bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamics and directional sensitivity of neck muscle spindle responses to head rotation
Authors: Chan Y. S. , Kasper J. , Wilson V. J.
Published: December 2017

With the use of floating electrodes we recorded from the C2 dorsal root ganglion of decerebrate cats during sinusoidal and trapezoidal head rotation. Fifty-one spontaneously firing afferents were identified as muscle spindle endings. Some were identified by their excitatory response to injection of succinylcholine, others by the similarity of their behavior to that of endings excited by the drug. Because afferent input to the ganglion was restricted by sectioning most nerve trunks, most spindle endings were presumably located in ventral and ventrolateral perivertebral muscles. The firing of each spindle afferent was modulated most effectively by tilting the head in a specific direction; this direction was termed its response vector. Responses to sine waves and trapezoids were then studied with stimuli oriented as closely as possible to the vertical plane of this vector. Most spindle afferents could be classified in one of two categories. Those with high gain, pronounced nonlinearity, and high dynamic index were called type A. Those classified as type B had low gain, a fairly linear response, and low dynamic index. In response to small (0.5 degrees) stimuli, type A endings had phase leads of approximately 40 degrees at frequencies of sinusoidal stimulation of 0.02-0.1 Hz, increasing to approximately 80 degrees at 4 Hz; with larger (2.5 degrees) stimuli, phase was advanced by an additional 10-20 degrees at all frequencies. Phase of type B responses was less advanced than that of type A responses. Gain slopes of the two types of endings were similar. Bode plots of spindle afferents strongly resembled those of upper cervical neurons whose activity is modulated by head rotation. Each spindle afferent had a response vector whose direction remained stable with time, different frequencies of stimulation, and different stimulus amplitudes. The distribution of response vectors covered approximately 270 degrees, with a gap near nose down pitch. Changing initial head position usually had little effect on the direction of an afferent's response vector or on response dynamics. However, stimulation far from the best plane could transform a type A into a type B response. This raises the possibility that type B receptors could be type A receptors best stimulated by yaw and with only low sensitivity to stimulation in vertical planes. Type A receptors have all the properties of spindle primaries. The identification of type B receptors remains uncertain, because they may include secondary afferents as well as primaries stimulated far from their best three-dimensional vector.(ABSTRACT TRUNCATED AT 400 WORDS)
Characterization of neuronal responses to noxious visceral and somatic stimuli in the medial lumbosacral spinal cord of the rat
Authors: Ness T. J. , Gebhart G. F.
Published: December 2017

The cutaneous receptive fields, long ascending projections, and responses to colorectal distension (20-100 mmHg) and tail movement of 252 neurons in spinal segments L6-S1 were characterized in pentobarbital- or halothane-N2O anesthetized, physiologically intact male rats. Seventeen additional neurons were studied in spinalized rats. Neurons studied were located within 0.5 mm of the midline at depths 0.2-1.4 mm from the spinal cord dorsum and included the area immediately dorsal and lateral to the central canal. Colorectal distension and/or antidromic invasion from the contralateral ventral quadrant of the cervical spinal cord were used as search stimuli. One hundred seventeen neurons responded to noxious colorectal distension; many had long ascending projections and convergent somatic input from deep joint receptors, ipsilateral perianal/scrotal cutaneous receptive fields, or both. Stimulus-response functions (SRFs) of 45 neurons to graded colorectal distension were linear, allowing extrapolation of threshold distending pressures to neuronal response. Neurons responsive to colorectal distension were subdivided into four classes based on their initial response colorectal distension (75-80 mmHg, 20 s). Short-latency abrupt (SL-A) neurons were excited at short latency by colorectal distension; activity abruptly returned to base line following termination of distension. Most SL-A neurons had long ascending projections, convergent somatic receptive fields, and 4/6 tested were excited by bradykinin administered intraarterially. The threshold distending pressure, estimated from the SRFs of 19 SL-A neurons, extrapolated to 2.7 mmHg. Short-latency sustained (SL-S) neurons were also excited at short latency by colorectal distension, but responses were sustained for 4–120 s following termination of distension. Most SL-S neurons had long ascending projections, convergent somatic receptive fields, and 18/20 tested were excited by intraarterial bradykinin. The threshold distending pressure, estimated from the SRFs of 20 SL-A neurons, extrapolated to 17.0 mmHg. Long-latency (LL) neurons were excited by colorectal distension at long latency following the onset of distension. No LL neurons had demonstrable long ascending projections, and few had convergent excitatory somatic fields. Three of five LL neurons were excited by intraarterial bradykinin. The threshold distending pressure, estimated from the SRFs of six LL neurons, extrapolated to 9.8 mmHg. Inhibited (INHIB) neurons were spontaneously active and were inhibited by colorectal distension.(ABSTRACT TRUNCATED AT 400 WORDS)
4-Aminopyridine produces epileptiform activity in hippocampus and enhances synaptic excitation and inhibition
Authors: Rutecki P. A. , Lebeda F. J. , Johnston D.
Published: December 2017

Using extra- and intracellular recording techniques, we investigated the epileptiform activity induced by low concentrations (5 and 10 microM) of bath-applied 4-aminopyridine (4-AP) in the CA3 subfield of rat hippocampal slices. We also studied the effects of 4-AP on the excitatory and inhibitory synaptic conductance changes in CA3 neurons produced by mossy fiber stimulation. Low concentrations of 4-AP induced spontaneously occurring epileptiform discharges at extracellular potassium concentrations between 1 and 10 mM. In contrast, picrotoxin and bicuculline produced spontaneous epileptiform discharges at extracellular potassium concentrations between 5 and 10 mM. The paroxysmal depolarizing shift (PDS) induced by 4-AP was also investigated. At potentials between -40 and -10 mV, the waveform of the PDS consisted of a depolarizing component enveloped by a hyperpolarizing component. The amplitude of the depolarizing component of the PDS was a monotonic function of the membrane potential, and the mean measured reversal potential was -25.7 mV. Under voltage-clamp conditions, the measured conductance associated with the depolarizing component of the PDS averaged 110 nS, with a reversal potential of -14.1 mV. Application of 5 microM 4-AP produced an increase in the inhibitory synaptic conductance change calculated from currents measured 15 ms following mossy fiber stimulation. The mean value increased from 35.2 to 58.1 nS (P less than 0.05) without a significant change in reversal potential. A concentration of 10 microM 4-AP also produced an increase in this inhibitory synaptic conductance change (from 53.3 to 66.3 nS, P less than 0.05) but caused a significant depolarization of the reversal potential (from -66.5 to -61.6 mV, P less than 0.05). This change in reversal potential may reflect a prolongation of the excitatory synaptic currents produced by 4-AP that contributes to the current measured 15 ms from the stimulus. Following application of either 5 or 10 microM 4-AP, there were no significant changes in the resting potential or input resistance of the neurons studied. Application of 5 microM 4-AP also significantly increased the amplitude of the measured excitatory synaptic conductance change produced by mossy fiber stimulation (from 27.9 to 44.1 nS, P less than 0.05) without producing a change in the reversal potential. In 5 of 21 neurons studied, a long-lasting outward synaptic current was present at holding potentials near rest following mossy fiber stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)
Evidence for a fatigue-induced reflex inhibition of motoneuron firing rates
Authors: Woods J. J. , Furbush F. , Bigland-Ritchie B.
Published: December 2017

1. In previous studies on the adductor pollicis and biceps brachii muscles we suggested that motoneuron firing rates are inhibited by a reflex from the muscle during fatigue, since: the firing rates decline during a sustained maximal voluntary contraction (MVC); recovery of MVC firing rates is prevented if the fatigued state of the muscle is preserved for 3 min by local occlusion of its blood supply; and full recovery occurs during this time once the blood supply to the peripheral muscle is restored. These findings were confirmed in the present study for quadriceps contractions. 2. These results do not necessarily imply an inhibitory reflex. The lower firing rates recorded from the muscle fibers during an MVC following 3 min of postfatigue ischemia may have been caused by either reduced subject effort (decreased muscle activation by the CNS) or impaired peripheral impulse transmission under these conditions. The present experiments, carried out on the quadriceps and adductor pollicis muscles, were designed to test this alternative explanation. 3. For both muscles, MVC contractions were sustained for 40 s with a blood pressure cuff inflated to 200 mmHg. This was followed by 3 min ischemic rest and a second 20-s MVC before cuff release. Three minutes after the blood supply to the muscle was restored a third 20-s MVC was made. Single shocks were delivered to the muscle throughout to record twitches from the relaxed muscle (Tr) before and after each MVC, and any twitches super-imposed on the voluntary contractions (Ts). The degree to which the muscle could be activated by voluntary effort was assessed from the ratio [1 - Ts/Tr]. For adductor pollicis, changes in the amplitude of the evoked M-waves were also measured. 4. Spike frequencies were only recorded during quadriceps experiments. These declined by 30% during the initial 40-s MVC. No recovery was seen in the second MVC following 3 min ischemic rest, but full recovery occurred within 3 min of cuff release. 5. Failure to retain full muscle activation was frequently seen in all three MVCs. However, for many well-motivated subjects twitch occlusion showed no reduction in the degree to which either the adductor pollicis or quadriceps muscles could be activated voluntarily during the MVC executed after 3 min of ischemic rest compared with that performed 3 min after the blood supply had been restored.(ABSTRACT TRUNCATED AT 400 WORDS)
Activity-evoked increases in extracellular potassium modulate presynaptic excitability in the CA1 region of the hippocampus
Authors: Poolos N. P. , Mauk M. D. , Kocsis J. D.
Published: December 2017

1. The effects of stimulus-evoked potassium release on the excitability of presynaptic axons were studied in the rat hippocampal slice preparation. Extracellular stimulation and recording in the stratum radiatum of CA1 yielded a characteristic field potential corresponding to the compound action potential of nonmyelinated afferents and subsequent postsynaptic activation of pyramidal cells. 2. Repetitive stimulation (1 s; 2-100 Hz) produced biphasic changes in the excitability of the afferents. Initial responses showed increased conduction velocity and variably increased amplitude; subsequent responses showed progressively decreasing conduction velocity and amplitude tending toward conduction block. Decreases in excitability were maximal at the end of stimulation and were more pronounced with higher stimulation frequencies. 3. When synaptic transmission was abolished with superfusate containing elevated [Mg2+] (6 mM) and decreased [Ca2+] (0.25 mM), kynurenic acid (1 mM), or adenosine (100 microM), the ability of the fibers to follow repetitive stimulation was enhanced, as indicated by a reduction in amplitude decrement of the presynaptic volley. The decrease in conduction velocity at the end of stimulation was less than half that obtained with intact postsynaptic activity. 4. Concomitant with changes in the excitability of CA1 afferents, the concentration of extracellular potassium ( [K+]o) increased up to 7 mM, as recorded in the stratum radiatum with potassium ion-sensitive microelectrodes. When postsynaptic activity was blocked, activity-evoked rises in [K+]o were reduced to less than 25% of their former value. This suggests that activity-evoked increases in [K+]o derive predominantly from postsynaptic elements. 5. Superfusion of solutions containing elevated [K+] produced biphasic changes in the excitability of CA1 afferents that were qualitatively similar to those produced by repetitive stimulation. Elevated [K+]o below 6 mM produced increased excitability, whereas [K+]o above 6 mM yielded decreased excitability. 6. These results demonstrate that in the CA1 region of the hippocampus, significant rises in [K+]o occur with activity and derive predominantly from postsynaptic elements. The conduction properties of CA1 afferents are sensitive to the level of [K+]o, whether altered artificially or by activity. These effects may constitute a mechanism of postsynaptic modulation of presynaptic conduction operating within a broad range of afferent firing frequencies in the hippocampus.
In-parallel and in-series behavior of human muscle spindle endings
Authors: Burke D. , Aniss A. M. , Gandevia S. C.
Published: December 2017

1. The responses of 62 putative muscle spindle afferents innervating the pretibial flexor muscles of normal human subjects were studied during graded twitch contractions of the receptor-bearing muscle to search for possible in-series coupling between spindle endings and motor units. 2. The majority of afferents (n = 57) responded unequivocally in an in-parallel manner to the twitch contractions, regardless of contraction strength. There were two patterns of in-parallel response: afferents without background activity discharged during the relaxation phase of the twitch; afferents with a background discharge were transiently silenced during the contraction phase and resumed their discharge on the relaxation phase. 3. Evidence of in-series coupling was found for five afferents during submaximal twitch contractions, to which each afferent responded in a mixed “biphasic” manner, with increases in discharge during both the contraction and relaxation phases of the twitch. Background discharge, response to stretch, and response during isometric voluntary contractions suggested that four of the afferents innervated primary spindle endings and the fifth a secondary spindle ending. 4. It is argued that the five atypical spindle endings responded in an ambiguous manner during twitch contractions of the receptor-bearing muscle because there was an in-series mechanical coupling between motor units and the spindle. The incidence of demonstrable in-series responses has serious implications for the mechanisms of spindle activation during normal motor behavior, but has only minor implications for the use of the twitch test to identify muscle spindle endings.
Gaze control in humans: eye-head coordination during orienting movements to targets within and beyond the oculomotor range
Authors: Guitton D. , Volle M.
Published: December 2017

Gaze, the direction of the visual axis in space, is the sum of the eye position relative to the head (E) plus head position relative to space (H). In the old explanation, which we call the oculocentric motor strategy, of how a rapid orienting gaze shift is controlled, it is assumed that 1) a saccadic eye movement is programmed with an amplitude equal to the target's offset angle, 2) this eye movement is programmed without reference to whether a head movement is planned, 3) if the head turns simultaneously the saccade is reduced in size by an amount equal to the head's contribution, and 4) the saccade is attenuated by the vestibuloocular reflex (VOR) slow phase. Humans have an oculomotor range (OMR) of about +/- 55 degrees. The use of the oculocentric motor strategy to acquire targets lying beyond the OMR requires programming saccades that cannot be made physically. We have studied in normal human subjects rapid horizontal gaze shifts to visible and remembered targets situated within and beyond the OMR at offsets ranging from 30 to 160 degrees. Heads were attached to an apparatus that permitted short unexpected perturbations of the head trajectory. The acceleration and deceleration phases of the head perturbation could be timed to occur at different points in the eye movement. 4. Single-step rapid gaze shifts of all sizes up to at least 160 degrees (the limit studied) could be accomplished with the classic single-eye saccade and an accompanying saccadelike head movement. In gaze shifts less than approximately 45 degrees, when head motion was prevented totally by the brake, the eye attained the target. For larger target eccentricities the gaze shift was interrupted by the brake and the average eye saccade amplitude was approximately 45 degrees, well short of the OMR. Thus saccadic eye movement amplitude was neurally, not mechanically, limited. When the head's motion was not perturbed by the brake, the eye saccade amplitude was a function of head velocity: for a given target offset, the faster the head the smaller the saccade. For gaze shifts to targets beyond the OMR and when head velocity was low, the eye frequently attained the 45 degrees position limit and remained there, immobile, until gaze attained the target.(ABSTRACT TRUNCATED AT 400 WORDS)
Effects of interaural time delays of noise stimuli on low-frequency cells in the cat's inferior colliculus. II. Responses to band-pass filtered noises
Authors: Chan J. C. , Yin T. C. , Musicant A. D.
Published: December 2017

1. We studied cells in the central nucleus of the inferior colliculus of the cat that were sensitive to interaural time delays (ITDs) in order to evaluate the influence of the stimulus spectrum of noise signals. Stimuli were sharply filtered low-, high-, and band-pass noise signals whose cutoff frequencies and bandwidths were systematically varied. The responses to ITDs of these noise signals were compared with responses obtained to ITDs of broadband noise and pure tones. 2. The discharge rate in response to band-pass noise as a function of ITD was usually a cyclic function with decreasing peak amplitudes at longer ITDs. The reciprocal of the mean interval between adjacent peaks indicated how rapidly the response rate varied with ITD and was termed the response frequency (RF). This RF was approximately equal to the median frequency of the stimulus spectrum filtered by the cell's sync-rate curve, which was the product of the synchronization to interaural phase and the discharge rate plotted against frequency. This suggests that the RF was determined by all the spectral components in the stimulus that fell within the frequency range in which the cell's response was synchronized. The contribution of each component was proportional to the sync-rate for that frequency. 3. The central peak of the ITD function usually fell within the physiological range of ITDs (+/- 400 microseconds). The location of this peak did not vary significantly with changes in stimulus spectrum by comparison with responses to tones of different frequency. Its shape also remained constant, except for a decrease in width when high-frequency components within the range of the sync-rate curve were added to the stimulus. A few cells responded with a minimal discharge instead of a maximal near-zero ITD, and this central minimum had similar properties as the central peak. The amplitude of the secondary peaks of the ITD function decreased as the stimulus bandwidth that overlapped the sync-rate curve broadened. 4. The sum of the ITD functions to two band-pass signals was similar to that of a broadband signal whose spectrum was composed of the sum of the band-pass spectra. 5. From these binaural responses we could make inferences about the response characteristics of the monaural inputs to binaural neurons. We then verified these predictions by studying responses of low-frequency trapezoid body fibers to band-pass noises.
Models of synchronized hippocampal bursts in the presence of inhibition. I. Single population events
Authors: Traub R. D. , Miles R. , Wong R. K.
Published: December 2017

1. We constructed model networks with 520 or 1,020 cells intended to represent the CA3 region of the hippocampus. Model neurons were simulated in enough detail to reproduce intrinsic bursting and the electrotonic flow of currents along dendritic cables. Neurons exerted either excitatory or inhibitory postsynaptic actions on other cells. The network models were simulated with different levels of excitatory and inhibitory synaptic strengths in order to study epileptic and other interesting collective behaviors in the system. 2. Excitatory synapses between neurons in the network were powerful enough so that burst firing in a presynaptic neuron would evoke bursting in its connected cells. Since orthodromic or antidromic stimulation evokes both a fast and a slow phase of inhibition, two types of inhibitory cells were simulated. The properties of these inhibitory cells were modeled to resemble those of two types of inhibitory cells characterized by dual intracellular recordings in the slice preparation. 3. With fast inhibition totally blocked, a stimulus to a single cell lead to a synchronized population burst. Thus the principles of our epileptic synchronization model, developed earlier, apply even when slow inhibitory postsynaptic potentials (IPSPs) are present, as apparently occurs in the epileptic hippocampal slice. The model performs in this way because bursting can propagate through several generations in the network before slow inhibition builds up enough to block burst propagation. This can occur, however, only if connectivity is sufficiently large. With very low connection densities, slow IPSPs will prevent the development of full synchronization. 4. We performed multiple simulations in which the fast inhibitory conductance strength was kept fixed at various levels while the strength of the excitatory synapses was varied. In each simulation, we stimulated either one or four cells. For each level of inhibition, the peak number of cells bursting depended sensitively on excitatory synaptic strength, showing a sudden increase as this strength reached a critical level. The critical excitation, which depended on the level of inhibition, corresponded to the level at which bursting can propagate from cell to cell at the particular level of inhibition. 5. We performed an analogous series of simulations in which the strength of excitatory synapses was held constant while the strength of fast inhibitory synapses was varied, stimulating a single neuron in each case. These simulations correspond to experiments that have been done in the hippocampal slice as low doses of picrotoxin are washed into a slice, gradually abolishing fast inhibition.(ABSTRACT TRUNCATED AT 400 WORDS)
Active contraction of nerve bundle and identification of a nerve-contractor motoneuron in Aplysia
Authors: Umitsu Y. , Matsumoto H. , Koike H.
Published: December 2017

1. The active contraction or shortening of the nerves of Aplysia kurodai and Aplysia juliana was examined. 2. A particular neuron in the abdominal ganglion controlled the contractions of the nerves, and the neuron was identified as a gill- and siphon-contractor motoneuron previously identified as L7. This was based on the following observations, which agreed closely with those reported for L7: the position, shape, and color of the cell body of the neuron; the synaptic and antidromic activation of the neuron by stimulation of various nerves; and the configurations of the major axons as revealed by dye injection into the soma of the neuron. Finally, the activation of the neuron contracted the gill, and the characteristics of the contraction were those reported for L7. 3. L7 was the only neuron we could find in the abdominal ganglion that directly controlled the contractions of the nerves. This was supported by the following observations: 1) direct or synaptic activation of L7 made the nerves shorter in a firing frequency-dependent manner. 2) Even single action potentials of L7 contracted the nerves. 3) When L7 was destroyed, no contractions of the nerves were observed however strongly a stimulation was applied. 4) When every synaptic connection in the abdominal ganglion was blocked by bathing the ganglion in Cafree artificial seawater, direct or spontaneous activation of L7 still made the nerves shorter. 4. A sensitive marker, cobaltic-lysine complex solution, was injected into the cell body of L7, and many fine axonal branches were newly found in the epineurium of the nerves. With the use of spike-triggered averaging, small potentials were recorded from the contracting nerves. This suggested that the action potentials were conducted along the newly found fine branches of the axon to innervate the epineurial muscles. 5. We found that L7 is a multifunctional motoneuron that contracts nerves.
Central sites involved in lateral hypothalamus conditioned neural responses to acoustic cues in the rat
Authors: Nakamura K. , Ono T. , Tamura R.
Published: December 2017

1. Unit activity in the lateral hypothalamus (LHA) of the rat was recorded during discrimination learning of cue-tone stimuli (CTS) predicting glucose (CTS1+) or intracranial self-stimulation (ICSS) (CTS2+) as positive reinforcement or electric shock (CTS1-) or tail pinch (CTS2-) as negative reinforcement. The same action, licking, was used as the behavioral response to all stimuli. Procaine hydrochloride, a local anesthetic, was microinjected into the ventral tegmental area (VTA) and the amygdala (AM). LHA neuron responses and licking were analyzed to investigate the afferent input pathway(s) responsible for LHA neural responses to conditioning CTSs in positive reinforcement and to identify the central site involved in CTS learning. Although the animals were restrained, there was no respiratory, cardiac rate, or blood pressure evidence of stress. The headholder was specially designed in our laboratory to avoid pain or discomfort to the animal. The subjects would often, after the first few sessions, voluntarily enter into position in the apparatus, presumably to obtain the reward available during the experiments. 2. In positive reinforcement, a rat was rewarded by 5 microliters of glucose or ICSS when it licked a spout. The rat licked for glucose after CTS1+ or for ICSS after CTS2+. In negative reinforcement, an aversive stimulus, either electric shock or tail pinch, was applied if the rat did not lick the spout. The electric shock and tail pinch were maintained weak enough to produce an avoidance ratio less than 20-30%, averaged in all trials. The rat licked to avoid electric shock after CTS1- or tail pinch after CTS2-. 3. Of 271 LHA neurons analyzed, 202 (74.5%) responded to either or both rewarding and aversive stimuli. The number of neurons that responded to only rewarding stimuli was relatively large (105/271), and the number that responded similarly to both rewarding and aversive stimuli was small (29/271). The effects of both glucose and ICSS, and the effects of both electric shock and tail pinch, were usually similar in neurons analyzed for both rewarding and aversive stimulation. Of 271 neurons, 173 responded differentially to rewarding and aversive stimuli. 4. Neural and behavioral responses were recorded before, during, and after local anesthesia of the VTA in 15 rats and of the AM in 14 rats. Injections of 0.3-0.8 microliters of 5% procaine hydrochloride or 0.9% saline were made at a rate of 0.3 microliters/min through guide cannulae chronically implanted in the VTA and AM, ipsilateral to the recording and ICSS sites in 29 rats that self-stimulated.(ABSTRACT TRUNCATED AT 250 WORDS)
Action-potential discharge in hippocampal CA1 pyramidal neurons: current source-density analysis
Authors: Richardson T. L. , Turner R. W. , Miller J. J.
Published: December 2017

1. The site of origin of evoked action-potential discharge in hippocampal CA1 pyramidal neurons was investigated using the in vitro rat hippocampal slice preparation. 2. Action-potential discharge in pyramidal cells was evoked by stimulation of efferent pyramidal cell fibers in the alveus (antidromic) or afferent synaptic inputs in stratum oriens (SO) or stratum radiatum (SR). Laminar profiles of evoked extracellular field potentials were recorded at 25-micron intervals along the entire dendrosomatic axis of the pyramidal cell and a one-dimensional current source-density analysis was applied. 3. Suprathreshold stimulation of the alveus evoked an antidromic population spike response and current sink with the shortest peak latency in stratum pyramidale or proximal stratum oriens. A biphasic positive/negative potential associated with a current source/sink was recorded in dendritic regions, with both components increasing in peak latency with distance from the border of stratum pyramidale. 4. Suprathreshold stimulation of SO or SR evoked a population spike response superimposed upon the underlying synaptic depolarization at all levels of the dendrosomatic axis. The shortest latency population spike and current sink were recorded in stratum pyramidale or proximal stratum oriens. In dendritic regions, a biphasic positive/negative potential and current source/sink conducted with increasing latency from the border of stratum pyramidale. 5. A direct comparison of alvear- and SR-evoked responses revealed a basic similarity in population spike potentials and associated sink/source relationships at both the somatic and dendritic level and a similar shift in peak latency of spike components along the pyramidal cell axis. 6. It is concluded that the initial site for generation of a spike along the dendrosomatic axis of the pyramidal cell following antidromic or orthodromic stimulation is in the region of the cell body layer (soma or axon hillock). Action-potential discharge in dendritic regions then occurs as the result of a subsequent retrograde spike invasion of basal and apical dendritic arborizations.
Dynamics and Directional Sensitivity of Neck Muscle Spindle Responses to Head Rotation
Authors: Chan Y. S. , Kasper J. , Wilson V. J.
Published: December 2017

Y. S. Chan, J. Kasper, and V. J. Wilson, “Dynamics and Directional Sensitivity of Neck Muscle Spindle Responses to Head Rotation.” Taiwan was incorrectly added to the present address of Y. S. Chan on page 1728. The correct address is Dept. of Physiology, Faculty of Medicine, University of Hong Kong, Hong Kong.
Signal transmission in the catfish retina. V. Sensitivity and circuit
Authors: Sakai H. M. , Naka K.
Published: December 2017

1. We analyzed the light-evoked responses of retinal neurons by means of a white-noise technique. Horizontal and bipolar cells produced a modulation response that was linearly related to a modulation of the mean luminance of a large field of light. The first-order kernels were capable of reproducing the cells' modulation response with a fair degree of accuracy. The amplitude as well as the waveform of the kernels changed with the change in the mean luminance. This is a parametric change and is a form of field adaptation. As the time constant of the parametric change was much longer than that of the modulation response (memory), neurons were assumed to be at a dynamic steady state at a given mean luminance. 2. With the presence of a steady annular illumination, the first-order kernel derived from stimulation with a small spot of light became faster in peak response time and larger in amplitude. For horizontal-cell somas and bipolar cells, the surround also linearized their modulation response. This surround enhancement has been seen in all the cone-driven retinal cells except the receptor and horizontal cell axon, in which a steady surround decreased the amplitude of the spot-evoked kernel but shortened the peak response time. 3. A change in the modulation depth did not affect either the amplitude or the wave-form of the first-order kernels from the horizontal and bipolar cells. In the amacrine and ganglion cells, on the other hand, the amplitude of kernels was related inversely to the depth of modulation. These cells were more sensitive to the modulation of a small modulation depth. 4. A static nonlinearity appeared when signals were transmitted to the amacrine cells. The nonlinearity was first produced in the type-C amacrine cells by a process, which could be modeled by squaring the bipolar cell response. A gamut of more complex second-order nonlinearities found in type-N amacrine cells could be modeled by a band-pass filtering of the type-C cell response. Linear components in the bipolar cells and nonlinear components in the amacrine cells are encoded into spike trains in the ganglion cells. Thus, under our simple stimulus regimen, the ganglion cells transformed the results of the preganglionic signal processing into a spike train without much modification. 5. We propose a tentative diagram of the signal flow in the cone-driven catfish retinal neurons based on this and previous studies.(ABSTRACT TRUNCATED AT 400 WORDS)
Voltage spread in an identified interneuron of the barnacle's visual system
Authors: Oland L. A. , Stuart A. E. , Hayashi J. H. , Callaway J. C.
Published: December 2017

1. The interneuron that is postsynaptic to barnacle photoreceptors (the inverting, or I-cell) receives similar synaptic input from the receptors onto its two distinct and separate arbors. We compared the spread of light-evoked synaptic potentials from the proximal and distal arbors with the cell's soma in order to ascertain how well voltages spread in this cell. 2. The proximal and distal arbors are connected by a commissural process approximately 200 microns in length and 2 microns in diameter. Voltages spreading from the distal arbor along this process were 20–60% of their original value, and delayed 15–20 ms, when recorded at the cell's soma. 3. The reversal potential of the receptor's input to the distal arbor, determined by injecting current into the soma, appeared substantially negative (-150 mV) to that of the identical input to the proximal arbor (-80 mV). Assuming identical reversal potentials in the two arbors, this difference indicates that more current must be injected into the I-cell's soma to change the voltage of the distal arbor to a given potential than to change that of the proximal arbor to the same potential. 4. Comparison of input from a lateral eye to the ipsilateral arbor with that from the median eye to the same arbor indicates that these two inputs are at an electrically equivalent distance from the soma. 5. Uneven illumination of the eyes may, through local conductance changes, cause the arbors to function independently, even to the point where one arbor may depolarize when the other is hyperpolarized.
Response variability of X- and Y-cells in the dorsal lateral geniculate nucleus of the cat
Authors: Sestokas A. K. , Lehmkuhle S.
Published: December 2017

1. We measured the variability of neural responses in the dorsal lateral geniculate nucleus (dLGN) of the anesthetized, paralyzed cat during repeated visual stimulation with sinusoidal grating patterns. Results are reported for 11 X-cells and 16 Y-cells recorded in laminae A and A1. 2. The responses of most X- and Y-cells varied markedly from trial to trial. The standard deviations of prestimulus, base-line discharge rate. In contrast, the standard deviations of poststimulus responses increased only slightly or not at all with increases in mean discharge rate. 3. Standard deviations of poststimulus responses to optimal stimuli were about one-third the size of mean discharge rates. Relative variability (standard deviation/mean) increased markedly and in nonlinear fashion with decreases in response amplitude, which resulted in considerable overlap of base-line and poststimulus response distributions when stimuli were less than optimal.
Vestibuloocular reflex inhibition and gaze saccade control characteristics during eye-head orientation in humans
Authors: Pelisson D. , Prablanc C. , Urquizar C.
Published: December 2017

1. In natural conditions, gaze (i.e., eye + head) orientation is a complex behavior involving simultaneously the eye and head motor systems. Thus one of the key problems of gaze control is whether or not the vestibuloocular reflex (VOR) elicited by head rotation and saccadic eye movement linearly add. 2. Kinematics of human gaze saccades within the oculomotor range (OMR) were quantified under different conditions of head motion. Saccades were visually triggered while the head was fixed or passively moving at a constant velocity (200 deg/s) either in the same direction as, or opposite to, the saccade. Active eye-head coordination was also studied in a session in which subjects were trained to actively rotate their head at a nearly constant velocity during the saccade and, in another session, during natural gaze responses. 3. When the head was passively rotated toward the visual target, both maximum and mean gaze velocities increased with respect to control responses with the head fixed; these effects increased with gaze saccade amplitude. In addition, saccade duration was reduced so that corresponding gaze accuracy, although poorer than for control responses, was not dramatically affected by head motion. 4. The same effects on gaze velocity were present during active head motion when a constant head velocity was maintained throughout saccade duration, and gaze saccades were as accurate as with the head fixed. 5. During natural gaze responses, an increased gaze velocity and a decreased saccade duration with respect to control responses became significant only for gaze displacement larger than 30 degrees, due to the negligible contribution of head motion for smaller responses. 6. When the head was passively rotated in the opposite direction to target step, gaze saccades were slower than those obtained with the head fixed; but their average accuracy was still maintained. 7. These results confirm a VOR inhibition during saccadic eye movements within the OMR. This inhibition, present in all 16 subjects studied, ranged from 40 to 96% (for a 40 degree target step) between subjects and increased almost linearly with target step amplitude. Furthermore, the systematic difference between instantaneous VOR gain estimated at the time of maximum gaze velocity and mean VOR gain estimated over the whole saccadic duration indicates a decay of VOR inhibition during the ongoing saccade. 8. A simplified model is proposed with a varying VOR inhibition during the saccade. It suggests that VOR inhibition is not directly controlled by the saccadic pulse generator.(ABSTRACT TRUNCATED AT 400 WORDS)
Muscle-specific decrease in presynaptic calcium dependence and clearance during neuromuscular transmission in aged rats
Authors: Smith D. O.
Published: December 2017

1. Calcium regulation in the vicinity of synaptic release sites was measured indirectly at the neuromuscular junction of diaphragm, soleus, and extensor digitorum longus (EDL) muscles of rats 10 (mature adult) and 25-27 mo of age. 2. The rate of miniature end-plate potentials (MEPPs) per nerve terminal increased by 79% with age in EDL but did not change significantly in diaphragm or soleus; since MEPP rate depends, in part, on resting steady-state intracellular Ca2+ levels, ([Ca2+]i), it was inferred that these levels may be elevated by at least 16% in the aged EDL tissue. 3. The double-logarithmic relationship between extracellular Ca2+ ([Ca2+]e), and quantal release (m) was determined for [Ca2+]e between 0.5 and 1.2 mM. The slope (n) of this relationship was 4.1 and 3.2 in EDL muscles from the younger and the older animals, respectively; this difference was significant statistically. 4. A static model of the saturable cooperative relationship between [Ca2+]e and m was used to evaluate possible causes of the age-related change in this relationship. Changes resembling those seen in EDL during aging could be produced by relatively slight variations in the amount of Ca2+ entering the cell, intracellular buffering capacity, and several other related aspects of Ca2+ availability. The observed changes could not, however, be attributed quantitatively to increased steady-state [Ca2+]i. 5. The decay rates of synaptic facilitation and of posttetanic augmentation were prolonged by 164 and 227%, respectively, in EDL during aging. Since both of these phenomena have been attributed to residual Ca2+, it was inferred that rates of Ca2+ clearance from synaptic release sites were correspondingly slower in aged EDL. 6. Each of these age-associated changes in Ca2+ regulation was observed only in EDL and not in diaphragm or soleus. This specificity may be related to progressive disuse of EDL (a fast-twitch leg muscle), and consequently decreased expression of Ca2+-regulatory enzymes, during aging.
Cholinergic mechanisms in the reticular control of transmission in the cat lateral geniculate nucleus
Authors: Francesconi W. , Muller C. M. , Singer W.
Published: December 2017

1. We examined the hypothesis that the ascending reticular arousal system influences thalamic transmission through a cholinergic mechanism. Extra- and intracellular recordings were obtained from neurons of the dorsal lateral geniculate nucleus (LGNd) and the perigeniculate nucleus (PGN) of cats anesthetized either with N2O and pentobarbital or with N2O and halothane. We compared the effects that electrical stimulation of the mesencephalic reticular formation (MRF) and ionophoretically applied acetylcholine (ACh) have on spontaneous and evoked activity of individual neurons and tested whether these effects could be antagonized by ionophoretic administration of the muscarinic receptor blocker scopolamine. The effects of ionophoretically applied glutamate (GLU), N-methyl-D-aspartate, and bicuculline were examined in addition. 2. The prominent effects in LGNd relay cells of both ACh application and of MRF stimulation were an enhancement of the resting discharge, a facilitation of the excitatory responses to light, a reduction of the amplitude and duration of evoked inhibitory episodes, and a blockade of postinhibitory rebound burst. These latter effects resembled those induced with bicuculline. Under barbiturate anesthesia neither ACh application nor MRF stimulation elicited discharges when the excitatory input from the retina was blocked. Ionophoretic application of hte muscarinic antagonist scopolamine abolished the effects of ACh ionophoresis in all relay cells tested (n = 20), and in 10 cells it also antagonized completely the effects of MRF stimulation. In the remaining cells scopolamine reduced the effects of MRF stimulation. 3. Increasing the depth of anesthesia reduced or abolished the effects of ACh application and MRF stimulation on the cells' resting activity but did not interfere with the facilitation of evoked responses. 4. The effects of the excitatory amino acids GLU and NMDA differed from those of MRF stimulation and ACh application, since the former always enhanced both spontaneous and evoked discharges but neither shortened phases of evoked inhibition nor abolished postinhibitory rebound bursts. 5. There was a high correlation between the effectiveness of MRF stimulation and ACh application in individual neurons. On the average, the facilitation of evoked responses was more pronounced in X- than in Y-cells, and the fraction of cells responding with an increase of resting activity to both procedures was considerably higher among X- than among Y-cells.(ABSTRACT TRUNCATED AT 400 WORDS)
Taste responses in the parabrachial pons of decerebrate rats
Authors: Di Lorenzo P. M.
Published: December 2017

1. Behavioral studies have shown that chronic decerebrate rats retain the capacity to react appropriately to gustatory stimuli (12), but do not form taste-illness associations (13). Little is known, however, about the effects of decerebration on the processing of gustatory information. The present experiment was designed to investigate this issue in the parabrachial nucleus of the pons (PbN). 2. Rats were decerebrated at the supracollicular level under ketamine and ether anesthesia and were prepared for electrical recording in the PbN. Thereafter, animals were maintained under Flaxedil, and wound edges were frequently treated with lidocaine. Heart rate, core temperature, and CO2 were monitored throughout each experiment. Control subjects were treated identically, except that they were not decerebrated. 3. Sapid solutions of NaCl (0.1 M), HCl (0.01 M), sucrose (0.5 M), saccharin sodium (0.004 M), and quinine HCl (.01 M) were used as taste stimuli. After a 10-s base line, each stimulus was bathed over the tongue for 10 s followed by a 10-s wait and a 20-s rinse of distilled water. The intertrial interval was at least 2 min. 4. Gustatory responses from 32 parabrachial units in 13 decerebrate rats were recorded. These were compared with responses in 31 units from the PbN of 16 intact rats. 5. Analysis of response profiles of PbN units in decerebrate rats showed that these units produced smaller responses to NaCl and HCl and larger responses to saccharin sodium compared with units in intact rats. 6. Despite changes in response magnitude, the temporal patterns of response (phasic-tonic relationships) were not different in PbN units in decerebrate rats compared with controls. Differences in the length of responses were, however, apparent. Responses to saccharin sodium were longer, response to NaCl, HCl and sucrose were shorter, and responses to quinine HCl were unchanged. 7. Results of a multidimensional scaling analysis of the response profiles across units showed that "taste spaces" for decerebrate and intact rats were similar. Units in each group were meaningfully placed near stimuli that evoked the best response in a given unit. Units that did not respond well to any stimulus were placed close together regardless of their best stimulus in both taste spaces. 8. Responses to the termination of the taste stimulus (OFF-responses) were observed in PbN units in the decerebrate rat but not in units from the intact rat. Twenty-one OFF-responses were recorded in 14 units; 6 of these occurred in the absence of a response to the stimulus.(ABSTRACT TRUNCATED AT 400 WORDS)