bluuebunny/crossref_metadata_2025 huggingface dataset:
Ca2+-Induced Ca2+Release Mediates a Slow Post-Spike Hyperpolarization in Rabbit Vagal Afferent Neurons
Authors: Moore Kimberly A. , Cohen Akiva S. , Kao Joseph P. Y. , Weinreich Daniel
Published: December 2017

Moore, Kimberly A., Akiva S. Cohen, Joseph P. Y. Kao, and Daniel Weinreich. Ca2+-induced Ca2+release mediates a slow post-spike hyperpolarization in rabbit vagal afferent neurons. J. Neurophysiol. 79: 688–694, 1998. The relation between Ca2+-induced Ca2+release (CICR) elicited by action potentials (APs) and a Ca2+-dependent slow post-spike hyperpolarization (AHPslow) in acutely dissociated adult rabbit nodose neurons was studied using microfluorimetric calcium measurements in conjunction with standard intracellular current- and voltage-clamp recording techniques. The magnitude of the AP-induced transient increase in [Ca2+]i(ΔCat) was used to monitor CICR. There was a close correlation between the magnitude of the ΔCatand the AHPslowcurrent over the range of 1–16 APs ( r = 0.985). Functional CICR blockers, ryanodine (10 μM), thapsigargin (100 nM), 2,5-di( t-butyl)hydroquinone (10 μM) or cyclopiazonic acid (10 μM), selectively reduced the peak amplitude of the AHPslow≥91%. In five neurons, simultaneous recordings of the ΔCatand the AHPslowrevealed that both responses were blocked in parallel. These findings indicate that CICR is necessary for the generation of the AHPslowin rabbit nodose neurons. The ΔCatrises and decays significantly faster than the AHPslow. This temporal disparity suggests that activation of the AHPslowby Ca2+may require additional signal transduction steps.
Comparison of Two Methods of Producing Adaptation of Saccade Size and Implications for the Site of Plasticity
Authors: Scudder Charles A. , Batourina Ekatherina Y. , Tunder George S.
Published: December 2017

Scudder, Charles A., Ekatherina Y. Batourina, and George S. Tunder. Comparison of two methods of producing adaptation of saccade size and implications for the site of plasticity. J. Neurophysiol. 79: 704–715, 1998. Saccade accuracy is known to be maintained by adaptive mechanisms that progressively reduce any visual error that consistently exists at the end of saccades. Experimentally, the visual error is induced using one of two paradigms. In the first, the horizontal and medial recti of trained monkeys are tenectomized and allowed to reattach so that both muscles are paretic. After patching the unoperated eye and forcing the monkey to use the “paretic eye,” saccades initially undershoot the intended target, but gradually increase in size until they almost acquire the target in one step. In the second, the target of a saccade is displaced in midsaccade so that the saccade cannot land on target. Again saccade size adapts until the target can be acquired in one step. Because adaptation with the latter paradigm is very rapid but adaptation using the former is slow, it has frequently been questioned whether or not the two forms of adaptation depend on the same neural mechanisms. We show that the rate of adaptation in both paradigms depends on the number of possible visual targets, so that when this variable is equated, adaptation occurs at similar rates in both paradigms. To demonstrate further similarities between the result of the two paradigms, an experiment using intrasaccadic displacements was conducted to show that rapid adaptation possesses the capacity to produce gain changes that vary with orbital position. The relative size of intrasaccadic displacements were graded with orbital position so as to mimic the position-dependent dysmetria initially produced by a single paretic extraocular muscle. Induced changes in saccade size paralleled the size of the displacements, being largest for saccades into one hemifield and being negligible for saccades into the other hemifield or in the opposite direction. Collectively, the data remove the rational for asserting that adaptation produced by the two paradigms depends on separate neural mechanisms. We argue that adaptation produced by both paradigms depends on the cerebellum.
Organization of Recurrent Inhibition and Facilitation in Motor Nuclei Innervating Ankle Muscles of the Cat
Authors: Turkin Vladimir V. , Monroe Katrina S. , Hamm Thomas M.
Published: December 2017

Turkin, Vladimir V., Katrina S. Monroe, and Thomas M. Hamm. Organization of recurrent inhibition and facilitation in motor nuclei innervating ankle muscles of the cat. J. Neurophysiol. 79: 778–790, 1998. The distribution of recurrent inhibition and facilitation to motor nuclei of muscles that act at the cat ankle joint was compared with the locomotor activity and mechanical action of those muscles described in published studies. Emphasis was placed on motor nuclei whose muscles have a principal action about the abduction—adduction axis and the pretibial flexors: tibialis posterior (TP), peroneus longus (PerL), peroneus brevis (PerB), the anterior part of tibialis anterior (TA) and extensor digitorum longus (EDL). Most intracellular recordings in spinalized, unanesthetized decerebrate cats showed only inhibitory or excitatory responses to antidromic stimulation of peripheral nerves, but mixed effects were also seen. Recurrent effects among motor nuclei of ankle abductors and adductors were not distributed uniformly. TP motoneurons received recurrent inhibition from most other nuclei active in stance and stimulation of the TP nerve inhibited these motor nuclei. Although PerB motoneurons are also active during stance, they received primarily facilitation from most motor nuclei. PerL received mixtures of inhibition and facilitation from all sources. Stimulation of the nerves to PerL, PerB, and peroneus tertius (PerT) produced weak recurrent inhibition and facilitation, even in homonymous motoneurons and motoneurons of Ia synergists. The ankle flexors TA and EDL displayed different patterns of recurrent inhibition and facilitation. TA motoneurons received prominent homonymous inhibition and inhibition from semitendinosus (St). EDL, whose activity profile differs from TA and which also acts at the digits, did not receive strong recurrent inhibition from either TA or St, nor did stimulation of the EDL nerve produce much inhibition. The distribution of recurrent inhibition and facilitation is correlated with the pattern of locomotor activity, but with exceptions that suggest an influence of mechanical action, particularly in the antagonistic interactions between TP and PerB. The extended pattern of recurrent inhibition, the reduction or absence of inhibition produced by motor nuclei with individualized functions or digit function and the prevalence of facilitation suggest that the recurrent Renshaw system is organized into inhibitory and disinhibitory projections that participate in the control of sets of motor nuclei engaged in rhythmic and stereotyped movements.
Role of Frontal Eye Fields in Countermanding Saccades: Visual, Movement, and Fixation Activity
Authors: Hanes Doug P. , Patterson Warren F. , Schall Jeffrey D.
Published: December 2017

Hanes, Doug P., Warren F. Patterson II, and Jeffrey D. Schall. Role of frontal eye fields in countermanding saccades: visual, movement, and fixation activity. J. Neurophysiol. 79: 817–834, 1998. A new approach was developed to investigate the role of visual-, movement-, and fixation-related neural activity in gaze control. We recorded unit activity in the frontal eye fields (FEF), an area in frontal cortex that plays a central role in the production of purposeful eye movements, of monkeys ( Macaca mulatta) performing visually and memory-guided saccades. The countermanding paradigm was employed to assess whether single cells generate signals sufficient to control movement production. The countermanding paradigm consists of a task that manipulates the monkeys' ability to withhold planned saccades combined with an analysis based on a race model that provides an estimate of the time needed to cancel the movement that is being prepared. We obtained clear evidence that FEF neurons with eye movement-related activity generate signals sufficient to control the production of gaze shifts. Movement-related activity, which was growing toward a trigger threshold as the saccades were prepared, decayed in response to the stop signal within the time required to cancel the saccade. Neurons with fixation-related activity were less common, but during the countermanding paradigm, these neurons exhibited an equally clear gaze-control signal. Fixation cells that had a pause in firing before a saccade exhibited elevated activity in response to the stop signal within the time that the saccade was cancelled. In contrast to cells with movement or fixation activity, neurons with only visually evoked activity exhibited no evidence of signals sufficient to control the production of gaze shifts. However, a fraction of tonic visual cells exhibited a reduction of activity once a saccade command had been cancelled even though the visual target was still present in the receptive field. These findings demonstrate the use of the countermanding paradigm in identifying neural signatures of motor control and provide new information about the fine balance between gaze shifting and gaze holding mechanisms.
Discharge Characteristics of Vestibular Saccade Neurons in Alert Monkeys
Authors: Kaneko Chris R. S. , Fukushima Kikuro
Published: December 2017

Kaneko, Chris R. S. and Kikuro Fukushima. Discharge characteristics of vestibular saccade neurons in alert monkeys. J. Neurophysiol. 79: 835–847, 1998. We previously described a class of neurons, located in and around the interstitial nucleus of Cajal of the cat, that discharged during vestibular stimulation and before saccades. We called these neurons vestibular saccade neurons (VSNs). In the present study, we characterized similar neurons in the monkey. These neurons discharged before vertical saccades and during vertical vestibular stimulation as well as vertical smooth pursuit. Like cat VSNs, the discharge metrics of these VSNs were poorly related to saccade metrics and showed only occasional, weak sensitivity to eye position. They discharged most intensely (on-direction) for movements that were either upward or downward, and their on-directions were consistent during pitch and pursuit but not for eye position. For saccades, the correlation coefficient of number of spikes and vertical saccade size varied from 0.08 to 0.90 with a mean of ∼0.6. The average sensitivity (i.e., slope) of the number of spikes and vertical saccade size linear regression was 0.3 ± 0.2 spike/deg. Average correlations between peak discharge rate and peak saccade velocity and between burst duration and saccade duration were 0.5 and 0.4; sensitivities were 0.2 ± 0.2 spike per s per deg/s and 0.6 ± 0.5 ms/ms, respectively. Average vestibular sensitivities during 0.5 Hz, ±10° sinusoidal pitch while the animals suppressed their vestibular ocular reflex were 0.97 spike/s per deg/s for up VSNs and 0.66 spike/s per deg/s for down VSNs. The average static position sensitivity for the population of 39 VSNs tested was 0.55 spike/s per deg. The average gain for VSNs tested during 0.5 Hz, ±10° sinusoidal smooth pursuit tracking was 1.4 spike/s per deg/s. As we could not identify analogous neurons in the region of the monkey ponto-medullary junction, we conclude that horizontal on-direction VSNs do not exist in the monkey. We discuss a possible functional role for VSNs and similar neurons described in previous studies and conclude that these neurons are most likely involved with the process of neural integration (in a mathematical sense) of velocity-coded inputs from a variety of oculomotor subsystems and are not a pivotal element in saccade generation.
Reflexes From the Superficial Peroneal Nerve During Walking in Stroke Subjects
Authors: Zehr E. P. , Fujita K. , Stein R. B.
Published: December 2017

Zehr, E. P., K. Fujita, and R. B. Stein. Reflexes from the superficial peroneal nerve during walking in stroke subjects. J. Neurophysiol. 79: 848–858, 1998. The function of ipsilateral cutaneous reflexes was studied with short trains of stimuli presented pseudorandomly to the superficial peroneal nerve (SP; innervates the top of the foot) during treadmill walking in neurologically intact (NI) subjects and subjects who had had a stroke. Ankle and knee joint angles together with electromyograms (EMG) of tibialis anterior (TA), soleus (SOL), medial gastrocnemius (MG), vastus lateralis (VL), and biceps femoris (BF) muscles were recorded. Net reflex EMG and kinematic responses to stimulation were quantified in each of the 16 parts of the step cycle and responses compared between the stroke and NI subjects. Stimulation strongly suppressed extensor muscles throughout stance in the stroke subjects. TA muscle showed a significant suppression during swing phase that was correlated with reduced ankle dorsiflexion in both stroke and NI subjects. BF reflexes were facilitatory during parts of swing and VL reflexes were suppressive throughout stance in the stroke subjects. There was a significant correlation between BF facilitation and knee flexion during swing, which was stronger in NI subjects. We conclude that only part of the stumble correction to foot dorsum electrical stimulation observed in NI subjects is maintained after stroke, and that new, suppressive responses are seen.
Representation of Binaural Spatial Cues in Field L of the Barn Owl Forebrain
Authors: Cohen Yale E. , Knudsen Eric I.
Published: December 2017

Cohen, Yale E. and Eric I. Knudsen. Representation of binaural spatial cues in Field L of the barn owl forebrain. J. Neurophysiol. 79: 879–890, 1998. This study examined the representation of spatial information in the barn owl Field L, the first telencephalic processing stage of the classical auditory pathway. Field L units were recorded extracellularly, and their responses to dichotically presented interaural time differences (ITD) and interaural level differences (ILD) were tested. We observed a variety of tuning profiles in Field L. Some sites were not sensitive to ITD or ILD. Other sites, especially those in the high-frequency region, were highly selective for values of ITD and ILD. These sites had multipeaked (commonly called “phase ambiguous”) ITD tuning profiles and were tuned for a single value of ILD. The tuning properties of these sites are similar to those seen in the lateral shell of the central nucleus of the inferior colliculus. Although the tuning properties of Field L sites were similar to those observed in the inferior colliculus, the functional organization of this spatial information was fundamentally different. Whereas in the inferior colliculus spatial information is organized into global topographics maps, in Field L spatial information is organized into local clusters, with sites having similar binaural tuning properties grouped together. The representation of binaural cues in Field L suggests that it is involved in auditory space processing but at a lower level of information processing than the auditory archistriatum, a forebrain area that is specialized for processing spatial information, and that the levels of information processing in the forebrain space processing pathway are remarkably similar to those in the well-known midbrain space processing pathway.
Adrenergic Modulation of GABAA Receptor-Mediated Inhibition in Rat Sensorimotor Cortex
Authors: Bennett B. D. , Huguenard J. R. , Prince D. A.
Published: December 2017

Bennett, B. D., J. R. Huguenard, and D. A. Prince. Adrenergic modulation of GABAA receptor-mediated inhibition in rat sensorimotor cortex. J. Neurophysiol. 79: 937–946, 1998. The effect of adrenoceptor activation on pharmacologically isolated monosynaptic inhibitory postsynaptic currents (IPSCs) detected in layer V pyramidal neurons was examined by using whole cell voltage-clamp in a slice preparation of rat sensorimotor cortex. Epinephrine (EPI; 10 μM) reversibly altered the amplitude of evoked IPSCs (eIPSCs) in slices from postnatal day 9–12 (P9–12) and P15–18 rats. The effects of EPI were heterogeneous in both age groups, and in individual cases an enhancement, a depression or no effect of eIPSCs was observed, although depression was observed more commonly in the younger age group. The effects of EPI on eIPSC amplitude were likely mediated through presynaptic mechanisms because they occurred in the absence of any alteration in the current produced by direct application of γ-aminobutyric acid (GABA), or in input resistance. EPI always elicited an increase in the frequency of spontaneous IPSCs (sIPSCs) irrespective of whether or not it induced any change in the amplitude of eIPSCs in the same neuron. The increase in sIPSC frequency was blocked by phentolamine (10 μM) but not by propranolol (10 μM), supporting the conclusion that EPI-mediated effects on sIPSC frequency result from activation of α-adrenoceptors located on presynaptic inhibitory interneurons. In a subpopulation of neurons (3/9) from P15–18 rats, EPI increased both the amplitude and frequency of miniature IPSCs (mIPSCs) recorded in the presence of tetrodotoxin (TTX) and under conditions where postsynaptic EPI effects were blocked, suggesting activation of adrenoceptors on presynaptic terminals in these cells. Results of these experiments are consistent with an action of EPI at adrenoceptors located on presynaptic GABAergic interneurons. Adrenergic activation thus has multiple and complex influences on excitability in cortical circuits, some of which are a consequence of interactions that regulate the strength of GABAergic inhibition.
Directionality and Inhibition in Crayfish Tangential Cells
Authors: Glantz Raymon M.
Published: December 2017

Glantz, Raymon M. Directionality and inhibition in crayfish tangential cells. J. Neurophysiol. 79: 1157–1166, 1998. The purpose of this study was to characterize the inhibitory mechanism(s) associated with directionally selective motion detection (DS) in nonspiking tangential cells of crayfish optic lobe. The experiments employed intracellular recording of synaptic potentials elicited with sinewave gratings and pharmacological techniques. Previous studies established that tangential cells are subject to bicuculline-sensitive GABA-mediated inhibition. In this study DS was reduced by 90% by bicuculline. The reduction in DS was accompanied by a substantial increase in the response to null-direction motion. Bicuculline also altered the response to pulses of illumination. The magnitude and time course of inhibition were derived from the time varying difference between the control light response and that elicited during bicuculline perfusion. Both the inhibitory delay (relative to excitation) and the inhibitory amplitude are close to the expectations of a linear model of DS. The inhibition is not prolonged with respect to excitation but its risetime is ∼2.5 times longer. The result implies a longer time constant in the inhibitory pathway relative to that in the excitatory pathway and places limits on the frequency response of inhibition and DS. The velocity-dependence of DS is related to the time course of inhibition. The stimulus drift velocity eliciting maximum directionality is inversely proportional to the inhibitory delay. Bicuculline did not influence orientation selectivity. It is concluded that the quantitative features of bicuculline-sensitive, GABA-mediated inhibition are consistent with a linear model of DS.
Impact of Synaptic Unreliability on the Information Transmitted by Spiking Neurons
Authors: Zador Anthony
Published: December 2017

Zador, Anthony. Impact of synaptic unreliability on the information transmitted by spiking neurons. J. Neurophysiol. 79: 1219–1229, 1998. The spike generating mechanism of cortical neurons is highly reliable, able to produce spikes with a precision of a few milliseconds or less. The excitatory synapses driving these neurons are by contrast much less reliable, subject both to release failures and quantal fluctuations. This suggests that synapses represent the primary bottleneck limiting the faithful transmission of information through cortical circuitry. How does the capacity of a neuron to convey information depend on the properties of its synaptic drive? We address this question rigorously in an information theoretic framework. We consider a model in which a population of independent unreliable synapses provides the drive to an integrate-and-fire neuron. Within this model, the mutual information between the synaptic drive and the resulting output spike train can be computed exactly from distributions that depend only on a single variable, the interspike interval. The reduction of the calculation to dependence on only a single variable greatly reduces the amount of data required to obtain reliable information estimates. We consider two factors that govern the rate of information transfer: the synaptic reliability and the number of synapses connecting each presynaptic axon to its postsynaptic target (i.e., the connection redundancy, which constitutes a special form of input synchrony). The information rate is a smooth function of both mechanisms; no sharp transition is observed from an “unreliable” to a “reliable” mode. Increased connection redundancy can compensate for synaptic unreliability, but only under the assumption that the fine temporal structure of individual spikes carries information. If only the number of spikes in some relatively long-time window carries information (a “mean rate” code), an increase in the fidelity of synaptic transmission results in a seemingly paradoxical decrease in the information available in the spike train. This suggests that the fine temporal structure of spike trains can be used to maintain reliable transmission with unreliable synapses.
Neurons in the Posterior Interposed Nucleus of the Cerebellum Related to Vergence and Accommodation. I. Steady-State Characteristics
Authors: Zhang Hongyu , Gamlin Paul D. R.
Published: December 2017

Zhang, Hongyu and Paul D. R. Gamlin. Neurons in the posterior interposed nucleus of the cerebellum related to vergence and accommodation. I. Steady-state characteristics. J. Neurophysiol. 79: 1255–1269, 1998. The present study used single-unit recording and electrical microstimulation techniques in alert, trained rhesus monkeys to examine the involvement of the posterior interposed nucleus (IP) of the cerebellum in vergence and accommodative eye movements. Neurons related to vergence and ocular accommodation were encountered within a circumscribed region of the IP and their activity during changes in viewing distance was characterized. The activity of these neurons increased with decreases in vergence angle and accommodation (the far-response) but none showed changes in activity during changes in conjugate eye position and we therefore term them “far-response neurons.” Far-response neurons were found within a restricted region of the IP that extended ∼1 mm rostrocaudally and mediolaterally and 2 mm dorsal to the fourth ventricle. Microstimulation of this far-response region of the IP with low currents (<30 μA) often elicited divergence and accommodation for far. The behavior of 37 IP far-response neurons was examined during normal binocular viewing, during monocular viewing (blur cue alone), and during binocular viewing with accommodation open-loop (disparity cue alone). The activity of all cells was modulated under all three conditions. However, the change in activity of some of these neurons was significantly different under these three viewing conditions. The behavior of 70 IP far-response neurons was compared during normal binocular viewing and during viewing in which the accommodative response was significantly dissociated from the vergence response. The data from these two conditions was pooled and multiple regression analyses for each neuron generated two coefficients expressing the activity of the neuron relative to the vergence and to accommodative response respectively. On the basis of these coefficients, the overall activity of the neurons were classified as follows: 34 positively correlated with divergence, 11 positively correlated with far accommodation, 14 positively correlated with divergence and far accommodation, 9 positively correlated with divergence and accommodation, and 2 positively correlated with convergence and far accommodation. The results of this study demonstrate the involvement of a specific region of the posterior interposed nucleus of the cerebellum in vergence and accommodation. IP far-response neurons are active for vergence and accommodation irrespective of whether or not these eye movements are elicited by blur or disparity cues. The data in the present study strongly suggest that this cerebellar region is a far-response region that is involved in vergence as well as accommodative eye movements.
Locomotor Capacity Attributable to Step Training Versus Spontaneous Recovery After Spinalization in Adult Cats
Authors: de Leon R. D. , Hodgson J. A. , Roy R. R. , Edgerton V. R.
Published: December 2017

de Leon, R. D., J. A. Hodgson, R. R. Roy, and V. R. Edgerton. Locomotor capacity attributable to step training versus spontaneous recovery after spinalization in adult cats. J. Neurophysiol. 79: 1329–1340, 1998. Locomotor performance, hindlimb muscle activity and gait patterns during stepping were studied in step-trained and non-trained female, adult spinal cats. Changes in locomotor characteristics relative to prespinalization bipedal and quadrupedal stepping patterns were used to evaluate the effects of step training on the capacity to execute full weight-bearing stepping after spinalization. Step training consisted of full weight-bearing stepping of the hindlimbs at the greatest range of treadmill speeds possible at any given stage of locomotor recovery. In the initial stages of training the limbs were assisted as needed to execute successful steps. On the basis of two behavioral criteria, the maximum speed of treadmill stepping and the number of successful steps per unit time, the ability to step was at least 3 times greater in animals trained to step versus those allowed to recover spontaneously, i.e., the non-trained. The greater success in stepping was reflected in several physiological and kinematic properties. For example, the amplitude of electromyograph (EMG) bursts in the tibialis anterior (an ankle dorsiflexor), the amount of extension at the end of both the stance (E3) and swing (E1) phases of the step cycle, and the amount of lift of the hindlimb during swing were greater in step-trained than in non-trained spinal cats. The changes that occurred in response to training reflected functional adaptations at specific phases of the step cycle, e.g., enhanced flexor and extensor function. The improved stepping capacity attributable to step training is interpreted as a change in the probability of the appropriate neurons being activated in a temporally appropriate manner. This interpretation, in turn, suggests that step training facilitated or reinforced the function of extant sensorimotor pathways rather than promoting the generation of additional pathways. These results show that the capacity of the adult lumbar spinal cord to generate full weight-bearing stepping over a range of speeds is defined, in large part, by the functional experience of the spinal cord after supraspinal connectivity has been eliminated. These results have obvious implications with regards to 1) the possibility of motor learning occurring in the spinal cord; 2) the importance of considering “motor experience” in assessing the effect of any postspinalization intervention; and 3) the utilization of use-dependent interventions in facilitating and enhancing motor recovery.
Different Contributions of GABAAand GABACReceptors to Rod and Cone Bipolar Cells in a Rat Retinal Slice Preparation
Authors: Euler Thomas , Wässle Heinz
Published: December 2017

Euler, Thomas and Heinz Wässle. Different contributions ofGABAAand GABACreceptors to rod and cone bipolar cells in a rat retinal slice preparation. J. Neurophysiol. 79: 1384–1395, 1998. Whole cell currents were recorded from rod and cone bipolar cells in a slice preparation of the rat retina. Use of the gramicidin D perforated-patch technique prevented loss of intracellular compounds. The recorded cells were identified morphologically by injection with Lucifer yellow. During the recordings, the cells were isolated synaptically by extracellular cobalt. To distinguish the γ-aminobutyric acid (GABA) receptors pharmacologically, theGABAAreceptor antagonist, bicuculline, and the GABACreceptor antagonist, 3-aminopropyl(methyl)phosphinic acid, were used. In all bipolar cells tested, application of GABA induced postsynaptic chloride currents that hyperpolarized the cells from their resting potential of about −40 mV. GABA was applied at different concentrations to allow for the different affinity of GABA at GABAAand GABACreceptors. At a GABA concentration of 25 μM, in the case of rod bipolar cells, ∼70% of the current was found to be mediated by GABACreceptors. In the case of cone bipolar cells, only ∼20% of the current was mediated by GABACreceptors. Furthermore, this GABAC-mediated fraction varied among the different morphological types of cone bipolar cells, supporting the hypothesis of distinct functional roles for the different types of cone bipolar cells. There is evidence that the efficacy of GABACreceptors is modulated by glutamate through metabotropic glutamate receptors. We tested this hypothesis by applying agonists of metabotropic glutamate receptors (mGluR)1/5 to rod bipolar cells. The specific agonist (±)-trans-azetidine-2,4-dicarboxylic acid and the potent mGluR agonist quisqualic acid reduced the amplitude of the GABACresponses by 10–30%. This suggests a functional role for the modulation of GABACreceptors by the metabotropic glutamate receptors mGluR1/5.
Swelling-Induced Arachidonic Acid Release via the 85-kDa cPLA2in Human Neuroblastoma Cells
Authors: Basavappa Srisaila , Pedersen Stine F. , Jørgensen Nanna K. , Ellory J. Clive , Hoffmann Else K.
Published: December 2017

Basavappa, Srisaila, Stine F. Pedersen, Nanna K. Jørgensen, J. Clive Ellory, and Else K. Hoffmann. Swelling-induced arachidonic acid release via the 85-kDa cPLA2in human neuroblastoma cells. J. Neurophysiol. 79: 1441–1449, 1998. Arachidonic acid or its metabolites have been implicated in the regulatory volume decrease (RVD) response after hypotonic cell swelling in some mammalian cells. The present study investigated the role of arachidonic acid (AA) during RVD in the human neuroblastoma cell line CHP-100. During the first nine minutes of hypo-osmotic exposure the rate of3H-arachidonic acid (3H-AA) release increased to 250 ± 19% (mean ± SE, n = 22) as compared with cells under iso-osmotic conditions. This release was significantly inhibited after preincubation with AACOCF3, an inhibitor of the 85-kDa cytosolic phospholipase A2(cPLA2). This indicates that a PLA2, most likely the 85-kDa cPLA2is activated during cell swelling. In contrast, preincubation with U73122, an inhibitor of phospholipase C, did not affect the swelling-induced release of3H-AA. Swelling-activated efflux of36Cl and3H-taurine were inhibited after preincubation with AACOCF3. Thus the swelling-induced activation of cPLA2may be essential for stimulation of both36Cl and3H-taurine efflux during RVD. As the above observation could result from a direct effect of AA or its metabolite leukotriene D4(LTD4), the effects of these agents were investigated on swelling-induced36Cl and3H-taurine effluxes. In the presence of high concentrations of extracellular AA, the swelling-induced efflux of36Cl and3H-taurine were inhibited significantly. In contrast, addition of exogenous LTD4had no significant effect on the swelling-activated36Cl efflux. Furthermore, exogenous AA increased cytosolic calcium levels as measured in single cells loaded with the calcium sensitive dye Fura-2. On the basis of these results we propose that cell swelling activates phospholipase A2and that this activation via an increased production of AA or some AA metabolite(s) other than LTD4is essential for RVD.
Impact of Spontaneous Synaptic Activity on the Resting Properties of Cat Neocortical Pyramidal Neurons In Vivo
Authors: Paré Denis , Shink Eric , Gaudreau Hélène , Destexhe Alain , Lang Eric J.
Published: December 2017

Paré, Denis, Eric Shink, Hélène Gaudreau, Alain Destexhe, and Eric J. Lang. Impact of spontaneous synaptic activity on the resting properties of cat neocortical pyramidal neurons in vivo. J. Neurophysiol. 79: 1450–1460, 1998. The frequency of spontaneous synaptic events in vitro is probably lower than in vivo because of the reduced synaptic connectivity present in cortical slices and the lower temperature used during in vitro experiments. Because this reduction in background synaptic activity could modify the integrative properties of cortical neurons, we compared the impact of spontaneous synaptic events on the resting properties of intracellularly recorded pyramidal neurons in vivo and in vitro by blocking synaptic transmission with tetrodotoxin (TTX). The amount of synaptic activity was much lower in brain slices (at 34°C), as the standard deviation of the intracellular signal was 10–17 times lower in vitro than in vivo. Input resistances ( R ins) measured in vivo during relatively quiescent epochs (“control R ins”) could be reduced by up to 70% during periods of intense spontaneous activity. Further, the control R ins were increased by ∼30–70% after TTX application in vivo, approaching in vitro values. In contrast, TTX produced negligible R in changes in vitro (∼4%). These results indicate that, compared with the in vitro situation, the background synaptic activity present in intact networks dramatically reduces the electrical compactness of cortical neurons and modifies their integrative properties. The impact of the spontaneous synaptic bombardment should be taken into account when extrapolating in vitro findings to the intact brain.
Activation of Presynaptic GABAB Receptors Inhibits Evoked IPSCs in Rat Magnocellular Neurons In Vitro
Authors: Mouginot Didier , Kombian Samuel B. , Pittman Quentin J.
Published: December 2017

Mouginot, Didier, Samuel B. Kombian, and Quentin J. Pittman. Activation of presynaptic GABAB receptors inhibits evoked IPSCs in rat magnocellular neurons in vitro. J. Neurophysiol. 79: 1508–1517, 1998. Whole cell recordings (nystatin-perforated patch) were carried out on magnocellular neurons of the rat supraoptic nucleus (SON) to study the modulation of inhibitory postsynaptic currents (IPSCs) by γ-aminobutyric acid-B (GABAB) receptors. Field stimulation adjacent to the SON in the presence of kynurenic acid, evoked monosynaptic GABAergic IPSCs. Baclofen reversibly reduced the amplitude of the IPSCs in a dose-dependent manner (EC50: 0.68 μM) without apparent effect on the holding current ( V h = −80 mV) or input resistance and altered neither the kinetic properties, nor the reversal potential of IPSCs. Concomittant to IPSC depression, baclofen enhanced the paired-pulse ratio for two consecutive IPSCs [interstimulus interval (ISI): 50 ms], an effect consistent with a presynaptic locus of action. Both actions of baclofen were abolished by CGP35348 (500 μM), a GABAB receptor antagonist. In testing for involvement of synaptically activated presynaptic GABAB receptors, we only recorded paired-pulse facilitation at most ISIs tested (50–500 ms), suggesting that the classical GABAB autoreceptors may not normally be activated in our conditions. However, enhancement of local GABA concentration by perfusion of a GABA uptake inhibitor (NO-711) revealed an action of endogenous GABA at these presynaptic GABAB receptors. The nonselective K+ channel blocker Ba2+ abolished baclofen's effect and pertussis toxin (PTX) pretreatment (200–500 ng/ml for 18–24 h) was ineffective in blocking the baclofen-induced inhibition, making an involvement of PTX-sensitive G protein unlikely. The present results show that presynaptic GABAB receptors that are coupled to PTX-insensitive G-proteins may be activated by endogenous GABA under conditions of reduced GABA uptake, thus regulating the inhibitory synaptic input to SON.
4 T-fMRI Study of Nonspatial Shifting of Selective Attention: Cerebellar and Parietal Contributions
Authors: Le Tuong Huu , Pardo José V. , Hu Xiaoping
Published: December 2017

Le, Tuong Huu, José V. Pardo, and Xiaoping Hu. 4 T-fMRI study of nonspatial shifting of selective attention: cerebellar and parietal contributions. J. Neurophysiol. 79: 1535–1548, 1998. Regional blood oxygenation in the cerebellum and posterior cerebral cortices was monitored with functional magnetic resonance imaging (fMRI) at four Tesla while 16 normal subjects performed three tasks with identical visual stimulation: fixation; attention focused upon either stimulus shape or color and sustained during blocks of trials (sustained attention); and rapid, serial shifts in attention between stimulus shape or color within blocks of trials (shifting attention). The stimuli were displayed centrally for 100 ms followed by a central fixation mark for 900 ms. Each stimulus was either a circle or a square displayed in either red or green. Attention shifting required switching between color and shape information after each target detection and occurred on average once every three seconds. Subjects pressed a response key upon detecting the target; reaction time and response accuracy were recorded. Two protocols for T2*-weighted echo-planar imaging were optimized, one with a surface coil for the cerebellum alone and the other with a volume coil for imaging both cerebellum and posterior brain structures (parietal, occipital, and part of temporal cortices). Because fMRI of the cerebellum is particularly susceptible to cardiac and respiratory fluctuations, novel techniques were applied to isolate brain activation signals from physiological noise. Functional activation maps were generated for contrasts of 1) sustained attention to color minus fixation; 2) sustained attention to shape minus fixation; and 3) shifting attention minus sustained attention (to color and shape; i.e., summed across blocks of trials). Consistent with the ease of these tasks, subjects performed with >80% accuracy during both sustained attention and shifting attention. Analysis of variance did not show significant differences in false alarms or true hits across either attentional condition. A subgroup of subjects whose performance data were recorded during ten minutes of continuous practice did not show significant changes over time. Both contrasts between the conditions of sustained attention to color or to shape as compared with the fixation condition showed significant bilateral activation in occipital and inferior temporal regions (Brodmann areas 18, 19, and 37). The anterior medial cerebellum was also significantly activated ipsilateral to the finger used for responding. The principal comparison of interest, the contrast between the condition of shifting attention and the condition of sustained attention produced significant and reproducible activation: lateral cerebellar hemisphere (ansiform lobule: Crus I Anterior and Crus I Posterior; left Crus I Posterior); cerebellar folium; posterior superior parietal lobule (R and L); and cuneus and precuneus (R and L).
Integrative Visuomotor Behavior Is Associated With Interregionally Coherent Oscillations in the Human Brain
Authors: Classen Joseph , Gerloff Christian , Honda Manabu , Hallett Mark
Published: December 2017

Classen, Joseph, Christian Gerloff, Manabu Honda, and Mark Hallett. Integrative visuomotor behavior is associated with interregionally coherent oscillations in the human brain. J. Neurophysiol. 79: 1567–1573, 1998. Coherent electrical brain activity has been demonstrated to be associated with perceptual events in mammals. It is unclear whether or not it is also a mechanism instrumental in the performance of sensorimotor tasks requiring the continuous processing of information between primarily executive and receptive brain areas. In particular it is unknown whether or not interregional coherent activity detectable in electroencephalographic (EEG) recordings on the scalp reflects interareal functional cooperativity in humans. We studied patterns of changes in EEG-coherence associated with a visuomotor force-tracking task in seven subjects. Interregional coherence of EEG signals recorded from scalp regions overlying the visual and the motor cortex increased in comparison to a resting condition when subjects tracked a visual target by producing an isometric force with their right index finger. Coherence between visual and motor cortex decreased when the subjects produced a similar motor output in the presence of a visual distractor and was unchanged in a purely visual and purely motor task. Increases and decreases of coherence were best differentiated in the low beta frequency range (13–21 Hz). This observation suggests a special functional significance of low frequency oscillations in information processing in large-scale networks. These findings substantiate the view that coherent brain activity underlies integrative sensorimotor behavior.
Conopressin Affects Excitability, Firing, and Action Potential Shape Through Stimulation of Transient and Persistent Inward Currents in Mulluscan Neurons
Authors: van Soest Paul F. , Kits Karel S.
Published: December 2017

van Soest, Paul F. and Karel S. Kits. Conopressin affects excitability, firing, and action potential shape through stimulation of transient and persistent inward currents in mulluscan neurons. J. Neurophysiol. 79: 1619–1632, 1998. The molluscan vasopressin/oxytocin-related neuropeptide conopressin activates two persistent inward currents in neurons from the anterior lobe of the right cerebral ganglion of Lymnaea stagnalis that are involved in the control of male copulatory behavior. The low-voltage–activated (LVA) current is activated at a wide range of membrane potentials, its amplitude being only weakly voltage dependent. The high-voltage–activated (HVA) current is activated at potentials positive to −40 mV only and shows a steep voltage dependence. Occurrence of both currents varies from cell to cell, some expressing both and others only the HVA current. In most neurons that have the LVA current, a conopressin-independent persistent inward current ( INSR) is found that resembles the HVA current in its voltage dependence. The functional importance of the LVA and HVA currents was studied under current-clamp conditions in isolated anterior lobe neurons. In cells exhibiting both current types, the effect of activation of the LVA current alone was investigated as follows: previously recorded LVA current profiles were injected into the neurons, and the effects were compared with responses induced by conopressin. Both treatments resulted in a strong depolarization and firing activity. No differences in firing frequency and burst duration were observed, indicating that activation of the LVA current is sufficient to evoke bursts. In cells exhibiting only the HVA current, the effect of conopressin on the response to a depolarizing stimulus was tested. Conopressin reversibly increased the number of action potentials generated by the stimulus, suggesting that the HVA current enhances excitability and counteracts accommodation. Conopressin enhanced action potential broadening during depolarizing stimuli in many neurons. Voltage-clamp experiments performed under ion-selective conditions revealed the presence of transient sodium and calcium currents. Using the action potential clamp technique, it was shown that both currents contribute to the action potential. The calcium current, which is activated mainly during the repolarizing phase of the action potential, is augmented by conopressin. Thus conopressin may directly modulate the shape of the action potential. In summary, conopressin may act simultaneously on multiple inward currents in anterior lobe neurons of Lymnaea to affect firing activity, excitability, and action potential shape.
Control of Grasp Stability When Humans Lift Objects With Different Surface Curvatures
Authors: Jenmalm Per , Goodwin Antony W. , Johansson Roland S.
Published: December 2017

Jenmalm, Per, Antony W. Goodwin, and Roland S. Johansson. Control of grasp stability when humans lift objects with different surface curvatures. J. Neurophysiol. 79: 1643–1652, 1998. In previous investigations of the control of grasp stability, humans manipulated test objects with flat grasp surfaces. The surfaces of most objects that we handle in everyday activities, however, are curved. In the present study, we examined the influence of surface curvature on the fingertip forces used when humans lifted and held objects of various weights. Subjects grasped the test object between the thumb and the index finger. The matching pair of grasped surfaces were spherically curved with one of six different curvatures (concave with radius 20 or 40 mm; flat; convex with radius 20, 10, or 5 mm) and the object had one of five different weights ranging from 168 to 705 g. The grip force used by subjects (force along the axis between the 2 grasped surfaces) increased with increasing weight of the object but was modified inconsistently and incompletely by surface curvature. Similarly, the duration and rate of force generation, when the grip and load forces increased isometrically in the load phase before object lift-off, were not influenced by surface curvature. In contrast, surface curvature did affect the minimum grip forces required to prevent frictional slips (the slip force). The slip force was smaller for larger curvatures (both concave and convex) than for flatter surfaces. Therefore the force safety margin against slips (difference between the employed grip force and the slip force) was higher for the higher curvatures. We conclude that surface curvature has little influence on grip force regulation during this type of manipulation; the moderate changes in slip force resulting from changes in curvature are not fully compensated for by changes in grip force.
Innervation Territories of Single Sympathetic C Fibers in Human Skin
Authors: Schmelz M. , Schmidt R. , Bickel A. , Torebjörk H. E. , Handwerker H. O.
Published: December 2017

Schmelz, M., R. Schmidt, A. Bickel, H. E. Torebjörk, and H. O. Handwerker. Innervation territories of single sympathetic C fibers in human skin. J. Neurophysiol. 79: 1653–1660, 1998. Microneurography techniques were used to record action potentials from unmyelinated nerve fibers (C fibers) in the cutaneous fascicles of the peroneal nerve in healthy volunteers. C units were identified by their long latency responses to electrical stimulation of their terminals in the skin. Their responsiveness to mechanical or heat stimuli applied to the skin or to sympathetic reflex provocation tests was determined by transient slowing of conduction velocity following activation (marking technique). In a sample of 381 C units, 59 were unresponsive to mechanical and thermal stimulation of their endings, but responded to sympathetic reflex provocation tests, e.g., arousal or deep inspiration. They were classified as sympathetic efferent units. On average, conduction velocities of sympathetic units were lower (0.78 ± 0.12 m/s, mean ± SD) than those of mechano-heat (CMH) or mechanoresponsive (CM) afferent C units (0.91 ± 0.14 m/s). Endings of most of the sympathetic units were located in the skin of toes or in the foot dorsum. Innervation territories of 16 sympathetic units were mapped by means of conditioning transcutaneous electrical stimuli. Twelve units had one continuous skin territory, whereas two units had two and two other units had three and five separate territories, respectively. The mean innervated area was 128 mm2(range: 24–350 mm2). Innervation territories of sympathetic units were of approximately the same size in different skin regions on the lower leg, foot, or toes. Based on responses to whole body cooling and warming, two units were tentatively classified as vasoconstrictor and sudomotor units, respectively. Eleven units were tested for responsiveness to iontophoresis of acetylcholine in their innervation territories. In five of them, activity was induced that was not due to central reflex activity but instead due to antidromic activation from the peripheral terminals. Iontophoresis of saline or histamine was ineffective. These findings confirm the existence of excitatory cholinergic receptors in the terminal membrane of some sympathetic units, possibly sudomotors.