bluuebunny/crossref_metadata_2025 huggingface dataset:
Fast-to-Slow Conversion Following Chronic Low-Frequency Activation of Medial Gastrocnemius Muscle in Cats. I. Muscle and Motor Unit Properties
Authors: Gordon T. , Tyreman N. , Rafuse V. F. , Munson J. B.
Published: December 2017

Gordon, T., N. Tyreman, V. F. Rafuse, and J. B. Munson. Fast-to-slow conversion following chronic low-frequency activation of medial gastrocnemius muscle in cats. I. Muscle and motor unit properties. J. Neurophysiol. 77: 2585–2604, 1997. This study of cat medial gastrocnemius (MG) muscle and motor unit (MU) properties tests the hypothesis that the normal ranges of MU contractile force, endurance, and speed are directly associated with the amount of neuromuscular activity normally experienced by each MU. We synchronously activated all MUs in the MG muscle with the same activity (20 Hz in a 50% duty cycle) and asked whether conversion of whole muscle contractile properties is associated with loss of the normal heterogeneity in MU properties. Chronically implanted cuff electrodes on the nerve to MG muscle were used for 24-h/day stimulation and for monitoring progressive changes in contractile force, endurance, and speed by periodic recording of maximal isometric twitch and tetanic contractions under halothane anesthesia. Chronic low-frequency stimulation slowed muscle contractions and made them weaker, and increased muscle endurance. The most rapid and least variable response to stimulation was a decline in force output of the muscle and constituent MUs. Fatigue resistance increased more slowly, whereas the increase in time to peak force varied most widely between animals and occurred with a longer time course than either force or endurance. Changes in contractile force, endurance, and speed of the whole MG muscle accurately reflected changes in the properties of the constituent MUs both in extent and time course. Normally there is a 100-fold range in tetanic force and a 10-fold range in fatigue indexes and twitch time to peak force. After chronic stimulation, the range in these properties was significantly reduced and, even in MU samples from single animals, the range was shown to correspond with the slow (type S) MUs of the normal MG. In no case was the range reduced to less than the type S range. The same results were obtained when the same chronic stimulation pattern of 20 Hz/50% duty cycle was imposed on paralyzed muscles after hemisection and unilateral deafferentation. The findings that the properties of MUs still varied within the normal range of type S MUs and were still heterogeneous despite a decline in the variance in any one property indicate that the neuromuscular activity can account only in part for the wide range of muscle properties. It is concluded that the normal range of properties within MU types reflects an intrinsic regulation of properties in the multinucleated muscle fibers.
Spatial and Temporal Integration of Signals in Foveal Line Orientation
Authors: Westheimer Gerald , Ley Eric J.
Published: December 2017

Westheimer, Gerald and Eric J. Ley. Spatial and temporal integration of signals in foveal line orientation. J. Neurophysiol. 77: 2677–2684, 1997. The discrimination of the orientation of a line improves with line length, reaching an optimum when a foveal line is ∼0.5° long. We studied the effect of eliminating sections of the line, of displacing them out of alignment, and of delaying them. Orientation discrimination thresholds are only a little elevated when a 25-arcmin line is replaced by three equally spaced collinear 5-arcmin segments. Two collinear 5-arcmin segments show better thresholds than a single one when they are separated by as much as 20 arcmin. But thresholds are impaired by bringing line segments out of collinearity by as little as 1 arcmin. Asynchrony of up to 50 ms can be tolerated, but when the middle segment of a three-line pattern is delayed by ∼100 ms there is active inhibition, thresholds being now higher than when the middle segment is absent. It is concluded that for signals to address the orientation discrimination mechanism optimally, they have to be contained inside a narrow spatial corridor and be presented within a time window of ∼50 ms, but that some spatial summation can take place over a length of ≥0.5° in the fovea. Because short lines made of black and white collinear segments do not have good orientation thresholds, whereas longer and interrupted lines do, it is concluded that what is involved is potentiating interaction between collinearly arranged neurons with identical orientation selectivity rather than summation of signals within the receptive fields of single neurons.
Abnormal Access of Axial Vibrotactile Input to Deafferented Somatosensory Cortex in Human Upper Limb Amputees
Authors: Kew John J. M. , Halligan Peter W. , Marshall John C. , Passingham Richard E. , Rothwell JOHN C. , Ridding Michael C. , Marsden C. David , Brooks David J.
Published: December 2017

Kew, John J. M., Peter W. Halligan, John C. Marshall, Richard E. Passingham, John C. Rothwell, Michael C. Ridding, C. David Marsden, and David J. Brooks. Abnormal access of axial vibrotactile input to deafferented somatosensory cortex in human upper limb amputees. J. Neurophysiol. 77: 2753–2764, 1997. We studied two human subjects with total deafferentation of one upper limb secondary to traumatic multiple cervical root avulsions. Both subjects developed a phantom limb and underwent elective amputation of the paralyzed, deafferentated limb. Psychophysical study revealed in each subject an area of skin in the pectoral region ipsilateral to the amputation where vibrotactile stimulation (VS) elicited referred sensations (RS) in the phantom limb. Positron emission tomography was then used to measure regional cerebral blood flow changes during VS of the pectoral region ipsilateral to the amputation with RS and during VS of a homologous part of the pectoral region adjacent to the intact arm without RS. A voxel-based correlation analysis was subsequently used to study functional connectivity. VS of the pectoral region adjacent to the intact arm was associated with activation of the dorsal part of the contralateral primary somatosensory cortex (S1) in a position consistent with the S1 trunk area. In contrast, VS of the pectoral region ipsilateral to the amputation with RS was associated with activation of the contralateral S1 that extended from the level of the trunk representation ventrally over distances of 20 and 12 mm, respectively, in the two subjects. The area of S1 activated during VS of the digits in a normal control subject was coextensive with the ventral S1 region abnormally activated during VS of the ectopic phantom representation in the two amputees, suggesting that the deafferented digit or hand/arm area had been activated by sensory input from the pectoral region. Correlation analysis showed an abnormal pattern of intrinsic connectivity within the deafferented S1 hand/arm area of both amputees. In one subject, the deafferented S1 was functionally connected with 3 times as many S1 voxels as the normally afferented S1. This abnormal functional connectivity extended in both the rostrocaudal and ventrodorsal dimensions. The results demonstrate that sensory input delivered to the axial body surface may gain access to the S1 hand/arm area in some humans who have suffered extensive deafferentation of this area. The findings are consistent with the hypothesis that deafferentation of an area of S1 may result in activation of previously dormant inputs from body surfaces represented in immediately adjacent parts of S1. The results also provide evidence that changes in functional connectivity between these adjacent areas of the cortex play a role in the somatotopic reorganization.
Convergent Chemical and Electrical Synaptic Inputs From Proprioceptive Afferents Onto an Identified Intersegmental Interneuron in the Crayfish
Authors: Nagayama Toshiki , Aonuma Hitoshi , Newland Philip L.
Published: December 2017

Nagayama, Toshiki, Hitoshi Aonuma, and Philip L. Newland. Convergent chemical and electrical synaptic inputs from proprioceptive afferents onto an identified intersegmental interneuron in the crayfish. J. Neurophysiol. 77: 2826–2830, 1997. Synaptic transmission between proprioceptive afferents from a chordotonal organ in the tailfan of the crayfish and an identified ascending interneuron, interneuron A, in the terminal abdominal ganglion was analyzed. Interneuron A is part of a disynaptic pathway from primary afferent neurons to the lateral giant interneuron involved in producing the characteristic ballistic escape behavior of crayfish. Interneuron A received short and long latency excitatory postsynaptic potentials (EPSPs) from chordotonal afferents. Short latency EPSPs occurred with little central synaptic delay, were unchanged by hyperpolarizing current injection of −2 nA, and remained at a constant amplitude when the nervous system was bathed in saline with a low calcium concentration or saline containing the nicotinic antagonist curare. These EPSPs are thus thought to be mediated by electrical transmission. Longer latency potentials were increased in amplitude by hyperpolarizing current injection, reduced in amplitude when the nervous system was bathed in low-calcium saline, and also reduced by bath application of saline containing curare. These potentials are thus thought to be mediated by chemical transmission. The functional significance of the dual modes of transmission at a key synapse in the escape circuitry is discussed.
Response Variability and Timing Precision of Neuronal Spike Trains In Vivo
Authors: Reich Daniel S. , Victor Jonathan D. , Knight Bruce W. , Ozaki Tsuyoshi , Kaplan Ehud
Published: December 2017

Reich, Daniel S., Jonathan D. Victor, Bruce W. Knight, Tsuyoshi Ozaki, and Ehud Kaplan. Response variability and timing precision of neuronal spike trains in vivo. J. Neurophysiol. 77: 2836–2841, 1977. We report that neuronal spike trains can exhibit high, stimulus-dependent temporal precision even while the trial-to-trial response variability, measured in several traditional ways, remains substantially independent of the stimulus. We show that retinal ganglion cells and neurons in the lateral geniculate nucleus (LGN) of cats in vivo display both these aspects of firing behavior, which have previously been reported to be contradictory. We develop a simple model that treats neurons as “leaky” integrate-and-fire devices and show that it, too, can exhibit both behaviors. We consider the implications of our findings for the problem of neural coding.
Processing of Interaural Intensity Differences in the LSO: Role of Interaural Threshold Differences
Authors: Park T. J. , Monsivais P. , Pollak G. D.
Published: December 2017

Park, T. J., P. Monsivais, and G. D. Pollak. Processing of interaural intensity differences in the LSO: role of interaural threshold differences. J. Neurophysiol. 77: 2863–2878, 1997. Cells in the lateral superior olive (LSO) are known to be sensitive to interaural intensity differences (IIDs) in that they are excited by IIDs that favor the ipsilateral ear and inhibited by IIDs that favor the contralateral ear. For each LSO neuron there is a particular IID that causes a complete inhibition of discharges, and the IID of complete inhibition varies from neuron to neuron. This variability in IID sensitivity among LSO neurons is a key factor that allows for the coding of a variety of IIDs among the population of cells. A fundamental question concerning the coding of IIDs is: how does each cell in the LSO derive its particular IID sensitivity? Although there have been a large number of neurophysiological studies on the LSO, this question has received little attention. Indeed, the only reports that have directly addressed this question are those of Reed and Blum, who modeled the binaural properties of LSO neurons and proposed that the IID at which discharges are completely suppressed should correspond to the difference in threshold between the excitatory, ipsilateral and inhibitory, contralateral inputs that innervate each LSO cell. The main purpose of this study was to test the threshold difference hypothesis proposed by Reed and Blum by recording responses to monaural stimulation and to IIDs from single cells in the LSO of the mustache bat. Our results show that although the IID sensitivities of some LSO cells correspond to the difference in threshold between the excitatory and inhibitory ears, in the majority of cells the difference in thresholds did not correspond to the cell's IID sensitivity. The results lead us to propose two models to account for IID sensitivities. One model is similar to that proposed by Reed and Blum and emphasizes differences in the thresholds of the excitatory and inhibitory inputs. This model accounts for the minority of cells in which the IID of complete inhibition corresponded to the difference in threshold of the inputs from the two ears. The other model, which accounts for the cells in which the IID of complete inhibition did not correspond to the difference in the thresholds of the inputs from the two ears (the majority of cells), places emphasis on differences in latencies of the excitatory and inhibitory inputs. The models incorporate features that are concordant with the known properties of the neurons that project to the LSO and together can account for the diversity of IID sensitivities among the population of LSO neurons.
Excitation of the Brain Stem Pedunculopontine Tegmentum Cholinergic Cells Induces Wakefulness and REM Sleep
Authors: Datta Subimal , Siwek Donald F.
Published: December 2017

Datta, Subimal and Donald F. Siwek. Excitation of the brain stem pedunculopontine tegmentum cholinergic cells induces wakefulness and REM sleep. J. Neurophysiol. 77: 2975–2988, 1997. Considerable evidence suggests that brain stem pedunculopontine tegmentum (PPT) cholinergic cells are critically involved in the normal regulation of wakefulness and rapid eye movement (REM) sleep. However, much of this evidence comes from indirect studies. Thus, although involvement of PPT cholinergic neurons has been suggested by numerous investigations, the excitation of PPT cholinergic neurons causal to the behavioral state of wakefulness and REM sleep has never been directly demonstrated. In the present study we examined the effects of three different levels of activation of PPT cholinergic cells in wakefulness and sleep behavior. The effects of glutamate on the activity of PPT cholinergic cells were studied by microinjection of one of the three different doses of l-glutamate (0.3, 1.0, and 3.0 μg) or saline (vehicle control) into the PPT cholinergic cell compartment while quantifying the effects on wakefulness and sleep in free moving chronically instrumented cats. All microinjections were made during wakefulness and were followed by 4 h of recording. Polygraphic records were scored for wakefulness, slow-wave sleep states 1 and 2, slow-wave sleep with pontogeniculooccipital waves, and REM sleep. Dependent variables quantified after each microinjection included the percentage of recording time spent in each state, the latency to onset of REM sleep, the number of episodes per hour for REM sleep, and the duration of each REM sleep episode. A total of 48 microinjections was made into 12 PPT sites in six cats. Microinjection of 0.3- and 1.0-μg doses of l-glutamate into the cholinergic cell compartment of the PPT increased the total amount of REM sleep in a dose-dependent manner. Both doses of l-glutamate increased REM sleep at the expense of slow-wave sleep but not wakefulness. Microinjection of 3.0 μg l-glutamate kept animals awake for 2–3 h by eliminating slow-wave and REM sleep. The results show that the microinjection of the excitatory amino acid l-glutamate into the PPT cholinergic cell compartments can increase wakefulness and/or REM sleep depending on the l-glutamate dosage. These findings unambiguously confirm the hypothesis that the excitation of the PPT cholinergic cells is causal to the generation of wakefulness and REM sleep.
Adenosine Modulation of Calcium Currents and Presynaptic Inhibition of GABA Release in Suprachiasmatic and Arcuate Nucleus Neurons
Authors: Chen Gong , van den Pol Anthony N.
Published: December 2017

Chen, Gong and Anthony N. van den Pol. Adenosine modulation of calcium currents and presynaptic inhibition of GABA release in suprachiasmatic and arcuate nucleus neurons. J. Neurophysiol. 77: 3035–3047, 1997. Adenosine modulation of calcium channel currents and synaptic γ-aminobutyrate (GABA) release was investigated with whole cell voltage-clamp recordings in rat suprachiasmatic nucleus (SCN) and arcuate nucleus cultures ( n = 94). In SCN cultures, ∼70% of the neurons showed a reversible inhibition of whole cell barium currents on the application of adenosine or its analogues. Adenosine at 1 μM reduced the amplitude of the barium currents by ∼27%. In contrast to the significant reduction in the amplitude, the rising and decaying phases of the barium currents, and the inverted bell shape of the current-voltage curve of the barium currents, were not changed by adenosine. The adenosine A1 receptor agonist N6-cyclopentyladenosine (CPA; 100 nM) and the adenosine A2 receptor agonist N6-[2-(3,5-dimethoxyphenyl)-ethyl]adenosine (DPMA; 100 nM) inhibited the barium currents by 21% and 16%, respectively, in SCN neurons, indicating both A1 and A2 receptor actions. The A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (100 nM) significantly reduced the effect of CPA but did not change the effect of DPMA on the barium currents. In the presence of tetrodotoxin to block action potentials, the frequency, but not the amplitude, of miniature inhibitory postsynaptic currents was significantly reduced (46%) by 1 μM adenosine, suggesting a presynaptic mechanism of adenosine action. In support of this suggestion, the postsynaptic GABA receptor responses were not influenced by 1 μM adenosine in the majority of SCN neurons. Most solitary self-innervating SCN neurons in microisland cultures were GABAergic. In these cells, the evoked autaptic GABA release (inhibitory postsynaptic current) was significantly inhibited by adenosine (37%), CPA (27%), and DPMA (28%), indicating that both A1 and A2 receptors were present in presynaptic axons. Similar to the effect in SCN neurons, adenosine inhibited both barium currents and GABA release in arcuate neurons. The reduction of whole cell barium currents by adenosine (1 μM), CPA (100 nM), and DPMA (100 nM) was 24, 17, and 19%, respectively. In solitary self-innervating arcuate neurons, adenosine inhibited the evoked GABA release (inhibitory postsynaptic current) by ∼48%. We conclude that both adenosine A1 and A2 receptors are present in the SCN and arcuate nucleus of the hypothalamus. Adenosine inhibits calcium currents and presynaptically reduces inhibitory GABA neurotransmission.
Functional Organization of the Projection From Area 2 to Area 4γ in the Cat
Authors: Caria Marcello A. , Kaneko Takeshi , Kimura Akihisa , Asanuma Hiroshi
Published: December 2017

Caria, Marcello A., Takeshi Kaneko, Akihisa Kimura, and Hiroshi Asanuma. Functional organization of the projection from area 2 to area 4γ in the cat. J. Neurophysiol. 77: 3107–3114, 1997. It has been shown that tetanic stimulation of area 2 of the somatosensory cortex produces long-term potentiation in neurons in area 4γ, and this has been suggested as the basis of learning new motor skills. The purpose of this study was to further elucidate the characteristics of this projection by the use of evoked potentials in area 4γ elicited by intracortical microstimulation of area 2. The experiments were carried out in cats and the following results were obtained. 1) In six animals, stimulation of a given site in area 2 elicited evoked potentials in a restricted region of area 4γ, the size of which ranged from 1 to 1.5 mm2. These responses were labeled “localized responses.” The evoked potentials were recorded from the superficial layers of the cortex, and were positive monophasic in shape. 2) In 16 animals, stimulation of a given site in area 2 elicited a focal response that was surrounded by smaller positive and monophasic potentials of <50% amplitude that spread broadly over area 4γ. These responses were labeled “graded responses.” 3) The sites that produced focal evoked potentials in area 4γ extended along the direction of the radial fibers in area 2. These sites were defined as most effective segments (MESs). 4) The receptive fields of neurons along the MES in area 2 were similar to those of neurons recorded at the foci of the evoked potentials in area 4γ. The results demonstrate that some of the projections from area 2 to area 4γ are highly specific and that the somatosensory and motor areas that are connected by these specific projections receive functionally related peripheral input. These results are discussed in relation to possible mechanisms underlying motor learning.
Afferent Inputs Modulate the Activity of a Rhythmic Burst Generator in the Rat Disinhibited Spinal Cord In Vitro
Authors: Bracci E. , Beato M. , Nistri A.
Published: December 2017

Bracci, E., M. Beato, and A. Nistri. Afferent inputs modulate the activity of a rhythmic burst generator in the rat disinhibited spinal cord in vitro. J. Neurophysiol. 77: 3157–3167, 1997. Application of strychnine and bicuculline to the isolated spinal cord of the neonatal rat induces spontaneous bursting of regular rhythmicity (cycle period ∼30 s). This phenomenon is important because it shows that a spinal network, made up by excitatory connections only, generates a very reliable rhythmic pattern. To find out how signals from the periphery or higher centres might influence the operation of the rhythmogenic network, the present experiments examined whether synaptic inputs from dorsal root (DR) or ventrolateral (VL) afferent fibers could modulate this spontaneous rhythmicity. This issue was addressed with intracellular recording from motoneurons or extracellular recording from ventral roots after eliciting bursting with strychnine plus bicuculline. Single electrical shocks (0.1 ms; intensity 1–4 times threshold) applied to one DR reset spontaneous bursting without altering its period or duration. Repetitive stimulations at periods ranging from 20 to 2 s entrained bursts on a 1:1 basis. Burst duration was shorter at lower stimulation periods whereas burst amplitude was unchanged. The lowest stimulation period compatible with burst entrainment depended on stimulus strength. At stimulation periods <2-s entrainment was always lost and spontaneous bursts unexpectedly returned even if electrical pulses still elicited ventral root reflexes. Such spontaneous bursts had similar properties as those recorded in the absence of electrical pulses. Analogous results were obtained with VL stimulations. It is concluded that the spinal rhythmogenic network was highly susceptible to external synaptic inputs, which paced burst generation whereas burst duration was adapted to interstimulus interval. A scheme is provided to explain the modulatory role of synaptic inputs as well as the escape of bursting from fast stimulus entrainment in terms of a rhythmogenic network functionally separated from reflex pathways activated by DR or VL tracts.
Role of Calcium Conductances on Spike Afterpotentials in Rat Trigeminal Motoneurons
Authors: Kobayashi Masayuki , Inoue Tomio , Matsuo Ryuji , Masuda Yuji , Hidaka Osamu , Kang Youngnam , Morimoto Toshifumi
Published: December 2017

Kobayashi, Masayuki, Tomio Inoue, Ryuji Matsuo, Yuji Masuda, Osamu Hidaka, Youngnam Kang, and Toshifumi Morimoto. Role of calcium conductances on spike afterpotentials in rat trigeminal motoneurons. J. Neurophysiol. 77: 3273–3283, 1997. Intracellular recordings were obtained from rat trigeminal motoneurons in slice preparations to investigate the role of calcium conductances in the depolarizing and hyperpolarizing spike afterpotential (ADP and mAHP, respectively). The mAHP was suppressed by bath application of 1 μM apamin, 2 mM Mn2+, and 2 mM Co2+, and also by intracellular injection of ethylene glycol-bis(b-aminoethylenether)- N,N,N′,N′-tetraacetic acid (EGTA), suggesting that the potassium conductance generating the mAHP is activated by Ca2+ influx. Mn2+ (2 mM) or Cd2+ (500 μM) reduced the ADP, whereas the ADP amplitude was increased by raising extracellular Ca2+ concentration from 2 to 8 mM by bath application of Ba2+ (0.5–5 mM) and by intracellular injection of EGTA. This would suggest that Ca2+ itself is likely to be the charge carrier generating the ADP. Focal application of ω-conotoxin GVIA (10–30 μM) suppressed the mAHP and enhanced the ADP, whereas focal application of ω-agatoxin IVA (10–100 μM) reduced the ADP amplitude without apparent effects on the mAHP. We conclude that Ca2+ influx through ω-agatoxin IVA–sensitive calcium channels is at least in part responsible for the generation of the ADP and that Ca2+ influx through ω-conotoxin GVIA–sensitive calcium channels contributes to the generation of the mAHP. Because of the selective suppression of the ADP and mAHP by ω-agatoxin IVA and ω-conotoxin GVIA, respectively, it is suggested that both calcium channels are separated geometrically in rat trigeminal motoneurons.
Two Parallel Signaling Pathways Couple 5HT1A Receptors to N- and L-Type Calcium Channels in C-Like Rat Dorsal Root Ganglion Cells
Authors: Cardenas Carla G. , Mar Lucinda P. Del , Scroggs Reese S.
Published: December 2017

Cardenas, Carla G., Lucinda P. Del Mar, and Reese S. Scroggs. Two parallel signaling pathways couple 5HT1A receptors to N- and L-type calcium channels in C-like rat dorsal root ganglion cells. J. Neurophysiol. 77: 3284–3296, 1997. The coupling of serotonin receptors to Ca2+ channels was studied in a subpopulation of acutely isolated rat dorsal root ganglion (DRG) cell bodies (type 1 DRG cells), which have membrane properties similar to C-type nociceptive sensory neurons. In these cells, serotonin (5HT) inhibited high-threshold Ca2+ channel current and decreased action potential duration. The inhibitory effects of 5HT and the 5HT1A agonist 8-OH-DPAT were shown to be antagonized by the 5HT1A antagonists spiperone and pindolol, respectively, indicating involvement of a 5HT1A receptor. Several observations suggest that 5HT1A receptors couple to N- and L-type Ca2+ channels by two different signaling pathways in type 1 DRG cells. The inhibition of Ca2+ channel currents produced by 10 μM 5HT occurred in two phases, an initial slowing of current activation rate (kinetic slowing), which was complete within 10 s, and a simultaneous reduction in steady state current amplitude (steady state inhibition), which peaked in ∼1 min. The kinetic slowing, but not steady state inhibition, was reversed by a positive prepulse to +70 mV (prepulse). Blockade of N-type Ca2+ channels selectively reduced the kinetic slowing and its reversal by prepulses. Chelation of intracellular Ca2+ or blockade of L-type Ca2+ channels selectively reduced the steady state inhibition. Recordings using the cell-attached patch configuration suggest that steady state inhibition required a component that was diffusible in the cytosol, while kinetic slowing occurred via a membrane delimited pathway. The application of 5HT to the cell body outside the patch pipette reduced macroscopic Ca2+ channel currents in 33% of small-diameter DRG cells tested, indicating the participation of a cytosolic diffusible component. Application of 5HT (a membrane impermeant compound) outside the patch pipette produced steady state inhibition only, whereas similar application of membrane permeant 5HT1A agonists, 8-OH-DPAT or 5-methoxy- N, N-dimethyl-tryptamine, produced kinetic slowing and steady state inhibition. Together these data suggest that 5HT1A receptors couple negatively to Ca2+ channels via two pathways: a membrane-delimited pathway that couples to N-channels and actuates voltage-sensitive kinetic slowing and a pathway dependent on a cytosolic diffusible component and free intracellular Ca2+, which couples to L channels and actuates steady state inhibition.
Dynamics of Neurons Controlling Movements of a Locust Hind Leg III. Extensor Tibiae Motor Neurons
Authors: Newland Philip L. , Kondoh Yasuhiro
Published: December 2017

Newland, Philip L. and Yasuhiro Kondoh. Dynamics of neurons controlling movements of a locust hind leg. III. Extensor tibiae motor neurons. J. Neurophysiol. 77: 3297–3310, 1997. Imposed movements of the apodeme of the femoral chordotonal organ (FeCO) of the locust hind leg elicit resistance reflexes in extensor and flexor tibiae motor neurons. The synaptic responses of the fast and slow extensor tibiae motor neurons (FETi and SETi, respectively) and the spike responses of SETi were analyzed with the use of the Wiener kernel white noise method to determine their response properties. The first-order Wiener kernels computed from soma recordings were essentially monophasic, or low passed, indicating that the motor neurons were primarily sensitive to the position of the tibia about the femorotibial joint. The responses of both extensor motor neurons had large nonlinear components. The second-order kernels of the synaptic responses of FETi and SETi had large on-diagonal peaks with two small off-diagonal valleys. That of SETi had an additional elongated valley on the diagonal, which was accompanied by two off-diagonal depolarizing peaks at a cutoff frequency of 58 Hz. These second-order components represent a half-wave rectification of the position-sensitive depolarizing response in FETi and SETi, and a delayed inhibitory input to SETi, indicating that both motor neurons were directionally sensitive. Model predictions of the responses of the motor neurons showed that the first-order (linear) characterization poorly predicted the actual responses of FETi and SETi to FeCO stimulation, whereas the addition of the second-order (nonlinear) term markedly improved the performance of the model. Simultaneous recordings from the soma and a neuropilar process of FETi showed that its synaptic responses to FeCO stimulation were phase delayed by about −30° at 20 Hz, and reduced in amplitude by 30–40% when recorded in the soma. Similar configurations of the first and second-order kernels indicated that the primary process of FETi acted as a low-pass filter. Cross-correlation between a white noise stimulus and a unitized spike discharge of SETi again produced well-defined first- and second-order kernels that showed that the SETi spike response was also dependent on positional inputs. An elongated negative valley on the diagonal, characteristic of the second-order kernel of the synaptic response in SETi, was absent in the kernel from the spike component, suggesting that information is lost in the spike production process. The functional significance of these results is discussed in relation to the behavior of the locust.
Functional MRI of Pain- and Attention-Related Activations in the Human Cingulate Cortex
Authors: Davis Karen D. , Taylor Stephen J. , Crawley Adrian P. , Wood Michael L. , Mikulis David J.
Published: December 2017

Davis, Karen D., Stephen J. Taylor, Adrian P. Crawley,Michael L. Wood, and David J. Mikulis. Functional MRI of pain- and attention-related activations in the human cingulate cortex. J. Neurophysiol. 77: 3370–3380, 1997. The aims of the study were to use functional magnetic resonance imaging (fMRI) to 1) locate pain-related regions in the anterior cingulate cortex (ACC) of normal human subjects and 2) determine whether each subject's pain-related activation is congruent with ACC regions involved in attention-demanding cognitive processes. Ten normal subjects underwent fMRI with a 1.5-T standard commercial MRI scanner. A conventional gradient echo technique was used to obtain data from a single 4-mm sagittal slice of the left ACC, ∼3.5 mm from midline. For each subject, interleaved sets of 6 images were obtained during a pain task, an attention-demanding task, and at rest, for a total of 36 images per task. Pain of different intensities was evoked via electrical stimulation of the right median nerve. The attention-demanding task consisted of silent word generation (verbal fluency). Additional experiments obtained data from the right ACC. A pixel-by-pixel statistical analysis of task versus rest images was used to determine task-related activated regions. The pain task resulted in a 1.6–4.0% increase in mean signal intensity within a small region of the ACC. The exact location of this activation varied from subject to subject, but was typically in the posterior part of area 24. The signal intensity changes within this region correlated with pain intensity reported by the subject. The attention-demanding tasks increased the mean signal intensity by 1.3–3.3% in a region anterior and/or superior to the pain-related activation in each subject. The activated region was typically larger than the pain-related activation. In some cases this activation was at or superior to the ACC border, near the supplementary motor area. These regions did not show any pain-intensity-related activation. In one subject both right and left ACC were imaged, revealing bilateral ACC activation during the attention task but only contralateral pain-related activation. These findings shed light on pain- and attention-related cognitive processes. The results provide evidence for a region in the posterior part of the ACC that is involved in pain and a more anterior region involved in other attention-demanding cognitive tasks.
Physiological Evidence for Local Excitatory Synaptic Circuits in the Rat Hypothalamus
Authors: Boudaba Cherif , Schrader Laura A. , Tasker Jeffrey G.
Published: December 2017

Boudaba, Cherif, Laura A. Schrader, and Jeffrey G. Tasker. Physiological evidence for local excitatory synaptic circuits in the rat hypothalamus. J. Neurophysiol. 77: 3396–3400, 1997. We conducted whole cell voltage-clamp and current-clamp recordings in slices of rat hypothalamus to test for local excitatory synaptic circuits. Local excitatory inputs to neurons of the paraventricular nucleus (PVN) and supraoptic nucleus (SON) were studied with the use of electrical and chemical stimulation. Extracellular electrical stimulation provided indirect evidence of local excitatory circuits. Single stimuli evoked multiple excitatory postsynaptic potentials (EPSPs) or excitatory postsynaptic currents (EPSCs) in some PVN and SON cells, invoking polysynaptic excitatory inputs. Repetitive stimulation (10–20 Hz, 2–10 s) elicited long afterdischarges of EPSPs/EPSCs, suggesting a potentiation of upstream synapses in a polysynaptic circuit. Bath application of metabotropic glutamate receptor agonists provided more conclusive evidence for local excitatory circuits. Metabotropic receptor activation caused an increase in the frequency of EPSPs/EPSCs that was blocked by tetrodotoxin, suggesting that it was mediated by activation of local presynaptic excitatory neurons. The local excitatory inputs to SON and PVN neurons were mediated by glutamate release, because the EPSPs/EPSCs elicited with electrical stimulation and metabotropic receptor activation were blocked by ionotropic glutamate receptor antagonists. Finally, glutamate microstimulation furnished the most direct demonstration of local excitatory synaptic circuits. Glutamate microstimulation of perinuclear sites elicited an increase in the frequency of EPSPs/EPSCs in 13% of the PVN and SON neurons tested. Two sites provided most of the local excitatory synaptic inputs to PVN neurons, the dorsomedial hypothalamus and the perifornical region. These experiments provide converging physiological evidence for local excitatory synaptic inputs to hypothalamic neurons, inputs that may play a role in pulsatile hormone release.
Control of Forces Applied by Individual Fingers Engaged in Restraint of an Active Object
Authors: Burstedt Magnus K. O. , Birznieks Ingvars , Edin Benoni B. , Johansson Roland S.
Published: December 2017

Burstedt, Magnus K. O., Ingvars Birznieks, Benoni B. Edin, and Roland S. Johansson. Control of forces applied by individual fingers engaged in restraint of an active object. J. Neurophysiol. 78: 117–128, 1997. We investigated the coordination of fingertip forces in subjects who used the tips of two fingers to restrain an instrumented manipulandum with horizontally oriented grip surfaces. The grip surfaces were subjected to tangential pulling forces in the distal direction in relation to the fingers. The subjects used either the right index and middle fingers (unimanual grasp) or both index fingers (bimanual grasp) to restrain the manipulandum. To change the frictional condition at the digit-object interfaces, either both grip surfaces were covered with sandpaper or one was covered with sandpaper and the other with rayon. The forces applied normally and tangentially to the grip surfaces were measured separately at each plate along with the position of the plates. Subjects could have performed the present task successfully with many different force distributions between the digits. However, they partitioned the load in a manner that reflected the frictional condition at the local digit-object interfaces. When both digits contacted sandpaper, they typically partitioned the load symmetrically, but when one digit made contact with rayon and the other with sandpaper, the digit contacting the less slippery material (sandpaper) took up a larger part of the load. The normal forces were also influenced by the frictional condition, but they reflected the average friction at the two contact sites rather than the local friction. That is, when friction was low at one of the digit-object interfaces, only the applied normal forces increased at both digits. Thus sensory information related to the local frictional condition at the respective digit-object interfaces controlled the normal force at both digits. The normal:tangential force ratio at each digit appeared to be a controlled variable. It was adjusted independently at each digit to the minimum ratio required to prevent frictional slippage, keeping an adequate safety margin against slippage. This was accomplished by the scaling of the normal forces to the average friction and by partitioning of the load according to frictional differences between the digit-object interfaces. In conclusion, by adjusting the normal:tangential force ratios to the local frictional condition, subjects avoided excessive normal forces at the individual digit-object interfaces, and by partitioning the load according the frictional difference, subjects avoided high normal forces. Thus the local frictional condition at the separate digit-object interfaces is one factor that can strongly influence the distribution of forces across digits engaged in a manipulative act.
Electrophysiological Properties of Lumbar Motoneurons in the α-Chloralose-Anesthetized Cat During Carbachol-Induced Motor Inhibition
Authors: Xi Ming-Chu , Liu Rong-Huan , Yamuy Jack , Morales Francisco R. , Chase Michael H.
Published: December 2017

Xi, Ming-Chu, Rong-Huan Liu, Jack Yamuy, Francisco R. Morales, and Michael H. Chase. Electrophysiological properties of lumbar motoneurons in the α-chloralose-anesthetized cat during carbachol-induced motor inhibition. J. Neurophysiol. 78: 129–136, 1997. The present study was undertaken 1) to examine the neuronal mechanisms responsible for the inhibition of spinal cord motoneurons that occurs in α-chloralose-anesthetized cats following the microinjection of carbachol into the nucleus pontis oralis (NPO), and 2) to determine whether the inhibitory mechanisms are the same as those that are responsible for the postsynaptic inhibition of motoneurons that is present during naturally occurring active sleep. Accordingly, the basic electrophysiological properties of lumbar motoneurons were examined, with the use of intracellular recording techniques, in cats anesthetized with α-chloralose and compared with those present during naturally occurring active sleep. The intrapontine administration of carbachol resulted in a sustained reduction in the amplitude of the spinal cord Ia monosynaptic reflex. Discrete large-amplitude inhibitory postsynaptic potentials (IPSPs), which are only present during the state of active sleep in the chronic cat, were also observed in high-gain recordings from lumbar motoneurons after the injection of carbachol. During carbachol-induced motor inhibition, lumbar motoneurons exhibited a statistically significant decrease in input resistance, membrane time constant and a reduction in the amplitude of the action potential's afterhyperpolarization. In addition, there was a statistically significant increase in rheobase and in the delay between the initial-segment (IS) and somadendritic (SD) portions of the action potential (IS-SD delay). There was a significant increase in the mean motoneuron resting membrane potential (i.e., hyperpolarization). The preceding changes in the electrophysiological properties of motoneurons, as well as the development of discrete IPSPs, indicate that lumbar motoneurons are postsynaptically inhibited after the intrapontine administration of carbachol in cats that are anesthetized with α-chloralose. These changes in the electrophysiological properties of lumbar motoneurons were found to be comparable with those that take place during the atonia of active (rapid-eye-movement) sleep in chronic cats. The present results support the conclusion that the neural system that is responsible for motor inhibition during naturally occurring active sleep can also be activated in α-chloralose-anesthetized cats following the injection of carbachol into the NPO.
Hyperpolarization-Activated Currents in the Growth Cone and Soma of Neonatal Rat Dorsal Root Ganglion Neurons in Culture
Authors: Wang Z. , Den Berg R. J. Van , Ypey D. L.
Published: December 2017

Wang, Z., R. J. Van Den Berg, and D. L. Ypey. Hyperpolarization-activated currents in the growth cone and soma of neonatal rat dorsal root ganglion neurons in culture. J. Neurophysiol. 78: 177–186, 1997. Dissociated dorsal root ganglion neuron growth cones and somata from neonatal rats were voltage and current clamped with the use of the perforated-patch whole cell configuration to study the occurrence and properties of slow hyperpolarization-activated currents ( I h) at both regions. Under voltage-clamp conditions I h, blockable by 2 mM extracellular CsCl, was present in 33% of the growth cones tested. Its steady-state activation as a function of voltage could be fitted with a single Boltzmann function with a midpoint potential of −97 mV. The time course of current activation could be best described by a double-exponential function. The magnitude of the fully activated conductance was 3.5 nS and the reversal potential amounted to −29 mV. At the soma, I h was found in 80% of the somata tested, which is much higher than occurrence at the growth cone. The steady-state activation curve of I h at the soma, fitted with a single Boltzmann function, had a midpoint potential of −92 mV, which was more positive than that in the growth cone. The double-exponential activation of the current was faster than in the growth cone. The fully activated conductance of 5.1 nS and the reversal potential of −27 mV were not significantly different from the values obtained at the growth cone. Membrane hyperpolarization by current-clamp pulses elicited depolarizing sags in 30% and 78% of the tested growth cones and somata, respectively, which is in agreement with our voltage-clamp findings. Termination of the hyperpolarizing current pulse evoked a transient membrane depolarization or an action potential at both sites. Application of 2 mM extracellular CsCl hyperpolarized the membrane potential reversibly by ∼5 mV and blocked the depolarizing sags and action potentials following the current injections at these regions. Thus I h contributes to the resting membrane potential and modulates the excitability of both the growth cone and the soma. Intracellular perfusion with the second messenger adenosine 3′,5′-cyclic monophosphate (cAMP) was only possible at the soma by the use of the conventional whole cell configuration. Addition of 100 μM cAMP to the pipette solution shifted the midpoint potential of the I h activation curve from −108 to −78 mV. The current activation time course was also accelerated. The reversal potential and the fully activated conductance underlying I h were not changed by cAMP. These results imply that cAMP primarily affects the gating kinetics of I h. Our results show for the first time quantitative differences in I h properties and occurrence at the growth cone and soma membrane. These differences may reflect differences in intracellular cAMP concentration and in the expression of I h.
Physiological Identification of the Targets of Cartwheel Cells in the Dorsal Cochlear Nucleus
Authors: Golding Nace L. , Oertel Donata
Published: December 2017

Golding, Nace L. and Donata Oertel. Physiological identification of the targets of cartwheel cells in the dorsal cochlear nucleus. J. Neurophysiol. 78: 248–260, 1997. The integrative contribution of cartwheel cells of the dorsal cochlear nucleus (DCN) was assessed with intracellular recordings from anatomically identified cells. Recordings were made, in slices of the cochlear nuclei of mice, from 58 cartwheel cells, 22 fusiform cells, 3 giant cells, 5 tuberculoventral cells, and 1 cell that is either a superficial stellate or Golgi cell. Cartwheel cells can be distinguished electrophysiologically from other cells of the cochlear nuclei by their complex spikes, which comprised two to four rapid action potentials superimposed on a slower depolarization. The rapid action potentials were blocked by tetrodotoxin ( n = 17) and were therefore mediated by voltage-sensitive sodium currents. The slow spikes were eliminated by the removal of calcium from the extracellular saline ( n = 3) and thus were mediated by voltage-sensitive calcium currents. The spontaneous and evoked firing patterns of cartwheel cells were distinctive. Cartwheel cells usually fired single and complex spikes spontaneously at irregular intervals of between 100 ms and several seconds. Shocks to the DCN elicited firing that lasted tens to hundreds of milliseconds. With the use of these distinctive firing patterns, together with a pharmacological dissection of postsynaptic potentials (PSPs), possible targets of cartwheel cells were identified and the function of the connections was examined. Not only cartwheel and fusiform cells, but also giant cells, received patterns of synaptic input consistent with their having originated from cartwheel cells. These cell types responded to shocks of the DCN with variable trains of PSPs that lasted hundreds of milliseconds. PSPs within these trains appeared both singly and in bursts of two to four, and were blocked by 0.5 or 1 μM strychnine ( n = 4 cartwheel, 4 fusiform, and 2 giant cells), indicating that cartwheel cells are likely to be glycinergic. In contrast with cartwheel cells, which are weakly excited by glycinergic input, glycinergic PSPs consistently inhibited fusiform and giant cells. Tuberculoventral cells and the putative superficial stellate cell received little or no spontaneous synaptic activity. Shocks to the DCN evoked synaptic activity that lasted ∼5 ms. These cells therefore probably do not receive input from cartwheel cells. In addition, the brief firing of tuberculoventral cells and of the putative superficial stellate cell in response to shocks indicates that these cells are unlikely to contribute to the late, glycinergic synaptic potentials observed in cartwheel, fusiform, and giant cells.