bluuebunny/crossref_metadata_2025 huggingface dataset:
Physiological characterization of spinohypothalamic tract neurons in the lumbar enlargement of rats
Authors: Burstein R. , Dado R. J. , Cliffer K. D. , Giesler G. J.
Published: December 2017

1. Ninety-six neurons in the lumbar enlargement of urethananesthetized rats were antidromically activated from the contralateral hypothalamus. The antidromic stimulating electrode was moved systematically within the hypothalamus until antidromic activation could be produced with currents of less than or equal to 50 microA (18.6 +/- 10.8 microA; mean +/- SD). The points at which antidromic activation thresholds were lowest were found in several regions of the hypothalamus but were concentrated in the optic tract and the supraoptic decussation. 2. The recording locations of 79 spinohypothalamic tract (SHT) neurons were marked and recovered. Twenty-nine were located in the superficial dorsal horn (SDH), 42 in the deep dorsal horn (DDH), 4 in the intermediate zone, and 2 in the gray matter surrounding the central canal. Two additional marks were located in the dorsal lateral funiculus (DLF). 3. The responses of 46 SHT neurons were examined during innocuous and noxious mechanical stimulation of their receptive fields. Forty-eight percent of recorded SHT neurons responded to both innocuous and noxious stimuli (wide dynamic range, WDR) and 39% responded only to noxious stimuli (high threshold, HT). Therefore 87% of SHT neurons responded preferentially or exclusively to noxious mechanical stimulation. Nine percent of SHT neurons responded exclusively to innocuous manipulation of joints and muscles. Four percent of SHT neurons responded only to innocuous tactile stimul (low threshold, LT). WDR, HT, and LT neurons were recorded widely throughout the dorsal horn; no relationship was found between the locations of recording sites in the dorsal horn and the response types of the neurons. SHT neurons that responded to stimulation of muscle, tendon, or joint were recorded deep in the gray matter. 4. The effects of heating the receptive fields were determined for 25 SHT neurons. Fourteen (56%) responded to thermal stimuli. Six (43%) of the responsive neurons responded at low frequencies to innocuous warming (38-41 degrees C) but more vigorously to noxious (greater than or equal to 45 degrees C) heating. The other eight responded only to noxious heat. Eighteen percent (3/17) of tested SHT neurons were activated by noxious cooling of their receptive fields. 5. Cutaneous receptive fields of most recorded SHT neurons were small, typically involving areas as small as two or three toes on the ipsilateral hindlimb; the largest receptive fields covered the entire paw. These findings indicate that relatively precise information about the location of innocuous and noxious stimuli is conveyed directly to the hypothalamus by SHT neurons.(ABSTRACT TRUNCATED AT 400 WORDS)
Discharge patterns of human C-fibers induced by itching and burning stimuli
Authors: Handwerker H. O. , Forster C. , Kirchhoff C.
Published: December 2017

1. The aim of this investigation was to study the peripheral neural mechanisms of the C-fiber-mediated modalities of burning pain and itch by the use of microneurography of human unmyelinated afferents. 2. Sixteen stable recordings of single C-fibers and 6 multiunit recordings were obtained from the superficial radial nerves of volunteers. All units were excited by stimulating their receptive fields with von Frey bristles (range 10-600 mN), and all but four units were also driven by radiant heat stimulation. 3. Histamine was iontophoretically applied to the receptive fields of these units for 20 or 30 s and was found to provoke itching sensations lasting several minutes, together with wheal and flare responses. Subsequently a solution containing 20 or 30% mustard oil was applied to the receptive field of the respective unit, which provoked a sensation of burning pain. 4. One-half of the units were excited by histamine, and the median discharge rates derived from interspike intervals ranged from approximately 0.1 to 0.8 Hz. Mustard oil-induced activity was observed in all histamine-sensitive units and also in three single units and in one multiunit recording that revealed no histamine response. Median interval-derived discharge rates ranged from 0.2 to 1.2 Hz. 5. Analysis of the interspike interval distribution and of the autocorrelation function derived from the chemically induced discharges of single units provided no evidence for an encoding of itch and burning pain in different discharge patterns of units responding to histamine and to mustard oil.(ABSTRACT TRUNCATED AT 250 WORDS)
Relationship of intrinsic connections to forelimb movement representations in monkey motor cortex: a correlative anatomic and physiological study
Authors: Huntley G. W. , Jones E. G.
Published: December 2017

1. Intracortical microstimulation (ICMS) and horseradish peroxidase (HRP) histochemistry were combined to examine the relationship between intrinsic connections and intracortical microstimulation sites eliciting evoked movements in the forelimb representation of adult macaque monkey motor cortex. 2. The distribution of sites from which stimulation-evoked movements about individual forelimb joints were elicited under anesthesia varied considerably among animals. Identical movements could often be elicited from multiple, noncontiguous sites. 3. After single, small extracellular HRP injections at sites from which thumb movement was evoked, small groups of retrogradely labeled cells and dense patches of axon terminations were found scattered across a wide area of the forelimb representation. Terminal patches were discontinuous and arose from horizontal, intracortical axons. 4. Correlating the HRP labeling with the physiologically defined movement maps revealed a profuse set of intrinsic, bidirectional connections that connect digit representations and representations of movements about the wrist, elbow, and shoulder. 5. HRP injections placed in the forelimb representation close to the physiologically defined face representation resulted in virtually no retrogradely labeled cells or terminal fiber labeling that crossed into the face representation. A patch of anterolaterally placed label that was present may be the dissociated rostrolateral arm area of other authors. 6. Taken together, these data suggest that extensive, horizontally oriented, intrinsic axon collaterals provide inputs to many different forelimb movement representations and may be recruited during complex movements to coordinate the activity of motor cortical zones whose predominant output is to forelimb muscle groups acting synchronously.
Computer simulations of N-methyl-D-aspartate receptor-induced membrane properties in a neuron model
Authors: Brodin L. , Traven H. G. , Lansner A. , Wallen P. , Ekeberg O. , Grillner S.
Published: December 2017

1. To evaluate the role of N-methyl-D-aspartate (NMDA) receptors in simulations of the lamprey spinal locomotor network, we developed a computer-simulated electrical model of a neuron that contains NMDA channels in addition to voltage-gated Na+, K+, and Ca2+ channels and Ca(2+)-activated K+ channels [K(Ca) channels]. 2. The voltage dependence of the Mg2+ block of the Na(+)-K+ current flow through the NMDA channel was modeled according to a scheme of open-channel block. To account for the regulation of K(Ca) channels by NMDA and membrane voltage, we modeled two separate Ca2+ pools that had different voltage dependencies and dynamics. 3. Pacemaker-like membrane potential oscillations could be elicited in the model neuron, which resembled those observed experimentally in the presence of bath-applied NMDA and tetrodotoxin. The effect of changing different channel parameters were tested to determine under which conditions such membrane potential oscillations could occur. 4. The oscillation amplitude was determined by the potential levels at which the NMDA channels and voltage-dependent K+ channels, respectively, were activated. The oscillation frequency and the relative durations of the de- and hyperpolarized phases of the oscillations were determined by the balance between the depolarizing (NMDA channels) and hyperpolarizing [K(Ca) channels] currents. 5. Simulated alterations of the Mg2+ concentration and the K+ conductance as well as injection of constant current caused changes of the oscillations corresponding to those observed experimentally. The de- and hyperpolarizing phases could be reset by brief current pulses. 6. We conclude that the present model can account for the effects of bath-applied NMDA on spinal neurons. This permits an incorporation of NMDA-receptor-mediated properties in simulation models of the lamprey locomotor network.
Neuronal activity related to visually guided saccades in the frontal eye fields of rhesus monkeys: comparison with supplementary eye fields
Authors: Schall J. D.
Published: December 2017

1. The purpose of this study was to analyze the response properties of neurons in the frontal eye fields (FEF) of rhesus monkeys (Macaca mulatta) and to compare and contrast the various functional classes with those recorded in the supplementary eye fields (SEF) of the same animals performing the same go/no-go visual tracking task. Three hundred ten cells recorded in FEF provided the data for this investigation. 2. Visual cells in FEF responded to the stimuli that guided the eye movements. The visual cells in FEF responded with a slightly shorter latency and were more consistent and phasic in their activation than their counterparts in SEF. The receptive fields tended to emphasize the contralateral hemifield to the same extent as those observed in SEF visual cells. 3. Preparatory set cells began to discharge after the presentation of the target and ceased firing before the saccade, after the go/no-go cue was given. These neurons comprised a smaller proportion in FEF than in SEF. In contrast to their counterparts in SEF, the preparatory set cells in FEF did not respond preferentially in relation to contralateral movements, even though most responded preferentially for movements in one particular direction. The time course of the discharge of the FEF set cells was similar to that of their SEF counterparts, except that they reached their peak level of activation sooner. The few preparatory set cells in FEF tested with both auditory and visual stimuli tended to respond preferentially to the visual targets, whereas, in contrast, most set cells in SEF were bimodal. 4. Sensory-movement cells represented the largest population of cells recorded in FEF, responding in relation to both the presentation of the targets and the execution of the saccade. Although some of these sensory-movement cells resembled their counterparts in SEF by exhibiting a sustained elevation of activity, most of the FEF sensory-movement cells gave two discrete bursts, one after the presentation of the target and another before and during the saccade. Like their counterparts in SEF, the sensory-movement cells tended to be tuned for saccades into the contralateral hemifield, but this tendency was more pronounced in FEF than in SEF. The FEF sensory-movement cells discharged more briskly, with a shorter latency relative to the presentation of the target, than their counterparts in SEF. In addition, the FEF sensory-movement neurons reached their peak activation sooner than SEF sensory-movement neurons. Most FEF sensory-movement cells exhibited different patterns of activation in response to visual and auditory targets.(ABSTRACT TRUNCATED AT 400 WORDS)
A model of a CA3 hippocampal pyramidal neuron incorporating voltage-clamp data on intrinsic conductances
Authors: Traub R. D. , Wong R. K. , Miles R. , Michelson H.
Published: December 2017

1. We have developed a 19-compartment cable model of a guinea pig CA3 pyramidal neuron. Each compartment is allowed to contain six active ionic conductances: gNa, gCa, gK(DR) (where DR stands for delayed rectifier), gK(A), gK(AHP), and gK(C). THe conductance gCa is of the high-voltage activated type. The model kinetics for the first five of these conductances incorporate voltage-clamp data obtained from isolated hippocampal pyramidal neurons. The kinetics of gK(C) are based on data from bullfrog sympathetic neurons. The time constant for decay of submembrane calcium derives from optical imaging of Ca signals in Purkinje cell dendrites. 2. To construct the model from available voltage-clamp data, we first reproduced current-clamp records from a model isolated neuron (soma plus proximal dendrites). We next assumed that ionic channel kinetics in the dendrites were the same as in the soma. In accord with dendritic recordings and calcium-imaging data, we also assumed that significant gCa occurs in dendrites. We then attached sections of basilar and apical dendritic cable. By trial and error, we found a distribution (not necessarily unique) of ionic conductance densities that was consistent with current-clamp records from the soma and dendrites of whole neurons and from isolated apical dendrites. 3. The resulting model reproduces the Ca(2+)-dependent spike depolarizing afterpotential (DAP) recorded after a stimulus subthreshold for burst elicitation. 4. The model also reproduces the behavior of CA3 pyramidal neurons injected with increasing somatic depolarizing currents: low-frequency (0.3-1.0 Hz) rhythmic bursting for small currents, with burst frequency increasing with current magnitude; then more irregular bursts followed by afterhyperpolarizations (AHPs) interspersed with brief bursts without AHPs; and finally, rhythmic action potentials without bursts. 5. The model predicts the existence of still another firing pattern during tonic depolarizing dendritic stimulation: brief bursts at less than 1 to approximately 12 Hz, a pattern not observed during somatic stimulation. These bursts correspond to rhythmic dendritic calcium spikes. 6. The model CA3 pyramidal neuron can be made to resemble functionally a CA1 pyramidal neuron by increasing gK(DR) and decreasing dendritic gCa and gK(C). Specifically, after these alterations, tonic depolarization of the soma leads to adapting repetitive firing, whereas stimulation of the distal dendrites leads to bursting. 7. A critical set of parameters concerns the regulation of the pool of intracellular [Ca2+] that interacts with membrane channels (gK(C) and gK(AHP)), particularly in the dendrites.(ABSTRACT TRUNCATED AT 400 WORDS)
Electrophysiological study of spinothalamic inputs to ventrolateral and adjacent thalamic nuclei of the cat
Authors: Yen C. T. , Honda C. N. , Jones E. G.
Published: December 2017

1. Extracellular and intracellular methods were used to record from fibers and neurons in the ventral lateral (VL) and adjacent nuclei of the cat thalamus. The receptive fields of the recorded units were analyzed and the units tested for inputs from the medial lemniscus (ML) and spinothalamic tract (STT) by electrical stimulation of the dorsal columns (DC) and ventrolateral funiculus (VLF) at the C2-3 spinal level. 2. Thirty-eight STT fibers were isolated in the thalamus. Their conduction velocities ranged from 15 to 75 m/s (mode 36 m/s). Adequate stimuli were found for 23 of these fibers. Seventeen were low-threshold (LT), 3 were wide-dynamic-range (WDR), and 3 were high-threshold (HT) units. 3. Five STT fibers were intra-axonally injected. Three were sufficiently well filled for analysis of their terminal fields. An intermediate-velocity STT fiber (conduction velocity 38 m/s) had a 4.3-microns axon and a single large terminal field in the central lateral nucleus (CL). The other two STT fibers were smaller, with diameters of 2.5 and 2.3 microns, conduction velocities of 15 and 19 m/s, and terminal fields made up of a few small boutons at the borders of the ventral posterior lateral nucleus (VPL). 4. Of 319 neurons isolated, 14 out of 129 (10.8%) in VL, 14 out of 76 (18.4%) in the VPL or ventral posterior medial (VPM) nucleus, 27 out of 64 (42.2%) in the CL nucleus, and 5 out of 50 (10%) in the reticular nucleus (R) responded at latencies less than 50 ms to VLF stimuli. A train of three pulses was more effective in driving VLF-responding neurons in all these nuclei than a single pulse. VLF-responding cells were widely dispersed in VL, concentrated in a focus in CL, and distributed around the borders of VPL. Most of those in VL and a small number in CL could be antidromically activated by stimulation of motor cortex. 5. Latencies of presynaptic responses (STT fibers) to VLF stimulation were short and varied from 0.8 to 3.9 ms (mode 1.6 ms). Despite this, very few fast-responding neurons were found. These were six VPL neurons (2.5 to 4 ms), one VL neuron (3 ms), and four CL neurons (3-4 ms). The initial spike latencies of the majority of thalamic neurons responding to VLF stimulation appeared in two peaks, one between 6 and 8 ms and the other at 10-15 ms.(ABSTRACT TRUNCATED AT 400 WORDS)
Saccade-related activity in the lateral intraparietal area. I. Temporal properties; comparison with area 7a
Authors: Barash S. , Bracewell R. M. , Fogassi L. , Gnadt J. W. , Andersen R. A.
Published: December 2017

1. The cortex of the inferior parietal lobule (IPL) contains neurons whose activity is related to saccadic eye movements. The exact role of the IPL in relation to saccades remains, however, unclear. In this and the companion paper, we approach this problem by quantifying many of the spatial and temporal parameters of the saccade-related (S) activity. These parameters have hitherto been largely unstudied. 2. The activity of single neurons was recorded from Macaca mulatta monkeys while they were performing a delayed-saccade task. The analysis presented here is based on 161 neurons recorded from the lateral intraparietal area (LIP), a recently defined subdivision of the IPL; and 54 neurons recorded from the neighboring part of the IPL, area 7a. Overall, 409 IPL neurons were isolated in this study. 3. The typical activity of IPL neurons during the delayed-saccade task has three basic phases: light sensitive (LS), memory (M), and S. These basic phases are common to neurons of both areas LIP and 7a. In each phase (LS, M, and S), individual neurons may or may not be active. Most LIP neurons, however, are active in more than one phase. 4. To compare the activity levels of different neurons, the actual firing rate was weighted by each neuron's background level, yielding an "activity index" for each neuron, in each phase of the task. We calculated the activity index for the LS and M phases and for three phases related to the saccade: a presaccadic (Pre-S), a saccade-coincident (S-Co), and a postsaccadic (Post-S) phase. For area LIP neurons the median values of the activity index were high for the LS, M, Pre-S, and S-Co activities, and slightly lower in the Post-S period. In area 7a the median values were low for the LS phase and, in particular, for the M and Pre-S phases, somewhat higher coincident with the saccade, and high post-saccadically. 5. In area LIP, in each phase, 49-63% of the neurons had excitatory activity, and 10-17% had inhibitory responses. 6. In contrast, in area 7a excitatory responses were most frequent in the Post-S phase (56%). Excitation was particularly infrequent during M (28%) and Pre-S (22%). The incidence of inhibitory responses varied too (4-18%). The time course of inhibition was roughly opposite that of excitation; the highest frequency of inhibitory responses occurred during the saccade.(ABSTRACT TRUNCATED AT 400 WORDS)
Synaptic potentials evoked by convergent somatosensory and corticocortical inputs in raccoon somatosensory cortex: substrates for plasticity
Authors: Smits E. , Gordon D. C. , Witte S. , Rasmusson D. D. , Zarzecki P.
Published: December 2017

1. "Unmasking" of weak synaptic connections has been suggested as a mechanism for the early changes in cortical topographic maps that follow alterations of sensory activity. For such a mechanism to operate, convergent sensory inputs must already exist in the normal cortex. 2. We tested for topographic and cross-modality convergence in primary somatosensory cortex of raccoon. The representation of glabrous skin of forepaw digits was chosen because, even though it is dominated by inputs from the glabrous skin of a single digit, it nevertheless comes to respond to stimulation of other digits when, e.g., a digit is removed. 3. Intracellular recordings were made from 109 neurons in the representation of glabrous skin of digit 4. Neurons were tested for somatosensory inputs with electrical and natural stimulation of digits. 4. Excitatory postsynaptic potentials (EPSPs) were evoked in 100% of the neurons (109/109) by electrical stimulation of glabrous skin of digit 4, and in 79% (31 of 39) by vibrotactile stimulation. 5. Glabrous skin of digit 4 was not the sole source of somatosensory inputs. A minority of neurons generated EPSPs after electrical stimulation of hairy skin of digit 4 (10 of 98 neurons, 10%). Electrical stimulation of digits 3 or 5 evoked EPSPs in 22 of 103 neurons (21%). Natural stimulation (vibrotactile or hair bending) was also effective in most of these latter cases (digit 3, 6/7; digit 5, 9/10). 6. Intracortical microstimulation of the "heterogeneous zone" was used to test for corticocortical connections to neurons in the glabrous zone.(ABSTRACT TRUNCATED AT 250 WORDS)
Ocular responses to translation and their dependence on viewing distance. I. Motion of the observer
Authors: Schwarz U. , Miles F. A.
Published: December 2017

1. The horizontal eye movements induced by acceleration along the interaural axis were recorded from five monkeys (Macaca mulatta) by the use of the electromagnetic search-coil technique. Animals sat on a sled that was moved briefly in darkness along a linear track (bell-shaped acceleration profile: peak, 400 mm/s2; duration, 200 ms). Immediately before acceleration, animals fixated one of five target lights located at distances ranging from 16 to 150 cm. During fixation, the horizontal positions of both eyes were used to check vergence, while accommodation was monitored with an infrared optometer. 2. Sled motion induced eye movements that were generally smooth and compensatory, e.g., rightward sled motion elicited leftward eye movement. We attribute these responses to a translational vestibuloocular reflex (TVOR) that senses the sled motion through the otolith organs. However, in three animals, these responses were preceded by weak anticompensatory movements (duration, less than 40 ms; amplitude, less than 10% of the maximum compensatory response). 3. Geometry indicates that, during brief sled motion, the eye movements required to keep gaze aligned on a particular location ("full" compensation) are inversely proportional to the viewing distance. Response measures based on the computed eye velocity profiles, such as the velocity achieved at specific times ("time slices") or the peak values of the estimated covariance functions, all indicated that compensatory responses were a linear function of the inverse of the prior viewing distance. Cross-correlation analyses indicated that the effect of the prior viewing distance was to scale responses, although detailed spectral analyses revealed that high-frequency components (greater than 10 Hz) tended to scale less vigorously than lower ones. 4. The adequacy of the compensatory eye movements was assessed by calculating the gain (response recorded/response required for full compensation). Regardless of the response measure used, gains varied considerably from one animal to another and, in some particular animals, from one direction to another but showed a general tendency to increase with viewing distance. For example, on the basis of the peak eye velocity achieved within 250 ms of the onset of sled motion, mean gain at 16 cm was 0.74 (range, 0.48-1.01), whereas at 150 cm it was 1.25 (range, 0.67-1.73). 5. Using wedge prisms to dissociate vergence and accommodation indicated that ocular responses to sled motion were sensitive to selective increases in either vergence (base-out prism with the most distant target) or accommodation (base-in prism with the nearest target). However, the magnitude of the effects showed considerable variability from one animal to another and, in some particular animals, from one direction to another.(ABSTRACT TRUNCATED AT 400 WORDS)
Transient reversal of the stretch reflex in human arm muscles
Authors: Lacquaniti F. , Borghese N. A. , Carrozzo M.
Published: December 2017

1. Load perturbation responses can violate the law of reciprocal innervation between antagonist muscles under particular conditions. Thus flexor and extensor muscles of wrist and elbow joints are reflexly coactivated by the impact of a ball on the hand during a catching task. The aim of this study was to determine whether reflex coactivation can be preset within the central nervous system (CNS) or whether it is entirely due to the peripheral stimulus. To this end, we studied the behavior of stretch reflex responses of arm muscles evoked by torque motor perturbations applied before and during the catching task. 2. Subjects were instructed to catch a ball dropped from 1.6 m. A torque motor delivered perturbations to the elbow joint, resulting in angular motion at both elbow and wrist joints because of their dynamic mechanical coupling. Two series of experiments were performed that differed in the perturbation waveform. In the first series, a single torque pulse could be randomly applied at different times during the task. The corresponding responses were recovered by subtracting the average of the unperturbed trials from the averages of perturbed trials. In the second series of experiments, a train of pseudorandom pulses was applied continuously during each trial. The time-varying impulse responses were computed at 20-ms intervals by cross-correlation methods. 3. The pattern of the short-latency electromyographic responses evoked by either single pulses or pseudorandom perturbations obeyed the law of reciprocal innervation of antagonist muscles under basal conditions. However, the pattern of the responses evoked by the same perturbations around the time of ball impact on the hand consisted of a substantial coactivation of both stretched and shortening muscles. Reflex coactivation resulted from response patterns that differed at different joints. At the elbow, reflex coactivation resulted from a transient reversal of the direction of the short-latency responses of flexor muscles, with little changes of the responses of extensor muscles. At the wrist, instead, reflex coactivation resulted from simultaneous changes in the response waveform of both flexor and extensor muscles. 4. The peripheral conditions associated with the applied perturbations were constant before the time of ball impact. Thus, because the changes of the stretch reflex responses began before that time, they must have been generated within the CNS. It is here hypothesized that the reversal of the reflex responses is centrally gated by switching from the pathways of reciprocal inhibition to those of coactivation of antagonist alpha-motoneurons.(ABSTRACT TRUNCATED AT 400 WORDS)
Excitatory transmission in the basolateral amygdala
Authors: Rainnie D. G. , Asprodini E. K. , Shinnick-Gallagher P.
Published: December 2017

1. Intracellular current-clamp recordings obtained from neurons of the basolateral nucleus of the amygdala (BLA) were used to characterize postsynaptic potentials elicited through stimulation of the stria terminalis (ST) or the lateral amygdala (LA). The contribution of glutamatergic receptor subtypes to excitatory postsynaptic potentials (EPSPs) were analyzed by the use of the non N-methyl-D-aspartate (non-NMDA) antagonist, 6-cyano-7-nitro-quinoxaline-2,3-dione (CNQX), and the NMDA antagonist, (DL)-2-amino-5-phosphonovaleric acid (APV). 2. Basic membrane properties of BLA neurons determined from membrane responses to transient current injection showed that at the mean resting membrane potential (RMP; -67.2 mV) the input resistance (RN) and time constant for membrane charging (tau) were near maximal, and that both values were reduced with membrane hyperpolarization, suggesting an intrinsic regulation of synaptic efficacy. 3. Responses to stimulation of the ST or LA consisted of an EPSP followed by either a fast inhibitory postsynaptic potential (f-IPSP) only, or by a fast- and subsequent slow-IPSP (s-IPSP). The EPSP was graded in nature, increasing in amplitude with increased stimulus intensity, and with membrane hyperpolarization after DC current injection. Spontaneous EPSPs were also observed either as discrete events or as EPSP/IPSP waveforms. 4. In physiological Mg2+ concentrations (1.2 mM), at the mean RMP, the EPSP consisted of dual, fast and slow, glutamatergic components. The fast-EPSP (f-EPSP) possessed characteristics of kainate/quisqualate receptor activation, namely, the EPSP increased in amplitude with membrane hyperpolarization, was insensitive to the NMDA receptor antagonist, APV (50 microM), and was blocked by the non-NMDA receptor antagonist, CNQX (10 microM). In contrast, the slow-EPSP (s-EPSP) decreased in amplitude with membrane hyperpolarization, was insensitive to CNQX (10 microM), and was blocked by APV (50 microM), indicating mediation by NMDA receptor activation. 5. In the presence of CNQX (10 microM), ST stimulation evoked an APV-sensitive s-EPSP. In contrast, LA stimulation evoked a f-IPSP, which when blocked by subsequent addition of bicuculline methiodide (BMI; 30 microM) revealed a temporally overlapping APV-sensitive s-EPSP. These data suggest that EPSP amplitude and duration are determined, in part, by the shunting of membrane conductance caused by a concomitant IPSP. 6. Superfusion of either CNQX or APV in BLA neurons caused membrane hyperpolarization and blockade of spontaneous EPSPs and IPSPs, suggesting that these compounds may act to block tonic excitatory amino acid (EAA) release within the nucleus, and that a degree of feed-forward inhibition occurs within the nucleus.(ABSTRACT TRUNCATED AT 400 WORDS)
Physiological properties of primary sensory neurons appropriately and inappropriately innervating skin in the adult rat
Authors: Lewin G. R. , McMahon S. B.
Published: December 2017

1. We have studied the physiology of sensory neurons innervating skin of the rat hindlimb, in three groups of animals: 1) normal animals; 2) animals in which the sural nerve (Sn) had regenerated to its original cutaneous target; and 3) animals in which the gastrocnemius muscle nerve (Gn) had previously been cut and cross anastomosed with the distal stump of the cut Sn so that its axons regenerated to a foreign target, skin. 2. Single-unit recordings were made from 222 afferents in normal, intact animals. They had conduction velocities of 0.5-53.1 m/s. The conduction velocity distribution had distinct peaks at approximately 37.5, 2.5, and 1.25 m/s, presumably corresponding to A alpha beta-, A delta-, and C-fiber populations. Eighty-two percent of the characterized myelinated fibers had low-threshold mechanosensitive receptive fields, whereas 16% were high threshold, and only 2% appeared to have no receptive field. The very large majority of low-threshold mechanosensitive receptive fields (87%) were rapidly adapting hair follicle afferents. 3. In animals with regenerated Sn, 308 afferents were recorded with conduction velocities of 0.4-58.8 m/s. However, the mean conduction velocity was lower than in control animals (P less than 0.05), and only one peak, at 27.5 m/s, was apparent for myelinated fibers. Eighty-six percent of myelinated fibers were low-threshold mechanosensitive afferents, 8.5% were high-threshold mechanoreceptors (HTMRs), and 5.5% appeared to have no receptive fields. Fewer low-threshold mechanoreceptors (LTMRs; compared with controls) were activated by hair movement (63 vs. 87%). Most of the remainder appeared to be field receptors (which were therefore more commonly observed here than in normal animals). 4. In animals in which the Gn had regenerated to skin, 430 afferents were recorded. These had conduction velocities ranging from 0.6 to 71.4 m/s, and again only one peak was apparent in the myelinated conduction velocity histogram, at approximately 17.5 m/s. Of the myelinated fibers, 79% had low-threshold mechanosensitive receptive fields in skin and 10% high-threshold mechanosensitive receptive fields. The remaining 11% apparently had no receptive field (cf. 5.5% in regenerated Sn). In contrast to normal or regrown sural afferents, only 58% of low-threshold gastrocnemius afferents in skin were rapidly adapting. Of the 42% slowly adapting afferents, many surprisingly responded to hair movement. Thus some gastrocnemius afferents seemed to have retained the adaptation properties characteristic of muscle afferents. Also surprisingly, given that the Gn contains fewer fibers than the Sn, receptive-field areas were not significantly different from regrown or normal sural fibers.(ABSTRACT TRUNCATED AT 400 WORDS)
Corticostriatal transformations in the primate somatosensory system. Projections from physiologically mapped body-part representations
Authors: Flaherty A. W. , Graybiel A. M.
Published: December 2017

1. The basal ganglia of primates receive somatosensory input carried largely by corticostriatal fibers. To determine whether map-transformations occur in this corticostriatal system, we investigated how electrophysiologically defined regions of the primary somatosensory cortex (SI) project to the striatum in the squirrel monkey (Saimiri sciureus). Receptive fields in the hand, mouth, and foot representations of cortical areas 3a, 3b, and 1 were mapped by multiunit recording; and small volumes of distinguishable anterograde tracers were injected into different body-part representations in single SI areas. 2. Analysis of labeled projections established that at least four types of systematic remapping occur in the primate corticostriatal system. 1) An area of cortex representing a single body part sends fibers that diverge to innervate multiple regions in the putamen, forming branching, patchy fields that are densest in the lateral putamen. The fields do not form elongated cylindrical forms; rather, they are nearly as extended mediolaterally as they are rostrocaudally. 2) Cortical regions representing hand, mouth, and foot send globally somatotopic, nonoverlapping projections to the putamen, but regions with closely related representations (such as those of the thumb and 5th finger in area 3b) send convergent, overlapping corticostriatal projections. The overlap is fairly precise in the caudal putamen, but in the rostral putamen the densest zones of the projections do not overlap. 3) Regions representing homologous body parts in different SI cortical areas send projections that converge in the putamen. This was true of paired projections from areas 3a and 3b, and from areas 3b and 1. Thus corticostriatal inputs representing distinct somatosensory submodalities can project to the same local regions within the striatum. Convergence is not always complete, however: in the rostral putamen of two cases comparing projections from areas 3a and 1, the densest zones of the projections did not overlap. 4) All projections from SI avoid striosomes and innervate discrete zones within the matrix. 3. These experiments demonstrate that the somatosensory representations of the body are reorganized as they are projected from SI to the somatosensory sector of the primate putamen. This remapping suggests that the striatal representation of the body may be functionally distinct from that of each area of SI. The patchy projections may provide a basis for redistribution of somatosensory information to discrete output systems in the basal ganglia. Transformations in the corticostriatal system could thus be designed for modulating different movement-related programs.
Slow inactivation of a TEA-sensitive K current in acutely isolated rat thalamic relay neurons
Authors: Huguenard J. R. , Prince D. A.
Published: December 2017

1. Voltage-gated K currents were studied in relay neurons (RNs) acutely isolated from somatosensory (VB) thalamus of 7- to 14-day-old rats. In addition to a rapidly activated, transient outward current, IA, depolarizations activated slower K+ currents, which were isolated through the use of appropriate ionic and pharmacological conditions and measured via whole-cell voltage-clamp. 2. At least two slow components of outward current were observed, both of which were sensitive to changes in [K+]o, as expected for K conductances. The first, IK1, had an amplitude that was insensitive to holding potential and a relatively small conductance of 150 pS/pF. It was blocked by submillimolar levels of tetraethylammonium [TEA, 50%-inhibitory concentration (IC50 = 30 microM)] and 4-aminopyridine (4-AP, 40 microM). In the absence of intracellular Ca2+ buffering, the amplitude of IK1 was both larger and dependent on holding potential, as expected for a Ca(2+)-dependent current. Replacement of [Ca2+]o by Co2+ reduced IK1, although the addition of Cd2+ to Ca(2+)-containing solutions had no effect. 3. The second component, IK2, had a normalized conductance of 2.0 nS/pF and was blocked by millimolar concentrations of TEA (IC50 = 4 mM) but not by 4AP. The kinetics of IK2 were analogous to (but much slower than) those of IA in that both currents displayed voltage-dependent activation and voltage-independent inactivation. IK2 was not reduced by the addition of Cd2+ to Ca(2+)-containing solutions or by replacement of Ca2+ by Co2+. 4. IK2 had a more depolarized activation threshold than IA and attained peak amplitude with a latency of approximately 100 ms at room temperature. IK2 decay was nonexponential and could be described as the sum of two components with time constants (tau) near 1 and 10 s. 5. IK2 was one-half steady-state inactivated at a membrane potential of -63 mV, near the normal resting potential for these cells. The slope factor of the Boltzman function describing steady-state inactivation was 13 mV-1, which indicates that IK2 varies in availability across a broad voltage range between -100 and -20 mV. 6. Activation kinetics of IK2 were voltage dependent, with peak latency shifting from 300 to 50 ms in the voltage range -50 to +30 mV. Deinactivation and deactivation were also voltage dependent, in contrast to inactivation, which showed little dependence on membrane potential. Increase in temperature sped the kinetics of IK2, with temperature coefficient (Q10) values near 3 for activation and inactivation. Heating increased the amplitude of IK2 with a Q10 value near 2.(ABSTRACT TRUNCATED AT 400 WORDS)
Visual activity in areas V3a and V3 during reversible inactivation of area V1 in the macaque monkey
Authors: Girard P. , Salin P. A. , Bullier J.
Published: December 2017

1. Behavioral studies in the monkey and clinical studies in humans show that some visuomotor functions are spared in case of a V1 lesion. This residual vision appears to be subserved at least partially by visual activity in extrastriate cortex. Earlier studies have demonstrated that neurons in area V2 lose their visual responses when V1 is reversibly inactivated. On the other hand, Rodman and collaborators have recently shown that neurons in the middle temporal area (area MT) remain visually responsive when V1 is lesioned or inactivated. The purpose of the present study was to determine whether area MT is unique among extrastriate cortical areas in containing visually responsive neurons in the absence of input from area 17. 2. A circular part of the opercular region of area V1 was reversibly inactivated by cooling with a Peltier device. In that condition, 149 sites were recorded in the retinotopically corresponding regions of areas V3 and V3a. 3. About 30% of sites in area V3a still responded to visual stimulation when V1 was inactivated. On the contrary, nearly all sites in area V3 ceased to fire to visual stimulation. Receptive-field properties were assessed with qualitative measures; for most single cells or multiunit sites that responded during V1 inactivation, these properties did not change during cooling. 4. These results suggest that area V3a could take part in spared visuomotor abilities in case of a lesion of V1. Areas V3a and MT are both part of the occipitoparietal pathway, which suggests that the residual vision observed after a lesion of area 17 may depend mostly on this pathway.
Discharge patterns of trigeminal commissural last-order interneurons during fictive mastication in the rabbit
Authors: Donga R. , Lund J. P.
Published: December 2017

1. The aim of these experiments was to examine the physiological properties and patterns of firing of trigeminal interneurons during fictive mastication in anesthetized and paralyzed rabbits. Antidromic stimulation was used to show that the 82 interneurons projected to the area of the contralateral fifth nerve motor nucleus (NVmot). 2. Straight-line conduction velocities calculated from stereotaxic coordinates of the stimulating and recording electrodes for 63 interneurons were found to range between 3.7 and 16.3 m/s (mean, 9.5 m/s). 3. Histological reconstructions of recording electrode tracks showed that the interneurons observed in this study were located in the lateral brain stem in or just medial to the rostral trigeminal sensory nuclei, including the intertrigeminal (NVint) and supratrigeminal (NVs) areas, the main sensory nucleus of the fifth nerve (NVsnpr), the rostral subdivision of the oral nucleus of the spinal trigeminal tract (NVor tau), and the rostral part of the parvocellular reticular nucleus (NRpc alpha). 4. Forty-six interneurons were shown to have low-threshold (LT) peripheral receptive fields, and 41 of these (88%) were in the oral cavity. Most of the responses were rapidly adapting. 5. Twenty-eight interneurons changed their pattern of firing during cortically induced fictive mastication. The discharge frequency of 20 neurons varied in phase with the fictive masticatory motor output, which was recorded from central ends of cut hypoglossal nerves (XII) and/or from the NVmot. Others were briefly excited and then inhibited (n = 2), only inhibited (n = 4), or tonically excited during fictive mastication (n = 2). Fifteen others were unaffected by this test. 6. It was found that the rhythmically active neurons could be further subdivided into two categories: those receiving short-latency excitatory input from the masticatory area of the cortex (n = 11) and those that did not (n = 9). No obvious differences in peripheral receptive fields for neurons in these categories were found. 7. We suggest that these phasically active premotor neurons are part of the circuitry generating the rhythmic masticatory pattern, specifically those that directly control the bursts of firing of the trigeminal motoneurons (burst generators, BGs). Their properties allow them to integrate sensory information and descending commands with the masticatory rhythm that is probably generated in midline brainstem reticular nuclei.
M-wave of the toad electroretinogram
Authors: Katz B. J. , Wen R. , Zheng J. B. , Xu Z. A. , Oakley B.
Published: December 2017

1. In the retina, two distinct, light-evoked releases of K+ have been described. One takes place in the outer plexiform layer (OPL) and is termed the "distal K+ increase." The other takes place in the inner plexiform layer (IPL) and is termed the "proximal K+ increase." Although the distal K+ increase generates the electroretinogram (ERG) b-wave, the contribution of the much larger proximal K+ increase to the ERG is less well understood. In this paper we detail our investigation of the proximal K+ increase and its contribution to the ERG. We describe an ERG component, the M-wave, which had not heretofore been observed in the diffuse-flash, vitreal ERG. 2. We studied the proximal K+ increase and the ERG M-wave in the isolated retina preparation of the toad, Bufo marinus. We used K(+)-sensitive microelectrodes, as well as conventional intra- and extracellular microelectrodes, to record K+ changes, the local (or intraretinal) ERG, the vitreal ERG, and Muller cell responses. 3. As in earlier studies of the amphibian and cat M-wave, we readily observed an M-wave in the intraretinal, or local, ERG (LERG). The M-wave we studied had characteristics similar to those of M-waves that were previously described. Specifically, we found that the M-wave was generated by a Muller cell response to the proximal K+ increase and that both the proximal K+ increase and the LERG M-wave were spatially tuned. 4. We used the aspartate receptor agonist, N-methyl-DL-aspartate (NMA), to reveal that an M-wave is present in the vitreal ERG. Researchers who previously investigated the M-wave were unable to identify an M-wave in the vitreal ERG. We found that the toad ERG M-wave was a small, positive potential that was partially obscured by the much larger b-wave and slow PIII components. 5. We observed that picrotoxin (PTX) had an excitatory effect on inner retina, as evidenced by an enhanced proximal K+ increase and an enhanced M-wave. This result indicates that it is likely that GABAergic inhibition in inner retina plays an important role in retinal processing in the toad. 6. At threshold, we found that the ERG consisted mainly of an M-wave, indicating that the amphibian threshold ERG is driven by proximal retina. This result is analogous to previous observations of the threshold ERG in cat. However, in cat, the M-wave and threshold response have been described as distinct ERG components.(ABSTRACT TRUNCATED AT 400 WORDS)
Effects on wrist and digit muscle activity from microstimuli applied at the sites of rubromotoneuronal cells in primates
Authors: Cheney P. D. , Mewes K. , Widener G.
Published: December 2017

1. The purpose of this study was to use the techniques of spike- and stimulus-triggered averaging (SpTA and StTA, respectively) to examine the output organization of individual rubromotoneuronal (RM) cells in relation to clusters of neighboring cells. SpTA of electromyographic (EMG) activity in awake monkeys reveals the target muscles of an individual recorded neuron, whereas StTA reveals the target muscles of the neuronal aggregate activated by the stimulus. 2. Three questions were of particular interest. First, does the pattern of poststimulus facilitation (PStF) across forearm muscles match the pattern of postspike facilitation (PSpF)? Second, does the output of RM cell aggregates tested with StTA favor forearm extensor muscles, as reported for individual RM cells in the companion paper? Third, how do RM poststimulus effects compare with corticomotoneuronal (CM) poststimulus effects? 3. Microstimuli were applied at the sites of 37 RM cells, identified by SpTA of EMG activity in awake monkeys performing an alternating wrist movement task. 4. The magnitudes of PStF at 5, 10, and 20 microA were, respectively, 4.3, 10.1, and 13.7 times greater than PSpF of the same muscles, reflecting activation, by the stimulus, of multiple RM cells. RM cell PStF was weaker than CM PStF. 5. The onset latency of poststimulus suppression (PStS) exceeded that of PStF. For example, at 20 microA the difference was 2.6 ms, comparable with the difference between PSpF and postspike suppression (PSpS). 6. The patterns of poststimulus effects on forearm flexor and extensor muscles were categorized in the same manner as postspike effects. Three major patterns were observed: 1) pure facilitation, 2) reciprocal suppression, and 3) cofacilitation of extensors and flexors. 7. The profile of PStF across synergist muscles was broadly similar to that of PSpF. At 83% of sites, the muscle with the greatest PSpF was also the muscle with the greatest PStF. At 30% of sites (11 of 37), the set of muscles with PStF (muscle field) exactly matched the set with PSpF. Overall, the level of discrepancies in SpTAs versus StTAs computed at the same RM cell sites was 27%. Most of these discrepancies could be attributed to muscles with the weakest effects. 8. The fact that the poststimulus muscle fields at many RM cell sites matched the postspike fields at the same sites, even though the poststimulus effects were greater in magnitude and were mediated by more cells, suggests clustering of RM cells with similar target motoneuron pools.(ABSTRACT TRUNCATED AT 400 WORDS)