bluuebunny/crossref_metadata_2025 huggingface dataset:
Physiological properties of motoneurons innervating different muscle unit types in rat gastrocnemius
Authors: Gardiner P. F.
Published: December 2017

1. The contractile properties of gastrocnemius muscle units and the electrophysiological properties of their innervating motoneurons were examined in anesthetized adult male Sprague-Dawley rats in situ, using conventional microelectrode techniques. 2. Muscle units (n = 70) were classified as fast (F) or slow (S) on the basis of the degree of force summation during stimulation at 25 Hz, as well as fatigue resistance, in response to current injection into innervating motoneurons. S units categorized using these criteria were also found to invariably demonstrate twitch half-relaxation times (RT1/2) > 28 ms, with F units demonstrating RT1/2 < 27 ms. Some overlap was present between F and S units in twitch time-to-peck tension (TPT). 3. S muscle units were innervated by motoneurons with significantly higher afterhyperpolarization (AHP) times-to-peak and half-decay times, AHP amplitudes, and input resistances than F units. Motoneurons innervating S units also demonstrated slower mean axon conduction velocity than F units. 4. F units were further classified as fast fatiguing (FF), fast fatigue-resistant (FR), or fast intermediate (FI) on the basis of their fatigue resistance. Muscle unit forces were different among the unit types such that FF > FI > FR > S. Twitch TPT and RT1/2 differed such that FF < FI, FR < S. 5. No differences among FF, FI, and FR units were found for measures of AHP time course, AHP amplitude, rheobase, or input resistance. The only motoneuron property that differed among F unit types was axon conduction velocity, which was lower for FF than for FI and FR units. 6. The best relationships between muscle unit and motoneuron physiological properties were between expression of twitch time course, which included RT1/2 and AHP half-decay time (r = 0.73 to 0.74). S units always had AHP half-decay times > 20 ms, whereas for F units, values never exceeded 19 ms. Correlations between these variables increased when only S units were considered (r = 0.86-0.97), and were weak and not significant among F units only. 7. The only other significant correlations between muscle unit and motoneuron properties > 0.5 were between input resistance and expressions of twitch time course (r = 0.56-0.66). These relationships were nonexistent when type S units were not included in the analysis. 8. A sample of tibial motoneurons (n = 98) that innervated hindlimb muscles other than gastrocnemius was combined with the gastrocnemius motoneurons to examine interrelationships among motoneuron properties.(ABSTRACT TRUNCATED AT 400 WORDS)
Coincidence detection by binaural neurons in the chick brain stem
Authors: Joseph A. W. , Hyson R. L.
Published: December 2017

1. Neurons in nucleus laminaris (NL) of birds are the first to receive binaural information and are presumed to play a role in encoding interaural time differences (ITDs). We studied extracellular single-unit responses of NL neurons in slices of the auditory brain stem of the chick. The afferents to NL were activated by electrical stimulation of nucleus magnocellularis (NM) or the auditory nerve. Changes in responses were measured as the delay between trains of bilateral stimuli (the simulated interaural time difference or S-ITD, n = 26) was varied and as the interstimulus interval and stimulus amplitude were varied (n = 61). 2. The probability of an action potential and the action-potential latency varied as a function of interstimulus interval. Most NL neurons showed a greater response probability and a shorter response latency to an interstimulus interval between 2.5 and 3.5 ms. The interstimulus interval that produced the minimum response latency was slightly longer than the interval that produced the maximum response probability. In contrast, NM neurons (n = 4) showed no preferred rate, instead, the probability of firing increased as the interstimulus interval increased. 3. Responses to bilateral stimulation showed that NL neurons can act as coincidence detectors. NL neurons responded most reliably when activated simultaneously by their two inputs and, at favorable S-ITDs, two subthreshold inputs combined to produce an action potential. 4. NL neurons also exhibited inhibition during bilateral stimulation. At unfavorable S-ITDs a subthreshold input combined with a suprathreshold input produced fewer action potentials than evoked by the suprathreshold input alone. 5. The latency of the bilateral response varied as a function of S-ITD. At S-ITDs near coincidence the latency of the bilateral response was shorter than the latency of either of the unilateral responses. Away from coincidence, the latency of the bilateral response was largely determined by the latency of the stronger unilateral response. When the unilateral responses were of similar strength, the earlier stimulus determined the latency of the bilateral response. 6. The range of S-ITDs producing a maximal response varied as a function of stimulus strength but was never less than approximately 300 microseconds. This is greater than the maximum possible ITD of sound calculated for the chick's head size. From these data we hypothesize that, in the chick, single units cannot uniquely encode ITDs, but rather ITDs may be coded by the proportion of maximally firing cells along an isofrequency band in NL.
Spontaneous burst firing in cat primary auditory cortex: age and depth dependence and its effect on neural interaction measures
Authors: Eggermont J. J. , Smith G. M. , Bowman D.
Published: December 2017

1. Neural activity was recorded with two independent electrodes separated by 0.5-2 mm, aligned in parallel, and advanced perpendicular to the surface of the cat auditory cortex. Because the experiments were part of a study into laminar interaction the difference in recording depths for the two independently movable electrodes was never > 100 microns. Multi-unit activity on each electrode was separated on-line into single-unit spike-trains with a maximum variance spike sorting algorithm. Off-line controls on the quality of the spike-train separation were routinely performed. The first aim of this study was to describe the age dependence of spontaneous burst firing and to explore if and how it could be explained by age dependent changes in firing rate. The second aim was to investigate a potential layer dependence on burst firing. The third aim was to describe the effect of burst-removal procedures on the shape, strength, and width of the cross-correlogram and to investigate whether an age dependence in burst firing might account for the previously reported age dependence in correlation strengths. 2. Recordings were made from 237 single units from primary auditory cortex in nine adult cats and from 67 units in seven kittens age 10-52 days. The incidence of burst firing as a function of firing rate, age and depth of recording and unit characteristic frequency was investigated. In addition the effect of burst firing on the strength and width of the central peak in 471 neural pair correlograms was analyzed. 3. Burst firing could be distinguished at many different time scales; bursts lasting of the order of 10 s contained bursts with durations of the order of 1 s, which in turn contained bursts of 30-50-ms duration. The analysis in this paper was restricted to the short-duration bursts. 4. Burst firing on the short-time scale of 50 ms was characterized by relatively well defined intervals between the first two spikes (3-15 ms) followed by higher-order intervals with large spread (range 4-50 ms) but with increasing modal interval value. The typical adult five-spike burst template featured spikes at 0, 3.3, 14.6, 27.2, and 34.8 ms. Burst with fewer spikes showed larger intervals between the first three spikes. 5. The probability of occurrence of isolated spikes, pairs, triplets, etc. showed a power-law dependence on firing rate with a coefficient that was significantly lower than expected under Poisson firing conditions.(ABSTRACT TRUNCATED AT 400 WORDS)
A cortical EEG frequency with a REM-specific increase in amplitude
Authors: Campbell I. G. , Feinberg I.
Published: December 2017

1. We used period/amplitude (PA) analysis to survey electroencephalography (EEG) across vigilance states in the Sprague-Dawley rat. We found a fast cortical EEG frequency band, which we designate rho, whose wave amplitude in rapid eye movement (REM) was elevated above the levels in both waking and nonrapid eye movement (NREM). Rho wave amplitudes in NREM and waking were similar. 2. Rho occurred between 20 and 30 Hz, which appears to be a transitional range. In the 5-Hz band below rho, EEG wave amplitudes are higher in both NREM and REM than in waking; above 30 Hz, amplitudes are higher in waking and REM than in NREM. The augmented amplitude of rho in REM may result from a unique point of interaction of EEG mechanisms of sleep and waking. 3. In addition to its theoretical interest, rho is of practical value for scoring REM sleep. It could obviate the need to record hippocampal theta EEG, eliminating electrode penetration of the brain and reducing the number of leads required to classify rat vigilance states.
Effects of vasoactive intestinal polypeptide on the response properties of cells in area 17 of the cat visual cortex
Authors: Murphy P. C. , Grieve K. L. , Sillito A. M.
Published: December 2017

1. Vasoactive intestinal polypeptide (VIP) was iontophoretically applied to a population of 90 single cells in the primary visual cortex (area 17) of the cat. Response magnitude, response selectivity, spontaneous activity, and the ratio between the visual response and spontaneous activity (signal-to-noise ratio) of the cells were assessed quantitatively before and during drug application. 2. VIP had little effect in the absence of visual stimulation, with only 29/90 (32%) of the cells showing a change of even 1 sp/s in their spontaneous activity. In contrast it had a clear effect on the visual responses of the majority (73/90, 81%) of the cells tested. 3. VIP produced a substantial change (i.e., > or = 40%) in optimal response magnitude for 57 of the affected cells. Of these 65% were facilitated, usually with no change or an improvement in signal-to-noise ratio and direction selectivity. The remaining cells were inhibited, with more variable effects on their visual response characteristics, and were found predominantly in the superficial laminae. 4. The effects of VIP bore a remarkable resemblance to those reported previously for the muscarinic action of acetylcholine (ACh). VIP and a muscarinic cholinergic agonist, either ACh or acetyl-beta-methacholine (MeCh), were therefore applied in turn to a group of 40 cells. In 23 cases VIP and the muscarinic agonist were also applied simultaneously. 5. The effects of VIP and the cholinergic agonist matched in 92% of the cases where both drugs were effective. That is to say, cells that were facilitated by VIP were facilitated also by ACh or MeCh, and vice versa. In many instances there was a clear similarity in the pattern as well as the direction of the effects produced by the two substances. The result of simultaneous application was generally additive. 6. These data suggest that VIP and ACh activate very similar postsynaptic mechanisms, and share a closely related function at the level of individual cortical cells. Thus VIP may facilitate the responses of both the excitatory and the inhibitory components of the cortical circuit, leading to an overall increase in responsiveness and selectivity. In contrast to the cholinergic input from the basal forebrain, however, the VIP-positive cortical cells are likely to exert a very localized influence, over a circumscribed region of the cortex, in response to the presence of an effective visual stimulus.
The neuropeptide red pigment concentrating hormone affects rhythmic pattern generation at multiple sites
Authors: Dickinson P. S. , Mecsas C. , Hetling J. , Terio K.
Published: December 2017

1. The cardiac sac network, which controls the rhythmic contractions of the cardiac sac in the foregut of crustaceans, is distributed throughout the stomatogastric nervous system, including the oesophageal ganglion (OG), the commissural ganglia (CGs), and the stomatogastric ganglion (STG). A red pigment-concentrating hormone (RPCH)-like peptide is likewise widely distributed. 2. The effects that bath application of the neuropeptide RPCH to the different ganglia has on the cardiac sac pattern were studied. 3. RPCH applied to the STG, the OG, or the CGs elicited bursting activity in all the known components of the cardiac sac pattern, including the two motor neurons, cardiac sac dilators 1 and 2 (CD1 and CD2), and the inferior ventricular nerve (ivn) fibers. 4. A cardiac sac pattern was also elicited when RPCH was applied to either the STG, the OG, or the CGs after synapses in that ganglion had been blocked by low Ca2+ saline containing 20 mM Co2+. 5. These data suggest that the ivn fibers are sensitive to RPCH and respond to it by generating bursting activity at or near their terminals in all four ganglia. 6. Application of RPCH to either the STG or the OG also caused an increase in the amplitude of the postsynaptic potential (PSP) from the ivn fibers to both CD1 and CD2. The increase was largest in the ganglion to which the RPCH was applied. 7. Repeated stimulation of the ivn, mimicking the bursts that occur during cardiac sac activity, also caused an increase in PSP amplitude, and so facilitation resulting from activation of ivn bursting could account for a portion of the increased amplitude seen in RPCH.(ABSTRACT TRUNCATED AT 250 WORDS)
Role of HCO3- ions in depolarizing GABAA receptor-mediated responses in pyramidal cells of rat hippocampus
Authors: Grover L. M. , Lambert N. A. , Schwartzkroin P. A. , Teyler T. J.
Published: December 2017

1. Activation of GABAA receptors can produce both hyperpolarizing and depolarizing responses in CA1 pyramidal cells. The hyperpolarizing response is mediated by a Cl- conductance, but the ionic basis of the depolarizing response is not clear. We compared the GABAA receptor-mediated depolarizations induced by synaptically released gamma-aminobutyric acid [GABA; depolarizing inhibitory postsynaptic potentials (dIPSPs)] with those produced by exogenous GABA (depolarizing GABA responses). Short trains of high-frequency (200 Hz) stimuli were used to generate dIPSPs. We found that dIPSPs generated by trains of stimuli and depolarizing responses to exogenous GABA were accompanied by a conductance increase and had a similar reversal potential, indicating a similar ionic basis for both responses. 2. We wished to determine whether an HCO3- current contributed to the GABAA-mediated depolarizations. We found that dIPSPs and depolarizing GABA responses were sensitive to perfusion with HCO3(-)-free medium. Interpretation of these data was complicated by the mixed nature of the responses: dIPSPs were invariably accompanied by conventional, Cl(-)-mediated fast hyperpolarizing IPSPs (fIPSPs), and response to exogenous GABA usually consisted of biphasic hyperpolarizing and depolarizing responses. However, it was sometimes possible to elicit responses to GABA that appeared purely depolarizing (monophasic depolarizing GABA responses). 3. We analyzed monophasic depolarizing GABA responses and found no change in reversal potential when slices were perfused with HCO(3-)-free medium. We also made whole-cell recordings from CA1 pyramidal cells, attempting to reduce [HCO3-]i, and compared the reversal potential for monophasic depolarizing GABA responses with similar responses recorded with fine intracellular microelectrodes. We found no difference in reversal potential. We also examined effects of the carbonic anhydrase inhibitor acetazolamide (ACTZ) on depolarizing GABA responses. ACTZ reduced these responses but did not change their reversal potential. 4. Effects of HCO(3-)-free medium were not specific to GABAA receptor-mediated responses. GABAB receptor-mediated slow IPSPs (sIPSPs) were also reduced, as were excitatory postsynaptic potentials (EPSPs). Analyses of field potentials and spontaneous fIPSPs suggested a decrease in presynaptic excitability during perfusion with HCO(3-)-free medium. In addition, pyramidal cells showed decreased input resistance when perfused with HCO(3-)-free medium. 5. The sensitivity of GABAA receptor-mediated depolarizations to HCO(3-)-free medium can be explained by a decrease in presynaptic excitability and an increased resting conductance in postsynaptic neurons.(ABSTRACT TRUNCATED AT 400 WORDS)
Nucleus Z: a somatosensory relay to motor thalamus
Authors: Mackel R. , Miyashita E.
Published: December 2017

1. It was the aim of this study to show that nucleus Z of the cat medulla acts as a relay between the spinal cord and the ventral lateral (VL) nucleus of the motor thalamus. For this purpose, extracellular recordings were made from neurons that were antidromically identified by stimulation in the rostral thalamus, particularly VL, and orthodromically activated by electrical stimulation of the spinal cord and/or natural stimulation of the hindlimb. The electrophysiological work was complemented by anatomic work. Here, wheat germ agglutinin-horseradish peroxidase (WGA-HRP) was injected into nucleus Z and the termination sites of bulbothalamic projections were anterogradely labeled. 2. A total of 120 neurons were antidromically identified as projecting to thalamus: 101 to VL and 19 outside VL. The recording sites in nucleus Z were marked by dye injection or by electrolytic lesion. They were confined to a small region (roughly 1 mm in diameter), 2.8-3.7 mm rostral to obex, 2.9-3.8 mm lateral from the midline, and from the surface of the medulla to a depth of 1 mm. The antidromic latencies ranged between 0.8 and 3.2 ms, with no difference in latencies associated with location of neurons in nucleus Z or thalamic projection sites. 3. Injection of WGA-HRP labeled fibers and axon terminals in the contralateral thalamus. Terminal labeling was densest in the lateral parts of the mid- and caudal region of the VL nucleus and, to a lesser extent, in the adjacent rostrodorsal part of the ventro-posterior lateral (VPL) nucleus. The sites of terminal labeling in VL corresponded with location of antidromic stimulation sites. 4. Orthodromic activation of nucleus Z neurons was tested in response to electrical stimulation of the ipsilateral dorsolateral funiculus (which includes the dorsal spinocerebellar tract) and/or the dorsal columns. All neurons responded to stimulation of the dorsolateral funiculus (45/45). The responsiveness of 44 neurons was tested to stimulation of the dorsal columns. Only 8 of 44 tested responded with a discharge. The orthodromic latencies of unitary discharges ranged from 1.1 to 4.4 ms to stimulation of the dorsolateral funiculus, and from 1.1 to 4.9 ms to stimulation of the dorsal columns. Most responses are likely to be monosynaptic. Differences in latencies were not associated with location of recording sites or thalamic projection sites of nucleus Z neurons. 5. The responsiveness of many neurons (n = 84) was tested to natural stimulation of the ipsilateral hindlimb (which provides the sensory input to nucleus Z).(ABSTRACT TRUNCATED AT 400 WORDS)
Two modes of interspike interval shortening by brief transient depolarizations in cat neocortical neurons
Authors: Reyes A. D. , Fetz E. E.
Published: December 2017

1. The effects of small, brief depolarizing pulses and excitatory postsynaptic potentials (EPSPs) on neuronal firing were examined in layer V neurons in slices of cat sensorimotor cortex. During intracellular recording, brief depolarizing current pulses (duration, 0.5-2.0 ms; amplitude, 0.1-4.0 nA) were injected in neurons to produce pulse potentials (PPs) with a near-linear rise to a peak (0.08-3.6 mV; rise time = pulse duration) followed by an exponential decay. These PPs resembled EPSPs evoked by electrical stimulation of adjacent sites. When injected in neurons that were induced to discharge tonically, the PPs shortened the interspike intervals (ISIs) in two ways, depending on their time of arrival in the ISI. 2. Toward the end of the ISI, the PPs crossed a time-varying firing level, thereby directly evoking action potentials and shortening the ISIs. These directly evoked spikes occurred during the rise or peak of the PPs. The absolute firing level increased with the membrane trajectory during the latter part of the ISI. 3. PPs that appeared earlier in the ISI did not cross firing level directly but could nevertheless shorten the ISI by a slow regenerative process. The indirectly evoked spikes occurred after the peak of the PPs, at latencies whose magnitude and variability increased as the PPs appeared at successively earlier times in the ISI. PPs that occurred during the initial portion (approximately the 1st 3rd) of the ISI did not affect ISI duration. 4. Stimulus-evoked EPSPs shortened the ISIs in a manner similar to that of PPs. Like PPs, EPSPs caused direct crossings late in the ISI and indirect crossings earlier. Comparison of the mean and maximum ISI shortenings and the range of delays in which the PPs and EPSPs consistently produced ISI shortenings revealed no systematic differences. These similarities suggest that PPs may be used to simulate the ISI shortenings caused by EPSPs. 5. To characterize possible mechanisms underlying the ISI shortening, we examined the PP shapes at different times in the ISI. PPs immediately following a spike were smaller and decayed more rapidly than those evoked by the same current at rest. Late in the ISI, when the membrane potential was > 5 mV above rest, the PP height exceeded that of the PP at rest. This amplitude increase may be due to activation of the persistent sodium current.(ABSTRACT TRUNCATED AT 400 WORDS)
Wipe and flexion reflexes of the frog. I. Kinematics and EMG patterns
Authors: Schotland J. L. , Rymer W. Z.
Published: December 2017

1. We evaluated the hypothesis that the neural control of complex motor behaviors is simplified by building movement sequences from a series of simple neural "building blocks." In particular, we compared two reflex behaviors of the frog, flexion withdrawal and the hindlimb-hindlimb wipe reflex, to determine whether a single neural circuit that coordinates flexion withdrawal is incorporated as the first element in a sequence of neural circuits comprising the wipe. The neural organization of these two reflexes was compared using a quantitative analysis of movement kinematics and muscle activity patterns [electromyograms (EMGs)]. 2. The three-dimensional coordinates of the position of the foot over time and the angular excursion of hip, knee, and ankle joints were recorded using a WATSMART infrared emitter-detector system. These data were quantified using principal-components analysis to provide a measure of the shape (eigenvalues) and orientation (eigen-vector coefficients) of the movement trajectories. The latencies and magnitudes of EMGs of seven muscles acting at the hip, knee, and ankle were analyzed over the interval from EMG onset to movement onset, and EMG magnitudes during the initial flexion of the limb. These variables were compared during flexion withdrawal and the initial flexion movement of the limb during the hindlimb-hindlimb wipe reflex (before the onset of the frequently rhythmic portion when the stimulus is removed) when the two reflexes were elicited from comparable stimulus locations. 3. In both the flexion reflex and the initial movement segment of the wipe reflex, the foot moves along a relatively straight line. However, the foot is directed to a more rostral and lateral position during flexion than during wipe. All three joints flex during flexion withdrawal, whereas during the wipe, the knee and ankle joints flex but the angular excursion of the hip joint may vary. The different orientations of the movement trajectories are associated with EMG patterns that differ in both timing and magnitude between the two reflexes. 4. The differences in the kinematics and EMG patterns of the two reflexes during unrestrained movements make it unlikely that the neural circuit that coordinates flexion withdrawal is incorporated as the first element in the sequence of neural circuits underlying the wipe reflex. 5. Unlike the wipe reflex, during flexion withdrawal there is no apparent constraint on the accuracy of placement at the end of the movement, yet the animals nevertheless achieved consistent final positions of both the foot and of each joint. The implications of these findings with respect to the controlled variables are discussed.
Wipe and flexion reflexes of the frog. II. Response to perturbations
Authors: Schotland J. L. , Rymer W. Z.
Published: December 2017

1. To evaluate the hypothesis that the neural control of sensorimotor transformations may be simplified by using a single control variable, we compared the movement kinematics and muscle activity patterns [electromyograms (EMGs)] of the frog during flexion withdrawal and the hind limb-hind limb wipe reflex before and after adding an external load. In addition, the flexibility of spinal cord circuitry underlying the hind limb-hind limb wipe reflex was evaluated by comparing wipes before and after removal of one of the contributing muscles by cutting a muscle nerve. 2. The kinematics of the movements were recorded using a WATSMART infrared emitter-detector system and quantified using principal-components analysis to provide a measure of the shape (eigenvalues) and orientation (eigenvector coefficients) of the movement trajectories. The neural pattern coordinating the movements was characterized by the latencies and magnitudes of EMGs of seven muscles acting at the hip, knee, and ankle. These variables were compared 1) during flexion withdrawal and the initial movement segment of the limb during the hind limb-hind limb wipe reflex in both unrestrained movements and in movements executed when a load equal to approximately 10% of the animal's body weight was attached to a distal limb segment and 2) during the initial movement segment of the wipe reflex before and after cutting the nerve to the knee flexor-hip extensor, iliofibularis. 3. Addition of the load had no discernible effect on the end-point position of the foot during either reflex. However, during the loaded flexion reflex, the ankle joint did not move until after the hip and knee joints had moved to their normal positions. This delayed flexion of the ankle was accompanied by large increases in the magnitude of EMG activity in two ankle muscles that exceeded the levels found during unrestrained movements. Significant changes in the temporal organization of the EMG pattern accompanied the change in joint angle relations during flexion withdrawal. 4. Despite the addition of an external load, all animals successfully and reliably removed the stimulus during the wipe reflex, and the relative timing of both the EMG pattern and joint angle motion was preserved. 5. Immediately after section of the nerve to a single muscle (iliofibularis), all animals successfully and reliably removed the stimulus during the wipe reflex. The relative timing of muscle activation was preserved, accompanied by a reduction in the activity level of gluteus magnus, a muscle with action reciprocal to iliofibularis.(ABSTRACT TRUNCATED AT 400 WORDS)
Miniature excitatory synaptic currents corrected for dendritic cable properties reveal quantal size and variance
Authors: Ulrich D. , Luscher H. R.
Published: December 2017

1. Non-NMDA (N-Methyl-D-aspartate) receptor mediated miniature excitatory synaptic currents (mEPSCs) were recorded from motoneurons in organotypic cultures of embryonic rat spinal cord. 2. Amplitude histograms of mEPSCs were unimodal and skewed toward larger events. The mean of the modes of the amplitude histograms was -18 pA with a maximal amplitude range of -4 to -160 pA for individual mEPSCs. 3. Current transients to a short voltage pulse were used to estimate the passive cable parameters of the motoneurons. The mean membrane time constant (tau) and the mean electrotonic length (L) were 20 and 0.96 ms, respectively. 4. The amplitudes of the mEPSCs were corrected for imperfect space and voltage clamp. The resulting amplitude histograms could be fitted by the sum of two Gaussian curves, revealing a mean quantal size of -48 pA with a coefficient of variation (cv) of 0.28. 5. Our data suggest that quantal size and its variance are masked by the cable properties of the neurons and that simultaneous release of elementary quanta occurs occasionally.
Timing of medullary late-inspiratory neuron discharges: vagal afferent effects indicate possible off-switch function
Authors: Cohen M. I. , Huang W. X. , Barnhardt R. , See W. R.
Published: December 2017

1. In decerebrate paralyzed cats, we observed the responses of ventral and dorsal medullary inspiratory (I) neurons to two types of vagal afferent input that shorten neural I: lung inflation and vagal electrical stimulation. 2. A study population of 15 I neurons whose firing patterns suggested involvement in the inspiratory OFF-switch (IOS) was selected on the basis of two criteria: late onset of firing and excitation by vagal inputs. 3. Firing in relation to the end of I showed two types of response to vagal inputs. The pre-expiratory onset time (time from initial spike to end of I) was either unchanged (type 1 response in 5/15 neurons) or significantly changed (type 2 response in 10/15 neurons). 4. It is suggested that type 1 neurons, whose firing patterns remain closely locked to the end of I despite considerable changes of I duration, are involved in promoting the IOS, whereas type 2 neurons are either not involved (e.g., late-onset premotor neurons) or are involved at an earlier temporal processing stage.
Exploring parameter space in detailed single neuron models: simulations of the mitral and granule cells of the olfactory bulb
Authors: Bhalla U. S. , Bower J. M.
Published: December 2017

1. Detailed compartmental computer simulations of single mitral and granule cells of the vertebrate olfactory bulb were constructed using previously published geometric data. Electrophysiological properties were determined by comparing model output to previously published experimental data, mainly current-clamp recordings. 2. The passive electrical properties of each model were explored by comparing model output with intracellular potential data from hyperpolarizing current injection experiments. The results suggest that membrane resistivity in both cells is nonuniform, with somatas having a substantially lower resistivity than the dendrites. 3. The active properties of these cells were explored by incorporating active ion channels into modeled compartments. On the basis of evidence from the literature, the mitral cell model included six channel types: fast sodium, fast delayed rectifier (Kfast), slow delayed rectifier (K), transient outward potassium current (KA), voltage- and calcium-dependent potassium current (KCa), and L-type calcium current. The granule cell model included four channel types: rat brain sodium, K, KA, and the non-inactivating muscarinic potassium current (KM). Modeled channels were based on the Hodgkin-Huxley formalism. 4. Representative kinetics for each of the channel classes above were obtained from the literature. The experimentally unknown spatial distributions of each included channel were obtained by systematic parameter searches. These were conducted in two ways: large-scale simulation series, in which each parameter was varied in turn, and an adaptation of a multidimensional conjugate gradient method. In each case, the simulated results were compared wtih experimental data using a curve-matching function evaluating mean squared differences of several aspects of the simulated and experimental voltage waveforms. 5. Systematic parameter variations revealed a single distinct region of parameter space in which the mitral cell model best fit the data. This region of parameter space was also very robust to parameter variations. Specifically, optimum performance was obtained when calcium and slow K channels were concentrated in the glomeruli, with a lower density in the soma and proximal secondary dendrites. The distribution of sodium and fast potassium channels, on the other hand, was highest at the soma and axon, with a much lighter distribution throughout the secondary dendrites. The KA and KCa channels were also concentrated near the soma. 6. The parameter search of the granule cell model was much less restrained by experimental data. Several parameter regimes were found that gave a good match to the data.(ABSTRACT TRUNCATED AT 400 WORDS)
An electrophysiological study of dorsal horn neurons in the spinal cord of rats with an experimental peripheral neuropathy
Authors: Laird J. M. , Bennett G. J.
Published: December 2017

1. Extracellular single-unit recordings have been made from 295 dorsal horn neurons in the lumbar enlargement of rat spinal cord; 191 neurons in 20 rats with an experimental peripheral neuropathy, and 104 in 10 sham-operated rats. Recordings were made 9-11 days after inducing the neuropathy by tying four loose ligatures around the sciatic nerve in the nerve-injured rats or performing a sham procedure in the sham-operated rats. 2. A survey of the general properties of all neurons encountered was made in the 10 sham-operated rats (104 neurons) and compared with those seen in 17 of the nerve-injured animals (180 neurons). The vast majority (87%; 156/180) of neurons recorded in the nerve-injured animals showed abnormal characteristics; these included responses to very gentle mechanical stimulation of the nerve-injury site and to manipulations that resulted in movement of this site such as extension of the leg and probing of the skin and muscle of the thigh (53%), absence of detectable peripheral receptive fields (RFs; 56%), and very high spontaneous activity (7%). In the sham-operated rats none of the neurons recorded could be activated by gentle mechanical stimulation of the sciatic nerve, and only 6% had no detectable peripheral RF. 3. In the nerve-injured animals, 31% (55/180) of cells had both a peripheral RF, and a response to gentle mechanical stimulation of the nerve-injury site. All cells of this type tested (n = 5) showed very prolonged responses (up to 10 min long) to 15 s pinch stimuli applied to the RF and to 15 s gentle tapping of the injury site. The majority of cells in this group were excited by noxious stimuli (71%; 39/55) and had C-fiber inputs (60%; 33/55). 4. The mean threshold temperatures for evoking responses to heat stimuli in cells tested in nerve-injured rats and in sham-operated animals were not different. However, there was a group of neurons in the nerve-injured rats that had low thresholds, failed to encode stimulus intensity, and did not have a C-fiber input. 5. There were significantly fewer neurons excited by low-intensity stimulation of the skin in the nerve-injured (24%; 43/180) than in the sham-operated rats (71%; 74/104). Measurements of mechanical threshold with von Frey hairs showed that, although the mean threshold did not change, none of the cells tested in the nerve-injured animals had thresholds < 12 mN, whereas the lowest threshold recorded in the sham-operated animals was 0.2 mN.(ABSTRACT TRUNCATED AT 400 WORDS)
The peptide FMRFa terminates a discharge in Aplysia bag cell neurons by modulating calcium, potassium, and chloride conductances
Authors: Fisher T. , Lin C. H. , Kaczmarek L. K.
Published: December 2017

1. Electrical stimulation of an afferent nerve triggers a 30-min period of firing of action potentials in the bag cell neurons of Aplysia californica. This afterdischarge causes the animal to undergo a long-lasting sequence of stereotyped reproductive behaviors culminating in laying of eggs. The connective sheath surrounding the clusters of bag cell neurons is interspersed with a network of particles that are immunoreactive to an antiserum raised against the tetrapeptide neurotransmitter Phe-Met-Arg-Phe-amide (FMRFa). Because the sheath is known to be rich in processes from the bag cell neurons, these data suggest that an FMRFa-like peptide may be located in neuronal processes that are in close contact with those of the bag cell neurons. 2. Application of FMRFa to bag cell neurons in intact abdominal ganglia effectively suppresses the onset of the afterdischarge in response to electrical stimulation and terminates an ongoing afterdischarge in a reversible manner. 3. Application of FMRFa to isolated bag cell neurons in primary cell culture causes an attenuation of the amplitude of evoked action potentials. This could be attributed in part to an attenuation of the voltage-activated calcium current, which in voltage-clamp experiments was found to be reduced by 10-40%. 4. Application of FMRFa to bag cell neuron in primary culture also causes a hyperpolarization of the membrane potential by activating an outward current with a reversal potential of approximately -67 mV. Ion substitution experiments, together with application of channel blockers, indicate that this current is carried by both potassium and chloride ions. Activation of this current is suppressed by treatment of the cells with either a cyclic AMP analogue or a phorbol ester activator of protein kinase C. 5. FMRFa exerts a powerful inhibitory influence on the bag cell neurons by altering the properties of ion currents involved in both the generation of action potentials and control of the resting potential. This suggests that this neuropeptide plays a role in the regulation of the onset of afterdischarge in vivo.
Inhibition in ON-OFF directionally selective ganglion cells of the rabbit retina
Authors: Amthor F. R. , Grzywacz N. M.
Published: December 2017

1. We have investigated the inhibitory mechanisms modulating the extracellularly recorded responses of ON-OFF directionally selective (DS) ganglion cells of the rabbit retina. Our investigations used both moving spots and apparent motion. The latter was produced by both prolonged light steps, which simulate movement of an edge, and light flashes, which simulate movement of a spot or slit. 2. Within the excitatory receptive-field center of DS ganglion cells, apparent motion with prolonged light steps elicits null-direction inhibition whose strength rises to 90% of maximum in 160 +/- 110 ms (7 cells) and then decays slowly, remaining above baseline longer than 2,000 ms for short interslit distances. 3. Prolonged light steps are generally effective for inhibiting any given excitatory receptive-field locus from an ovate-shaped area that extends asymmetrically in the direction that would be previously traversed by null-direction moving objects. This inhibitory area is typically larger than one-half the size of the receptive-field center. The strength of the inhibition is greater at short than long distances within this area. 4. The rise and fall times of the null-direction inhibition elicited by apparent motion using prolonged light steps are somewhat faster at large than short interslit distances. 5. Short light flashes (at sufficiently long interslit delays) elicit inhibition not only from the same asymmetric, ovate-shaped inhibitory field as long steps of light, but also from loci completely surrounding the second slit. This implies that the asymmetric, null-direction-specific inhibition is due to a temporally sustained mechanism. The symmetric inhibition elicited by short flashes may be due to the presence of the antagonistic surround mechanism within the receptive-field center. The apparent absence of this surround inhibition for preferred-direction apparent motion during prolonged light steps may be due to masking by facilitation that is strongly evoked by long steps, but not flashes of light (see accompanying paper). 6. The relatively slow rise time and sustained time course of the inhibition elicited by null-direction apparent motion within the excitatory receptive field center appears to distinguish it from the inhibition elicited by stimulation within the receptive field surround, which has a much faster rise time and more transient time course. However, the sustained, null-direction inhibitory mechanism that can be elicited by prolonged light steps within the excitatory receptive field center extends into the surround on the side of the receptive-field center previously traversed during null-direction motion.(ABSTRACT TRUNCATED AT 400 WORDS)
Position-specific adaptation in complex cell receptive fields of the cat striate cortex
Authors: Marlin S. , Douglas R. , Cynader M.
Published: December 2017

1. Responses of complex cells in cat striate cortex were studied with flashed light slit stimuli. The responses to slits flashed in different positions in the receptive field were assessed quantitatively before and after periods of prolonged stimulation of one small region of the receptive field. This type of prolonged stimulation resulted in reduced responsivity over a limited zone within the complex cell receptive field. 2. The adaptation-induced responsivity decrement was generally observed in both the ON and OFF response profiles but could also be restricted to one or the other. In general, the magnitude of the response decrements was greatest in the ON response profiles. The adaptation-induced response decrement did not necessarily spread throughout the receptive field but was restricted to a small region surrounding the adapted receptive field position (RFP). Adaptation spread equally widely across the ON and OFF response profiles despite the smaller adaptation effects in the OFF profile. 3. The adaptation effects from repeated stimulation at a single RFP did not spread symmetrically across the receptive field, and a given cell's preferred direction of motion indicated the direction of the asymmetric spread of the adaptation. RFPs that would be stimulated by a light slit originating at the point of adaptation and moving in the preferred direction (preferred side) showed greater adaptation-induced response decrements than did RFPs that would be stimulated by a light slit moving in the opposite direction from the point of adaptation (nonpreferred side). There was significant enhancement of responses at some RFPs on the non-preferred side of the point of adaptation. This asymmetric spread of adaptation could be caused by adaptation of inhibitory connections that contribute to complex cell direction selectivity. 4. The asymmetry of adaptation was significantly different for the ON and OFF response profiles. The asymmetric spread of adaptation for the ON response profile was similar to that observed previously in simple cells with greater decrements in the preferred direction side of the point of adaptation. However, the OFF response profiles showed less directional asymmetry in the spread of adaptation and showed greater decrements at RFPs in the nonpreferred direction side of the point of adaptation. 5. The similarity between the spread of adaptation in simple and complex cells suggests that the adaptation in these cells is occurring through a common mechanism. The directional asymmetry of the spread of adaptation is likely due to a local postsynaptic mechanism of adaptation rather than presynaptic transmitter depletion.
Electrical coupling of mechanoreceptor afferents in the crayfish: a possible mechanism for enhancement of sensory signal transmission
Authors: el Manira A. , Cattaert D. , Wallen P. , DiCaprio R. A. , Clarac F.
Published: December 2017

1. Central electrical coupling between primary afferent axons was investigated in an in vitro preparation of the crayfish thoracic locomotor system by using intracellular recordings. 2. Intracellular injection of the dye Lucifer yellow in single afferents resulted in staining of one to three additional afferents through dye-coupling. Three-dimensional confocal imaging of dye-coupled axons revealed a large zone of close apposition that may correspond to the gap junction site. 3. A depolarization preceding the spike in one sensory terminal was shown to facilitate the excitatory postsynaptic potential occurring in postsynaptic motoneurons. Further, a spike in one afferent axon can depolarize other, electrically coupled, axons above spike threshold, resulting in an increased number of active afferents. 4. The electrical coupling occurred between sensory afferents of similar function. It may therefore serve to facilitate sensory signal transmission from functionally homologous afferents onto postsynaptic target neurons.
Ionic mechanisms for the subthreshold oscillations and differential electroresponsiveness of medial entorhinal cortex layer II neurons
Authors: Klink R. , Alonso A.
Published: December 2017

1. Layer II of the medial entorhinal cortex is composed of two electrophysiologically and morphologically distinct types of projection neurons: stellate cells (SCs), which are distinguished by rhythmic subthreshold oscillatory activity, and non-SCs. The ionic mechanisms underlying their differential electroresponsiveness, particularly in the subthreshold range of membrane potentials, were investigated in an "in vitro" slice preparation. 2. In both SCs and non-SCs, the apparent membrane input resistance was markedly voltage dependent, respectively decreasing or increasing at hyperpolarized or subthreshold depolarized potential levels. Thus the neurons displayed inward rectification in the hyperpolarizing and depolarizing range. 3. In the depolarizing range, inward rectification was blocked by tetrodotoxin (TTX, 1 microM) in both types of neurons and thus shown to depend on the presence of a persistent low-threshold Na+ conductance (gNap). However, in the presence of TTX, pronounced outward rectification became manifest in the subthreshold depolarizing range of membrane potentials (positive to -60 mV) in the SCs but not in the non-SCs. 4. The rhythmic subthreshold membrane potential oscillations that were present only in the SCs were abolished by TTX and not by Ca2+ conductance block with Cd2+ or Co2+. Subthreshold oscillations thus rely on the activation of voltage-gated Na+, and not Ca2+, conductances. The Ca2+ conductance block also had no effect on the subthreshold outward rectification. 5. Prominent time-dependent inward rectification in the hyperpolarizing range in the SCs persisted after Na(+)- and Ca2+ conductance block. This rectification was not affected by Ba2+ (1 mM), but was blocked by Cs+ (1-4 mM). Therefore, it is most probably generated by a hyperpolarization-activated cationic current (Q-like current). However, the Q-like current appears to play no major role in the generation of subthreshold rhythmic membrane potential oscillations, because these persisted in the presence of Cs+. 6. On the other hand, in the SCs, the fast, sustained, outward rectification that strongly developed (after Na+ conductance block) at the oscillatory voltage level was not affected by Cs+ but was blocked by Ba2+ (1 mM). Barium was also effective in blocking the subthreshold membrane potential oscillations. 7. In the non-SCs, which do not generate subthreshold rhythmic membrane potential oscillations or manifest subthreshold outward rectification in TTX, Ca2+ conductance block abolished spike repolarization and caused the development of long-lasting Na(+)-dependent plateau potentials at a high suprathreshold voltage level. At this level, where prominent delayed rectification is present, the Na+ plateaus sustained rhythmic membrane potential oscillations.(ABSTRACT TRUNCATED AT 400 WORDS)