bluuebunny/crossref_metadata_2025 huggingface dataset:
Large amplitude variability of GABAergic IPSCs in melanotropes from Xenopus laevis: evidence that quantal size differs between synapses
Authors: Borst J. G. , Lodder J. C. , Kits K. S.
Published: December 2017

1. We made in situ whole-cell recordings from melanotropes in the intermediate lobe of the pituitary gland of Xenopus laevis. Melanotropes received spontaneous synaptic inputs that had a fast rise time and a much slower decay. These inputs were GABAergic inhibitory postsynaptic currents (IPSCs): they followed the reversal potential for chloride ions and they were blocked by the gamma-aminobutyric acid-A (GABAA) receptor antagonist bicuculline. 2. Because of the very low baseline noise it was possible to see discrete levels in the tails of IPSCs that corresponded to the opening of one or more synaptic GABAA receptor channels. "All-points" histograms of the IPSCs showed that the chord conductance of the channels in the tails of the IPSCs was 21.6 +/- 0.6 pS (mean +/- SE, n = 6). 3. The amplitudes of the spontaneous IPSCs were very variable, ranging from 3 to 390 pA at a holding potential of -80 mV. The average of the median amplitudes was -67.5 +/- 5.9 pA (n = 28). The amplitude distributions of the IPSCs were well described by the sum of two lognormal distributions with large SDs. The average of the means of the first lognormal distribution was 27.8 +/- 5.3 pA (n = 10); the average of the SDs was 24.7 +/- 8.1 pA. For the second lognormal distribution these values were 87.0 +/- 13.4 and 33.7 +/- 7.4 pA. An average of 41.8 +/- 6.9% of the IPSCs originated from the first lognormal distribution. 4. The large variability in the amplitudes of spontaneous IPSCs was not the result of presynaptic action potentials because it was not reduced by tetrodotoxin (TTX), Ca(2+)-free extracellular solution, or the combined application of TTX and Mn2+. 5. The time course of the IPSCs from the first and the second lognormal distributions were very similar: averages of the median 20- to 80% rise times were 585 +/- 64 and 488 +/- 28 microseconds, respectively (n = 8), whereas the decays were well described by the sum of two exponential functions, with fast time constants of 8.9 +/- 1.1 (n = 7) and 9.3 +/- 3.3 ms and slow time constants of 29.5 +/- 3.3 and 31.7 +/- 2.6 ms, respectively. 6. The decay of the IPSCs was voltage dependent; it was approximately 3 times slower at a holding potential of +40 mV than at -80 mV (n = 5).(ABSTRACT TRUNCATED AT 400 WORDS)
Ionic conductances of monkey solitary cone inner segments
Authors: Yagi T. , Macleish P. R.
Published: December 2017

1. The membrane properties of cone inner segments dissociated enzymatically from monkey retina were studied under voltage-clamp conditions using patch pipettes in the whole-cell clamp configuration. 2. A noninactivating, voltage-gated calcium current was evoked at potentials positive to -60 mV and peaked between -30 and -20 mV when barium was substituted for calcium. Cadmium (50 microM) but not nickel (50 microM) blocked the current. 3. A large calcium-activated anion current (IAn) was observed when the membrane potential was set to a level between -60 and 30 mV. The reversal potential of IAn was 0 mV with chloride as the sole anion and about -30 and -40 mV when methanesulfonate and D-aspartate, respectively, replaced intracellular chloride to set the equilibrium potential for chloride at -50 mV. IAn inactivated and oscillated when the membrane potential was maintained at depolarized levels, contrary to calcium-activated anionic currents seen in photoreceptors of other species. 4. A sustained-type potassium current was activated by depolarizations positive to -50 mV. The time course of activation and deactivation were voltage dependent. This potassium current was partially blocked by 20 mM tetraethylammonium ions. 5. A transient potassium current was activated by depolarizations positive to -20 mV. This current was blocked by 4-aminopyridine (2 mM) and inactivated with a time constant of approximately 500 ms. The amplitude in response to voltage steps to 45 mV was decreased by prepulses to voltages more positive than -30 mV. 6. Hyperpolarization negative to -65 mV activated an inward current that was completely blocked by external cesium (10 mM). The reversal potential suggested a conductance mechanism permeable to both sodium and potassium ions. 7. A calcium-activated potassium current, which was found in salamander photoreceptors, was not detected. 8. The presence of these conductances is expected to influence the membrane potential and the time course of the light response in monkey cones.
Processing of amplitude-modulated signals that mimic echoes from fluttering targets in the inferior colliculus of the little brown bat, Myotis lucifugus
Authors: Condon C. J. , White K. R. , Feng A. S.
Published: December 2017

1. Neurophysiological recordings were undertaken to determine how neurons in the central nucleus of the inferior colliculus (ICc) of the little brown bat, Myotis lucifugus, extract amplitude modulations that span across a series of tone pulses (i.e., signals that simulate echoes from fluttering targets). Two types of stimuli were presented to the bats. The first served as a control and consisted of an unmodulated train of tone pulses having different repetition rates (TPu, 5-400 pulses per second). The second was a train of tone pulses that were sinusoidally amplitude modulated (TPm, 5-110 Hz) across sequential pulses. The modulated trains of pulses were presented at five different repetition rates (25, 50, 100, 200, and 400 pulses per second) encompassing the range of biosonar emission rates in these bats at different stages of target-directed flight. 2. One hundred fifty-two single neurons were isolated in the ICc of M. lucifugus; their basic response properties and temporal firing patterns were characterized. The best frequencies (BFs) ranged from 10 to 80 kHz and the minimum thresholds at BF were distributed widely (10-95 dB SPL). The frequency tuning selectivity ranged widely, from very broadly tuned (Q10dB = 1.3) to narrowly tuned (Q10dB = 89). Units with very narrow frequency tuning (Q values > 20) were restricted to BFs of 30-50 kHz. The temporal firing pattern of ICc units could be categorized into primary-like (PL), chopper (C), onset-immediate (OI), and onset-late (OL). 3. In response to TPu ICc units exhibited varying degrees of response selectivities as evidenced by their count-based response functions (using the spike count as a measure) versus repetition rate. The count-based response functions of ICc units exhibited five filtering characteristics including band-pass, low-pass, high-pass, band-suppression, and all-pass characteristics. The temporal firing pattern of a unit showed certain correlations with its count-based response function. For example, the majority of OI and OL units, and about half of the C units, showed tuned band-pass response functions. The remaining C and onset types showed mostly low-pass response functions. In contrast, PL neurons showed mostly high-pass response functions, but one third displayed band-pass response functions. 4. The ability of ICc neurons to time-lock their discharges to the individual pulses in a train was characterized by using the synchronization coefficient (SC) as a measure. The SC was plotted against the repetition rate to construct units' synchronization-based response function.(ABSTRACT TRUNCATED AT 400 WORDS)
Defense reaction in the pond snail Planorbis corneus. III. Response to input from statocysts
Authors: Arshavsky Y. I. , Deliagina T. G. , Okshtein I. L. , Orlovsky G. N. , Panchin Y. V. , Popova L. B.
Published: December 2017

1. In the intact pond snail Planorbis corneus, a rapid tilt in any plane evoked a defense reaction consisting of a fast movement of the shell towards the head, shortening of the foot, inhibition of locomotion and of rhythmical feeding movements. This reaction was similar to the first phase of the general defense reaction of Planorbis to cutaneous stimulation. 2. A method has been developed for inclination of the isolated CNS in space (up to 90 degrees) and simultaneous intracellular recordings from different neurons. 3. The statocyst receptor cells (SRCs) responded both phasically and tonically to the tilt. The SRCs differ in their spatial zones of sensitivity. 4. Essential manifestations of the defense reaction to the input from statocysts could be observed in the in vitro preparation of the CNS isolated with statocysts. Both tilting of the CNS and electrical stimulation of individual SRCs elicited an excitatory response in numerous neurons from different ganglia, including motor neurons (MNs) of the columellar muscle. This response was of "all-or-none" nature, and could be evoked by electrical stimulation of any SRC. The response was followed by a long (10-20 s) period of refractoriness. 5. Activation of SRCs resulted also in excitation of the giant dopaminergic cell in the left pedal ganglion (related to the control of respiration), in inhibition of the feeding rhythm generator, and in inhibition of the pedal neurons responsible for activation of the ciliary locomotor system. 6. Combined stimulation of two inputs able to evoke a defense reaction, i.e., those from the statocyst and from cutaneous nerve, revealed a strong interdependence of their central effects.(ABSTRACT TRUNCATED AT 250 WORDS)
The regulation of chloride homeostasis in the small nonspiking visual interneurons of the fly compound eye
Authors: Uusitalo R. O. , Weckstrom M.
Published: December 2017

1. We have used intracellular recordings and ionophoretic injections in vivo to investigate the ion exchange mechanisms responsible for the maintenance of the ion gradients in the large monopolar cells (LMCs) of the first optic ganglion of the blowfly, Calliphora vicinia. 2. Ionophoretic chloride injections caused a rapid approximately 20-mV depolarization of the resting potential (Erp) and abolished or even reversed the light-ON response (OR), which is caused by histamine-gated chloride conductance, as the chloride equilibrium potential (ECl) was increased beyond the Erp, i.e., 50 mV upward. Ionophoretic sodium injections were found to mimic the action of the ionophoretic chloride injections and thus also to cause chloride accumulation inside the cell. 3. Ionophoretic injections of bicarbonate only had the effect of hyperpolarizing the Erp by 5-15 mV for 1-25 s, but chloride gradient, i.e., ECl remained unchanged. Intracellular proton load caused depolarization of the Erp by 15 +/- 5 mV (mean +/- SE) for 20-25 s and a slight 15 +/- 5-mV decrease of the peak OR. Ionophoretic injections of potassium, acetate, and furosemide failed to cause any physiological effect. 4. The time constant for the recovery of the peak OR after sodium load increased linearly as a function of injected charge whereby the time constant for the recovery after chloride accumulation increased slowly up to 50 nC of injected charge, after which it increased rapidly, possibly indicating substrate inhibition. The time constant for the recovery of peak OR after sodium load was from 5 to 65 nC greater than that of chloride.(ABSTRACT TRUNCATED AT 250 WORDS)
Mammalian voltage-activated calcium channel currents are blocked by Pb2+, Zn2+, and Al3+
Authors: Busselberg D. , Platt B. , Michael D. , Carpenter D. O. , Haas H. L.
Published: December 2017

1. The effects of the di- and trivalent trace metal cations, Pb2+, Zn2+, and Al3+, on voltage-activated calcium channel currents recorded from cultured rat dorsal root ganglion neurons were determined. 2. All three cations blocked transient and sustained components of the voltage-gated calcium channel currents elicited by a voltage jump from -80 mV to 0 mV, but the trace metals differed in threshold, reversibility, and specificity, and in actions on the different components. 3. Pb2+ was most effective in reducing the voltage-activated calcium channel currents. Threshold concentration for Pb2+ was < 0.1 microM. The threshold for Zn2+ action was < 5 microM and that for Al3+ was approximately 20 microM. Total blockade (> 80%) was obtained with concentrations > 1 microM Pb2+, and 150-200 microM Zn2+ or Al3+. Half of the current was blocked with 0.6 microM Pb2+, 69 microM Zn2+, and 84 microM Al3+. The Hill slope for Pb2+ and Zn2+ action was approximately 1, whereas for Al3+ it was close to 3. 4. Al3+ blockade was clearly use dependent, whereas this was not the case for either Pb2+ or Zn2+. 5. The blockade by none of these metals was totally reversible. The best recovery was obtained upon wash after exposure to Pb2+ (> or = 60%), some recovery was seen with Zn2+ (> or = 50%), but there was little or no recovery after application of Al3+. 6. With Zn2+ or Al3+ in the external solution the current-voltage relation often shifted to depolarized voltages.(ABSTRACT TRUNCATED AT 250 WORDS)
Muscle activation patterns for reaching: the representation of distance and time
Authors: Buneo C. A. , Soechting J. F. , Flanders M.
Published: December 2017

1. The timing and intensity of phasic muscle activation were related to the distance of reaching movements of the human arm. We dissociated phasic components of muscle activation from complete muscle activation waveforms by subtracting waveforms obtained during very slow movements. 2. We recorded electromyographic (EMG) activity from elbow and/or shoulder muscles as standing subjects reached forward and upward to targets at four distances. Accuracy was deemphasized and no terminal corrections were allowed. In the first part of the experiment subjects were asked to move at their preferred speed. In the second part of the experiment they were asked to move using a range of speeds. 3. In the first part of the experiment subjects moved faster to more distant targets but they also increased movement time as a nearly linear function of target distance. The slope of this function was very similar across subjects. The phasic EMG waveforms for different distances appeared to be similar in shape but of variable duration. EMG time base was quantified using a correlation technique that identified the time base scale factor that best superimposed a given trace with a template. This technique revealed that the slope of the relation between EMG time base and target distance was not the same for all muscles. 4. In the second part of the experiment, where subjects moved to each target at a range of specified speeds, time base scaling was again significantly different for different muscles. The scaling differed most dramatically between anterior deltoid and medial head of triceps. 5. EMG intensity was more strongly related to movement time than to distance. We quantified the correspondence of distance and movement time to phasic EMG intensity using a multiple regression analysis of all distances and speeds, assuming a power relation. Distance exponents were positive and movement time exponents were larger and negative. This implies that movement time is more important than distance in its relation to EMG intensity.
Motion sensitivity in the nucleus of the basal optic root of the pigeon
Authors: Wolf-Oberhollenzer F. , Kirschfeld K.
Published: December 2017

1. Single-unit responses to large-field movement (angular velocity, w = 0.25-42 degrees/s) of sine-wave gratings of different spatial wavelength (lambda = 5.2-41 degrees) and contrast have been recorded in the nucleus of the basal optic root (nBOR) of the accessory optic system (AOS) of the pigeon. 2. The steady-state response to moving sine-wave gratings increases with increasing contrast to reach a saturation level at 25%. 3. Generally the steady-state responses of the cells passed through a maximum when stimulated at various velocities. In 12 of the 15 cells tested with six different velocities and four different spatial wavelengths, the location of the response maximum on the velocity scale depended on the spatial wavelength (lambda) used. That is, in these cells the response depends on the temporal frequency (tf = w/lambda) of the stimulus and not on its velocity alone. This is in agreement with the prediction of the theory of motion detection according to the basic version of the correlation scheme. 4. The temporal frequency for maximal response of individual cells shifts to higher values when the contrast of the sine-wave gratings is reduced to 5%. 5. The steady-state response of 16 of the recorded directional selective cells (53) is modulated with the temporal frequency of the stimulus, regardless of the phase of the grating at the beginning of its movement. 6. In phasic-tonically responding cells, the phasic response peak decays to the steady-state level with a time constant that becomes shorter as the temporal frequency of the stimulus increases. 7. The basic version of the correlation scheme includes only the time constant of one low-pass filter. Therefore the phasic response is expected to decay to the steady-state level with one and the same time constant, and the position of the maximal response on the temporal frequency scale should not be influenced by a change of pattern contrast. According to the model, phase-dependent modulations of the steady-state response should occur only when the spatial wavelength of the stimulus pattern is large compared with the sampling base of the underlying detector. Consequently the results given in points 4-6 cannot be described by a basic version of the correlation scheme.
Modeling three-dimensional velocity-to-position transformation in oculomotor control
Authors: Schnabolk C. , Raphan T.
Published: December 2017

Pages 623–638: C. Schnabolk and T. Raphan, “Modeling three-dimensional velocity-to-position transformation in oculomotor control.” Page 629, matrix Gp of Equation 44 should read:

See PDF for Equation
Responses of macaque STS neurons to optic flow components: a comparison of areas MT and MST
Authors: Lagae L. , Maes H. , Raiguel S. , Xiao D. K. , Orban G. A.
Published: December 2017

1. We recorded and tested quantitatively 65 middle temporal (MT) and 82 middle superior temporal (MST) cells in paralyzed and anesthetized monkeys. 2. Responses to the three elementary optic flow components (EFCs)--rotation, deformation, and expansion/contraction--and to translation (in the display) were compared after optimization of stimulus direction, speed, size, and position. As a control responses to flicker were measured. 3. Response windows were adapted in correspondence with our finding that latencies of MT and MST cells decrease with increasing speed for all types of motion. 4. There was a response continuum in MT as well as in MST cells. Compared with translation, MST cells responded significantly more to rotation but less to flicker than MT cells. MST cells were significantly more direction selective for expansion/contraction than MT cells. 5. MST cells generally responded to fewer motion types than MT cells. 6. Position invariance of EFC direction selectivity was tested over a region of the visual field centered on the translation receptive field (RF). Direction selectivity for an EFC was not position invariant in MT cells but it was invariant in 40% of the MST cells tested. These cells were considered EFC selective. 7. Most EFC-selective MST cells were selective for a single EFC, possibly combined with translation. Few of them were selective for deformation. 8. EFC selectivity was also speed invariant and EFC-selective MST cells usually had RFs summating inputs over wide portions of the visual field. 9. EFC-selective MST cells with similar selectivities were clustered.
Modulation of transient outward potassium current by GTP, calcium, and glutamate in horizontal cells of the Xenopus retina
Authors: Akopian A. , Witkovsky P.
Published: December 2017

1. Membrane currents of luminosity horizontal cells (L-HCs) and chromatic horizontal cells (C-HCs) isolated from the Xenopus retina were characterized using the whole-cell patch-clamp technique. 2. The current-voltage curve for the L-HC had a characteristic negative slope conductance in the voltage range of -30 to -10 mV that was not evident in the C-HC. 3. A transient outward 4-aminopyridine-sensitive potassium current (A-current) was the most prominent current in C-HCs but was also present in L-HCs. A-current characteristics in the two horizontal cell (HC) classes were closely similar. Its threshold of activation was above -45 mV. The half-voltage of inactivation was close to -70 mV. The decay of the A-current was fit by a single exponential with time constants of 30 and 40 ms at depolarizing voltage steps to -10 and +30 mV, respectively. 4. The voltage for 50% A-current inactivation shifted toward negative potentials shortly after we established the whole-cell configuration. This shift was changed to more positive potentials by internal application of guanosine 5'-triphosphate, resulting in a significant overlap of A-current activation and inactivation functions near -40 mV, which is well within the normal operating range of the HC. 5. Internal application of the G-protein activator GTP gamma S shifted the voltage-dependent inactivation of the A-current toward positive potentials by +15 mV. In contrast, GDP beta S shifted the inactivation curve by about -10 mV, similar to what was observed in untreated cells. 6. GTP and GTP gamma S increased the rate of recovery from inactivation and slowed down the rate of inactivation of the A-current enabled by a depolarizing prepulse. 7. Glutamate superfused in the bath solution significantly accelerated the rate of inactivation of A-current induced by depolarizing prepulses. The rate of A-current recovery from inactivation, however, was not affected by glutamate. 8. Removal of calcium from the bath solution reversibly decreased the amplitude of the A-current without a significant shift in its threshold of activation.
Gustatory neural coding in the monkey cortex: the quality of saltiness
Authors: Scott T. R. , Plata-Salaman C. R. , Smith-Swintosky V. L.
Published: December 2017

1. We analyzed the activity of single neurons in the insularopercular cortex of four alert cynomolgus monkeys in response to the oral application of four basic taste stimuli (glucose, NaCl, HCl, and quinine HCl) and fruit juice and to a range of 17 sodium and lithium salts with a variety of anions. 2. Neurons responsive to gustatory stimulation were encountered in an area of 34.5 mm3 (2.0 mm A-P x 2.5 mm M-L x 6.9 mm D-V). Taste cells composed 46 (4.5%) of the 1,028 neurons whose sensitivities were tested. Nongustatory cells included those responsive to mouth movements (20.4%), tactile stimulation in the mouth (3.4%), and visual approach of the stimulus (0.7%). The functions of the remaining 71.0% could not be determined. 3. The mean spontaneous discharge rate of these cortical taste cells was 4.4 spikes/s (range, 0.1–23.8 spikes/s). The mean breadth-of-tuning coefficient was a moderate 0.72 (range, 0.15–1.00). Inhibitory responses were nearly nonexistent. 4. There was no evidence that taste cells with similar functional characteristics were clustered within the cortex, i.e., there was no apparent topographic organization of taste qualities. 5. The 46 taste cells were divisible into three functional types, based on their response profiles to the four basic stimuli used here. The types could be characterized as sweet-, salt-, and quinine-oriented. 6. A taste space was generated from correlations among the response profiles evoked by the stimulus array. The 17 salts formed a coherent group from which the other basic stimuli were separated. Glucose was closest to the salt group, followed by quinine and HCl. 7. Within the salt group, the four halides (NaCl, LiCl, NaBr, LiBr) formed a tight cluster; the 11 stimuli with acetate, citrate, phosphate, sulfate, and tartrate anions joined with monosodium glutamate and Na bicarbonate to form two closely related clusters; Na succinate was somewhat distinct from the others, and Na carbonate was most separate. 8. The relative qualities of the salts did not relate systematically to anionic size, promotion of sodium transport, or molar conductivity. 9. The configuration of stimuli in this taste space was compared with that in a space derived from human descriptions of the relative similarities of many of these same stimuli. Using the position of NaCl as a reference, the distances to all other stimuli common to the two studies was measured.(ABSTRACT TRUNCATED AT 400 WORDS)
The role of GABA-mediated inhibition in the rat ventral posterior medial thalamus. II. Differential effects of GABAA and GABAB receptor antagonists on responses of VPM neurons
Authors: Lee S. M. , Friedberg M. H. , Ebner F. F.
Published: December 2017

1. Changes in the response properties of 106 ventral posterior medial (VPM) units were assessed after iontophoretic blockade of gamma-aminobutyric acid-A or -B (GABAA or GABAB) receptor-mediated inhibition using bicuculline methiodide (BIC) or 2-hydroxy-saclofen (2-OH-S), respectively. 2. The iontophoretic administration of either BIC or 2-OH-S did not alter significantly the average spontaneous firing rate of VPM neurons for current intensities between 40 and 80 nA. The presence of 10 mM 2-OH-S (60 nA) was effective in completely reversing the depressant effects of the selective GABAB receptor agonist, baclofen, on the spontaneous activity of VPM neurons. 3. The effect of BIC on whisker-evoked responses was a preferential enhancement in the responses elicited by the whisker giving rise to the highest probability response (center receptive field whisker or CRF). The effect of 2-OH-S (40-80 nA iontophoretic currents) was to increase the responsiveness of VPM neurons to the stimulation of whiskers in all parts of the receptive field (RF), although its influence was much more pronounced in the peripheral areas of the RF (surround receptive field whisker or SRF). This preferential enhancement of SRF-whisker responses after the blockade of GABAB receptor-mediated inhibition resulted in a 2.3-fold increase in the average RF size of VPM neurons; no statistically significant increases in the size of the RF were seen in the presence of BIC. 4. The primary influence of BIC and, to a lesser degree, 2-OH-S was to prolong the response duration of VPM neurons to CRF whisker stimulation. Under our recording conditions, approximately 25% of VPM neurons in normal animals responded with sustained discharges. In the presence of BIC and 2-OH-S, the percent of VPM units that could be classified as tonically responding increased to 82% and 67%, respectively. 5. The proportion of VPM neurons that was selective to the deflection of whiskers in a particular direction (87%) was not altered in the presence of BIC or 2-OH-S. 6. BIC was effective in antagonizing GABA-mediated inhibition within the first 40 ms of a stimulus; BIC was completely ineffective in reversing a late suppression seen between 80 and 140 ms. In contrast, no statistically significant changes in the initial GABA-mediated inhibition were seen in the presence of 2-OH-S, but 2-OH-S was partially effective in antagonizing the late suppression of responses in VPM neurons.(ABSTRACT TRUNCATED AT 400 WORDS)
Computer simulations of the effects of different synaptic input systems on the steady-state input-output structure of the motoneuron pool
Authors: Heckman C. J.
Published: December 2017

1. The effects of different types of synaptic input on the steady-state input-output relations of the mammalian motoneuron pool were investigated by the use of computer simulations. The properties of the simulated motor units and their synaptic inputs were based as closely as possible on the experimental data from studies in the cat hindlimb. 2. Three basic types of synaptic input systems were simulated: postsynaptic, presynaptic, and neuromodulatory. The effects of these inputs on three aspects of the system input-output structure were studied: gain, precision, and motor-unit type utilization. 3. The gain analyses were based on a simulation of the steady-state homonymous Ia input. The gain of this steady-state Ia “reflex” was found to be determined largely by the slope of the pool input-output function. Precision was evaluated in two ways, from the amplitudes of the quantal steps due to motor-unit recruitment and from the sensitivity of the input-output function to noise. The pattern of motor-unit type utilization allowed indirect assessment of fatigue resistance: the larger the percentage of force generated by FF units, the lower the fatigue resistance. 4. A uniformly distributed input (i.e., one that generates equal input in all motoneurons) generates outputs that are solely determined by the intrinsic properties of the motor units. Thus the gain, precision, and motor-unit type patterns generated by a uniform input were used as the basis with which the effects of all other input systems were compared. 5. Postsynaptic excitatory inputs with nonuniform distributions within the pool did influence gain. The greatest effect was the increase mediated by the rubrospinal excitatory input (27% increase at 30% of maximal force). However, this input also greatly decreased both fatigue resistance and precision, due to increased activation of FF units at low force levels. In contrast, the Ia input slightly decreased gain (12% decrease at 30% of maximum force) while slightly increasing fatigue resistance and precision. 6. The simulated neuromodulatory input was based on the monoaminergic reticulospinal effect on motoneurons. Gain was generally increased by the monoaminergic input. However, the magnitude of the increase strongly depended on whether the monoaminergic effects were largest on S units (giving a 20% increase at 30% of maximum force), equal on all types (52%), or largest on FF units (102%). Presynaptic inhibition reduced gain with no effect whatsoever on fatigue resistance or precision. 7. Therefore Ia reflex gain was modifiable by all three types of input: postsynaptic, presynaptic, and neuromodulatory.(ABSTRACT TRUNCATED AT 400 WORDS)
A novel long-latency response of locus coeruleus neurons to noxious stimuli: mediation by peripheral C-fibers
Authors: Hirata H. , Aston-Jones G.
Published: December 2017

1. Extracellular recordings were obtained from single presumed noradrenergic neurons in the nucleus locus coeruleus (LC) in response to percutaneous electrical foot shock (FS) stimulation in the rat. We employed long-duration stimulus pulses to examine the possible contribution of peripheral C-fibers to evoked activity in LC. 2. As in previous studies, 0.5-ms FS stimuli produced a short-latency excitatory response (onset 20.8 ms) followed by a prolonged postactivation inhibition. However, 2.0- or 5.0-ms FS stimuli yielded an additional late excitatory response. 3. The onset and termination latency of this late excitatory response were approximately 200 and 400 ms, respectively, after the FS. The conduction velocity for this late response (peripheral plus central pathway) was estimated to be < 1.2 m/s. 4. The percentages of LC neurons that exhibited a significant late response was 4% (3/85) with 0.5-ms stimuli, 53% (31/59) with 2.0-ms stimuli, and 73% (47/64) with 5.0-ms FS stimuli. 5. The average number of spikes evoked per FS stimulus (presented at 0.5 Hz) increased from the 1st to the 21st FS stimulus. This increased response occurred selectively in the late, not in the early, response. This result was interpreted to represent a “windup” phenomenon reflected at the level of LC. 6. Direct application of capsaicin onto the sciatic nerve reduced the average magnitude of the late response of LC neurons to 17% of control 42.5 min after application. The magnitude of the short-latency response components showed little or no change. 7. Averaged compound action potential (cAP) recordings from the sciatic nerve revealed that C-fiber responses were more consistently observed and much larger with 5.0-ms compared with 0.5-ms FS stimuli. 8. C-fiber cAPs were reduced or eliminated after application of capsaicin distal to the recording site with a time course similar to that of the late response of LC neurons, with little or no effect on A-fiber cAPs. 9. These data show that a previously undescribed long-latency response of LC neurons to noxious FS stimulation in rat results from C-fiber activation in the sciatic nerve. This late response may be involved in generating descending noradrenergic analgesia induced by electrical stimulation of the foot pad or other body regions. Future studies of the pharmacology of this late response to noxious stimuli in LC may aid in developing new therapies for the treatment of acute or chronic pain.
Antidromic responses of single units from the spiral ganglion
Authors: Brown M. C.
Published: December 2017

1. Antidromic responses of single units in the guinea pig spiral ganglion were recorded in response to shocks to the auditory nerve root. The orthodromic responses of these units were also recorded in response to sound. The aim of this study was 1) to classify units according to their response patterns to shocks and to sound and 2) to propose anatomic types that might correlate with these responses. The four classes of units were as follows: type I, olivocochlear (OC), long-latency: locked, and long-latency: jittering. 2. Type I units responded antidromically to shocks with little jitter and short latency. Their responses to sound were also of short latency and had irregular interspike intervals. Some of these units had complex spike waveforms. These units likely correspond to type I primary afferent neurons, the majority population of spiral ganglion cells. 3. One-third of the OC units responded to shocks, with little jitter and intermediate latency (2 ms). OC unit responses to sound were of long latency and had regular interspike intervals. These units likely correspond to efferent neurons that originate in the superior olivary complex of the brain and end on outer hair cells in the cochlea. 4. Long-latency: locked units responded to shocks with little jitter and long latency (4–11 ms). Many of these units had complex spike waveforms and most did not respond to high-level noise bursts. Long-latency: locked units may correspond to type II spiral ganglion neurons. 5. Long-latency: jittering units responded to shocks with a jitter of several milliseconds and long latency. Some of these units responded to sound in a pattern reminiscent of OC units. These units may constitute a subgroup of OC units that respond to shocks via activation of the reflex pathway from the cochlea to the superior olive and back out to the cochlea. 6. Further data were collected on the type I response to shocks. Antidromic spikes lacked the inflections seen on the waveforms that are typically seen on orthodromic spikes. Type I shock responses depended on shock level and duration and were reduced when a click preceded the shock by approximately 2 ms. Several type I characteristics depended on the rate of spontaneous discharge: for units of low and medium spontaneous rates (when compared with units of high rates), the shock thresholds were lower, shock latencies were longer, and the probability of firing repetitive spikes to a single shock was higher.(ABSTRACT TRUNCATED AT 400 WORDS)
Proprioceptive coordination of movement sequences: role of velocity and position information
Authors: Cordo P. , Carlton L. , Bevan L. , Carlton M. , Kerr G. K.
Published: December 2017

1. Recent studies have shown that the CNS uses proprioceptive information to coordinate multijoint movement sequences; proprioceptive input related to the kinematics of one joint rotation in a movement sequence can be used to trigger a subsequent joint rotation. In this paper we adopt a broad definition of “proprioception,” which includes all somatosensory information related to joint posture and kinematics. This paper addresses how the CNS uses proprioceptive information related to the velocity and position of joints to coordinate multijoint movement sequences. 2. Normal human subjects sat at an experimental apparatus and performed a movement sequence with the right arm without visual feedback. The apparatus passively rotated the right elbow horizontally in the extension direction with either a constant velocity trajectory or an unpredictable velocity trajectory. The subjects' task was to open briskly the right hand when the elbow passed through a prescribed target position, similar to backhand throwing in the horizontal plane. The randomization of elbow velocities and the absence of visual information was used to discourage subjects from using any information other than proprioceptive input to perform the task. 3. Our results indicate that the CNS is able to extract the necessary kinematic information from proprioceptive input to trigger the hand opening at the correct elbow position. We estimated the minimal sensory conduction and processing delay to be 150 ms, and on the basis of this estimate, we predicted the expected performance with different degrees of reduced proprioceptive information. These predictions were compared with the subjects' actual performances, revealing that the CNS was using proprioceptive input related to joint velocity in this motor task. To determine whether position information was also being used, we examined the subjects' performances with unpredictable velocity trajectories. The results from experiments with unpredictable velocity trajectories indicate that the CNS extracts proprioceptive information related to both the velocity and the angular position of the joint to trigger the hand movement in this movement sequence. 4. To determine the generality of proprioceptive triggering in movement sequences, we estimated the minimal movement duration with which proprioceptive information can be used as well as the amount of learning required to use proprioceptive input to perform the task. The temporal limits for proprioceptive processing in this movement task were established by determining the minimal movement time during which the task could be performed.(ABSTRACT TRUNCATED AT 400 WORDS)
Influence of stimulus level on acoustic motion-direction sensitivity in barn owl midbrain neurons
Authors: Wagner H. , Trinath T. , Kautz D.
Published: December 2017

1. Many neurons in the owl's midbrain are able to discriminate by their responses the motion of an acoustic source in one direction, the preferred direction, from the motion of the source in the opposite direction, the null direction. This differential response can be understood by the action of an acoustic motion detector. However, the motion detector would work in an effective way only if the motion direction-sensitive responses of a cell were largely independent of stimulus level. 2. We investigated the level dependence of acoustic motion sensitivity in midbrain neurons with standard extracellular recording techniques. We used an apparent motion paradigm with sounds moving clockwise or counterclockwise in the horizontal plane or stationary sounds for stimulation from free-field speakers. In most cases we added a constant level of background noise to the stimuli having a variable level. Thus we could analyze the responses as a function of the signal-to-noise ratio. 3. Moving and stationary sounds yielded similar response thresholds and similar dynamic ranges. 4. When the background level was changed the response threshold changed accordingly, so that the response threshold always occurred at a constant signal-to-noise ratio independent of background level. 5. The preferred direction of all cells was independent of stimulus level and some 22 percent of the cells showed a directional bias of their response at threshold. In no cell was a change in the preferred direction observed when stimulus level was varied. Typically, however, the motion direction sensitivity, measured by a signed directionality index, was not maximal at threshold. However, the dynamic range, i.e., the range of stimulus levels over which motion direction sensitivity changed, was < or = 20 dB in most cases. Therefore these cells are indeed able to encode motion direction largely independently of stimulus level. 6. We discuss the data within the framework of the acoustic motion detector mentioned above and with respect to earlier reports on acoustic motion sensitivity in the owl and other animals.
Electrotonic profiles of interneurons in stratum pyramidale of the CA1 region of rat hippocampus
Authors: Thurbon D. , Field A. , Redman S.
Published: December 2017

1. Whole-cell recordings have been made from interneurons located in stratum pyramidale in the CA1 region of the hippocampus. The responses of these interneurons to brief current pulses were recorded; the neurons were filled with biocytin and their morphology was reconstructed. 2. The interneurons were identified as basket cells on the basis of the regional distribution of their axon collateral network and their location in stratum pyramidale. 3. A compartmental model of the reconstructed neuron was made, and the specific membrane resistivity (Rm), specific cytoplasmic resistivity (Ri), and somatic shunt leakage resistance (Rs) determined by adjusting these parameters until an optimal fit was obtained between the compartmental model's current pulse response and the recorded current pulse response of the neuron. 4. This procedure was successful for six neurons, giving Rm from 7 to 66 k omega cm2, Ri from 52 to 484 omega cm, and Rs from 84 M omega to infinity. The specific membrane capacitance was assumed to be 1 microF/cm2. The electrotonic length of the apical dendrites was 1.06 +/- 0.4, and for the basal dendrites it was 0.51 +/- 0.26 (mean +/- SD). 5. Although the total surface area of the interneurons and the physical length of their dendrites was much smaller than for CA1 pyramidal neurons, their electrotonic profiles were similar. Neurons with small physical profiles cannot be assumed to be more electrotonically compact than larger neurons, especially if the dendrites of the smaller neurons have a proportional reduction in diameter. 6. Two neurons did not require a somatic leakage conductance in their electrical representation. This suggests that when a somatic leakage conductance is required, it is an artifact resulting from electrode damage, rather than a requirement caused by a lower resistivity of the somatic membrane compared with the dendritic membrane. 7. Simulations of synaptic currents evoked in the dendrites of these interneurons while the soma is voltage clamped indicate large errors will occur in the time course measurements and amplitude of these currents. Also the ratio of N-methyl-D-aspartate:alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (NMDA:AMPA) currents at these synapses calculated from currents recorded at the soma will be in error because of the differential attenuation of the faster AMPA currents compared with the NMDA currents.
Saccadic burst neurons in the fastigial nucleus are not involved in compensating for orbital nonlinearities
Authors: Ohtsuka K. , Sato H. , Noda H.
Published: December 2017

1. To test whether the cerebellum is involved in compensating for orbital nonlinearities, we recorded discharges of saccadic burst neurons in the fastigial oculomotor region (FOR) during both centrifugal and centripetal saccades in two trained macaque monkeys. 2. We also investigated the metrics of centrifugal and centripetal saccades with the same amplitude while output signals from the fastigial nucleus were blocked by muscimol, an agonist of inhibitory neurotransmitter gamma-aminobutyric acid (GABA), injected into the FOR. 3. We studied discharges of 32 fastigial neurons that were inhibited by microstimulation of the oculomotor vermis. These neurons exhibited unique burst responses during contralaterally and ipsilaterally directed saccades, as shown in our previous report. The discharge pattern, the peak burst frequency, the burst lead time, and the burst duration were consistent, regardless of initial eye position. 4. The muscimol injection produced hypermetric saccades toward the injection side and hypometric saccades to the opposite side, regardless of whether saccade was centripetally or centrifugally directed. 5. These findings suggest that the FOR is not involved in the compensation of saccade metrics for orbital nonlinearities.
Stance control in the chronic spinal cat
Authors: Pratt C. A. , Fung J. , Macpherson J. M.
Published: December 2017

1. A longitudinal study of the control of quiet and perturbed stance was conducted before and for 1 yr after complete spinal transection (T12) in a cat trained to stand on a moveable force platform. 2. With daily training, the spinal cat recovered full weight support and some intermittent control of lateral stability within 1 mo. Within the second month postspinalization, the spinal cat achieved the ability to maintain independent, unassisted stance (no external support or stimulation) for up to 45 s during quiet stance, as well as for 62–97% of the trials of horizontal translations of the support surface. 3. Control of lateral stability in the spinal cat was severely compromised, however, as eventually the spinal cat always lost its balance. Head movements and the tendency for the hindlimbs to initiate stepping movements were more destabilizing than platform translations. 4. Our preliminary results indicate that the recovery of partial lateral stability of the hindquarters in the spinal cat is the product of passive muscle properties and segmental reflexes, which, in isolation can provide only limited balance control in the chronic spinal cat.
Differences in voltage-dependent sodium currents exhibited by superficial and deep layer neurons of guinea pig entorhinal cortex
Authors: Fan S. , Stewart M. , Wong R. K.
Published: December 2017

1. Sodium currents were studied using whole-cell voltage-clamp techniques in neurons acutely isolated from superficial (II/III) and deep (V/VI) layers of guinea pig entorhinal cortex. 2. Sodium currents were larger (peak amplitude) in superficial than in deep layer cells under the same conditions: -1939 +/- 780 (SD) pA (N = 6) versus -307 +/- 257 pA (N = 6). Specific membrane conductance was calculated to be 12.3 +/- 9.6 mS/cm2 for superficial layer cells and 1.4 +/- 0.9 mS/cm2 for deep layer cells. 3. Sodium currents could be activated in superficial layer cells from potentials as depolarized as -20 mV, whereas no significant currents could be activated in deep neurons from potentials more depolarized than about -50 mV. Using a protocol consisting of a 25-ms prepulse and a 20 ms test pulse, the inactivation curves for superficial layer cells were found to be shifted toward more depolarized potentials by an average of 15 mV (V50 = -59.8 +/- 3.8 mV compared with -75.7 +/- 12.0 mV for deep cells). This produced a region of overlap with the activation curves for superficial cells. 4. Over a range of about -50 to -20 mV in superficial layer cells, the region of overlap of the activation and inactivation curves, a sodium current could be activated, which did not fully inactivate during the test pulse (average peak amplitude: -89.5 +/- 48.7 pA; crossover voltage: -39.2 +/- 2.0 mV). Voltage steps to more depolarized potentials, outside the voltage “window”, permitted complete inactivation of the sodium current.(ABSTRACT TRUNCATED AT 250 WORDS)