bluuebunny/crossref_metadata_2025_split huggingface dataset:
Selective, Activity-Dependent Uptake of Histamine into an Arthropod Photoreceptor
Authors: Stuart Ann E. , Morgan Jennifer R. , Mekeel Harold E. , Kempter Elizabeth , Callaway Joseph C. 
Published: April 2018

The synapses made by many arthropod photoreceptors are disinhibitory and use histamine as their transmitter. Because decreases and not increases in the cleft concentration of transmitter constitute the important event at these synapses, a transporter to clear the cleft of histamine would seem particularly crucial to signal transfer. We report here that3H-histamine is taken up selectively into barnacle photoreceptors by a Na+-dependent mechanism, presumably a transporter. Using light microscopic autoradiography, we observe heavy label over axons and presynaptic terminals of these neurons when they are stimulated during uptake. The radioactivity taken up was identified as3H-histamine by thin layer chromatography; no metabolites were detected, even after 5 hr. Radiolabeled 5-hydroxytryptamine and GABA are not taken up by the photoreceptor.3H-histamine uptake into photoreceptors is decreased markedly by an excess of unlabeled histamine and by chlorpromazine and phenoxybenzamine. Unexpectedly for uptake dependent on the Na+gradient, photoreceptor terminals label more intensely in the light (when depolarized) than in the dark (when hyperpolarized). Glia label more strongly than photoreceptors in dark-incubated preparations. The presence of presynaptic uptake strengthens the evidence that histamine is the neurotransmitter of arthropod photoreceptors and provides a mechanism by which this synapse could recycle transmitter, control its steady-state cleft concentration, and clear it from the cleft in response to decreases in its release from the photoreceptors.
Transgenic Expression of Embryonic MAP2 in Adult Mouse Brain: Implications for Neuronal Polarization
Authors: Marsden Kathryn M. , Doll Thierry , Ferralli Jacqueline , Botteri Florence , Matus Andrew 
Published: April 2018

The major neuronal microtubule-associated protein MAP2 is selectively localized in dendrites, where its expression is under strong developmental regulation. To learn more about its potential effects on neuronal morphogenesis and its sorting within the neuronal cytoplasm, we have raised transgenic mice that express high levels of the embryonic form, MAP2c, in the adult brain. One transgenic line expressed higher levels of MAP2c than endogenous adult MAP2. This had no detectable effect on either the arrangement or morphology of neurons, suggesting that although MAP2c is necessary for neuronal morphogenesis it is not involved in its regulation. Like endogenous adult MAP2, transgenic MAP2c was present in dendrites but not axons, indicating that the signal responsible for its cytoplasmic sorting is contained within the 1.5 kb of its coding sequence.In situhybridization with specific probes showed that transgenic MAP2c mRNA was limited to cell bodies. Thus, the dendritic localization of MAP2c protein cannot be the result of previous transport of its mRNA but must depend on a signal associated with the protein itself. Furthermore, because the amino acid sequence of MAP2c is present in all forms of MAP2, this signal is also contained within adult high-MrMAP2 protein. This raises the possibility that, rather than the conventional scheme of mRNA sorting preceding protein localization, the transport of adult MAP2 mRNA into dendrites could depend on it being part of a translation complex in which the targeting signal is on the nascent protein.
Regenerative Proliferation in Organ Cultures of the Avian Cochlea: Identification of the Initial Progenitors and Determination of the Latency of the Proliferative Response
Authors: Warchol Mark E. , Corwin Jeffrey T. 
Published: April 2018

Sensory hair cells in the cochleae of birds are regenerated after the death of preexisting hair cells caused by acoustic overstimulation or administration of ototoxic drugs. Regeneration involves renewed proliferation of cells in an epithelium that is otherwise mitotically quiescent. To determine the identity of the first cells that proliferate in response to the death of hair cells and to measure the latency of this proliferative response, we have studied hair-cell regeneration in organ culture. Cochleae from hatchling chicks were placed in culture, and hair cells were killed individually by a laser microbeam. The culture medium was then replaced with a medium that contained a labeled DNA precursor. The treated cochleae were incubated in the labeling media for different time periods before being fixed and processed for the visualization of proliferating cells. The first cells to initiate DNA replication in response to the death of hair cells were supporting cells within the cochlear sensory epithelium. All of the labeled supporting cells were located within 200 μm of the hair-cell lesions. These cells first entered S-phase ∼16 hr after the death of hair cells. The results indicate that supporting cells are the precursors of regenerated hair cells and suggest that regenerative proliferation of supporting cells is triggered by signals that act locally within the damaged epithelium.
Spatially Restricted Increase in Polysialic Acid Enhances Corticospinal Axon Branching Related to Target Recognition and Innervation
Authors: Daston Maryellen M. , Bastmeyer Martin , Rutishauser Urs , O’Leary Dennis D. M. 
Published: April 2018

The polysialic acid (PSA) modification of the neural cell adhesion molecule (NCAM) has been shown to alter the responses of developing axons to their environment. We have studied the potential role of PSA in regulating the innervation of the spinal cord by corticospinal axons, which occurs by a delayed formation of collateral branches from the parent axons. Developmental changes in the distribution of PSA were examined immunohistochemically using light and electron microscopy. Whereas NCAM is distributed along the entire pathway of rat corticospinal axons as they grow from the cortex to the spinal cord, PSA-modified NCAM does not become evident until later. When PSA becomes evident, it is restricted to the distal segment of these axons from the caudal hindbrain through the spinal cord. The increase in PSA on corticospinal axons coincides with the time that they begin to form collateral branches in the spinal cord. This unique spatiotemporal distribution of PSA suggests its involvement in corticospinal axon branching. To test this hypothesis, PSA was selectively removed by anin vivoinjection of endoneuraminidase N. This treatment did not seem to interfere with the pathfinding of corticospinal axons; however, PSA removal delayed the onset of collateral branching by corticospinal axons within the spinal cord and later diminished the magnitude of branching. These findings indicate a role for PSA in the regulation of interstitial axon branching, a crucial step in the process of target recognition and innervation by corticospinal axons.
Multiple Channel Types Contribute to the Low-Voltage-Activated Calcium Current in Hippocampal CA3 Pyramidal Neurons
Authors: Avery Robert B. , Johnston Daniel 
Published: April 2018

Hippocampal neurons exhibit low-voltage-activated (LVA) and high-voltage-activated (HVA) calcium currents. We characterized the LVA current by recording whole-cell Ca2+currents from acutely isolated rat hippocampal CA3 pyramidal neurons in 2 mmCa2+.Long depolarizing steps to −50 mV revealed two components to the LVA current: transient and sustained. The transient phase had a fast decay time constant of 59 msec. The sustained phase persisted throughout the depolarization, even for steps lasting several seconds. The transient current was inhibited by the classic T-type channel antagonists Ni2+and amiloride. The anticonvulsant phenytoin preferentially blocked the sustained phase, but ethosuximide had no effect. Steady-state inactivation of the transient component was half-maximal at −80 mV.Nimodipine, an L-type channel antagonist, partly inhibited the sustained current. BayK-8644, an L-type channel agonist, potentiated the sustained current. Calciseptine, another L-type channel antagonist, inhibited the sustained component. ω-Conotoxin-MVIIC, a nonselective toxin for HVA channels, had no effect on either of the LVA current components. ω-Grammotoxin-SIA, another nonselective toxin, partially inhibited the sustained component. The voltage dependence of activation of the nimodipine-sensitive current could be fit with a single Boltzmann, consistent with a homogenous population of L-type channels in CA3 neurons. Half-maximal activation of the nimodipine-sensitive current occurred at −30 mV, considerably more negative than the remaining HVA current.These results suggest that in physiologic Ca2+more than one type of Ca2+channel contributes to the LVA current in CA3 neurons. The transient current is carried by T-type channels. The sustained current is carried, at least in part, by dihydropyridine-sensitive channels. Thus, the designation “low-voltage-activated” should not be limited to T-type channels. These findings challenge the traditional designation of L-type channels as exclusively HVA and reveal a possible role in subthreshold Ca2+signaling.
Induction of Hippocampal Long-Term Depression Requires Release of Ca2+from Separate Presynaptic and Postsynaptic Intracellular Stores
Authors: Reyes Magali , Stanton Patric K. 
Published: April 2018

Studies have suggested that an increase in intracellular [Ca2+] is necessary for the induction of both long-term potentiation (LTP) and long-term depression (LTD) of synaptic transmission, and that release of Ca2+from intracellular storage pools can be necessary to induce LTP. We investigated whether release of Ca2+from intracellular stores also is required for the induction of LTD at Schaffer collateral–CA1 synapses in hippocampal slices. Both thapsigargin (1 μm) and cyclopiazonic acid (1 μm), compounds that deplete all intracellular Ca2+pools by blocking ATP-dependent Ca2+uptake into intracellular compartments, blocked the induction, but not maintenance, of LTD by low-frequency stimulation (LFS) (1 Hz/15 min) without affecting baseline synaptic transmission. Washout of the reversible inhibitor cyclopiazonic acid restored the ability to induce LTD. In contrast, thapsigargin did not blockdepotentiationof LTP by 1 Hz LFS, suggesting that LTP causes a reduction in the threshold [Ca2+] necessary for LTD. Selective depletion of the ryanodine receptor-gated Ca2+pool by bath application of ryanodine (10 μm) also blocked the induction of LTD, indicating a requirement for Ca2+-induced Ca2+release. Impalement of CA1 pyramidal neurons with microelectrodes containing thapsigargin (500 nmto 200 μm) prevented the induction of LTD at synapses on that neuron without blocking LTD in the rest of the slice. In contrast, similar filling of CA1 pyramidal neurons with ryanodine (2 μmto 5 mm) did not block the induction of LTD. From these data, we conclude that the induction of LTD requires release of Ca2+both from apresynapticryanodine-sensitive pool and frompostsynaptic(presumably IP3-gated) stores.
Lipocalin-Type Prostaglandin D Synthase (β-Trace) Is Located in Pigment Epithelial Cells of Rat Retina and Accumulates within Interphotoreceptor Matrix
Authors: Beuckmann Carsten T. , Gordon William C. , Kanaoka Yoshihide , Eguchi Naomi , Marcheselli Victor L. , Gerashchenko Dimitry Y. , Urade Yoshihiro , Hayaishi Osamu , Bazan Nicolas G. 
Published: April 2018

Glutathione-independent prostaglandin D synthase, identical to β-trace, (a major CSF protein), is localized in the CNS. This enzyme, lipocalin-type prostaglandin D synthase, is a member of the lipocalin family of secretory proteins that transport small lipophilic substances. This enzyme’s activity in adult rat retina was enriched sixfold in retinal pigment epithelium (RPE) and even more in interphotoreceptor matrix (IPM), all higher than brain. Western blots with anti-lipocalin-type prostaglandin D synthase showed three distinct immunoreactive bands. In the retinal cytosolic fraction, only one band was observed (Mr25,000); in IPM, the larger component occurred (Mr26,000). The RPE membrane-bound fraction showed two bands (Mr20,000 and 23,000), indicating synthesis, and the cytosolic fraction contained two bands (Mr23,000 and 26,000), indicating modification for release into IPM. At least two glycosylation sites occurred on the prostaglandin D synthase moiety, explaining the three immunoreactive bands in Western blots. Immunohistochemistry with polyclonal antibodies against this lipocalin-type enzyme showed intense localization in RPE, but less in photoreceptor outer and inner segments.In situhybridization showed mRNA specifically expressed in RPE. Thus, lipocalin-type prostaglandin D synthase is predominantly expressed in RPE and actively accumulated in IPM. This may demonstrate gene sharing because, while catalyzing prostaglandin D2synthesis, it may perform an additional, unrelated role in IPM. This enzyme is secreted from the RPE into IPM from which it is then taken up by photoreceptors. However, the nature of its ligand(s) is not known; they may be retinoids and/or docosahexanoic acid.
Rin, a Neuron-Specific and Calmodulin-Binding Small G-Protein, and Rit Define a Novel Subfamily of Ras Proteins
Authors: Lee Ching-Hsien J. , Della Neil G. , Chew Christina E. , Zack Donald J. 
Published: April 2018

cDNAs encoding two novel 25 kDa Ras-like proteins, Rit and Rin, were isolated from mouse retina using a degenerate PCR-based cloning strategy. Using the expressed sequence tag database, human orthologs were also obtained and sequenced. The protein sequences of Rit and Rin, which are 64% identical, are more similar to each other than to any known Ras protein. Their closest homologs in the databases areMucor racemosusRas2 and Ras3, to which they show ∼48% identity. Rit and Rin both bind GTPin vitro. An unusual feature of their structure is that they lack a known recognition signal for C-terminal lipidation, a modification that is generally necessary for plasma membrane association among the Ras subfamily of proteins. Nonetheless, transiently expressed Rit and Rin are plasma membrane-localized. Both proteins contain a C-terminal cluster of basic amino acids, which could provide a mechanism for membrane association. Deletion analysis suggested that this region is important for Rit membrane binding but is not necessary for Rin. Rit, like most Ras-related proteins, is ubiquitously expressed. Rin, however, is unusual in that it is expressed only in neurons. In addition, Rin binds calmodulin through a C-terminal binding motif. These results suggest that Rit and Rin define a novel subfamily of Ras-related proteins, perhaps using a new mechanism of membrane association, and that Rin may be involved in calcium-mediated signaling within neurons.
Functional Organization for Direction of Motion and Its Relationship to Orientation Maps in Cat Area 18
Authors: Shmuel Amir , Grinvald Amiram 
Published: April 2018

The goal of this study was to explore the functional organization of direction of motion in cat area 18. Optical imaging was used to record the activity of populations of neurons. We found a patchy distribution of cortical regions exhibiting preference for one direction over the opposite direction of motion. The degree of clustering according to preference of direction was two to four times smaller than that observed for orientation. In general, direction preference changed smoothly along the cortical surface; however, discontinuities in the direction maps were observed. These discontinuities formed lines that separated pairs of patches with preference for opposite directions. The functional maps for direction and for orientation preference were closely related; typically, an iso-orientation patch was divided into regions that exhibited preference for opposite directions, orthogonal to the orientation. In addition, the lines of discontinuity within the direction map often connected points of singularity in the orientation map. Although the organization of both domains was related, the direction and the orientation selective responses were separable; whereas the selective response according to direction of motion was nearly independent of the length of bars used for visual stimulation, the selective response to orientation decreased significantly with decreasing length of the bars. Extensive single and multiunit electrical recordings, targeted to selected domains of the functional maps, confirmed the features revealed by optical imaging. We conclude that significant processing of direction of motion is performed early in the cat visual pathway.
Dynamics of Induction and Expression of Long-Term Synaptic Facilitation inAplysia
Authors: Mauelshagen Juliane , Parker Gretchen R. , Carew Thomas J. 
Published: April 2018

Serotonin (5HT)-induced short-term facilitation and long-term facilitation (STF and LTF) of the monosynaptic connection between tail sensory neurons (SNs) and motor neurons (MNs) inAplysiahave been useful in delineating possible cellular mechanisms contributing to short-term and long-term memory. Previous work from our laboratory showed that LTF can be produced in the absence of STF, suggesting that these processes may be functionally independent. In the present study, we explored this hypothesis by examining the temporal relationship between STF and LTF. We recorded intracellularly from pairs of monosynaptically connected SNs and MNs in isolated pleural–pedal ganglia. In the first experimental series, we followed the time course of LTF across a 24 hr period after its induction by five applications of 10 μm5HT. STF completely decayed to baseline several hours before the expression of LTF. This biphasic expression profile of STF and LTF further supports the hypothesis that LTF is not a simple elaboration of STF. In the second experimental series, we monitored the immediate expression of facilitation during and after different numbers of 5HT applications. We identified a rapidly decaying STF (lasting 15–30 min) after one to four pulses of 50 μm5HT and a unique, prolonged intermediate-term facilitation (ITF; lasting up to 90 min) after five pulses of 50 μm5HT. These results raise the possibility that STF, ITF, and LTF may reflect components of different memory phases in the intact animal.
Song- and Order-Selective Neurons in the Songbird Anterior Forebrain and their Emergence during Vocal Development
Authors: Doupe Allison J. 
Published: April 2018

Auditory experience is critical for vocal learning in songbirds as in humans. Therefore, in a search for neural mechanisms for song learning and recognition, the auditory response properties of neurons in the anterior forebrain (AF) pathway of the songbird brain were investigated. This pathway plays an essential but poorly understood role during the period of song development when auditory feedback is most crucial.Single-unit recordings demonstrated that both the lateral magnocellular nucleus of the anterior neostriatum (LMAN) and Area X (X) contain auditory neurons in adult male finches. These neurons are strongly selective for both spectral and temporal properties of song; they respond more robustly to the bird’s own song (BOS) than to songs of conspecific individuals, and they respond less well to the BOS if it is played in reverse. In addition, X neurons are more broadly responsive than LMAN neurons, suggesting that responses to song become progressively more refined along this pathway.Both X and LMAN of young male finches early in the process of song learning (30–45 d old) also contain song-responsive auditory neurons, but these juvenile neurons lack the song and order selectivity present in adult birds. The spectral and temporal selectivity of the adult AF auditory neurons therefore arises during development in neurons that are initially broadly song-responsive. These neurons provide one of the clearest examples of experience-dependent acquisition of complex stimulus selectivity. Moreover, the auditory properties of the AF circuit suggest that one of its functions may be to mediate the auditory learning and feedback so essential to song development.
Nervous System-Specific Expression of a Novel Serine Protease: Regulation in the Adult Rat Spinal Cord by Excitotoxic Injury
Authors: Scarisbrick Isobel A. , Towner Melvin D. , Isackson Paul J. 
Published: April 2018

A full-length cDNA clone of a previously unidentified serine protease, myelencephalon-specific protease (MSP), has been isolated by using a PCR cloning strategy and has been shown to be expressed in a nervous system and spinal cord-specific pattern. Sequence analysis demonstrated that MSP is most similar in sequence to neuropsin, trypsin, and tissue kallikrein and is predicted to have trypsin-like substrate specificity. MSP mRNA was found to be ∼10-fold greater in the CNS of the rat and human, as compared with most peripheral tissues, and within the CNS was found to be highest by a factor of four in the medulla oblongata and spinal cord. Levels of mRNA encoding tissue plasminogen activator (tPA) also were elevated in the spinal cord but were more widespread in peripheral tissues as compared with MSP.In the adult rat lumbosacral spinal cord,in situlocalization of MSP mRNA demonstrated 2-fold higher levels in the white, as compared with the gray, matter. MSP mRNA expression was shown to increase 3-fold in the white matter and 1.5-fold in the gray laminae at 72 hr after intraperitoneal injection of the AMPA/kainate glutamate receptor-specific agonist, kainic acid (KA). MSP mRNA remained elevated in the ventral gray matter, including expression associated with the motor neurons of lamina IX, at 7 d after the initial excitotoxic insult. Together, these observations indicate that MSP is in a position to play a fundamental role in normal homeostasis and in the response of the spinal cord to injury.
DNA Replication and Postreplication Mismatch Repair in Cell-Free Extracts from Cultured Human Neuroblastoma and Fibroblast Cells
Authors: David Pascale , Efrati Edna , Tocco Georges , Krauss Sharon Wald , Goodman Myron F. 
Published: April 2018

DNA synthesis and postreplication mismatch repair were measuredin vitrousing cell-free extracts from cultured human SY5Y neuroblastoma and WI38 fibroblast cells in different growth states. All extracts, including differentiated SY5Y and quiescent WI38 fibroblasts, catalyzed SV40 origin-dependent DNA synthesis, totally dependent on SV40 T-antigen. Thus, although differentiated neuroblastoma and quiescent fibroblasts cells were essentially nondividing, their extracts were competent for DNA replication using DNA polymerases δ, α, and possibly ε, with proliferating cell nuclear antigen. Nonreplicative DNA synthesis and lesion bypass by either α- or β-polymerases were detected independently in extracts using primed or gapped single-stranded DNA templates. Long-patch postreplication mismatch repair was measured for the first time in neuroblastoma cell-free extracts. Extracts from subconfluent and high-density SY5Y cells catalyzed postreplication mismatch repair with efficiencies comparable to those of HeLa cell extracts. No significant differences were observed in repair between SY5Y differentiated and undifferentiated cell extracts. Mismatch repair efficiencies were threefold lower in extracts from subconfluent WI38 cells, and repair in WI38 quiescent cells was fourfold less than in subconfluent cells, suggesting that mismatch repair may be regulated. The spectrum of mismatch repair in SY5Y extracts closely resembled the mismatch removal specificities of HeLa extracts: T · G and G · G mismatches were repaired most efficiently; C · A, A · A, A · G and a five-base loop were repaired with intermediate efficiency; repair of G · A, C · C, and T · T mismatches was extremely inefficient.