bluuebunny/crossref_metadata_2025 huggingface dataset:
The Synaptophysin–Synaptobrevin Complex: a Hallmark of Synaptic Vesicle Maturation
Authors: Becher Anja , Drenckhahn Anne , Pahner Ingrid , Margittai Martin , Jahn Reinhard , Ahnert-Hilger Gudrun
Published: April 2018

Exocytosis of synaptic vesicles requires the formation of a fusion complex consisting of the synaptic vesicle protein synaptobrevin (vesicle-associated membrane protein, or VAMP) and the plasma membrane proteins syntaxin and soluble synaptosomal-associated protein of 25 kDa (or SNAP 25). In search of mechanisms that regulate the assembly of the fusion complex, it was found that synaptobrevin also binds to the vesicle protein synaptophysin and that synaptophysin-bound synaptobrevin cannot enter the fusion complex. Using a combination of immunoprecipitation, cross-linking, andin vitrointeraction experiments, we report here that the synaptophysin–synaptobrevin complex is upregulated during neuronal development. In embryonic rat brain, the complex is not detectable, although synaptophysin and synaptobrevin are expressed and are localized to the same nerve terminals and to the same pool of vesicles. In contrast, the ability of synaptobrevin to participate in the fusion complex is detectable as early as embryonic day 14. The binding of synaptoporin, a closely related homolog of synaptophysin, to synaptobrevin changes in a similar manner during development. Recombinant synaptobrevin binds to synaptophysin derived from adult brain extracts but not to that derived from embryonic brain extracts. Furthermore, the soluble cytosol fraction of adult, but not of embryonic, synaptosomes contains a protein that induces synaptophysin–synaptobrevin complex formation in embryonic vesicle fractions. We conclude that complex formation is regulated during development and is mediated by a posttranslational modification of synaptophysin. Furthermore, we propose that the synaptophysin–synaptobrevin complex is not essential for exocytosis but rather provides a reserve pool of synaptobrevin for exocytosis that can be readily recruited during periods of high synaptic activity.
Distinct Signaling Pathways Mediate Touch and Osmosensory Responses in a Polymodal Sensory Neuron
Authors: Hart Anne C. , Kass Jamie , Shapiro Jonathan E. , Kaplan Joshua M.
Published: April 2018

TheCaenorhabditis elegansASH sensory neurons mediate responses to nose touch, hyperosmolarity, and volatile repellent chemicals. We show here that distinct signaling pathways mediate the responses to touch and hyperosmolarity. ASH neurons distinguish between these stimuli because habituation to nose touch has no effect on the response to high osmolarity or volatile chemicals (1-octanol). Mutations inosm-10eliminate the response to hyperosmolarity but have no effect on responses to nose touch or to volatile repellents. OSM-10 is a novel cytosolic protein expressed in ASH and three other classes of sensory neurons. Mutations in two other osmosensory-defective genes,eos-1andeos-2, interact genetically withosm-10. Our analysis suggests that nose touch sensitivity and osmosensation occur via distinct signaling pathways in ASH and that OSM-10 is required for osmosensory signaling.
The 5′-Flanking Region of the Mouse Adenylyl Cyclase Type VIII Gene Imparts Tissue-Specific Expression in Transgenic Mice
Authors: Muglia Lisa M. , Schaefer Michele L. , Vogt Sherri K. , Gurtner Gregory , Imamura Atsuko , Muglia Louis J.
Published: April 2018

The calcium-stimulated adenylyl cyclases (ACs) play a central role in stimulus-dependent modification of synaptic function. The type VIII AC (AC8) is one of three mammalian calcium-stimulated isoforms, each of which is expressed in a region-specific manner in the CNS. To delineate the DNA sequences responsible for appropriate targeting of AC8 expression, we report here the complete structure of the AC8 gene and define the pattern of expression of the full-length cDNA and its splice variants. In addition to expression within the brain, robust expression of AC8 was also found in the lung. Byin situhybridization, we have found the highest expression of AC8 mRNA within the olfactory bulb, thalamus, habenula, cerebral cortex, and hypothalamic supraoptic and paraventricular nuclei. By generating transgenic mice whose expression of β-galactosidase is controlled by the AC8 5′-flanking DNA sequences, we demonstrate that the DNA sequences within the 10 kb preceding exon 1 are critical for establishment of this region-specific pattern. This spectrum of sites of production is unique to AC8 among the calcium-stimulated adenylyl cyclases and suggests nonredundant functions with other adenylyl cyclases in neuroendocrine regulation and/or behavior.
In VitroAnalog of Operant Conditioning inAplysia. I. Contingent Reinforcement Modifies the Functional Dynamics of an Identified Neuron
Authors: Nargeot Romuald , Baxter Douglas A. , Byrne John H.
Published: April 2018

Previously, an analog of operant conditioning inAplysiawas developed using the rhythmic motor activity in the isolated buccal ganglia. This analog expressed a key feature of operant conditioning, namely a selective enhancement in the occurrence of a designated motor pattern by contingent reinforcement. Different motor patterns generated by the buccal central pattern generator were induced by monotonic stimulation of a peripheral nerve (i.e., n.2,3). Phasic stimulation of the esophageal nerve (E n.) was used as an analog of reinforcement. The present study investigated the neuronal mechanisms associated with the genesis of different motor patterns and their modifications by contingent reinforcement. The genesis of different motor patterns was related to changes in the functional states of the pre-motor neuron B51. During rhythmic activity, B51 dynamically switched between inactive and active states. Bursting activity in B51 was associated with, and predicted, characteristic features of a specific motor pattern (i.e., pattern I). Contingent reinforcement of pattern I modified the dynamical properties of B51 by decreasing its resting conductance and threshold for eliciting plateau potentials and thus increased the occurrences of pattern I-related activity in B51. These modifications were not observed in preparations that received either noncontingent reinforcement (i.e., yoke control) or no reinforcement (i.e., control). These results suggest that a contingent reinforcement paradigm can regulate the dynamics of neuronal activity that is centrally programmed by the intrinsic cellular properties of neurons.
In VitroAnalog of Operant Conditioning inAplysia. II. Modifications of the Functional Dynamics of an Identified Neuron Contribute to Motor Pattern Selection
Authors: Nargeot Romuald , Baxter Douglas A. , Byrne John H.
Published: April 2018

Previously, an analog of operant conditioning was developed using the buccal ganglia ofAplysia, the probabilistic occurrences of a specific motor pattern (i.e., pattern I), a contingent reinforcement (i.e., stimulation of the esophageal nerve), and monotonic stimulation of a peripheral nerve (i.e., n.2,3). This analog expressed a key feature of operant conditioning (i.e., selective enhancement of the probability of occurrence of a designated motor pattern by contingent reinforcement). In addition, the training induced changes in the dynamical properties of neuron B51, an element of the buccal central pattern generator. To gain insights into the neuronal mechanisms that mediate features of operant conditioning, the present study identified a neuronal element that was critically involved in the selective enhancement of pattern I. We found that bursting activity in cell B51 contributed significantly to the expression of pattern I and that changes in the dynamical properties of this cell were associated with the selective enhancement of pattern I. These changes could be induced by an explicit association of reinforcement with random depolarization of B51. No stimulation of n.2,3 was required. These results indicate that the selection of a designated motor pattern by contingent reinforcement and the underlying neuronal plasticity resulted from the association of reinforcement with a component of central neuronal activity that contributes to a specific motor pattern. The sensory stimulus that allows for occurrences of different motor acts may not be critical for induction of plasticity that mediates the selection of a motor output by contingent reinforcement in operant conditioning.
Coding of Sound Envelopes by Inhibitory Rebound in Neurons of the Superior Olivary Complex in the Unanesthetized Rabbit
Authors: Kuwada Shigeyuki , Batra Ranjan
Published: April 2018

Most natural sounds (e.g., speech) are complex and have amplitude envelopes that fluctuate rapidly. A number of studies have examined the neural coding of envelopes, but little attention has been paid to the superior olivary complex (SOC), a constellation of nuclei that receive information from the cochlear nucleus. We studied two classes of predominantly monaural neurons: those that displayed a sustained response to tone bursts and those that gave only a response to the tone offset. Our results demonstrate that the off neurons in the SOC can encode the pattern of amplitude-modulated sounds with high synchrony that is superior to sustained neurons. The upper cutoff frequency and highest modulation frequency at which significant synchrony was present were, on average, slightly higher for off neurons compared with sustained neurons. Finally, most sustained and off neurons encoded the level of pure tones over a wider range of intensities than those reported for auditory nerve fibers and cochlear nucleus neurons. A traditional view of inhibition is that it attenuates or terminates neural activity. Although this holds true for off neurons, the robust discharge when inhibition is released adds a new dimension. For simple sounds (i.e., pure tones), the off response can code a wide range of sound levels. For complex sounds, the off response becomes entrained to each modulation, resulting in a precise temporal coding of the envelope.
The Superior Olivary Nucleus and Its Influence on Nucleus Laminaris: A Source of Inhibitory Feedback for Coincidence Detection in the Avian Auditory Brainstem
Authors: Yang Lichuan , Monsivais Pablo , Rubel Edwin W
Published: April 2018

Located in the ventrolateral region of the avian brainstem, the superior olivary nucleus (SON) receives inputs from nucleus angularis (NA) and nucleus laminaris (NL) and projects back to NA, NL, and nucleus magnocellularis (NM). The reciprocal connections between the SON and NL are of particular interest because they constitute a feedback circuit for coincidence detection. In the present study, the chick SON was investigated.In vivotracing studies show that the SON projects predominantly to the ipsilateral NM, NL, and NA.In vitrowhole-cell recording reveals single-cell morphology, firing properties, and postsynaptic responses. SON neurons are morphologically and physiologically suited for temporal integration; their firing patterns do not reflect the temporal structure of their excitatory inputs. Of most interest, direct stimulation of the SON evokes long-lasting inhibition in NL neurons. The inhibition blocks both intrinsic spike generation and orthodromically evoked activity in NL neurons and can be eliminated by bicuculline methiodide, a potent antagonist for GABAAreceptor-mediated neurotransmission. These results strongly suggest that the SON provides GABAergic inhibitory feedback to laminaris neurons. We discuss a mechanism whereby SON-evoked GABAergic inhibition can influence the coding of interaural time differences for sound localization in the avian auditory brainstem.
Effect of Chronic High-Dose Exogenous Cortisol on Hippocampal Neuronal Number in Aged Nonhuman Primates
Authors: Leverenz James B. , Wilkinson Charles W. , Wamble Molly , Corbin Shannon , Grabber Jo Ellen , Raskind Murray A. , Peskind Elaine R.
Published: April 2018

Chronic exposure to increased glucocorticoid concentrations appears to lower the threshold for hippocampal neuronal degeneration in the old rat. It has been proposed that increased brain exposure to glucocorticoids may lower the threshold for hippocampal neuronal degeneration in human aging and Alzheimer’s disease. Here, we asked whether chronic administration of high-dose cortisol to older nonhuman primates decreases hippocampal neuronal number as assessed by unbiased stereological counting methodology. SixteenMacaca nemestrina(pigtailed macaques) from 18 to 29 years of age were age-, sex-, and weight-matched into pairs and randomized to receive either high-dose oral hydrocortisone (cortisol) acetate (4–6 mg/kg/d) or placebo in twice daily palatable treats for 12 months. Hypothalamic–pituitary–adrenal activity was monitored by measuring plasma adrenocorticotropin and cortisol, 24 hr urinary cortisol, and CSF cortisol. Urinary, plasma, and CSF cortisol were elevated, and plasma adrenocorticotropin was reduced in the active treatment group. Total hippocampal volume, subfield volumes, subfield neuronal density, and subfield total neuronal number did not differ between the experimental groups. These findings suggest that chronically elevated cortisol concentrations, in the absence of stress, do not produce hippocampal neuronal loss in nonhuman primates.
Nicotinic Receptor Activation Excites Distinct Subtypes of Interneurons in the Rat Hippocampus
Authors: McQuiston A. Rory , Madison Daniel V.
Published: April 2018

We examined the function of nicotinic acetylcholine receptors (nAChRs) in interneurons of area CA1 of the rat hippocampus. CA1 interneurons could be classified into three categories based on nicotinic responses. The first class was depolarized by α7 nAChRs, found in all layers of CA1 and as a group, had axonal projections to all neuropil layers of CA1. The second class had both fast α7 and slow non-α7 nAChR depolarizing responses, was localized primarily to the stratum oriens, and had axonal projections to the stratum lacunosum-moleculare. The third group had no nicotinic response. This group was found in or near the stratum pyramidale and had axonal projections almost exclusively within and around this layer. Low concentrations (500 nm) of nicotine desensitized fast and slow nAChR responses. These findings demonstrate that there are distinct subsets of interneurons with regard to nicotinic receptor expression and with predictable morphological properties that suggest potential cellular actions for nicotinic receptor activation in normal CNS function and during nicotine abuse.
Selective Color Constancy Deficits after Circumscribed Unilateral Brain Lesions
Authors: Rüttiger Lukas , Braun Doris I. , Gegenfurtner Karl R. , Petersen Dirk , Schönle Paul , Sharpe Lindsay T.
Published: April 2018

The color of an object, when part of a complex scene, is determined not only by its spectral reflectance but also by the colors of all other objects in the scene (von Helmholtz, 1886; Ives, 1912; Land, 1959). By taking global color information into account, the visual system is able to maintain constancy of the color appearance of the object, despite large variations in the light incident on the retina arising from changes in the spectral content of the illuminating light (Hurlbert, 1998; Maloney, 1999). The neural basis of this color constancy is, however, poorly understood. Although there seems to be a prominent role for retinal, cone-specific adaptation mechanisms (von Kries, 1902; Pöppel, 1986; Foster and Nascimento, 1994), the contribution of cortical mechanisms to color constancy is still unclear (Land et al., 1983; D’Zmura and Lennie, 1986). We examined the color perception of 27 patients with defined unilateral lesions mainly located in the parieto-temporo-occipital and fronto-parieto-temporal cortex. With a battery of clinical and specially designed color vision tests we tried to detect and differentiate between possible deficits in central color processing. Our results show that color constancy can be selectively impaired after circumscribed unilateral lesions in parieto-temporal cortex of the left or right hemisphere. Five of 27 patients exhibited significant deficits in a color constancy task, but all of the 5 performed well in color discrimination or higher-level visual tasks, such as the association of colors with familiar objects. These results indicate that the computations underlying color constancy are mediated by specialized cortical circuitry, which is independent of the neural substrate for color discrimination and for assigning colors to objects.
Hypothalamic Hypocretin (Orexin): Robust Innervation of the Spinal Cord
Authors: van den Pol Anthony N.
Published: April 2018

Hypocretin (orexin) is synthesized by neurons in the lateral hypothalamus and has been reported to increase food intake and regulate the neuroendocrine system. In the present paper, long descending axonal projections that contain hypocretin were found that innervate all levels of the spinal cord from cervical to sacral segments, as studied in mouse, rat, and human spinal cord and not previously described. High densities of axonal innervation are found in regions of the spinal cord related to modulation of sensation and pain, notably in the marginal zone (lamina 1). Innervation of the intermediolateral column and lamina 10 as well as strong innervation of the caudal region of the sacral cord suggest that hypocretin may participate in the regulation of both the sympathetic and parasympathetic parts of the autonomic nervous system. Double-labeling experiments in mice combining retrograde transport of diamidino yellow after spinal cord injections and immunocytochemistry support the concept that hypocretin-immunoreactive fibers in the cord originate from the neurons in the lateral hypothalamus. Digital-imaging physiological studies with fura-2 detected a rise in intracellular calcium in response to hypocretin in cultured rat spinal cord neurons, indicating that spinal cord neurons express hypocretin-responsive receptors. A greater number of cervical cord neurons responded to hypocretin than another hypothalamo-spinal neuropeptide, oxytocin. These data suggest that in addition to possible roles in feeding and endocrine regulation, the descending hypocretin fiber system may play a role in modulation of sensory input, particularly in regions of the cord related to pain perception and autonomic tone.
Long-Term Effects of Transcranial Magnetic Stimulation on Hippocampal Reactivity to Afferent Stimulation
Authors: Levkovitz Yechiel , Marx Julia , Grisaru Nimrod , Segal Menahem
Published: April 2018

Transcranial magnetic stimulation (TMS) has become a promising treatment of affective disorders in humans, yet the neuronal basis of its long-lasting effects in the brain is still unknown. We studied acute and lasting effects of TMS on reactivity of the rat hippocampus to stimulation of the perforant path. Application of TMS to the brain of the anesthetized rat caused a dose-dependent transient increase in population spike (PS) response of the dentate gyrus to perforant path stimulation. In addition, TMS caused a marked decrease in inhibition and an increase in paired-pulse potentiation of reactivity to stimulation of the perforant path. Also, TMS suppressed the ability of fenfluramine (FFA), a serotonin releaser, to potentiate PS response to perforant path stimulation. Chronic TMS did not affect single population spikes but caused an increase in paired-pulse potentiation, which was still evident 3 weeks after the last of seven daily TMS treatments. After chronic TMS, FFA was ineffective in enhancing reactivity to perforant path stimulation, probably because it lost the ability to release serotonin. In addition, the β adrenergic receptor agonist isoproterenol, which caused an increase in PS in the control rats, failed to do so in the TMS-treated rats. These results indicate that TMS produces a long-term reduction in efficacy of central modulatory systems.
Mechanisms of Neural Synchrony in the Septohippocampal Pathways Underlying Hippocampal Theta Generation
Authors: Bland Brian H. , Oddie Scott D. , Colom Luis V.
Published: April 2018

Using urethane-anesthetized rats, 18 simultaneously recorded septohippocampal cell pairs (36 individual cells), each classified as theta-related according to the criteria of Colom and Bland (1987), were studied during four spontaneously occurring hippocampal field conditions: (1) large amplitude irregular activity (LIA) only; (2) the transition from LIA to theta; (3) theta only; and (4) the transition from theta to LIA. The main objective was to study the temporal relationships and degree of neural synchrony between the discharges of the cell pairs, using both time-averaged and time-dependent joint peristimulus time histogram correlation techniques, during the four conditions, to determine their contribution to the control of oscillation and synchrony (theta) in the hippocampus. The study demonstrated that the transition from the LIA state to the theta field state in the hippocampus required a temporal sequence of changes in theta-related cellular activity occurring on average 500 msec preceding the transition: (1) the medial septum inhibits hippocampal theta-OFF cells; (2) medial septal tonic theta-ON cells provide tonic depolarizing inputs to initiate membrane potential oscillations (MPOs) in hippocampal phasic theta-ON cells, whereas medial septal phasic theta-ON cells synchronize the MPOs of hippocampal phasic theta-ON cells and the discharges of hippocampal tonic theta-ON cells. Much of the time preceding the LIA to theta transition is accounted for by recruitment of these theta-related cell populations. Conversely, “turning off” the theta state occurs abruptly and involves the medial septal disinhibition of hippocampal theta-OFF cells.
Cytosolic Ca2+Changes duringIn VitroIschemia in Rat Hippocampal Slices: Major Roles for Glutamate and Na+-Dependent Ca2+Release from Mitochondria
Authors: Zhang Yanlong , Lipton Peter
Published: April 2018

This work determined Ca2+transport processes that contribute to the rise in cytosolic Ca2+duringin vitroischemia (deprivation of oxygen and glucose) in the hippocampus. The CA1 striatum radiatum of rat hippocampal slices was monitored by confocal microscopy of calcium green-1. There was a 50–60% increase in fluorescence during 10 min of ischemia after a 3 min lag period. During the first 5 min of ischemia the major contribution was from Ca2+entering via NMDA receptors; most of the fluorescence increase was blocked by MK-801. Approximately one-half of the sustained increase in fluorescence during 10 min of ischemia was caused by activation of Ca2+release from mitochondria via the mitochondrial 2Na+–Ca2+exchanger. Inhibition of Na+influx across the plasmalemma using lidocaine, low extracellular Na+, or the AMPA/kainate receptor blocker CNQX reduced the fluorescence increase by 50%. The 2Na+–Ca2+exchange blocker CGP37157 also blocked the increase, and this effect was not additive with the effects of blocking Na+influx. When added together, CNQX and lidocaine inhibited the fluorescence increase more than CGP37157 did. Thus, during ischemia, Ca2+entry via NMDA receptors accounts for the earliest rise in cytosolic Ca2+. Approximately 50% of the sustained rise is attributable to Na+entry and subsequent Ca2+release from the mitochondria via the 2Na+–Ca2+exchanger. Sodium entry is also hypothesized to compromise clearance of cytosolic Ca2+by routes other than mitochondrial uptake, probably by enhancing ATP depletion, accounting for the large inhibition of the Ca2+increase by the combination of CNQX and lidocaine.
Manganese Superoxide Dismutase Mediates the Early Release of Mitochondrial Cytochrome C and Subsequent DNA Fragmentation after Permanent Focal Cerebral Ischemia in Mice
Authors: Fujimura Miki , Morita-Fujimura Yuiko , Kawase Makoto , Copin Jean-Christophe , Calagui Bernard , Epstein Charles J. , Chan Pak H.
Published: April 2018

Recent studies have shown that release of mitochondrial cytochrome c is a critical step in the apoptosis process. We have reported that cytosolic redistribution of cytochrome cin vivooccurred after transient focal cerebral ischemia (FCI) in rats and preceded the peak of DNA fragmentation. Although the involvement of reactive oxygen species in the cytosolic redistribution of cytochrome cin vitrohas been suggested, the detailed mechanism by which cytochrome c release is mediatedin vivohas not yet been established. Also, the role of mitochondrial oxidative stress in cytochrome c release is unknown. These issues can be addressed using knock-out mutants that are deficient in the level of the mitochondrial antioxidant manganese superoxide dismutase (Mn-SOD). In this study we examined the subcellular distribution of the cytochrome c protein in both wild-type mice and heterozygous knock-outs of the Mn-SOD gene (Sod2 −/+) after permanent FCI, in which apoptosis is assumed to participate. Cytosolic cytochrome c was detected as early as 1 hr after ischemia, and correspondingly, mitochondrial cytochrome c showed a significant reduction 2 hr after ischemia (p< 0.01). Cytosolic accumulation of cytochrome c was significantly higher in Sod2 −/+ mice compared with wild-type animals (p< 0.05).N-benzyloxycarbonyl-val-ala-asp-fluoromethyl ketone (z-VAD.FMK), a nonselective caspase inhibitor, did not affect cytochrome c release after ischemia. A significant amount of DNA laddering was detected 24 hr after ischemia and increased in Sod2 −/+ mice. These data suggest that Mn-SOD blocks cytosolic release of cytochrome c and could thereby reduce apoptosis after permanent FCI.
Activities of the Primary and Supplementary Motor Areas Increase in Preparation and Execution of Voluntary Muscle Relaxation: An Event-Related fMRI Study
Authors: Toma Keiichiro , Honda Manabu , Hanakawa Takashi , Okada Tomohisa , Fukuyama Hidenao , Ikeda Akio , Nishizawa Sadahiko , Konishi Junji , Shibasaki Hiroshi
Published: April 2018

Brain activity associated with voluntary muscle relaxation was examined by applying event-related functional magnetic resonance imaging (fMRI) technique, which enables us to observe change of fMRI signals associated with a single motor trial. The subject voluntarily relaxed or contracted the right upper limb muscles. Each motor mode had two conditions; one required joint movement, and the other did not. Five axial images covering the primary motor area (M1) and supplementary motor area (SMA) were obtained once every second, using an echoplanar 1.5 tesla MRI scanner. One session consisted of 60 dynamic scans (i.e., 60 sec). The subject performed a single motor trial (i.e., relaxation or contraction) during one session in his own time. Ten sessions were done for each task. During fMRI scanning, electromyogram (EMG) was monitored from the right forearm muscles to identify the motor onset. We calculated the correlation between the obtained fMRI signal and the expected hemodynamic response. The muscle relaxation showed transient signal increase time-locked to the EMG offset in the M1 contralateral to the movement and bilateral SMAs, where activation was observed also in the muscle contraction. Activated volume in both the rostral and caudal parts of SMA was significantly larger for the muscle relaxation than for the muscle contraction (p< 0.05). The results suggest that voluntary muscle relaxation occurs as a consequence of excitation of corticospinal projection neurons or intracortical inhibitory interneurons, or both, in the M1 and SMA, and both pre-SMA and SMA proper play an important role in motor inhibition.
Leukemia Inhibitory Factor Augments Neurotrophin Expression and Corticospinal Axon Growth after Adult CNS Injury
Authors: Blesch A. , Uy H. S. , Grill R. J. , Cheng J.-G. , Patterson P. H. , Tuszynski M. H.
Published: April 2018

The cytokine leukemia inhibitory factor (LIF) modulates glial and neuronal function in development and after peripheral nerve injury, but little is known regarding its role in the injured adult CNS. To further understand the biological role of LIF and its potential mechanisms of action after CNS injury, effects of cellularly delivered LIF on axonal growth, glial activation, and expression of trophic factors were examined after adult mammalian spinal cord injury. Fibroblasts genetically modified to produce high amounts of LIF were grafted to the injured spinal cords of adult Fischer 344 rats. Two weeks after injury, animals with LIF-secreting cells showed a specific and significant increase in corticospinal axon growth compared with control animals. Furthermore, expression of neurotrophin-3, but not nerve growth factor, brain-derived neurotrophic factor, glia cell line-derived neurotrophic factor, or ciliary neurotrophic factor, was increased at the lesion site in LIF-grafted but not in control subjects. No differences in astroglial and microglial/macrophage activation were observed. Thus, LIF can directly or indirectly modulate molecular and cellular responses of the adult CNS to injury. These findings also demonstrate that neurotrophic molecules can augment expression of other trophic factorsin vivoafter traumatic injury in the adult CNS.
Patterns of Synchronization in the Superior Colliculus of Anesthetized Cats
Authors: Brecht Michael , Singer Wolf , Engel Andreas K.
Published: April 2018

Sensorimotor transformations in the mammalian superior colliculus (SC) are mediated by large sets of distributed neurons. For such distributed coding systems, stimulus superposition poses problems attributable to the merging of neural populations coding for different stimuli. Such superposition problems could be overcome by synchronization of neuronal discharges, because it allows the selection of a subset of distributed responses for further joint processing. To assess the putative role of such a temporal binding mechanism in the SC, we have applied correlation analysis to visually evoked collicular activity. We performed recordings of single-unit and multiunit activity in the SC of anesthetized and paralyzed cats with multiple electrodes. Autocorrelation analysis revealed that collicular neurons often discharged in broad (20–100 msec) bursts or with an oscillatory patterning in the α- and β-frequency range. Significantly modulated cross-correlograms were observed in 50% (128 of 258) of the collicular multiunit recording pairs, and for these pairs significant correlations occurred in 44% of the stimulation epochs. For the single-unit pairs, significant interactions were observed in 14 of 48 cases studied (29%). Collicular cross-correlograms were often oscillatory, and these oscillations covered a broad frequency range of up to 100 Hz, with a predominance of oscillation frequencies in the α- and β-range. In the majority of the significant correlograms (64%) the phase lag of the center peak was <5 msec. The probability of collicular synchronization increased with the overlap of the receptive fields and the proximity of the recording sites. Correlations were also observed between cells in the superficial and deep SC layers. Collicular synchronization required activation of the respective cells with a single coherent stimulus and broke down when the neurons were activated with two different stimuli. These data are consistent with the notion that collicular synchrony could define assemblies of functionally related cells.
Calcium-Activated Potassium Conductances Contribute to Action Potential Repolarization at the Soma But Not the Dendrites of Hippocampal CA1 Pyramidal Neurons
Authors: Poolos Nicholas P. , Johnston Daniel
Published: April 2018

Evidence is accumulating that voltage-gated channels are distributed nonuniformly throughout neurons and that this nonuniformity underlies regional differences in excitability within the single neuron. Previous reports have shown that Ca2+, Na+, A-type K+, and hyperpolarization-activated, mixed cation conductances have varying distributions in hippocampal CA1 pyramidal neurons, with significantly different densities in the apical dendrites compared with the soma. Another important channel mediates the large-conductance Ca2+-activated K+current (IC), which is responsible in part for repolarization of the action potential (AP) and generation of the afterhyperpolarization that follows the AP recorded at the soma. We have investigated whether this current is activated by APs retrogradely propagating in the dendrites of hippocampal pyramidal neurons using whole-cell dendritic patch-clamp recording techniques. We found noICactivation by back-propagating APs in distal dendritic recordings. Dendritic APs activatedIConly in the proximal dendrites, and this activation decayed within the first 100–150 μm of distance from the soma. The decay ofICin the proximal dendrites occurred despite AP amplitude, plus presumably AP-induced Ca2+influx, that was comparable with that at the soma. Thus we conclude thatICactivation by action potentials is nonuniform in the hippocampal pyramidal neuron, which may represent a further example of regional differences in neuronal excitability that are determined by the nonuniform distribution of voltage-gated channels in dendrites.
The Electrical Properties of Auditory Hair Cells in the Frog Amphibian Papilla
Authors: Smotherman Michael S. , Narins Peter M.
Published: April 2018

The amphibian papilla (AP) is the principal auditory organ of the frog. Anatomical and neurophysiological evidence suggests that this hearing organ utilizes both mechanical and electrical (hair cell-based) frequency tuning mechanisms, yet relatively little is known about the electrophysiology of AP hair cells. Using the whole-cell patch-clamp technique, we have investigated the electrical properties and ionic currents of isolated hair cells along the rostrocaudal axis of the AP.

Electrical resonances were observed in the voltage response of hair cells harvested from the rostral and medial, but not caudal, regions of the AP. Two ionic currents,ICaandIK(Ca), were observed in every hair cell; however, their amplitudes varied substantially along the epithelium. Only rostral hair cells exhibited an inactivating potassium current (IA), whereas an inwardly rectifying potassium current (IK1) was identified only in caudal AP hair cells.

Electrically tuned hair cells exhibited resonant frequencies from 50 to 375 Hz, which correlated well with hair cell position and the tonotopic organization of the papilla. Variations in the kinetics of the outward current contribute substantially to the determination of resonant frequency.ICaandIK(Ca)amplitudes increased with resonant frequency, reducing the membrane time constant with increasing resonant frequency. We conclude that a tonotopically organized hair cell substrate exists to support electrical tuning in the rostromedial region of the frog amphibian papilla and that the cellular mechanisms for frequency determination are very similar to those reported for another electrically tuned auditory organ, the turtle basilar papilla.
Fast Excitatory Synaptic Transmission Mediated by Nicotinic Acetylcholine Receptors inDrosophilaNeurons
Authors: Lee Daewoo , O’Dowd Diane K.
Published: April 2018

Difficulty in recording from single neuronsin vivohas precluded functional analyses of transmission at central synapses inDrosophila, where the neurotransmitters and receptors mediating fast synaptic transmission have yet to be identified. Here we demonstrate that spontaneously active synaptic connections form between cultured neurons prepared from wild-type embryos and provide the first direct evidence that both acetylcholine and GABA mediate fast interneuronal synaptic transmission inDrosophila. The predominant type of fast excitatory transmission between cultured neurons is mediated by nicotinic acetylcholine receptors (nAChRs). Detailed analysis of cholinergic transmission reveals that spontaneous EPSCs (sEPSCs) are composed of both evoked and action potential-independent [miniature EPSC (mEPSC)] components. The mEPSCs are characterized by a broad, positively skewed amplitude histogram in which the variance is likely to reflect differences in the currents induced by single quanta. Biophysical characteristics of the cholinergic mEPSCs include a rapid rise time (0.6 msec) and decay (τ = 2 msec). Regulation of mEPSC frequency by external calcium and cobalt suggests that calcium influx through voltage-gated channels influences the probability of ACh release. In addition, brief depolarization of the cultures with KCl can induce a calcium-dependent increase in sEPSC frequency that persists for up to 3 hr after termination of the stimulus, illustrating one form of plasticity at these cholinergic synapses. These data demonstrate that cultured embryonic neurons, amenable to both genetic and biochemical manipulations, present a unique opportunity to define genes/signal transduction cascades involved in functional regulation of fast excitatory transmission at interneuronal cholinergic synapses inDrosophila.
Alternative Splicing of a Short Cassette Exon in α1BGenerates Functionally Distinct N-Type Calcium Channels in Central and Peripheral Neurons
Authors: Lin Zhixin , Lin Yingxin , Schorge Stephanie , Pan Jennifer Qian , Beierlein Michael , Lipscombe Diane
Published: April 2018

The N-type Ca channel α1Bsubunit is localized to synapses throughout the nervous system and couples excitation to release of neurotransmitters. In a previous study, two functionally distinct variants of the α1Bsubunit were identified, rnα1B-band rnα1B-d, that differ at two loci;four amino acids [SerPheMetGly (SFMG)] in IIIS3–S4 and two amino acids [GluThr (ET)] in IVS3–S4. These variants are reciprocally expressed in rat brain and sympathetic ganglia (Lin et al., 1997a). We now show that the slower activation kinetics of rnα1B-b(ΔSFMG/+ET) compared with rnα1B-d(+SFMG/ΔET) channels are fully accounted for by the insertion of ET in IVS3–S4 and not by the lack of SFMG in IIIS3–S4. We also show that the inactivation kinetics of these two variants are indistinguishable. Through genomic analysis we identify a six-base cassette exon that encodes the ET site and with ribonuclease protection assays demonstrate that the expression of this mini-exon is essentially restricted to α1BRNAs of peripheral neurons. We also show evidence for regulated alternative splicing of a six-base exon encoding NP in the IVS3–S4 linker of the closely related α1Agene and establish that residues NP can functionally substitute for ET in domain IVS3–S4 of α1B. The selective expression of functionally distinct Ca channel splice variants of α1Band α1Asubunits in different regions of the nervous system adds a new dimension of diversity to voltage-dependent Ca signaling in neurons that may be important for optimizing action potential-dependent transmitter release at different synapses.
TheCaenorhabditis elegans unc-49Locus Encodes Multiple Subunits of a Heteromultimeric GABA Receptor
Authors: Bamber Bruce A. , Beg Asim A. , Twyman Roy E. , Jorgensen Erik M.
Published: April 2018

Ionotropic GABA receptors generally require the products of three subunit genes. By contrast, the GABA receptor needed for locomotion inCaenorhabditis elegansrequires only theunc-49gene. We clonedunc-49and demonstrated that it possesses an unusual overlapping gene structure.unc-49contains a single copy of a GABA receptor N terminus, followed by three tandem copies of a GABA receptor C terminus. Using a single promoter,unc-49generates three distinct GABAAreceptor-like subunits by splicing the N terminus to each of the three C-terminal repeats. This organization suggests that the three UNC-49 subunits (UNC-49A, UNC-49B, and UNC-49C) are coordinately rescued and therefore might coassemble to form a heteromultimeric GABA receptor. Surprisingly, only UNC-49B and UNC-49C are expressed at high levels, whereas UNC-49A expression is barely detectable. Green fluorescent protein-tagged UNC-49B and UNC-49C subunits are coexpressed in muscle cells and are colocalized to synaptic regions. UNC-49B and UNC-49C also coassemble efficiently inXenopusoocytes and HEK-293 cells to form a heteromeric GABA receptor. Together these data argue that UNC-49B and UNC-49C coassemble at theC. elegansneuromuscular junction. Thus,C. elegansis able to encode a heteromeric GABA receptor with a single locus.
Mutant Presenilin-1 Induces Apoptosis and Downregulates Akt/PKB
Authors: Weihl Conrad C. , Ghadge Ghanashyam D. , Kennedy Scott G. , Hay Nissim , Miller Richard J. , Roos Raymond P.
Published: April 2018

Most early onset cases of familial Alzheimer’s disease (AD) are caused by mutations in presenilin-1 (PS1) and presenilin-2 (PS2). These mutations lead to increased β-amyloid formation and may induce apoptosis in some model systems. Using primary cultured hippocampal neurons (HNs) and rat pheochromocytoma (PC12) cells transiently transfected with replication-defective recombinant adenoviral vectors expressing wild-type or mutant PS1, we demonstrate that mutant PS1s induce apoptosis, downregulate the survival factor Akt/PKB, and affect several Akt/PKB downstream targets, including glycogen synthase kinase-3β and β-catenin. Expression of a constitutively active Akt/PKB rescues HNs from mutant PS1-induced neuronal cell death, suggesting a potential therapeutic target for AD. Downregulation of Akt/PKB may be a mechanism by which mutant PS1 induces apoptosis and may play a role in the pathogenesis of familial AD.
Voltage-Activated K+Channels and Membrane Depolarization Regulate Accumulation of the Cyclin-Dependent Kinase Inhibitors p27Kip1and p21CIP1in Glial Progenitor Cells
Authors: Ghiani Cristina A. , Yuan Xiaoqing , Eisen Alex M. , Knutson Peter L. , DePinho Ronald A. , McBain Chris J. , Gallo Vittorio
Published: April 2018

Neural cell development is regulated by membrane ion channel activity. We have previously demonstrated that cell membrane depolarization with veratridine or blockage of K+channels with tetraethylammonium (TEA) inhibit oligodendrocyte progenitor (OP) proliferation and differentiation (Knutson et al., 1997); however the molecular events involved are largely unknown. Here we show that forskolin (FSK) and its derivative dideoxyforskolin (DFSK) block K+channels in OPs and inhibit cell proliferation. The antiproliferative effects of TEA, FSK, DFSK, and veratridine were attributable to OP cell cycle arrest in G1 phase. In fact, (1) cyclin D accumulation in synchronized OP cells was not affected by K+channel blockers or veratridine; (2) these agents prevented OP cell proliferation only if present during G1 phase; and (3) G1 blockers, such as rapamycin and deferoxamine, mimicked the anti-proliferative effects of K+channel blockers. DFSK also prevented OP differentiation, whereas FSK had no effect. Blockage of K+channels and membrane depolarization also caused accumulation of the cyclin-dependent kinase inhibitors p27Kip1and p21CIP1in OP cells. The antiproliferative effects of K+channel blockers and veratridine were still present in OP cells isolated from INK4a−/−mice, lacking the cyclin-dependent kinase inhibitors p16INK4aand p19ARF. Our results demonstrate that blockage of K+channels and cell depolarization induce G1 arrest in the OP cell cycle through a mechanism that may involve p27Kip1and p21CIP1and further support the conclusion that OP cell cycle arrest and differentiation are two uncoupled events.
Immortalized Human Dorsal Root Ganglion Cells Differentiate into Neurons with Nociceptive Properties
Authors: Raymon Heather K. , Thode Silke , Zhou Jiuying , Friedman Glenn C. , Pardinas Jose R. , Barrere Christian , Johnson Randolph M. , Sah Dinah W. Y.
Published: April 2018

A renewable source of human sensory neurons would greatly facilitate basic research and drug development. We had established previously conditionally immortalized human CNS cell lines that can differentiate into functional neurons (Sah et al., 1997). We report here the development of an immortalized human dorsal root ganglion (DRG) clonal cell line, HD10.6, with a tetracycline-regulatable v-myconcogene. In the proliferative condition, HD10.6 cells have a doubling time of 1.2 d and exhibit a neuronal precursor morphology. After differentiation of clone HD10.6 for 7 d in the presence of tetracycline, v-mycexpression was suppressed, and >50% of the cells exhibited typical neuronal morphology, stained positively for neuronal cytoskeletal markers, and fired action potentials in response to current injection. Furthermore, this cell line was fate-restricted to a neuronal phenotype; even in culture conditions that promote Schwann cell or smooth muscle differentiation of neural crest stem cells, HD10.6 differentiated exclusively into neurons. Moreover, differentiated HD10.6 cells expressed sensory neuron-associated transcription factors and exhibited capsaicin sensitivity. Taken together, these data indicate that we have established an immortalized human DRG cell line that can differentiate into sensory neurons with nociceptive properties. The cell line HD10.6 represents the first example of a human sensory neuronal line and will be valuable for basic research, as well as for the discovery of novel drug targets and clinical candidates.
Brain Mechanisms of Propofol-Induced Loss of Consciousness in Humans: a Positron Emission Tomographic Study
Authors: Fiset Pierre , Paus Tomás , Daloze Thierry , Plourde Gilles , Meuret Pascal , Bonhomme Vincent , Hajj-Ali Nadine , Backman Steven B. , Evans Alan C.
Published: April 2018

In the present study, we used positron emission tomography to investigate changes in regional cerebral blood flow (rCBF) during a general anesthetic infusion set to produce a gradual transition from the awake state to unconsciousness. Five right-handed human volunteers participated in the study. They were given propofol with a computer-controlled infusion pump to achieve three stable levels of plasma concentrations corresponding to mild sedation, deep sedation, and unconsciousness, the latter defined as unresponsiveness to verbal commands. During awake baseline and each of the three levels of sedation, two scans were acquired after injection of an H215O bolus. Global as well as regional CBF were determined and correlated with propofol concentrations. In addition, blood flow changes in the thalamus were correlated with those of the entire scanned volume to determine areas of coordinated changes.

In addition to a generalized decrease in global CBF, large regional decreases in CBF occurred bilaterally in the medial thalamus, the cuneus and precuneus, and the posterior cingulate, orbitofrontal, and right angular gyri. Furthermore, a significant covariation between the thalamic and midbrain blood flow changes was observed, suggesting a close functional relationship between the two structures.

We suggest that, at the concentrations attained, propofol preferentially decreases rCBF in brain regions previously implicated in the regulation of arousal, performance of associative functions, and autonomic control. Our data support the hypothesis that anesthetics induce behavioral changes via a preferential, concentration-dependent effect on specific neuronal networks rather than through a nonspecific, generalized effect on the brain.