bluuebunny/crossref_metadata_2025 huggingface dataset:
The actions of hydrogen sulfide on dorsal raphe serotonergic neurons in vitro
Authors: Kombian S. B. , Reiffenstein R. J. , Colmers W. F.
Published: December 2017

1. The actions of hydrogen sulfide (HS-) on membrane and synaptic properties of dorsal raphe (DR) serotonergic cells were studied in the in vitro brain stem slice preparation, using intracellular sharp microelectrode and whole-cell recording techniques. 2. Sulfide produced two reversible, concentration-dependent effects on resting membrane properties of DR cells: (1) 14% responded to HS- with a slow onset hyperpolarization or an outward current accompanied by an conductance increase in voltage clamp (holding potential = -60 mV; monophasic outward cell) or (2) 39% responded with a rapid-onset depolarization corresponding to a weakly voltage-dependent inward current showing little or no change in conductance between -115 and -40 mV (monophasic inward cell). In addition, 29.5% showed both the above effects, responding first with a rapid-onset depolarization and then a sustained hyperpolarization. Such cells had membrane currents very similar to those seen in the monophasic inward and outward cells (biphasic cells). Finally, 17.5% of DR cells had no measurable postsynaptic membrane response to HS-. 3. The outward current induced in the presence of HS- had a reversal potential of about -90 mV when recorded either with 2 M KCl or 145 mM potassium gluconate in the pipette and was accompanied by an increase in conductance, suggesting that it is caused by an elevated conductance to K+. 4. This current was sensitive to the removal of external Ca2+ and blockade by Cd2+, suggesting that it is activated by an elevation in internal [Ca2+]. It was also blocked by apamin or Ba2+ and Cs+, both of which revealed an underlying inward current. The outward current was insensitive to the application of a large variety of antagonists to other known voltage- and calcium-dependent K+ channels. Elevation of intracellular ATP using a patch pipette did not prevent the activation of the outward current. 5. HS- reversibly suppressed a voltage-dependent outward current activated in the voltage range of -50 to -40 mV. This current was also blocked by 10 mM tetraethylammonium, suggesting that HS- suppresses the delayed rectifier in DR cells. 6. The inward current could be observed in the presence of HS- not only in monophasic inward cells but also in monophasic outward or biphasic cells whose outward current was selectively blocked. This inward current was sensitive to the removal of extracellular Ca2+, or the the application of relatively low concentrations of Cd2+, suggesting that it is carried by Ca2+. Both these manipulations also blocked the outward current in monophasic outward or biphasic cells.(ABSTRACT TRUNCATED AT 400 WORDS)
Effects of ear plugging on single-unit azimuth sensitivity in cat primary auditory cortex. I. Evidence for monaural directional cues
Authors: Samson F. K. , Clarey J. C. , Barone P. , Imig T. J.
Published: December 2017

1. Single-unit recordings were carried out in primary auditory cortex (AI) of barbiturate-anesthetized cats. Neurons, sensitive to sound direction in the horizontal plane (azimuth), were identified by their responses to noise bursts, presented in the free field, that varied in azimuth and sound pressure level (SPL). SPLs typically varied between 0 and 80 dB and were presented at each azimuth that was tested. Each azimuth-sensitive neuron responded well to some SPLs at certain azimuths and did not respond well to any SPL at other azimuths. This report describes AI neurons that were sensitive to the azimuth of monaurally presented noise bursts. 2. Unilateral ear plugging was used to test each azimuth-sensitive neuron's response to monaural stimulation. Ear plugs, produced by injecting a plastic ear mold compound into the concha and ear canal, attenuated sound reaching the tympanic membrane by 25-70 dB. Binaural interactions were inferred by comparing responses obtained under binaural (no plug) and monaural (ear plug) conditions. 3. Of the total sample of 131 azimuth-sensitive cells whose responses to ear plugging were studied, 27 were sensitive to the azimuth of monaurally presented noise bursts. We refer to these as monaural directional (MD) cells, and this report describes their properties. The remainder of the sample consisted of cells that either required binaural stimulation for azimuth sensitivity (63/131), because they were insensitive to azimuth under unilateral ear plug conditions or responded too unreliably to permit detailed conclusions regarding the effect of ear plugging (41/131). 4. Most (25/27) MD cells received either monaural input (MD-E0) or binaural excitatory/inhibitory input (MD-EI), as inferred from ear plugging. Two MD cells showed other characteristics. The contralateral ear was excitatory for 25/27 MD cells. 5. MD-E0 cells (22%, 6/27) were monaural. They were unaffected by unilateral ear plugging, showing that they received excitatory input from one ear, and that stimulation of the other ear was without apparent effect. On the other hand, some monaural cells in AI were insensitive to the azimuth of noise bursts, showing that sensitivity to monaural directional cues is not a property of all monaural cells in AI. 6. MD-EI cells (70%, 19/27) exhibited an increase in responsiveness on the side of the plugged ear, showing that they received excitatory drive from one ear and inhibitory drive from the other. MD-EI cells remained azimuth sensitive with the inhibitory ear plugged, showing that they were sensitive to monaural directional cues at the excitatory ear.(ABSTRACT TRUNCATED AT 400 WORDS)
Computer simulations of NMDA and non-NMDA receptor-mediated synaptic drive: sensory and supraspinal modulation of neurons and small networks
Authors: Traven H. G. , Brodin L. , Lansner A. , Ekeberg O. , Wallen P. , Grillner S.
Published: December 2017

1. The segmental locomotor network in lamprey can generate the rhythmic burst pattern underlying locomotion when it is driven via synaptic glutamate receptors. Lower rates of activity can be evoked by activation of N-methyl-D-aspartate (NMDA) receptors, whereas a rapid activity can only be induced by non-NMDA receptors [kainate/alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)]. The reticulospinal and sensory inputs are known to act via both NMDA and non-NMDA receptors, but it is unclear how these inputs can provide an appropriate control of the locomotor rate. We have examined the effects of different types of excitatory synaptic input to neurons of the locomotor network with the use of a computer-simulated electrical neuron model, with Na+, K+, Ca(2+)-dependent K+ channels, and with inherent oscillatory properties linked to the NMDA conductance. Synapses were modeled as a modulated ionic conductance in the membrane of the postsynaptic cell comprising a voltage-dependent NMDA component (Na+, K+, Ca2+ conductances) of long duration, and/or a non-NMDA component (Na+, K+ conductance) of short duration. 2. By using two neurons to drive a postsynaptic cell with non-NMDA-type synapses, a continuous range of firing frequencies could be evoked in the postsynaptic cell, by altering the firing rate of the presynaptic cells. If a single presynaptic neuron was used, there was a tendency toward spike synchronization between the pre- and postsynaptic cells. 3. When a postsynaptic neuron was driven via NMDA synapses, an oscillatory burst activity could be evoked. The rate of the oscillations was, however, little affected by the presynaptic firing rate. When a drive neuron with mixed (NMDA and non-NMDA) synapses was used, the rate of the oscillations could be changed within a limited frequency range by altering the presynaptic firing rate. By adding another larger drive neuron, having a larger rheobase current and mixed synapses with smaller relative NMDA components, the frequency range of the postsynaptic oscillations could be markedly increased. The frequency range depended on the parameters selected for each of the two types of mixed synapses. 4. A small rhythm-generating neuronal network, comprising six cells connected as the principal interneurons of the lamprey spinal locomotor network, was used to test the role of a tonic NMDA and non-NMDA receptor activation to drive the network and produce bursting.(ABSTRACT TRUNCATED AT 400 WORDS)
A caffeine- and ryanodine-sensitive Ca2+ store in avian sensory neurons
Authors: Ivanenko A. , Baring M. D. , Airey J. A. , Sutko J. L. , Kenyon J. L.
Published: December 2017

1. We identified and studied the function of ryanodine receptors in neurons isolated from dorsal root ganglia (DRG) of 10-day-old chick embryos. 2. A monoclonal antibody (mAb 34C) that recognizes all known ryanodine receptor isoforms in skeletal and cardiac muscle and CNS identified ryanodine receptor-like immunoreactivity in cultured DRG neurons. 3. Using the permeabilized patch technique to record membrane currents, we found that calcium currents were followed by a current with characteristics of a Ca(2+)-activated Cl- current (ICl(Ca)) in approximately two-thirds of the neurons. In these cells, acute application of 10 mM caffeine activated a similar ICl(Ca) and this effect was inhibited by 10 microM ryanodine. The activation of ICl(Ca) by caffeine was not dependent on extracellular Ca2+. These data suggest that caffeine raises intracellular free Ca2+ (Cai2+) by activating the release of Ca2+ from an intracellular store and that this Ca2+ activates the membrane conductance responsible for ICl(Ca). 4. The magnitude of ICl(Ca) activated by depolarization was not affected by ryanodine, implying that the Ca2+ that activates ICl(Ca) in this protocol is supplied by the Ca2+ current without amplification by a ryanodine-sensitive mechanism such as Ca(2+)-induced Ca2+ release. 5. We also used indo-1 to measure Cai2+ in DRG neurons. Ten millimolar caffeine caused a transient increase in Cai2+ that was inhibited by 10 microM ryanodine. 6. The ability of caffeine to elevate Cai2+ and activate ICl(Ca) was reduced at higher temperatures, suggesting increased Ca2+ sequestration. 7. These data demonstrate the existence of an intracellular store of Ca2+ that can be mobilized by a caffeine- and ryanodine-sensitive mechanism. The release of Ca2+ from this store can elevate Cai2+ and modulate membrane conductances.
Fictive swimming elicited by electrical stimulation of the midbrain in goldfish
Authors: Fetcho J. R. , Svoboda K. R.
Published: December 2017

1. We developed a fictive swimming preparation of goldfish that will allow us to study the cellular basis of interactions between swimming and escape networks in fish. 2. Stimulation of the midbrain in decerebrate goldfish produced rhythmic alternating movements of the body and tail similar to swimming movements. The amplitude and frequency of the movements were dependent on stimulus strength. Larger current strengths or higher frequencies of stimulation produced larger-amplitude and/or higher-frequency movements. Tail-beat frequency increased roughly linearly with current strength over a large range, with plateaus in frequency sometimes evident at the lowest and highest stimulus strengths. 3. Electromyographic (EMG) recordings from axial muscles on opposite sides at the same rostrocaudal position showed that stimulation of the midbrain led to alternating EMG bursts, with bursts first on one side, then the other. These bursts occurred at a frequency equal to the tail-beat frequency and well below the frequency of brain stimulation. EMG bursts recorded from rostral segments preceded those recorded from caudal segments on the same side of the body. The interval between individual spikes within EMG bursts sometimes corresponded to the interval between brain stimuli. Thus, whereas the frequency of tail beats and EMG bursts was always much slower than the frequency of brain stimulation, there was evidence of individual brain stimuli in the pattern of spikes within bursts. 4. After paralyzing fish that produced rhythmic movement on midbrain stimulation, we monitored the motor output during stimulation of the midbrain by using extracellular recordings from spinal motor nerves. We characterized the motor pattern in detail to determine whether it showed the features present in the motor output of swimming fish. The fictive preparations showed all of the major features of the swimming motor pattern recorded in EMGs from freely swimming fish. 5. The motor nerves, like the EMGs produced by stimulating midbrain, showed rhythmic bursting at a much lower frequency than the brain stimulus. Bursts on opposite sides of the body alternated. The frequency of bursting ranged from 1.5 to 13.6 Hz and was dependent on stimulus strength, with higher strengths producing faster bursting. Activity in rostral segments preceded activity in caudal ones on the same side of the body. Some spikes within bursts of activity occurred at the same frequency as the brain stimulus, but individual brain stimuli were not as evident as those seen in some of the EMGs. 6. The duration of bursts of activity in a nerve was positively and linearly correlated with the time between successive bursts (cycle time).(ABSTRACT TRUNCATED AT 400 WORDS)
Oscillatory properties of the central pattern generator for locomotion in neonatal rats
Authors: Sqalli-Houssaini Y. , Cazalets J. R. , Clarac F.
Published: December 2017

1. The oscillatory properties of the lumbar spinal networks that generate locomotor activity in mammals were studied. These experiments were performed on an in vitro isolated spinal cord preparation from newborn rats. Adding to the saline serotonin (5-HT) and N-methyl-D-aspartate (NMDA) excitatory amino acid receptor agonist (N-methyl-D,L-aspartate, NMA) induced rhythmic locomotor-like activity that was recorded in the ventral roots. 2. The period of the rhythmic locomotor-like activity could be set by combining the neurotransmitters at various concentrations. The combined transmitters also acted on the instantaneous variations of the period value. The stability of the period from one cycle to another increased when 5-HT was mixed with NMA compared with the activity induced by bath application of the compound alone. 3. K(+)-induced depolarizations were used to set the neuron membrane potential. These systematic changes in the K+ concentration resulted in a change in the period value. 4. Stimulation of the dorsal roots reset the ongoing rhythm. Phase-response curves were drawn up that showed that the spinal networks exhibit a differential sensitivity to the same stimulus depending on the phase at which the stimulus is applied. The free-running activity could be entrained by the cyclic volleys of sensory discharges. Entrainment occurred, on average, between -28 and 36% of the rest period. Because the lumbar segments were completely isolated by means of a sucrose blockade of all descending neuronal activity, the entrainment of the locomotor activity must take place directly at the lumbar level. 5. In conclusion, our data show that, at birth, the rhythmic activity produced by the spinal networks is based on a neuronal architecture that displays oscillatory properties. At this early age, the peripheral sensory afferents have already established connections with the central pattern generator. These sensory inputs are able to control the cycling activity of the spinal networks step by step.
Firing behavior of brain stem neurons during voluntary cancellation of the horizontal vestibuloocular reflex. I. Secondary vestibular neurons
Authors: Cullen K. E. , McCrea R. A.
Published: December 2017

1. The single-unit activity of vestibular neurons was recorded in alert squirrel monkeys. The monkeys had been trained to track a small visual target by generating smooth pursuit eye movements and to cancel their vestibuloocular reflex (VOR) by fixating a head stationary target. The monkeys were seated on a vestibular turntable, and their heads were held in the plane of the horizontal semicircular canals. The responses of 45 type I vestibular neurons whose activity was related to ipsilateral horizontal head movements were recorded. In 19 of 30 cells tested, electrical stimulation (0.1-ms monophasic pulses, < or = 800 microA) of the ipsilateral vestibular nerve evoked a spike at a monosynaptic latency (0.7-1.3 ms). 2. The spiking behavior of each cell was recorded during several behavioral paradigms: 1) spontaneous eye movements, 2) horizontal smooth pursuit of a target that was moved sinusoidally +/- 20 degrees/s at 0.5 Hz, 3) horizontal VOR during 0.5-Hz sinusoidal turntable rotations +/- 40 degrees/s (VORs), and 4) voluntary cancellation of the sinusoidal VOR by fixation of a head-stationary target during 0.5-Hz sinusoidal turntable rotation at +/- 40 degrees/s in the light (VORCs). 3. The response of most (34) of the units was recorded during unpredictable 100-ms steps in head acceleration (400 degrees/s2) that were generated while the monkey was fixating a target light. The acceleration steps were generated either when the monkey was stationary (VORt paradigm) or when the turntable was already rotating, and the monkey was canceling its VOR (VORCt paradigm). Smaller eye movements were evoked when the acceleration step was generated during VOR cancellation. 4. Type I vestibular units were grouped into two classes on the basis of the relationship of their firing rate to eye movements. The discharge rate of 20 "pure vestibular" units was not clearly related to eye movements. The remaining 25 units were classified as position-vestibular-pause (PVP) neurons. PVP neurons increased their firing rate during contralateral eye movements and during ipsilateral turntable rotations, and paused during saccadic eye movements. 5. Most (17/20) pure vestibular neurons generated the same response to vestibular stimuli when the monkeys canceled their VOR as they did during the VOR in both the sinusoidal and acceleration step paradigms. 6. The head velocity sensitivity of most (19/24) PVP neurons was reduced by 20-60% during VORCs, compared with their response during the VORs. The PVP neurons whose sensitivity of head movements was reduced during VORCs also exhibited a reduced vestibular sensitivity during VORCt.(ABSTRACT TRUNCATED AT 400 WORDS)
Increased propensity for nonsynaptic epileptiform activity in immature rat hippocampus and dentate gyrus
Authors: Roper S. N. , Obenaus A. , Dudek F. E.
Published: December 2017

1. Low-[Ca2+] bursting was studied in hippocampal slices from immature and adult rats to test the hypothesis that the increased seizure susceptibility of the immature brain involves nonsynaptic mechanisms. Extracellular recordings were obtained from area CA1 of the hippocampus and from the dentate gyrus in slices from rats 6-9 days old (1 wk), 11-15 days old (2 wk), 19-23 days old (3 wk), and > 60 days old (adult). These slices were exposed to a low-[Ca2+] solution that included the calcium chelator, ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA), and the excitatory amino acid antagonists, 6,7-dinitroquinoxaline-2,3-dione (DNQX) and DL-2-amino-5-phosphonopentanoic acid (AP-5). They were also exposed to a hyposmolar low-[Ca2+] solution (diluted with 20% H2O by volume), which induced or intensified the bursting. The propensity for nonsynaptic bursting and the characteristics of the bursts were compared between age groups. 2. The 1-wk group showed no bursting activity under any treatment condition in either CA1 or the dentate gyrus. Bursting occurred more frequently in the 2- and 3-wk groups than in the adult group in both CA1 and the dentate gyrus. 3. In CA1 the duration of the bursts was longer in the 2- and 3-wk groups as compared with the adult group. The number of population spikes per burst was also higher in slices from immature rats in dilute low-[Ca2+] solution. These findings demonstrate that nonsynaptic bursting in area CA1 is more robust in tissue from immature rats than adults.(ABSTRACT TRUNCATED AT 250 WORDS)
Broad directional tuning in spinal projections to the cerebellum
Authors: Bosco G. , Poppele R. E.
Published: December 2017

1. Spinocerebellar neurons that project in the dorsal spinocerebellar tract (DSCT) receive mono- and polysynaptic inputs from specific sensory receptors in the hindlimb, and they project mossy fiber terminals to the cerebellar vermis. We examined the functional organization of these neurons and found that it relates to whole-limb parameters like limb posture and direction of limb movement. 2. We recorded the activity of 444 DSCT units during passive perturbations of the hind foot in anesthetized cats. The movements were either confined a single joint (the ankle; 234 cells) or involved the entire hindlimb (210 cells). The cells exhibited opposite responses for opposite directions of whole-limb movement, but a variety of response patterns for opposite directions of movement at one joint. We interpret the result to imply that the population encodes information about the whole limb rather than single joints. 3. Most of the 78 neurons recorded during passive limb placements (63%) responded to changes in limb length and also changes in limb orientation. In fact, the activity of most of the cells was broadly tuned with respect to the direction of passive limb movements generated by moving the hind foot in the sagittal plane. Changes in unit activity could be described by a cosine tuning function with respect to foot positions (72% of responses) and directions of foot movement (50%). 4. The similarity of this behavior to that of neurons in the motor cortex and cerebellar nuclei recorded during voluntary movements is consistent with a common neural code to represent the sensorimotor parameters of limb movement.
On the synchronous activity induced by 4-aminopyridine in the CA3 subfield of juvenile rat hippocampus
Authors: Avoli M. , Psarropoulou C. , Tancredi V. , Fueta Y.
Published: December 2017

1. Extracellular field potential and intracellular recordings were made in the CA3 subfield of hippocampal slices obtained from 10- to 24-day-old rats during perfusion with artificial cerebrospinal fluid (ACSF) containing the convulsant 4-aminopyridine (4-AP, 50 microM). 2. Three types of spontaneous, synchronous activity were recorded in the presence of 4-AP by employing extracellular microelectrodes positioned in the CA3 stratum (s.) radiatum: first, inter-ictal-like discharges that lasted 0.2-1.2 s and had an occurrence rate of 0.3-1.3 Hz; second, ictal-like events (duration: 3-40 s) that occurred at 4-38 x 10(-3) Hz; and third, large-amplitude (up to 8 mV) negative-going potentials that preceded the onset of the ictal-like events and thus appeared to initiate them. 3. None of these synchronous activities was consistently modified by addition of antagonists of the N-methyl-D-aspartate (NMDA) receptor to the ACSF. In contrast, the non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 2-10 microM) reversibly blocked interictal- and ictallike discharges. The only synchronous, spontaneous activity recorded in this type of medium consisted of the negative-going potentials that were abolished by the GABAA receptor antagonists bicuculline methiodide (5-20 microM) or picrotoxin (50 microM). Hence they were mediated through the activation of the GABAA receptor. 4. Profile analysis of the 4-AP-induced synchronous activity revealed that the gamma-aminobutyric acid (GABA)-mediated field potential had maximal negative amplitude in s. lacunosum-moleculare, attained equipotentiality at the border between s. radiatum and s. pyramidale, and became positive-going in s. oriens. These findings indicated that the GABA-mediated field potential presumably represented a depolarization occurring in the dendrites of CA3 pyramidal cells. 5. This conclusion was supported by intracellular analysis of the 4-AP-induced activity. The GABA-mediated potential was reflected by a depolarization of the membrane of CA3 pyramidal cells that triggered a few variable-amplitude, fractionated spikes or fast action potentials. By contrast, the ictal-like discharge was associated with a prolonged depolarization during which repetitive bursts of action potentials occurred. Short-lasting depolarizations with bursts of action potentials occurred during each interictal-like discharge. 6. The GABA-mediated potential recorded intracellularly in the presence of CNQX consisted of a prolonged depolarization (up to 12 s) that was still capable of triggering a few fast action potentials and/or fractionated spikes.(ABSTRACT TRUNCATED AT 400 WORDS)
Neural encoding of single-formant stimuli in the cat. I. Responses of auditory nerve fibers
Authors: Wang X. , Sachs M. B.
Published: December 2017

1. We have studied auditory responses to a set of speech-related narrowband sounds, single-formant stimuli (SFSs), in populations of auditory nerve fibers (ANFs). An analytic method was developed to extract the envelope of temporal discharge patterns of the ANF responses to nonsinusoidally modulated stimuli, whose spectra have multiple clusters of components. Such responses are often encountered in the auditory system when complex stimuli are used and have traditionally been studied by analyzing the fundamental component of the responses. 2. The envelope modulation in the SFSs is shown to be represented by the response patterns of ANFs. When the whole ANF population is considered, the information on modulation in stimulus envelope does not disappear at the highest sound level tested at all best frequencies (BFs) we studied (1-10 kHz). The representation is the best at medium sound levels and degrades at high sound levels. Low/medium-spontaneous rate (SR) ANFs showed greater envelope modulation in their responses at high sound levels than do high-SR ANFs. The quality of the representation at high sound levels is, on average, proportional to BF threshold of an ANF. On the basis of populations of ANFs with all SRs, the envelope modulation in the SFSs is represented over a wide range of sound levels. 3. We found that low-BF ANFs differ from high-BF ANFs in representing envelope modulation in the SFSs. For ANFs with BFs less than approximately 6 kHz, information on stimulus envelope is not only contained in spectral components near direct current but also in components at the vicinities of frequencies equal to BF and its multiples. In fact, for ANFs with BFs < 3 kHz, the contribution from spectral components centered at BF to overall response modulation is greater than that from spectral components near direct current. These findings indicate that, by using measures solely based on the fundamental component, the amount of modulation in the responses to narrowband stimuli is underestimated for low-BF ANFs. 4. Off-BF stimulation of ANFs with SFSs was found to result in increased envelope modulation in responses at high sound levels. The further away the stimulus is centered relative to unit BF, the greater the modulation it induces, provided that the stimulus is capable of exciting the unit. An SFS centered as close as 15% off unit BF can produce a significant increase in the modulation of responses at very high sound levels.(ABSTRACT TRUNCATED AT 400 WORDS)
Adaptive control for backward quadrupedal walking. III. Stumbling corrective reactions and cutaneous reflex sensitivity
Authors: Buford J. A. , Smith J. L.
Published: December 2017

1. Four cats were trained to walk backward (BWD) and forward (FWD) on a motorized treadmill. Mechanical (taps) or electrical (pulses) stimuli were applied to the dorsal or ventral aspect of the hind paw during swing or stance. Hindlimb kinematic data, obtained by digitizing 16-mm high-speed film, were synchronized with computer-analyzed electromyograms (EMG) recorded from anterior biceps femoris (ABF), vastus lateralis (VL), lateral gastrocnemius (LG), tibialis anterior (TA), and semitendinosus (ST). Responses to taps and pulses, as well as the modulation in cutaneous reflex sensitivity to pulses, were described for both walking directions and stimulus locations. 2. After dorsal taps that obstructed FWD swing, the hindlimb initially drew back away from the obstacle with knee flexion and ST activation, ankle extension with TA suppression and LG activation, and hip extension with ABF facilitation. Next, the limb was raised over the obstacle with resumed TA activity and enhanced knee and ankle flexion, and then compensatory knee and ankle extension positioned the limb for the ensuing stance phase. 3. For ventral taps that obstructed BWD swing, the initial response also tended to draw the limb away from the obstacle with hip and ankle flexion and TA facilitation and reduced knee flexion with weak VL facilitation and suppression of ST activity. Next, ST activity resumed as knee and ankle flexion raised the limb over the obstacle, and then compensatory extension completed the swing phase for BWD walking. Thus the initial kinematic and EMG responses to obstacles were opposite for BWD versus FWD swing, and these responses were consistent with active avoidance of the obstacles. Responses during BWD walking were subtle, however, compared with those for FWD. 4. After nonobstructing taps (ventral FWD, dorsal BWD), ST and TA activation and knee and ankle flexion were coincident, demonstrating that the aforementioned differences in responses to obstructing obstacles were not simply location dependent. Regardless of the direction of walking or the location of stimulation, taps applied during stance had little immediate kinematic effect, but the subsequent swing phase was usually exaggerated, as if the response was programmed to avoid any lingering obstacle. 5. Electrical pulses did not elicit the full-blown responses typically evoked by taps. The sequencing in activation of ST and TA characteristic after laps was absent after pulses, and there were rarely dramatic kinematic responses to pulses like those easily elicited by taps. There were, in fact, few differences in responses to electrical stimulation for BWD versus FWD walking.(ABSTRACT TRUNCATED AT 400 WORDS)
Sensitization of the gill and siphon withdrawal reflex of Aplysia: multiple sites of change in the neuronal network
Authors: Trudeau L. E. , Castellucci V. F.
Published: December 2017

1. Recent studies have emphasized the major contribution of interneuronal transmission to the mediation and learning-associated modulation of the gill and siphon withdrawal (GSW) reflex of Aplysia. We wish to provide more direct support for the hypothesis that inhibitory junctions are crucial sites of plasticity. 2. In parallel experiments we investigated modulation at five major sites of synaptic transmission in the GSW network: 1) from sensory neurons to motor neurons, 2) from sensory neurons to excitatory interneurons (INTs+) 3) from INTs+ to motor neurons (MNs), 4) from inhibitory interneurons (INTs-) to INTs+, and 5) from INTs+ to INTs-. 3. While recording simultaneously from a single sensory neuron of the LE cluster, an INT+, and a MN, we found that both LE-MN and LE-INTs+ synapses were facilitated by the activation of modulator neurons by stimulation of the left pleuroabdominal connective (185 and 93%, respectively) as well as by serotonin (5-HT) (191 and 84%). Junctions of the second type were therefore less facilitated. The difference in the magnitude of facilitation at these two sites is an indication of a branch-specific, differential efficacy in the modulation of different central synapses made by a single neuron. 4. Although INT(+)-MN junctions have the capacity to display marked posttetanic potentiation, they are not significantly potentiated after connective stimulation. Sensitization of the GSW reflex is therefore not necessarily accompanied by a modification of transmission at these synapses. 5. Inhibitory transmission to INTs+ is significantly reduced by connective stimulation (36%) and by 5-HT (71%). This supports the hypothesis that a reduction of feedback inhibition into INTs+ is a major mechanism of reflex sensitization and may account for the increased evoked firing of INTs+ that is observed after connective stimulation. 6. The excitatory input to INTs- is selectively decreased by 5-HT (50%) and by the molluscan neuropeptide small cardioactive peptide B (38%). This latter effect, which could produce disinhibition of INTs+, may explain the previous observation that this peptide is able to potentiate the evoked input to MNs of the reflex at a concentration (1 microM) that fails to modify monosynaptic sensory-motor transmission. 7. These results indicate that transmission through a small neuronal network that mediates a withdrawal reflex in Aplysia may be modulated at multiple sites and by different mechanisms. These mechanisms include: 1) branch-specific facilitation of sensory neuron outputs and 2) inhibition of INT(-)-INT+ inhibitory postsynaptic potentials by endogenous modulatory neurons and by 5-HT.(ABSTRACT TRUNCATED AT 400 WORDS)
Estimation of passive horizontal linear whole-body displacement in humans
Authors: Israel I. , Chapuis N. , Glasauer S. , Charade O. , Berthoz A.
Published: December 2017

1. Passive linear self-motion estimation along the X and Y axes was investigated in human subjects. 2. A target was viewed from a distance of 0.8 or 2.4 m from the starting point. Subjects were then blindfolded and transported toward the target on a distance of 3.2 m and back to the start. Acceleration was constant: +/- 0.2 or +/- 1 m/s2. The subjects pushed a button on both outward and return paths, when they passed the previously seen target. 3. The results showed anticipation of the target on the outward path, and not on the return. This was identical for both axes and both accelerations. 4. The data are in accord with a model of double integration of the otolith signal, suggesting that linear path integration is a basic sensory mechanism.
The effect of bilateral cold block of the primate face primary somatosensory cortex on the performance of trained tongue-protrusion task and biting tasks
Authors: Lin L. D. , Murray G. M. , Sessle B. J.
Published: December 2017

1. Studies using ablation, intracortical microstimulation (ICMS) and surface stimulation, and single-neuron recordings have suggested that the primate primary somatosensory cortex (SI) may play an important role in movement control. Our aim was to determine whether bilateral inactivation of face SI would indeed interfere with the control of tongue or jaw-closing movements. 2. Effects of reversible inactivation by cooling of face SI was investigated in two monkeys trained to perform both a tongue-protrusion task and a biting task. The cooling experiments were carried out after the orofacial representation within SI was identified by systematically defining the mechanoreceptive field of single neurons recorded in face SI. The deficits in the tongue or jaw-closing movement were evaluated by the success rates for the monkeys' performance of both tasks and by the force and electromyographic (EMG) activity recorded from the masseter, genioglossus, and digastric muscles associated with the tasks. 3. During bilateral cooling of face SI, there was a statistically significant reduction in the success rates for the performance of the tongue-protrusion task in comparison with control series of trials while the thermodes used to cool face SI were kept at 37 degrees C. Detailed analyses of force and EMG activity showed that the principal deficit was the inability of the monkeys to maintain a steady tongue-protrusive force in the force holding period during each trial and to exert a consistent tongue-protrusion force between different trials. The task performance returned to control protocol levels at 4 min after commencement of rewarming. 4. Identical cooling conditions did not significantly affect the success rates for the performance of the biting task. Although the extent of the deficit was not severe enough to cause a significant reduction in successful rates for the biting task, cooling did significantly affect the ability of the monkeys to maintain a steady force in the holding period during each trial and to exert a consistent force between different trials. In one monkey the success rate of the biting task was also not affected by bilaterally cooling of face SI with a pair of larger thermodes placed on the dura over most of the face SI, face primary motor cortex (face MI), and adjacent cortical regions.(ABSTRACT TRUNCATED AT 400 WORDS)
N-methyl-D-aspartate (NMDA) and non-NMDA receptor antagonists block the hyperexcitability of dorsal horn neurons during development of acute arthritis in rat's knee joint
Authors: Neugebauer V. , Lucke T. , Schaible H. G.
Published: December 2017

1. In 22 anesthetized rats we studied the involvement of N-methyl-D-aspartate (NMDA) and non-NMDA receptors in the generation and maintenance of hyperexcitability in spinal cord neurons with knee input that develops in the course of an acute inflammation in the knee. In all experiments one neuron with knee input was identified, and the responses to mechanical stimuli and the receptive fields were monitored before and after induction of inflammation by the intra-articular injections of kaolin and carrageenan into the joint cavity. In most experiments multibarrel electrodes were used to administer specific NMDA and non-NMDA antagonists ionophoretically close to the neuron to test their effects on the inflammation-evoked changes. 2. Six neurons in the deep dorsal horn in six rats were used to establish the time course of the development of hyperexcitability in the untreated animal. In control periods of up to 3 h, the responses to mechanical stimuli and the receptive fields were stable. After induction of inflammation, the neurons developed increased responsiveness to mechanical stimuli applied to the injected knee but also to mechanical stimuli applied to the ipsilateral ankle and paw (including a reduction in the mechanical threshold in nociceptive specific neurons). The receptive fields expanded in five out of six neurons. The changes of responsiveness occurred mainly in the 2nd to 3rd h after the injection of kaolin. 3. In four rats three to four intravenous injections of the NMDA antagonist ketamine (2 mg/kg) were given during the injections of kaolin and carrageenan and in the following periods (up to 101 min postkaolin). During this treatment none of the four neurons exhibited the changes of responsiveness that were usually seen in control animals, although swelling of the knee developed in the same fashion as in control rats. Similarly, the generation of hyperexcitability was prevented when the NMDA antagonists ketamine and DL-2-amino-5-phosphonovalerate (AP5) were administered ionophoretically (ketamine in 4, AP5 in 2 rats) during the injections of kaolin and carrageenan and up to 100 min postkaolin. The doses of ketamine and AP5 were sufficient to reduce the responses to NMDA, whereas the responses to the non-NMDA agonist alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) were not influenced. 4. The ionophoretic application of the non-NMDA antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) during the injections of the kaolin and carrageenan and up to 103 min postkaolin also prevented the generation of hyperexcitability in six neurons in six rats.(ABSTRACT TRUNCATED AT 400 WORDS)
L-type calcium channels in type I cells of the rat carotid body
Authors: Fieber L. A. , McCleskey E. W.
Published: December 2017

1. Whole-cell and cell-attached patch-clamp recordings were made from enzymatically isolated type I cells from the carotid body of adult rats. Voltage-dependent K+ and Ca2+ channels were observed, but there was no detectable Na+ current. In this respect, rat carotid body cells are unlike those from rabbit, which have Na+ currents and Na(+)-dependent action potentials. 2. The observed Ca2+ channels had the following properties: 1) activation requires voltage steps above -20 mV; 2) little inactivation occurred with holding voltages below -40 mV; 3) one single-channel conductance of 21 pS was found with 90 or 110 mM Ba2+ in the cell-attached pipette and this was the only conductance observed; 4) open probability was increased by the dihydropyridine Ca2+ channel agonist Bay K 8644 and was decreased by the antagonist nifedipine; and 5) omega-conotoxin had little or no effect on the channels. These are properties expected of L-type Ca2+ channels. 3. To investigate whether these voltage-dependent channels would be available for opening on membrane depolarization, we measured the type I cell resting membrane potential noninvasively using unitary openings of the L-type Ca2+ channel with Bay K 8644 in the cell-attached pipette. Resting potentials ranged from -62 to -13 mV, with a mean of -32 mV in 12 cells. 4. Judging from single-channel conductance and pharmacology, the Ca2+ current is mostly, if not solely, carried by L channels. Thus it should be possible to use modulators of L channel activity to determine the role of Ca2+ channels in stimulus-secretion coupling in the rat carotid body.
Voltage dependence and activation kinetics of pharmacologically defined components of the high-threshold calcium current in rat neocortical neurons
Authors: Brown A. M. , Schwindt P. C. , Crill W. E.
Published: December 2017

1. As a first step toward identification of the functional significance of the spatial distribution of calcium channels we examined the high voltage-activated calcium current (HVA current) in acutely isolated pyramidal neurons from rat sensorimotor cortex using whole-cell voltage clamp. The goals of this study were (1) to determine whether the pharmacologically separable components of the HVA current differed in voltage dependence or activation kinetics and (2) to develop an empirical model that could predict the HVA current evoked by action potentials or other physiological responses. 2. Cells with short dendrites were chosen for study. Input resistance averaged 3.5 +/- 0.4 (SE) G omega. Specific membrane resistance averaged 51.9 +/- 6.8 K omega-cm2 on the basis of estimated membrane surface area. 3. Using 2 mM calcium in the extracellular solution, we evoked the HVA current by depolarizations positive to -45 mV from a holding potential of -60 mV, a potential where the low-threshold calcium current is fully inactivated. Maximum HVA current amplitude (484.9 +/- 42.3 pA) occurred near -15 mV. The evoked current was completely and reversibly blocked by 200 microM cadmium. 4. Tail current amplitude at a fixed potential increased as a sigmoidal function of prepulse potential. A plot of normalized tail current amplitude, taken as the fraction of HVA channels open at each prepulse potential, was best described by a Boltzmann function (maximum slope: e-fold per 11.3 mV; half activation: -24.6 mV) raised to the power of 2. This relation was not altered by extracellular application of 5 microM nifedipine or 10 microM omega-conotoxin, each of which reduced a separate component of the HVA current uniformly at all potentials. We conclude that the pharmacologically separable components of the HVA current do not differ significantly in voltage dependence. 5. The time course of current onset during a step depolarization was best described by second-order activation kinetics. Activation time constants ranged from a maximum of 1.2 ms at -40 mV to 0.3 ms at +25 mV. Neither activation nor tail current time constants were altered by extracellular application of 5 microM nifedipine or 10 microM omega-conotoxin. After application of 1 microM Bay K 8644 tail current decay was best described by a fast time constant similar to control values and a slow time constant. We conclude that the pharmacologically separable components of the HVA current in these neurons do not differ significantly in kinetics.(ABSTRACT TRUNCATED AT 400 WORDS)
Motor-unit recruitment in self-reinnervated muscle
Authors: Cope T. C. , Clark B. D.
Published: December 2017

1. Recruitment order of motor units in self-reinnervated medial gastrocnemius (MG) muscles was studied in decerebrate cats 16 mo after surgical reunion of the cut MG nerve. Pairs of MG motor units were isolated by dual microelectrode penetration of ventral roots to measure their recruitment sequence during cutaneous reflexes in relation to their physiological properties. 2. Physiological properties of reconstituted motor units appeared normal, as expected. Also normal were the relationships among these properties: twitch and tetanic tension tended to increase with axonal conduction velocity and decrease with twitch contraction time. A small fraction of motor units (10/116) in reinnervated muscles produced either no measurable tension or unusually large amounts of tension compared with controls. This was the only distinct feature of the sample of reconstituted units. 3. In muscles reinnervated after nerve section, stretch was notably ineffective in eliciting reflex contraction of MG muscles or their constituent motor units (only 5/116 units). Incomplete recovery from nerve section was probably the cause of this impairment, because stretch reflexes were readily evoked in adjacent untreated muscles and in one reinnervated MG muscle that was studied 16 mo after nerve crush. In contrast with the ineffectiveness of muscle stretch, sural nerve stimulation succeeded in recruiting 49/116 units, a proportion fairly typical of normal MG muscles. 4. The contractions of the first unit recruited in cutaneous reflexes tended to be slower and less forceful than those of the other unit in a pair. By these measures, recruitment obeyed the size principle. This recruitment order with respect to unit contractile properties was not significantly different (P > 0.05) between untreated and reinnervated muscles but was significantly (P < 0.005) different from random order in both groups. The same recruitment pattern was observed for pairs of motor units sampled from the muscle reinnervated after nerve crush, whether units were recruited by muscle stretch or sural nerve stimulation. 5. The usual tendency for motor units with slower conduction velocity (CV) to be recruited in sural nerve reflexes before those with faster CV was not strong in reinnervated muscles. After nerve section the proportion of units exhibiting the usual recruitment pattern was not significantly different (P > 0.05) from a random pattern for CV. 6. The central finding is that the normal recruitment patterns recover from nerve injury in a muscle that is reinnervated by its original nerve. By contrast, stretch reflexes do not recover well from nerve section, and this deficiency may contribute to motor disability.
Short- and long-term synaptic depression in rat neostriatum
Authors: Lovinger D. M. , Tyler E. C. , Merritt A.
Published: December 2017

1. We have examined plasticity at glutamatergic synapses on neurons in slices of neostriatum, a forebrain area involved in movement and cognitive function. 2. High-frequency stimulation of afferent inputs to neostriatal neurons induced depression of glutamatergic synaptic transmission. Depression could be induced using either prolonged trains or short repetitive bursts of high-frequency stimulation. Depression developed within seconds after such stimulation. Responses recovered to baseline levels within 10 min in most slices but persisted for up to 60 min in others. 3. Postsynaptic passive electrical properties and the ability to elicit action potentials by postsynaptic depolarization were not altered during depression. 4. The magnitude and time course of depression was similar whether postsynaptic responses were mediated by alpha amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) or N-methyl-D-aspartate (NMDA) type glutamate receptors. Depression was not altered by antagonism of AMPA or NMDA receptors or potentiation of AMPA receptor function with aniracetam. 5. Depression was blocked by treatments that increase transmitter release including increased extracellular Ca2+, application of 4-aminopyridine, or application of phorbol ester. 6. Our findings indicate that glutamatergic synapses in neostriatum are capable of expressing a form of synaptic depression that may involve decreased glutamate release.