bluuebunny/crossref_metadata_2025 huggingface dataset:
Role of primate medial vestibular nucleus in long-term adaptive plasticity of vestibuloocular reflex
Authors: Lisberger S. G. , Miles F. A.
Published: December 2017

1. Fifteen hundred and thirty cells were recorded in the medial vestibular nucleus (MVN) of alert monkeys whose vestibuloocular reflex (VOR) had been adapted to one of two kinds of spectacles. The “high-gain” sample was recorded from monkeys that had worn 2.0 x telescopic spectacles; the gain of the VOR in the dark (eye velocity divided by head velocity) was greater than 1.5. The “low-gain” sample was recorded from monkeys that had worn goggles providing a visual field that was fixed with respect to the freely turning head; the gain of the VOR was less than 0.4. 2. Cells showing modulation of firing rate related to imposed head velocity were grouped into four categories: pure vestibular (10), vestibular-plus-saccade (10), vestibular-plus-position (10), and vestibular-plus-head/body (24). Sensitivity to head velocity was measured from averaged responses to sinusoidal, 0.4-Hz whole-body oscillation in the horizontal plane. Almost all cells (98%) having increased firing during ipsilateral head rotation received inputs from the horizontal semicircular canals. Conversely, 82% of cells having increased firing during contralateral head rotation received inputs from the vertical canals. 3. There were no statistically significant differences in resting discharge rate, phase shift, or sensitivity to head velocity between the high- and low-gain samples of any of the cell types. Nonetheless, there was a consistent tendency, evident in all the functionally defined cell groups, for the sensitivity to be about 20% greater in the high-gain samples. However, this difference is small by comparison with the fourfold difference in VOR gain. 4. Detailed scrutiny of the response properties of individual cells suggested that the small differences in sensitivity reflect small changes distributed throughout the population, rather than large and potentially significant changes within a small sub-population. 5. Our data indicate that large, adaptive changes in the gain of the VOR are accompanied by only minor changes in the vestibular sensitivity and no changes in the phase shift or resting discharge rates of cells in the MVN. It remains possible that large changes in vestibular sensitivity occurred in cells we did not sample or in subgroups we could not identify. We argue that this is unlikely and that the major changes underlying VOR plasticity occur after the first central synapse in the VOR pathways.
Tetrapartite classification of motor units of cat tibialis posterior
Authors: McDonagh J. C. , Binder M. D. , Reinking R. M. , Stuart D. G.
Published: December 2017

The results of this study and its precedents suggest that the tetrapartite classification scheme might have universal applicability to at least the muscle units of cat hindlimb muscles and perhaps any mammalian muscle in which fiber typing reveals the presence of FG, FI, FOG, and type SO fibers. A possible exception to this generalization involves a small (n = 18) but thoroughly examined sample of muscle units from the first deep lumbrical muscle of the cat's foot, which led Kernell et al. (30) to conclude that the FF, FR, and S classification scheme was not directly applicable to that muscle. However, histochemical fiber typing is not yet available for that muscle. Furthermore, more extensive sampling, use of a different stimulation regime in the fatigue test, and a more detailed analysis of the sag property might well reveal that the tetrapartite classification scheme is indeed appropriate for units of cat foot muscles.
Muscle architecture and force-velocity characteristics of cat soleus and medial gastrocnemius: implications for motor control
Authors: Spector S. A. , Gardiner P. F. , Zernicke R. F. , Roy R. R. , Edgerton V. R.
Published: December 2017

1. Isometric and isotonic contractile parameters of the soleus (SOL) and medial gastrocnemius (MG) muscles of seven adult cats were studied. In addition, architectural characteristics of six contralateral pairs of these ankle extensors were determined. 2. The in situ peak isometric tetanic tension developed by the MG at the Achilles tendon is nearly 5 times (9,846 vs 2,125 g) that of the SOL muscle. However, when differences between the MG and SOL in fiber length (2.01 vs 3.66 cm), muscle mass (9.80 vs. 3.31 g), and angle of pinnation (21.4 vs. 6.4 degrees) are considered, the specific tensions of these muscles are similar (approximately 2.3 kg x cm-2). 3. When the effects of muscle architecture are eliminated, the nearly threefold greater maximum isotonic shortening velocity (Vmax) of sarcomeres of the MG (38.2 micron/s) relative to the SOL (13.4 micron/s) is presumably due to intrinsic differences in the biochemical properties of these muscle. However, the Vmax developed by the MG at the Achilles tendon (258.6 mm/s) during a shortening contraction is only 1.5 times that of the SOL (176.3 mm/s) due to the influence of these muscles' specific architectures. 4. Variations in geometrical characteristics of the SOL and MG are consonant with the relative amounts of participation of these muscles during posture, locomotion, and jumping. Posture requires the development of low forces for prolonged periods for which the SOL seems best suited both architecturally and physiologically. The MG, relatively inactive during quiet standing, becomes responsible for a greater percentage of tension and shortening speed during plantar flexion (E3) as gait speeds increase, which is consistent with this muscle's greater tension- and velocity-generating capacity. 5. At high speeds of locomotion (3.0 m/s) and jumping, the shortening velocities developed at the end of E3 (approximately 20-40 ms before paw off) exceed Vmax of the SOL. Consequently, the SOL, although electrically active, cannot contribute to the tensions required to generate the shortening velocities dictated by these movements. 6. These data demonstrate the influence of the differing geometries of the SOL and MG on the roles of these muscles in generating forces at varying velocities, as demanded by the dynamics of the movement.
Neuronal activity in prepositus nucleus correlated with eye movement in the alert cat
Authors: Lopez-Barneo J. , Darlot C. , Berthoz A. , Baker R.
Published: December 2017

1. In nine alert chronically prepared cats the activity of 177 neurons was recorded in the prepositus nucleus during either spontaneous eye movement or that induced by natural vestibular and optokinetic stimulation. 2. In 116 cells, eye position and/or eye velocity was precisely and unequivocally encoded whatever the origin of the eye movement. These cells were separated into different populations according to the eye movement variable encoded and the directionality of the neuronal response. The firing rates of the remaining 61 cells were loosely related to eye movements because a variety of discharge patterns were observed during identical eye movements. In the latter case, some other unmeasured variable (e.g., neck or visual) was suggested to be encoded in the firing frequency. 3. Discharge rate changed before the eyes began to move and reached a new steady level during fixation following a saccade into a particular direction of the orbit. The ondirection was horizontal for 59% of the neurons, vertical for 17%, and oblique for 24%. 4. Regardless of their preferred direction, the discharge rate in 19% of the neurons was closely proportional to eye position. The range in sensitivity was from 1.1 to 7.5 spikes X s-1/deg. Weak velocity responses were occasionally observed during the slow phase of vestibular and optokinetic nystagmus including during saccades. This class of neurons exhibited a very regular interspike interval for a given position of fixation. Since mainly eye position was encoded, these cells were called position neurons. 5. Other prepositus neurons showed both position and velocity sensitivity during saccades and fixation. Their firing rate encoded eye position over the same range as above and also coded velocity during the slow phase of vestibular and optokinetic nystagmus. Depending on the weighting between the position and velocity proportionality constants, these neurons were classified into position-velocity (48%) or velocity-position (33%) groups. 6. The distribution of the above responses led to the conclusion that the prepositus nucleus plays a role in vertical and horizontal spatial integration. The predominance of horizontal activity suggested that the nucleus may be a significant site underlying genesis of horizontal eye position.
Activity of omnipause neurons in alert cats during saccadic eye movements and visual stimuli
Authors: Evinger C. , Kaneko C. R. , Fuchs A. F.
Published: December 2017

1. In the cats trained to follow a target spot with their eyes, activity was recorded from omnipause neurons (OPNs). OPNs discharge at a relatively high steady tonic rate (50-130 spikes/s) during visual fixation and smooth-pursuit eye movements but exhibit a complete cessation of discharge that begins before saccades in any direction. They are located in a compact region of the dorsal pontine tegmentum near the midline, just rostral to the abducens nucleus. 2. The average duration of the horizontal or vertical component of a saccade increases monotonically with pause duration, but a given pause duration is associated with a large range of individual saccade parameters and the timing of the pause, such as the latency from the pause onset to saccade onset or the interval from the maximum saccade velocity to the end of the pause, is no better. However, OPNs can be divided into two distinct groups on the basis of the timing of the pause relative to the parameters of the saccade. One group ceases discharging 32.4 +/- 4.6 ms, on average, before the saccade, while the second pauses 18.2 +/- 3.4 ms before the saccade. 3. Microstimulation at the site of OPNs affects the occurrence and trajectory of saccades but not smooth pursuit or fixation. Sustained electrical stimulation (20 micro A) lasting several seconds prevents the occurrence of saccades while brief trains (10-60 ms), timed to occur early in the saccade, interrupt it in midflight for the duration of the train. The latency to the interruption is about 26 ms. These data support the view that OPNs tonically inhibit the saccadic machinery between saccades and must be turned off to allow a saccade to occur. 4. Almost every (65 of 69) feline OPN exhibited a brief transient increase in activity for visual stimuli moving in any direction with a wide range of velocities. A moving 1 degree spot was generally more effective than a moving full-field, striped background. All units also showed a transient increase in firing when the spot was turned either on or off. Receptive fields plotted with the spot were greater than 250 deg2 and always included the area centralis. Two-thirds of the cells tested also responded to auditory stimuli. 5. Interaction between the excitatory visual input and the saccade-related pause was tested by comparing OPN activity and the saccadic trajectory during eye movements in the dark versus the light and by presenting brief flashes of light during a saccade. During saccades in the dark, the steady firing of OPNs was less than during saccades in the light. Only by stabilizing a flashed spot of light to occur on the area centralis at the beginning of the saccade was it possible to activate an OPN artificially to interrupt the saccade in midflight. Therefore, rather than being instrumental in specifically controlling the saccade trajectory, the visual input, along with the auditory and other sensory inputs, probably serves, under normal visual conditions, to help establish the tonic rate of OPNs. 6...
Presynaptic inhibition, EPSP amplitude, and motor-unit type in triceps surae motoneurons in the cat
Authors: Zengel J. E. , Reid S. A. , Sypert G. W. , Munson J. B.
Published: December 2017

1. Composite group Ia excitatory postsynaptic potentials (EPSPs) produced by heteronymous nerve stimulation were recorded from triceps surae motoneurons of barbiturate-anesthetized cats. Motoneuron rheobase, input resistance, and axonal conduction velocity were measured, and motor units were classified on the basis of the mechanical responses of their muscle units. 2. The amplitude of EPSPs recorded from 33 medial gastrocnemius (MG) motoneurons ranged from 0.6 to 4.3 mV. The mean EPSP amplitude differed among the major MG motor-unit types, increasing in the order fast twitch, fast fatiguing (FF); fast twitch, fatigue resistant (FR); slow twitch, fatigue resistant (S) (FF less than FR less than S). The amplitude of EPSPs recorded from 15 soleus motoneurons ranged from 0.3 to 3.4 mV, with a mean of 1.4 mV. 3. Presynaptic inhibition of EPSPs was produced by trains of conditioning volleys in the posterior biceps-semitendinosus (PBST) nerve. In 33 MG cells PBST conditioning stimulation reduced the amplitude of EPSPs by 11-50%, with a mean inhibition of 27%. The amplitude of EPSPs in 15 soleus motoneurons was decreased by 5-84%, with a mean inhibition of 37%. 4. When the magnitude of presynaptic inhibition was expressed as percent inhibition, there was no relation between presynaptic inhibition and either motor-unit type or the amplitude of the EPSP. However, when presynaptic inhibition was expressed as the absolute amount of inhibition in millivolts, the magnitude of inhibition was highly correlated with EPSP amplitude both across the entire triceps surae population (MG, lateral gastrocnemius, soleus) as well as within each muscle population. This correlation was also significant within the MG FF and FR motor-unit populations. 5. We conclude that EPSP amplitude and not motor-unit type is the major determinant of the magnitude of presynaptic inhibition. However, because of the effect of motor-unit type on EPSP amplitude, the net effect is that presynaptic inhibition increases in the order FF less than FR less than S.
Increase in Purkinje cell gain associated with naturally activated climbing fiber input
Authors: Ebner T. J. , Yu Q. X. , Bloedel J. R.
Published: December 2017

These experiments were designed to test the hypothesis that climbing fiber inputs evoked by a peripheral stimulus increase the responsiveness of Purkinje cells to mossy fiber inputs. This hypothesis was based on a previous series of observations demonstrating that spontaneous climbing fiber inputs are associated with an accentuation of the Purkinje cell responses to subsequent mossy fiber inputs (10, 12). Furthermore, short-term nonpersistent interactions between climbing and mossy fiber inputs have been an important aspect of many theories of cerebellar function (5, 7, 8, 12, 36). Extracellular unitary recordings were made from Purkinje cells in lobule V of decerebrate, unanesthetized cats. To activate mossy and climbing fiber inputs, the forepaw was passively flexed by a Ling vibrator system. A data analysis was developed to sort the simple spike trials into two groups, based on the presence or absence of complex spikes activated by the stimulus. In addition, during those trials in which complex spikes were activated, the simple spike train was aligned on the occurrence of the complex spike. For each simple spike response to the forepaw input, the average firing rate during the response was compared to background both in those trials in which complex spikes were activated and in those in which they were not. The ratio of the response amplitudes in the histograms constructed from these two groups of trials permitted a quantification of the change in responsiveness when climbing fiber inputs were activated. The results show that both excitatory and inhibitory simple spike responses are accentuated when associated with the activation of a complex spike. Using an arbitrary level of a gain change ratio of 120% as indicating a significant modification, 64% of the response components analyzed increased their amplitude when climbing fiber input was present. Simple spike response components occurring prior to complex spike activation were usually not accentuated, although in a few cells the amplitude of this component of the response increased. In addition, in a small number of cells the occurrence of complex spikes was associated with a new simple spike component. For excitatory responses, the magnitude of the gain change ratio was shown to be inversely related to the amplitude of the simple spike response evoked by the mossy fiber inputs. The data obtained is consistent with the hypothesis that the climbing fiber input is associated with an increase in the responsiveness of Purkinje cells to mossy fiber inputs. The increased responsiveness occurs whether the simple spike modulation evoked by the peripheral stimulus is excitatory or inhibitory. The change in responsiveness is short term and nonpersistent. It is argued that the activation of climbing fiber inputs to the cerebellar cortex is associated with an increase in the gain of Purkinje cells to mossy fiber inputs activated by natural peripheral stimuli.
Corticotectal and corticothalamic efferent projections of SIV somatosensory cortex in cat
Authors: Stein B. E. , Spencer R. F. , Edwards S. B.
Published: December 2017

Substantial corticotectal (and corticothalamic) projections from the cortex of the anterior ectosylvian sulcus (AES) were demonstrated in the cat using the axonal transport methods of autoradiography and horseradish peroxidase. The corticotectal projection arises nearly exclusively from medium-large pyramidal cells in lamina V. One of the densest projecting areas of the AES is the rostral aspect of its superior bank, where a fourth somatotopic representation (SIV) has recently been demonstrated. It terminates in the intermediate and deep laminae of the superior colliculus, where somatic cells are located. The pathway is bilateral but much heavier ipsilaterally than contralaterally. In contrast to the substantial corticotectal projection from SIV and adjacent tissue, there was no unequivocal evidence for a corticotectal projection from traditional somatosensory cortex SI-SIII. This finding, that somatosensory projections to the cat superior colliculus arise from an area outside of SI-SIII, was unexpected on the basis of what is known about visual corticotectal projections. However, it is consistent with the patterns of other cortical projections that terminate in the intermediate and deep laminae of this structure and with the absence of demonstrable corticotectal influences from SI to SIII in this animal. These data are in contrast to demonstrations by other investigators that there is a corticotectal projection from SI cortex in rodents. Apparently there is a fundamental species difference in the organization of descending somatosensory pathways. A corticothalamic projection of the AES was also observed. This descending projection appeared to form a shell of labeled cells and fibers around the ventrobasal complex, but unequivocal terminal labeling within the ventrobasal complex could not be demonstrated. Dense terminal labeling was apparent in the posterior group of thalamic nuclei (PO) where thalamocortical afferents to the AES originate.
Binaural interaction in low-frequency neurons in inferior colliculus of the cat. I. Effects of long interaural delays, intensity, and repetition rate on interaural delay function
Authors: Kuwada S. , Yin T. C.
Published: December 2017

Detailed, quantitative studies were made of the interaural phase sensitivity of 197 neurons with low best frequency in the inferior colliculus (IC) of the barbiturate-anesthetized cat. We analyzed the responses of single cells to interaural delays in which tone bursts were delivered to the two ears via sealed earphones and the onset of the tone to one ear with respect to the other was varied. For most (80%) cells the discharge rate is a cyclic function of interaural delay at a period corresponding to that of the stimulating frequency. The cyclic nature of the interaural delay curve indicates that these cells are sensitive to the interaural phase difference. These cells are distributed throughout the low-frequency zone of the IC, but they are less numerous in the medial and caudal zones. Cells with a wide variety of response patterns will exhibit interaural phase sensitivities at stimulating frequencies up to 3,100 Hz, although above 2,500 Hz the number of such cells decrease markedly. Using dichotic stimuli we could study the cell's sensitivity to the onset delay and interaural phase independently. The large majority of IC cells respond only to changes in interaural phase, with no sensitivity to the onset delay. However, a small number (7%) of cells exhibit a sensitivity to the onset delay as well as to the interaural phase disparity, and most of these cells show an onset response. The effects of changing the stimulus intensity equally to both ears or of changing the interaural intensity difference on the mean interaural phase were studied. While some neurons are not affected by level changes, others exhibit systematic phase shifts for both average and interaural intensity variations, and there is a continuous distribution of sensitivities between these extremes. A few cells also showed systematic changes in the shape of the interaural delay curves as a function of interaural intensity difference, especially at very long delays. These shifts can be interpreted as a form of time-intensity trading. A few cells demonstrated orderly changes in the interaural delay curve as the repetition rate of the stimulus was varied. Some of these changes are consonant with an inhibitory effect that occurs at stimulus offset. The responses of the neurons show a strong bias for stimuli that would originate from he contralateral sound field; 77% of the responses display mean interaural phase angles that are less than 0.5 of a cycle, which are delays to the ipsilateral tone.(ABSTRACT TRUNCATED AT 400 WORDS)
Direct projections from vestibular nuclei to facial nucleus in cats
Authors: Shaw M. D. , Baker R.
Published: December 2017

Postsynaptic potentials were recorded from motoneurons in the facial nucleus in response to stimulation of the vestibular and trigeminal nerves. The motoneurons were identified by antidromic activation from their peripheral axons. Disynaptic excitatory and inhibitory postsynaptic potentials (EPSPs and IPSPs) and mixed EPSP/IPSPs were recorded in response to vestibular nerve stimulation, ranging in latency from 0.9 to 2.1 ms, with most at 1.5 ms. Activity in secondary vestibular axons recorded within the facial nucleus occurred at a latency of 0.7-1.1 ms. The amplitudes of the vestibular postsynaptic potentials were small, generally less than a millivolt, but double shocks produced marked summation. The average time to peak of ipsilateral vestibular EPSPs, 1.1 ms, was faster than that of either ipsilateral IPSPs, 1.6 ms, or contralateral EPSPs, 1.4 ms. The double-spiked vestibular activity was detectable in double-peaked PSPs. Disynaptic EPSPs, ranging in latency from 2.0 to 3.0 ms, were recorded in response to trigeminal nerve stimulation. The average time to peak was 1.3 ms. The multiple-spiked activity of the trigeminal neurons was detectable in multipeaked EPSPs. Inhibitory ipsilateral effects (Vi IPSPs) were recorded twice as often as excitatory ipsilateral effects (Vi EPSPs), being found in 29% versus 15% of the motoneurons. Contralateral effects were found in 13% of the motoneurons studied, and almost all were excitatory. Analysis of synaptic potential shapes suggested that the excitatory and inhibitory vestibular synapses probably contact distal dendrites preferentially, with the excitatory connections being somewhat closer to the soma. The trigeminal inputs probably contact the facial motoneurons more extensively near the soma. Horseradish peroxidase was injected into the facial nucleus, and retrograde uptake by vestibular neurons was studied. The majority of filled vestibular neurons was ipsilateral to the injection site, especially in the medial vestibular nucleus, ventral y group, and supravestibular nucleus. On the contralateral side, filled vestibular cells were found almost exclusively in the medial nucleus. Filled cells were also noted in the trigeminal nucleus, predominantly ipsilaterally at all rostrocaudal levels. We have demonstrated monosynaptic projections to facial motoneurons from both vestibular and trigeminal nuclei. The trigeminal input is likely to be involved in facial reflexes, especially blinking and grimacing. The afferent vestibular population overlaps that going to the oculomotor and cervical motoneurons; these projections may be collaterals of single vestibular neurons.4+.
Response properties of neurons in posterior parietal cortex of monkey during visual-vestibular stimulation. I. Visual tracking neurons
Authors: Kawano K. , Sasaki M. , Yamashita M.
Published: December 2017

Extracellular recordings were obtained from 163 visual tracking neurons in area 7a or PG (24) of alert monkeys. The firing patterns were observed during movements of the chair in which the monkey was seated with its head fixed and of a visual target that the monkey was trained to fixate continuously. Horizontal visual tracking neurons were classified into three groups, A, B, and C, on the basis of the following two discharge characteristics: directional preference for visual tracking and response to horizontal sinusoidal oscillation of the chair in the dark. Those neurons that did not respond to chair oscillations in the dark were classified as type A (26/53). Of the remainder, those that responded with the same directional preference as during visual tracking were classified as type B (19/53), and those that showed the opposite directional preference were classified as type C (8/53). When the target and the chair were oscillated together and the monkey canceled the vestibuloocular reflex (VOR) (combined eye and head tracking), most of the visual tracking neurons (types A and B, 32/38) continued to respond in the same way as during visual tracking when the chair was stationary. Type C neurons showed only weak responses. When the monkey fixated an earth-fixed target while the chair was oscillated sinusoidally (VOR target task), responses of the types A and B neurons were much smaller than during visual tracking, while type C neurons were clearly modulated. The results suggest that visual tracking neurons receive information concerning the smooth-pursuit command during combined eye and head (gaze) movements; some also receive vestibular information in addition to the pursuit command information.
Tonic neck reflex of the decerebrate cat: response of spinal interneurons to natural stimulation of neck and vestibular receptors
Authors: Wilson V. J. , Ezure K. , Timerick S. J.
Published: December 2017

In order to investigate the neural basis of the tonic neck reflex, we studied the response of neurons in the cervical spinal cord of decerebrate, paralyzed cats to neck rotation about the longitudinal axis (roll), to vestibular stimulation produced by roll tilt, and to a combination of these stimuli. Most neurons were outside the motoneuron nuclei and were arbitrarily classified as interneurons. Three types of preparation were used--one with intact labyrinths, one acutely labyrinthectomized, and one with acute spinal transection. The activity of 115 neurons recorded extracellularly was modulated by sinusoidal neck rotation in the range 0.02-4 Hz; their behavior was sufficiently linear for sinusoidal analysis. The phase and gain of the responses of neurons in all three preparations were similar except that the absolute gain in cats with intact labyrinths was higher than that of the others. The location of neurons in segments C4-C8 was mainly in laminae 7-8. Some neurons were excited by rotation of the chin to the ipsilateral side (type I) and others by contralateral chin rotation (type II). The dynamic behavior of type I and type II neurons was the same; phase was flat over most of the frequency range and close to the phase of peak neck rotation, while gain enhancement occurred at higher frequencies. This behavior was similar to that of the neckforelimb reflex evoked in unparalyzed intact-labyrinth and labyrinthectomized cats. In cats with intact labyrinths, vestibular input to neurons whose activity was modulated by the neck stimulus was studied using whole-body roll tilt. Many neurons received otolith input; some received canal input. Neck and vestibular inputs to spinal neurons always had opposite polarities (complementary inputs). Thus, type I neurons were always excited by tilt to the ipsilateral side (ipsilateral ear down) while type II neurons were excited by tilt to the contralateral side. Combined neck and vestibular stimulation indicated that the dynamic behavior of neurons was determined by a linear summation of the responses to these stimuli. Interaction of neck and vestibular input at the neuron level was similar to that observed previously at the reflex level in forelimb extensor muscles.(ABSTRACT TRUNCATED AT 400 WORDS)
An electrophysiological study of inferior mesenteric ganglion of the dog
Authors: King B. F. , Szurszewski J. H.
Published: December 2017

Intracellular recordings were made in vitro from 430 sympathetic neurons in the inferior mesenteric ganglion (IMG) of the dog. Ganglion cells had resting membrane potentials between -35 and -70 mV; input resistance (Rin) was approximately 22 M omega. Cell rheobase to depolarizing current was 0.3 nA, and the action potential elicited was 80-100 mV in amplitude followed by an afterhyperpolarization of up to 15 mV in size, which decayed to the resting membrane potential over a range of 50-500 ms. Neurons were classified as either phasic (188 of 280) or tonic (92 of 280) firing cells, depending on their discharge pattern in response to depolarizing current. Two hundred eight of 430 neurons showed continuous electrical activity in the form of spontaneous excitatory postsynaptic potentials, 2-5 mV in amplitude. Continuous electrical activity was unaffected by tetrodotoxin (3 X 10(-6) M) but abolished by hexamethonium (10(-4) M). A small number of cells (21 of 430) adopted a repetitive firing pattern not associated with injury discharge. These cells may have been pacemaking neurons. Stimulation of peripheral and central nerves resulted in multiple synaptic input to ganglion cells. There was marked convergence of excitatory fibers to any one cell. Evoked synaptic potentials were abolished by hexamethonium (10(-4) M). Synaptic input from peripheral and central nerves could not be correlated with location of postganglionic neurons in the IMG. The possibility of neuronal intercommunication and dissemination of central and peripheral commands is discussed.
Intensity and frequency characteristics of pacinian corpuscles. II. Receptor potentials
Authors: Bolanowski S. J. , Zwislocki J. J.
Published: December 2017

Intensity characteristics that relate receptor- (generator) potential amplitude to vibration amplitude and frequency characteristics that relate either the stimulus intensity required for a criterion response or the phase angle between the stimulus and the receptor potential to vibration frequency have been obtained from isolated pacinian corpuscles removed from cat mesentery. The intensity characteristics of signal-averaged receptor potentials in response to sinusoidal displacements were found to be linear at low stimulus levels and to saturate at higher ones. At the higher levels, an asymmetric full-wave rectification was often found, the degree of which varied among receptors. The receptor-potential waveforms showed a time-dependent hysteresis in response to every stimulus cycle at moderate and high stimulus levels. An average intensity characteristic is given. The measured amplitude-frequency characteristics for a constant magnitude of the receptor potential below the neural spike threshold were found to be U-shaped functions. The averaged (n = 7) amplitude-frequency characteristic generated at a constant criterion response had a best frequency of 370 Hz and a bandwidth of Q3 dB equal to 0.8. The phase-frequency characteristics of the receptor potentials below spike threshold exhibited two populations of responses. Both populations underwent phase changes of about 300 degrees as the vibration frequency was increased from 20 Hz to 1.0 kHz but were separated by 180 degrees. An average (n = 8) phase-frequency characteristic is shown. For a constant neural firing rate, the relationship between receptor-potential amplitude and stimulus frequency was also U-shaped. Several qualitative physiological models are presented in relation to previously reported anatomical evidence (14, 18, 19, 32, 45). For the intensity domain, it is suggested that the cytoplasmic extensions that protrude from the unmyelinated portion of the corpuscle axon into the hemilamellar clefts are responsible for the asymmetric full-wave rectification and the response polarity in the phase-frequency characteristics. It is the asymmetric full-wave rectification and consequent receptor-potential waveforms that produce the 2 spikes/stimulus cycle plateaus in the characteristics relating firing rate to stimulus intensity described in the preceding paper (5). An additional model, based on the recovery of spike threshold, suggests how the plateaus in the firing rate-intensity characteristics (5) are produced. For the frequency domain, three filters in cascade can account for the frequency characteristic obtained with a constant firing rate criterion (see Ref. 5).(ABSTRACT TRUNCATED AT 400 WORDS)
Origins of tooth pulp-evoked far-field and early near-field potentials in the cat
Authors: Dong W. K. , Chudler E. H.
Published: December 2017

Electrical stimulation of the mandibular canine tooth pulp in barbiturate-anesthetized cats activated myelinated A-beta-fibers in the inferior alveolar (dental) nerve and evoked a complex pattern of short-latency potentials that were recorded epidurally from the cortex. Three far-field components ( FFPs designated I, IIa,b, and IIIa,b) and two early near-field components ( ENFPs designated P1 and N1) were identified from computer-averaged potentials recorded over the contralateral lateral sigmoid gyrus or ipsilateral presylvian /anterior coronal gyri. Several corroborative lines of evidence indicated that tooth pulp-evoked FFPs and ENFPs originate from the following generator sources: I, inferior alveolar (dental) nerve/semilunar (gasserian) ganglion; IIa,b, trigeminal lemniscal fibers from the principal (main) sensory nucleus; IIIa,b, thalamocortical fibers from the thalamic ventral posteromedial nucleus; P1, N1, cytoarchitectural area 3 on the banks of the coronal or orbital sulcus. The latencies and waveforms of volume-conducted, surface-recorded potentials were not significantly different from those recorded at putative generator sites along the trigeminal lemniscal projection system. The short latencies and distribution of surface- and depth-recorded tooth pulp-evoked potentials suggested bilateral, trisynaptic paths from peripheral nerve to cortical neurons. Amplitude measurements of FFPs and ENFPs recorded at the cortical, epidural surface were compared to calculated values based on a mathematical model of two concentric spheres of inhomogeneous media in which a single equivalent dipole is radially oriented at some distance from the center. The morphology and distribution of FFPs and ENFPs are discussed in relationship to source geometry. Surface- and depth-recorded tooth pulp-evoked potentials had recovery functions that were covariant with rates of stimulation. In addition, stimulation of putative generator sites along the trigeminal lemniscal system reproduced portions of the tooth pulp-evoked surface-recorded potentials. Selective ablation of trigeminal cortical area 3 abolished ENFPs and lesions of lemniscal brain stem sites abolished FFPs . Disruption of extralemniscal brain stem sites had no effect on the surface-recorded evoked potentials examined. These findings and other supporting evidence from previous studies imply that the projection of fast-conducting tooth pulp input to the cortex may subserve a nonnociceptive modality and participate in sensorimotor integration.
Relations among threshold, spike height, electrode distance, and conduction velocity in electrical stimulation of certain medullospinal neurons
Authors: Hentall I. D. , Zorman G. , Kansky S. , Fields H. L.
Published: December 2017

This report describes how the threshold for extracellular, electrical stimulation of cell bodies in the rat's rostromedial medulla depends on the distance to the stimulating electrode. A monopolar microelectrode both delivered current pulses near medullospinal neurons and, after decay of the stimulus artifact, detected whether an orthodromic spike had occurred by collision of that spike with a suitably timed antidromic spike initiated at the thoracic spinal cord. The liminal current and the height of antidromic spikes were noted at a series of vertical electrode positions. Regression analysis was performed to determine whether threshold and the inverse of peak-to-peak spike height varied more as the radial distance or its square. The square relationship provided a much better fit for threshold and a marginally better fit for the inverse of spike height. The spatial decline in excitability (K2) averaged 859 microA/mm2, falling within the range of values found for fibers and cell bodies in other studies. The constant of spatial decline in spike height (C2) in millivolts per square millimeter was positively correlated with K2. Both C2 and K2 were negatively correlated with conduction velocity. From threshold distance curves fitted by regression analysis, the mean separation of sites of spike maxima and threshold minima along each electrode path was 16 micron; the estimated distance from these sites to, respectively, the loci of spike generation and spike excitation were positively correlated and similar. The variation of C2 and K2 with conduction velocity may be due either to an influence of the size and shape of the dendritic tree on the spatial decrement of excitability and spike height or to a confounding in the studied equations of the space-independent effect of the size of a cell body on spike height and excitability.
Activity of commissural interneurons in spinal cord of Xenopus embryos
Authors: Soffe S. R. , Clarke J. D. , Roberts A.
Published: December 2017

Horseradish peroxidase- (HRP) filled microelectrodes have been used to examine the anatomy and physiology of "commissural interneurons," a morphologically defined class of spinal cord interneuron in Xenopus laevis embryos. Commissural interneurons have unipolar cell bodies in the dorsal half of the spinal cord. Their dendrites lie in the mid to ventral parts of the lateral tracts and their axons cross the cord ventrally, T branch, and ascend and descend on the opposite side of the cord. Recordings were made from animals immobilized in tubocurarine and responding to natural stimulation with three patterns of fictive motor activity. During episodes of fictive swimming, commissural interneurons are phasically excited to fire 1 spike/cycle in phase with motor discharge on the same side and receive a midcycle inhibitory postsynaptic potential (IPSP) in phase with motor discharge on the opposite side. Rhythmic activity is superimposed on a background depolarization. During periods of synchrony, phasic excitatory input doubles in frequency so that cells fire with half the swimming cycle period. The background depolarization is generally stronger than during swimming. During periods of fictive struggling, evoked by electrical stimulation of the skin, commissural interneurons fire a burst of spikes per cycle, cells being relatively hyperpolarized when motoneurons on the opposite side are active. In response to ipsilateral skin stimulation, some cells receive an IPSP at a latency of 12-20 ms. This precedes the onset of fictive locomotion. We discuss how anatomy and activity of commissural interneurons is suitable for a reciprocal inhibitory role.
Effects of continuous noise backgrounds on rate response of auditory nerve fibers in cat
Authors: Costalupes J. A. , Young E. D. , Gibson D. J.
Published: December 2017

This study describes the effects of broadband background noise on the average discharge rate to best-frequency (BF) tones of auditory nerve fibers in the cat. The effects of exposure to long-term continuous noise are compared to the effects of noise gated on and off simultaneously with test tones. Addition of background noise causes a shift of the dynamic portion of tone-evoked rate versus level functions to higher tone intensities. The shift occurs at a mean rate of 0.61 dB of shift for each 1-dB increment in noise level. The rate of shift is independent of best frequency and spontaneous discharge rate. The noise level at which the shift begins is frequency dependent and is consistent with the frequency-dependent bandwidths of auditory nerve fiber tuning curves. The adjustment of the dynamic range shows many similarities to two-tone suppression. Therefore, it is most likely that it is caused by suppression of the response to the BF test tone by energy present in the noise at surrounding frequencies. At high noise levels, the ability of auditory nerve fibers to respond to test tones is limited by the rate response to the noise. As noise level increases, the discharge rate it evokes approaches a fiber's saturation rate and ultimately eliminates the fiber's ability to respond to test tones. Low spontaneous rate fibers, which have been shown to have higher thresholds and wider dynamic range (17,29), are significantly more resistant to saturation by high noise levels. Exposure to broadband noise prior to onset of test tones produces an overall decrement in response rate. This phenomenon is similar to the effects of short-term adaptation (32) and seems to develop independently of the shift of dynamic range. At high noise levels, previous exposure to the noise produces a small dynamic range shift. This effect is similar to that produced by suppression but is smaller. The effect is occluded in continuous noise backgrounds by the adjustment of sensitivity produced by suppression.
Features of laminar and somatotopic organization of lumbar spinal cord units receiving cutaneous inputs from hindlimb receptive fields
Authors: Light A. R. , Durkovic R. G.
Published: December 2017

Single-unit recordings from 312 units of lamina I-VII of the lumbar spinal cord of unanesthetized, decerebrate, T8 spinal cats were used to determine the somatotopic and laminar organization of spinal neurons responding to cutaneous stimulation of the hindlimb. Properties of cells confined to different Rexed laminae (I-VII) were shown to differ in several respects, including responses to variations in stimulus intensity, receptive-field areas, spontaneous frequencies, and central delays. Spinal cord neurons with similarly localized cutaneous receptive fields were found to be organized in sagittally oriented rectangular columns. These columns were 7 to at least 20 mm long (rostral-caudal axis), 0.5-1.0 mm wide, and could encompass laminae I-VII in depth. Touch, pressure, and pinch were effective excitatory inputs into each column subserving a given receptive-field location. A map of the somatotopic organization of units in the horizontal plane is presented, which in general confirms previous reports and in particular deals with the organization of units with receptive fields on the plantar cushion and individual toes.
Heterogeneity of group Ia synapses on homonymous alpha-motoneurons as revealed by high-frequency stimulation of Ia afferent fibers
Authors: Collins W. F. , Honig M. G. , Mendell L. M.
Published: December 2017

Excitatory postsynaptic potentials (EPSPs) were recorded in medial gastrocnemius (MG) motoneurons following intraaxonal electrical stimulation of single spindle afferent fibers in anesthetized cats. High-frequency bursts of 32 shocks were delivered to the afferent axon and the EPSPs were averaged in the motoneuron. EPSP amplitude generally changed during the burst, in some cases increasing and in other cases decreasing, depending on the connection. Interpretation of these changes was complicated by potentiation of the initial EPSPs in the burst that occurred with the repeated bursts. The extent of the potentiation varied from connection to connection. The magnitude of facilitation or depression during a burst of standard frequency (167 Hz) was determined by comparison of EPSPs at the end of the burst with the mean EPSP obtained during low-frequency stimulation (18 Hz). Large amplitude EPSPs tended to depress, whereas the small amplitude EPSPs facilitated. Facilitation was more prevalent in motoneurons with large rheobases and depression was more often observed in small rheobase motoneurons. The use of partial correlations, which was necessary because of the inverse correlation between EPSP amplitude and motoneuron rheobase, revealed that facilitation-depression behavior during repetitive stimulation is correlated primarily with EPSP amplitude rather than with motoneuron rheobase. Acute transection of the spinal cord resulted in no change in motoneuron rheobase but considerable enlargement of mean EPSP amplitude at low frequencies of stimulation. A significant increase in the amount of depression during repetitive stimulation was noted under these conditions. These results indicate considerable heterogeneity in the response of individual connections to repetitive stimulation. We suggest that this heterogeneity results from differences in transmitter release at different connections. This heterogeneity must also have functional consequences related to susceptibility for firing of different motoneurons under various physiological conditions that can include afferent discharge frequencies equivalent to those used in this study.
Stability of new electrical connections between adult Helisoma neurons is influenced by preexisting neuronal interactions
Authors: Bulloch A. G. , Kater S. B. , Miller H. R.
Published: December 2017

The factors responsible for the selective stability of new electrical connections between regenerating, adult Helisoma neurons (5, 6) were examined. In particular the alternative hypotheses that the normal reduction in strength of a specific connection is dependent on the formation of a new stable connection or the maintenance of a preexisting connection were tested. To this end, single neurons were eliminated either by microdissection or photoinactivation. Formation of stable 5-5 [i.e., left neuron 5 (L5) to right neuron 5 (R5)] coupling was prevented by removal of a single neuron 5 soma. The time course of the normally transient neuron 5-4 connection in these ganglia, however, was the same as that of control preparations. Thus the 5-4 connection is transient even when stable 5-5 coupling is unable to develop. After removal of a single neuron 4 soma, however, the 5-4 connection was stabilized. This was despite the concurrent development of stable 5-5 coupling in these preparations. Similar results were obtained when neurons were eliminated by photoinactivation, a procedure that kills axonal processes in addition to the neuronal cell body. Morphological examination of untreated neurons by Lucifer Yellow CH stain showed that neurite outgrowth was not prevented by either of the techniques employed to eliminate single neurons. It is concluded that the development of the new, stable 5-5 electrical connection does not influence the transient nature of the 5-4 connection. The presence of both neurons 4, however, which have a preexisting connection, is required for reduction of 5-4 coupling. Thus preexisting neurons and/or their connections appear to play a role in the stability of new connections in this adult nervous system.