bluuebunny/crossref_metadata_2025 huggingface dataset:
Ca2+ Current in Rabbit Carotid Body Glomus Cells Is Conducted by Multiple Types of High-Voltage–Activated Ca2+ Channels
Authors: Overholt Jeffrey L. , Prabhakar Nanduri R.
Published: December 2017

Overholt, Jeffrey L. and Nanduri R. Prabhakar. Ca2+ current in rabbit carotid body glomus cells is conducted by multiple types of high-voltage–activated Ca2+ channels. J. Neurophysiol. 78: 2467–2474, 1997. Carotid bodies are sensory organs that detect changes in arterial oxygen. Glomus cells are presumed to be the initial sites for sensory transduction, and Ca2+-dependent neurotransmitter release from glomus cells is believed to be an obligatory step in this response. Some information exists on the Ca2+ channels in rat glomus cells. However, relatively little is known about the types of Ca2+ channels present in rabbit glomus cells, the species in which most of the neurotransmitter release studies have been performed. Therefore we tested the effect of specific Ca2+ channel blockers on current recorded from freshly dissociated, adult rabbit carotid body glomus cells using the whole cell configuration of the patch-clamp technique. Macroscopic Ba2+ current elicited from a holding potential of −80 mV activated at a V m of approximaely −30 mV, peaked between 0 and +10 mV and did not inactivate during 25-ms steps to positive test potentials. Prolonged (≈2 min) depolarized holding potentials inactivated the current with a V 1/2 of −47 mV. There was no evidence for T-type channels. On steps to 0 mV, 6 mM Co2+ decreased peak inward current by 97 ± 1% (mean ± SE). Nisoldipine (2 μM), 1 μM ω-conotoxin GVIA, and 100 nM ω-agatoxin IVa each blocked a portion of the macroscopic Ca2+ current (30 ± 5, 33 ± 5, and 19 ± 3% after rundown correction, respectively). Simultaneous application of these blockers revealed a resistant current that was not affected by 1 μMω-conotoxin MVIIC. This resistant current constituted 27 ± 5% of the total macroscopic Ca2+ current. Each blocker had an effect in every cell so tested. However, the relative proportion of current blocked varied from cell to cell. These results suggest that L, N, P, and resistant channel types each conduct a significant proportion of the macroscopic Ca2+ current in rabbit glomus cells. Hypoxia-induced neurotransmitter release from glomus cells may involve one or more of these channels.
Interaction Between Tetanus Long-Term Potentiation and Hypoxia-Induced Potentiation in the Rat Hippocampus
Authors: Lyubkin M. , Durand D. M. , Haxhiu M. A.
Published: December 2017

Lyubkin, M., D. M. Durand, and M. A. Haxhiu. Interaction between tetanus long-term potentiation and hypoxia-induced potentiation in the rat hippocampus. J. Neurophysiol. 78: 2475–2482, 1997. The interaction between tetanus-induced long-term potentiation (LTP) and hypoxia-induced potentiation was investigated by performing extracellular recordings in the CA1 region of rat hippocampus using a two-pathway design. Hippocampal slices were placed in an interface chamber containing artificial cerebrospinal fluid (ACSF) solution with high magnesium concentration. Hypoxia was induced by replacing the 5% CO2-95% O2gas mixture with 5% CO2-95% N2for 2 min. Tetanus-LTP was induced with 1-s, 100-Hz current pulses. Significant hypoxia-induced potentiation of the slope of the dendritic excitatory postsynaptic potential (EPSP) was found in ACSF containing 2 mM of magnesium 2, 27 ± 10% (mean ± SE; n = 16; P < 0.01) with no change in the mean amplitude of the presynaptic volley. All experiments in which a stable control baseline was obtained were used for data analysis. The data show that short episodes (2 min) of hypoxia can induce LTP of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-mediated synaptic transmission. The present study demonstrated that after tetanus-LTP, 33 ± 3% ( n = 10; P < 0.01), hypoxia further potentiated the field EPSP slopes by a mean value of 16 ± 5% ( n = 10; P < 0.05). Moreover, using a two-pathway design, we showed that hypoxia produced similar potentiation in both the control [19 ± 5%; n = 10; P < 0.01) and tetanus-induced LTP pathway, and the total potentiation produced by a combination of tetanus then hypoxia, 63 ± 13% ( n = 10; p < 0.01), was significantly larger ( P < 0.01) than hypoxia alone. These data suggest that hypoxia-induced potentiation is additive with tetanus-LTP. Occlusion experiments were performed to verify whether the mechanisms responsible for hypoxia-induced potentiation are independent of preexisting synaptic levels induced by high-frequency stimulation. Hypoxia produced significant potentiation (23 ± 7%; n = 7; P < 0.05) after successful occlusion of the LTP pathway. Therefore, because the magnitude of hypoxia-induced potentiation is both independent of preexisting synaptic levels and also additive, synaptic specificity associated with LTP is preserved. The magnitude of tetanus-LTP induced 20 min after hypoxia (15 ± 4%; n = 10) was significantly smaller ( P < 0.01) relative to LTP after normoxic conditions (33 ± 3%; n = 10). Additionally, hypoxia blocked the transient, robust potentiation occurring during the early phase of LTP induction. This study suggests that although hypoxia modifies neuronal processing by general excitation, synaptic specificity associated with tetanus-LTP still is preserved. However, hypoxia can disrupt neuronal processing by inhibiting new modification of synaptic transmission.
Properties of Carbachol-Induced Oscillatory Activity in Rat Hippocampus
Authors: Williams John H. , Kauer Julie A.
Published: December 2017

Williams, John H. and Julie A. Kauer. Properties of carbachol-induced oscillatory activity in rat hippocampus. J. Neurophysiol. 78: 2631–2640, 1997. The recent resurgence of interest in carbachol oscillations as an in vitro model of theta rhythm in the hippocampus prompted us to evaluate the circuit mechanisms involved. In extracellular recordings, a regularly spaced bursting pattern of field potentials was observed in both CA3 and CA1 subfields in the presence of carbachol. Removal of the CA3 region abolished oscillatory activity observed in CA1, suggesting that the oscillatory generator is located in CA3. An α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonist, 6,7-dinitroquinoxaline-2,3-dione (DNQX), blocked carbachol oscillations, indicating that AMPA receptor-mediated synaptic currents are necessary for the population oscillation. Moreover, the spread of oscillatory activity into CA1 required intact N-methyl-d-aspartate receptors. These data are more consistent with epileptiform bursting than with theta rhythm described in vivo. In the presence of carbachol, individual CA3 pyramidal cells exhibited a slow, rhythmic intrinsic oscillation that was not blocked by DNQX and that was enhanced by membrane hyperpolarization. We hypothesize that this slower oscillation is the fundamental oscillator that participates in triggering the population oscillation by exciting multiple synaptically connected CA3 neurons. γ-aminobutyric acid-A (GABAA) receptors are not necessary for carbachol to elicit synchronous CA3 field events but are essential to the bursting pattern observed. Neither GABABnor metabotropic glutamate receptors appear to be necessary for carbachol oscillations. However, both nicotinic and M1 and M3 muscarinic cholinergic receptors contribute to the generation of this activity. These results establish the local circuit elements and neurotransmitter receptors that contribute to carbachol-induced oscillations and indicate that carbachol-induced oscillations are fundamentally distinct from theta rhythm in vivo.
Effects of Pb2+ on Delayed-Rectifier Potassium Channels in Acutely Isolated Hippocampal Neurons
Authors: Madeja Michael , Muβhoff Ulrich , Binding Norbert , Witting Ute , Speckmann Erwin-Josef
Published: December 2017

Madeja, Michael, Ulrich Muβhoff, Norbert Binding, Ute Witting, and Erwin-Josef Speckmann. Effects of Pb2+ on delayed-rectifier potassium channels in acutely isolated hippocampal neurons. J. Neurophysiol. 78: 2649–2654, 1997. The effects of Pb2+ on delayed-rectifier potassium currents were studied in acutely isolated hippocampal neurons (CA1 neurons, CA3 neurons, granule cells) from the guinea pig using the patch-clamp technique in the whole cell configuration. Pb2+ in micromolar concentrations decreased the potassium currents in a voltage-dependent manner, which appeared as a shift of the current-voltage relation to positive potentials. The effect was reversible after washing. The concentration-responsiveness measured in CA1 neurons revealed an IC50 value of 30 μmol/l at a potential of −30 mV. The half-maximal shift of the current-voltage relation was reached at 33 μmol/l and the maximal obtainable shift was 13.4 mV. For the different types of hippocampal neurons, the shift of the current-voltage relation was distinct and was 7.9 mV in CA1 neurons, 13.7 mV in CA3 neurons, and 14.2 mV in granule cells with 50 μmol/l Pb2+. The effects described here of Pb2+ on the potassium currents in hippocampal neurons and the differences between the types of hippocampal neurons correspond with the known properties and distributions of cloned potassium channels found in the hippocampus. As a whole, our results demonstrate that Pb2+ in micromolar concentration is a voltage-dependent, reversible blocker of delayed-rectifier potassium currents of hippocampal neurons. This effect has to be taken into consideration as a possible contributing mechanism for the neurological symptoms of enhanced brain activity seen during Pb2+ intoxication.
Response Sensitivity and Voltage Gain of the Rod- and Cone-Bipolar Cell Synapses in Dark-Adapted Tiger Salamander Retina
Authors: Yang Xiong-Li , Wu Samuel M.
Published: December 2017

Yang, Xiong-Li and Samuel M. Wu. Response sensitivity and voltage gain of the rod- and cone-bipolar cell synapses in dark-adapted tiger salamander retina. J. Neurophysiol. 78: 2662–2673, 1997. Rods, cones, and bipolar cells were recorded in superfused, flat-mounted isolated retinas of the larval tiger salamander, Ambystoma tigrinum, under dark-adapted conditions. Voltage responses of 24 rods, 15 cones, and 41 bipolar cells in dark-adapted retinas to 500 nm light steps of various intensities were listed and fitted with hyperbolic functions, and their step sensitivities and relative sensitivities (log σ) were estimated. In the linear response-intensity ranges, the step sensitivity of rods, SS (rod), is −1.0 mV photon−1 μm2 s or 0.034 mV Rh*−1 s rod and that of the cones, S S (cone), is ∼0.00146 mV photon−1 μm2 s or 0.000048 mV Rh*−1 s rod. The rod and cone responses were relatively homogenous with little variations in response amplitude and sensitivity. In contrast, bipolar cell responses were heterogenous with large variations in response amplitude and sensitivity. The maximum response amplitude of bipolar cells varied from 5 to 25 mV, and the relative response sensitivity (log σ) varied >6 log units (−8.11 to −2.32). The step sensitivity of bipolar cells in the linear response-intensity range varied from 0.0000438 to 51.82 mV photon−1 μm2 s. Bipolar cells in dark-adapted tiger salamander retinas fell into two groups according to their relative sensitivities with very few cells falling in the intermediate light intensity region. The mixed bipolar cells (DBCM and HBCM) exhibited relative response sensitivity ranged from −8.11 to −5.54, and step sensitivity ranged from 1.22 to 51.82 mV photon−1 μm2 s. The cone-driven bipolar cells (DBCC and HBCC) exhibited relative response sensitivity ranged from −3.45 to −2.32, and step sensitivity ranged from 0.0000438 to 0.00201 mV photon-1 μm2 sec. The chord voltage gain of the rod-DBCM or rod-HBCM synapses near the rod dark membrane potential ranged from 1.14 to 48.43 and that of the cone-DBCC or cone-HBCC synaptic gain near the cone dark membrane potential ranged from 0.03 to 1.38. The highest voltage gains were found near the rod or cone dark membrane potentials. By the use of linear subtraction method, we studied the synaptic inputs from cones to five mixed bipolar cells, and the voltage gains of the cone synapses in each of the bipolar cells were very close to the voltage gain of the rod synapses. This result suggests that although the responses of mixed bipolar cells are mediated mainly by rods when lights of short and medium wavelengths are used, their responses to long wavelength lights (>650 nm) are mediated by both rods and cones with comparable synaptic gains. Functional roles of the mixed and cone-driven bipolar cells in information processing in dark-adapted retinas are discussed.
Mechanisms of Potentiation by Calcium-Calmodulin Kinase II of Postsynaptic Sensitivity in Rat Hippocampal CA1 Neurons
Authors: Shirke Aneil M. , Malinow Roberto
Published: December 2017

Shirke, Aneil M. and Roberto Malinow. Mechanisms of potentiation by calcium-calmodulin kinase II of postsynaptic sensitivity in rat hippocampal CA1 neurons. J. Neurophysiol. 78: 2682–2692, 1997. Preactivated recombinant α-calcium–calmodulin dependent multifunctional protein kinase II (CaMKII*) was perfused internally into CA1 hippocampal slice neurons to test the effect on synaptic transmission and responses to exogenous application of glutamate analogues. After measurement of baseline transmission, internal perfusion of CaMKII* increased synaptic strength in rat hippocampal neurons and diminished the fraction of synaptic failures. After measurement of baseline responses to applied transmitter, CaMKII* perfusion potentiated responses to kainate but not responses to N-methyl-d-aspartate. Internal perfusion of CaMKII*potentiated the maximal effect of kainate. Potentiation byCaMKII* did not change the time course of responses to kainate, whereas increasing response size by pharmacologically manipulating desensitization or deactivation rate constants significantly altered the time course of responses. Nonstationary fluctuation analysis of responses to kainate showed a decrease in the coefficient of variation after potentiation by CaMKII*. These data support the hypothesis that CaMKII increases postsynaptic responsiveness by increasing the available number of active α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid/kainate channels and suggests that a similar process may occur during the expression of long-term potentiation.
NMDA Receptor Involvement in Neuroplastic Changes Induced By Neonatal Capsaicin Treatment in Trigeminal Nociceptive Neurons
Authors: Chiang Chen Yu , Hu James W. , Sessle Barry J.
Published: December 2017

Chiang, Chen Yu, James W. Hu, and Barry J. Sessle. NMDA receptor involvement in neuroplastic changes induced by neonatal capsaicin treatment in trigeminal nociceptive neurons. J. Neurophysiol. 78: 2799–2803, 1997. This study examines whether 1) the neonatal loss of C-fiber afferents results in neuroplastic changes in the mechanoreceptive field (RF) properties and spontaneous activity of nociceptive neurons in trigeminal subnucleus caudalis (medullary dorsal horn) of adult rats, and that 2) N-methyl-d-aspartic acid (NMDA) receptor mechanisms are involved in these neuroplastic changes. Compared with vehicle-treated (i.e., control, CON) rats, capsaicin-treated (CAP) rats showed a marked increase in neuronal spontaneous activity and RF size per se, but these neuroplastic changes could be significantly reduced by MK-801 (1 mg/kg, iv), a noncompetitive NMDA receptor antagonist; RF size and spontaneous activity remained unchanged in CON rats after MK-801 administration and in CAP rats after vehicle (saline, iv). Administration of 7-chlorokynurenic acid intrathecally (5 μg/10 μl), an antagonist of strychnine-insensitive glycine binding sites on the NMDA receptor, also significantly reduced neuronal RF size and spontaneous activity in CAP rats, but not in CON rats. These data provide evidence that C-fiber afferents play a role in shaping the properties of nociceptive neurons and that the neuroplastic changes involve NMDA receptor mechanisms.
Intrinsic Membrane Characteristics Distinguish Two Subsets of Nociceptive Modulatory Neurons in Rat RVM
Authors: Zagon Aniko , Meng Xianwei , Fields Howard L.
Published: December 2017

Zagon, Aniko, Xianwei Meng, and Howard L. Fields. Intrinsic membrane characteristics distinguish two subsets of nociceptive modulatory neurons in rat RVM. J. Neurophysiol. 78: 2848–2858, 1997. Pain modulating neurons of the rostral ventromedial medulla (RVM) include three physiologically distinct classes of neurons in intact, anesthetized animals: on and off cells that change their activity before the onset of withdrawal reflexes and neutral cells, which have activity unrelated to withdrawal reflexes. A previous in vitro intracellular study demonstrated that the RVM contains two types of neurons that are distinguished by their action-potential characteristics. The present in vivo intracellular study examined whether these intracellularly recorded action-potential characteristics are correlated with the physiological response properties of RVM neurons recorded. RVM neurons exhibited two distinct types of action potentials in vivo. Fast-spike (FS) neurons ( n = 30) had short-duration action potentials (0.27 ± 0.02 (SE) ms at half amplitude) and biphasic afterhyperpolarizations with a characteristic rapid overshooting spike repolarization. Slow-spike (SS) neurons ( n = 25) had longer duration action potentials (0.44 ± 0.02 ms at half-amplitude) due to a slower-spike repolarization rate and monophasic afterhyperpolarization. on and off cell classes included both FS and SS neurons. FS on and off neurons had an early onset response to noxious heat stimulation. SS on and off cells showed a delayed onset response to noxious heat. neutral cells ( n = 13) were all SS cells. Among the SS neurons, only neutral cells had action potentials longer than 0.45 ms ( n = 9). FS and SS neurons were intermingled throughout the RVM. The majority of intracellularly labeled cells ( n = 15) had fusiform somata with two to five fine caliber primary dendrites and a predominantly mediolateral orientation of the long axis of their dendritic tree. All labeled FS on cells ( n = 5) had large, multipolar somata with four to nine large caliber primary dendrites. The present study defines in vivo membrane and morphological characteristics of RVM neurons that correlate with physiological differences and may be used for identification of nociceptive modulatory RVM neurons in slice preparations.
Perceptual Learning of Spatial Localization: Specificity for Orientation, Position, and Context
Authors: Crist Roy E. , Kapadia Mitesh K. , Westheimer Gerald , Gilbert Charles D.
Published: December 2017

Crist, Roy E., Mitesh K. Kapadia, Gerald Westheimer, and Charles D. Gilbert. Perceptual learning of spatial localization: specificity for orientation, position, and context. J. Neurophysiol. 78: 2889–2894, 1997. Discrimination of simple visual attributes can improve significantly with practice. We have trained human observers to perform peripherally presented tasks involving the localization of short line segments and examined the specificity of the learning for the visual location, orientation, and geometric arrangement of the trained stimulus. Several weeks of training resulted in dramatic threshold reductions. The learning was specific for the orientation and location of the trained stimulus, indicating the involvement of the earliest cortical stages in the visual pathway where the orientation and location of stimuli are mapped with highest resolution. Furthermore, improvement was also specific for both the configuration of the trained stimulus and the attribute of the stimulus that was under scrutiny during training. This degree of specificity suggests that the learning cannot be achieved by cortical recruitment alone, as proposed in current models, but is likely to involve a refinement of lateral interactions within the cortex and possibly a gating of lower level changes by attentional mechanisms.
Functional Development of Intrinsic Properties in Ganglion Cells of the Mammalian Retina
Authors: Wang Guo-Yong , Ratto G.-M. , Bisti Silvia , Chalupa Leo M.
Published: December 2017

Wang, Guo-Yong, G.-M. Ratto, Silvia Bisti, and Leo M. Chalupa. Functional development of intrinsic properties in ganglion cells of the mammalian retina. J. Neurophysiol. 78: 2895–2903, 1997. Sensory neurons manifest pronounced changes in excitability during maturation, but the factors contributing to this ubiquitous developmental phenomenon are not well understood. To assess the contribution of intrinsic membrane properties to such changes in excitability, in the present study whole cell patch-clamp recordings were made from developing ganglion cells in the intact retina of postnatal rats. During a relatively brief developmental period (postnatal days P7-P27) ganglion cells exhibited pronounced changes in the discharge patterns generated by depolarizing current injections. The youngest cells (P7-P17) typically responded to maintained depolarizations with only a single spike or a rapidly adapting discharge pattern. In contrast, the predominant response mode of more mature cells (P21-P27) was a series of repetitive discharges that lasted for the duration of the depolarization period, and by P25 all cells responded in this manner. These functional changes characterized all three morphologically defined cell classes identified by intracellular labeling with Lucifer yellow.

To determine if expression of the potassium current ( I a) and the kinetics of the Na-channel related to the increased excitability of developing ganglion cells described above, current- and voltage-clamp recordings were made from individual neurons. The different firing patterns manifested by developing retinal ganglion cells did not reflect the presence or absence of the I a conductance, although cells expressing I a tended to generate spikes of shorter duration. With maturation the speed of recovery from inactivation of the Na current increased markedly and this related to the increased excitability of developing ganglion cells. Neurons yielding only a single spike to maintained depolarization were characterized by the slowest speed of recovery; cells with rapidly adapting discharges showed a faster recovery and those capable of repetitive firing recovered fastest from Na-channel inactivation. It is suggested that these changes in intrinsic membrane properties may relate to the different functional roles subserved by ganglion cells during development.
Kinetics of Muscarinic Reduction of I sAHP in Hippocampal Neurons: Effects of Acetylcholinesterase Inhibitors
Authors: Zhang Y. , Carlen P. L. , Zhang L.
Published: December 2017

Zhang, Y., P. L. Carlen, and L. Zhang. Kinetics of muscarinic reduction of I sAHP in hippocampal neurons: effects of acetylcholinesterase inhibitors. J. Neurophysiol. 78: 2999–3007, 1997. The present experiments were designed to elucidate the time frame in which an evoked cholinergic impulse decreases the Ca2+-dependent K+ current ( I sAHP) in hippocampal CA1 neurons, and to determine to what extent acetylcholinesterase (AChE) inhibitors enhance the efficacy of the cholinergic impulse. Whole cell voltage-clamp recordings were performed on hippocampal CA1 neurons of rat brain slices and I sAHPs were evoked by constant depolarizing pulses. Cholinergic afferent fibers in stratum oriens were stimulated electrically and the time interval between the afferent stimulus and the depolarizing pulse was varied from 1 to 30 s. In slices perfused with the standard external medium, the afferent stimulus caused a profound decrease in the following I sAHP only when the stimulus preceded the depolarizing pulse by 1–2 s. The stimulus was without effects on the I sAHP when applied ≥5s before the depolarizing pulse. The effects of the afferent stimulus were greatly enhanced in CA1 neurons exposed to the catalytic AChE inhibitors neostigmine, physostigmine, or 9-amino-1,2,3,4-tetrahydro-acridine. A substantial decrease in the I sAHP was observed even when the stimulus preceded the depolarizing pulse by ≥30 s. However applications of peripheral site AChE inhibitors decamethonium and propidium caused only minor or no enhancement of the I sAHP reduction after the afferent stimulus. We suggest in physiological conditions that muscarinic modulation of ionic conductances of CNS neurons has a limited time course after a cholinergic impulse and that the modulation is greatly enhanced and prolonged when catalytic activities of AChEs are suppressed pharmacologically.
Functional Analysis of the Sensory Motor Pathway of Resistance Reflex in Crayfish. II. Integration of Sensory Inputs in Motor Neurons
Authors: Ray Didier Le , Clarac François , Cattaert Daniel
Published: December 2017

Le Ray, Didier, François Clarac, and Daniel Cattaert. Functional analysis of the sensory motor pathway of resistance reflex in crayfish. II. Integration of sensory inputs in motor neurons. J. Neurophysiol. 78: 3144–3153, 1997. The in vitro preparation of the fifth thoracic ganglion of the crayfish was used to analyze the connections supporting the monosynaptic reflex responses recorded from the depressor motor neurons (Dep MNs). Dep MNs are directly connected by the release-sensitive afferents from a proprioceptor, the coxo-basipodite chordotonal organ (CBCO), which is released by upward movements of the leg. Sine-wave movements, applied to the CBCO strand from the most released position, allowed us to stimulate the greatest part of release-sensitive CBCO fibers. Systematic intracellular recordings from all Dep MNs performed in high divalent cation saline allowed us to determine the connections between CBCO afferents and their postsynaptic Dep MNs: it highlighted the sequential activation of the different Dep MNs involved in the monosynaptic reflex. The convergence of different sensory afferents onto a given Dep MN, and the divergence of a given sensory afferent onto several Dep MNs illustrates the complexity of the sensory-motor reflex loops involved in the control of locomotion and posture. Electrophysiological experiments and simulations were performed to analyze the mechanisms by which Dep MNs integrate the large amount of sensory input that they receive. Paired intracellular recording experiments demonstrated that postsynaptic response shapes characteristic of both phasic and phaso-tonic afferents could be induced by varying the presynaptic firing frequency, whatever the postsynaptic Dep MN. Compartment model simulations were used to analyze the role of the sensory-motor synapse characteristics in the summation properties of postsynaptic MN. They demonstrated the importance of the postsynaptic compartment geometry, because large postsynaptic compartments allowed to generate greater excitatory postsynaptic potential (EPSP) summations than small ones. The results presented show that velocity information is the most effective to elicit large compound EPSPs in MNs. We therefore suggest that the negative feedback reflex is mainly based on the detection of leg movements.
Temporal Summation of C-Fiber Afferent Inputs: Competition Between Facilitatory and Inhibitory Effects on C-Fiber Reflex in the Rat
Authors: Gozariu Manuela , Bragard Dominique , Willer Jean-Claude , Le Bars Daniel
Published: December 2017

Gozariu, Manuela, Dominique Bragard, Jean-Claude Willer, and Daniel Le Bars. Temporal summation of C-fiber afferent inputs: competition between facilitatory and inhibitory effects on C-fiber reflex in the rat. J. Neurophysiol. 78: 3165–3179, 1997. Long-lasting facilitations of spinal nociceptive reflexes resulting from temporal summation of nociceptive inputs have been described on many occasions in spinal, nonanesthetized rats. Because noxious inputs also trigger powerful descending inhibitory controls, we investigated this phenomenon in intact, halothane-anesthetized rats and compared our results with those obtained in other preparations. The effects of temporal summation of nociceptive inputs were found to be very much dependent on the type of preparation. Electromyographic responses elicited by single square-wave electrical shocks (2 ms, 0.16 Hz) applied within the territory of the sural nerve were recorded in the rat from the ipsilateral biceps femoris. The excitability of the C-fiber reflex recorded at 1.5 times the threshold ( T) was tested after 20 s of electrical conditioning stimuli (2 ms, 1 Hz) within the sural nerve territory. During the conditioning procedure, the C-fiber reflex was facilitated (wind-up) in a stimulus-dependent fashion in intact, anesthetized animals during the application of the first seven conditioning stimuli; thereafter, the magnitude of the responses reached a plateau and then decreased. Such a wind-up phenomenon was seen only when the frequency of stimulation was 0.5 Hz or higher. In spinal, unanesthetized rats, the wind-up phenomenon occurred as a monotonic accelerating function that was obvious during the whole conditioning period. An intermediate picture was observed in the nonanesthetized rat whose brain was transected at the level of the obex, but the effects of conditioning were profoundly attenuated when such a preparation was anesthetized. In intact, anesthetized animals the reflex was inhibited in a stimulus-dependent manner during the postconditioning period. These effects were not dependent on the frequency of the conditioning stimulus. Such inhibitions were blocked completely by transection at the level of the obex, and in nonanesthetized rats were then replaced by a facilitation. A similar long-lasting facilitation was seen in nonanesthetized, spinal rats. It is concluded that, in intact rats, an inhibitory mechanism counteracts the long-lasting increase of excitability of the flexor reflex seen in spinal animals after high-intensity, repetitive stimulation of C-fibers. It is suggested that supraspinally mediated inhibitions also participate in long term changes in spinal cord excitability after noxious stimulation.
Mathematical Model of the Human Jaw System Simulating Static Biting and Movements After Unloading
Authors: Slager G.E.C. , Otten E. , van Eijden T.M.G.J. , van Willigen J. D.
Published: December 2017

Slager, G.E.C., E. Otten, T.M.G.J. van Eijden, and J. D. van Willigen. Mathematical model of the human jaw system simulating static biting and movements after unloading. J. Neurophysiol. 78: 3222–3233, 1997. When the resistance to a forceful isometric bite is suddenly removed in unloading experiments, the bite force drops to zero and the mandible reaches a constant velocity. This occurs at an initial bite force of 100 N after ∼12 ms when the incisors have moved 4.5 mm. Reflex activity is far too slow to limit the velocity at impact. To explore the influence of other factors (cocontraction, force-length properties, and force-velocity properties of the muscles) on the velocity at impact, a numerical forward dynamic model of the jaw system is formulated. Unloading experiments in different experimental conditions were simulated with the model. Most parameter values of the model are based on physiological data, both from literature and a data basis from a human cadaver study. Other parameter values were found by optimally fitting the model results to data from the unloading experiments. The model analysis shows that the limitation of the jaw velocity mainly may be due to the force-velocity properties of the jaw-closing muscles. Force-length properties of the jaw muscles hardly contribute to the impact velocity. The compliance of tendinous sheets in the jaw muscles is unfavorable for the reduction in impact velocity, whereas cocontraction of jaw-opening and -closing muscles helps to limit impact velocity. The force-velocity propertiesof the muscles provide a quick mechanism for dealing withunexpected closing movements and so avoid damage to the dental elements.
Electrophysiological Properties of Rat Pontine Nuclei Neurons In Vitro. I. Membrane Potentials and Firing Patterns
Authors: Schwarz Cornelius , Möck Martin , Thier Peter
Published: December 2017

Schwarz, Cornelius, Martin Möck, and Peter Thier. Electrophysiological properties of rat pontine nuclei neurons in vitro. I. Membrane potentials and firing patterns. J. Neurophysiol. 78: 3323–3337, 1997. We used a new slice preparation of rat brain stem to establish the basic membrane properties of neurons in the pontine nuclei (PN). Using standard intracellular recordings, we found that pontine cells displayed a resting membrane potential of −63 ± 6 mV (mean ± SD), an input resistance of 53 ± 21 MΩ, a membrane time constant of 5.3 ± 2.4 ms and were not spontaneously active. The current-voltage relationship of most of the PN neurons showed the characteristics of inward rectification in both depolarizing and hyperpolarizing directions. A prominent feature of the firing of pontine neurons was a marked firing rate adaptation, which eventually caused the cells to cease firing. Several types of membrane conductances possibly contribute to this feature. For one, a medium and a slow type of afterhyperpolarization (AHP) control the pattern of firing. The medium AHP was partly susceptible to blockade of calcium influx, whereas it was abolished completely by blockade of potassium channels with tetraethylammonium, indicating that it is based on at least two conductances: a calcium-dependent and a calcium-independent one. The slow AHP was carried by potassium ions and could be blocked effectively by preventing calcium influx into the cell. It was present after single spikes but was strongest after a high-frequency spike train. Calcium entry into the cell was mediated by high-threshold calcium channels that were detected by the generation of calcium spikes under blockade of potassium channels. Furthermore, the early phase of the firing rate adaptation was shown to be related to the time course of a slow, tetrodotoxin (TTX)-sensitive, persistent sodium potential, which was activated already in the subthreshold range of membrane potentials. This potential was time dependent and imposed as a depolarizing “hump” with a maximum occurring in most cases between 50 and 100 ms after stimulus onset. In the suprathreshold range, it generated plateau potentials following fast spikes, if potassium channels were blocked. After the complete adaptation of the firing rate, PN neurons were observed to display irregular fluctuations of the membrane potential, which sometimes reached firing threshold thereby eliciting an irregular low-frequency spike train. As these fluctuations could be blocked with TTX, they probably are based on the persistent sodium currents. The opposing drive in hyperpolarizing direction may be provided by strong outward currents that generated a marked outward rectification in the current-voltage relationship under TTX. In conclusion, PN neurons show complex membrane properties that are reminiscent in many ways to cerebrocortical “regular firing” neurons.
Regulation of N- and L-Type Ca2+Channels in Adult Frog Sympathetic Ganglion B Cells by Nerve Growth Factor In Vitro and In Vivo
Authors: Lei Saobo , Dryden William F. , Smith Peter A.
Published: December 2017

Lei, Saobo, William F. Dryden, and Peter A. Smith. Regulation of N- and L-type Ca2+channels in adult frog sympathetic ganglion B cells by nerve growth factor in vitro and in vivo. J. Neurophysiol. 78: 3359–3370, 1997. To examine mechanisms responsible for the long-term regulation of Ca2+-channels in an adult neuron, changes in whole cell Ba2+current ( IBa) were examined in adult bullfrog sympathetic ganglion B cells in vitro. Cells were cultured at low density in defined, serum free medium. After 15 days, total IBawas similar to the initial value, whereas IBadensity was reduced by ∼36%, presumably due to an increase in neuronal surface area. By contrast, IBadensity remained constant after 6–15 days in the presence of murine β-NGF (200 ng/ml), and total IBawas almost doubled. Inclusion of cytosine arabinoside (Ara-C; 10 μM) to inhibit proliferation of nonneuronal cells, did not affect the survival of neurons in the absence of nerve growth factor (NGF) nor did it attenuate IBa. Ara-C did not prevent the effect of NGF on IBa. There were three independent components to the action of NGF; during 6–9 days, it increased ω-conotoxin-GVIA–sensitive N-type IBa( IBa,N); increased nifedipine-sensitive L-type IBa( IBa,L) and decreased inactivation of the total Ba2+conductance ( gBa). The latter effect involved a selective decrease in the amplitude of one of the four kinetic components that describe the inactivation process. Total IBawas also 55.8% larger than control in the somata of B cells acutely dissociated from leopard frogs that had received prior subcutaneous injections of NGF. By contrast, injection of NGF antiserum decreased total IBaby 29.4%. There was less inactivation of gBain B cells from NGF-injected animals than in cells from animals injected with NGF antiserum ( P < 0.001). These data suggest that NGF-like molecule(s) play(s) a role in the maintenance of IBain an adult amphibian sympathetic neuron; the presence of NGF may allow the neuron to maintain a constant relationship between cell size and current density. They also show that IBainactivation in an adult neuron can be modulated in a physiologically relevant way by an extracellular ligand.
Right-Left Interactions Between Rostral Scratch Networks Generate Rhythmicity in the Preenlargement Spinal Cord of the Turtle
Authors: Currie Scott N. , Gonsalves Gregory G.
Published: December 2017

Currie, Scott N. and Gregory G. Gonsalves. Right-left interactions between rostral scratch networks generate rhythmicity in the preenlargement spinal cord of the turtle. J. Neurophysiol. 78: 3479–3483, 1997. We examined the rhythmogenic capacity of the midbody D3–D7spinal cord during stimulation of the rostral scratch reflex in turtles. Fictive scratching was recorded bilaterally as electroneurograms (ENGs) from prehindlimb enlargement nerves [transverse D7(TD7) and oblique D7(OD7)] and hip flexor nerves (HF). TD7and OD7innervate transverse- and oblique-abdominus muscles, respectively. D3-end preparations had intact spinal cords caudal to a D2–D3transection site. Unilateral stimulation of the rostral receptive field in D3-end preparations evoked rhythmic bursting in the ipsilateral (ipsi) HF nerve and bilateral rhythmic discharge in the TD7and OD7nerves. Right HF bursts were coactive with right TD7and left OD7bursts and alternated with left TD7and right OD7bursts. D3–D7preparations received a second spinal transection at the caudal end of segment D7, thus resulting in activation of strictly preenlargement circuitry in response to rostral scratch stimulation and preventing activation of hindlimb enlargement circuitry in segments D8–S2. D3–D7preparations responded to unilateral stimulation with modulated or tonic discharge in the ipsi TD7and contralateral (contra) OD7nerves. In contrast, bilateral stimulation reestablished robust bursting in which coactive right TD7-left OD7bursts alternated with coactive left TD7-right OD7bursts. These data imply that TD7circuit modules make 1) crossed excitatory connections with contra OD7circuitry, 2) crossed inhibitory connections with contra TD7circuitry, and 3) uncrossed inhibitory connections with ipsi OD7circuitry. Our results also suggest that bilateral stimulation evokes rhythmic alternation in the preenlargment cord by simultaneously exciting reciprocally inhibitory circuit modules.
Local Field Potential Oscillations in Primate Cerebellar Cortex During Voluntary Movement
Authors: Pellerin Jean-Pierre , Lamarre Yves
Published: December 2017

Pellerin, Jean-Pierre and Yves Lamarre. Local field potential oscillations in primate cerebellar cortex during voluntary movement. J. Neurophysiol. 78: 3502–3507, 1997. Sustained oscillations of 13–18 Hz were observed in local field potentials (LFPs) in the cerebellar cortex of a behaving monkey. These oscillations, which appeared to be generated in the granular cell layer, were particularly prominent in the paramedian lobule. The oscillatory activity decreased during drowsiness or extreme arousal and occurred most often when the animal was immobile but alert. In a task requiring the animal to move the arm ∼1 s after an auditory cue, the oscillations stopped some 150–200 ms after the cue, resumed 200–300 ms later, and stopped again 50–100 ms before movement onset. This modulation pattern was observed with consistency only when the animal responded reliably to the auditory cue. The results suggest that the cerebellum could be involved in some higher level of integration particularly during complex sensorimotor behavior.
Long-Term Plasticity at Excitatory Synapses on Aspinous Interneurons in Area CA1 Lacks Synaptic Specificity
Authors: Cowan A. I. , Stricker C. , Reece L. J. , Redman S. J.
Published: December 2017

Cowan, A. I., C. Stricker, L. J. Reece, and S. J. Redman. Long-term plasticity at excitatory synapses on aspinous interneurons in area CA1 lacks synaptic specificity. J. Neurophysiol. 79: 13–20, 1998. The synaptic specificity of long-term potentiation (LTP) was examined at synapses formed on aspinous dendrites of interneurons whose somata were located in the pyramidal cell layer of hippocampal area CA1. Intracellular recordings from slices prepared from rats were used to monitor excitatory postsynaptic potentials (EPSPs) elicited by extracellular stimulation in stratum radiatum. Two synaptic inputs were evoked at 0.5 Hz by stimulating axons adjacent to stratum pyramidale and s. lacunosum-moleculare. After obtaining baseline recordings (≥10 min), one of the EPSPs was conditioned. The protocol involved tetanic stimulation, sometimes combined with somatic depolarization. Low-frequency stimulation of the two pathways was then resumed and EPSPs were recorded for <30 min. We observed both homosynaptic and heterosynaptic changes in synaptic strength. LTP and long-term depression (LTD) were seen in both pathways and all possible combinations of changes in the two EPSPs were observed, including heterosynaptic LTP associated with either homosynaptic LTP or LTD. Intracellular 1,2-bis (2-aminophenoxy)-ethane- N, N, N′, N′-tetraacetic acid (10 mM) abolished alterations in synaptic strength. When axons in s. radiatum synapse onto a spiny pyramidal cell, synaptic specificity of LTP is preserved. However the results obtained from aspinous interneurons show that synaptic specificity of LTP is lost. These results are consistent with the hypothesis that spines provide postsynaptic mechanism(s) for conferring specificity to LTP.
Vibration-Induced Postural Posteffects
Authors: Wierzbicka M. M. , Gilhodes J. C. , Roll J. P.
Published: December 2017

Wierzbicka, M. M., J. C. Gilhodes, and J. P. Roll. Vibration-induced postural posteffects. J. Neurophysiol. 79: 143–150, 1998. It generally is known that vibration of various muscles in free-standing subjects evokes a spatially oriented postural response. Furthermore, it recently has been shown that when a vibratory stimulus is terminated, a powerful involuntary contraction of the previously vibrated muscle often occurs that, under the isotonic condition, is accompanied by movement of a limb. The aim of this study was to explore effects of a low-amplitude mechanical vibration, applied in a seated position, on the standing posture. The 30-s vibration was applied bilaterally at the ankle level to anterior or posterior tendons and at the cervical level in front or back of the neck, at one site only at a time. Center of pressure trajectories were monitored during quiet stance for ≤19 min after the offset of vibration, and these measurements were compared with a previbration control trial. The results clearly indicate that vibration produced in all subjects strong, long-lasting dynamical modification of posture mainly in the anterior-posterior direction. Spatial orientation of the induced postvibratory shift in posture was dependent on the vibration side. We conclude that sustained Ia sensory inflow, evoked by vibration, has a powerful after-effect on the motor system at the postural level.
Envelope Coding in the Lateral Superior Olive. III. Comparison With Afferent Pathways
Authors: Joris Philip X. , Yin Tom C. T.
Published: December 2017

Joris, Philip X. and Tom C. T. Yin. Envelope coding in the lateral superior olive. III. Comparison with afferent pathways. J. Neurophysiol. 79: 253–269, 1998. Binaural cues for spatial localization of complex high-frequency sounds are interaural level and time differences (ILDs and ITDs). We previously showed that cells in the lateral superior olive (LSO) are sensitive to ITDs in the envelope of sinusoidally amplitude-modulated (AM) signals up to a modulation frequency of only ∼800 Hz. To understand the limitations in this ITD-sensitivity, we here compare responses to monaural modulation in LSO and its input pathways, derived from cochlear nucleus and medial nucleus of the trapezoid body. These pathways have marked functional and morphological specializations, suggestive of adaptations for timing. Afferent cell populations were identified on the basis of electrophysiological signatures, and for each population, average firing rate and synchronization to AM tones were compared with auditory-nerve fibers and LSO cells. Except for an increase in modulation gain in some subpopulations, synchronization of LSO afferents was very similar to that in auditory nerve fibers in its dependency on sound pressure level (SPL), modulation depth, and modulation frequency. Distributions of cutoff frequencies of modulation transfer functions were largely coextensive with the distribution in auditory nerve. Group delays, measured from the phase of the response modulation as a function of modulation frequency, showed an orderly dependence on characteristic frequency and cell type and little dependence on SPL. Similar responses were obtained to a modulated broadband carrier. Compared with their afferents, LSO cells synchronized to monaurally modulated stimuli with a higher gain but often over a narrower range of modulation frequencies. Considering the scatter in afferent and LSO cell populations, ipsi- and contralateral responses were well matched in cutoff frequency and magnitude of delays. In contrast to their afferents, LSO cells show a decrease in average firing rate at high modulation frequencies. We conclude that the restricted modulation frequency range over which LSO cells show ITD-sensitivity does not result from loss of envelope information along the afferent pathway but is due to convergence or postsynaptic effects at the level of the LSO. The faithful transmission of envelope phase-locking in LSO afferents is consistent with their physiological and morphological adaptations, but these adaptations are not commensurate with the rather small effects of physiological ITDs reported previously, especially when compared with effects of ILDs. We suggest that these adaptations have evolved to allow a comparison of instantaneous amplitude fluctuations at the two ears rather than to extract interaural timing information per se.