bluuebunny/crossref_metadata_2025 huggingface dataset:
Responses of pigeon vestibulocerebellar neurons to optokinetic stimulation. II. The 3-dimensional reference frame of rotation neurons in the flocculus
Authors: Wylie D. R. , Frost B. J.
Published: December 2017

1. The complex spike activity of Purkinje cells in the flocculus in response to rotational flowfields was recorded extracellularly in anesthetized pigeons. 2. The optokinetic stimulus was produced by a rotating “planetarium projector.” A light source was placed in the center of a tin cylinder, which was pierced with numerous small holes. A pen motor oscillated the cylinder about its long axis. This apparatus was placed above the bird's head and the resultant rotational flow-field was projected onto screens that surrounded the bird on all four sides. The axis of rotation of the planetarium could be oriented to any position in three-dimensional space. 3. Two types of responses were found: vertical axis (VA; n = 43) neurons responded best to visual rotation about the vertical axis, and H-135i neurons (n = 34) responded best to rotation about a horizontal axis. The preferred orientation of the horizontal axis was at approximately 135 degrees ipsilateral azimuth. VA neurons were excited by rotation about the vertical axis producing forward (temporal to nasal) and backward motion in the ipsilateral and contralateral eyes, respectively, and were inhibited by rotation in the opposite direction. H-135i neurons in the left flocculus were excited by counterclockwise rotation about the 135 degrees ipsilateral horizontal axis and were inhibited by clockwise motion. Thus, the VA and H-135i neurons, respectively, encode visual flowfields resulting from head rotations stimulating the ipsilateral horizontal and ipsilateral anterior semicircular canals. 4. Sixty-seven percent of VA and 80% of H-135i neurons had binocular receptive fields, although for most binocular cells the ipsilateral eye was dominant. Binocular stimulation resulted in a greater depth of modulation than did monocular stimulation of the dominant eye for 69% of the cells. 5. Monocular stimulation of the VA neurons revealed that the best axis for the contralateral eye was tilted back 11 degrees, on average, to the best axis for ipsilateral stimulation. For the H-135i neurons, the best axes for monocular stimulation of the two eyes were approximately the same. 6. By stimulating circumscribed portions of the monocular receptive fields of the H-135i neurons with alternating upward and downward largefield motion, it was revealed that the contralateral receptive fields were bipartite. Upward motion was preferred in the anterior 45 degrees of the contralateral field, and downward motion, was preferred in the central 90 degrees of the contralateral visual field.(ABSTRACT TRUNCATED AT 400 WORDS)
Activity induced elevations of intracellular calcium concentration in neurons of the deep cerebellar nuclei
Authors: Muri R. , Knopfel T.
Published: December 2017

1. Depolarization-induced changes in the cytosolic free calcium concentration ([Ca2+]i) were examined in slice-cultured neurons of the deep cerebellar nuclei by combined intracellular and multisite fura-2 recording techniques. 2. Firing of tetrodotoxin (TTX)-sensitive action potentials induced by depolarizing current pulses caused large elevations in somatic as well as proximal dendritic [Ca2+]i. In the dendrites, rise and decay times of [Ca2+]i were faster than in the soma. [Ca2+]i changes associated with depolarizations to < or = -40 mV in the presence of TTX were small compared with changes induced by Na+ spike firing, suggesting that Ca2+ influx through high voltage-activated Ca2+ channels is a major cause for Na+ spike-associated [Ca2+]i increases. 3. During sustained Na+ spike firing at a constant frequency (> 20 Hz), [Ca2+]i approached a constant level, after approximately 1 s in the dendrites and 2 s in the soma, respectively. The amplitude of the attained level was positively correlated with the firing frequency. We suggest that during tonic activity [Ca2+]i reaches a steady state determined by Ca2+ influx and extrusion. 4. TTX-resistant plateau potentials caused substantially greater [Ca2+]i increases in the dendrites than in the soma. In the dendrites, plateau-associated Ca2+ transients were comparable in amplitude to Ca2+ transients triggered by short (50 ms) Na+ spike trains, in the soma, they were considerably smaller. 5. Low-threshold spikes (LTSs) in association with a burst of Na+ spikes induced a sharp increase in [Ca2+]i both in the soma and in dendrites.(ABSTRACT TRUNCATED AT 250 WORDS)
Face recognition in human extrastriate cortex
Authors: Allison T. , Ginter H. , McCarthy G. , Nobre A. C. , Puce A. , Luby M. , Spencer D. D.
Published: December 2017

1. Twenty-four patients with electrodes chronically implanted on the surface of extrastriate visual cortex viewed faces, equiluminant scrambled faces, cars, scrambled cars, and butterflies. 2. A surface-negative potential, N200, was evoked by faces but not by the other categories of stimuli. N200 was recorded only from small regions of the left and right fusiform and inferior temporal gyri. Electrical stimulation of the same region frequently produced a temporary inability to name familiar faces. 3. The results suggest that discrete regions of inferior extrastriate visual cortex, varying in location between individuals, are specialized for the recognition of faces. These "face modules" appear to be intercalated among other functionally specific small regions.
Enhancement of neural synchronization in the anteroventral cochlear nucleus. II. Responses in the tuning curve tail
Authors: Joris P. X. , Smith P. H. , Yin T. C.
Published: December 2017

1. Discharges of neurons in the peripheral auditory system contain information about the temporal features of acoustic stimuli. Phase-locking of neurons in the anteroventral cochlear nucleus (AVCN) is usually reported to be less robust than in auditory nerve (AN) fibers, which provide their major input. In a companion paper we reported that some cells in AVCN of the cat show enhanced phase-locking compared with the AN when stimulated at the frequency to which they are most sensitive [characteristic frequency (CF)]. We called neurons "high-sync" when they showed vector strengths (R, a measure of phase-locking) > or = 0.9. Here we report phase-locking properties to stimuli at frequencies below CF. 2. Horseradish peroxidase-filled glass micropipettes or metal microelectrodes were inserted into the trapezoid body (TB), which is the large output tract of the AVCN. Acoustically driven fibers were classified on the basis of the shape of the poststimulus time (PST) histograms to short tone bursts at CF. We then presented low-frequency tones of increasing SPL and determined the maximum R value at 500 Hz (R500) for each fiber. Using the same experimental protocol we studied phase-locking in the ANs of two animals because maximal R values at the tuning curve tail have not been reported for AN fibers. 3. Although phase-locking in AN fibers is usually assumed to be independent of CF, we found that fibers with CF > 2 kHz tended to have higher R500 values than fibers with CF < or = 2 kHz. Moreover, R500 was > or = 0.9 in 20% (42 of 196) of the fibers studied and could be as high as 0.95. This population of fibers was defined as having "high-sync tails" and consisted almost entirely of fibers with low or medium spontaneous rate. 4. High-CF TB fibers stimulated at 500 Hz showed very high phase-locking. High-sync tails (R500 > or = 0.9) were found in 41 of 70 TB fibers. For a subset of these fibers (1/3 in total: 23 of 70) phase-locking was higher than is ever observed in the AN (R500 > or = 0.95); these fibers were defined as showing synchronization "enhancement." Virtually all fibers showing synchronization enhancement had primary-like-with-notch (PLN) PST histograms. Chopper and primary-like fibers showed high-sync tails for CFs > 3 kHz. 5. Synchronization filter functions were obtained for high-CF AN fibers by determining maximum synchronization for a range of stimuli below CF.(ABSTRACT TRUNCATED AT 400 WORDS)
Sound localization after unilateral lesions of inferior colliculus in the ferret (Mustela putorius)
Authors: Kelly J. B. , Kavanagh G. L.
Published: December 2017

1. The ability of ferrets to localize sounds in space was determined before and after large unilateral lesions of the inferior colliculus. Three animals sustained restricted lesions that destroyed the inferior colliculus caudally but spared some tissue rostrally. These restricted lesions did not extend substantially beyond the cytoarchitectonic boundaries of the inferior colliculus. Four animals received more extensive lesions that destroyed all of the inferior colliculus, including the rostral pole. These lesions also involved to various degrees other midbrain structures, including the dorsal nucleus of the lateral lemniscus and the lateral tegmentum. Psychophysical curves and minimum audible angles were obtained for midline and left and right lateral fields. Comparisons were made of deficits ipsilateral and contralateral to the lesion. 2. The animals were tested in a semicircular apparatus with loudspeakers located at various positions around the periphery. Separate sound localization tests were conducted for midline, left, and right field positions. In each test the animals were trained first to discriminate between speakers separated by 60 degrees. They were then tested with progressively smaller angles of speaker separation to obtain their psychophysical threshold (minimum audible angle). All critical tests of sound localization were based on the ability of animals to identify the location of a 45-ms noise burst presented at the beginning of each trial. Correct responses were rewarded by delivery of a small quantity of water from spouts located around the perimeter of the apparatus. 3. Unilateral lesions restricted to the inferior colliculus had relatively little effect on sound localization. All three animals with restricted lesions were still capable of localizing a single noise burst and minimum audible angles were similar before and after surgery for midline, left, and right field tests. There was no difference in postoperative performance ipsilateral and contralateral to the lesion site. 4. More extensive unilateral lesions that included the dorsal nucleus of the lateral lemniscus and the lateral tegmentum as well as the inferior colliculus resulted in severe deficits in sound localization. Each of the four animals with large unilateral lesions had a substantial impairment in sound localization in the field contralateral to the lesion site. Postoperative performance in the contralateral field was too low to obtain a minimum audible angle for these animals. Midline sound localization was also affected in some cases but ipsilateral sound localization was only slightly affected.
Effects of anoxia on rat midbrain dopamine neurons
Authors: Mercuri N. B. , Bonci A. , Johnson S. W. , Stratta F. , Calabresi P. , Bernardi G.
Published: December 2017

1. Dopamine-containing neurons of the rat midbrain were recorded intracellularly in vitro. Anoxia (2-5 min) caused reversible membrane hyperpolarization (4-25 mV), which blocked spontaneous firing of action potentials. Under voltage clamp, anoxia produced an outward current (100-1,000 pA) associated with an increase in the apparent input conductance. 2. The mean reversal potential of the anoxia-induced response at 2.5 and 12.5 mM [K+] was -86 and -66 mV, respectively. 3. The effect of anoxia was not blocked by tetrodotoxin (TTX), saclofen, (-)sulpiride, or strychnine. Superfusate containing low calcium (0.5 mM CaCl2 and 10 mM MgCl2 or 0.5-1 mM CaCl2 and 1 mM CoCl2) or low sodium (25-40% of control) reduced the anoxia-induced outward current. 4. Extracellular barium (0.1-1 mM) blocked the anoxia-induced hyperpolarization/outward current. Other K+ channel blockers (tetraethylammonium, apamin, quinine, and glibenclamide) failed to reduce anoxia-induced current. 5. When the dopamine-containing neurons were loaded with cesium (1-2 mM), anoxia caused a reversible membrane depolarization and a block of the firing activity. This depolarization was voltage dependent; it was decreased or blocked by the hyperpolarization of the membrane. 6. Perfusion of the cells with 0.5-1 microM TTX did not affect the membrane depolarization/inward current caused by anoxia. These were also present when the cells were treated with the excitatory amino acid receptor antagonists D,L-2-amino-5-phosphonovalerate (APV) (30 microM) and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) (10 microM). 7. The exposure of the neurons with low-sodium, low-calcium solutions reversibly reduced the depolarizing/inward effects of anoxia.(ABSTRACT TRUNCATED AT 250 WORDS)
Weak excitation and simultaneous inhibition induce long-term depression in hippocampal CA1 neurons
Authors: Yang X. D. , Connor J. A. , Faber D. S.
Published: December 2017

1. Weak excitation to rat hippocampal CA1 neurons via Schaffer collaterals at a frequency of 0.1 or 0.2 Hz accompanied by repeated brief exposures to the inhibitory transmitter gamma-amino-butyric acid (GABA) causes a long-term depression (LTD, up to 90% of the control) of the stimulated pathway. This depression can be reversed by high-frequency stimulation. 2. Although inhibition is necessary for the induction of this LTD, the depression can be produced with either the GABAA or the GABAB receptor agonists. 3. This conjunctive LTD could not be blocked by the N-methyl-D-aspartate receptor antagonist, 2-amino-5-phosphonovaleric acid. 4. It was, however, blocked by the metabotropic glutamate receptor antagonist L-2-amino-3-phosphonopropionic acid and (RS)-alpha-methyl-4-carboxyphenylglycine, indicating that activation of a metabotropic glutamate receptor is necessary for the LTD. Induction also appeared to require an intracellular Ca2+ increase. 5. Because GABAergic inhibition often modulates glutamatergic transmission in the brain, we propose that this form of synaptic modification is of potential importance for neural plasticity.
Proprioceptive coordination of movement sequences: discrimination of joint angle versus angular distance
Authors: Bevan L. , Cordo P. , Carlton L. , Carlton M.
Published: December 2017

1. The purpose of these experiments was to determine the accuracy with which human subjects could discriminate proprioceptive (nonretinotopic) targets during movement. The targets were located at either a specified angle in joint space, or a specified angular distance from an initial joint angle. 2. In these experiments the right elbows of normal human subjects were passively extended from either predictable or unpredictable starting angles. The subjects were instructed to open the right hand to indicate that the elbow was passing through a target joint angle or a target angular distance. The subjects were not given visual information about the location of the elbow, so they had to rely on proprioceptive input to perform this task. The target (criterion joint angle or angular distance) was learned by the use of proprioception during 8-15 practice trials. 3. Four experiments were conducted. In three experiments the target was located at a constant joint angle, and in the fourth experiment the target was located at a constant angular distance from the starting angle. The starting angle in all four experiments was pseudorandomly varied from trial to trial. 4. On the basis of an analysis of constant errors, subjects were more accurate at discriminating angular distance than joint angle. The slope of the relationship between the starting position and the constant errors was dictated by the task requirement. 5. In the distance discrimination experiment, when the starting angle was more flexed than the intermediate (i.e., central) position, the subjects slightly overshot the target distance. Conversely, when the starting angle was more extended than the intermediate position, the subjects slightly undershot the target distance. 6. In the joint angle discrimination experiments, the opposite results were obtained. Subjects overshot the target when the starting position of the elbow was more extended than the intermediate starting position, and they undershot the target when the starting position was more flexed than the intermediate starting position. The amplitude of these systematic errors increased when the subjects were unaware that the initial angle of their elbow was variable. 7. It is concluded that, in kinesthetic tasks of this type, the discrimination of angular distance is more accurate than the discrimination of joint angle. We hypothesize that the nervous system extracts kinematic information related to both joint angle and angular distance from proprioceptors, and that the encoding and or decoding of angular distance is more accurate than that of absolute joint angle.(ABSTRACT TRUNCATED AT 400 WORDS)
The roles of GABAergic and glycinergic inhibition on binaural processing in the dorsal nucleus of the lateral lemniscus of the mustache bat
Authors: Yang L. , Pollak G. D.
Published: December 2017

1. We studied the monaural and binaural response properties of 99 neurons in the dorsal nucleus of the lateral lemniscus (DNLL) of the mustache bat before and during the iontophoretic application of antagonists that blocked gamma-aminobutyric acid-A (GABAA) receptors (bicuculline) or glycine receptors (strychnine). All cells were driven by monaural stimulation of the contralateral ear, whereas monaural stimulation of the ipsilateral ear never evoked discharges. The binaural properties of 81 neurons were determined by holding the intensity constant at the contralateral ear and presenting a variety of intensities to the ipsilateral ear. This procedure generated interaural intensity disparity (IID) functions and allowed us to determine the effect of ipsilaterally evoked inhibition on a constant excitatory drive evoked by the contralateral ear. 2. One of the main findings is that the IID functions in the majority of DNLL neurons were not affected by application of either strychnine or bicuculline. Blocking glycinergic inhibition with strychnine had no effect on the IID functions in 75% of the cells studied. However, strychnine did change the IID functions in approximately 25% of the DNLL population. In those cells glycinergic inhibition appeared to be partially, or, in a few cases, entirely responsible for the ipsilaterally evoked spike suppression. In contrast, blocking GABAergic inhibition with bicuculline had no discernible effect on the ipsilaterally evoked spike suppression in any of the excitatory/inhibitory cells that we recorded. GABAergic inhibition, therefore, plays no role in the formation of IID functions of neurons in the DNLL. Furthermore, the results suggest that glycinergic inhibition also does not contribute to the suppression of spikes evoked by stimulation of the contralateral ear in the vast majority of DNLL neurons. 3. Although the majority of IID functions were not influenced when either GABAergic or glycinergic innervation was blocked, ipsilateral stimulation alone evoked both a glycinergic and GABAergic inhibition in most DNLL cells. These inhibitory events were demonstrated in 18 other cells by evoking discharges with the iontophoretic application of glutamate. Stimulating the ipsilateral ear alone under these conditions caused a suppression of the glutamate-evoked discharges. Furthermore, the spike suppression persisted for a period of time that was longer than the duration of the tone burst at the ipsilateral ear. 4. The application of bicuculline or strychnine had different effects on the glutamate-elicited spikes. Bicuculline reduced the duration of the inhibition, and it was always the latter portion of the inhibition that was abolished by bicuculline. In more than half of the cells studied strychnine also reduced the duration of the inhibition.(ABSTRACT TRUNCATED AT 400 WORDS)
Reconstruction of hippocampal CA1 pyramidal cell electrophysiology by computer simulation
Authors: Warman E. N. , Durand D. M. , Yuen G. L.
Published: December 2017

1. We have developed a 16-compartment model that reproduces most of the features of the CA1 pyramidal cell electrophysiology observed experimentally. The model was constructed using seven active ionic conductances: gNa, gCa, gDR, gCT, gA, gM, and gAHP whose kinetics have been, inferred, in most cases, from the available voltage-clamp data obtained from these cells. We focussed the simulation on the initial and late accommodation, the slow depolarization potential and the spike broadening during repetitive firing, because their mechanisms are not well understood. 2. Current-clamp records were reproduced by iterative adjustments to the ionic maximum conductances, scaling and/or “reshaping” of the gates' time constant within the experimental voltage-clamp data, and shifting the position of the steady-state gate opening. The final properties of the ionic channels were not significantly different from the voltage-clamp experiments. 3. The resulting model reproduces all four after-potentials that have been recorded to follow activation of the cell. The fast, medium, and slow after-hyperpolarization potentials (AHPs) were, respectively, generated by ICT, IM, and IAHP. Furthermore, the model suggests that the mechanisms underlying the depolarization after potential (DAP) is mostly due to passive recharging of the soma by the dendrites. 4. The model also reproduces most of the firing features experimentally observed during injection of long current pulses. Model responses showed a small initial decrease in the firing frequency during a slow underlying depolarization potential, followed by a more significant frequency decrease. Moreover, a gradual broadening of the action potential and loss of the fast AHP were also observed during the initial high-frequency firing, followed, as the firing frequency decreased, by a gradual recovery of the spikes' original width and fast AHP amplitude increase. 5. A large reduction of the K repolarizing current was required to reproduce the spike broadening and reduction of the fast AHP experimentally observed in CA1 cells during repetitive firing responses. The incorporation of a transient Ca- and voltage-dependent K current (ICT) into the model successfully reproduced these experimental observations. In contrast, we were unable to reproduce this phenomenon when a large persistent Ca- and voltage-dependent K current (generally named IC) was included in the model. These results suggest that there is a strong contribution to action-potential repolarization and fast AHP by a transient Ca- and voltage-dependent K current (ICT). 6. The two accommodation steps were induced by a progressively enlargement of two K currents IM (initial) and IAHP (late).(ABSTRACT TRUNCATED AT 400 WORDS)
Neuropharmacological mechanisms underlying rhythmical discharge in trigeminal interneurons during fictive mastication
Authors: Inoue T. , Chandler S. H. , Goldberg L. J.
Published: December 2017

1. We have examined the effects of iontophoretic application of antagonists to excitatory amino acid (EAA) receptors, as well as glycine and gamma-aminobutyric acid (GABA), on rhythmically active (RA) brain stem neurons during cortically induced masticatory activity (RMA) in the anesthetized guinea pig. Ten of these neurons were antidromically activated at latencies of 0.3–0.9 ms by stimulation of the trigeminal motor nucleus (MoV). 2. RA neurons were divided into closer and opener type according to the phase of activation during RMA. Iontophoretic application of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), a specific non-N-methyl-D-aspartate (NMDA) receptor antagonist, suppressed discharge of both closer and opener type RA neurons during RMA. In contrast, iontophoretic application of 3-((1)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP), a specific NMDA receptor antagonist, was not effective in suppressing discharge of most opener type RA neurons but did reduce activity of closer type RA neurons. 3. Spike discharge of most RA neurons was time locked to each cortical stimulus during RMA. Some of the RA neurons were activated at a short latency to short pulse train stimulation of the cortex in the absence of RMA. In most cases CNQX reduced such time-locked responses during RMA and greatly reduced discharge evoked by short pulse stimulation of the cortex in all cases. In contrast, CPP was not as effective in suppressing either the time-locked responses during RMA or the discharge evoked by short pulse train stimulation of the cortex. 4. D,L-Homocysteic acid (HCA) application produced low level maintained discharge in RA neurons before RMA induction. When RMA was evoked in combination with HCA, rhythmical burst discharges with distinct interburst periods during the opening phase of RMA were observed in most closer type RA neurons. In contrast, during RMA in combination with HCA application, opener type RA neurons showed burst discharges that were modulated during the RMA cycle but lacked distinct interburst periods during the closer phase of the cycle. 5. During application of strychnine (STR), a glycine antagonist, discharge of closer type RA neurons increased in the opener phase of RMA during continuous HCA application. In contrast, bicuculline methiodide (BIC), a GABA antagonist, did not increase unit discharge of closer type RA neurons in the opener phase of RMA. 6. It is concluded that closer type RA neurons receive, alternatively, EAA-mediated excitatory and glycine-mediated inhibitory masticatory synaptic drive signals during RMA.(ABSTRACT TRUNCATED AT 400 WORDS)
Classification of taste responses in brain stem: membership in fuzzy sets
Authors: Erickson R. P. , Di Lorenzo P. M. , Woodbury M. A.
Published: December 2017

1. Classification methods in sensory systems in general, and gustation in particular, tend to place each of the relevant objects, such as stimuli or neurons, into one class each. Some of these methods are based on the responsiveness of neurons to various stimuli; in these, each group must contain a variety of nonidentical members because of the individuality of each neuron or stimulus. 2. The “fuzzy” set method is appropriate for more accurate classification in such heterogeneous populations. In this method each member is given graded membership in several sets rather than membership in only one set. In the present paper we subjected previously published data on the responses of individual taste neurons to a variety of stimuli to fuzzy set analysis. 3. We found that the amounts of response of 46 neurons in the solitary nucleus of the rat to NaCl, HCl, sucrose, quinine HCl, and KCl could accurately be accounted for by giving each a grade of membership in three sets; the same held in the parabrachial nucleus of the rat for the responses of 41 neurons to the first four of these stimuli. The response was calculated as the sum of the products of the stimulus times neuron ratings in each set. 4. Temporal patterns of response have often been related, but with only moderate success, to the identity of the stimulus or neuron. These patterns could be accurately accounted for with the present method. Each of the products of designated parts of the stimulus ratings times the neuron ratings gave the basis for accurate description of the temporal course of the response of each neuron to each stimulus. 5. This method appears to account for the varieties of amount and temporal pattern of response of taste neurons with a simple mathematical process of few parameters. This suggests that within the known complexities of receptor mechanisms and mechanisms of neural processing, the neural message is reduced to a rather simple form. 6. The fuzzy set approach, which is based on disclosing underlying sets rather than placement of heterogeneous members into one of several essentialistic groups, may be useful in disclosure of the underlying mechanisms producing the neural responses in taste.
Membrane properties and synaptic responses of interneurons located near the stratum lacunosum-moleculare/radiatum border of area CA1 in whole-cell recordings from rat hippocampal slices
Authors: Williams S. , Samulack D. D. , Beaulieu C. , LaCaille J. C.
Published: December 2017

1. The membrane properties and synaptic inputs of interneurons, located at the stratum (s.) lacunosum-moleculare and radiatum border (L-M) of the CA1 region, were examined with the use of current-clamp whole-cell recordings in rat hippocampal slices. 2. Biocytin-labeled L-M interneurons had nonpyramidal somata and aspinous, often beaded, dendrites that arborized in s. lacunosum-moleculare and radiatum, sometimes as far as s. moleculare of the dentate gyrus. Their axon coursed and branched in s. lacunosum-moleculare and radiatum. Axon collaterals were also observed traversing the hippocampal fissure and arborizing in s. moleculare of the dentate gyrus and s. radiatum of the CA3 region. 3. Several membrane properties of interneurons were typically nonpyramidal: they had large input resistances, short-duration action potentials followed by prominent fast afterhyperpolarizations, and responded to hyperpolarizing current pulses with little membrane rectification. L-M interneurons showed significant anodal break responses, and their mean membrane time constant was 33 ms. After-depolarizations elicited by subthreshold depolarizing current pulses were larger in amplitude and decayed more slowly at depolarized than hyperpolarized membrane potentials. 4. The majority of L-M interneurons (35 of 49 cells) were silent at resting membrane potentials, whereas other displayed either spontaneous single action potentials (n = 12) or rhythmic bursts (n = 2). The rhythmic bursts were insensitive to the N-methyl-D-aspartate (NMDA) and non-NMDA excitatory amino acid receptor antagonists, 2-amino-5-phosphonopentanoic acid (AP-5; 50 microM) and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; 20 microM), respectively. Both spontaneous single action potentials and burst firing were blocked by membrane hyperpolarization, suggesting that they were intrinsically rather than synaptically generated. 5. L-M interneurons responded with regular sustained firing to depolarizing current pulses at resting membrane potential. However, at more hyperpolarized membrane potentials (near -75 mV), depolarizing current pulses elicited action-potential firing with a delayed onset. This suggests that voltage-sensitive, transient outward currents may be activated in L-M interneurons from hyperpolarized membrane potentials. 6. Electrical stimulation of s. radiatum or lacunosum-moleculare elicited predominantly long-duration excitatory postsynaptic potentials (EPSPs; n = 20 cells), or both EPSPs and inhibitory postsynaptic potentials (IPSPs; n = 17 cells). In most L-M interneurons (35/37), with increasing intensities, up to two action potentials were elicited. Occasionally, larger bursts (3–5 action potentials) were observed (n = 2). 7. The multiphasic components of the synaptic responses became more evident when stimulations were repeated at different membrane potentials.(ABSTRACT TRUNCATED AT 400 WORDS)
Synchronous bursting in a subset of interneurons inhibitory to the goldfish Mauthner cell: synaptic mediation and plasticity
Authors: Charpier S. , Behrends J. C. , Chang Y. T. , Sur C. , Korn H.
Published: December 2017

1. Presynaptic activity in the inhibitory network impinging on the Mauthner (M-) cell was investigated in the goldfish medulla in vivo using extra- and intracellular recordings. The inhibitory presynaptic volley elicited by stimulation of the contralateral vestibular nerve consisted of multiple successive peaks at high frequency (up to 1,000 Hz). Less pronounced multicomponent responses were recorded after antidromic activation of the M-cell. Such high-frequency “oscillatory” field potentials also occurred spontaneously. 2. In intracellular recordings, a subset of inhibitory interneurons showed evoked and spontaneous burst discharge. Burst action potentials were correlated with the peaks in the extracellular volley, suggesting that repetitive firing of these cells is synchronized. Nonbursting cells, on the other hand, fired single action potentials in response to vestibular stimuli and were not activated via the M-cell collateral network. 3. Bursting cells were determined morphologically to be part of the feedback inhibitory circuit. Their responses to stimulation of the contralateral vestibular nerve thus suggest the existence of a crossed excitatory pathway to these interneurons. 4. Vestibular-evoked excitatory postsynaptic potentials (EPSPs) in bursting interneurons had a short latency of 0.781 +/- 0.08 ms (mean +/- SD, n = 18) but reached threshold at 2.25 +/- 1 ms (n = 21). These characteristics are suggestive of a chemically mediated EPSP. Indeed, the evoked synchronous repetitive activity of these cells was prevented by superfusion with excitatory amino-acid receptor antagonists. 5. Bursting neurons showed several characteristics that differentiate them from nonbursting cells, including brief action potentials, plateau responses, and intense spontaneous subthreshold activity. 6. With extracellular recordings, tetanization of contralateral vestibular primary afferents evoked a long-lasting potentiation of oscillatory population responses in 11 of 27 cases. Furthermore in three experiments, the frequency of occurrence of spontaneous bursts was enhanced and a similar facilitation was detected at the intracellular level. 7. We conclude that a subset of interneurons in this inhibitory network is capable of repetitive discharges and that evoked as well as spontaneous firing in this population is synchronized. Although electrical coupling between interneurons may mediate synchronization and intrinsic membrane properties may promote burst activity, our data suggest strongly that repetitive firing requires chemically mediated transmission. Furthermore they indicate that the mechanisms underlying evoked as well as spontaneous bursting in this population show activity-dependent plasticity.
Effect of muscimol microinjections into the prepositus hypoglossi and the medial vestibular nuclei on cat eye movements
Authors: Mettens P. , Godaux E. , Cheron G. , Galiana H. L.
Published: December 2017

1. For horizontal eye movements, previous observations led to the hypothesis that the legendary neural integrator necessary for correct gaze holding, adequate vestibuloocular reflex (VOR), and optokinetic nystagmus, was located in the region of the complex formed by the nucleus prepositus hypoglossi (NPH) and the medial vestibular nucleus (MVN). 2. The aim of the present study was to test the respective contributions of the NPH, of the rostral part of the MVN, which contains most second-order vestibular neurons, and of the central part of the MVN to the horizontal integrator. 3. An injection of muscimol was used to inactivate each of these three zones in the cat's brain. Muscimol is a gamma-aminobutyric acid (GABA) agonist. By binding to GABAA receptors, it induces a hyperpolarization of the neurons that nullifies their activity. Muscimol was injected into the brain stem of the alert cat through a micropipette by an air pressure system. 4. The search coil technique was used to record spontaneous eye movements and the VOR induced by rotating a turntable at a constant velocity. VOR was analyzed by a new method: transient analysis of vestibular nystagmus. 5. A unilateral injection of muscimol into the NPH induced a bilateral gaze-holding failure: saccades were followed by a centripetal postsaccadic drift. A vestibular imbalance was also present but it was moderate and variable. The VOR responses were distorted drastically. Through transient analysis of vestibular nystagmus, that distortion was revealed to be due more to a failure of the neural integrator than to an alteration of the vestibular input to the neural integrator. The responses to a rotation either toward the injected side or in the opposite direction were asymmetrical. The direction of that asymmetry was variable. 6. A unilateral injection of muscimol into the rostral part of the MVN caused a vestibular imbalance: in complete darkness, a nystagmus appeared, whose linear slow phases were directed toward the side of injection. 7. A unilateral injection of muscimol into the central part of the MVN induced a syndrome where a severe bilateral gaze-holding failure was combined with a vestibular imbalance. In the light, saccades were followed by a bilateral centripetal postsaccadic drift. In complete darkness, a nystagmus was observed, whose curved slow phases were directed towards the side of injection. The VOR responses were distorted drastically. Here again, that distortion was revealed by our analysis to be due more to a failure of the neural integrator than to an alteration of the vestibular input to the neural integrator.(ABSTRACT TRUNCATED AT 400 WORDS)
Gramicidin perforated patch-clamp technique reveals glycine-gated outward chloride current in dissociated nucleus solitarii neurons of the rat
Authors: Rhee J. S. , Ebihara S. , Akaike N.
Published: December 2017

1. The inhibitory response of exogenously applied glycine was investigated in freshly dissociated rat nucleus tractus solitarii neurons under whole cell configuration using new perforated patch-clamp technique termed "gramicidin perforated patch technique," which maintains intact intracellular Cl- concentrations. 2. Using the gramicidin perforated patch technique, at a holding potential (VH) of -45 mV, glycine induced outward currents in a concentration-dependent manner with a EC50 of 4.0 x 10(-5) M and at a Hill coefficient of 1.5. In contrast, using the nystatin perforated patch technique, glycine induced inward currents at the same VH in a concentration-dependent manner with an EC50 of 4.9 x 10(-5) M and at a Hill coefficient of 1.2. 3. The glycine-induced outward currents were blocked by strychnine in a concentration dependent manner with an IC50 of 2.2 x 10(-8) M. The blockade was competitive. 4. The current-voltage relationship for the 10(-5) M glycine response showed a clear outward rectification. 5. Ten-fold change of extracellular Cl- with a large impermeable anion resulted in a 65 mV shift of the reversal potential of glycine-induced currents (EGly), indicating that the membrane behaves like a Cl- electrode in the presence of glycine. 6. The intracellular Cl- activity calculated from the EGly ranged from 7.3 to 18.2 mM, with a mean value of 13.3 mM. 7. The values of EGly in the individual neurons were significantly negative to the resting membrane potentials, suggesting the existence of active transport of Cl-.
Pronounced changes in the activity of nociceptive modulatory neurons in the rostral ventromedial medulla in response to prolonged thermal noxious stimuli
Authors: Morgan M. M. , Fields H. L.
Published: December 2017

1. Brain regions that inhibit nociception can be activated by various environmental stimuli, including prolonged noxious stimuli. The present study tested the effect of such a prolonged noxious stimulus on the activity of nociceptive modulatory neurons in the rostral ventromedial medulla (RVM). These neurons, called ON- and OFF-cells because of their respective burst and pause in activity associated with nocifensor reflexes, have been shown to facilitate and inhibit nociception, respectively. 2. Single-unit activity of ON- and OFF-cells was assessed in lightly halothane- or barbiturate-anesthetized rats exposed to prolonged noxious heat (50 degrees C water). This prolonged noxious stimulus caused an increase in ON-cell and a decrease in OFF-cell activity regardless of anesthetic (halothane or barbiturate) or stimulus location (hindpaw or tail). 3. Surprisingly, and despite the consistent changes in RVM cell activity, the prolonged noxious stimulus caused different effects depending on the reflex used to assess nociception. The hindpaw withdrawal reflex was facilitated when the tail was immersed in hot water, whereas the tail flick reflex was inhibited when the hindpaw was immersed in hot water (see preceding manuscript). Lidocaine inactivation of the RVM shortened the latency for both reflexes but had no effect on tail flick inhibition produced by the noxious conditioning stimulus. In contrast, lidocaine inactivation of the RVM completely reversed the hindpaw reflex facilitation produced by tail heat, indicating the involvement of RVM ON-cells in facilitation of this reflex. 4. These data demonstrate that RVM neurons respond in a consistent manner to noxious stimuli whether applied for a brief or prolonged time: ON-cell activity increases and OFF-cell activity decreases. Moreover, the activation of RVM ON-cells produced by a noxious stimulus is sufficient to enhance some nocifensor reflexes, whereas neural structures other than the RVM appear to mediate the antinociceptive effects produced by a prolonged noxious stimulus.
cAMP-independent effects of 8-(4-parachlorophenylthio)-cyclic AMP on spike duration and membrane currents in pleural sensory neurons of Aplysia
Authors: Sugita S. , Baxter D. A. , Byrne J. H.
Published: December 2017

1. The serotonergic modulation of pleural sensory neurons in Aplysia is mediated via two second messenger systems: the adenosine cyclic monophosphate/protein kinase A (cAMP/PKA) and diacylglycerol/protein kinase C systems. Often membrane permeable derivatives of cAMP, such as 8-(4-parachlorophenylthio)-cAMP (pcpt-cAMP), have been used to investigate the role of cAMP/PKA in modulating sensory neurons. In light of recent findings that pcpt-cAMP may have cAMP-independent actions, we have reexamined the effects of pcpt-cAMP on the action potential and membrane currents of the sensory neurons. 2. Although pcpt-cAMP (500 microM to 1 mM) and serotonin (5-HT; 10 microM) induced comparable measures of spike broadening (an average increase above baseline of 29 and 40%, respectively), the broadening produced by the two was qualitatively different. Serotonin-induced broadening developed slowly over 9-12 min, was most prominent during later phases of the spike repolarization, and reduced the spike afterhyperpolarization. In contrast, pcpt-cAMP-induced broadening developed rapidly, was rather uniform throughout the repolarization phase of the spike, delayed the peak of the action potential, and increased the afterhyperpolarization. 3. Preexposure of sensory neurons to 5-HT did not occlude further spike broaden by subsequent application of pcpt-cAMP. Indeed the effects of the two were additive. In addition, the effects of pcpt-cAMP were not mimicked by another analogue of cAMP, 8-bromo-cAMP. Interestingly, most of the effects of pcpt-cAMP on the action potential were mimicked by 8-(4-parachlorophenyl-thio)-guanosine cyclic monophosphate (pcpt-cGMP), but not by 8-bromo-cGMP. 4. During voltage-clamp pulses to 20 mV, pcpt-cAMP reduced the membrane current throughout the voltage-clamp pulse, which was qualitatively different from the modulation of the membrane current by 5-HT. In addition, the pcpt-cAMP-induced reduction in the membrane current at the beginning of the pulse was much greater than that induced by 5-HT. Moreover, preexposure of sensory neurons to 5-HT did not occlude further reduction in the membrane current by subsequent application of pcpt-cAMP. 5. These results suggest that pcpt-cAMP has some mechanisms of action that are not shared by 5-HT or cAMP but are shared by pcpt-cGMP. In addition, these findings provide further evidence that results obtained with this compound should be interpreted with caution.
Identification of molecular components of A-type channels activating at subthreshold potentials
Authors: Serodio P. , Kentros C. , Rudy B.
Published: December 2017

1. Xenopus oocytes injected with rat brain mRNA express a transient K+ current similar to the A current that activates transiently near the threshold for Na+ action potential generation (ISA) seen in somatic recordings from neurons. We used hybrid arrest with antisense oligonucleotides to investigate which of the cloned K+ channel proteins might be components of the channels responsible for the ISA expressed from brain mRNA. An oligonucleotide complementary to a sequence common to all known mammalian Shal-related mRNAs [KV4.1, KV4.2, and KV4.3 (the nomenclature of Sh K+ channel genes of Chandy and colleagues was used in this paper)] blocked the expression of the ISA. An oligonucleotide complementary only to the KV4.2 mRNA, the most abundant Shal-related transcript in rat brain RNA preparations, was also quite efficient in arresting the expression of the ISA from brain. These experiments indicate that Shal-related proteins are important components of the channels carrying the ISA expressed in oocytes injected with brain mRNA. However, there are several significant differences between this ISA and the currents expressed in the same oocytes by in vitro transcribed KV4.1 or KV4.2 cRNA. Most of these differences are eliminated if KV4.1 or KV4.2 cRNA is coinjected with brain poly-(A) RNA treated with antisense oligonucleotides which arrest the expression of the ISA, or with a 2–4Kb rat brain poly-(A) RNA fraction which does not express detectable K+ currents under the same recording conditions. These data support the hypothesis that ISA channels such as those expressed from brain mRNA contain Shal proteins that can be modified by proteins encoded in RNAs that by themselves do not express K+ currents.
Dissociation between perception and visuomotor transformation during reproduction of remembered distances
Authors: Gentilucci M. , Negrotti A.
Published: December 2017

1. In complete darkness subjects were presented with two visual stimuli whose distance was randomly varied. The subjects were required to reproduce the interstimulus remembered distance in two conditions. In one condition (reproduction by pointing) they pointed to a virtual position in space. In the other condition (visual reproduction) they used two other visual stimuli. One of them was fixed, and the other could be manually moved. Constant and variable errors were measured in the two conditions. 2. Constant error varied between the two conditions. In the pointing task subjects slightly overestimated the shorter distances, and underestimated the longer ones. During visual reproduction, they consistently overestimated all distances, and the error of overestimation tended to increase with distance. Statistical comparison between the errors in the two conditions was significant. Variable error increased with distance in both conditions, but did not show any significant difference between the two tasks. 3. The results of the present experiment support the hypothesis that perception and visuo-motor transformation are two separate processes in which the same object attributes are independently analysed. However, the finding that variable error did not change between the two tasks suggests that some stages are common to the two processes.