bluuebunny/crossref_metadata_2025 huggingface dataset:
Aβ Fibers Mediate Cutaneous Reflexes During Human Walking
Authors: van Wezel B.M.H. , van Engelen B.G.M. , Gabreëls F.J.M. , Gabreëls-Festen A.A.W.M. , Duysens J.
Published: December 2017

During human gait, transmission of cutaneous reflexes from the foot is controlled specifically according to the phase of the step cycle. These reflex responses can be evoked by nonnociceptive stimuli, and therefore it is thought that the large-myelinated and low-threshold Aβ afferent fibers mediate these reflexes. At present, this hypothesis is not yet verified. To test whether Aβ fibers are involved the reflex responses were studied in patients with a sensory polyneuropathy who suffer from a predominant loss of large-myelinated Aβ fibers. The sural nerve of both patients and healthy control subjects was stimulated electrically at a nonnociceptive intensity during the early and late swing phases while they walked on a treadmill. The responses were studied by recording electromyographic (EMG) activity of the biceps femoris (BF) and tibialis anterior (TA) of the stimulated leg. In both phases, large facilitatory responses were observed in the BF of the healthy subjects. These facilitations were reduced significantly in the BF of the patients, indicating that Aβ fibers mediate these reflexes. In TA similar results were obtained. The absolute response magnitude across the two phases was significantly smaller for the patients than for the healthy subjects. The TA responses for the healthy subjects were on average facilitatory during early swing and suppressive during end swing. Both facilitations and suppressions were considerably smaller for the patients, indicating that both types of responses are mediated by Aβ fibers. It is concluded that low-threshold Aβ sensory fibers mediate these reflexes during human gait. The low threshold and the precise phase-dependent control of these responses suggest that these responses are important in the regulation of gait. The loss of such reflex activity may be related to the gait impairments of these patients.
Cerebellar Ataxia: Torque Deficiency or Torque Mismatch Between Joints?
Authors: Bastian A. J. , Zackowski K. M. , Thach W. T.
Published: December 2017

Prior work has shown that cerebellar subjects have difficulty adjusting for interaction torques that occur during multi-jointed movements. The purpose of this study was to determine whether this deficit is due to a general inability to generate sufficient levels of phasic torque inability or due to an inability to generate muscle torques that predict and compensate for interaction torques. A second purpose was to determine whether reducing the number of moving joints by external mechanical fixation could improve cerebellar subjects' targeted limb movements. We studied control and cerebellar subjects making elbow flexion movements to touch a target under two conditions: 1) a shoulder free condition, which required only elbow flexion, although the shoulder joint was unconstrained and 2) a shoulder fixed condition, where the shoulder joint was mechanically stabilized so it could not move. We measured joint positions of the arm in the sagittal plane and electromyograms (EMGs) of shoulder and elbow muscles. Elbow and shoulder torques were estimated using inverse dynamics equations. In the shoulder free condition, cerebellar subjects made greater endpoint errors (primarily overshoots) than did controls. Cerebellar subjects' overshoot errors were largely due to unwanted flexion at the shoulder. The excessive shoulder flexion resulted from a torque mismatch, where larger shoulder muscle torques were produced at higher rates than would be appropriate for a given elbow movement. In the shoulder fixed condition, endpoint errors of cerebellar subjects and controls were comparable. The improved accuracy of cerebellar subjects was accompanied by reduced shoulder flexor muscle activity. Most of the correct cerebellar trials in the shoulder fixed condition were movements made using only muscles that flex the elbow. Our findings suggest that cerebellar subjects' poor shoulder control is due to an inability to generate muscle torques that predict and compensate for interaction torques, and not due to a general inability to generate sufficient levels of phasic torque. In addition, reducing the number of muscles to be controlled improved cerebellar ataxia.
Nicotinic EPSCs in Intact Rat Ganglia Feature Depression Except If Evoked During Intermittent Postsynaptic Depolarization
Authors: Sacchi Oscar , Rossi Maria Lisa , Canella Rita
Published: December 2017

The involvement of the postsynaptic membrane potential level in controlling synaptic strength at the ganglionic synapse was studied by recording nicotinic fast synaptic currents (EPSCs) from neurons in the intact, mature rat superior cervical ganglion, using the two-electrode voltage-clamp technique. EPSCs were evoked by 0.05-Hz supramaximal stimulation of the preganglionic sympathetic trunk over long periods; their peak amplitude (or synaptic charge transfer) over time appeared to depend on the potential level of the neuronal membrane where the nicotinic receptors are embedded. EPSC amplitude remained constant ( n = 6) only if ACh was released within repeated depolarizing steps of the postganglionic neuron, which constantly varied between −50 and −20 mV in consecutive 10-mV steps, whereas it decreased progressively by 45% ( n = 9) within 14 min when the sympathetic neuron was held at constant membrane potential. Synaptic channel activation, channel ionic permeation and depolarization of the membrane in which the nicotinic receptor is localized must occur simultaneously to maintain constant synaptic strength at the ganglionic synapse during low-rate stimulation (0.03–1 Hz). Different posttetanic (20 Hz for 10 s) behaviors were observed depending on the mode of previous stimulation. In the neuron maintained at constant holding potential during low-rate stimulation, the depressed EPSC showed posttetanic potentiation, recovering ∼23% of the mean pretetanic values ( n = 10). The maximum effect was immediate in 40% of the neurons tested and developed over a 3- to 6-min period in the others; thereafter potentiation vanished within 40 min of 0.05-Hz stimulation. In contrast, no statistically significant synaptic potentiation was observed when EPSC amplitudes were kept constant by repeated −50/−20-mV command cycles ( n = 12). It is suggested that, under these conditions, posttetanic potentiation could represent an attempt at recovering the synaptic strength lost during inappropriate functioning of the ganglionic synapse.
Three-Dimensional Vestibuloocular Reflex of the Monkey: Optimal Retinal Image Stabilization Versus Listing's Law
Authors: Misslisch Hubert , Hess Bernhard J. M.
Published: December 2017

If the rotational vestibuloocular reflex (VOR) were to achieve optimal retinal image stabilization during head rotations in three-dimensional space, it must turn the eye around the same axis as the head, with equal velocity but in the opposite direction. This optimal VOR strategy implies that the position of the eye in the orbit must not affect the VOR. However, if the VOR were to follow Listing's law, then the slow-phase eye rotation axis should tilt as a function of current eye position. We trained animals to fixate visual targets placed straight ahead or 20° up, down, left or right while being oscillated in yaw, pitch, and roll at 0.5–4 Hz, either with or without a full-field visual background. Our main result was that the visually assisted VOR of normal monkeys invariantly rotated the eye around the same axis as the head during yaw, pitch, and roll (optimal VOR). In the absence of a visual background, eccentric eye positions evoked small axis tilts of slow phases in normal animals. Under the same visual condition, a prominent effect of eye position was found during roll but not during pitch or yaw in animals with low torsional and vertical gains following plugging of the vertical semicircular canals. This result was in accordance with a model incorporating a specific compromise between an optimal VOR and a VOR that perfectly obeys Listing's law. We conclude that the visually assisted VOR of the normal monkey optimally stabilizes foveal as well as peripheral retinal images. The finding of optimal VOR performance challenges a dominant role of plant mechanics and supports the notion of noncommutative operations in the oculomotor control system.
Mechanisms Involved in Tetanus-Induced Potentiation of Fast IPSCs in Rat Hippocampal CA1 Neurons
Authors: Shew T. , Yip S. , Sastry B. R.
Published: December 2017

In the present study, possible mechanisms involved in the tetanus-induced potentiation of γ-aminobutyric acid-A (GABA-A) receptor-mediated inhibitory postsynaptic currents (IPSCs) were investigated using the whole cell voltage-clamp technique on CA1 neurons in rat hippocampal slices. Stimulations (100 Hz) of the stratum radiatum, while voltage-clamping the membrane potential of neurons, induces a long-term potentiation (LTP) of evoked fast IPSCs while increasing the number but not the amplitude of spontaneous IPSCs (sIPSCs). The potentiation of fast IPSCs was input specific. During the period of IPSC potentiation, postsynaptic responses produced by 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol hydrochloride and baclofen, GABA-A and GABA-B agonists respectively, were not significantly different from control. CGP 36742, a GABA-B antagonist, blocked the induction of tetanus-induced potentiation of evoked and spontaneous IPSCs, while GTPγS, an activator of G proteins, substitution for GTP in the postsynaptic recording electrode did not occlude potentiation. Since GABA-B receptors work through G proteins, our results suggest that pre- but not postsynaptic GABA-B receptors are involved in the potentiation of fast IPSCs. A tetanus delivered when GABA-A responses were completely blocked by bicuculline suggests that GABA-A receptor activation during tetanus is not essential for the induction of potentiation. Rp-cAMPs, an antagonist of protein kinase A (PKA) activation, blocks the induction of potentiation of fast IPSCs. Forskolin, an activator of PKA, increases baseline evoked IPSCs as well as the number of sIPSCs, and a tetanic stimulation during this enhancement uncovers a long-term depression of the evoked IPSC. Sulfhydryl alkylating agents, N-ethylmaleimide and p-chloromercuribenzoic acid, which have been found to presynaptically increase GABA release and have been suggested to have effects on proteins involved in transmitter release processes occurring in nerve terminals, occlude tetanus-induced potentiation of evoked and spontaneous IPSCs. Taken together our results suggest that LTP of IPSCs originates from a presynaptic site and that GABA-B receptor activation, cyclic AMP/PKA activation and sulfhydryl-alkylation are involved. Plasticity of IPSCs as observed in this study would have significant implications for network behavior in the hippocampus.
Polarized Synaptic Interactions Between Intercalated Neurons of the Amygdala
Authors: Royer Sébastien , Martina Marzia , Paré Denis
Published: December 2017

The intercalated (ITC) cell masses are small GABAergic cell clusters interposed between the basolateral (BL) complex and central (CE) nucleus of the amygdala. ITC cells receive excitatory afferents from the BL complex and generate feed-forward inhibition in the CE nucleus. Recently it was shown that ITC cells could gate impulse traffic between the BL complex and CE nucleus in a spatiotemporally differentiated manner. In addition, it was hypothesized that lateromedial inhibitory interactions between different ITC cell clusters played a critical role in this respect. Given the potential importance of such conditional computations, the present study aimed to characterize the connectivity existing among ITC cells. To this end, whole cell recordings of ITC neurons were obtained under visual guidance in coronal slices of the guinea pig amygdala. Electrical stimuli applied in the BL complex primarily elicited excitatory responses when they were applied at the same lateromedial level or more medially than the recorded ITC cells. As the stimulation site was moved laterally, the character of the response shifted toward inhibition. Both bicuculline and non- N-methyl-d-aspartate receptor antagonists abolished this BL-evoked inhibition, suggesting that it was not mediated by BL inhibitory cells projecting to ITC neurons. In keeping with this, local glutamate injections in and around the ITC clusters revealed that the most effective site to inhibit ITC cells were ITC clusters located laterally with respect to the recorded one. The activation of more medial ITC clusters evoked much smaller responses. Thus, connections between ITC clusters tend to run in a lateromedial direction. To identify the source of these directionally polarized synaptic interactions, the morphological features of ITC cells were analyzed by intracellular injection of Neurobiotin. This analysis revealed that the dendritic tree and axonal arbor of ITC cells are asymmetric in the lateromedial plane. In particular, their laterally directed dendrites were longer than the medial ones, whereas their laterally directed axon collaterals were shorter than the medial ones. It is concluded that the morphological asymmetry of ITC cells accounts for the directional polarization of inter-ITC connections. The significance of these findings for the gating of information transfer from the BL complex to the CE nucleus is discussed.
Task-Related Modulation of Visual Cortex
Authors: Huk Alexander C. , Heeger David J.
Published: December 2017

We performed a series of experiments to quantify the effects of task performance on cortical activity in early visual areas. Functional magnetic resonance imaging (fMRI) was used to measure cortical activity in several cortical visual areas including primary visual cortex (V1) and the MT complex (MT+) as subjects performed a variety of threshold-level visual psychophysical tasks. Performing speed, direction, and contrast discrimination tasks produced strong modulations of cortical activity. For example, one experiment tested for selective modulations of MT+ activity as subjects alternated between performing contrast and speed discrimination tasks. MT+ responses modulated in phase with the periods of time during which subjects performed the speed discrimination task; that is, MT+ activity was higher during speed discrimination than during contrast discrimination. Task-related modulations were consistent across repeated measurements in each subject; however, significant individual differences were observed between subjects. Together, the results suggest 1) that specific changes in the cognitive/behavioral state of a subject can exert selective and reliable modulations of cortical activity in early visual cortex, even in V1; 2) that there are significant individual differences in these modulations; and 3) that visual areas and pathways that are highly sensitive to small changes in a given stimulus feature (such as contrast or speed) are selectively modulated during discrimination judgments on that feature. Increasing the gain of the relevant neuronal signals in this way may improve their signal-to-noise to help optimize task performance.
Endomorphin-1 and Endomorphin-2 Modulate Responses of Trigeminal Neurons Evoked by N-Methyl-d-Aspartic Acid and Somatosensory Stimuli
Authors: Wang Xiao-Min , Zhang Kai-Ming , Long Layron O. , Flores Carmina A. , Mokha Sukhbir S.
Published: December 2017

The present study investigated the modulation of N-methyl-d-aspartate (NMDA)-evoked and peripheral cutaneous stimulus-evoked responses of trigeminal neurons by endomorphins, endogenous ligands for the μ-opioid receptor. Effects of endomorphins, administered microiontophoretically, were tested on the responses of nociceptive neurons recorded in the superficial and deeper dorsal horn of the medulla (trigeminal nucleus caudalis) in anesthetized rats. Endomorphin-1 and endomorphin-2 predominantly reduced the NMDA-evoked responses, producing an inhibitory effect of 54.1 ± 2.96% (mean ± SE; n = 34, P < 0.001) in 92% (34/37) of neurons and 63.6 ± 3.61% ( n = 32, P< 0.001) in 91% (32/35) of neurons, respectively. The inhibitory effect of endomorphins was modality specific; noxious stimulus-evoked responses were reduced more than nonnoxious stimulus-evoked responses. Naloxone applied at iontophoretic current that blocked the inhibitory effect of [d-Ala2, N-Me-Phe4, Gly5-ol]-enkephalin, reduced the peak inhibitory effect of endomorphins on the NMDA- and natural stimulus-evoked responses. We suggest that endomorphins by acting at μ-opioid receptor selectively modulate noxious stimulus-evoked responses in the medullary dorsal horn.
Phase-Dependent Filtering of Sensory Information in the Oscillatory Olfactory Center of a Terrestrial Mollusk
Authors: Inoue Tsuyoshi , Watanabe Satoshi , Kawahara Shigenori , Kirino Yutaka
Published: December 2017

With electrophysiological techniques, we found phase-dependent modification of the efficacy of signal transmission in the procerebrum (PC), the oscillatory olfactory center, of the terrestrial mollusk Limax marginatus and elucidated its neuronal mechanism. Previous studies have indicated that about 105PC neurons can be classified into only two types: bursting (B) neurons and nonbursting (NB) neurons, and both types of neurons have ongoing and phase-locked periodic oscillation of their membrane potentials. On olfactory nerve stimulation, excitatory postsynaptic potentials (EPSPs) were evoked with a constant latency in NB neurons, while EPSPs with a variable latency were evoked in B neurons. These findings suggest a monosynaptic connection from the olfactory nerve to NB neurons, but a polysynaptic connection between the olfactory nerve and B neurons. This polysynaptic transmission is most likely mediated by NB neurons because the olfactory nerve makes synaptic connection only with NB neurons in the PC. The latency of the evoked EPSPs in B neurons depended on the phase of the PC oscillatory activity, presumably because of the oscillation of the intervening NB neurons. These results suggest that the efficacy of olfactory nerve–B neuron polysynaptic transmission is regulated by the activity level of the phasically oscillating NB neurons. Thus, the intrinsic oscillation in the PC can serve as a filter for olfactory information conveyed from the olfactory nerve as a train of neuronal spikes. This filtering system may also produce a phase-dependent modification by the olfactory input of the PC oscillation frequency.
NT-3 Evokes an LTP-Like Facilitation of AMPA/Kainate Receptor–Mediated Synaptic Transmission in the Neonatal Rat Spinal Cord
Authors: Arvanov Viktor L. , Seebach Bradley S. , Mendell Lorne M.
Published: December 2017

Neurotrophin-3 (NT-3) is a neurotrophic factor required for survival of muscle spindle afferents during prenatal development. It also acts postsynaptically to enhance the monosynaptic excitatory postsynaptic potential (EPSP) produced by these fibers in motoneurons when applied over a period of weeks to the axotomized muscle nerve in adult cats. Similar increases in the amplitude of the monosynaptic EPSP in motoneurons are observed after periodic systemic treatment of neonatal rats with NT-3. Here we show an acute action of NT-3 in enhancing the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA/kainate) receptor–mediated fast monosynaptic EPSP elicited in motoneurons by dorsal root (DR) stimulation in the in vitro hemisected neonatal rat spinal cord. The receptor tyrosine kinase inhibitor K252a blocks this action of NT-3 as does the calcium chelator bis-( o-aminophenoxy)- N, N, N′, N′-tetraacetic acid (BAPTA) injected into the motoneuron. The effect of NT-3 resembles long-term potentiation (LTP) in that transient bath application of NT-3 to the isolated spinal cord produces a long-lasting increase in the amplitude of the monosynaptic EPSP. An additional similarity is that activation of N-methyl-d-aspartate (NMDA) receptors is required to initiate this increase but not to maintain it. The NMDA receptor blocker MK-801, introduced into the motoneuron through the recording microelectrode, blocks the effect of NT-3, indicating that NMDA receptors in the motoneuron membrane are crucial. The effect of NT-3 on motoneuron NMDA receptors is demonstrated by its enhancement of the depolarizing response of the motoneuron to bath-applied NMDA in the presence of tetrodotoxin (TTX). The potentiating effects of NT-3 do not persist beyond the first postnatal week. In addition, EPSPs with similar properties evoked in the same motoneurons by stimulation of descending fibers in the ventrolateral funiculus (VLF) are not modifiable by NT-3 even in the initial postnatal week. Thus, NT-3 produces synapse-specific and age-dependent LTP-like enhancement of AMPA/kainate receptor–mediated synaptic transmission in the spinal cord, and this action requires the availability of functional NMDA receptors in the motoneuron.
An Associational Model of Birdsong Sensorimotor Learning II. Temporal Hierarchies and the Learning of Song Sequence
Authors: Troyer Todd W. , Doupe Allison J.
Published: December 2017

Understanding the neural mechanisms underlying serially ordered behavior is a fundamental problem in motor learning. We present a computational model of sensorimotor learning in songbirds that is constrained by the known functional anatomy of the song circuit. The model subsumes our companion model for learning individual song “syllables” and relies on the same underlying assumptions. The extended model addresses the problem of learning to produce syllables in the correct sequence. Central to our approach is the hypothesis that the Anterior Forebrain Pathway (AFP) produces signals related to the comparison of the bird's own vocalizations and a previously memorized “template.” This “AFP comparison hypothesis” is challenged by the lack of a direct projection from the AFP to the song nucleus HVc, a candidate site for the generator of song sequence. We propose that sequence generation in HVc results from an associative chain of motor and sensory representations (motor → sensory → next motor … ) encoded within the two known populations of HVc projection neurons. The sensory link in the chain is provided, not by auditory feedback, but by a centrally generated efference copy that serves as an internal prediction of this feedback. The use of efference copy as a substitute for the sensory signal explains the ability of adult birds to produce normal song immediately after deafening. We also predict that the AFP guides sequence learning by biasing motor activity in nucleus RA, the premotor nucleus downstream of HVc. Associative learning then remaps the output of the HVc sequence generator. By altering the motor pathway in RA, the AFP alters the correspondence between HVc motor commands and the resulting sensory feedback and triggers renewed efference copy learning in HVc. Thus, auditory feedback-mediated efference copy learning provides an indirect pathway by which the AFP can influence sequence generation in HVc. The model makes predictions concerning the role played by specific neural populations during the sensorimotor phase of song learning and demonstrates how simple rules of associational plasticity can contribute to the learning of a complex behavior on multiple time scales.
Intermittency in the Control of Continuous Force Production
Authors: Slifkin Andrew B. , Vaillancourt David E. , Newell Karl M.
Published: December 2017

The purpose of the current investigation was to examine the influence of intermittency in visual information processes on intermittency in the control continuous force production. Adult human participants were required to maintain force at, and minimize variability around, a force target over an extended duration (15 s), while the intermittency of on-line visual feedback presentation was varied across conditions. This was accomplished by varying the frequency of successive force-feedback deliveries presented on a video display. As a function of a 128-fold increase in feedback frequency (0.2 to 25.6 Hz), performance quality improved according to hyperbolic functions (e.g., force variability decayed), reaching asymptotic values near the 6.4-Hz feedback frequency level. Thus, the briefest interval over which visual information could be integrated and used to correct errors in motor output was approximately 150 ms. The observed reductions in force variability were correlated with parallel declines in spectral power at about 1 Hz in the frequency profile of force output. In contrast, power at higher frequencies in the force output spectrum were uncorrelated with increases in feedback frequency. Thus, there was a considerable lag between the generation of motor output corrections (1 Hz) and the processing of visual feedback information (6.4 Hz). To reconcile these differences in visual and motor processing times, we proposed a model where error information is accumulated by visual information processes at a maximum frequency of 6.4 per second, and the motor system generates a correction on the basis of the accumulated information at the end of each 1-s interval.
Development of Spontaneous Glycinergic Currents in the Mauthner Neuron of the Zebrafish Embryo
Authors: Ali Declan W. , Drapeau Pierre , Legendre Pascal
Published: December 2017

We used whole cell and outside-out patch-clamp techniques with reticulospinal Mauthner neurons of zebrafish embryos to investigate the developmental changes in the properties of glycinergic synaptic currents in vivo from the onset of synaptogenesis. Miniature inhibitory postsynaptic currents (mIPSCs) were isolated and recorded in the presence of TTX (1 μM), kynurenic acid (1 mM), and bicuculline (10 μM) and were found to be sensitive to strychnine (1 μM). The mIPSCs were first observed in 26–29 h postfertilization (hpf) embryos at a very low frequency of ∼0.04 Hz, which increased to ∼0.5 Hz by 30–40 hpf, and was ∼10 Hz in newly hatched (>50 hpf) larvae, indicating an accelerated increase in synaptic activity. At all embryonic stages, the amplitudes of the mIPSCs were variable but their means were similar (∼100 pA), suggesting rapid formation of the postsynaptic matrix. The 20–80% rise times of mIPSCs in embryos were longer (0.6–1.2 ms) than in larvae (∼0.3 ms), likely due to slower diffusion of glycine at the younger, immature synapses. The mIPSCs decayed with biexponential (τoff1and τoff2) time courses with a half-width in 26–29 hpf embryos that was longer and more variable than in older embryos and larvae. In 26- to 29-hpf embryos, τoff1was ∼15 ms and τoff2was ∼60 ms, representing events of intermediate duration; but occasionally long mIPSCs were observed in some cells where τoff1was ∼40 ms and τoff2was ∼160 ms. In 30–40 hpf embryos, the events were faster, with τoff1∼ 9 ms and τoff2∼ 40 ms, and in larvae, events declined somewhat further to τoff1∼ 4 ms and τoff2∼ 30 ms. Point-per-point amplitude histograms of the decay of synaptic events at all stages resulted in the detection of similar single channel conductances estimated as ∼45 pS, indicating the presence of heteromeric glycine receptors (GlyRs) from the onset of synaptogenesis. Fast-flow (1 ms) application of a saturating concentration of glycine (3–10 mM) to outside-out patches obtained at 26–29 hpf revealed GlyR currents that decayed biexponentially with time constants resembling the values found for intermediate and long mIPSCs; by 30–40 hpf, the GlyR currents resembled fast mIPSCs. These observations indicate that channel kinetics limited the mIPSC duration. Our data suggest that glycinergic mIPSCs result from the activation of a mixture of fast and slow GlyR subtypes, the properties and proportion of which determine the decay of the synaptic events in the embryos.
Dendritic Calcium Accumulation Associated With Direction-Selective Adaptation in Visual Motion-Sensitive Neurons In Vivo
Authors: Kurtz Rafael , Dürr Volker , Egelhaaf Martin
Published: December 2017

Motion adaptation in directionally selective tangential cells (TC) of the fly visual system has previously been explained as a presynaptic mechanism. Based on the observation that adaptation is in part direction selective, which is not accounted for by the former models of motion adaptation, we investigated whether physiological changes located in the TC dendrite can contribute to motion adaptation. Visual motion in the neuron's preferred direction (PD) induced stronger adaptation than motion in the opposite direction and was followed by an afterhyperpolarization (AHP). The AHP subsides in the same time as adaptation recovers. By combining in vivo calcium fluorescence imaging with intracellular recording, we show that dendritic calcium accumulation following motion in the PD is correlated with the AHP. These results are consistent with a calcium-dependent physiological change in TCs underlying adaptation during continuous stimulation with PD motion, expressing itself as an AHP after the stimulus stops. However, direction selectivity of adaptation is probably not solely related to a calcium-dependent mechanism because direction-selective effects can also be observed for fast moving stimuli, which do not induce sizeable calcium accumulation. In addition, a comparison of two classes of TCs revealed differences in the relationship of calcium accumulation and AHP when the stimulus velocity was varied. Thus the potential role of calcium in motion adaptation depends on stimulation parameters and cell class.
Horizontal-Plane Arm Movements With Direction Reversals Performed by Normal Individuals and Individuals With Down Syndrome
Authors: Almeida Gil Lúcio , Corcos Daniel M. , Hasan Ziaul
Published: December 2017

We examined the systematic variation in shoulder and elbow torque, as well as movement kinematics, for horizontal-plane arm movements with direction reversals performed by normal individuals and individuals with Down syndrome. Eight neurologically normal individuals and eight individuals with Down syndrome performed horizontal, planar reversal movements to four different target locations. The four locations of the targets were chosen such that there is a systematic increase in elbow interaction torque for each of the four different target locations. This systematic increase in interaction torque has previously been shown to lead to progressively larger movement reversal errors, and trajectories that do not show a sharp reversal of direction, for movements to and from the target in patients who have proprioceptive abnormalities. We computed joint torques at the elbow and shoulder and found a high correlation between elbow and shoulder torque for the neurologically normal subjects. The ratio of joint torques varied systematically with target location. These findings extend previously reported findings of a linear synergy between shoulder and elbow joints for a variety of point-to-point movements. There was also a correlation between elbow and shoulder torque in individuals with Down syndrome, but the magnitude of the correlation was less. The ratio of joint torques changed systematically with target direction in individuals with Down syndrome but was slightly different from the ratio observed for neurologically normal individuals. The difference in the ratio was caused by the generation of proportionately more elbow torque than shoulder torque. The fingertip path of individuals with Down syndrome showed a sharp reversal in moving toward and then away from the target. In this respect, they were similar to neurologically normal individuals but dissimilar to individuals with proprioceptive deficits. Finally, we observed that individuals with Down syndrome spend proportionately more time in the vicinity of the target than normal individuals. Collectively these results show that there is a systematic relationship between joint torques at the elbow and shoulder. This relationship is present for reversal movements and is also present in individuals with Down syndrome.
Step, Swim, and Scratch Motor Patterns in the Turtle
Authors: Earhart Gammon M. , Stein Paul S. G.
Published: December 2017

The turtle generates a variety of coordinated hindlimb movements, including different forms of locomotion and scratching. The intact turtle produces forward step, forward swim, and backpaddle. Following spinal cord transection, rostral, pocket, and caudal scratches can be evoked by mechanical stimulation of the shell. Comparisons of the kinematics and motor patterns of these six behaviors provide insights regarding neuronal mechanisms underlying their production. All six behaviors were characterized by alternating hip flexion and extension and by an event during which force was exerted against a substrate. The portion of the cycle occupied by hip flexion or extension movement varied across behaviors. Hip extension occupied well over half the cycle period in the forward step and the caudal scratch. The cycle was split into approximately half hip flexion and half hip extension for the forward swim, the backpaddle, and the rostral scratch. Hip flexion occupied over half the cycle in the pocket scratch. The swim and scratch forms had curvilinear, crescent-shaped toe trajectories and a single burst of monoarticular knee extensor activity during each cycle. The forward step had a linear toe trajectory and two bursts of knee extensor activity during each cycle, one during swing and one during stance. Timing of monoarticular knee extensor onset was similar for: the forward swim, the rostral scratch, and the swing phase burst of forward step; the pocket scratch and the stance phase burst of forward step; and the backpaddle and the caudal scratch. Amplitudes of muscle activity varied among the six behaviors; high amplitudes of activity were associated with events during which force was exerted against a substrate. These times of force exertion were: stance phase in the forward step, powerstroke in the forward swim and the backpaddle, and rubs of the limb against the shell in the scratch forms. The six behaviors studied represent a range of parameter values, as evidenced by relative durations of hip flexion to hip extension, knee extensor phasing, and electromyogram (EMG) amplitudes. This range of behaviors could be produced by assembling different combinations of neurons from a common pool, with all six behaviors likely sharing some basic circuitry. The extent of shared circuitry may be greater between behaviors with similar timing, e.g., backpaddle and caudal scratch.
Vestibulospinal and Reticulospinal Neuronal Activity During Locomotion in the Intact Cat. I. Walking on a Level Surface
Authors: Matsuyama Kiyoji , Drew Trevor
Published: December 2017

To examine the function of descending brain stem pathways in the control of locomotion, we have characterized the discharge patterns of identified vestibulo- and reticulospinal neurons (VSNs and RSNs, respectively) recorded from the lateral vestibular nucleus (LVN) and the medullary reticular formation (MRF), during treadmill walking. Data during locomotion were obtained for 44 VSNs and for 63 RSNs. The discharge frequency of most VSNs (42/44) was phasically modulated in phase with the locomotor rhythm and the averaged peak discharge frequency ranged from 41 to 165 Hz (mean = 92.8 Hz). We identified three classes of VSNs based on their discharge pattern. Type A, or double peak, VSNs (20/44 neurons, 46%) showed two peaks and two troughs of activity in each step cycle. One of the peaks was time-locked to the activity of extensor muscles in the ipsilateral hindlimb while the other occurred anti-phase to this period of activity. Type B, or single pause, neurons (13/44 neurons, 30%) were characterized by a tonic or irregular discharge that was interrupted by a single pronounced and brief period of decreased activity that occurred just before the onset of swing in the ipsilateral hindlimb; some type B VSNs also exhibited a brief pulse of activity just preceding this decrease. Type C, or single peak, neurons (9/44 neurons, 23%) exhibited a single period of increased activity that, in most cells, was time-locked to the burst of activity of either extensor or flexor muscles of a single limb. The population of RSNs that we recorded included neurons that showed phasic activity related to the activity of flexor or extensor muscles [electromyographically (EMG) related, 26/63, 41%], those that were phasically active but whose activity was not time-locked to the activity of any of the recorded muscles (13/63, 21%) and those that were completely unrelated to locomotion (24/63, 38%). Most of the EMG-related RSNs showed one (15/26) or two (11/26) clear phasic bursts of activity that were temporally related to either flexor or extensor muscles. The discharge pattern of double-burst RSNs covaried with ipsilateral and contralateral flexor muscles. Peak averaged discharge activity in these EMG-related RSNs ranged from 4 to 98 Hz (mean = 35.2 Hz). We discuss the possibility that most VSNs regulate the overall activity of extensor muscles in the four limbs while RSNs provide a more specific signal that has the flexibility to modulate the activity of groups of flexor and extensor muscles, in either a single or in multiple limbs.
Slow Synaptic Inhibition Mediated by Metabotropic Glutamate Receptor Activation of GIRK Channels
Authors: Dutar Patrick , Petrozzino Jeffrey J. , Vu Huan M. , Schmidt Marc F. , Perkel David J.
Published: December 2017

Glutamate is the predominant excitatory neurotransmitter in the vertebrate CNS. Ionotropic glutamate receptors mediate fast excitatory actions whereas metabotropic glutamate receptors (mGluRs) mediate a variety of slower effects. For example, mGluRs can mediate presynaptic inhibition, postsynaptic excitation, or, more rarely, postsynaptic inhibition. We previously described an unusually slow form of postsynaptic inhibition in one class of projection neuron in the song-control nucleus HVc of the songbird forebrain. These neurons, which participate in a circuit that is essential for vocal learning, exhibit an inhibitory postsynaptic potential (IPSP) that lasts several seconds. Only a portion of this slow IPSP is mediated by GABAB receptors. Since these cells are strongly hyperpolarized by agonists of mGluRs, we used intracellular recording from brain slices to investigate the mechanism of this hyperpolarization and to determine whether mGluRs contribute to the slow synaptic inhibition. We report that mGluRs hyperpolarize these HVc neurons by activating G protein–coupled, inwardly-rectifying potassium (GIRK) channels. MGluR antagonists blocked this response and the slow synaptic inhibition. Thus, glutamate can combine with GABA to mediate slow synaptic inhibition by activating GIRK channels in the CNS.
Angiotensin II Increases Neuronal Delayed Rectifier K+Current: Role of 12-Lipoxygenase Metabolites of Arachidonic Acid
Authors: Zhu Mingyan , Natarajan Rama , Nadler Jerry L. , Moore Jennifer M. , Gelband Craig H. , Sumners Colin
Published: December 2017

Angiotensin II (Ang II) elicits an Ang II type 2 (AT2) receptor–mediated increase in voltage-dependent delayed rectifier K+current ( IKV) in neurons cultured from newborn rat hypothalamus and brain stem. In previous studies, we have determined that this effect of Ang II is mediated via a Gi protein, activation of phospholipase A2(PLA2), and generation of arachidonic acid (AA). AA is rapidly metabolized within cells via lipoxygenases (LO), cyclooxygenase (COX) or p450 monooxygenase enzymes, and the metabolic products are known regulators of K+currents and channels. Thus in the present study, we have investigated whether the AT2receptor–mediated effects of Ang II on neuronal IKVrequire AA metabolism and if so, which metabolic pathways are involved. The data presented here indicate that the stimulatory actions of Ang II and AA on neuronal IKVare attenuated by selective blockade of 12-LO enzymes. However, the effects of Ang II are not altered by blockade of 5-LO or p450 monooxygenase enzymes. Furthermore, the actions of Ang II are mimicked by a 12-LO metabolite of AA, but 5-LO metabolites such as leukotriene B4and C4do not alter neuronal IKV. These data indicate that the AT2receptor–mediated stimulation of neuronal IKVis partially mediated through 12-LO metabolites of AA.
Discharge Pattern of Renal Sympathetic Nerve Activity in the Conscious Rat: Spectral Analysis of Integrated Activity
Authors: Kunitake Takato , Kannan Hiroshi
Published: December 2017

We investigated the periodic characteristics of bursting discharge in renal sympathetic nerve activity (RSNA) in conscious rats. Employing a discrete fast Fourier transform algorithm, a power spectrum analysis was used to quantify periodicities present in rectified and integrated RSNA whose signal-to-noise ratio in the recordings was greater than six. In conscious rats with intact baroreceptors, RSNA was characterized by four frequency components occurring at about 0.5, 1.5, 6, and 12 Hz, which corresponded to the low-frequency fluctuation of heart rate, respiration, and frequency of heart beat, and its harmonics, respectively. After intravenous infusion of sodium nitroprusside (SNP) to elicit reflex increases in RSNA and heart rate, the power for the component at 6 Hz followed the changes in heart beat frequency and was significantly increased, while those for the three other components were attenuated or experienced no change. In sino-aortic denervated (SAD) conscious rats, all four components were abolished, and the power spectrum was well fitted by a flat or Lorentzian curve, suggesting an almost random pattern. Only a respiratory-related component, which suggested common central modulation, appeared sporadically for short periods but was absent for the most part. Therefore most of this component together with the low-frequency component was also likely due to the baroreceptor-dependent peripheral modulation. The activity was sorted in 15 subgroups on the basis of spike amplitudes in the RSNA. Each subgroup showed frequency characteristics similar to the whole nerve activity. These results suggest that all periodicity in the RSNA of conscious rats with intact baroreceptors is caused by the baroreceptor input.
Formal and Attribute-Specific Information in Primary Visual Cortex
Authors: Reich Daniel S. , Mechler Ferenc , Victor Jonathan D.
Published: December 2017

We estimate the rates at which neurons in the primary visual cortex (V1) of anesthetized macaque monkeys transmit stimulus-related information in response to three types of visual stimulus. The stimuli—randomly modulated checkerboard patterns, stationary sinusoidal gratings, and drifting sinusoidal gratings—have very different spatiotemporal structures. We obtain the overall rate of information transmission, which we call formal information, by a direct method. We find the highest information rates in the responses of simple cells to drifting gratings (median: 10.3 bits/s, 0.92 bits/spike); responses to randomly modulated stimuli and stationary gratings transmit information at significantly lower rates. In general, simple cells transmit information at higher rates, and over a larger range, than do complex cells. Thus in the responses of V1 neurons, stimuli that are rapidly modulated do not necessarily evoke higher information rates, as might be the case with motion-sensitive neurons in area MT. By an extension of the direct method, we parse the formal information into attribute-specific components, which provide estimates of the information transmitted about contrast and spatiotemporal pattern. We find that contrast-specific information rates vary across neurons—about 0.3 to 2.1 bits/s or 0.05 to 0.22 bits/spike—but depend little on stimulus type. Spatiotemporal pattern-specific information rates, however, depend strongly on the type of stimulus and neuron (simple or complex). The remaining information rate, typically between 10 and 32% of the formal information rate for each neuron, cannot be unambiguously assigned to either contrast or spatiotemporal pattern. This indicates that some information concerning these two stimulus attributes is confounded in the responses of single neurons in V1. A model that considers a simple cell to consist of a linear spatiotemporal filter followed by a static rectifier predicts higher information rates than are found in real neurons and completely fails to replicate the performance of real cells in generating the confounded information.
Androgens and Isolation From Adult Tutors Differentially Affect the Development of Songbird Neurons Critical to Vocal Plasticity
Authors: Livingston Frederick S. , Mooney Richard
Published: December 2017

Song learning in oscine birds occurs during a juvenile sensitive period. One idea is that this sensitive period is regulated by changes in the electrophysiological properties of neurons in the telencephalic song nucleus lateral magnocellular nucleus of the anterior neostriatum (LMAN), a structure critical for song development but not adult singing. A corollary of this idea is that manipulations affecting the pace and quality of song learning will concomitantly affect the development of LMAN′s electrophysiological properties. Manipulations known to affect song development include treating juvenile male zebra finches with exogenous androgens, which results in abnormally truncated adult songs, and isolation of the juvenile from adult tutors and their songs, which extends the sensitive period for song learning. Previously, we showed that synaptic transmission in LMAN changes over normal song development and that these changes are accelerated or retarded, respectively, by androgen treatment and isolation from an adult tutor. The intrinsic properties of LMAN neurons afford another potential target for regulation by steroid hormones and experience of adult tutors. Indeed previous studies showed that the capacity for LMAN neurons to fire action potentials in bursts, due to a low-threshold calcium spike, and the width of single action potentials in LMAN, wane over development. Here we analyzed these and other intrinsic electrophysiological features of LMAN neurons over normal development, then tested whether either early androgen treatment or isolating juveniles from adult tutors affected the timing of these changes. The present study shows that androgen but not isolation treatment alters the developmental time at which LMAN neurons progress from the bursting to nonbursting phenotype. In addition, other intrinsic properties, including the half-height spike width and the magnitude of the spike afterhyperpolarization (AHP), were found to change markedly over development but only changes to the AHP were androgen sensitive. Interestingly of all of the synaptic and intrinsic electrophysiological properties in LMAN studied to date, only the half-height spike width continues to change in the late juvenile stages of song learning. Furthermore raising juveniles in isolation from an adult tutor transiently delays the maturation of this property. The present results underscore that beyond their effects on LMAN′s synaptic properties, both androgens and adult tutor experience are potent and selective regulators of the intrinsic properties of LMAN neurons.