bluuebunny/crossref_metadata_2025 huggingface dataset:
Chronic Morphine Treatment Alters Endogenous Opioid Control of Hippocampal Mossy Fiber Synaptic Transmission
Authors: Harrison John M. , Allen Richard G. , Pellegrino Michael J. , Williams John T. , Manzoni Olivier J.
Published: December 2017

Synaptic adaptations are thought to be an important component of the consequences of drug abuse. One such adaptation is an up-regulation of adenylyl cyclase that has been shown to increase transmitter release at several inhibitory synapses. In this study the effects of chronic morphine treatment were studied on mossy fiber synapses in the guinea pig hippocampus using extracellular field potential recordings. This opioid-sensitive synapse was chosen because of the known role of the adenylyl cyclase cascade in the regulation of glutamate release. Long-term potentiation (LTP) at the mossy fiber synapse was enhanced after chronic morphine treatment. In control animals, opioid antagonists increased LTP but had no effect in morphine-treated guinea pigs. In contrast, the long-lasting depression of transmission induced by a mGluR agonist and CA1 LTP were not altered. Chronic morphine treatment neither caused tolerance to μ- and κ-receptor–mediated inhibition at the mossy fiber synapse nor modified total hippocampal dynorphin levels. The results suggest that the phasic inhibition of glutamate transmission mediated by endogenous opioids is reduced after chronic exposure to morphine.
Muscle Tone Facilitation and Inhibition After Orexin-A (Hypocretin-1) Microinjections Into the Medial Medulla
Authors: Mileykovskiy Boris Y. , Kiyashchenko Lyudmila I. , Siegel Jerome M.
Published: December 2017

Orexins/hypocretins are synthesized in neurons of the perifornical, dorsomedial, lateral, and posterior hypothalamus. A loss of hypocretin neurons has been found in human narcolepsy, which is characterized by sudden loss of muscle tone, called cataplexy, and sleepiness. The normal functional role of these neurons, however, is unclear. The medioventral medullary region, including gigantocellular reticular nucleus, alpha (GiA) and ventral (GiV) parts, participates in the induction of locomotion and muscle tone facilitation in decerebrate animals and receives moderate orexinergic innervation. In the present study, we have examined the role of orexin-A (OX-A) in muscle tone control using microinjections (50 μM, 0.3 μl) into the GiA and GiV sites in decerebrate rats. OX-A microinjections into GiA sites, previously identified by electrical stimulation as facilitating hindlimb muscle tone bilaterally, produced a bilateral increase of muscle tone in the same muscles. Bilateral lidocaine microinjections (4%, 0.3 μl) into the dorsolateral mesopontine reticular formation decreased muscle rigidity and blocked muscle tone facilitation produced by OX-A microinjections into the GiA sites. The activity of cells related to muscle rigidity, located in the pedunculopontine tegmental nucleus and adjacent reticular formation, was correlated positively with the extent of hindlimb muscle tone facilitation after medullary OX-A microinjections. OX-A microinjections into GiV sites were less effective in muscle tone facilitation, although these sites produced a muscle tone increase during electrical stimulation. In contrast, OX-A microinjections into the gigantocellular nucleus (Gi) sites and dorsal paragigantocellular nucleus (DPGi) sites, previously identified by electrical stimulation as inhibitory points, produced bilateral hindlimb muscle atonia. We propose that the medioventral medullary region is one of the brain stem target for OX-A modulation of muscle tone. Facilitation of muscle tone after OX-A microinjections into this region is linked to activation of intrinsic reticular cells, causing excitation of midbrain and pontine neurons participating in muscle tone facilitation through an ascending pathway. Moreover, our results suggest that OX-A may also regulate the activity of medullary neurons participating in muscle tone suppression. Loss of OX function may, therefore, disturb both muscle tone facilitatory and inhibitory processes at the medullary level.
Developmental Changes in the Density of Ionic Currents in Antennal-Lobe Neurons of the Sphinx Moth,Manduca sexta
Authors: Mercer Alison R. , Hildebrand John G.
Published: December 2017

Early in metamorphic adult development, action potentials elicited from Manduca sexta antennal lobe neurons are small in amplitude, long in duration, and calcium dependent. As development proceeds, the action potential waveform becomes larger in amplitude, shorter in duration, and increasingly sodium dependent. Whole cell voltage-clamp analysis of Manduca antennal-lobe neurons in vitro has been used to identify voltage-activated currents that contribute to developmental changes in the electrical excitability of these cells. Proximal Branching neurons [putative projection (output) neurons] and Rick Rack neurons (putative local antennal-lobe interneurons) are examined in detail early (pupal stage 5) and late (pupal stage 14) in adult metamorphosis. In both cell types, four voltage-gated and two calcium-dependent ionic currents have been identified. Cell-type–specific changes in the density of sodium, calcium, and potassium currents correlate temporally with changes in cell excitability and spike waveform. Developmental changes in ionic current profiles are accompanied also by the emergence of cell-type–specific response characteristics in the cells. Together with the accompanying paper, this study provides an important foundation for examining the impact of developmental changes in electrical excitability on the growth, electrical properties and connectivity of neurons in central olfactory pathways of the moth.
Role of Arcuate Frontal Cortex of Monkeys in Smooth Pursuit Eye Movements. I. Basic Response Properties to Retinal Image Motion and Position
Authors: Tanaka Masaki , Lisberger Stephen G.
Published: December 2017

Anatomical and physiological studies have shown that the “frontal pursuit area” (FPA) in the arcuate cortex of monkeys is involved in the control of smooth pursuit eye movements. To further analyze the signals carried by the FPA, we examined the activity of pursuit-related neurons recorded from a discrete region near the arcuate spur during a variety of oculomotor tasks. Pursuit neurons showed direction tuning with a wide range of preferred directions and a mean full width at half-maximum of 129°. Analysis of latency using the “receiver operating characteristic” to compare responses to target motion in opposite directions showed that the directional response of 58% of FPA neurons led the initiation of pursuit, while 19% led by 25 ms or more. Analysis of neuronal responses during pursuit of a range of target velocities revealed that the sensitivity to eye velocity was larger during the initiation of pursuit than during the maintenance of pursuit, consistent with two components of firing related to image motion and eye motion. FPA neurons showed correlates of two behavioral features of pursuit documented in prior reports. 1) Eye acceleration at the initiation of pursuit declines as a function of the eccentricity of the moving target. FPA neurons show decreased firing at the initiation of pursuit in parallel with the decline in eye acceleration. This finding is consistent with prior suggestions that the FPA plays a role in modulating the gain of visual-motor transmission for pursuit. 2) A stationary eccentric cue evokes a smooth eye movement opposite in direction to the cue and enhances the pursuit evoked by subsequent target motions. Many pursuit neurons in the FPA showed weak, phasic visual responses for stationary targets and were tuned for the positions about 4° eccentric on the side opposite to the preferred pursuit direction. However, few neurons (12%) responded during the preparation or execution of saccades. The responses to the stationary target could account for the behavioral effects of stationary, eccentric cues. Further analysis of the relationship between firing rate and retinal position error during pursuit in the preferred and opposite directions failed to provide evidence for a large contribution of image position to the firing of FPA neurons. We conclude that FPA processes information in terms of image and eye velocity and that it is functionally separate from the saccadic frontal eye fields, which processes information in terms of retinal image position.
Role of L-Type Ca2+ Channels in Transmitter Release From Mammalian Inner Hair Cells. II. Single-Neuron Activity
Authors: Robertson Donald , Paki Bardia
Published: December 2017

Previously reported changes in the gross sound-evoked cochlear potentials after intracochlear perfusion of nimodipine suggest that dihydropyridine-sensitive Ca2+ channels (L-type) control the sound-evoked release of transmitter from the inner hair cells of the mammalian cochlea. In the present study, we combined recording of the action potentials of single primary auditory afferent neurons with intracochlear perfusion to further investigate the role of voltage-gated Ca2+ channels at this synapse. Spontaneous action potential firing rates were depressed by the L-type channel blocker nimodipine, but were elevated by S(−) BAY K8644, an L-type channel agonist. Sound-evoked responses of single primary afferents were depressed by nimodipine in a manner that was consistent with a block at the inner hair cell-afferent dendrite synapse. Perfusions with solutions containing the N-type channel blocker conotoxin GVIA did not differ in their effects from control artificial perilymph perfusions. The results extend the conclusions of the earlier study by showing that L-type Ca2+channels are primarily responsible for controlling both spontaneous and sound-evoked transmitter release from inner hair cells. In addition it was found that afferent neurons with widely different spontaneous firing rates were all sensitive to nimodipine and to BAY K8644, suggesting that the multiple synaptic outputs of each inner hair cell are under the control of only one major type of Ca2+ channel.
Dendritic Resonance in Rat Neocortical Pyramidal Cells
Authors: Ulrich Daniel
Published: December 2017

Dendritic integration of synaptic signals is likely to be an important process by which nerve cells encode synaptic input into spike output. However, the response properties of dendrites to time-varying inputs are largely unknown. Here, I determine the transfer impedance of the apical dendrite in layer V pyramidal cells by dual whole cell patch-clamp recordings in slices of rat somatosensory cortex. Sinusoidal current waveforms of linearly changing frequencies (0.1–25 Hz) were alternately injected into the soma or apical dendrite and the resulting voltage oscillations recorded by the second electrode. Dendrosomatic and somatodendritic transfer impedances were calculated by Fourier analysis. At near physiological temperatures ( T∼35°C), the transfer impedance had a maximal magnitude at low frequencies ( f res ∼6 Hz). In addition, voltage led current up to ∼3 Hz, followed by a current lead over voltage at higher frequencies. Thus the transfer impedance of the apical dendrite is characterized by a low-frequency resonance. The frequency of the resonance was voltage dependent, and its strength increased with dendritic distance. The resonance was completely abolished by the I h channel blocker ZD 7288. Dendrosomatic and somatodendritic transfer properties of the apical dendrite were independent of direction or amplitude of the input current, and the responses of individual versus distributed inputs were additive, thus implying linearity. For just threshold current injections, action potentials were generated preferentially at the resonating frequency. I conclude that due to the interplay of a sag current ( I h) with the membrane capacitance, layer V pyramids can act as linear band-pass filters with a frequency preference in the theta frequency band.
Gain Control in Human Smooth-Pursuit Eye Movements
Authors: Churchland Anne K. , Lisberger Stephen G.
Published: December 2017

In previous experiments, on-line modulation of the gain of visual-motor transmission for pursuit eye movements was demonstrated in monkeys by showing that the response to a brief perturbation of target motion was strongly enhanced during pursuit relative to during fixation. The present paper elaborates the properties of on-line gain control by recording the smooth-pursuit eye movements of human subjects during tracking of a spot target. When perturbations consisted of one cycle of a 5-Hz sine wave, responses were significantly larger during pursuit than during fixation. Furthermore, responses grew as a function of eye/target velocity at the time of the perturbation and of perturbation amplitude. Thus human pursuit, like monkey pursuit, is modulated by on-line gain control. For larger perturbations consisting of a single sine wave at 2.8 Hz, ±19°/s, the degree of enhancement depended strongly on the phase of the perturbation. Enhancement was present when “peak-first” perturbations caused the target speed to increase first and was attenuated when “peak-last” perturbations caused target speed to decrease first. This effect was most profound when the perturbation was 2.8 Hz, ±19°/s but was also present when the amplitude of the peak-last perturbation was ±5o/s. For peak-last perturbations, the eye velocity evoked by the later peak of the perturbation was inversely related to that evoked by the preceding trough of the perturbation. We interpret these effects of perturbation phase as evidence that peak-last perturbations cause a decrease in the on-line gain of visual-motor transmission for pursuit. We conclude that gain control is modulated dynamically as behavioral conditions change. Finally, when perturbations were presented as a sequence of three large, peak-last sine waves starting at the onset of target motion at 10°/s, repeating the conditions used in prior studies on humans, we were able to replicate the prior finding that the response to the perturbations was equal during pursuit and fixation. We conclude that on-line gain control modulates human pursuit and that it can be probed most reliably with small, brief perturbations that do not affect the on-line gain themselves.
K+ Currents Generated by NMDA Receptor Activation in Rat Hippocampal Pyramidal Neurons
Authors: Shah Mala M. , Haylett Dennis G.
Published: December 2017

Long lasting outward currents mediated by Ca2+-activated K+ channels can be induced by Ca2+ influx through N-methyl-d-aspartate (NMDA)-receptor channels in voltage-clamped hippocampal pyramidal neurons. Using specific inhibitors, we have attempted to identify the channels that underlie these outward currents. At a holding potential of −50 mV, applications of 1 mM NMDA to the soma of cultured hippocampal pyramidal neurons induced the expected inward currents. In 44% of cells tested, these were followed by outward currents (average amplitude 60 ± 7 pA) that peaked 2.5 s after the initiation of the inward NMDA currents and decayed with a time constant of 1.4 s. In 43% of those cells exhibiting an outward current, SK channel inhibitors, UCL 1848 (100 nM) and apamin (100 nM) abolished the outward current. In the remainder of the cells, the outward currents were either insensitive or only partly inhibited (44 ± 4%) by 100 nM UCL 1848. In these cells, the outward currents were reduced by the slow afterhyperpolarization (sAHP) inhibitors, muscarine (3 μM; 43 ± 9%), UCL 1880 (3 μM; 34 ± 10%), and UCL 2027 (3 μM; 57 ± 6%). Neither the BK channel inhibitor, charybdotoxin (100 nM), nor the Na+/K+ ATPase inhibitor, ouabain (100 μM), reduced these outward currents. Irrespective of the pharmacology, the time course of the outward current did not differ. Interestingly, no correlation was observed between the presence of a slow apamin-insensitive afterhyperpolarization and an outward current insensitive to SK channel blockers following NMDA-receptor activation. It is concluded that an NMDA-mediated rise in [Ca2+]i can result in the activation of apamin-sensitive SK channels and of the channels that underlie the sAHP. The activation of these channels may, however, depend on their location relative to NMDA receptors as well as on the spatial Ca2+ buffering within individual neurons.
Effects of Pedunculopontine Nucleus (PPN) Stimulation on Caudal Pontine Reticular Formation (PnC) Neurons In Vitro
Authors: Homma Yutaka , Skinner R. D. , Garcia-Rill E.
Published: December 2017

Stimulation of the pedunculopontine nucleus (PPN) is known to induce changes in arousal and postural/locomotor states. Previously, PPN stimulation was reported to induce prolonged responses (PRs) in extracellularly recorded PnC neurons in the decerebrate cat. The present study used intracellular recordings in semihorizontal slices from rat brain stem ( postnatal days 12–21) to determine responses in PnC neurons following PPN stimulation. Two-thirds (65%) of PnC neurons showed PRs after PPN stimulation. PnC neurons with PRs had higher amplitude afterhyperpolarizations (AHP) than non-PR (NPR) neurons. Both PR and NPR neurons were of mixed cell types characterized by “A” and/or “LTS,” or neither of these types of currents. PnC cells showed decreased AHP duration with age, due mostly to decreased AHP duration in NPR cells. The longest mean duration PRs were induced by stimulation at 60 and 90 Hz compared with 10 or 30 Hz. Maximal firing rates in PnC cells during PRs were induced by PPN stimulation at 60 Hz compared with 10, 30, or 90 Hz. BaCl2superfusion blocked PPN stimulation-induced PRs, suggesting that PRs may be mediated by blockade of potassium channels, in keeping with increased input resistance observed during PRs. Depolarizing pulses failed to elicit, and hyperpolarizing pulses failed to reset, PPN stimulation-induced PRs, suggesting that PRs may not be plateau potentials. Pharmacological testing revealed that nifedipine superfusion failed to block PPN stimulation-induced PRs; i.e., PRs may not be calcium channel-dependent. The muscarinic cholinergic agonist carbachol induced depolarization in most PR neurons tested, and the muscarinic cholinergic antagonist scopolamine reduced or blocked PPN stimulation-induced PRs in some PnC neurons, suggesting that some PRs may be due to muscarinic receptor activation. The nonspecific ionotropic glutamate receptor antagonist kynurenic acid failed to block PPN stimulation-induced PRs, as did the metabotropic glutamate receptor antagonist (R, S)-αmethyl-4-carboxyphenylglycine, suggesting that PRs may not be mediated by glutamate receptors. These findings suggest that PPN stimulation-induced PRs may be due to increased excitability following closing of muscarinic receptor-sensitive potassium channels, allowing PnC neurons to respond to a transient, frequency-dependent depolarization with long-lasting stable states. PPN stimulation appears to induce PRs using parameters known best to induce locomotion. This mechanism may be related to switching from one state to another (e.g., locomotion vs. standing or sitting, waking vs. non-REM sleep or REM sleep).
Control of Foot Trajectory in Human Locomotion: Role of Ground Contact Forces in Simulated Reduced Gravity
Authors: Ivanenko Y. P. , Grasso R. , Macellari V. , Lacquaniti F.
Published: December 2017

We studied the changes of vertical contact forces, lower limb kinematics, and electromyographic activity (EMG) at different speeds and gravitational loads. To this end healthy subjects were asked to walk on a motorized treadmill while the percentage of body weight unloaded (body weight support, BWS) was modified in steps by means of a well-characterized unloading system. BWS was set at 0, 35, 50, 75, 95, or 100% of body weight. Walking speed was 0.7, 1.1, 2, 3, or 5 km/h. We found that changing BWS between 0 and 95% resulted in drastic changes of kinetic parameters but in limited changes of the kinematic coordination. In particular, the peak vertical contact forces decreased proportionally to BWS; at 95%-BWS they were 20-fold smaller than at 0% and were applied at the forefoot only. Also, there were considerable changes of the amplitude of EMG activity of all tested lower limb muscles and a complex re-organization of the pattern of activity of thigh muscles. By contrast, the corresponding variation of the parameters that describe shape and variability of the foot path was very limited, always <30% of the corresponding values at 0 BWS. Moreover, the planar co-variation of the elevation angles was obeyed at all speed and BWS values. Minimum variance of limb trajectory occurred at 3 km/h. At 100% BWS, subjects stepped in the air, their feet oscillating back and forth just above but never contacting the treadmill. In this case, step-to-step variability of foot path was much greater than at all other BWS levels but was restored to lower values when minimal surrogate contact forces were provided during the “stance” phase. The results did not depend on the specific instruction given to the subject. Therefore we conclude that minimal contact forces are sufficient for accurate foot trajectory control.
Two Types of Network Oscillations and Their Odor Responses in the Primary Olfactory Center of a Terrestrial Mollusk
Authors: Inokuma Yasuko , Inoue Tsuyoshi , Watanabe Satoshi , Kirino Yutaka
Published: December 2017

We identified two classes of network oscillations with different frequency ranges in the tentacle ganglion (TG), the primary olfactory center of the terrestrial mollusk Limax marginatus, and investigated the responses of these oscillations to odor inputs. A recent study indicated that there are serotonergic terminals in the TG. We found that when serotonin was applied to the TG, the spontaneous network oscillation of about 1.5 Hz in the TG changed its oscillatory frequency to 0.5 Hz. These two oscillations are distinct, because 1) in most cases, the application of serotonin to the TG initially inhibited the 1.5-Hz oscillation and subsequently generated the slow 0.5-Hz oscillation; and 2) occasionally, the application of serotonin did not inhibit the spontaneous 1.5-Hz oscillation, resulting in the coexistence of two network oscillations. Thus the TG has two different oscillatory dynamics. We named the spontaneous 1.5-Hz oscillation the fast oscillation (FO), and the serotonin-induced 0.5-Hz oscillation the slow oscillation (SO). By calculating the spatial coherence of the TG oscillations, we found that the FO is a noncoherent oscillatory mode and the SO is a coherent oscillatory mode. Finally, odor presentation to the olfactory receptors selectively modulated the SO by decreasing the oscillatory amplitude, but the FO was not modulated by the odor input. These results indicate that 1) the TG has two oscillatory states (FO and SO) and these states are changed by the extracellular level of serotonin, and 2) these two oscillatory states have different responses to odors.
Intrinsic Neuronal Properties of the Chick Nucleus Angularis
Authors: Soares Daphne , Chitwood Raymond A. , Hyson Richard L. , Carr Catherine E.
Published: December 2017

In vitro whole cell recording revealed intrinsic firing properties and single-cell morphology in the cochlear nucleus angularis (NA) of the chick. We classified three major classes of neurons: one-spike, damped, and tonic. A delayed inward rectifying current was observed in all classes during hyperpolarization injections. One-spike neurons responded with a single spike to depolarizing current injection and had small (stubby) radiate dendritic trees. Damped neurons responded with only a few spikes at the onset of positive current injection. More positive current inputs led to a damped response. Damped cell dendrites had a planar orientation parallel to the isofrequency axis in NA. Tonic cells produced trains of action potentials in response to a depolarizing current injection. Three variations of the tonic type had multipolar morphology, with dendrites oriented either radially (I and III) or perpendicular to the tonotopic axis (II; vertical). Tonics I and III differed in the shape of their action potential undershoot. Thus NA is both physiologically and morphologically heterogeneous.
Sensory Integration in Presynaptic Inhibitory Pathways During Fictive Locomotion in the Cat
Authors: Ménard Ariane , Leblond Hugues , Gossard Jean-Pierre
Published: December 2017

The aim of this study is to understand how sensory inputs of different modalities are integrated into spinal cord pathways controlling presynaptic inhibition during locomotion. Primary afferent depolarization (PAD), an estimate of presynaptic inhibition, was recorded intra-axonally in group I afferents ( n = 31) from seven hindlimb muscles in L6–S1 segments during fictive locomotion in the decerebrate cat. PADs were evoked by stimulating alternatively low-threshold afferents from a flexor nerve, a cutaneous nerve and a combination of both. The fictive step cycle was divided in five bins and PADs were averaged in each bin and their amplitude compared. PADs evoked by muscle stimuli alone showed a significant phase-dependent modulation in 20/31 group I afferents. In 12/20 afferents, the cutaneous stimuli alone evoked a phase-dependent modulation of primary afferent hyperpolarization (PAH, n = 9) or of PADs ( n = 3). Combining the two sensory modalities showed that cutaneous volleys could significantly modify the amplitude of PADs evoked by muscle stimuli in at least one part (bin) of the step cycle in 17/31 (55%) of group I afferents. The most common effect (13/17) was a decrease in the PAD amplitude by 35% on average, whereas it was increased by 17% on average in the others (4/17). Moreover, in 8/13 afferents, the PAD reduction was obtained in 4/5 bins i.e., for most of the duration of the step cycle. These effects were seen in group I afferents from all seven muscles. On the other hand, we found that different cutaneous nerves had quite different efficacy; the superficial peroneal (SP) being the most efficient (85% of trials) followed by Saphenous (60%) and caudal sural (44%) nerves. The results indicate that cutaneous interneurons may act, in part, by modulating the transmission in PAD pathways activated by group I muscle afferents. We conclude that cutaneous input, especially from the skin area on the dorsum of the paw (SP), could subtract presynaptic inhibition in some group I afferents during perturbations of stepping (e.g., hitting an obstacle) and could thus adjust the influence of proprioceptive feedback onto motoneuronal excitability.
T-Type Calcium Channel α1G and α1H Subunits in Human Retinoblastoma Cells and Their Loss After Differentiation
Authors: Hirooka Kazuyuki , Bertolesi Gabriel E. , Kelly Melanie E. M. , Denovan-Wright Eileen M. , Sun Xiaolu , Hamid Jawed , Zamponi Gerald W. , Juhasz Alexander E. , Haynes Lawrence W. , Barnes Steven
Published: December 2017

Human retinoblastoma cells are multipotent retinal precursor cells capable of differentiating into photoreceptors, neurons, and glia. The current-voltage relation of the undifferentiated cells is dominated by a transient inward current that disappears shortly after differentiation. In 20 mM Ba2+-containing bath solutions, the current has an activation midpoint near −25 mV and appears to be fully inactivated at −20 mV. Sr2+and Ca2+ are preferred charge carriers relative to Ba2+, and the current vanishes in the absence of these divalent cations. Cd2+ blocks the current with an IC50 of 160 μM, and Ni2+ blocks in a biphasic manner with IC50s of 22 and 352 μM. The current is unaffected when sodium is replaced with other monovalent cations, and it is insensitive to nifedipine, ω-conotoxin GVIA, ω-agatoxin IVA, and ω-conotoxin MVIIC. RT-PCR revealed the presence of α1G and α1H mRNA in undifferentiated cells, but following differentiation, a striking reduction of both α1G and α1H mRNA was found, and this was paralleled by the loss of T-type Ca channel currents. α1I subunit mRNA levels were low in undifferentiated and differentiated cells. These results suggest that T-type Ca channels could play a role in undifferentiated retinoblastoma cell physiology since α1G and α1H Ca channel subunit expression is reduced in cells that have differentiated and exited the cell cycle.
AMRP Peptides Modulate a Novel K+ Current in Pleural Sensory Neurons of Aplysia
Authors: McDearmid Jonathan R. , Brezina Vladimir , Weiss Klaudiusz R.
Published: December 2017

Modulation of Aplysia mechanosensory neurons is thought to underlie plasticity of defensive behaviors that are mediated by these neurons. In the past, identification of modulators that act on the sensory neurons and characterization of their actions has been instrumental in providing insight into the functional role of the sensory neurons in the defensive behaviors. Motivated by this precedent and a recent report of the presence of Aplysia Mytilusinhibitory peptide-related (AMRP) neuropeptides in the neuropile and neurons of the pleural ganglia, we sought to determine whether and how pleural sensory neurons respond to the AMRPs. In cultured pleural sensory neurons under voltage clamp, AMRPs elicited a relatively rapidly developing, then partially desensitizing, outward current. The current exhibited outward rectification; in normal 10 mM K+, it was outward at membrane potentials more positive than −80 mV but disappeared without reversing at more negative potentials. When external K+ was elevated to 100 mM, the AMRP-elicited current reversed around −25 mV; the shift in reversal potential was as expected for a current carried primarily by K+. In the high-K+ solution, the reversed current began to decrease at potentials more negative than −60 mV, creating a region of negative slope resistance in the I-V relationship. The AMRP-elicited K+ current was blocked by extremely low concentrations of 4-aminopyridine (4-AP; IC50= 1.7 × 10−7 M) but was not very sensitive to TEA. In cell-attached patches, AMRPs applied outside the patch—thus presumably through a diffusible messenger—increased the activity of a K+ channel that very likely underlies the macroscopic current. The single-channel current exhibited outward rectification, and the open probability of the channel decreased with hyperpolarization; together, these two factors accounted for the outward rectification of the macroscopic current. Submicromolar 4-AP included in the patch pipette blocked the channel by reducing its open probability without altering the single-channel current. Based on the characteristics of the AMRP-modulated K+ current, we conclude that it is a novel current that has not been previously described in Aplysia mechanosensory neurons. In addition to this current, two other AMRP-elicited currents, a slow, 4-AP-resistant outward current and a Na+-dependent inward current, were occasionally observed in the cultured sensory neurons. Responses consistent with all three currents were observed in sensory neurons in situ in intact pleural ganglia.
Effect of Strength and Speed of Torque Development on Balance Recovery With the Ankle Strategy
Authors: Robinovitch Stephen N. , Heller Britta , Lui Andrew , Cortez Jeffrey
Published: December 2017

In the event of an unexpected disturbance to balance, the ability to recover a stable upright stance should depend not only on the magnitude of torque that can be generated by contraction of muscles spanning the lower extremity joints but also on how quickly these torques can be developed. In the present study, we used a combination of experimental and mathematical models of balance recovery by sway (feet in place responses) to test this hypothesis. Twenty-three young subjects participated in experiments in which they were supported in an inclined standing position by a horizontal tether and instructed to recover balance by contracting only their ankle muscles. The maximum lean angle where they could recover balance without release of the tether (static recovery limit) averaged 14.9 ± 1.4° (mean ± SD). The maximum initial lean angle where they could recover balance after the tether was unexpectedly released and the ankles were initially relaxed (dynamic recovery limit) averaged 5.9 ± 1.1°, or 60 ± 11% smaller than the static recovery limit. Peak ankle torque did not differ significantly between the two conditions (and averaged 116 ± 32 Nm), indicating the strong effect on recovery ability of latencies in the onset and subsequent rates of torque generation (which averaged 99 ± 13 ms and 372 ± 267 N · m/s, respectively). Additional experiments indicated that dynamic recovery limits increased 11 ± 14% with increases in the baseline ankle torques prior to release (from an average value of 31 ± 18 to 54 ± 24 N · m). These trends are in agreement with predictions from a computer simulation based on an inverted pendulum model, which illustrate the specific combinations of baseline ankle torque, rate of torque generation, and peak ankle torque that are required to attain target recovery limits.
Excitatory Mechanisms in the Suprachiasmatic Nucleus: The Role of AMPA/KA Glutamate Receptors
Authors: Michel Stephan , Itri Jason , Colwell Christopher S.
Published: December 2017

A variety of evidence suggests that the effects of light on the mammalian circadian system are mediated by direct retinal ganglion cell projection to the suprachiasmatic nucleus (SCN). This synaptic connection is glutamatergic and the release of glutamate is detected by both N-methyl-d-asparate (NMDA) and amino-methyl proprionic acid/kainate (AMPA/KA) iontotropic glutamate receptors (GluRs). It is well established that NMDA GluRs play a critical role in mediating the effects of light on the circadian system; however, the role of AMPA/KA GluRs has received less attention. In the present study, we sought to better understand the contribution of AMPA/KA-mediated currents in the circadian system based in the SCN. First, whole cell patch-clamp electrophysiological techniques were utilized to measure spontaneous excitatory postsynaptic currents (sEPSCs) from SCN neurons. These currents were widespread in the SCN and not just restricted to the retino-recipient region. The sEPSC frequency and amplitude did not vary with the daily cycle. Similarly, currents evoked by the exogenous application of AMPA onto SCN neurons were widespread within the SCN and did not exhibit a diurnal rhythm in their magnitude. Fluorometric techniques were utilized to estimate AMPA-induced calcium (Ca2+) concentration changes in SCN neurons. The resulting data indicate that AMPA-evoked Ca2+transients were widespread in the SCN and that there was a daily rhythm in the magnitude of AMPA-induced Ca2+transients that peaked during the night. By itself, blocking AMPA/KA GluRs with a receptor blocker decreased the spontaneous firing of some SCN neurons as well as reduced resting Ca2+levels, suggesting tonic glutamatergic excitation. Finally, immunohistochemical techniques were used to describe expression of the AMPA-preferring GluR subunits GluR1 and GluR2/3s within the SCN. Overall, our data suggest that glutamatergic synaptic transmission mediated by AMPA/KA GluRs play an important role throughout the SCN synaptic circuitry.
Developmental Regulation of Neuronal KCaChannels by TGFβ1: An Essential Role for PI3 Kinase Signaling and Membrane Insertion
Authors: Lhuillier Loic , Dryer Stuart E.
Published: December 2017

TGFβ1 is a target-derived factor responsible for the developmental expression of large-conductance Ca2+-activated K+(KCa) channels in ciliary neurons of the chick ciliary ganglion. The acute effects of TGFβ1 on KCachannels are mediated by posttranslational events and require activation of the MAP kinase Erk. Here we show that TGFβ1 evokes robust phosphorylation of Akt/PKB, a protein kinase dependent on the products of phosphatidylinositol 3-OH kinase (PI3K). TGFβ1-evoked stimulation of KCachannels is blocked by the PI3K inhibitors wortmannin and LY294002. These drugs also inhibit TGFβ1 effects on Akt/PKB phosphorylation but have no effect on TGFβ1-evoked Erk activation. Application of the MEK1 inhibitor PD98059 blocked TGFβ1 effects on Erk but had no effect on Akt/PKB phosphorylation. These results indicate that PI3K and Erk represent parallel signaling cascades activated by TGFβ1 in ciliary neurons. The effects of TGFβ1 on functional expression of KCaare blocked by the microtubule inhibitors colchicine and nocodazole, by botulinum toxins A and E, and by brefeldin-A, an agent that disrupts the Golgi apparatus. These data indicate that translocation of a membrane protein, possibly Slowpoke (SLO), is required for the acute posttranslational effects of TGFβ1 on KCachannels. Confocal immunofluorescence studies with three different SLO antisera showed robust expression of SLO in multiple intracellular compartments of embryonic day 9–13 ciliary neurons, including the cell nucleus. These data suggest that TGFβ1 evokes insertion of SLO channels into the plasma membrane as a result of signaling cascades that entail activation of Erk and PI3K.
Regulation of the Retinal Bipolar Cell mGluR6 Pathway by Calcineurin
Authors: Snellman Josefin , Nawy Scott
Published: December 2017

Glutamate produces a hyperpolarizing postsynaptic potential inon bipolar cells by binding to the metabotropic receptor mGluR6 and subsequently closing a cation-selective channel. It has been proposed that Ca2+influx through the cation channel triggers a depression of the synaptic potential. Here we report that this Ca2+-mediated depression requires activation of calcineurin, a Ca2+/calmodulin-regulated phosphatase. We measured glutamate-evoked currents ( Iglu) with whole cell recordings ofon bipolar cells in light-adapted retinal slices. Depression of Igluby Ca2+was prevented by inhibitors of calcineurin or by tightly buffering Ca2+with bis-( o-aminophenoxy)- N,N,N′,N′-tetraacetic acid (BAPTA). However, when cells were dialyzed with BAPTA and a Ca2+-independent form of calcineurin (CaN420), depression of Igluwas restored. Similarly, CaN420 induced depression of Igluduring continuous glutamate application, a protocol that ordinarily prevents depression. Analysis of changes in the amplitude of the cation-selective current ( Icat) of cells that were dialyzed with high Ca2+(1 μM), or with BAPTA and CaN420, indicates that Ca2+depresses Igluby reducing Icatand that calcineurin acts via the same mechanism. Ca2+-mediated depression of Igluwas not found to involve CaMKII, as inhibitors of CaMKII did not prevent this depression nor did they affect the sensitivity of the response to small changes in the concentration of mGluR6 agonist. Our data suggest that Ca2+and calcineurin may play an adaptive role at the synapse between photoreceptor and on bipolar cells, closing postsynaptic cation channels that are opened by a drop in synaptic glutamate levels during prolonged photoreceptor illumination.
Responses of Reticulospinal Neurons in Intact Lamprey to Pitch Tilt
Authors: Pavlova E. L. , Deliagina T. G.
Published: December 2017

In the swimming lamprey, a postural control system maintains a definite orientation of the animal's longitudinal axis in relation to the horizon (pitch angle). Operation of this system is based on vestibular reflexes. Important elements of the postural network are the reticulospinal (RS) neurons, which are driven by vestibular input and transmit commands for postural corrections from the brain stem to the spinal cord. Here we describe responses to vestibular stimulation (rotation of the animal in the pitch plane) in RS neurons of intact lampreys. The activity of neurons was recorded from their axons in the spinal cord by chronically implanted arrays of macroelectrodes. From the multielectrode recordings of mass activity, discharges in individual axons were extracted by means of a spike-sorting program, and the axon position in the spinal cord and its conduction velocity were determined. Vestibular stimulation was performed by rotating the animal in steps of 45° throughout 360° or by periodical “trapezoid” tilts between the nose-up and -down positions. Typically, the RS neurons exhibited both dynamic responses (activity during movement) and static responses (activity in a new sustained position). The neurons were classified into two groups according to their pattern of response. Group up neurons responded preferentially to nose-up rotation with maximal activity at 0–135° up. Group down neurons responded preferentially to nose-down rotation with maximal activity at 0–135° down. Neurons of the two groups also differed in the position of their axons in the spinal cord and axonal conduction velocity. An increase in water temperature, which presumably causes a downward turn in swimming lampreys, affected the activity in the up anddown groups differently, so that the ratio upresponses to down responses increased. We suggest that theup and down groups mediate the opposing vestibular reflexes and cause the downward and upward turns of the animal, respectively. The lamprey will stabilize the orientation in the pitch plane at which the effects of up and downgroups are equal to each other. In addition to the main test (rotation in the pitch plane), the animals were also tested by rotation in the transverse (roll) plane. It was found that 22% of RS neurons responding to pitch tilts also responded to roll tilts. The overlap between the pitch and roll populations suggests that the RS pathways are partly shared by the pitch and roll control systems.
Inhibitory Synchronization of Bursting in Biological Neurons: Dependence on Synaptic Time Constant
Authors: Elson Robert C. , Selverston Allen I. , Abarbanel Henry D. I. , Rabinovich Mikhail I.
Published: December 2017

Using the dynamic clamp technique, we investigated the effects of varying the time constant of mutual synaptic inhibition on the synchronization of bursting biological neurons. For this purpose, we constructed artificial half-center circuits by inserting simulated reciprocal inhibitory synapses between identified neurons of the pyloric circuit in the lobster stomatogastric ganglion. With natural synaptic interactions blocked (but modulatory inputs retained), these neurons generated independent, repetitive bursts of spikes with cycle period durations of ∼1 s. After coupling the neurons with simulated reciprocal inhibition, we selectively varied the time constant governing the rate of synaptic activation and deactivation. At time constants ≤100 ms, bursting was coordinated in an alternating (anti-phase) rhythm. At longer time constants (>400 ms), bursts became phase-locked in a fully overlapping pattern with little or no phase lag and a shorter period. During the in-phase bursting, the higher-frequency spiking activity was not synchronized. If the circuit lacked a robust periodic burster, increasing the time constant evoked a sharp transition from out-of-phase oscillations to in-phase oscillations with associated intermittent phase-jumping. When a coupled periodic burster neuron was present (on one side of the half-center circuit), the transition was more gradual. We conclude that the magnitude and stability of phase differences between mutually inhibitory neurons varies with the ratio of burst cycle period duration to synaptic time constant and that cellular bursting (whether periodic or irregular) can adopt in-phase coordination when inhibitory synaptic currents are sufficiently slow.
Muscarinic Activation of a Cation Current and Associated Current Noise in Entorhinal-Cortex Layer-II Neurons
Authors: Shalinsky Mark H. , Magistretti Jacopo , Ma Li , Alonso Angel A.
Published: December 2017

The effects of muscarinic stimulation on the membrane potential and current of in situ rat entorhinal-cortex layer-II principal neurons were analyzed using the whole cell, patch-clamp technique. In current-clamp experiments, application of carbachol (CCh) induced a slowly developing, prolonged depolarization initially accompanied by a slight decrease or no significant change in input resistance. By contrast, in a later phase of the depolarization input resistance appeared consistently increased. To elucidate the ionic bases of these effects, voltage-clamp experiments were then carried out. In recordings performed in nearly physiological ionic conditions at the holding potential of −60 mV, CCh application promoted the slow development of an inward current deflection consistently associated with a prominent increase in current noise. Similarly to voltage responses to CCh, this inward-current induction was abolished by the muscarinic antagonist, atropine. Current-voltage relationships derived by applying ramp voltage protocols during the different phases of the CCh-induced inward-current deflection revealed the early induction of an inward current that manifested a linear current/voltage relationship in the subthreshold range and the longer-lasting block of an outward K+current. The latter current could be blocked by 1 mM extracellular Ba2+, which allowed us to study the CCh-induced inward current ( ICCh) in isolation. The extrapolated reversal potential of the isolated ICChwas ≈0 mV and was not modified by complete substitution of intrapipette K+with Cs+. Moreover, the extrapolated ICChreversal shifted to approximately −20 mV on removal of 50% extracellular Na+. These results are consistent with ICChbeing a nonspecific cation current. Finally, noise analysis of ICChreturned an estimated conductance of the underlying channels of ∼13.5 pS. We conclude that the depolarizing effect of muscarinic stimuli on entorhinal-cortex layer-II principal neurons depends on both the block of a K+conductance and the activation of a “noisy” nonspecific cation current. We suggest that the membrane current fluctuations brought about by ICChchannel noise may facilitate the “theta” oscillatory dynamics of these neurons and enhance firing reliability and synchronization.
Suppression by Zinc of AMPA Receptor-Mediated Synaptic Transmission in the Retina
Authors: Zhang Dao-Qi , Ribelayga Christophe , Mangel Stuart C. , McMahon Douglas G.
Published: December 2017

Zinc is strikingly co-localized with glutamate-containing vesicles in the synaptic terminals of retinal photoreceptors, and it is thought to be co-released with glutamate onto postsynaptic neurons such as horizontal cells and bipolar cells. Here we examined exogenous zinc modulation of glutamate receptors on cultured retinal horizontal cells using patch-clamp recording and endogenous zinc effect on intact horizontal cells using intracellular recording techniques. Application of 3, 30, and 300 μM zinc reduced the whole cell peak current of response to 200 μM glutamate by 2, 30, and 56%, respectively. Zinc suppression of glutamate response persisted in the presence of 10 μM cyclothiazide (CTZ). Glutamate responses of outside-out patches were completely abolished by 30 μM 1-(4-aminophenyl)-4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine (GYKI 52466), and the receptor desensitization was blocked by 30 μM CTZ, indicating that receptor target for the zinc action on horizontal cells is α-amino-3-hydroxy-5-methyl-4-isoxazoleproponic acid (AMPA) receptors. Zinc decreased the amplitude of outside-out patch peak current without an effect on either its 10–90% rise time or the rate of receptor desensitization. Dose-response curves for glutamate show that zinc reduced the maximal current evoked by glutamate and increased EC50 from 50 ± 3 to 70 ± 6 μM without changing the Hill coefficient. Chelation of endogenous zinc with 1 mM Ca-EDTA depolarized horizontal cells in the intact retina by 3 mV, consistent with relief of the partial glutamate receptor inhibition by zinc. Overall, the results describe a unimodal form of zinc modulation of AMPA-type glutamate receptor responses not previously described in native neuronal preparations and a novel role for endogenous zinc in modulating neurotransmission.