bluuebunny/crossref_metadata_2025 huggingface dataset:
Generation and coordination of heartbeat timing oscillation in the medicinal leech. II. Intersegmental coordination
Authors: Peterson E. L.
Published: December 2017

1. A network of four pairs of interneurons, HN(1)-HN(4), times the heartbeat of the medicinal leech. The following model accounts for the stable phase relationships in the network and the network's response to perturbation, entrainment, and stimulation. 2. There are two centers of oscillation, one the HN(3) pair in the third ganglion, the other the HN(4) pair in the fourth ganglion. 3. The two other pairs, HN(1) and HN(2), couple the oscillation of the HN(3) pair with that of the HN(4) pair, thereby guaranteeing that a coherent time signal is sent to the rest of the heartbeat system. 4. The HN(1) and HN(2) pairs can play this coupling role because they have impulse-initiation sites in the third and fourth ganglia and have input and output connections with the HN(3) and HN(4) pairs. 5. In the context of the network, the intrinsic frequency of the HN(4) pair appears to be higher than that of the HN(3) pair. Coupled, the two pairs strike a stable compromise in which the HN(4) pair leads the HN(3) pair.
Projection of single pulmonary stretch receptors to solitary tract region
Authors: Berger A. J. , Averill D. B.
Published: December 2017

1. Central projections of single slowly adapting pulmonary stretch receptors were mapped in the medulla by the technique of spike-triggered averaging of extracellular field potentials. Discharge of pulmonary stretch receptors was recorded in continuity from the nodose ganglion; this activity provided the trigger for an averaging computer. 2. These pulmonary stretch receptors were characterized by a linear increase in firing rate in response to increases in transpulmonary pressure, an adaptation index, and peripheral axonal and intramedullary conduction velocities. 3. In accordance with the terminology used by Munson and Sypert (21), three types of electrical potentials were observed for the projection of a pulmonary stretch receptor in the medulla. Axonal potentials were recorded when the brain stem electrode was in the vicinity of the afferent axon. Terminal potentials were recorded when the electrode was adjacent to terminations of the afferent axon. Focal synaptic potentials were recorded when the electrode was near postsynaptic units receiving input from the pulmonary stretch receptor. Maxima of terminal potentials were recorded in a region 1 mm rostral to the obex in the medial nucleus of the tractus solitarius (six cases), in the ventrolateral nucleus of the tractus solitarius (three cases), and in an area just dorsolateral to the tractus solitarius (two cases). Focal synaptic potentials for five pulmonary stretch receptors were observed in a region 1 mm rostral to obex. Maxima of these potentials were recorded in the medial nucleus of tractus solitarius (two cases), in the ventrolateral nucleus of tractus solitarius (two cases), and in an area just dorsolateral to the tractus solitarius (one case). 4. Occasionally both terminal and focal synaptic potentials were observed for the same pulmonary afferent. The difference in the latencies of these potentials fell within the range previously reported for monosynaptic connections of muscle spindle Ia and group II afferents for alpha-motoneurons. This suggests that the afferents of pulmonary stretch receptors have monosynaptic connections with neurons in the medial nucleus of the tractus solitarius, in the ventrolateral nucleus of the tractus solitarius, and in an area dorsolateral to the tractus solitarius.
Functional properties of neurons in middle temporal visual area of the macaque monkey. II. Binocular interactions and sensitivity to binocular disparity
Authors: Maunsell J. H. , Van Essen D. C.
Published: December 2017

1. Electrophysiological recordings were made in the middle temporal visual area (MT) of five macaque monkeys. Binocularity and selectivity for disparity were examined using a computer-driven stimulator to activate each eye independently. Results were obtained from 91 single units in MT. 2. Most units in MT receive approximately balanced inputs from the two eyes, and very few could be driven through only one eye. 3. In one type of test for disparity selectivity, units were examined with stimuli that had different but fixed horizontal disparities, thereby simulating frontoparallel movements at different distances from the animal. About two-thirds of ;the units tested for fixed disparity selectivity (52/76) showed pronounced sensitivity to horizontal disparity. Most of these units could be grouped into the same four classes of disparity-tuned units that have previously been described in V1 and V2 of the macaque: near, far, tuned excitatory, and tuned inhibitory. 4. Twenty units were tested for sensitivity to vertical stimulus disparity, which does not normally contribute to stereopsis. Most were as sensitive to vertical disparities as to horizontal. 5. Units were also tested for selectivity for stimuli that moved with changing disparity, simulating trajectories with components of motion toward or away from the animal (motion in depth). No units were found to be truly selective for motion in depth. Units tuned for fixed disparity could appear to prefer motion in depth if tested only with trajectories whose common center point was far from the unit's optimal fixed disparity. However, we do not consider this to represent genuine selectivity for motion in depth, since 1) the responses ara adequately and more easily explained in terms of selectivity for fixed disparity and 2) the best overall response of these units is to frontoparallel motion at the optimal fixed disparity. This observation bears importantly on the interpretation of motion in depth selectivity in previous investigations. 6. The presence of a substantial degree of selectivity for fixed disparity in MT, together with previously demonstrated selectivities for direction and speed, indicates that MT is well suited for the analysis of motion in three-dimensional space.
Synaptic interactions between mammalian central neurons in cell culture. I. Reversal potential for excitatory postsynaptic potentials
Authors: Macdonald R. L. , Pun R. Y. , Neale E. A. , Nelson P. G.
Published: December 2017

Intracellular recording and stimulation techniques were used to study the electrical properties of neurons in cell cultures from fetal mouse spinal cord (SC). The morphology of SC neurons and the distribution on SC neurons of boutons formed by synaptically connected SC or dorsal root ganglion (DRG) neurons were demonstrated with horseradish peroxidase (HRP) injection. Postsynaptic polarization in conjunction with synaptic activation of SC neurons was used to determine the reversal potential for excitatory postsynaptic potentials (EPSPs). Tetraethylammonium ions were injected postsynaptically in order to obtain reversal of the EPSPs. Both SC-SC and DRG-SC excitatory connections could be reversed by postsynaptic depolarization. The average reversal potential for the SC-SC EPSP was -4 +/- 12.2 (SD) mV and that for the DRG-SC EPSP was +8 +/- 7.9 (SD) mV, a statistically significant difference (Wilcoxon two-sample rank; P less than 0.05). Scatter was quite large, particularly for the SC-SC connection. While some neurons gave clear electrophysiological evidence of significant dendritic effects, the average total electrotonic length was small (0.58 +/- 0.65 (SD) of a length constant). The morphological extent of the dendrites of SC neurons was substantially less than that of mature motoneurons in vivo. We concluded that both SC-SC and DRG-SC EPSPs were mediated by a conventional conductance increase and that most synaptic input was not far removed electrically from the recording site in the neuron cell body.
Neuronal pathways for activation of inhibitory interneurons in pyriform cortex of the rabbit
Authors: Satou M. , Mori K. , Tazawa Y. , Takagi S. F.
Published: December 2017

The neuronal pathways responsible for the fast inhibitory postsynaptic potentials (IPSPs) elicited in principal cells in the pyriform cortex (PC) by volleys from the olfactory bulb (OB), the lateral olfactory tract (LOT), the anterior commissure (AC), and the deep-lying structures of the PC (DPC) were studied in the rabbit. The central latencies of the fast IPSPs (measured from the onset of the monosynaptic excitatory postsynaptic potential (EPSP) elicited by volleys through the LOT) ranged between 3.0 and 9.3 ms (5.5 +/- 1.3 (SD) ms; n = 54) in the case of OB shocks and between 4.5 and 6.5 ms (5.1 +/- 0.7 (SD) ms; n = 7) in the case of LOT shocks. The onset latencies of the fast IPSPs were between 2.5 and 11.8 ms (5.1 +/- 1.8 (SD) ms; n = 66) in the case of DPC shocks and between 3.5 and 10.1 ms (5.8 +/- 1.5 (SD) ms; n = 61) in the case of AC shocks. The conditioning OB or LOT shocks almost completely eliminated the LOT-evoked fast IPSP when the testing shock was applied at the peak period of the conditioning slow IPSP. The conditioning OB shocks also eliminated the initial part of the OB-evoked fast IPSP, leaving the later part of the fast IPSP almost unchanged. Thus, the onset latency of the OB-evoked fast IPSP was lengthened by 7.1 +/- 2.9 (SD) ms (n = 35) by the conditioning OB shock. The conditioning OB or DPC shocks left the peak amplitude of the DPC-evoked fast IPSP almost unaffected. Similarly, the conditioning OB or AC shocks left the peak amplitude of the AC-evoked fast IPSP almost unaffected. The conditioning OB, DPC, or AC shocks had only a slight influence on the onset latency of the DPC- or AC-evoked fast IPSPs. Rhythmical steps at intervals of 3-5 ms were observed in the rising phase of the OB-evoked fast IPSP. This was interpreted as a result of a repetitive impingement of interneuronal discharges on the impaled cells. Spatial facilitation was observed among the fast IPSPs evoked by volleys from the OB, DPC, and AC when shocks were applied at suitable intervals. A slight facilitation was also seen between the LOT-evoked fast IPSP and the DPC- or AC-evoked fast IPSP. These results were interpreted as a result of the convergence of excitatory synaptic inputs onto the presumed inhibitory interneurons from the four structures of the brain. A temporal facilitation of the fast IPSPs was observed when the OB, DPC, or AC shocks were applied repetitively at short intervals. This suggests a temporal facilitation of the spike discharges of the presumed inhibitory interneurons under similar conditions. From these results, criteria were determined for identifying the inhibitory interneurons.
Posttetanic potentiation of group Ia EPSPs: possible mechanisms for differential distribution among medial gastrocnemius motoneurons
Authors: Lev-Tov A. , Pinter M. J. , Burke R. E.
Published: December 2017

We have reinvestigated the phenomenon of posttetanic potentiation (PTP) of group Ia monosynaptic excitatory postsynaptic potentials (EPSPs) in medial gastrocnemius (MG) alpha-motoneurons of pentobarbital-anesthetized cats. The results generally confirm earlier reports by Luscher and colleagues (43, 44) of a negative correlation between the maximum percentage potentiation of Ia EPSP amplitude (Pmax) and 1) the mean amplitude of the pretetanic control EPSP in the same cell and 2) the input resistance of the postsynaptic motoneuron. These negative correlations, which we will refer to as "differential distribution of PTP" within the MG motor pool, were less strong in the present work than reported by Luscher et al. (43, 44). We also found a relatively strong negative correlation between posttetanic EPSP depression, assessed by the amplitude of the first posttetanic EPSP, and the level of Pmax subsequently attained. We found no evidence that posttetanic depression is caused by failure of presynaptic action potentials. We investigated a second type of depression, referred to as "specific" synaptic depression, in which the second EPSP of paired responses (interval 250 ms) is, on average, smaller in peak amplitude than the first EPSP. This phenomenon appears to reflect decreases in the probability of transmitter release from previously activated synapses. Specific synaptic depression was consistently increased when paired responses were conditioned by a high-frequency tetanus. This is most easily explained by postulating that PTP results, at least in part, from an increase in the statistical probability of transmitter liberation from group Ia synapses that are activated (i.e., presumably invaded by action potentials) both before and after afferent tetanization. On the basis of the present results and other available evidence, we conclude that the differential distribution of PTP can be explained by two main factors: 1) the nonlinear relation between conductance and voltage changes inherent in all chemical synapses and 2) systematic variations in the properties of group Ia synapses that innervated different motoneurons, which remain to be clarified.
Response characteristics of lateral hypothalamic neurons to odors in unanesthetized rabbits
Authors: Kogure S. , Onoda N.
Published: December 2017

Extracellular responses of 103 neurons to eight odors were studied in the lateral hypothalamic area (LHA) of unanesthetized rabbits. In response to electrical stimulation of the olfactory bulb (OB), 97 units were excited with latencies of 3.7-68.0 ms (mean, 19.4 ms) and the activity of 6 units was suppressed. In the LHA, 90 units of 103 were found that responded to from one to eight odors. The number of units that responded to three odors was the most numerous (22%) among these odor-sensitive units. Lateral hypothalamic (LH) neurons showed high response probabilities to cineole (0.72), cyclotene (0.68), and isovaleric acid (0.54). Of the recorded units, 94% showed an excitatory-type response to both electrical stimulation of the OB and odor stimuli of the olfactory mucosa, while only 6% showed an inhibitory-type response to both stimuli. These results suggest that the olfactory effect on the LHA is predominantly excitatory. Responses to a concentration series of odors were examined in 24 LH neurons. In most cases, response intensity did not increase monotonically with increasing odor concentration. Instead, the concentration-response curves of most units showed a peak or inflections during the concentration series. Compared with results obtained from other olfactory structures in different species, it appears that LH neurons do not contribute much to odor discrimination in rabbits.
Effect of eye rotation on visual-field map onto superior colliculus and visual cortex
Authors: Gordon B. , Moran J. , Presson J.
Published: December 2017

We used multiunit recording to assess the effect of rotating one eye approximately 90 degrees at about the time of normal eye opening. Rotation of the eye did not alter the topography of the retinal maps onto visual cortex or superior colliculus. The intorted eye drove cells at most recording points in the contralateral visual cortex and superior colliculus. In its ipsilateral colliculus the intorted eye drove cells at about 10% of the recording points; that is, the temporal retina of this eye was quite ineffective in driving collicular cells. In its ipsilateral cortex the intorted eye drove cells at about 30% of the recording sites. The unoperated eye drove cells at all locations in both colliculus and cortex on both sides of the brain. The effects of extorsion were studied only in the superior colliculus. Extorsion and intorsion produced similar results except that extorsion produced a less severe deficit in the ability of the temporal retina to drive cells in its ipsilateral colliculus. Cutting all the extraocular muscles without eye rotation was studied only in the colliculus and produced results similar to those produced by intorsion and extorsion. However, the temporal retina of the operated eye was more effective after muscle cut alone than after intorsion or extorsion. Forcing the animal to use the rotated right eye alone on alternate days during the first 3 mo of life did not decrease the deficits. Almost all recording sites in the right colliculus were driven only by the unoperated left eye. If the left eye was sutured when the right eye was rotated, only the right eye drove cells in the left colliculus, but the two eyes were about equally effective in the right colliculus; however, rather few sites in the right colliculus were binocularly driven. We conclude that both extraocular muscle section and eye rotation reduce the effectiveness of the uncrossed input from the operated eye to the superior colliculus and visual cortex. The effects on the superior colliculus are, however, greater.
Action potential in neurons of motor nerve net of Cyanea (Coelenterata)
Authors: Anderson P. A. , Schwab W. E.
Published: December 2017

Neurons of the motor nerve net of the jellyfish Cyanea were impaled with microelectrodes for intracellular recordings. The cells have conventional, negative resting potentials and produce variable-amplitude action potentials with complex waveforms. The variability and complexity of these spikes is due to the superimposition of two classes of Ca2+-dependent potentials on an otherwise fast, clean action potential. Repetitive stimulation and ionic manipulation reveal that most superimposed potentials are chemically induced excitatory postsynaptic potentials (EPSPs). These account for the complexity and variability of the action potential. The remaining potential is interpreted as a Ca2+ component of the action potential. The action potential is a Na+-dependent but tetrodotoxin- (TTX) insensitive event. Repolarization is achieved by two pharmacologically distinct mechanisms: a tetraethylammonium- (TEA) and 4-amino-pyridine- (4-AP) sensitive K+ efflux and a delayed, Ca2+-activated, K+ efflux. The latter is responsible for the afterhyperpolarization that follows the action potential. The results indicated that these neurons are physiologically conventional. This is interesting in view of the phylogenetic primitiveness of the preparation and important, since it means that this preparation can provide generally useful information on chemical synaptic physiology.
Responses of medullary reticulospinal neurons to sinusoidal stimulation of labyrinth receptors in decerebrate cat
Authors: Manzoni D. , Pompeiano O. , Stampacchia G. , Srivastava U. C.
Published: December 2017

The electrical activity of 168 individual neurons located in the medullary reticular formation, namely, in the medial aspects of the nucleus reticularis gigantocellularis, magnocellularis, and ventralis, has been recorded in precollicular decerebrate cats during sinusoidal tilt about the longitudinal axis of the whole animal, leading to stimulation of labyrinth receptors. In particular, 93 neurons were activated antidromically by stimulation of the spinal cord at T12 and L1 (1RS neurons); the remaining 75 neurons were not activated antidromically (RF neurons). Among these medial reticular neurons tested, 64 of 93 (i.e., 69%) 1RS neurons and 49 of 75 (i.e., 65%) RF neurons responded to slow rotation of the animal at the standard frequency of 0.026 Hz and at the peak amplitude of displacement of 10 degrees. A periodic modulation of firing rate of the units was observed during the sinusoidal stimulus. In particular, 71 of 113 units (i.e., 63%) were excited during side-up and depressed during side-down tilt, whereas 24 of 113 units (i.e., 21%) showed the opposite behavior. In both instances, the peak of the responses occurred with an average phase lead of about +25 degrees with respect to the extreme side-up or side-down position of the animal. The remaining 18 units (i.e., 16%) showed a prominent phase shift of the peak of their response with respect to animal position. Within the explored region of the medulla, the proportion of units excited during side-up tilt was higher at caudal levels, whereas that of the units excited during side-down tilt was higher at rostral levels. Units displaying intermediate phase angle of the responses predominated at intermediate levels of the medulla. Responses to animal tilt were detectable at 1 degree of peak displacement. The gain (impulses x s-1 x deg-1) of the responses of reticulospinal neurons did not change by increasing the peak amplitude of tilt from 5 to 20 degrees at the fixed frequency of 0.026 Hz. This finding indicates that the system was relatively linear with respect to the amplitude of displacement. By varying the frequency of stimulation from 0.008 to 0.32 Hz at the fixed amplitude of 10 degrees, two populations of reticulospinal neurons were observed. In the first, the gain and the phase angle of response remained relatively unmodified against changes in frequencies: these positional responses were attributed to stimulation of macular receptors.(ABSTRACT TRUNCATED AT 400 WORDS)
Electrotonic parameters of rat dentate granule cells measured using short current pulses and HRP staining
Authors: Durand D. , Carlen P. L. , Gurevich N. , Ho A. , Kunov H.
Published: December 2017

The passive electrotonic parameters of nerve cells in the dentate gyrus of the rat were studied in vitro. Intracellular recordings from 30 granule cells and 3 pyramidal basket cells followed by intracellular injection of horseradish peroxidase (HRP), allowed calculations of input resistance (RN), membrane time constant (tau m), electrotonic length (L), ratio of dendritic to somatic conductance (rho), membrane specific capacitance and resistance (Rm, Cm), and specific axoplasmic resistance (Ri). The analysis of the voltage decays from long saturating (100 ms) and short (0.5 ms) current pulses showed that the short-pulse method gave better resolution for the measurement of the time constants and avoided some of the time-dependent nonlinearities but required larger currents than the long pulse. Morphological analysis of 49 branching points taken from the dendritic trees of granule cells showed that the branching power, n, is equal to 1.56 +/- 0.186 and was fairly constant throughout the tree. Given the fact that all dendrites have approximately the same length and number of branch points, the granule cell dendritic tree can be meaningfully collapsed into an equivalent cable. Moreover, electrophysiological data suggested that the cable had a "sealed" end or at least a high-impedance termination. Based on an equivalent cable model with a sealed end and a lumped soma impedance, a method was implemented to analyze the multiexponential decays from hyperpolarizing current pulses and to solve the equations of the model. This was done successfully in only 40% of the cells and yielded the following mean values for L = 1.13 and rho = 7.58. From the measurements of the soma surface area (S) and the equivalent cable diameter (D), the average specific membrane parameters were calculated: Rm = 2,726 alpha x cm2, Cm = 5.24 microF/cm2, Ri = 101 alpha x cm. The input resistance and time constant of the granule cells as measured from the short-pulse technique averaged to RN 58.57 M alpha and tau m = 16.21 ms. The failure of the model to fit 60% of the cells was interpreted to be due to the presence of a somatic shunt resulting from electrode injury, tonic synaptic activity, a lower somatic membrane specific resistance, or electronic coupling.(ABSTRACT TRUNCATED AT 400 WORDS)
Motor-unit discharge rates in maximal voluntary contractions of three human muscles
Authors: Bellemare F. , Woods J. J. , Johansson R. , Bigland-Ritchie B.
Published: December 2017

Single motor<unit firing rates have been recorded during maximal voluntary contractions using tungsten microelectrodes. Over 300 units from four subjects were sampled from each of three muscles. These were the biceps brachii, adductor pollicis, and soleus, chosen because of known differences in their fiber<type composition and contractile properties. In all cases the contraction maximality was assured by delivering single supramaximal shocks during the voluntary contractions. All motor units were deemed to have already been fully activated if no additional force resulted. Thus for each muscle, the firing rates elicited by a maximal voluntary effort are sufficient to generate a fully fused tetanus in each motor unit. For the biceps brachii and adductor pollicis muscles, the mean firing rates (+/- SD) were 31.1 +/- 10.1 and 29.9 +/- 8.6 Hz, respectively, while for soleus they were only 10.7 +/- 2.9 HZ. For each muscle the firing rates distribution covered approximately a four-fold range about the mean value. The mean firing rates for each muscle varied roughly in proportion to their respective twitch contraction and half relaxation times. These contractile time measurements for both biceps brachii and adductor pollicis agreed well with the mean values reported for human fast-twitch motor units, while those for soleus fell in the range observed for human slow-twitch units. An argument is presented that suggests that, in response to voluntary effort, the range of discharge rates of each motor-unit pool is limited to those only just sufficient to produce maximum force in each motor unit. This suggestion is based on the relationship between the range of motor-unit firing frequencies observed during maximum voluntary contractions, their range of contraction times, and the stimulation frequencies required for maximum force generation. The implications of this hypothesis for motor control are discussed.
Columnar organization of directionally selective cells in visual area MT of the macaque
Authors: Albright T. D. , Desimone R. , Gross C. G.
Published: December 2017

We recorded from single neurons in visual area MT of the macaque in order to examine the spatial distribution of its directionally selective cells. The animals were paralyzed and anesthetized with nitrous oxide. All MT neurons (n = 614) responded better to moving stimuli than to stationary stimuli. For 55% of the neurons, responses to moving stimuli were independent of stimulus color, shape, length, or orientation. For the remaining cells, stimulus length affected the response magnitude and tuning bandwidth but not the preferred direction. MT neurons were divided into four categories on the basis of their sensitivity to moving stimuli: 60% responded exclusively to one direction of motion, 24% responded best to one direction with a weaker response in the opposite direction, 8% responded equally well to two opposite directions of motion, and 8% responded equally well to all directions of motion. The direction preferences of successively sampled cells on a penetration either changed by small increments or occasionally by approximately 180 degrees. Thus, there is a systematic representation of direction of motion. The representation of axis of motion, i.e., the orientation of the path along which a stimulus moves, is more continuous than the representation of direction of motion. There was a systematic relationship between penetration angle and rate of change of preferred axis of motion, indicating that cells with a similar axis of motion preference are arranged in vertical columns. Furthermore, axis of motion columns appear to exist in the form of continuous slabs in area MT. The size of these slabs is such that 180 degrees of axis of motion are represented in 400-500 micron of cortex. There was also a systematic relationship between penetration angle and frequency of 180 degrees reversals, indicating that cells with a similar direction of motion preference are also organized in vertical columns and cells with opposite direction preferences are located in adjacent columns within a single axis of motion column. Just as in macaque striate cortex where approximately 500 micron of cortex contain the mechanism for the local analysis of stimulus orientation, so in MT approximately 500 micron of cortex contain the mechanism for the local analysis of stimulus motion.
A reevaluation of intervestibular nuclear coupling: its role in vestibular compensation
Authors: Galiana H. L. , Flohr H. , Jones G. M.
Published: December 2017

Recent experimental observations indicate that pathways interconnecting the bilateral vestibular nuclei (VN) may provide positive-feedback loops for signals across the midline. The implications of such positive feedback are considered in the context of vestibular compensation. A simple conceptual model of the interconnected VN is studied analytically, based on the hypothesis that the restoration of central symmetry is achieved via changes of neural gain in closed commissural loops. A wide variety of experimental conditions related to vestibular compensation are investigated. Analytic model predictions are compared to behavioral and neurophysiological findings in the literature. The results show that organized control over commissural gains in closed loops coupling the bilateral VN is fully compatible with all phenomena cited in the article. In particular, such a mechanism for vestibular compensation can reconcile observations such as the fact that Bechterew phenomena and decompensation can both be elicited from the compensated state. Placing the site of vestibular compensation in pathways linking the VN has many implications. Other forms of central neural plasticity (e.g., vestibuloocular reflex (VOR) gain plasticity) may rely on a similar principle, since modulation of transmidline coupling can be a very powerful means of altering responses in a bilateral nervous system.
Signals in vestibular nucleus mediating vertical eye movements in the monkey
Authors: Tomlinson R. D. , Robinson D. A.
Published: December 2017

The action potentials of single neurons were recorded extracellularly throughout the rostral vestibular nuclei and subadjacent reticular formation in three alert, juvenile, rhesus monkeys. Neuronal responses were tested during a) sinusoidal pitch oscillations in darkness, b) cancellation of the vestibuloocular reflex (VOR) during similar oscillations by fixation of a target moving with the head, c) sinusoidal vertical smooth pursuit, d) vertical saccades, and e) fixation with the head stationary. Eye movements were measured using the magnetic field-search coil technique. Of the 527 neurons isolated, 318 responded to pitch oscillation and/or vertical eye movements. The latter cells could be classified into six categories. Of this group, 273 cells were recorded from for sufficient time to allow them to be fully tested and form the basis of this report. Cells were classified as follows: pure-vestibular cells with firing rates modulated only by head velocity (15%), vestibular-pause cells that were similar to the pure-vestibular cells but paused for saccades in all directions (10%), gaze-velocity cells that modulated their rates in proportion to vertical eye velocity in space (7%), position cells with rates modulated by changes in eye position in the head but that did not burst or pause during saccades (33%), position-burst cells that also carried an eye-position signal but did burst during saccades in one direction and paused in the opposite direction (15%), and position-vestibular-pause cells that carried signals proportional to eye position in the head and head velocity and paused during all saccades (20%). Most cells that carried an eye-position signal also carried an eye-velocity signal during pursuit. Position and position-burst cells could be divided into two subcategories. Position cells that also reported head velocity represented 20% of the total sample, while those without head-velocity signals made up the remaining 13%. Position-burst cells were divided into two subcategories based on their behavior during pitch oscillation in darkness. Both carried eye-velocity signals during pursuit, but only one type (8% of the total sample) also carried an eye-velocity signal during vestibular eye movements in the dark, while the other (7%) did not. Some cells in all six categories except the pure-vestibular cells responded antidromically to stimulation of the medial longitudinal fasciculus (MLF). Only the position-vestibular-pause, position-burst, and gaze-velocity cells, however, were judged to be commonly antidromically activated, suggesting that these three cell types are the major contributors to the MLF from the rostral vestibular nuclei.(ABSTRACT TRUNCATED AT 400 WORDS)
Rat hippocampal neurons in culture: potassium conductances
Authors: Segal M. , Barker J. L.
Published: December 2017

Two-electrode voltage-clamp methodology was used to analyze voltage-dependent ionic conductances in 81 rat hippocampal neurons grown in culture for 4-6 wk. Pyramidal and multipolar cells with 15- to 20-micron-diameter cell bodies were impaled with two independent KCl electrodes. The cells had resting potentials of -30 to -60 mV and an average input resistance of about 30 M omega. A depolarizing command applied to a cell maintained in normal medium invariably evoked a fast (2-10 ms) inward current that saturated the current-passing capacity of the system. This was blocked in a reversible manner by application of tetrodotoxin (TTX) (0.1-1.0 microM) near the recorded cell. In the presence of TTX, a depolarizing command evoked a rapidly rising (3-5 ms), rapidly decaying (25 ms) transient outward current reminiscent of "IA" reported in molluscan neurons. This was followed by a more slowly activating (approximately 100 ms) outward current response of greater amplitude that decayed with a time constant of about 2-3 s. These properties resemble those associated with the K+ conductance, IK, underlying delayed rectification described in many excitable membranes. IK was blocked by extracellular application of tetraethylammonium (TEA) but was insensitive to 4-aminopyridine (4-AP) at concentrations that effectively eliminated IA. IA, in turn, was only marginally depressed by TEA. Unlike IK, IA was completely inactivated when the membrane was held at potentials positive to -50 mV. Inactivation was completely removed by conditioning hyperpolarization at -90 mV. A brief hyperpolarizing pulse (10 ms) was sufficient to remove 95% of the inactivation. IA activated on commands to potentials more positive than -50 mV. The inversion potential of the ionic conductance underlying IA and IK was in the range of the K+ equilibrium potential, EK, as measured by the inversion of tail currents; and this potential was shifted in a depolarizing direction by elevated [K+]0. Thus, both current species reflect activation of membrane conductance to K+ ions. Hyperpolarizing commands from resting potentials revealed a time- and voltage-dependent slowly developing inward current in the majority of cells studied. This membrane current was observed in cells exhibiting "anomalous rectification" and was therefore labeled IAR. It was activated at potentials negative to -70 mV with a time constant of 100-200 ms and was not inactivated. A return to resting potential revealed a tail current that disappeared at about EK. IAR was blocked by extracellular CS+ and was enhanced by elevating [K+]0. It thus appears to be carried by inward movement of K+ ions.(ABSTRACT TRUNCATED AT 400 WORDS)
An electromyographic analysis of compartments in cat lateral gastrocnemius muscle during unrestrained locomotion
Authors: English A. W.
Published: December 2017

Cat lateral gastrocnemius (LG) muscle is composed of four compartments, each of which is supplied by a primary branch of the LG muscle nerve and each of which contains a discrete population of motor units/muscle fiber types. The activation patterns of these different motor-unit populations were examined from recordings made using selective electromyographic (EMG) electrodes, which were carefully placed into the different LG compartments. Recordings were made as the cats stepped overground along a wooden walkway at a variety of different stepping speeds. Electrical activity was correlated with stepping movements using high-speed cinematography. A number of different activation patterns of the different compartments were noted during stepping. In one such pattern, more intense EMG activity was found in distal than proximal compartments at slow stepping speeds, but at moderate to fast stepping speeds the intensity of activity in proximal compartments was equal to or greater than in distal compartments. In other patterns, a less consistent relationship between compartment EMG intensity and stepping speed was observed. These results are generally consistent with an orderly pattern of activation of motor units in the LG during stepping but also indicate that more than one activation pattern exists.
Activity of trigeminothalamic neurons in medullary dorsal horn of awake monkeys trained in a thermal discrimination task
Authors: Bushnell M. C. , Duncan G. H. , Dubner R. , He L. F.
Published: December 2017

We analyzed the activity of 51 trigeminothalamic neurons in the medullary dorsal horn (trigeminal nucleus caudalis) of monkeys during the performance of behavioral tasks requiring the monkeys to discriminate innocuous and noxious thermal stimuli applied to the face and to detect the onset of visual stimuli. Static properties of trigeminothalamic neurons in behaving monkeys were similar to those in anesthetized monkeys. Responses to passively presented mechanical and thermal stimuli, receptive-field properties, and conduction velocities did not differ in the awake and anesthetized states. For most wide dynamic range and nociceptive-specific trigeminothalamic neurons, there was a negative correlation between the magnitude of thermally evoked activity and behavioral latencies to discriminate 47 and 49 degrees C stimuli. Thus, both groups of neurons provide information that could be used by the monkey to discriminate noxious thermal stimuli. The magnitude of thermal responses of trigeminothalamic neurons was modulated by the behavioral significance of the stimulus. Behaviorally relevant thermal stimuli presented during the thermal discrimination task produced a greater neuronal response than equivalent irrelevant thermal stimuli presented between behavioral trials or presented while the monkey performed the visual detection task. Neurons whose activity is modulated by behavioral state are likely to be involved in discrimination of thermal stimuli, since the activity of these neurons correlates with the behavioral response to the stimuli and information from the modulated neurons is sent to the thalamus. Some trigeminothalamic neurons that exhibited somatosensory responses also responded to behaviorally relevant stimuli and events associated with trial initiation and receipt of reward in the behavioral tasks. Similar events outside a behavioral task evoked no neuronal responses. These task-related responses were similar to those described previously for medullary dorsal horn neurons not identified as to projection sites (14).(ABSTRACT TRUNCATED AT 400 WORDS)
Central compensation of vestibular deficits. II. Influences of roll tilt on different-size lateral vestibular neurons after ipsilateral labyrinth deafferentation
Authors: Pompeiano O. , Xerri C. , Gianni S. , Manzoni D.
Published: December 2017

The activity of 168 Deiters' neurons projecting to lumbosacral segments of the spinal cord has been recorded in precollicular decerebrate cats after ipsilateral acute (aVN) or chronic vestibular neurectomy (cVN), and their response characteristics to sinusoidal stimulation of contralateral labyrinth receptors at the standard parameters (roll tilt at 0.026 Hz, 10 degrees peak displacement) have been related to cell size inferred from the conduction velocity of the corresponding axons. These findings were compared with those elicited in decerebrate cats with both vestibular nerves intact. In all experimental conditions, the higher the coefficient of variation (CV) of the vestibulospinal neurons, reflecting a more irregular unit discharge, the lower was the mean discharge rate at rest. However, the proportion of regularly discharging units (with the lowest CV) decreased after aVN but increased after cVN. The relation found in control experiments, i.e., the faster the conduction velocity of vestibulospinal axon the lower was the unit discharge at rest, was lost after aVN due to a decrease in resting discharge rate of the slow neurons. The mean discharge rate of these units, however, recovered after cVN, so that the negative correlation between resting discharge rate and axonal conduction velocity was reestablished. After aVN, the decrease in resting discharge rate of the slow vestibulospinal neurons was not associated with significant changes in gain (impulses per second per degree) of the unit responses to standard parameters of tilt, so that the sensitivity of these units (percentage change of the mean discharge rate per degree) increased; on the other hand, the resting discharge rate of the fast neurons, which remained almost unchanged after aVN, was associated with a significant increase in gain, thus leading to an average increase in response sensitivity of these units.(ABSTRACT TRUNCATED AT 400 WORDS)
A voltage-clamp analysis of currents underlying cyclic AMP-induced membrane modulation in isolated peptidergic neurons of Aplysia
Authors: Kaczmarek L. K. , Strumwasser F.
Published: December 2017

A variety of chemical and electrophysiological evidence indicates that the onset of afterdischarge and the subsequent profound enhancement of spike broadening that occur in the bag cell neurons of Aplysia are related to an increase in adenosine 3',5'-monophosphate-(cAMP) dependent protein phosphorylation. We have now used a two-electrode voltage clamp to study the properties of isolated bag cell neurons in cell culture and their response to 8 benzylthio-cAMP (8BTcAMP) and N6-n-butyl 8BTcAMP. These membrane-permeant and phosphodiesterase-resistant cAMP analogs induce spontaneous discharge and spike broadening in both the intact bag cell cluster and isolated bag cell neurons in cell culture. The dominant inward current in these cultured cells was found to be the calcium current, Ica, which was abolished by Co2+ (20 mM) or Ni2+ (10 mM) and could be observed in Na+-free media. In a minority of cells (2 of 12), in normal ionic media, a transient inward current was observed that was unaffected by Co2+ and Ni2+ and probably represents a sodium current. The three characterized potassium currents, the delayed rectifying current IK, the calcium-dependent current IC, and the early transient current IA, distinguished by their differing pharmacological and voltage-activation properties, were present in all healthy cells. Three effects of the cyclic AMP analogs (0.5 mM) on the electrical properties of these cells were 1) the emergence of a region of negative slope resistance in the steady-state I-V relations, 2) a depression of the net sustained outward currents due to depolarizing commands, and 3) a marked reduction in IA. When outward currents had been largely suppressed using high concentrations of tetraethylammonium (TEA) ions (100-460 mM) no effects of the cyclic AMP analogs could be observed on peak inward currents using NA+ and Ca2+ or Ba2+ as carriers of inward current. At least part of these electrical effects of the cyclic AMP analogs could be accounted for by a depression of a delayed potassium current and the A current.
Motor organization in pharynx of Helix pomatia
Authors: Peters M. , Altrup U.
Published: December 2017

Identified motor neurons in the buccal ganglia of Helix pomatia and pharynx muscles innervated by them were studied with intracellular recording and cobalt staining. Retrograde cobalt staining via the buccal nerves indicated that neurons occupy relatively constant positions within the ganglia. With intracellular cobalt staining it was shown that the shape of a representative motor neuron (B4) is similar in different preparations. In some cases, however, deviations from the normal pattern of axon distribution were found. Presumed motor endings of neuron B4 in the muscle were also visualized with intracellular staining. Recordings from individual motor neurons show typical phase relationships of spontaneous spike activity. Most motor neurons are active in the retraction phase of the radula. Only excitatory motor neurons were found. Most neurons directly supply more than one muscle. Amplitude of excitatory junction potentials (EJP) and plasticity at neuromuscular junctions from one neuron are similar in different muscles. Single muscle fibers receive polyneuronal innervation. Activity of single motor neurons already leads to muscle contraction even without spiking of the muscle cells. Muscle tension depends on integrated EJP size. Most motor neurons supply typical combinations of a set of muscles. Thus, several muscles can be activated synchronously by activity of a single motor neuron. In this way muscle combinations are predetermined morphologically by the peripheral branching patterns of the respective neurons.
Properties of deep spinothalamic tract cells in the rat, with special reference to ventromedial zone of lumbar dorsal horn
Authors: Menetrey D. , de Pommery J. , Roudier F.
Published: December 2017

Spinothalamic tract cells lying at the base of the dorsal horn or in deeper areas were identified in the rat at the lumbar spinal cord level by injecting horseradish peroxidase or stimulating posterior thalamic areas. Two groups of neurons were delineated; each constituted a homogeneous population of cells in terms of electrophysiological properties. Ventromedial dorsal horn cells lay at the base of the dorsal horn in its most medial aspect. They constitute a densely packed formation, which in the rat's ascending pathway system is restricted to the spinothalamic tract. Their main characteristics were a) ongoing activity, which consisted of small groups of spikes occurring at regular intervals, with a maximal discharge during ankle extension; b) unilateral receptive fields, which were restricted to the distal parts of the limb and involved both proprioceptive (ankle, joint digits) and exteroceptive (foot skin) structures; c) input of innocuous origin (midrange articular movement, touch, pressure) that was excitatory and input of noxious cutaneous origin (radiant heat) that was inhibitory; the same areas of foot skin were thus potentially either excitatory or inhibitory, depending on the nature of the stimulus applied; d) ankle flexion could differentially modulate both ongoing activity and excitatory responses from distal parts of the limb, inhibiting the former and potentiating the latter. In consequence, the ability of these cells to be driven by both proprioceptive and cutaneous inputs from limb extremities as well as by interactions of these inputs would appear to be very favorable for informing the central nervous system about limb position in both passive postural changes and the step cycle. It is suggested that they supply the thalamus with integrated information about locomotion. Lamina VII cells also constituted a subpopulation of neurons with very homogeneous electrophysiological properties. They were characterized by widespread inhibitory receptive fields, possibly spanning both hindlimbs and the ipsilateral forelimb. Inhibition was most effective when the stimulus (pressure, pinch) was intense and applied to proximal parts of the hindlimb. Ongoing activity consisted of spikes set at regular intervals and sometimes related to midrange movements of the knee. Although the significance of the widespread inhibitory receptive fields remains unclear, it has been suggested that these neurons are involved in the transmission of proprioceptive information.(ABSTRACT TRUNCATED AT 400 WORDS)