bluuebunny/crossref_metadata_2025 huggingface dataset:
The motor-unit population of the cat tenuissimus muscle
Authors: Lev-Tov A. , Pratt C. A. , Burke R. E.
Published: December 2017

1. We studied the organization of motor units in the tenuissimus (TEN) muscle of pentobarbital-anesthetized cats. The cat TEN is a long, delicate straplike muscle that spans hip and knee, which has a very flat length-tension curve through 22 mm of length change. 2. The TEN motor nucleus, labeled by retrograde transport of several forms of horseradish peroxidase, was composed of 8-31 cells in different cats, of which about half were, on average, in the size range of alpha-motoneurons. TEN motoneurons were scattered through the ventrolateral portion of lamina IX, over a rostrocaudal distance of up to 6.5 mm, making it relatively easy to isolate individual TEN motor axons for single motor-unit stimulation. 3. Individual TEN muscle units were classified into four groups [fast-twitch, fatigable (FF), intermediate, fatigue-resistant (Fint), fast-twitch, fatigue-resistant (FR), and slow-twitch, fatigue resistant (S)] on the basis of "sag" and fatigue index mechanical properties, as in other cat hindlimb muscles. There was a relatively large proportion of Fint units (28%) in the TEN sample, and the range of tetanic tension (approximately 19-fold) was much smaller than found in other cat hindlimb muscles. 4. A majority of TEN muscle fibers could be classified into the three major histochemical types (IIB, IIA, and I) found in other cat muscles, but a substantial minority remained "unclassified." A single type Fint muscle unit was successfully depleted of glycogen for histochemical study. It exhibited a typical type IIB histochemical profile. 5. Despite its unusual morphology, the cat TEN contains the same types of motor units found in larger, more "typical" limb muscles.
Characteristics and functional identification of saccadic inhibitory burst neurons in the alert monkey
Authors: Scudder C. A. , Fuchs A. F. , Langer T. P.
Published: December 2017

1. With the use of single-unit recording, the reticular formation immediately caudal to the abducens nucleus was searched for saccadic burst neurons in alert, trained rhesus monkeys. We recorded 80 short- and long-lead burst neurons, investigated their connections, and quantitatively analyzed their discharge characteristics. 2. Like excitatory burst neurons located rostral to the abducens, these caudal burst neurons fire optimally for ipsilaterally directed saccades, fire less for vertical saccades, and fire minimally, if at all, for contralateral saccades. The direction associated with the maximum number of spikes was approximately along the horizontal axis (1 +/- 12 degrees (SD); n = 33). 3. The first spike of the burst led the saccade by 2-120 ms, depending on the unit. Neurons were divided into short lead (45%) and long lead (55%) using a burst-lead criterion of 15 ms. In the on-direction, the discharges of both types exhibited strong correlations between number of spikes in the burst and size of the horizontal saccade component; duration of the burst and duration of the saccade; and peak frequency of the burst and peak velocity of the saccade. These relations were looser for long-lead neurons than for short-lead neurons. 4. Horseradish peroxidase injected into the abducens nucleus retrogradely labeled cells in the contralateral reticular formation where burst neurons were recorded, showing that cells in this region make crossed monosynaptic connections. There was good agreement between the limits of this region, as determined physiologically and anatomically. 5. Microstimulation at the locus of recorded burst neurons elicited EMG potentials in the contralateral lateral rectus muscle of the appropriate sign and latency for a monosynaptic inhibitory projection to abducens motoneurons. Stimulation also elicited eye movements consistent with inhibition of the contralateral lateral rectus. 6. It is argued that these characteristics make it likely that the short-lead neurons are the source of the afference which generate the pause in contralateral abducens motoneuron firing during adducting saccades. These neurons are therefore analogous to the inhibitory burst neurons (IBNs) found in the cat. The characteristics of long-lead burst neurons, particularly their lead, make them less likely to subserve this function. These cells might be better suited to providing input to omnipause neurons or to the short-lead IBNs.
Effects of muscle shortening on the responses of cat tendon organs to unfused contractions
Authors: Horcholle-Bossavit G. , Jami L. , Petit J. , Vejsada R. , Zytnicki D.
Published: December 2017

1. The discharges from individual Golgi tendon organs of peroneus tertius and brevis muscles were recorded in anesthetized cats. Responses to unfused isometric contractions of single motor units and combinations of motor units were compared with responses to contractions eliciting muscle shortening (i.e., shortening contractions). 2. In 75% of the examined instances, the effect of muscle shortening during unfused contractions was a slight decrease in tendon organ activation, in keeping with the reduction of contractile tension recorded at the muscle tendon. In other instances there was either no change in tendon organ response or, in less than 10% of instances, a slight increase For two motor units eliciting similar activation of a given tendon organ under isometric conditions, the effect of shortening contraction was not necessarily the same. 3. The reductions observed in tendon organ discharges upon muscle shortening were less than proportional to the reductions of contractile tension and difficult to correlate with the properties of motor units, as determined under isometric conditions. The present observations suggest three main reasons for this lack of relation. 4. The first reason depended on the properties of motor units, in that the relation between length changes and tension changes was not the same for all units. Two motor units developing similar isometric tensions did not necessarily produce the same degree of muscle shortening. Some units produced relatively significant shortening without much loss of tension. 5. Second, the dynamic sensitivity of tendon organs is known to exert a major influence on their responses to isometric unfused contractions, accounting for 1:1 driving of discharge during tension oscillations and high frequency bursts upon abrupt increase of tension. Although less tension was produced and the rate of tension development was slower in shortening contractions, similar manifestations of the dynamic sensitivity of tendon organs were observed. In such cases, the responses of tendon organs were the same whether or not the muscle shortened during contraction. 6. Third, when several motor units were stimulated in combination, the unloading influences of in-parallel units were facilitated by muscle shortening so that unloading effects, which were hardly visible under isometric conditions became evident during shortening contractions.
Membrane properties of cell types within guinea pig basal forebrain nuclei in vitro
Authors: Griffith W. H.
Published: December 2017

1. Neurons in the nucleus of the diagonal band of Broca (nDBB) and ventral portion of the medial septum (MS) were studied using intracellular recording and single-electrode voltage clamp (SEVC) techniques in an in vitro brain slice preparation. Cell types could be operationally divided into three categories: cells with a slow postspike afterhyperpolarization (SAHP cell, 40%), neurons with a fast AHP (FAHP cells, 53%), and a third cell group recorded infrequently (7% of the cells) that fired in a burst pattern. Double-labeling techniques have shown that SAHP cells stain positively for acetylcholinesterase (AChE) and are presumably cholinergic (22). The present study provides a more detailed analysis of the passive and active membrane properties of SAHP and FAHP types within these forebrain nuclei. 2. SAHP cells were characterized by a postspike afterhyperpolarization (AHP) with an amplitude of 10-20 mV and duration of approximately 600 ms at -65 mV. In the voltage range of -60--70 mV, the AHP decayed as a single exponential function with a time constant of 170 +/- 53 ms (n = 10). However, many neurons at these membrane potentials exhibited an AHP decay that was a multiple exponential function lasting for seconds. The null potential of the SAHP was approximately -90 mV and shifted by 25 mV in 9 mM KCl, a value closely predicted for a potassium (K+) conductance. The SAHP was reversibly blocked by cadmium (Cd2+), suggesting the SAHP was mediated by a calcium (Ca2+)-activated K+ conductance. 3. FAHP cells displayed afterhyperpolarizations of smaller amplitude (5-10 mV) and duration (5-50 ms) that reversed at approximately -85 mV. Elevating extracellular K+ concentration [Ko] to 6 mM shifted the reversal 13 mV more positive. Cd2+ also reduced the AHP in these cells suggesting a second faster Ca2+-activated K+ conductance may be present. 4. Both SAHP and FAHP cells had similar input resistances and resting membrane potentials but markedly different action-potential characteristics. SAHP cells had a spike duration of 1.4 ms and a prominent shoulder on the falling phase of the SAHP cell action potentials that was reduced by Cd2+. In contrast, FAHP cells had an average spike duration of 0.63 ms that was unaffected by Cd2+. 5. The passive electrical cable properties of both cell types were characterized. Equivalent electrotonic length of the dendrites (L) and the dendritic-to-somatic conductance ratio (rho) were calculated for different cell groups. SAHP cells displayed average L values of 0.61, and the average rho was 2.13. Similar values of 0.69 and 2.14 were calculated for L and rho, respectively, in FAHP cells.(ABSTRACT TRUNCATED AT 400 WORDS)
Relative contributions of passive equilibrium and active transport to the distribution of chloride in mammalian cortical neurons
Authors: Thompson S. M. , Deisz R. A. , Prince D. A.
Published: December 2017

1. Active and passive factors affecting the chloride gradient of cortical neurons were assessed using intracellular recordings from neurons in slices of cingulate cortex maintained in vitro. The chloride equilibrium potential (ECl-) was estimated indirectly from the reversal potentials of responses to perisomatic gamma-aminobutyric acid (GABA) application and the Cl(-)-dependent inhibitory postsynaptic potential (IPSP). Under control conditions the mean resting potential (Vm; -69.7 mV) was not significantly different than the mean IPSP reversal potential (EIPSP; -70.1 mV). 2. Increasing the external potassium concentration ([K+]o) from 1 to 10 mM shifted the mean EIPSP from -80.4 to -61.8 mV. The mean EIPSP was approximately equal to the mean Vm at all [K+]oS. The conditions of Donnan equilibrium are not met in [K+]o less than 10 mM. 3. Polarization of Vm up to 20 mV away from EIPSP for 4 min with maintained current injection had no significant effect on EIPSP. 4. The GABA reversal potential was maintained 37-52 mV less negative than Vm after equilibration in saline in which the external chloride concentration had been reduced from 133 to 5 mM by substitution with isethionate. Vm and input resistance were not significantly different from control values in cells recorded under these conditions. 5. We conclude that Cl- is not passively distributed in cortical neurons, perhaps due to a low resting Cl- permeability. 6. Impalement with electrodes containing 2 M KCl resulted in a rapid 10 mV depolarizing shift in EIPSP that then remained relatively constant. Intracellular iontophoresis of Cl- resulted in a further depolarizing shift of EIPSP of 5-10 mV that returned to control in less than 1 min. The time course of recovery of IPSP amplitude could be fit with a single exponential having a mean time constant of 6.9 +/- 1.5 s and was independent of the amount of Cl- injected or stimulation frequency. 7. Reductions in temperature from 37 to 32 degrees C significantly increased the mean time constant of IPSP recovery from Cl- injection to 11.1 +/- 3.3 s, corresponding to Q10 = 2.6.(ABSTRACT TRUNCATED AT 400 WORDS)
Nonequivalent cylinder models of neurons: interpretation of voltage transients generated by somatic current injection
Authors: Rose P. K. , Dagum A.
Published: December 2017

1. Numerical methods were used to simulate the voltage responses to an intrasomatic current step of neuronal models that incorporated tapering dendrites, dendrites of unequal electrotonic length, nonlinear membrane properties, and regional differences in specific membrane resistivity (Rm). A "peeling" technique was used to estimate the time constants (tau 0 and tau 1) and coefficients (a0 and a1) of the first two exponential terms of the series of exponential terms whose sum represented the slope of the voltage response. 2. The electrotonic structure of models with a uniform Rm was calculated using equations derived by Rall or Johnston or Brown et al. The adequacy of these methods were tested using a wide variety of models that conformed to the equivalent cylinder approximation of Rall. Johnston's method provided the most reliable estimate of electrotonic length (L) and the ratio of the dendritic conductance to the somatic conductance (rho). However, if L exceeded 2 and rho was eight or larger, the equations derived by Johnston could frequently not be solved due to small errors in the peeled values of tau 0, tau 1, a0, and a1. Although the method suggested by Brown et al. could be applied to all models, this method invariably underestimated L and rho. These errors were particularly large for model neurons with L values of 1.5 or larger and rho values of four or larger. Estimates of L using Rall's method were only reliable if rho was large and L was two or less. 3. Changing the geometry of the dendritic tree (dendritic tapering or dendrites of unequal L) or the addition of a time- and voltage-dependent conductance designed to mimic a sag process commonly seen in spinal motoneurons caused systematic changes in tau 0, tau 1, a0, and a1. The sag process always led to an underestimate of tau 0 even after applying a correction procedure. On the other hand, the ratio, tau 0/tau 1, was not affected by the sag process or dendritic tapering.(ABSTRACT TRUNCATED AT 400 WORDS)
Compartmentalization of motor units in the cat neck muscle, biventer cervicis
Authors: Armstrong J. B. , Rose P. K. , Vanner S. , Bakker G. J. , Richmond F. J.
Published: December 2017

1. The neck muscle biventer cervicis is supplied by five separate nerve bundles that originate from segments C2-C5 and enter the muscle at different rostrocaudal levels. We have used the glycogen-depletion method to investigate the distribution of muscle fibers supplied by each nerve bundle and also the extent of motor-unit territories supplied by single motoneurons in the C3 segment. 2. Prolonged intermittent stimulation of each nerve bundle produced glycogen depletion in a compartment of muscle fibers that ran only a fraction of the whole-muscle length. The depleted compartment was separated by tendinous inscriptions from adjacent, serially arranged compartments that were supplied by different nerve bundles. Thus the muscle was divided into five in-series compartments, arranged in the same rostrocaudal sequence as the nerves by which they were supplied. 3. Six fast, glycolytic (FG) and five fast, oxidative-glycolytic (FOG) motor units were depleted by repetitive intracellular stimulation of their antidromically identified motoneurons in the C3 segment. The fibers of each motor unit were confined to a striplike subvolume whose cross-sectional area was only 20-40% of that for the whole compartment in which it was located. Single motor units contained an average of 408 extrafusal fibers (range: 262-582 fibers), and these were distributed with an average density of 20 fibers/mm2 in cross sections through their motor domains. No significant differences were found between the numbers or densities of fibers in FG and FOG motor units. 4. The specialized in-series organization of compartments has functional implications because the forces generated by one compartment of motor units must be transmitted through other in-series compartments of muscle fibers rather than directly onto skeletal attachments. The confined distribution of muscle fibers belonging to a single motor unit suggests that an additional level of organization may exist within individual compartments. The implications of these features for the physiological behavior and neural control of biventer cervicis are discussed.
Electrotonic architecture of type-identified alpha-motoneurons in the cat spinal cord
Authors: Fleshman J. W. , Segev I. , Burke R. B.
Published: December 2017

1. Measurements of input resistance (RN), time constant (tau 0), and electrotonic length (Lpeel) were derived from intracellular voltage changes produced by injection of current pulses in six type-identified triceps surae alpha-motoneurons. The motoneurons were labeled with horseradish peroxidase and subsequently reconstructed and measured from serial sections. These quantitative morphological and physiological data were incorporated into detailed computer models of the motoneurons. 2. Steady-state and dynamic models were used to determine values for specific membrane resistivity (Rm) that matched the experimental estimates of RN, tau 0, and Lpeel for each motoneurons. The models were based on the following assumptions 1) the membrane was electrically passive, 2) cytoplasmic resistivity (Ri) was 70 omega-cm, and 3) "sealed-end" boundary conditions were present at dendritic terminations. We also considered the nature and magnitude of possible errors introduced by using linear (passive) computer models to match responses from motoneurons with nonlinear (i.e., voltage-dependent) conductances. 3. If we assume that the experimental measurements of RN and tau 0 were correct, uniform Rm values that reproduced the experimentally measured RN required widely varying values of Cm (1.4-8.6 microF/cm2) to match the experimental tau 0. Furthermore, the electrotonic distance to dendritic terminals was generally much greater than expected from physiological estimates of Lpeel. However, if we assumed that the RN measurements could have been underestimated by as much as 30% and that Cm = 1.0 microF/cm2, it was possible to choose spatially uniform Rm that matched the observed tau 0 in three of six cases. 4. Relaxing the assumption of spatially uniform membrane resistivity permitted us to reconcile the anatomical and physiological characteristics of all six motoneurons. Two qualitatively different models of Rm nonuniformity gave equally good fits to the experimental results 1) a step-wise increase in Rm from a low value at the soma to a much higher but uniform value over the entire dendritic tree, and 2) a monotonic increase in Rm from soma to distal dendrites as a sigmoidal function of path distance along the dendrites. The step and sigmoidal models of the spatial distribution of Rm generated different electrotonic architectures in motoneuron dendritic trees, but both gave essentially identical electrical responses at the soma.(ABSTRACT TRUNCATED AT 400 WORDS)
Theory of dynamic similarity in neuronal systems
Authors: MacGregor R. J. , Tajchman G.
Published: December 2017

1. The techniques of dynamic similarity from the engineering science of fluid mechanics are applied to neuronal systems to suggest how to scale down critical parameters (such as numbers of constituent cells and synapses, synaptic strengths, thresholds, etc.) from naturally occurring systems to computer models. 2. The interconnectivity of a prototypical neuronal junction is defined in terms of the total number of projecting fibers, receiving cells, synapses, and directly connected cell fiber pairs. Critical derivative parameters are defined in terms of these, including: a global convergence factor, alpha ij, which is the ratio of the numbers of projecting fibers to receiving cells; and an interconnectivity completeness parameter or microscopic convergence/divergence parameter, gamma ij, which measures both the percentage of cells to which a given sending fiber projects (and the percentage of fibers from which a given cell receives) and the percentage of cell fiber combinations which are directly connected. 3. Analysis of the differential equations governing neuroelectric activity in constituent neurons suggests the definition of a sensitivity parameter complex, sigma ij (with components eta ij and mu ij) for each ij junction. These numbers represent the ratio of synaptic drive to current leakage in nonactive neurons. 4. A model for quasi-steady firing suggests the definition of a parameter, rho *j, which may be used to characterize the level of activity in a given neuronal population in terms of its synaptic drive and system parameters. It may be considered as the neuronal analog of the Reynolds number in fluid mechanics. 5. The analysis implies that computer models of neuronal systems should be scaled so as to keep the parameters alpha ij, gamma ij, and sigma ij for every junction at the same values as in the corresponding junctions of naturally occurring system being modeled. Equations for a scaling factor, chi, numbers of constituent synapses, thresholds, etc., are provided. The scaling method is illustrated by a computer simulation example and by application to the junction of the perforant path fibers to the granule cells of the hippocampus. 6. The analysis shows that there is a fundamental trade-off in scaled down computer models between verisimilitude at the level of network interconnectivity and verisimilitude at the level of individual neuronal dynamics. 7. The approach of dynamic similarity is discussed with respect to compression of free parameters and predictive comparison of naturally occurring systems.
Single vibrissal cortical column in SI cortex of rat and its alterations in neonatal and adult vibrissa-deafferented animals: a quantitative 2DG study
Authors: Kossut M. , Hand P. J. , Greenberg J. , Hand C. L.
Published: December 2017

1. A quantitative 2-[14C]deoxy-D-glucose (2DG) autoradiographic study was undertaken to determine the functional (metabolic) organization of an individual column in the first somatosensory cortex (SI) of the awake restrained rat. Manual or mechanically controlled brush stroking of a single vibrissa (typically C3) was used in order to evoke neural activity and increase glucose utilization in a single cortical barrel in lamina IV and in adjacent supra- and infragranular layers in register with the single cortical barrel labeling in lamina IV. 2. The single activated vibrissal column was found to extend from layer I to the superficial half of layer VI of the contralateral SI cortex and was fusiform in shape, being of largest diameter (650-micron) in layer IV and smallest diameter (200 micron) in layer VI. 3. This single metabolic column was not uniform in its density of labeling. The greatest local cerebral metabolic rate of glucose (LCMRG) was found in layer IV (170 mumol.100 g-1.min-1), layers II-III, and V had, on the average, similar LCMRG values (115 mumol.100 g-1.min-1), which decreased with distance from layer IV. 4. The functional (metabolic) columnar activity center situated in layer IV corresponded in size to the appropriate anatomical barrel as determined from thionin-stained sections. Increased metabolic activity was not strictly confined to the candle-pin-shaped column but extended tangentially as radiating fingerlike projections toward the neighboring barrels. 5. In cortical layers other than IV, the metabolic column was less prominently labeled, and the metabolic activity also branched in the tangential plane. The labeling pattern profile in upper layers was characterized by numerous lateral spreading fingerlike projections of increased glucose metabolism. 6. Neonatal follicle lesions sparing only C3 vibrissa caused a great increase (125%) in cortical territory driven by the spared whisker with a concomitant loss of columnar shape and decrease in intensity of metabolic activity in response to its stimulation. 7. Similar lesions in adult rats produced a significant increase (40%) in dimensions of the spared C3 cortical column, which was, however, smaller than that produced after neonatal lesions. The metabolic activation of layer Vb in the spared C3 column was increased (17%) compared with that of the control column.(ABSTRACT TRUNCATED AT 400 WORDS)
Fluctuations in spontaneous discharge of hippocampal theta cells during sleep-waking states and PCPA-induced insomnia
Authors: Mushiake H. , Kodama T. , Shima K. , Yamamoto M. , Nakahama H.
Published: December 2017

1. The spontaneous activity of hippocampal theta cells in head-restrained cats was recorded during slow-wave sleep (SWS), paradoxical sleep (PS), and the attentive state of bird watching (BW). We also recorded theta cell activity during a state of insomnia with pontogeniculoocipital (PGO) waves, which was induced by the administration of p-chlorophenylalanine (PCPA), a selective inhibitor of serotonin synthesis. 2. The time-dependent structure of fluctuations in theta cell activity was evaluated by power spectral analysis and Markovian analysis. The coefficient of variation for these time series was used as a measure of the variability of theta cell activity, which indicates the relative amplitude of fluctuations. 3. During SWS, theta cell activity showed a larger variability and a flat spectrum, i.e., low Markovian properties. During PS, this activity exhibited smaller variability and high spectral density in a low-frequency band (0.01-1.0 Hz), i.e., high Markovian properties. During BW, variability, spectral and Markovian properties were intermediate. 4. The firing pattern of theta cells during PCPA-induced insomnia was similar to that during PS. However, after the administration of either a serotonin agonist, 5-Methoxy-N,N-dimethyltryptamine, or a choline antagonist, atropine sulfate, theta cell activity no longer exhibited PS-like fluctuations, revealing instead a firing pattern similar to that during SWS. 5. During PS and PCPA-induced insomnia, not only the unit activity of theta cells, but PGO activity and theta wave frequency exhibited slow fluctuations, i.e., the high spectral density in the low-frequency band (0.01-1.0 Hz). 6. Cross-correlation analyses were performed between the fluctuations in theta cell activity, theta wave frequency, and PGO activity. These fluctuations correlated with each other during both PS and PCPA-induced insomnia. Bursts of PGO waves especially contributed to these cross-correlations. 7. These results suggest, first, that the slow fluctuations of the theta cell activity during PS and PCPA-induced insomnia is the physiological expression of the removal of aminergic influences and, secondly, that they are dependent on cholinergic mechanisms, including PGO generators.
Convergence of heterotopic nociceptive information onto subnucleus reticularis dorsalis neurons in the rat medulla
Authors: Villanueva L. , Bouhassira D. , Bing Z. , Le Bars D.
Published: December 2017

1. In anesthetized rats recordings were made from neurons in the medulla caudal to the obex. In the medullary dorsal horn, typical trigeminal noxious specific, nonnoxious specific, and convergent neurons were found. In nucleus cuneatus, typical dorsal column units were recorded. In subnucleus reticularis dorsalis (SRD), recordings were made from neurons which exhibited convergence of nociceptive inputs from the entire body. In subnucleus reticularis ventralis (SRV) we recorded both from neurons with spontaneous activity that were either unaffected or inhibited by noxious stimuli applied to various parts of the body and from respiratory neurons. The present paper deals particularly with the nature of the stimuli that activated reticular neurons exhibiting nociceptive convergence. 2. Neurons with nociceptive convergence could be activated by mechanical, thermal, or chemical noxious stimuli applied to widespread areas of the body. By using percutaneous electrical stimulation, we found that they responded to the activation of peripheral fibers in the A delta- and C-range. Two neuronal subpopulations were defined according to the way in which SRD neurons responded to the electrical stimuli, namely: "neurons with total nociceptive convergence" (TNC) and "neurons with partial nociceptive convergence" (PNC). 3. The great majority (84%) of TNC neurons did not exhibit spontaneous activity and none of these neurons gave responses to heterosensory (flashes, whistle sounds) or proprioceptive stimuli. Most (88%) did not respond to any kind of innocuous cutaneous stimuli. By contrast, the entire population of TNC neurons responded to noxious mechanical, thermal, and visceroperitoneal stimuli. In the majority of cases (71%) long-lasting afterdischarges were observed following cessation of the application of the nociceptive stimulus. 4. All the TNC neurons responded to suprathreshold percutaneous electrical stimulation (2-ms duration) with two peaks of activation no matter which part of the body was stimulated. By stimulating two regions of the tail, 100 mm apart, we determined that the early and late peaks of activation were triggered by activities in peripheral fibers with mean conduction velocities of 10.8 +/- 0.5 and 0.74 +/- 0.05 (SE) m/s, respectively, i.e., A delta- and C-fibers. The mean thresholds for obtaining A delta-fiber components were found in the 0.4-0.7-mA range; the mean thresholds for obtaining C-fiber components were found in the 6-7.5- and 3-4-mA range for the face and the other parts of the body, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)
Relations of motor cortex neural discharge to kinematics of passive and active elbow movements in the monkey
Authors: Flament D. , Hore J.
Published: December 2017

1. Bedingham and Tatton recently reported that in cats trained not to resist imposed limb perturbations, some motor cortex (area 4) neurons responded predominantly to acceleration or jerk (the third derivative of position). The questions arose whether motor cortex neurons responding to higher derivatives of limb displacement exist in the primate in a resist-perturbation task and, if so, whether discharge of such neurons responds to the same kinematics in active (voluntary) movements. 2. To answer these questions we studied the discharge patterns of 203 motor cortex neurons that responded to torque pulse perturbations about the elbow and fired during active elbow flexions and extensions in four monkeys. Detailed analysis was performed on 66 neurons that responded reciprocally in both situations. 3. Reciprocal neurons discharged at short latency (20-40 ms) for one direction of arm perturbation. For the opposite direction they were initially silent or inhibited and then discharged at a variety of latencies but in apparent relation to limb kinematics. Based on the timing and overall pattern of their discharge the majority of neurons (68%) were classified as being acceleration-like. 4. Twenty-four (36%) of these reciprocal neurons had only sensory (kinematic)-like properties in active movements, i.e., they discharged after (and not before) movement onset. Discharge of these neurons followed the timing, but not the magnitude, of acceleration (20 neurons) or velocity (4 neurons). The discharge of these neurons also had a static component as the arm was held stationary. 5. Twenty-nine (44%) of reciprocal neurons commenced firing before movement onset for one direction of active movement, while for the opposite direction their discharge occurred after movement onset. Thus their discharge appeared to be muscle-related: both when the muscle was contracting as an agonist and stretched as an antagonist. 6. Although in these tasks discharge of MCNs could be generated either by sensory feedback or by motor responses, the strong response sensitivity of many neurons to acceleration supports the hypothesis that feedback based on higher derivatives of limb displacement could represent a "predictive" control system for accurate regulation of limb motion.
Unitary conductance changes at teleost Mauthner cell glycinergic synapses: a voltage-clamp and pharmacologic analysis
Authors: Faber D. S. , Korn H.
Published: December 2017

1. The magnitude and kinetics of inhibitory postsynaptic currents (IPSCs) evoked in the goldfish Mauthner (M-) cell by intracellular stimulation of identified presynaptic interneurons (unitary responses) and by activation of the recurrent collateral network were determined with single-and double electrode voltage-clamp techniques. 2. The peak magnitude of the inhibitory conductance changes were 5610 +/- 4800 nS (mean +/- SD; n = 13) for the collateral response, and 144 +/- 44 nS (n = 7) for the unitary IPSCs. These synaptic conductances, which are due to the opening of Cl- channels, were independent of the degree of Cl- -loading of the M-cell. 3. The peak amplitude of the collateral inhibitory postsynaptic potential (IPSP) was a constant fraction (0.52 +/- 0.06) of the driving force, which was determined from current-voltage plots for both types of IPSCs and ranged from 10 to 37 mV. These findings confirm indirect measurements from previous current-clamp studies and validate the normalization procedure used to previously calculate synaptic conductances from IPSP amplitudes, a method that therefore may be applicable to other central neurons. 4. At the resting membrane potential, the rise time of the unitary IPSCs was 0.34 +/- 0.07 ms (n = 18), whereas their decay was exponential, with a time constant of 5.7 +/- 1.1 ms (n = 16). 5. Iontophoretic and intramuscular applications of the glycine antagonist strychnine reduced or blocked M-cell inhibitory responses, without altering the excitability of the presynaptic neurons, or the driving force. 6. Amplitude fluctuations of unitary IPSPs recorded during partial blockade by strychnine were analyzed according to a binomial model of quantal transmitter release. In one experimental series, comparison of the binomial parameters before and after applying the antagonist indicated that only quantal size, q, was reduced, whereas n, the number of available release units, and p, the probability of release, were unaffected by strychnine. In a second series, the individual presynaptic cells were injected with horseradish peroxidase (HRP), and it was found that the correlation between n and the number of stained presynaptic boutons and, therefore, of active zones, was maintained in the presence of the drug. No evidence was found for silent synapses in these conditions. 7. The quantal conductance, gq, was estimated from the binomially derived quantal size, in millivolts, and the voltage-clamp measurements of the IPSP driving force and M-cell input conductance. gq averaged 21.5 nS in control conditions and 12.3 nS in the presence of strychnine.(ABSTRACT TRUNCATED AT 400 WORDS)
Physiological responses of rat plantaris motor units to overload induced by surgical removal of its synergists
Authors: Olha A. E. , Jasmin B. J. , Michel R. N. , Gardiner P. F.
Published: December 2017

1. Rat plantaris muscles were subjected to chronic overload by the surgical removal of the soleus and most of the gastrocnemius muscles. Twelve to 16 wk later whole muscle and motor unit (ventral root dissection technique) contractile properties as well as histochemistry were determined. 2. Motor units were categorized as fast, fatigable (FF), fast, intermediate fatigue-resistant (FI), fast, fatigue-resistant (FR), and slow (S) based on contractile characteristics. Muscle fibers were identified as type I and type II according to myofibrillar ATPase staining. 3. Whole muscles demonstrated increases in wet weight, tetanic force, proportion of type I fibers, and mean cross-sectional areas of both type I and II fibers, as a result of chronic overload. 4. Tetanic tension increased by the same relative magnitude in all motor units whereas twitch tension remained unchanged. A significant change in the proportions of the motor unit types occurred in overloaded muscles, such that the latter contained higher proportions of FF and S units, and lower proportions of FI and FR units, than normal muscles. 5. The fatigue profile of a composite constructed from a summation of motor unit responses revealed that the overloaded plantaris displayed fatigue resistance similar to that of the normal plantaris for a given absolute force output. 6. Glycogen-depleted fibers of hypertrophied single motor units demonstrated uniform myofibrillar ATPase and SDH staining characteristics suggesting that metabolic adaptations among fibers of the same unit were similar after 12-16 wk of overload. 7. The finding that overload caused a uniform increase in the tetanic strength of all motor units, whereas alterations in fatigue resistance varied in degree and direction among unit types, demonstrate that these two properties are not controlled in parallel in this model. The smallest units maintain or even increase their fatigue resistance during the hypertrophic process, whereas high threshold units actually decrease in fatigue resistance.
A comparison of supramammillary and medial septal influences on hippocampal field potentials and single-unit activity
Authors: Mizumori S. J. , McNaughton B. L. , Barnes C. A.
Published: December 2017

1. A comparison was made between the influences of supramammillary (SUM) and medial septal (MS) nuclei on hippocampal physiology in Nembutal-anesthetized rats. Specifically, the effects of prestimulation of the SUM or MS on the perforant path-dentate field potential, on spontaneous activity of single units, and on perforant path-induced unit activation were assessed. Another series of experiments addressed the issue of whether the SUM and MS effects on the perforant path-dentate field response are independent. 2. Prestimulation of the SUM or MS significantly facilitated the perforant path-dentate population spike with no clear effect on the field excitatory postsynaptic potential (EPSP) recorded in the subgranular zone of the dentate hilus. Prestimulation of either nucleus also reduced the threshold for spike onset. The major differences between the two spike facilitation effects were the magnitude of the change and possibly the optimal interstimulus intervals required to obtain the effects. 3. Acute transection of the ipsilateral column of fornix or dorsal fornix eliminated the SUM population spike facilitation effect. MS lesion or dorsal fornix/fimbria transection eliminated the MS spike facilitation effect. The MS lesion did not alter the effects of SUM prestimulation. Cingulum or medial forebrain bundle transection affected neither SUM- nor MS-mediated spike facilitation. Thus the SUM and MS influences on the dentate field response appear to be independent of one another. The relevant SUM afferents travel through the ipsilateral column of fornix and dorsal fornix, whereas MS afferents project through the dorsal fornix/fimbria. 4. Single units recorded in stratum granulosum (SG) were assessed with respect to several parameters. These included the mean firing rate, whether or not excitation occurred prior to the field population spike and at lower threshold, and whether or not a driven unit responded to a second perforant path stimulus delivered at short latency following the first (during the period of population spike depression). The latter parameter in particular appeared to separate SG cells into two classes. The cells that were not activated during the second field potential were classified as granule cells, whereas those that were activated were classified as basket cells. Based on this distinction, significant differences were also found between the two cell classes on the other parameters. In particular, cells classified as granule cells often had very low firing rates.(ABSTRACT TRUNCATED AT 400 WORDS)
Monaural and binaural response properties of neurons in the inferior colliculus of the rabbit: effects of sodium pentobarbital
Authors: Kuwada S. , Batra R. , Stanford T. R.
Published: December 2017

1. We studied the effects of sodium pentobarbital on 22 neurons in the inferior colliculus (IC) of the rabbit. We recorded changes in the sensitivity of these neurons to monaural stimulation and to ongoing interaural time differences (ITDs). Monaural stimuli were tone bursts at or near the neuron's best frequency. The ITD was varied by delivering tones that differed by 1 Hz to the two ears, resulting in a 1-Hz binaural beat. 2. We assessed a neuron's ITD sensitivity by calculating three measures from the responses to binaural beats: composite delay, characteristic delay (CD), and characteristic phase (CP). To obtain the composite delay, we first derived period histograms by averaging, showing the response at each stimulating frequency over one period of the beat frequency. Second, the period histograms were replotted as a function of their equivalent interaural delay and then averaged together to yield the composite delay curve. Last, we calculated the composite peak or trough delay by fitting a parabola to the peak or trough of this composite curve. The composite delay curve represents the average response to all frequencies within the neuron's responsive range, and the peak reflects the interaural delay that produces the maximum response. The CD and CP were estimated from a weighted fit of a regression line to the plot of the mean interaural phase of the response versus the stimulating frequency. The slope and phase intercept of this regression line yielded estimates of CD and CP, respectively. These two quantities are thought to reflect the mechanism of ITD sensitivity, which involves the convergence of phase-locked inputs on a binaural cell. The CD estimates the difference in the time required for the two inputs to travel from either ear to this cell, whereas the CP reflects the interaural phase difference of the inputs at this cell. 3. Injections of sodium pentobarbital at subsurgical dosages (less than 25 mg/kg) almost invariably altered the neuron's response rate, response latency, response pattern, and spontaneous activity. Most of these changes were predictable and consistent with an enhancement of inhibitory influences. For example, if the earliest response was inhibitory, later excitation was usually reduced and latency increased. If the earliest response was excitatory, the level of this excitation was unaltered or slightly enhanced, and changes in latency were minimal. 4. The neuron's response pattern also changed in a predictable way. For example, a response with an inhibitory pause could either change to a response with a longer pause or to a response with an onset only.(ABSTRACT TRUNCATED AT 400 WORDS)
Functional properties of monkey caudate neurons. III. Activities related to expectation of target and reward
Authors: Hikosaka O. , Sakamoto M. , Usui S.
Published: December 2017

1. The present paper reports complex neural activities in the monkey caudate nucleus that precede and anticipate visual stimuli and reward in learned visuomotor paradigms. These activities were revealed typically in the delayed saccade task in which memory and anticipation were required. We classified these activities according to their relationships to the task. 2. Activity related to expectation of a cue (n = 46) preceded the presentation of a spot of light (target cue) that signified the future location of saccade target. When the target cue was delayed, the activity was prolonged accordingly. The same spot of light was preceded by no activity if it acted as a distracting stimulus. 3. The sustained activity (n = 80) was a tonic discharge starting after the target cue as if holding the spatial information. 4. The activity related to expectation of target (n = 109) preceded the appearance of the target whose location was cued previously. It started with or after a saccade to the cued target location and ended with the appearance of the target. The activity was greater when the target was expected to appear in the contralateral visual field. 5. The activity related to expectation of reward (n = 57) preceded a task-specific reward. It started with the appearance of the final target and ended with the reward. In most cases, the activity was nonselective for how the monkey obtained the reward, i.e., by visual fixation only, by a saccade, or by a hand movement. The activity was dependent partly on visual fixation. 6. A few neurons showed tonic activity selectively before lever release and are thus considered to be related to the preparation of hand movements. 7. The activity related to breaking fixation (n = 33) occurred phasically if the monkey broke fixation, aborting the trial. 8. Activity related to reward (n = 104) was a phasic discharge that occurred before or after a reward of water was delivered. The activity was not simply related to a specific movement involved in the reward-obtaining behavior (eye, hand, or mouth movement). 9. Fixation-related activity (n = 72) was tonic activity continuing as long as the monkey attentively fixated a spot of light. It was dependent on reward expectancy in most cases. 10. The present results, together with those in the preceding papers, indicate that the activities of individual caudate neurons--sensory, motor, or cognitive--are dependent on specific contexts of learned behavior.(ABSTRACT TRUNCATED AT 400 WORDS)
Lateral tegmental field neurons of cat medulla: a source of basal activity of raphespinal sympathoinhibitory neurons
Authors: Barman S. M. , Gebber G. L.
Published: December 2017

1. We tested the hypothesis that sympathoinhibitory (SI) neurons in the lateral tegmental field (LTF) of the cat medulla exert their actions over a pathway that includes raphe neurons whose axons innervate the thoracic intermediolateral nucleus (IML). 2. We recorded from 32 LTF neurons with sympathetic nerve-related activity [as demonstrated with spike-triggered averaging of inferior cardiac sympathetic nerve discharge (SND)] whose firing rate increased during the inhibition of SND produced by baroreceptor reflex activation. These neurons were classified as SI in function. 3. Twenty-three of these 32 LTF-SI neurons were antidromically activated by microstimulation of the raphe nuclei, 2-4 mm rostral to the obex and 3-4.5 mm below the dorsal surface of the medulla. The threshold current for eliciting the longest-latency antidromic responses [18.9 +/- 2.4 (SE) ms] was increased when the stimulating microelectrode was moved more dorsally in the midline. With one exception, these neurons could not be antidromically activated by stimulation of sites either 1.5-2.0 mm lateral to the midline, contralateral to the site of unit recording or raphe sites caudal to the obex. Threshold stimuli applied 2-4 mm rostral to the obex and 1 mm lateral to the midline, ipsilateral to the site of unit recording, elicited antidromic responses whose onset latencies were shorter than those produced by raphe stimulation. These data support the view that the axons of LTF-SI neurons terminated in the region of the raphe that contains SI neurons whose axons innervate the IML. 4. We recorded from 32 raphe neurons with sympathetic nerve-related activity whose firing rate increased during baroreceptor reflex activation. These neurons were classified as SI in function. Twenty-five of the 32 raphe-SI neurons were antidromically activated by microstimulation of the third thoracic (T3) IML. Seven (including 5 with spinal axons) of 24 raphe-SI neurons tested were synaptically activated by microstimulation of the region of the LTF containing SI neurons. The modal onset latency of synaptic activation was 22.8 +/- 8.4 ms. This value is close to the difference in spontaneous firing times (26 ms on the average) of LTF-SI and raphe-SI neurons, relative to the peak of the cardiac-related burst of SND. 5. Taken together, these data are consistent with the hypothesis that LTF-SI neurons are a source of the background discharges of raphespinal-SI neurons. 6. Thirteen raphe-SI neurons were antidromically activated by stimulation of both the medulla and T3 IML.(ABSTRACT TRUNCATED AT 400 WORDS)