bluuebunny/crossref_metadata_2025 huggingface dataset:
The vestibular nerve of the chinchilla. V. Relation between afferent discharge properties and peripheral innervation patterns in the utricular macula
Authors: Goldberg J. M. , Desmadryl G. , Baird R. A. , Fernandez C.
Published: December 2017

1. The relation between the discharge properties of utricular afferents and their peripheral innervation patterns was studied in the chinchilla by the use of intra-axonal labeling techniques. Fifty-three physiologically characterized units were injected with horseradish peroxidase (HRP) or lucifer yellow CH (LY) and their labeled processes were traced to the utricular macula. For most labeled neurons, the discharge regularity, background discharge, and sensitivity to externally applied galvanic currents were determined, as were the gain (g2 Hz) and phase (phi 2 Hz) of the response to 2-Hz sinusoidal linear forces. Terminal fields were reconstructed and fibers were classified as calyx (n = 13) or dimorphic units (n = 40). No bouton units were recovered. Calyx units were confined to the striola. Dimorphic units were located in the striola (n = 8), the juxtastriola (n = 7), or the peripheral extrastriola (n = 25). 2. To determine whether the intra-axonal sample was representative, the physiological properties of labeled utricular units were compared with those of a larger sample of extracellularly recorded units. A comparison was also made between the morphology of intra-axonally labeled units and those labeled by the extracellular injection of HRP into the vestibular nerve. Most of the discrepancies between the intra-axonal and either extracellular sample can be explained by assuming that small-diameter fibers are underrepresented in the former sample. Dimorphic fibers labeled intra-axonally had more bouton endings and larger terminal trees than did those labeled extracellularly. The latter differences may reflect a sampling bias in the extracellular material. 3. Calyx units were irregularly discharging. The discharge regularity of dimorphic units was related to their macular locations. Only 1/8 dimorphic units in the striola was regularly discharging. The ratio increases to 3/7 in the juxtastriola and to 23/25 in the peripheral extrastriola. Among dimorphic units, there is a tendency for irregularly discharging afferents to have fewer bouton endings. The trend is far from perfect because it is possible to pick a subsample of dimorphic units that have similar numbers of boutons and, yet, have discharge patterns that range from regular to irregular. 4. Published morphological polarization maps can be used to predict the excitatory tilt directions of a unit from its macular location. Predictions were confirmed in 39/41 labeled afferents. 5. The galvanic sensitivity (beta *) of an afferent, irrespective of its peripheral innervation pattern or its epithelial location, was strongly correlated with a normalized coefficient of variation (CV*).(ABSTRACT TRUNCATED AT 400 WORDS)
Activity-dependent neuromodulation in Aplysia neuron R15: intracellular calcium antagonizes neurotransmitter responses mediated by cAMP
Authors: Kramer R. H. , Levitan I. B.
Published: December 2017

1. The effect of electrical activity on the response to the neuromodulators serotonin (5-HT) and the neuropeptide egg-laying hormone (ELH) was studied in the Aplysia bursting pacemaker neuron R15. 2. Previous work has shown that 5-HT and ELH augment R15s bursting activity by enhancing two ionic currents, an inwardly rectifying K+ current (IR) and a voltage-gated Ca2+ current (ICa), and that the enhancement of the currents is mediated by the intracellular second-messenger adenosine 3',5'-cyclic monophosphate (cAMP). Here we show that both spontaneous action potentials and voltage-clamp depolarizations suppress the modulation by 5-HT and ELH of these currents. Both spontaneous and evoked depolarizations decrease the magnitude and dramatically speed the decay of the modulation of IR and ICa. 3. The depolarization-induced suppression is blocked by intracellular ethylene glycol-bis(beta-aminoethyl ether)N,N,N',N',-tetraacetic acid (EGTA), indicating that the suppression is Ca-dependent. The suppression is specific for responses mediated by cAMP; a non-cyclic AMP-mediated response to acetylcholine is not affected by depolarizing pulses. 4. The Ca-dependent suppression of IR modulation differs from the Ca-dependent suppression of ICa modulation. Ca2+ influx decreases the sensitivity of IR to neuromodulators without reducing the maximal response elicited by high concentrations of neuromodulators. In contrast, Ca2+ not only decreases the sensitivity of ICa but also reduces the maximal effect elicited by high concentrations of neuromodulators. We have shown previously that intracellular Ca2+ also inactivates the basal IR and ICa in neuron R15 by distinct mechanisms. The inactivation of IR is due to an antagonistic action of Ca2+ on cAMP metabolism, whereas the inactivation of the basal ICa is due primarily to a more direct action of Ca2+, perhaps on the Ca channels themselves. 5. We also studied the interaction between action potentials and neuromodulator released onto R15 from an endogenous source: bag cell neurons, which release large amounts of ELH during an intense "afterdischarge." IR and ICa become greatly enhanced during the afterdischarge, even though R15 continually fires action potentials. In addition, Ca-dependent inactivation of IR is suppressed during the afterdischarge. We suggest that the bag cells release an amount of ELH sufficient to temporarily saturate the cAMP-mediated enhancement of IR and that this temporarily prevents the suppressive effects of Ca2+ on IR. 6. The activity-dependent suppression of neuromodulation in neuron R15 is an example of neuronal plasticity that results from interactions between intracellular messengers.(ABSTRACT TRUNCATED AT 400 WORDS)
Mechanism of potassium uptake in neuropile glial cells in the central nervous system of the leech
Authors: Wuttke W. A.
Published: December 2017

1. Ion-selective double-barreled microelectrodes (ISME) were used to measure intracellular K+ (aKi), Na+ (aNai), and Cl- (aCli) activities of neuropile glial (NG) cells in the central nervous system of the medicinal leech Hirudo medicinalis. Ion fluxes were induced by an increase in extracellular K+ concentration [( K+]o) and analyzed to elucidate the ionic mechanism of the K+ uptake occurring under such conditions. 2. In addition, the K+ concentration of the extracellular space of the nerve cell body region (NCBR) and the neuropile (N) was measured with neutral carrier K(+)-ISME. In normal saline (4 mM K+), a concentration of 4.2 mM was measured in both extracellular spaces. No differences between the K+ concentration of the bathing fluid and the extracellular spaces were found at higher (i.e., 10 and 40 mM) K+ concentrations. 3. In normal saline, the mean membrane potential (Em) was -68 mV, and the mean aKi, aNai, and aCli were found to be 77, 10, and 7 mM, respectively. The corresponding equilibrium potentials were -81, 56, and -66 mV. The chloride equilibrium potential (ECl) was similar to Em, and it is concluded that chloride is passively distributed across the NG cell membrane. 4. When [K+]o was transiently increased 10-fold (i.e., to 40 mM), aKi and a Cli increased transiently by 22 and 25 mM, respectively, and the membrane depolarized to -28 mV, which was similar to both K+ equilibrium potential (EK) and ECl. The KCl uptake was accompanied by a transient decrease in aNai to 5 mM. 5. After incubation for at least 1 h in Na(+)-free saline, NG cells accumulated K+ in the absence of extracellular Na+ to levels similar to those observed in the presence of Na+. Therefore the uptake of K+ was not dependent on external--and probably also internal--Na+. 6. Changes in cell volume induced by the increase in [K+]o were estimated by loading NG cells with choline and monitoring its intracellular concentration with Corning-K(+)-ISME. In saline containing 40 mM K+, NG cell volume increased to approximately 150% of its volume in normal saline. 7. It is concluded that the mechanism of K+ uptake in NG cells is by passive KCl and water influx, which causes cell swelling.
Visual responses of Purkinje cells in the cerebellar flocculus during smooth-pursuit eye movements in monkeys. II. Complex spikes
Authors: Stone L. S. , Lisberger S. G.
Published: December 2017

1. We report the complex-spike responses of two groups of Purkinje cells (P-cells). The cell were classified according to their simple-spike firing during smooth eye movements evoked by visual and vestibular stimuli with the use of established criteria (Lisberger and Fuchs 1978; Stone and Lisberger 1990). During pursuit with the head fixed, ipsi gaze-velocity P-cells (GVP-cells) showed increased simple-spike firing when gaze moved toward the side of the recording, whereas down GVP-cells showed increased simple-spike firing when gaze moved downward. 2. During pursuit of sinusoidal target motion, the complex-spike firing rate was modulated out-of-phase with the simple-spike firing rate. Ipsi GVP-cells showed increased complex-spike firing during pursuit away from the side of the recording, and down GVP-cells showed increased complex-spike firing during upward pursuit. The strength of the complex-spike response increased as a function of the frequency of sinusoidal target motion. 3. GVP-cells showed directionally selective complex-spike responses during the initiation of pursuit to ramp target motion. Ipsi GVP-cells had increased complex-spike firing 100 ms after the onset of contralaterally directed target motion and decreased complex-spike activity after the onset of ipsilaterally directed target motion. Down GVP-cells had increased complex-spike firing 100 ms after the onset of upward target motion and decreased firing after the onset of downward target motion. As during sinusoidal target motion, each cell's simple- and complex-spike responses had the opposite directional preferences. 4. When the monkeys fixated a stationary target during a transient vestibular stimulus, the retinal slip caused by the 14-ms latency of the vestibuloocular reflex (VOR) affected the complex-spike firing rate. For ipsi GVP-cells, ipsilateral head motion caused transient contralateral image motion and an increase in complex-spike firing. The same vestibular stimulus in darkness caused an almost identical eye movement but had no effect on complex-spike firing. We conclude that complex spikes in ipsi GVP-cells are driven by contralaterally directed image motion. 5. To determine the events surrounding complex-spike firing during pursuit, we triggered averages of eye and target velocity on the occurrence of complex spikes during pursuit of sine-wave target motion. The averages revealed a transient pulse of retinal image motion that peaked approximately 100 ms before the complex spike. We conclude that complex spikes during steady-state pursuit are driven by the retinal slip associated with imperfect pursuit.(ABSTRACT TRUNCATED AT 400 WORDS)
Regulation of heartbeat in Lymnaea by motoneurons containing FMRFamide-like peptides
Authors: Buckett K. J. , Peters M. , Dockray G. J. , Van Minnen J. , Benjamin P. R.
Published: December 2017

1. Intracellular stimulation of single neurons in the Lymnaea CNS was carried out to identify heart motoneurons. 2. Two of the identified motoneurons, the E heart excitor (Ehe) cells, were shown to contain Phe-Met-Arg-Phe-NH2 (FMRFamide)-like peptides by immunocytochemical staining of dye-marked neurons and by radioimmunoassay (RIA) applied to extracts of single dissected cells. 3. Bursts of spikes in the Ehe cells increased heart rate, beat amplitude and muscle tonus. This response was mimicked by perfusion of exogenous FMRFamide at low concentration (10(-6) to 5 x 10(-8) M) through the interior of the intact heart. 4. Application of selective antagonists to 5-hydroxytryptamine (5-HT) and dopamine failed to block Ehe cardiac effects. 5. Detailed evidence that the Ehe cells were heart motoneurons was obtained. 1) Anatomic mapping using the dye Lucifer yellow showed Ehe cells had peripheral projections restricted mainly to the intestinal nerve, the only nerve known to innervate the heart. 2) Perfusion of the CNS with a saline containing Co2+ blocked central chemical synapses but did not affect activity of Ehe cells on the heart. 3) Simultaneous intracellular recordings from Ehe cells and auricle muscle fibers showed unitary excitatory junction potentials following with constant latency from spikes in Ehe cells. 6. The present study elucidates the role of FMRFamide in cardioregulation and provides the first evidence that it acts as an excitatory neurotransmitter on the snail heart.
Sensitivities of cells in anteroventral cochlear nucleus of cat to spatiotemporal discharge patterns across primary afferents
Authors: Carney L. H.
Published: December 2017

1. This study tested the hypothesis that a cell in the anteroventral cochlear nucleus (AVCN) that receives convergent input from auditory nerve (AN) fibers can be sensitive to the temporal pattern of discharges on the set of AN fibers providing its input. 2. The temporal discharge pattern across the population of low-frequency AN fibers was manipulated by varying the phase spectra of complex stimuli that had fixed, flat magnitude spectra. By introducing a phase shift with variable slope at a particular frequency, the relative times of discharge of phase-locked neurons with different characteristic frequencies (CFs) could be varied. In this manner the overall spatiotemporal discharge pattern across the array of AN fibers was systematically manipulated. 3. Some low-frequency cells in the AVCN were sensitive to changes in the slope of the phase transition of the complex stimulus. The cells that were sensitive came from several different cell types in the AVCN. Their responses were consistent with the hypothesis that these cells were sensitive to the temporal relationships between discharges on their primary inputs and that they received inputs with different CFs, because the phase shifts introduced relative time differences between different frequencies. 4. Other cells were not sensitive to the degree of phase shift of the stimulus. This insensitivity implied either that these cells received inputs of the same, or nearly the same, CF, or that they were not sensitive to the time differences introduced by these changes in the phase spectra, or both. 5. The cells that were sensitive to the manipulations of the phase spectrum were located in the posterior region of anterior AVCN and in the posterior region of AVCN and thus were presumably either globular bushy, small spherical bushy, or stellate cells. No sensitive cells were located in the most anterior region of the AVCN, where large spherical bushy cells are located. 6. Temporal discharge patterns across the AN population in response to complex stimuli change as a function of level. Accordingly, the sensitivity of neurons to changes in the phase transitions of the complex stimuli used in this study was often affected by the level of the stimulus. 7. The sensitivity to changes in the phase spectrum was a frequency-specific effect. That is, a cell was most sensitive to changes made in phase that were centered near its CF and less sensitive to changes in phase that were introduced at frequencies below or above CF.(ABSTRACT TRUNCATED AT 400 WORDS)
Event-related potentials in the retina and optic tectum of fish
Authors: Bullock T. H. , Hofmann M. H. , Nahm F. K. , New J. G. , Prechtl J. C.
Published: December 2017

1. Compound field potentials were recorded with up to 18 microelectrodes in comb, brush, or spear arrays on and in the optic tectum and with suction electrodes from the distal stump of the cut optic nerve and from the optic nerve head in the opened eye in elasmobranchs and teleosts. Diffuse light flashes of different durations and submaximal intensities were delivered in trains with regular or irregular interstimulus intervals (ISI). 2. Event-related potentials (ERPs) are visible in single trials and begin at 50-200 ms after an "oddball" flash, especially one that is slightly weaker, briefer, or delayed by as little as 6% of ISI, compared with the more frequent stimulus. ERPs to the opposite condition are not of the same form or size. 3. One or more stimuli were omitted from a train or the train terminated after various conditioning times. Deflections occur beyond the expected visual-evoked potentials (VEPs) to the last flash and are called omitted-stimulus potentials (OSPs). They occur on schedule--approximately 100 ms after the next flash would be due--almost independent of intensity, duration, or conditioning time. They are considered to be ERPs without any necessary implication or denial of a temporally specific expectation. 4. Three components of OSP occur alone or in combination: an initial fast peak, a slow wave, and an oscillatory spindle up to ls or more in duration. This resembles the OFF response to steady light. 5. All these components are already present in the retina with optic nerve cut. 6. The same mean ISI with a high proportion of jitter gives OSPs with only slightly longer latencies and smaller amplitudes; the OSP acts as though the retina makes an integrated prediction of ISI, intensity, and duration. 7. During a conditioning train the equilibrium between excitation and inhibition after each flash changes according to frequency, intensity, duration, and conditioning time; the VEP reflects this in a shape unique to the ISI; inhibition increases rapidly after each flash and then decays slowly according to the recent mean ISI. This allows rebound disinhibition after missing, weak, or delayed flashes (OSP or ERP) or causes an altered VEP after a longer or stronger oddball. 8. It seems unlikely that the OSP or oddball ERP in fish tectum is equivalent to mammalian ERPs under the same regime or signals higher cognitive events, because they are already present in the retina, require flash frequencies greater than 1 Hz, and grow with frequency up to and beyond flicker fusion.(ABSTRACT TRUNCATED AT 400 WORDS)
Inhibition of sensory responses of cat inferior olive neurons produced by stimulation of red nucleus
Authors: Weiss C. , Houk J. C. , Gibson A. R.
Published: December 2017

1. The sensory responsiveness of cells in the inferior olive is known to be suppressed during certain phases of active movement. These experiments were designed to test the possibility that activity in the rubrospinal pathway contributes to this suppression. We recorded from cells sensitive to light touch located in one of the divisions of the inferior olive, the rostral dorsal accessory olive (rDAO), in cats anesthetized with pentobarbitol sodium. Responsiveness to peripheral stimuli was tested during and after trains of conditioning stimuli delivered to the rubrospinal pathway. 2. All 44 cells in our sample of rDAO neurons showed an inhibition of responsiveness to peripheral stimuli after conditioning stimulation of the rubrospinal pathway. Typical conditioning trains consisted of 0.2-ms pulses at 200 Hz for 100 ms. The mean current required for a reduction in firing probability to 0.5 was 31 microA. Slight increases in intensity often completely inhibited responses to peripheral stimuli. 3. Inhibition of responsiveness showed a delayed time course. Peak inhibition occurred approximately 50 ms after the last pulse in the conditioning train. In many cases there was no demonstrable inhibition during the conditioning train. Increases of train frequency, train duration, or stimulus intensity produced stronger and broader periods of olivary inhibition. 4. The lowest threshold points for eliciting rDAO inhibition coincided with either the magnocellular red nucleus (RNm) or the rubrospinal tract (RST). Stimulation at RST sites produced inhibition of responses in the contralateral but not in the ipsilateral rDAO. Transection of the RST in the upper brain stem blocked the inhibition produced by red-nucleus stimulation without altering the inhibition produced by tract stimulation caudal to the transection. The inhibitory effects thus appear to be caused by activation of the rubrospinal pathway. 5. The inhibitory timing observed in this study may be appropriate for explaining the suppression of olivary responsiveness to contact that has been observed in awake animals. Bursts of movement-related, red nucleus discharge often cease approximately 50 ms before the end of movement. This timing would allow peak inhibition to develop at approximately the time of contact with an object at the end of a goal-directed limb movement.
Basal forebrain projections to somatosensory cortex in the cat
Authors: Barstad K. E. , Bear M. F.
Published: December 2017

1. This investigation was designed to identify the source of cholinergic basal forebrain projections to somatosensory cortex in the cat. 2. Injections of horseradish peroxidase (HRP) into cortical areas 3a, 3b, and 1 after a 36 to 48-h survival period, labeled neurons in the basal forebrain. The distribution of retrogradely labeled neurons was compared with the distribution of cells labeled by choline acetyltransferase immunocytochemistry. Most retrogradely labeled neurons in the basal telencephalon were found on the border between the globus pallidus and adjacent structures. Sometimes labeled neurons were also found in both limbs of the diagonal band of Broca. 3. Excitotoxin lesions of these regions of the basal telencephalon led to a profound depletion of acetylcholinesterase-containing axons in primary somatosensory cortex. 4. These data lay necessary groundwork for tests of the hypothesis that the cholinergic projection modulates experience-dependent modifications in adult cat somatosensory cortex.
Organization of sensory discrimination and response selection in choice and nonchoice conditions: a study using cerebral evoked potentials in normal humans
Authors: Goodin D. S. , Aminoff M. J. , Shefrin S. L.
Published: December 2017

1. It has been suggested that the long-latency "event-related" cerebral evoked potentials (ERPs) reflect certain aspects of the neural processing underlying sensory discrimination in a two-choice reaction time task. The present paper examines the hypothesis that the coupling of these ERPs to sensory discrimination is variable and that the discrimination process is completed at different points during the course of cerebral processing, depending on the actual requirements of the task. 2. We recorded the cerebral evoked potentials and electromyogram (EMG) of the responding muscle in five different reaction time tasks, each requiring sensory discrimination and response selection of varying complexity. In the Choice condition two stimuli were presented, and two separate responses were required. In the two Go-No Go conditions two stimuli were presented, but a response was required to only one or the other of the stimuli. In the two Simple conditions only one stimulus was presented, and one response was required. 3. Under both Choice and Go-No Go conditions, the frequency histogram of the onset latency of the compound muscle action potential for the response to the frequent tone showed a bimodal distribution without overlap, suggesting that there were two distinct types of responder: fast and slow. The comparable histograms for the onset latency of the response to the rare tone also showed a bimodal distribution, but the mean onset latency was prolonged relative to the response to the frequent tone, and the mean separation was less so that the two distributions overlapped each other. 4. Despite the marked difference in response latencies between the fast and slow responders, there was no appreciable difference in cerebral evoked responses between the two groups. Moreover, in response to the frequent tone, all slow responders and, likewise, all fast responders had similar onset latencies of the averaged EMG activity regardless of condition. Nonetheless, fast or slow responders to the frequent tone on one block of trials were also fast or slow responders, respectively, to the rare tone on the same block of trials. 5. These results suggest that two separate sensory discrimination processes are occurring; the first relating to the presence or absence of the frequent (expected) stimulus, and the second relating to the presence or absence of the rare stimulus. The response to each tone can either be generated immediately after that tone is positively identified or, when accuracy is required, can be delayed until both stimuli have been successfully discriminated by the subject.
Differential modulation of single voltage-gated calcium channels by cholinergic and adrenergic agonists in adult hippocampal neurons
Authors: Fisher R. , Johnston D.
Published: December 2017

1. Pharmacologic agents known to modulate long-term potentiation (LTP) at the mossy fiber-to-CA3 pyramidal neuron synapse were tested for their effects on the activity of single voltage-gated calcium channels in adult CA3 pyramidal neurons. 2. Single-channel current recordings of three types of voltage-gated calcium channels were made from acutely exposed CA3 pyramidal neurons of the adult guinea pig hippocampus. 3. The beta-adrenergic agonist isoproterenol (10 microM), which is known to enhance LTP, increased the activity of the two high-threshold calcium channels (N and L) with no striking effect on the low-threshold (T) channel. 4. The muscarinic agonists carbachol and muscarine (1-10 microM), the latter of which has been shown to inhibit LTP, decreased the probability of opening of L channels, increased the probability of opening of T channels, and had no effect on N channels. The effects were blocked by 0.1 microM atropine. 5. These results are consistent with the hypothesis that neuromodulation of mossy fiber LTP occurs, at least in part, through the modulation of postsynaptic, voltage-gated calcium channels.
Twitch properties of human thenar motor units measured in response to intraneural motor-axon stimulation
Authors: Thomas C. K. , Johansson R. S. , Westling G. , Bigland-Ritchie B.
Published: December 2017

1. The twitch properties of human thenar motor units were examined in response to intraneural motor-axon stimulation. Force components of thumb abduction and flexion were measured before and after tetanic stimulation. The magnitude, direction, and time derivatives of resultant forces, together with axon conduction velocities, were calculated for each unit. 2. Various indexes of contraction and relaxation rate were measured including contraction time (time from force onset to peak), one-half relaxation time (time from peak force to one-half that value), normalized maximum contraction and normalized maximum relaxation rates (peak positive and negative time derivatives of the force signal normalized to twitch force), and the times at which these maximum rates occurred. 3. For different units, the directions of resultant forces were approximately evenly distributed between thumb abduction and flexion. At the onset of the experiment, initial twitch forces ranged from 3 to 34 mN, contraction times from 35 to 80 ms, and one-half relaxation times from 25 to 108 ms. 4. Resultant twitch forces were positively correlated to normalized maximum relaxation rates, but not to other rate indexes or to conduction velocity. The various contraction rate measures were correlated to each other, but generally not to relaxation rates. 5. After the first test involving tetanic stimulation, the twitches of most units were potentiated and slowed, especially their relaxation phase. However, the extent of these changes varied considerably between units. In general, units with weak initial forces potentiated most, some up to three-fold. These changes in twitch properties were denoted posttetanic twitch potentiation.(ABSTRACT TRUNCATED AT 250 WORDS)
A comparison of human thenar motor-unit properties studied by intraneural motor-axon stimulation and spike-triggered averaging
Authors: Thomas C. K. , Bigland-Ritchie B. , Westling G. , Johansson R. S.
Published: December 2017

1. Measurements of twitch contractile properties of human motor units recorded by spike-triggered averaging may be distorted by partial fusion between twitches, because motor units seldom fire at rates below 8-10 Hz. The effects of this fusion were examined by comparing the responses of 27 human thenar motor units when their motor axons were stimulated at 1, 8, and 10 Hz. 2. Resultant forces were calculated from the abduction and flexion force components, together with various contraction and relaxation rate indexes as reported previously. Values for single twitches were compared to measurements made from the unfused force fluctuations ("apparent twitches") of the same units recorded during 8 and 10 Hz stimulation. 3. For all units, stimulation at 8 and 10 Hz caused partial twitch fusion. At 10 Hz, mean values for "apparent twitch" forces, contraction times (CT), and one-half relaxation times (1/2RT) were reduced to 44, 76, and 52% of the corresponding values measured from separate twitches evoked by 1 Hz stimulation. Similar but smaller reductions were seen at 8 Hz. 4. Slow units, with initial twitch CT greater than 60 ms, showed significantly more distortion of all "apparent twitch" parameters when stimulated at both 8 and 10 Hz, compared to fast units (less than 50 ms). 5. The potentiated abduction force component data were compared with abduction forces obtained previously by spike-triggered averaging from the same muscle group. Mean force obtained by spike-triggered averaging ("STA twitch" force: 21 mN) was significantly larger than that measured in abduction in response to either 1 or 10 Hz motor-axon stimulation (14 mN, 6 mN, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)
Interocular torsional disparity and visual cortical development in the cat
Authors: Isley M. R. , Rogers-Ramachandran D. C. , Shinkman P. G.
Published: December 2017

1. The present experiments were designed to assess the effects of relatively large optically induced interocular torsional disparities on the developing kitten visual cortex. Kittens were reared with restricted visual experience. Three groups viewed a normal visual environment through goggles fitted with small prisms that introduced torsional disparities between the left and right eyes' visual fields, equal but opposite in the two eyes. Kittens in the +32 degrees goggle rearing condition experienced a 16 degrees counterclockwise rotation of the left visual field and a 16 degrees clockwise rotation of the right visual field; in the -32 degrees goggle condition the rotations were clockwise in the left eye and counterclockwise in the right. In the control (0 degree) goggle condition, the prisms did not rotate the visual fields. Three additional groups viewed high-contrast square-wave gratings through Polaroid filters arranged to provide a constant 32 degrees of interocular orientation disparity. 2. Recordings were made from neurons in visual cortex around the border of areas 17 and 18 in all kittens. Development of cortical ocular dominance columns was severely disrupted in all the experimental (rotated) rearing conditions. Most cells were classified in the extreme ocular dominance categories 1, 2, 6, and 7. Development of the system of orientation columns was also affected: among the relatively few cells with oriented receptive fields in both eyes, the distributions of interocular disparities in preferred stimulus orientation were centered near 0 degree but showed significantly larger variances than in the control condition.(ABSTRACT TRUNCATED AT 250 WORDS)
Reduction of Ib autogenetic inhibition in motoneurons during contractions of an ankle extensor muscle in the cat
Authors: Zytnicki D. , Lafleur J. , Horcholle-Bossavit G. , Lamy F. , Jami L.
Published: December 2017

1. Triceps surae and plantaris (Pl) motoneurons were recorded intracellularly in chloralose or pentobarbital sodium (Nembutal)-anesthetized cats during unfused tetanic contractions of gastrocnemius medialis muscle (GM) produced by stimulating either a cut branch of the GM nerve or the muscle directly. 2. In alpha-motoneurons, during a series of GM twitches at 10/s, contraction-induced inhibitory potentials, probably the result of input from Golgi tendon organs (autogenetic inhibition), rapidly subsided before the end of the series. In contrast, excitatory potentials, probably the result of the activation of spindle primary endings during relaxation from contraction, persisted. 3. In gastrocnemius lateralis-soleus (GL-S) and Pl motoneurons lacking an excitatory connection with Ia afferents from GM, the sustained contraction of this muscle also elicited a declining inhibition. Rapid reduction of contraction-induced autogenetic inhibition was also observed in homonymous gamma-motoneurons. During unfused tetanic contractions lasting 0.5-4s, inhibitory potentials quickly subsided, but an abrupt increase in contractile force elicited a new series of decreasing inhibitory potentials. 4. The assumption that the inhibition induced by GM unfused tetanic contractions was due to activation of homonymous Ib afferents was supported by observations of the effects of electrical stimulation of the GM nerve. In Pl motoneurons lacking an excitatory connection with Ia afferents from GM, repetitive trains applied to the GM nerve, at a strength just above threshold for group I fibers, elicited rapidly declining inhibitory potentials similar to those produced by GM contraction. It was verified that during such stimulation, the amplitude of the group I afferent volleys did not decrease. 5. Reduction of contraction-induced Ib inhibition during sustained GM contraction was still present after a low spinalization of the preparation. As GM tendon organ discharges were verified to persist throughout prolonged contractions, the observed decline of autogenetic inhibition is likely to depend on a spinal mechanism, possibly involving presynaptic inhibition of Ib afferents and/or mutual inhibition of Ib-inhibitory interneurons.
Kinetic properties of T-type Ca2+ currents in isolated rat hippocampal CA1 pyramidal neurons
Authors: Takahashi K. , Ueno S. , Akaike N.
Published: December 2017

1. T-type Ca2+ channels producing a transient inward current were studied in pyramidal neurons acutely isolated from the ventral portion of rat hippocampal CA1 region. Membrane currents were recorded by the suction-pipette technique, which allows for internal perfusion under a single-electrode voltage clamp. 2. In all cells superfused with external solution containing 10 mM Ca2+, the T-type Ca2+ current was evoked by step depolarization to potentials more positive than -60 mV from a holding potential of -100 mV and reached a peak in the current-voltage relationship around -30 mV at 20–22 degrees C. 3. Activation and inactivation processes of T-type Ca2+ current were highly potential dependent, and the latter was fitted by a single exponential function. 4. Steady-state inactivation of T-type Ca2+ current could be fitted by a Boltzmann's equation with a slope factor of 6.0 and a half-inactivated voltage of -79 mV. 5. Recovery from inactivation of T-type Ca2+ current was not a single exponent. The major component of recovery (60-90% of total) was voltage sensitive with a time constant of 215 ms at -100 mV. 6. Amplitude of the T-type Ca2+ current depended on the external Ca2+ concentration. The ratio of peak amplitude in the individual current-voltage relationships of Ca2+, Ba2+, and Sr2+ currents passing through T-type Ca2+ channel was 1.0:0.85:1.32. The current kinetics were much the same. 7. All kinetic properties, including activation and inactivation, as well as the amplitude of T-type Ca2+ current, were temperature sensitive with Q10 (temperature coefficient) values of 1.7–;2.5.(ABSTRACT TRUNCATED AT 250 WORDS)
Differentiation of NG108-15 cells alters channel conductance and desensitization kinetics of the 5-HT3 receptor
Authors: Shao X. M. , Yakel J. L. , Jackson M. B.
Published: December 2017

1. NG108-15 cells undergo morphological differentiation in response to appropriate culture conditions. We have used patch clamp techniques to compare responses mediated by the 5-HT3 receptor in differentiated and undifferentiated NG108-15 cells. 2. In differentiated cells, desensitization of 5-hydroxytryptamine (5-HT) responses was much slower than in undifferentiated cells. Desensitization in differentiated cells was also highly variable, with half-times varying by greater than 40-fold. Rapidly desensitized responses in differentiated cells were qualitatively similar to the responses of undifferentiated cells. 3. In outside-out patches from undifferentiated cells, single channel currents could be seen after 5-HT application. These channels had a conductance of 12 pS. The 5-HT-activated channels in differentiated cells were too small to observe at the single-channel level. Noise analysis indicated that the channel conductance was approximately 4 pS. In differentiated cells, both rapidly and slowly desensitized responses were generated by channels with essentially the same conductance. 4. The 5-HT responses of differentiated cells were also distinguished from those of undifferentiated cells on the basis of the voltage dependence of desensitization and the curvature of the current-voltage curve. 5. NG108-15 cells can produce different receptor subtypes, which may be expressed in different tissues or at different stages of development. These variations in receptor behavior suggest that there are at least two distinct mechanisms for regulation of the 5-HT3 receptor.
Lead and zinc block a voltage-activated calcium channel of Aplysia neurons
Authors: Busselberg D. , Evans M. L. , Rahmann H. , Carpenter D. O.
Published: December 2017

1. The effects of Pb2+ and Zn2+ on the peak of the voltage-activated calcium current of Aplysia neurons were examined. Calcium currents were reversibly blocked by Pb2+ at concentrations that did not significantly affect potassium and sodium currents and by Zn2+ at concentrations associated with a delay and reduction of peak sodium and potassium currents. 2. The block by both was concentration dependent, and percentage blockade was reduced in elevated Ca2+. The threshold Pb2+ concentration for blockade in 20 mM Ca artificial sea water (ASW) was approximately 1 microM, whereas for Zn2+ it was 2 mM. The Hill coefficient for Pb2+ action was near 1.0 under all conditions, whereas for Zn2+ it was 1.4-1.6. 3. With addition of Pb2+, the voltage at which peak calcium current was generated shifted to hyperpolarized voltages, an effect similar to that caused by reduction of Ca2+ concentration in the absence of Pb2+. Zn2+ shifted the voltage at which peak current was generated in a depolarizing direction. 4. Pb2+ did not significantly change inactivation but shifted the voltage dependence of activation to hyperpolarized voltages in a dose-dependent manner. Zn2+ shifted both activation and inactivation in a depolarizing direction in a dose-dependent fashion. 5. The blockade of calcium currents by Pb2+ but not Zn2+ was highly voltage dependent and increased with depolarization. 6. Our results suggest that Pb2+ is a specific, potent, competitive, and reversible blocker of calcium currents. These observations are consistent with a competition by Pb2+ with Ca2+ at a binding site within the calcium channel. In contrast, the blockade of calcium currents by Zn2+ is probably through actions at fixed charge sites external to the channel.
Computer simulation of the steady-state input-output function of the cat medial gastrocnemius motoneuron pool
Authors: Heckman C. J. , Binder M. D.
Published: December 2017

1. A pool of 100 simulated motor units was constructed in which the steady-state neural and mechanical properties of the units were very closely matched to the available experimental data for the cat medial gastrocnemius motoneuron pool and muscle. The resulting neural network generated quantitative predictions of whole system input-output functions based on the single unit data. The results of the simulations were compared with experimental data on normal motor system behavior in humans and animals. 2. We considered only steady-state, isometric conditions. All motoneurons received equal proportions of the synaptic input, and no feedback loops were operative. Thus the intrinsic properties of the motor unit population alone determined the form of the system input-output function. Expressing the synaptic input in terms of effective synaptic current allowed the simulated motoneuron input-output functions to be specified by well-known firing rate-injected current relations. The motor unit forces were determined from standard motor unit force-frequency relations, and the system output at any input level was assumed to be the linear sum of the forces of the active motor units. 3. The steady-state input-output function of the simulated motoneuron pool had a roughly sigmoidal shape that was quite different from those derived from previous recruitment models, which did not incorporate frequency modulation. Frequency modulation in combination with the skewed distribution of thresholds (low values much more frequent than high) restricted upward curvature to low input levels, whereas frequency modulation alone was responsible for the final gradual approach to the maximum force output. 4. Sensitivity analyses were performed to assess the importance of several assumptions that were required to deal with gaps and uncertainties in the available experimental data. The shape of the input-output function was not critically dependent on any of these assumptions, including those specifying linear summation of inputs and outputs. 5. A key assumption of the model was that systematic variance in motor unit properties was much more important than random variance for determining the input-output function. Addition of random variance via Monte Carlo techniques showed that this assumption was correct. These results suggest that the output of a motoneuron pool should be quite tolerant of random variance in the distribution of synaptic inputs and yet substantially altered by any systematic differences, such as unequal distribution of inputs among different motor unit types.(ABSTRACT TRUNCATED AT 400 WORDS)
Synaptic responses of guinea pig and rat central amygdala neurons in vitro
Authors: Nose I. , Higashi H. , Inokuchi H. , Nishi S.
Published: December 2017

1. To investigate postsynaptic potentials (PSPs), we made intracellular recordings from neurons of the amygdaloid central nucleus in slices from the guinea pig and rat brains maintained in vitro. The results from guinea pigs and rats were very similar. 2. In the presence of bicuculline (20 microM), focal electrical stimulation of the amygdaloid basal nucleus with low intensities elicited short-latency excitatory PSPs (EPSPs) followed by long-latency EPSPs. The short-latency EPSP was selectively blocked by 6-cyano-7-nitroquinoxaline-2,3-dion (CNQX; 10-20 microM). The long-latency EPSP was preferentially abolished by D,L-2-amino-5-phosphonovaleric acid (D,L-APV; 40 microM) and was augmented by removal of extracellular Mg2+. The compound EPSP reversed at -4 mV, which was close to -1 mV, the reversal potential for pressure-ejected glutamate (Glu). 3. When the intensity of the focal stimulation was increased in the presence of bicuculline (20 microM), CNQX (20 microM), and D,L-APV (50 microM), a second EPSP with a short latency and a prolonged duration could be evoked in approximately 65% of the neurons. The EPSPs were reversibly blocked by d-tubocurarine (50 microM) or hexamethonium (200 microM) but were unaffected by atropine (1 microM) or a 5-hydroxytryptamine type 3 receptor antagonist, ICS-205930 (5-10 microM). In these neurons, acetylcholine (ACh; 1-3 mM) caused a depolarization, associated with a decreased input resistance. 4. In the presence of CNQX (20 microM) and D,L-APV (50 microM), single focal stimulation of the dorsolateral subdivision in the central nucleus with low intensities elicited a depolarizing inhibitory PSP (IPSP). The IPSP was reversibly abolished by bicuculline (20-40 microM). The reversal potential (-63 mV) for the IPSP was similar to the reversal potential (-61 mV) for the response to gamma-aminobutyric acid (GABA) applied by pressure ejection. 5. In the presence of bicuculline (20-40 microM) and CNQX (20 microM), a repetitive focal stimulus with high intensities delivered to the dorsolateral subdivision produced a hyperpolarizing PSP followed by a slow depolarization in most neurons. Of putative inhibitory amino acid transmitters, glycine (Gly; 3 mM) produced only a hyperpolarization, associated with a decrease in input resistance. Strychnine (1-2 microM) reversibly blocked both the Gly hyperpolarization and the synaptically evoked hyperpolarization. The reversal potential of -81 mV for the hyperpolarizing PSP was close to -82 mV for the Gly hyperpolarization. The reversal potential for the Gly response was shifted to less negative values by increasing the external K+ concentration or decreasing the extracellular Cl- concentration.(ABSTRACT TRUNCATED AT 400 WORDS)
Behavior of upper cervical inspiratory propriospinal neurons during fictive vomiting
Authors: Nonaka S. , Miller A. D.
Published: December 2017

1. The role of upper cervical inspiratory (UCI)-modulated neurons in respiratory muscle control during vomiting was examined by recording the impulse activity of these neurons during fictive vomiting in decerebrate, paralyzed cats. Fictive vomiting was identified by a characteristic series of bursts of coactivation of phrenic and abdominal muscle nerves, elicited either by electrical stimulation of supradiaphragmatic vagal nerve afferents or by emetic drugs, which would be expected to produce expulsion of gastric contents in nonparalyzed animals. 2. Data were recorded from 43 propriospinal UCI neurons, located in the C1-C3 spinal segments near the border of the intermediate gray matter and lateral funiculus, which were antidromically activated with floating pin electrodes placed in the ipsilateral lateral funiculus, usually at T1-T3. Some cells (9/21 tested) were also activated from the upper lumbar cord (L1). During respiration, most neurons (n = 40) had an augmenting discharge pattern during inspiration. In addition, more than one-half (55%) fired tonically during the remainder of the respiratory cycle. About 40% of UCI neurons showed variations in their firing pattern during the noninspiratory portion of respiration. These latter two properties of UCI neurons were not observed in dorsal and ventral respiratory group (DRG and VRG-, respectively) bulbospinal inspiratory (I) neurons previously recorded under similar conditions. 3. During fictive vomiting, the firing pattern of most UCI neurons fell into one of three main categories. More than one-half (53%) were active in phase with bursts of phrenic discharge and were thus classified as Active-type cells.(ABSTRACT TRUNCATED AT 250 WORDS)