bluuebunny/crossref_metadata_2025 huggingface dataset:
Rotational kinematics of the human vestibuloocular reflex. I. Gain matrices
Authors: Tweed D. , Sievering D. , Misslisch H. , Fetter M. , Zee D. , Koenig E.
Published: December 2017

1. This series of three papers aims to describe the three-dimensional, kinematic input-output relations of the rotational vestibuloocular reflex (VOR) in humans, and to identify the functional advantages of these relations. In this first paper the response to sinusoidal rotation in darkness at 0.3 Hz, maximum speed 37.5%/s, was quantified by the use of the three-dimensional analogue of VOR gain: a 3 x 3 matrix where each element describes the dependence of one component (torsional, vertical, or horizontal) of eye velocity on one component of head velocity. 2. The three matrix elements indicating collinear gains (i.e., dependence of torsional eye velocity on torsional head velocity, vertical on vertical, and horizontal on horizontal) were smaller than the -1's required for optimal retinal image stabilization. Of these three the torsional gain was weakest: -0.37 for rotation about an earth-vertical axis, versus -0.73 and -0.64 for vertical and horizontal gains. Matrix elements indicating cross talk were mostly negligible. There was a tendency to leftward eye rotation in response to clockwise head motion, but this was not statistically significant. 3. VOR responses were compared for rotation about earth-vertical and earth-horizontal axes. The varying otolith input due to the rotation of the gravity vector relative to the head during earth-horizontal axis rotation made no difference to the collinear gains. 4. There were no consistent phase leads or lags except for a torsional phase lead of up to 10 degrees, usually more marked for clock-wise head rotation versus counterclockwise, and for oblique axis rotations versus purely torsional. 5. Torsional gain was magnified, averaging -0.52, when the torsional component of head rotation was only a small part of a predominantly vertical or horizontal rotation, i.e., when the axis of head rotation was near the frontal plane. Because most natural head rotations occur about such axes, the torsional VOR is probably somewhat stronger than the response to pure torsion would suggest. 6. The speed of eye rotation in response to a given stimulus varied widely among subjects, but the direction of rotation was much more uniform. For head rotations about oblique axes out of the frontal plane, there was a systematic misalignment of eye and head axes, with eye axes tilted toward the frontal plane. These findings can be explained on the basis of a strategy where the VOR balances the muscular effort of rotating the eyes against the cost of retinal slip.
Rotational kinematics of the human vestibuloocular reflex. II. Velocity steps
Authors: Tweed D. , Fetter M. , Sievering D. , Misslisch H. , Koenig E.
Published: December 2017

1. Gain matrices were used to quantify the three-dimensional vestibuloocular reflex (VOR) in five human subjects who were accelerated over 1 s and then spun at a constant 150 degrees/s for 29 s in darkness. Rotations were torsional, vertical and horizontal, about earth-vertical and earth-horizontal axes. 2. Elements on the main diagonal of the gain matrices were much smaller than the optimal value of -1, and torsional gain was weaker than vertical or horizontal. Off-diagonal elements, indicating cross talk, were minimal except for a small but consistent horizontal response to torsional head rotation. 3. Downward slow phases were more than twice as fast as upward at the start of rotation about both earth-vertical and earth-horizontal axes, but the asymmetry vanished later in the rotation. 4. During earth-vertical-axis rotation, all matrix elements decayed to zero. The main-diagonal torsional and vertical gains waned with time constants close to that of the cupula (6.7 and 7.3 s). Velocity storage prolonged the horizontal response to horizontal head rotation (time constant 14.2 s) but not the horizontal response to torsion (7.7 s). A simple explanation is that velocity storage acts on a central estimate of head motion that accurately distinguishes horizontal from torsional and that the inappropriate horizontal eye velocity response to torsion occurs because of cross talk downstream from velocity storage. 5. During earth-horizontal-axis rotation, the torsional, vertical, and horizontal main-diagonal elements declined, with time constants of 7.6, 8.2, and 7.9 s, to maintained nonzero values, all equal to about -0.1. Off-diagonal elements, including the horizontal response to torsion, decayed to zero, so that the otolith-driven reflex, late in the rotation, was equally strong in all dimensions and almost free of detectable cross talk. 6. The difference between gain curves over the course of earth-vertical- and earth-horizontal-axis rotations was not constant but increased with time, suggesting that the VOR response to earth-horizontal-axis rotation is not a simple sum of canal and otolith reflexes.
Reorganization of cortical blood flow and transcranial magnetic stimulation maps in human subjects after upper limb amputation
Authors: Kew J. J. , Ridding M. C. , Rothwell J. C. , Passingham R. E. , Leigh P. N. , Sooriakumaran S. , Frackowiak R. S. , Brooks D. J.
Published: December 2017

1. Two complimentary techniques were used to study cortical function in six human upper limb amputees: positron emission tomographic (PET) measurements of regional cerebral blood flow (rCBF) were made in subjects during limb movements to study activation of the primary motor (M1), primary somatosensory (S1), and association cortices; and electromyographic responses to transcranial magnetic stimulation (TMS) were measured in proximal upper limb muscles to assess the excitability of corticospinal neurons in subjects at rest. 2. To explore possible cortical mechanisms governing the phantom limb phenomenon, PET and TMS findings were compared between subjects with acquired, traumatic upper limb amputations (n = 3), in whom phantom limb symptoms were prominent, and congenital upper limb amputees (n = 3) without phantom limbs. 3. Paced shoulder movements were associated with significant blood flow increases in the contralateral M1/S1 cortex of both groups of amputees. In traumatic amputees, these increases were present over a wider area and were of significantly greater magnitude in the partially deafferented cortex contralateral to the amputation. In congenital amputees blood flow increases were also present over a wider area in the partially deafferented M1/S1 cortex, but their magnitude was not significantly different from that in the normally afferented M1/S1 cortex. 4. Abnormal blood flow increases also were present in the partially deafferented M1/S1 cortex of traumatic amputees during movement of the ipsilateral, intact arm. Abnormal ipsilateral M1/S1 responses were not present during movement of the intact arm in the congenital group. 5. TMS studies showed that the abnormal blood flow increases in the partially deafferented M1 cortex of traumatic amputees were associated with increased corticospinal excitability.(ABSTRACT TRUNCATED AT 250 WORDS)
Grouping of somatosensory neurons in the spinal cord and the gracile nucleus of the rat by cluster analysis
Authors: Leem J. W. , Lee B. H. , Willis W. D. , Chung J. M.
Published: December 2017

1. A set of 11 cutaneous stimuli defined previously to differentiate among different types of cutaneous sensory receptors in the rat hindpaw was also effective in differentially activating second-order sensory neurons in the dorsal horn and the gracile nucleus of rats. 2. All sampled units were responsive to more than 1 of the 11 stimuli. However, none responded to innocuous warming or cooling stimuli. Therefore further analysis was restricted to responses to nine of the selected stimuli. 3. Cluster analysis of the responses to nine selected innocuous and noxious mechanical stimuli and noxious thermal stimuli yielded seven classes that seemed functionally distinct from each other: a class of high-threshold neurons, three classes of convergent (wide dynamic range) neurons, a class of a mixture of poorly responsive neurons and neurons receiving Pacinian inputs, and two classes of low-threshold neurons. 4. High-threshold neurons responded predominantly to noxious mechanical and thermal stimuli and presumably received an input from both mechanically and thermally sensitive nociceptors. These cells were located in the dorsal horn, and some were spinothalamic tract cells. Wide dynamic range neurons were excited by innocuous and noxious stimuli, but better by noxious stimuli. These classes of cells were either in the dorsal horn (some were spinothalamic tract cells) or in the nucleus gracilis.(ABSTRACT TRUNCATED AT 250 WORDS)
Pacemaker behavior of respiratory neurons in medullary slices from neonatal rat
Authors: Johnson S. M. , Smith J. C. , Funk G. D. , Feldman J. L.
Published: December 2017

1. We have hypothesized that pacemaker neurons in the pre-Botzinger complex (pre-BotC) form the kernel for respiratory rhythm generation. A prediction of this hypothesis is that oscillatory behavior in some respiratory neurons could persist in the absence of synaptic transmission. In this study we used extracellular recording of neuronal activity in slice preparations from neonatal rat medulla that generate respiratory rhythm in vitro to determine 1) whether pacemaker properties are present in pre-BotC and unique to respiratory neurons, 2) whether pacemaker properties are common to all respiratory neurons, and 3) the spatiotemporal patterns of pacemaker neuron activity. 2. Whole cell recordings from respiratory neurons verified that bathing the slices in a low-Ca2+/high-Mg2+ solution (low-Ca2+ solution) eliminated endogenous respiratory synaptic inputs and electrically evoked synaptic inputs. 3. Sixty-three neurons spontaneously generated rhythmic bursts of action potentials in low-Ca2+ solution. After we switched to control solution to reactivate the respiratory network, these neurons were classified on the basis of their spike discharge patterns relative to the respiratory cycle as: 1) inspiratory (I) neurons (n = 41), 2) tonic expiratory (tonic E) neurons (n = 4), and 3) tonic neurons (n = 18). 4. In other experiments we tested I and tonic E neurons identified first in control solution for bursting behavior in low-Ca2+ solution. Several I neurons (n = 5 of 33), but none of the tonic E neurons (n = 0 of 13), continued to burst rhythmically. 5. Bursting and nonbursting respiratory neurons were distributed throughout the ventrolateral reticular formation within the pre-BotC as well as in the ventral respiratory group (VRG) immediately caudal to the pre-BotC. 6. We conclude that subpopulations of VRG neurons in vitro have rhythmic bursting properties when synaptic transmission is abolished. Respiratory neurons, especially I neurons, were the most prevalent class of bursting cells. Only a small percentage of respiratory neurons, however, had pacemaker properties. These findings are consistent with the hypothesis that the respiratory oscillator includes specialized neurons with intrinsic oscillatory properties.
Substance P potentiates calcium channel modulation by somatostatin in chick sympathetic ganglia
Authors: Golard A. , Role L. , Siegelbaum S. A.
Published: December 2017

1. The whole cell patch clamp was used to measure calcium current in isolated chick sympathetic ganglion neurons. Previous results showed that somatostatin inhibits calcium currents (ICa) in a voltage-dependent manner. The effect of somatostatin rapidly desensitizes. In addition, the action of somatostatin on the calcium current is inhibited by activation of protein kinase C (PKC). Because substance P (SP) has been shown to activate PKC in the chick sympathetic neurons, we here test the effects of SP on the calcium current and on the modulatory action of somatostatin. 2. At a concentration of 1 microM, SP had small, variable effects on ICa. 3. SP in the presence of guanosine 5'-triphosphate-gamma-S, or at higher concentrations (10 microM), inhibited ICa in a voltage-dependent manner, similar to the action of somatostatin. 4. Rather than inhibiting the action of somatostatin, SP (1 microM) potentiated the response to somatostatin. This effect of SP was only observed after the response to somatostatin had partially desensitized. SP had no effect on nondesensitized responses to somatostatin. 5. Desensitization of the somatostatin response involved a shift in its dose-response curve toward higher somatostatin concentrations as well as a decrease in the maximal response. SP appears to counteract the shift of the dose-response curve selectively. 6. The potentiation of the somatostatin response by SP is blocked by 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7), but not by Calphostin C, Compound 5, k252a, protein kinase C (PKC)19-36, or adenylyl-imidodiphosphate (AMP-PNP), suggesting that phosphorylation is not involved and that the H-7 action does not depend on kinase inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)
Participation of the caudal fastigial nucleus in smooth-pursuit eye movements. I. Neuronal activity
Authors: Fuchs A. F. , Robinson F. R. , Straube A.
Published: December 2017

1. We recorded single-unit activity from neurons of an output of the cerebellum, the fastigial nucleus, in two rhesus macaques while the monkeys tracked small moving targets with their eyes. Many neurons in the caudal part of the fastigial nucleus exhibited a modulation in their discharge rates when smooth-pursuit eye movements were elicited by either sinusoidal or step-ramp motions of a small target. 2. The pursuit direction that elicited the most vigorous modulation in unit firing to sinusoidal target motion could be horizontal, vertical, or oblique. Most often, the preferred direction was in the contralateral and/or downward direction (50 of 69 neurons) or in the ipsilateral and/or upward direction (13 of 69). 3. For units whose preferred smooth-pursuit directions were either contralateral/downward or ipsilateral/upward during sinusoidal pursuit, peak firing as measured by the phase shift of periodic modulation at 0.5-0.8 Hz occurred near the time of peak velocity. The discharge of 80% of the neurons with contralateral/downward preferred directions preceded eye velocity by an average of -27 degrees; thus these neurons discharged maximally during eye acceleration. In contrast, neurons with ipsilateral/upward preferred directions lagged peak velocity by an average of +10.5 degrees and therefore discharged during eye deceleration. 4. The average eye velocity sensitivity for sinusoidal pursuit between 0.5 and 0.8 Hz was 0.83 +/- 0.57 (SD) spikes/s per degrees/s. We also tested 36 units during pursuit at a variety of frequencies in their preferred directions and found that firing rates increased monotonically with peak eye velocity. However, the firing rate saturated at velocities ranging from 20 to 60 degrees/s for different units. 5. When a monkey tracked a step-ramp target motion, three discharge patterns emerged in the 27 units tested. Just over half of the units discharged a burst of spikes that preceded (average lead of 27.4 +/- 17 ms) and lasted throughout the initial third of the eye acceleration; the burst was followed by a subsequent steady firing that continued after the eye had accelerated to its steady velocity. Fewer neurons discharged a burst that began late in the acceleration and was followed by steady firing. Occasional neurons showed only a gradual increase in firing rate during acceleration followed by a steady discharge. 6. Thirty of the 31 fastigial smooth-pursuit units tested also were modulated during sinusoidal yaw and/or pitch oscillations while the animals fixated a spot that rotated with them.(ABSTRACT TRUNCATED AT 400 WORDS)
Pharmacological analysis of the cholinergic input to the locust VPLI neuron from an extraocular photoreceptor system
Authors: Baines R. A. , Bacon J. P.
Published: December 2017

1. The brain of the locust contains an extraocular photoreceptor (EOP), which provides the major synaptic excitation to the vasopressin-like immunoreactive (VPLI) interneuron of the suboesophageal ganglion. Although the precise location of the EOP remains unknown, its activity can be determined indirectly by intracellular recording from the VPLI neuron. The excitatory drive to the VPLI neuron occurs only in darkness and is absent in the light. 2. The EOP is preferentially sensitive to light of wavelength 494 +/- 7 (SD) nm (blue-green) and has an absorption spectrum characteristic of a rhodopsin-like photopigment. 3. In the presence of high divalent saline (20 mM Ca2+ and Mg2+), the VPLI neuron receives excitatory input in the light. This indicates that the excitatory input to the VPLI neuron is from a tonically active descending input, which normally is inhibited by the light-induced activation of the presynaptic EOP. 4. Stimulation of the connectives while recording the resultant excitatory postsynaptic potential (EPSP) evoked in VPLI shows that the descending input projects beyond the suboesophageal ganglion, extending as far as the metathoracic ganglion. 5. Pharmacological analysis shows that the descending input to the VPLI neuron is cholinergic: acetylcholine (ACh) strongly depolarizes the neuron and eserine, an ACh esterase inhibitor, markedly potentiates the synaptic excitation of the VPLI neuron. 6. Nicotinic and muscarinic receptor antagonists show that the excitation of VPLI consists of two pharmacologically discrete components. Nicotinic ACh receptors mediate a fast depolarization, whereas muscarinic ACh receptors evoke a more sustained depolarization. Accordingly, both a fast and slow depolarization can be evoked selectively in VPLI by direct application of either nicotine or muscarine. 7. Voltage-clamp analysis shows that the fast EPSP evoked current is similar to that produced by nicotine in that it decreases linearly with membrane depolarization. The current associated with the sustained depolarization is similar to that evoked by muscarine, increasing nonlinearly with membrane depolarization. 8. Activity of the descending input, or application of muscarine, lowers the spike-initiation threshold of the VPLI neuron, thereby increasing its excitability. 9. It is concluded that the presence of two ACh receptor subtypes act synergistically to allow continuous activity of the VPLI neuron for sustained periods (i.e., throughout the hours of darkness).
Tuning specificities to aliphatic odorants in mouse olfactory receptor neurons and their local distribution
Authors: Sato T. , Hirono J. , Tonoike M. , Takebayashi M.
Published: December 2017

1. Odor responses to two homologous series of n-fatty acids (nFA) and n-aliphatic alcohols (nAA) with a straight chain of three to nine carbons were examined by measuring odor-induced [Ca2+]i increase in mouse olfactory receptor neurons (ORNs) isolated by the tissue-printing method. 2. One-third of the ORNs responsive to nFA and/or nAA were alternately sensitive to either type of odorant. Their sensitivities were usually near maximal for one or two odorants and decreased with differences in the carbon chain length from the tuned odorants. 3. Two-thirds of the ORNs responsive to nFA and/or nAA were sensitive to both types of odorants. Most of them were also tuned to one or two odorants in each series with similar carbon chain lengths and showed a decrease of sensitivity with increasing stereochemical discrepancy, similar to nFA/nAA discriminating ORNs. 4. In 10 of 20 non-nFA/nAA discriminating ORNs, the sensitivity to nFA was > 10 times greater than to nAA, and 80% of them were localized in a central region of olfactory epithelium on the septum wall where ORNs preferentially project to the dorsomedial or centromedial regions of the olfactory bulb. In addition, the sensitivity to three series of n-aliphatic odorants with an added amino group was examined. Sensitivity became higher as the electronegativity of the functional groups increased, suggesting that a hydrogen bond might partly mediate affinity in one type of non-nFA/nAA discriminating ORNs. 5. The diversity in odorant tuning specificity and sensitivity of the individual ORNs indicated that their receptor sites were finely tuned to the stereochemical structures of numerous odorants by changes in the three-dimensional size and intermolecular positions of the hydrophobic domains for hydrophobic bond, as well as the proton-acceptor or donor for the hydrogen bond and the electrical charge for the ionic bond. 6. The subpopulation of ORNs tuned to an individual odorant increased as the length of carbon chain of the odorant increased from three to nine. This tendency was more marked for nFA than for nAA in the case of non-nFA/nAA discriminating ORNs. 7. Data obtained by the in vitro approach using the tissue-printing method suggested that three or more subtypes of ORNs, which were similar in some cases and significantly different in other cases, were located within close proximity to one another.
Sodium-dependent receptor current in a new mechanoreceptor preparation
Authors: Juusola M. , Seyfarth E. A. , French A. S.
Published: December 2017

1. Intracellular microelectrodes recorded the receptor potential and receptor current in the neurons of spider slit sense organs during mechanical stimulation of the slits. 2. Mechanical stimulation produced two patterns of action potential discharge, corresponding to the two groups of neurons described previously by electrical stimulation. 3. Tetrodotoxin eliminated the action potentials and revealed a receptor potential with both static and adapting components. Voltage clamp gave an inward receptor current with a similar time course. 4. Replacement of sodium ions in the bath reversibly eliminated the receptor current, indicating that it is carried by sodium ions. However, this effect was comparatively slow, suggesting that the tips of the sensory dendrites lie in a chemically restricted environment.
Stimulus-evoked changes of extra- and intracellular pH in the leech central nervous system. II. Mechanisms and maintenance of pH homeostasis
Authors: Rose C. R. , Deitmer J. W.
Published: December 2017

1. We have studied extracellular pH (pHe) and intracellular pH (pHi) changes evoked by repetitive electrical side nerve stimulation (20 Hz, 1 min) in segmental ganglia of the leech Hirudo medicinalis using double-barreled, pH-sensitive microelectrodes to elucidate the involvement of neurotransmitters, of carbonic anhydrase, and of active acid/base transport on the extracellular H+ homeostasis. In saline buffered with 5% CO2-24 mM HCO3-, the stimulation induced a small and brief alkalinization followed by an acidification in the extracellular spaces (ECS), whereas neurons acidified and glial cells alkalinized (see previous paper). 2. Blocking synaptic transmitter release by superfusion with 20 mM Mg2+ saline (CO2/HCO3(-)-free) led to a reversible reduction of both activity-induced pHe changes by approximately 90% and to a complete suppression of the intracellular acidification of neurons. After application of the glutamate/kainate receptor blocker 6-cyano-7-dinitroquinozaline-2,3-dione (CNQX, 50 microM) to CO2/HCO3(-)-free saline, the stimulus-evoked pHe changes were reversibly reduced. The gamma-aminobutyric acid-A (GABAA) receptor antagonist picrotoxin (50 microM) led to an amplification of the extracellular alkalinization in the presence of CO2/HCO3-. Bath application of the excitatory transmitter agonists carbachol or kainate to CO2/HCO3(-)-free saline induced biphasic alkaline-acid transients in the ECS; the inhibitory transmitters GABA and serotonin had no detectable effects on the pHe (saline buffered with CO2/HCO3-).(ABSTRACT TRUNCATED AT 250 WORDS)
In vivo responses of single olfactory receptor neurons in the channel catfish, Ictalurus punctatus
Authors: Kang J. , Caprio J.
Published: December 2017

1. We report for the first time in any teleost, a quantitative in vivo study of recordings from single olfactory receptor neurons (ORNs) in the channel catfish, Ictalurus punctatus, with odorant stimuli. 2. Responses of 69 spontaneously active single ORNs were recorded simultaneously with the electroolfactogram (EOG). Recording times ranged from 10 to 72 min per receptor cell with an average of 24 +/- 15 (SD) min/cell. The averaged spontaneous frequency ranged from < 1 to 12 action potentials/s with a mean frequency of 4.7 +/- 2.5 action potentials/s. 3. Catfish ORNs responded to the odorant stimuli (amino acids, bile salts, and ATP) with either an excitation or suppression of the background neural activity. Suppressive responses were encountered more frequently than excitatory responses, suggesting that suppressive responses also play an important role in olfactory coding. 4. Excitatory and suppressive responses to the different odorants were elicited from the same ORN, suggesting that different olfactory receptor molecules and different transduction pathways exist in the same ORN.
Short- and long-range neuronal synchronization of the slow (< 1 Hz) cortical oscillation
Authors: Amzica F. , Steriade M.
Published: December 2017

1. Multisite, extra- and intracellular recordings were carried out in cats under ketamine and xylazine anesthesia to assess the degree of synchrony and time relations among cellular activities in various neocortical fields during a slow (< 1 Hz) oscillation consisting of long-lasting depolarizing and hyperpolarizing phases. 2. Recordings were performed from visual areas 17, 18, 19, and 21, association suprasylvian areas 5 and 7, motor pericruciate areas 4 and 6, as well as some related thalamic territories, such as the lateral geniculate (LG), perigeniculate (PG), and rostral intralaminar nuclei. We used spike analyses (auto- and cross-correlograms) to reveal rhythmicities, time relations and coherence properties, analyses of field potentials recorded through the same microelectrodes as used for unit discharges (auto-and cross-correlation functions and their spectral equivalents), and spike-triggered averages. The results are based on 194 groups of neurons with a total of 591 neurons. Seventeen groups included intracellular recordings of cortical neurons with membrane potentials more negative than -60 mV and overshooting action potentials. 3. The most obvious and frequent signs of neuronal synchrony were found within and between association areas 5 and 7 and 18/19 and 21. Closely located cells or neuronal pools were also "closer" in time. The shortest mean time lag was found between cells within adjacent foci (1-2 mm) of areas 5 and 7 and was 12 +/- 11.2 (SE) ms, with more caudal neurons preceding the rostral ones in 70% of cases. In visual cortical fields, the time lag between areas 18/19 and 21 neurons was 27.6 +/- 36 ms, between areas 17 and 21 was 36.2 +/- 47.8 ms, and between areas 18/19 and 17 was 40 +/- 73 ms. In the majority of cases, neuronal firing in area 21 preceded that in areas 18/19. The longest time lags were found in distant recordings from visual and motor areas, with a mean of 124 +/- 86.8 ms, although in some cell groups the time intervals between neuronal firing in areas 18/19 or 21 and areas 4 or 6 were as short as approximately 20 ms. 4. Similar time relations were found in those instances in which the unit firing of the same cortical neuron was used as reference in spike triggered averages and was related to the field potential recorded from an adjacent area before impaling a neuron and, thereafter, to membrane potential fluctuations after impaling the cell. 5. The PG reticular thalamic neurons reflected the slow cortical oscillation in 75% of multisite recordings.(ABSTRACT TRUNCATED AT 400 WORDS)
Modulation of epileptiform activity by metabotropic glutamate receptors in immature rat neocortex
Authors: Burke J. P. , Hablitz J. J.
Published: December 2017

1. Intracellular and extracellular recordings were obtained from neocortical brain slices of immature rats (postnatal days 9-16) maintained in vitro. Spontaneous and evoked epileptiform discharges (termed paroxysmal depolarizing shifts or PDSs) were recorded from upper cortical laminae (layers II-III) after exposure to the gamma-aminobuturic acid-A receptor antagonist, bicuculline methiodide. The effects of mGluR activation on PDS duration, spontaneous frequency, and threshold for evoking a PDS were determined. Putative mGluR agonists and antagonists also were tested. 2. Bath application of the mGluR agonist (1S,3R)-1-aminocyclopentane-1,3-dicarboxylate (ACPD, 50-200 mM) elicited biphasic, time-dependent effects on evoked and spontaneous epileptiform discharges. At times early in drug wash-in, ACPD increased PDS duration and spontaneous PDS frequency. In > 60% of the slices, the spontaneous PDSs became regular. Subsequently, ACPD reduced PDS duration and increased the stimulus threshold for evoking a PDS, suggesting that the actions of ACPD were dose dependent. 3. Investigation of the concentration-dependence revealed that sustained low ACPD concentrations (5 microM) elicited only facilitatory actions, whereas higher concentrations were suppressive. These observations suggest the activation of different mGluR subtypes, which may be localized differentially at pre- and postsynaptic sites. 4. Bath application of the mGluR agonists, L-2-amino-4-phosphonobutyrate or (2S,3S,4S)-alpha-(carboxycyclopropyl) glycine, produced only suppressive effects on epileptiform activity in the immature neocortex. L-2-amino-3-phosphonopropionate was an ineffective antagonist of ACPD-mediated modulation of epileptiform activity. Application of the putative antagonist, alpha-methyl-4-carboxyphenylglycine (MCPG), failed to antagonize the biphasic actions of ACPD. MCPG had suppressive effects of epileptiform activity, suggesting activation of mGluRs by endogenous agonists. 5. Simultaneous recordings from deeper and upper cortical layers indicated that the initial negativity of both evoked and spontaneous PDSs began in deeper cortical layers under control conditions and in the presence of ACPD. Intracellular records from neurons in deeper layers displayed two distinct patterns of activity during mGluR activation. Most deep layer neurons received a barrage of excitatory postsynaptic potentials before a spontaneous PDS during ACPD application. A small population of neurons depolarized and entered a tonically firing mode, which was interrupted by spontaneous PDSs. Different neuronal populations, possible expressing different mGluR subtypes or coupling mechanisms, may play integral roles in the induction and generation of epileptiform activities. 6. Thapsigargin or dantrolene, agents thought to block release of Ca2+ from intracellular stores, were both applied for periods < or = min.(ABSTRACT TRUNCATED AT 400 WORDS)
Biophysical and pharmacological characterization of inwardly rectifying K+ currents in rat spinal cord astrocytes
Authors: Ransom C. B. , Sontheimer H.
Published: December 2017

1. Whole cell and cell-attached patch-clamp recordings were obtained from rat spinal cord astrocytes maintained in culture for 6-14 days. It was found that the resting conductance in these astrocytes is primarily due to inwardly rectifying K+ (Kir) channels. 2. Two types of astrocytic Kir channels were identified with single-channel conductances of approximately 28 and approximately 80 pS, respectively. Channels displayed some voltage dependence in their open probability, which was largest (0.8-0.9) near the K+ equilibrium potential (Ek) and decreased at more negative potentials. The resting potential closely followed Ek, so it can be assumed that Kir channels have a high open probability at the resting potential. 3. The conductance of inwardly rectifying K+ currents (Kir) depended strongly on [K+]o and was approximately proportional to the square-root of [K+]o. 4. Kir currents inactivated in a time- and voltage-dependent manner. The Na+ dependence of inactivation was studied with ion substitution experiments. Replacement of [Na+]o with choline or Li+ removed inactivation. This dependence of current inactivation on [Na+]o resembles the previously described block of Kir channels in other systems by [Na+]o. 5. Kir currents were also blocked in a dose-dependent manner by Cs+ (Kd = 189 microM at -140 mV), Ba2+ (Kd = 3.5 microM), and tetraethylammonium (TEA; 90% block at 10 mM) but were insensitive to 4-aminopyridine (4-AP; 5 mM). In the current-clamp mode, Ba2+ and TEA inhibition of Kir currents was associated with a marked depolarization, suggesting that Kir channel activity played a role in the establishment of the negative resting potential typical of astrocytes. 6. These biophysical features of astrocyte inwardly rectifying K+ channels are consistent with those properties required for their proposed involvement in [K+]o clearance: 1) high open probability at the resting potential, 2) increasing conductance with increasing [K+]o, and 3) rectification, e.g., channel closure, at positive potentials. It is proposed, therefore, that the dissipation of [K+]o following neuronal activity is mediated primarily by the activity of astrocytic Kir channels.
Functional neural regeneration in the feeding system of Aplysia: behavioral recovery correlated with changes in buccal motor output
Authors: Scott M. L. , Li Y. , Kirk M. D.
Published: December 2017

1. We tested for functional neural regeneration in the feeding system of Aplysia after bilateral transections or crushes of the cerebral-buccal connectives (CBCs) with the use of behavioral analyses and electrophysiological recordings. 2. Both types of lesion selectively abolished rhythmic consummatory behavior, dramatically increasing bite latency and interbite interval, and decreasing bite magnitude. Appetitive feeding behavior was not affected. 3. About 2 wk after CBC crush, bite latency, bite magnitude, and interbite interval began to recover, as rhythmic biting reappeared; complete recovery of rhythmic biting occurred within 60 days. Rhythmic biting never recovered after transection of the CBCs. 4. The recovery of rhythmic biting was correlated with changes in buccal motor output, which were assessed with the use of in vivo recordings from buccal nerve 4 in freely moving Aplysia. Initially, some bursting in nerve 4 occurred without overt bites; with full recovery of biting, a 1:1 correspondence between bursts in nerve 4 and overt bites returned. 5. CBC lesions caused a functional separation between biting and swallowing; at early times postlesion, subjects displayed apparently normal rhythmic swallowing even though rhythmic biting had been eliminated. However, there was a disruption of the 1:1 correspondence between nerve 4 bursts and swallows, which persisted until consummatory feeding fully recovered. 6. Transection of the CBCs in animals that had fully recovered from a previous CBC crush again abolished rhythmic biting, suggesting that the recovery of consummatory feeding behavior was due to functional neural regeneration of cerebral-buccal connections.
Statomotor system in the marine mollusk Clione limacina
Authors: Panchin Y. V. , Sadreev R. I. , Arshavsky Y. I.
Published: December 2017

1. In the marine mollusk Clione limacina the "statomotor system" (named by analogy with the oculomotor system) has been found. This system includes a muscle that is directly attached to the statocysts connecting them with each other and with the inner surface of the body. 2. The statocyst muscle consists of four electrically coupled, mononuclear cells. Statocyst muscle cells do not generate spike-like potentials but only excitatory junctional potentials. 3. The motor input to the statocyst muscle correlates with the activity of the locomotor generator. This suggests that in the soft-bodied Clione contraction of the statocyst muscle stabilizes the statocysts into a standard "working" position in relation to coordinates of the body. This statocyst stabilization is important for Clione's spatial orientation during swimming.
Suppression of the corrective response to loss of ground support by stimulation of extensor group I afferents
Authors: Hiebert G. W. , Whelan P. J. , Prochazka A. , Pearson K. G.
Published: December 2017

1. When a hind leg of a walking cat fails to contact the ground at the end of swing, the limb is rapidly lifted and replaced in an attempt to seek support. In this investigation we tested the hypothesis that one factor in the initiation of this corrective response is the absence of signals from the group I afferents of extensor muscles. 2. Experiments were performed on decerebrate cats walking on a treadmill. The corrective response to loss of ground support occurred when one hind leg stepped into a hole cut into the treadmill belt. Group I afferents in various extensor nerves were stimulated via implanted cuff electrodes when the foot entered the hole. 3. Stimulation of extensor group I afferents suppressed the corrective flexion response. Instead of a flexor burst being generated soon after the foot entered the hole, extensor activity was maintained for a period exceeding the duration of the stimulus trains. The onset of the corrective response occurred at a relatively fixed latency of 70 ms after the end of the short stimulus trains (200-400 ms) provided that the contralateral limb was still in stance phase. For longer stimulus trains (500-1,000 ms) that terminated during or just prior to the swing phase of the contralateral leg, the onset of ipsilateral flexor activity occurred only after the contralateral leg had regained support. 4. We conclude that the absence of signals from group I afferents when a foot fails to contact the ground allows the locomotor rhythm generator to re-initiate a flexor burst to produce the corrective response.(ABSTRACT TRUNCATED AT 250 WORDS)
Nonlinear behavior of muscle reflexes at the human ankle joint
Authors: Stein R. B. , Kearney R. E.
Published: December 2017

1. Pulse inputs (similar to tendon jerks) were applied to the human ankle joint with the use of a hydraulic actuator. Inputs of only 1-2 degrees could elicit large responses (> 20% of maximum voluntary contraction). The magnitude of the response depended nonlinearly on a number of factors: the amplitude, direction, and duration of the pulse; the angle of the ankle; and the level of voluntary activation of the ankle muscles. 2. Pulses that flexed or extended the ankle could both produce reflex torques in the same direction (extensor torque). Although an extension of the ankle did not itself produce a response, it could affect the response to a subsequent flexion for up to 1 s. 3. The influence of random perturbations on the stretch reflex at the ankle was assessed. Responses to pulse displacements alone and to pulses superimposed on random perturbations were compared at the same level of voluntary activity. Reflex responses decreased in a graded manner with increasing amplitude or bandwidth of the random perturbations. 4. These results demonstrate that stretch reflexes can generate substantial torques, but in a highly nonlinear manner. In particular, passive joint movements markedly alter stretch reflex gain, and these changes must be considered in interpreting the functional significance of reflex actions.
Activities of spinal neurons during brain stem-dependent fictive swimming in lamprey
Authors: Buchanan J. T. , Kasicki S.
Published: December 2017

1. We made intracellular microelectrode recordings of membrane potential from spinal neurons during fictive swimming elicited by brief electrical shocks to the spinal cord in a brain stem-spinal cord preparation of the adult silver lamprey (Ichthyomyzon unicuspis). 2. We characterized membrane potential activities recorded during brain stem-dependent fictive swimming in five spinal cell types: myotomal motoneurons, lateral interneurons (inhibitory neurons with ipsilateral descending axons), CC interneurons (neurons with contralateral and caudal projecting axons), edge cells (intraspinal stretch receptors), and dorsal cells (primary mechanosensory neurons with cell bodies in the spinal cord). The membrane potential activities were compared with data from previous reports recorded during fictive swimming in the isolated spinal cord with fictive swimming induced by superfusion with D-glutamate. 3. Compared with the same cell types recorded during D-glutamate-induced fictive swimming in brain stem-dependent fictive swimming, the motoneurons and CC interneurons had significantly larger trough-to-peak amplitudes of membrane potential oscillations, whereas lateral interneurons were not significantly different in amplitude. The timings of the membrane potential oscillations and of cell spiking were not significantly different in the two preparations, with the exception that motoneurons in brain stem-dependent fictive swimming were significantly earlier by approximately 10% of a cycle. Edge cells had only weak or no oscillatory activities, and dorsal cells had no detectable input during brain stem-dependent fictive swimming. These findings are similar to those in D-glutamate-induced fictive swimming.(ABSTRACT TRUNCATED AT 250 WORDS)
Efferent-mediated protection from acoustic overexposure: relation to slow effects of olivocochlear stimulation
Authors: Reiter E. R. , Liberman M. C.
Published: December 2017

1. The present study attempts to resolve discrepancies in the reported role of olivocochlear (OC) efferent activation in protecting the inner ear from acoustic overstimulation: in previous studies, activating the OC system in guinea pigs reduced the threshold shift caused by 1 min monaural exposure to a 10-kHz tone; whereas unilateral OC activation in cats had no effect on threshold shifts following binaural exposure to a 10 min 6-kHz tone. 2. In this study, anesthetized and curarized guinea pigs were exposed either monaurally or binaurally to tones of different duration (1-5 min), frequency (6 to 10 kHz) and intensity (105-118 dB SPL). For each exposure condition, threshold shifts were compared among ears with different levels of OC activation: in some cases, the OC bundle (OCB) was electrically stimulated during (and/or before) the acoustic overexposure; in others, the OCB was cut before the exposure; in control cases, the OCB was neither cut nor electrically stimulated. 3. Electrical stimulation of the OCB delivered simultaneously with acoustic overstimulation produced significant reductions in threshold shift only for acoustic exposures at higher frequencies (8 and 10 kHz) and shorter durations (1 and 2 min). The protective effects on 1-min exposures could be extinguished by prior stimulation of the OCB, i.e., if the OC stimulation was turned on 4 min before the acoustic overexposure.(ABSTRACT TRUNCATED AT 250 WORDS)
Spino (trigemino) parabrachiohypothalamic pathway: electrophysiological evidence for an involvement in pain processes
Authors: Bester H. , Menendez L. , Besson J. M. , Bernard J. F.
Published: December 2017

1. Parabrachiohypothalamic (PB-H) neurons (n = 71) were recorded with extracellular micropipettes in the parabrachial (PB) area and were antidromically driven from the ventromedial nucleus (VMH) or the retrochiasmatic area (RCh) of the hypothalamus, in the anesthetized rat. The spontaneous activity of these neurons was very low, (10th percentile < median frequency < 90th percentile were 0.01 < 0.2 < 7 Hz). The axons of these neurons exhibited a very slow conduction velocity in the range of 0.2-1.4 m/s, i.e., corresponding to thin unmyelinated fibers. 2. Most PB-H neurons (89%) were located in the mesencephalic division of the PB area (mPB) mainly in the superior lateral (mPBsl) and external lateral (mPBel) subnuclei. 3. These units were separated in three groups: 1) a group of nociceptive-specific (NS) neurons (49%) activated by mechanical and/or thermal (heat) cutaneous stimuli only in noxious range; 2) a group of inhibited neurons (7%), not activated by any of the mechanical or thermal cutaneous stimuli but inhibited, by at least one of these stimuli, which had to be in noxious range; and 3) a group of nonresponsive neurons (44%). 4. The NS neurons responded exclusively to mechanical (pinch or squeeze) and/or thermal (waterbath or waterjet > 44 degrees C) noxious stimuli with a rapid onset, a marked and sustained activation, and generally no afterdischarge. The magnitude of the responses was between 2 and 30 Hz with a mean value of 14.8 +/- 1.4 Hz (mean +/- SE, n = 49). These neurons exhibited a clear capacity to encode thermal stimuli in the noxious range: 1) the stimulus-response function was always positive and monotonic; 2) the slope of the mean curve increased up to a maximum (between 46 and 50 degrees C) then beyond the slope decreased; and 3) the mean threshold was 44.3 +/- 2.2 degrees C. 5. The excitatory receptive fields of the NS neurons were often large including all (22% of the population) or several (67% of the population) parts of the body. In the few remaining cases (11%) they were restricted to one part of the body. In addition, in several cases, noxious stimuli applied outside the excitatory receptive field were found to strongly inhibit the discharge of NS neurons. 6. Most NS neurons responded to intense transcutaneous electrical stimulation with two peaks of activation.(ABSTRACT TRUNCATED AT 400 WORDS)
Sparseness of the neuronal representation of stimuli in the primate temporal visual cortex
Authors: Rolls E. T. , Tovee M. J.
Published: December 2017

1. To analyze the selectivity and the sparseness of firing to visual stimuli of single neurons in the primate temporal cortical visual area, neuronal responses were measured to a set of 68 visual stimuli in macaques performing a visual fixation task. The population of neurons analyzed had responses that occurred primarily to faces. The stimuli included 23 faces, and 45 nonface images of real-world scenes, so that the function of this brain region could be analyzed when it was processing natural scenes. 2. The neurons were selected to meet the previously used criteria of face selectivity by responding more than twice as much to the optimal face as to the optimal nonface stimulus in the set. Application of information theoretic analyses to the responses of these neurons confirmed that their responses contained much more information about which of 20 face stimuli had been seen (on average 0.4 bits) than about which (of 20) nonface stimuli had been seen (on average 0.07 bits). 3. The sparseness of the representation of a scene or object provided by each of these neurons (which can be thought of as the proportion of stimuli to which the neuron responds, and which is fundamental to understanding the network operation of the system) can be defined as [formula: see text] where ri is the firing rate to the ith stimulus in the set of n stimuli. The sparseness has a maximal value of 1.0. It was found that the sparseness of the representation of the 68 stimuli by each neuron had an average across all neurons of 0.65. This indicates a rather distributed representation. 4. If the spontaneous firing rate was subtracted from the firing rate of the neuron to each stimulus, so that the changes of firing rate, i.e., the responses of the neurons, were used in the sparseness calculation, then the "response sparseness" had a lower value, with a mean of 0.33 for the population of neurons, or 0.60 if calculated over the set of faces. 5. Multidimensional scaling to produce a stimulus space represented by this population of neurons showed that the different faces were well separated in the space created, whereas the different nonface stimuli were grouped together in the space. 6. The information analyses and multidimensional scaling provided evidence that what was made explicit in the responses of these neurons was information about which face had been seen.(ABSTRACT TRUNCATED AT 400 WORDS)