bluuebunny/crossref_metadata_2025 huggingface dataset:
Response patterns and postspike effects of peripheral afferents in dorsal root ganglia of behaving monkeys
Authors: Flament D. , Fortier P. A. , Fetz E. E.
Published: December 2017

1. The activity of single afferent units was recorded in cervical dorsal root ganglia (DRG) in two macaque monkeys as they generated alternating flexion and extension torques about the wrist during a step-tracking task. During these isometric and auxotonic muscle contractions, electromyographic (EMG) activity was recorded with electrode pairs in up to 12 independent forearm muscles. Spike-triggered averages (STAs) of rectified EMG activity were used to identify afferents that were associated with correlated facilitation of active muscles. 2. Our aim was to find peripheral afferents producing postspike effects in muscles and to compare their properties with those of corticomotoneuronal (CM) and rubromotoneuronal (RM) cells previously obtained under identical behavioral conditions. We documented the timing, magnitude and distribution of their postspike facilitation (PSF) of forearm muscles and investigated the response properties of task-related units. 3. Of 125 afferent units tested with STAs, 68 showed PSF of EMG activity in at least one muscle. Fifty-nine DRG units provided sufficiently long recordings to generate averages with greater than or equal to 2,000 triggers, the minimum number considered to demonstrate reliable effects. Of these 59 units, 29 (49%) were associated with facilitation of forearm muscle activity. 4. Many STAs showed a gradual increase in EMG activity starting before or near the afferent trigger spike; often superimposed on this broad facilitation was a sharply rising PSF starting at a longer latency. The earliest poststimulus facilitation evoked by single microstimuli delivered in DRG occurred in stimulus-triggered averages at a latency of 3.5 ms. In STAs the broad facilitation beginning at latencies shorter than the responses to electrical stimulation was attributed to synchronous discharges in other afferent units. The sharper postspike EMG increases occurring with latencies of greater than or equal to 3.5 ms were identified as PSF produced by the afferent. The PSF parameters documented in this study were measured after subtracting the effects of synchrony facilitation. 5. PSF of EMG activity began at a mean latency of 5.8 +/- 0.3 (SE) ms and peaked at a mean latency of 7.5 +/- 0.3 (SE) ms. In previous studies, the PSFs from CM and RM cells had mean onset latencies of 6.3 and 5.6 ms, respectively, and mean peak latencies of 10.2 and 9.1 ms. 6. A measure of the PSF amplitude is the mean percent increase (MPI), defined as the increase of the PSF above its base measured as a percentage of the prespike baseline mean.(ABSTRACT TRUNCATED AT 400 WORDS)
Dynamic reconfiguration of brain stem neural assemblies: respiratory phase-dependent synchrony versus modulation of firing rates
Authors: Lindsey B. G. , Hernandez Y. M. , Morris K. F. , Shannon R. , Gerstein G. L.
Published: December 2017

1. The objective of this work was to determine whether configurations of midline brain stem neural assemblies change during the respiratory cycle. 2. Spike trains of several single neurons were recorded simultaneously in anesthetized, paralyzed, bilaterally vagotomized, artificially ventilated cats. Data were analyzed with cross-correlational and gravity methods. 3. Sequential samples from each of eight groups of neurons known to contain synchronously discharging neurons exhibited temporal variations in that synchrony. 4. Gravity analysis of short (less than 200-s) samples of spike train data revealed 20 pairs of clustered particles that were not predicted from cross-correlation analysis of the parent data sets (greater than 20 min). 5. Twenty-nine groups of three to eight simultaneously monitored neurons, each with at least two synchronously discharging neurons, were analyzed for evidence of respiratory phase-dependent modulation of that coordinated activity. Spikes from successive interleaved inspiratory and expiratory intervals were analyzed separately. 6. Neurons pairs in 11 groups were more synchronous during the inspiratory interval; six groups had pairs that were more synchronous during the expiratory period. In two groups, different pairs were synchronous in different respiratory phases. In 11 of the 26 pairs that exhibited phase-dependent differences in synchrony, neither neuron had a respiratory-modulated firing rate as judged by either the cycle-triggered histogram or an analysis of variance of their firing rates. 7. Configurations of respiratory-related brain stem neural networks changed with time and the phases of breathing. Neurons with no apparent respiratory modulation of their individual firing rates collectively exhibited respiratory phase-dependent modulation of their impulse synchrony.(ABSTRACT TRUNCATED AT 250 WORDS)
Neuronal responses to static texture patterns in area V1 of the alert macaque monkey
Authors: Knierim J. J. , van Essen D. C.
Published: December 2017

1. We recorded responses from neurons in area V1 of the alert macaque monkey to textured patterns modeled after stimuli used in psychophysical experiments of pop-out. Neuronal responses to a single oriented line segment placed within a cell's classical receptive field (CRF) were compared with responses in which the center element was surrounded by rings of elements placed entirely outside the CRF. The orientations of the surround elements either matched the center element, were orthogonal to it, or were random. 2. The addition of the textured surround tended to suppress the response to the center element by an average of 34%. Overall, almost 80% of the 122 cells analyzed in detail were significantly suppressed by at least one of the texture surrounds. 3. Cells tended to respond more strongly to a stimulus in which there was a contrast in orientation between the center and surround than to a stimulus lacking such contrast. The average difference was 9% of the response to the optimally oriented center element alone. For the 32% of the cells showing a statistically significant orientation contrast effect, the average difference was 28%. 4. Both the general suppression and orientation contrast effects originated from surround regions at the ends of the center bar as well as regions along the sides of the center bar. 5. The amount of suppression induced by the texture surround decreased as the density of the texture elements decreased. 6. Both the general suppression and the orientation contrast effects appeared early in the population response to the stimuli. The general suppression effect took approximately 7 ms to develop, whereas the orientation contrast effect took 18-20 ms to develop. 7. These results are consistent with a possible functional role of V1 cells in the mediation of perceptual pop-out and in the segregation of texture borders. Possible anatomic substrates of the effects are discussed.
Spontaneous nystagmus and gaze-holding ability in monkeys after intravitreal picrotoxin injections
Authors: Ariel M. , Tusa R. J.
Published: December 2017

1. Eye movements were measured in three rhesus monkeys after monocular intravitreal injections of picrotoxin, a gamma-aminobutyric acid (GABA) antagonist. The effects of this drug were tested when the animals were in a completely dark room, when they performed a smooth pursuit task, and when they viewed either a stationary pattern or a full-field optokinetic pattern rotating horizontally. 2. Between 15 and 20 min after the injection, a sustained conjugate spontaneous nystagmus developed in the dark, with the slow-phase movement in the temporal-to-nasal direction with respect to the injected eye. Peak slow-phase velocity ranged from 15 to 45 degrees/s. The nystagmus persisted for at least 1 h but stopped by the next day. 3. In a well-lit room, the nystagmus was completely suppressed, even during monocular viewing with the injected eye. When the lights were turned off, the slow-phase velocity of the spontaneous nystagmus slowly increased to a steady-state level within 70-120 s. 4. Horizontal smooth pursuit eye movements to a 1 degree target light moving in front of the animal +/- 20 degrees to either side of center of gaze at constant speeds were normal. Target speeds ranging from 15 to 60 degrees/s for both monocular and binocular viewing conditions were used. Binocular and monocular optokinetic nystagmus (OKN) to a full-field drum rotating at a constant velocity (5-90 degrees/s) were also normal. The initial pursuit and steady-state components of OKN were measured, as well as the velocity-storage component (optokinetic after nystagmus, OKAN).(ABSTRACT TRUNCATED AT 250 WORDS)
Effects of ganglionic satellite cells and NGF on the expression of nicotinic acetylcholine currents by rat sensory neurons
Authors: Mandelzys A. , Cooper E.
Published: December 2017

1. We have investigated two factors that affect the expression of nicotinic acetylcholine (ACh) currents on neonatal rat sensory neurons: an influence derived from ganglionic satellite cells, and nerve growth factor (NGF). 2. With the use of whole-cell patch-clamp techniques on rat nodose neurons, we have measured the proportion of neurons sensitive to ACh and have quantified their ACh current densities. The majority (60%) of nodose neurons from neonatal animals do not express nicotinic acetylcholine receptors (nAChRs); the remaining 40% had ACh current densities that ranged from 0.4 to 93 pA/pF. Furthermore, neither the proportion nor the ACh current densities change over the first two postnatal weeks in vivo. 3. The expression of ACh currents by these neurons in vivo is controlled, in part, by an influence from the ganglionic satellite cells: culturing neurons in the absence of other cell types results in an increase in the proportion of ACh-sensitive neurons, whereas coculturing neurons with their satellite cells maintains functional nAChR expression in its in vivo state. Furthermore, satellite cells are not required continually, as a brief exposure to this influence, either in vivo or in culture, is sufficient to exert its effect on functional nAChR expression. 4. On removal of this satellite cell influence, the neurons respond to NGF treatment by increasing their ACh current densities: the median ACh current density for neurons grown for 2-3 wk with NGF was 32.5 pA/pF, whereas, the median ACh current density for neurons cultured without NGF for the same time was 4.5 pA/pF.(ABSTRACT TRUNCATED AT 250 WORDS)
Ionic currents of morphologically distinct peptidergic neurons in defined culture
Authors: Meyers D. E. , Graf R. A. , Cooke I. M.
Published: December 2017

1. The X-organ sinus gland is a major peptidergic neurosecretory system in Crustacea, analogous to the vertebrate hypothalamoneurohypophyseal system. Neuronal somata isolated from the crab (Cardisoma carnifex) X-organ and maintained in primary culture in unconditioned, fully defined medium show immediate regenerative outgrowth. Outgrowth occurring as broad lamellipodia ("veiled") distinguishes neurons consistently showing crustacean hyperglycemic hormone immunoreactivity. Neurons that are immunoreactive against molt-inhibiting hormone and red pigment concentrating hormone antisera give rise to branched neurites ("branched"). 2. The whole-cell variation of the patch-clamp technique was used to study the electrophysiology of these two cell types 24-48 h after plating. Under current clamp, only veiled neurons fired overshooting action potentials either spontaneously or in response to depolarization. 3. Under voltage clamp, net current was predominantly outward. When solutions that suppressed outward current were used, only veiled neurons showed significant inward current. These included a tetrodotoxin (TTX)-sensitive Na current and a slow (time to peak 6-10 ms at 0 mV) Cd-sensitive Ca current (ICa) that was activated at potentials less than -30 mV, was maximal at 0 to +20 mV, and did not reverse at potentials up to +60 mV. 4. In TTX, the form of the Ca current I(V) curve was unchanged by changes of holding potential between -40 and -80 mV, and 75-100% of ICa was available from -40 mV. 5. ICa inactivated slowly and incompletely. Analysis with two-pulse regimes suggested that both inactivation and facilitation mechanisms were present. 6. Outward current was examined in the presence and absence of 0.5 mM Cd2+ (1 microM TTX was always present in the external medium). Cd2+ ions slightly reduced the peak outward current, usually by less than 10% (Vc = -10 to +20 mV; Vh = -80 mV). All additional observations were in the presence of TTX and Cd2+. 7. Both cell types expressed a 4-aminopyridine (4-AP)-sensitive transient current, analogous to IA, and a slower-rising (minimum time to peak 20 ms), sustained current that was partially sensitive to tetraethylammonium, analogous to IK. 8. The mean Vh at which IA was half inactivated was -46 mV, and the mean time constant for removal of inactivation was 46 ms.(ABSTRACT TRUNCATED AT 400 WORDS)
Characterization of descending facilitation and inhibition of spinal nociceptive transmission from the nuclei reticularis gigantocellularis and gigantocellularis pars alpha in the rat
Authors: Zhuo M. , Gebhart G. F.
Published: December 2017

1. Descending influences produced by focal electrical stimulation in the nuclei reticularis gigantocellularis (NGC) and gigantocellularis pars alpha (NGC alpha) on spinal nociceptive transmission and the dorsoventral region of spinal white matter mediating stimulation-produced modulation were examined in pentobarbital sodium-anesthetized, paralyzed rats. Spinal units studied responded to mechanical stimuli and noxious heating (50 degrees C) of cutaneous receptive fields confined to the glabrous skin of the ipsilateral hind foot. Recording sites were located in laminae I-VI of the L3-L5 spinal segments. 2. Electrical stimulation in the NGC or NGC alpha produced both facilitation and inhibition of responses of spinal units to noxious heating of the skin. At 33 of 57 stimulation sites in the NGC and NGC alpha, electrical stimulation produced biphasic effects, facilitating responses at lesser intensities (5-25 microA) and inhibiting responses at greater intensities (50-100 microA). At 21 other sites in the NGC and NGC alpha, electrical stimulation (5-100 microA) only inhibited, and at 3 sites stimulation (5-100 microA) only facilitated responses of spinal units to noxious heating of the skin. 3. Electrical stimulation in the NGC or NGC alpha contralateral to the spinal recording site produced the same magnitude of facilitation/inhibition or inhibition of spinal nociceptive transmission as did stimulation in the ipsilateral NGC and NGC alpha. 4. The latencies to descending facilitation and inhibition of spinal nociceptive transmission from the NGC and NGC alpha were estimated by a cumulative sum technique to be 232 and 80 ms, respectively. 5. Responses of spinal units to graded heating (42-50 degrees C) of the skin exhibited positively accelerating stimulus-response functions (SRF) throughout the temperature range tested. Electrical stimulation at lesser, "facilitating" intensities produced a parallel, leftward shift of the SRF, whereas stimulation at greater, "inhibitory" intensities significantly decreased the slope of the SRF without affecting the threshold for response. 6. To determine whether activation of cell bodies in the NGC or NGC alpha were capable of replicating the effects of electrical stimulation, L-glutamate was microinjected into sites where electrical stimulation facilitated at lesser and inhibited at greater intensities the responses of spinal units to 50 degrees C heating of the skin. L-Glutamate (5 nmol) produced a rapid onset, short-lasting and reproducible facilitation of nociceptive transmission; glutamate microinjection into the same site at a greater dosage (50 nmol) inhibited responses of the same spinal units.(ABSTRACT TRUNCATED AT 400 WORDS)
Motor cortical activity during drawing movements: single-unit activity during sinusoid tracing
Authors: Schwartz A. B.
Published: December 2017

1. This study examines the neuronal activity of motor cortical cells associated with the production of arm trajectories during drawing movements. Three monkeys were trained to perform two tasks. The first task ("center----out" task) required the animal to move its arm in different directions from a center start position to one of eight targets spaced at equal angular intervals and equal distances from the origin. Movements to each target were in a constant direction, and the average rate of neuronal discharge with movements to different targets varied in a characteristic pattern. A cosine tuning function was used to map each cell's discharge rate to the direction of arm movement. This function spanned all movement directions, with a peak firing rate in the cell's preferred direction. 2. The second task ("tracing" task) required the animal to trace curved figures consisting of sine waves of different spatial frequencies and amplitudes. Both the speed and direction changed continuously throughout these movements. The cosine tuning function derived from the center----out task was used to model the activity of the cell during the tracing of sinusoids in the second task. Sinusoidal data were divided into 20-ms bins; instantaneous direction, speed, and discharge rate were analyzed bin by bin. This provided a way to compare directly the tuning parameters during a task with constant direction to a task where the direction varied continuously. 3. Movement direction as it changed during the tracing task was an important factor in the discharge pattern of cells that had discharge patterns that could be represented by the cosine tuning function. 4. The modulation of discharge rate during figure tracing depended on both the cell's preferred direction and the orientation of the figure. The activity of cells with preferred directions perpendicular to the axis of the sinusoidal figure was most modulated, whereas the activity of those cells with preferred directions aligned to the figure's axis was least modulated. 5. The cells with modulated activity tended to have firing rates that differed from the predicted cosine tuning function during the sinusoidal movements for those portions of the trajectory where the movement direction was in the cell's preferred direction. 6. Finger speed during figure tracing varied inversely with path curvature with the same relation that has been found during human drawing. To assess the relation of instantaneous speed to discharge rate, the component of the discharge pattern related to direction was subtracted from the total discharge.(ABSTRACT TRUNCATED AT 400 WORDS)
Analysis and modeling of the multisegmental coordination of shortening behavior in the medicinal leech. I. Motor output pattern
Authors: Wittenberg G. , Kristan W. B.
Published: December 2017

1. To understand how a multisegmental animal coordinates motor activity over more than one segment, we studied shortening behavior in the medicinal leech, in which several segments contract longitudinally in response to a moderately strong mechanical stimulus. 2. We first demonstrated that the neuronal activity responsible for shortening behavior occurred in semi-intact and isolated nerve cord preparations, and then characterized the responses of motor neurons in isolated preparations. The motor output during shortening was simultaneous excitation of motor neurons innervating dorsal longitudinal muscle and of motor neurons innervating ventral longitudinal muscle. 3. The stronger the stimulus, the more segments produced the shortening motor output, with the segments nearest the stimulus recruited first. 4. Although the shortening response was produced in several segments near the site of stimulation, it was never produced in the stimulated segment, where the local bending motor output pattern was produced. The motor pattern suggests that shortening, initially considered a very simple behavior, requires the involvement of at least few segmentally iterated interneurons.
Nociceptive neurons in area 24 of rabbit cingulate cortex
Authors: Sikes R. W. , Vogt B. A.
Published: December 2017

1. Single-unit responses in area 24 of cingulate cortex were examined in halothane-anesthetized rabbits during stimulation of the skin with transcutaneous electrical (TCES, 3-10 mA), mechanical (smooth or serrated forceps to the dorsal body surface or graded pressures of 100-1,500 g to the stabilized ear) and thermal (> 25 degrees C) stimulation. 2. Of 542 units tested in cingulate cortex, 150 responded to noxious TCES (> or = 6 mA), 93 of 221 units tested responded to noxious mechanical (serrated forceps) and 9 of 47 units tested responded to noxious heat (> 43 degrees C) stimuli. Twenty-five percent of the units that responded to noxious mechanical stimuli also responded to noxious heat stimuli. The only innocuous stimulus that evoked activity in cingulate cortex was a "tap" to the skin and this was effective for 11 of 14 tested units. 3. In 74 units that produced excitatory responses to TCES of the contralateral ear, response latency was 166 +/- 11.3 (SE) ms and response duration was 519 +/- 52.1 ms. 4. Twenty of the 150 units that responded to noxious TCES were initially inhibited. These responses were usually < 1 s in duration (17 of 20 units), whereas responses in the other 3 lasted for over 20 s. 5. Most units had broad receptive fields, because noxious mechanical stimuli anywhere on the dorsal surface of the rabbits, including the face and ears, evoked responses. A small number of units for which the entire body surface was tested (3 of 15 units) had receptive fields limited to the ears, rostral back, and forepaws. 6. Fifteen of 33 units tested had no preferential responses to noxious TCES of the ipsilateral and contralateral ears. Of the remaining units, 10 had a greater response to contralateral and 8 had a greater response to ipsilateral stimuli. 7. The locations of 186 units were histologically verified. Most nociceptive cingulate units were in dorsal area 24b in layers III (n = 35), II (n = 13), or V (n = 9). 8. Cortical knifecut lesions were made in five rabbits to determine if the responses in area 24 were dependent on lateral or posterior cortical inputs. These lesions did not alter the percentage of units driven by noxious stimuli nor response latency. 9. Injections of lidocaine were made into medial parts of the thalamus in six animals and injection and recording sites analyzed histologically.(ABSTRACT TRUNCATED AT 400 WORDS)
Development of glutamate and NMDA sensitivity of neurons within the cochlear nuclear complex of kittens
Authors: Walsh E. J. , McGee J. , Fitzakerley J. L.
Published: December 2017

1. The effects of glutamate, N-methyl-D-aspartate (NMDA), and NMDA receptor antagonists, D-alpha-aminoadipate (D alpha AA) and 2-amino-5-phosphonovalerate (APV), microionophoretically applied onto neurons in the caudal divisions (posteroventral and dorsal subnuclei) of the cochlear nuclear complex (CN), were investigated during postnatal development in kittens with the use of extracellular techniques. From birth through postnatal day 7, microionophoretically applied glutamate elevated the acoustically evoked discharge rates of nearly 80% of neurons studied. Although fewer neurons were studied with the use of NMDA, approximately 65% of these responded to this glutamatergic agonist, and no developmental changes in the percentage of responsive neurons were observed. The actions of NMDA antagonists were studied in a relatively small number of neurons, and results support the supposition that glutamate, or a glutamate-like substance, acts as a CN neurotransmitter throughout postnatal life. 2. Approximately 64% of CN neurons encountered among neonatal animals were unresponsive to acoustic stimulation, even at the highest output levels available (> 120 dB SPL). That percentage declined monotonically during the next three postnatal days, such that approximately 23% of neurons encountered were unresponsive to acoustic stimulation on the third day. Essentially all encountered neurons were responsive to acoustic stimulation by the middle of the second postnatal week. Under conditions of simultaneous glutamate and acoustic stimulation, neurons in this general class of “acoustically unresponsive” neurons segregated into two groups. Glutamate increased spontaneous discharge rate in 45% of the neurons studied, however, these units remained acoustically unresponsive during combined sound and excitatory amino acid stimulation (group A1). In the second group (A2), 55% of the neurons that were acoustically unresponsive under control (sound alone) conditions responded to the acoustic component of the combined acoustic and glutamate stimulation (the experimental condition) in a frequency-dependent manner. A2 neurons exhibited temporal firing patterns characteristic of acoustically responsive neurons of corresponding age, suggesting that these neurons are functionally connected to the auditory periphery, whereas A1 neurons are not. 3. Dose-response curves were either sigmoidal or linear over the range that measurements were made, and maximum discharge rates evoked by high doses of glutamate in the youngest animals studied tended to be lower than those produced by acoustic stimulation alone in older animals. These results suggest that intrinsic properties contribute to the mechanism(s) that limits neuronal responsiveness. Average dose-response curve slopes were higher for neurons recorded from older animals, also indicating that intrinsic properties regulating dynamic response range are acquired postnatally in the kitten CN.(ABSTRACT TRUNCATED AT 400 WORDS)
Neuronal responses to stimulation of the cervix, uterus, colon, and skin in the rat spinal cord
Authors: Berkley K. J. , Hubscher C. H. , Wall P. D.
Published: December 2017

1. Previous studies in the rat have shown that the hypogastric nerve conveys input from the cervix and uterus mainly to the T13-L3 segments of the spinal cord, whereas the pelvic nerve conveys input from the cervix and vaginal canal mainly to the L6-S2 segments. 2. To study the effects of this input, the dorsal horns of the T13-L1, L6-S2, and L4-L5 segments in 13 decerebrate, T10-spinalized, unanesthetized, and paralyzed adult female rats in estrus were searched for neurons responsive to gentle mechanical stimulation of the cervix. The 87 neurons found were then further tested for their responses to gentle mechanical stimulation of the skin and to distension of both uterine horns, distension of the colon, and shearing stimulation of the colon and vaginal canal. 3. Neurons responsive to cervix stimulation, primarily by excitation, were readily found in the ventral part of the dorsal horn in T13-L1 and throughout the dorsal horn in L6-S2. Cervix-responsive neurons were less readily found throughout the dorsal horn in L4-L5, where 25% were inhibited by the stimulation. All but one neuron had cutaneous receptive fields. 4. The 30 cervix-responsive neurons in T13-L1 had large bilateral cutaneous receptive fields covering the perineum and hind-limbs. Most (76%) also responded, primarily by excitation, to uterine distension, as well as to colonic stimulation (59%). More than half were activated by both types of stimulation. 5. The 33 cervix-responsive neurons in L6-S2 had cutaneous receptive fields in the same regions as those in T13-L1, but generally smaller, particularly for neurons in the dorsal part of the dorsal horn, many of whose receptive fields were confined to the perineum. The L6-S2 neurons also exhibited less convergent input from other visceral structures, particularly the uterus. Fewer neurons (42%) responded to uterine distension, mostly by being inhibited, whereas about the same proportion (51%) responded with excitation to colonic stimulation. Only 24% responded to both uterus and colon. 6. All 24 cervix-responsive neurons in medial L4-L5 had small cutaneous receptive fields on the toes, and the neurons received less convergent input from other visceral structures (25% from the uterus, 33% from the colon, 13% from both). 7. These results indicate the presence of an extensive system of neurons throughout the caudal spinal cord of the rat, concentrated in separated thoracolumbar and lumbosacral segments, that is concerned with input from the reproductive tract.(ABSTRACT TRUNCATED AT 400 WORDS)
Effects of transient depolarizing potentials on the firing rate of cat neocortical neurons
Authors: Reyes A. D. , Fetz E. E.
Published: December 2017

1. The effects of excitatory postsynaptic potentials (EPSPs) on interspike intervals (ISIs) of neocortical neurons can be mimicked by pulse potentials (PPs) produced by current injection. The present report documents the dependence of the ISI shortening on the amplitudes of PPs and EPSPs and on the firing rate of the affected neuron. 2. In rhythmically firing necortical neurons, the ISI shortenings caused by PPs arriving at specific times in the ISI can be described by a shortening-delay (S-D) curve. The S-D curve yields three measures of the PPs' ability to shorten the ISI: 1) the mean ISI shortening, S; 2) the maximum shortening, Smax; and 3) the effective interval, defined as the portion of the ISI in which the PP consistently shortens the ISI. For PPs ranging between 80 microV and 3.6 mV (and cells firing at 25 imp/s), the mean shortening increased with amplitude h as S (ms) = 1.2*h (mV)1.24 (r = 0.94; P < 0.01). Smax increased linearly with amplitude as 4.9 ms/mV (r = 0.86, P < 0.01). The effective interval (as a percentage of the ISI) increased slightly with PP amplitude and had a mean value of 65 +/- 21% (mean +/- SD). 3. S-D curves obtained with stimulus-evoked EPSPs varied with EPSP amplitude in a manner similar to those of PPs. The relations obtained for stimulus-evoked EPSPs were not statistically different from those obtained for PPs in the same cells. 4. To determine the effect of firing rate. PPs were applied while neurons fired at frequencies ranging from 8 to 71 imp/s. Both S and Smax were approximately inversely proportional to the baseline firing rate (fo) and could be described as: S or Smax = kfo-m. The mean value of the exponent m (+/- SD) was 0.96 +/- 0.25 for S and 1.2 +/- 0.4 for Smax. These values were not statistically different from a value of 1 (1 group, 2-tailed t test). The effective interval did not vary significantly with firing rate. 5. The dependence of S on PP amplitude and baseline firing rate was incorporated into an expression for the average change in firing rate (delta f) produced by PPs occurring at rate fs: delta f = 0.03 h1.24 fs. The delta f increased with PP amplitude but did not vary significantly with the baseline firing rate. The values of delta f calculated from the S-D curves matched the values that were computed directly from the spike trains.(ABSTRACT TRUNCATED AT 400 WORDS)
Differential electroresponsiveness of stellate and pyramidal-like cells of medial entorhinal cortex layer II
Authors: Alonso A. , Klink R.
Published: December 2017

1. The electroresponsive properties of neurons from layer II of the rat medial entorhinal cortex (MEC) were studied by intracellular recording under current clamp in an in vitro brain slice preparation. From a total of 184 cells that fulfilled our criteria for recording stability, two groups of projection neurons were distinguished on the basis of their intrinsic biophysical properties and morphological characteristics (demonstrated by intracellular biocytin injection; n = 34). 2. Stellate cells (SCs) were the most abundant (69%). They were highly electroresponsive, and minimal changes (1-3 mV) of membrane potential generated an active response. Subthreshold depolarizing or hyperpolarizing current pulse injection always caused the membrane potential to attain an early peak and then sag to a lower level. Depolarization-induced "sags" were larger and determined early firing in all cells. The voltage-current relationship of SCs was markedly non-linear, demonstrating robust inward rectification in the hyperpolarizing and depolarizing range. 3. SCs generated persistent rhythmic subthreshold voltage oscillations on DC depolarization positive to -60 mV. The mean frequency of the oscillations was 8.6 Hz (theta range) at a membrane potential of approximately -55 mV, at which level occasional single spiking also occurred. At slightly more positive potentials, a striking 1- to 3-Hz repetitive bursting pattern emerged. This consisted of nonadapting trains of spikes ("clusters") interspersed with subthreshold oscillations that had a mean frequency of 21.7 Hz (beta range). 4. Nonstellate cells (39%; mostly pyramidal-like) displayed time-dependent inward rectification that was less pronounced than that of SCs, and minimal depolarization-induced sags. On threshold depolarization, firing was always preceded by a slowly rising ramp depolarization and thus occurred with a long delay. Inward rectification in the depolarizing range was very pronounced. However, non-SCs did not generate persistent rhythmic subthreshold oscillatory activity or spike clusters. 5. Of the electrophysiological parameters quantified, spike threshold, spike duration, depolarizing afterpotential amplitude and apparent membrane time constant demonstrated statistically significant differences between SCs and non-SCs. 6. The repetitive hiring properties in response to square current pulses of short duration (< 500 ms) were also different between SCs and non-SCs. First, most SCs displayed a bilinear frequency-current (f-I) relationship for only the first interspike interval, whereas most non-SCs displayed a bilinear relationship for all intervals. Second, SCs had a much steeper primary f-I slope for early intervals than non-SCs. Finally, SCs displayed more pronounced and faster spike frequency adaptation than non-SCs.(ABSTRACT TRUNCATED AT 400 WORDS)
Electrophysiology of cat association cortical cells in vivo: intrinsic properties and synaptic responses
Authors: Nunez A. , Amzica F. , Steriade M.
Published: December 2017

1. The intrinsic properties and synaptic responses of association cortical neurons (n = 179) recorded from cat's areas 5 and 7 were studied in vivo. Intracellular recordings were performed under urethane anesthesia. Resting membrane potential (Vm) was -71.7 +/- 1.2 (SE) mV, amplitude of action potential was 83.7 +/- 2.3 mV, and input resistance was 18.4 +/- 1.8 M omega. Cells were identified ortho- and antidromically from lateroposterior and centrolateral thalamic nuclei and from homotopic foci in the contralateral cortex. Physiologically identified neurons were intracellularly stained with Lucifer yellow (LY) and found to be pyramidal-shaped elements (n = 21). 2. We classified the neurons as regular-spiking and intrinsically bursting cells. Regular-spiking cells were further classified as slow- and fast-adapting according to the adaptation of spike frequency during long-lasting depolarizing current pulses. 3. Regular-spiking, slow-adapting neurons had a monophasic afterhyperpolarization (AHP) or a biphasic AHP with fast and medium components (FAHP, mAHP). Slow-adapting behavior was observed in 84% (n = 119) of the regular-spiking cells. 4. Regular-spiking, fast-adapting cells only fired a train of spikes at the beginning of the pulse. Thereafter, the Vm remained as a depolarizing plateau, occasionally triggering some spikes. These neurons had a monophasic AHP and represented 16% (n = 23) of the regular-spiking neurons. 5. Intrinsically bursting neurons (n = 37) were observed in 20% of neocortical cells at depolarized Vm. Their action potential was followed by a marked depolarizing afterpotential (DAP). Rhythmic (4-10 Hz) bursts occurred during long-lasting depolarizing current pulses. 6. Small (3-10 mV), fast (1.5-4 ms), all-or-none depolarizing potentials were triggered by depolarizing current pulses. They are tentatively regarded as dendritic spikes recorded from the soma because their rate of occurrence changed as a function of the Vm and they were eventually blocked by hyperpolarization. 7. Synaptic stimulation of either thalamic or homotopic contralateral cortical areas elicited a sequence of excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs). Two components of the EPSP were revealed. At a hyperpolarized Vm, the initial component of the EPSP increased in amplitude, whereas the secondary component was blocked. Repetitive (10 Hz) stimulation of the thalamus or contralateral cortex elicited incremental responses. The augmentation phenomenon was due to an increase in the secondary component of the EPSP. The cortically elicited augmenting responses survived extensive thalamic lesions. A short IPSP and a long-lasting IPSP were evoked by thalamic or cortical stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)
Excitatory amino acid neurotransmission at sensory-motor and interneuronal synapses of Aplysia californica
Authors: Trudeau L. E. , Castellucci V. F.
Published: December 2017

1. Although the gill and siphon withdrawal reflex of Aplysia has been used as a model system to study learning-associated changes in synaptic transmission, the identity of the neurotransmitter released by the sensory neurons and excitatory interneurons of the network mediating this behavior is still unknown. The identification of the putative neurotransmitter of these neurons should facilitate further studies of synaptic plasticity in Aplysia. 2. We report that sensory-motor transmission within this circuit is mediated through the activation of an excitatory amino acid receptor that is blocked by the non-N-methyl-D-aspartate excitatory amino acid receptor antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and 1-(4-chlorobenzoyl)-piperazine-2,3-dicarboxylic acid (CBPD). Compound postsynaptic potentials evoked in motor neurons by electrical stimulation of the siphon nerve were blocked by 92% with CNQX (75 microM) and 89% with CBPD (75 microM). 3. Simultaneous intracellular recordings were obtained from sensory neurons, excitatory interneurons, and motor neurons. Monosynaptic excitatory postsynaptic potentials (EPSPs) evoked in motor neurons by an action potential in a sensory neuron were blocked by 86% with CNQX (75 microM) and 71% with CBPD (75 microM). The two antagonists also blocked monosynaptic interneuronal EPSPs onto motor neurons by 65% and 67%, respectively. 4. Potential agonists of the synaptic receptors were puff-applied in the intact abdominal ganglion. Homocysteic acid (HCA) was found to mimic the action of the synaptically released transmitter because it strongly excites motor neurons. This effect was blocked by CNQX. Kainate and domoic acid were also effective agonists. 5. The actions of L- and D-glutamate as well as quisqualate were found to be mainly hyperpolarizing, whereas aspartate and (+/-)-amino-3-hydroxy-5-methylisoxazole-4-propionic acid had no effect. 6. Several reasons may be proposed to explain the inability of puff-applied glutamate to excite effectively the postsynaptic neurons in the intact ganglion. It is possible nonetheless that other endogenous amino acids such as HCA act as neurotransmitters at these synapses.
Estrogen-sensitive neurons in the female rat ventral tegmental area: a dual route for the hormone action
Authors: Sakamoto Y. , Suga S. , Sakuma Y.
Published: December 2017

1. Electrical stimulation of the ventral part of the midbrain central gray (CG) elicited antidromic action potentials in 136 neurons in the ventral tegmental area (VTA) of 23 urethan-anesthetized ovariectomized female rats. 2. Antidromic action potentials were positive-negative biphasic and completed mostly within 2.4 ms. Many had a notch in their initial positive deflection, at which antidromic potentials often failed to propagate into the neuronal soma. 3. The latency for antidromic activation ranged 1.0-10.5 ms, and the threshold was 100-1,700 microA. The relative refractory period was 0.8-2.8 ms. In 23 neurons (17%) gradual changes in stimulus intensity caused latency jumps, suggesting that their axons terminate or spread into branches in stimulation sites. 4. The parameters for antidromic activation were compared among 12 animals with a subcutaneous Silastic capsule of estrogen and 11 others with a blank capsule. Estrogen raised the mean threshold from 675 +/- 40 (SE) microA (n = 69) to 908 +/- 40 microA (n = 67). At the same time, estrogen significantly decreased the probability of the antidromic propagation from 63 to 41%. No changes were detected in the latency or the refractory period. 5. The probability distribution of the threshold was different in ovariectomized animals from that in estrogen-treated animals. Estrogen increased the number of cells with thresholds in the 1,300- to 1,500-microA range. 6. The probability of antidromic propagation was stable in each neuron to stimuli repeated at 1.0 Hz. Electrical stimulation of the preoptic area (POA) with a 30-s train of 50-microA pulses at 100 Hz increased the probability of antidromic propagation into the soma.(ABSTRACT TRUNCATED AT 250 WORDS)
Declining inhibition in ipsi- and contralateral lumbar motoneurons during contractions of an ankle extensor muscle in the cat
Authors: Lafleur J. , Zytnicki D. , Horcholle-Bossavit G. , Jami L.
Published: December 2017

1. Motoneurons of pretibial ankle flexor and knee flexor and extensor muscles were recorded intracellularly in chloralose- or pentobarbitone-anesthetized cats during sustained submaximal contractions of either ipsi- or contralateral gastrocnemius medialis muscle (GM). 2. In a majority of ipsilateral motoneurons, a sustained GM contraction elicited inhibitory potentials that quickly subsided before the end of the contraction. An abrupt increase in contractile force could elicit a new series of inhibitory potentials, which declined again in spite of a maintained force level. 3. Contraction-induced effects were only exceptionally detected in contralateral triceps surae and plantaris motoneurons. In a small number of pretibial flexor and knee flexor and extensor motoneurons, declining inhibitions were observed during sustained contractions of the contralateral GM muscle. 4. At the onset of GM contractions, a variety of motoneurons uniformly receive inhibitory inputs that are quickly filtered out. Although the functional significance of this widespread initial inhibition remains to be elucidated, its rapid decline seems useful to allow subsequent recruitment of motor units as may be required for coordination of posture and movement. 5. Tendon organs are activated during muscle contraction, but it is not certain whether Ib inputs from GM can account for all the effects observed. Contribution of other afferents was considered and tested using a different experimental approach. The companion paper reports observations suggesting that effects elicited by group II afferents may cooperate in the contraction-induced inhibition of motoneurons.
Cerebellar ataxia and muscle spindle sensitivity
Authors: Gorassini M. , Prochazka A. , Taylor J. L.
Published: December 2017

1. The cerebellum has long been known to participate in movement control. One of the enduring theories of cerebellar function is that it "tunes" and coordinates sensorimotor traffic in other parts of the CNS. In particular, it has been implicated in the control of the sensitivity of muscle spindle stretch receptors through the fusimotor system. 2. The stretch sensitivity of spindle primary endings can be varied approximately over a 10-fold range by fusimotor efferent action. For many years it has been believed that cerebellar dysfunction is associated with reduced drive to the fusimotor system and that this in turn causes hypotonia by reducing the reflex excitation of alpha-motoneurons by spindle afferents. 3. The data on which this hypothesis is based were obtained in anesthetized or decerebrate animals. Little direct information is available on animals or humans performing voluntary movements and exhibiting ataxia or other cerebellar symptoms. 4. We tested the hypothesis by recording from nine muscle spindle afferents in behaving cats before and during reversible inactivation of cerebellar interpositus and dentate nuclei. In normal cats fusimotor action varies with motor task, greatly altering spindle stretch sensitivity. We investigated whether this same range of task-related sensitivity manifested itself during ataxia. 5. We found that the full range of spindle sensitivity was still present during ataxia. We therefore conclude that the cerebellar nuclei studied are not primarily responsible for fusimotor control, nor is the ataxia primarily caused by disordered proprioceptive sensitivity.
Models of recruitment and rate coding organization in motor-unit pools
Authors: Fuglevand A. J. , Winter D. A. , Patla A. E.
Published: December 2017

1. Isometric muscle force and the surface electromyogram (EMG) were simulated from a model that predicted recruitment and firing times in a pool of 120 motor units under different levels of excitatory drive. The EMG-force relationships that emerged from simulations using various schedules of recruitment and rate coding were compared with those observed experimentally to determine which of the modeled schemes were plausible representations of the actual organization in motor-unit pools. 2. The model was comprised of three elements: a motoneuron model, a motor-unit force model, and a model of the surface EMG. Input to the neuron model was an excitatory drive function representing the net synaptic input to motoneurons during voluntary muscle contractions. Recruitment thresholds were assigned such that many motoneurons had low thresholds and relatively few neurons had high thresholds. Motoneuron firing rate increased as a linear function of excitatory drive between recruitment threshold and peak firing rate levels. The sequence of discharge times for each motoneuron was simulated as a random renewal process. 3. Motor-unit twitch force was estimated as an impulse response of a critically damped, second-order system. Twitch amplitudes were assigned according to rank in the recruitment order, and twitch contraction times were inversely related to twitch amplitude. Nonlinear force-firing rate behavior was simulated by varying motor-unit force gain as a function of the instantaneous firing rate and the contraction time of the unit. The total force exerted by the muscle was computed as the sum of the motor-unit forces. 4. Motor-unit action potentials were simulated on the basis of estimates of the number and location of motor-unit muscle fibers and the propagation velocity of the fiber action potentials. The number of fibers innervated by each unit was assumed to be directly proportional to the twitch force. The area of muscle encompassing unit fibers was proportional to the number of fibers innervated, and the location of motor-unit territories were randomly assigned within the muscle cross section. Action-potential propagation velocities were estimated from an inverse function of contraction time. The train of discharge times predicted from the motoneuron model determined the occurrence of each motor-unit action potential. The surface EMG was synthesized as the sum of all motor-unit action-potential trains. 5. Two recruitment conditions were tested: narrow (limit of recruitment < 50% maximum excitation) and broad recruitment range conditions (limit of recruitment > 70% maximum excitation).(ABSTRACT TRUNCATED AT 400 WORDS)