bluuebunny/crossref_metadata_2025 huggingface dataset:
Medial Olivocochlear Efferent System in Humans Studied With Amplitude-Modulated Tones
Authors: Maison Stéphane , Micheyl Christophe , Collet Lionel
Published: December 2017

Maison, Stéphane, Christophe Micheyl, and Lionel Collet. Medial olivocochlear efferent system in humans studied with amplitude-modulated tones. J. Neurophysiol. 77: 1759–1768, 1997. Evoked otoacoustic emissions (EOAEs) are assumed to be generated by outer hair cells (OHCs). It is now generally accepted that EOAEs represent a means of functional exploration of the active micromechanical properties of OHCs. Efferent fibers of the medial olivocochlear system (MOCS) are connected along the sides and the bases of OHCs. Some studies have shown that a suppression effect on EOAE amplitude is induced by the MOCS neurons during contralateral stimulation, presumably by modification of OHC motility. The contralateral acoustic stimuli used in experiments on the EOAE suppression effect have consisted mainly of sounds without a slow temporal fluctuation in their envelopes (broad-band noise, narrow-band noise, pure tones, or clicks). To elucidate further the parameters of MOCS activation, in the present study we looked at the contralateral suppression effect of amplitude-modulated (AM) tones. The results showed that EOAE amplitude was reduced with AM tones compared with no contralateral acoustic stimulation. The suppression effect mainly depended on three parameters. 1) Contralateral stimulation intensity: EOAE suppression occurred only with intensities ≥40 dB SL. 2) The greater the modulation depth, the greater the suppression effect: statistical analysis showed a significant effect for 75 and 100% modulation depth. 3) The 100- and 140-Hz modulation frequencies gave the greatest suppression effect for 100 and 75% modulation depths. The suppression effect was frequency specific. The greatest decreases were observed when the carrier frequency of the contralateral AM tone was close to the frequency of the EOAE under study, i.e., 1 and 2 kHz. Acoustic cross talk and middle ear effects, which cannot be completely excluded, are discussed. However, the demonstrated frequency specificity of the EOAE suppression effect, together with observed presence of contralateral EOAE suppression in patients without stapedial reflex and the very weak intensities used (i.e., below acoustic reflex threshold), suggested that it was unlikely that the observed effects were due merely to middle ear reflexes. Our results confirm further the contralateral suppression effect on human cochlea mechanisms and show that the suppression effect can be influenced by amplitude modulations of the suppressor, characteristic of sounds in the environment.
Functional Role of Ca2+Currents in Graded and Spike-Mediated Synaptic Transmission Between Leech Heart Interneurons
Authors: Lu Jin , Dalton John F. , Stokes Darrell R. , Calabrese Ronald L.
Published: December 2017

Lu, Jin, John F. Dalton, IV, Darrell R. Stokes, and Ronald L. Calabrese. Functional role of Ca2+currents in graded and spike-mediated synaptic trnasmission between leech heart interneurons. J. Neurophysiol. 77: 1779–1794, 1997. We used intracellular recording and single electrode voltage-clamp techniques to explore Ca2+currents and their relation to graded and spike-mediated synaptic transmissions in leech heart interneurons. Low-threshold Ca2+currents (activation begins below −50 mV) consist of a rapidly inactivating component ( ICaF) and a slowly inactivating component ( ICaS). The apparent inactivation kinetics of ICaFappears to be influenced by Ca2+; both the substitution of Ca2+(5 mM) with Ba2+(5 mM) in the saline and the intracellular injection of the rapid Ca2+chelator, bis-( o-aminophenoxy)- N,N,N′,N′-tetraacetic acid (BAPTA), from the recording microelectrode, significantly increase its apparent inactivation time constant. The use of saline with a high concentration of Ba2+(37.5 mM) permitted exploration of divalent ion currents over a broader activation range, by acting as an effective charge carrier and significantly blocking outward currents. Ramp and pulse voltage-clamp protocols both reveal a rapidly activating and inactivating Ba2+current ( IBaF) and a less rapidly activating and slowly inactivating Ba2+current with a broad activation range ( IBaS). Low concentrations of Cd2+(100–150 μM) selectively block IBaS, without significantly diminishing IBaF. The current that remains in Cd2+lacks the characteristic delayed activation peak of IBaSand inactivates with two distinct time constants. IBaFappears to correspond to a combination of ICaFand ICaS, i.e., to low-threshold Ca2+currents, that can be described as T-like. IBaSappears to correspond to a Ca2+current with a broad activation range, which can be described as L-like. Cd2+(100 μM) selectively blocks spike-mediated synaptic transmission between heart interneurons without significantly interfering with low-threshold Ca2+currents and plateau formation in or graded synaptic transmission between heart interneurons. Blockade of spike-mediated synaptic transmission between reciprocally inhibitory heart interneurons with Cd2+(150 μM), in otherwise normal saline, prevents the expression of normal oscillations (during which activity in the two neurons consists of alternating bursts), so that the neurons fire tonically. We conclude that graded and spike-mediated synaptic transmission may be relatively independent processes in heart interneurons that are controlled predominantly by different Ca2+currents. Moreover, spike-mediated synaptic inhibition appears to be required for normal oscillation in these neurons.
Evidence for Functional Metabotropic Glutamate Receptors in the Dorsal Cochlear Nucleus
Authors: Molitor Scott C. , Manis Paul B.
Published: December 2017

Molitor, Scott C. and Paul B. Manis. Evidence for functional metabotropic glutamate receptors in the dorsal cochlear nucleus. J. Neurophysiol. 77: 1889–1905, 1997. The parallel fibers (PFs) of the dorsal cochlear nucleus (DCN) molecular layer use glutamate as a neurotransmitter. Although metabotropic glutamate receptors (mGluRs) have been identified on cells postsynaptic to the PFs, little is known about the effects of mGluR activation in PF synaptic transmission in the DCN. To investigate these effects, PF-evoked field potentials were recorded from the DCN in guinea pig brain stem slice preparations. The α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor-mediated components of the field response were reversibly depressed by bathing the slice in the mGluR agonists (±)-aminocyclopentane-1,3-dicarboxylic acid (trans-ACPD) or (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid [(1S,3R)-ACPD]. A similar depression was produced by the mGluR1/5 agonist (RS)-3,5-dihydroxyphenylglycine, but not by the mGluR2/3 agonist (2S,1′S,2′S)-2-(carboxycyclopropyl)glycine or by the mGluR4/6/7/8 agonist l(+)-2-amino-4-phosphonobutyric acid. In addition to the AMPA component, an N-methyl-d-aspartate (NMDA) receptor-dependent component of the field potentials could be identified when the slices were bathed in a low magnesium solution. Under these conditions, the ACPD-induced depression of the AMPA component did not completely recover, whereas the depression of the NMDA component usually recovered and potentiated in some slices. Intracellular recordings of PF-evoked responses were obtained to ascertain which neuronal populations were affected by mGluR activation. Activation of mGluRs produced a reversible depression of PF-evoked responses in cartwheel cells that was not accompanied by any changes in paired-pulse facilitation. The PF-evoked responses recorded from pyramidal cells were unaffected by mGluR activation. Both cell types exhibited a reversible depolarization during (1S,3R)-ACPD application. Subsequent experiments explored the involvement of protein kinases in mediating the effects of mGluRs. The protein kinase C (PKC) activator phorbol-12,13-diacetate partially inhibited the mGluR-mediated depression of the field response;however, the PKC inhibitor 2-[1-(3-dimethylaminopropyl)-1H-indol-3-yl]-3-(1H-indol-3-yl)-maleimide or the protein kinaseA inhibitor N-[2-(( p-bromocinnamyl)amino)ethyl]-5-isoquinolinesulfonamide had little effect on the actions of (1S,3R)-ACPD. These results demonstrate that functional mGluRs are present at PF synapses and are capable of modulating PF synaptic transmission in the DCN.
Neural Mechanisms of Reflex Reversal in Coxo-Basipodite Depressor Motor Neurons of the Crayfish
Authors: Ray Didier Le , Cattaert Daniel
Published: December 2017

Le Ray, Didier and Daniel Cattaert. Neural mechanisms of reflex reversal in coxo-basipodite depressor motor neurons of the crayfish. J. Neurophysiol. 77: 1963–1978, 1997. The in vitro preparation of the fifth thoracic ganglion of the crayfish was used to investigate the mechanisms underlying the reflex reversal in a sensory-motor pathway. Sensory afferent neurons from the coxo-basipodite chordotonal organ (CBCO), which senses vertical movements of the limb, connect monosynaptically with basal limb motor neurons (MNs). In tonically active preparation, stretching the CBCO (corresponding to downward movements of the leg) stimulates the levator MNs, whereas releasing the CBCO activates the depressor (Dep) MNs. These reflexes, opposed to the imposed movement, are termed resistance reflexes. By contrast, during fictive locomotion, the reflexes are reversed and termed assistance reflexes. Intracellular recordings from all 12 Dep MNs were performed in single experiments. It allowed us to characterize three types of Dep MNs according to their response to CBCO imposed step-and-ramp movements: 8 of the 12 Dep MNs are resistance MNs that are depolarized during release of the CBCO and are connected monosynaptically to release-sensitive CBCO neurons; 1 Dep MN is an assistance MN that is depolarized during stretching of the CBCO and is connected monosynaptically to exclusively velocity-coding stretch-sensitive CBCO neurons; in our experimental conditions, 3 Dep MNs do not display any response to CBCO stimulation. Assistance reflex interneurons (ARINs), involved in polysynaptic assistance reflexes recorded from depressor MNs, are presented. During low-velocity (0.05 mm/s) stretching ramps imposed on the CBCO, ARINs display compound excitatory postsynaptic potentials (EPSPs), whereas during high-velocity (0.25 mm/s) ramps, they display a mixed excitatory and inhibitory response. Whereas a single MN generally receives monosynaptic EPSPs from three to six CBCO neurons, ARINs receive monosynaptic EPSPs from up to eight velocity-coding stretch-sensitive CBCO neurons. In addition, ARINs receive disynaptic inhibitory phasic inputs from stretch-sensitive CBCO afferents. Injection of a depolarizing current pulse into ARINs elicits a fast transient voltage-dependent depolarization. Its time to peak decreases, and its peak amplitude increases with increasing current intensity. ARINs likely are to be connected directly to Dep MNs. The synaptic delay between these nonspiking ARINs and Dep MNs is short (<2 ms) and constant. The postsynaptic EPSP amplitude increases with increasing current pulse intensity injected into ARIN. The dual sensory control (excitatory and inhibitory) makes it likely that ARIN represents a key element in reflex reversal control.
Locomotion of the Hindlimbs After Neurectomy of Ankle Flexors in Intact and Spinal Cats: Model for the Study of Locomotor Plasticity
Authors: Carrier Lynda , Brustein Edna , Rossignol Serge
Published: December 2017

Carrier, Lynda, Edna Brustein, and Serge Rossignol. Locomotion of the hindlimbs after neurectomy of ankle flexors in intact and spinal cats: a model for the study of locomotor plasticity. J. Neurophysiol. 77: 1979–1993, 1997. To study the potential plasticity of locomotor networks in the spinal cord, an important issue for locomotor rehabilitation after spinal injuries, we have investigated the locomotor performance of cats before and after a unilateral denervation of the ankle flexors tibialis anterior (TA) and extensor digitorum longus (EDL) both in cats with intact spinal cord and after spinalization. The effects of the inactivation of the ankle flexors were studied in three cats with intact spinal cord during periods of 4–7 wk. Cats adapted their locomotor performance very rapidly within a few days so that the locomotor behavior appeared to be unchanged practically. However, kinematic analyses of video records often revealed small but consistent increase in knee and/or hip flexion. These changes were accompanied by some increase in the amplitude of knee and hip flexor muscle activity. Cats maintained a regular and symmetrical walking pattern over the treadmill for several minutes. Two of these cats then were spinalized at T13 and studied for ∼1 mo afterward. Whereas normally cats regain a regular and symmetrical locomotor pattern after spinalization, these cats had a disorganized and asymmetrical locomotor pattern with a predominance of knee flexion and absence of plantar foot contact of the denervated limb. Another cat first was spinalized and allowed to recuperate a regular symmetrical locomotor performance. Then it also was submitted to the same unilateral ankle flexor inactivation and studied for ∼50 days. The cat maintained a well-organized symmetrical gait although there was almost no ankle flexion on the denervated side. There was no exaggerated knee hyperflexion and gait asymmetry as seen in the two previous cats spinalized only after they had adapted to the denervation of ankle flexors. It is concluded that, after muscle denervation, locomotor adaptation is achieved through changes occurring at different levels. Because cats spinalized after adaptation to the neurectomy had an asymmetrical locomotor pattern dominated by hyperflexion, it is suggested that the spinal circuitry has been modified during the adaptive process, presumably through the action of corrective supraspinal inputs. Indeed spinal cats do not normally display such abnormal hyperflexions, and neither did the one cat denervated after spinalization. On the other hand, because the modified locomotor pattern in the spinal state is not functional and contains only some aspects of the compensatory response seen before spinalization, it is suggested that the complete functional adaptation observed in intact cats after peripheral nerve lesions may depend on changes occurring at the spinal and the supraspinal levels.
Modulation of Jaw Muscle Spindle Discharge During Mastication in the Rabbit
Authors: Masuda Y. , Morimoto T. , Hidaka O. , Kato T. , Matsuo R. , Inoue T. , Kobayashi M. , Taylor A.
Published: December 2017

Masuda, Y., T. Morimoto, O. Hidaka, T. Kato, R. Matsuo, T. Inoue, M. Kobayashi, and A. Taylor. Modulation of jaw muscle spindle discharge during mastication in the rabbit. J. Neurophysiol. 77: 2227–2231, 1997. Discharges of jaw muscle spindles were recorded during chewing carrot from mesencephalic trigeminal nucleus (Mes V) in the awake rabbit to evaluate contribution of the muscle spindles to the development of complete sequences of masticatory movements. The Mes V spindle units were divided into two types according to the maximum firing rates during mastication, with a dividing line at 200 Hz; high-frequency units and low-frequency units. Although both types of units fired maximally during the jaw-opening phase of chewing cycles, their firing rates and pattern varied according to three sequential stages of mastication (stages I, IIa, and IIb). The high-frequency units often increased firing before the start of mastication and built up firing in the first few chewing cycles. Their maximal firing rate was sometimes lower during stage IIa (chewing stage) than during stage I (ingestion stage) and stage IIb (preswallowing stage), although the jaw movements were greater in stage IIa than in other stages. The phase relationship of the firing to a jaw movement cycle in stage IIa was consistent in individual units. The low-frequency units did not build up activity before the onset of movements. They fired mostly during the jaw-opening phase, but the peak of firing did not necessarily coincide with the time of maximal opening. It was concluded that the difference in the firing pattern among masticatory stages may be ascribed to a stage-dependent modulation of both fusimotor activity and jaw movement pattern.
No Clock Signal in the Discharge of Neurons in the Deep Cerebellar Nuclei
Authors: Keating J. G. , Thach W. T.
Published: December 2017

Keating, J. G. and W. T. Thach. No clock signal in the discharge of neurons in the deep cerebellar nuclei. J. Neurophysiol. 77: 2232–2234, 1997. We examined the spike activity of deep cerebellar nuclear cells recorded from awake, behaving monkeys to determine if there was a tendency for periodic discharge at or near 10 Hz. Data were obtained from four Rhesus monkeys trained to perform either targeted flexions and extensions of the wrist in relation to a visual cue (2 monkeys) or instrumented digit movements and natural reaches (2 monkeys). We determined the interspike intervals of 274 isolated cells. We looked for periodicity by autocorrelating the interval data and Fourier transforming the resulting autocorrelation function. The autocorrelograms and the Fourier transforms failed to reveal periodicity at or near 10 Hz for any cell. This lack of oscillatory discharge in deep nuclear cells of the cerebellum is consistent with our previously reported results that the complex spike of the Purkinje cell is aperiodic. Our failure to observe a clocklike timing signal in awake, behaving animals in either the Purkinje cell complex spike or the deep nuclear cell discharge argues against a popular idea that the inferior olive may act through the cerebellum as a motor clock.
Visuospatial Properties of Ventral Premotor Cortex
Authors: Graziano Michael S. A. , Hu Xin Tian , Gross Charles G.
Published: December 2017

Graziano, Michael S. A., Xin Tian Hu, and Charles G. Gross. Visuospatial properties of ventral premotor cortex. J. Neurophysiol. 77: 2268–2292, 1997. In macaque ventral premotor cortex, we recorded the activity of neurons that responded to both visual and tactile stimuli. For these bimodal cells, the visual receptive field extended from the tactile receptive field into the adjacent space. Their tactile receptive fields were organized topographically, with the arms represented medially, the face represented in the middle, and the inside of the mouth represented laterally. For many neurons, both the visual and tactile responses were directionally selective, although many neurons also responded to stationary stimuli. In the awake monkeys, for 70% of bimodal neurons with a tactile response on the arm, the visual receptive field moved when the arm was moved. In contrast, for 0% the visual receptive field moved when the eye or head moved. Thus the visual receptive fields of most “arm + visual” cells were anchored to the arm, not to the eye or head. In the anesthetized monkey, the effect of arm position was similar. For 95% of bimodal neurons with a tactile response on the face, the visual receptive field moved as the head was rotated. In contrast, for 15% the visual receptive field moved with the eye and for 0% it moved with the arm. Thus the visual receptive fields of most “face + visual” cells were anchored to the head, not to the eye or arm. To construct a visual receptive field anchored to the arm, it is necessary to integrate the position of the arm, head, and eye. For arm + visual cells, the spontaneous activity, the magnitude of the visual response, and sometimes both were modulated by the position of the arm (37%), the head (75%), and the eye (58%). In contrast, to construct a visual receptive field that is anchored to the head, it is necessary to use the position of the eye, but not of the head or the arm. For face + visual cells, the spontaneous activity and/or response magnitude was modulated by the position of the eyes (88%), but not of the head or the arm (0%). Visual receptive fields anchored to the arm can encode stimulus location in “arm-centered” coordinates, and would be useful for guiding arm movements. Visual receptive fields anchored to the head can likewise encode stimuli in “head-centered” coordinates, useful for guiding head movements. Sixty-three percent of face + visual neurons responded during voluntary movements of the head. We suggest that “body-part-centered” coordinates provide a general solution to a problem of sensory-motor integration: sensory stimuli are located in a coordinate system anchored to a particular body part.
Role of Potassium and Calcium in the Generation of Cellular Bursts in the Dentate Gyrus
Authors: Pan Enhui , Stringer Janet L.
Published: December 2017

Pan, Enhui and Janet L. Stringer. Role of potassium and calcium in the generation of cellular bursts in the dentate gyrus. J. Neurophysiol. 77: 2293–2299, 1997. Epileptiform activity, which appears to be endogenous, has been recorded in the granule cells of the dentate gyrus before the onset of synchronized seizure activity and has been termed cellular bursts. It has been postulated that an increase in input to the dentate gyrus causes a local increase in extracellular K+ concentration ([K+]o) and a decrease in [Ca2+]o that results in this cellular bursting. The first test of this hypothesis is to determine whether the cellular bursts appear in ionic conditions that occur in vivo before the onset of synchronized epileptic activity. This hypothesis was tested in vitro by varying the ionic concentrations in the perfusing solution and recording changes in the granule cells of the dentate gyrus. Intra- and extracellular recordings were made in the dentate gyri of hippocampal slices prepared from anesthetized adult Sprague-Dawley rats. Increasing the extracellular potassium or decreasing the extracellular calcium of the perfusing solution caused three forms of spontaneous activity to appear: depolarizing potentials, action potentials, and cellular bursts. Increasing potassium or decreasing calcium also caused the granule cells to depolarize and reduced their input resistance. No synchronized extracellular field activity was detected. Simultaneously increasing potassium and decreasing calcium caused cellular bursts to appear at concentrations recorded in vivo before the onset of synchronized reverberatory seizure activity.
Two-Tone Distortion on the Basilar Membrane of the Chinchilla Cochlea
Authors: Robles Luis , Ruggero Mario A. , Rich Nola C.
Published: December 2017

Robles, Luis, Mario A. Ruggero, and Nola C. Rich. Two-tone distortion on the basilar membrane of the chinchilla cochlea. J. Neurophysiol. 77: 2385–2399, 1997. Basilar membrane responses to pairs of tones were measured, with the use of a laser velocimeter, in the basal turn of the cochlea in anesthetized chinchillas. Frequency spectra of basilar membrane responses to primary tones with frequencies (f1, f2) close to the characteristic frequency (CF) contain prominent odd-order two-tone distortion products (DPs) at frequencies both higher and lower than CF (such as 2f1 − f2, 3f1 − 2f2, 2f2 − f1 and 3f2 − 2f1). For equal-level primaries with frequencies such that 2f1 − f2 equals CF, the magnitude of the2f1 − f2 DP grows with primary level at linear or faster rates at low stimulus levels, but it saturates or decreases slightly at higher levels. For a fixed level of one of the primary tones, the magnitude of the 2f1 − f2 DP is a nonmonotonic function of the level of the other primary tone. For low intensities of the variable tone, the2f1 − f2 DP grows at a rate of ∼2 dB/dB with f1 level and 1 dB/dB with f2 level. DP magnitudes decrease rapidly with increasing primary frequency ratio (f2/f1) at low stimulus levels. For more intense stimuli, DP magnitudes remain constant or decrease slowly over a wide range of frequency ratios until a critical value is reached, at which DP magnitudes fall with slopes as steep as −300 dB/octave. As stimulus level grows, DP phases increasingly lag for large f2/f1 ratios, but exhibit leads for small f2/f1 ratios. Cochlear exposure to an intense tone that produces large sensitivity losses for the primary frequencies (but only small losses for tones with frequency equal to 2f1 − f2) causes a substantial decrease in magnitude of the 2f1 − f2 DP. This result demonstrates that the 2f1 − f2 DP originates at the basilar membrane region with CFs corresponding to the primary frequencies and propagates to the location with CF equal to the DP frequency. 2f1 − f2 DPs on the basilar membrane resemble those measured in human psychophysics in most respects. However, the magnitude of basilar membrane DPs does not show the nonmonotonic dependence on f2/f1 ratio evident in DP otoacoustic emissions.
Pharmacological Evidence for Two Types of Postsynaptic Glycinergic Receptors on the Mauthner Cell of 52-h-Old Zebrafish Larvae
Authors: Legendre P.
Published: December 2017

Legendre, P. Pharmacological evidence for two types of postsynaptic glycinergic receptors on the Mauthner cell of 52-h-old zebrafish larvae. J. Neurophysiol. 77: 2400–2415, 1997. The presence of homooligomeric and heterooligomeric glycine receptors (GlyRs) on the Mauthner (M) cell in the isolated medulla of 52-h-old zebrafish larvae was investigated by analysis of the effects of picrotoxin on glycine-gated channels and on glycinergic miniature inhibitory postsynaptic currents (mIPSCs). Two functionally different GlyRs have been previously described on the M cell. The effects of picrotoxin on these two GlyRs were first analyzed by measuring the relative change in their total open probability ( NPo) with picrotoxin concentration. Picrotoxin had no significant effect on the glycine channel with a single conductance level of 40–46 pS. In contrast, picrotoxin application decreased the NPoof the GlyR with multiple subconductance levels. On this GlyR, picrotoxin decreased in a concentration-dependent manner the occurrence of the 80- to 86-pS substate (median inhibiting concentration = 0.89 μM) and had no apparent effect on the 40- to 46-pS opening probability. Opening frequency and the mean open times of the 80- to 88-pS main conductance state were reduced in the presence of 10 μM picrotoxin, but their relative weight remained unchanged. These effects of picrotoxin were not voltage dependent. Picrotoxin also modified 40- to 46-pS kinetics. At 100 μM, picrotoxin evoked voltage-independent flickering during channel openings. Short and long mean open times were significantly decreased, whereas the relative proportion of long mean open times was increased. The medium closed time was decreased, whereas medium burst duration was increased. The burst frequency remained unchanged. Spontaneous glycinergic mIPSCs were recorded in the presence of 1 μM tetrodotoxin + 25 μM bicuculline (holding potential = −50 mV). Application of 10 μM picrotoxin did not change the frequency of the synaptic activity, whereas it decreased the amplitude of large mIPSCs. No effect was observed on the time to peak (0.8 ms) or the mean decay time constant (τd= 7.7 ms). Increasing picrotoxin concentration to 100 μM resulted in a decrease of mIPSC frequency (35.6%), amplitude (39.8%), and τd(from 7.7 to 5 ms). These results suggest that these two functionally different GlyRs correspond to α1homooligomeric-like and α1/β-heterooligomeric-like GlyRs, and that both are synaptically activated. Variation in the proportions of GlyR subtypes from one synapse to another could partly account for the broad amplitude distribution of mIPSCs recorded from the zebrafish M cell.
Local and Propagated Dendritic Action Potentials Evoked by Glutamate Iontophoresis on Rat Neocortical Pyramidal Neurons
Authors: Schwindt Peter C. , Crill Wayne E.
Published: December 2017

Schwindt, Peter C. and Wayne E. Crill. Local and propagated dendritic action potentials evoked by glutamate iontophoresis on rat neocortical pyramidal neurons. J. Neurophysiol. 77: 2466–2483, 1997. Iontophoresis of glutamate at sites on the apical dendrite 278–555 μm from the somata of rat neocortical pyramidal neurons evoked low-threshold, small, slow spikes and/or large, fast spikes in 71% of recorded cells. The amplitude of the small, slow spikes recorded at the soma averaged 9.1 mV, and their apparent threshold was <10 mV positive to resting potential. Both their amplitude and their apparent threshold decreased as the iontophoretic site was moved farther from the soma. These spikes were not abolished by somatic hyperpolarization. When the somata of cells displaying these small spikes were voltage clamped at membrane potentials that prevented somatic or axonic firing, corresponding current spikes could be evoked all-or-none by dendritic depolarization, indicating that the small, slow spikes arose in the dendrite. Similar responses were not observed during somatic depolarization evoked by current pulses or glutamate iontophoresis. These small, slow spikes were abolished by blocking voltage-gated Ca2+ channels but not by blocking Na+ channels or N-methyl-d-aspartate receptors. We conclude that these Ca2+ spikes occurred in a spatially restricted region of the dendrite and were not actively propagated to the soma. In the presence of 10 mM tetraethylammonium chloride, the amplitudes of the iontophoretically evoked Ca2+ spikes were large, similar to those of the Ca2+ spikes evoked by somatic current injection, but their apparent thresholds were 63% lower. We conclude that dendritic K+ channels normally prevent the active propagation of Ca2+ spikes along the dendrite. In 36% of recorded cells dendritic glutamate iontophoresis evoked a Na+ spike with an apparent threshold 63% lower than those evoked by somatic current injection or somatic glutamate iontophoresis. Blockade of these low-threshold Na+ spikes by pharmacological or electrophysiological means often revealed underlying small dendritic Ca2+ spikes. When cells displaying the low-threshold Na+ spikes were voltage clamped at membrane potentials that prevented firing of the soma or axon, corresponding tetrodotoxin-sensitive current spikes could be evoked all-or-none by dendritic depolarization. We conclude that these low-threshold Na+ spikes were initiated in the dendrite, probably by local Ca2+ spikes, and subsequently propagated actively to the soma. Most cells displaying dendritic Na+ spikes fired multiple bursts of action potentials during tonic dendritic depolarization, whereas somatic depolarization of the same cells evoked only regular firing. We discuss the implications of dendritic Ca2+ and Na+ spikes for synaptic integration and neural input-output relations.
Fast-to-Slow Conversion Following Chronic Low-Frequency Activation of Medial Gastrocnemius Muscle in Cats. II. Motoneuron Properties
Authors: Munson John B. , Foehring Robert C. , Mendell Lorne M. , Gordon Tessa
Published: December 2017

Munson, John B., Robert C. Foehring, Lorne M. Mendell, and Tessa Gordon. Fast-to-slow conversion following chronic low-frequency activation of medial gastrocnemius muscle in cats. II. Motoneuron properties. J. Neurophysiol. 77: 2605–2615, 1997. Chronic stimulation (for 2–3 mo) of the medial gastrocnemius (MG) muscle nerve by indwelling electrodes renders the normally heterogeneous MG muscle mechanically and histochemically slow (type SO). We tested the hypothesis that motoneurons of MG muscle thus made type SO by chronic stimulation would also convert to slow phenotype. Properties of all single muscle units became homogeneously type SO (slowly contracting, nonfatiguing, nonsagging contraction during tetanic activation). Motoneuron electrical properties were also modified in the direction of type S, fatigue-resistant motor units. Two separate populations were identified (on the basis of afterhyperpolarization, rheobase, and input resistance) that likely correspond to motoneurons that had been fast (type F) or type S before stimulation. Type F motoneurons, although modified by chronic stimulation, were not converted to the type S phenotype, despite apparent complete conversion of their muscle units to the slow oxidative type (type SO). Muscle units of the former type F motor units were faster and/or more powerful than those of the former type S motor units, indicating some intrinsic regulation of motor unit properties. Experiments in which chronic stimulation was applied to the MG nerve cross-regenerated into skin yielded changes in motoneuron properties similar to those above, suggesting that muscle was not essential for the effects observed. Modulation of group Ia excitatory postsynaptic potential (EPSP) amplitude during high-frequency trains, which in normal MG motoneurons can be either positive or negative, was negative in 48 of 49 chronically stimulated motoneurons. Negative modulation is characteristic of EPSPs in motoneurons of most fatigue-resistant motor units. The general hypothesis of a periphery-to-motoneuron retrograde mechanism was supported, although the degree of control exerted by the periphery may vary: natural type SO muscle appears especially competent to modify motoneuron properties. We speculate that activity-dependent regulation of the neurotrophin-(NT) 4/5 in muscle plays an important role in controlling muscle and motoneuron properties.
Order of Application Determines the Interaction Between Phorbol Esters and GTP-γ-S in Dorsal Raphe Neurons: Evidence That the Effect of 5-HT Is Modified Upstream of the G Protein Ca Channel Interaction
Authors: Chen Yuan , Penington Nicholas J.
Published: December 2017

Chen, Yuan and Nicholas J. Penington. Order of application determines the interaction between phorbol esters and GTP-γ-S in dorsal raphe neurons: evidence that the effect of 5-HT is modified upstream of the G protein Ca channel interaction. J. Neurophysiol. 77: 2697–2703, 1997. Phorbol esters activating protein kinase C (PKC) partially uncouple the inhibitory effect of serotonin (5-HT) from serotonergic neuron Ca2+current. Presently the site of action of PKC is not known and may be the receptor, G protein, or ion channel. We recorded Ca2+current from acutely isolated neurons with the use of the patch-clamp technique to study the site of action of PKC. Activation of the G protein with internal guanosine 5′-O-(3-thiotriphosphate) (GTP-γ-S) occluded the response to 5-HT, but unexpectedly this effect was not reversed by the addition of the phorbol ester phorbol 12-myristate 13-acetate (PMA) despite the voltage-dependent reversal of the effect of GTP-γ-S by long depolarizing steps to +80 mV. PMA was, however, able to partially reverse 5-HT-induced inhibition of Ca2+current. The rate of reinhibition of the Ca2+current (related to the concentration of activated G proteins) by GTP-γ-S after the addition of PMA at −50 mV was identical to the rate when only GTP-γ-S was present.By contrast, when cells were exposed first to PMA, and thenGTP-γ-S was perfused into the cell, GTP-γ-S lost about half of its ability to activate the G protein. The rate of reinhibition of the Ca2+current by internal GTP-γ-S was also reduced in cells pretreated with PMA. The original result in which PMA did not reverse the action of GTP-γ-S suggested that the channel was not the functional site of action of PMA, nor was the site on the G protein that binds to the channel, but it did not rule out the receptor. When the receptor was bypassed, after prior PKC activation, it was found that direct activation of the G protein by a nonhydrolyzable analogue of GTP was reduced; taken as a whole, this indicates that in dorsal raphe, and perhaps other neurons, the site of the critical phosphorylation may be on the G protein and possibly at the GTP binding site.
Low-Amplitude Oscillations in the Inferior Olive: A Model Based on Electrical Coupling of Neurons With Heterogeneous Channel Densities
Authors: Manor Yair , Rinzel John , Segev Idan , Yarom Yosef
Published: December 2017

Manor, Yair, John Rinzel, Idan Segev, and Yosef Yarom. Low-amplitude oscillations in the inferior olive: a model based on electrical coupling of neurons with heterogeneous channel densities. J. Neurophysiol. 77: 2736–2752, 1997. The mechanism underlying subthreshold oscillations in inferior olivary cells is not known. To study this question, we developed a single-compartment, two-variable, Hodgkin-Huxley-like model for inferior olive neurons. The model consists of a leakage current and a low-threshold calcium current, whose kinetics were experimentally measured in slices. Depending on the maximal calcium and leak conductances, we found that a neuron model's response to current injection could be of four qualitatively different types: always stable, spontaneously oscillating, oscillating with injection of current, and bistable with injection of current. By the use of phase plane techniques, numerical integration, and bifurcation analysis, we subdivided the two-parameter space of channel densities into four regions corresponding to these behavioral types. We further developed, with the use of such techniques, an empirical rule of thumb that characterizes whether two cells when coupled electrically can generate sustained, synchronized oscillations like those observed in inferior olivary cells in slices, of low amplitude (0.1–10 mV) in the frequency range 4–10 Hz. We found that it is not necessary for either cell to be a spontaneous oscillator to obtain a sustained oscillation. On the other hand, two spontaneous oscillators always form an oscillating network when electrically coupled with any arbitrary coupling conductance. In the case of an oscillating pair of electrically coupled nonidentical cells, the coupling current varies periodically and is nonzero even for very large coupling values. The coupling current acts as an equalizing current to reconcile the differences between the two cells' ionic currents. It transiently depolarizes one cell and/or hyperpolarizes the other cell to obtain the regenerative response(s) required for the synchronized oscillation. We suggest that the subthreshold oscillations observed in the inferior olive can emerge from the electrical coupling between neurons with different channel densities, even if the inferior olive nucleus contains no or just a small proportion of spontaneously oscillating neurons.
Ocular Dominance in Human V1 Demonstrated by Functional Magnetic Resonance Imaging
Authors: Menon Ravi S. , Ogawa Seiji , Strupp John P. , Uǧurbil Kâmil
Published: December 2017

Menon, Ravi S., Seiji Ogawa, John P. Strupp, and Kâmil Uǧurbil. Ocular dominance in human V1 demonstrated by functional magnetic resonance imaging. J. Neurophysiol. 77: 2780–2787, 1997. Very high resolution functional magnetic resonance imaging (fMRI) at a 4 Tesla (T) magnetic field was used to map ocular dominance regions in the human visual cortical layers using the blood oxygen level dependent (BOLD) contrast mechanism. The fMRI response from primary visual cortex (V1) exhibited a distribution of ocular dominance reminiscent of the single-cell recordings of Hubel and Wiesel. Pixels could be grouped into seven categories varying from left-only response to binocular-only response to right-only responses. Nonspecific responses were found in the MRI-visible draining veins as well as in the parenchyma. Although large vessel BOLD signals are easily detectable, regardless of field strength, they demonstrate a fMRI response to photic input that could not be used to distinguish ocular dominance. The difference in BOLD response between a region activated by one eye and that activated by the other is only 2.9% on average. This necessitates the use of a difference paradigm to visualize the regions of ocular dominance accurately. The data show that BOLD-based fMRI is sensitive to neuronal activity in cortical columns when using differential techniques, opening up the possibility of mapping specialized populations of neurons in humans that are not accessible to electrophysiological or other methods of invasive mapping.
Encoding of Binocular Disparity by Complex Cells in the Cat's Visual Cortex
Authors: Ohzawa Izumi , Deangelis Gregory C. , Freeman Ralph D.
Published: December 2017

Ohzawa, Izumi, Gregory C. DeAngelis, and Ralph D. Freeman. Encoding of binocular disparity by complex cells in the cat's visual cortex. J. Neurophysiol. 77: 2879–2909, 1997. To examine the roles that complex cells play in stereopsis, we have recorded extracellularly from isolated single neurons in the striate cortex of anesthetized paralyzed cats. We measured binocular responses of complex cells using a comprehensive stimulus set that encompasses all possible combinations of positions over the receptive fields for the two eyes. For a given position combination, stimulus contrast could be the same for the two eyes (2 bright or 2 dark bars) or opposite (1 bright and 1 dark). These measurements provide a binocular receptive field (RF) profile that completely characterizes complex cell responses in a joint domain of left and right stimulus positions. Complex cells typically exhibit a strong selectivity for binocular disparity, but are only broadly selective for stimulus position. For most cells, selectivity for disparity is more than twice as narrow as that for position. These characteristics are highly desirable if we assume that a disparity sensor should exhibit position invariance while encoding small changes in stimulus depth. Complex cells have nearly identical binocular RFs for bright and dark stimuli as long as the sign of stimulus contrast is the same for the two eyes. When stimulus contrast is opposite, the binocular RF also is inverted such that excitatory subregions become suppressive. We have developed a disparity energy model that accounts for the behavior of disparity-sensitive complex cells. This is a hierarchical model that incorporates specific constraints on the selection of simple cells from which a complex cell receives input. Experimental data are used to examine quantitatively predictions of the model. Responses of complex cells generally agree well with predictions of the disparity energy model. However, various types of deviations from the predictions also are found, including a highly elongated excitatory region beyond that supported by a single energy mechanism. Complex cells in the visual cortex appear to provide a next level of abstraction in encoding information for stereopsis based on the activity of a group of simple-type subunits. In addition to exhibiting narrow disparity tuning and position invariance, these cells seem to provide a partial solution to the stereo correspondence problem that arises in complex natural scenes. Based on their binocular response properties, these cells provide a substantial reduction in the complexity of the correspondence problem.
Responses to Glutamate in Rat Taste Cells
Authors: Bigiani A. , Delay R. J. , Chaudhari N. , Kinnamon S. C. , Roper S. D.
Published: December 2017

Bigiani, A., R. J. Delay, N. Chaudhari, S. C. Kinnamon, and S. D. Roper. Responses to glutamate in rat taste cells. J. Neurophysiol. 77: 3048–3059, 1997. We studied taste transduction in sensory receptor cells. Specifically, we examined the actions of glutamate, a significant taste stimulus, on the membrane properties of taste cells by applying whole cell patch-clamp techniques to cells in rat taste buds isolated from foliate and vallate papillae. In 55 of 91 taste cells, bath-applied glutamate, at concentrations that elicit taste responses in the intact animal (10–20 mM), produced one of two different responses when the cell membrane was held near its presumed resting potential, −85 mV. “Sustained” glutamate responses were observed in the majority of taste cells (51 of 55) and consisted of an outward current (reduction of the maintained inward current). Sustained glutamate responses were voltage dependent, were decreased by membrane depolarization, and were accompanied by a reduction in membrane conductance. An analysis of the reversal potential of sustained responses in different ionic conditions and the effect of ion substitutions suggested that the currents were carried by cations. The data suggest that sustained responses are mediated by the closure of nonselective cation channels. Other taste cells (4 of 55) responded to glutamate with a transient inward current—so-called “transient” responses. Transient glutamate responses were voltage dependent and Na+ dependent, and appeared to be generated by nonspecific cation channels activated by glutamate. l(+)-2-amino-4-phosphonobutyric acid (l-AP4), a specific agonist of a metabotropic glutamate receptor (mGluR4) recently identified in rat taste cells and believed to be involved in taste transduction, mimicked the sustained glutamate responses. These findings indicate that glutamate, at concentrations at or slightly above threshold for taste in rats, produces two different membrane currents. The properties of these two responses suggest that there may be two different sets of nonspecific cation channels in taste cells, one closed by glutamate (sustained response) and the other opened (transient response). Our findings on the effect of l-AP4 suggest that the sustained response is the membrane mechanism mediating, at least in part, taste transduction for glutamate.
Electrophysiological Analysis of Dorsal Root Ganglion Neurons Pre- and Post-Coexpression of Green Fluorescent Protein and Functional 5-HT3Receptor
Authors: Smith George M. , Berry Richard L. , Yang Jay , Tanelian Darrell
Published: December 2017

Smith, George M., Richard L. Berry, Jay Yang, and Darrell Tanelian. Electrophysiological analysis of dorsal root ganglion neurons pre- and post-coexpression of green fluorescent protein and functional 5-HT3receptor. J. Neurophysiol. 77: 3115–3121, 1997. Aequorea green fluorescent protein (GFP) is an excellent marker to examine genetically altered live cells in whole animals or culture. Its potential use in identifying genetically modified neurons, however, has not been investigated extensively. To examine the usefulness, toxicity, and potential electrophyiological effects of GFP expression in neurons, we generated adenovirus containing the mGFP4 cDNA. One week after virus transfection of dorsal root ganglion neurons (DRG), 10% of postnatal DRG neurons appeared brightly fluorescent, labelling the soma and neurites. Temporal examination of these neurons demonstrated no toxicity to DRG neurons even after several weeks in culture with repeated daily epifluorescent exposure. Electrophysiological analysis and comparison of control and viral exposed (GFP− and GFP+) DRG neurons did not demonstrate any differences in whole cell resistance, resting potential, action potential (AP) threshold, AP duration, AP amplitude, or whole cell capacitance. To investigate the usefulness of GFP as a marker for identifying neurons genetically altered to express a novel neurotransmitter receptor, a second adenovirus construct was generated containing both GFP and serotonin type 3 (5-HT3) receptor cDNAs. Transfection of DRG neurons with this virus produced an inward current in the presence of serotonin only in DRG neurons that were GFP-positive. It is concluded that adenoviral transfection of neurons with GFP, for cellular labeling, and coexpression of GFP-neurotransmitter constructs are safe, nontoxic, methods for electrophysiologically investigating neurons over several weeks. The uniqueness of the vector used in these experiments is that it was constructed to express GFP in a second cassette so that it would label the transduced cells, but have no potential for interfering with the function of the foreign 5-HT3receptor.