bluuebunny/crossref_metadata_2025 huggingface dataset:
Neurons in the rat spinal trigeminal complex driven by corneal nociceptors: receptive-field properties and effects of noxious stimulation of the cornea
Authors: Pozo M. A. , Cervero F.
Published: December 2017

1. A survey of the receptive-field properties of neurons in the spinal trigeminal complex driven by stimulation of corneal afferents has been carried out. The afferent inputs to these neurons from the cornea and from the adjacent skin were studied as well as changes in the excitability of the cells and in the size of their receptive fields after thermal noxious stimulation of the cornea. 2. Single-unit electrophysiological recordings were made in pentobarbitone anesthetized rats from 54 neurons all of which were activated by mechanical stimulation of the ipsilateral cornea. Seventeen of these neurons were activated only by corneal stimulation and the other 37 had an additional cutaneous receptive field in the periorbital skin. Of the 37 neurons with a cutaneous receptive field, 29 were activated exclusively by noxious stimulation of the skin (Class 3) and the remaining 8 were driven by both innocuous and noxious cutaneous stimuli (Class 2). 3. All of the neurons were located in the ventro-lateral area of a region of the spinal trigeminal complex between +0.5 mm and -1.0 mm from the obex. This area corresponds to the most caudal part of subnucleus interpolaris, the transition zone between interpolaris and caudalis and the rostral half of subnucleus caudalis. Most neurons were located in the superficial layers of this part of the spinal trigeminal complex. No differences were observed between the locations of the recording sites of neurons with an exclusive corneal input and those with a corneal and a cutaneous receptive field.(ABSTRACT TRUNCATED AT 250 WORDS)
Ionic basis for endogenous rhythmic patterns induced by activation of N-methyl-D-aspartate receptors in neurons of the rat nucleus tractus solitarii
Authors: Tell F. , Jean A.
Published: December 2017

1. Activation of N-methyl-D-aspartate (NMDA) receptors in caudal nucleus tractus solitarii (cNTS) neurons elicited endogenous rhythmic activities. We used an in vitro brain stem slice preparation to determine the ionic mechanisms underlying the generation of these activities. 2. Using intracellular recordings, we found several ionic conductances to be responsible for the electrophysiological properties of cNTS neurons. After addition of tetrodotoxin (TTX) to the perfusate, cNTS neurons were still able to generate action potentials (APs). Because these APs were suppressed by the addition of cobalt or by the reduction of calcium, they were likely due to calcium currents (ICa). In addition, the amplitude of the afterhyperpolarization (AHP) that followed a train of TTX-resistant APs was reduced in both low-calcium and cobalt-containing saline. It was therefore suggested that calcium-activated potassium (IKCa) currents were involved in the AHP. Accordingly, application of apamin, a blocker of slow IKCa, also decreased the AHP. cNTS neurons exhibited a delayed excitation phenomenon, characterized by a ramplike depolarization that delayed the onset of neuronal firing, when they were depolarized from hyperpolarizing potential. The underlying current was presumed to be an A-current (IKA), because this phenomenon was suppressed during application of 4-aminopyridine (4-AP). 3. Application of NMDA elicited different types of discharge patterns in cNTS neurons: a repetitive firing at depolarized levels of membrane potential (above -60 mV) and rhythmic patterns characterized by either rhythmic bursting or rhythmic single discharges at hyperpolarized levels (within membrane potential range of -60 to -85 mV). In all neurons, rhythmic patterns were superimposed on oscillations of membrane potential. They were characterized by a sudden shift of membrane potential, followed by a ramp-shaped phase of depolarization that preceded spike elicitation. Addition of TTX to the saline did not suppress NMDA-induced oscillations. Therefore rhythmic patterns were not driven by synaptic mechanisms but resulted from endogenous properties of cNTS neurons. 4. APs superimposed on NMDA-induced depolarizations presented the same characteristics as those elicited by positive current pulses. NMDA-elicited oscillations of membrane potential were eliminated by removing magnesium from the saline. Therefore oscillation generation was based primarily on the NMDA channel properties. 5. Intrinsic conductances of cNTS neurons interacted with NMDA-gated conductances to shape the depolarization waveform. Because removal of calcium from the saline suppressed endogenous oscillations, ICa currents were required for the expression of rhythmic activities. IKCa currents were involved in the repolarization phase of oscillations because apamin increased the duration of the oscillations.(ABSTRACT TRUNCATED AT 400 WORDS)
Mechanosensory inputs to the central pattern generators for locomotion in the lamprey spinal cord: resetting, entrainment, and computer modeling
Authors: McClellan A. D. , Jang W.
Published: December 2017

1. Mechanoreceptors in the lamprey spinal cord have inputs to the central pattern generator (CPG) for locomotion. In the present study, imposed sinusoidal and pulsed movements were applied to the end of the in vitro lamprey spinal cord to excite the mechanoreceptors so that the relationship between entrainment and resetting of the locomotor rhythm could be examined. 2. The range over which the locomotor rhythm could be entrained by sinusoidal movements was asymmetric and occurred mostly at movement cycle times below the resting cycle time. During entrainment at the shortest cycle times, the movement phases were relatively small. 3. The phase response curves (PRCs) displayed the greatest shortening of cycle times (phase advance) for movement pulses applied during the first half of the locomotor cycle, whereas movement pulses applied during the second half of the cycle were largely ineffective. The amplitude of phase shifts in the PRC correlated with the ranges of cycle times over which entrainment occurred. 4. During resetting from movement pulses applied early in the cycle, the burst and interburst parts of the cycle shortened by about the same percentage. In addition, resetting effects occurred simultaneously along the spinal cord, suggesting a rapid distribution of timing information. 5. A computer model of the CPGs, consisting of left and right oscillators and inputs from mechanosensory elements, produced entrainment ranges that were symmetric around the resting cycle time. The PRCs from the model showed phase advance for movement pulses applied during the first half of the cycle and phase delay for pulses applied during the second half of the cycle. 6. Because of the asymmetric experimental PRCs for the lamprey spinal cord, gating was incorporated into the cooffter model such that oscillators on one side of the model gated inputs from mechanosensory elements on the same side. With gating, the model produced entrainment ranges that were asymmetric and confined to cycle times below the resting cycle time. The PRCs still showed phase advance for pulses applied at the beginning of the cycle, and the amount of phase delay produced during the second half of the cycle was substantially reduced compared with the simulations without gating.
Tactile activity in primate primary somatosensory cortex during active arm movements: cytoarchitectonic distribution
Authors: Prud'homme M. J. , Cohen D. A. , Kalaska J. F.
Published: December 2017

1. Cells were recorded in areas 3b and 1 of the primary somatosensory cortex (SI) of three monkeys during active arm movements. Successful reconstructions were made of 46 microelectrode penetrations, and 298 cells with tactile receptive fields (RFs) were located as to cytoarchitectonic area, lamina, or both. 2. Area 3b contained a greater proportion of cells with slowly adapting responses to tactile stimuli and fewer cells with deep modality inputs than did area 1. Area 3b also showed a greater level of movement-related modulation in tactile activity than area 1. Other cell properties were equally distributed in the two areas. 3. The distribution of cells with low-threshold tactile RFs that also responded to lateral stretch of the skin or to passive arm movements was skewed toward deeper laminae than for tactile cells that did not respond to those manipulations. 4. The variation of activity of tactile neurons during arm movements in different directions was weaker in the superficial laminae than in deeper cortical laminae. 5. Cells with only increases in activity during arm movements were preferentially but not exclusively located in middle and superficial layers. Cells with reciprocal responses were found mainly in laminae III and V, whereas cells with only decreases in activity were concentrated in lamina V. 6. Overall, active arm movements evoke directionally tuned tactile and “deep” activity in areas 3b and 1, in particular in the deeper cortical laminae that are the source of the descending output pathways from SI.
Repetitive stimulation induced potentiation of excitatory transmission in the rat dorsal horn: an in vitro study
Authors: Jeftinija S. , Urban L.
Published: December 2017

1. The effects of repetitive stimulation of primary afferents in lumbar dorsal roots on synaptic transmission in the dorsal horn (DH) were studied in a rat spinal cord slice-dorsal root ganglion (DRG)-peripheral nerve trunk preparation by the use of intracellular recording from neurons (n = 115) of the spinal dorsal horn (depth 147 +/- 139, mean +/- SD). All DH neurons were excited synaptically by electrical stimulation of the dorsal root or the peripheral nerve trunk. The electrical shocks were calibrated to produce activation either of large fibers (10–20 V, 0.02 ms) or the whole fiber population including unmyelinated afferents (supramaximal stimulus: > 35 V, 0.5 ms). Postsynaptic potentials induced by low intensity repetitive stimulation of primary afferents at frequencies below 5 Hz failed to produce a prolonged change in the resting membrane potential. In 97/115 DH neurons, slow excitatory postsynaptic potentials (EPSP)--evoked by high intensity low-frequency repetitive stimulation (0.1–2 Hz) of primary afferents--summated, producing a prolonged cumulative depolarization. In the remaining 18/115 DH neurons, high intensity low-frequency stimulation produced a cumulative hyperpolarizing response. 2. In 22 of 97 neurons that responded to high intensity repetitive stimulation with a cumulative depolarization, wind-up in the firing of action potentials was recorded. In all but two experiments, neurons that responded with wind-up to stimulation of one root responded with wind-up to stimulation of the adjacent dorsal root. In 14/22 wind-up neurons, the synaptic response to high intensity stimulation of primary afferents was composed of a short latency EPSP, followed by an inhibitory postsynaptic potential (IPSP), followed by a slow EPSP. The decrease of the amplitude and duration of the IPSP obtained during train stimulation did not seem to contribute to facilitation of transmission induced by repetitive stimulation. 3. The wind-up in firing of action potentials was followed by a prolonged potentiation of synaptic transmission in tetanized synapses. A test of other, adjacent primary afferents revealed that these synapses in the neurons in the superficial laminae had not undergone potentiation. This “synaptic specificity” of post-wind-up potentiation suggested that the mechanism for the induction of stimulation-dependent changes in the excitability of the DH neuron is presynaptic to the recorded-from neuron. 4. In a concentration of 0.5 microM and higher, tetrodotoxin (TTX) applied to sensory neurons selectively blocked action potentials in large myelinated primary afferents.(ABSTRACT TRUNCATED AT 400 WORDS)
Microstimulation of the medullary reticular formation during fictive locomotion
Authors: Perreault M. C. , Rossignol S. , Drew T.
Published: December 2017

1. The present study was designed to determine the effects of microstimulation of the medullary reticular formation (MRF) on the locomotor activity of the cat in the absence of phasic afferent feedback from the limbs. To this end, both short (33 ms) and long (200 ms) trains of stimuli (trains of 0.2-ms pulses at 330 Hz, 35 microA) were applied at 43 loci in the MRF (P:6–12 mm; L:0.5–1.5 mm), and in 3 loci in the medial longitudinal fasciculus (P7.5, L < 0.5 mm) during fictive locomotion in the decerebrate and paralyzed cat. The locomotor pattern was monitored by recording the activity of representative flexor and extensor muscle nerves from each of the four limbs. 2. Short trains of stimuli evoked transient excitatory and/or inhibitory responses in extensor and flexor nerves of each limb that were incorporated into the locomotor pattern. In the majority of sites, excitatory responses were obtained in the motor nerves to both flexor and extensor muscles of the fore- and hindlimbs. The exception to this rule was the ipsilateral triceps, in which the predominant response was inhibitory. The amplitude of these responses was dependent on the time of the locomotor cycle at which the stimulus was delivered, and it was always maximum during the period of activity of the respective nerve. 3. The shortest latency response in the nerves to different muscles of the forelimb averaged between 5.6 and 7.3 ms; for the hindlimbs the values were between 6.9 and 9.3 ms. 4. Changing the depth at which the stimulation was applied in any one trajectory usually produced changes only in the amplitude of the evoked responses but occasionally also caused a change in the sign of these responses, especially in the most ventral regions of the MRF. 5. At 72% of the loci (31/43), short trains of stimulation also changed the duration of the activity in the recorded nerves. These changes were often (20/31 loci) sufficiently strong to alter the duration of the overall locomotor cycle. If one considers only the largest changes produced at each locus, stimulation during the period of ipsilateral extensor activity produced an average reduction in the ipsilateral locomotor cycle duration of 12.8 +/- 8.8% (mean +/- SD), whereas stimulation when the ipsilateral flexor nerve was active produced an average increase in locomotor cycle duration of 27.1 +/- 20.8%. 6. Long trains of stimuli produced similar but larger effects than the shorter trains and always reset the locomotor rhythm.(ABSTRACT TRUNCATED AT 400 WORDS)
Spatiotemporally differential inhibition of pyramidal cells in the cat motor cortex
Authors: Kang Y. , Kaneko T. , Ohishi H. , Endo K. , Araki T.
Published: December 2017

1. The spatiotemporal pattern of inhibition in the cat motor cortex was studied in in vitro slice preparations in the presence of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and 2-amino-5-phosphonovaleric acid (APV). 2. After intracortical microstimulation (0.5–6 microA), fast and slow inhibitory postsynaptic potentials (IPSPs) were produced in layers II–VI pyramidal cells and selectively reduced with bicuculline methiodide and phaclofen, respectively. 3. Fast IPSPs were maximally produced by stimulation of the same layer where their cell bodies were located, and they decreased in amplitude as the more superficial layer was stimulated. In contrast, slow IPSPs were maximally produced by stimulation of layer II regardless of the location of the recorded pyramidal cell and decreased in amplitude as the deeper layer was stimulated. 4. The reduction of amplitude of fast IPSPs, in response to a vertical shift of the stimulation site toward more superficial layers, was always correlated with an increase in rise time and with a shift of the reversal potential to a more hyperpolarized level. 5. When the stimulation site was moved horizontally to the more lateral site, fast IPSPs increased in latency and decreased in amplitude gradually without appreciable changes in rise time. Fast IPSPs could be evoked from horizontally remote sites of up to 800–1,200 microns. 6. Inhibitory interneurons, which are responsible for evoking fast IPSPs, appear to be distributed through almost all layers to send horizontally spreading parallel axons making synaptic contacts at different electrotonic distances along apical dendrites of single pyramidal cells. 7. Horizontal spreads were much less in slow IPSPs (< 340–680 microns). The time-to-peak of slow IPSPs produced in layer V pyramidal cells (159.5 +/- 6.8 ms, mean +/- SD, n = 10) was significantly (P < 0.0001) longer than that in layers II and III pyramidal cells (128.5 +/- 7.5 ms, n = 7). Asymmetric reversal properties of slow IPSPs were seen, suggesting the spatial dispersion of synaptic inputs along apical dendrites of pyramidal cells. 8. In layer V pyramidal cells, the time-to-peak of slow IPSPs decreased with increasing membrane hyperpolarization, indicating that the later portion of slow IPSPs was more sensitive to the membrane-potential change than the early portion. This further indicates that the late portion of slow IPSPs is generated at synapses on the more proximal dendrite of pyramidal cells than the early portion, contrary to that expected from the Rall's model of passive dendrite under the condition of synchronous inputs.(ABSTRACT TRUNCATED AT 400 WORDS)
Simulator for neural networks and action potentials: description and application
Authors: Ziv I. , Baxter D. A. , Byrne J. H.
Published: December 2017

1. We describe a simulator for neural networks and action potentials (SNNAP) that can simulate up to 30 neurons, each with up to 30 voltage-dependent conductances, 30 electrical synapses, and 30 multicomponent chemical synapses. Voltage-dependent conductances are described by Hodgkin-Huxley type equations, and the contributions of time-dependent synaptic conductances are described by second-order differential equations. The program also incorporates equations for simulating different types of neural modulation and synaptic plasticity. 2. Parameters, initial conditions, and output options for SNNAP are passed to the program through a number of modular ASCII files. These modules can be modified by commonly available text editors that use a conventional (i.e., character based) interface or by an editor incorporated into SNNAP that uses a graphical interface. The modular design facilitates the incorporation of existing modules into new simulations. Thus libraries can be developed of files describing distinctive cell types and files describing distinctive neural networks. 3. Several different types of neurons with distinct biophysical properties and firing properties were simulated by incorporating different combinations of voltage-dependent Na+, Ca2+, and K+ channels as well as Ca(2+)-activated and Ca(2+)-inactivated channels. Simulated cells included those that respond to depolarization with tonic firing, adaptive firing, or plateau potentials as well as endogenous pacemaker and bursting cells. 4. Several types of simple neural networks were simulated that included feed-forward excitatory and inhibitory chemical synaptic connections, a network of electrically coupled cells, and a network with feedback chemical synaptic connections that simulated rhythmic neural activity. In addition, with the use of the equations describing electrical coupling, current flow in a branched neuron with 18 compartments was simulated. 5. Enhancement of excitability and enhancement of transmitter release, produced by modulatory transmitters, were simulated by second-messenger-induced modulation of K+ currents. A depletion model for synaptic depression was also simulated. 6. We also attempted to simulate the features of a more complicated central pattern generator, inspired by the properties of neurons in the buccal ganglia of Aplysia. Dynamic changes in the activity of this central pattern generator were produced by a second-messenger-induced modulation of a slow inward current in one of the neurons.
Potassium currents in mammalian and avian isolated type I semicircular canal hair cells
Authors: Rennie K. J. , Correia M. J.
Published: December 2017

1. Type I vestibular hair cells were isolated from the cristae ampullares of the semicircular canals of the Mongolian gerbil (Meriones unguiculatus) and the white king pigeon (Columba livia). Dissociated type I cells were distinguished from type II hair cells by their neck to plate ratio (NPR) and their characteristic amphora shape. 2. The membrane properties of gerbil and pigeon type I hair cells were studied in whole-cell voltage- and current-clamp using the perforated patch technique with amphotericin B as the perforating agent. 3. In whole-cell current-clamp, the average zero-current potential, Vz, measured for pigeon type I hair cells, was -70 +/- 7 (SD) mV (n = 18) and -71 +/- 11 mV (n = 83) for gerbil type I hair cells. 4. At Vz, for both gerbil and pigeon type I hair cells, a potassium current (IKI) was > or = 50% activated. This current deactivated rapidly when the membrane potential was hyperpolarized below -90 mV. 5. IKI was blocked by externally applied 4-aminopyridine (4-AP) (5 mM) and by internally applied 20 mM tetraethylammonium (TEA). It was also reduced when 4 mM barium was present in the external solution. The degree of block by barium increased as the membrane potential became more positive. External cesium (5 mM) blocked the inward component of IKI. When IKI was pharmacologically blocked, Vz depolarized by approximately 40 mV. Therefore IKI appears to be a delayed rectifier and to set the more negative Vz noted for isolated type I hair cells when compared to isolated type II hair cells, which do not have IKI. 6. A second, smaller potassium current was present at membrane potential depolarizations above -40 mV. This current was blocked by 30-50 mM, externally applied TEA, 100 microM quinidine, 100 nM apamin, but not 100 nM charybdotoxin, indicating that this is a calcium-activated potassium current, IK(Ca), different from the maxi-K calcium-activated potassium current found in most other hair cells.
Length and width tuning of neurons in the cat's primary visual cortex
Authors: DeAngelis G. C. , Freeman R. D. , Ohzawa I.
Published: December 2017

1. The classically defined receptive field of a visual neuron is the area of visual space over which the cell responds to visual stimuli. It is well established, however, that the discharge produced by an optimal stimulus can be modulated by the presence of additional stimuli that by themselves do not produce any response. This study examines inhibitory influences that originate from areas located outside of the classical (i.e., excitatory) receptive field. Previous work has shown that for some cells the response to a properly oriented bar of light becomes attenuated when the bar extends beyond the receptive field, a phenomenon known as end-inhibition (or length tuning). Analogously, it has been shown that increasing the number of cycles of a drifting grating stimulus may also inhibit the firing of some cells, an effect known as side-inhibition (or width tuning). Very little information is available, however, about the relationship between end- and side-inhibition. We have examined the spatial organization and tuning characteristics of these inhibitory effects by recording extracellularly from single neurons in the cat's striate cortex (Area 17). 2. For each cortical neuron, length and width tuning curves were obtained with the use of rectangular patches of drifting sinusoidal gratings that have variable length and width. Results from 82 cells show that the strengths of end- and side-inhibition tend to be correlated. Most cells that exhibit clear end-inhibition also show a similar degree of side-inhibition. For these cells, the excitatory receptive field is surrounded on all sides by inhibitory zones. Some cells exhibit only end- or side-inhibition, but not both. Data for 28 binocular cells show that length and width tuning curves for the dominant and nondominant eyes tend to be closely matched. 3. We also measured tuning characteristics of end- and side-inhibition. To obtain these data, the excitatory receptive field was stimulated with a grating patch having optimal orientation, spatial frequency, and size, whereas the end- or side-inhibitory regions were stimulated with patches of gratings that had a variable parameter (such as orientation). Results show that end- and side-inhibition tend to be strongest at the orientation and spatial frequency that yield maximal excitation. However, orientation and spatial frequency tuning curves for inhibition are considerably broader than those for excitation, suggesting that inhibition is mediated by a pool of neurons.(ABSTRACT TRUNCATED AT 400 WORDS)
Modulation of high-threshold transmission between heart interneurons of the medicinal leech by FMRF-NH2
Authors: Simon T. W. , Schmidt J. , Calabrese R. L.
Published: December 2017

1. We examined high-threshold synaptic transmission between oscillatory pairs of leech heart interneurons. Inhibitory postsynaptic currents (IPSCs) could be reliably evoked by depolarizing the presynaptic neuron in voltage clamp from a holding potential of -35 mV. At this presynaptic potential, the Ca2+ currents underlying graded transmission are completely inactivated, and we conclude that a high-threshold Ca2+ current is extant in heart interneurons. Further evidence for this was that inhibitory postsynaptic currents were blocked when Co2+ replaced Ca2+ in the saline and thus high-threshold transmission was dependent on the presence of external Ca2+. 2. When IPSCs were evoked by a 200-ms duration voltage step from a holding potential of -35 mV in the presynaptic neuron, the time course of turn-on of the IPSC consisted of a fast (time-to-peak = 17.5 +/- 1.93 (SE) ms [n = 7]) and a slow (time-to-peak = 250 +/- 28.5 ms [n = 8]) component. FMRF-NH2 reduced the amplitude of the fast component but did not affect the slow component. When the presynaptic voltage step was ended the IPSC turned off with a single exponential time course. FMRF-NH2 slowed the time course of turn-off of the IPSC. 3. When IPSCs were evoked by a 1500-ms duration voltage step from a holding potential of -35 mV in the presynaptic neuron, these IPSCs peaked around 300 ms. Following the peak, the IPSC decayed with a single exponential time course. FMRF-NH2 accelerated the time course of this decay. At potentials of 0 mV and +5 mV, FMRF-NH2 produced a significant decrease in the peak current and at potentials of -5 mV and 0 mV, produced a significant decrease in the current integral. 4. High-threshold IPSCs could also be evoked by a spike in the presynaptic neuron. Bath application of 1 microM FMRF-NH2 decreased the amplitude of the spike-evoked IPSC and slowed the time course of its falling phase. 5. We examined the effect of FMRF-NH2 on the quantal synaptic transmission. Bath-application of FMRF-NH2 increased binomial p, the probability of release, and decreased binomial n, the number of units available for release. FMRF-NH2 had no effect on q, the unit size, when calculated from the distributions of PSPs, and increased the coefficient of variation (CV). 6. The lack of a change in q and the increase in CV suggested that FMRF-NH2 acted at a presynaptic location.(ABSTRACT TRUNCATED AT 400 WORDS)
Functional characteristics of spontaneously active neurons in rat dorsal cochlear nucleus in vitro
Authors: Waller H. J. , Godfrey D. A.
Published: December 2017

1. The cochlear nucleus of rat brain stem slices was explored with extracellular microelectrodes to determine the distribution and characteristics of spontaneously active neurons. 2. In mapping experiments few spontaneously active neurons were found in anteroventral or posteroventral divisions of the cochlear nucleus. In contrast, spontaneously active neurons (N = 648) were widely distributed in the dorsal cochlear nucleus (DCN), especially its more superficial part. The density (neurons per penetration) was greatest 100-400 microns from the lateral surface of DCN, corresponding approximately to the fusiform soma layer and closely adjacent portions of the molecular and deeper regions. In penetrations with active neurons as many as 13 were found, with a mean of 4.3 neurons per penetration. Activity was found along the entire dorsomedial-ventrolateral extent of the nucleus, across the tonotopic representation. 3. Most neurons were readily categorized according to the spike interval pattern as regular (40%), bursting (30%), or irregular (30%). Regular and bursting patterns were highly stable, but few bursting neurons were found in relatively inactive slices. Although there was extensive overlap in location, bursting neurons were significantly closer to the lateral edge of the slice. Also, they were more likely to have initially negative action potentials than regular or irregular neurons. 4. A high density of spontaneous firing, including regular, bursting, and irregular patterns, was observed in slices containing only DCN and adjacent fiber tracts, with other nuclear structures trimmed away. 5. When the K+ concentration of the perfusion medium was decreased from 6.25 to 3.25 mM firing rates of regular neurons decreased moderately without changes in pattern. In contrast, firing rates of most bursting and irregular neurons showed large increases, and bursts were prolonged. 6. When the K+ concentration was increased from 6.25 to 9.25 or 12.25 mM regular neurons showed moderate increases in rate without changes in pattern. Effects on firing rates differed among bursting and irregular neurons, but bursts usually increased in frequency and decreased in duration, and irregular neurons showed some burst firing. 7. When Ca2+ was decreased to 0.2 mM and Mg2+ increased to 3.8 or 7.8 mM regular neurons did not change in pattern of firing although firing rates increased or decreased moderately. Bursting neurons showed large increases in the durations of the bursts. Firing rates of bursting neurons usually increased during 0.2 mM Ca2+ -3.8 mM Mg2+ but typically decreased, after an initial rise, during 0.2 mM Ca2+ -7.8 mM Mg2+.(ABSTRACT TRUNCATED AT 400 WORDS)
Corrective responses to loss of ground support during walking. II. Comparison of intact and chronic spinal cats
Authors: Hiebert G. W. , Gorassini M. A. , Jiang W. , Prochazka A. , Pearson K. G.
Published: December 2017

1. The preceding study described a corrective response in cats when one hind leg steps into a hole. In this investigation we examine the extent to which this behavior is organized at the spinal level by comparing the responses elicited in intact and chronic spinal cats. 2. Adult cats were trained to step bipedally with their hind legs on a treadmill. After training, the responses to stepping into a hole cut in the treadmill belt were monitored with a video recorder and by recording electromyograms from muscles in both hind legs. The responses to stepping into the hole were also recorded in chronic spinal cats that had recovered the ability to step with their hind legs a few weeks after spinalization. 3. The behavioral responses in the two groups of animals differed in two respects. First, the latency of the onset of the flexion movement to remove the foot from the hole was shorter in intact animals (70-150 ms in intact vs. 130-350 ms in spinal animals). Second, the flexion movement in the intact animals was stronger. The exaggerated flexion movement in intact animals lifted the paw well clear of the hole and allowed support to be regained on the treadmill belt. The weaker flexion movement in spinal animals was usually insufficient to lift the paw completely from the hole. 4. Differences in the motor patterns recorded from flexor muscles during the corrective response in intact and spinal animals correspond with the differences in the kinematics. First, the onset of flexor activity after the foot entered the hole was delayed by approximately 100 ms in spinal animals relative to intact animals. Second, in intact animals the magnitudes of flexor bursts were increased relative to the flexor bursts associated with the swing phase during stepping, whereas in spinal animals flexor bursts during the corrective response resembled those occurring during swing. 5. Similarities in the duration and the timing of bursts in different flexor muscles in intact and spinal animals during the corrective response and during swing indicated that the corrective response involves activation of the spinal system that normally produces swing phase flexor activity. We conclude that activation of this system is facilitated by input from supraspinal structures during the corrective response in intact animals. 6. In all intact animals and three of five spinal animals, support of the hindquarters when the foot entered the hole was maintained by the contralateral leg.(ABSTRACT TRUNCATED AT 400 WORDS)
Calcium currents in turtle retinal ganglion cells. I. The properties of T- and L-type currents
Authors: Liu Y. , Lasater E. M.
Published: December 2017

1. Voltage-activated calcium currents from single, isolated turtle retinal ganglion cells were characterized with standard whole cell patch clamp techniques. Calcium current amplitude was increased with the use of 10 mM extracellular Ca2+, whereas sodium and potassium currents were pharmacologically suppressed. 2. A transient component, expressed in approximately 39% of the cells recorded from, closely resembled the T-type calcium current described previously in other tissues. This component activated at low voltages (around -50 mV from a holding potential of -70 mV) and inactivated with a time constant 10-30 ms at -20 mV; the inactivation was strongly voltage dependent. Substitution of Ca2+ with Ba2+ reduced this current in most cases or had no effect in some instances. Surprisingly, the transient calcium current was potentiated by Bay-K 8644 and inhibited by nifedipine in some of the ganglion cells tested. 3. A sustained component, which activated at between -20 and -10 mV from a holding potential of -70 mV, was found in all ganglion cells from which we recorded. This component was substantially larger when equimolar Ba2+ replaced Ca2+ as the charge carrier, and was sensitive to the dihydropyridine agonist Bay-K 8644 and the antagonist nifedipine. Thus the sustained current in turtle retinal ganglion cells was similar to the L-type calcium current described in chick DRG neurons. However, unlike the typical L-type current, this component in turtle ganglion cells showed an inactivation that was highly dependent on the intracellular free Ca2+ concentration but not the membrane potential. 4. Synthetic omega-conotoxin MVIIC selectively blocked the sustained calcium current while sparing the transient component. It could completely block the sustained current that was resistant to nifedipine in some cells. Thus there may exist several different high voltage-activated calcium channels in turtle retinal ganglion cells.
GTP modulates run-up of whole-cell Ca2+ channel current in a Ca(2+)-dependent manner
Authors: Wagner J. J. , Alger B. E.
Published: December 2017

1. Whole-cell voltage-clamp recordings were obtained from CA1 neurons acutely dissociated from rat hippocampus to study the effects of guanosine 5'-triphosphate (GTP) on the gradual increase in Ca2+ channel current amplitude that takes place over several minutes after breaking in to whole-cell mode ("run-up"). 2. Including GTP (500 microM) in the patch pipette significantly prolonged the duration of run-up of peak Ca2+ channel current to its maximum value compared with controls without GTP when the recording solutions contained Ca2+. On the other hand, GTP significantly enhanced run-up when Mg2+ and Ba2+ were substituted for intracellular and extracellular Ca2+, respectively. 3. The enhancement of run-up of the current in the Mg/Ba condition appeared to be due both to an initial increase in current amplitude that was complete within 30 s after break in and to a more rapid initial rate of run-up when compared with the Ca2+ condition. GTP did not affect the absolute maximum amplitudes of the currents in either Ca2+ or Ba2+ conditions. 4. We conclude that an early GTP-dependent modulation of Ca2+ channel current is qualitatively altered, depending on whether Ca2+ or Ba2+ is used as the charge carrier. Evidence of this modulation is apparent within seconds after rupture of the membrane patch. Conceivably, influences occurring during the period of "equilibration" with electrode contents could alter subsequent regulatory steps.
Spinothalamic and spinohypothalamic tract neurons in the cervical enlargement of rats. III. Locations of antidromically identified axons in the cervical cord white matter
Authors: Dado R. J. , Katter J. T. , Giesler G. J.
Published: December 2017

1. Fifty-five neurons in the cervical enlargement (C6-C8) of urethan-anesthetized rats were antidromically activated from the contralateral posterior diencephalon. In all cases, antidromic thresholds were < or = 30 microA. The locations of the axons of these neurons within the white matter of segments C2-C6 were determined by tracking systematically using a second antidromic stimulating electrode. 2. The recording locations of 51 neurons were marked and recovered. Twenty neurons were recorded in the superficial dorsal horn (SDH) and 31 were in the deep dorsal horn (DDH). Eighty-three lowest threshold points for antidromic activation within the white matter of segments C2-C6 were determined for these 51 neurons. The mean antidromic threshold at these points was 9.5 +/- 0.5 (SE) microA. For 26 neurons, the lowest threshold point for antidromic activation was determined at one segmental level. We also attempted to determine whether individual axons maintained their position as they ascended through the cervical cord white matter. In 25 cases, lowest threshold points were determined at two or more segmental levels. 3. In segments C5-C6, 88% (7/8) of the lowest threshold points of the examined axons were located in the contralateral ventral funiculus, indicating that the majority of examined axons crossed the midline within one or two segments. 4. In segments C3-C4, 32% (14/44) of all examined axons were found in the dorsal lateral funiculus (DLF) and 66% (29/44) were within the ventral quadrant [ventral lateral funiculus (VLF) and ventral funiculus (VF)]. Sixty-nine percent (11/16) of the axons of neurons recorded in the SDH were located in the contralateral DLF and 31% (5/16) were located in the ventral quadrant (VQ). In contrast, only 11% (3/28) of the axons of neurons recorded in the DDH were located in the contralateral DLF and 86% (24/28) were located in the VQ. Therefore, in segments C3-C4, the locations of axons differed significantly. Those from neurons recorded in the SDH were located primarily in the DLF and those from neurons recorded in the DDH were located principally in the VQ. 5. In segment C2, 74% (23/31) of all examined axons were found in the DLF, 23% (7/31) were in the VQ, and 3% (1/31) were in the dorsal horn. Thus, the percentage of all examined axons in the DLF in C2 was approximately 2.5 times greater than it was in C3-C4.(ABSTRACT TRUNCATED AT 400 WORDS)
A model for dendritic Ca2+ accumulation in hippocampal pyramidal neurons based on fluorescence imaging measurements
Authors: Jaffe D. B. , Ross W. N. , Lisman J. E. , Lasser-Ross N. , Miyakawa H. , Johnston D.
Published: December 2017

1. High-speed fluorescence imaging was used to measure intracellular Ca2+ concentration ([Ca2+]i) changes in hippocampal neurons injected with the Ca(2+)-sensitive indicator fura-2 during intrasomatic and synaptic stimulation. The results of these experiments were used to construct a biophysical model of [Ca2+]i dynamics in hippocampal neurons. 2. A compartmental model of a pyramidal neuron was constructed incorporating published passive membrane properties of these cells, three types of voltage-gated Ca2+ channels characterized from adult hippocampal neurons, voltage-gated Na+ and K+ currents, and mechanisms for Ca2+ buffering and extrusion. 3. In hippocampal pyramidal neurons imaging of Na+ entry during electrical activity suggests that Na+ channels, at least in sufficient density to sustain action potentials, are localized in the soma and the proximal part of the apical dendritic tree. The model, which incorporates this distribution, demonstrates that action potentials attenuate steeply in passive distal dendritic compartments or distal dendritic compartments containing Ca2+ and K+ channels. This attenuation was affected by intracellular resistivity but not membrane resistivity. 4. Consistent with fluorescence imaging experiments, a non-uniform distribution of Ca2+ accumulation was generated by Ca2+ entry through voltage-gated Ca2+ channels opened by decrementally propagating Na+ action potentials. Consequently, the largest increases in [C2+]i were produced in the proximal dendrites. Distal voltage-gated Ca2+ currents were activated by broad, almost isopotential action potentials produced by reducing the overall density of K+ channels. 5. Simulations of subthreshold synaptic stimulation produced dendritic Ca2+ entry by the activation of voltage-gated Ca2+ channels. In the model these Ca2+ signals were localized near the site of synaptic input because of the attenuation of synaptic potentials with distance from the site of origin and the steep voltage-dependence of Ca2+ channel activation. 6. These simulations support the hypotheses generated from experimental evidence regarding the differential distribution of voltage-gated Ca2+ and Na+ channels in hippocampal neurons and the resulting voltage-gated Ca2+ accumulation from action and synaptic potentials.
Visual response properties of single neurons in the temporal pole of behaving monkeys
Authors: Nakamura K. , Matsumoto K. , Mikami A. , Kubota K.
Published: December 2017

1. The responses of single neurons in the anterior part of the temporal cortex in monkeys, mainly the temporopolar cortex, area 36, and the most anterior part of area TE of von Bonin and Bailey (1947) (these areas were designated here as the temporal pole), were examined during the performance of a visual recognition memory task. The visual stimulus (sample stimulus) was presented when the monkey pressed a lever. The same sample stimulus was presented one to four times and, thereafter, a new stimulus was presented. The monkeys were trained to discriminate the new stimulus from the sample stimulus and to release the lever in response to the new stimulus. We used colored photographs of natural objects (human faces, monkeys, foods, and non-food objects) as complex visual stimuli or computer-generated two-dimensional shapes (a red square, a green circle, etc.) as simple visual stimuli. 2. In total, the activity of 311 neurons was recorded, and 225 of these responded to at least one visual stimulus. All visually responsive neurons were located in the ventral part of the temporal pole including the banks of the superior temporal sulcus. 3. The relationship between the monkey's eye movements and visual responses was investigated. Visual response properties, such as the number of spikes, onset latency, and response duration, were stable regardless of the monkey's eye positions and movements if the eyes were directed to the display. We also examined the receptive field property of neurons (n = 3). The neurons tested in the temporal pole tended to have a large receptive field (24 x 24 degrees). 4. The neurons tended to respond to different stimuli in different magnitudes. In each case, the maximal responses were elicited by complex, colored photographs, whereas simple, two-dimensional colored shapes elicited little or no responses. In 21% of the cases (47/225), the magnitude of the maximal response was significantly larger than for any of the other responses. 5. An achromatic version of the stimulus that induced the maximal response was tested in 53 neurons. About 80% of the neurons (41/53) responded to the achromatic stimulus at a magnitude that was not significantly different from the response to the original stimulus. In 12 neurons, the removal of color did significantly decrease the magnitude of the response. When other colors were tested, 3 of 9 neurons were found to code for color. 6. In 21 of these 53 neurons, a portion (the left-, right-, upper-, or lower-half) of the stimulus was also tested.(ABSTRACT TRUNCATED AT 400 WORDS)
Inertial representation of angular motion in the vestibular system of rhesus monkeys. I. Vestibuloocular reflex
Authors: Angelaki D. E. , Hess B. J.
Published: December 2017

1. The spatial organization of the vestibuloocular reflex (VOR) was studied in six rhesus monkeys by applying fast, short-lasting, passive head and body tilts immediately after constant-velocity rotation (+/- 90 degrees/s) about an earth-vertical axis. Two alternative hypotheses were investigated regarding the reference frame used for coding angular motion. 1) If the vestibular system is organized in head-centered coordinates, postrotatory eye velocity would decay invariably along the direction of applied head angular acceleration. 2) Alternatively, if the vestibular system codes angular motion in inertial, gravity-centered coordinates, postrotatory eye velocity would decay along the direction of gravity. 2. Horizontal VOR was studied with the monkeys upright. Pitch (roll) tilts away from upright elicited a transient vertical (torsional) VOR and shortened the time constant of the horizontal postrotatory slow phase velocity. In addition, an orthogonal torsional (after pitch tilts) or vertical (after roll tilts) response gradually built up. As a result, the eye velocity vector transiently deviated in the roll (pitch) plane and then gradually rotated in the same direction as gravity in the pitch (roll) head plane until the orthogonal component reached a peak value. Subsequently, the residual postrotatory eye velocity decayed along a line parallel to gravity. 3. The time constant of the horizontal postrotatory response was maximal in upright position (21.5 +/- 5.7 s, mean +/- SD) and minimal after tilts to prone (3.8 +/- 0.7 s), supine (4.5 +/- 1.2 s), and ear-down (5.2 +/- 1.6 s) positions. A similar dependence on head orientation relative to gravity characterized the dynamics of the resultant eye velocity vector in the pitch and roll planes. 4. Torsional VOR was studied with the monkeys in supine or prone position. Pitch (yaw) tilts from the supine or prone position toward upright (ear-down) position elicited a transient vertical (horizontal) VOR and shortened the time constant of the torsional postrotatory response while a horizontal (vertical) orthogonal component slowly built up. As a result the eye velocity vector gradually rotated in the pitch (yaw) plane until the orthogonal component reached a peak value. Subsequently residual postrotatory eye velocity decayed along a line parallel to gravity. 5. The time constant of the torsional postrotatory response in supine/prone positions was 16.5 +/- 6.8 s. After tilts from supine/prone positions toward upright position, time constants decreased and were minimal after tilts to upright position (2.7 +/- 0.7 s).(ABSTRACT TRUNCATED AT 400 WORDS)