bluuebunny/crossref_metadata_2025 huggingface dataset:
Topographical distribution and functional properties of cortically induced rhythmical jaw movements in the monkey (Macaca fascicularis)
Authors: Huang C. S. , Hiraba H. , Murray G. M. , Sessle B. J.
Published: December 2017

1. The lateral part of the pericentral cortex of both hemispheres in three awake monkeys was explored with intracortical microstimulation (ICMS) using short trains (T/S; 200-microseconds pulses at 333 Hz for 35 ms, less than or equal to microA) and long trains (C/S; 200-microseconds pulses at 50 Hz for 3 s, less than or equal to 60 microA). In both hemispheres of one of these monkeys, the responsiveness of single cortical neurons to stimulation of the orofacial region was tested at the same intracortical sites where ICMS was applied. 2. Movements were evoked from four physiologically defined cortical regions: the primary face motor cortex (MI), the primary face somatosensory cortex (SI), the principal part of the cortical masticatory area (CMAp) which was located in the precentral gyrus lateral to MI, and a deep part of the cortical masticatory area (CMAd) which was located in the inferior face of the frontal operculum. 3. Two types of cortically induced movements were observed: a single twitch movement and EMG activity of the orofacial muscles that was evoked by T/S at a short latency (10–45 ms) and rhythmical jaw movements (RJMs) which were only evoked by C/S. 4. RJMs were evoked at C/S frequencies ranging from 20 to 300 Hz. At movement threshold, the frequency of the cortically induced RJMs varied from 0.7 to 1.5 Hz and usually increased with the increase of C/S intensity up to 2 times movement threshold. The vertical amplitude of RJMs was also stimulus dependent, and at movement threshold it ranged from 3 to 9 mm. 5. The movement patterns of the cortically induced RJMs remained constant during the course of C/S but could be differentiated in the frontal plane into ipsilateral- (RJMi), vertical-(RJMv), and contralateral- (RJMc) directed movements. These three different patterns of RJMs were associated with different patterns of masticatory muscle activity. 6. Each cortical region contained many sites from which RJMs could be induced (so-called RJM sites). The RJMi sites were more numerous than RJMc sites in all regions except SI and were located anterolateral or lateral to the RJMc sites in each region; the RJMv sites were scattered throughout each cortical region. 7. In MI, C/S elicited RJMs from 94 intracortical sites from which short-latency twitch movements could also be evoked by T/S.(ABSTRACT TRUNCATED AT 400 WORDS)
Esophageal mechanoreceptors in the feeding system of the pond snail, Lymnaea stagnalis
Authors: Elliott C. J. , Benjamin P. R.
Published: December 2017

1. We identify esophageal mechanoreceptor (OM) neurons of Lymnaea with cell bodies in the buccal ganglia and axons that branch repeatedly to terminate in the esophageal wall. 2. The OM cells respond phasically to gut distension. Experiments with a high magnesium/low calcium solution suggest that the OM neurons are primary mechanoreceptors. 3. In the isolated CNS preparation, the OM cells receive little synaptic input during the feeding cycle. 4. The OM cells excite the motoneurons active in the rasp phase of the feeding cycle. 5. The OM cells inhibit each of the identified pattern-generating and modulatory interneurons in the buccal ganglia. Experiments with a saline rich in magnesium and calcium suggest that the connections are monosynaptic. 6. Stimulation of a single OM cell to fire at 5-15 Hz is sufficient to terminate the feeding rhythm in the isolated CNS preparation. 7. We conclude that these neurons play a role in terminating feeding behavior.
Light-evoked increases in [K+]o in proximal portion of the dark-adapted cat retina
Authors: Frishman L. J. , Steinberg R. H.
Published: December 2017

1. The scotopic threshold response (STR) and slow negative response are negative-going potentials in the dark-adapted electroretinogram (ERG) of the cat eye that originate proximal to the photoreceptors and are present at threshold and with dim illuminations. The present paper examines the hypothesis that these events are associated with Muller cell responses to potassium released by proximal retinal neurons by measuring light-dependent changes in extracellular K+ concentration [( K+]o, in proximal retina. 2. Extracellular field potentials and changes in [K+]o, evoked in response to diffuse illumination of the dark-adapted retina, were recorded with a double-barreled K+-sensitive microelectrode placed in the retina at different depths. The vitreal ERG was recorded at the same time. 3. The dynamic range of the light-evoked increases in [K+]o, recorded in proximal retina from threshold to saturation, was strikingly similar to that of the STR and slow negative response. The threshold for the [K+]o increase was near that of the most sensitive ganglion cells, and the response saturated approximately 2.4 log units below rod saturation. Also, onset latencies and rates of rise for the increases in [K+]o and the field potentials in proximal retina followed similar functions of intensity. 4. The depth distribution of the light-evoked [K+]o increases resembled that of the STR. The increases in [K+]o were largest and fastest in proximal retina where the STR was largest. This was true both for very low intensity stimuli, below the threshold for PII (DC-component and b-wave) in distal retina, and for stimulus intensities near STR saturation, where PII (DC-component) was present. For stimuli of intensities near rod saturation, when the b-wave was present in distal retina, there was a small fast increase in [K+]o at light onset in distal retina and a slower increase in proximal retina. Both increases were truncated by spread of the large light-evoked decrease in [K+]o in subretinal space that is known to cause the c-wave in the ERG and slow PIII in neural retina. 5. The duration of the increases in [K+]o in proximal retina was more sustained than the proximal field potentials. In response to stimuli of 2-4 s, the field potential began to recover toward base line after about 300 ms, whereas the increases in [K+]o remained at maximal levels until stimulus offset.(ABSTRACT TRUNCATED AT 400 WORDS)
Induction of paroxysmal discharges in the dentate gyrus: frequency dependence and relationship to afterdischarge production
Authors: Stringer J. L. , Williamson J. M. , Lothman E. W.
Published: December 2017

1. Electrical-stimulus trains activated hippocampal circuits in urethan-anesthetized rats. Responses were monitored with recordings of extracellular potentials and with measurements of the extracellular potassium ([K+]o). Stimulating electrodes were placed in the CA3 region contralateral to the recording electrode (cCA3) and in the ipsilateral angular bundle (AB) while recording in the CA1 pyramidal-cell layer or the granule-cell layer of the dentate gyrus. Patterns of maximal activation were identified. 2. In the CA1 region, maximal activation was indicated by the presence of 10- to 15-mV population spikes, a smooth rise in [K+]o of 5-6 mM above base-line levels of 3 mM, and a negative shift of the sustained DC potential of 2-4 mV. The dentate gyrus was considered to be maximally activated when bursts of large-amplitude (20-40 mV) population spikes were present. These population spikes were associated with a secondary rise in [K+]o to 6-8 mM above base line and an abrupt negative shift of the DC potential of 5-8 mV. 3. Maximal activation depended on the stimulus intensity, frequency, and duration. Trains of 10-Hz stimuli were used to determine the lowest stimulus intensity needed to elicit complete activation in CA1 and in the dentate gyrus. At this intensity, afterdischarges were not produced, and these responses could be elicited repeatedly. 4. By the use of this threshold stimulus intensity, cCA3 stimulation produced a rapid and progressive augmentation of CA1 responses until maximal activation was reached. In comparison, stimulation of the AB could produce the same end result, but the appearance of CA1 population spikes was delayed. Stimulation of the AB produced a steady increase in the evoked granule-cell population spike until the appearance of the paroxysmal large-amplitude population spikes. In contrast, cCA3 stimulation produced two positive evoked responses in the dentate gyrus before the paroxysms of population spikes began. 5. The frequency dependence of the responses was determined by giving stimulus trains ranging from 2 to 100 Hz. Stimulation of cCA3 produced population spikes in CA1 up to 100 Hz that were all associated with the same peak rise in [K+]o. AB stimulation only produced CA1 responses with stimulation frequencies between 15 and 25 Hz. The paroxysmal dentate population spikes were generated by stimulus frequencies between 15 and 30 Hz with both AB and cCA3 stimulation. 6. Unilateral colchicine injections caused a loss of dentate granule cells and a loss of maximal dentate activation on the side of the injection.(ABSTRACT TRUNCATED AT 400 WORDS)
Excitatory neurotransmission activates voltage-dependent properties in neurons in spinal motor system of lamprey
Authors: Alford S. , Sigvardt K. A.
Published: December 2017

1. Ventral horn neurons were studied under voltage clamp during episodes of sensory-evoked rhythmic coactivation in the in vitro lamprey spinal cord-tailfin preparation in the presence of strychnine. 2. Voltage clamp under a range of holding potentials during episodes of rhythmic coactivation revealed inward currents coincident with ventral root bursting in the same hemisegment and an apparent reversal potential of about -10 mV. 3. The current-voltage relationship of the peak inward current during each burst of this activity demonstrated a marked voltage dependency. 4. The voltage dependence of the inward current was eliminated by the specific NMDA-receptor blocker, APV, and by removal of Mg2+ from the bathing solution. 5. At depolarized potentials a long-lasting outward current could be observed, indicating an apparent voltage-dependent conductance for K+ and/or Cl-. This current was also blocked by APV and increased by the removal of Mg2+. 6. These results provide evidence that during rhythmic coactivation in strychnine, endogenous release of excitatory amino acid transmitter induces nonlinear conductance properties in ventral horn neurons by the activation of NMDA receptors. The results provide additional evidence that such activation contributes to the membrane potential oscillations that underlie rhythmic locomotory activity.
Chronic epileptic foci in vitro in hippocampal slices from rats with the tetanus toxin epileptic syndrome
Authors: Jefferys J. G.
Published: December 2017

1. Minute doses of tetanus toxin were injected into the hippocampi of rats, under pentobarbitone anesthesia, to induce a chronic experimental epilepsy. The effects of this treatment were studied in vitro in hippocampal slices prepared 1-60 days after injection. 2. Epileptic activity was preserved in these slices in vitro, closely resembling that seen in vivo. Epileptiform afterdischarges were evoked by stimulation after survival times of greater than or equal to 3 days from injection. Spontaneous synchronous epileptic discharges were recorded from 7 days after injection. Both kinds of epileptiform activity were found with survival times up to 36 days but not beyond 44 days. This time course resembles the waxing and waning of the epileptic syndrome in vivo. 3. Two distinct types of spontaneous burst were seen. The first was a simple burst lasting 100-300 ms, reminiscent of the "interictal spike" of the clinical electroencephalogram. The second was much more prolonged, lasting several seconds. It consisted of a simple burst followed by a series of discrete afterbursts at 3-6/s and resembled the early stages of an epileptic seizure. Both types of burst were associated with slow field potentials that were positive at the cell-body layer. 4. Both the interictal and the seizure-like spontaneous epileptic discharges originated in the CA3b/c pyramidal cell region and propagated at 0.1-0.25 m/s along the cell layer toward the CA1 region. They occurred at very variable intervals, ranging from 20 s to 30 min. 5. Spontaneous epileptic bursts occurred in media containing 3 mM [K+]o to 5 mM in one-third of experiments during the period 1-4 wk after injection. Spontaneous bursts could be induced by increasing [K+]o to 5 mM in two-thirds of the remaining slices, which initially had produced evoked afterdischarges. 6. Intracellular recordings revealed that spontaneous field bursts were invariably associated with paroxysmal depolarization shifts (PDSs) and bursts of action potentials, suggesting that almost all the pyramidal cells in the region were recruited into the epileptic discharges. In some cells, smaller abnormal depolarizations were also seen; they were clearly larger than the spontaneous synaptic potentials but were not associated with field potentials. They may have been due to a more limited recruitment of pyramidal cells into partially synchronous bursts. 7. The tetanus toxin experimental epileptic syndrome differs from chronic models described previously in retaining in the hippocampal slice in vitro much of the spontaneous epileptic activity seen in vivo in the freely moving chronically epileptic rat.(ABSTRACT TRUNCATED AT 400 WORDS)
Serotonergic modulation of two potassium currents in the pleural sensory neurons of Aplysia
Authors: Baxter D. A. , Byrne J. H.
Published: December 2017

1. The properties of membrane currents that were modulated by serotonin (5-HT) were investigated with two-electrode voltage-clamp techniques in sensory neuron somata isolated from the pleural ganglion of Aplysia californica. The modulatory effects of 5-HT were revealed by computer subtraction of current responses elicited in the presence of 5-HT from current responses elicited prior to the application of 5-HT. The complexities of the resulting 5-HT difference currents (I5-HT) suggested that 5-HT modulated more than one component of membrane current. 2. The 5-HT difference currents appeared to have at least two distinct components. One component was clearly evident at membrane potentials more negative than -10 mV was relatively voltage independent and did not inactivate. A second component was activated at membrane potentials more positive than -10 mV, had complex kinetics, and was highly voltage dependent. In an attempt to identify the membrane currents that were modulated by 5-HT, we compared the pharmacologic sensitivity of I5-HT to that of previously described K+ currents. 3. The two components of I5-HT had different sensitivities to agents that block K+ currents. The relatively voltage-independent component of I5-HT was not blocked by 2 mM 4-aminopyridine (4-AP) and was relatively insensitive to tetraethylammonium (TEA) (estimated Kd of 92 mM). In contrast, the voltage-dependent component of I5-HT was blocked by 4-AP (2 mM) and moderate concentrations of TEA (estimated Kd of 5 mM). 4. The K+ current blockers that were used to examine I5-HT were also used to examine voltage-activated membrane currents. Externally applied TEA blocked the delayed or voltage-dependent K+ current (IK.V) with an estimated dissociation constant (Kd) of 8 mM and a membrane current similar to the Ca2+-activated K+ current (IK.Ca) with an estimated Kd of 0.4 mM. In addition, externally applied 4-AP (2 mM) blocked IK.V. Thus TEA and 4-AP were equipotent in blocking both IK.V and the voltage-dependent component of I5-HT. 5. The suggestion that I5-HT contained multiple components was supported further by examining the modulatory effects of adenosine 3',5'-cyclic monophosphate (cAMP) that mediates some actions of 5-HT on membrane currents in these cells. cAMP difference currents (IcAMP) were similar to the relatively voltage-independent component of I5-HT. The subsequent addition of 5-HT to solutions already containing cAMP resulted in 5-HT difference currents similar to the voltage-dependent component of I5-HT.(ABSTRACT TRUNCATED AT 400 WORDS)
Interlimb coordination of leg-muscle activation during perturbation of stance in humans
Authors: Dietz V. , Horstmann G. A. , Berger W.
Published: December 2017

1. Electromyographic (EMG) responses were recorded in both legs, along with corresponding joint movements, after uni- and bilateral perturbations during stance on a treadmill with split belts. Displacements were directed forward, backward, or in opposing directions. They were induced by randomly timed ramp impulses at one of four different rates of treadmill acceleration. 2. Unilateral perturbations directed backward were followed by a bilateral gastrocnemius-EMG response, forward-directed perturbations by a bilateral tibialis anterior-EMG response. The amplitude of these responses was dependent on the rate of treadmill acceleration. Relative to the response of the displaced leg, the amplitude of the EMG response on the nondisplaced side was smaller when a gastrocnemius EMG response was induced, and about equal when the tibialis anterior muscle was activated. The onset latencies were shorter on the displaced side (displaced leg 75-96 ms, non-displaced leg 93-112 ms). 3. Bilateral perturbations in one direction were followed by larger EMG responses in both legs (in the gastrocnemius for backward-directed impulses, in the tibialis anterior for forward-directed impulses). For a given acceleration rate, their amplitude was about equal to the sum of the EMG amplitude of the displaced leg and that of the nondisplaced leg obtained during unilateral displacement. The inverse result was obtained when the legs were simultaneously displaced in opposite directions: EMG responses in both legs were significantly smaller than those obtained after unilateral displacement. 4. It is concluded that a unilateral displacement evokes reflex EMG responses in the synergistic muscles of both legs, which are graded according to the size of the proprioceptive input from the primarily displaced joint. During bilateral displacements, the activity induced by the respective contralateral leg is linearly summed or subtracted, depending on whether the legs are displaced in the same or in opposite directions. In view of the short latencies of these bilateral responses, it would seem that they are mediated by a spinal mechanism. 5. Distinct differences in the behavior of the antagonistic leg muscles were observed: 1) the coactivation of the contralateral leg muscle was significantly smaller when the gastrocnemius was stretched unilaterally, whereas it was about equal for the tibialis anterior; and 2) the gastrocnemius EMG responses were closely correlated with the displacement velocity, whereas the tibialis anterior response was more closely correlated with acceleration, i.e., the tibialis anterior response was more dynamic in nature.(ABSTRACT TRUNCATED AT 400 WORDS)
Bifurcation analysis of nonlinear retinal horizontal cell models. I. Properties of isolated cells
Authors: Winslow R. L.
Published: December 2017

1. Bifurcation theory is used to study properties of nonlinear analytical and computational models of isolated retinal horizontal cells. The analytical model is based on the published data of Shingai and Christensen describing steady-state I-V characteristics of horizontal cells isolated from catfish (Ictalurus punctatus) retina. The computational model is based on I-V characteristics of distinct macroscopic membrane currents observed in horizontal cells isolated from goldfish (Carassius auratus) retina. Slow-model dynamics are analyzed assuming that excitatory processes occur rapidly with respect to the time course of inactivation of the inward Ca2+ and outward K+ currents. 2. A global bifurcation diagram plotting the location and stability properties of critical points as a function of photoreceptor-evoked horizontal-cell postsynaptic membrane conductance Gsyn is derived for the analytical model. The automated bifurcation analysis software AUTO is used to compute global bifurcation diagrams for the computational model. Bifurcation diagrams exhibit a bistable regime at small Gsyn values characterized by two stable and one unstable critical point and a monostable regime at larger Gsyn values characterized by a single globally attracting stable critical point. The transition between bistable and monostable behavior occurs at a Gsyn value of roughly 0.9 nS for the computational model and 1.7 nS for the analytical model. Estimates of horizontal-cell glutamate-channel conductance suggest that this transition corresponds to the activation of as few as 400-700 glutamate channels. Dark-evoked release of neurotransmitter from photoreceptors may therefore set horizontal-cell synaptic conductance Gsyn to a value within the monostable regime. 3. Photoreceptor-evoked horizontal-cell membrane conductance, total Ca2+ channel conductance, and inactivation of the inward Ca2+ current are shown to be the major factors controlling the bifurcation structure of the computational model. Inactivation of the inward Ca2+ current is required to account for the dark resting potential of horizontal cells as well as light-evoked hyperpolarizing responses. Inactivation of the outward K+ current has little effect on model properties. 4. Isolated horizontal cells generate Ca2+ action potentials whereas cells in the intact retina normally do not. Simple procedures for modeling the slow dynamics of isolated horizontal-cell Ca2+ action potentials are described.(ABSTRACT TRUNCATED AT 400 WORDS)
Influence of central set on human postural responses
Authors: Horak F. B. , Diener H. C. , Nashner L. M.
Published: December 2017

1. The effect of central set on automatic postural responses was studied in humans exposed to horizontal support-surface perturbations causing forward sway. Central set was varied by providing subjects with prior experience of postural stimulus velocities or amplitudes under 1) serial and random conditions, 2) expected and unexpected conditions, and 3) practiced and unpracticed conditions. In particular, the influence of central-set conditions was examined on the pattern and magnitude of six leg and trunk electromyograph (EMG) activations and associated ankle torque responses to postural perturbations with identical stimulus parameters. 2. The scaling of initial agonist integrated EMG (IEMG) and torque responses to postural perturbation amplitude disappeared when perturbation amplitudes were randomized. This finding suggests that the initial magnitude of postural responses were centrally set to anticipated postural perturbation amplitudes based on sequential experience with the stimulus. 3. Expectation of postural stimulus amplitude had a significant effect on initial torque responses; subjects overresponded when a larger perturbation was expected and underresponded when a smaller perturbation was expected. Expectation of postural stimulus velocity had a smaller effect on initial torque responses, and subjects consistently overresponded when the velocity of the perturbation was unexpected. This difference in amplitude and velocity expectation may be because of the capacity to encode stimulus velocity, but not amplitude information, into the earliest postural responses of the current trial. The relative strength of amplitude and velocity central-set effects varied widely with individual subjects. 4. Central-set conditions did not affect initial EMG response latencies (100 +/- 20 ms, mean +/- SD) or the relative onset of proximal and distal agonists and antagonists. Unexpected or unpracticed stimulus amplitudes, however, were associated with significant late activation of ankle antagonist, tibialis. Thus errors in initial response magnitude because of central-set effects appear to be partially corrected by reciprocal antagonist activity. Agonist IEMG, however, did not always reflect significant changes in torque responses with central-set conditions. 5. Expectation of postural stimulus amplitude and velocity had two different types of effects on the magnitudes of postural responses: 1) a directionally specific, central-set effect consisting of either increased or decreased responses, depending on expectation of stimulus amplitude; and 2) a nonspecific enhanced response to novel stimulus velocities with a gradual reduction when a velocity was presented repeatedly. Two different neural mechanisms are proposed for these two adaptive effects. 6. Reduction of postural response magnitude and antagonist activity during practice may be partially explained by adaptive mechanisms based on expectation because of prior experience with stimulus velocity and amp
A comparative study of the changes in receptive-field properties of multireceptive and nocireceptive rat dorsal horn neurons following noxious mechanical stimulation
Authors: Laird J. M. , Cervero F.
Published: December 2017

1. Single-unit electrical activity has been recorded from 42 dorsal horn neurons in the sacral segments of the rat's spinal cord. The sample consisted of 20 multireceptive (class 2) cells with both A- and C-fiber inputs and 22 nocireceptive (class 3) cells. All neurons had cutaneous receptive fields (RFs) on the tail. 2. The RF sizes of the cells and their response thresholds to mechanical stimulation of the skin were determined before and after each of a series of 2-min noxious mechanical stimuli. Up to five such stimuli were delivered at intervals ranging from 10 to 60 min. In most cases, only one cell per animal was tested. 3. The majority of neurons were tested in barbiturate-anesthetized animals. However, to test whether or not this anesthetic influenced the results obtained, experiments were also performed in halothane-anesthetized and decerebrate-spinal preparations. The results from these experiments are considered separately. 4. All of the neurons responded vigorously to the first noxious pinch stimulus and all but one to the rest of the stimuli in the series. The responses of the neurons varied from stimulus to stimulus, but there were no detectable trends in the two groups of cells. 5. The RFs of the class 2 cells showed large increases (624.3 +/- 175.8 mm2, mean +/- SE) after the application of the pinch stimuli. The RFs of the class 3 neurons, which were initially smaller than those of the class 2 cells, either did not increase in size or showed very small increases after the pinch stimuli (38.3 +/- 11.95 mm2, mean +/- SE). 6. Some cells in both groups (6/10 class 2 cells and 7/16 class 3 cells) showed a decrease in mechanical threshold as a result of the noxious mechanical stimulus, but none of the class 3 cells' thresholds dropped below 20 mN into the low-threshold range. 7. The results obtained in the halothane-anesthetized and decerebrate-spinal animals were very similar to those seen in the barbiturate-anesthetized experiments, with the exception that in the decerebrate-spinal animals, the RFs of the class 2 cells were initially larger and showed only small increases.(ABSTRACT TRUNCATED AT 400 WORDS)
Synchronized excitation and inhibition driven by intrinsically bursting neurons in neocortex
Authors: Chagnac-Amitai Y. , Connors B. W.
Published: December 2017

1. The cellular mechanisms of synchronous synaptic activity were studied in isolated slices of rat SmI neocortex in which gamma-aminobutyric acid (GABA)-mediated inhibition was slightly suppressed. Intracellular measurements were made from single neurons, and extracellular recordings monitored the timing and intensity of population events. 2. Neurons in cortical layers II-VI were classified by the attributes of their single action potentials and repetitive firing patterns during injection of intracellular current pulses. Regular-spiking (RS) cells occurred in all layers and had relatively long-duration spikes and strong frequency adaptation. Intrinsically bursting (IB) cells occurred only in layers IV and V and generated bursts of greater than or equal to 3 spikes; some IB cells of lower-layer V produced repetitive bursts during long depolarizing pulses. Fast-spiking (FS) cells had brief spikes and little or no adaptation and fired at high frequencies. 3. When GABAA-mediated inhibition was slightly reduced with low doses of bicuculline methiodide (BMI, 0.8-1.0 microM), synchronous events were evoked by stimulating layer VI with single shocks. Synchronous events were characterized by prominent, often all-or-none extracellular field potentials that propagated horizontally for variable distances up to several millimeters. Large field potentials were invariably correlated with excitatory and inhibitory postsynaptic potentials (EPSPs and IPSPs) in single neurons. Both PSPs and field potentials often had long (up to 250 ms) and variable latencies, and sometimes two or more events were generated by single stimuli. In all cases the PSPs and field potentials were synchronous. Both field potentials and single cells sometimes generated short epochs (3-7 peaks) of rhythmic events at 20-50 Hz. 4. The physiological class of single neurons was correlated with the relative dominance of excitation and inhibition during each synchronous event. In phase with each synchronous event, most RS cells were very strongly inhibited with only small amounts of concurrent excitation. By contrast, IB cells were strongly and consistently excited, with relatively little inhibition. FS cells were also phasically excited. 5. Anatomic studies have identified RS and IB cells as pyramidal cells and FS cells as GABAergic nonpyramidal cells. This implies that, during the synchronous events of the present study, the majority of pyramidal cells were dominated by IPSPs. Synchronous excitation of FS cells, the presumed inhibitory interneurons, is consistent with this. Only a subset of the pyramidal neurons, almost all of them IB cells of the middle layers, displayed strong, synchronous excitation and clusters of action potentials.(ABSTRACT TRUNCATED AT 400 WORDS)
Swimming in Aplysia brasiliana: behavioral and cellular effects of serotonin
Authors: Parsons D. W. , Pinsker H. M.
Published: December 2017

1. Aplysia brasiliana is a marine mollusk that swims by repeated metachronal flapping movements of its bilateral fleshy parapodia. Animals with bilateral cerebropedal connective (CPC) lesions do not swim when suspended above the substrate, although tonic CPC stimulation can elicit normal parapodial flapping. Although the parapodial opener-phase (POP) cells, a previously identified group of neurons, fire synchronous bursts of efferent spikes in-phase with parapodial opening movements in both intact animals and dissected preparations, they are not likely to be primary parapodial motoneurons. These cells receive one or more large, apparently monosynaptic excitatory postsynaptic potentials (EPSPs) during CPC stimulation that are effective in producing the swimming motor program (SMP). 2. In suspended CPC-lesioned animals, injections of serotonin (5-HT) that produce an average hemolymph concentration of 10(-5) M induced full-amplitude parapodial flapping. Selected episodes of flapping were similar in frequency to normal suspended swimming. 3. In suspended CPC-lesioned animals, 5-HT injections elicited an apparently normal swimming motor program that was associated with synchronous bursts of large-amplitude efferent spikes in the parapodial nerves. In many semi-intact preparations, exposing the circumoesophageal ganglia to 5-HT elicited a similar rhythmic motor program, but usually at a lower frequency than during normal swimming or during tonic CPC stimulation. 4. In isolated-ganglion preparations, bath application of 5-HT produced immediate depolarization and tonic firing of individual POP neurons, followed by smooth and regular bursting in the apparent absence of synaptic input. In such preparations, the motor program elicited by bath-applied 5-HT differed from the one elicited by tonic CPC stimulation in that the 5-HT-elicited rhythmic bursting usually was not synchronous in different POP neurons. Tonic CPC stimulation during bath applications of 5-HT produced immediate synchronization of bursts among the POP neurons. 5. Hyperpolarization (or depolarization) of a POP neuron during bath application of 5-HT increased (or decreased) the burst period, but membrane polarization did not change the burst period elicited during tonic CPC stimulation.
Spatial summation of heat-induced pain: influence of stimulus area and spatial separation of stimuli on perceived pain sensation intensity and unpleasantness
Authors: Price D. D. , McHaffie J. G. , Larson M. A.
Published: December 2017

1. Psychophysical experiments were initiated to determine the possible influence of increasing stimulus size on perceived pain intensity. Six trained human subjects (5 male, 1 female) made visual analogue scale (VAS) ratings for pain-sensation intensity and unpleasantness in response to nociceptive thermal stimuli. Test stimuli consisted of 5-s duration heat pulses (45-50 degrees C in 1 degrees increments) delivered by one, two, or three contact thermal probes (1 cm2 each) applied to the medial aspect of the anterior forearm. 2. The area of skin receiving noxious thermal stimuli was changed by randomly varying the number of thermodes activated. The effects of varying the distance between the thermal probes also were evaluated. In the first series of experiments, thermal-probe separation was kept close to 0; in subsequent experimental series, the thermodes were separated by either 5 or 10 cm. 3. In each experimental series, considerable spatial summation occurred in both pain-sensation intensity and unpleasantness dimensions of pain. This summation occurred throughout the nociceptive thermal range of 45-50 degrees C and was larger at suprathreshold temperatures (greater than or equal to 47 degrees C) than those near threshold (less than or equal to 46 degrees C). Unlike spatial summation of perceived warmth, that of pain was not characterized by systematic changes in power-function exponents but as approximately upward parallel displacements in double-logarithmic coordinates. 4. Thermal-probe separation over a range of 0-10 cm had no effects on spatial summation of pain-sensation intensity or pain unpleasantness. In contrast, increasing thermal-probe separation increased the subjects' ability to discriminate differences in stimulus size and their ability to detect correctly the number of thermal probes activated. 5. Because affective VAS ratings of unpleasantness were linearly related to, but distinctly and systematically less than, VAS ratings of pain-sensation intensity, it was clear that subjects responded quite differently to these two pain dimensions. Affective judgements were not additionally influenced by thermal probe separation and hence by the ability to perceive stimulus size or number of thermal probes activated. 6. The results indicate that powerful spatial-summation mechanisms exist for heat-induced pain. Spatial summation of pain is likely to be subserved both by local integration mechanisms at the level of single spinothalamic-tract neurons and by recruitment of central nociceptive neurons, because spatial summation of pain occurred to approximately equal extents under conditions of thermode separations over a distance of at least 20 cm.
Kinesthetic control of a multijoint movement sequence
Authors: Cordo P. J.
Published: December 2017

1. The individual joint rotations of a movement sequence might be controlled either by a central motor plan or by motion-dependent (i.e., kinesthetic) sensory input. Most previous research has focused on how the nervous system uses central motor plans to control movement sequences. This study examined how the nervous system uses kinesthetic input to control a multijoint movement sequence. 2. Human subjects were trained to extend the elbow horizontally at 22 degrees/s and to open the hand as the elbow passed through a 2 degrees-wide target zone. Different distances to the target zone were used to examine a wide range of movement times of the elbow to target zone (i.e., 150-1,500 ms). 3. A hydraulic apparatus simulated a spring resistance to the elbow extension. In some trials, the spring constant was unexpectedly increased or decreased just before the subject initiated the elbow extension, causing the elbow to slow down or speed up. Because these changes in spring constant were randomly imposed and because no visual feedback was available, subjects had to use kinesthetic input to control this motor task. 4. The experimental subjects employed two different strategies for the use of kinesthetic input to control this motor task. In the first strategy, the subjects used kinesthetic input related to the elbow rotation to detect and correct velocity errors caused by the changes in spring constant. The onset of error correction varied between 92 and 196 ms after the appearance of velocity errors. The proportion of the error corrected by the time the elbow reached the target zone varied between 31 and 78%, depending on the movement time to the target zone. However, because this correction for velocity errors was neither instantaneous nor complete, the changes in spring constant caused leads and lags in the time that the elbow reached the target zone. 5. In the second strategy, subjects used kinesthetic input related to the elbow rotation to advance or delay the onset of the hand movement, thereby compensating for leads and lags in the arrival of the elbow at the target zone. These adjustments in the triggering time of the hand movement allowed subjects to open the hand while the elbow was in the target zone. This kinesthetic triggering mechanism was effective for elbow rotations reaching the target zone within 150-1,500 ms. 6. These results suggest that, to fully understand how multijoint movement sequences are controlled by the nervous system, sensory mechanisms must be considered in addition to central mechanisms.
Visual motion response properties of neurons in dorsolateral pontine nucleus of alert monkey
Authors: Suzuki D. A. , May J. G. , Keller E. L. , Yee R. D.
Published: December 2017

1. In this study we sought to characterize the visual motion processing that exists in the dorsolateral pontine nucleus (DLPN) and make a comparison with the reported visual responses of the middle temporal (MT) and medial superior temporal (MST) areas of the monkey cerebral cortex. The DLPN is implicated as a component of the visuomotor interface involved with the regulation of smooth-pursuit eye movements, because it is a major terminus for afferents from MT and MST and also the source of efferents to cerebellar regions involved with eye-movement control. 2. Some DLPN cells were preferentially responsive to discrete (spot and bar) visual stimuli, or to large-field, random-dot pattern motion, or to both discrete and large-field visual motion. The results suggest differential input from localized regions of MT and MST. 3. The visual-motion responses of DLPN neurons were direction selective for 86% of the discrete visual responses and 95% of the large-field responses. Direction tuning bandwidths (full-width at 50% maximum response amplitude) averaged 107 degrees and 120 degrees for discrete and large-field visual motion responses, respectively. For the two visual response types, the direction index averaged 0.95 and 1.02, indicating that responses to stimuli moving in preferred directions were, on average, 20 and 50 times greater than responses to discrete or large-field stimulus movement in the opposite directions, respectively. 4. Most of the DLPN visual responses to movements of discrete visual stimuli exhibited increases in amplitude up to preferred retinal image speeds between 20 and 80 degrees/s, with an average preferred speed of 39 degrees/s. At higher speeds, the response amplitude of most units decreased, although a few units exhibited a broad saturation in response amplitude that was maintained up to at least 150 degrees/s before the response decreased. Over the range of speeds up to the preferred speeds, the sensitivity of DLPN neurons to discrete stimulus-related, retinal-image speed averaged 3.0 spikes/s per deg/s. The responses to large-field visual motion were less sensitive to retinal image speed and exhibited an average sensitivity of 1.4 spikes/s per deg/s before the visual response saturated. 5. DLPN and MT were quantitatively comparable with respect to degree of direction selectivity, retinal image speed tuning, and distribution of preferred speeds. Many DLPN receptive fields contained the fovea and were larger than those of MT and more like MST receptive fields in size.(ABSTRACT TRUNCATED AT 400 WORDS)
Recurrent inhibition to and from motoneurons innervating the flexor digitorum and flexor hallucis longus muscles of the cat
Authors: Hamm T. M.
Published: December 2017

1. Recurrent inhibitory postsynaptic potentials (IPSPs) to and from motoneurons innervating the flexor digitorum longus (FDL) and flexor hallucis longus (FHL) muscles of the cat were investigated to determine whether recurrent inhibitory projections involving these motoneurons are similar--as would be consistent with the Ia and anatomic synergism of FDL and FHL--or are dissimilar, as are the activities of these muscles during locomotion (O'Donovan et al. 1982). 2. Composite recurrent IPSPs were recorded in several species of motoneurons innervating hindlimb muscles in response to stimulation of a number of muscle nerves in cats allowed to become unanesthetized after ischemic decapitation. 3. No recurrent IPSPs from stimulation of the FDL nerve were observed in motoneurons innervating FDL, FHL, lateral gastrocnemius-soleus (LG-S), medial gastrocnemius (MG), plantaris (Pl), tibialis anterior (TA), or extensor digitorum longus (EDL). 4. The recurrent IPSPs produced by stimulation of FHL were larger and found more frequently in LG-S than in FDL motoneurons. Recurrent inhibition from FHL was also greater in Pl than in FDL motoneurons. 5. The recurrent IPSPs produced by stimulation of LG-S, PL, and MG were larger in FHL than in FDL motoneurons, and those from LG-S and MG were found more frequently in FHL than in FDL motoneurons. 6. Stimulation of the TA nerve produces recurrent IPSPs in FDL but not in FHL motoneurons. A few FDL and FHL cells (6 of 23 and 9 of 34, respectively) received small (less than 0.5 mV) recurrent IPSPs from stimulation of the EDL nerve.(ABSTRACT TRUNCATED AT 250 WORDS)
The spino(trigemino)pontoamygdaloid pathway: electrophysiological evidence for an involvement in pain processes
Authors: Bernard J. F. , Besson J. M.
Published: December 2017

1. Neurons were recorded in the parabrachial (PB) area, located in the dorsolateral region of the pons (with the use of extracellular micropipette), in the anesthetized rat. Parabrachioamygdaloid (PA) neurons (n = 67) were antidromically identified after stimulation in the centralis nucleus of the amygdala (Ce). The axons of these neurons exhibit a very slow conduction velocity, between 0.26 and 1.1 m/s, i.e., in the unmyelinated range. 2. These PA neurons were located in a restricted region of the PB area: the subnuclei external lateral (PBel) and external medial (PBem). A relative somatotopic organization was found in this region. 3. These units were separated into two groups: 1) a group of nociceptive-specific (NS) neurons (69%), which responded exclusively to noxious stimuli, and 2) a group of nonresponsive (NR) neurons (31%). 4. The NS neurons exhibited low or lacked spontaneous activity. They responded exclusively to mechanical (pinch or squeeze) and/or thermal (waterbath or waterjet greater than 44 degrees C) noxious stimuli with a marked and sustained activation with a rapid onset and generally without afterdischarge. Noxious thermal stimuli generally induced a stronger response than the noxious mechanical stimuli. These neurons exhibited a clear capacity to encode thermal stimuli in the noxious range: 1) the stimulus-response function was always positive and monotonic; 2) the slope of the curve progressively increased up to a maximum where it was very steep, then the steepness of the slope decreased close to the maximum response; and 3) the mean threshold was 44.1 +/- 2 degrees C, and the point of steepest slope of the mean curve was around 47 degrees C. 5. The excitatory receptive fields of the NS neurons were large in the majority (70%) of the cases and included several areas of the body. A more marked activation was often obtained from stimuli applied to one part of the body, denoted as the preferential receptive field (PRF). In the other cases (30%), the excitatory receptive field was relatively small (SRF) and restricted to one part of the body (the tail, a paw, a hemiface, or the tongue). Both the PRF and SRF were more often located on the contralateral side. In addition, noxious stimuli applied outside the excitatory receptive field were found to strongly inhibit the responses of NS neurons. 6. All the NS neurons responded to intense transcutaneous electrical stimulation applied to the PRF or SRF with two peaks of activation.(ABSTRACT TRUNCATED AT 400 WORDS)
Effect of passive eye position changes on retinogeniculate transmission in the cat
Authors: Lal R. , Friedlander M. J.
Published: December 2017

1. Extracellular recordings were made from single neurons in layer A of the left dorsal lateral geniculate nucleus (LGNd) of anesthetized and paralyzed adult cats. Responses to retinotopically identical visual stimuli (presented through the right eye) were recorded at several positions of the left eye in its orbit. Visual stimuli consisted of drifting sinusoidal gratings of optimal temporal and spatial frequencies at twice threshold contrast. Visual stimulation of the left eye was blocked by a variety of methods, including intravitreal injection of tetrodotoxin (TTX). The change in position of the left eye was achieved by passive movements in a randomized and interleaved fashion. Of 237 neurons studied, responses were obtained from 143 neurons on 20-100 trials of identical visual stimulation at each of six eye positions. Neurons were classified as X- or Y- on the basis of a standard battery of physiological tests (primarily linearity of spatial summation and response latency to electrical stimulation of the optic chiasm). 2. The effect of eye position on the visual response of the 143 neurons was analyzed with respect to the number of action potentials elicited and the peak firing rate. Fifty-seven (40%) neurons had a significant effect [by one-factor repeated-measure analysis of variance (ANOVA), P less than 0.05] of eye position on the visual response by either criterion (number of action potentials or peak firing rate). Of these 57 neurons, 47 had a significant effect (P less than 0.05) with respect to the number of action potentials and 23 had a significant effect (P less than 0.05) by both criteria. Thus the permissive measure by either criterion and the conservative measure by both criteria resulted in 40% and 16%, respectively, of all neurons' visual responses being significantly affected by eye position. 3. For the 47 neurons with a significant effect of eye position (number of action potentials criterion), a trend analysis of eye position versus visual response showed a linear trend (P less than 0.05) for 9 neurons, a quadratic trend (P less than 0.05) for 32 neurons, and no significant trend for the 6 remaining neurons. The trends were approximated with linear and nonlinear gain fields (range of eye position change over which the visual response was modulated). The gain fields of individual neurons were compared by measuring the normalized gain (change in neuronal response per degree change of eye position). The mean normalized gain for the 47 neurons was 4.3. 4. The nonlinear gain fields were generally symmetric with respect to nasal versus temporal changes in eye position.(ABSTRACT TRUNCATED AT 400 WORDS)