bluuebunny/crossref_metadata_2025 huggingface dataset:
Fixation cells in monkey superior colliculus. I. Characteristics of cell discharge
Authors: Munoz D. P. , Wurtz R. H.
Published: December 2017

1. We studied the role of the superior colliculus (SC) in the control of visual fixation by recording from cells in the rostral pole of the SC in awake monkeys that were trained to perform fixation and saccade tasks. 2. We identified a subset of neurons in three monkeys that we refer to as fixation cells. These cells increased their tonic discharge rate when the monkey actively fixated a visible target spot to obtain a reward. This sustained activity persisted when the visual stimulation of the target spot was momentarily removed but the monkey was required to continue fixation. 3. The fixation cells were in the rostral pole of the SC. As the electrode descended through the SC, we encountered visual cells with foveal and parafoveal receptive fields most superficially, saccade-related burst cells with parafoveal movement fields below these visual cells, and fixation cells below the burst cells. From this sequence in depth, the fixation cells appeared to be centered in the deeper reaches of the intermediate layers, and this was confirmed by small marking lesions identified histologically. 4. During saccades, the tonically active fixation cells showed a pause in their rate of discharge. The duration of this pause was correlated to the duration of the saccade. Many cells did not decrease their discharge rate for small-amplitude contraversive saccades. 5. The saccade-related pause in fixation cell discharge always began before the onset of the saccade. The mean time from pause onset to saccade onset for contraversive saccades and ipsiversive saccades was 36.2 and 33.0 ms, respectively. Most fixation cells were reactivated before the end of contraversive saccades. The mean time from saccade terminatioN to pause end was -2.6 ms for contraversive saccades and 9.9 ms for ipsiversive saccades. The end of the saccade-related pause in fixation cell discharge was more tightly correlated to saccade termination, than pause onset was to saccade onset. 6. After the saccade-related pause in discharge, many fixation cells showed an increased discharge rate exceeding that before the pause. This increased postsaccadic discharge rate persisted for several hundred milliseconds. 7. The discharge rate of fixation cells was not consistently altered when the monkey actively fixated targets requiring different orbital positions. 8. Fixation cells discharged during smooth pursuit eye movements as they did during fixation. They maintained a steady tonic discharge during pursuit at different speeds and in different directions, provided the monkey looked at the moving target.(ABSTRACT TRUNCATED AT 400 WORDS)
Virtual-space receptive fields of single auditory nerve fibers
Authors: Poon P. W. , Brugge J. F.
Published: December 2017

1. Sounds reaching the tympanic membranes are first modified by the acoustic properties of the torso, head, and external ear. For certain frequencies in the incident sound there results a complex, direction-dependent spatial distribution of sound pressure at the eardrum such that, within a sound field, localized areas of pressure maxima are flanked by areas of pressure minima. Listeners may use these spatial maxima and minima in localizing the source of a sound in space. The results presented describe how information about this spatial pressure pattern is transmitted from the cochlea to the central auditory system via single fibers of the auditory nerve. 2. Discharges of single fibers of the auditory nerve were studied in Nembutal-anesthetized cats [characteristic frequencies (CFs) ranged from 0.4 to 40 kHz]. Click stimuli were derived from sound-pressure waveforms that were generated by a loudspeaker placed at 1,800 locations around the cat's head and recorded at the tympanic membrane with miniature microphones. Recorded signals were converted to acoustic stimuli and delivered to the ear via a calibrated and sealed earphone. The full complement of signals is referred to as "virtual acoustic space," and the spatial distribution of discharges to this array of signals is referred to as a "virtual-space receptive field" (VSRF). 3. Fibers detect both pressure maxima and pressure minima in virtual acoustic space. Thus VSRFs take on complex shapes. 4. VSRFs of fibers of the same or similar CF having low spontaneous rates had the same overall pattern as those from high-spontaneous rate (HSR) fibers. For HSR fibers, the VSRF is obscured by the high background spike activity. 5. Comparison of the VSRF and isolevel contour maps of the stimulus derived at various frequencies revealed that auditory nerve fibers most accurately extract spectral information contained in the stimulus at a frequency close to or slightly higher than CF.
Parallel, interdependent channels for location and orientation in sensorimotor transformations for reaching and grasping
Authors: Soechting J. F. , Flanders M.
Published: December 2017

1. Subjects were presented with a cylinder, whose orientation with respect to the vertical and location in space varied from trial to trial. They grasped a similar cylinder in their hands and were instructed to align the grasped cylinder with the target cylinder. In some experiments the task was performed from memory, and subjects attempted to reproduce both location and orientation of the cylinder. In others, they attempted to reproduce only its orientation, either from memory or while the cylinder was in view. 2. Multivariate linear regression analysis was used to determine persistent and variable errors in performance. This analysis related the subjects' performance (reproduced orientation) to target parameters (location and orientation). 3. We have interpreted the experimental results starting from the assumption that there are two parallel neural processes underlying reaching and grasping: one relating proximal arm motion to target location and the other relating distal hand motion to target orientation. 4. Variable errors did not vary with task conditions, even when subjects were asked to dissociate target orientation from target location by matching target orientation with the arm at the side, irrespective of the location of the target. This finding suggests that the neural transformations involving target location and target orientation are performed in parallel. 5. Persistent errors did vary with task condition. The subjects made the largest errors in matching target orientation when the target was in view, but they were asked to match its orientation at a location that differed from that of the target. These errors depended mostly on the elevation of the target and on its slant (inclination relative to the vertical). They were related to the posture of the arm in a manner that suggested that matching orientation is influenced by both extrinsic (spatial) and intrinsic (arm posture) parameters. 6. The fact that persistent errors depend on target location and on arm posture as well as on target orientation implies that the neural transformation from target orientation to hand orientation is not independent of the transformation dealing with target location.
Membrane properties of rat subicular neurons in vitro
Authors: Mattia D. , Hwa G. G. , Avoli M.
Published: December 2017

1. Conventional intracellular recordings were performed in rat hippocampal slices to investigate the electrophysiological properties of subicular neurons. These cells had a resting membrane potential (RMP) of -66 +/- 7.2 mV (mean +/- SD; n = 50), input resistance of 23.6 +/- 8.2 M omega (n = 51), time constant of 7.1 +/- 1.9 ms (n = 51), action potential amplitude of 85.8 +/- 13.8 mV (n = 50), and duration of 2.9 +/- 1.2 ms (n = 48). Analysis of the current-voltage relationship revealed membrane inward rectification in both depolarizing and hyperpolarizing direction. The latter type was readily abolished by Cs+ (3 mM; n = 6 cells). 2. Injection of depolarizing current pulses of threshold intensity induced in all subicular neurons (n = 51) recorded at RMP a burst of two to three fast action potentials (frequency = 212.7 +/- 90 Hz, n = 13 cells). This burst rode on a slow depolarizing envelope and was followed by an afterhyperpolarization and later by regular spiking mode once the pulse was prolonged. Similar bursts were also generated upon termination of a hyperpolarizing current pulse. 3. The slow depolarization underlying the burst resembled a low-threshold response, which in thalamic cells is caused by a Ca2+ conductance and is contributed by the Cs(+)-sensitive inward rectifier. However, bursts in subicular cells persisted in medium containing the Ca(2+)-channel blockers Co2+ (2 mM) and Cd2+ (1 mM) (n = 5 cells) but disappeared during application of TTX (1 microM; n = 3 cells). Hence they were mediated by Na+. Blockade of the hyperpolarizing inward rectification by Cs+ did not prevent the rebound response (n = 3 cells). 4. Our findings demonstrate that intrinsic bursts, presumably related to a "low-threshold" Na+ conductance are present in rat subicular neurons. Similar intrinsic characteristics have been suggested to underlie the rhythmic activity described in other neuronal networks, although in most cases the low-threshold electrogenesis was caused by Ca2+. We propose that the bursting mechanism might play a role in modulating incoming signals from the classical hippocampal circuit within the limbic system.
Ion channels in human axons
Authors: Scholz A. , Reid G. , Vogel W. , Bostock H.
Published: December 2017

1. Until now, no direct electrophysiological information has been available on the molecular basis of human nerve excitability. We here report patch-clamp recordings, both single- and multichannel, from acutely dissociated human axons. 2. Voltage-dependent sodium channels with a conductance gamma = 13 pS (measured in Ringer at room temperature) are found in the nodal area. 3. There are several types of voltage-dependent potassium channels: I channels (gamma = 34 pS), F channels (gamma = 50 pS), and channels with small conductance (gamma = 7-9 pS, all measured in high potassium solution). Most of them are closely similar to those already reported in Xenopus and rat axons; in addition a 200-pS, calcium-dependent potassium channel, similar to that in Xenopus, is present. 4. Differences between the electrical behavior of human axons and those of other species are probably not due to the presence of fundamentally different channel types, but may be due to differences in channel density or distribution. 5. As well as increasing our understanding of the basis of excitability in human nerve, this method may prove useful in the investigation of inherited and other human neuropathies.
Focal attention produces spatially selective processing in visual cortical areas V1, V2, and V4 in the presence of competing stimuli
Authors: Motter B. C.
Published: December 2017

1. The activity of single neurons was recorded in Macaca mulatta monkeys while they performed tasks requiring them to select a cued stimulus from an array of three to eight stimuli and report the orientation of that stimulus. Stimuli were presented in a circular array centered on the fixation target and scaled to place a single stimulus element within the receptive field of the neuron under study. The timing of the cuing event permitted the directing of visual attention to the spatial location of the correct stimulus before its presentation. 2. The effects of focal attention were examined in cortical visual areas V1, V2, and V4, where a total of 672 neurons were isolated with complete studies obtained for 94 V1, 74 V2, and 74 V4 neurons with receptive-field center eccentricities in the range 1.8-8 degrees. Under certain conditions, directed focal attention results in changes in the response of V1, V2, and V4 neurons to otherwise identical stimuli at spatially specific locations. 3. More than one-third of the neurons in each area displayed differential sensitivity when attention was directed toward versus away from the spatial location of the receptive field just before and during stimulus presentation. Both relative increases and decreases in neural activity were observed in association with attention directed at receptive-field stimuli. 4. The presence of multiple competing stimuli in the visual field was a major factor determining the presence or absence of differential sensitivity. About two-thirds of the neurons that were differentially sensitive to the attending condition in the presence of competing stimuli were not differentially sensitive when single stimuli were presented in control studies. For V1 and V2 neurons the presence of only a few (3-4) competing stimuli was sufficient for a majority of the neurons studied; a majority of the V4 neurons required six to eight stimuli in the array before significant differences between attending conditions occurred. 5. For V1 and V2 neurons the neuronal sensitivity differences between attending conditions were observed primarily at or near the peak of the orientation tuning sensitivity for each neuron; the differences were evident over a broader range of orientations in V4 neurons. 6. In conclusion, neural correlates of focal attentive processes can be observed in visual cortical processing in areas V1 and V2 as well as area V4 under conditions that require stimulus feature analysis and selective spatial processing within a field of competing stimuli.(ABSTRACT TRUNCATED AT 400 WORDS)
Respiratory modulation of the activity in postganglionic neurons supplying skeletal muscle and skin of the rat hindlimb
Authors: Habler H. J. , Janig W. , Krummel M. , Peters O. A.
Published: December 2017

1. The respiratory modulation of activity in postganglionic neurons of the lumbar sympathetic outflow to skeletal muscle and hairy skin of the hindlimb was studied in anesthetized rats, either breathing spontaneously or paralyzed and artificially ventilated, using single- and multifiber recordings. The activity of the neurons was analyzed with respect to the phrenic nerve discharges or with respect to the cycle of artificial ventilation under various experimental conditions. 2. In total, 19 single and 62 multiunit preparations supplying skeletal muscle and 42 single and 95 multiunit preparations supplying skin were analyzed. Qualitatively, both populations and single- and multiunit preparations exhibited similar patterns. The majority (187/218 preparations) exhibited a depression of activity during inspiration and a peak of activity during expiration that was mostly accentuated during early expiration. The remainder exhibited a peak of activity at the transition between expiration and inspiration (n = 15) or showed no respiratory modulation (n = 16). 3. Respiratory modulation in the postganglionic neurons was similar in animals breathing spontaneously and in those that were paralyzed and artificially ventilated. 4. Systemic hypercapnia and asphyxia in most cases enhanced both the peak of activity during early expiration and the depression of activity during inspiration. 5. No peripheral (reflex) component mediated by arterial baroreceptors was found in vagotomized animals that was related to the cycle of artificial ventilation using a tidal volume of 1-2 ml and a ventilation frequency of 70 +/- 7 (SD) strokes, min-1. However, a small ventilation-related rhythm of arterial baroreceptor activity recorded from the aortic nerve was found under these conditions. 6. Respiratory modulation of postganglionic activity was similar before and after bilateral vagotomy. 7. It is concluded that respiratory modulation of sympathetic activity in rats is less differentiated than in cats. The observed differences between neurons supplying different targets are only quantitative. Possible mechanisms involved in the generation of respiratory modulation are discussed.
Mechanical properties of cat soleus muscle elicited by sequential ramp stretches: implications for control of muscle
Authors: Lin D. C. , Rymer W. Z.
Published: December 2017

1. Force changes in areflexive cat soleus muscle in decerebrate cats were recorded in response to two sequential constant velocity (ramp) stretches, separated by a variable time interval during which the length was held constant. Initial (i.e., prestretch) background force was generated by activating the crossed-extension reflex, and stretch reflexes were eliminated by section of ipsilateral dorsal roots. 2. For the initial 400-900 microns of the first stretch, the muscle exhibited high stiffness, classically termed "short-range stiffness." This high stiffness region was followed by an abrupt reduction in stiffness, called muscle "yield," after which force remained at a relatively constant level, achieving a plateau in force. This plateau force level depended largely on stretch velocity, but this dependence was much less than proportional to the increase in stretch velocity, in that a 10-fold increase in velocity produced < 2-fold increase in plateau force. 3. In experiments where the velocities of the two sequential ramp stretches were identical, the force plateau level was the same for each stretch, regardless of the time elapsed before the second stretch (varied from 0 to 500 ms). In contrast, measures of stiffness during the initial portion of the second stretch showed time-dependent magnitude reductions. However, stiffness recovered quickly after the first stretch was completed, returning to control values within 30-40 ms. 4. In one preparation, in which the velocities of the two sequential ramp stretches were different, the force plateau elicited during the second stretch exhibited velocity dependence comparable with that recorded in the earlier single velocity studies. Furthermore, muscle yield was still evident in the case where the force change was due solely to the change in velocity and where short-range stiffness had not yet recovered fully from the initial stretch. On the basis of these findings, we argue that the classical descriptions of short-range stiffness and yield are inadequate and that the change in force that has typically been called the muscle yield reflects a transition between short-range, transient elastic behavior to steady-state, essentially viscous behavior. 5. To examine changes in the muscle's mechanical stiffness during single ramp stretches, a single pulse perturbation was superimposed at various times before, during, and subsequent to the constant velocity stretch. The force increment elicited in response to each pulse decreased relative to the initial isometric value, remained essentially constant until the end of the ramp, and then returned to its prestretch magnitude shortly (30-40 ms) after stretch termination.(ABSTRACT TRUNCATED AT 400 WORDS)
A comparison of rat hippocampal mossy cells and CA3c pyramidal cells
Authors: Buckmaster P. S. , Strowbridge B. W. , Schwartzkroin P. A.
Published: December 2017

1. There is a long-standing debate about whether the large spiny cells in the hilar region of the hippocampus should be classified as pyramidal cells of Ammon's horn or as a distinct cell type of the dentate gyrus. The rationale for grouping these hilar neurons (termed "mossy cells") with pyramidal cells of Ammon's horn is shared characteristics. In the present study we have compared the morphological and physiological characteristics of mossy cells and nearby CA3c pyramidal cells with the use of a rat hippocampal slice preparation. 2. Biocytin-labeled neurons were examined on the basis of soma area, location, shape, number of primary dendrites, extent of dendritic spines, dendritic location, and axon trajectories. Mossy cells had larger soma areas than CA3c pyramidal cells, and they had more large complex spines (thorny excrescences) on their proximal dendrites and somata than CA3c pyramidal cells. Mossy cell dendritic trees and axon collaterals ramified in different regions of the hippocampus than dendrites and axons of CA3c pyramidal cells. 3. Intrinsic physiological properties, and spontaneous and evoked synaptic properties, were measured and compared. Mossy cells had significantly higher input resistances, smaller amplitude burst afterhyperpolarizations, smaller amplitude action potentials, less spike-frequency adaptation, and more anomalous rectification than CA3c pyramidal cells. 4. Mossy cells had spontaneous excitatory postsynaptic potentials (EPSPs) that were significantly higher in frequency and larger in amplitude than CA3c pyramidal cells. A larger proportion of mossy cells than CA3c pyramidal cells responded to perforant path stimulation with depolarizing postsynaptic potentials without any apparent hyperpolarization. Conversely, a smaller proportion of mossy cells than CA3c pyramidal cells responded to perforant path stimulation with inhibitory postsynaptic potentials (IPSPs), and spontaneous IPSPs were more difficult to detect in mossy cells. 5. The intrinsic physiological properties of mossy cells endow these cells with potent excitatory mechanisms but relatively fewer inhibitory control processes than CA3c pyramidal cells. Recordings of spontaneous and evoked PSPs suggest that mossy cells receive more excitatory input and less inhibitory input than CA3c pyramidal cells. These intrinsic and synaptic properties of mossy cells may explain this cell type's exceptional vulnerability to excitotoxic damage by intense afferent stimulation. 6. In summary, mossy cells were significantly different from CA3c pyramidal cells in many of their morphological, intrinsic physiological, and synaptic properties.(ABSTRACT TRUNCATED AT 400 WORDS)
Distribution of rubrospinal synaptic input to cat triceps surae motoneurons
Authors: Powers R. K. , Robinson F. R. , Konodi M. A. , Binder M. D.
Published: December 2017

1. We evoked steady-state synaptic potentials in triceps surae motoneurons of the cat by stimulating the hindlimb projection area of the contralateral magnocellular red nucleus at 200 Hz. We measured the effective synaptic currents (IN) underlying the synaptic potentials using a modified voltage-clamp technique. We also determined the effect of the rubrospinal input on the discharge rate of some of the motoneurons by inducing repetitive discharge with long injected current pulses during which the red nucleus stimulation was repeated. 2. At motoneuron resting potential, the distribution of IN from the red nucleus within the triceps surae pools was qualitatively similar to the distribution of synaptic potentials: 86% of the putative type F motoneurons received a net depolarizing IN from the red nucleus stimulation, whereas only 38% of the putative type S units did so. The mean values of IN were significantly different in the two groups [+4.1 +/- 5.0 nA (SD) for putative type F and -1.6 +/- 3.1 nA for putative type S]. 3. However, when the values of IN at threshold for repetitive firing were estimated, the distribution of IN from the red nucleus was quite different. At threshold, all of the putative type S units received hyperpolarizing IN but so did nearly half of the putative type F units. 4. As would be expected from the wide range of IN at threshold (-20 to +12 nA), the red nucleus input produced dramatically different effects on the discharge of different motoneurons.(ABSTRACT TRUNCATED AT 250 WORDS)
Periodic synchronized bursting and intracellular calcium transients elicited by low magnesium in cultured cortical neurons
Authors: Robinson H. P. , Kawahara M. , Jimbo Y. , Torimitsu K. , Kuroda Y. , Kawana A.
Published: December 2017

1. In Mg(2+)-free external solution, rat cortical neurons in cultured networks entered a stable firing mode, consisting of regular bursts of action potentials superimposed on long-lasting depolarizations. The average separation between bursts varied from culture to culture, but was usually between 5 and 20 s. The distribution of burst intervals followed a Gaussian or normal distribution, with a standard deviation of typically 10% of the average burst period. 2. A gradually depolarizing pacemaker potential was never observed between bursts, but the threshold for action potentials during the quiescent phase was > or = 10 mV above the resting potential. No progressive change in conductance or excitability was observed during the quiescent period. Intracellular stimulation of action potentials did not reproduce the long-lasting depolarization. 3. Switching from current clamp to voltage clamp at the resting potential revealed large postsynaptic currents, mainly excitatory but with a small inhibitory component, at the same phase and frequency as the spike bursts, showing that periodic synaptic input is responsible for the burst-depolarizations. The current could be eliminated by local application of 2-amino-5-phosphonovaleric acid (APV) or 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) to the postsynaptic cell. In the presence of tetrodotoxin, irregular miniature excitatory postsynaptic currents were observed. 4. A fluorescent calcium indicator (fluo-3, 100 microM) was included in the whole-cell pipette solution, to allow simultaneous electrical and calcium measurements in the same cell. In current clamp, transient intracellular calcium increases were found, which were synchronized to the spike bursts. The Ca2+ rise lasted as long as the action potential burst, and was followed by an exponential decay considerably slower than that of the membrane potential. Calcium transients disappeared during voltage clamp at the resting potential, suggesting that calcium influx through voltage-dependent calcium channels greatly exceeds that through synaptic channels. 5. Multisite Ca2+ recording, after loading with fluo-3 acetoxymethyl (AM) ester, revealed that the onsets of burst-related calcium transients were synchronized in all active cells of each view-field, to within approximately 20 ms. Occasionally, secondary rhythms were observed in which only a subset of cells participated. The times to peak and the decay times of calcium transients varied among synchronized cells. 6. The pharmacology of the burst-related calcium transients was investigated by bath application of a variety of compounds.(ABSTRACT TRUNCATED AT 400 WORDS)
Single channel recordings of Nt- and L-type Ca2+ currents in rat neurohypophysial terminals
Authors: Wang X. , Treistman S. N. , Lemos J. R.
Published: December 2017

1. Ca2+ currents through single channels in acutely dissociated nerve terminals from rat neurohypophyses were recorded using cell-attached patch recordings with 110 mM Ba2+ as the charge carrier. 2. One type (Nt, where the t denotes terminal) of single Ca2+ channel current was evoked only by depolarizing steps from holding potentials less negative than -50 mV. Because this channel opened primarily at the beginning of a 180-ms-long voltage pulse, the averaged ensemble current decayed rapidly (approximately 30 ms). Infrequently, the channel opened throughout such a long pulse, resulting in a long-lasting averaged ensemble current. The averaged channel open time constant (tau) was 0.34 ms and the two averaged closed time constants were 1.78 (tau 1) and 86.57 (tau 2) ms. The mean unitary slope conductance for this channel was 11 pS and its threshold for activation was approximately -10 mV. 3. The other type (L) of single Ca2+ channel current could be evoked in isolation by depolarizations from holding potentials more positive than or equal to -50 mV. This channel opened throughout an entire 180-ms-long voltage pulse. The averaged ensemble current, therefore, showed little inactivation. The averaged channel open-time constant was 0.49 ms and the two average closed time constants were 2.02 (tau 1) and 79.91 (tau 2) ms. The mean unitary slope conductance for this channel was 25 pS. 4. Bay K 8644 (5 microM), a dihydropyridine (DHP) Ca2+ channel agonist, increased the open probability of the larger-conductance L-type Ca2+ channel by prolonging the average duration (to 2.79 ms) of channel openings, but did not alter the single channel slope conductance. In contrast, the same concentration of Bay K 8644 did not affect the smaller-conductance Nt-type Ca2+ channel. The DHP Ca2+ channel antagonist nicardipine (5 microM), but not nifedipine (5 microM), reduced the open probability of the large-conductance L-type Ca2+ channel by shortening the duration (to 0.36 ms) of channel openings. 5. The voltage- and time-dependent properties of these two types of single Ca2+ channel currents are in close agreement with those of the two components of macroscopic Ca2+ currents previously reported using the "whole-terminal" recording method. Therefore these two types of single channels appear to underlie the macroscopic current. 6. Our studies suggest that the terminal Nt-type Ca2+ channel differs from the conventional somatic N- and T-type Ca2+ channels in some respects, and that the terminal L-type Ca2+ channel is similar to the conventional somatic L-type Ca2+ channel.(ABSTRACT TRUNCATED AT 400 WORDS)
Differential effects of cutaneous and deep application of inflammatory irritant on mechanoreceptive field properties of trigeminal brain stem nociceptive neurons
Authors: Yu X. M. , Sessle B. J. , Hu J. W.
Published: December 2017

1. The aim of this study was to determine whether there are differential neuroplastic effects of cutaneous and deep stimuli on the mechanoreceptive field (RF) properties of nociceptive brain stem neurons recorded in trigeminal (V) subnucleus caudalis. 2. A total of 31 caudalis neurons were functionally identified in anesthetized rats as nociceptive neurons receiving convergent cutaneous and deep afferent inputs, and the effects of the small-fiber excitant and inflammatory irritant mustard oil applied to either tongue muscle or facial skin were tested on their cutaneous and deep RFs. 3. The expression of neuroplasticity on the cutaneous and deep RFs of the neurons was found to depend on the site of application of this irritant. Mustard oil injected into the tongue muscle produced a significant and reversible expansion of both the cutaneous and deep RFs. In contrast, application of mustard oil to facial skin resulted in a significant and reversible expansion of the cutaneous RF, but no deep RF expansion occurred. 4. These findings suggest that considerable functional neuroplasticity of the cutaneous and deep RF properties of V nociceptive neurons can be induced by a peripheral inflammatory irritant and that deep inputs are especially effective in evoking these neuroplastic changes.
Synaptic transmission through cat lumbar ascending sensory pathways is suppressed during active sleep
Authors: Soja P. J. , Oka J. I. , Fragoso M.
Published: December 2017

1. Few data are available that describe the evoked activity of spinal cord sensory tract neurons as a function of behavioral state. Accordingly, experiments were performed in which ascending volleys were recorded extracellularly within the spinoreticular (SRT), spinothalamic (STT), and spinomesencephalic (SMT) tracts located in the ventrolateral reticular formation in response to low-intensity electrical stimulation of the contralateral sciatic nerve in the chronic unanesthetized, behaving cat during naturally occurring episodes of wakefulness, quite sleep, and active sleep. 2. During episodes of wakefulness and quite sleep sciatic nerve stimulation produced a low-amplitude and long-duration orthodromic field potential that did not differ in amplitude or waveform. However, during the corresponding episode of active sleep, the sciatic nerve-induced orthodromic field potential was markedly suppressed or abolished. 3. The effects of sustained microiontophoretic applications of inhibitory amino acid agonists, glycine, or gamma-aminobutyric acid during wakefulness or quite sleep markedly suppressed the antidromic field potential recorded from nearby VII motoneurons but did not alter the sciatic nerve-evoked orthodromic field potential, indicating that the sciatic response was recorded from ascending axons of passage emanating from lumbar spinal neurons. We suggest that lumbar neurons comprising the SRT, STT, and SMT tracts are subjected to a descending suppressor drive that is activated specifically during the behavioral state of active sleep.
Role of the caudal fastigial nucleus in saccade generation. II. Effects of muscimol inactivation
Authors: Robinson F. R. , Straube A. , Fuchs A. F.
Published: December 2017

1. We studied the effect of temporarily inhibiting neurons in the caudal fastigial nucleus in two rhesus macaques trained to make saccades to jumping targets. We placed injections of the gamma-aminobutyric acid (GABA) agonist muscimol unilaterally or bilaterally at sites in the caudal fastigial nucleus where we had recorded saccade-related neurons a few minutes earlier. 2. Unilateral injections (n = 9) made horizontal saccades to the injected side hypermetric and those to the other side hypometric (mean gain of 1.37 and 0.61, respectively, for 10 degrees target steps, and 1.26 and 0.81 for 20 degrees target steps; normal saccade gain was 0.96). Saccades to vertical targets showed a small but significant hypermetria and curved strongly toward the side of the injection. The trajectories and end points of all targeted saccades were more variable than normal. 3. After unilateral injections, centripetal saccades were slightly larger than centrifugal saccades (mean gains for ipsilateral saccades were 1.42 and 1.31, respectively, for 10 degrees target steps, and 1.37 and 1.15 for 20 degrees target steps). 4. Unilateral injections increased the average acceleration of ipsilateral saccades and decreased the acceleration of contralateral saccades. Injections decreased both the acceleration and deceleration of vertical saccades. 5. After dysmetric saccades, monkeys acquired the target with an abnormally high number of hypometric corrective saccades. Injection increased the average number of corrective saccades from 0.6 to 2.1 after 10 degrees horizontal target steps and from 0.8 to 2.1 after 20 degrees steps. The size of each successive corrective saccade in a series decreased, and the latency from the previous corrective saccade increased. 6. Bilateral injections (n = 2) of muscimol, in which we injected first into the left caudal fastigial nucleus and then, within 30 min, into the right, made all saccades hypermetric (mean gain for 10 degrees right, left, up, and down saccades was 1.18, 1.49, 1.43, and 1.10, respectively). Paradoxically, bilateral injection decreased both saccade acceleration and deceleration. Saccade trajectories and end points were more variable than normal. 7. To account for the effects of our injections, we propose that the activity of caudal fastigial neurons on one side normally helps to decelerate ipsilateral saccades and helps to accelerate contralateral saccades by influencing the feedback loop of the saccade burst generator in the brain stem. Without caudal fastigial activity the brain stem burst generator produces hypermetric, variable saccades. We therefore also propose that the influence of caudal fastigial neurons on the burst generator makes saccades more consistent and accurate.(ABSTRACT TRUNCATED AT 400 WORDS)
Fos-like immunoreactivity in the superficial medullary dorsal horn induced by noxious and innocuous thermal stimulation of facial skin in the rat
Authors: Strassman A. M. , Vos B. P. , Mineta Y. , Naderi S. , Borsook D. , Burstein R.
Published: December 2017

1. To examine further the ability of different classes of nociceptive and nonnociceptive primary afferent neurons to induce c-fos expression in central neurons, fos-like immunoreactivity was examined in the medullary dorsal horn (laminae I-IV) of the rat after facial application of a range of warming and cooling thermal stimuli. Urethan-anesthetized rats received 15 30-s thermal pulses (53, 50, 47, 41, 25, or 10 degrees C) applied to the vibrissal pad over a period of 30 min and were perfused 2 h after the end of stimulation. 2. Stimulation of 41 degrees C produced no significant increase in the number of fos-LI-labeled cells in lamina I or II compared with control (35 degrees C) animals. 3. Stimulation of 47 degrees C produced a significant increase in the number of fos-LI-labeled cells in both laminae I and II. Stimulation of 50 degrees C produced a significant increase in labeling, compared with that produced by 47 degrees C, which was primarily in lamina II. Stimulation of 53 degrees C produced no further increase in the number of labeled cells, compared with that produced by 50 degrees C, in lamina I or II. 4. In the cooling direction, 25 degrees C produced a significant increase in labeling above control levels in both lamina I and II, whereas 10 degrees C produced a further increase compared with 25 degrees C, which was restricted to lamina I. 5. None of the stimuli produced a significant increase in labeling in laminae III-IV. 6. The results are interpreted as providing evidence that low-threshold cold receptors, high-threshold cold receptors, and nociceptors are capable of inducing fos expression in dorsal horn neurons, whereas warm receptors are relatively ineffective. The results also provide evidence that neurons that receive input from C polymodal nociceptors are present in both laminae I and II, as are neurons that receive input from low-threshold cold receptors. Neurons that receive input from high-threshold cold receptors, but not from low-threshold cold receptors, appear to be located preferentially in lamina I. The shape of the curve relating fos-LI labeling to stimulus temperature in the warming direction is consistent with the expected pattern of recruitment of primary afferent nociceptors.
Posttetanic hyperpolarization produced by electrogenic Na(+)-K+ pump in lizard axons impaled near their motor terminals
Authors: Morita K. , David G. , Barrett J. N. , Barrett E. F.
Published: December 2017

1. The hyperpolarization that follows tetanic stimulation was recorded intra-axonally from the internodal region of intramuscular myelinated motor axons. 2. The peak amplitude of the posttetanic hyperpolarization (PTH) that followed stimulation at 20-100 Hz for < or = 35 s increased with increasing train duration, reaching a maximum of 22 mV. PTH decayed over a time course that increased from tens to hundreds of seconds with increasing train duration. For a given frequency of stimulation the time integral of PTH was proportional to the number of stimuli in the train, averaging 3-4 mV.s per action potential. 3. Ouabain (0.1-1 mM) and cyanide (1 mM) depolarized the resting potential and abolished PTH. Tetanic stimulation in ouabain was followed by a slowly decaying depolarization (probably due to extra-axonal K+ accumulation) whose magnitude and duration increased as the duration of the train increased. 4. Axonal input resistance showed no consistent change during PTH in normal solution but increased during PTH in the presence of 3 mM Cs+ (which blocks axonal inward rectifier currents). 5. PTH was abolished when bath Na+ was replaced by Li+ or choline. PTH persisted after removal of bath Ca2+ and addition of 2 mM Mn2+. 6. Removal of bath K+ abolished the PTH recorded after brief stimulus trains and greatly reduced the duration of PTH recorded after longer stimulus trains. 7. A brief application of 10 mM K+, which normally depolarizes axons, produced a ouabain-sensitive hyperpolarization in axons bathed in K(+)-free solution. 8. These observations suggest that in these myelinated axons PTH is produced mainly by activation of an electrogenic Na(+)-K(+)-ATPase, rather than by changes in K+ permeability or transmembrane [K+] gradients. This conclusion is supported by calculations showing agreement between estimates of Na+ efflux/impulse based on PTH measurements and estimates of Na+ influx/impulse based on nodal voltage-clamp measurements. Pump activity also appears to contribute to the resting potential. 9. The stimulus intensity required to initiate a propagating action potential increased during PTH but decreased during the posttetanic depolarization recorded in ouabain. Thus changes in axonal excitability after tetanic stimulation correlate with changes in the posttetanic membrane potential. 10. Action potentials that propagated during PTH had a larger peak amplitude and were followed by a larger and longer depolarizing afterpotential than action potentials elicited at the resting potential. This enhancement of the depolarizing afterpotential is consistent with previous reports of an increased superexcitable period after action potentials evoked during PTH.
Signal delay and input synchronization in passive dendritic structures
Authors: Agmon-Snir H. , Segev I.
Published: December 2017

1. A novel approach for analyzing transients in passive structures called "the method of moments" is introduced. It provides, as a special case, an analytic method for calculating the time delay and speed of propagation of electrical signals in any passive dendritic tree without the need for numerical simulations. 2. Total dendritic delay (TD) between two points (y, x) is defined as the difference between the centroid (the center of gravity) of the transient current input, I, at point y[tI(y)] and the centroid of the transient voltage response, V, at point x [tV(x)]. The TD measured at the input points is nonzero and is called the local delay (LD). Propagation delay, PD(y, x), is then defined as TD(y, x)--LD(y) whereas the net dendritic delay, NDD(y, 0), of an input point, y, is defined as TD(y, 0) - LD(0), where 0 is the target point, typically the soma. The signal velocity at a point x0 in the tree, theta(x0), is defined as [1/(dtv(x)/dx)[x = x0. 3. With the use of these definitions, several properties of dendritic delay exist. First, the delay between any two points in a given tree is independent of the properties (shape and duration) of the transient current input. Second, the velocity of the signal at any given point (y) in a given direction from (y) does not depend on the morphology of the tree "behind" the signal, and of the input location. Third, TD(y, x) = TD(x, y), for any two points, x, y. 4. Two additional properties are useful for efficiently calculating delays in arbitrary passive trees. 1) The subtrees connected at the ends of any dendritic segment can each be functionally lumped into an equivalent isopotential R-C compartment. 2) The local delay at any given point (y) in a tree is the mean of the local delays of the separate structures (subtrees) connected at y, weighted by the relative input conductance of the corresponding subtrees. 5. Because the definitions for delays utilize difference between centroids, the local delay and the total delay can be interpreted as measures for the time window in which synaptic inputs affect the voltage response at a target/decision point. Large LD or TD is closely associated with a relatively wide time window, whereas small LD or TD imply that inputs have to be well synchronized to affect the decision point. The net dendritic delay may be interpreted as the cost (in terms of delay) of moving a synapse away from the target point.(ABSTRACT TRUNCATED AT 400 WORDS)
Possible network interactions indicated by bilaterally coherent fast rhythms in expiratory recurrent laryngeal nerve discharges
Authors: Huang W. X. , Christakos C. N. , Cohen M. I. , He Q.
Published: December 2017

1. In a search for correlated fast rhythms in recurrent laryngeal (RL) expiratory (E) activities, we performed spectral and coherence analysis on bilateral RL nerve discharges in 54 midcollicular decerebrate, paralyzed cats. 2. Inspiratory (I) RL activities showed in almost all cases high-frequency oscillations (HFO, range 50-100 Hz) that were bilaterally coherent and also coherent to HFOs in phrenic (PHR) activities. In contrast, bilaterally coherent rhythms (range 24-54 Hz) in RLE discharges were found in only a fraction of the cats (6/54); in the other cats (48/54) such coherences were absent even though the auto-spectra showed the presence of similar fast rhythms on the two sides. The bilateral RLE coherences were associated with increased amplitude and prolonged duration of RLE activity, such as occurred following removal of phasic pulmonary stretch receptor inputs by vagotomy or by no-inflation. 3. Thus, although coherent fast rhythms are uncommon in RLE discharges, their occurrence under some conditions indicates the presence of short-time-scale interactions between neurons involved in this activity. This suggests that such rhythms are a general feature of neural networks.
Electrophysiological properties of identified classes of lamprey spinal neurons
Authors: Buchanan J. T.
Published: December 2017

1. As part of a continuing analysis of the mechanisms of the central pattern generator underlying fictive swimming in lamprey, a systematic survey of electrophysiological properties of lamprey neurons was made in the in vitro spinal cord preparation with the use of intracellular current-clamp recordings. A total of 70 neurons was included in the study, representing 6 classes of spinal neurons. The classes were myotomal motoneurons, three classes of interneurons involved in fictive swimming [lateral interneurons, nerve cells with contralateral and caudal projecting axons (CC interneurons), and excitatory interneurons], and two classes of interneurons involved in sensory processes (edge cells and giant interneurons). The recordings were done in quiescent preparations. 2. There was little or no significant difference among the cell classes with regard to resting potential, threshold potential, action-potential amplitude, or action-potential duration. 3. The voltage versus current relationships for the cells were fairly linear near resting potential, although most cells showed a slight tendency to rectify with depolarization above resting potential. This tendency was strongest among edge cells and lateral interneurons and weakest among motoneurons and CC interneurons. The input resistances, membrane time constants, and rheo-bases for the cell classes showed significant differences among some classes. For example, CC interneurons and excitatory interneurons had significantly higher input resistances than the other cell classes. 4. The late afterhyperpolarization following the action potential tended to be larger in amplitude with an earlier peak and a longer duration in edge cells and giant interneurons than in the other cell classes. 5. All cells responded to depolarizing current injections by firing action potentials, and almost all cells fired action potentials throughout the 400-ms current pulse. The cells exhibited adaptation resulting in increasing interspike intervals during the current pulse. The adaptation, however, was insufficient to terminate firing before the end of the current pulse. The relationship between frequency of firing and input current was generally monotonic with a tendency to saturate at higher current levels. 6. The general conclusion from this study is that the spinal neurons that partake in fictive swimming (motoneurons, lateral interneurons, CC interneurons, and excitatory interneurons) are similar in their resting and action-potential mechanisms. Their most prominent differences are in size-related properties. The sensory-related interneurons, especially the edge cells and to some extent the giant interneurons, exhibited more pronounced differences in their resting and action-potential properties when compared with the other cell classes.