bluuebunny/crossref_metadata_2025 huggingface dataset:
The effects of contrast on visual orientation and spatial frequency discrimination: a comparison of single cells and behavior
Authors: Skottun B. C. , Bradley A. , Sclar G. , Ohzawa I. , Freeman R. D.
Published: December 2017

We have compared the effects of contrast on human psychophysical orientation and spatial frequency discrimination thresholds and on the responses of individual neurons in the cat's striate cortex. Contrast has similar effects on orientation and spatial frequency discrimination: as contrast is increased above detection threshold, orientation and spatial frequency discrimination performance improves but reaches maximum levels at quite low contrasts. Further increases in contrast produce no further improvements in discrimination. We measured the effects of contrast on response amplitude, orientation and spatial frequency selectivity, and response variance of neurons in the cat's striate cortex. Orientation and spatial frequency selectivity vary little with contrast. Also, the ratio of response variance to response mean is unaffected by contrast. Although, in many cells, response amplitude increases approximately linearly with log contrast over most of the visible range, some cells show complete or partial saturation of response amplitude at medium contrasts. Therefore, some cells show a clear increase in slope of the orientation and spatial frequency tuning functions with increasing contrast, whereas in others the slopes reach maximum values at medium contrasts. Using receiver operating characteristic analysis, we estimated the minimum orientation and spatial frequency differences that can be signaled reliably as a response change by an individual cell. This analysis shows that, on average, the discrimination of orientation or spatial frequency improves with contrast at low contrasts more than at higher contrasts. Using the optimal stimulus for each cell, we estimated the contrast threshold of 48 neurons. Most cells had contrast thresholds below 5%. Thresholds were only slightly higher for nonoptimal stimuli. Therefore, increasing the contrast of sinusoidal gratings above approximately 10% will not produce large increases in the number of responding cells. The observed effects of contrast on the response characteristics of nonsaturating cortical cells do not appear consistent with the psychophysical results. Cells that reach their maximum response at low-to-medium contrasts may account for the contrast independence of psychophysical orientation and spatial frequency discrimination thresholds at medium and high contrasts.
Reorganization of the receptive fields of spinocervical tract neurons following denervation of a single digit in the cat
Authors: Wilson P. , Snow P. J.
Published: December 2017

The effect of acute and chronic section of the digital nerves of a single toe on the organization of low-threshold, mechanoreceptive fields of lumbosacral spinocervical tract (SCT) neurons has been studied in adult cats anesthetized with chloralose. The immediate effect of sectioning the digital nerves of a single toe is to produce a patch of dorsal horn in the medial region of the ipsilateral lumbosacral cord in which SCT neurons lack any peripheral receptive field when gentle hair movement or light touch of glabrous skin are used as stimuli. Other SCT neurons in the region may lose only part of their receptive fields. Between 30 and 70 days later most of the affected SCT neurons have established receptive fields. These are mainly on somatotopically inappropriate areas of skin medially and laterally adjacent to the denervated region. A small proportion of SCT neurons form discontinuous receptive fields. The relative somatotopic organization within the affected region remains unchanged. As there is no sign of regeneration of the sectioned nerves the new receptive fields must result from a central reorganization of excitatory inputs to SCT neurons. It is concluded that chronic peripheral nerve section affects the anatomical and physiological mechanisms underlying the formation of light touch receptive fields of dorsal horn neurons in the lumbosacral cord of the adult cat, but that the resulting reorganization of receptive fields is spatially restricted.
Modulation of pacemaker activity by IPSP and brief length perturbations in the crayfish stretch receptor
Authors: Buno W. , Fuentes J. , Barrio L.
Published: December 2017

We have studied the influences of brief stretches and releases and of inhibitory postsynaptic potentials (IPSPs) on pacemaker activity of the crayfish stretch receptor (RM1). Stimuli shift or reset the ongoing rhythm. Resettings were different if evaluated in interspike intervals containing perturbations, or in succeeding ones, and are referred to as early and late, respectively. Early resetting revealed that stretches and releases or IPSPs advance and delay, respectively, the next spike. With small stretches and releases or IPSPs, effects depend on the timing of the perturbation relative to the previous spike or phase, but above a characteristic mechanical perturbation amplitude the next spike fires at a fixed latency, invariant with the phase. Of particular interest was the finding that during late resetting the first successive intervals following stretches and releases or IPSPs were longer and shorter, respectively, than the period. This led, in approximately 50% of the cases, to a gradual recovery of the original pacemaker beat in the sense that spikes fire timed as if the early rhythm shift had not occurred. In conclusion, the recent firing history is essential in determining the RM1's response. The receptor's sensitivity is a complex nonlinear and periodic function of the pacemaker activity, and the response is due to interactions between pacemaker- and perturbation-induced transmembrane ionic currents. Although several alternative mechanisms may underly beat recovery, the results suggest that at least two coupled oscillators, one perturbable and the other not, provide a better explanation than a single oscillator. The physiological significance of resettings is unknown, but the early rhythm shift may synchronize RM1s in several segments when the animal's tail is moved, and conversely recovery would reduce synchrony, with obvious influences on shared postsynaptic neurons.
Histidine-rich basic peptide: a cardioactive neuropeptide from Aplysia neurons R3-14
Authors: Campanelli J. T. , Scheller R. H.
Published: December 2017

We have previously demonstrated that neurons R3-14 of the Aplysia abdominal ganglia specifically express a gene encoding a 108-amino acid neuropeptide precursor. This precursor is postranslationally processed by cleavage of a signal sequence and two internal dibasic residues resulting in three peptides. The peptide products are colocalized in dense core granules throughout the R3-14 processes that innervate the efferent vein of the gill and the auricle. Gel filtration and reverse phase high-pressure liquid chromatography (rpHPLC) were used to purify a 4.9-kDa peptide produced by the R3-14 neurons. We call this peptide the histidine-rich basic peptide (HRBP), which reflects its primary structure. In vitro tension measurements of cannulated Aplysia hearts revealed dose-dependent cardioexcitatory actions of HRBP. HRBP increased both beat frequency and amplitude with a threshold of 10(-7) M. HRBP increased the amplitude of ventricular contractions in a dose-dependent manner, whereas the frequency of contraction is unaffected. In contrast both the amplitude and frequency of auricular contractions were enhanced. High concentrations of HRBP also had a positive tonotropic effect on the auricle. HRBP was also demonstrated to have actions on tissue of the gut. Circular muscles of the crop adjacent to the anterior gizzard showed infrequent spontaneous contractions. Both HRBP and acetylcholine (ACh) induced repetitive contractions of this muscle. Circular muscles of the posterior gizzard had a high degree of spontaneous activity when continually perfused. Contraction amplitude and frequency was increased by HRBP and ACh, whereas contractility was inhibited by Phe-Met-Arg-Phe-amide (FMRFamide).
Noradrenaline-induced afterdepolarization in cat sympathetic preganglionic neurons in vitro
Authors: Yoshimura M. , Polosa C. , Nishi S.
Published: December 2017

Sympathetic preganglionic neurons of the intermediolateral nucleus were identified by antidromic stimulation in the slice of the T2 or T3 segment of the cat spinal cord. In normal Krebs solution, the action potential of these neurons had a shoulder on the repolarization phase and was followed by a long-lasting afterhyperpolarization (AHP). The AHP had a fast and a slow component. Superfusion of the slice with noradrenaline (NA), 10-50 microM, resulted in depression of the shoulder on the repolarization phase of the action potential, in the appearance of an afterdepolarization (ADP), which was absent in control conditions, and in depression of the slow component of the AHP. These effects were present whether the membrane potential of the sympathetic preganglionic neurons was decreased, increased, or not changed by NA. A typical ADP had time to peak of 50 ms and decay time of 200-500 ms; the amplitude was variable and large ADPs could be suprathreshold, causing repetitive firing. The amplitude and duration of the ADP increased with NA concentration. The appearance of the ADP seemed to be independent of the depressant effect of NA on the slow AHP. The ADP was associated with a decrease in neuron input resistance and was voltage dependent, being depressed in nonlinear fashion by membrane hyperpolarization. The ADP decreased in amplitude or disappeared within a range of membrane potentials from -70 to -90 mV. The ADP was reversibly suppressed by the Ca-channel blocker cobalt (2 mM), by low Ca Krebs (0.25 mM), and by iontophoretic injection of ethyleneglycol-bis(B-aminoethyl-ether)-N,N'-tetraacetic acid into the cell. Increasing Ca concentration from 2.5 to 10.0 mM had no effect. The ADP was unaffected by tetrodotoxin, at a concentration blocking the Na spike, but was suppressed in Na-free medium, even when the Ca spike was prolonged by tetraethylammonium 20 mM. Changes in external K concentration from 3.6 to 2.5 or 10.0 mM did not change the ADP. Increasing intracellular Cl concentration or decreasing extracellular Cl concentration had no effect on the ADP. It is concluded that the ADP, evoked by NA, is due to an increase in membrane conductance involving Na and Ca ions, possibly a Ca-activated Na conductance. The ADP provides a mechanism with which NA may modulate sympathetic preganglionic neuron responsiveness to excitatory synaptic inputs.
Single-cell neuronal model for associative learning
Authors: Gingrich K. J. , Byrne J. H.
Published: December 2017

Recently, a novel cellular mechanism, activity-dependent neuromodulation, was identified in sensory neurons mediating the gill and tail withdrawal reflexes in Aplysia. This mechanism may explain associative learning on a behavioral level. The present study was designed to mathematically model subcellular events that may underlie this mechanism and to examine the ability of the model to fit available empirical data. In this associative model, the reinforcing or unconditioned stimulus (US) leads to non-specific enhancement of transmitter release from sensory neurons by activating a cAMP cascade. Spike activity in sensory neurons, the conditioned stimulus (CS), transiently elevates intracellular Ca2+. The CS-triggered increases of intracellular Ca2+ “primes” the cyclase and amplifies the US-mediated cAMP synthesis. As a result of pairing specific amplification of cAMP levels, transmitter release is enhanced beyond that produced by unpaired stimuli or by application of the US alone. The model is capable of fitting empirical data on activity-dependent neuromodulation and predicts a characteristic interstimulus interval (ISI) curve. At the subcellular level, the model's ISI function is related to the time course of the buffering of intracellular Ca2+. The magnitude and duration of the pairing specific enhancement of transmitter release is related to the levels and time course of intracellular cAMP stimulation.
Postnatal development of electrical activity in the locus ceruleus
Authors: Nakamura S. , Kimura F. , Sakaguchi T.
Published: December 2017

1. A method for adapting a standard stereotaxic frame for use with neonatal rats as young as postnatal day 1 (PD 1) was devised, and single-unit extracellular recordings were obtained from neurons in the locus ceruleus (LC) in urethan-anesthetized rats during different stages in development from PD 1 to PD 34. 2. The spontaneous firing pattern of neonatal LC neurons was characterized by long silent periods punctuated by brief epochs of sporadic firing. At PD 7-14, LC neurons exhibited periodic occurrences of irregular firing that lasted for 20-30 s. By PD 20, the pattern and rate of spontaneous activity were virtually indistinguishable from that of adults. 3. Conditioning stimulation of the dorsal noradrenergic bundle (DNB), given 10-200 ms prior to a test stimulus to the DNB, markedly reduced the amplitude of the antidromic action potentials to the test stimulus and sometimes resulted in spike decomposition. This refractoriness of the soma-dendritic membrane of LC cells was significantly attenuated with development and approached adult levels after PD 18. 4. Antidromic responses elicited by DNB stimulation were followed by a phase of inhibition or inhibition-excitation. Postactivation excitation was most prominent in cells that were not spontaneously active, and decreased steadily throughout development, probably because of the steady increase in spontaneous firing rate seen during maturation. 5. Although the conduction velocity of LC axons increased steadily from birth through PD 26, conduction time remained unchanged. 6. Neonatal LC neurons were equally sensitive to noxious and nonnoxious somatosensory stimuli. As development proceeded, LC neurons became less sensitive to innocuous somatosensory stimuli such as air puffs and tactile stimuli while simultaneously becoming more sensitive to noxious stimuli. Auditory and visual stimuli became effective for the first time at PD 14 and PD 12, respectively. 7. These results indicate that the electrical activity of LC neurons in the developing brain is intimately related to input from peripheral sensory sources. Therefore, the influence of the LC on the developing brain may occur predominantly through sensory input.
Serotonin and forskolin increase an inwardly rectifying potassium conductance in cultured identified Aplysia neurons
Authors: Lotshaw D. P. , Levitan I. B.
Published: December 2017

1. The effect of serotonin (5-HT) and forskolin on an inwardly rectifying K+ conductance (IKR) was studied using voltage-clamp techniques in several identified Aplysia neurons isolated and maintained in primary cell culture. 2. Inward rectification was observed in the current-voltage relationship of the identified neurons R15, R2, B1, and B2 and was predominately due to IKR, as demonstrated by the dependence of inward rectification on the extracellular K+ concentration, instantaneous kinetics of the membrane current response to hyperpolarizing voltage clamp pulses, and voltage-dependent Ba2+ block of the inwardly rectifying current. 3. 5-HT increased IKR conductance between 100 and 400% in the identified neuron R15 in culture and increased IKR conductance approximately 50% in the identified neurons B1, B2, and R2 in culture. The adenylate cyclase activator, forskolin, plus a phosphodiesterase inhibitor, Ro 20-1724, also increased IKR conductance in these neurons. 4. 5-HT and forskolin modulated other ion conductances as well in all of these cultured neurons.
Different responses to small visual errors during initiation and maintenance of smooth-pursuit eye movements in monkeys
Authors: Morris E. J. , Lisberger S. G.
Published: December 2017

1. We have investigated the role of retinal and extraretinal signals in the initiation and maintenance of smooth-pursuit eye movements in trained rhesus monkeys. Visual targets were presented in open-loop conditions by using electronic feedback of eye position to form the command for target position. This allowed us to present stimuli that were stabilized with respect to the moving eye or to provide small, precisely controlled retinal position or velocity errors. 2. Pursuit was maintained with only small decreases in eye velocity if retinal errors were eliminated by stabilizing the tracking target in front of the fovea during pursuit at 15 degrees/s. This argues that the pursuit system employs “velocity memory” to maintain pursuit. We suggest that velocity memory is effected by an extraretinal signal derived from positive feedback of eye-velocity commands. 3. Small retinal position errors caused smooth eye accelerations if imposed during pursuit, but were ineffective for initiating the transition from steady fixation to pursuit. Small retinal velocity errors were effective both for initiating pursuit from steady fixation and for altering eye velocity during pursuit. 4. Retinal position errors were effective at changing smooth eye velocity in a variety of conditions that required prior activation of the pursuit system. These include pursuit with or without a stationary background, pursuit with a background that was stabilized with respect to the eye, pursuit with combined eye and head motion (cancellation of the vestibuloocular reflex), and use of pursuit to suppress optokinetic nystagmus. Position errors were ineffective during fixation of stationary targets, even if head motion was provided to evoke the smooth eye velocity of the vestibuloocular reflex. 5. We conclude that retinal position errors are effective only after the pursuit system has been activated. It follows that pursuit initiation involves an active transition from steady fixation and that this transition is normally triggered by retinal velocity errors but not by retinal position errors.
The inhibition of cat lateral superior olive unit excitatory responses to binaural tone bursts. II. The sustained discharges
Authors: Tsuchitani C.
Published: December 2017

1. Preliminary to extending a point process model of lateral superior olive (LSO) unit activity to describe the units' binaural responses, the statistical properties of their discharges to binaural tone bursts were studied. The hypothesis that stimulation of the contralateral ear results in the simple reduction of the ipsilateral input was also examined. Single-unit activity was recorded extracellularly from the LSO of the anesthetized cat. The sustained discharges to characteristic frequency (CF) tone bursts presented simultaneously to the two ears were examined to determine whether the fine temporal (statistical) properties of these discharges differed from those of the discharges elicited by stimulating the ipsilateral ear alone. 2. The major effect of simultaneously stimulating the contralateral ear was the inhibition (i.e., the reduction in the mean discharge rate) of the sustained discharges to the ipsilateral control stimulus. The temporal pattern of discharges to the ipsilateral stimulus was also affected by stimulation of the contralateral ear. The discharges to binaural stimulation were more irregular in pattern: they often produced bimodal or multimodal interval histograms where unimodal interval histograms had been produced by the discharges to the ipsilateral control stimulus alone. The hazard function, an estimate of the unit recovery function, also often differed in form for the binaural and monaural discharges. 3. The binaural discharges could be distinguished from an ipsilaterally elicited discharge of comparable mean rate: there was a greater incidence of “short” interspike intervals in the binaural discharge. These short interspike intervals occurred most frequently in the discharges to the ipsilateral control stimulus alone and infrequently in the discharges to an ipsilateral stimulus that produced a mean rate similar to that of the binaural discharge. Thus the dead time estimates derived from the binaural discharges were more similar to the estimates derived from the ipsilateral control discharges than to those derived from the comparable-rate ipsilaterally elicited discharges. 4. Although the measures of the recovery properties of LSO unit discharges differed under monaural and binaural stimulus conditions, the serial dependence observed between successive interspike intervals in the binaurally elicited discharges was similar to that in the ipsilaterally elicited discharges. The conditional mean function, an estimate of the serial dependence or unit shifting function, did not differ greatly in form for the monaural and binaural discharges.(ABSTRACT TRUNCATED AT 400 WORDS)
Acute inflammation of the knee joint in the cat alters responses of flexor motoneurons to leg movements
Authors: He X. , Proske U. , Schaible H. G. , Schmidt R. F.
Published: December 2017

1. This is a report of changes in reflex excitability of flexor motoneurons in response to innocuous mechanical stimuli following initiation of an acute experimental inflammation of the knee joint in the chloralose-anaesthetized cat spinalized at level T12. 2. Activity of functionally single alpha- or gamma- motoneurons, identified by ventral root stimulation, was recorded in filaments of the nerve to biceps semitendinosus before and after onset of an acute inflammation. The inflammation was evoked by injection into the knee cavity of the compounds kaolin and carrageenan. 3. Measurements were made of resting activity, responses to local pressure applied to parts of the upper or lower limb, and to flexion or extension movements at the knee joint before and after onset of the inflammation. In two experiments, one in which no inflammation was initiated, and another in which recordings were made only after the inflammation had fully developed, a survey of large numbers of neurons (44 alpha and 84 gamma) showed that under control conditions only 14% of alpha-motoneurons showed a response to mechanical stimulation compared with 41% of gamma-motoneurons. In the presence of an inflammation 41% of alpha-cells were responsive compared with 64% of gamma-cells. 4. Inflammation-induced changes in activity of motoneurons including both excitatory and inhibitory effects, took 1-2 h to fully develop. Excitatory effects included a rise in resting discharge, an increase in the response to local pressure, and an increased response to flexion and/or to extension of the knee. Inhibitory effects included falls in resting discharge and/or in the responses to leg movements. 5. For 35 cells identified as alpha-motoneurons and tested both before and after initiation of an inflammation, 20 remained unresponsive throughout the experiment, whereas 4 that had not responded during the control period began after inflammation to respond to local pressure and/or flexion/extension movements. Of 11 units that exhibited some response before inflammation, 8 showed an increase with inflammation, whereas 2 became unresponsive. 6. The inflammation had rather more dramatic effects on gamma-neurons. Many showed control responses to leg movements, and these were measurably modified by inflammation. Of 56 gamma-cells tested under control conditions, 26 were unresponsive to all stimuli, whereas 30 showed some form of response including activity during flexion and extension movements of the leg. Where responses were tested both before and after onset of an inflammation, 11 of 13 unresponsive units remained unresponsive.(ABSTRACT TRUNCATED AT 400 WORDS)
Electrophysiological characteristics of hamster dorsal root ganglion cells and their response to axotomy
Authors: Gurtu S. , Smith P. A.
Published: December 2017

1. The active and passive membrane properties of neurons in the lower lumbar (L6, L7) or sacral (S1) dorsal root ganglia from golden hamsters were examined in vitro by means of conventional intracellular recording techniques. Data were collected from neurons exhibiting action potentials (AP) of 70 mV or more in amplitude. 2. Cells with axonal conduction velocities (CV) greater than 20 m/s were termed fast-A-cells, those with CVs between 2.5 and 20 m/s were termed A-delta-cells, and those with CVs less than 1 m/s were termed C-cells. 3. Fast-A-cells usually exhibited short-duration APs (2.51 +/- 0.41 ms, n = 19) followed by short (less than 50 ms) afterhyperpolarizations (AHPs). C-cells usually exhibited long-duration APs (10.5 +/- 0.69 ms, n = 18) followed by long-duration AHPs (much greater than 50 ms). The characteristics of APs in A-delta-cells (AP mean duration 3.34 +/- 0.42 ms, n = 32) were intermediate between those of fast-A- and C-cells. Long AHPs (duration much greater than 50 ms) were manifest in 43.8% of A-delta-cells. 4. A time-dependent sag in hyperpolarizing electrotonic potentials (rectification) was found in 68.8% of fast-A-cells, 45.5% of A-delta-cells, and 62.5% of C-cells. 5. To examine neuronal properties 1-6 wk after transection of the sciatic nerve (axotomy), cells were reclassified as SAP (short action potential) cells and LAP (long action potential) cells. Cells in the SAP category had AP durations less than 5 ms and included all fast-A-cells and the majority of A-delta-cells. The LAP category included cells with AP durations greater than 8 ms contained only C-cells. 6. Axotomy failed to decrease the CV of LAP cells or A-delta-cells in the SAP group. The CV of LAP cells may have increased (P less than 0.05), whereas that of SAP cells was unchanged. 7. The duration of the AP and AHP of SAP cells were slightly increased (0.1 greater than P greater than 0.05), whereas AP and AHP duration of LAP cells were unchanged after axotomy. AHP amplitudes of all cell types tended to be smaller (0.1 greater than P greater than 0.05). Axotomy did not alter the resting membrane potential or reduce the incidence of rectification in any cell type. 8. Invasion of the soma by axonally evoked APs was impeded in all cell types after axotomy even though a decrease (P less than 0.05) in rheobase of SAP cells occurred.(ABSTRACT TRUNCATED AT 400 WORDS)
Gastric mill activity in the lobster. III. Effects of proctolin on the isolated central pattern generator
Authors: Heinzel H. G. , Selverston A. I.
Published: December 2017

1. The response of the isolated gastric central pattern generator (CPG) to bath application of proctolin is characterized and compared with the previously analyzed behavioral response. 2. Proctolin had an excitatory effect on the ongoing spontaneous rhythm of "combined" preparations, in which the stomatogastric ganglion (STG) is connected to the esophageal and commissural ganglia by the stomatogastric nerve (STN). The effect started between 20 s and 5 min and was characterized by strongly increased burst durations as well as increased spike rates in all units except the two lateral posterior gastric (LPG) motoneurons. The effect was strongest in the dorsal gastric (DG) and lateral gastric (LG) motoneurons and was accompanied by a phase change of the DG burst. DG continued spiking throughout large parts of the burst of LG and of the gastric mill (GM) motoneurons, which are antagonists of DG. 3. The threshold concentration was approximately 10(-10) M, and the effects were dose dependent and reversible. 4. LG and DG were identified as target cells for the action of proctolin. In LG regenerative plateau properties were induced, as revealed by its long-lasting plateau potentials, sensitivity for triggering inputs, and the occurrence of oscillatory prepotentials. An induction of endogenous bursting in DG was concluded from preparations, in which DG was cycling alone or bursting with a much shorter period duration than other gastric neurons. Hyperpolarization of DG, which normally has no or weak driving power within the gastric network, demonstrated that under the influence of proctolin, firing of DG can accelerate the gastric rhythm from a 27- to a 9-s period duration. 5. Proctolin does not only have a modulatory influence on an ongoing rhythm, but it also can trigger gastric activity. This function was first concluded from proctolin-treated STGs, which, unlike normal preparations, continue bursting if inputs via the STN are blocked. Finally, triggering was demonstrated directly, since isolated STGs that were not oscillating started a gastric rhythm after 20-30 min of perfusion with proctolin. 6. The proctolin-induced changes of the CPG activity in isolated preparations are in agreement with the effect on gastric mill chewing in the intact animal, in which, depending on the dose, different modes of chewing could be elicited.
Delay-tuned combination-sensitive neurons in the auditory cortex of the vocalizing mustached bat
Authors: Kawasaki M. , Margoliash D. , Suga N.
Published: December 2017

1. FM-FM neurons in the auditory cortex of the mustached bat are sensitive to a pair of frequency-modulated (FM) sounds that simulates an FM component of the orientation sound and an FM component of the echo. These neurons are tuned to particular delays between the two FM components, suggesting an encoding of target range information. The response properties of these FM-FM neurons, however, have previously been studied only with synthesized orientation sounds and echoes delivered from a loud-speaker as substitutes for the bat's own orientation sounds and corresponding echoes. In this study, the combination sensitivity and delay tuning of FM-FM neurons were examined while the bat was actively vocalizing. 2. When the bat produced orientation sounds in an anechoic environment, or synthesized single FM echoes were delivered to a silent bat, the FM-FM neurons showed weak or no response. In contrast, when synthesized FM echoes were delivered with a particular delay from the FM component of the vocalized orientation sounds, the FM-FM neurons exhibited strong facilitative responses. 3. In both the vocalizing bats and the silent bats with substituted synthesized orientation sounds, all FM-FM neurons tested responded preferentially to the same echo harmonic (FM2, FM3, or FM4). 4. In vocalizing bats, FM-FM neurons showed maximum response to an echo FM component delivered with a particular delay (best delay) from an FM component in the orientation sound. Best delays measured with vocalized orientation sounds were nearly the same as those measured with synthesized orientation sounds. 5. The equivalent effect of a vocalized orientation sound and a synthesized FM1 component on the activity of FM-FM neurons indicates that, during echolocation, the FM1 component in the vocalized orientation sound stimulates the auditory system and conditions the FM-FM neurons to be sensitive to echoes with particular delays from the vocalized orientation sounds. 6. The amount of vocal self-stimulation to the inner ear by the bat's own vocalized sounds was measured by recording cochlear microphonic potentials (CMs). Spectral analysis of CM indicated that the amount of vocal self-stimulation by each harmonic of an orientation sound was equivalent to a sound of 70 dB sound pressure level (SPL) for the first harmonic (H1), 91 dB SPL for H2, 83 dB SPL for H3, and 70 dB SPL for H4, when the amplitude of the vocalized sound was 117 dB SPL at 5 cm in front of the bat's mouth.
Differential conduction at axonal bifurcations. I. Effect of electrotonic length
Authors: Stockbridge N. , Stockbridge L. L.
Published: December 2017

1. Frequency-dependent differential conduction of action potentials into one daughter branch of the squid giant axon is demonstrated. 2. This differential conduction arises from differences in the electrotonic length of the daughters, rather than inhomogeneities in membrane properties. 3. It may therefore be a more general phenomenon in the nervous system than is differential conduction which does depend upon membrane inhomogeneities.
Three-dimensional sensitivity and caudal projection of neck spindle afferents
Authors: Kasper J. , Schor R. H. , Yates B. J. , Wilson V. J.
Published: December 2017

1. We recorded from neck muscle spindle afferents in the C2 dorsal root ganglion of the decerebrate cat using floating electrodes. The afferents presumably innervated mainly ventral and ventrolateral perivertebral muscles, and sternocleidomastoid. Stimuli consisted of combinations of rotatory head movements about the roll/pitch or pitch/yaw axes. An important difference from our earlier experiments (10) was the addition of yaw movement to the stimulus paradigm making possible a three-dimensional analysis of afferent behavior. 2. For each afferent we determined the most effective direction of tilt (orientation of the response vector) in three dimensions by using sinusoidal stimuli that combined pitch and roll, or pitch and yaw, or by measuring the gains to responses to roll, pitch, and yaw rotation. 3. Most afferents were sensitive to rotation around all three axes; pitch and yaw were usually more effective than roll. There was no indication of clustering of response vectors, as might be expected if the receptors were located in a small number of muscles each of which has receptors aligned in a homogeneous direction. 4. The responses of afferents were further studied using sinusoidal and trapezoidal stimuli aligned as closely as possible with the orientation of their response vector. The availability of the yaw stimulus made receptor classification based on response linearity, gain, and dynamic index more reliable than in our earlier experiments (10). 5. Muscle spindle responses were divided into three categories: A, B, and ambiguous. The evidence suggests that category A are probably spindle primary receptors and category B are secondaries. Ambiguous receptors have intermediate properties. 6. The caudal projection of spindle afferents was examined by delivering antidromic stimuli with a movable electrode on the surface of the ipsilateral dorsal column. Eighteen percent of the afferents projected to C4, and 14% as far as C5. Long caudal projections can be found in A, B, and ambiguous receptors with a range of directional sensitivities. 7. The evidence suggests that C2 spindle afferents make synapses in the midcervical segments with interneurons and propriospinal neurons that are part of the intraspinal pathway of the tonic neck reflex.
Effects of acute dorsal spinal hemisection on motoneuron discharge in the medial gastrocnemius of the decerebrate cat
Authors: Powers R. K. , Rymer W. Z.
Published: December 2017

1. The discharge of single alpha-motoneuron axons was recorded from small cut filaments of the medial gastrocnemius (MG) muscle nerve in the decerebrated cat preparation before and after a dorsal hemisection of the thoracic spinal cord. The remainder of the MG muscle nerve was left intact, and muscle force and multiunit electromyographic (EMG) activity were recorded along with alpha-motoneuron discharge, while motor output was varied by manual stimulation of the contralateral hindlimb. 2. We recorded activity in 32 motoneurons before and after the spinal lesion, and pre- and postlesion recruitment forces and minimum firing rates were determined for 30 of these. Postlesion decreases in minimum firing rates were observed in 25/30 motoneurons, and decreases in recruitment force were seen in 21/30 motoneurons. The remaining motoneurons, which generally had low presection recruitment forces and minimum rates, exhibited postlesion increases in both parameters (see below). 3. The effects of the spinal lesion on the recruitment force and minimum firing rate of a motoneuron were related to the prelesion values of these parameters; the largest postlesion decreases were seen in motoneurons with the highest prelesion rates and recruitment forces. Spinal lesions thus acted to shift and compress the range of recruitment forces and minimum firing rates, so that after the lesion all motoneurons tended to exhibit discharge behavior typical of that seen only in the lowest threshold motoneurons before the lesion. In addition, motoneurons with low prelesion recruitment forces (less than 1.0 N of active force) generally showed an increase in recruitment force after the lesion, indicating that the lesion may have led to changes in the prelesion recruitment order. Direct evidence of recruitment reversals was obtained in 4/14 experiments where two or more motoneurons were followed pre- and postlesion. 4. The lesion-induced changes in motoneuron discharge characteristics were associated with changes in the relations between muscle force, rectified EMG, and motoneuron rate. Postlesion discharge rates were always significantly lower than the prelesion rates when compared over the same range of EMG levels. This postlesion drop in discharge rates was generally associated with inefficient force production, as evidenced by a significant drop in muscle force for matched EMG levels. 5. The degree of discharge synchrony in MG motoneurons was assessed by calculating a spike-triggered average (STA) between axonal discharge and multiunit rectified EMG. Significant STA peaks were rare before the lesion (4/32 motoneurons) but were quite common after the lesion (29/32 motoneurons).(ABSTRACT TRUNCATED AT 400 WORDS)
Responses of mitral/tufted cells to orthodromic and antidromic electrical stimulation in the olfactory bulb of the tiger salamander
Authors: Hamilton K. A. , Kauer J. S.
Published: December 2017

1. Responses evoked by electrical stimulation of the olfactory nerve and olfactory tracts were analyzed in 46 output cells of the salamander olfactory bulb, in vivo. Labeling of several cells with horseradish peroxidase indicated that they were mitral and/or tufted neurons. The responses contained reproducible sequences of depolarizing and hyperpolarizing potentials, which changed with increases in stimulus intensity. 2. Stimulation of the nerve with intensities subthreshold for evoking spikes in the recorded cell resulted in a small depolarization followed by a period of hyperpolarization, during which spontaneous spikes were suppressed. With suprathreshold stimulus intensities, a single spike or often a burst of spikes was evoked, followed by a complex prolonged hyperpolarization. When full spikes were blocked by injecting hyperpolarizing current through the recording electrode, an excitatory postsynaptic potential (EPSP) with two major components and sometimes a fast prepotential were observed at the beginning of the response. Amplitudes of the EPSP and hyperpolarization increased with graded increases in stimulus intensity. In tests with paired stimulus volleys, spike generation was inhibited for at least 1 s and often for several seconds during the hyperpolarization. 3. Stimulation of the tracts with intensities subthreshold for evoking spikes in the recorded cell resulted in a complex prolonged hyperpolarization. With suprathreshold stimulus intensities, a single spike was evoked, followed by a similar period of hyperpolarization. When full spikes were blocked by injecting hyperpolarizing current through the recording electrode, a small antidromic spike, presumably generated in the axon or initial segment, was often observed. Amplitude of the hyperpolarization increased with graded increases in stimulus intensity. In tests with paired volleys, generation of a full antidromic spike was inhibited for a period that usually began 20-30 ms, following the spike evoked by the conditioning stimulus and lasted 100-500 ms. Full antidromic spikes were evoked prior to the period of inhibition and small antidromic spikes were evoked during the period. 4. The mean latencies of single evoked spikes or the first spikes of bursts decreased from 22 to 17 ms with increases in the intensity of nerve stimulation and from 7 to 6 ms with increases in the intensity of tract stimulation. Only decreases in orthodromic latency were significant at P less than or equal to 0.05, as determined by one-sided t tests between the means of responses subdivided according to response pattern and relative stimulus intensity.(ABSTRACT TRUNCATED AT 400 WORDS)
Influence of stimulus parameters on human postural responses
Authors: Diener H. C. , Horak F. B. , Nashner L. M.
Published: December 2017

1. The role of sensory information in shaping muscle activation patterns to postural perturbations in humans was investigated by varying velocity, amplitude, or duration of the perturbing stimulus. Ten normal subjects were exposed to 120 backward translations of the support surface under conditions of varying velocities (10-35 cm/s, constant amplitude), varying amplitudes (1.2-12 cm, constant velocity), or varying durations (40-800 ms). The effects of perturbation parameters on movement kinematics and EMG latencies, patterns, and integrated areas in six trunk and leg muscles were examined. Integrated EMG activity was normalized across subjects and the early (first 75 ms), middle (second 75 ms), and late (last 350 ms) components were analyzed separately. 2. Ankle, knee, and hip angle trajectories and surface reactive forces suggest that a relatively consistent movement strategy was scaled to the perturbation velocities and amplitudes applied. 3. Short-duration perturbations (75 ms) evoked a single burst of muscle activity (75-100 ms duration) in gastrocnemius, hamstrings, paraspinal, and rectus abdominis muscles at latencies too long to be explained by simple stretch reflexes. EMG latencies, patterns, and integrated areas were independent of the velocity and amplitude of the short-duration perturbations, suggesting a minimal time to incorporate peripheral velocity information into the triggered response. 4. For translations lasting longer than 75 ms, the integrated areas of the early agonist EMG bursts were positively correlated with stimulus velocity. The integrated area of later, more tonic EMG components were best correlated with stimulus amplitude. These relationships were found in both distal (stretched) muscles and in proximal muscles. Absolute latencies (94-145 ms), intersegmental latencies (18-29 ms), and burst durations (75-100 ms) were not influenced by the velocity or amplitude of the stimulus. 5. These results suggest that the spatial and temporal organization of automatic postural responses may be organized independently of response intensity. Within a particular spatial-temporal pattern, the amount of muscle activation appears to be adjusted by sensory information, which specifies velocity and amplitude of the perturbation.
Temporally dependent changes in response properties of dorsal horn neurons after dorsolateral funiculus lesions
Authors: Pubols L. M. , Hirata H. , Brown P. B.
Published: December 2017

Previous studies in this laboratory have shown 1) that 19% of L6 and L7 dorsal horn cells in normal cats respond only with excitatory postsynaptic potentials (EPSPs) to sural nerve stimulation, and 2) that the distribution of dorsal horn neurons responding with impulses to sural nerve stimulation is increased in cats with chronic lateral funiculus lesions. The present study was undertaken to determine whether strengthening of subliminal sural nerve projections could account for the changes seen after lateral funiculus lesions and to explore the nature of these changes in greater detail. Ipsilateral L6 and L7 dorsal horn cells of cats with T12 dorsolateral funiculus (DLF) lesions were studied electrophysiologically at less than 1-30 days postoperatively (DPO) and were compared with similar cells recorded in normal cats. The major results were as follows. 1. Responsiveness to peripheral stimulation was depressed for up to 3 DPO following the lesions. 2. The percentage of L6 and L7 dorsal horn cells showing spontaneous activity was elevated at 3 DPO and declined to normal levels by 28 DPO. 3. The percentage of cells that responded to sural nerve stimulation increased over 3-30 DPO and was significantly greater than normal at 28-30 DPO. The increase in the percentage of cells giving impulses to sural nerve stimulation at 28-30 DPO was similar to the percentage of cells with subliminal responses to sural nerve stimulation in normal cats. A subpopulation of identified postsynaptic dorsal column neurons also showed a significant increase in the percentage that responded to sural nerve stimulation after DLF lesions. 4. The percentage of cells that had a cutaneous receptive field (RF) overlapping the region of skin innervated by the sural nerve also increased over time and was significantly greater than normal at 28-30 DPO. 5. Median low-threshold or high-threshold RF areas were not significantly greater than normal ipsilateral to DLF lesions at any survival time. 6. The proportions of low-threshold (LT), high-threshold (HT), and multireceptive (MR) cells were not significantly different from normal at any survival time from less than 1 to 30 DPO.(ABSTRACT TRUNCATED AT 400 WORDS)
Modulation of a subthreshold calcium current by the neuropeptide FMRFamide in Aplysia neuron R15
Authors: Kramer R. H. , Levitan E. S. , Carrow G. M. , Levitan I. B.
Published: December 2017

1. The effect of the endogenous neuropeptide FMRFamide (Phe-Met-Arg-Phe-amide) on the Aplysia bursting pacemaker neuron R15 was studied. Brief local applications of FMRFamide, both on R15 somata in situ, and on R15 somata that were isolated and maintained in primary cell culture, cause a hyperpolarization of the membrane potential and a suppression of spontaneous bursting or beating pacemaker activity. 2. Two-electrode voltage-clamp experiments revealed that FMRFamide decreases the amplitude of an inward current, which activates with depolarization starting at a membrane potential less depolarized than the threshold for action potentials. Previous studies have established that this subthreshold inward current is carried by calcium and is essential for the generation of bursting pacemaker activity in Aplysia neurons. The effect of FMRFamide on the subthreshold inward current of R15 is blocked by divalent cation calcium channel blockers, such as cobalt and manganese, and is unaffected by changing the external concentration of potassium or chloride ions, or addition of blockers of the calcium-activated potassium current, such as external tetraethylammonium or internal EGTA. 3. The subthreshold calcium current of R15 is also decreased by dopamine and by an unidentified synaptic neurotransmitter. These substances mimic and occlude the action of FMRFamide on the subthreshold calcium current, suggesting that all three transmitters converge to affect the same population of calcium channels in neuron R15. 4. The subthreshold calcium current is enhanced by neurotransmitters that elevate cyclic AMP in R15, including serotonin, and the Aplysia neuropeptide egg-laying hormone (ELH). Likewise, the effect of FMRFamide on the subthreshold calcium current is enhanced by serotonin, ELH, and a cyclic AMP analog, suggesting that FMRFamide and cyclic AMP have antagonistic actions on the same population of calcium channels in neuron R15. 5. We conclude that the suppression of spontaneous bursting or beating pacemaker activity in neuron R15 by FMRFamide is due to a decrease in the subthreshold calcium current. The subthreshold calcium current in R15 is a common target for modulation by many different transmitters, acting via several distinct molecular mechanisms.