bluuebunny/crossref_metadata_2025 huggingface dataset:
Epileptiform activity induced by changes in extracellular potassium in hippocampus
Authors: Rutecki P. A. , Lebeda F. J. , Johnston D.
Published: December 2017

Using extra- and intracellular recording techniques, we investigated the induction and frequency modulation of spontaneous epileptiform activity produced by changes in the concentration of extracellular potassium ([K+]o). This paper describes a quantitative relationship between [K+]o and the frequency of spontaneously occurring epileptiform events. Recordings were made from the CA3 subfield of the rat in vitro hippocampal slice preparation. Intracellular microelectrodes were filled with 2 M Cs2SO4 and connected to a 3-kHz, time-share, single-electrode current- and voltage-clamp device. The frequency of spontaneous epileptiform (interictal) discharges was determined from extracellular recordings as a function of [K+]o. Current- and voltage-clamp techniques were used to characterize the intracellular correlate of these epileptiform events. The frequency of bicuculline-induced spontaneous epileptiform discharges was dependent on [K+]o. Below 4 mM [K+]o, spontaneous discharges occurred sporadically in the presence of 10 microM bicuculline. Increasing [K+]o from 5 to 10 mM caused a fivefold increase in the rate of spontaneous discharges. Spontaneous epileptiform discharges also occurred in the absence of bicuculline when [K+]o was increased above 6.5 mM. The rate of these discharges was dependent on [K+]o in much the same way as the discharges induced by bicuculline. For any given [K+]o concentration greater than 6.5 mM, however, the resultant discharge rate was faster than that obtained when bicuculline was present in the bathing solution. Simultaneous intra- and extracellular recordings revealed that the spontaneous high-[K+]o-induced interictal discharge was accompanied by a large depolarization of the membrane potential that appeared similar to the paroxysmal depolarizing shift (PDS) seen with other convulsants. The intracellularly recorded event fulfilled the criteria for a synaptically mediated PDS. The waveform of the PDS was complex and dependent on the membrane potential. When the membrane potential was held at 0 mV, spontaneously occurring hyperpolarizing potentials were noted during the inter-PDS interval. These events were blocked by picrotoxin or bicuculline and were probably spontaneous inhibitory postsynaptic potentials. The complexity of the PDS waveform suggested that more than one synaptic conductance was involved in the generation of the PDS. The mean measured reversal potential of the depolarizing phase was -10.7 mV. Voltage-clamp techniques were used to measure the conductance underlying the depolarizing phase of the high-[K+]o-induced PDS. The mean measured conductance was 51.5 nS, with a reversal potential of -7.9 mV.(ABSTRACT TRUNCATED AT 400 WORDS)
Abolition of spindle oscillations in thalamic neurons disconnected from nucleus reticularis thalami
Authors: Steriade M. , Deschenes M. , Domich L. , Mulle C.
Published: December 2017

The effects of depriving thalamic relay and intralaminar nuclei from their reticularis thalami (RE) inputs were investigated in acute and chronic experiments on cat. In acutely prepared animals, two (frontal and parasagittal) thalamic transections were made; extracellular and intracellular recordings were performed in RE-disconnected thalamic nuclei. In chronic experiments, the RE nuclear complex was lesioned by means of kainic acid injections; the activity of RE-deprived thalamocortical neurons was extracellularly studied during wakefulness and synchronized sleep. Two features distinguish RE-deprived nuclei from normal thalamic nuclei: absence of spindle-wave rhythmicity and all-burst activity of neurons. The abolition of spindle-related rhythms (sequences of 7- to 14-Hz waves recurring periodically with a rhythm of 0.1-0.2 Hz) in RE-disconnected thalamic nuclei and ipsilateral neocortical areas contrasted with normal spindling rhythmicity in contralateral EEG leads. Spontaneously occurring, rhythmic, long-lasting inhibitory postsynaptic potentials (IPSPs), as observed in intact preparations, were no longer observed in RE-disconnected thalamic neurons. The remaining inhibitory events consisted of short-duration IPSPs. The possibility that RE nucleus is a pacemaker for spindling rhythms, imposing them through inhibitory projections to target thalamic areas, is supported by our concurrent experiments that indicate RE neurons preserve their rhythmicity after disconnection from their major (cortical and thalamic) input sources. RE-deprived thalamocortical neurons exclusively exhibit high-frequency spike bursts whose intrinsic structure is identical to that of intact thalamic relay cells. Instead of the spindle-related sequences of bursts seen in normal animals, the bursts of RE-disconnected thalamocortical neurons are single events, with a dramatic rhythmicity at 1-2 Hz. The presumed mechanism of this rhythmicity is the periodic activation of a low-threshold somatic conductance whose deinactivation is brought about by temporal integration of short-lasting IPSPs. It is known that high-frequency spike bursts of thalamic relay neurons result from hyperpolarization of cell membrane. We blocked the underlying inhibitory events by bicuculline and reversibly changed the all-burst activity of RE-disconnected neurons into a tonic mode. Since the only activity of RE-deprived thalamocortical neurons consists of burst discharges, we hypothesize that local-circuit GABAergic neurons are released from inhibition after RE disconnection or lesion.
Role of intramuscular receptors in the awareness of limb position
Authors: Clark F. J. , Burgess R. C. , Chapin J. W. , Lipscomb W. T.
Published: December 2017

We studied proprioception with the ankle joint and the metacarpophalangeal (MCP) joint of the index finger of humans by use of a method that could distinguish a position sense from a movement sense. The test measured how subjects' ability to detect a fixed displacement of a joint varied with the rate of joint rotation. A position sense should not depend on the speed of joint placement; therefore slow rates of movement should not degrade subjects' ability to sense joint displacements. However, in the absence of a position sense, subjects would presumably rely on movement signals that do depend on the rate of rotation, and their ability to detect displacements should decrease when rate decreases. Subjects could sense small displacements of the ankle (+/- 3.5 degrees) and the MCP joint (+/- 2.5 degrees lateral excursions) with no decrement in performance at speeds as low as 0.25 degrees/min for the ankle and 0.5 degrees/min for the MCP joint (the slowest tested thus far). The findings confirm the existence of a position sense with these joints. Block of the ulnar nerve at the wrist, which paralyzes the interosseous muscles that adduct and abduct the MCP joint but presumably leaves skin and joint mechanisms unaffected, substantially impaired subjects' ability to detect the lateral excursions at slow speeds. Performance fell sharply at speeds less than 128 degrees/min and leveled off at approximately 20% detections at speeds less than 4 degrees/min. Increasing displacement to +/- 7 degrees did not improve performance. Block of the common peroneal nerve at the knee, which paralyzes the ankle dorsiflexor muscles, substantially impaired subjects' ability to detect the +/- 3.5 degrees displacements at slow speeds when the foot was positioned to slacken the plantarflexion muscles (which were not affected by the block). Performance fell sharply at speeds less than 256 degrees/min and approached zero at speeds less than 16 degrees/min. However, positioning the foot to stretch the plantarflexor muscles restored subjects' performance to near normal. Local anesthetic injected into the MCP joint space produced no observable effect on the ability to detect either slow or fast excursions. The joint anesthesia went unnoticed by the subject. We conclude that independent and separable senses exist for limb position and limb movement and that normal position sense requires sensory inputs from the muscles.
Presynaptic inhibition produced by an identified presynaptic inhibitory neuron. II. Presynaptic conductance changes caused by histamine
Authors: Kretz R. , Shapiro E. , Bailey C. H. , Chen M. , Kandel E. R.
Published: December 2017

We have examined the morphology and pharmacology of the L32 neurons, identified cells that mediate presynaptic inhibition in the Aplysia abdominal ganglion, to gain insight into the putative transmitter released by the L32 cells. We analyzed the fine structure of the synaptic release sites of L32 cells stained with horseradish peroxidase. Each varicosity of L32 was found to contain two general classes of vesicles. One class of vesicles is large (mean long diameter of 98 nm) and contains an electron-dense core that typically filled or nearly filled each vesicle profile. The second class of vesicles is smaller (mean long diameter of 67 nm) and relatively electron lucent. The size, distribution, and morphology of the vesicle population in L32's terminals was similar to that described at the synapses of the identified histaminergic neuron C2 in Aplysia (2). These morphological observations suggested that L32 cells might be histaminergic. Among the various putative transmitters tested, histamine was most effective in mimicking the postsynaptic effects of L32 cells onto L10, and onto other follower cells of L32 in the abdominal ganglion. Histamine also caused inhibition of transmitter output from L10. Both the IPSP produced by L32 in L10 and the response of L10 to histamine could be reversibly blocked by cimetidine, a histamine antagonist in Aplysia (14). These results support, but do not establish the identification of histamine as the putative transmitter of L32 cells. Histamine mimics the action of L32 in mediating presynaptic inhibition allowing us to examine in more detail the conductance changes in L10 underlying presynaptic inhibition. Voltage-clamp analysis revealed that histamine blocked the voltage-dependent Ca2+ current and increased a voltage-dependent K+ current in L10, much as did L32. Both of these changes are likely to act synergistically to inhibit transmitter release. Reduction of Ca2+ current in L10 would directly inhibit transmitter release from L10 directly by decreasing the amount of Ca2+ entering during spike depolarization. The increase in K+ current would act indirectly to reduce transmitter release from L10, by hyperpolarizing L10 and decreasing the amplitude and duration of spikes in L10, as well as reducing the steady-state Ca2+ influx. These results support the idea that in Aplysia presynaptic inhibition is caused primarily by a direct transmitter-mediated reduction in presynaptic Ca2+ current and secondarily by a hyperpolarization of the presynaptic neuron due to a transmitter-mediated increase in a K+ current.(ABSTRACT TRUNCATED AT 400 WORDS)
Differential effects of low-frequency depression, vibration-induced inhibition, and posttetanic potentiation on H-reflexes and tendon jerks in the human soleus muscle
Authors: Van Boxtel A.
Published: December 2017

A comparison was made between the effects of repetition rate, muscle vibration, and tetanic stimulation of the tibial nerve on H-reflexes and tendon (T) jerks elicited in the relaxed soleus muscle of normal human. H- and T-reflexes with electromyographic (EMG) potentials of equivalent amplitude were elicited alternately in the same leg to ensure identical experimental conditions. H- and T-reflexes of identical EMG amplitude showed isometric twitch tensions of identical amplitude and time course. H- and T-reflexes were elicited at different repetition rates ranging from once every 6 s to 2/s. H-reflexes showed a significantly stronger low-frequency depression than T-reflexes. Inhibition of H- and T-reflexes was induced by 2-min vibration at 100 Hz of ankle extensors, ankle flexors, or knee flexors. Vibration of ankle extensors and flexors induced a stronger inhibition than vibration of knee flexors. In all three conditions, inhibition of H-reflexes was stronger than inhibition of T-reflexes. The difference was relatively greater during vibration of ankle extensors and flexors than during vibration of knee flexors. When tested together, the effects of low-frequency depression and vibration-induced inhibition of H- and T-reflexes were found to be independent if reflex amplitudes were expressed as a percentage of the control reflex amplitude. The cessation of vibration of ankle extensors was followed by a gradual recovery of H-reflexes from inhibition. On the contrary, T-reflexes showed a marked potentiation. Such postvibratory effects were generally not observed following vibration of ankle or knee flexors. When postvibratory effects were tested during low-frequency depression, percent postvibratory depression of H-reflexes and percent postvibratory potentiation of T-reflexes were found to be independent of the degree of low-frequency depression. Tetanic stimulation of the tibial nerve for 20 s at 200 Hz resulted in posttetanic potentiation (PTP) of H- and T-reflexes, the former being stronger than the latter. The extent of the changes in H- and T-reflex EMG amplitudes, due to changes in repetition rate, vibration, or tetanic stimulation, was generally inversely related to the intensity of the electrical or mechanical reflex stimuli. The observed discrepancies between the induced changes in H- and T-reflex amplitudes are interpreted in terms of the differences in afferent inputs between the two reflexes that were suggested by Burke and his colleagues (9-11).(ABSTRACT TRUNCATED AT 400 WORDS)
The detailed somatotopic organization of the dorsal horn in the lumbosacral enlargement of the cat spinal cord
Authors: Wilson P. , Meyers D. E. , Snow P. J.
Published: December 2017

The somatotopic organization of spinocervical tract cells and unidentified dorsal horn neurons that lie in the same depth range as the spinocervical tract cells has been examined in detail in the lumbosacral enlargement of cats anesthetized with alpha-chloralose. Only gentle hair movement or light touch of glabrous skin were used as stimuli. Within the region of the dorsal horn containing these neurons there is a precise somatotopic organization. However, there is considerable variation between animals in the relationship between the somatotopic map and the lumbosacral segmental boundaries. The somatotopic map described here is considered to be restricted to a 300- to 500-micron thick lamina. In the medial half to two-thirds of this lamina in the L6 and L7 segments the toes are represented in a rostrocaudal sequence from toe 2 to toe 5. Over the most medial 200-500 micron of this part of the dorsal horn are found cells that respond to stimulation of the glabrous skin of the toe pads and the central pad. The toe representation is surrounded by a strip of foot representation, which is in turn surrounded by a strip of leg representation. The most lateral part of the lamina curves ventrally in the L6 and L7 segments and contains a continuous rostrocaudal representation of the skin of the thigh. In this region are found both spinocervical tract cells and unidentified dorsal horn neurons with receptive fields on the thigh. The skin of the hindlimb is represented such that a line of discontinuity runs down the posteromedial thigh, leg, and foot. Skin lateral to this line is represented caudally, while skin medial to it is represented rostrally.
Activity of pars reticulata neurons of monkey substantia nigra in relation to motor, sensory, and complex events
Authors: Schultz W.
Published: December 2017

The behavioral involvement of neurons in the pars reticulata of the substantia nigra (SNpr) in sensory and motor processes was investigated in order to contribute to the understanding of behavior-related neuronal mechanisms in the basal ganglia, of which the SNpr is a major output station. Electrophysiological properties of SNpr neurons were studied with extracellular recordings from single neurons in monkeys performing in a behavioral GO/NO-GO paradigm, employing significant auditory and visual stimuli, forelimb reaching movements, and mouth movements. Neurons in the SNpr discharged impulses of 0.6 to 1.0 ms in duration, at rates of 23 to 145/s (median 68/s). They contrasted with dopaminergic pars compacta neurons of substantia nigra, which discharged longer impulses at rates below 8/s. Two-thirds of more than 100 quantitatively and statistically evaluated SNpr neurons showed changes with temporal relationships to at least one of the events of the behavioral task. One-fifth of all neurons covaried with more than one event. The largest group of task-related neurons increased or decreased activity with contralateral forelimb movements (46% of all neurons). Most of them covaried with large forward reaching of the arm, and only the minority covaried with distal forearm manipulation. None of the SNpr neurons resembled in their changes the timing of activity of single muscles. Many neurons also showed changes with ipsilateral movements, in a similar fashion as on the contralateral side. Changes began rarely before and mostly with or after onset of muscle activity in prime movers. Changes were quantitatively moderate, rarely exceeding a doubling of discharge rate with increases and reductions by 50% with decreases. Movement relations did not appear to be due to somatosensory input. Some neurons increased or decreased their activity in relation to mouth movements (16% of all neurons). Changes were quantitatively moderate as in the case of movement relationships. Nine percent of all neurons decreased their activity after an acoustic preparatory signal and 9% after a light stimulus indicating the GO or NO-GO situation. Latencies were 50-150 ms (median 90 ms) for the auditory and 80-200 ms (median 120 ms) for the visual responses. Twelve percent of all neurons increased or decreased their activity during the waiting and preparation period, which lay between an initial sensory signal and the permission to move for reward.(ABSTRACT TRUNCATED AT 400 WORDS)
Voltage-clamp analysis of a Ca2+- and voltage-dependent chloride conductance in cultured mouse spinal neurons
Authors: Owen D. G. , Segal M. , Barker J. L.
Published: December 2017

Current and voltage-clamp recordings were made at room temperature from cultured mouse spinal neurons using conventional two-electrode voltage-clamp techniques and electrodes filled with either 3 M KCl, 3 M CsCl, or 3 M Cs2SO4. In the presence of tetraethylammonium and tetrodotoxin, “fast” (rapidly rising and falling) action potentials (FAP) of variable duration were recorded in most neurons. “Slow” (slowly rising and falling) depolarizing potentials (SDP) occurred in 23% of the cells, when using KCl-filled electrodes, and in 82% of the cells with CsCl-filled electrodes. The SDP was frequently preceded by an FAP, although in some cells activation of the SDP occurred before the FAP threshold was reached and in a graded fashion. Both the FAP and SDP were abolished by Cd2+ and other Ca2+ antagonists. In cells exhibiting SDPs, voltage-clamp analysis revealed a sustained (noninactivating) inward current (Isin) during depolarizing steps to potentials more positive than -45 mV. Repolarizing steps resulted in slowly decaying inward tail currents (Itail). Both Isin and Itail were abolished in solutions nominally free of Cao2+, or containing Ca2+-channel antagonists. Bao2+ did not support Isin. The data indicated a U-shaped activation curve for Isin, peaking at about -10 mV. Activation of Isin occurred exponentially with a time constant of approximately 140 ms at -23 mV, becoming faster at more depolarized potentials (ca. 50 ms at -2 mV). Deactivation was slow, giving rise to tail currents lasting seconds. In some cases deactivation could be described by a single exponential process, although frequently the kinetics were more complex. Deactivation was faster at hyperpolarized potentials and sensitive to extracellular ([Ca2+]o), duration of activating voltage steps, and the degree of activation of Isin. Using CsCl-filled electrodes, the reversal potential (Erev) for Isin was -1.7 mV (SEM 3.5 mV, n = 20). Erev always corresponded to the reversal potential for gamma-aminobutyric acid-evoked currents in the same cell. In experiments in which Cs2SO4-filled electrodes were used, Erev was estimated to be -44 mV (SEM 2.3 mV, n = 9). Neither complete substitution of Nao+ with choline ions nor elevation of [K+]o 10-fold significantly affected the estimated Erev. However, substitution of Cl0- with isethionate or methanesulphonate increased the amplitude of inward currents (recorded with CsCl-filled electrodes) and shifted Erev to more depolarized potentials. The results indicate that Cl- are the primary charge carriers for this current and that Cai2+ is required for its activation, leading us to identify it as ICl(Ca).(ABSTRACT TRUNCATED AT 400 WORDS)
Afterhyperpolarization mechanisms in cat sympathetic preganglionic neuron in vitro
Authors: Yoshimura M. , Polosa C. , Nishi S.
Published: December 2017

A long-lasting afterhyperpolarization (AHP) follows the antidromic or current-induced action potential of sympathetic preganglionic neurons (SPNs) studied in slices of cat spinal cord maintained in vitro. Duration and amplitude of the AHP that follows a single spike were 2.8 +/- 0.3 s and 16.0 +/- 0.7 mV (mean +/- SE), respectively. In most cases two components could be distinguished, an initial faster and usually larger component [fast (F) AHP] followed by a slowly decaying component [slow (S) AHP]. An increase in membrane conductance was associated with the AHP. The amplitude of both components increased with membrane depolarization and decreased with hyperpolarization. Both fast and slow component were nullified at a voltage of -90 mV in 3.6 mM K+. Peak AHP amplitude decreased as K+ was increased from 1.5 to 7.0 mM. The null point for both fast (F) AHP and slow (S) AHP shifted in the depolarizing or hyperpolarizing direction when K+ was increased or decreased, respectively. These data suggest that an increase in K+-conductance is the mechanism underlying the AHP. The two components of the AHP could be separated by their differential sensitivity to superfusion with the Ca2+-channel blocker cobalt (2 mM) or with low Ca2+ (0.25 mM). These procedures resulted in an AHP of much shorter duration (330 ms, range 150-600), presumably the FAHP. These observations indicate that a Ca2+-activated K+-conductance is likely to be involved in the generation of the SAHP. The FAHP was depressed during superfusion with tetraethylammonium (TEA) (20 mM) and intracellular cesium injection. The SAHP was enhanced by TEA and enhanced or depressed by cesium. In 3.6 mM K+ the FAHP reversed in polarity at membrane voltages more negative than -90 mV. This component had an approximately linear relation of amplitude to membrane potential. The SAHP did not reverse in most cells. In the few cases in which it reversed, the change in amplitude for a given change in membrane voltage was much smaller on the negative than on the positive side of the null potential. Thus the SAHP shows voltage-dependent, nonlinear characteristics. This difference in behavior of the two components was also observed when the null point was displaced in high or low K+. In the presence of tetrodotoxin (TTX) the AHP persisted in temporal association with a high-threshold, TTX-resistant, cobalt-sensitive spike. During the time course of the AHP the efficacy of synaptic input decreased, suggesting that the AHP has an important role in regulating the firing rate of the SPN.
Reflex influences on muscle spindle activity in relaxed human leg muscles
Authors: Gandevia S. C. , Miller S. , Aniss A. M. , Burke D.
Published: December 2017

The study was designed to determine whether low-threshold cutaneous and muscle afferents from the foot reflexly activate gamma-motoneurons innervating relaxed muscles of the leg. In 15 experiments multiunit recordings were made from 21 nerve fascicles innervating triceps surae or tibialis anterior. In a further nine experiments the activity of 19 identified single muscle spindle afferents was recorded, 13 from triceps surae, 5 from tibialis anterior, and 1 from extensor digitorum longus. Trains of electrical stimuli (5 stimuli, 300 Hz) were delivered to the sural nerve at the ankle (intensity, twice sensory threshold) and the posterior tibial nerve at the ankle (intensity, 1.1 times motor threshold for the small muscles of the foot). In addition, a tap on the appropriate tendon at varying times after the stimuli was used to assess the dynamic responsiveness of the afferents under study. The conditioning electrical stimuli did not change the discharge of single spindle afferents. Recordings of rectified and averaged multiunit activity also revealed no change in the overall level of background neural activity following the electrical stimuli. The afferent responses to tendon taps did not differ significantly whether or not they were preceded by stimulation of the sural or posterior tibial nerves. These results suggest that low-threshold afferents from the foot do not produce significant activation of fusimotor neurons in relaxed leg muscles, at least as judged by their ability to alter the discharge of muscle spindle afferents. As there may be no effective background activity in fusimotor neurons innervating relaxed human muscles, it is possible that these inputs from the foot could influence the fusimotor system during voluntary contractions when the fusimotor neurons have been brought to firing threshold. In one subject trains of stimuli were delivered to the posterior tibial nerve at painful levels (30 times motor threshold). They produced an acceleration of the discharge of a spindle in soleus at a latency of approximately 125 ms, in advance of detectable activity in skeletomotor neurons and before an increase in muscle length was noted. It presumably resulted from activation of gamma-motoneurons innervating soleus by small myelinated afferents (A-delta range).
Gustatory responses in the frontal opercular cortex of the alert cynomolgus monkey
Authors: Scott T. R. , Yaxley S. , Sienkiewicz Z. J. , Rolls E. T.
Published: December 2017

The responses of 165 single taste neurons in the anterior operculum of the alert cynomolgus monkey were analyzed. Chemicals were deionized water, blackcurrant juice, and the four basic taste stimuli: glucose, NaCl, HCl, and quinine HCl. Taste-evoked responses could be recorded from an opercular region that measured approximately 4.0 mm in its anteroposterior extent, 2.0 mm mediolaterally, and 3.0 mm dorsoventrally. Within this area, taste-responsive neurons were sparsely distributed such that multiunit activity was rarely encountered and neuronal isolation was readily achieved. Intensity-response functions were determined for nine cells.In each case, the lowest concentration of the dynamic response range conformed well to human electrophysiological and psychophysical thresholds for the basic taste stimuli. There was some evidence of chemotopic organization. Cells that responded best to glucose tended to be distributed toward the anterior operculum, whereas most acid-sensitive neurons were located more posteriorly. The proportion of cells responding best to NaCl peaked in the middle of the area, whereas quinine sensitivity was rather evenly distributed throughout. Opercular neurons in the monkey showed moderate breadth of sensitivity compared with taste cells of other species and at other synaptic levels. A breadth-of-tuning coefficient was calculated for each neuron. This is a metric that can range from 0.0 for a cell that responds specifically to only one of the four basic stimuli to 1.0 for one that responds equally to all four stimuli. The mean coefficient for 165 cells in the operculum was 0.67 (range = 0.12-0.99). Efforts were made to determine whether neurons could be divided into a discrete number of types, as defined by their responsiveness to the stimulus array used here. It was concluded that most taste cells may be assigned to a small number of groups, each of which is statistically independent of the others, but within which the constituent neurons are not identical. An analysis of taste quality indicated that the sweet and salty stimuli evoked patterns of activity that were significantly intercorrelated. Similarly, patterns representing HCl, quinine HCl, and water were related.
Cat area 17. III. Response properties and orientation anisotropies of corticotectal cells
Authors: Weyand T. G. , Malpeli J. G. , Lee C. , Schwark H. D.
Published: December 2017

The receptive field properties of antidromically identified corticotectal (CT) cells in area 17 were explored in the paralyzed, anesthetized cat. To compare these with another population of infragranular cells, we also examined the receptive field properties of cells in layer 6. Sixty percent of our sample of CT cells showed increased response to increased stimulus length (length summation) and were classified as standard complex cells. The other 40% showed little or no length summation, were generally end stopped, and were classified as special complex cells. Standard and special complex CT cells have complementary orientation anisotropies: the distribution of orientation preferences of standard complex cells is biased toward obliquely oriented stimuli, whereas special complex cells are biased toward horizontally and vertically oriented stimuli. The receptive fields of the cells in our sample were primarily along the horizontal meridian so we cannot determine if these anisotropies are defined relative to the vertical meridian or relative to the meridian passing through the receptive field. The effects of these anisotropies in preferred orientation are minimized by the broad orientation tuning of CT cells. There was no simple relationship between the direction bias of CT cells and the reported direction bias of tectal cells. In contrast to the heterogeneity of corticotectal cells, layer 6 cells uniformly showed strong length summation, tight orientation tuning, and little spontaneous activity.
Quantitative characterization of ceruleospinal inhibition of nociceptive transmission in the rat
Authors: Jones S. L. , Gebhart G. F.
Published: December 2017

A total of 51 dorsal horn units responsive to heat were isolated and their receptive fields characterized (i.e., response properties and adequate stimuli determined) in pentobarbital-anesthetized, paralyzed rats. In 39 of the 51 units, the descending inhibition of heat-evoked activity produced by focal electrical stimulation in the locus ceruleus/subceruleus (LC/SC) was examined. All units studied responded to mechanical stimulation, to electrical stimulation of the ipsilateral tibial nerve at intensities supramaximal to activate A-alpha, delta- and C-fibers, and to noxious heating (50 degrees C) of the footpad. The cutaneous receptive fields of all units were confined to the glabrous skin of the toes and footpad. All neurons examined were located in the dorsal horn of the spinal cord in laminae I-VI. Tracking experiments established that inhibition of heat-evoked dorsal horn unit activity could be reliably produced by focal electrical stimulation in both the contralateral and ipsilateral LC/SC. The inhibition produced by electrical stimulation in the LC/SC was intensity-, pulse duration-, and frequency-dependent. In six experiments, the efficacy of LC/SC stimulation-produced inhibition of heat-evoked activity was compared using two pulse durations (100 and 400 microseconds); greater inhibition of heat-evoked activity was produced at lower intensities of stimulation at the 400-microseconds pulse duration. In 10 experiments, the frequency of stimulation was varied (25-200 Hz); stimulation at a frequency of 100 Hz resulted in maximal inhibition of heat-evoked activity for stimulation sites both inside (n = 7) and outside (n = 3) the LC/SC. Inhibition of heat-evoked dorsal horn unit activity could be reliably produced by focal electrical stimulation in sites inside the LC/SC (n = 18). Significant descending inhibition of noxious heat-evoked spinal neuronal activity could also be produced by stimulation in pontine sites located outside the LC/SC, however, not as reliably. Systematic electrode tracks were made through the pons, using a searching stimulus of 100 microA, to locate sites medial, lateral, and ventral to the LC/SC from which significant descending inhibition could be produced. Stimulation in 156 sites outside the LC/SC at 100 microA produced inhibition of heat-evoked spinal unit activity to 50% of control or less in only 37 sites. Descending inhibition was characterized quantitatively from 14 of these 37 sites; the mean intensities of stimulation to inhibit heat-evoked activity to 50% of control were experimentally determined, and the mean thresholds of stimulation for inhibition and the mean recruitment indices were calculated.(ABSTRACT TRUNCATED AT 400 WORDS)
Changes in neuronal activity of the monkey precentral cortex during preparation for movement
Authors: Lecas J. C. , Requin J. , Anger C. , Vitton N.
Published: December 2017

The aim of this study was to analyze the changes in neuronal activity of the motor cortex associated with preparation for movement. Monkeys were trained to perform a between-hands choice-reaction time (RT) task. They pressed upon two levers with both hands and, after a preparatory period of 1-s duration initiated by a warning tone, they must point at either a left- or right-located target, when illuminated as a response signal, with either the left or right hand. The level of preparation for performing either sided movement was changed by manipulating, across block of trials, the relative probabilities for the left and right hands to point at the corresponding target. When considering behavioral data averaged over daily sessions, it was found that RT significantly decreased as response probability increased, whereas movement time (MT) was not affected. However, large changes in this rule were observed when data collected within a single session were considered. Response probability manipulation was acting on RT alone in 27% of sessions, on MT alone in 19% of sessions, and on both RT and MT in 17% of sessions. Statistically significant trial-by-trial correlations between RT and MT were found; of positive sign for 34% of sessions and of negative sign for 12% of sessions. Electromyographic recordings from the biceps and triceps brachii showed that muscle activity remained stable during the preparatory period, both muscles of the performing arm began to be coactivated about 70-130 ms before the lever release, biceps activation being progressively larger than that of the triceps, and the rising slope of biceps activation was steeper for short than for long RTs. Single-cell recording techniques were used to study the neuronal activity of primary motor cortex during the performance of the task. One hundred and fifteen units in area 4, whose activity was recorded during a whole experimental session, were selected for further analysis. Disregarding 4% of units which did not exhibit any movement-related change in activity, it was found that twenty-one percent of units were related to contralateral movements only, 2% to ipsilateral movements only, and 73% to both sided movements. Among this last subset, 27% of units exhibited reciprocal movement-related changes in activity, the most often an excitation for contralateral movements and an inhibition for ipsilateral movements, and 50% of units exhibited a movement-related change in activity in the same direction for both movements, the most often an excitation.(ABSTRACT TRUNCATED AT 400 WORDS)
Sensorimotor integration in the primate superior colliculus. I. Motor convergence
Authors: Jay M. F. , Sparks D. L.
Published: December 2017

Orienting movements of the eyes and head are made to both auditory and visual stimuli even though in the primary sensory pathways the locations of auditory and visual stimuli are encoded in different coordinates. This study was designed to differentiate between two possible mechanisms for sensory-to-motor transformation. Auditory and visual signals could be translated into common coordinates in order to share a single motor pathway or they could maintain anatomically separate sensory and motor routes for the initiation and guidance of orienting eye movements. The primary purpose of the study was to determine whether neurons in the superior colliculus (SC) that discharge before saccades to visual targets also discharge before saccades directed toward auditory targets. If they do, this would indicate that auditory and visual signals, originally encoded in different coordinates, have been converted into a single coordinate system and are sharing a motor circuit. Trained monkeys made saccadic eye movements to auditory or visual targets while the activity of visual-motor (V-M) cells and saccade-related burst (SRB) cells was monitored. The pattern of spike activity observed during trials in which saccades were made to visual targets was compared with that observed when comparable saccades were made to auditory targets. For most (57 of 59) V-M cells, sensory responses were observed only on visual trials. Auditory stimuli originating from the same region of space did not activate these cells. Yet, of the 72 V-M and SRB cells studied, 79% showed motor bursts prior to saccades to either auditory or visual targets. This finding indicates that visual and auditory signals, originally encoded in retinal and head-centered coordinates, respectively, have undergone a transformation that allows them to share a common efferent pathway for the generation of saccadic eye movements. Saccades to auditory targets usually have lower velocities than saccades of the same amplitude and direction made to acquire visual targets. Since fewer collicular cells are active prior to saccades to auditory targets, one determinant of saccadic velocity may be the number of collicular neurons discharging before a particular saccade.
Development of taste responses in the rat parabrachial nucleus
Authors: Hill D. L.
Published: December 2017

Extracellular responses from neurons in the parabrachial nuclei (PBN) were studied in rats 4 days old to adulthood during chemical stimulation of the tongue with monochloride salts, citric and hydrochloric acids, sucrose, sodium saccharin, and quinine hydrochloride. Multiunit taste responses were recorded in rats at 4-7 days of age and single-unit responses were recorded from 121 neurons in four other age groups of 14-20 days, 25-35 days, 50-60 days, and adults. PBN neurons in rats 4-7 days old consistently responded to 0.1 M solutions of NH4Cl and NaCl, to 0.5 M solutions of NH4Cl, NaCl, and KCl, and to 1.0 M sucrose, 0.1 M sodium saccharin, 0.1 M citric acid, and 0.1 N HCl. They often did not respond, however, to 0.1 M KCl and 0.01 M quinine hydrochloride. Single PBN neurons in rats 14 days old and older characteristically responded to all stimuli, which consisted of 0.1 and 0.5 M salts, acids, sucrose, sodium saccharin, and quinine hydrochloride. Thus no developmental differences occurred in the number of stimuli to which neurons responded after rats were 14 days old. With the exception of responses to hydrochloric acid, there were significant increases in response frequencies to all stimuli after 14 days of age. Average response frequencies to NH4Cl and citric acid increased after 20 days of age and those to NaCl, LiCl, KCl, sucrose, sodium saccharin, and quinine hydrochloride increased after 35 days of age. Average response frequencies for hydrochloric acid did not alter after 14 days of age. The proportion of single PBN neurons that responded maximally to specific monochloride salts did not change during development. Most single neurons in all age groups responded equally well to NH4Cl, NaCl, and LiCl. No PBN neuron responded maximally to KCl. Developmental differences in response frequencies of third-order gustatory neurons in the PBN generally reflect developmental response changes in first-order neurons of the chorda tympani nerve and second-order neurons of the solitary nucleus. However, unique developmental changes are evident in the PBN. Thus the ontogenetic changes that occur in PBN responses likely relate to modifications of lower-order peripheral and central nervous system afferents and peripheral receptor sensitivities.
Motor units and histochemistry in rat lateral gastrocnemius and soleus muscles: evidence for dissociation of physiological and histochemical properties after reinnervation
Authors: Gillespie M. J. , Gordon T. , Murphy P. R.
Published: December 2017

A reexamination of the question of specificity of reinnervation of fast and slow muscle was undertaken using the original "self" nerve supply to the fast lateral gastrocnemius (LG) and slow soleus muscles in the rat hindlimb. This paradigm takes advantage of the unusual situation of a common nerve branch, which supplies both a fast and slow muscle, and of the opportunity to keep the reinnervating nerve in its normal position. In addition it provides a test of the effects of cross-reinnervation among muscles of the same functional group. The properties of soleus and LG muscles and of individual muscle units were characterized in normal rats and in rats 4-14 mo after cutting the lateral gastrocnemius-soleus (LGS) nerve and suture of the proximal stump to the dorsal surface of the LG muscle. Individual muscle units were functionally isolated by stimulation of single motor axons to LG or soleus muscle contained in teased filaments in the L4 and L5 ventral roots. Motor units were classified as fast contracting fatiguable (FF), fast contracting fatigue resistant (FR), and slow (S) on the basis of criteria described in the cat by Burke et al. and applied to rat muscle units by Gillespie et al. Muscle fibers were classified as fast glycolytic (FG), fast oxidative glycolytic (FOG), and slow oxidative (SO) on the basis of histochemical staining for myosin ATPase, nicotinamide-adenine dinucleotide diaphorase (NADH-D), and alpha-glycerophosphate (alpha-GPD). Reinnervated muscles developed less force and weighed less in accordance with having fewer than normal motor units and having lost denervated muscle fibers. Normal LG contained a small proportion of S-type motor units (9%), whereas the majority (80%) of control soleus units were S type. After reinnervation, each muscle contained similar proportions of fast and slow motor units with S-type units constituting 30% of units in both muscles. When compared with the normal motor-unit sample, there was no significant change in average twitch and tetanic force in reinnervated muscles for each type of motor unit. However, the range within each type was greater, and there was considerable overlap between types. Twitch contraction time was inversely correlated with force in normal and reinnervated muscles as shown previously in self- and cross-reinnervated LGS in the cat. Changes in proportions of motor units in reinnervated LG were accompanied by corresponding changes in histochemical muscle types. This contrasted with reinnervated soleus in which the proportion of muscle fiber types was not significantly changed from normal despite significant change in motor-unit proportions.(ABSTRACT TRUNCATED AT 400 WORDS)
Synaptic potentials of primary afferent fibers and motoneurons evoked by single intermediate nucleus interneurons in the cat spinal cord
Authors: Rudomin P. , Solodkin M. , Jimenez I.
Published: December 2017

Spike-triggered averaging of dorsal and ventral root potentials was used in anesthetized cats to disclose possible synaptic connections of spinal interneurons in the intermediate nucleus with afferent fibers and/or motoneurons. With this method we have been able to document the existence of a distinct group of interneurons whose activity was associated with the recording of inhibitory potentials in the ventral roots (iVRPs), but not with negative dorsal root potentials (nDRPs). The iVRPs had mean durations of 60.8 +/- 22.1 ms and latencies between 1.7 and 5.1 ms relative to the onset of the interneuronal spikes. Within this group of neurons it was possible to characterize two categories depending on their responses to segmental inputs. Most type A interneurons were mono- or disynaptically activated by group I muscle afferents and polysynaptically by low threshold (1.08-1.69 X T) cutaneous fibers. Type B interneurons were instead polysynaptically activated by group II muscle and by cutaneous fibers with thresholds ranging from 1.02 to 3.1 X T. Whenever tested, both type A and B interneurons could be antidromically activated from Clarke's columns. There was a second group of interneurons whose activity was associated with the generation of both iVRPs and nDRPs. These potentials had mean durations of 107.5 +/- 35.6 and 131.5 +/- 32 ms, respectively, and onset latencies between 1.7 and 6.1 ms. The interneurons belonging to this group, which appear not to send axonal projections to Clarke's column, could be classified in three categories depending on their responses to peripheral inputs. Type C interneurons responded mono- or disynaptically to group I muscle volleys and polysynaptically to intermediate threshold (1.22-2.7 X T) cutaneous afferents. Type D interneurons were polysynaptically activated by group II muscle afferents (2.3-8.5 X T) and by intermediate threshold (1.4-3 X T) cutaneous fibers and type E interneurons only by group I muscle afferents with mono- or disynaptic latencies. A third group of interneurons produced nDRPs without iVRPs. The nDRPs had onset latencies varying from 1.9 to 6.2 ms and mean durations of 130.0 +/- 34.6 ms. These neurons (type F) showed spontaneous and evoked bursts of activity and were not antidromically activated from Clarke's column. They responded to stimulation of low- and intermediate-threshold cutaneous fibers (1.04-2.9 X T) with mono- and polysynaptic latencies, but not by group I muscle fibers. Type F interneurons appear to be located in more superficial layers than all the other interneurons.(ABSTRACT TRUNCATED AT 400 WORDS)
Kinematic and electromyographic responses to perturbation of a rapid grasp
Authors: Cole K. J. , Abbs J. H.
Published: December 2017

Kinematic and electromyographic responses of the thumb and index finger to load-induced extension of the thumb during a rapid precision grasp of the thumb and finger were studied in four human subjects. Angular position of the index finger metacarpophalangeal (MP) and proximal interphalangeal (PIP) joints was recorded along with the linear position of the thumb tip (TH). Myoelectric activity was recorded from flexor pollicis longus, flexor digitorum superficialis, first dorsal interosseous, and extensor digitorum communis. Loads that extended the thumb were applied ranging from 125 ms prior to movement onset to movement onset. For loads applied earlier than 50 ms before movement onset, the amount of flexion of TH was reduced compared with control trials. Contact between the finger and thumb was attained nonetheless due to an altered trajectory of the fingertip that was generated by reduced flexion of PIP and increased flexion of MP. These finger responses appear to be functional in that contact of the finger pulp on the more distal pulp of the thumb was preserved. With loads delivered near onset of the grasp, there was increased PIP flexion, rather than reduced PIP flexion. These responses to later loads occurred despite greatly reduced magnitudes of TH flexion compared with loads delivered well before onset of the gasp movements. Thus reduced PIP flexion observed with early loads was not simply the result of finger biomechanics. The thumb flexor muscle increased activity 45-55 ms after onset of the load, whereas responses of the finger flexors began 65 ms after load onset. Response magnitudes decreased as loads were introduced nearer to movement onset. Measured reaction times of the finger muscles to thumb extension stimuli averaged 154 ms, which indicated that the responses of the finger muscles were not voluntary responses to the thumb extension. Afferent information generated by perturbation of the thumb during a grasp movement can influence the activity of intrinsic and extrinsic muscles to yield apparently functional compensations in the closing movements. However, temporal limitations exist that appear to offer greater constraints on the use of afferent signals for controlling rapid movements than for sustained grasp.