bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantitative characterization and spinal pathway mediating inhibition of spinal nociceptive transmission from the lateral reticular nucleus in the rat
Authors: Janss A. J. , Gebhart G. F.
Published: December 2017

1. The modulation of spinal nociceptive transmission from the lateral reticular nucleus (LRN) was characterized for 47 spinal dorsal horn neurons in pentobarbital-anesthetized, paralyzed rats. All 47 units studied had receptive fields confined to the glabrous skin of the plantar surface of the ipsilateral hind foot and responded to mechanical stimulation as well as noxious heating (50 degrees C). Rostral projections contained in the ventrolateral quadrant of the cervical spinal cord were demonstrated for 15 of the 47 units by antidromic invasion. Glutamate- and stimulation-produced descending inhibition, the spinal pathway, and tonic descending inhibition from the LRN were systematically examined. 2. Inhibition of unit responses to heating of the skin by electrical stimulation in the LRN varied with the intensity, pulse duration (100 or 400 microseconds), and frequency (25–100 Hz) of stimulation. Greater inhibition was produced at lower intensities of stimulation with the 400-microseconds pulse duration and a frequency of 100 Hz. The effects of stimulation on spontaneous activity and responses to heat were compared in 16 experiments; inhibition of spontaneous activity was intensity dependent and did not differ significantly in magnitude from stimulation-produced inhibition of responses to heating of the skin. 3. Tracking experiments established that stimulation in the ipsilateral and contralateral ventrolateral medulla reliably attenuated unit responses to noxious heating of the skin and that stimulation in the LRN produced maximal inhibition at a low intensity of stimulation. Descending inhibition was quantitatively characterized from sites within (n = 32) and outside (n = 30) the LRN. Both the extrapolated mean stimulation threshold for inhibition and mean intensity inhibiting unit responses to heat to 50% of control were significantly lower for sites in the LRN. 4. The responses of seven spinal units to graded noxious heating of the skin were studied; all exhibited linear monotonic stimulus-response functions (SRFs) throughout the temperature range examined (42–50 degrees C). Electrical stimulation in the LRN significantly decreased the slope (42 +/- 4% of control) of the SRFs and increased the neuronal response threshold (2.0 +/- 0.7 degrees C). 5. S-glutamate (50 nmol, 0.5 microliter) was microinjected into stimulation sites within (n = 15) and distant from (n = 6) the LRN. Glutamate produced a transient (less than 7 min) but significant attenuation of neuronal responses to heat to 35 +/- 6% of control only when microinjected into the LRN.(ABSTRACT TRUNCATED AT 400 WORDS)
Interval coding and band-pass filtering at oculomotor synapses in crayfish
Authors: Glantz R. M. , Nudelman H. B.
Published: December 2017

1. Crayfish exhibit steady-state compensatory eyestalk rotations in response to rotations of the organism or the visual surround. For stimuli in the vertical planes (pitch or roll) the visual reflexes are mediated by identified visual interneurons [sustaining fibers (SFs)], which synapse on identified oculomotor neurons (Mns) (18). 2. The optimal visual stimulus is broad-field intense illumination (simulated skylight) distributed over the dorsal half of the cornea. These stimuli are also optimal for eliciting a regular pacing discharge in SFs with dorsal receptive fields (17). Since a unique discharge pattern is associated with the reflex stimulus, we proposed that the pacing discharge interval encodes the stimulus condition and is optimal for driving the motoneuron discharge. 3. The cross-correlation of SF and Mn impulse trains exhibit large peaks (or troughs) at short latencies associated with strong excitatory (or inhibitory) interactions and “secondary effects” at longer delays associated with the periodicity of the Mn impulse train. The secondary peaks and troughs indicate delayed periods of elevated or depressed Mn excitability synchronized to the reference train (SF) events. From the structure of the cross-correlograms and the motoneuron autocorrelograms we predicted that the spike-to-spike synaptic throughput should be differentially sensitive to the various classes of SF interspike intervals. 4. The hypotheses were tested with logical-correlation functions that directly measure the relative synaptic efficacy of several classes of SF intervals during a continuous train at constant mean rate. The results indicate that the SF-to-Mn excitatory synapse is maximally driven by SF impulses separated by approximately 85 ms. These events are about 2.5 times as effective as the impulses associated with short intervals (less than 20 ms) and 1.4 times as effective as the spikes of long intervals (250 ms). The optimal interval in the various preparations is highly to correlated to the period of the Mn discharge and the SF modal interspike interval. Inhibitory synapses are also differentially sensitive to the SF interspike intervals, but they exhibit summation rather than depression in response to short interspike intervals. 5. These results are generally consistent with previously formulated relationships (39), which govern the synaptic modulation of pacemakers and may apply to any synaptic interaction in which the postsynaptic neuron exhibits a regular discharge. 6. Combinations of long and short intervals with the same mean rate as the optimal interval are not as effective in driving the SF-to-Mn synapse.(ABSTRACT TRUNCATED AT 400 WORDS)
Vertical vestibuloocular reflex in cat: asymmetry and adaptation
Authors: Snyder L. H. , King W. M.
Published: December 2017

1. We studied eye velocity during the first 2 s of the vertical vestibuloocular reflex (VOR) elicited from cats placed on their sides (90 degrees roll position) and rotated about an earth vertical axis. Vestibular stimuli were presented in the dark and consisted of brief trapezoidal velocity profiles. Eye movements were recorded with a magnetic search coil, and eye velocity was analyzed with high temporal resolution. 2. The first 2 s of upward or downward eye velocity after the onset of head rotation was characterized and compared. Adaptive changes in VOR gain (eye/head velocity) were then induced, and upward and downward eye velocity responses were again compared. 3. The early time course of the vertical VOR was complex. After a latency of approximately 15 ms, eye velocity increased rapidly until it was equal in magnitude and opposite in direction to head velocity. The peak eye velocity decayed within less than 1 s to a plateau of slow-phase eye velocity (SPEV) equal to approximately -0.6 times the head velocity. Peak upward and downward eye velocity was symmetric. The transition from peak to plateau was more rapid for the downward VOR (slow phases downward) than for the upward VOR (slow phases upward). The plateau attained by upward SPEV was approximately 15% higher than the plateau attained by downward SPEV. 4. VOR gain adaptation was symmetric. The percentage change in adapted upward eye velocity equalled the percentage change in adapted downward eye velocity. Both peak and plateau SPEV adapted, but peak eye velocity adapted less than plateau eye velocity. VOR latency was unchanged by adaptation. 5. The trajectory of the VOR response to steps of head velocity could be divided into an invariant and a variant interval. The invariant interval consisted of the initial approximately 15 ms of the eye movement. Neither direction of head movement (upward vs. downward) nor adaptation of the VOR gain effected the eye movement trajectory during the invariant interval. The variant interval began approximately 30 ms after the onset of head movement and approximately 15 ms after the onset of eye movement. In unadapted animals, downward eye speed exceeded upward eye speed during the variant interval. In adapted animals, eye speed during the variant interval, but not during the invariant interval, diverged from eye speed in the unadapted state. We suggest that the initial invariant interval (approximately 15 ms) of the eye movement response trajectory may represent the direct response of the classically described three-neuron arc.(ABSTRACT TRUNCATED AT 400 WORDS)
Slow conductances in neurons from cat sensorimotor cortex in vitro and their role in slow excitability changes
Authors: Schwindt P. C. , Spain W. J. , Foehring R. C. , Chubb M. C. , Crill W. E.
Published: December 2017

1. The electrophysiological and pharmacological properties of slow afterpotentials in large layer V neurons from cat sensorimotor cortex were studied in an in vitro slice preparation using intracellular recording and single-microelectrode voltage clamp. These properties were used to assess the role of afterpotential mechanisms in prolonged excitability changes. 2. The mean duration of a slow afterhyperpolarization (sAHP) was 13.5 s following 100 spikes evoked at 100 Hz. Its time course was best described by two exponential components, which decayed with time constants of several hundred milliseconds (the early sAHP) and several seconds (the late sAHP). The amplitude of both the early and late components were sensitive to membrane potential and raised extracellular K+ concentration [( K+]o). 3. The early sAHP was reduced when divalent cations were substituted for Ca2+, whereas the late sAHP was unaffected. We conclude that a Ca2+-mediated K+ conductance is responsible for much of the early sAHP. In the presence of tetrodotoxin (TTX), 1-s voltage-clamp steps were used to evoke slow AHPs or outward ionic currents. These AHPs and currents were abolished in Ca2+-free perfusate, but they had a maximum duration of only a few seconds. Thus the slowest outward currents we could observe during voltage clamp in TTX were responsible only for the early sAHP. 4. The possible role of an electrogenic Na+-K+ pump in the late sAHP was examined by applying ouabain to the slice. Ouabain did not reduce selectively the late sAHP, and its effect was best explained by a decrease in intracellular K+ concentration and an increase in [K+]o. 5. Muscarinic and beta-adrenergic agonists reduced or abolished the entire (early and late) sAHP. Neither type of agonist affected the Ca2+-dependent, apamin-sensitive medium-duration afterhyperpolarization (35). We conclude that both the Ca2+-mediated K+ conductance underlying the early sAHP and the Ca2+-independent mechanisms underlying the late sAHP are sensitive to at least two classes of transmitter agonists. 6. We focused on the muscarinic effects. When concentrations greater than 5 microM were employed, the entire (early and late) sAHP was replaced by a slow afterdepolarization (sADP). Muscarine reduced the sAHP directly by reducing the underlying outward ionic currents and indirectly by causing the sADP. The sADP was Ca2+-mediated, since it was abolished by Ca2+-free perfusate but not by TTX. 7. The ionic currents underlying the sAHP and the sADP influenced excitability for seconds following evoked repetitive firing.(ABSTRACT TRUNCATED AT 400 WORDS)
Influence of anomalous rectifier activation on afterhyperpolarizations of neurons from cat sensorimotor cortex in vitro
Authors: Schwindt P. C. , Spain W. J. , Crill W. E.
Published: December 2017

1. Large neurons from layer V of cat sensorimotor cortex (Betz cells) were studied to determine the influence of the anomalous rectifier current (IAR) on slow afterhyperpolarizations (AHPs). The neurons were examined using intracellular recording and single-microelectrode voltage clamp in an in vitro brain slice preparation. 2. A faster medium-duration AHP (mAHP) and slower AHP (sAHP) followed repetitive firing (22, 23). The amplitude of the mAHP often increased or remained constant during membrane potential hyperpolarization. The membrane potential trajectory resulting solely from IAR activation was similar to the mAHP. 3. Postrepetitive firing voltage clamp was used to measure directly slowly decaying K+ currents (IK) and IAR at different membrane potentials. IK exhibited both a fast and slow decay. The time constants of the fast decay of IK and IAR activation were similar. IAR increased with hyperpolarization or raised extracellular K+ concentration [( K+]o), whereas both the fast and slow components of IK reversed or nulled near -100 mV and behaved as pure K+ currents in response to raised [K+]o. 4. To determine the precise contribution of IK and IAR to the AHP waveform, theoretical AHPs were computed using a quantitative model based on voltage-clamp measurements. The calculated AHPs were qualitatively similar to measured AHPs. The amplitude of the mAHP showed little change with hyperpolarization because of the increasing dominance of IAR at more negative membrane potentials. The sAHP was little affected by IAR activation. 5. Several model parameters subject to biological variation among Betz cells were varied in the calculations to determine their importance in the AHP waveform. With IK parameters held constant, the amplitude and time course of the mAHP depended on resting potential, membrane time constant, the kinetics of the anomalous rectifier conductance (GAR), and the maximum value of GAR. IAR activation could result in a biphasic AHP even when the fast decay of IK was omitted from the calculations. 6. A wider variation of model parameters revealed behavior that may be relevant to other neurons. Certain values of membrane or IAR activation time constants resulted in a monophasic AHP even when the fast decay of IK was present. The decay of a biphasic AHP could reflect either the onset of IAR or the fast decay of IK, depending on the relative value of their time constants. Procedures are outlined to discriminate between these possibilities using current clamp methods.(ABSTRACT TRUNCATED AT 400 WORDS)
Responses of feline trigeminal spinal tract nucleus neurons to stimulation of the middle meningeal artery and sagittal sinus
Authors: Davis K. D. , Dostrovsky J. O.
Published: December 2017

1. Extracellular single-unit activity was recorded from 250 trigeminal (V) spinal tract nucleus neurons that were excited by electrical stimulation of the middle meningeal artery (MMA) and/or sagittal sinus (SS) in anesthetized cats. One hundred and thirty of these neurons were located in the V subnucleus caudalis (Vc), and the remaining 120 neurons were located in the V subnucleus oralis (Vo) or rostral part of the V subnucleus interpolaris (Vi). In many cases these neurons were also examined for the existence of orofacial receptive fields (RFs) by applying mechanical stimuli to the orofacial region. 2. The mean minimum latencies to suprathreshold electrical stimulation of the MMA and the SS were similar for Vc and Vo/Vi neurons. Excitation of Vc neurons occurred at latencies of 14.3 +/- 1.0 (n = 102) and 17.4 +/- 1.6 ms (n = 36) to MMA and SS stimulation, respectively. Excitation of Vo/Vi neurons occurred at latencies of 12.4 +/- 0.9 (n = 86) and 16.4 +/- 1.1 ms (n = 58) to MMA and SS stimulation, respectively. These latencies correspond to mean conduction velocities of approximately 5.2 and 4.0 m/s to MMA and SS stimulation, respectively. 3. Mechanical stimulation of the vessels evoked neuronal responses in five of eight MMA-activated neurons tested and three of five SS-activated neurons tested. 4. Almost all of the neurons tested (127 of 131) had peripheral RFs, and all were in the orofacial region. Nearly all (95%) Vc neurons had RFs within or including the ophthalmic facial region. The RFs of most (67%) Vo/Vi neurons also had RFs within or including ophthalmic regions, but in some cases were only within maxillary and/or mandibular regions. 5. Most of the Vc neurons (87%) were classified on the basis of their cutaneous inputs as nociceptive. The incidence of nociceptive neurons in Vo/Vi was also high (61%), although less than in Vc. In both the Vc and Vo/Vi neuronal populations, MMA-activated neurons were more likely to have nociceptive peripheral inputs than SS-activated neurons. 6. Histological reconstruction of recording sites indicated that the MMA- and/or SS-activated Vc neurons were concentrated in the lateral half of laminae III-V. The responsive neurons at the level of Vo/rostral Vi were not confined to any particular portion of these subnuclei. 7. These findings indicate that sensory afferents that innervate the dural arteries and venous sinuses are capable of activating neurons throughout the V spinal tract nucleus.(ABSTRACT TRUNCATED AT 400 WORDS)
Swimming in Aplysia brasiliana: identification of parapodial opener-phase and closer-phase neurons
Authors: Parsons D. W. , Pinsker H. M.
Published: December 2017

1. In freely behaving Aplysia brasiliana, spontaneous swimming in the laboratory occurred primarily in the dark hours of the day-night cycle. Suspending an intact animal above the substrate elicited continuous parapodial flapping with the same frequency and amplitude as spontaneous swimming. Parapodial flapping with decreased frequency and amplitude could still be elicited by suspending minimally dissected, but not more radically dissected, preparations. 2. In otherwise intact animals, severing the cerebropedal connective (CPC) bilaterally abolished suspended parapodial flapping, but normal flapping was elicited by tonic stimulation of the distal CPC. In minimally dissected preparations, tonic CPC stimulation elicited parapodial flapping, but with reduced frequency and amplitude. 3. During normal parapodial flapping, chronically implanted electrodes on parapodial nerves recorded the swimming motor program (SMP). The whole-nerve SMP consisted of rhythmic bursts of large-amplitude efferent units in phase with parapodial opening, with no observable activity during parapodial closing. By contrast, simultaneous electromyogram (EMG) recordings from antagonistic parapodial muscles showed antiphasic bursts of activity during opening and closing. The SMP was inhibited by touching food to the animals' lips. 4. Parapodial nerve backfills, using nickel chloride, labeled several cell clusters in the ipsilateral pedal ganglion. Two of these clusters were located caudally: one tightly clustered medial group had large cell bodies, and another, more distributed, lateral group had small cell bodies. The two clusters were identified in semi-intact preparations and isolated brains, using tonic CPC stimulation to elicit a fictive SMP recorded in parapodial nerves, and intracellular electrodes to characterize and stain individual cells. 5. The large parapodial opener-phase (POP) neurons were normally silent. At the onset of CPC stimulation, POP neurons depolarized and fired tonically, and then burst rhythmically in phase with each other, and one for one with large-amplitude axon spikes observed extracellularly in parapodial nerves during the fictive SMP. Intracellular firing of POP cells, singly or in pairs, never produced observable papapodial movements or one-for-one responses in parapodial muscles. Lucifer yellow-filled POP neurons showed a process (with a pronounced rostral loop) that gave off many short, fine neurites in the pedal neuropile before branching into two or three axons projecting into different parapodial nerves. 6. The smaller parapodial closer-phase (PCP) neurons normally discharged tonically at low frequencies.(ABSTRACT TRUNCATED AT 400 WORDS)
Natural groupings of primate spinothalamic neurons based on cutaneous stimulation. Physiological and anatomical features
Authors: Surmeier D. J. , Honda C. N. , Willis W. D.
Published: December 2017

1. Two hundred and twenty-one spinothalamic tract (STT) neurons in the lumbar spinal cord of anesthetized monkeys were studied. The majority of the recordings were in laminae IV-VI. Thirteen of these neurons were intracellularly injected with horseradish peroxidase and histologically reconstructed. 2. A standard series of four mechanical cutaneous stimuli, which ranged in intensity from innocuous brushing to tissue-damaging pinching, were used to test the mechanical responsiveness of STT neurons. The mean alterations in discharge rate produced by these test stimuli when delivered to a neuron's excitatory receptive field were used as response measures. 3. Univariate and bivariate analyses of these response measures failed to reveal natural groupings of STT neurons. To assess whether natural groupings dependent upon shared multivariate response patterns were present, a k-means cluster analysis of the responses was performed. 4. Because an assumption about the type of coding used by the STT system had to be made prior to clustering, two independent analyses were performed. One approach assumed a labeled line coding model; response magnitudes were determined within the context of the neuron under study (within-neuron analysis). The other approach assumed a population coding model; response magnitudes were determined within the context of the STT population (across-neuron analysis). 5. The within-neuron analysis suggested that the STT sample could be partitioned into four groups. The smallest group (n = 18, 8%) responded primarily to brushing but often had a convergent nociceptive input; this group was referred to as type I. A second group (n = 31, 14%) had strong responses to low-intensity stimuli, particularly pressure, and modestly larger responses to noxious stimuli; this group was referred to as type II. The clustering in these two groups was relatively weak, reflecting some heterogeneity in response pattern. 6. The largest within-neuron group (n = 108, 49%) was most responsive to noxious stimuli but had a saturating response function; because of their apparent role in coding intermediate intensity stimuli, this group was referred to as type III. The fourth group (n = 64, 29%) responded best to the most intense stimulus used; this group was referred to as type IV. 7. The across-neuron analysis also suggested that the STT sample could be partitioned into four groups. The largest group (n = 122, 55%) had relatively weak responses to all the cutaneous stimuli; this group was referred to as type A. 8. All of the remaining across-neuron groups had mean responses at or above the mean for all cutaneous stimuli.(ABSTRACT TRUNCATED AT 400 WORDS)
Reflex changes in muscle spindle discharge during a voluntary contraction
Authors: Aniss A. M. , Gandevia S. C. , Burke D.
Published: December 2017

1. This study was undertaken to determine whether low-threshold cutaneous and muscle afferents from mechanoreceptors in the foot reflexly affect fusimotor neurons innervating the plantar and dorsiflexors of the ankle during voluntary contractions. 2. Recordings were made from 29 identified muscle spindle afferents innervating triceps surae and the pretibial flexors. Trains of electrical stimuli (5 stimuli, 300 impulses per second) were delivered to the sural nerve at the ankle (intensity: 2-4 times sensory threshold) and to the posterior tibial nerve at the ankle (intensity: 1.5-3 times motor threshold for the small muscles of the foot). The stimuli were delivered while the subject maintained an isometric voluntary contraction of the receptor-bearing muscle, sufficient to accelerate the discharge of each spindle ending. This ensured that the fusimotor neurons directed to the ending were active and influencing the spindle discharge. The effects of these stimuli on muscle spindle discharge were assessed using raster displays, frequencygrams, poststimulus time histograms (PSTHs) and cumulative sums ("CUSUMs") of the PSTHs. Reflex effects onto alpha-motoneurons were determined from poststimulus changes in the averaged rectified electromyogram (EMG). Reflex effects of these stimuli onto single-motor units were assessed in separate experiments using PSTHs and CUSUMs. 3. Electrical stimulation of the sural or posterior tibial nerves at nonnoxious levels had no significant effect on the discharge of the 14 spindle endings in the pretibial flexor muscles. The electrical stimuli also produced no significant change in discharge of 11 of 15 spindle endings in triceps surae. With the remaining four endings in triceps surae, the overall change in discharge appeared to be an increase for two endings (at latencies of 60 and 68 ms) and a decrease for two endings (at latencies of 110 and 150 ms). The difference in the incidence of the responses of spindle endings in tibialis anterior and in triceps surae was significant (P less than 0.05, chi 2 test). 4. For both triceps surae and pretibial flexor muscles the electrical stimuli to sural or posterior tibial nerves had clear effects on the alpha-motoneuron pool, whether assessed using surface EMG or the discharge of single-motor units. Based on EMG recordings using intramuscular wire electrodes, the reflex effects differed for the gastrocnemii and soleus. 5. In this study, reflex changes in the discharge of human spindle endings were more difficult to demonstrate than comparable changes in the discharge of alpha-motoneurons.(ABSTRACT TRUNCATED AT 400 WORDS)
The functional anatomy of the receptive fields of rabbit C polymodal nociceptors
Authors: Kenins P.
Published: December 2017

1. The rabbit saphenous nerve was split into small strands to enable recording from single polymodal nociceptive C receptors. 2. The cutaneous receptive field was explored with textile fiber sized probes of diameter 20-50 microns, with buckling loads from 75 to 150 mgf. It was found that the classical 'hot spot', as defined by nylon monofilament von Frey hairs, is composed of a large number of active areas if a smaller stimulating probe is used. 3. Studies of spatial and temporal interaction established that C polymodal nociceptors respond best to slow movements and that each area of the receptive field acts independently of surrounding areas. 4. Moisture on the skin was shown to increase the discharge to a standard stimulus, probably by its softening effect on the stratum corneum. Glueing the probe to the skin showed that compressive force is not the major stimulus. 5. These results support the contention that fabric-evoked prickle is the result of individual stiff fabric hairs exceeding nociceptor threshold at their point of contact with the skin rather than some complex interaction of fabric properties.
Transcutaneous electrical stimulation and the sensation of prickle
Authors: Garnsworthy R. K. , Gully R. L. , Kenins P. , Westerman R. A.
Published: December 2017

1. A high-voltage low-current transcutaneous electrical stimulating device was constructed and tested for its suitability to evaluate fabric-evoked prickle sensitivity in a population of 162 subjects. The initial sensation experienced by subjects with this device was the unpleasant sensation of prickle. 2. Single-unit recordings from the rabbit saphenous nerve established that at threshold most unmyelinated cutaneous receptors, both C low-threshold mechanoreceptive and polymodal nociceptive, were activated by the device. 3. Threshold measurements showed that there was no relationship of electrical threshold to atopic status, nor to fabric prickle threshold. It was concluded that our device preferentially excites unmyelinated afferents, but is not useful as a screening device for fabric intolerance.
A frequency and time domain study of the horizontal and vertical vestibuloocular reflex in the pigeon
Authors: Anastasio T. J. , Correia M. J.
Published: December 2017

1. The horizontal and vertical vestibuloocular reflex (HVOR and VVOR, respectively) was studied in four chronically instrumented pigeons. Eye movements were measured using the magnetic search-coil technique and were produced by rotation in the dark. During the rotation paradigms, the pigeons were either pharmacologically aroused (using amphetamine) or drug free (normal). The pigeon HVOR and VVOR were tested using step and sinusoidal rotational stimulation. The range of frequencies (0.03-6.0 Hz) and the magnitude of the sinusoidal stimuli were chosen to match those used in a previous study of the responses of semicircular canal primary afferents (SCPAs) in unanesthetized (i.e., normal) pigeons. 2. The gain of the HVOR and VVOR in both normal and aroused pigeons was independent of stimulus magnitude (6-30 degrees/s) over the frequency range tested. In aroused pigeons, the frequency independent gain (G) of the HVOR (G = 0.6) and VVOR (G = 0.9) was roughly twice that for normal pigeons. Pigeon VOR phase under all combinations of orientation and arousal level was independent of stimulus magnitude except at the lowest frequency tested (0.03 Hz). At this frequency, phase lead decreased as stimulus magnitude increased for the HVOR and VVOR in both normal and aroused pigeons. 3. The step and sinusoidal gains were greater for the VVOR than for the HVOR under the same level of arousal. Neither the gain nor the dominant time constant of the VOR (tau vor) differed for rotation direction (clockwise or counterclockwise) for the HVOR or VVOR in normal or aroused pigeons. 4. The mean value of tau vor was 4.0 +/- 0.5 (SE) s as estimated from frequency response data and 4.3 +/- 0.4 s as estimated from step response data for the HVOR and VVOR in both normal and aroused pigeons. In comparison, the mean value of the dominant or cupular time constant (tau c) of normal pigeon SCPAs was approximately 10 s as estimated from frequency response data. These results indicate that tau vor is shorter than tau c in the pigeon. 5. At higher frequencies, the pigeon HVOR and VVOR exhibit an increasing phase lag unaccompanied by a gain change--characteristics produced by a pure time delay. The value of this time delay was about 7 ms for both the HVOR and VVOR in both normal and aroused pigeons. The HVOR and VVOR in normal and aroused pigeons lacked the higher frequency lead characteristics present in the frequency responses of most pigeon SCPAs.
The effects of acetylcholine on response properties of cat somatosensory cortical neurons
Authors: Metherate R. , Tremblay N. , Dykes R. W.
Published: December 2017

1. Two-hundred thirty-three single neurons were isolated and studied in somatosensory cortex of cats anesthetized with pentobarbital sodium or urethane. Two-hundred and three were studied during iontophoretic administration of acetylcholine (ACh), 173 during administration of glutamate, and 24 during administration of atropine. 2. Fifty-six percent of the 218 neurons tested responded to somatic stimuli. Another 21% did so during glutamate administration. In 11 cases ACh iontophoresis uncovered a receptive field in a previously unresponsive cell. 3. Forty-six percent of the 160 cells tested responded to thalamic stimulation. Another 17% did so in the presence of glutamate, but 19 cells responded to neither cutaneous nor thalamic stimuli. 4. Sixteen percent of the 203 cells tested were overtly excited by ACh and the responses to somatic stimulation of 29% were modulated by administration of ACh. Cells displaying overt excitation and/or modulation of responses were said to be cholinoceptive and made up 39% of the sample. These cells were located in all cortical layers. 5. Cholinoceptive neurons were more likely than noncholinoceptive cells to be driven by thalamic stimulation. 6. The changes observed during ACh administration tended to be facilitatory: an enhanced responsiveness to somatic stimuli, an increased firing rate, or an increased receptive-field size. However, in 10 of the 203 cases tested one or more of these variables decreased. 7. The enhanced responsiveness during ACh administration was a robust phenomenon; responses were often increased by as much as 200% and the discharge pattern was altered so that bursts of impulses following stimulation were more common. 8. ACh tended to enhance one attribute of a cell selectively rather than to act as a general excitant. 9. ACh is a powerful neuromodulatory agent in somatosensory cortex that, when released in specific behavioral states, should enhance the responsiveness of cortical neurons.
Differential conduction at axonal bifurcations. II. Theoretical basis
Authors: Stockbridge N.
Published: December 2017

1. Numerical methods are employed to describe unbranched and branched axons like those employed in the previous paper (13). The model axon consists of a set of conical-section membrane patches having identical Hodgkin-Huxley (6) properties and which are connected by a finite-difference approximation to the cable equation (7). 2. Frequency-dependent differential conduction is shown to occur in both unbranched and branched axons in the model, much as observed experimentally. 3. The effect is shown to occur when one limb is electrically shorter than another and results from differences in the way in which axial current entering such branches is distributed between membrane area near the bifurcation and membrane area far away.
Enlarged motor units resulting from partial denervation of cat hindlimb muscles
Authors: Luff A. R. , Hatcher D. D. , Torkko K.
Published: December 2017

1. It was the aim of this study to determine the extent to which a mammalian motoneuron can sprout in a partially denervated muscle, which motor unit types are involved in sprouting, and whether polyneuronal innervation exists between sprouted units. 2. The fast-twitch flexor digitorum longus (FDL) and slow-twitch soleus were partially denervated by unilateral section of the L7 ventral root in 12-wk-old kittens. After approximately 100 days single motor units were isolated, and their isometric contractile characteristics were determined. FDL units were also tested for their resistance to fatigue and categorized as fast-twitch, fatiguing fibers (FF), fast-twitch, fatigue-resistant fibers (FR), and slow-twitch, fatigue-resistant fibers (S). The presence of polyneuronal innervation was investigated between pairs of like and unlike units. 3. The extent of the original denervation was variable and was estimated from the distribution of motor axons innervating the muscle via the L7 and S1 (soleus) or L6 and L7 (FDL) ventral roots on the contralateral side. In soleus, denervations ranged from 75 to 98%; in FDL, 60 to 97% (denervations less than 60% were not investigated). In general, motor-unit force increased in proportion to the extent of the denervation. 4. Within soleus, unit force increased to over 2 N, which was about 16 times greater than the average for a normal muscle (133 mN). However, most units increased in force to between five and 12 times normal. 5. Within FDL, the force development of type S units was unaffected by partial denervation. Type FF units increased by up to 11 times (4.3 N) compared with normal FF units (395 mN) with most increasing between two and four times. FR units exhibited the greatest relative increase in force [up to 19 times (4.3 N) compared with normal (225 mN)]. Most units were two to seven times the normal. 6. A few FDL units were glycogen depleted, the muscles frozen, and cross sections prepared for histochemical analysis. This indicated that the largest units contained approximately 5,000 fibers, and there was little fiber hypertrophy. In the extensively denervated soleus muscle, large numbers of small, presumably denervated fibers were observed. The innervation ratio of several large units was determined indirectly using mean fiber area. This gave estimates of 3,000-4,000 fibers for the largest units. Again, fiber hypertrophy contributed little to the increase in unit force. It was concluded that the increased force of units in both muscles was largely attributable to terminal and axonal sprouting of the intact motor axons. 7. No evidence for polyneuronal innervation was found in either FDL or soleus muscle.(ABSTRACT TRUNCATED AT 400 WORDS)
Effects of temporomandibular joint stimulation on nociceptive and nonnociceptive neurons of the cat's trigeminal subnucleus caudalis (medullary dorsal horn)
Authors: Broton J. G. , Hu J. W. , Sessle B. J.
Published: December 2017

1. The extracellular activity of 196 single neurons in subnucleus caudalis (medullary dorsal horn) of the trigeminal (V) spinal tract nucleus was examined in chloralose-anesthesized, paralyzed cats. Electrical, mechanical, and algesic chemical stimuli were applied to the exposed temporomandibular joint (TMJ) in order to activate TMJ afferents. Seventy-eight neurons were studied that responded to electrical stimulation of the TMJ at a mean latency of 9.9 +/- 4.8 (SD) ms. 2. All neurons with TMJ input received additional afferent input, predominantly from facial skin or intraoral sites. Caudalis neurons were classified on the basis of their cutaneous mechanoreceptive field properties as low-threshold mechanoreceptive (LTM), wide dynamic range (WDR), or nociceptive specific (NS); a few neurons unresponsive to cutaneous stimuli were responsive to manipulation of deep subcutaneous structures. A sample of caudalis neurons was tested for responsiveness to electrical TMJ stimulation after the mechanoreceptive field properties of the neurons were determined. In this sample, 24% of the LTM neurons, 29% of the WDR neurons, 36% of the NS neurons, and 57% of the neurons with input from deep structures were responsive to TMJ stimulation. The WDR and NS neurons with TMJ inputs had mechanoreceptive field properties and laminar locations in caudalis that were comparable to those previously described for cutaneous nociceptive neurons in caudalis; also in accordance with recent studies, 74% of the neurons tested showed convergence of tooth pulp and/or hypoglossal (XII) nerve afferent inputs. 3. In contrast to the LTM neurons, the WDR and NS neurons were especially responsive to intense mechanical and algesic chemical stimulation of the TMJ as well as to electrical stimulation of TMJ afferents. For example, 71% of the WDR and NS neurons excited by electrical stimulation of the TMJ afferents and tested for their responsiveness to injections of algesic chemicals (7% NaCl, KCl, bradykinin, histamine) into the TMJ responded to at least one of these chemicals. The temporal characteristics of these responses were quantified. 4. The TMJ afferent inputs to the WDR and NS neurons were considered to be predominantly of a nociceptive character because of (1) the long latency and high threshold of most TMJ-evoked responses, which are consistent with previous demonstrations that small-diameter afferents predominantly supply the TMJ and, (2) the preferential responsiveness to noxious mechanical and chemical stimulation of TMJ afferents of neurons which were functionally identified as cutaneous nociceptive neurons.(ABSTRACT TRUNCATED AT 400 WORDS)
Pharmacological modulation of the rod pathway in the cat retina
Authors: Muller F. , Wassle H. , Voigt T.
Published: December 2017

1. In the intact cat eye, the responses of ganglion cells to light stimulation were recorded extracellularly and the actions of iontophoretically applied 2-amino-4-phosphonobutyrate (APB), a potent agonist at ON-bipolars, and of strychnine, a glycine antagonist, were investigated. 2. Under light-adapted conditions, the activity of ON-center ganglion cells is decreased by APB but is increased by strychnine. APB and strychnine act independently of one another. 3. The activity of light-adapted OFF-center ganglion cells is increased by APB and by strychnine. The light response remains clearly modulated. Strychnine blocks the action of simultaneously applied APB. The results are in agreement with the action of a push-pull mechanism, according to which ON-cone-bipolars provide a glycinergic input into OFF-center ganglion cells. 4. Under dark-adapted conditions, APB blocks the light responses of both ON-center and OFF-center ganglion cells. The discharge rate of ON-center ganglion cells is completely suppressed; OFF-center ganglion cells show a high maintained discharge. 5. Strychnine blocks the scotopic light response of OFF-center ganglion cells and blocks the action of simultaneously applied APB. The light response of ON-center ganglion cells is hardly affected by strychnine. 6. The effects of strychnine on OFF-center ganglion cells are in agreement with the hypothesis that the glycinergic AII amacrine cells modulate the activity of the scotopic OFF-channel. 7. Intravitreally applied APB abolished the scotopic b-wave of the electroretinogram at concentrations of 100 microM. 8. Our data suggest that as in rabbit (10) the rod bipolars in cat retina are depolarizing (ON) bipolar cells.
Corticotectal circuit in the cat: a functional analysis of the lateral geniculate nucleus layers of origin
Authors: Colby C. L.
Published: December 2017

1. The dorsal lateral geniculate nucleus (LGN) of the cat is a major thalamic relay between the retina and several visual cortical areas. These cortical areas in turn project to the superior colliculus (SC). The aim of the present experiment was to determine which LGN layers provide a necessary input to the corticotectal circuit. 2. Individual layers of the LGN were reversibly inactivated by microinjection of cobalt chloride during recording of visual responses in the retinotopically corresponding part of the superior colliculus. 3. For cells driven through the contralateral eye, inactivation of layer A or the medial interlaminar nucleus (MIN) had little effect on visual responsiveness in the superior colliculus. In contrast, inactivation of layer C abolished visual responses at one-quarter of the SC recording sites, reduced responses at another quarter, and left half of the recording sites unaffected. 4. For cells driven through the ipsilateral eye, inactivation of layer C1 or the MIN had no effect. Inactivation of layer A1 uniformly reduced visual responses in the superior colliculus and usually abolished them entirely. 5. These results are compatible with previous work showing that cortical input to the SC originates from Y-cells. They indicate that two of the five Y-cell containing layers (A1 and C) provide major inputs to the corticotectal circuit. The results suggest that layer A1 is functionally allied to layer C as well as to layer A.
An intracellular study of time-dependent cardiovascular afferent interactions in nucleus tractus solitarius
Authors: Mifflin S. W. , Felder R. B.
Published: December 2017

1. We used a model of bilateral carotid sinus nerve (CSN) stimulation to investigate cardiovascular afferent interactions in nucleus tractus solitarius (NTS) in anesthetized cats. In some instances, interactions with afferent inputs from vagus or renal nerves were also examined. 2. Intracellular recordings were made from 88 NTS neurons activated by electrical stimulation of one or both CSNs. Excitatory (EPSPs), inhibitory (IPSPs), and combined excitatory and inhibitory (EPSP/IPSP) postsynaptic membrane potential responses to ipsilateral CSN stimulation were observed. The input from opposite CSN (30 of 34 neurons tested) or from other ipsilateral afferent sources (vagus nerve, 10 tested; renal nerve, 9 tested) was qualitatively the same as that from ipsilateral CSN. 3. Conditioning tests demonstrated that the response (EPSP, IPSP, or EPSP/IPSP) evoked by a test stimulus to one CSN was reduced in amplitude and/or duration by a prior stimulus (1-5 pulses) to the same (82 of 85 neurons) or to the opposite (30 of 37 neurons) CSN at conditioning intervals ranging from 50 to 550 ms. For cells in which CSN stimulation evoked an EPSP, this inhibitory interaction occurred with no change in resting membrane potential and no change in input resistance. For cells in which CSN stimulation evoked an IPSP, the inhibitory interaction persisted beyond the duration of the CSN evoked IPSP. 4. We infrequently (3 cells) observed an excitatory interaction, in which the conditioning stimulus resulted in rhythmic depolarization of the neuron and a facilitated action potential response to an appropriately timed test stimulus. 5. During continuous CSN stimulation, postsynaptic potentials (PSPs) evoked by ipsilateral CSN were abolished in the steady state at stimulus frequencies of 5-20 Hz (n = 14). In cells that received a convergent input from contralateral CSN, the PSP evoked by contralateral CSN was usually (6 of 8 tested) abolished at lower stimulus frequencies (median difference = 5.0 Hz). 6. We conclude that individual NTS neurons frequently have the same PSP response to peripheral afferent inputs of different origins. Time-dependent interactions among cardiovascular afferent inputs that evoke PSPs of like kind may determine the nature of the integrated signal conveyed from NTS to subsequent cardiovascular related central nuclei. Both inhibitory and, less frequently, excitatory time-dependent interactions between cardiovascular afferent inputs occur. The absence of membrane potential changes associated with the inhibitory interaction suggests it may be mediated by disfacilitation.
Structure-function relationships in the primate superior colliculus. II. Morphological identity of presaccadic neurons
Authors: Moschovakis A. K. , Karabelas A. B. , Highstein S. M.
Published: December 2017

1. Microelectrodes filled with horseradish peroxidase (HRP) were inserted in the superior colliculus (SC) of alert squirrel monkeys. Spontaneous eye movements were monitored in the dark during recording and intraaxonal injection of fibers carrying presaccadic signals. 2. Analysis of the relationship between neuronal activity and saccadic parameters indicates that saccade-related neurons can be functionally classified into: 1) vectorial long-lead burst neurons (n = 31), and 2) directional long-lead burst neurons. 3. Vectorial long-lead burst neurons have little if any spontaneous activity and burst intensely before spontaneous saccades within their movement fields with a latency of approximately 20 ms. Their cell bodies were recovered mostly (4/5) in the stratum opticum of the SC. The mediolateral and anteroposterior location of these tectal long-lead burst neurons (TLLBs) together with their movement fields are consistent with existing descriptions of the motor map of the deeper tectal layers. Due to their somatodendritic morphology and pattern of axonal trajectories, TLLBs belong to the T group of tectal efferent neurons that was described in our companion report. Through its branched axonal system each TLLB can relay a signal coding intended eye displacement to reticular targets of the predorsal bundle (PDB), contralateral tectum, ipsilateral mesencephalic reticular formation (MRF), and rostrally located ipsilateral targets of the SC, besides participating in intratectal information processing. 4. Recovered tectal neurons (n = 4) with activity not related to spontaneous saccades participate in the predorsal and ventral ascending tectofugal bundles as well as the projection to the ipsilateral mesencephalic reticular formation. They do not participate in the commissural projection of the SC and need not have recurrent collaterals. Due to their somatodendritic morphology and pattern of axonal trajectories, these cells belong to the X group of tectal efferent neurons that was described in the preceding paper. 5. Recovered cells of origin of directional long-lead burst fibers recorded in the SC (n = 5) are located in the tectorecipient portion of the MRF and their axonal terminals are entirely contained within the SC. The high-frequency portion of the discharge of these reticulotectal long-lead burst neurons (RTLLBs) precedes most contraversive saccades by approximately 19 ms.(ABSTRACT TRUNCATED AT 400 WORDS)