bluuebunny/crossref_metadata_2025 huggingface dataset:
Responses of pigeon horizontal semicircular canal afferent fibers. I. Step, trapezoid, and low-frequency sinusoid mechanical and rotational stimulation
Authors: Dickman J. D. , Correia M. J.
Published: December 2017

1. The horizontal semicircular canals of anesthetized (barbiturate/ketamine) pigeons were stimulated by rotational and by mechanical stimulation. 2. The mechanical stimulation consisted of making a small (less than 1 mm) fistula in the lateral part of the bony horizontal semicircular canal and, after inserting a probe coupled to a piezoelectric micropusher through the fistula, providing controlled indentation of the exposed membranous horizontal semicircular duct. 3. Extracellular action potentials from single horizontal semicircular canal primary afferent (HCA) fibers were recorded during sinusoidal rotational and during step, ramp, and sinusoidal mechanical stimulation. 4. The mean spontaneous discharge rate of 160 horizontal canal afferents was 86 +/- 4 (SE) spikes/s. This rate was not significantly different from that reported previously for pigeon HCA fibers recorded with the horizontal canal intact (i.e., no fistula introduced). 5. Sinusoidal mechanical indentation of the horizontal semicircular duct produced clearly entrained action potentials on 36 HCA fibers for a range of peak displacements from +/- 0.5 to +/- 30 microns. Action potentials were never modulated on afferents (n greater than 100) identified as innervating the anterior and posterior semicircular canals or the otolith organs during mechanical stimulation of the horizontal semicircular canal, even for displacements as large as 30 microns. 6. Intensity functions relating peak firing frequency (spikes per second) and peak probe displacement (micrometers) for 1.0-Hz sinusoidal mechanical stimulation were linear over the range 1.0-5.0 microns. The most sensitive units (6/36, 17%) showed response saturation as the stimulus magnitude was extended to 7 microns and beyond. 7. In 15 of 36 units, both mechanical and rotational sinusoidal stimulation (1.0 Hz) were applied to the same unit. The duct indentation magnitudes were 1.0, 2.5, 5.0, and 7.0 microns and the rotational velocities were 5, 10, and 20 deg/s. The constant of proportionality found to equate the peak response produced by rotational to that elicited by mechanical stimulation was 7.0 deg.sec-1/1.0 microns. 8. Bode plots and best-fit transfer functions of the frequency response (0.05-10.0 Hz) of 14 HCAs exposed to both mechanical and rotational stimulation were nearly identical. 9. Parameters for best-fit transfer functions, responses to step, and trapezoidal duct displacements were in excellent agreement with previous rotational studies carried out using the pigeon. 10. Although the mechanisms by which focal identation of the horizontal membranous duct produce responses have not yet been determined, primary afferent responses using this method of stimulation are directly comparable with rotatory stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)
Ammonium decreases excitatory synaptic transmission in cat spinal cord in vivo
Authors: Raabe W.
Published: December 2017

1. Glutamine is thought to be a precursor of the pool of glutamate that is used as synaptic transmitter. NH4+ inhibits glutaminase, the enzyme presumed to cleave glutamine into glutamate in synaptic terminals. Therefore a decrease by NH4+ of excitatory synaptic transmission in hippocampus was suggested to be due to the inability to utilize glutamine as a precursor for glutamate and subsequent transmitter depletion. This study reexamines the effects of NH4+ on excitatory synaptic transmission. 2. The effects of NH4+ on excitatory synaptic transmission from low-threshold afferent fibers, presumably Ia-afferent fibers, to motoneurons was investigated in the spinal cord of anesthetized cats in vivo. 3. Action potentials of low-threshold afferent fibers were recorded at the entry of the dorsal roots into the spinal cord. An extracellular electrode within a motoneuron nucleus recorded the action potential of low-threshold afferent fibers and the extracellular monosynaptic excitatory postsynaptic potential, i.e., the focal synaptic potential (FSP). This extracellular electrode also recorded the antidromic field potential (AFP) in response to ventral root stimulation. Electrodes on the ventral roots recorded the monosynaptic reflex (MSR) and the monosynaptic excitatory postsynaptic potential in motoneurons electrotonically conducted into the ventral roots (VR-EPSP). 4. Intravenous infusion of ammonium acetate (AA) reversibly decreased MSR, VR-EPSP, and FSP, i.e., decreased excitatory synaptic transmission. 5. The decrease of VR-EPSP and FSP was accompanied initially by a decrease of conduction and, eventually, a conduction block in presynaptic terminals of low-threshold afferent fibers. 6. The decreases of VR-EPSP and FSP were also accompanied by the transient appearance of a reflex discharge, triggered by VR-EPSPs of decreased amplitude, and changes of the AFP indicating increased invasion of motoneuron somata by antidromic action potentials. 7. It is suggested that NH4+ depolarizes intraspinal Ia-afferent fibers and motoneurons. This depolarization initially decreases and then blocks conduction of action potentials into the presynaptic terminals of Ia-afferent fibers. The conduction block prevents the release of excitatory transmitter and decreases excitatory synaptic transmission. 8. The suggested depolarizing action of NH4+ may be due to K+-like ionic properties of NH4+ and/or an inhibition of K+-uptake into astrocytes. 9. The conduction block in presynaptic terminals of low-threshold afferent fibers can fully explain the decrease of excitatory synaptic transmission by NH4+. Because of the conduction block in presynaptic terminals, this study does not permit a conclusion as to an inhibition by NH4+ fo the utilization of glutamine as a precursor for glutamate used as synaptic transmitter.
Characterization of an early afterhyperpolarization after a brief train of action potentials in rat hippocampal neurons in vitro
Authors: Williamson A. , Alger B. E.
Published: December 2017

1. In rat hippocampal pyramidal cells in vitro, a brief train of action potentials elicited by direct depolarizing current pulses injected through an intracellular recording electrode is followed by a medium-duration afterhyperpolarization (mAHP) and a longer, slow AHP. We studied the mAHP with the use of current-clamp techniques in the presence of dibutyryl cyclic adenosine 3',5'-monophosphate (cAMP) to block the slow AHP and isolate the mAHP. 2. The mAHP evoked at hyperpolarized membrane potentials was complicated by a potential generated by the anomalous rectifier current, IQ. The mAHP is insensitive to chloride ions (Cl-), whereas it is sensitive to the extracellular potassium concentration ([K+]o). 3. At slightly depolarized levels, the mAHP is partially Ca2+ dependent, being enhanced by increased [Ca2+]o and BAY K 8644 and depressed by decreased [Ca2+]o, nifedipine, and Cd2+. The Ca2(+)-dependent component of the mAHP was also reduced by 100 microM tetraethylammonium (TEA) and charybdotoxin (CTX), suggesting it is mediated by the voltage- and Ca2(+)-dependent K+ current, IC. 4. Most of the Ca2(+)-independent mAHP was blocked by carbachol, implying that IM plays a major role. In a few cells, a small Ca2(+)- and carbachol-insensitive mAHP component was detectable, and this component was blocked by 10 mM TEA, suggesting it was mediated by the delayed rectifier current, IK. The K+ channel antagonist 4-aminopyridine (4-AP, 500 microM) did not reduce the mAHP. 5. We infer that the mAHP is a complex potential due either to IQ or to the combined effects of IM and IC. The contributions of each current depend on the recording conditions, with IC playing a role when the cells are activated from depolarized potentials and IM dominating at the usual resting potential. IQ is principally responsible for the mAHP recorded at hyperpolarized membrane potentials.
Proton-gated sodium current in parasympathetic ganglion cells of frog heart
Authors: Kim D. K. , Tateishi N. , Akaike N.
Published: December 2017

1. The proton-gated current was investigated in whole-cell configuration of the neurons isolated from bullfrog heart parasympathetic ganglia with the use of the "concentration-clamp" technique, which combines intracellular perfusion and extremely rapid exchange of external solution within 1-2 ms, under a single-electrode voltage-clamp condition. 2. In all isolated neurons, a "step" decrease in extracellular pH (pHo) induced a transient inward current that was followed by a complete inactivation within 1 s. 3. The proton-gated current increased in a sigmoidal fashion as pHo decreased. In the external solution containing 2 mM Ca2+, the threshold of current activation was at pHo 7.4, and the maximum response appeared at pHo 6.5-5.5. The dissociation constant (Kd) and Hill coefficient were 7.1 and 3.2, respectively. 4. The proton-gated current was reduced by decreasing the extracellular Na+ concentration. In the absence of K+, the current produced by reduced extracellular pH reversed at the Na+ equilibrium potential (ENa), indicating that the current was carried by Na+. 5. Kinetics of both the activation and inactivation phases of proton-induced current were single exponential. The time constants of activation (tau a) and inactivation (tau i) had no potential dependence but decreased slightly by decreasing pHo. 6. In the inactivation curve of the proton-induced current obtained by decreasing pHo from various conditioning pHos to 6.5, the half-maximum inactivation occurred at pHo 7.75. 7. The proton-gated current was suppressed as the extracellular Ca2+ concentration [( Ca2+]o) increased from 0.1 to 10 mM, and the half inhibition occurred at greater than 10 mM [Ca2+]o.(ABSTRACT TRUNCATED AT 250 WORDS)
Modulation of spinal nociceptive transmission from nuclei tractus solitarii: a relay for effects of vagal afferent stimulation
Authors: Ren K. , Randich A. , Gebhart G. F.
Published: December 2017

1. The effects of electrical and chemical stimulation in the nucleus tractus solitarii (NTS) on spinal nociceptive transmission were examined in pentobarbital sodium-anesthetized, paralyzed rats. These studies also examined the role of the NTS as a relay for the effects of vagal afferent stimulation (VAS) on spinal nociceptive transmission. All 75 neurons studied were located in laminae I-VI in the L3-L5 spinal segments, with receptive fields on the glabrous skin of the plantar surface of the ipsilateral hindpaw. The units responded to mechanical (low and/or high intensities) and thermal stimuli (42-52 degrees C). 2. Electrical stimulation in the NTS either ipsilateral or contralateral to the spinal unit inhibited neuronal responses to noxious thermal stimuli. The magnitude of inhibition did not significantly differ as a function of either ipsilateral (15 units) or contralateral (12 units) NTS stimulation (NTSS) as indicated by extrapolated thresholds for inhibition of responses to heat, intensities to produce 50% inhibition of responses to heat, and the slope of recruitment lines for inhibition. Tracking experiments also revealed that stimulation in the area ventral to the NTS produced a greater magnitude of inhibition of these units than did NTSS. 3. NTSS significantly decreased the slope of the stimulus-response functions (SRFs) of dorsal horn units to graded thermal stimuli (42-52 degrees C), whereas response threshold was unaffected by NTSS. The apparent latency of NTSS to produce inhibition of unit responses to heating of the hindpaw was determined to be 50 +/- 10 ms (mean +/- SE). 4. Microinjection of 50 nmol of glutamate into the NTS ipsilateral to the spinal unit also inhibited neuronal responses to thermal stimuli in 17/21 units; responses of 2/21 units were facilitated. Inhibition typically lasted 4-7 min and was shown to be dose-volume dependent. 5. The effects of VAS and NTSS on spinal nociceptive transmission were directly compared. The responses of 17 units to 50 degrees C heating of the hindpaw were facilitated by low and inhibited by greater intensities of VAS (Biphasic units); the responses of 12 units were only inhibited by VAS (Inhib units); three were only facilitated (Facil units), and 2 were unaffected by VAS. In contrast, NTSS generally inhibited the same spinal units, although modest facilitation was produced by NTSS contralateral to the recording site. NTSS produced greater inhibition of the Biphasic units than did VAS, shown by a leftward shift of the recruitment line of inhibition and greater inhibition at the same intensity of electrical stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)
Retinal image motion alone does not control disconjugate postsaccadic eye drift
Authors: Kapoula Z. , Optican L. M. , Robinson D. A.
Published: December 2017

1. In these experiments, postsaccadic ocular drift was induced by postsaccadic motion of the visual scene. In the most important case, the scene was moved in one eye but not the other. Six human subjects viewed the interior of a full-field hemisphere filled with a random-dot pattern. During training, eye movements were recorded by the electrooculogram. A computer detected the end of every saccade and immediately moved the pattern horizontally in the same or, in different experiments, in the opposite direction as the saccade. The pattern motion was exponential with an amplitude of 25% of the size of the antecedent saccade and a time constant of 50 ms. Before and after 3-4 h of such training, movements of both eyes were measured simultaneously by the eye coil-magnetic field method while subjects looked between stationary targets for calibration, explored the visual pattern with saccades, or made saccades in the dark to measure the effects of adaptation on postsaccadic ocular drift. The amplitude of this drift was expressed as a percentage of the size of the antecedent saccade. 2. In monocular experiments, subjects viewed the random-dot pattern with one eye. The other eye was patched. With two subjects, the pattern drifted backward in the direction opposite to the saccade; with the third, it drifted onward. The induced ocular drift was exponential, always in the direction to reduce retinal image motion, had zero latency, and persisted in the dark. After training, drift in the dark changed by 6.7% in agreement with our prior study with binocular vision, which produced a change of 6.0%. 3. In a dichoptic arrangement, one eye regarded the moveable random-dot pattern; the other, through mirrors, saw a different random-dot pattern (with similar spacing, contrast, and distance) that was stationary. These visual patterns were not fuseable and did not evoke subjective diplopia. In this case, the induced change in postsaccadic drift in the same three subjects was only 4.8%. In all cases the changes in postsaccadic drift were conjugate--they obeyed Hering's law. 4. Normal human saccades are characterized by essentially no postsaccadic drift in the abducting eye and a pronounced onward drift (approximately 4%) in the adducting eye. After training, this abduction-adduction asymmetry was preserved in the light and dark with monocular or dichoptic viewing, indicating again that all adaptive changes were conjugate. 5. When the subjects viewed the adapting stimulus after training, the zero-latency, postsaccadic drift always increased from levels in the dark.(ABSTRACT TRUNCATED AT 400 WORDS)
Concentration-jump experiments with NMDA antagonists in mouse cultured hippocampal neurons
Authors: Benveniste M. , Mienville J. M. , Sernagor E. , Mayer M. L.
Published: December 2017

1. Voltage-clamp experiments were used to study N-methyl-D-aspartic acid (NMDA) receptor antagonists applied by fast perfusion to mouse hippocampal neurons in dissociated culture. 2. Preincubation with the NMDA antagonists zinc (3-30 microM) and magnesium (30-300 microM) reduced subsequent responses to 100 microM NMDA applied together with these antagonists. No time dependence of antagonism was observed when responses were measured at the start and at the end of NMDA pulses 1.25-1.5 s in duration. 3. Two competitive antagonists of similar affinity in equilibrium experiments, D-2-amino-5-phosphonopentanoic acid (D-AP5) and 3-((+-)-2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP), had different profiles of action when applied as described above. With D-AP5, pulses of NMDA produced fast-on, fast-off responses, of reduced amplitude, similar to the effect of Zn and Mg. Responses to NMDA in the presence of CPP were also of reduced amplitude but, in addition, showed slow activation, such that the antagonist action of CPP decreased with time after the application of NMDA. 4. In the presence of 3 microM glycine and NMDA receptor antagonists with activity at the glycine modulatory site, either kynurenic acid (Kyn), 7-chlorokynurenic acid (7Cl-Kyn), or 5-chloro-indole-2-carboxylic acid (5Cl-I2CA), NMDA-evoked responses showed apparent use-dependent antagonism, such that the peak response to NMDA was much greater than the equilibrium response. A similar effect was produced by preincubation with low concentrations of glycine (less than 300 nM), which enhances desensitization of responses to NMDA. The apparent use-dependent action of glycine antagonists could be reversed on raising the glycine concentration and did not vary appreciably with changes in membrane potential over the range -60 to +50 mV. 5. Concentration-jump application of NMDA antagonists, in the presence of 100 microM NMDA and 3 microM glycine, were used to study antagonist association and dissociation kinetics directly. For D-AP5 and CPP, the dissociation rate was independent of antagonist concentration, and approximately 15 times faster for D-AP5 (19.6 s-1) than for CPP (1.36 s-1). The association rate for D-AP5 and CPP increased with antagonist concentration in a linear manner over the range 3-30 microM and was slower for CPP than for D-AP5, consistent with their similar potency at equilibrium. 6. In contrast to results obtained with CPP and D-AP5, the association rate for 7Cl-Kyn was approximately 3 times slower than the dissociation rate and did not change with concentration of antagonist.(ABSTRACT TRUNCATED AT 400 WORDS)
Temporal correlations in sensory-synaptic interactions: example in crayfish stretch receptors
Authors: Barrio L. C. , Buno W.
Published: December 2017

1. The effects of inhibitory postsynaptic potential (IPSP) barrages on coding of sinusoidal length inputs were investigated in slowly and rapidly adapting stretch receptors of crayfish (RM1 and RM2, respectively). To examine the contribution of postsynaptic firings, a description was obtained of the temporal correlations between sensory stimuli, pre- and postsynaptic spikes, plus the relative position of the latter. In this analysis, the times between an IPSP and the closest spike preceding or following it are known, respectively, as phase (phi) and cophase (theta). 2. Interactions were similar in RM1 and RM2. The usual effect was the expected increased postsynaptic interval durations, but special consequences were also evoked. With regular IPSPs there were epochs including inhibitory (S) and postsynaptic (R) spikes and fixed "alternations" at S/R times the IPSP rate. S/R ratios were usually 1:1 and 1:2, more rarely 2:1. There were sudden postsynaptic interval duration changes, or "jumps," between successive alternation ratios where inhibitory effects increased or decreased. With 1:1 and 1:2 ratios there was a gradual "sliding," or phi increase-theta decrease, at the pull and the opposite at the release. The theta and phi roughly paralleled the control postsynaptic intervals and the inhibited-minus-control differences, respectively, when sliding was present. Sliding disappeared, and phi and theta tended to become invariant, with 2:1 ratio. 3. Irregular IPSP increased postsynaptic interval irregularities and eliminated alternations. Phase values were irregularly distributed, but theta and control postsynaptic intervals were similar irrespective of pattern.(ABSTRACT TRUNCATED AT 250 WORDS)
Background-induced flicker enhancement in cat retinal horizontal cells. II. Spatial properties
Authors: Nelson R. , Pflug R. , Baer S. M.
Published: December 2017

1. Intracellular recordings have been made from cat retinal horizontal cells stimulated with flickering test spots. Dim backgrounds increase flicker amplitudes in response to small but not large test stimuli. 2. This background-induced flicker enhancement has been measured for different slit- and square-test stimulus widths and the results compared with two spatial models for the enhancement effect. 3. In the "dark test-region" model it is argued that rods within the test region are unresponsive to background stimuli because of prior saturation by the test stimulus. Background-evoked rod signals decay passively from regions outside the test stimulus through a syncytial network into the recording site, where they act on the cone-to-horizontal-cell synapse, increasing its gain. 4. In the "changing length-constant" model rod signals reduce the length constant of a syncytial network by uncoupling the cells within it. This causes an increased response to small but not large test stimuli. 5. Both models are analytically evaluated with the use of a conductive-sheet approximation to the syncytial network. Expressions are derived for network polarization [(V(0, 0)] as a function of stimulus size. The specific stimulus shapes considered are disks, rectangles, slits, and squares in both bright and dark varieties. From these expressions predictions of response enhancement as a function of stimulus size are made for both models. 6. The dark test-region model provides for an exponential decay of flicker enhancement as a function of slit width but a steeper-than-exponential decay with the width of squares, in close agreement with experimental data. 7. The changing length-constant model makes qualitatively similar predictions. Flicker enhancement declines nearly exponentially with slit width. For square-shaped test stimuli the predicted decline of flicker enhancement with size is somewhat shallower than either the dark test-region-model curve or the experimentally determined curve. 8. As recorded in the same set of cells and under the same set of stimulus conditions (with the use of both slit- and square-test stimuli), the mean length constant of the peak-to-peak flicker component in the horizontal-cell response is 168 +/- 18 (SE) microns with the background and 232 +/- 45 microns in the dark. The mean length constant for the background-induced flicker enhancement, as fit by dark test-region-model curves, is 186 +/- 22 microns (n = 9).(ABSTRACT TRUNCATED AT 250 WORDS)
Role of arachidonic acid in depolarization-induced modulation of ion currents in Aplysia giant neurons
Authors: Carlson R. O. , Levitan I. B.
Published: December 2017

1. The effects of membrane depolarization on inward currents subsequently elicited by hyperpolarization were studied with the use of two-electrode, voltage-clamp techniques in the giant neurons LP1 and R2 of Aplysia. 2. Several successive sets of brief depolarizing pulses, or bursts, were used to depolarize the giant neurons. Two distinct inward currents elicited by hyperpolarization were found to be altered after these sets of depolarizing pulses. These currents were distinguished by their voltage dependence, reversal potential, and sensitivity to 1 mM BaCl2. One of the inward currents was increased after depolarization. It was outwardly rectifying, reversed at -50 mV, and not blocked by Ba2+, suggesting it was a chloride current (ICl). The other inward current, which was decreased after depolarization, was inwardly rectifying, reversed at -70 mV, and completely inhibited by Ba2+. These are characteristics of the inwardly rectifying potassium current (IR), a current previously described to be inhibited after depolarization in Aplysia neuron R 15. Depolarization typically increased the putative ICl and decreased IR for minutes, with the decrease in IR consistently outlasting the increase in an initial brief net increase in inward current followed by a long-lasting decrease. 3. Several criteria suggest arachidonic acid (AA) may mediate depolarization-induced modulation of IR. Previously, free AA has been shown to constitutively inhibit IR in the resting state. Also, depolarization has been reported to stimulate liberation of AA from storage in Aplysia ganglia. Consistent with previous results in neuron R 15, depolarization-induced modulation of IR in giant neurons was dependent on external calcium. Indomethacin and 4-bromophenacylbromide (BPB), pharmacologic agents that activate IR through inhibition of AA turnover, altered the effect of depolarization on IR. In contrast serotonin (5HT), which activates IR through adenosine 3',5'-cyclic monophosphate (cAMP), did not alter the effect of depolarization. Also, extended perfusion with bovine serum albumin (BSA), which strips AA from lipid storage in neurons, decreased the depolarization-induced modulation of IR. We conclude that the calcium influx accompanying depolarization activates the phospholipase responsible for liberation of AA from phospholipid, and the liberated AA then acts to inhibit IR. The molecular mechanism of this AA-mediated inhibition remains to be determined. 4. Depolarization-induced modulation of ICl was also dependent on external calcium but was not affected by BPB and only slightly decreased with indomethacin. This suggested AA was probably not involved in this modulation. However, 5HT opposed the modulation of IC1 induced by previous depolarization, suggesting cAMP may be involved in this effect of depolarization.
Behavior of accessory abducens and abducens motoneurons during eye retraction and rotation in the alert cat
Authors: Delgado-Garcia J. M. , Evinger C. , Escudero M. , Baker R.
Published: December 2017

1. The activity of both accessory abducens (Acc Abd) and abducens (Abd) motoneurons (Mns) was recorded in the alert cat during eye retraction and rotational eye movements. Cats were fitted with two scleral coils, one measured rotational eye movements directly and the other retraction by distinguishing the translational component. 2. Acc Abd and Abd Mns were identified following antidromic activation from electrical stimulation of the ipsilateral VIth nerve. 3. In response to corneal air puffs, bursts of spikes were produced in all (n = 30) Acc Abd Mns. The burst began 7.2 +/- 1.2 (SD) ms after onset of the air puff and 8.9 +/- 1.9 ms before eye retraction. 4. Acc Abd Mns were silent throughout all types of rotational eye movements, and tonic activity was not observed during intervals without air-puff stimulation. 5. In contrast, all (n = 50) identified Abd Mns exhibited a burst and/or pause in activity preceding and during horizontal saccades as well as a tonic activity proportional to eye position. 6. Only 10% of Abd Mns fired a weak burst of spikes in response to air-puff stimulation. 7. We conclude that Acc Abd Mns are exclusively involved in eye retraction in the cat and that only a few Abd Mns have an eye-retraction signal added to their eye position and velocity signals. Thus any rotational eye-movement response described in retractor bulbi muscle must result from innervation by Mns located in the Abd and/or the oculomotor nuclei. 8. The organization of the prenuclear circuitry and species variation are discussed in view of the nictiating membrane extension response measured in associative learning.
Mechanisms of depolarizing inhibition at the crayfish giant motor synapse. I. Electrophysiology
Authors: Edwards D. H.
Published: December 2017

1. Mechanisms of depolarizing synaptic inhibition were investigated at the crayfish giant motor synapse with the use of two-electrode current- and voltage-clamp techniques. Depolarizing inhibitory postsynaptic potentials (d-IPSPs) of between 5 and 15 mV in amplitude are produced there in the motor giant motoneuron (MoG) by motor giant inhibitor (MoGI) interneurons. 2. Three mechanisms of inhibition are activated by the d-IPSP: inactivation of a voltage-sensitive inward current (probably sodium), activation of the delayed rectifier, and reverse bias of the electrically rectifying giant motor synapse (GMS). These mechanisms supplement the inhibition produced by a gamma-aminobutyric acid (GABA)-mediated increase in postsynaptic conductance. 3. The d-IPSP is produced by a fast-rising increase in postsynaptic membrane conductance that peaks at 10 microS and lasts nearly 100 ms. 4. An 8-ms, 10-mV depolarizing prepulse inactivated 90% of the inward current evoked by a subsequent step to 33 mV above rest potential, which was -70 mV. d-IPSPs having similar amplitudes should have similar effects on the inward current evoked by an excitatory postsynaptic potential (EPSP). 5. The input resistance of MoG decreased by greater than 60% when the cell was depolarized to 11 mV above rest. This resistance change corresponds to delayed rectification, which should also contribute to the increase in input conductance during a d-IPSP. 6. Depolarization of MoG by 10 mV reduced the excitatory postsynaptic current through the GMS by up to 30%. The reduction in synaptic current occurs because postsynaptic depolarization reduces the transynaptic driving force and increases the reverse bias of the electrically rectifying synapse.(ABSTRACT TRUNCATED AT 250 WORDS)
Reflex activation of muscle spindles in human pretibial muscles during standing
Authors: Aniss A. M. , Diener H. C. , Hore J. , Burke D. , Gandevia S. C.
Published: December 2017

1. Experiments were performed in standing subjects to determine whether low-threshold cutaneous and muscle afferents from mechanoreceptors in the human foot reflexly influence fusimotor neurons innervating pretibial flexor muscles. Recordings were made from 30 identified muscle-spindle afferents, four tendon-organ afferents, and one alpha-motor axon innervating the pretibial flexor muscles. The subjects stood without support or vision on a force platform while trains of electrical stimuli (5 stimuli, 300 Hz) were delivered at nonpainful intensities to the sural nerve or to the posterior tibial nerve at the ankle. 2. Seventeen of the 30 spindle endings had no background discharge, and none was activated by the sural or posterior tibial stimuli. Five silent afferents were given a background discharge by sustained pressure on the relevant tendon, but with two the discharge was dominated by a tremor rhythm obscuring any reflex response to the stimuli. Based on peristimulus time histograms (PSTHs), the sural stimuli then produced increases in discharge of two of the remaining three endings at latencies of 84 and 90 ms. These effects could not be explained by muscle stretch and are presumed to have been fusimotor mediated. 3. When the subjects stood freely without support or vision, 13 muscle-spindle endings had a background discharge, but with three endings tremor developed at the ankle and dominated the spindle discharge. Sural stimuli affected the discharge of five of nine endings unaffected by tremor. With three of these endings, there were changes in discharge that could be explained by muscle stretch.(ABSTRACT TRUNCATED AT 250 WORDS)
Functional organization within the medullary reticular formation of intact unanesthetized cat. II. Electromyographic activity evoked by microstimulation
Authors: Drew T. , Rossignol S.
Published: December 2017

1. The present study has examined the detailed organization of the medullary reticular formation (MRF) as revealed by microstimulation (33-ms trains of 0.2-ms duration pulses at 330 Hz and 35 microA or less) in the intact, chronically implanted, unanesthetized cat. Stimulus-locked electromyographic (EMG) responses were recorded from flexors and extensors of each of the four limbs, as well as bilaterally from muscles of the neck and back, during stimulation of the same 592 loci that formed the basis of the preceding article. 2. The thresholds of the responses were different for each group of muscles, with, on the average, the neck muscles being activated at the lowest range of currents, 13.8-16.5 microA; forelimb muscles at 16.9-17.9 microA; back muscles at 25.4-25.7 microA; and hindlimb muscles at 21.1-25.7 microA. 3. Whereas stimulation within the MRF evoked movement of the head only to the stimulated side (preceding article), analysis of the EMG responses showed there was frequently bilateral activation of the neck muscles. Similarly, even though stimulation produced predominantly ipsilateral elbow flexion and contralateral elbow extension, most loci caused cocontraction of antagonistic muscles at these joints. Cocontraction was also frequently observed for the hindlimbs. Reciprocal activation of antagonistic muscles was less frequent but was observed in the ipsilateral forelimb as well as in both hindlimbs; it was never observed in the contralateral forelimb. 4. Although excitatory responses were observed from widespread regions for all of the muscles under study, those regions of the MRF that evoked the strongest responses in each muscle showed a large degree of segregation. Muscles of the ipsilateral forelimb were most strongly activated from the rostrodorsal MRF, whereas muscles of the contralateral forelimb were most strongly effected by stimulation caudoventrally. Muscles of the hindlimbs were more strongly activated from the rostral brain stem, although with some exceptions. Responses in axial muscles were evoked from widespread regions of the brain stem but were concentrated further caudally than were the limb muscles. 5. Excitatory responses were much more prevalent than inhibitory responses and were evoked from all regions of the MRF, including the most caudal and ventral areas. The shortest latency responses in each track were, on the average, as follows: 6.6-8.8 ms for the neck; 11.2-13.4 ms for the forelimbs; 13.8-14.2 ms for the back; and 15.9-17.2 ms for the hindlimbs. Inhibitory responses were also evoked from widely distributed regions, which were intermingled with those loci evoking excitatory responses.(ABSTRACT TRUNCATED AT 400 WORDS)
Ensemble discharge from Golgi tendon organs of cat peroneus tertius muscle
Authors: Horcholle-Bossavit G. , Jami L. , Petit J. , Vejsada R. , Zytnicki D.
Published: December 2017

1. The responses of individual tendon organs of the cat peroneus tertius muscle to motor-unit contractions were recorded in anesthetized cats during experiments in which all the Ib-afferent fibers from the muscle had been prepared for recording in dorsal root filaments. This was possible because the cat peroneus tertius only contains a relatively small complement of approximately 10 tendon organs. 2. Motor units of different physiological types were tested for their effects on the whole population of tendon organs in the muscle. Effects of unfused tetanic contractions were tested under both isometric and anisometric conditions. Each motor unit activated at least one tendon organ, and each tendon organ was activated by at least one motor unit. Individual slow-type units were found to act on a single or two receptors, whereas a fast-type unit could activate up to six tendon organs. 3. In one experiment, the effects of 8 motor units on 10 tendon organs were examined. One fast-twitch, fatigue resistant (FR)-type unit acted on six tendon organs, of which four were also activated by another FR unit. The contraction of each unit, on its own, elicited a range of individual responses, from weak to strong. The discharge frequencies of individual responses displayed no clear relation with the strength of contraction, nor did they accurately represent the shape of force profiles. But when all the discharges were pooled, a fairly good correspondence appeared between variations of contractile force and variations of averaged discharge frequencies.(ABSTRACT TRUNCATED AT 250 WORDS)
GABA actions within the caudal cochlear nucleus of developing kittens
Authors: Walsh E. J. , McGee J. , Fitzakerley J. L.
Published: December 2017

1. The effects of gamma-aminobutyric acid (GABA), microionophoretically applied onto neurons within the dorsal and posteroventral divisions (i.e., caudal regions) of the cochlear nucleus (CN), were studied during postnatal development in kittens with the use of extracellular recording techniques. Approximately 80% of all neurons encountered within the caudal CN responded to exogenously applied GABA regardless of neuronal response type or postnatal age. 2. GABA reduced acoustically evoked as well as spontaneous discharge rates in a dose-dependent manner at all ages studied, and generally abolished discharge activity at sufficiently high doses (i.e., ejection currents). Dose-response curves generated during acoustic stimulation by varying GABA ejection current were sigmoidal at all ages studied, and the range of slopes relating discharge rate to applied currents increased during the first 10 postnatal days. 3. Neural thresholds to acoustic stimuli were elevated, and slopes of discharge-rate-versus-sound-pressure-level curves were depressed regardless of age when GABA was microionophoresed onto CN neurons. 4. GABA's capacity to reduce spontaneous or acoustically evoked discharge rates was a voltage-dependent phenomenon directly related to control discharge rates (i.e., efficacy was high when discharge rates were high) for neurons recorded from both immature and mature animals. 5. A small set of neurons recorded from animals younger than 2 wk exhibited prolonged GABA "activation" and "deactivation" times (i.e., times required to achieve 90% of the maximal effect evoked by GABA and to recover from that effect, respectively) and may represent a group of actively differentiating units. 6. Bicuculline microionophoresis effectively blocked the actions of exogenously applied GABA and endogenous GABA, which, presumably, was synaptically released as a result of acoustic stimulation. The actions of bicuculline were dose dependent in animals ranging in age from 2 postnatal days to adulthood. These results suggest that recognition sites for GABA and bicuculline and the ionophore associated with the GABA receptor are present and functionally coupled in the caudal CN before the developmental period during which the full complement of inhibitory projections form synaptic contacts with these cells.
Classification of the temporal discharge patterns of single auditory neurons in the dorsal medullary nucleus of the northern leopard frog
Authors: Hall J. C. , Feng A. S.
Published: December 2017

1. The dorsal medullary nucleus (DMN) of frogs is the presumed homolog of the mammalian cochlear nucleus (CN). Like the CN, the DMN is the sole target of centrally projecting primary auditory-nerve fibers and the first central auditory-processing center. To study the transformation of acoustic information in the DMN, we have utilized relatively simple stimuli--tone bursts--to detail the temporal discharge patterns of DMN neurons that can be compared with those shown by auditory-nerve fibers. 2. Based on the shape of poststimulus time (PSTH) and interspike interval (ISIH) histograms, we observed six distinctive discharge patterns to tone bursts presented at the best excitatory frequency (BEF), 10 dB above threshold. Four of these (primary-like type 1-4) resembled discharge patterns seen at the level of the auditory nerve, whereas two (phasic and phasic burst) were only observed in the DMN. 3. At stimulus levels of 20-30 dB above BEF threshold several phasic neurons became tonic responders, whereas several primary-like type-2 cells gave "pauser" discharges. The response patterns of the remaining cells were intensity independent. 4. We further showed that many of the single-unit discharge patterns were related to other neuronal response properties; specifically, spontaneous firing rate, intensity-rate functions, threshold, latency, BEF, and sharpness of tuning (Q10). 5. The implications of our findings are discussed with respect to 1) the transformation of acoustic information as it is passed from the auditory nerve to the DMN, and 2) the functional organization of the DMN.
A chromatic horizontal cell in the Xenopus retina: intracellular staining and synaptic pharmacology
Authors: Stone S. , Witkovsky P. , Schutte M.
Published: December 2017

1. We identified a chromatic-type horizontal cell (C-cell) in the Xenopus retina by intracellular dye injection with Lucifer yellow or horseradish peroxidase (HRP). C-cells hyperpolarized in response to blue light and depolarized in response to red light. 2. In either photopic or mesopic states, moderate-intensity blue and red stimuli evoked responses that were inverted with respect to each other but of similar waveform and latency. In the presence of a bright green adapting field, the maximal voltage (Vmax) of the hyperpolarizing and depolarizing response component approached 30 mV; the kinetics of both waveforms were fast, and the hyperpolarizing response was followed by a small depolarizing overshoot at light OFF. Thus the blue-sensitive photoreceptor is capable of initiating large visual signals under photopic conditions when transmission from green-sensitive rods is suppressed. Under mesopic conditions (no adapting field) the kinetics of both waveforms were slower. The Vmax of the hyperpolarizing response reached 30-40 mV, whereas the cone-mediated depolarization saturated at 15 mV. 3. Both response components of the C-cell showed large receptive fields with no center-surround antagonism. 4. The C-cell perikaryon was located in the distal inner nuclear layer. It emitted four to seven long, tapering processes that ran horizontally for 90-100 microns. Two kinds of terminal dendrites, short and long, extended from the tapering processes toward the layer of photoreceptor bases. 5. Glycine (5-10 mM) completely eliminated the depolarizing response of the C-cell, whereas the hyperpolarizing component was unaffected. In contrast, gamma-aminobutyric acid (GABA; 5-10 mM) had no obvious effect on either component. 6. The C-cell light response was modified in two stages by cis-2,3-piperidine dicarboxylic acid (cis-PDA; 0.5-5 mM): first the depolarizing response disappeared; then the membrane potential hyperpolarized concomitant with a large reduction or elimination of the hyperpolarizing light response. In contrast, DL-2-amino-4-phosphonobutyric acid (APB) had no obvious effect on either response component or the membrane potential of the cell. 7. Our pharmacological findings are consistent with the view that the hyperpolarizing response in the C-cell is mediated by direct synaptic input from a blue-sensitive photoreceptor. The depolarizing response mediated by the red-sensitive cone could be explained by a direct synapse from the red cone or an indirect pathway involving luminosity (L-type) horizontal cells.
Potassium currents in the inner segment of single retinal cone photoreceptors
Authors: Maricq A. V. , Korenbrot J. I.
Published: December 2017

1. The K+ currents of cone inner segments isolated from the retina of a lizard were studied with the use of tight-seal electrodes in the whole cell configuration. To conduct these studies other identified currents in the cell were blocked. Co2+ blocked a voltage-dependent Ca2+ current and a Ca2(+)-dependent Cl- current, and Cs+ blocked an inward-rectifying current partially carried by K+. 2. The cells sustained a voltage-dependent K+ current that was blocked by tetraethylammonium (TEA)+ and had characteristics typical of the delayed rectifier. However, we found no evidence for the existence of “A”-type K+ currents or Ca2(+)-dependent K+ currents. 3. The delayed-rectifier current was nearly ideally selective for K+. Increasing external K+ concentration 10-fold shifted the reversal potential by 55 mV. 4. Analysis of the voltage dependence of the activation of the delayed-rectifier current revealed the existence of two distinct subclasses of this current. We referred to them as IdrL and IdrH for low and high threshold of voltage activation. 5. IdrL activated at voltages above -70 mV. Its dependence on voltage was described by Boltzmann's function with average half-maximum activation at -51 mV and steepness factor k = 7.5 mV. IdrH activated at voltages above -50 mV. Its dependence on voltage was described by Boltzmann's function with average half-maximum activation at -4.6 mV and steepness factor k = 17.1 mV. 6. Of nine cells analyzed in detail, one demonstrated IdrH alone, whereas the remaining had a variable mixture of the two current subtypes. At maximum activation the current through IdrL ranged between 0.3 and 0.5 of the total delayed-rectifier current. 7. The kinetics of activation of the total delayed-rectifier current were described by the sum of two exponentials the amplitudes and time constants of which were voltage dependent. However, the kinetics of the current subtypes were not resolved individually. The current inactivated slowly with a single-exponential time course that was voltage dependent. 8. The voltage dependence of the delayed-rectifier current indicates the current is active in a cone photoreceptor in the dark. The current is 20-30 pA in amplitude at the dark-membrane potential and outwardly directed. 9. IdrL may generate a rapid relaxation of photovoltages activated by dim lights--those that hyperpolarize the membrane by only a few millivolts. The delayed-rectifier currents help shape the action potentials that can be generated in isolated cone photoreceptors
Inhibition of lobster olfactory receptor cells by an odor-activated potassium conductance
Authors: Michel W. C. , McClintock T. S. , Ache B. W.
Published: December 2017

1. Whole cell current-clamp recordings show that odors not only depolarize but may also hyperpolarize lobster olfactory receptor cells. Odor-evoked hyperpolarizations occurred in 36% of 178 receptor cells examined. Cell-attached recordings of action potentials followed by current-clamp recordings in the same cell indicate that depolarizing and hyperpolarizing responses were associated with increases (excitation) and decreases (inhibition) in action potential frequency, respectively. Since odorants that hyperpolarized one receptor cell depolarized other cells and since individual cells may be both excited and inhibited, the inhibitory and excitatory nature of the response must be conferred by the odorant-receptor and transduction processes expressed by the receptor cell. 2. The input resistance dropped from 1.73 G omega at rest to 1.45 G omega during odor-evoked hyperpolarization, and the membrane time constant correspondingly decreased from 114 to 61 ms. The increased conductance persisted throughout the stimulation period (5 s). 3. Shifting the K+ reversal to a more negative potential by lowering the [K+]o from 14 to 2.8 mM increased the magnitude of hyperpolarization. The hyperpolarization could be reversibly blocked by dendritic treatment with 5-10 mM 4-aminopyridine (4-AP) or 10 mM cesium ion, but not by 10 mM tetraethylammonium (TEA). 4. Substituting 80% of the [Cl-]o with NO3- increased the amplitude of the hyperpolarization. Based on a calculated equilibrium potential of -32 mV for chloride, an increase in chloride conductance in a low [Cl-]o environment should have decreased the magnitude of the response. Presumably the change in [Cl-]o acts through the dendritic steady-state chloride conductance to shift the membrane potential further from the reversal potential for K+.(ABSTRACT TRUNCATED AT 250 WORDS)