bluuebunny/crossref_metadata_2025 huggingface dataset:
Fetal Transplants Rescue Axial Muscle Representations in M1 Cortex of Neonatally Transected Rats That Develop Weight Support
Authors: Giszter Simon F. , Kargo William J. , Davies Michelle , Shibayama Motohide
Published: December 2017

Giszter, Simon, William Kargo, Michelle Davies, and Motohide Shibayama. Fetal transplants rescue axial muscle representations in M1 cortex of neonatally transected rats that develop weight support. J. Neurophysiol. 80: 3021–3030, 1998. Intraspinal transplants of fetal spinal tissue partly alleviate motor deficits caused by spinal cord injury. How transplants modify body representation and muscle recruitment by motor cortex is currently largely unknown. We compared electromyographic responses from motor cortex stimulation in normal adult rats, adult rats that received complete spinal cord transection at the T8–T10 segmental level as neonates (TX rats), and similarly transected rats receiving transplants of embryonic spinal cord (TP rats). Rats were also compared among treatments for level of weight support and motor performance. Sixty percent of TP rats showed unassisted weight-supported locomotion as adults, whereas ∼30% of TX rats with no intervention showed unassisted weight-supported locomotion. In the weight-supporting animals we found that the transplants enabled motor responses to be evoked by microstimulation of areas of motor cortex that normally represent the lumbar axial muscles in rats. These same regions were silent in all TX rats with transections but no transplants, even those exhibiting locomotion with weight support. In weight-supporting TX rats low axial muscles could be recruited from the rostral cortical axial representation, which normally represents the neck and upper trunk. No operated animal, even those with well-integrated transplants and good weight-supported locomotion, had a hindlimb motor representation in cortex. The data demonstrate that spinal transplants allow the development of some functional interactions between areas of motor cortex and spinal cord that are not available to the rat lacking the intervention. The data also suggest that operated rats that achieve weight support may primarily use the axial muscles to steer the pelvis and hindlimbs indirectly rather than use explicit hindlimb control during weight-supported locomotion.
Development of Ionic Currents Underlying Changes in Action Potential Waveforms in Rat Spinal Motoneurons
Authors: Gao Bao-Xi , Ziskind-Conhaim Lea
Published: December 2017

Gao, Bao-Xi and Lea Ziskind-Conhaim. Development of ionic currents underlying changes in action potential waveforms in rat spinal motoneurons. J. Neurophysiol. 80: 3047–3061, 1998. Differentiation of the ionic mechanism underlying changes in action potential properties was investigated in spinal motoneurons of embryonic and postnatal rats using whole cell voltage- and current-clamp recordings. Relatively slow-rising, prolonged, largely Na+-dependent action potentials were recorded in embryonic motoneurons, and afterdepolarizing potentials were elicited in response to prolonged intracellular injections of depolarizing currents. Action potential amplitude, as well as its rates of rise and repolarization significantly increased, and an afterhyperpolarizing potential (AHP) became apparent immediately after birth. Concurrently, repetitive action potential firing was elicited in response to a prolonged current injection. To determine the ionic mechanism underlying these changes, the properties of voltage-gated macroscopic Na+, Ca2+, and K+ currents were examined. Fast-rising Na+ currents ( I Na) and slow-rising Ca2+ currents ( I Ca) were expressed early in embryonic development, but only I Na was necessary and sufficient to trigger an action potential. I Na and I Ca densities significantly increased while the time to peak I Na and I Ca decreased after birth. The postnatal increase in I Na resulted in overshooting action potential with significantly faster rate of rise than that recorded before birth. Properties of three types of outward K+ currents were examined: transient type-A current ( I A), noninactivating delayed rectifier-type current ( I K), and Ca2+-dependent K+ current ( I K(Ca)). The twofold postnatal increase in I K and I K(Ca) densities resulted in shorter duration action potential and the generation of AHP. Relatively large I A was expressed early in neuronal development, but unlike I K and I K(Ca) its density did not increase after birth. The three types of K+ channels had opposite modulatory actions on action potential firing behavior: I K and I A increased the firing rate, whereas I K(Ca) decreased it. Our findings demonstrated that the developmental changes in action potential waveforms and the onset of repetitive firing were correlated with large increases in the densities of existing voltage-gated ion channels rather than the expression of new channel types.
Transformation of Binaural Response Properties in the Ascending Auditory Pathway: Influence of Time-Varying Interaural Phase Disparity
Authors: Spitzer Matthew W. , Semple Malcolm N.
Published: December 2017

Spitzer, Matthew W. and Malcolm N. Semple. Transformation of binaural response properties in the ascending auditory pathway: influence of time-varying interaural phase disparity. J. Neurophysiol. 80: 3062–3076, 1998. Previous studies demonstrated that tuning of inferior colliculus (IC) neurons to interaural phase disparity (IPD) is often profoundly influenced by temporal variation of IPD, which simulates the binaural cue produced by a moving sound source. To determine whether sensitivity to simulated motion arises in IC or at an earlier stage of binaural processing we compared responses in IC with those of two major IPD-sensitive neuronal classes in the superior olivary complex (SOC), neurons whose discharges were phase locked (PL) to tonal stimuli and those that were nonphase locked (NPL). Time-varying IPD stimuli consisted of binaural beats, generated by presenting tones of slightly different frequencies to the two ears, and interaural phase modulation (IPM), generated by presenting a pure tone to one ear and a phase modulated tone to the other. IC neurons and NPL–SOC neurons were more sharply tuned to time-varying than to static IPD, whereas PL–SOC neurons were essentially uninfluenced by the mode of stimulus presentation. Preferred IPD was generally similar in responses to static and time-varying IPD for all unit populations. A few IC neurons were highly influenced by the direction and rate of simulated motion, but the major effect for most IC neurons and all SOC neurons was a linear shift of preferred IPD at high rates—attributable to response latency. Most IC and NPL–SOC neurons were strongly influenced by IPM stimuli simulating motion through restricted ranges of azimuth; simulated motion through partially overlapping azimuthal ranges elicited discharge profiles that were highly discontiguous, indicating that the response associated with a particular IPD is dependent on preceding portions of the stimulus. In contrast, PL–SOC responses tracked instantaneous IPD throughout the trajectory of simulated motion, resulting in highly contiguous discharge profiles for overlapping stimuli. This finding indicates that responses of PL–SOC units to time-varying IPD reflect only instantaneous IPD with no additional influence of dynamic stimulus attributes. Thus the neuronal representation of auditory spatial information undergoes a major transformation as interaural delay is initially processed in the SOC and subsequently reprocessed in IC. The finding that motion sensitivity in IC emerges from motion-insensitive input suggests that information about change of position is crucial to spatial processing at higher levels of the auditory system.
Anatomy and Physiology of the Primate Interstitial Nucleus of Cajal. II. Discharge Pattern of Single Efferent Fibers
Authors: Dalezios Y. , Scudder C. A. , Highstein S. M. , Moschovakis A. K.
Published: December 2017

Dalezios, Y., C. A. Scudder, S. M. Highstein, and A. K. Moschovakis. Anatomy and physiology of the primate interstitial nucleus of Cajal. II. Discharge pattern of single efferent fibers. J. Neurophysiol. 80: 3100–3111, 1998. Single efferent fibers of the interstitial nucleus of Cajal (NIC) were characterized physiologically and injected with biocytin in alert behaving monkeys. Quantitative analysis demonstrated that their discharge encodes a constellation of oculomotor variables. Tonic and phasic signals were related to vertical (up or down) eye position and saccades, respectively. Depending on how they encoded eye position, saccade velocity, saccade size, saccade duration, and smooth-pursuit eye velocity, fibers were characterized as regular or irregular, bi- or unidirectionally modulated, more or less sensitive, and reliable or unreliable. Further, fibers that did not burst for saccades (tonic) and fibers the eye-position and saccade-related signals of which increased in the same (in-phase) or in the opposite (anti-phase) directions were encountered. A continuum of discharge properties was the rule. We conclude that NIC efferent fibers send a combination of eye-position, saccade-, and smooth-pursuit-related signals, mixed in proportions that differ for different fibers, to targets of the vertical neural integrator such as extraocular motoneurons.
Annexin I Is a Local Mediator in Neural-Endocrine Feedback Control of Inflammation
Authors: Green Paul G. , Strausbaugh Holly J. , Levine Jon D.
Published: December 2017

Green, Paul G., Holly J. Strausbaugh, and Jon D. Levine. Annexin I is a local mediator in neural-endocrine feedback control of inflammation. J. Neurophysiol. 80: 3120–3126, 1998. Activation of primary afferent nociceptors induces a neural endocrine–mediated inhibition of the inflammatory response via a circuit that includes ascending spinal pathways and activation of the hypothalamic-pituitary adrenal (HPA) axis. This circuit inhibits sympathetic neuron-dependent plasma extravasation (PE) in the rat knee joint produced by bradykinin (BK), but not sympathetic neuron–independent PE produced by platelet activating factor (PAF). Noxious (25 mA) but not non-noxious (2.5 mA) electrical stimulation significantly increased plasma corticosterone concentrations, and intravenous infusion of corticosterone (5 μg/min) mimicked inhibition of BK-induced PE produced by noxious stimulation. However, perfusion of corticosterone locally through the knee joint, at doses that do not have a systemic action (i.e., ≤1 μM), did not inhibit BK-induced PE. Annexin I (lipocortin-1), a 37-kDa member of a family of phospholipid and calcium binding proteins, can mediate local anti-inflammatory effects of glucocorticoids via a mechanism that is partially dependent on inhibition of phospholipase A2activity and adhesion and transmigration of polymorphonuclear leukocytes. Because BK-induced PE is dependent on both polymorphonuclear leukocytes and phospholipase A2activity, we tested the hypothesis that the action of corticosterone to inhibit BK-induced PE is mediated by stimulating the production and release of annexin I. Perfusion of BK (150 nM) through the rat knee joint induces a rapid and sustained increase in PE. Co-perfusion of BK with annexin I (100 ng/ml) through the knee joint mimics the inhibition of BK-induced PE produced by noxious electrical stimulation or by intravenous corticosterone. Co-perfusion of BK with annexin I antibody (LCPS1, 1:60 dilution) prevented the inhibition of BK-induced PE produced by noxious electrical stimulation or intravenous corticosterone adminstration. PAF-induced PE, which is not dependent on polymorphonuclear leukocytes, was not inhibited by local perfusion of annexin I. These data suggest that the inhibitory effect of C-fiber activity on BK-induced PE, acting via an HPA circuit, is mediated by annexin I in the knee joint.
Red Nucleus Stimulation Inhibits Within the Inferior Olive
Authors: Horn K. M. , Hamm T. M. , Gibson A. R.
Published: December 2017

Horn, K. M., T. M. Hamm, and A. R. Gibson. Red nucleus stimulation inhibits within the inferior olive. J. Neurophysiol. 80: 3127–3136, 1998. In the anesthetized cat, electrical stimulation of the magnocellular red nucleus (RNm) inhibits responses of rostral dorsal accessory olive (rDAO) neurons to cutaneous stimulation. We tested the hypothesis that RNm-mediated inhibition occurs within the inferior olive by using stimulation of the ventral funiculus (VF) of the spinal cord in place of cutaneous stimulation of the hindlimb. Fibers in the VF terminate on hindlimb rDAO neurons, so inhibition of this input would have to occur within the olive. rDAO responses elicited by VF stimulation were inhibited by prior stimulation of the RNm, indicating that inhibition occurs within the olive. In contrast, evoked potentials recorded from the VF or dorsal columns following hindlimb stimulation were not affected by prior stimulation of RNm, indicating that stimulation of the RNm does not inhibit olivary afferents at spinal levels. RNm stimulation that inhibited rDAO responses had little effect on evoked somatosensory responses in thalamus, indicating that inhibition generated by activity in RNm may be specific to rDAO. To test limb specificity of RNm-mediated inhibition, conditioning stimulation was applied to the dorsolateral funiculus at thoracic levels, which selectively activates RNm neurons projecting to the lumbar cord. Stimulation at thoracic levels inhibited evoked responses from hindlimb but not forelimb regions of rDAO, suggesting that inhibitory effects of RNm activity are limb specific. Several studies have reported that olivary neurons have reduced sensitivity to peripheral stimulation during movement; it is likely that RNm-mediated inhibition occurring within the olive contributes to this reduction of sensitivity. Inhibition of rDAO responses by descending motor pathways appears to be a salient feature of olivary function.
Transmitter Concentration at a Three-Dimensional Synapse
Authors: Rao-Mirotznik Rukmini , Buchsbaum Gershon , Sterling Peter
Published: December 2017

Rao-Mirotznik, Rukmini, Gershon Buchsbaum, and Peter Sterling. Transmitter concentration at a three-dimensional synapse. J. Neurophysiol. 80: 3163–3172, 1998. At intensities from starlight to 1000-fold brighter, the mammalian rod synapse transmits a binary signal, the capture of 0 or 1 photon. Zero is signified by tonic exocytosis, and 1 is signified by a brief pause. The synapse is three dimensional: vesicles discharge at the apex of a deep cleft created by the invagination of four postsynaptic processes. Two horizontal cell spines bearing α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors reach near to the release sites (16 nm), and two bipolar dendrites bearing mGluR6 receptors end far from the release sites (up to 640 nm). We considered two hypotheses for signal transfer: transmitter quanta might be integrated in the cleft and sensed as a steady concentration (high for 0 and low for 1); or quanta might be sensed at the postsynaptic membrane as discrete postsynaptic potentials (PSPs) and integrated within the dendrite. We calculate from a passive diffusion model that the invagination empties rapidly (τ ∼ 1.7 ms). Further calculations suggest that a glutamate concentration high enough to hold a bipolar cell in darkness at one end of its response range would require ∼4,000 vesicles/s. On the other hand, the glutamate pulse from a single vesicle would reach both nearby AMPA receptors (low affinity) and distant mGluR6 receptors (high affinity) at spatiotemporal concentrations matched to their apparent binding affinities. Thus one vesicle could evoke a discrete PSP in all four postsynaptic processes. We calculate from a stochastic model that PSPs could transfer the binary signal at ∼100 vesicles/s. Thus dendritic integration of unitary PSPs is both plausible and 40-fold more efficient than the alternative mechanism. The rod's deep invagination, rather than serving to pool transmitter, may serve to prevent “spillover” of transmitter to neighboring rods. Spillover, by pooling the noise from neighboring rods, would impair transmission of their binary signals.
Inhibition Evoked From Primary Afferents in the Electrosensory Lateral Line Lobe of the Weakly Electric Fish (Apteronotus leptorhynchus)
Authors: Berman Neil J. , Maler Leonard
Published: December 2017

Berman, Neil J. and Leonard Maler. Inhibition evoked from primary afferents in the electrosensory lateral line lobe of the weakly electric fish ( Apteronotus leptorhynchus). J. Neurophysiol. 80: 3173–3196, 1998. The responses of two types of projection neurons of the electrosensory lateral line lobe, basilar (BP) and nonbasilar (NBP) pyramidal cells, to stimulation of primary electrosensory afferents were determined in the weakly electric fish, Apteronotus leptorhynchus. Using dyes to identify cell type, the response of NBP cells to stimulation of primary afferents was inhibitory, whereas the response of BP cells was excitation followed by inhibition. γ-Aminobutyric acid (GABA) applications produced biphasic (depolarization then hyperpolarization) responses in most cells. GABAA antagonists blocked the depolarizing effect of GABA and reduced the hyperpolarizing effect. The GABAB antagonists weakly antagonized the hyperpolarizing effect. The early depolarization had a larger increase in cell conductance than the late hyperpolarization. The conductance changes were voltage dependent, increasing with depolarization. In both cell types, baclofen produced a slow small hyperpolarization and reduced the inhibitory postsynaptic potentials (IPSPs) evoked by primary afferent stimulation. Tetanic stimulation of primary afferents at physiological rates (100–200 Hz) produced strongly summating compound IPSPs (∼500-ms duration) in NBP cells, which were usually sensitive to GABAA but not GABAB antagonists; in some cells there remained a slow IPSP that was unaffected by GABAB antagonists. BP cells responded with excitatory or mixed excitatory + inhibitory responses. The inhibitory response had both a fast (∼30 ms, GABAA) and long-lasting slow phase (∼800 ms, mostly blocked by GABAA antagonists). In some cells there was a GABAA antagonist-insensitive slow IPSP (∼500 ms) that was sensitive to GABAB antagonists. Application of glutamate ionotropic receptor antagonists blocked the inhibitory response of NBP cells to primary afferent stimulation and the excitatory response of BP cells but enhanced the BP cell slow IPSP; this remaining slow IPSP was reduced by GABAB antagonists. Unit recordings in the granule cell layer and computer simulations of pyramidal cell inhibition suggested that the duration of the slow GABAA inhibition reflects the prolonged firing of GABAergic granule cell interneurons to primary afferent input. Correlation of the results with known GABAergic circuitry in the electrosensory lobe suggests that the GABAergic type 2 granule cell input to both pyramidal cell types is via GABAA receptors. The properties of the GC2 GABAA input are well suited to their putative role in gain control, regulation of phasicness, and coincidence detection. The slow GABAB IPSP evoked in BP cells is likely due to ovoid cell input to their basal dendrites.
Different VAMP/Synaptobrevin Complexes for Spontaneous and Evoked Transmitter Release at the Crayfish Neuromuscular Junction
Authors: Hua Shao-Ying , Raciborska Dorota A. , Trimble William S. , Charlton Milton P.
Published: December 2017

Hua, Shao-Ying, Dorota A. Raciborska, William S. Trimble, and Milton P. Charlton. Different VAMP/synaptobrevin complexes for spontaneous and evoked transmitter release at the crayfish neuromuscular junction. J. Neurophysiol. 80: 3233–3246, 1998. Although vesicle-associated membrane protein (VAMP/synaptobrevin) is essential for evoked neurotransmitter release, its role in spontaneous transmitter release remains uncertain. For instance, many studies show that tetanus toxin (TeNT), which cleaves VAMP, blocks evoked transmitter release but leaves some spontaneous transmitter release. We used recombinant tetanus and botulinum neurotoxin catalytic light chains (TeNT-LC, BoNT/B-LC, and BoNT/D-LC) to examine the role of VAMP in spontaneous transmitter release at neuromuscular junctions (nmj) of crayfish. Injection of TeNT-LC into presynaptic axons removed most of the VAMP immunoreactivity and blocked evoked transmitter release without affecting nerve action potentials or Ca2+influx. The frequency of spontaneous transmitter release was little affected by the TeNT-LC when the evoked transmitter release had been blocked by >95%. The spontaneous transmitter release left after TeNT-LC treatment was insensitive to increases in intracellular Ca2+. BoNT/B-LC, which cleaves VAMP at the same site as TeNT-LC but uses a different binding site, also blocked evoked release but had minimal effect on spontaneous release. However, BoNT/D-LC, which cleaves VAMP at a different site from the other two toxins but binds to the same position on VAMP as TeNT, blocked both evoked and spontaneous transmitter release at similar rates. The data indicate that different VAMP complexes are employed for evoked and spontaneous transmitter release; the VAMP used in spontaneous release is not readily cleaved by TeNT or BoNT/B. Because the exocytosis that occurs after the action of TeNT cannot be increased by increased intracellular Ca2+, the final steps in neurotransmitter release are Ca2+independent.
Locomotor Modulation of Disynaptic EPSPs From the Mesencephalic Locomotor Region in Cat Motoneurons
Authors: Degtyarenko A. M. , Simon E. S. , Burke R. E.
Published: December 2017

Degtyarenko, A. M., E. S. Simon, and R. E. Burke. Locomotor modulation of disynaptic EPSPs from the mesencephalic locomotor region in cat motoneurons. J. Neurophysiol. 80: 3284–3296, 1998. When low-frequency tetanization of the mesencephalic locomotor region (MLR) produce fictive locomotion in unanesthetized, decerebrate cats, each MLR stimulus produces a distinctive cord dorsum potential (CDP) and oligosynaptic excitatory postsynaptic potentials (EPSPs) in many lumbosacral motoneurons. The average segmental latency from the initial CDP wave [mean delay from stimulus: 4.3 ± 0.9 (SD) ms] to the onset of detectable MLR EPSPs was 1.6 ± 0.4 ms, suggesting a disynaptic segmental connection. In gastrocnemius/soleus, flexor hallucis longus, flexor digitorum longus, tibialis anterior, and posterior biceps-semitendinosus motoneurons (35/38 cells), MLR EPSPs either appeared or were enhanced during the phase of fictive stepping in which the target motoneurons were depolarized and the motor pool was active (the on phase), with parallel changes between EPSP amplitudes and membrane depolarization. In contrast, MLR stimulation produced small (1/10) or no EPSPs in extensor digitorum longus (EDL) motoneurons, with no on phase enhancement (4/10) or oligosynaptic inhibitory postsynaptic potentials during the on phase (5/10). Eight of 10 flexor digitorum longus (FDL) cells exhibited membrane depolarization in the early flexion phase of fictive stepping, and five of these showed parallel enhancement of disynaptic MLR EPSPs during early flexion. Three cases were studied when the FDL motor pool exhibited exclusively extensor phase firing. In these cases, the disynaptic MLR EPSPs were enhanced only during the extensor phase, accompanied by membrane depolarizations. We conclude that the last-order interneurons that produce disynaptic MLR EPSPs may well participate in producing the depolarizing locomotor drive potentials (LDPs) found in hindlimb motoneurons during fictive locomotion. However, the absence of linkage between MLR EPSP enhancement and LDP depolarizations in EDL motoneurons suggests that other types of excitatory interneurons also must be involved at least in some motor pools. We compared these patterns with the modulation of disynaptic EPSPs produced in FDL cells by stimulation of the medial longitudinal fasciculus (MLF). In all seven FDL motoneurons tested, disynaptic MLF EPSPs appeared only during the extension phase, regardless of when the FDL motoneurons were active. The fact that the modulation patterns of MLR and MLF disynaptic EPSPs is different in FDL motoneurons indicates that the two pathways do not converge on common last-order interneurons to that motor pool.
Neuronal Discriminator Formed by Metabotropic γ-Aminobutyric Acid Receptors
Authors: Zhang Jian , Tian Ning , Slaughter Malcolm M.
Published: December 2017

Zhang, Jian, Ning Tian, and Malcolm M. Slaughter. Neuronal discriminator formed by metabotropic γ-aminobutyric acid receptors. J. Neurophysiol. 80: 3365–3368, 1998. Neurotransmitters function in one of two modes, promoting either inhibition or excitation. However, the metabotropic γ-aminobutyric acid receptor (GABABR) system can switch between these modes. In the presence of a small excitatory stimulus, the GABABR mediates a shunting inhibition that suppresses excitation. However, in the presence of a strong excitatory stimulus, the GABABR potentiates the response. This bipartite action is accomplished by linking the GABABR to two electrogenic mechanisms; one activates an outward current and another reduces an outward current. As a consequence, the GABABR serves as a discriminator that reduces the influence of weak signals while augmenting responses to strong signals. In retinal ganglion cells, this mechanism acts to promote the communication of phasic information.
Damping in Reflexively Active and Areflexive Lengthening Muscle Evaluated With Inertial Loads
Authors: Lin David C. , Rymer W. Zev
Published: December 2017

Lin, David C. and W. Zev Rymer. Damping in reflexively active and areflexive lengthening muscle evaluated with inertial loads. J. Neurophysiol. 80: 3369–3372, 1998. Studies of active areflexive muscle have shown that during a constant velocity stretch the increment in force elicited by an incremental length change falls dramatically after a few hundred micrometers of stretch, a finding labeled as “muscle yield.” The mechanical behavior after the yield was like a viscous damper, in that force varied only with velocity. In light of these observations, our aims were to determine whether viscous properties are also evident under more physiological conditions, specifically under inertial loading, and to evaluate the damping action of reflexively intact compared with that of deafferented muscle. The active soleus muscle in a decerebrate cat was forcibly stretched by a simulated inertia with a specified initial velocity. We compared muscle length changes when afferent pathways were intact with those recorded after cutting the dorsal roots. Our findings were that areflexive muscle showed highly damped responses, with large changes in mean muscle length, indicative of high viscosity relative to stiffness. In contrast, reflexively active muscle produced lightly damped oscillations, with minimal changes in mean length, reflecting low viscosity and high stiffness. It appears that the stretch reflect modifies the relative contributions of elastic and viscous-like forces, maintaining elasticity, which in turn sustains oscillations. These differences highlight tradeoffs between positional and velocity regulation, in that elastic properties of reflexively active muscle promote oscillations with modest change in mean muscle length, whereas viscous-like properties of areflexive muscle produce damped responses, with poor positional regulation.
Cultured Insect Mushroom Body Neurons Express Functional Receptors for Acetylcholine, GABA, Glutamate, Octopamine, and Dopamine
Authors: Cayre M. , Buckingham S. D. , Yagodin S. , Sattelle D. B.
Published: December 2017

Cayre, M., S. D. Buckingham, S. Yagodin, and D. B. Sattelle. Cultured insect mushroom body neurons express functional receptors for acetylcholine, GABA, glutamate, octopamine, and dopamine. J. Neurophysiol. 81: 1–14, 1999. Fluorescence calcium imaging with fura-2 and whole cell, patch-clamp electrophysiology was applied to cultured Kenyon cells (interneurons) isolated from the mushroom bodies of adult crickets ( Acheta domesticus) to demonstrate the presence of functional neurotransmitter receptors. In all cells investigated, 5 μM acetylcholine (ACh, n = 52) evoked an increase in intracellular free calcium ([Ca2+]i). Similar effects were observed in response to 10 μM nicotine. The ACh response was insensitive to atropine (50 μM) but was reduced by mecamylamine (50 μM) and α-bungarotoxin (α-bgt, 10 μM). ACh-induced inward ion currents ( n = 28, EACh∼0 mV) were also blocked by 1 μM mecamylamine and by 1 μM α-bgt. Nicotine-induced inward currents desensitized more rapidly than ACh responses. Thus functional α-bgt–sensitive nicotinic ACh receptors are abundant on all Kenyon cells tested, and their activation leads to an increase in [Ca2+]i. γ-Aminobutyric acid (GABA, 100 μM) triggered a sustained decrease in [Ca2+]i. Similar responses were seen with a GABAAagonist, muscimol (100 μM), and a GABABagonist, 3-APPA (1 mM), suggesting that more than one type of GABA receptor can affect [Ca2+]i. This action of GABA was not observed when the extracellular KCl concentration was lowered. All cells tested ( n = 26) with patch-clamp electrophysiology showed picrotoxinin (PTX)-sensitive, GABA-induced (30–100 μM) currents with a chloride-sensitive reversal potential. Thus, an ionotropic PTX-sensitive GABA receptor was found on all Kenyon cells tested. Most (61%) of the 54 cells studied responded to l-glutamate (100 μM) application either with a biphasic increase in [Ca2+]ior with a single, delayed, sustained [Ca2+]iincrease. Nearly all cells tested (95%, n = 19) responded to (100 μM) l-glutamate with rapidly desensitizing, inward currents that reversed at approximately −30 mV. Dopamine (100 μM) elicited either a rapid or a delayed increase in [Ca2+]iin 63% of the 26 cells tested. The time course of these responses varied greatly among cells. Dopamine failed to elicit currents in patch-clamped cells ( n = 4). A brief decrease in [Ca2+]iwas induced by octopamine (100 μM) in ∼54% of the cells tested ( n = 35). However, when extracellular CaCl2was lowered, octopamine triggered a substantial increase in [Ca2+]iin 35% of the cells tested ( n = 26). No octopamine-elicited currents were detected in patched-clamped cells ( n = 10).
P42/44 MAP Kinase Inhibitor PD98059 Attenuates Multiple Forms of Synaptic Plasticity in Rat Dentate Gyrus In Vitro
Authors: Coogan Andrew N. , O'Leary Deirdre M. , O'Connor John J.
Published: December 2017

Coogan, Andrew N., Deirdre M. O'Leary, and John J. O'Connor. P42/44 MAP kinase inhibitor PD98059 attenuates multiple forms of synaptic plasticity in rat dentate gyrus in vitro. J. Neurophysiol. 81: 103–110, 1999. The effects of the specific p42/44 mitogen-activated protein (MAP) kinase cascade inhibitor, PD98059, were investigated on three types of long-term potentiation (LTP) in the medial perforant path of the rat dentate gyrus in vitro: LTP induced by 1) high-frequency stimulation (HFS-LTP), 2) application for 10 min of the K+ channel blocker, tetraethylammonium chloride (TEA-LTP), and 3) application of the metabotropic glutamate receptor (mGluR) agonist (S)-dihydrophenylglycine (S-DHPG) for 2 min (DHPG-LTP). Bath perfusion of PD98059 (50 μM) for 1 h inhibited HFS-LTP (111 ± 5%, mean ± SE, at 90 min posttetanus in test slices compared with 144 ± 5% in control slices; n = 6–7). Concentrations of 10 and 20 μM PD98059 had no effect on HFS-LTP ( n = 6). PD98059 (50 μM) had no effect on the isolated N-methyl-d-aspartate excitatory postsynaptic potential (NMDA-EPSP) or on the maintenance phase of HFS-LTP. PD98059 (50 μM) did not affect paired-pulse depression (PPD; interstimulus intervals of 10 and 100 ms) of synaptic transmission as is typically observed in the medial perforant path of the dentate gyrus. Bath application of (S)-DHPG (40 μM) for 2 min gave rise to a potentiation of the EPSPs slope (148 ± 4% at 1 h post-DHPG wash out; n = 5). Pretreatment of slices with PD98059 (50 μM) inhibited the DHPG-LTP (98 ± 3% at 1 h post-DHPG wash out; n = 5). The TEA-LTP (125 ± 4% at 1 h post-TEA wash out; n = 6) was found to be both d-2-amino-5-phosphonopentanoic acid (d-AP5; 100 μM) and nifedipine (20 μM) independent. However, the T type voltage-dependent calcium-channel blocker, NiCl2 (50 μM), completely inhibited the observed potentiation. The mGluR receptor antagonist α-methyl-4-carboxy-phenyl glycine (MCPG; 100 μM) and PD98059 (50 μM) caused a complete block of the TEA-LTP. These data show for the first time an involvement of the p42/44 MAP kinase in the induction and expression of both an NMDA-dependent and two forms of NMDA-independent LTP in the dentate gyrus.
Studies on the Corticospinal Control of Human Walking. I. Responses to Focal Transcranial Magnetic Stimulation of the Motor Cortex
Authors: Capaday Charles , Lavoie Brigitte A. , Barbeau Hugues , Schneider Cyril , Bonnard Mireille
Published: December 2017

Capaday, Charles, Brigitte A. Lavoie, Hugues Barbeau, Cyril Schneider, and Mireille Bonnard. Studies on the corticospinal control of human walking. I. Responses to focal transcranial magnetic stimulation of the motor cortex. J. Neurophysiol. 81: 129–139, 1999. Experiments were done to determine the extent to which the corticospinal tract is linked with the segmental motor circuits controlling ankle flexors and extensors during human walking compared with voluntary motor tasks requiring attention to the level of motor activity. The motor cortex was activated transcranially using a focal magnetic stimulation coil. For each subject, the entire input-output (I-O) curve [i.e., the integral of the motor evoked-potential (MEP) versus stimulus strength] was measured during a prescribed tonic voluntary contraction of either the tibialis anterior (TA) or the soleus. Similarly, I-O curves were measured in the early part of the swing phase, or in the early part of the stance phase of walking. The I-O data points were fitted by the Boltzmann sigmoidal function, which accounted for ≥80% of total data variance. There was no statistically significant difference between the I-O curves of the TA measured during voluntary ankle dorsiflexion or during the swing phase of walking, at matched levels of background electromyographic (EMG) activity. Additionally, there was no significant difference in the relation between the coefficient of variation and the amplitude of the MEPs measured in each task, respectively. In comparison, during the stance phase of walking the soleus MEPs were reduced on average by 26% compared with their size during voluntary ankle plantarflexion. Furthermore, during stance the MEPs in the inactive TA were enhanced relative to their size during voluntary ankle plantarflexion and in four of six subjects the TA MEPs were larger than those of the soleus. Finally, stimulation of the motor cortex at various phases of the step cycle did not reset the cycle. The time of the next step occurred at the expected moment, as determined from the phase-resetting curve. One interpretation of this result is that the motor cortex may not be part of the central neural system involved in timing the motor bursts during the step cycle. We suggest that during walking the corticospinal tract is more closely linked with the segmental motor circuits controlling the flexor, TA, than it is with those controlling the extensor, soleus. However, during voluntary tasks requiring attention to the level of motor activity, it is equally linked with the segmental motor circuits of ankle flexors or extensors.
Dopamine Modulates Inwardly Rectifying Hyperpolarization-Activated Current (I h) in Cultured Rat Olfactory Receptor Neurons
Authors: Vargas Gricelly , Lucero Mary T.
Published: December 2017

Vargas, Gricelly and Mary T. Lucero. Dopamine modulates inwardly rectifying hyperpolarization-activated current ( I h) in cultured rat olfactory receptor neurons. J. Neurophysiol. 81: 149–158, 1999. The presence of dopamine receptors in olfactory receptor neurons (ORNs) suggests that odor sensitivity may be modulated by neurotransmitters at the level of primary sensory neurons. Using standard patch-clamp techniques on rat ORNs, we found that 1 μM dopamine, 500 μM SQ 22536 (SQ, an adenylyl cyclase inhibitor), 20 and 50 μM quinpirole (a selective dopamine D2 receptor agonist), and 1 mM adenosine 3′,5′-cyclic monophosphate (cAMP) modulate the hyperpolarization-activated current I h. On hyperpolarizing from a holding potential of −58 mV, a small Cs+-sensitive inwardly rectifying current ( I h) was observed. Increases in extracellular K+ increased I h amplitude without shifting its voltage dependence of activation, whereas increases in temperature produced an increase in I h amplitude and a hyperpolarizing shift in the activation curve. Application of 1 μM dopamine reversibly shifted I h activation to more negative potentials and decreased I h current amplitudes. These effects were blocked by concomitant application of dopamine with sulpiride, a selective dopamine D2 receptor antagonist. The effects of dopamine were mimicked by quinpirole. Quinpirole (20 μM) decreased I h current amplitude, but was without effect on I h voltage dependence of activation. However, 50 μM quinpirole produced both a reduction of I h peak currents and a hyperpolarizing shift in the activation curve for I h. External application of the adenylyl cyclase inhibitor SQ 22536 produced a reversible decrease in peak currents but had no effect on I h voltage dependence of activation, whereas internal application of cAMP shifted I h activation to more depolarized potentials. Because I h modulates cell excitability and spike frequency adaptation, our findings support a role for dopamine in modulating the sensitivity and output of rat ORNs to odorants.
Current-Source Density Analysis in the Rat Olfactory Bulb: Laminar Distribution of Kainate/AMPA- and NMDA-Receptor-Mediated Currents
Authors: Aroniadou-Anderjaska Vassiliki , Ennis Matthew , Shipley Michael T.
Published: December 2017

Aroniadou-Anderjaska, Vassiliki, Matthew Ennis, and Michael T. Shipley. Current-source density analysis in the rat olfactory bulb: laminar distribution of kainate/AMPA- and NMDA-receptor-mediated currents. J. Neurophysiol. 81: 15–28, 1999. The one-dimensional current-source density method was used to analyze laminar field potential profiles evoked in rat olfactory bulb slices by stimulation in the olfactory nerve (ON) layer or mitral cell layer (MCL) and to identify the field potential generators and the characteristics of synaptic activity in this network. Single pulses to the ON evoked a prolonged (≥400 ms) sink (S1ON) in the glomerular layer (GL) with corresponding sources in the external plexiform layer (EPL) and MCL and a relatively brief sink (S2ON) in the EPL, reversing in the internal plexiform and granule cell layers. These sink/source distributions suggested that S1ONand S2ONwere generated in the apical dendrites of mitral/tufted cells and granule cells, respectively. The kainate/AMPA-receptor antagonist CNQX (10 μM) reduced the early phase of S1ON, blocked S2ON, and revealed a low amplitude, prolonged sink at the location of S2ONin the EPL. Reduction of Mg2+, in CNQX, enhanced both the CNQX-resistant component of S1ONand the EPL sink. This EPL sink reversed below the MCL, suggesting it was produced in granule cells. The NMDA-receptor antagonist APV (50 μM) reversibly blocked the CNQX-resistant field potentials in all layers. Single pulses were applied to the MCL to antidromically depolarize the dendrites of mitral/tufted cells. In addition to synaptic currents of granule cells, a low-amplitude, prolonged sink (S1mcl) was evoked in the GL. Corresponding sources were in the EPL, suggesting that S1mclwas generated in the glomerular dendritic tufts of mitral/tufted cells. Both S1mcland the granule cell currents were nearly blocked by CNQX (10 μM) but enhanced by subsequent reduction of Mg2+; these currents were blocked by APV. S1mclalso was enhanced by γ-aminobutyric acid-A-receptor antagonists applied to standard medium; this enhancement was reduced by APV. ON activation produces prolonged excitation in the apical dendrites of mitral/tufted cells, via kainate/AMPA and NMDA receptors, providing the opportunity for modulation and integration of sensory information at the first level of synaptic processing in the olfactory system. Granule cells respond to input from the lateral dendrites of mitral/tufted cells via both kainate/AMPA and NMDA receptors; however, in physiological concentrations of extracellular Mg2+, NMDA-receptor activation does not contribute significantly to the granule cell responses. The glomerular sink evoked by antidromic depolarization of mitral/tufted cell dendrites suggests that glutamate released from the apical dendrites of mitral/tufted cells may excite the same or neighboring mitral/tufted cell dendrites.
Responses of Neurons in the Nucleus of the Basal Optic Root to Translational and Rotational Flowfields
Authors: Wylie Douglas R. W. , Frost Barrie J.
Published: December 2017

Wylie, Douglas R. W. and Barrie J. Frost. Responses of Neurons in the nucleus of the basal optic root to translational and rotational flowfields. J. Neurophysiol. 81: 267–276, 1999. The nucleus of the basal optic root (nBOR) receives direct input from the contralateral retina and is the first step in a pathway dedicated to the analysis of optic flowfields resulting from self-motion. Previous studies have shown that most nBOR neurons exhibit direction selectivity in response to large-field stimuli moving in the contralateral hemifield, but a subpopulation of nBOR neurons has binocular receptive fields. In this study, the activity of binocular nBOR neurons was recorded in anesthetized pigeons in response to panoramic translational and rotational optic flow. Translational optic flow was produced by the “translator” projector described in the companion paper, and rotational optic flow was produced by a “planetarium projector” described by Wylie and Frost. The axis of rotation or translation could be positioned to any orientation in three-dimensional space. We recorded from 37 cells, most of which exhibited a strong contralateral dominance. Most of these cells were located in the caudal and dorsal aspects of the nBOR complex and many were localized to the subnucleus nBOR dorsalis. Other units were located outside the boundaries of the nBOR complex in the adjacent area ventralis of Tsai or mesencephalic reticular formation. Six cells responded best to rotational flowfields, whereas 31 responded best to translational flowfields. Of the rotation cells, three preferred rotation about the vertical axis and three preferred horizontal axes. Of the translation cells, 3 responded best to a flowfield simulating downward translation of the bird along a vertical axis, whereas the remaining 28 responded best to flowfields resulting from translation along axes in the horizontal plane. Seventeen of these cells preferred a flowfield resulting from the animal translating backward along an axis oriented ∼45° to the midline, but the best axes of the remaining eleven cells were distributed throughout the horizontal plane with no definitive clustering. These data are compared with the responses of vestibulocerebellar Purkinje cells.
Mapping Membrane Potential Transients in Crayfish (Procambarus clarkii) Optic Lobe Neuropils With Voltage-Sensitive Dyes
Authors: Yagodin Sergey , Collin Carlos , Alkon Daniel L. , Sheppard Norman F. , Sattelle David B.
Published: December 2017

Yagodin, Sergey, Carlos Collin, Daniel L. Alkon, Norman F. Sheppard, Jr., and David B. Sattelle. Mapping membrane potential transients in crayfish ( Procambarus clarkii) optic lobe neuropils with voltage-sensitive dyes. J. Neurophysiol. 81: 334–344, 1999. Voltage-sensitive dyes NK 2761 and RH 155 were employed (in conjunction with a 12 × 12 photodiode array) to study membrane potential transients in optic lobe neuropils in the eye stalk of the crayfish Procambarus clarkii. By this means we investigated a pathway linking deutocerebral projection neurons, via hemiellipsoid body local interneurons, to an unidentified target (most likely neurons processing visual information) in the medulla terminalis. Rapid (10- to 20-ms duration), transient changes in absorption with the characteristics of action potentials were recorded from the optic nerve and the region occupied by deutocerebral projection neurons after stimulation of the olfactory globular tract in the optic nerve and were blocked by 1 μM tetrodotoxin. Action potentials appeared to propagate to the glomerular layer of the hemiellipsoid body where synaptic responses were recorded from a restricted region of the hemiellipsoid body occupied by dendrites of hemiellipsoid body neurons. Action potentials were also recorded from processes of hemiellipsoid body neurons located in the medulla terminalis. Synaptic responses in the hemiellipsoid body and medulla terminalis were eliminated by addition to the saline of 500 μM Cd2+or 20 mM Co2+, whereas the action potential attributed to branches of deutocerebral projection neurons in the hemiellipsoid body remained unaffected. Action potentials of hemiellipsoid body neurons in the medulla terminalis evoked postsynaptic potentials (50- to 200-ms duration) with an unidentified target in the medulla terminalis. Transient absorption signals were not detected in either the internal or external medulla nor were they recorded from other parts of the optic lobes in response to electrical stimulation of axons of the deutocerebral projection neurons. Functional maps of optical activity, together with electrophysiological and pharmacological findings, suggest that γ-aminobutyric acid affects synaptic transmission in glomeruli of the hemiellipsoid body. Synapses of the olfactory pathway located in the medulla terminalis may act as a “filter,” modifying visual information processing during olfactory stimulation.