bluuebunny/crossref_metadata_2025 huggingface dataset:
Response of commissural and other upper cervical ventral horn neurons to vestibular stimuli in vertical planes
Authors: Endo K. , Kasper J. , Wilson V. J. , Yates B. J.
Published: December 2017

1. To study their contribution to the vestibulocollic reflex, we have studied, in decerebrate paralyzed cats, the effect of sinusoidal vestibular stimulation in multiple vertical planes on the spontaneous activity of neurons in the C3 ventral horn. Antidromic microstimulation was used to identify 17/42 neurons as commissural; 10 of these were confirmed to have a projection to the contralateral ventral horn. 2. Dynamics of the responses of spontaneously firing neurons were studied with 0.05–1 Hz sinusoidal stimuli delivered near the plane of rotation that produced maximal modulation of neuron activity (response vector orientation). On the basis of their responses, we classified 38 neurons as receiving otolith, semicircular canal, or otolith + canal input. All three response types were found among commissure and nonantidromic neurons. 3. Two-thirds of neuron response vector orientations pointed contralaterally. They were either near the anterior or posterior canal planes or in the roll quadrant. In the case of neurons with input from canals, the latter indicates convergence from the vertical canals on the same side. There were almost no vectors in the pitch quadrants. The distribution of response vector orientations resembles that seen in the vestibular nuclei and pontomedullary reticular formation, suggesting that commissural neurons may not make a new contribution to spatial processing in the vertical vestibulocollic reflex. 4. It is presumed that commissural neurons are premotor. If so, some have the properties to be in the pathway between the contralateral utricle and neck motoneurons. More generally, their actions could modify the effectiveness of vestibulospinal and reticulospinal fibers that have similar spatial properties and make synapses with neck motoneurons.
Neural interaction in cat primary auditory cortex II. Effects of sound stimulation
Authors: Eggermont J. J.
Published: December 2017

1. The effect of auditory stimulation with click trains, noise bursts, amplitude-modulated noise bursts, and amplitude-modulated tone bursts on the correlation of firing of 1,290 neuron pairs recorded on one or two electrodes in primary auditory cortex of the cat was investigated. A distinction was made between neural synchrony (the correlation under stimulus conditions) and neural correlation (the correlation under spontaneous or under stimulus conditions after correction for stimulus-related correlations). For neural correlation 63% of the single-electrode pairs showed a unilateral excitation component, often combined with a common-input peak, and only 11% of the dual electrode pairs showed this unilateral excitation. 2. Under poststimulus conditions the incidence of correlograms with clear peaks was high for single-electrode pairs (80–90% range) and somewhat lower for dual-electrode pairs (50–60% range). The strength of the neural correlation for poststimulus conditions, from 0.5 to 2 s after a 1-s stimulus, was comparable with that obtained for 15-min continuous silence, suggesting that aftereffects of stimulation had largely disappeared after 0.5 s. A stationary analysis of the correlation coefficient corroborated this. 3. Two stimulus-correction procedures, one based on the shift predictor and the other based on the joint peristimulus-time histogram (JPSTH) were compared. The mean value of the neural correlation under stimulus conditions obtained after applying the poststimulus time (PST) predictor was on average 20% larger than the mean value obtained after application of the shift predictor; however, this was not significantly different at the 0.05 level. There were no differences in the shape of the correlograms. This suggests that the less time-consuming shift predictor-based stimulus-correction procedure can be used for cortical neurons. 4. Under stimulus conditions neural correlation coefficients could be < or = 50% smaller than for spontaneous conditions. The strength of the stimulus-corrected neural correlation was inversely related to the relative size of the stimulus predictor (compared with the neural synchrony) and thus to the effectiveness of stimulation. This suggests that the assumption of additivity of stimulus and connectivity effects on neural synchrony is generally violated both for shift predictor and PST predictor procedures. 5. The neural correlogram peaks were narrower for single-electrode pairs than for dual-electrode pairs both under stimulus and spontaneous conditions. Under stimulus conditions the peaks were generally narrower than under spontaneous firing conditions.(ABSTRACT TRUNCATED AT 400 WORDS)
Reinnervated muscles fail to produce stretch reflexes
Authors: Cope T. C. , Bonasera S. J. , Nichols T. R.
Published: December 2017

1. We studied the stretch-evoked reflex organization of hind limb muscles in two decerebrate cats 36 mo after unilateral section and immediate surgical repair of the common nerve supplying the lateral gastrocnemius (LG) and soleus (S) muscles. 2. The production of considerable reflex force by reinnervated muscles in response to electrical stimulation of uninjured nerves indicated substantial functional recovery of motor units. However, reduction in the responsiveness of reinnervated muscles to stretch of the untreated medial gastrocnemius (MG) muscle indicated some deficit in recovery of normal synaptic integration. 3. Stretch failed to elicit autogenic excitation of the reinnervated S and LG. This failure was observed whether the reinnervated muscles were quiescent or contracting in other reflexes. 4. The heterogenic reflex organization of reinnervated muscles was abnormal. Stretch of the reinnervated S failed to evoke heterogenic reflexes both in the untreated MG and in the reinnervated LG. Stretch of the reinnervated LG failed to produce excitation of MG. 5. These findings demonstrate deficiencies in proprioceptive feedback from reinnervated muscles and lead us to expect incomplete recovery of motor function after nerve section.
Monosynaptic and disynaptic connections in the utriculo-ocular reflex arc of the cat
Authors: Uchino Y. , Ikegami H. , Sasaki M. , Endo K. , Imagawa M. , Isu N.
Published: December 2017

1. Connections from the utricular (UT) nerve to motoneurons and interneurons in the ipsilateral abducens (AB) nucleus were studied in anesthetized and decerebrated cats. Bipolar electrodes were fixed on the left UT nerve under visual observation. The other branches of the vestibular nerve and the facial nerve were transected in the left inner ear. 2. Stimulation of the UT nerve evoked a small positive-negative (P/N) deflection and a negative (N1) potential in the vestibular nuclei, with mean latencies of 0.56 and 0.84 ms, respectively. In the AB nucleus a small P/N deflection with a mean latency of 0.72 ms was recorded, which was considered as a incoming volley of the UT nerve. 3. Excitatory postsynaptic potentials (EPSPs) were recorded from AB motoneurons with short latencies after UT nerve stimulation. They were classified into two types, M and D. M-type EPSPs, which followed repetitive high-frequency stimuli and were recorded from the majority of AB motoneurons, had latencies ranging from 0.9 to 1.2 ms. Double shocks to the UT nerve evoked EPSPs that had the same latency. It was suggested that the AB motoneurons had monosynaptic connections with the UT nerve. D-type EPSPs, which were recorded from most of the AB motoneurons, had slightly longer latencies ranging from 1.2 to 1.8 ms. They showed temporal facilitation when double shocks were provided to the UT nerve. They did not follow repetitive high-frequency stimuli (< or = 2.5-ms interval). It was suggested that D-type EPSPs were di-synaptically evoked via secondary vestibular neurons. Interneurons in the AB nucleus had the same characteristics as AB motoneurons.(ABSTRACT TRUNCATED AT 250 WORDS)
Subthreshold frequency selectivity in avian auditory thalamus
Authors: Strohmann B. , Schwarz D. W. , Puil E.
Published: December 2017

1. We studied the frequency responses of neurons in the nucleus ovoidalis (OV), the principal thalamic auditory relay nucleus of the chicken, in the subthreshold range of membrane potentials. The frequency response is the impedance amplitude profile evident in the voltage response to a broadband stimulus. The stimulus was a deterministic periodic current input of small amplitude, sweeping through a specified frequency range. We used whole-cell, tight-seal recording techniques in slices to study the voltage responses and membrane properties in current and voltage clamp. 2. Generally, low-frequency resonant humps with peak impedances of approximately 6 Hz characterized the frequency responses of OV neurons. This resonance was the principal determinant for frequency selectivity in the majority of OV neurons expressing only a tonic mode of firing. 3. The 6-Hz resonance was voltage dependent and most distinct where the activation ranges of a hyperpolarization activated inward current (IH) and a persistent Na+ current tend to overlap. The potential range for optimal resonance often included the resting potential. 4. Application of the Na+ current antagonist, tetrodotoxin, blocked the persistent Na+ current and most of the resonant hump at depolarized levels but did not affect the resonant peak along the frequency axis. Thus the persistent Na+ current may serve to amplify the resonance. 5. Extracellular application of Cs+, but not Ba2+, blocked a voltage sag during pulsed hyperpolarization as well as the IH current. Application of Cs+ also eliminated the 6-Hz resonance. An IH seems, therefore, instrumental for the resonance. 6. A minority of neurons that expressed low-threshold Ca2+ spikes and burst firing at hyperpolarized states displayed voltage oscillations at 2-4 Hz, spontaneously or in response to pulsatile stimuli. Application of Ni2+ blocked the oscillations and the low-threshold spikes, presumably produced by a T-type Ca2+ current. The resonance at 6 Hz, however, was only slightly affected by Ni2+. A T-type current, therefore, is critical for the 2- to 4-Hz oscillations. 7. Membrane resonance may dominate the power spectrum of subthreshold potential fluctuations. The resonance demonstrated in vitro may be stabilized by experimental procedures; its frequency may be different and more variable in vivo. Resonances in thalamic neurons may play a role in auditory signal processing in birds.
Opening of large-conductance calcium-activated potassium channels by the substituted benzimidazolone NS004
Authors: McKay M. C. , Dworetzky S. I. , Meanwell N. A. , Olesen S. P. , Reinhart P. H. , Levitan I. B. , Adelman J. P. , Gribkoff V. K.
Published: December 2017

1. We used electrophysiological techniques to examine the effects of 5-trifluoromethyl-1-(5-chloro-2-hydroxyphenyl)-1,3-dihydro-2H-benzimidaz ole- 2-one (NS004) on large-conductance calcium-activated potassium (BK) channels. 2. We used recordings from excised membrane patches (cell-attached and inside-out single-channel configurations) and whole-cell patch-clamp recordings to examine the effects of NS004 on single BK channels and whole-cell outward currents, respectively, in rat GH3 clonal pituitary tumor cells. We also tested NS004 on voltage-clamped BK channels isolated from rat brain plasma membrane preparations and reconstituted into planar lipid bilayers. Finally, we used two-electrode voltage-clamp techniques to study the effects of NS004 on currents expressed in Xenopus laevis oocytes by the recently described Slo BK clone from Drosophila. 3. In GH3 cells and in Xenopus oocytes expressing the Slo gene product NS004 produced an increase in an iberiotoxin- or tetraethylammonium-sensitive whole-cell outward current, respectively. NS004 produced a significant increase in the activity of single GH3 cell BK channels and rat brain BK channels reconstituted into planar lipid bilayers. In both systems this was characterized by an increase in channel mean open time, a decrease in interburst interval, and an apparent increase in channel voltage/calcium sensitivity. 4. These data indicate that NS004 could be useful for investigating the biophysical and molecular properties of BK channels and for determining the functional consequences of the opening of BK channels.
A hyperpolarization-activated cation conductance in lobster olfactory receptor neurons
Authors: Corotto F. S. , Michel W. C.
Published: December 2017

1. The current underlying inward rectification in lobster olfactory receptor neurons was investigated with the use of whole-cell patch-clamp techniques. Inward rectification could most likely result from an inwardly rectifying potassium conductance or a hyperpolarization-activated cation conductance. To distinguish between these possibilities, the current underlying inward rectification was examined with respect to its sensitivity to extracellular Cs+ and Ba2+, time course of activation, and reversal potential. 2. In current clamp, injection of negative current led to a hyperpolarization followed by a partial return (sag) toward the initial holding potential. The rate and magnitude of the sag depended on the magnitude of the hyperpolarizing current with larger currents leading to larger, faster depolarizing sags. In voltage clamp, hyperpolarizing steps elicited a slowly activating, noninactivating inward current clamp. Both the sag and the slow inward current were blocked reversibly by extracellular application of 5 mM CsCl but were unaffected by 2 mM BaCl2. 3. The rate of inward current activation was best approximated by a single exponential function with time constants that were voltage dependent, ranging from 7.8 s at-69 mV to 248 ms at-114 mV. 4. Cells normally exhibited an average input resistance of 0.99 G omega over the range of-69 to-114 mV. With the hyperpolarization-activated inward current blocked by 5 mM CsCl, the average input resistance increased to 2.12 G omega over the same range. 5. Analysis of tail currents revealed that the average predicted reversal potential of the hyperpolarization-activated inward current was 1.7 mV and was not affected significantly by a shift in ECl.(ABSTRACT TRUNCATED AT 400 WORDS)
Na(+)-Ca2+ exchanger-like immunoreactivity and regulation of intracellular Ca2+ levels in fish retinal ganglion cells
Authors: Bindokas V. P. , Yoshikawa M. , Ishida A. T.
Published: December 2017

1. We have used two experimental approaches to examine regulation of intracellular calcium ion levels in fish retinal ganglion cells. In the first set of experiments, we ratio-imaged fura-2 emission intensity to estimate the concentration of free intracellular calcium ions ([Ca2+]i) in isolated goldfish retinal ganglion cells depolarized by increases in extracellular levels of potassium ions ([K+]o), in the presence and absence of extracellular sodium ions (Na+). Stepwise increases in [K+]o from 5 mM to as high as 60 mM produced stepwise increases in [Ca2+]i. These increases were sustained in the absence of external Na+, but transient and smaller in the presence of external Na+. The decline of [Ca2+]i in high-K, Na(+)-containing saline could be reversed by application of the ionophore monensin, or by replacement of external Na+ with either N-methyl-D-glucamine or lithium. In Na(+)-containing saline, [Ca2+]i fell to control levels after [K+]o was restored to control levels. 2. In the second set of experiments, we assessed Na(+)-Ca2+ exchanger-like immunoreactivity in goldfish retinal ganglion cells with the use of a polyclonal antiserum directed against Na(+)-Ca2+,K+ exchanger purified from bovine rod outer segments. This antiserum specifically stained the somata, neurites, and growth cones of isolated ganglion cells, the outer segments of rod photoreceptors, and (on Western blots prepared from mechanically isolated rods) protein displaying an apparent molecular mass of 210 kDa. 3. These results provide measurements of changes in [Ca2+]i of retinal ganglion cells depolarized in Na(+)-containing saline, and the distribution and apparent molecular weight of Na(+)-Ca2+ exchanger-like immunoreactivity in teleost retina.(ABSTRACT TRUNCATED AT 250 WORDS)
Synaptic mediation from cutaneous mechanical nociceptors
Authors: Schneider S. P. , Perl E. R.
Published: December 2017

1. Responses of dorsal horn neurons to cutaneous mechanical stimulation were studied in an in vitro preparation of hamster spinal cord with partially intact innervation from an isolated patch of hairy skin. Stable extracellular and intracellular recordings were obtained from cells with different mechanoreceptive properties similar to those reported for other species in vivo. Analyses were made of the intracellular responses of 25 dorsal horn neurons activated selectively by mechanical stimulation to the skin patch. 2. Bath application of the broad spectrum, excitatory amino acid (EAA) receptor antagonist, kynurenic acid (1 mM) blocked excitation of 7 of 8 high-threshold mechanoreceptive units by either cutaneous nerve volleys or mechanical stimulation of the skin. This concentration of kynurenic acid suppressed peripherally evoked responses in 8 of 14 neurons responsive to innocuous mechanical stimuli. 3. High-threshold mechanoreceptive neurons of the superficial dorsal horn exhibited one of three distinctive patterns of postsynaptic potentials in response to electrical stimulation of cutaneous afferent fibers: 1) a simple fast excitatory postsynaptic potential (EPSP), 2) a fast EPSP with a prolonged decay phase lasting between 100 and 1,000 ms, and 3) a multiphasic response dissociable on the basis of stimulus strength consisting of a fast EPSP followed by a hyperpolarizing inhibitory postsynaptic potential (IPSP) (duration 80–100 ms). Gentle mechanical stimuli initiated inhibition from areas adjacent to the high-threshold mechanically excitatory field; this suggests that membrane hyperpolarization in these neurons was evoked by input from low-threshold mechanoreceptors. 4. Bath application of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 10 microM), a competitive EAA antagonist selective for non-N-methyl-D-aspartate (non-NMDA) receptor subtypes, substantially or completely (56–100%) suppressed EPSPs evoked from cutaneous afferent fibers in high-threshold mechanoreceptive neurons. CNQX also decreased the membrane depolarization, the frequency of EPSPs, and the frequency of action potentials evoked by mechanical stimulation of the receptive field. 5. CNQX (10 microM) or kynurenic acid (1 mM) had considerably weaker effects on IPSPs than on EPSPs evoked from the periphery in superficial dorsal horn neurons. IPSP amplitudes were unchanged by these agents in some neurons and decreased by only 20–25% in others. 6. We conclude that L-glutamate acting on non-NMDA receptors mediates fast synaptic excitation of superficial dorsal horn neurons from peripheral mechanical nociceptors with myelinated fibers. Furthermore, the observations imply either an agent other than L-glutamate or one acting at different membrane receptors is a synaptic mediator for other peripheral afferent units including some activated by innocuous mechanical stimuli.
Arm position constraints when throwing in three dimensions
Authors: Hore J. , Watts S. , Tweed D.
Published: December 2017

1. Overarm throwing is a skilled multijoint movement with potentially many degrees of freedom. Considering only the arm > or = 7 degrees of freedom are involved (shoulder 3, elbow 2, wrist 2). For each arm segment 3 degrees of freedom are potentially required to specify its angular position (orientation) at any moment during a throw. Simplification of the control problem for the CNS would occur if there were constraints on these degrees of freedom. The objective was to determine whether such constraints exist at ball release when throwing at targets in different directions using only the arm. 2. The angular positions in three dimensions of the distal phalanx of the middle finger, the hand, the forearm, and the upper arm were simultaneously recorded with search coils as subjects sat with a fixed trunk and threw balls at nine targets in an approximate +/- 40 degree work space. Ball release was signaled by microswitches on the proximal and distal phalanges of the middle finger (proximal and distal triggers). 3. On throwing at any one target the hand at ball release adopted a similar orientation for each throw, i.e., for a particular vertical and horizontal angular position the hand adopted a similar torsional position. On throwing at targets throughout the work space, angular position (rotation) vectors describing hand positions in space at ball release were confined to a two-dimensional surface rather than a three-dimensional volume. This constraint in hand torsion occurred near and at ball release but not throughout the entire throw. It was not due to mechanical factors because such a surface was not obtained when subjects deliberately twisted their arms when throwing. Thus at ball release during a "natural" throw the hand was constrained to 2 of its possible 3 angular degrees of freedom. 4. The same constraint was also found for finger, forearm, and upper arm angular positions in space at ball release as determined at both the proximal and distal triggers. A consequence is that at ball release the entire arm was constrained to 2 of its possible 7 degrees of freedom. 5. The two-dimensional position vector surface for each arm segment was similar to that obtained when pointing with a straight arm at the same targets. In both cases they showed torsion and were twisted like the surface obtained by rotations around the horizontal and vertical axes of a Fick gimbal. However, in some subjects the throwing surfaces were tilted from the vertical.(ABSTRACT TRUNCATED AT 400 WORDS)
Activators of protein kinase C mimic serotonin-induced modulation of a voltage-dependent potassium current in pleural sensory neurons of Aplysia
Authors: Sugita S. , Baxter D. A. , Byrne J. H.
Published: December 2017

1. In the pleural mechanoafferent sensory neurons of Aplysia, serotonin (5-HT)-induced spike broadening consists of at least two components: a cAMP and protein kinase A (PKA)-dependent, rapidly developing component and a protein kinase C (PKC)-dependent, slowly developing component. Voltage-clamp experiments were conducted to identify currents that are modulated by PKC and thus may contribute to the slowly developing component of 5-HT-induced spike broadening. 2. We compared the effects of phorbol esters, activators of PKC, on membrane currents with those of 5-HT. Bath application of 5-HT had complex modulatory effects on currents elicited by voltage-clamp pulses to potentials > 0 mV. The kinetics of both activation and inactivation of the membrane currents were slowed by 5-HT. This led to a decrease in an outward current at the beginning of the voltage-clamp pulse and an increase at the end of the pulse. Previous work has shown that these effects represent, in part, the modulation of a large, voltage-dependent K+ current (IK,V) by 5-HT. 3. Active phorbol esters mimicked some of the actions of 5-HT on membrane currents in that they slowed activation and inactivation kinetics of current responses to voltage-clamp pulses more positive than 0 mV. This led to a decrease in an outward current at the beginning of the pulse and an increase at the end of the pulse. Because inactive phorbols did not mimic the actions of 5-HT, the effects of active phorbol esters appeared to be PKC specific. In addition, preexposure of the sensory neurons to active phorbol esters appeared to occlude the modulatory actions of 5-HT on IK,V. Thus it is likely that modulation of IK,V by 5-HT is mediated, at lease in part, by PKC. 4. To further characterize which currents were modulated by PKC, low concentrations of tetraethylammonium (TEA, 2 mM) were used to block Ca(2+)-activated K+ current (IK,Ca). Low TEA partially blocked the phorbol ester-induced increase of the outward current at the end of voltage-clamp pulses. These results agreed with previous reports that activation of PKC enhanced a fast component of IK,Ca in these sensory neurons. Such an enhancement would lead to an increase in outward current that should be blocked by low TEA. Low TEA, however, did not affect phorbol ester-induced decrease of the outward current at the beginning of pulse, where the predominant current is IK,V, which is less sensitive to TEA.(ABSTRACT TRUNCATED AT 400 WORDS)
Response variability of single cells in the dorsal lateral geniculate nucleus of the cat. Comparison with retinal input and effect of brain stem stimulation
Authors: Hartveit E. , Heggelund P.
Published: December 2017

1. We studied the degree and source of response variability in different classes of cell in the dorsal lateral geniculate nucleus (dLGN). The response of single cells to a series of contrasts of a stationary flashing light spot was measured. The variability analyses were based on the mean and SD of the response to a number of repeated stimulus presentations. The relative variability was expressed by the coefficient of variation (Cv; SD/mean). 2. At a given contrast, the Cv for lagged cells was larger than for nonlagged cells. No difference was found between the Cv of X and Y cells. The magnitude of the Cv was about the same as previously found for cells in striate cortex. Accordingly, little variability is added at the cortical level. The Cv decreased with increasing contrast showing that the reliability of response and the signal-to-noise ratio was improved with increasing contrast. 3. For some cells, the retinal input was determined by recording S potentials in addition to action potentials. The Cv of the retinal input was smaller than the Cv of the dLGN cells at a given contrast. Thus in the paralyzed and anesthetized preparation, variability was added at the geniculate relay. 4. The additional variability was related to modulatory input from the brain stem. This was shown by comparing Cv versus contrast curves for the dLGN cells obtained during electrical stimulation of the peribrachial region of the brain stem (PBR) with corresponding curves obtained without PBR stimulation. During PBR stimulation, which presumably mimics the effects of arousal on the dLGN cell, the Cv at a given contrast was reduced toward the value for the retinal input to the cell. Furthermore PBR stimulation increased the signal-to-noise-ratio of the cell to the level of the retinal input. 5. When Cv was plotted against response rather than against contrast, approximately the same function was found for the various dLGN cell classes. This indicated that the variability basically depended on firing rate rather than on stimulus contrast. No difference of Cv was seen between lagged and nonlagged cells at a given level of response. The difference found at a given level of contrast reflected differences in firing rate of the two cell classes. During PBR stimulation, there was no clear difference between the Cvs of the dLGN cell and its retinal input at a given level of response.(ABSTRACT TRUNCATED AT 400 WORDS)
Phase-locked response characteristics of single neurons in the frog "cochlear nucleus" to steady-state and sinusoidal-amplitude-modulated tones
Authors: Feng A. S. , Lin W. Y.
Published: December 2017

1. We made extracellular recordings from 164 single neurons in the frog dorsal medullary nucleus (DMN), a homologue of the cochlear nucleus. Phase-locked responses to tones at the unit's characteristic frequency (CF) and to off-CF tones were evaluated. We also stimulated units with tones at CF that were amplitude modulated sinusoidally between 5 and 1,000 Hz and examined responses to these stimuli. 2. Results showed that single neurons in the frog DMN displayed phase-locked discharges to tones at frequencies < or = 800 Hz. Phase-locking was robust at low frequencies (< 400 Hz) and became poorer at higher frequencies; the variation of the synchronization coefficient (SC) with frequency typically showed a low-pass characteristic. 3. The capacity of phase-locking to tones was correlated with the functional classification of a DMN neuron and the firing rate of its CF response. Primarylike neurons exhibited various degrees of phase-locked discharges to tones at off-CF frequencies. The average upper cutoff frequency, i.e., the frequency at which the SC dropped to 0.5 of maximum value, differed for the three classes of primarylike neurons. The average cutoff frequency was respectively 183, 325, and 536 Hz for primarylike neurons that displayed low (PL-1), intermediate (PL-2), and high (PL-3) steady-state firing rates to CF stimulation. The phasic neurons showed poor phase-locking capacities at all tone frequencies. 4. The frequency range of phase-locking to amplitude-modulated stimuli was also different for the different cell types, as evidenced by the units' modulation transfer functions (MTFs). The primarylike neurons exhibited mostly all-pass or low-pass sync-based MTFs. The mean upper cutoff frequencies for primarylike neurons having low-pass MTFs were 155 Hz for PL-1 neurons, 176 Hz for PL-2 neurons, and 218 Hz for PL-3 neurons. Pauser, chopper, phasic, and phasic-burst neurons gave mostly low-pass MTFs having a mean upper cutoff frequency of 219, 235, 242, and 251 Hz, respectively. 5. The phase-locking ability of DMN neurons to tones and to amplitude-modulated stimuli are compared with those of frog's primary afferent fibers and with those of avian and mammalian cochlear nucleus neurons. The significance of results in terms of sound localization and sound pattern recognition is discussed.
Factors contributing to the decay of the stimulus-evoked IPSC in rat hippocampal CA1 neurons
Authors: Roepstorff A. , Lambert J. D.
Published: December 2017

1. Monosynaptic gamma-aminobutyric acid-A (GABAA)-mediated inhibitory postsynaptic currents (IPSCs) were evoked in CA1 pyramidal neurons in the hippocampal slice preparation by direct stimulation of the interneurons in the presence of glutamatergic blockers and intracellular QX-314 to block GABAB-mediated postsynaptic inhibition. 2. Paired-pulse stimulation was used to activate presynaptic GABAB autoreceptors and thereby reduce the amount of transmitter release. This caused paired-pulse depression, persisting for > 3 s, and maximal at interpulse intervals between 100 and 250 ms where peak current (Ipeak) was decreased by 29.7% and decay time (t1/2) was decreased by 44.7%. There was clear correlation between changes in Ipeak and t1/2 at all interpulse intervals. 3. With paired-pulse stimulation, the decay of the second IPSC in most cells (12/18) could be resolved into two components, Ifast and Islow, each decaying monoexponentially with tau fast = 14.10 ms and tau slow = 58.87 ms. The faster decay during paired-pulse depression was predominantly caused by a larger Ifast fraction, which accounted for 27.5% of Ipeak in a single control IPSC and 79.3% at an interpulse interval of 250 ms. 4. Reducing the probability for transmitter release at all active sites by reducing [Ca2+]o from 2 mM to 1 mM decreased Ipeak by 49.7%, reduced paired-pulse depression, and partly mimicked the changes in decay kinetics seen after activation of presynaptic GABAB receptors. Lowering the stimulating intensity to 10% of the maximal value decreased Ipeak by 73.8%, but hardly affected the decay of the IPSC and the paired-pulse depression. 5. Application of the selective blocker of GABA uptake, tiagabine (20-50 microM), increased t1/2 of a single IPSC by 114% without affecting Ipeak. The increase was caused solely by an increase in tau slow of 141%. On the other hand, the benzodiazepine agonist midazolam (2 microM), selectively increased tau fast. It therefore is suggested that tau fast reflects the kinetics of the GABAA receptor/ionophore complex and tau slow the efficiency of the GABA uptake system. 6. The findings show that GABA activates postsynaptic receptors throughout the tail of a single IPSC. This could be caused by reactivation of synaptic receptors or activation of extrasynaptic receptors. The decay therefore is limited mainly by the efficiency of the uptake system. An IPSC that is maximally depressed by paired-pulse stimulation is mediated primarily by a single activation of synaptic receptors, and the decay is limited mainly by the kinetics of the GABAA receptor/ionophore complex.(ABSTRACT TRUNCATED AT 400 WORDS)
Direct demonstration of functional disconnection by anoxia of inhibitory interneurons from excitatory inputs in rat hippocampus
Authors: Congar P. , Khazipov R. , Ben-Ari Y.
Published: December 2017

1. We studied the effects of anoxia on excitatory and inhibitory postsynaptic currents (EPSCs and IPSCs) evoked by electrical stimulation in the stratum radiatum in concomitantly recorded pyramidal cells and interneurons of the CA1 region of rat hippocampal slices. We used the blind whole cell patch-clamp technique, and anoxia was induced by switching perfusion of the slice from oxygenated artificial cerebral spinal fluid (ACSF) to ACSF saturated with 95% N2-5% CO2 for 4-6 min. 2. As in pyramidal neurons, anoxia induced in interneurons outward currents, during and shortly after the anoxic episode. Both currents were, however, significantly larger in interneurons than in pyramidal neurons. 3. EPSCs are more rapidly depressed by anoxia in interneurons than in simultaneously recorded pyramidal cells. 4. In pyramidal neurons, polysynaptic IPSCs (pIPSCs) evoked by conventional distant stimulation (> 1 mm) are more sensitive to anoxia then EPSCs. In contrast, in interneurons, anoxia blocks with a similar latency EPSCs and polysynaptic IPSCs. 5. To determine whether this block of pIPSCs in pyramidal cells is due to a shift in driving force or a change in conductance, we examined the current (I/V) relationships. The block by anoxia of pIPSCs is due to a reduction of IPSC conductance (> 98%) that occlude other events including the shift of IPSCs reversal potential (ECl).(ABSTRACT TRUNCATED AT 250 WORDS)
Representation of moving tactile stimuli in the somatic sensory cortex of awake monkeys
Authors: Ruiz S. , Crespo P. , Romo R.
Published: December 2017

1. We have studied how neurons of primary somatic sensory (SI) cortex encode the direction and speed of moving tactile stimuli delivered to the glabrous skin of the contralateral hand. 2. From a total of 178 neurons recorded in SI cortex of 3 awake Macaca mulatta monkeys, 103 were selected for quantitative analysis. Forty-six neurons had slowly adapting (SA) responses, 43 quickly adapting (QA), and 14 mixed SA-QA properties. All possessed cutaneous receptive fields on the distal segments of digits 2, 3, or 4. Receptive fields were scanned with a metal probe (2 mm diam, hemispheric tip) in four different directions (0, 90, 180, and 270 degrees), over a fixed traverse distance of 6 mm, at a variety of speeds (4-100 mm/s), and with a static normal force of 20 g by means of a computer-controlled tactile stimulator. 3. Most neurons gave statistically significant differences in mean impulse rate during the moving stimuli (Wilcoxon, P < 0.01), in at least one of the four directions, compared with the control (nonstimulus) period. The Kruskal-Wallis test (P < 0.01) and the direction index (DI > 35%) determined that about one-half of SI cortical neurons showed significant differences in mean impulse rates associated with the direction of the stimuli at the speeds of 23, 50, and 100 mm/s, and about one-third at 4 mm/s. 4. We determined how the temporal covariance of the neural activity was associated with the parameters of the moving stimuli by calculating the coefficients of the Karhunen-Loeve (KL) transform for each set of stimulus responses. Decomposition of the neural activity into principal components indicated that approximately 85% of the impulse train variance during the stimulus responses was contained in the 1st 10 coefficients of the KL transform for the speeds of 23, 50, and 100 mm/s, and approximately 75% at the speed of 4 mm/s. The line spectra calculated from the coefficients of the KL transform showed that the variance contained in the impulse trains in about one-half of the neurons is related to the stimuli. 5. We investigated how the temporal covariance of the neuronal activity was correlated with the direction of the stimulus, by fitting the first coefficient of the KL transform to a weighting function model. This analysis showed that the first coefficient of the KL transform varied as an orderly function of the direction of the moving stimuli.(ABSTRACT TRUNCATED AT 400 WORDS)
Temporal and spatial characteristics of tonically active neurons of the primate's striatum
Authors: Aosaki T. , Kimura M. , Graybiel A. M.
Published: December 2017

1. Tonically active neurons (TANs) in the primate striatum develop transient responses to sensory conditioning stimuli during behavioral training in classical conditioning tasks. In this study we examined the temporal characteristics of such TAN responses and mapped the sites of TANs responding to auditory and visual conditioned stimuli in the striatum in macaque monkeys. We further mapped the locations of TANs recorded acutely in the squirrel monkey striatum in relation to the neurochemically distinguished striosome and matrix compartments of the striatum, and made quantitative comparisons between the densities and compartmental distributions of TANs and those of four major types of striatal interneuron identified by histochemical and immunohistochemical staining. 2. We made recordings from 858 TANs at different sites in the striatum in two behaving macaque monkeys at different times during training with auditory (click) and visual (light-emitting diode flash) conditioning stimuli. TANs distributed across large parts of the striatum developed responses to the conditioning stimuli. The responses comprised a decrement of tonic firing (pause) followed by a rebound excitation. Measurements were made of the onsets, offsets, and durations of the pauses of individual TANs and of the interspike intervals (ISIs) of the same cells. 3. The mean duration of the pause responses (268.3 ms) was greater than the mean ISI of the same neurons (181 ms), suggesting that the pause represents an active suppression of TAN firing. The coefficient of variation (CV) for the pause responses was 0.28, compared with a CV of 0.63 for the same cells' ISIs. The population CV for the pauses was 0.16, compared with a population CV of 0.20 for the ISIs. These data, together with temporal analysis of the responses and population histograms, suggest that the pauses became temporally aligned across large parts of the striatum after learning. Analyses of variance (ANOVAs) were carried out to determine whether there were differences in the onset and offset latencies of the pause response or in the durations of the pause responses for TANs at different sites. These analyses suggested that, with rare exceptions, there was no difference in the timing of the TAN responses across large (> 10 mm3) parts of the striatum. 4. Comparisons of TAN responses in different regions of the striatum showed that, for responses to a given modality of conditioned stimulus, there were no significant differences in pause offset times for TANs recorded in the caudate nucleus or putamen, or for TANs recorded in more anterior or more posterior parts of these nuclei.(ABSTRACT TRUNCATED AT 400 WORDS)
Excitatory postsynaptic currents and glutamate receptors in neonatal rat sympathetic preganglionic neurons in vitro
Authors: Krupp J. , Feltz P.
Published: December 2017

1. We obtained whole cell patch-clamp recordings from visually identified sympathetic preganglionic neurons (SPNs) in thin (200-300 microns) transverse spinal cord slices of neonatal rats (1-14 days postnatal). Exogenous application of glutamate (100 microM), N-methyl-D-aspartate (NMDA; 100 microM), kainate (100 microM), quisqualate (1 microM), and alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA; 50 microM) induced inward currents at a holding potential of -30 mV. 2. Excitatory postsynaptic currents (EPSCs) were evoked by electrical stimulation either in the dorsal horn or the lateral funiculus. They reversed at 1.2 +/- 4.6 (SD) mV and could in most cases (49 of 51) be separated into two components. 3. In the presence of DL-2-amino-5-phosphonovalerate (10-40 microM) the current-voltage (I-V) relationship of the remaining EPSC was linear. When stimulated in the lateral funiculus, its rise time (10-90%) and the time constant of the monoexponential decay were 1.6 +/- 1.0 and 5.5 +/- 2.7 ms, respectively. By contrast, when stimulated in the dorsal horn, this component had a rise time (10-90%) of 3.0 +/- 0.8 ms and a decay time constant of 13.7 +/- 7.6 ms. 4. We studied the NMDA receptor-mediated component of the EPSCs after superfusion of 6-cyano-7-nitroquinoxaline-2,3-dione (5 microM). The I-V relationship of this component had a region of negative slope conductance between -30 and -80 mV, which was abolished in Mg(2+)-free saline. The rise time (10-90%) ranged from 3.3 to 9.5 ms and the decay was biexponential. Both decay time constants increased with depolarization. Mg(2+)-free saline reduced this voltage sensitivity. 5. At a membrane potential of -80 mV and in 1 mM extracellular Mg2+, the NMDA receptor-mediated component represented 74.8 +/- 11.2% of the total charge carried by the EPSCs evoked by stimulation in the dorsal horn. In contrast, when stimulated from the lateral funiculus, 28.9 +/- 18.9% of the total charge carried during the EPSC was mediated by the NMDA receptor-mediated component. The contribution of the NMDA receptor-mediated component increased in both cases with depolarization. In addition, in 2 of 18 SPNs the EPSC evoked in the dorsal horn was exclusively carried by NMDA receptors. 6. We conclude that L-glutamate or a related substance mediates the fast excitatory input onto SPNs. Viscerosomatic and supraspinal inputs form synapses with different topographical locations on the SPN.(ABSTRACT TRUNCATED AT 400 WORDS)
Interaction between center and surround in rabbit retinal ganglion cells
Authors: Merwine D. K. , Amthor F. R. , Grzywacz N. M.
Published: December 2017

1. The interaction between the center and surround mechanisms of a variety of rabbit retinal ganglion cell classes was examined in extracellular single-unit recordings in an isolated eyecup preparation. Ganglion cell classes studied included on and off brisk sustained and transient, on and off sluggish sustained and transient, on-off and on directionally selective, orientationally selective, and large field units. The surround effects observed were qualitatively similar in all these ganglion cell classes. 2. The average response-versus-contrast functions for stimuli within the ganglion cells' receptive-field centers were relatively linear between threshold and saturation for all ganglion cell classes examined. The major effect of surround stimulation on the center response-versus-contrast function was a reduction in the slope of the linear portion of the curve, rather than a downward, parallel shift of the function. Stimulation of the surround had no systematically significant effect on the contrast threshold for the center spot, and, when it did have a significant effect, it sometimes decreased, rather than increased the magnitude of threshold. 3. Step changes in surround contrast were most effective when they were made simultaneously with step changes in the center; surround inhibition decreased significantly when it preceded stimulation of the center by > 100 ms and was generally ineffective when preceding the center by > 500 ms. The decrease in the inhibitory effect of surround stimulation was a monotonic function of delay between 0 and 500 ms. 4. Stimulation of the surround by step changes in the contrast of a sine-wave grating annulus produced qualitatively similar results to those obtained for pure luminance modulations. This suggests that the surround mechanism observed in these experiments was not due to pure luminance adaptation within the surround. The inhibitory effect of sine-wave gratings in the surround decreased monotonically as a function of spatial frequency. 5. Stimulation with a spot and an annulus that were both entirely within the ganglion cell's excitatory receptive-field center typically yielded nonadditive summation at contrasts whose linear sum of responses were below saturation. The effect of an annulus within the receptive-field center on responses elicited by a central spot quantitatively resembled the inhibition elicited from annuli in the inhibitory surround, after the excitatory center response due to the annulus was taken into account. These results suggest that the inhibiton elicited from the surrounds of the ganglion cells in these experiments extended into their receptive-field centers.(ABSTRACT TRUNCATED AT 400 WORDS)
Transformation of temporal discharge patterns in a ventral cochlear nucleus stellate cell model: implications for physiological mechanisms
Authors: Wang X. , Sachs M. B.
Published: December 2017

1. We have stimulated responses of stellate cells in the anteroventral cochlear nucleus (AVCN) to single-formant stimuli (SFSs) with the use of recorded auditory-nerve fiber (ANF) responses as inputs. In particular, two important features of temporal discharge patterns, the phase locking to best frequency (BF) tones and to stimulus envelopes, were examined in the model output. Our earlier experimental studies with SFSs found an enhancement of the envelope modulation in AVCN chopper units, presumably recorded from stellate cells, as compared with that of ANFs. 2. We simulated in the model three mechanisms for the enhancement in envelope modulation proposed earlier by us, namely, convergence of ANFs, temporal summation and inhibitory input. It was found that the convergence of multiple ANFs alone did not always lead to an enhancement in modulation depth, but was necessary for the model to produce other physiologically plausible envelope features; the temporal summation of subthreshold events can lead to an increase in modulation depth; and the somatic inhibition effectively reduced the envelope minimum and, as a result, increased the modulation depth. In addition, we found that, given the same input configuration, the closer the inputs were located to the soma, the greater modulation depth they produced at the model output. 3. Different types of convergence of ANF inputs were tested in our model. It was found that the convergence of both low and high spontaneous rate (SR) ANFs resulted in an enhancement in modulation depth over a wider range of sound level than that due to the convergence of ANFs from the same SR group.(ABSTRACT TRUNCATED AT 250 WORDS)
Effects of nerve injury on sympathetic excitation of A delta mechanical nociceptors
Authors: Bossut D. F. , Perl E. R.
Published: December 2017

1. The effects of sympathetic stimulation and close arterial injection of norepinephrine were tested on cutaneous myelinated-fiber (A delta) mechanical nociceptors [high-threshold mechanoreceptors-(MyHTMs)] from normal and from partially transsected nerves. 2. Neither sympathetic stimulation nor close arterial injection of norepinephrine (200 ng) excited MyHTMs (18) recorded from the uninjured great auricular nerve of adult rabbits. 3. MyHTMs (58) conducting across the site of partial cut lesions, made 2 to 28 days previously, had threshold and responsiveness to mechanical stimuli, receptive field organization, and absence of background discharge typical of such elements in normal nerve. 4. Four MyHTMs recorded from the injured nerves were excited by sympathetic stimulation and/or norepinephrine injection but only one gave more than two impulses within 60 s to either form of stimulation. 5. The meagerness of the sympathetic and adrenergic excitation of MyHTMs after nerve injury contrasts with that observed under similar conditions for C-fiber polymodal nociceptors. Therefore, induction of adrenergic responsiveness in nociceptors after partial denervation in cutaneous MyHTMs appears to be less important for mechanisms related to pathogenic pain than alterations in certain C-fiber nociceptors.