bluuebunny/crossref_metadata_2025 huggingface dataset:
Patterns of spontaneous discharge in primate spinothalamic neurons
Authors: Surmeier D. J. , Honda C. N. , Willis W. D.
Published: December 2017

1. The spontaneous discharge of 30 spinothalamic tract (STT) neurons in the lumbosacral spinal cord of anesthetized monkeys was studied. Interval, correlation, and spectral analyses were performed. 2. Three patterns of discharge were found; these were referred to as the SP1, SP2, and SP3 patterns. 3. The SP1 group had moderately regular discharge trains that were devoid of short-interval spike bursts. 4. The SP2 group had spike trains dominated by short-interval bursts without evidence of low-frequency rhythmicity. 5. The SP3 group had spike trains with features of both the SP1 and SP2 groups. 6. Some correlations were found between the mean discharge rate and stimulus-response classes previously defined by our group (25). Correlations were deduced from a parent data set of 221 STT neurons. Type 1 neurons, which were driven primarily by tactile afferents, were found to have significantly lower mean rates than other "within-neuron" groups. On the other hand, type C neurons, which had strong input from afferents signalling pressure and noxious stimuli, were found to have significantly higher mean rates than all other "across-neuron" classes. 7. A weak relationship was found between the pattern of discharge and the within-neuron stimulus-response classification. Neurons with a largely tactile coding orientation (types 1 and 2) were most frequently of the SP1 and SP2 classes, whereas neurons with a more prominent nociceptive input (types 3 and 4) were most frequently of the SP2 and SP3 classes. No relationship was apparent between discharge pattern and the across-neuron classes.
Somatotopic organization of forelimb representation in cervical enlargement of raccoon dorsal horn
Authors: Pubols B. H. , Hirata H. , West-Johnsrud L.
Published: December 2017

1. Somatosensory representation of the forelimb in the dorsal horn of spinal segments C5-T2 was examined in 13 North American raccoons anesthetized with pentobarbital sodium. Single- or multiple-unit responses to light mechanical stimulation were recorded at a total of 504 loci, which were subsequently reconstructed from stained, transverse sections. From these, dorsal view maps of forelimb representation in Rexed's laminae III and IV were synthesized. 2. There was a shifting, serial overlap of representations of different forelimb regions in both the rostrocaudal and mediolateral axes of the dorsal horn. The rostrocaudal progression of receptive fields was from preaxial forelimb to forepaw to postaxial forelimb, whereas the mediolateral progression was from the volar glabrous forepaw toward the trunk. 3. Representations of the glabrous surfaces of the digits and palm pads showed considerable overlap, with the digital representations extending more laterally, but the palmar representations extending more rostrally and caudally. One-third of all recording loci were devoted exclusively to glabrous skin representation. 4. Comparison with results of earlier studies in raccoons indicates that representation of a given digit or palm pad is more restricted in rostrocaudal extent in the dorsal horn than in the dorsal roots, and that, compared with various nuclear regions of the dorsal column-medial lemniscal system, the glabrous surfaces of the forepaw are underrepresented in the dorsal horn. 5. The results suggest that there is a dorsoventral modular organization of forelimb representation in the dorsal horn. These wedge-shaped modules from larger aggregates which represent major body subdivisions and which course sinuously in the rostrocaudal dimension.
Cable properties of spinal cord motoneurons in adult and aged cats
Authors: Engelhardt J. K. , Morales F. R. , Yamuy J. , Chase M. H.
Published: December 2017

1. The electrophysiological properties of spinal cord alpha-motoneurons were investigated in adult cats (1-3 yr old) and old cats (14-15 yr old) using intracellular recording techniques. Voltage transients following depolarizing pulses of current were analyzed according to the procedure described by Ito and Oshima (15). The input resistance of each cell, together with the passive electrical time constants, were used to estimate the electrotonic length and total cell capacitance of each motoneuron. 2. Adult and old motoneurons both exhibited an undershoot of the membrane potential following the cessation of a subthreshold depolarizing current pulse (15). The average time constant for the decay of this undershoot in membrane potential was statistically indistinguishable in motoneurons of adult and aged animals. 3. The average membrane time constant of motoneurons in aged cats was 19% longer than that of motoneurons in adult cats. 4. The average total cell capacitance of motoneurons in aged cats was 16% smaller than that of motoneurons in adult cats. 5. The average electrotonic length of old motoneurons was statistically indistinguishable from that of motoneurons in adult cats. 6. From these results, we conclude that there is an age-dependent increase in the membrane resistance and an age-dependent decrease in cell surface area of alpha-motoneurons of the lumbar spinal cord in aged cats. Both of these phenomena are believed to contribute to the age-dependent increase in input resistance that has been previously reported to occur in motoneurons in aged cats (18).
Cyclic AMP selectively reduces the N-type calcium current component of mouse sensory neurons in culture by enhancing inactivation
Authors: Gross R. A. , Macdonald R. L.
Published: December 2017

1. The single-electrode voltage-clamp technique was used to assess the effect of elevated intracellular cyclic AMP levels on the three calcium current components of mouse dorsal root ganglion (DRG) neurons in culture. 2. Neither forskolin, cholera toxin, nor 8-Br-cyclic AMP affected the isolated transient low-threshold (T) calcium current. 3. When calcium currents were evoked at clamp potentials (Vc) positive to -20 mV from holding potentials (Vh) near the resting membrane potential, the calcium current consisted primarily of the transient high-threshold (N) and the slowly inactivating high-threshold (L) calcium current components. Under these conditions forskolin, cholera toxin, and 8-Br-cyclic AMP reduced the peak calcium current but had little or no effect on the late (greater than or equal to 300 ms) calcium current. When calcium currents were evoked from very negative Vh, however, there was no effect of these compounds. 4. Forskolin had no effect on the voltage-dependence of the current-voltage relation, nor on the rate of recovery of the calcium current from inactivation. 5. In other experiments, current traces were fitted using a multiexponential curve-fitting program that determined the amplitudes and inactivation time constants (tau i) of the three calcium current components. Forskolin selectively reduced the magnitude of the (curve-fitted) N current, and reduced its tau i. 6. Forskolin also enhanced steady-state inactivation of the N current, producing a -7.5 mV shift in the steady-state inactivation curve. 7. Cholera toxin, forskolin, and 8-Br-cyclic AMP had similar effects on calcium currents in mouse DRG neurons in culture.(ABSTRACT TRUNCATED AT 250 WORDS)
Temporal coding of envelopes and their interaural delays in the inferior colliculus of the unanesthetized rabbit
Authors: Batra R. , Kuwada S. , Stanford T. R.
Published: December 2017

1. The difference in the time of arrival of a sound at the two ears can be used to locate its source along the azimuth. Traditionally, it has been thought that only the on-going interaural temporal disparities (ITDs) produced by sounds of lower frequency (approximately less than 2 kHz) could be used for this purpose. However, ongoing ITDs of low frequency are also produced by envelopes of amplitude-modulated (AM) tones. These ITDs can be detected and used to lateralize complex high-frequency sounds (1, 8, 12, 15, 22, 24, 26). Auditory neurons synchronize to the modulation envelope, but do so at progressively lower modulation frequencies at higher levels of the auditory pathway. Some neurons of the cochlear nucleus synchronize best to frequencies as high as 700 Hz, but those of the inferior colliculus (IC) exhibit their best synchrony below 200 Hz. Even though synchrony to higher modulation frequencies is reduced at higher levels of the auditory pathway, is information about ITDs retained? 2. We answered this question by extracellularly recording the responses of neurons in the IC of the unanesthetized rabbit. We used an unanesthetized preparation because anesthesia alters the responses of neurons in the IC to both monaurally presented tones and ITDs. The unanesthetized rabbit is ideal for auditory research. Recordings can be maintained for long periods, and the acoustic stimulus to each ear can be independently controlled. 3. We studied the responses of 89 units to sinusoidally AM tones presented to the contralateral ear. For each unit, we recorded the response at several modulation frequencies. The degree of phase locking to the envelope at each frequency was measured using the synchronization coefficient. Two measures were used to assess the range of modulation frequencies over which phase locking occurred. The "best AM frequency" was the frequency at which we observed the greatest phase locking. The "highest AM frequency" was the highest frequency at which significant phase locking (0.001 level) was observed. We could not assess synchrony to ipsilateral AM tones directly, because most units did not respond to ipsilateral stimulation. 4. We studied the sensitivity of 63 units to ITDs produced by the envelopes of AM tones. Sensitivity to ITDs was tested by presenting AM tones to the two ears that had the same carrier frequency, but modulation frequencies that differed by 1 Hz. Units that were sensitive to ITDs responded to this stimulus by varying their response rate cyclically at the difference frequency, i.e., 1 Hz.(ABSTRACT TRUNCATED AT 400 WORDS)
Loss of inhibition precedes delayed spontaneous seizures in the hippocampus after tetanic electrical stimulation
Authors: Kapur J. , Lothman E. W.
Published: December 2017

1. The electrophysiological consequences of a "continuous" hippocampal stimulation protocol consisting of 10-s-long stimulus trains administered every 11 s for 90 min to the hippocampus of urethane-anesthetized rats were studied. During the period of stimulation, there was an initial phase with tonic discharges occurring every 1-2 min followed by a secondary phase in which there were well-demarcated recurrent clonic seizures. 2. At the end of the 90 min stimulation period, 7 out of a total of 14 animals studied show epileptiform activity that lasted one-half hour. The other half show disappearance of epileptiform activity within 2 min after terminating the stimulus. In all the animals a quiescent period then followed. In 11 of the animals studied, spontaneous seizures reappeared after the quiescent period had been present for several hours. 3. A paired-pulse method that in previous studies had been shown to reflect the functional state of GABAergic inhibition was employed. Paired-pulse depression in the CA1 region of the hippocampus was measured before administration of stimulus trains, in the quiescent period following the trains, and during and after spontaneous seizures. By comparing indices of maximal inhibition under the various experimental conditions, estimates of the relative amount of inhibition lost could be made. 4. All animals showed reduction of paired-pulse depression in the quiescent period following stimulation when compared with prestimulation values.(ABSTRACT TRUNCATED AT 250 WORDS)
Components of the responses of a population of DSCT neurons determined from single-unit recordings
Authors: Osborn C. E. , Poppele R. E.
Published: December 2017

1. Impulse activity of single units belonging to the dorsal spinocerebella tract (DSCT) was recorded in response to electrical stimulation of peripheral muscle nerves at group I intensities. The responses for 187 units were determined using a spike train analysis technique that facilitates the comparison of poststimulus response time course across units (response probability function, RPF; 16). 2. The poststimulus changes in impulse activity were represented in the waveform of the RPF. Principal component analysis was used to determine the component waveforms that were common to the responses across units. The analysis showed that there were a few waveforms that dominated the majority of the responses (85% of the total variability was accounted for by five principal component waveforms). 3. A cluster analysis based on three principal component waveforms revealed seven major groups of responses according to the patterns of their poststimulus activity. These response types were composed of different combinations of short- or long-latency excitation and inhibition. The same clusters were formed regardless of response amplitude or the source of the stimulus. 4. The responses were characterized by three general features, revealed by the first three principal components. The primary feature was the sign of the response, either mostly excitatory or inhibitory. The second feature was a distinction between a short- (up to 15 ms) and long- (approximately 30 ms) latency to peak response, and the third feature was the appearance of two separate phases of opposite sign in some of the responses.(ABSTRACT TRUNCATED AT 250 WORDS)
Sets of synaptic currents paired by common presynaptic or postsynaptic neurons
Authors: Gardner D.
Published: December 2017

1. In the buccal ganglia of Aplysia, presynaptic neurons B4 and B5 produce similar inhibitory postsynaptic currents (PSCs) in several postsynaptic follower cells. Previous work has shown that both duration and amplitude of these PSCs vary, that each parameter may be altered transiently by manipulating presynaptic activity, and that these variations affect synaptic efficacy. 2. To permit synapse-to-synapse comparisons, the mean and coefficient of variation (CV) of both peak conductance (gpeak) and time constant of decay (tau) were determined for sets of synaptic currents evoked by direct intracellular stimulation of presynaptic neurons. For 56 synapses, gpeak = 0.40 +/- 0.33 (SD) microS for a CV of 0.83, and tau = 19.7 +/- 4.0 ms for a CV of 0.20. The synapse-to-synapse variability was within 5% of values obtained from a previous population. 3. The relative contributions of presynaptic and postsynaptic factors to efficacy and variability of PSCs were examined by recordings from two classes of three-cell networks and by comparing values of gpeak and tau at synapses sharing a common presynaptic or postsynaptic neuron. 4. In the first case, paired presynaptic inputs from B4 and B5 converged on a common postsynaptic cell. For 16 examples of this case, mean values of both gpeak and tau recorded in a single follower cell, but produced by different presynaptic neurons, were significantly closer than those recorded in different followers (P less than 0.001). The common postsynaptic cell did not constrain variability of these parameters; CVs for paired synapses were not significantly different from the population (P greater than 0.1).(ABSTRACT TRUNCATED AT 250 WORDS)
Characteristics of vagal esophageal tension-sensitive afferent fibers in the opossum
Authors: Sengupta J. N. , Kauvar D. , Goyal R. K.
Published: December 2017

1. Single-unit vagal afferent activity was recorded from 35 fibers that demonstrated evoked response to distension in the smooth muscle portion of the esophagus in anesthetized opossums. 2. The conduction velocities, measured in 22 fibers, varied from 1.0 to 21.33 m/s. Eight fibers (36%) had conduction velocities in the range of C-fibers (less than 2.5 m/s), whereas 14 (64%) had velocities in the range of A delta-fibers (3.16-21.33 m/s). All fibers were spontaneously active with an average discharge rate of 7.3 +/- 1.0 imp/s (mean +/- SE; range, 1.2-23 imp/s). 3. Esophageal distension produced a reproducible increase in discharge rate that adapted slowly to sustained distension. The average threshold pressure of the endings was 10 mmHg. The saturation pressure was 70 mmHg with cumulative, stepwise distension and 56 mmHg with graded, discrete distensions, respectively. 4. The discharge rate at the saturation pressure was 46 +/- 7 imp/s with cumulative, stepwise distensions and was 59 +/- 4 imp/s with graded, discrete distensions. The difference in maximum discharge between these two modes of distension was not statistically significant (P greater than 0.05). 5. Esophageal peristaltic contraction was associated with bursts of spike discharge with an average rate of 53.6 +/- 4.7 imp/s. 6. Two types of fibers were identified based on their duration of spike discharge associated with peristaltic contraction. The short-activity fibers showed a short duration of response consisting of approximately 3 s of spike bursts in response to swallows. These short-activity fibers were not activated by either stretch or contraction of the longitudinal esophageal muscle. The long-activity fibers showed a long duration of response consisting of approximately 10 s of activity in response to swallows. These long-activity fibers could be activated by longitudinal muscle stretch or contraction. 7. It is concluded that esophageal tension-sensitive mechano-receptors associated with vagal afferents are activated by physiological peristalsis and are present "in series" with either circular or longitudinal muscle layers.
Classical conditioning reduces amplitude and duration of calcium-dependent afterhyperpolarization in rabbit hippocampal pyramidal cells
Authors: Coulter D. A. , Lo Turco J. J. , Kubota M. , Disterhoft J. F. , Moore J. W. , Alkon D. L.
Published: December 2017

1. The afterhyperpolarization (AHP) that follows action potentials was studied in CA1 hippocampal pyramidal cells from classically conditioned and control rabbits. Measurements of the AHP were obtained with intracellular recordings from CA1 cells within hippocampal slices. 2. The AHP of rabbit CA1 pyramidal cells was found to be accompanied by a conductance increase. The AHP was reduced by bath applications of the calcium channel blockers, cadmium and cobalt, by bath application of the cholinergic agonist, carbamylcholine chloride, and intracellular injection of the calcium chelator, ethylene glycol-bis(B-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA). 3. The AHP was markedly reduced in cells from rabbits that were well-trained with the nictitating membrane conditioning procedure, as compared with cells from pseudoconditioned or naive control animals. The difference in AHP amplitudes between conditioned and control groups increased as the number of spikes elicited by the stimulation pulse increased from one to four. Both the duration (measured as the time constant of AHP decay) and amplitude of the AHP were reduced in cells from conditioned animals. 4. The reduced AHP in cells from conditioned animals remained reduced in a medium that contained 0.5 microM tetrodotoxin (TTX) and 5.0 mM tetraethylammonium chloride (TEA); the AHP following calcium spikes was measured under these conditions. Since this medium eliminated synaptic transmission elicited by Schaeffer collateral stimulation, the AHP reduction in pyramidal cells from conditioned animals was not due to a modification in synaptic properties. There were no significant differences in the mean voltage thresholds, amplitudes, or durations of calcium spikes between cells from animals in the three groups. Thus the AHP reduction appears to be due to a modification of a Ca2+ -dependent K+ conductance and was not due to a secondary effect of reductions in calcium conductances underlying the spike. 5. In medium containing TTX and TEA, the amount of injected current required to elicit a calcium spike (current threshold) was significantly greater in cells from conditioned animals than in cells from control animals. This increase in current threshold persisted in 4-aminopyridine (4-AP)-containing medium and so cannot be attributed entirely to conditioning-specific increases in the A-current. 6. The conditioning-specific AHP reduction resulted in increased excitability in cells from conditioned animals versus pseudoconditioned control animals. Cells from conditioned animals fired more spikes to trains of 100-ms depolarizing current pulses than did cells from controls.
Two populations of rhythmically bursting neurons in rat medial septum are revealed by atropine
Authors: Stewart M. , Fox S. E.
Published: December 2017

1. Previous findings, such as the sensitivity of the hippocampal theta rhythm to cholinergic manipulation, support a "pacemaker" role for the cholinergic cells of the medial septal nucleus and the vertical limb of the nucleus of the diagonal band (MSN-NDB). To explore the mechanism(s) of action of systemic antimuscarinic drugs in eliminating the theta rhythm, recordings of hippocampal EEG and rhythmic MSN-NDB neurons that fired in phase with the hippocampal theta rhythm were taken during the administration of atropine in urethane-anesthetized rats. 2. Twenty-two of 33 rhythmic MSN-NDB cells continued to burst at the theta rhythm frequency after administration of a dose of atropine (25 mg/kg iv) that was sufficient to eliminate the theta rhythm (atropine-resistant cells). The remaining 11 cells lost their rhythmic firing pattern over the same time course as the loss of the theta rhythm (atropine-sensitive cells). 3. Both types of rhythmic MSN-NDB cells could be antidromically driven from the fimbria/fornix with similar latencies (range, 0.5-4.0 ms). The extracellularly recorded spike waveforms were not useful in predicting the atropine sensitivity of a given cell. Atropine-resistant cells frequently had higher firing rates than atropine-sensitive cells, but there was sufficient overlap of the two groups to make this a poor predictor of sensitivity. 4. Cooling the fimbria/fornix reversibly eliminated the hippocampal theta rhythm, but had no effect on 21/25 rhythmic MSN-NDB cells tested. This indicates that the atropine-sensitive MSN-NDB cells do not depend on the periodic output from the hippocampus for their rhythmic firing. Recordings from pairs of rhythmic MSN-NDB cells during cooling and/or atropine administration showed unchanged phase relations at the theta rhythm frequency. In rats in which the septohippocampal system was exposed by aspirating the overlying brain tissue, direct application of atropine (10 mg/ml) to the septal nuclei reversibly eliminated the hippocampal theta rhythm. 5. The rhythmic cells of the MSN-NDB are apparently composed of at least two distinct types, both of which potentially contribute to the production of the theta rhythm in the hippocampus. Elimination of hippocampal theta rhythm after local septal atropine application suggests that the loss of rhythmic activity in the group of atropine-sensitive septal cells is sufficient for the elimination of the theta rhythm. A model of the septohippocampal connections necessary for the theta rhythm is presented.
Whole cell recording from lobster olfactory receptor cells: responses to current and odor stimulation
Authors: Schmiedel-Jakob I. , Anderson P. A. , Ache B. W.
Published: December 2017

1. The basic electrical properties of olfactory (antennule) receptor cells were studied in an in situ preparation of the spiny lobster using whole cell patch-clamp recording. 2. The current-voltage relationship of the cells was linear for membrane potentials between -150 and -40 mV and rectified at more positive membrane potentials. The input resistance at rest averaged 508 M omega. The cells displayed two time constants, with mean values of 29.8 and 8.2 ms. 3. Depolarizing current steps elicited fast, overshooting action potentials at a mean threshold of -32 mV from an imposed resting membrane potential of -65 mV. The action potentials were tetrodotoxin (TTX) and tetraethylammonium (TEA) sensitive, suggesting they are typical sodium/potassium action potentials. 4. Odor stimulation evoked slow, dose-dependent, depolarizing receptor potentials up to 50 mV in amplitude. In approximately 30% of cells tested, these led to repetitive spiking when the cells were depolarized beyond -45 to -30 mV. The amplitude of the receptor potential was graded as a linear function of the logarithm of the odor concentration. 5. The amplitude of the receptor potential varied linearly with the membrane potential between -70 and -30 mV. Extrapolated reversal potentials appeared to be normally distributed around a mean value of -3.6 mV. 6. The results collectively indicate that lobster olfactory receptor cells have electrical properties similar to, but not necessarily identical with, those currently envisaged for olfactory receptor cells in other species.
Dissection of the neuron network in the catfish inner retina. III. Interpretation of spike kernels
Authors: Korenberg M. J. , Sakai H. M. , Naka K.
Published: December 2017

1. Three independent sets of evidence have been obtained to show that similar first- and second-order light-evoked kernels are computed for the ganglion cell when the system output is taken to be either the spike train (discrete signal) or the postsynaptic potential (analog signal). In this paper we show that the similarity of postsynaptic potential (PSP) kernels and spike kernels is readily explained by assuming an underlying cascade structure for the neural information processing. The cascade structure enables spike kernels to be mathematically related very simply to the process of generating the postsynaptic potentials of ganglion cells. 2. Mathematical analysis of the cascade structure also suggests why spike kernels appear to differ slightly from PSP kernels. The relation between the two sets of kernels predicted from our analysis is substantiated here by experiment and reveals an interconnection between several of the signals measured. 3. Our experimental results, in particular, suggest that the neuronal circuitry leading from the light stimulus to the generation of ganglion cell spike discharges can be represented as follows: either a Wiener (LN) or a dynamic linear-static nonlinear-dynamic linear (LNL) structure is followed by a highly nonlinear process [static or brief-memory Hammerstein static-nonlinear dynamic-linear (NL) structure] of spike generation. Cross-correlation between the analog input and spike output enables identification of these structures.
Discrimination among odorants by single neurons of the rat olfactory bulb
Authors: Wellis D. P. , Scott J. W. , Harrison T. A.
Published: December 2017

1. Intracellular and extracellular recordings were made from rat olfactory bulb mitral and tufted cells during odor stimulation and during electrical stimulation of the olfactory nerve. Neurons were identified by horseradish peroxidase injections and/or antidromic activation. The presentation of multiple concentrations of at least one odorant in a cyclic artificial sniff paradigm, as reported previously (10), allowed the study of odor responses. This approach was extended to multiple odorants to compare their concentration-response profiles. This procedure avoids the problems of interpretation resulting from nonequivalence of the effective concentrations of different odorants used as stimuli that have characterized previous studies of odor quality effects. Comparisons of intracellular events and responses to electrical stimulation with the odor-induced spike train activity allow us to begin to delineate the local circuitry involved in generating odor-induced responses. 2. The concentration-response profiles of the 72 cells in the present study are comparable to those previously reported for output neurons of the olfactory bulb, showing ordered changes in the temporal patterning of spike activity with step changes in odor concentration. However, eight of the neurons exhibited inhibitory responses to lower concentrations, but excitation, at similar latency, to higher concentrations of the same odorant. These data emphasize that to study pattern changes induced by changing odor quality the influence of stimulus intensity must also be carefully examined. The data also provide evidence that the temporal pattern evoked by an odorant is probably not in itself the code for odor quality recognition. 3. Complete concentration-response profiles, including subthreshold concentrations, to more than one odorant show that, although responses to the different odorant can evolve systematically with concentration, the responses to different odorants can evolve through very different patterns. For example, in some cells, the response patterns to different odors were complementary in form. These results demonstrate that the patterned responses of olfactory bulb neurons can reflect changes in odor quality as well as intensity. 4. Intracellular recording was employed to compare the temporal patterning of spikes during odor stimulation with membrane potential changes. In some cases, the spike pattern was closely correlated with apparent postsynaptic potentials. However, there were several clear exceptions. In five cells, a prominent hyperpolarization, seen in the first sniff of a series of 10 consecutive sniffs, was associated with pauses in spike activity. In the following
Dendrotoxin blocks accommodation in frog myelinated axons
Authors: Poulter M. O. , Hashiguchi T. , Padjen A. L.
Published: December 2017

1. Intracellular microelectrode recordings from large sensory and motor myelinated axons in spinal roots of Rana pipiens were used to study the effects of dendrotoxin (DTX), a specific blocker of a fast activating potassium current (GKf1). 2. Dendrotoxin reduced the ability of myelinated sensory and motor axons to accommodate to a constant stimulus. A depolarizing current step, which normally evoked only one action potential, after dendrotoxin treatment (200-500 nM) produced a train of action potentials. These spike trains lasted 29 +/- 2.8 (SE) ms on average in sensory fibers (n = 18) and 40.2 +/- 4.5 ms in motor fibers (n = 9). 3. After dendrotoxin treatment, in addition to a reduction in the ability to accommodate to a constant stimulus, a slowing in the rate of action potential generation was evident (spike frequency adaptation). 4. Dendrotoxin had no effect on the rising phase of conducted action potentials evoked by peripheral stimulation. Together with a lack of effect on the absolute refractory period, these results indicate that dendrotoxin does not affect sodium channel activity. 5. The steady-state voltage/current relationship was unchanged in response to hyperpolarizing current pulses; however, there was a significant increase in cord resistance in response to depolarizing current steps, demonstrating that DTX decreases outward rectification. 6. A computer model based on Hodgkin and Huxley equations was developed, which included the three voltage-dependent potassium conductances described by Dubois. The model reproduced major experimental results: removal of the conductance, termed GKf1, reduced the accommodation in the early phase of a continuous stimulus, indicating that this current could be responsible for the early accommodation. The hypothesis that the slow potassium conductance GKs regulates late accommodation and action potential frequency adaptation is also supported by the computer model. 7. In summary, these results suggest that in amphibian myelinated sensory and motor axons, the activity of potassium conductances can account for accommodation and adaptation without involvement of sodium conductance activity.
Evidence that peaks in EMG averages can sometimes be caused by inhibition of motoneurons
Authors: Widmer C. G. , Lund J. P.
Published: December 2017

1. It has been reported that an excitatory response occurs before strong inhibition in masticatory muscles. We tested the hypothesis that this small monopolar wave in the EMG, called by us the early exteroceptive component (EEC), is in fact the first response to inhibition. 2. A mapping of the electrical activity of the masseter muscle was performed using a 3 x 4 matrix of surface electrodes with reference to the back of the neck. Subjects sat with the jaw closing muscles relaxed or contracting at approximately 75% of the maximum voluntary level. The chin was tapped to evoke a jaw jerk reflex and the EEC was elicited by electrical stimulation to the palate. 3. In addition, bipolar EMGs and jaw position were recorded at minimal bite forces and at contraction levels of 5, 10, 15, or 20 N. 4. Data were computer average, with and without rectification, for 32 stimuli. 5. The EEC [latency 12.1 +/- 1.0 (SD)ms] was found to have the same polarity, shape, and duration as the repolarizing wave of the stretch reflex. 6. After electrical stimulation, an increase of bite force was never observed during or immediately after the EEC. Instead, bite force began to decrease 5-7 ms after the onset of the EEC. 7. The amplitude of the EECs never exceeded the level of the peaks in the preceding background EMG, even when the left and right palatal electrodes were stimulated simultaneously at high intensity.(ABSTRACT TRUNCATED AT 250 WORDS)
Identification of excitatory interneurons contributing to generation of locomotion in lamprey: structure, pharmacology, and function
Authors: Buchanan J. T. , Grillner S. , Cullheim S. , Risling M.
Published: December 2017

1. In the in vitro preparation of the lamprey spinal cord, paired intracellular recordings of membrane potential were used to identify interneurons producing excitatory postsynaptic potentials (EPSPs) on myotomal motoneurons. 2. Seventy-nine interneurons (8.4% of all neuron-motoneuron pairs tested) elicited unitary EPSPs that followed one-for-one at short, constant latencies and were therefore considered monosynaptic according to conventional criteria. Evidence was obtained for selectivity and divergence of excitatory interneuron (EIN) outputs and for convergence of EIN input to motoneurons. 3. The neurotransmitter released by EINs may be an excitatory amino acid such as glutamate, because the EPSPs were depressed by antagonists of excitatory amino acids. 4. Intracellular dye injection revealed that EINs have small cell bodies (average 11 x 27 microns), transversely oriented dendrites, and thin (less than 3 microns) slowly conducting axons (0.7 m/s) that project caudally and ipsilaterally. One EIN exhibited a system of thin multi-branching axon collaterals with periodic swellings. Ultrastructurally, these swellings contained clear spherical vesicles, and they apposed postsynaptic membrane specializations. 5. During fictive locomotion, the membrane-potential oscillations of EINs were greater in amplitude than, but similar in shape and timing to, those of their postsynaptic motoneurons. EINs fired action potentials during fictive locomotion and contributed to the depolarization of motoneurons. 6. These interneurons are proposed to be a source of excitation to motoneurons and interneurons in the lamprey spinal cord, participating in motor activity including locomotion.
Vagal afferent modulation of spinal nociceptive transmission in the rat
Authors: Ren K. , Randich A. , Gebhart G. F.
Published: December 2017

1. The effects of vagal afferent stimulation (VAS) on spinal nociceptive transmission and the spinal pathway(s) mediating VAS-produced effects were examined in pentobarbital sodium- and urethane-anesthetized, paralyzed rats. The 60 units studied responded to mechanical stimuli and noxious heating (50 degrees C) of cutaneous receptive fields confined to the glabrous skin of the toes and footpads. Recording sites were located in laminae I-VI of the L3-L5 spinal segments. 2. VAS facilitated and inhibited neuronal responses to heat. In pentobarbital-anesthetized rats, responses of most (24/44) units were facilitated by low and inhibited by higher intensities of VAS. Responses of some units (15/44) were only inhibited and others (4/44) only facilitated by VAS. Inhibition produced by VAS was intensity-, pulse width-, frequency-, and stimulation duration-dependent. In urethane-anesthetized rats, responses of 6/16 units were initially facilitated, then inhibited as the intensity of VAS was increased; responses of nine units were inhibited by VAS. Quantitative comparisons of recruitment indices, mean thresholds for inhibition and mean intensities to inhibit unit responses to heat to 50% of control revealed no significant differences between the two anesthetic conditions. 3. The effects of VAS on neuronal responses to heat were dissociable from its effect on blood pressure. Regardless of the effect of VAS on unit responses to noxious heat, VAS consistently produced intensity-dependent depressor responses. The latencies to onset of inhibition and facilitation by VAS were determined by a cumulative sum technique and bin-by-bin analysis of peristimulus time histograms. The apparent latencies were 91 +/- 11 (SE) ms for inhibition and 278 +/- 59 ms for facilitation, both of which occurred before changes in blood pressure. Finally, microinjections of lidocaine into the ventrolateral funiculus (VLF) or transections of the dorsolateral funiculus (DLF) of the thoracic spinal cord attenuated VAS-produced effects on neuronal responses, but did not affect VAS-induced depressor responses. 4. The responses of 11 dorsal horn units to graded noxious heating of the skin were studied; the stimulus-response functions (SRF) were linear and monotonic throughout the temperature range examined (42-52 degrees C). VAS at intensities which inhibited unit responses to heat significantly decreased the slope of the SRF. VAS at intensities which facilitated unit responses to heat produced a leftward, parallel shift of the SRF.(ABSTRACT TRUNCATED AT 400 WORDS)
Bullfrog dorsal root ganglion cells having tetrodotoxin-resistant spikes are endowed with nicotinic receptors
Authors: Morita K. , Katayama Y.
Published: December 2017

1. Intracellular recordings were made from bullfrog dorsal root ganglion (DRG) neurons in vitro. They were divided into three types, As, Ar, and C, according to their conduction velocity and their sensitivity to tetrodotoxin [TTX (less than or equal to 1 microM)]; an As neuron had a fast conduction velocity (13-50 m/s, mean = 31 m/s, n = 73) and TTX-sensitive sodium soma spikes: an Ar neuron showed a fast conduction velocity (4-28 m/s, mean = 14 m/s, n = 52) and TTX-resistant sodium soma spikes; and a C neuron had a slow conduction velocity (0.16-0.8 m/s, mean = 0.4 m/s, n = 49) and TTX-resistant sodium-calcium soma spikes. 2. Superfusion of acetylcholine [ACh (0.3 microM-1 mM)] produced a fast depolarization in 70% of Ar and in 50% of C neurons. No As neuron showed a fast depolarization in response to ACh. The ACh-induced fast response persisted in calcium-free or TTX-containing solutions. 3. The response in both Ar and C neurons was similar except in time course; the response was always more rapid in C than in Ar neurons. The response was always associated with a decreased membrane resistance and reversed in polarity at about -30 mV. The reversal potential varied with both sodium and potassium concentrations of the superfusing solutions. 4. Nicotine, (+)-tubocurarine [(+)-TC], and hexamethonium reversibly blocked the ACh fast response.(ABSTRACT TRUNCATED AT 250 WORDS)
Receptor characteristics of periodontal mechanosensitive units supplying the cat's lower canine
Authors: Loescher A. R. , Robinson P. P.
Published: December 2017

1. Forces have been applied to the lower canine teeth of cats, and the range of directions over which single periodontal mechanoreceptors are sensitive (arc of sensitivity) has been determined. We have further studied the response of each unit to forces applied in the direction of maximum sensitivity and investigated whether there is any relationship between the properties of the unit and its location within the periodontal ligament. 2. Recordings were made from 91 single units dissected from the inferior alveolar nerve in six cats. The mean arc of sensitivity to a 0.5 N force applied at right angles to the long axis of the tooth was 312 degrees. The arc of sensitivity was dependent on the force applied and the threshold of the receptor. 3. More units responded maximally to forces applied in a distolingual direction than would have been expected had the responses been evenly distributed around the tooth. Thirty-four of the units were bidirectionally sensitive, 28 became active when the force was removed, and 20 were spontaneously active. 4. The force threshold decreased with increasing rates of force application. 5. The majority of the units (81%) were slowly adapting. The rapidly adapting units had significantly higher force thresholds. 6. Twenty-eight of the receptors could be localized in the periodontal ligament after removing bone overlying the tooth root. There was no apparent relationship between the distance of the receptor from the fulcrum and its arc of sensitivity, threshold, maximum frequency of discharge, or adaptation properties.
Properties of reinnervated periodontal mechanoreceptors after inferior alveolar nerve injuries in cats
Authors: Loescher A. R. , Robinson P. P.
Published: December 2017

1. The properties of periodontal mechanoreceptors supplying lower canine teeth in cats have been investigated 12 wk after the crushing or sectioning of the inferior alveolar nerve. Forces were applied at right angles to the crown of the tooth and recordings made from filaments dissected from the nerve central to the injury site. Data obtained from 41 units after nerve crush and 65 units after nerve section were compared with those from a series of control animals. 2. The range of directions to which each receptor was sensitive was significantly smaller after both nerve crush and nerve section. There were significantly more rapidly adapting units after both nerve crush (37%) and nerve section (34%) than in the controls (19%). 3. Force thresholds measured at three rates of application (20 N/s, 2 N/s, and 0.25 N/s) were significantly higher after nerve section but not after nerve crush. The maximum frequency of discharge was significantly reduced after both nerve crush and nerve section. 4. Bone was removed from over the roots of the teeth to localize receptors in the underlying periodontal ligament. Seventeen receptors were localized in the nerve crush group and 23 in the nerve section group, and their distribution appeared similar to that found in controls. The conduction velocities of these units were significantly reduced after nerve section but not after nerve crush. One unit in the nerve section group appeared to have branched and innervated receptors in two locations.
G protein is coupled to presynaptic glutamate and GABA receptors in lobster neuromuscular synapse
Authors: Miwa A. , Ui M. , Kawai N.
Published: December 2017

1. We have examined the effects of L-glutamate and gamma-aminobutyric acid (GABA) on the presynaptic membrane of spiny lobster by the use of intra-axonal recording near the nerve terminals. 2. Application of glutamate to the synaptic region produced hyperpolarization in the presynaptic membrane but depolarization in the postsynaptic membrane. The presynaptic glutamate potential (PGP) is generated by an activation of K+ channels, as evidenced by its dependence on external K+ concentration. 3. The PGP was not affected by a spider toxin (JSTX), which blocks the postsynaptic glutamate receptor. By contrast, pertussis toxin (IAP) effectively blocked the PGP without affecting the resting conductance channels or action potentials in the presynaptic membrane. 4. Guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S), a hydrolysis-resistant analogue of GTP, blocked the PGP, suggesting the involvement of a G protein in the generation of K+ current. 5. Application of GABA induced depolarization or hyperpolarization in the presynaptic axon depending on the resting membrane potential. By reducing external Cl-, GABA-induced hyperpolarizations were converted to depolarizations, indicating that they are mainly mediated by Cl-. 6. In contrast to GABA, baclofen consistently induced hyperpolarization in low Cl- solution as well as in normal solution. Baclofen-induced hyperpolarization was blocked by IAP, indicating the mediation of G protein. 7. These results suggest that the presynaptic membrane of lobster neuromuscular synapse has entirely different types of amino-acid receptors from those in the postsynaptic membrane. Both the excitatory and the inhibitory axonal membrane have glutamate ("glutamateB") and GABAB receptors, which activate K+ channels via G protein.(ABSTRACT TRUNCATED AT 250 WORDS)
Synaptic transmission between rat inferior olivary neurons and cerebellar Purkinje cells in culture
Authors: Hirano T.
Published: December 2017

1. Monosynaptic excitatory connections between rat inferior olivary neurons and cerebellar Purkinje cells were studied in culture. Cerebellar cells were dissociated and cultured with small pieces of tissue excised from inferior olivary region. 2. Stimulation of inferior olivary neurons elicited an all-or-none response, which resembled a climbing fiber response, in a whole-cell current-clamped Purkinje cell. Under a voltage-clamp condition of a Purkinje cell, large excitatory postsynaptic current (EPSC) was recorded. 3. The inward EPSC recorded at -50 mV decreased in amplitude as the membrane potential was set more positive and reversed to the outward current around -10 mV. The amplitude of the EPSC changed linearly with the membrane potential between -90 and 10 mV, both in Mg2(+)-free and Mg2(+)-containing solutions. 4. The EPSC was suppressed with excitatory amino acid antagonist kynurenate or gamma-D-glutamylglycine (DGG) at 1 mM. Specific N-methyl-D-aspartate (NMDA) antagonist, DL-2-amino-5-phosphonovalerate (APV), little affected the EPSC at 0.2 mM. 5. The results indicate that the functional synapses were formed between inferior olivary neurons and cerebellar Purkinje cells in culture and suggest that the major postsynaptic receptors at the synapse are excitatory amino acid receptors of non-NMDA type.