bluuebunny/crossref_metadata_2025 huggingface dataset:
Heterogeneous calcium currents and transmitter release in cultured mouse spinal cord and dorsal root ganglion neurons
Authors: Yu C. , Lin P. X. , Fitzgerald S. , Nelson P.
Published: December 2017

1. Calcium currents and transmitter release were studied in cocultures of fetal mouse neurons from the ventral half of the spinal cord (VH neurons) and from dorsal root ganglion (DRG neurons). The effects of BayK 8644 and omega-conotoxin on calcium currents and transmitter release were compared. 2. The presence of low voltage-activated (LVA) calcium current in both VH and DRG neurons is variable. Some cells exhibit only high voltage-activated (HVA) currents, whereas others show both HVA and LVA currents. 3. BayK 8644 did not affect LVA currents but strongly augmented both steady and transient components of the HVA calcium conductance. 4. omega-Conotoxin GVIA reduces both transient and steady components of the HVA but does not abolish either component even after 3 h of application. 5. Calcium currents that were resistant to omega-contoxin were augmented by BayK 8644. 6. Synaptic transmission between pairs of spinal cord neurons from the ventral half of the spinal cord (VH-VH connections) or between dorsal root ganglion neurons and VH neurons (DRG-VH connections) were studied with two-cell recording and stimulation techniques. 7. In approximately 70% of VH-VH connections and 50% of DRG-VH connections, BayK 8644 or its active optical isomer failed to affect transmitter output. Substantial augmentation of the remainder of the connections could be reliably produced by the dihydropyridines. Raised calcium in the extracellular medium produced augmentation of synaptic connections in all cases. BayK 8644 produced substantial, consistent augmentation of voltage-sensitive calcium channels in both VH and DRG neurons. 8. The toxin, omega-conotoxin, produced no consistent effect on excitatory or inhibitory postsynaptic potentials (EPSPs or IPSPs) elicited in VH neurons by stimulation of nearby VH neurons. VH EPSPs elicited by stimulation of nearby DRG neurons were reduced to approximately 50% of control values after 10 min of omega-conotoxin perfusion. Spontaneous and evoked synaptic activity could be recorded in VH neurons as long as 2 h after cultures were incubated in 0.5 microM omega-conotoxin. omega-Conotoxin produced a modest reduction in HVA currents in both VH and DRG neurons. 9. BayK 8644 did not produce consistent augmentation of transmission at the frog neuromuscular junction. omega-Conotoxin produced total blockade of transmission in this preparation. 10. We conclude that neither sustained nor inactivating high-threshold voltage-sensitive (HVA) calcium channels sensitive to BayK 8644 or omega-conotoxin such as those measured in the neuronal cell bodies are responsible for action-potential-evoked transmitter release from the majority of VH neurons.(ABSTRACT TRUNCATED AT 400 WORDS)
Habituation of an appetitive reflex in the honeybee
Authors: Braun G. , Bicker G.
Published: December 2017

1. The proboscis extension reflex is an appetitive component of the bee's feeding behavior that is elicited by touching one antenna with a droplet of sugar water. Repetitive stimulation leads to a decrement and finally to the disappearance of the response, which can be restored by stimulating the contralateral antenna. This behavioral plasticity conforms to essential parametric characteristics for habituation. 2. The response was quantified by recording extracellularly from a muscle involved in proboscis movement, by measuring the duration of the proboscis extension, or by determining the number of trials necessary to abolish any visible response. 3. Because habituation was restricted to the repetitively stimulated antenna and did not generalize to the contralateral hemisphere, the neural circuits mediating habituation may be confined to one hemisphere. 4. State dependence of habituation could be demonstrated by showing that hungry animals exhibited a smaller response decrement and required more trials until disappearance of the response compared with satiated animals. The initial response and the subsequent response decrement are separate components determined by satiation level and stimulus strength. 5. Depleting the nervous system of monoamines by the use of reserpine abolished the reflex in 30% of the animals and reduced responsiveness in the remainder. Injection of octopamine or its metabolic precursor tyramine restored the reflex in reserpinized unresponsive animals, and tyramine also enhanced the muscle-spike discharge of reserpinized, responsive animals. In undepleted animals, tyramine application also accelerated the rate of habituation of the reflex. We therefore propose that octopaminergic neurons participate in mediating food arousal and the state dependence of habituation and, in a separate process, influence the response decrement during habituation. 6. Application of an acetylcholine esterase (AChE) inhibitor and a cholinergic receptor blocker confirmed histochemical data that implicate cholinergic transmission in the reflex pathways. 7. The combined pharmacological dissection of the reflex and immunocytochemical investigations of its chemical architecture provide evidence that the proboscis extension reflex is mediated by nonaminergic and monoaminergic pathways operating in parallel.
Role of the rostral superior colliculus in active visual fixation and execution of express saccades
Authors: Munoz D. P. , Wurtz R. H.
Published: December 2017

1. In the rostral pole of the monkey superior colliculus (SC) a subset of neurons (fixation cells) discharge tonically when a monkey actively fixates a target spot and pause during the execution of saccadic eye movements. 2. To test whether these fixation cells are necessary for the control of visual fixation and saccade suppression, we artificially inhibited them with a local injection of muscimol, an agonist of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA). After injection of muscimol into the rostral pole of one SC, the monkey was less able to suppress the initiation of saccades. Many unwanted visually guided saccades were initiated less than 100 ms after onset of a peripheral visual stimulus and therefore fell into the range of express saccades. 3. We propose that fixation cells in the rostral SC form part of a fixation system that facilitates active visual fixation and suppresses the initiation of unwanted saccadic eye movements. Express saccades can only occur when activity in this fixation system is reduced.
Changes in the distributed temporal response properties of SI cortical neurons reflect improvements in performance on a temporally based tactile discrimination task
Authors: Recanzone G. H. , Merzenich M. M. , Schreiner C. E.
Published: December 2017

1. Temporal response characteristics of neurons were sampled in fine spatial grain throughout the hand representations in cortical areas 3a and 3b in adult owl monkeys. These monkeys had been trained to detect small differences in tactile stimulus frequencies in the range of 20-30 Hz. Stimuli were presented to an invariant, restricted spot on a single digit. 2. The absolute numbers of cortical locations and the cortical area over which neurons showed entrained frequency-following responses to behaviorally important stimuli were significantly greater when stimulation was applied to the trained skin, as compared with stimulation on an adjacent control digit, or at corresponding skin sites in passively stimulated control animals. 3. Representational maps defined with sinusoidal stimuli were not identical to maps defined with just-visible tapping stimuli. Receptive-field/frequency-following response site mismatches were recorded in every trained monkey. Mismatches were less frequently recorded in the representations of control skin surfaces. 4. At cortical locations with entrained responses, neither the absolute firing rates of neurons nor the degree of the entrainment of the response were correlated with behavioral discrimination performance. 5. All area 3b cortical locations with entrained responses evoked by stimulation at trained or untrained skin sites were combined to create population peristimulus time and cycle histograms. In all cases, stimulation of the trained skin resulted in 1) larger-amplitude responses, 2) peak responses earlier in the stimulus cycle, and 3) temporally sharper responses, than did stimulation applied to control skin sites. 6. The sharpening of the response of cortical area 3b neurons relative to the period of the stimulus could be accounted for by a large subpopulation of neurons that had highly coherent responses. 7. Analysis of cycle histograms for area 3b neuron responses revealed that the decreased variance in the representation of each stimulus cycle could account for behaviorally measured frequency discrimination performance. A strong correlation between these temporal response distributions and the discriminative performances for stimuli applied at all studied skin surfaces was even stronger (r = 0.98) if only the rising phases of cycle histogram were considered in the analysis. 8. The responses of neurons in area 3a could not account for measured differences in frequency discrimination performance. 9. These representational changes did not occur in monkeys that were stimulated on the same schedule but were performing an auditory discrimination task during skin stimulation. 10. It is concluded that by behaviorally training adult owl monkeys to discriminate the temporal features of a tactile stimulus, distributed spatial and temporal response properties of cortical neurons are altered.(ABSTRACT TRUNCATED AT 400 WORDS)
Strength increases from the motor program: comparison of training with maximal voluntary and imagined muscle contractions
Authors: Yue G. , Cole K. J.
Published: December 2017

1. This study addressed potential neural mechanisms of the strength increase that occur before muscle hypertrophy. In particular we examined whether such strength increases may result from training-induced changes in voluntary motor programs. We compared the maximal voluntary force production after a training program of repetitive maximal isometric muscle contractions with force output after a training program that did not involve repetitive activation of muscle; that is, after mental training. 2. Subjects trained their left hypothenar muscles for 4 wk, five sessions per week. One group produced repeated maximal isometric contractions of the abductor muscles of the fifth digit's metacarpophalangeal joint. A second group imagined producing these same, effortful isometric contractions. A third group did not train their fifth digit. Maximal abduction force, flexion/extension force and electrically evoked twitch force (abduction) of the fifth digit were measured along with maximal integrated electromyograms (EMG) of the hypothenar muscles from both hands before and after training. 3. Average abduction force of the left fifth digit increased 22% for the Imagining group and 30% for the Contraction group. The mean increase for the Control group was 3.7%. 4. The maximal abduction force of the right (untrained) fifth digit increased significantly in both the Imagining and Contraction groups after training (10 and 14%, respectively), but not in the Control group (2.3%). These results are consistent with previous studies of training effects on contralateral limbs. 5. The abduction twitch force evoked by supramaximal electrical stimulations of the ulnar nerve was unchanged in all three groups after training, consistent with an absence of muscle hypertrophy. The maximal force of the left great toe extensors for individual subjects remained unchanged after training, which argues against strength increases due to general increases in effort level. 6. Increases in abduction and flexion forces of the fifth digit were poorly correlated in subjects of both training groups. The fifth finger abduction force and the hypothenar integrated EMG increases were not well correlated in these subjects either. Together these results indicate that training-induced changes of synergist and antagonist muscle activation patterns may have contributed to force increases in some of the subjects. 7. Strength increases can be achieved without repeated muscle activation. These force gains appear to result from practice effects on central motor programming/planning. The results of these experiments add to existing evidence for the neural origin of strength increases that occur before muscle hypertrophy.
Stabilization of gaze during circular locomotion in darkness. II. Contribution of velocity storage to compensatory eye and head nystagmus in the running monkey
Authors: Solomon D. , Cohen B.
Published: December 2017

1. Yaw eye in head (Eh) and head on body velocities (Hb) were measured in two monkeys that ran around the perimeter of a circular platform in darkness. The platform was stationary or could be counterrotated to reduce body velocity in space (Bs) while increasing gait velocity on the platform (Bp). The animals were also rotated while seated in a primate chair at eccentric locations to provide linear and angular accelerations similar to those experienced while running. 2. Both animals had head and eye nystagmus while running in darkness during which slow phase gaze velocity on the body (Gb) partially compensated for body velocity in space (Bs). The eyes, driven by the vestibuloocular reflex (VOR), supplied high-frequency characteristics, bringing Gb up to compensatory levels at the beginning and end of the slow phases. The head provided substantial gaze compensation during the slow phases, probably through the vestibulocollic reflex (VCR). Synchronous eye and head quick phases moved gaze in the direction of running. Head movements occurred consistently only when animals were running. This indicates that active body and limb motion may be essential for inducing the head-eye gaze synergy. 3. Gaze compensation was good when running in both directions in one animal and in one direction in the other animal. The animals had long VOR time constants in these directions. The VOR time constant was short to one side in one animal, and it had poor gaze compensation in this direction. Postlocomotory nystagmus was weaker after running in directions with a long VOR time constant than when the animals were passively rotated in darkness. We infer that velocity storage in the vestibular system had been activated to produce continuous Eh and Hb during running and to counteract postrotatory afterresponses. 4. Continuous compensatory gaze nystagmus was not produced by passive eccentric rotation with the head stabilized or free. This indicates that an aspect of active locomotion, most likely somatosensory feedback, was responsible for activating velocity storage. 5. Nystagmus was compared when an animal ran in darkness and in light. the beat frequency of eye and head nystagmus was lower, and the quick phases were larger in darkness. The duration of head and eye quick phases covaried. Eye quick phases were larger when animals ran in darkness than when they were passively rotated. The maximum velocity and duration of eye quick phases were the same in both conditions. 6. The platform was counterrotated under one monkey in darkness while it ran in the direction of its long vestibular time constant.(ABSTRACT TRUNCATED AT 400 WORDS)
Midline and lateral field sound localization in the ferret (Mustela putorius): contribution of the superior olivary complex
Authors: Kavanagh G. L. , Kelly J. B.
Published: December 2017

1. The ability of ferrets to localize sound in space was determined before and after unilateral or bilateral lesions of the superior olivary complex (SOC). Lesions were made by pressure injection of kainic acid into the SOC through a stereotaxically positioned glass micropipette. The lesions destroyed the cell bodies in the superior olive without disrupting fibers of passage in the trapezoid body or other pathways in the auditory brain stem. The integrity of fibers was demonstrated by protargol staining of axonal processes and by the retrograde transport of horseradish peroxidase (HRP) from the inferior colliculus to other auditory brain stem nuclei. Behavioral tests were carried out separately for sound localization at midline and lateral field positions. Minimum audible angles were determined for single 45-ms noise bursts presented through paired loudspeakers positioned symmetrically around 0, -60, and +60 degrees azimuth. 2. Four ferrets received complete lesions of the left SOC, and two received complete lesions of the right SOC. In general, unilateral destruction of the superior olive resulted in impairments in sound localization in both left and right lateral fields. In some cases, deficits were also apparent on midline. Four additional animals received unilateral lesions that spared cells within the SOC. In most cases, deficits were apparent despite incomplete lesions of the SOC. The pattern of deficits was generally consistent with that found in animals with complete lesions. Most animals had difficulty localizing sounds in the lateral fields. 3. Four animals received bilateral lesions of the SOC. Three had complete or near-complete destruction of the superior olive on one side of the brain with relatively minor damage on the other side. Each of these animals exhibited behavioral deficits that were particularly severe ipsilateral to the more extensively damaged superior olive. One animal with complete bilateral destruction of the SOC was incapable of sound localization, even with 2-s noise bursts. This animal, however, suffered severe motor impairments after surgery that might have contributed to the apparent inability to localize sound. 4. Two animals with kainic acid lesions that caused little or no damage to the SOC were still capable of high levels of performance in tests of sound localization and had no elevation in minimum audible angles. These cases served as controls for the possible effects of nonspecific brain damage and demonstrated that kainic acid injections per se resulted in no obvious deficits in our test situation.(ABSTRACT TRUNCATED AT 400 WORDS)
Ion channels in spinal cord astrocytes in vitro. II. Biophysical and pharmacological analysis of two Na+ current types
Authors: Sontheimer H. , Waxman S. G.
Published: December 2017

1. Na+ currents expressed in astrocytes cultured from spinal cord were studied by whole cell patch-clamp recording. Two subtypes of astrocytes, pancake and stellate cells, were morphologically differentiated and showed expression of Na+ channels at densities that are unusually high for glial cells (2-8 channels/microns2) and comparable to cultured neurons. 2. Na+ currents in stellate and pancake astrocytes were comparable to neuronal Na+ currents with regard to Na(+)-current activation (tau m) and inactivation (tau h) time constants, which were equally fast in both astrocyte types. However, they differed with respect to voltage dependence of activation, and current-voltage (I-V) curves were approximately 10 mV more positive in stellate cells (-11.1 +/- 5.6 mV, mean +/- SD) than in pancake cells (19.7 +/- 4.5 mV). Steady-state activation (m infinity curves) was 16 mV more negative in pancake (mean V1/2 = -48.8 mV) than in stellate cells (mean V1/2 = -32.7 mV). 3. Steady-state inactivation (h infinity curves) of Na+ currents was distinctly different in the two astrocyte types. In stellate astrocytes h infinity curves had midpoints close to -65 mV (-64.6 +/- 6.5 mV), similar to most cultured neurons. In pancake astrocytes h infinity-curves were approximately 25 mV more negative, with midpoints close to -85 mV (84.5 +/- 9.5 mV). 4. The two forms of Na+ currents were additionally distinguishable by their sensitivity to tetrodotoxin (TTX). Na+ currents in stellate astrocytes were highly TTX sensitive [half-maximal inhibition (Kd) = 5.7 nM] whereas Na+ currents in pancake astrocytes were relatively TTX resistant, requiring 100- to 1,000-fold higher concentrations for blockage (Kd = 1,007 nM). 5. Na+ currents were fit by the Hodgkin-Huxley (HH) model. In pancake astrocytes, as in squid gigant axons, Na(+)-current kinetics could be well described with an m3h model, whereas in stellate astrocytes Na+ currents were better described with higher-order power terms for activation (m). On average, best fits were obtained using an m4h model. 6. Pancake astrocytes were capable of generating action-potential (AP)-like responses under current clamp whereas stellate astrocytes were not. The h infinity curve for APs shows that membrane potentials more negative than -70 mV are required to allow these responses to occur.(ABSTRACT TRUNCATED AT 400 WORDS)
K-dependent inhibition in the dentate-CA3 network of guinea pig hippocampal slices
Authors: Misgeld U. , Bijak M. , Brunner H. , Dembowsky K.
Published: December 2017

1. The occurrence of potassium-dependent inhibitory postsynaptic potentials (K-IPSPs) in relation to burst discharges induced by 4-aminopyridine (4-AP; 30 microM) was studied in CA3, granule and hilar neurons in guinea pig hippocampal slices with the use of paired extra- and/or intracellular recording. 2. Slow small (2-5 mV) and large (up to 30 mV) K-IPSPs were observed in CA3, granule and in some hilar neurons during 4-AP applications in the presence of blockers for fast synaptic transmission, picrotoxin (50 microM), and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; 5-10 microM). Amplitudes of K-IPSPs were linearly related to voltage, and they reversed in sign close to -100 mV, as expected for synaptic potentials generated by an increase in K-conductance. 3. In CA3 neurons, 4-AP applied in the presence of picrotoxin elicited burst discharges and K-IPSPs. CNQX blocked the burst discharge activity and increased the amplitude of K-IPSPs. 4. In granule cells, 4-AP applied in the presence of picrotoxin elicited K-IPSPs and only inconsistently small excitatory postsynaptic potentials (EPSPs). The EPSPs were blocked by CNQX, but CNQX application did not affect the K-IPSPs. However, in granule cells it could be observed that blockade of Cl-inhibition by picrotoxin in the presence of CNQX increased the amplitude of K-IPSPs. 5. In hilar neurons, 4-AP applied in the presence of picrotoxin elicited mainly burst discharges. CNQX blocked the burst discharges only in a few cells. In most hilar neurons K-IPSPs were observed at the beginning of the 4-AP effect, but subsequently K-IPSPs were replaced by burst discharges. 6. To determine the type of cells that burst in picrotoxin and 4-AP, neurons were stained intracellularly with horseradish peroxidase. Neurons stained in the granule cell layer did not burst and were morphologically identified as granule cells. Neurons stained in the hilar region burst and were nonpyramidal, nongranule cells. Bursting cells stained in the CA3 area were all pyramidal cells. 7. The hilar neurons varied considerably in size and dendritic organization. They could be classified as aspiny and spiny cells, the latter including mossy cells. 8. We conclude that K-dependent inhibition may explain the long-lasting IPSPs observed in in vivo recordings from hippocampal cells. In a hippocampal lamella, burst discharge activity of hilar neurons including presumed excitatory mossy cells is associated with inhibition of granule cells.(ABSTRACT TRUNCATED AT 400 WORDS)
Segmental organization of visceral and somatic input onto C3-T6 spinothalamic tract cells of the monkey
Authors: Hobbs S. F. , Chandler M. J. , Bolser D. C. , Foreman R. D.
Published: December 2017

1. Referred pain of visceral origin has three major characteristics: visceral pain is referred to somatic areas that are innervated from the same spinal segments as the diseased organ; visceral pain is referred to proximal body regions and not to distal body areas; and visceral pain is felt as deep pain and not as cutaneous pain. The neurophysiological basis for these phenomena is poorly understood. The purpose of this study was to examine the organization of viscerosomatic response characteristics of spinothalamic tract (STT) neurons in the rostral spinal cord. Interactions were determined among the following: 1) segmental location, 2) effects of input by cardiopulmonary sympathetic, greater splanchnic, lumbar sympathetic, and urinary bladder afferent fibers, 3) location of excitatory somatic field, e.g., hand, forearm, proximal arm, or chest, 4) magnitude of response to hair, skin, and deep mechanoreceptor afferent input, and 5) regional specificity of thalamic projection sites. 2. A total of 89 STT neurons in segments C3-T6 were characterized for responses to visceral and somatic stimuli. Neurons were activated antidromically from the contralateral ventroposterolateral oralis or caudalis nuclei of the thalamus. Cell responses to visceral and somatic stimuli were not different on the basis of the thalamic site of antidromic activation. Recording sites for 61 neurons were located histologically; 87% of lesion sites were located in laminae IV-VII or X. There was no relationship between response properties of the neurons and spinal laminar location. 3. Different responses to visceral stimuli were observed in three zones of the rostral spinal cord: C3-C6, C7-C8, and T1-T6. In C3-C6, urinary bladder distension (UBD) and electrical stimulation of greater splanchnic and lumbar sympathetic afferent fibers inhibited STT cells. Electrical stimulation of cardiopulmonary sympathetic afferents increased cell activity in C5 and C6 and either excited or inhibited STT cells in C3 and C4. In the cervical enlargement (C7-C8), STT cells generally were either inhibited or showed little response to stimulation of visceral afferent fibers. In T1-T6, input from greater splanchnic and cardiopulmonary sympathetic afferent nerves increased activity of STT cells. Lumbar sympathetic afferent input inhibited cells in T1-T2 and had little effect on cells in T3-T6, whereas UBD decreased cell activity in all segments studied. 4. In general, stimulation of somatic structures increased activity of STT neurons in segments that received primary afferent innervation from the excitatory somatic receptive field or in the segments immediately adjacent to these segments. Only input from the forelimb, especially the hand, markedly excited cells in C7 and C8.+
Primary motor cortical responses to perturbations of prehension in the monkey
Authors: Picard N. , Smith A. M.
Published: December 2017

1. Two monkeys were trained to grasp, lift, and hold an object within a vertical position window. A downward force-pulse perturbation was delivered during stationary object holding to simulate slip of the object due to gravity. The responses evoked by the perturbation were studied in 189 neurons of the hand area of the primary motor cortex. In addition, the slip-evoked responses were compared with the modulation of neural discharge with textures and weights described in the previous paper. 2. The perturbation evoked responses with sharp onsets in the majority of motor cortical neurons (115/189, 61%) active during the task. The majority of the responses were of sufficiently short latency (43.17 +/- 17.24 ms, mean +/- SD) to have participated in the reflex grip force increase that followed at latencies from 50 to 100 ms. 3. Although a similar proportion of neurons with cutaneous (43/70) or proprioceptive (35/59) receptive fields (RFs) were responsive to the perturbation, the cutaneous afferents provided a stronger excitation of motor cortical cells than the feedback originating from proprioceptive receptors. 4. The covariation of the neural discharge related to the surface texture of the grasped object and the responsiveness to object slip was studied in 89 cells tested with the perturbation and with more than one surface texture on unperturbed trials. Within this population, motor cortical cells with cutaneous RFs were more sensitive to the perturbation (25/31) than neurons receiving proprioceptive input (8/16). Furthermore, all (17/17) neurons with cutaneous RFs that were more active with the smooth than with the rough surface textures showed a vigorous response to the perturbation. 5. A detectable downward displacement of the object was not always necessary to excite neurons with cutaneous RFs and whose activity increased with the smooth textures. Their sensitivity to the perturbation was consistent with the hypothesis that the cutaneous afferent activity generated by object slips or shear forces on the skin contributed to the increased discharge when lifting objects of slippery surface textures. The activity of these slip- or shear-sensitive cells may have contributed to the reflex grip force increases and to the greater sustained muscular activity needed to lift smooth objects. 6. Ten cells that were excited by stroking of the glabrous skin of the hand decreased their discharge frequency during the task even though their RFs were in direct contact with the object. Most of these neurons (7/10) did not respond to the object slip, and three cells had very weak responses to the perturbation.(ABSTRACT TRUNCATED AT 400 WORDS)
Characterization and adaptive modification of the goldfish vestibuloocular reflex by sinusoidal and velocity step vestibular stimulation
Authors: Pastor A. M. , de la Cruz R. R. , Baker R.
Published: December 2017

1. The normal and adapted vestibuloocular reflex (VOR) of goldfish was characterized by means of sinusoidal, velocity step, and position step head rotations about the vertical axis. VOR adaptation was induced by short-term, 1- to 4-h, presentation of visual and vestibular stimuli that altered the ratio of eye to head velocity. 2. The VOR response measured with sinusoidal oscillations in the dark was close to ideal compensatory values over 2 decades (1/32-2 Hz). Gain approximated unity, and phase, in relation to the head, was nearly 180 degrees. The VOR was linear within the range of head velocity tested (4-64 degrees/s). 3. Head velocity steps from 1/8 to 1 Hz produced steplike eye velocity profiles that could be divided into an early acceleration-related "dynamic" component and a later constant-velocity "sustained" period frequently separated by a sag at approximately 0.1-0.15 s from the initiation of eye movement. The sustained response exhibited no decay during the constant-velocity component of the step. 4. Higher temporal resolution of the dynamic response showed the adducting eye movement to have a shorter latency, faster rise time, and larger peak gain than the abducting eye movement. The characteristics of this directional asymmetry were similar for position steps and electrical stimulation of the vestibular nerve. However, the asymmetry was not observed during sinusoidal head rotation, the sustained component of the step response, or after electrical stimulation of the VIth and IIIrd nerves. We conclude that this directional asymmetry is of central origin and may be largely due to the parallel vestibular and abducens internuclear neuron pathways onto medial rectus motoneurons. 5. The VOR adaptation process for both higher and lower eye velocity exhibited an exponential time course with time constants of 55 and 45 min, respectively. After continuous sinusoidal training for 4 h, VOR gain reached an asymptotic level 5% away from perfect suppression in the low-gain training, but 19% away from the actual performance in the high-gain paradigm. The time constant for VOR gain reversal was 5 h, and an asymptotic level 40% less than performance was reached within 10 h. 6. Adapted VOR gain was symmetrical for both directions of eye movement measured either during sinusoidal rotation or the sustained part of the velocity step. VOR adaptation also produced a comparable gain change in the nasal and temporal directions of the dynamic component, but this reflected the asymmetric characteristics observed in the preadapted condition.(ABSTRACT TRUNCATED AT 400 WORDS)
Cholinergic transmission at the first synapse of the circuit mediating the crayfish lateral giant escape reaction
Authors: Miller M. W. , Vu E. T. , Krasne F. B.
Published: December 2017

1. The chemical synapses between mechanoreceptor neurons and first-order interneurons in the lateral giant (LG) neuron escape circuit of the crayfish have plastic properties, some of which are believed to be the basis for behavioral habituation and sensitization. In this investigation pharmacological experiments were conducted to assess the role of cholinergic synaptic transmission in this pathway. 2. Arterial perfusion of the cholinergic agonist carbachol produced increased activity of many abdominal nerve cord units, including an identified first-order interneuron (interneuron A) in the LG circuit. A general increase in activity of interneurons in this circuit in the presence of certain cholinergic agonists was inferred from an increase in the frequency of occurrence of spontaneous excitatory postsynaptic potentials (EPSPs) recorded in the LG. 3. Cholinergic antagonists reduced the amplitude of spontaneous and evoked sensory neuron-to-interneuron A EPSPs and decreased the disynaptic (via 1st-order interneurons) component of evoked EPSPs in the LG. These effects indicate that postsynaptic cholinergic receptors are utilized in mechanosensory synaptic transmission to the first-order interneurons of this circuit. The relative potencies of the blockers tested (mecamylamine > picrotoxin >>> curare > atropine) suggest that the receptors on the interneurons belong to a previously characterized class of crustacean cholinergic receptors that resemble the ganglionic nicotinic subtype of vertebrates. 4. Nicotinic agonists (carbachol, tetramethylammonium hydroxide, 1,1-dimethyl-4-phenyl-piperazium iodide) produced depolarizing (decreased input resistance) responses on the LG neuron itself. These responses persisted during blockade of chemical transmission by cobalt. The presence of cholinergic receptors on the LG, a cell in which all known inputs mediating sensory excitation are electrical, is discussed. 5. Application of muscarinic agonists (pilocarpine, oxotremorine) resulted in a long-lasting reduction of the evoked sensory neuron-to-interneuron A EPSP and the disynaptic component of the evoked EPSP in the LG. No effects on the membrane potential or input resistance of the interneurons were detected. It is proposed that presynaptic receptors with a muscarinic profile are present on mechanosensory neurons and that these receptors mediate a reduction of transmitter release.
Groupings of nonpyramidal and pyramidal cells with specific physiological and morphological characteristics in rat frontal cortex
Authors: Kawaguchi Y.
Published: December 2017

1. Physiological and morphological properties of layer V non-pyramidal and pyramidal cells in isolated slices of frontal cortex from young rats (16-22 days postnatal) were studied by whole-cell, current-clamp recording of visualized cell bodies coupled with intracellular staining by biocytin at 26-27 degrees C. 2. Plotting of spike width at half amplitude against input resistance revealed two physiological categories of nonpyramidal cells. One class (n = 29) had input resistances lower than 400 M omega and spike widths at half amplitude shorter than 0.8 ms; the other (n = 22) had input resistances higher than 400 M omega and spike widths longer than 0.8 ms. According to their spike firing characteristics, the former are called fast-spiking (FS) cells, and the latter low-threshold spike (LTS) cells. 3. Resting potentials were more negative in FS cells than in LTS cells. Membrane time constants in LTS cells were four times larger than those of FS cells. Afterhyperpolarizations (AHPs) following action potentials consisted of a single component in FS cells, but two components with early and late peaks were observed in LTS cells. AHPs of FS cells had faster time-to-peak and larger amplitude than the early component of the AHPs of LTS cells. 4. Low-threshold spikes induced by depolarizing current pulses were observed at hyperpolarized potentials in LTS cells, but not in FS cells. The low-threshold spikes in LTS cells could be activated at hyperpolarized potentials by synaptic potentials. 5. Spike trains elicited by depolarizing current pulses in FS cells showed almost no spike-frequency adaptation, whereas those in LTS cells showed adaptation. 6. Excitatory postsynaptic potentials (EPSPs) of both groups of nonpyramidal cells contained N-methyl-D-aspartate (NMDA) receptor-mediated components. A combination of stimulation-induced EPSPs with depolarization caused repetitive firing in FS cells that was abolished by NMDA receptor blockers. Repetitive firing was not observed in LTS cells under these conditions. 7. The somal size of the two classes of nonpyramidal cells was similar. FS cells were all multipolar in shape, whereas LTS cells included both multipolar and bitufted types. The dendrites of some FS cells extended up into layers II/III, but there were also other FS cells with their dendrites restricted in layer V. Dendrites of LTS cells were mostly restricted to layer V. Dendrites of FS cells were mostly smooth, but those of LTS cells possessed a modest but consistent population of spines.(ABSTRACT TRUNCATED AT 400 WORDS)
PET study of voluntary saccadic eye movements in humans: basal ganglia-thalamocortical system and cingulate cortex involvement
Authors: Petit L. , Orssaud C. , Tzourio N. , Salamon G. , Mazoyer B. , Berthoz A.
Published: December 2017

1. The purpose of this work was to explore the cortical and subcortical mechanisms underlying the execution of voluntary saccadic eye movements in humans. 2. Normalized regional cerebral blood flow (NrCBF) was measured using positron emission tomography (PET) and H2(15O) bolus intravenous injections in four right-handed healthy volunteers at rest and while performing self-paced voluntary horizontal saccadic eye movements in total darkness. 3. Magnetic resonance imaging of each subject's brain was matched to PET images, allowing the detection of activation in individually defined anatomic regions of interest. Cortical regions were drawn according to gyri limits; subcortical structures were also defined. 4. Self-paced saccadic eye movements elicited bilateral NrCBF increases in the lenticular nuclei, including putamen and globus pallidus, and in the thalamus. At the cortical level, we found bilateral NrCBF increases in the precentral gyrus, the superior part of the median frontal gyrus that corresponds to the supplementary motor area. There was also a significant NrCBF increase in the cerebellar vermis. 5. Right fusiform and lingual gyri, right insula, and left cingulate gyrus were also activated during the execution of saccades. 6. These results indicate that the classical basal ganglia-thalamocortical motor loop previously described for skeletal movements may also be involved in simple saccadic eye movements in humans.
Human flexor reflex modulation during cycling
Authors: Brown D. A. , Kukulka C. G.
Published: December 2017

1. Human flexor reflex (HFR) responses were elicited during ergometer cycling in neurologically intact humans with the objective of understanding the influence of lower limb muscle activity on phase-dependent reflex modulation during movement. The experimental setup permitted control over background muscle activity and stimulus intensity without significantly interfering with the cycling motion. 2. All experiments involved cycling on an ergometer at a set rate and workload. A 333-Hz, 15-ms pulse train of electrical stimulation was randomly delivered to the skin over the tibial nerve at the ankle at selected lower limb positions. In the first group of experiments, subjects were stimulated at six cycling phases while pedaling with normal, phasic ankle activity (free-form cycling). The second and third group of experiments involved stimulation under static limb positioning conditions and during active pedaling while subjects were asked to maintain a consistent background level of isolated tibialis anterior (TA) or soleus (SOL) electromyographic (EMG) activity. 3. Control criteria were established to assure similar isolated muscle EMG levels and sensory stimulation intensities throughout the experiments. With the aid of the application of a lower extremity brace and visual EMG feedback, SOL and TA activity were confined by the subject to a narrow range during the task of cycling. Stimulus consistency was achieved through maintenance of flexor hallucis brevis M-waves to within an envelope encompassing the mean value +/- 5% of the maximum M-wave amplitude in all experimental conditions. 4. When the subject's limb was statically positioned, the HFR responses in the SOL muscle showed no significant changes in pattern when compared at various limb positions. During cycling with consistent SOL activity, a response waveform pattern of early-latency-long-duration depression was followed by a later-latency facilitation response in all positions except the initial power phase. The initial power phase was characterized by an additional early-latency facilitation in all but one subject. 5. In the TA muscle response, no change in onset latency (57.5 +/- 0.8 ms, mean +/- SD), waveform pattern, or response amplitude (7.9 +/- 1.1% maximal voluntary contraction, mean +/- SD) was observed during static limb positioning. Significant increases in response amplitude (P < 0.05) coupled with significant increases (9.2 ms, P < 0.05) in onset latency were seen during the transition from the recovery phase to the power phase during cycling. In addition, there was no correlation between the prestimulation baseline level and the onset latency during controlled TA cycling activity conditions.(ABSTRACT TRUNCATED AT 400 WORDS)
Rate of rise of the cumulative depolarization evoked by repetitive stimulation of small-caliber afferents is a predictor of action potential windup in rat spinal neurons in vitro
Authors: Sivilotti L. G. , Thompson S. W. , Woolf C. J.
Published: December 2017

1. The summation of depolarizing postsynaptic potentials (PSPs) evoked by stimulation of primary afferent fibers in lumbar dorsal roots was studied in dorsal and ventral horn neurons in the rat hemisected spinal cord in vitro with current-clamp intracellular recording techniques. PSPs evoked by activation of A delta and/or C fibers could summate after repetitive stimulation at low frequencies: this resulted in a progressive, long-lasting change in the neuronal membrane potential (Vm) (cumulative depolarization). Cumulative depolarization was not observed after stimulation at A beta-fiber intensity or at frequencies < 0.2 Hz. 2. Effective PSP summation resulting in a significant cumulative depolarization (> 5 mV) was observed only if the PSPs evoked were longer than 4 s. On the other hand, there was no correlation between the amplitude of cumulative depolarization achieved in a neuron and the absolute duration of the PSP or the neuronal resting membrane properties (Vm and input resistance). 3. With relation to the changes in Vm during the stimulation train, three patterns of response to repetitive stimuli could be detected in both dorsal horn (DH) and ventral horn (VH) neurons: 1) little or no depolarization throughout the train; 2) an initial depolarization, which either remained stationary or decayed to the resting Vm after the first 3-4 s of stimulation; or 3) a progressive cumulative depolarization increasing throughout the train. 4. Depolarizing the cell by DC current injection resulted in a steeper rise in Vm in response to repetitive stimuli in one half of VH neurons and in one out of nine DH neurons tested. 5. Action potential windup, an increase in the number of action potentials elicited by each stimulus as the train progresses, was observed both in DH and in VH cells. C-fiber strength stimulation was the most effective in eliciting windup. Windup was associated with Vm responses to repetitive stimulation belonging to the progressive cumulative depolarization pattern. Indeed, cumulative depolarizations that resulted in windup had significantly steeper slopes for the Vm trajectory than those that did not. In those neurons in which DC depolarization by intracellular current injection increased the slope of the Vm trajectory, DC depolarization could also bring about action potential windup. 6. These results indicate that, although the generation of long-lasting "slow" PSPs by high-threshold primary afferents is necessary for the summation of synaptic activity in the spinal cord at low frequencies, the rate and pattern of the summation does not depend on the absolute duration of the PSPs.(ABSTRACT TRUNCATED AT 400 WORDS)
Nociceptive responses in the neostriatum and globus pallidus of the anesthetized rat
Authors: Chudler E. H. , Sugiyama K. , Dong W. K.
Published: December 2017

1. Extracellular recordings were made from neurons in the neostriatum (caudate nucleus-putamen, CPu) and globus pallidus (GP) of anesthetized rats. Few cells (3%) were classified as low-threshold-mechanoreceptive (LTM) neurons. The majority (97%) of somatosensory CPu and GP neurons responded differentially or exclusively to noxious mechanical stimulation of the skin. Nociceptive neurons were classified into the following three groups on the basis of their response properties to noxious mechanical stimulation: wide-dynamic-range (WDR) neurons (21%); nociceptive-specific (NS) neurons (67%); and inhibited (INH) neurons (13%). 2. No differences in the response properties or in the proportions of WDR, NS, and INH neurons were found in the CPu compared with the GP. Nociceptive neurons were located most often along the CPu-GP border. Additionally, neurons of similar functional classification were often clustered within 200-400 microns of each other along a single microelectrode track. 3. The receptive fields of nociceptive CPu and GP neurons were often large and bilateral; some receptive fields encompassed the entire body. The trigeminal region, especially the perioral area, was included in the receptive fields of nociceptive neurons more often (62 of 63 cells) than any other part of the body. However, no preference for any particular division of the trigeminal nerve was observed in the receptive fields. Some neurons had receptive fields that were discontinuous. 4. Noxious pinching of the skin significantly increased the spontaneous neuronal discharge of WDR and NS neurons by an average of 482 and 221%, respectively. There were no significant differences between the discharge adaptation rates of WDR and NS neurons. Afterdischarge activity was observed in some WDR and NS neurons. INH neurons decreased their resting activity levels by an average of 43% after a noxious pinch. 5. The von Frey stimulus threshold of WDR neurons (11.0 g/mm2) was significantly lower than that of NS neurons (33.6 g/mm2) and INH neurons (32.6 g/mm2). Mean stimulus thresholds of WDR, NS, and INH neurons determined by using calibrated forceps were 1.6, 4.8, and 2.2 g/mm2, respectively. 6. Individual stimulus-response functions of nociceptive neurons were best fit by a negatively accelerating (logarithmic) curves. However, WDR neurons had significantly steeper slopes than NS neurons. 7. The results demonstrate that a large proportion of somatosensory neurons within the neostriatum and globus pallidus (especially along the CPu-GP border) receive nociceptive information. These data are discussed in relation to several putative afferent nociceptive pathways projecting to the CPu and GP.(ABSTRACT TRUNCATED AT 400 WORDS)