bluuebunny/crossref_metadata_2025 huggingface dataset:
Encoding of sound-source location and movement: activity of single neurons and interactions between adjacent neurons in the monkey auditory cortex
Authors: Ahissar M. , Ahissar E. , Bergman H. , Vaadia E.
Published: December 2017

1. Neuronal mechanisms for decoding sound azimuth and angular movement were studied by recordings of several single units in parallel in the core areas of the auditory cortex of the macaque monkey. The activity of 180 units was recorded during the presentation of moving and static sound stimuli. Both the activity of single units and the interactions between neighboring neurons in response to each stimulus were analyzed. 2. Sixty-two percent of the units showed significant modulation of their firing rates as a function of the stimulus azimuth. Contralateral stimuli were preferred by the majority (approximately 60%) of these neurons. Thirty-five percent of the units showed mild but statistically significant modulation of their firing rates, which was specifically attributed to the angular movement of the sound source. 3. Eighty-nine percent of the "movement-sensitive" units were also "azimuth sensitive." The sound source's azimuth determined the pattern of the response components (on, sustained, off), whereas the source's movement affected only the magnitude of these components, typically the sustained component. Most neurons for which the sustained response to static sounds was greater for contralateral than ipsilateral stimuli preferred moving sounds that were moving into the contralateral hemifield. 4. Cross-correlation analysis was carried out for 245 neuron pairs. Cross-correlograms were computed for each pair under all stimulus conditions to allow comparison of the neuronal interactions under the various conditions. The shapes of some correlograms (after subtraction of direct stimulus effects) were dependent on specific stimulus conditions, suggesting that the effective connectivity between these neurons depended on the location and/or movement of the sound stimuli. Furthermore, joint peristimulus time (JPST) analysis indicated that modifications of connectivity may be temporally related to the stimulus and may occur over short periods of time. These results could not have been predicted from analysis of the independent single-unit responses to the stimuli. 5. The data suggest that both firing rates and correlated activity between adjacent neurons in the auditory cortex encode sound location and movement.
Single-electrode voltage-clamp analysis of the N-methyl-D-aspartate component of synaptic responses in neocortical slices from children with intractable epilepsy
Authors: Wuarin J. P. , Peacock W. J. , Dudek F. E.
Published: December 2017

1. Synaptic transmission mediated by the N-methyl-D-aspartate (NMDA)-receptor type was studied in neocortex from children undergoing surgical treatment for intractable epilepsy. Intracellular recordings from pyramidal cells were obtained in slices of neocortical tissue by use of microelectrodes. Synaptic responses were induced by electrical stimulation and studied with current-clamp and single-electrode voltage-clamp techniques. The NMDA-receptor-mediated component of the synaptic responses was isolated by addition of 10 microM bicuculline and 30 microM 6-cyano-2,3-dihydroxy-7-nitroquinoxaline (CNQX) in the perfusion solution. 2. In the presence of bicuculline and CNQX, electrical stimulation evoked an excitatory postsynaptic potential (EPSP) in every recorded cell. The amplitude of this EPSP increased when membrane potential was depolarized with injected current. 3. All cells studied in voltage clamp were recorded with microelectrodes containing Cs+ and QX 314. To avoid contamination of the responses from voltage-dependent Ca2+ conductances, membrane potential was held at depolarized potentials until Ca2+ spiking inactivated completely. The evoked excitatory postsynaptic currents (EPSCs) measured at resting membrane potential ranged from 100 to 400 pA. The NMDA receptor-selective antagonist DL-2-amino-5-phosphonopentanoic acid (AP-5) reversibly decreased the current amplitude by 60% for 10 microM and 80% for 30 microM. 4. The current-voltage (I-V) relation showed a region of negative slope conductance between -100 and -20 mV. The largest currents (-250 to -900 pA) were recorded in the range of -45 to -20 mV and reversed between -10 and +10 mV. Removing Mg2+ from the perfusion solution decreased the negativity of the slope, which is consistent with a reduction in the voltage-dependent Mg2+ block of the NMDA-receptor channel. 5. The I-V plots obtained from cells recorded in the most abnormal tissue were averaged and compared with those from the least abnormal tissue. No significant difference was found between these two groups. The averaged plots from the youngest patients (8 and 10 mo old) and those from the oldest (5-15 yr old) patients were also compared, and the results from these two groups were not significantly different.(ABSTRACT TRUNCATED AT 400 WORDS)
FMRFamide effects on membrane properties of heart cells isolated from the leech, Hirudo medicinalis
Authors: Thompson K. J. , Calabrese R. L.
Published: December 2017

1. The effects of the cardioactive peptide FMRFamide were tested on enzymatically dissociated muscle cells isolated from hearts of the leech. These cells were normally quiescent, with resting potentials near -60 mV. 2. Superfusion of FMRFamide induced a strong depolarization in isolated heart cells (e.g., greater than 40 mV with 10(-6) M FMRFamide). The depolarization was maintained in the continued presence of peptide and persisted long after its removal. Less frequently, FMRFamide superfusion elicited an episodic polarization rhythm. 3. The response of isolated heart cells to bath-applied FMRFamide showed a 1- to 2-min latency. The latency decreased with repeated applications of FMRFamide. 4. The FMRFamide response was diminished by Na+ replacement but persisted with Ca2+ channel blockade. 5. In voltage-clamped heart cells (-60 mv), superfusion of FMRFamide elicited a slow inward current with a transient and a sustained component. 6. Current-voltage (I-V) curves during FMRFamide superfusion in normal leech saline showed that FMRFamide also enhanced voltage-dependent outward currents activated at depolarized levels. 7. Under conditions in which K+ currents were substantially blocked, the FMRFamide-dependent I-V curve was net inward from -90 to +50 mV. A voltage-dependent component was blocked by Co2+ and a linear component by Na+ replacement. 8. We conclude that FMRFamide elicits a persistent inward current with a Na+ component and in addition modulates both voltage-dependent Ca2+ and K+ currents that may contribute to the normal myogenic activity of leech heart muscle cells.
Local synaptic circuits and epileptiform activity in slices of neocortex from children with intractable epilepsy
Authors: Tasker J. G. , Peacock W. J. , Dudek F. E.
Published: December 2017

1. Single and dual intracellular recordings were performed in neocortical slices obtained from tissue samples surgically removed from children (8 mo to 15 yr) for the treatment of intractable epilepsy. Electrical stimulation and glutamate microapplication were used to study local synaptic inputs to pyramidal cells. 2. In recordings with potassium-acetate electrodes, activation of presynaptic neocortical neurons with glutamate microdrops did not elicit a clear increase in postsynaptic potentials (PSPs) but did suppress current-evoked repetitive spike firing in recorded neurons. Bicuculline (10 microM) blocked this effect, suggesting it was caused by the activation of presynaptic gamma-aminobutyric acid (GABA) cells. In recordings with KCl electrodes, glutamate microdrops elicited an increase in the frequency and amplitude of depolarizing PSPs. Bicuculline (5-10 microM) blocked the glutamate-evoked PSPs, suggesting they were reversed GABAA-receptor-mediated inhibitory postsynaptic potentials (IPSPs). In one cell recorded with a KCl electrode (total n = 8), current-evoked spike trains elicited afterdischarges of reversed IPSPs, thus revealing a recurrent inhibitory circuit. Therefore local inhibitory synaptic circuits were robust and could be observed in tissue from patients as young as 11 mo. 3. In addition to short-latency (10-25 ms), monosynaptic excitatory postsynaptic potentials (EPSPs), electrical stimulation at low intensities sometimes elicited delayed EPSPs (20-60 ms). When GABAA-receptor-mediated synaptic inhibition was partially reduced in bicuculline (5-10 microM), electrical stimulation evoked large EPSPs at long and variable latencies (100-300 ms). Glutamate microapplication caused an increase in the frequency and amplitude of EPSPs; preliminary results suggest that glutamate microdrops were less likely to evoke EPSPs in tissue from younger patients (8-12 mo) than in slices from patients greater than 4 yr. Evidence for local excitatory synaptic circuits was thus found when synaptic inhibition was partially reduced. 4. After further reduction of inhibition in bicuculline (5-50 microM), electrical stimulation elicited epileptiform bursts. In pairs of simultaneously recorded neurons, bursts were generated synchronously from long-latency EPSPs (100-300 ms) in slices from patients as young as 8 mo. Reflected EPSPs at very long and variable latencies (500-1,100 ms) and repetitive epileptiform bursts could be evoked synchronously in pairs of cells. Glutamate activation of local presynaptic neurons elicited robust epileptiform events in recorded cells. This was seen in slices from patients as young as 16 mo. 5. These data provide physiological evidence for the presence of local inhibitory and excitatory synaptic circuits in human neocortex at least as early as 11 and 8 mo, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)
Direct evidence for presynaptic inhibitory mechanisms in crayfish sensory afferents
Authors: Cattaert D. , el Manira A. , Clarac F.
Published: December 2017

1. The central control of sensory inputs from a proprioceptor [chordotonal organ (CO)] in the second joint [coxo-basipodite (CB)] of the fifth leg was studied in crayfish in vitro preparations (Fig. 1A). Simultaneous intracellular recordings from CBCO terminals (CBT) and postsynaptic motoneurons (MNs) were performed along with micropipette pressure ejection or bath application of gamma-aminobutyric acid (GABA), to study the presynaptic mechanisms at work in the CBT (Fig. 1B). 2. Two intracellular recordings were used to show that the spikes never overshoot, and that the more central the recording site within the neuropile, the smaller the spikes (Fig. 2). Only electrotonic conduction occurs, therefore, in the sensory afferents within the ganglion. 3. Pressure ejection of GABA close to the recording site of CBTs in the ganglion (Fig. 3A) gave rise to a membrane depolarization, the reversal potential of which was about -25 mV (Fig. 7), as well as to an increase in the membrane conductance (Fig. 3C) and a decrease in the orthodromic spike amplitude; moreover, it did not elicit either hyperpolarization, or any change in the membrane conductance of the postsynaptic MN (Fig. 3B), which indicates that pressure ejection of GABA affected only a restricted area around the CBT and not the postsynaptic MNs. 4. In CBT, spontaneous primary afferent depolarizations (PADs) occurred irregularly when the activity of the preparation was not rhythmic (Fig. 4A), and in bursts when the preparation displayed fictive locomotion (Fig. 4B). In the latter case, antidromic spikes were sometimes superimposed on PADs (Fig. 4D). The amplitude of the PADs was reduced when picrotoxin (PTX), a GABA antagonist, was applied (Fig. 5), which suggests that GABA may be involved in spontaneous PADs. The reversal potential of PADs was about -25 mV (Figs. 6 and 7). 5. During simultaneous recordings from a CBT and a monosynaptically related MN, GABA applied by pressure ejection close to the CBT (Fig. 8A) completely suppressed the excitatory postsynaptic potentials (EPSPs) elicited by CBT spikes in the MN (Fig. 8, B and D). This was due to a presynaptic mechanism because no change in the membrane potential or membrane conductance was observed in the MN (Fig. 8C) and most of the CBTs associated with a given MN were affected (Fig. 9). 6. Simultaneously recording from a CBT and a monosynaptically related MN demonstrated that, during bouts of PADs, the spike amplitude decreased in proportion to the PAD amplitude (Fig. 10A).(ABSTRACT TRUNCATED AT 400 WORDS)
Functional properties of single neurons in the face primary motor cortex of the primate. III. Relations with different directions of trained tongue protrusion
Authors: Murray G. M. , Sessle B. J.
Published: December 2017

1. In previous papers we presented evidence pointing to an important role for face motor cortex in the control of tongue movements. Intracortical microstimulation (ICMS) at many sites within face motor cortex evoked different types of tongue movement, and many neurons at these "tongue-MI" sites received intraoral mechanosensitive afferent input, and their activity was related to a tongue-protrusion task performed by a monkey. In view of the synergistic action of the various tongue muscles during tongue movement, we hypothesized that these different tongue-MI sites are recruited to effect the appropriate change in tongue shape and position during a tongue-protrusion movement. A prediction from this hypothesis is that variations in the direction of a tongue-protrusion movement should be associated with variations in the activities within the different tongue-MI efferent zones. Differences in efferent-zone activity should be reflected in differences in the firing rates of neurons that are located at these tongue-MI sites. 2. We trained two monkeys to perform a tongue-protrusion task at each of three directions. The tongue-protrusion task transducer was positioned at 0 degrees (Ts), 30 degrees to the left (Tlt), or 30 degrees to the right (Trt) from the midsagittal plane; the latter two positions were termed asymmetric tongue-protrusion task positions. Single neurons were recorded from tongue-MI during trials of tongue-protrusion task at each of two or three of the above positions. Some of the neurons were also studied during a biting task. In addition, neurons were tested for possible mechanosensitive afferent input. 3. Of the 66 neurons studied, 31 (45%) exhibited directional relations; that is, the change in firing rate between the pretrial period (PTP) and the task period for the tongue-protrusion task was significantly different for each neuron depending on the direction in which the activity of the neuron was studied. 4. The "directional" neurons exhibited a single preferred direction of firing in that the mean firing rate during one direction of tongue-protrusion task was significantly greater than for any other direction. Of the 20 neurons studied at all three directions of tongue-protrusion task, the mean firing rate of each of 18 was highest at one of the asymmetric positions, and 12 of these 18 neurons exhibited a monotonic decrease in absolute firing frequency from one asymmetric task direction to the other. 5. Thirteen of the neurons were also studied while the monkey performed the biting task. Most tongue-MI directional neurons were not related to the biting task.(ABSTRACT TRUNCATED AT 400 WORDS)
Functional connectivity between brain stem midline neurons with respiratory-modulated firing rates
Authors: Lindsey B. G. , Hernandez Y. M. , Morris K. F. , Shannon R.
Published: December 2017

1. Recent evidence supports the idea that neurons distributed along the midline of the brain stem contribute to the regulation of breathing. This study sought evidence for functional connections between midline neurons with respiratory-modulated firing rates. 2. Experiments were conducted on 38 anesthetized, paralyzed, bilaterally vagotomized, artificially ventilated cats. Planar arrays of tungsten microelectrodes were used to monitor spike trains of two or more midline neurons simultaneously in the regions of n. raphe obscurus, n. raphe pallidus, and n. raphe magnus. Efferent phrenic nerve activity was recorded. Data were analyzed with auto- and cross-correlograms and cycle-triggered histograms. Spike trains of neurons were also tested for respiratory modulation by an analysis of variance with the use of a subjects-by-treatments experimental design. 3. Of 584 neurons studied, 99.1% were tonic, i.e., they had firing probabilities greater than zero in all phases of the respiratory cycle. Fifty-three percent of the neurons had respiratory-modulated firing rates; 223 cells were more active during the expiratory (E) interval; 88 neurons were inspiratory (I)-related. The remaining cells were classified as having no respiratory-related modulation of firing rate (NRR). 4. The spike trains of 210 of 1,078 pairs (19.5%) of brain stem midline neurons exhibited short-time scale correlations indicative of paucisynaptic interactions. Primary cross-correlogram features included 129 central peaks, 45 offset peaks, two central troughs, and 57 offset troughs. Twenty-two of the neuronal pairs analyzed had both offset peaks and troughs. Correlograms from an additional 35 pairs of neurons had multiple peaks and troughs without a significant primary feature. 5. The frequency of correlations for neuron pairs composed of cells with respiratory-modulated firing rates was as follows: E-E, 40/185 (22%); E-I, 23/111 (21%); E-NRR, 45/297 (15%); I-I, 11/25 (44%); and I-NRR, 13/104 (13%). Twenty-two percent of the NRR pairs (79/357) exhibited short-time scale correlations. 6. Thirty pairs of neurons included a cell with an antidromically identified axonal projection extending to at least the third cervical segment. The mean estimated conduction velocity based on the single-site stimulation method was 26.5 +/- 9.9 (SD) m/s. 7. The results provide evidence for inhibitory and excitatory functional connections between midline brain stem neurons. Data support the hypothesis that the respiratory-modulated discharge patterns of midline neurons are, at least in part, a consequence of the synaptic actions of other midline cells.(ABSTRACT TRUNCATED AT 400 WORDS)
Respiratory-related neural assemblies in the brain stem midline
Authors: Lindsey B. G. , Hernandez Y. M. , Morris K. F. , Shannon R. , Gerstein G. L.
Published: December 2017

1. The initial objective of this study was to determine whether respiratory-related neural assemblies exist in the brain stem midline. A second goal was to seek evidence for concurrent relationships among the neurons that could generate the detected synchrony. 2. Experiments were conducted on anesthetized, paralyzed, bilaterally vagotomized, artificially ventilated cats. Spike trains of four to nine simultaneously monitored neurons were recorded in the regions of n. raphe obscurus-n. raphe pallidus and n. raphe magnus. 3. Data were analyzed with cycle-triggered histograms, cross-correlograms, snowflakes, and the gravitational representation. A significance test for the gravity method was developed and tested with spike trains generated by simulated networks with defined connections. 4. Ninety-three groups of neurons from 24 cats were studied. Thirty-nine groups from 19 cats included neurons that discharged synchronously on a millisecond time scale; less than or equal to 19 pairs of synchronously discharging neurons were found in one group. Twenty-seven of these 39 groups included neurons that had respiratory-modulated firing rates and discharged synchronously with other group members. Synchronous assemblies included cells monitored at rostral or caudal locations, or both. 5. Six classes of relationships were inferred from groups of neurons with multiple correlations: divergence (n = 11); convergence (n = 7); connections with opposite actions between neurons (n = 5); projections of synchronous neurons to separate targets (n = 5); projections to one neuron in a synchronous group (n = 4); and projections between two synchronous groups with common elements (n = 6). 6. The results document the existence of assemblies of synchronously discharging respiratory-related neurons in midline regions of the brain stem and suggest that divergent excitatory and inhibitory connections within the midline participate in the generation of that synchrony. Links between assemblies may operate to stabilize their collective activity in a particular state.
Knee joint input into the peripheral region of the ventral posterior lateral nucleus of cat thalamus
Authors: Hutchison W. D. , Luhn M. A. , Schmidt R. F.
Published: December 2017

1. Experiments were carried out in chloralose-anesthetized cats to study the responses of neurons in the lateral thalamus to excitation of afferent fibres from the knee joint. 2. Single- and multi-unit recordings were made with tungsten electrodes in dorsoventral penetrations through the ventral posterior lateral nucleus (VPL) during electrical stimulation of the medial articular nerve (MAN) of the cat's knee joint at an intensity sufficient to excite slowly conducting unmyelinated fibers. The locations of the recording sites were verified by recovering electrolytic lesion sites in histological sections (Nissl and cytochrome oxidase staining). 3. The average earliest latency for excitation of thalamic responses was 19.1 +/- 8.5 (SD) ms (n = 50). The threshold for excitation of most thalamic units was found to correspond to peripheral joint afferent fibers of the A-delta group. 4. The majority of neurons responding to MAN stimulation were found to be dorsal or ventral to the low-threshold cutaneous hindlimb region of the lateral division of the VPL (stereotaxic coordinates: AP 9.0-11.5; ML 7.0-9.5). In the ventral periphery of the VPL, most neurons responding to MAN stimulation (11/14) were wide dynamic range (WDR) with a discrete cutaneous receptive field on the hindpaw digits. Six WDR neurons were found dorsal to the hindlimb VPL with a convergent receptive field on the hindlimb (but not hindpaw digits). No nociceptive-specific knee joint units were found. 5. Other neurons were found dorsal to the hindlimb VPL with large receptive fields often encompassing the whole contralateral leg, including skin and deep hindlimb structures, possibly in a region described as the dorsal portion of the posterior complex (POd). Some neurons were found with no receptive field. 6. This study provides the first observations on the responses of lateral thalamic neurons to stimulation of the MAN of the cat knee joint. These results demonstrate a central pathway conveying impulses from specific deep joint afferents of the MAN to the peripheral region of the VPL and overlying region known as the POd, regions implicated in the transmission of nociceptive information.
Quantitative analysis of static strain sensitivity in human mechanoreceptors from hairy skin
Authors: Edin B. B.
Published: December 2017

1. Microelectrode recordings from 15 slowly adapting (SA) cutaneous mechanoreceptor afferents originating in hairy skin were obtained from the radial nerve in humans. 2. Controlled skin stretch was applied to the back of the hand that encompassed the physiological range of skin stretch during movements at the metacarpophalangeal (MCP) joints. 3. Both SA Group I and II afferents showed exquisite dynamic and static sensitivity to skin stretch. The median static strain sensitivity was 1.0 imp.s-1 per percent skin stretch for SAI units and 1.8 for SAII units. 4. Translated into sensitivity to movements at the MCP joint, both SAI and SAII afferents in the skin of the back of the hand displayed a positional sensitivity that was comparable with that reported for muscle spindle afferents. 5. These data give quantitative support to suggestions that skin receptors in the human hairy skin provide information on nearby joint configurations and therefore may play a specific role in proprioception, kinesthesia, and motor control.
Hypoglossal neural activity during licking and swallowing in the awake rat
Authors: Travers J. B. , Jackson L. M.
Published: December 2017

1. Thirty-five neurons in the hypoglossal nucleus (mXII) of the rat were characterized during licking and swallowing in response to fluid stimulation in an awake, freely moving preparation. Simultaneously recorded electromyographic (EMG) recordings from a subset of oropharyngeal muscles were obtained to delineate both the lick cycle and the occurrence of swallows. Most mXII neurons discharged with rhythmic bursts in phase with licking. Twenty-six of the 35 mXII neurons had bimodal interspike interval (ISI) histograms, reflecting rhythmic bursts and the absence of spontaneous activity. Three mXII cells with unimodal ISI histograms were rhythmically active during licking but had some spontaneous activity. Of the remaining six cells with unimodal ISI histograms, five had nonbursting modes of activity. 2. Phase relationships between neural and EMG activity during licking were determined by cross-correlation and compared with distributions of cross-correlations between lingual and masticatory EMG activity. A bimodal distribution of cross-correlations was obtained by cross-correlating EMG activity between lingual protrudor muscles [genioglossus (GG) or geniohyoid (GH)] and masticatory jaw-opener activity [anterior digastric (AD)] and cross-correlating lingual retractor activity [styloglossus (STY)] with anterior digastric EMG. A similar bimodal distribution of cross-correlations obtained between mXII neuron activity and AD contractions suggested that the majority of mXII neurons (30/35) could be classified as protrudor- or retractor-related. Neurons classified as protrudor-related cells were located ventrally in mXII; cells classified as retractor-related were more dorsally located, consistent with anatomic and physiological descriptions of the myotopic organization of mXII. 3. Ten mXII protrudor-related neurons responded with a mean of 4.9 +/- 2.2 (SD) action potentials per lick cycle and preceded the peak jaw-opening phase of licking by a mean of 22.3 ms. In contrast, the activity of 20 retractor-related mXII neurons lagged the jaw-opening phase of licking by a mean of 55.9 ms, with a mean of 5.5 +/- 3.4 (SD) action potentials occurring per lick cycle. Five other mXII neurons exhibited nonrhythmic activity during licking and could not be classified as protrudor- or retractor-related on the basis of cross-correlations with the AD. 4. The occurrence of a swallow decreased the licking frequency by 21%, corresponding to an increase of approximately 43 ms in the period between AD contractions.(ABSTRACT TRUNCATED AT 400 WORDS)
Recurrent collaterals of motoneurons projecting to distal muscles in the cat hindlimb
Authors: McCurdy M. L. , Hamm T. M.
Published: December 2017

1. Recurrent collaterals of motoneurons innervating muscles that have a role in control of the hindlimb digits were studied with neuroanatomic tracing methods to determine whether these motoneurons have simple recurrent collateral arbors in comparison with those of hip, knee, and ankle muscles. 2. Motoneurons innervating the hindlimb muscles plantaris (Pln), flexor hallucis longus (FHL), or flexor digitorum longus (FDL) were injected with 10% horseradish peroxidase. Recurrent collaterals were reconstructed from serial transverse sections. 3. No recurrent collaterals were observed in a sample of 10 FDL motoneurons. 4. FHL motoneurons had simple recurrent collateral arbors as assessed by number of first-order collaterals, number of collateral swellings, number of end branches, and the highest-order branch of individual collateral trees. Recurrent collateral arbors of Pln motoneurons were more complex than those of FHL motoneurons. Pln and FHL recurrent collateral arbors were less complex than those described for gastrocnemius-soleus, anterior tibial, and posterior biceps motoneurons. 5. These anatomic findings correspond well with electrophysiological results indicating that the recurrent inhibition produced by FHL motoneurons is weak and that FDL motoneurons do not produce recurrent inhibition. In addition, Pln motoneurons are reported to produce stronger recurrent inhibition than FHL motoneurons in many motor pools. 6. Consideration of these results with respect to the mechanical actions and patterns of motor activity observed in FDL, FHL, and Pln suggests that the complexity of recurrent collaterals of a motoneuron pool and the extent of its contribution to recurrent inhibition diminish with its involvement in the individualized control of the digits.
Reflex responses in active muscles elicited by stimulation of low-threshold afferents from the human foot
Authors: Aniss A. M. , Gandevia S. C. , Burke D.
Published: December 2017

1. Reflex responses were elicited in muscles that act at the ankle by electrical stimulation of low-threshold afferents from the foot in human subjects who were reclining supine. During steady voluntary contractions, stimulus trains (5 pulses at 300 Hz) were delivered at two intensities to the sural nerve (1.2-4.0 times sensory threshold) or to the posterior tibial nerve (1.1-3.0 times motor threshold for the intrinsic muscles of the foot). Electromyographic (EMG) recordings were made from tibialis anterior (TA), peroneus longus (PL), soleus (SOL), medial gastrocnemius (MG), and lateral gastrocnemius (LG) muscles by the use of intramuscular wire electrodes. 2. As assessed by averages of rectified EMG, stimulation of the sural or posterior tibial nerves at nonpainful levels evoked a complex oscillation with onset latencies as early as 40 ms and lasting up to 200 ms in each muscle. The most common initial responses in TA were a decrease in EMG activity at an onset latency of 54 ms for sural stimuli, and an increase at an onset latency of 49 ms for posterior tibial stimuli. The response of PL to stimulation of the two nerves began with a strong facilitation of 44 ms (sural) and 49 ms (posterior tibial). With SOL, stimulation of both nerves produced early inhibition beginning at 45 and 50 ms, respectively. With both LG and MG, sural stimuli produced an early facilitation at 52-53 ms. However, posterior tibial stimuli produced different initial responses in these two muscles: facilitation in LG at 50 ms and inhibition in MG at 51 ms. 3. Perstimulus time histograms of the discharge of 61 single motor units revealed generally similar reflex responses as in multiunit EMG. However, different reflex components were not equally apparent in the responses of different single motor units: an individual motor unit could respond slightly differently with a change in stimulus intensity or background contraction level. The multiunit EMG record represents a global average that does not necessarily depict the precise pattern of all motor units contributing to the average. 4. When subjects stood erect without support and with eyes closed, reflex patterns were seen only in active muscles, and the patterns were similar to those in the reclining posture. 5. It is concluded that afferents from mechanoreceptors in the sole of the foot have multisynaptic reflex connections with the motoneuron pools innervating the muscles that act at the ankle. When the muscles are active in standing or walking, cutaneous feedback may play a role in modulating motoneuron output and thereby contribute to stabilization of stance and gait.
Role of monkey midbrain near-response neurons in phoria adaptation
Authors: Morley J. W. , Judge S. J. , Lindsey J. W.
Published: December 2017

1. One striking characteristic of the way in which accommodation and convergence of the eyes are organized is that although the two responses are usually tightly coupled, a brief period of binocular viewing through prisms that require extra convergence brings about a persistent, adaptive alteration in the relationship between the two responses: the vergence during monocular viewing of a target at a given distance is biased in a convergent direction. We sought to discover the role of the near-response neurons we have previously described in the monkey midbrain in such phoria adaptation. 2. Phoria adaptation was produced in two monkeys by having them view binocularly stereoscopic targets under conditions that mimicked prism viewing, i.e., the mirrors of the stereoscope were set so as to require more convergence than that associated with a real target at the same distance as the images seen in the stereoscope. The activity of 57 near-response neurons located dorsally and dorsolaterally to the oculomotor nucleus was recorded before and after adaptation while the monkeys monocularly viewed targets at a range of distances. 3. Comparison of a neuron's response in normal binocular viewing with the response when the accommodation and vergence stimuli were in conflict allowed us to distinguish 24 neurons that behaved as though they were related exclusively to the vergence response. 5 neurons that behaved as though they were exclusively related to the accommodation response, and 12 neurons whose firing was not so simply related to either response. We were unable to classify the remaining 16 near-response cells by this method. 4. In accommodation-related neurons, the relationship between firing rate and accommodation did not alter, or only altered slightly, when the animal's phoria was adapted. 5. The relationship between firing rate and vergence was unaltered by phoria adaptation in only a small proportion of vergence-related neurons, showing that most neurons do not carry the entire signal responsible for phoria adaptation. On the other hand, in the majority of vergence-related neurons the relationship between firing rate and accommodation was altered by phoria adaptation, showing that most neurons do carry part of the phoria adaptation signal. 6. The implication is that the increase in vergence observed after adaptation is mediated at more than one site. A proportion of the phoria adaptation signal is present at the level of the midbrain vergence-related neurons, with the remainder of the signal being added later, presumably at the motoneurons.
APB suppresses synaptic input to retinal horizontal cells in fish: a direct action on horizontal cells modulated by intracellular pH
Authors: Takahashi K. , Copenhagen D. R.
Published: December 2017

1. Membrane potentials and cone-driven light responses were recorded from the H1-type horizontal cells in isolated retinas. Membrane potentials and intracellular pH were recorded also in enzymatically dissociated solitary horizontal cells. 2. In isolated retinas the glutamate analogue 2-amino-4-phosphonobutyrate (APB) hyperpolarized horizontal cells and reduced their light responses in a dose-dependent manner (5-200 microM). 3. The action of APB depended on the formulation of the saline; APB was effective in L-15 saline buffered with N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES) but not in a commonly used, nominally CO2-free bicarbonate/Tris-buffered saline. 4. The major factor controlling the potency of APB was intracellular pH. APB was ineffective during retinal perfusion with NH4Cl-containing or CO2-free bicarbonate saline, both of which are known to alkalinize cells. In contrast, APB was effective in salines formulated to acidify the retinal neurons. These included both HEPES and Tris-buffered salines containing a weak acid and bicarbonate/Tris-buffered saline gassed with CO2. 5. APB reduced the size of glutamate-evoked depolarizations in solitary horizontal cells but had no independent action in the absence of glutamate. This reduction of glutamate-induced depolarization was observed in salines formulated to block voltage-dependent calcium and potassium currents. 6. The magnitude of APB's antagonistic action on solitary horizontal cells increased in a dose-dependent manner from 10 to 200 microM. The antagonism was increased by intracellular acidification and was reduced or eliminated by alkalinization. 7. We conclude that APB can reduce glutamate-evoked and, by inference, the photoreceptor neurotransmitter-evoked depolarization of horizontal cells by acting directly on the horizontal cells. This effect of APB is modulated by intracellular pH.
Effects of the GABA uptake inhibitor tiagabine on inhibitory synaptic potentials in rat hippocampal slice cultures
Authors: Thompson S. M. , Gahwiler B. H.
Published: December 2017

1. The effects of the gamma-aminobutyric acid (GABA) uptake blocker tiagabine on inhibitory synaptic potentials (IPSPs) were examined with microelectrode and whole-cell recording from CA3 pyramidal cells in rat hippocampal slice cultures. 2. Tiagabine (10-25 microM) greatly prolonged the duration of monosynaptic IPSPs elicited in the presence of excitatory amino acid antagonists but had no effect on their amplitude. Part of the prolonged time course resulted from a GABAB receptor-mediated component that was not detectable under control conditions. 3. The mean decay time constant of the underlying GABAA receptor-mediated synaptic current was increased from 16 to 250 ms. Spontaneous miniature IPSPs recorded with whole-cell clamp were unaffected by tiagabine. Pentobarbital sodium, in contrast, increased the decay time constant of both evoked and spontaneous GABAA-mediated currents. 4. Tiagabine (25 microM) inhibited spontaneous and evoked epileptiform bursting induced by increasing the extracellular potassium concentration to 8 mM. 5. We conclude that GABA uptake plays a significant role in determining the time course of evoked IPSPs and also limits the likelihood that GABAB receptors are activated.
Neural responses to visual texture patterns in middle temporal area of the macaque monkey
Authors: Olavarria J. F. , DeYoe E. A. , Knierim J. J. , Fox J. M. , van Essen D. C.
Published: December 2017

1. We studied how neurons in the middle temporal visual area (MT) of anesthetized macaque monkeys responded to textured and nontextured visual stimuli. Stimuli contained a central rectangular ,figure- that was either uniform in luminance or consisted of an array of oriented line segments. The figure moved at constant velocity in one of four orthogonal directions. The region surrounding the figure was either uniform in luminance or contained a texture array (whose elements were identical or orthogonal in orientation to those of the figure), and it either was stationary or moved along with the figure. 2. A textured figure moving across a stationary textured background (,texture bar- stimulus) often elicited vigorous neural responses, but, on average, the responses to texture bars were significantly smaller than to solid (uniform luminance) bars. 3. Many cells showed direction selectivity that was similar for both texture bars and solid bars. However, on average, the direction selectivity measured when texture bars were used was significantly smaller than that for solid bars, and many cells lost significant direction selectivity altogether. The reduction in direction selectivity for texture bars generally reflected a combination of decreased responsiveness in the preferred direction and increased responsiveness in the null (opposite to preferred) direction. 4. Responses to a texture bar in the absence of a texture background (,texture bar alone-) were very similar to the responses to solid bars both in the magnitude of response and in the degree of direction selectivity. Conversely, adding a static texture surround to a moving solid bar reduced direction selectivity on average without a reduction in response magnitude. These results indicate that the static surround is largely responsible for the differences in direction selectivity for texture bars versus solid bars. 5. In the majority of MT cells studied, responses to a moving texture bar were largely independent of whether the elements in the bar were of the same orientation as the background elements or of the orthogonal orientation. Thus, for the class of stimuli we used, orientation contrast does not markedly affect the responses of MT neurons to moving texture patterns. 6. The optimum figure length and the shapes of the length tuning curves determined with the use of solid bars and texture bars differed significantly in most of the cells examined. Thus neurons in MT are not simply selective for a particular figure shape independent of whatever cues are used to delineate the figure.
Shunting of excitatory input to dentate gyrus granule cells by a depolarizing GABAA receptor-mediated postsynaptic conductance
Authors: Staley K. J. , Mody I.
Published: December 2017

1. Stimulation of the perforant path in the outer molecular layer of the adult rat dentate gyrus produced a depolarizing post-synaptic potential (DPSP) in granule cells when recorded using whole-cell techniques in the standard hippocampal slice preparation at 34 degrees C. The postsynaptic currents (PSCs) contributing to the DPSP were analyzed using specific receptor antagonists in current- and voltage-clamp recordings. 2. The DPSP reversal potential was dependent on the intracellular chloride concentration, and the amplitude of the DPSP was increased 55% after perfusion of the gamma-aminobutyric acid-A (GABAA) receptor antagonist bicuculline methiodide (BMI). The GABAA receptor-mediated PSC reversed at -66 mV, which was 19 mV positive to the resting membrane potential (-85 mV) but hyperpolarized relative to action potential threshold. At -35 mV, the GABAA PSC had a latency to peak of 12.9 ms after the stimulus and decayed monoexponentially with an average time constant of 23.4 ms. 3. The component of the PSC blocked by the Quis/AMPA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) had a latency to peak of 7.1 ms and decayed monoexponentially with a time constant of 9.9 ms at -35 mV. The N-methyl-D-aspartate (NMDA) receptor-mediated PSC, which was blocked by D-amino-5-phosphonovaleric acid (D-AP5), had a waveform that was similar to the GABAA PSC: the latency to peak was 16 ms and the decay was monoexponential with a time constant of 24.5 ms at -35 mV. 4. The ratio of the peak PSCs mediated by GABAA, Quis/AMPA, and NMDA receptors measured at -35 mV with cesium gluconate electrode solutions was 1:0.2:0.1. This ratio was essentially constant over the range of stimulus intensities that produced compound PSC amplitudes of 80-400 pA. 5. Measured at its reversal potential, the GABAA receptor-mediated postsynaptic conductance (GGABA-A) decreased the peak DPSP amplitude by 35%, shunted 50% of the charge transferred to the soma by the excitatory PSC, and completely inhibited the NMDA receptor-mediated component of the DPSP. 6. Simultaneous stimulation of presynaptic fibers from both the perforant path and interneurons results in a large depolarizing GGABA-A that inhibits the granule cell by shunting the excitatory PSCs. As predicted by models of shunting, the similar kinetics of the GABAA and NMDA PSCs leads to particularly effective inhibition of the NMDA PSC. The more rapid Quis/AMPA PSC is less affected by the GGABA-A, so that granule cell excitation under these conditions is primarily due to Quis/AMPA receptor activation.
Characterization of voltage-dependent calcium currents in mouse motoneurons
Authors: Mynlieff M. , Beam K. G.
Published: December 2017

1. Calcium channel currents were measured with the whole-cell patch clamp technique in cultured, identified mouse motoneurons. Three components of current were operationally defined on the basis of voltage dependence, kinetics, and pharmacology. 2. Test potentials to -50 mV or greater (10 mM external Ca2+) elicited a low-voltage activated T-type current that was transient (decaying to baseline in less than 200 ms) and had a relatively slow time to peak (20-50 ms). A 1-s prepulse to -45 mV produced approximately half-maximal inactivation of this T current. 3. Two high-voltage activated (HVA) components of current (1 transient and 1 sustained) were activated by test potentials to -20 mV or greater (10 mM external Ca2+). A 1-s prepulse to -35 mV produced approximately half-maximal inactivation of the transient component without affecting the sustained component. 4. When Ba2+ was substituted for Ca2+ as the charge carrier, activation of the HVA components was shifted in the hyperpolarizing direction, and the relative amplitude of the transient HVA component was reduced. 5. Amiloride (1-2 mM) caused a reversible, partial block of the T current without affecting the HVA components. 6. The dihydropyridine agonist isopropyl 4-(2,1,3-benzoxadiazol-4-yl)-1,4-dihydro-2,6-dimethyl-5-nitro-3- pyridine-carboxylate [(+)-SDZ 202-791, 100 nM-1 microM)] shifted the activation of the sustained component of HVA current to more negative potentials and increased its maximal amplitude. Additionally, (+)-SDZ 202-791 caused the appearance of a slowed component of tail current.(ABSTRACT TRUNCATED AT 250 WORDS)
Contribution of Ca and Ca-activated Cl channels to regenerative depolarization and membrane bistability of cone photoreceptors
Authors: Barnes S. , Deschenes M. C.
Published: December 2017

1. Cone photoreceptors in several vertebrate species generate Ca-dependent regenerative depolarizations (e.g., Ca spikes lasting up to 2 s) in response to current injection or surround illumination and may remain in a state of prolonged depolarization (e.g., a permanent plateau near 0 mV) after these stimuli. This paper, while confirming the role of Ca channels in the regenerative depolarization, demonstrates that Ca-activated Cl channels either enhance or hinder prolonged depolarization, depending on the value of the chloride equilibrium potential (ECl). 2. Current- and voltage-clamp recordings obtained with the whole-cell patch-clamp technique were compared in 158 isolated tiger salamander cones to determine the contribution of specific ion channel types to the two forms of depolarizing response. Cones dialyzed with CsCl or KCl intracellular solution (such that ECl = 0 mV) that had sustained negative slope regions in their current-voltage (I-V) relations recorded under voltage clamp, were, under current clamp, bistable with respect to their resting potential. Injection of approximately 20-pA steps of depolarizing current resulted in transitions from the negative stable membrane potential (near -50 mV) to a long lasting plateau around 0 mV. Injection of 200–300 pA of hyperpolarizing current could then force a return to the negative stable resting potential, although once repolarization occurred, current injection had to be reduced or terminated to prevent damaging hyperpolarization of the cell. 3. The inward currents accounting for the negative slope region of the I-V relation were carried in Ca and Ca-activated Cl channels. Specific block of Ca-activated Cl current (ICl(Ca)) by 100 microM niflumic acid (NFA) eliminated the prolonged depolarization, even though the negative slope conductance region in the I-V persisted and the cone could still produce the briefer Ca-dependent regenerative depolarizations. Application of 100 microM Cd2+ blocked both forms of depolarization. 4. Substitution of Ba2+, which among other actions did not activate ICl(Ca), usually supported regenerative depolarizations of shortened duration, demonstrating the role of Ca channels in the initial phase of these responses. 5. A difference was observed in the regenerative depolarization when ECl was shifted away from 0 mV, where it had been in the experiments described above. With ECl set to -40 or -60 mV by reduction of [Cl-] in the pipette, steady-state membrane bistability was eliminated and prolonged depolarization did not occur. Under these conditions, application of the Cl channel blocker NFA showed that ICl(Ca) contributes to membrane hyperpolarization.(ABSTRACT TRUNCATED AT 400 WORDS)