bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of lack of vision and of occipital lobectomy upon recovery from unilateral labyrinthectomy in rhesus monkey
Authors: Fetter M. , Zee D. S. , Proctor L. R.
Published: December 2017

1. We investigated the influence of visual experience upon vestibular compensation in monkeys. Two paradigms were used to elicit vestibular adaptation: artificially imposed motion of images upon the retina during head rotation and unilateral labyrinthectomy. Two groups of animals were investigated: monkeys that underwent a bilateral occipital lobectomy and intact monkeys without a cortical lesion. Occipital lobectomy alone caused only a minor change in the vestibuloocular reflex (VOR); the gain (eye vel/head vel) decreased slightly (10-15%) for high speeds of rotation (180-300 degrees/s). 2. In response to a 4-h period of continuous oscillation of the head (0.25 Hz, 30 degrees/s) with the visual scene made to move in phase with the head (X0 viewing) or out of phase with the head (X2 viewing), intact monkeys showed an average 40% decrease or increase, respectively, of the VOR gain measured in darkness. After occipital lobectomy this adaptive capability was diminished, primarily for increasing the VOR gain after X2 viewing (42% preop to 13% postop). 3. Unilateral labyrinthectomy in either occipital-lobectomized or in otherwise intact monkeys led to a static imbalance with initial (18- to 20-h postlesion) values of spontaneous nystagmus of 22-62 degrees/s measured in darkness and to a dynamic disturbance with an approximately 50% decrease of VOR gain. Compensation for both abnormalities was studied in three groups of animals: previously occipital-lobectomized monkeys kept in the light after labyrinthectomy, intact monkeys kept in the light after labyrinthectomy, and intact monkeys kept in the dark for 4 days after labyrinthectomy and then exposed to light. Spontaneous nystagmus disappeared at the same rate in each group of animals. VOR gain increased in the intact monkeys kept in the light after labyrinthectomy but not in the intact monkeys kept in the dark after labyrinthectomy until they were exposed to light. The occipital-lobectomized monkeys showed some recovery of VOR gain (approximately 25-40%), but only at low speeds of rotation (30-60 degrees/s). Occipital lobectomy performed in monkeys after they had already compensated for a labyrinthectomy caused the VOR gain to drop to values approximately 0.5 but without any recurrence of spontaneous nystagmus. 4. Our results indicate that visual experience after labyrinthectomy is essential for recovery of VOR gain but not for resolution of spontaneous nystagmus. Furthermore, geniculostriate pathways play a major role in providing information about high velocities of retinal image motion that is necessary for the acquisition of VOR gain adaptation.(ABSTRACT TRUNCATED AT 400 WORDS)
Neural mechanisms in vibrotactile adaptation
Authors: O'Mara S. , Rowe M. J. , Tarvin R. P.
Published: December 2017

1. Peripheral and central neural contributions to vibrotactile adaptation were investigated in decerebrate or anesthetized cats by recording from sensory nerve fibers associated with Pacinian corpuscle (PC) receptors and from central neurons of the dorsal column nuclei that receive their input from vibration-sensitive receptors of the forelimb footpads. Responsiveness of units was assessed using 1-s duration, test vibration stimuli delivered with 1- to 2-mm-diam probes at different times following adapting trains of vibration (usually 300 Hz) that lasted from less than 1 min up to 50 min. 2. Cuneate neuron responsiveness underwent marked depression following prior vibration. The extent of the depression and the time course of recovery in responsiveness were dependent on the intensity and duration of the adapting vibratory stimulus. The recovery time course (often several minutes) was approximately exponential and resembled the reported time course of subjective vibrotactile adaptation obtained in psychophysical experiments. 3. Response depression in PC fibers was only seen at low amplitudes of the test vibration and displayed a brief time course of recovery in comparison with that seen in cuneate neurons. It is therefore unlikely to account for the adaptation time course either in cuneate neurons or at a subjective level. Furthermore, as the adaptation seen in PC fiber responses had a similar time course in both cutaneous and mesenteric PC fibers it is unlikely that mechanical changes in the skin contribute significantly to the adaptation in PC fiber responses to vibration. 4. The time course of afferent-induced inhibition following long periods of prior vibration was too brief to account for the response adaptation in cuneate neurons. 5. As the long-term response depression in cuneate neurons following their prior activation was seen for inputs from unconditioned sites within the neuron's excitatory receptive field, as well as from the conditioned site, it appears that the response adaptation is attributable to changes in the central neuron or in synaptic processes associated with the central neuron. It is proposed that this adaptation may be due to an increase in extracellular potassium ion concentration that alters the responsiveness of the central neurons.
Efferent neurons and suspected interneurons in binocular visual cortex of the awake rabbit: receptive fields and binocular properties
Authors: Swadlow H. A.
Published: December 2017

1. In fully awake rabbits the stability of the two eyes was monitored and was sufficient to enable receptive-field analysis of antidromically identified efferent neurons and suspected interneurons in the binocular segment of visual area 1. Efferent neurons analyzed included callosal efferent neurons (CC neurons, n = 52), neurons projecting to visual area 2 (CV2 neurons, n = 35), corticotectal neurons (CT neurons, n = 43), and corticogeniculate neurons (CG neurons, n = 51). Six additional neurons projected a branching axon to both the corpus callosum and visual area 2. 2. Most CC and CV2 neurons were found in layer 2-3 and had receptive fields of the simple type. Only two corticocortical neurons with complex receptive fields were found. Orientation tuning ranges of CC and CV2 simple cells were similar and end stopping was prevalent in both CC (62%) and CV2 (45%) neurons. Axonal conduction velocities of CC and CV2 neurons were low (mean = 3.5 and 1.4 m/s, respectively) and visually nonresponsive CC neurons (19%) had conduction velocities that were significantly lower than visually responsive neurons. Spontaneous firing rates of corticocortical neurons were low (mean less than 1 spike/s) and these neurons responded to a lower range of stimulus velocities than did corticofugal neurons. 3. Most CG neurons had simple receptive fields and none had a complex field. Orientation tuning ranges of these neurons were comparable to those of CC and CV2 neurons, but a significantly smaller proportion (12%) were end stopped. Both spontaneous firing rates (mean = less than 1 spike/s) and axonal conduction velocities (mean = 2.4 m/s) of CG neurons were low and, as was found for CC neurons, visually nonresponsive CG neurons (25%) had significantly lower conduction velocities than did visually responsive neurons. 4. CT neurons had receptive fields that were predominantly complex (37%), motion/uniform (28%), or simple (26%). Conduction velocities (mean = 10.9 m/s) and spontaneous firing rates (mean = 7 spikes/s) of CT neurons of all receptive-field types were much higher than those of CC, CV2, and CG neurons. 5. An additional class of neurons was studied that responded synaptically at a short latency to electrical stimulation of the dorsal lateral geniculate nucleus (LGNd) with a burst of three or more spikes at frequencies of 600-900 Hz. These neurons showed a high degree of synaptic convergence, also responding synaptically with a high-frequency burst of spikes to stimulation of both visual area 2 and the corpus callosum.(ABSTRACT TRUNCATED AT 400 WORDS)
Aftereffects in the responses of cat muscle spindles and errors of limb position sense in man
Authors: Gregory J. E. , Morgan D. L. , Proske U.
Published: December 2017

1. This is a report of two series of experiments, one, observations on muscle spindles in the anesthetized cat, the other, based on the animal observations, concerned with limb-position sense in human subjects. 2. When the cat soleus muscle is contracted at a short length and then after a brief period is brought to an intermediate length, the integrated afferent activity recorded in dorsal roots is maintained at a high level. If the contraction is applied while the muscle is held at a long length, the subsequent level of afferent activity back at the intermediate length is much lower. A similar result is obtained if large amplitude vibration of the muscle is used instead of contraction. Recordings from single afferents confirm that these alterations in discharge could be attributed to the primary and secondary endings of muscle spindles. 3. Following the proposal that the resting discharge of muscle spindles contributes to the sense of limb position in man, we have used a sequence of contractions or periods of vibration of biceps and triceps brachii followed by an arm-matching task to look for errors in limb position consistent with the patterns of muscle afferent discharge observed in the animal experiments. 4. Blindfolded subjects were told to contract biceps of one, the test arm, with the arm flexed. After the arm had relaxed, it was placed by the experimenter at an intermediate angle that the subject was asked to match with the other, indicator arm. Then the subject was asked to contract triceps with the arm extended, and the matching task was repeated. 5. The hypothesis was that contracting a muscle while it was short raised the level of afferent discharge coming from it when the arm was moved to an intermediate position so that the muscle would be perceived as more stretched and the arm felt to be displaced further than it really was. Thus, when biceps was contracted with the arm flexed, this would lead the arm in the intermediate position to be perceived as more extended than it really was. When triceps was contracted with the arm extended, this would lead the arm in the intermediate position to be perceived as more flexed than it really was.(ABSTRACT TRUNCATED AT 400 WORDS)
Receptive-field properties and morphological characteristics of the superior collicular neurons that project to the lateral posterior and dorsal lateral geniculate nuclei in the hamster
Authors: Mooney R. D. , Nikoletseas M. M. , Ruiz S. A. , Rhoades R. W.
Published: December 2017

1. Intracellular recording, antidromic activation, and horseradish peroxidase (HRP) injection techniques were employed to characterize the receptive-field properties and morphology of the superior collicular (SC) neurons in the hamster that projected to the lateral posterior nucleus (LP) or the dorsal lateral geniculate body (LGNd). 2. Twenty-three tecto-LP and 21 tecto-LGNd cells were successfully characterized, filled with HRP, and recovered. Additional physiological information was obtained from four tecto-LP and five tecto-LGNd neurons in which HRP injections did not completely label the cell, but did provide information as to the laminar location of the soma. Recovered neurons were classified as wide-field or narrow-field vertical cells, marginal cells, stellate cells, or horizontal cells on the basis of their soma-dendritic morphology. They were categorized as stationary responsive (SR), movement sensitive (MV), or directionally selective (DS) on the basis of their physiological responses (3, 37). 3. The somas of the recovered tecto-LP cells were located, with two exceptions, in, or near, the borders of the stratum opticum (SO). Tecto-LGNd neurons, with two exceptions, had their cell bodies in the upper one-half of the stratum griseum superficiale (SGS). Fifty-two percent of the recovered tecto-LP cells were wide-field vertical cells, 22% were narrow-field vertical cells, 13% were stellate cells, 9% were horizontal cells, and 4% could not be classified according to the scheme that we employed. Twenty-four percent of the recovered tecto-LGNd cells were marginal cells, 24% were stellate cells, 38% were narrow-field vertical cells, 5% were horizontal cells, 5% were wide-field vertical cells, and 5% could not be classified. The difference between the distributions of morphological cell types that contributed to the tecto-LGNd and tecto-LP pathways was statistically significant (chi 2 = 15.8, P less than 0.01). 4. Sixty-seven percent of the tecto-LP cells had MV receptive fields, 11% were DS, 7% had SR fields, and 15% were unresponsive. The distribution of receptive-field types for tecto-LGNd cells was somewhat different: 54% had SR fields, 15% were MV, 19% were DS, 4% were somatosensory, 4% were unresponsive, and 4% were incompletely classified. These differences between tecto-LP and tecto-LGNd cells were statistically significant (chi 2 = 18.4, P less than 0.001). The strongest correlation between morphology and receptive-field type was observed for the wide-field vertical cells that projected to LP. All but one of these had MV receptive fields.(ABSTRACT TRUNCATED AT 400 WORDS)
Contribution of GABAergic inhibition to the response characteristics of auditory units in the avian forebrain
Authors: Muller C. M. , Scheich H.
Published: December 2017

1. We tested the contribution of GABAergic inhibition to the response characteristics of 213 neurons in the auditory telencephalon of chronically prepared nonanesthetized chickens. Extracellular recordings were obtained with multibarrel glass electrodes containing a tungsten wire. Auditory stimuli consisted of tones, two-tone combinations, and noise bursts presented either free field or via earphones. 2. Response properties of the neurons were studied both before and during iontophoretic application of GABA, glutamate, bicuculline methiodide (BIC), and acetylcholine. 3. During BIC application excitatory responses were facilitated. With the exception of transient off-responses, which occasionally appeared only in the BIC condition, the temporal response patterns to tone stimuli at the units' best frequency usually were unaltered. In no case was an inhibitory response component to binaurally presented pure tones antagonized by BIC. 4. BIC iontophoresis enlarged the isointensity-response areas of the vast majority of neurons in the structures of the auditory forebrain lying postsynaptic to the thalamorecipient layer L2. This effect was not obtained when neurons were depolarized to perithreshold levels with glutamate. 5. Two-tone stimulation resulted in a suppression of the excitatory response to a neuron's best frequency when the second frequency lay outside the excitatory response area. In lamina L2, the frequency range inducing two-tone suppression was narrow, and the suppressive effect was not antagonized by BIC. In the postsynaptic layers, frequencies up to three octaves from the neurons' best frequency induced two-tone suppression that was sensitive to BIC. In addition, these neurons also displayed a BIC-insensitive suppression similar to the one seen in layer L2. 6. Neurons displaying no or only a poor response to white-noise stimulation strongly responded to this wide-band stimulus during BIC iontophoresis. 7. Neurons without tone responses usually displayed clear response areas to tones during BIC application. Iontophoretic application of acetylcholine, but not glutamate, also induced such tone responses. Two-tone combinations with frequencies lying within the response areas observed in the BIC condition elicited excitatory responses after full recovery from the BIC application. 8. During BIC iontophoresis nonmonotonic intensity-response functions were converted to monotonic functions in most of the neurons studied. 9. A model of GABAergic inhibitory interactions is proposed that is based on two independent GABAergic systems.(ABSTRACT TRUNCATED AT 400 WORDS)
Organization of auditory cortex in the albino rat: binaural response properties
Authors: Kelly J. B. , Sally S. L.
Published: December 2017

1. The binaural response properties of neurons in the auditory cortex of the albino rat were examined using microelectrode mapping techniques. Characteristic frequencies, binaural response classes, and interaural intensity differences for binaural interaction were determined for multiple electrode penetrations across the cortical surface. The location of electrode penetrations was determined by reference to the cortical vascular pattern in individual animals. 2. When examined over a wide range of interaural intensities binaural responses could be classified as one of the following types: summation, i.e., excited by stimulation of either ear alone and facilitated by stimulation of both ears together (35.3%); suppression, i.e., excited by contralateral stimulation, unaffected by ipsilateral stimulation alone, but inhibited under binaural stimulus conditions (42.2%); mixed, i.e., facilitated by binaural stimulation at near threshold levels, but strongly inhibited by increased sound pressure levels in the ipsilateral ear (18.5%); or other, i.e., responses that could not be classified as any other type (4%). 3. Neurons of the summation and suppression class often exhibited binaural interaction when the intensities at both ears were approximately equal. The modal interaural intensity difference for both response types was between 0 and +5 dB. Neurons of the mixed interaction class were facilitate at near equal dichotic intensity but suppressed when the intensity in the ipsilateral ear was increased. The modal value was between 0 and +5 dB for summation and +20 dB for suppression. 4. Summation, suppression, and mixed binaural response types were found over a wide range of sound frequencies from 1 to 40 kHz. There was some tendency for summation responses to prevail at lower frequencies and suppression responses to prevail at higher frequencies but the differences were not large. Generally, responses from each of the three binaural classes were well represented over the rat's hearing range. 5. Cells of the same binaural response type were grouped together to form aggregates of summation, suppression, or mixed interaction patterns. Cortical areas with similar binaural response properties appeared in some cases to extend across isofrequency contours.
Spatial patterns of olfactory bulb single-unit responses to learned olfactory cues in young rats
Authors: Wilson D. A. , Leon M.
Published: December 2017

1. Neonatal rat pups were classically conditioned to an odor stimulus from postnatal day 1 (PN1) to PN18. Tactile stimulation (stroking) was used as the unconditioned stimulus. On PN19, mitral/tufted cell single-unit responses to the conditioned odor were examined in both conditioned and control pups. Recordings were made from mitral/tufted cells in two regions of the olfactory bulb: 1) an area typically associated with focal [14C]2-deoxyglucose (2-DG) uptake in response to the conditioned odor and 2) an area distant from focal 2-DG uptake to the conditioned odor. Animals were anesthetized with urethane and were naturally respiring during the single-unit recording procedure. 2. Changes in mitral/tufted cell firing rate in response to odors in both bulbar regions and all training groups were classified as either excitatory, suppressive, or no response. This response classification was used to compare response patterns to the conditioned odor between bulbar regions and training groups. 3. Classical conditioning selectively modified the response patterns of mitral/tufted cells to the conditioned odor when those cells were associated with regions of focal 2-DG uptake for that odor. Mitral/tufted cells demonstrated significantly more suppressive and fewer excitatory responses to the conditioned odor than cells in control pups. Response patterns to a novel odor were not similarly modified. 4. Response patterns of mitral/tufted cells distant from the focal region of 2-DG uptake to the conditioned odor were not modified by conditioning compared with control pups. 5. The difference in response pattern between cells in the 2-DG focus and cells distant to the 2-DG focus was apparent within 500 ms of the stimulus onset. Given the respiratory rate of these pups (2 Hz), these data suggest that the modified response pattern occurred on the first inhalation of the learned odor. 6. These data demonstrate that both spatial and temporal patterns of olfactory bulb output neuron activity are used in the coding of olfactory information in the bulb. Furthermore, these spatial/temporal response patterns can be modified by early learning.
Effects of attention and stimulus interaction on visual responses of inferior temporal neurons in macaque
Authors: Sato T.
Published: December 2017

1. Extracellular discharges were recorded from neurons in the inferior temporal cortex (area TE) of three macaque monkeys while they performed visual fixation and pattern discrimination tasks. For the pattern discrimination task, monkey was trained to release the lever quickly at the onset of one of two pattern stimuli and to release the lever at the dimming of the other pattern. During this task, neutral light stimulus (light bar) to which the monkey was not required to respond was presented once a trial either prior to the onset of the discriminandum or during presentation of the pattern that dimmed later. The neuronal activities evoked by the neutral stimulus under these two conditions were compared. 2. When the discriminanda were located at the center or at 5 degrees in the contralateral visual field, one-half of the neurons showed significantly smaller responses to the neutral stimulus when it was presented during presentation of the dimming pattern than when it was presented prior to the onset of the discriminandum. 3. The suppressive effect depended on the location of the two stimuli. When the neutral stimulus was located in the ipsilateral visual field and the pattern was located in the contralateral visual field, the response to the neutral stimulus was suppressed. However, when the pattern was located in the ipsilateral visual field (5 degrees visual angle), still within the receptive field for many neurons, the suppressive effect of the pattern on the response to the neutral stimulus in the contralateral visual field was almost undetectable. 4. When the pattern was located nearer the fovea than was the neutral stimulus, the suppressive effect was greater than when the pattern was located more peripherally to the neutral stimulus. Different from the receptive field of more primary visual neurons, this suppressive effect did not appear to be related to the neuron's responsiveness to the patterns nor to precise stimulus location in the receptive field. 5. The magnitude of suppression by the attended pattern on the visual response during the pattern discrimination task correlated with the suppression noted in the presence of a fixation spot during the fixation tasks, while the animals did not fixate on the attended pattern. The response of some neurons to the neutral stimulus prior to pattern presentation during the pattern discrimination task was enhanced slightly compared with the response recorded during the simple fixation task.(ABSTRACT TRUNCATED AT 400 WORDS)
Organization and properties of neurons in a visual area within the insular cortex of the cat
Authors: Hicks T. P. , Benedek G. , Thurlow G. A.
Published: December 2017

1. Extracellular recordings from 304 neurons were obtained with carbon fiber-containing multibarrel micropipettes. The cells were isolated in the insula in cats anesthetized with barbiturate and immobilized with gallamine triethiodide. Cells were tested with visual stimuli in the form of bars of light, moving edges, and square-wave, drifting grating patterns. 2. The spatial extent of the visually responsive region of insular cortex was assessed and was found to be limited to a surface area of approximately 6-8 mm2, the perimeter being delimited caudally by visually unresponsive cortex of the anterior sylvian gyrus, rostrally by the cortex surrounding the posterior third of the orbital sulcus (ventral bank), dorsally by the rostral extension of the dorsal bank of the anterior ectosylvian sulcus, and ventrally by a visually unresponsive zone bounded by a region about 2 mm2 ventrolateral from the anterior ectosylvian sulcal infolding. Furthermore, a group of unimodal, visually responsive cells often was found in the upper bank of the anterior rhinal sulcus. 3. The possibility of there being a visuotopic organization of insular neurons was examined by analyzing the distribution of receptive-field representation of neurons in sequential penetrations, as well as by searching for spatial progressions in the locations of visually responsive areas within the region. No such clear-cut organization was found among the cells of the insula. 4. Visually responsive neurons were encountered in groups, within electrode penetrations. These groupings were roughly segregated into three distinct levels within the depth of the cortex: the first between the pial surface and 600 micron, the second between 1,100 micron and 1,800 micron, and the third between 2,000 micron and 2,500 micron. 5. Neurons were classified according to their velocity sensitivity, directional preference, orientation sensitivity, length preference, modality specificity, response to electrical stimulation of extrageniculostriate regions, and response to light stimulation in the presence of microiontophoretically administered bicuculline methiodide (BMI). 6. Cells of superficial layers tended to exhibit a preference for high-velocity movements of light bars (600 degrees s-1), whereas those of deeper laminae generally preferred relatively lower velocity movements (60 degrees s-1). The clear preferences of many cells for certain directions of movement within the 360 degrees arc suggested the presence of a dynamic orientation sensitivity. 7. Proportionately more cells preferred moving bars (57%) to small moving spots (43%).(ABSTRACT TRUNCATED AT 400 WORDS)
Synaptic organization of the tectal-facial pathways in the cat. I. Synaptic potentials following collicular stimulation
Authors: Vidal P. P. , May P. J. , Baker R.
Published: December 2017

1. The synaptic pathways underlying tectal influence over pinna movements were studied using an acute electrophysiological approach. Under pentobarbital anesthesia, postsynaptic potentials were recorded intracellularly in antidromically identified, cat facial motoneurons following electrical stimulation of the superior colliculus. How collicular topography is reflected in these synaptic potentials was examined using multiple stimulation sites. The pathways responsible for tectally evoked synaptic potentials were studied by making acute brain stem lesions and by intra-axonal horseradish peroxidase (HRP) staining. 2. Monosynaptic excitatory potentials (EPSPs) with latencies ranging from 0.7 to 1.1 ms and amplitudes that were always less than 1 mV were recorded in motoneurons following stimulation of the contralateral superior colliculus. Larger disynaptic EPSPs ranging in latency from 1.2 to 2.0 ms were recorded both in isolation and in association with monosynaptic EPSPs. In addition, disynaptic inhibitory synaptic potentials (IPSPs) with latencies ranging from 1.5 to 2.5 ms were observed, often in combination with monosynaptic EPSPs. Both disynaptic EPSPs and IPSPs were graded, augmented by multiple stimuli and found in all categories of motoneurons. 3. Stimulation of the ipsilateral superior colliculus produced nearly the same spectrum of potentials and latencies as did contralateral tectal stimulation. Occlusion between ipsi- and contralaterally evoked IPSPs suggests there might be a common element in the inhibitory disynaptic pathways. 4. More discrete populations of facial motoneurons were investigated. Specifically, motoneurons innervating the platysma and orbicularis oculi muscles, the intrinsic ear muscles, and muscles that move the vibrissae all displayed tectally elicited mono- and di-synaptic potentials. Collicular input was not restricted to motoneurons involved in orienting the pinnae. 5. The presence, polarity, and amplitude of the synaptic potentials evoked in individual facial motoneurons exhibited variations that were related to the site of stimulation in either the ipsi- or contralateral colliculus. These variations are compatible with the idea that the collicular input to facial motoneurons is topographically organized. 6. Acute lesions at the level of the superior olive indicated that the pathway producing the contralateral monosynaptic EPSPs runs, near the midline, ipsilateral to the target facial nucleus, whereas the contralateral disynaptic and the ipsilateral mono- and disynaptic pathways lie further lateral.(ABSTRACT TRUNCATED AT 400 WORDS)
Nonlinear systems analysis of the hippocampal perforant path-dentate projection. II. Effects of random impulse train stimulation
Authors: Berger T. W. , Eriksson J. L. , Ciarolla D. A. , Sclabassi R. J.
Published: December 2017

1. Nonlinear systems analytic techniques were used to characterize transformational properties of the network of neurons activated by perforant path input to the rabbit hippocampus. Trains of 4,064 impulses with randomly varying interimpulse intervals were used to stimulate perforant path fibers, and amplitudes of evoked dentate granule cell population spikes were measured. Interimpulse intervals of the random stimulus train were determined by a Poisson distribution with a mean interimpulse interval of 500 ms, and with intervals ranging from 1 to 5,000 ms. The response of dentate granule cells to this stimulation was assumed to reflect activity in the larger hippocampal network, because other subpopulations of neurons activated monosynaptically and polysynaptically within the hippocampal formation contribute to granule cell excitability through multiple feedforward and feedback pathways. System properties were characterized both for halothane anesthetized and chronically implanted, unanesthetized preparations. 2. Second-order kernel analysis showed that population spike amplitude was highly dependent on interimpulse interval. When population spikes of all latencies were included in the same analysis, stimulation impulses produced near-total suppression of spike amplitude when they were preceded 10-20 ms by another impulse in the train. Spike suppression extended to approximately 50 ms and was inversely related to length of the interimpulse interval. Suppression of granule cell response to intervals within the range of 10-50 ms was not influenced by halothane anesthesia. 3. Interstimulus intervals greater than approximately 50 ms resulted in a facilitation of population spike amplitude, with maximum facilitation occurring in response to intervals of 90-100 ms. The magnitude of maximum facilitation was significantly greater for anesthetized (129%) than for unanesthetized (74%) preparations. The range of intervals resulting in facilitation for unanesthetized animals could extend to 1,000-1,100 ms (average range, 61-714 ms). This was much greater than observed for population spikes recorded from anesthetized animals (50-364 ms), which exhibited suppression in response to intervals of approximately 300-700 ms. 4. Further analysis revealed that the nature of nonlinearities in population spike amplitude may depend on spike latency. For example, population spikes of "short" latency (3-4 or 4-5 ms, depending on the animal) exhibited only facilitation in response to interstimulus intervals of 1-4 ms.(ABSTRACT TRUNCATED AT 400 WORDS)
Electrophysiology of mammalian tectal neurons in vitro. II. Long-term adaptation
Authors: Llinás R. , Lopez-Barneo J.
Published: December 2017

1. The long-term adaptation of repetitive firing in guinea pig superior colliculus neurons was studied in a mesencephalic slice preparation using intracellular recording techniques. 2. This long-term adaptation was characterized by a decrease in the number of action potentials generated by a depolarizing pulse of constant amplitude applied at frequencies of 0.5-2 Hz. Long-term adaptation appeared in all cells tested regardless of whether they showed short-term spike frequency adaptation during each pulse. 3. Long-term adaptation had a close-to-exponential time course with a time constant of 4.085 +/- 0.675 s (mean +/- SD, n = 8). This phenomenon developed more rapidly as the stimulus frequency increased and was paralleled by a progressive hyperpolarization of the membrane potential which, at the termination of the train of stimuli, remained 6-10 mV more negative than the resting value. 4. The hyperpolarization and the spike frequency adaptation recovered spontaneously in approximately 60 s. The time constant of recovery was 14.66 +/- 1.189 s (n = 4). 5. The afterhyperpolarization (AHP) was also paralleled by a decrease in the input resistance of the cells. This response and the adaptation disappeared after removal of Ca2+ or after addition of Cd2+ to the external solution. This suggests that Ca2+ entry during trains of action potentials activates a Ca2+-dependent K+ conductance with an unusually slow kinetics. 6. This conductance appears to differ from other Ca2+-dependent K+ conductances in that it was blocked by 4-aminopyridine. 7. The properties of this long-term adaptation are remarkably similar to those reported for visual habituation; thus this newly described K+ conductance may be pertinent to the understanding of this behavioral phenomenon.
Maximum tension predicts relative endurance of fast-twitch motor units in the cat
Authors: Botterman B. R. , Cope T. C.
Published: December 2017

1. The relationships between maximum tetanic tension (P0), endurance time, and axonal conduction velocity (CV) were investigated in fast-twitch motor units of the cat flexor carpi radialis (FCR) and medial gastrocnemius (MG) muscles, and in one flexor digitorum longus (FDL) muscle. Endurance time was the length of time that a unit could maintain 25% of its maximum tetanic tension during a sustained contraction. Motor-unit tension was "clamped" at 25% of maximum by altering the stimulation rate of a unit's motor axon through computer feedback control. 2. In individual experiments, including the one investigated FDL muscle, an inverse relation was consistently found between maximum tension and endurance time. Pooled data from the FCR and MG muscles also resulted in significant correlations between maximum tetanic tension and endurance time. 3. Following the force-clamp contraction, some motor units were subjected to the standard fatigue test of Burke and colleagues (6). Motor units were classified as type FR (fast twitch, fatigue resistant) or type FF* (fast twitch, fast fatiguing after the force-clamp contraction). For both type FR and FF* units, maximum tetanic tension and endurance time were found to be inversely related. However, no correlation was found between maximum tetanic tension and fatigue index for type FR units. Only when all type F (FR + FF*) units were considered as a population was there a significant correlation between these two properties. 4. Other investigators have shown that maximum tetanic tension and axonal conduction velocity are highly correlated with the recruitment order of motoneurons (e.g., Refs. 2, 26). Endurance time was found to be more tightly coupled with contraction strength than with conduction velocity. In 12 of 14 experiments, significant Spearman rank correlation coefficients were found between endurance time and tension, whereas significant correlations were found in only 3 of 14 experiments for endurance time and conduction velocity. 5. Pairs of motor units isolated from the same muscle were formed to see if the unit with the smaller tension had the slower conduction velocity and the longer endurance time. Across all muscles, the probability that the unit with the smallest tension had the greatest endurance time was 0.91 (441 of 487 pairs). By contrast, the probability that the least forceful unit of the pair had the slowest conduction velocity was 0.61. 6. In four experiments, pairs of type-identified units were examined. Among FR-FR pairs, the least forceful unit had the greatest endurance time in 88% of 43 pairs. For FF*-FF* pairs, the percentage was somewhat lower, 72% of 29 pairs.(ABSTRACT TRUNCATED AT 400 WORDS)
Changes in motor cortex neural discharge associated with the development of cerebellar limb ataxia
Authors: Hore J. , Flament D.
Published: December 2017

1. The relation between changes in motor cortex neural (MCN) discharge and the development of limb ataxia during cerebellar dysfunction was studied in 4 Cebus monkeys. Elbow movements with decreased accelerations or with tremor were produced by reversible cerebellar nuclear cooling. Discharge from 160 neurons was analyzed in detail. 2. During cerebellar cooling 37 of 80 neurons that discharged before movement onset decreased their phasic, but not their tonic, activity. This could not be explained by decreased peak velocities during cerebellar cooling. It is suggested that this decreased phasic discharge is related to the less abrupt onset and smaller magnitude of agonist EMG activity, and to the decreased initial accelerations, without decreased peak velocities, observed in limb movements during cerebellar dysfunction. This view implies that the cerebellum is involved in some way in the generation of commands to agonist alpha-motoneurons. 3. No evidence was found that 3- to 4-Hz cerebellar intention tremor is driven by a purely central oscillator. All 28 neurons that discharged strongly in relation to cerebellar tremor in movements responded strongly and reciprocally to limb perturbations. 4. A number of changes were observed during cerebellar nuclear cooling in kinematically related neural discharge associated with disordered elbow movements: an increase in discharge of some velocity- and acceleration-like neurons, a decrease in (reciprocal) inhibition, and a shift from an acceleration-like to a velocity-like discharge in some neurons. 5. Fourteen of 29 neurons with muscle-like discharge patterns discharged in a servoassistance-like manner during cerebellar dysfunction that was consistent with them contributing to tremor. 6. The results indicate that a variety of disorders, i.e., in the generation of central commands that initiate movements and in the regulation of the gain and phase of proprioceptive feedback, contribute to the development of limb ataxia during cerebellar dysfunction.
Single-unit activity in bulbar reticular formation during food ingestion in chronic cats
Authors: Hiraba K. , Taira M. , Sahara Y. , Nakamura Y.
Published: December 2017

1. Single-unit activity was recorded from 215 neurons in the medial bulbar reticular formation during the masticatory sequence, from intake to deglutition, of 3 kinds of food (cat food pellets, canned fish, and milk) in 8 chronically prepared, unanesthetized, spontaneously respiring cats with their head fixed to a stereotaxic apparatus without pain or pressure. The firing patterns were compared to the simultaneously recorded EMGs of the jaw-closing and -opening muscles and to the jaw movement. 2. Fifty neurons changed their firing patterns during mastication. Nine neurons increased and one neuron decreased or stopped firing coincident with the masticatory sequence without an apparent rhythmical modulation of frequency corresponding with the masticatory rhythm (nonphasic group). The firing pattern of the remaining 40 neurons was modulated in phase with jaw movement (phasic group); 34 neurons either showed a spike burst or attained the highest firing frequency during the jaw-opening phase (opening type), while 6 neurons did so during the jaw-closing phase (closing type). The firing patterns of each neuron were essentially the same regardless of the kind of food ingested, except for 2 opening-type neurons that showed a rhythmical burst during mastication of solid food and tonic activity during lapping milk. 3. For 16 phasic neurons, there were significant correlations between some aspects of the firing pattern and a parameter of the movement during ingestion of solid food and/or milk. With one exception, these relationships did not appear to be due to sensory feedback. 4. We detected a monosynaptic excitatory projection from 3 opening-type neurons to the anterior digastric motoneurons, and monosynaptic inhibitory projections to the temporal or masseter motoneurons from 3 other opening-type neurons, by spike-triggered averaging of the full-wave rectified EMG of the jaw-closing and -opening muscles. No monosynaptic projections from the closing-type neurons or nonphasic group neurons to either jaw-opener or -closer motoneurons were detected. 5. The instantaneous firing frequency of all 3 inhibitor premotor neurons was positively correlated with the opening velocity, and the firing of 2 was also related to the jaw displacement.(ABSTRACT TRUNCATED AT 400 WORDS)
Membrane currents of retinal bipolar cells in culture
Authors: Lasater E. M.
Published: December 2017

1. Retinal bipolar cells were isolated from white bass retinas and maintained in a cell culture preparation. Two morphological types of bipolar cells were observed in cell culture. These were labeled large- and small-bipolar cells based mainly on the size of their somata and primary dendrites. Two types of small-bipolar cells were observed. Isolated bass bipolar cells are very similar to those described in the intact retina. 2. Under current clamp, to depolarizing current injection, small-bipolar cells produced a spike followed by a plateau. Large-bipolar cells showed a slow depolarization to a plateau level. 3. Voltage-gated membrane currents were studied using whole-cell patch-clamp techniques. Channel blocking agents were used to define the ion channels found in the membranes of these cells. 4. The large-bipolar cells were found to possess an A-current, a calcium current, and a calcium-dependent potassium current. 5. Large bipolar cells also possessed an inward rectifier that did not correspond to any previously described. 6. The two types of small-bipolar cells were found to have very similar membrane properties to one another. They lacked a large A-current but possessed a slowly activating, outward rectifying potassium current. Similar to the large-bipolar cells, they showed a calcium current and a calcium-activated potassium current. 7. The inward rectifier of small-bipolar cells was characterized as an H-current. 8. The results suggest that the membrane currents of bipolar cells set a narrow operating range about which the cells function in the intact retina. In addition these currents help shape the responses of bipolar cells to light stimuli but do not confer ON or OFF properties.
Temporal coding of resonances by low-frequency auditory nerve fibers: single-fiber responses and a population model
Authors: Carney L. H. , Yin T. C.
Published: December 2017

1. We recorded responses of low-frequency auditory nerve fibers (characteristic frequency (CF) less than 3 kHz) in the cat to resonant stimuli with varied natural frequencies, damping coefficients, and sound pressure levels. Responses to resonances were synchronized to frequencies lying between the peak frequency of the stimulus spectrum and a frequency near the fiber's CF. The frequency of the dominant synchrony in the response varied systematically as a function of the stimulus parameters. 2. More lightly damped resonances, which have sharp spectral peaks, elicited synchrony closer to the peak frequency, whereas the broader peaks of more highly damped resonances elicited synchrony closer to the fiber's CF. Thus as the stimulus was varied from an undamped tone to a highly damped transient, the dominant component of the synchronized response moved from the peak frequency of the stimulus toward the CF of the fiber. The trajectory of the dominant component varied as a function of stimulus level, with higher levels resulting in synchrony biased toward the peak of the stimulus spectrum over a wider range of damping. 3. The frequency tuning and synchronization characteristics of a fiber, along with the stimulus parameters, determined the temporal properties of its response to complex stimuli. Using reverse correlation (revcor) filters to characterize the tuning and synchronization of auditory nerve fibers, we were able to predict the temporal properties of responses to resonant stimuli. 4. A parametric model was fit to measured revcor functions derived from responses of auditory nerve fibers to wideband noise. In this way, a bank of model revcor filters was developed based on our population of measured filters. 5. The filter bank was used to model the response of a population of auditory nerve fibers to resonances. Temporal patterns present in the response of a population of fibers encoded the parameters of resonant stimuli. 6. The model revcor filter bank provided a means of studying temporal response patterns of the population of fibers to other complex sounds. 7. The output of the population model is a representation of the temporal information provided by the auditory periphery to the central nervous system; thus it provides a potentially useful tool for testing hypotheses concerning the processing of temporal information by the central auditory system.(ABSTRACT TRUNCATED AT 400 WORDS)
The development of transmission at an identified molluscan synapse. I. The emergence of synaptic plasticities
Authors: Pawson P. A. , Chase R.
Published: December 2017

1. A monosynaptic, chemical synapse exists between two identified neurons in the subesophageal ganglia of the pulmonate mollusc, Achatina fulica. The snail undergoes a direct development, i.e., there is no intervening metamorphic period. The presynaptic (V2) and postsynaptic (RPr1) cells are two of the largest neurons found in the ganglia. The development of transmission at this synapse was studied from the last one-third of embryonic life to adulthood. 2. Synaptic transmission was studied by eliciting an action potential in V2 and recording the resultant excitatory postsynaptic potential (EPSP) in RPr1. In a train of repetitive stimuli, the ratio of the mean amplitude of the second EPSP to that of the first EPSP (EPSP2/EPSP1) is always greater than 1, indicating that short-term facilitation is present at all developmental ages studied. Following the initial short-term facilitation, embryonic synapses undergo a profound synaptic depression. Postembryonically there is a progressive increase in the amount of frequency facilitation with age, suggesting that the synapse shows a developmental trend towards an increased capacity for transmitter release. 3. In contrast to the progressive growth of frequency facilitation, the amplitude of the first EPSP in a series of responses (EPSP1) is not significantly related to age. 4. When transmitter release is reduced to approximately 25% of normal levels by a low-Ca2+/high-Mg2+ saline, the synaptic depression that is observed in the younger synapses disappears and is replaced by an adult-like frequency facilitation. 5. The adult synapse displays a phenomenon similar to posttetanic potentiation, which we refer to as the "retention of frequency facilitation." If an initial train of 150 stimuli at 0.2 Hz is followed by a second, identical train after an interval of 1 h, the postsynaptic response is greater during the second train than during the first. This phenomenon only becomes apparent in the second month after hatching, indicating that this separate synaptic plasticity develops at a different rate than does frequency facilitation.