording in hippocampal slices (at 33–34°C). Population spikes and field EPSPs were depressed by 4–5 min bath applications of 50–100 μmCN (IC50was 18 μmfor spikes and 72 μmfor EPSPs). The actions of CN were reversibly suppressed by the adenosine antagonists 8-sulfophenyltheophylline (8-SPT; 10 μm) and 8-cyclopentyl-1,3-dipropylxanthine (DPCPX; 0.2 μm), potentiated by the adenosine transport inhibitor dipyridamole (0.5 μm), but unaffected by the KATPchannel blocker glyburide (10 μm). Therefore the CN-induced reductions of synaptic efficacy and postsynaptic excitability—demonstrated by synaptic input:output plots—are mediated mainly by adenosine. In whole-cell or intracellular recordings, CN depressed EPSCs and elicited an increase in input conductance and an outward current, the reversal potential of which was approximately −90 mV (indicating that K+was the major carrier). These effects also were attenuated by 8-SPT. In the presence of 1 mmBa, CN had no significant postsynaptic action; Cs (2 mm) also prevented CN-induced outward currents but only partly blocked the increase in conductance. Another 8-SPT-sensitive action of CN was to depress hyperpolarization-activated slow inward relaxations (Q current). At room temperature (22–24°C), although it did not change holding current and slow inward relaxations, CN raised the input conductance; this effect also was prevented by 8-SPT (10 μm), but not by glyburide (10 μm). Adenosine release thus appears to be the major link between acute CN poisoning and early depression of CNS synaptic function.
Development of Multisensory Neurons and Multisensory Integration in Cat Superior Colliculus
Authors: Wallace Mark T. , Stein Barry E.
Published: April 2018

The development of multisensory neurons and multisensory integration was examined in the deep layers of the superior colliculus of kittens ranging in age from 3 to 135 d postnatal (dpn). Despite the high proportion of multisensory neurons in adult animals, no such neurons were found during the first 10 d of postnatal life. Rather, all sensory-responsive neurons were unimodal. The first multisensory neurons (somatosensory–auditory) were found at 12 dpn, and visually responsive multisensory neurons were not found until 20 dpn. Early multisensory neurons responded weakly to sensory stimuli, had long latencies, large receptive fields, and poorly developed response selectivities. Most surprising, however, was their inability to integrate combinations of sensory cues to produce significant response enhancement (or depression), a characteristic feature of the adult. Responses to combinations of sensory cues differed little from responses to their modality-specific components.

At 28 dpn an abrupt physiological change was noted. Some multisensory neurons now integrated combinations of cross-modality cues and exhibited significant response enhancements when these cues were spatially coincident and response depressions when the cues were spatially disparate. During the next 2 months the incidence of multisensory neurons, and the proportion of these neurons capable of adult-like multisensory integration, gradually increased. Once multisensory integration appeared in a given neuron, its properties changed little with development. Even the youngest integrating neurons showed superadditive enhancements and spatial characteristics of multisensory integration that were indistinguishable from the adult. Nevertheless, neonatal and adult multisensory neurons differed in the manner in which they integrated temporally asynchronous stimuli, a distribution that may reflect the very different behavioral requirements at different ages. The possible maturational role of corticotectal projections in the abrupt gating of multisensory integration is discussed.
Functional Roles of Dopamine D2and D3Autoreceptors on Nigrostriatal Neurons Analyzed by Antisense KnockdownIn Vivo
Authors: Tepper James M. , Sun Bao-Cun , Martin Lynn P. , Creese Ian
Published: April 2018

Two different 19-mer antisense oligodeoxynucleotides complementary to the initial coding regions of dopamine D2or D3receptor mRNA were infused unilaterally into the substantia nigra of rats for 3–6 d to suppress synthesis of D2and/or D3receptors on substantia nigra dopaminergic neurons, thereby producing specific reductions of D2and/or D3receptors. Autoradiographic receptor binding revealed that D2and D3antisense oligodeoxynucleotides specifically and significantly reduced D2or D3binding in the ipsilateral substantia nigra, respectively, without affecting dopamine receptor binding in the neostriatum. Either D2or D3antisense oligodeoxynucleotides greatly attenuated the ability of apomorphine to inhibit dopaminergic neuronsin vivo, an effect that was potentiated by simultaneous administration of D2and D3antisenses. Despite these effects, neither the rate nor the pattern of spontaneous activity of antisense-treated nigrostriatal neurons differed from those in the control groups. The proportion of antidromic responses consisting of full spikes from antisense-treated rats was significantly greater, and the mean antidromic threshold was significantly lower than in controls, indicating that autoreceptor knockdown increased both somatodendritic and terminal excitability. These data demonstrate that selective reduction of specific dopamine receptor subtypes by antisense infusion can be effectedin vivo, and that nigrostriatal neurons express both D2and D3autoreceptors at their somatodendritic and axon terminal regions. Although the somatodendritic and terminal autoreceptors modulate dendritic and terminal excitability, respectively, the interaction of endogenously released dopamine with somatodendritic autoreceptors does not appear to exert a significant effect on spontaneous activity in anesthetized rats.
An Escalating Dose “Binge” Model of Amphetamine Psychosis: Behavioral and Neurochemical Characteristics
Authors: Segal David S. , Kuczenski Ronald
Published: April 2018

Stimulant-induced psychosis is most frequently associated with a chronic, high-dose, multiple daily (“binge”) exposure pattern of stimulant abuse. To simulate these conditions, rats were exposed to escalating doses of amphetamine (Escalating Dose phase, 1.0–8.0 mg/kg) before multiple daily injections of relatively high doses of the drug (Run phase, 8.0 mg/kg/2 hr × 4 injections). Behavior was monitored continuously during the course of these treatments as well as during subsequent amphetamine challenges at various times after discontinuation of drug treatment. With the Escalating Dose–Run pattern of administration, a unique behavioral profile emerged in which tolerance occurred to the amount of time spent engaged in continuous focused stereotypy simultaneous with a profound increase in ambulatory activity that appeared agitated and disorganized. Parallelin vivomicrodialysis studies showed progressively declining extracellular dopamine and serotonin responses, both within and between successive runs, whereas the norepinephrine response remained relatively unaltered. We propose that this model more closely resembles clinical manifestations of amphetamine psychosis and that the alterations may reflect a shift in the relative activation of mesolimbic and nigro-striatal dopamine pathways.
Apomorphine-Susceptible and Apomorphine-Unsusceptible Wistar Rats Differ in Their Susceptibility to Inflammatory and Infectious Diseases: A Study on Rats with Group-Specific Differences in Structure and Reactivity of Hypothalamic–Pituitary–Adrenal Axis
Authors: Kavelaars Annemieke , Heijnen Cobi J. , Ellenbroek Bart , van Loveren Henk , Cools Alexander
Published: April 2018

Variability in susceptibility to diseases is a well known phenomenon that has been attributed to genetic and environmental factors. At the level of the immune system, the reactivity of two types of T helper cells (Th1 and Th2 cells) plays an important role in determining disease susceptibility. Inflammatory (autoimmune) diseases are stimulated by cytokines produced by Th1 cells. Th2 cytokines stimulate antibody production (e.g., IgE) and eosinophilia as observed in allergic reactions or during parasitic infections. We describe here that the reactivity in a Th1 or a Th2 disease model significantly differs between individual rats that show group-specific differences in reactivity of the hypothalamic–pituitary–adrenal (HPA) axis, as well as in their behavioral responses to stress.

We used two outbred lines of Wistar rats, apomorphine-susceptible rats that have a relatively hyperreactive HPA axis (APO-SUS) and apomorphine-unsusceptible rats that have a relatively hyporeactive HPA axis (APO-UNSUS). APO-SUS, but not APO-UNSUS, rats generated a vigorous, Th2-dependent IgE response after infection with the nematodeTrichinella spiralis. In contrast, APO-UNSUS, but not APO-SUS, rats were susceptible for Th1-mediated experimental autoimmune encephalomyelitis. Investigation of cytokine responses of splenocytes revealed that the ratio of mRNA expression for Th1-derived interferon (IFN)-γ and mRNA expression of Th2-derived interleukin-4 (IL-4) was significantly smaller in APO-SUS than in APO-UNSUS rats.

In conclusion, individual differences in structure and reactivity of the neuroendocrine system co-occur with group-specific differences in susceptibility to inflammatory and infectious diseases.
μ-Opioid Receptors Are Localized to Extrasynaptic Plasma Membranes of GABAergic Neurons and Their Targets in the Rat Nucleus Accumbens
Authors: Svingos Adena L. , Moriwaki Akiyoshi , Wang Jia Bei , Uhl George R. , Pickel Virginia M.
Published: April 2018

The activation of μ-opioid receptors in the nucleus accumbens (Acb) produces changes in locomotor and rewarding responses that are believed to involve neurons, including local γ-aminobutyric acid (GABA)ergic neurons. We combined immunogold–silver detection of an antipeptide antiserum against the cloned μ-opioid receptor (MOR) and immunoperoxidase labeling of an antibody against GABA to determine the cellular basis for the proposed opioid modulation of GABAergic neurons in the rat Acb. MOR-like immunoreactivity (MOR-LI) was localized prominently to plasma membranes of neurons having morphological features of both spiny and aspiny cells, many of which contained GABA. Of 351 examples of profiles that contained MOR-LI and GABA labeling, 65% were dendrites. In these dendrites, MOR-LI was seen mainly along extrasynaptic portions of the plasma membrane apposed to unlabeled terminals and/or glial processes. Dually labeled dendrites often received convergent input from GABAergic terminals and/or from unlabeled terminals forming asymmetric excitatory-type synapses. Of all profiles that contained both MOR and GABA immunoreactivity, 28% were axon terminals. MOR-containing GABAergic terminals and terminals separately labeled for MOR or GABA formed synapses with unlabeled dendrites and also with dendrites containing MOR or GABA. Our results indicate that MOR agonists could modulate the activity of GABA neurons in the Acb via receptors located mainly at extrasynaptic sites on dendritic plasma membranes. MOR ligands also could alter the release of GABA onto target dendrites that contain GABA and/or respond to opiate stimulation.
Identification of the Single Channels that Underlie the N-Type and L-Type Calcium Currents in Bullfrog Sympathetic Neurons
Authors: Elmslie Keith S.
Published: April 2018

Most of the whole-cell calcium current of frog sympathetic neurons is an N-type current, blocked by ω-conotoxin GVIA (ωCGVIA). Thus, these cells should be an excellent system to study the properties of single N-type channels. However, a channel that is active near −10 mV in isotonic Ba2+, originally identified as “N-type,” corresponds more closely to a ωCGVIA-resistant component of the whole-cell current observed in 100 mmBa2+. That conclusion would imply that the true single-channel correlate of the macroscopic N-current remains to be identified in frog sympathetic neurons. I report here recordings from cell-attached patches of a calcium channel that activates in the appropriate voltage range (>0 mV, in isotonic Ba2+) and is blocked by ωCGVIA. This channel has a slope conductance of 20 pS (range, 17–25 pS) and a single-channel current of −1.3 pA at 0 mV. Other channels active in the same voltage range (24 pS, −1.3 pA at 0 mV) were identified as L-type channels because they exhibited long openings after repolarization in the presence of 1 μmBay K 8644 and were resistant to ωCGVIA. A third channel type (13–19 pS) was distinguished by current amplitude (−0.6 pA at 0 mV) and strong inactivation at −40 mV. The similarity in slope conductance among these channels demonstrates that distinguishing them requires the consideration of additional properties. The ωCGVIA-sensitive channel can be identified as an N-type calcium channel.
Signal Transduction Mediated by the Truncated trkB Receptor Isoforms, trkB.T1 and trkB.T2
Authors: Baxter Gregory T. , Radeke Monte J. , Kuo Richard C. , Makrides Victoria , Hinkle Beth , Hoang Richard , Medina-Selby Angelica , Coit Doris , Valenzuela Pablo , Feinstein Stuart C.
Published: April 2018

The trkB family of transmembrane proteins serves as receptors for BDNF and NT-4/5. The family is composed of a tyrosine kinase-containing isoform as well as several alternatively spliced “truncated receptors” with identical extracellular ligand-binding domains but very small intracellular domains. The two best-characterized truncated trkB receptors, designated as trkB.T1 and trkB.T2, contain intracellular domains of only 23 and 21 amino acids, respectively. Although it is known that the tyrosine kinase isoform (trkB.FL) is capable of initiating BDNF and NT-4/5-induced signal transduction, the functional role or roles of the truncated receptors remain enigmatic. At the same time, the potential importance of the truncated receptors in the development, maintenance, and regeneration of the nervous system has been highlighted by recent developmental and injury paradigm investigations. Here we have used trkB cDNA transfected cell lines to demonstrate that both trkB.T1 and trkB.T2 are capable of mediating BDNF-induced signal transduction. More specifically, BDNF activation of either trkB.T1 or trkB.T2 increases the rate of acidic metabolite release from the cell, a common physiological consequence of many signaling pathways. Further, these trkB.T1- and trkB.T2-mediated changes occur with kinetics distinct from changes mediated by trkB.FL, suggesting the participation of at least some unique rate-limiting component or components. Mutational analysis demonstrates that the isoform-specific sequences within the intracellular domains of each receptor are essential for signaling capability. Finally, inhibitor studies suggest that kinases are likely to be involved in the trkB.T1 and trkB.T2 signaling pathways.
Nonuniform Distribution of Ca2+Channel Subtypes on Presynaptic Terminals of Excitatory Synapses in Hippocampal Cultures
Authors: Reid Christopher A. , Clements John D. , Bekkers John M.
Published: April 2018

Several subtypes of Ca2+channel support the release of glutamate at excitatory synapses. We investigated the pattern of colocalization of these subtypes on presynaptic terminals in hippocampal cultures. N-type (conotoxin GVIA-sensitive) or P/Q-type (agatoxin IVA-sensitive) Ca2+channels were blocked selectively, and the reduction in transmitter release probability (Pr) was measured with MK-801. The antagonists completely blocked release at some terminals, reducedPrat others, and failed to affect the remainder. In contrast, nonselective reduction of presynaptic Ca2+influx by adding Cd2+or lowering external Ca2+reducedPruniformly at all terminals. We conclude from these results that the mixture of N-type and P/Q-type channels varies markedly between terminals on the same afferent. The distribution of Ca2+channel subtypes was the same for high and lowPrterminals. Given that Ca2+channel subtypes are affected differentially by neuromodulators, these findings lead to the possibility of terminal-specific modulation of synaptic function.
Cyclo-Oxygenase-2 Gene Expression in Neurons Contributes to Ischemic Brain Damage
Authors: Nogawa Shigeru , Zhang Fangyi , Ross M. Elizabeth , Iadecola Costantino
Published: April 2018

Cyclo-oxygenase-2 (COX-2), a rate-limiting enzyme for prostanoid synthesis, is induced during inflammation and participates in inflammation-mediated cytotoxicity. Cerebral ischemia is followed by an inflammatory reaction that plays a role in the evolution of the tissue damage. We studied whether COX-2 is induced after cerebral ischemia and if so, whether such expression contributes to ischemic brain damage. The middle cerebral artery was occluded in rats, and the ischemic area was sampled for analysis 3–96 hr later. COX-2 mRNA was determined by the competitive reverse-transcription PCR. COX-2 mRNA was upregulated in the ischemic hemisphere, but not contralaterally, beginning 6 hr after ischemia. The upregulation reached a maximum at 12 hr, at which time a fivefold induction of the message occurred. Twenty-four hours after ischemia, the concentration of prostaglandin E2was elevated in the injured brain by 292 ± 57% (n= 6). COX-2 immunoreactivity was observed in neurons at the medial edge of the ischemic area. Administration of the COX-2 inhibitor NS-398 attenuated the elevation in prostaglandin E2in the postischemic brain and reduced the volume of the infarct by 29 ± 6% (p< 0.05). Thus, cerebral ischemia leads to upregulation of COX-2 message, protein, and reaction products in the injured hemisphere. The data implicate COX-2 in the mechanisms of delayed neuronal death at the infarct border and provide the rationale for neuroprotective strategies employing COX-2 inhibitors.
Reduction of K+Uptake in Glia Prevents Long-Term Depression Maintenance and Causes Epileptiform Activity
Authors: Janigro Damir , Gasparini Sonia , D’Ambrosio Raimondo , McKhann II Guy , DiFrancesco Dario
Published: April 2018

Extracellular cesium causes synchronous, interictal-like bursting and prevents maintenance of long-term depression (LTD) in the CA1 hippocampal region. We have investigated the cellular mechanisms underlying cesium actions. Whole-cell recordings showed that brief (2 min) bath exposures to cesium caused pyramidal cell hyperpolarization associated with decreased membrane conductance attributable to blockade of an inward h-type current. After prolonged (>2 min) exposures, a late depolarizing response was observed; this effect was not associated with changes in cell membrane conductance. Recordings from interneurons revealed that Ihis expressed in a subpopulation of cells and that cesium effects on interneurons expressing Ihare comparable to those observed in pyramidal cells. Consistent with this effect, cesium decreased the early component of the IPSP recorded in pyramidal cells. Interneurons lacking Ihwere not affected by cesium but developed a depolarizing response when drug applications were paired to orthodromic stimulation. We concluded that cesium actions on LTD and cesium-induced epileptiform activity were not attributable exclusively to its direct effects on neurons. Recordings from hippocampal slice astrocytes revealed that cesium interfered with glial electrical responses during LTD induction. Cesium blocked glial inwardly rectifying potassium channels and increased the amplitude and duration of stimulation-evoked [K+]outincreases. Thus, the effects of cesium on CA1 synchronization and synaptic plasticity appear to be mediated predominantly by blockade of glial voltage-dependent potassium uptake.
Medial Superior Temporal Area Neurons Respond to Speed Patterns in Optic Flow
Authors: Duffy Charles J. , Wurtz Robert H.
Published: April 2018

The speed of visual motion in optic flow fields can provide important cues about self-movement. We have studied the speed sensitivities of 131 neurons in the dorsal region of the medial superior temporal area (MSTd) that responded to either radial or circular optic flow stimuli. The responses of more than two-thirds of these neurons were strongly modulated by changes in the mean speed of motion in optic flow stimuli, with response profiles resembling simple filter characteristics. When we removed the normal gradient of speeds in optic flow (slower speeds in the center, faster speeds in the periphery), approximately two-thirds of the neurons showed changes in their responses. When the speed gradient was altered rather than eliminated, almost nine in 10 neurons preferred either a normal speed gradient or an inverted one (slower speeds near the periphery) over stimuli with no speed gradient. These speed gradient preferences do not come simply from different speed preferences in the central and peripheral segments of the stimulus area. Rather, these speed gradient preferences seemed to reflect interactions between simultaneously presented speeds within an optic flow stimulus. The sensitivity of MSTd neurons to patterns of speed, as well as patterns of direction, strengthens the view that these neurons are well suited to the analysis of optic flow. Sensitivity to speed gradients in optic flow might contribute to neuronal mechanisms for spatial orientation during self-movement and for representing the three-dimensional structure of the visual environment.
Differential Expression of α-Gustducin in Taste Bud Populations of the Rat and Hamster
Authors: Boughter Jr. John D. , Pumplin David W. , Yu Chengsi , Christy Robert C. , Smith David V.
Published: April 2018

The G-protein subunit α-gustducin, which is similar to rod transducin, has been implicated in the transduction of both sweet- and bitter-tasting substances. In rodents, there are differences in sensitivity to sweet and bitter stimuli in different populations of taste buds. Rat fungiform taste buds are more responsive to salts than to sweet stimuli, whereas those on the palate respond predominantly to sweet substances. In contrast, hamster fungiform taste buds are more sensitive to sweet-tasting stimuli. Taste buds in the vallate and foliate papillae of both species are sensitive to bitter compounds. These differences in sensitivity should be reflected in the numbers of gustducin-containing cells in different taste bud populations. We examined taste buds in the rat and hamster for immunoreactivity to an antibody against α-gustducin. Immunofluorescence of labeled taste cells was examined by confocal microscopy, and the cells were counted. Gustducin-positive cells were seen in all taste bud regions; they were spindle-shaped, with circular cross-sections and apical processes that extended to the taste pore. Cells with this characteristic shape in rat vallate taste buds are Type II (light) cells. In the rat, taste buds of the fungiform papillae had fewer gustducin-positive cells (3.1/taste bud) than those of other regions, including the posterior tongue and palate (>8.9/taste bud). Hamster fungiform taste buds contained twice as many gustducin-expressing cells (6.8/taste bud) as those of the rat. These data support the hypothesis that α-gustducin is involved in the transduction of both sweet- and bitter-tasting stimuli by mammalian taste receptor cells.
Estrogen Modifies an Electrocommunication Signal by Altering the Electrocyte Sodium Current in an Electric Fish,Sternopygus
Authors: Dunlap Kent D. , McAnelly M. Lynne , Zakon Harold H.
Published: April 2018

Many species of electric fish emit sexually dimorphic electrical signals that are used in gender recognition. InSternopygus, mature females produce an electric organ discharge (EOD) that is higher in frequency and shorter in pulse duration than that of mature males. EOD pulse duration is determined by ion currents in the electrocytes, and androgens influence EOD pulse duration by altering the inactivation kinetics of the electrocyte sodium current. We examined whether estrogen modulates the female-specific EOD and, if so, whether it regulates EOD pulse duration by acting on the same androgen-sensitive ion current in the electrocytes. We implanted gonadectomizedSternopyguswith either empty SILASTIC capsules (control), one capsule filled with estradiol-17β (E2; low dose), or three capsules of E2(high dose). Twelve days after implantation, E2-treated fish had plasma E2levels ∼3.3-fold (low dose) or ∼7.1-fold (high dose) higher than controls. After implantation, both E2-treated groups had higher EOD frequency and shorter EOD pulse duration than controls and their own preimplantation values. Through immunocytochemistry, we identified immunoreactive estrogen receptors in the nuclei of electrocytes, indicating that these cells are directly responsive to estrogen. In addition, voltage-clamp studies showed that E2affected the electrocyte ion currents kinetics: the sodium inactivation time constant was significantly lower in E2-treated fish than in controls. Thus, sexual dimorphism in the electrocommunication signal results, at least in part, from estrogens and androgens acting in opposite directions on the same ion current in the electrocytes.
Inhibition of GABAASynaptic Responses by Brain-Derived Neurotrophic Factor (BDNF) in Rat Hippocampus
Authors: Tanaka Tatsuro , Saito Hiroshi , Matsuki Norio
Published: April 2018

Brain-derived neurotrophic factor (BDNF) is one of neurotrophins involved in the development and maintenance of both the peripheral nervous system and CNS. Although the expression of BDNF and its receptor TrkB still occurs in the adult stage, their physiological role in the mature CNS is not fully understood. In the present study we examined in detail the possibility that BDNF modulates synaptic neurotransmissions by using patch-clamp technique in rat hippocampal CA1 region. BDNF (20–100 ng/ml) did not show any appreciable effect on evoked EPSCs, but it markedly reduced both evoked and spontaneous IPSCs within 5 min, and the reduction persisted while BDNF was present. BDNF also attenuated GABAAreceptor-mediated response to applied GABA. However, BDNF failed to attenuate IPSCs when the postsynaptic pyramidal neuron was loaded intracellularly with 200 nmK252a, an alkaloid that inhibits the kinase activity of Trk receptor family, through the patch pipette. Intracellular application of 200 nmK252b, a weaker inhibitor of Trk-type kinase, did not affect the inhibition. The attenuating effect also was prevented by postsynaptic injection of U73122 (5 μm), a broad-spectrum PLC inhibitor, and by strong chelation of intracellular Ca2+with 10 mmBAPTA. These data suggest that BDNF modulates GABAAsynaptic responses by postsynaptic activation of Trk-type receptor and subsequent Ca2+mobilization in the CNS.
Preferential Interaction of ω-Conotoxins with Inactivated N-type Ca2+Channels
Authors: Stocker Jonathan W. , Nadasdi Laszlo , Aldrich Richard W. , Tsien Richard W.
Published: April 2018

The selective block of N-type Ca2+channels by ω-conotoxins has been a hallmark of these channels, critical in delineating their biological roles and molecular characteristics. Here we report that the ω-conotoxin-channel interaction depends strongly on channel gating. N-type channels (α1B, α2, and β1) expressed inXenopusoocytes were blocked with a variety of ω-conotoxins, including ω-CTx-GVIA, ω-CTx-MVIIA, and SNX-331, a derivative of ω-CTx-MVIIC. Changes in holding potential (HP) markedly altered the severity of toxin block and the kinetics of its onset and removal. Notably, strong hyperpolarization renders ω-conotoxin block completely reversible. These effects could be accounted for by a modulated receptor model, in which toxin dissociation from the inactivated state is ∼60-fold slower than from the resting state. Because ω-conotoxins act exclusively outside cells, our results suggest that voltage-dependent inactivation of Ca2+channels must be associated with an externally detectable conformational change.
A Hierarchy of Hu RNA Binding Proteins in Developing and Adult Neurons
Authors: Okano Hirotaka J. , Darnell Robert B.
Published: April 2018

The Hu proteins are a group of antigens targeted in an immune-mediated neurodegenerative disorder associated with cancer. We have cloned and characterized four members of theHugene family from mouse. We find that theHugenes encode a large number of alternatively spliced transcripts to produce a series of related neuron-specific RNA binding proteins. Despite this complexity, we have discerned several ordered features ofHuexpression. In the embryo, specificHugenes are expressed in a hierarchy during early neurogenesis. In the E16 developing cortex,mHuBis induced in very early postmitotic neurons exiting the ventricular zone,mHuDis expressed in migrating neurons of the intermediate zone, andmHuCis expressed in mature cortical plate neurons. Such a hierarchy suggests distinct functional roles for each gene in developing neurons. In the adult, all neurons express some set ofHumRNA and protein. However, specific patterns are evident such that individual neuronal types in the hippocampus, cerebellum, olfactory cortex, neocortex, and elsewhere express from one to severalHugenes. The complexity of potential protein variants within a gene family and of differentHufamily members within a neuron suggests a diverse array of function. Given the strong homologies among the Hu proteins, theDrosophilaneurogenic geneelav, and theDrosophilasplicing factorsxl, we predict that different combinations of Hu proteins determine different neuron-specific aspects of post-transcriptional RNA regulation. Our findings of specific developmental patterns of expression and the correlation between immune targeting of the Hu proteins and adult neurodegenerative disease suggest that the Hu proteins are critical in both the proper development and function of mature neurons.
Heterogeneous Topographic and Cellular Distribution of Huntingtin Expression in the Normal Human Neostriatum
Authors: Ferrante Robert J. , Gutekunst Claire-Anne , Persichetti Francesca , McNeil Sandra M. , Kowall Neil W. , Gusella James F. , MacDonald Marcy E. , Beal M. Flint , Hersch Steven M.
Published: April 2018

A striking heterogeneous distribution of topographic and cellular huntingtin immunoreactivity was observed within the human neostriatum using three distinct huntingtin antibodies. Patchy areas of low huntingtin immunoreactivity were present in both the caudate nucleus and putamen, surrounded by an intervening area of greater immunoreactivity. Comparison of huntingtin immunoreactivity with contiguous serial sections stained for enkephalin and calbindin D28k immunoreactivities showed that the topographic heterogeneity of huntingtin immunostaining corresponded to the patch (striosome) and matrix compartments within the striatum. Huntingtin immunoreactivity was confined primarily to neurons and neuropil within the matrix compartment, whereas little or no neuronal or neuropil huntingtin immunostaining was observed within the patch compartment. There was marked variability in the intensity of huntingtin immunolabel among medium-sized striatal neurons, whereas a majority of large striatal neurons were only faintly positive or without any immunoreactivity. Combined techniques for NADPH-diaphorase enzyme histochemistry and huntingtin immunocytochemistry, as well as double immunofluorescence for either nitric oxide synthase or calbindin D28k in comparison with huntingtin expression, revealed a striking correspondence between calbindin D28k and huntingtin immunoreactivities, with little or no colocalization between NADPH-diaphorase or nitric oxide synthase neurons and huntingtin expression. These observations suggest that the selective vulnerability of spiny striatal neurons and the matrix compartment observed in Huntington’s disease is associated with higher levels of huntingtin expression, whereas the relative resistance of large and medium-sized aspiny neurons and the patch compartments to degeneration is associated with low levels of huntingtin expression.
Intracellular Acidification Reversibly Reduces Endocytosis at the Neuromuscular Junction
Authors: Lindgren Clark A. , Emery Dennis G. , Haydon Philip G.
Published: April 2018

The close spatial and temporal coupling of endocytosis and exocytosis in nerve terminals has made it difficult to elucidate the mechanisms and the regulation of endocytosis per se. Despite significant advances in our knowledge of the molecules involved in endocytosis, it has not yet been possible to selectively manipulate endocytosis in nerve terminals. We report that the substitution of propionate for chloride in the saline bathing a lizard neuromuscular junction reduces internal pH and reversibly blocks activity-dependent endocytosis. When intraterminal pH is reduced by ∼0.7 pH units, the uptake of FM1-43 in nerve terminals, but not activity-dependent destaining, is reduced. Normalization of intracellular pH by removing the propionate, raising extracellular pH, or adding ammonium chloride immediately restores FM1-43 uptake. Electron microscopy indicates that intracellular acidification reversibly reduces activity-dependent endocytosis in nerve terminals, because depolarization in propionate saline leads to a depletion of vesicles and the appearance of large intramembraneous infoldings.
Differential Expression of Connexins during Neocortical Development and Neuronal Circuit Formation
Authors: Nadarajah B. , Jones A. M. , Evans W. H. , Parnavelas J. G.
Published: April 2018

Gap junctions are membrane channels that mediate the direct passage of ions and molecules between adjacent cells. Recent tracer coupling and optical recording studies have revealed the presence of gap junction-mediated communication between neurons during neocortical development. We have visualized gap junctions in the developing rat cerebral cortex with electron microscopy and studied the pattern of expression and cellular localization of connexins 26, 32, and 43 that take part in their formation. We found that these connexins (Cxs) are expressed differentially during development, and their patterns of expression are correlated with important developmental events such as cell proliferation, migration, and formation of cortical neuronal circuits. Specifically, we observed that the developmental profile of Cx 26 during the first 3 weeks of postnatal life matched closely the development of neuronal coupling, suggesting that coupled neurons use this gap junction protein during circuit formation in the cortex. The subsequent diminution of Cx 26 was mirrored by an increase in Cx 32 immunoreactivity, which became pronounced at the late stages of cortical maturation. In contrast, Cx 43 was localized in the cortex throughout the period of development. Its localization in radial glial fibers closely associated with migrating neurons suggests that this Cx may be involved in neuronal migration.
baxDeficiency Prevents the Increased Cell Death of Immature Neurons inbcl-x-Deficient Mice
Authors: Shindler Kenneth S. , Latham Cecelia B. , Roth Kevin A.
Published: April 2018

The intracellular balance between pro- and antiapoptotic members of the Bcl-2 gene family is thought to regulate cell death. Targeted disruption ofbcl-x, a death repressing member, causes massive cell death of immature neurons in the developing mouse CNS, whereas targeted disruption ofbax, a proapoptotic member, blocks the death of specific populations of sympathetic and motor neurons. In the present study, mice deficient in both Bcl-xLand Bax (bcl-x−/−/bax−/−) are used to examine the relative significance and potential interactions of Bcl-xLand Bax during early CNS development.bcl-x−/−/bax−/−mice demonstrate greatly reduced levels of apoptosis bothin vivoandin vitrocompared with the CNS of Bcl-xL-deficient mice, as assessed by histology and terminal deoxytransferase-mediated deoxyuridine triphosphate nick end-labeling. Bax-deficient mice, however, contain occasional apoptotic cells in the developing CNS, and cultures of bax-deficient telencephalic cells demonstrate similar levels of apoptosis as wild-type cultures. These results suggest that Bax critically interacts with Bcl-xLto regulate survival of immature neurons, but indicate that other cell death regulating proteins, in addition to Bcl-xLand Bax, also function during CNS development.
Transcranial Magnetic Stimulation during Positron Emission Tomography: A New Method for Studying Connectivity of the Human Cerebral Cortex
Authors: Paus Tomáš , Jech Robert , Thompson Christopher J. , Comeau Roch , Peters Terry , Evans Alan C.
Published: April 2018

We describe a new technique permitting the mapping of neural connections in the living human brain. The method combines two well established tools of brain research: transcranial magnetic stimulation (TMS) and positron emission tomography (PET). We use TMS to stimulate directly a selected cortical area while simultaneously measuring changes in brain activity, indexed by cerebral blood flow (CBF), with PET. The exact location of the stimulation site is achieved by means of frameless stereotaxy. In the first study using this technique, we found significant positive correlations between CBF and the number of TMS pulse trains at the stimulation site, namely the left frontal eye field (FEF) and, most importantly, in the visual cortex of the superior parietal and medial parieto-occipital regions. The pattern of these distal effects was consistent with the known anatomic connectivity of the monkey FEF. We suggest that the combined TMS/PET technique offers an objective tool for assessing the state of functional connectivity without requiring the subject to engage in any specific behavior.
Negative Feedback Neuroendocrine Control of Inflammatory Response in the Rat is Dependent on the Sympathetic Postganglionic Neuron
Authors: Green Paul G. , Jänig Wilfrid , Levine Jon D.
Published: April 2018

Negative feedback control of inflammation is mediated by activation of nociceptive afferents that in turn activates the hypothalamic-pituitary-adrenal axis to release corticosteroids. Plasma extravasation (PE) produced by the potent inflammatory mediator, bradykinin (BK), but not that induced by another potent inflammatory mediator, platelet-activating factor (PAF), is inhibited by released corticosterone. Because bradykinin, but not PAF, produces PE by a mechanism that is, in part, dependent on the sympathetic postganglionic neuron (SPGN) terminal, we tested the hypothesis that the negative feedback control of inflammation is dependent on the SPGN terminal in the inflamed tissue. In sympathectomized rats, the residual (i.e., SPGN-independent) PE in the knee joint produced by BK was not inhibited by noxious electrical stimulation. Furthermore, intravenous administration of corticosterone potently inhibited, with a similar time-course, the SPGN-dependent, but not the SPGN-independent, component of BK-induced PE. Neither electrical stimulation nor corticosterone inhibited PAF-induced PE. Finally, corticosterone’s actions do not appear to be mediated by release of norepinephrine from the SPGN terminal, because neither the α-adrenergic receptor antagonist phentolamine nor the β2-adrenergic receptor antagonist ICI 118,551 antagonized the inhibition of BK-induced PE by corticosterone. We conclude that in the rat knee joint, negative feedback control of the inflammatory response is dependent on the presence of the SPGN terminal. Further, our data suggest that a significant component of corticosteroid-induced inhibition of PE produced by inflammatory mediators is SPGN-dependent.
Stimulus-Dependent Neuronal Oscillations and Local Synchronization in Striate Cortex of the Alert Cat
Authors: Gray Charles M. , Viana Di Prisco Gonzalo
Published: April 2018

Neuronal responses to visual stimuli that are correlated on a millisecond time scale are well documented in several areas of the mammalian visual cortex. This coherent activity often takes the form of synchronous rhythmic discharges ranging in frequency from 20 to 70 Hz. We performed experiments to determine the incidence and properties of this rhythmic activity in the striate cortex of alert cats and to compare this activity to similar data collected in the striate cortex of anesthetized cats. The results demonstrate that optimal visual stimuli evoke robust, locally synchronous, 20–70 Hz oscillatory responses in the striate cortex of cats that are fully alert and performing a visual fixation task. The oscillatory activity is stimulus dependent, largely absent during periods of spontaneous activity, and shows a systematic increase in frequency with increasing stimulus velocity. Thus, the synchronous oscillatory activity observed in this and earlier studies cannot be explained as an artifact of anesthesia nor as a phenomenon that occurs independent of visual stimulation. Rather, it is a robust process that is present in the alert state and is dependent on the presence and specific properties of visual stimuli.
SEROTONERGIC Pontomedullary Neurons Are Not Activated by Antinociceptive Stimulation in the Periaqueductal Gray
Authors: Gao Keming , Kim Yoo-Hang Hugh , Mason Peggy
Published: April 2018

The antinociceptive and cardiovascular effects of midbrain periaqueductal gray (PAG) stimulation are mediated through a relay in the pontomedullary raphe magnus (RM) and adjacent nucleus reticularis magnocellularis (NRMC). To test whether the neurons important in mediating PAG-evoked effects areserotonergic, the responses of pontomedullaryserotonergic-likecells to PAG stimulation were tested.serotonergic-likeneurons (n= 21) were recorded extracellularly in halothane-anesthetized Sprague Dawley rats. Serotonergic-like neurons were distinguished by their slow and steady background discharge. Two neurons that were physiologically characterized asserotonergic-likewere intracellularly labeled and processed for serotonin immunoreactivity; both cells tested contained immunoreactive serotonin. Train stimulation of sites within the midbrain PAG, at intensities of ≤50 μA, suppressed the tail withdrawal from noxious heat and evoked changes in blood pressure and heart rate. Noserotonergic-likecells were activated by single-pulse or short-train (two to five pulses) stimulation of the PAG at antinociceptive intensities. In most cases,serotonergic-likecells were unaffected by long-train stimulation (5–6 sec) of the PAG, which produced antinociception and cardiovascular changes. In contrast, >50% of the cells in two nonserotonergic-like cell classes were activated at short latency by such PAG stimulation. In conclusion, monosynaptic excitation ofserotonergiccells in RM/NRMC is unlikely to be necessary for the nociceptive and autonomic modulatory effects of PAG stimulation.
Phase Locking to High Frequencies in the Auditory Nerve and Cochlear Nucleus Magnocellularis of the Barn Owl,Tyto alba
Authors: Köppl Christine
Published: April 2018

The auditory system of the barn owl is an important model for temporal processing on a very fast time scale and for the neural mechanisms and circuitry underlying sound localization. Phase locking has been shown to be the behaviorally relevant temporal code. This study examined the quality and intensity dependence of phase locking in single auditory nerve fibers of the barn owl to define the input to the known brainstem circuit for temporal processing. For direct comparison in the same individuals, recordings were also obtained from the relevant next higher center, the nucleus magnocellularis (NM). Phase locking was regularly seen at sound pressure levels (SPL) below those eliciting an increase in spike rate, thus providing an additional cue for signal detection. The quality of phase locking, expressed as vector strength, decreased with increasing frequency. Auditory nerve fibers showed an unusual step-like decline with a prominent plateau in the mid-frequency range (1.5–3 kHz), indicating that some specialization enables the owl to halt the deterioration and extend phase locking to frequencies up to 10 kHz, above the range commonly observed in other species. Phase locking in the NM was consistently inferior to that of auditory-nerve fibers at frequencies above 1 kHz, suggesting that the synapse plays a limiting role in temporal precision. The response delays, or group delays, derived from the phase-versus-frequency functions of auditory nerve fibers were not consistent with the unusual spatial frequency representation in the owl cochlea. This questions the common assumption that group delays reflect cochlear wave travel times.