bluuebunny/crossref_metadata_2025 huggingface dataset:
Opposite Functions of Histamine H1 and H2 Receptors and H3 Receptor in Substantia Nigra Pars Reticulata
Authors: Zhou Fu-Wen , Xu Jian-Jun , Zhao Yu , LeDoux Mark S. , Zhou Fu-Ming
Published: May 2006

The substantia nigra pars reticulata (SNr) is a key basal ganglia output nucleus. Inhibitory outputs from SNr are encoded in spike frequency and pattern of the inhibitory SNr projection neurons. SNr output intensity and pattern are often abnormal in movement disorders of basal ganglia origin. In Parkinson’s disease, histamine innervation and histamine H3 receptor expression in SNr may be increased. However, the functional consequences of these alterations are not known. In this study, whole cell patch-clamp recordings were used to elucidate the function of different histamine receptors in SNr. Histamine increased SNr inhibitory projection neuron firing frequency and thus inhibitory output. This effect was mediated by activation of histamine H1 and H2 receptors that induced inward currents and depolarization. In contrast, histamine H3 receptor activation hyperpolarized and inhibited SNr inhibitory projection neurons, thus decreasing the intensity of basal ganglia output. By the hyperpolarization, H3 receptor activation also increased the irregularity of the interspike intervals or changed the pattern of SNr inhibitory neuron firing. H3 receptor–mediated effects were normally dominated by those mediated by H1 and H2 receptors. Furthermore, endogenously released histamine provided a tonic, H1 and H2 receptor–mediated excitation that helped keep SNr inhibitory projection neurons sufficiently depolarized and spiking regularly. These results suggest that H1 and H2 receptors and H3 receptor exert opposite effects on SNr inhibitory projection neurons. Functional balance of these different histamine receptors may contribute to the proper intensity and pattern of basal ganglia output and, as a consequence, exert important effects on motor control.
Coordinated Turn-and-Reach Movements. I. Anticipatory Compensation for Self-Generated Coriolis and Interaction Torques
Authors: Pigeon Pascale , Bortolami Simone B. , DiZio Paul , Lackner James R.
Published: May 2006

When reaching movements involve simultaneous trunk rotation, additional interaction torques are generated on the arm that are absent when the trunk is stable. To explore whether the CNS compensates for such self-generated interaction torques, we recorded hand trajectories in reaching tasks involving various amplitudes and velocities of arm extension and trunk rotation. Subjects pointed to three targets on a surface slightly above waist level. Two of the target locations were chosen so that a similar arm configuration relative to the trunk would be required for reaching to them, one of these targets requiring substantial trunk rotation, the other very little. Significant trunk rotation was necessary to reach the third target, but the arm's radial distance to the body remained virtually unchanged. Subjects reached at two speeds—a natural pace (slow) and rapidly (fast)—under normal lighting and in total darkness. Trunk angular velocity and finger velocity relative to the trunk were higher in the fast conditions but were not affected by the presence or absence of vision. Peak trunk velocity increased with increasing trunk rotation up to a maximum of 200°/s. In slow movements, peak finger velocity relative to the trunk was smaller when trunk rotation was necessary to reach the targets. In fast movements, peak finger velocity was ∼1.7 m/s for all targets. Finger trajectories were more curved when reaching movements involved substantial trunk rotation; however, the terminal errors and the maximal deviation of the trajectory from a straight line were comparable in slow and fast movements. This pattern indicates that the larger Coriolis, centripetal, and inertial interaction torques generated during rapid reaches were compensated by additional joint torques. Trajectory characteristics did not vary with the presence or absence of vision, indicating that visual feedback was unnecessary for anticipatory compensations. In all reaches involving trunk rotation, the finger movement generally occurred entirely during the trunk movement, indicating that the CNS did not minimize Coriolis forces incumbent on trunk rotation by sequencing the arm and trunk motions into a turn followed by a reach. A simplified model of the arm/trunk system revealed that additional interaction torques generated on the arm during voluntary turning and reaching were equivalent to ≤1.8 g (1 g = 9.81 m/s2) of external force at the elbow but did not degrade performance. In slow-rotation room studies involving reaching movements during passive rotation, Coriolis forces as small as 0.2 g greatly deflect movement trajectories and endpoints. We conclude that compensatory motor innervations are engaged in a predictive fashion to counteract impending self-generated interaction torques during voluntary reaching movements.
Differential Contribution of Reticulospinal Cells to the Control of Locomotion Induced By the Mesencephalic Locomotor Region
Authors: Brocard Frédéric , Dubuc Réjean
Published: May 2006

In lampreys as in other vertebrates, the reticulospinal (RS) system relays inputs from the mesencephalic locomotor region (MLR) to the spinal locomotor networks. Semi-intact preparations of larval sea lamprey were used to determine the relative contribution of the middle (MRRN) and the posterior (PRRN) rhombencephalic reticular nuclei to swimming controlled by the MLR. Intracellular recordings were performed to examine the inputs from the MLR to RS neurons. Stimulation of the MLR elicited monosynaptic excitatory responses of a higher magnitude in the MRRN than in the PRRN. This differential effect was not attributed to intrinsic properties of RS neurons. Paired recordings showed that at threshold intensity for swimming, spiking activity was primarily elicited in RS cells of the MRRN. Interestingly, cells of the PRRN began to discharge at higher stimulation intensities only when MRRN cells had reached their maximal discharge rate. Glutamate antagonists were ejected in either nucleus to reduce their activity. Ejections over the MRRN increased the stimulation threshold for evoking locomotion and resulted in a marked decrease in the swimming frequency and the strength of the muscle contractions. Ejections over the PRRN decreased the frequency of swimming. This study provides support for the concept that RS cells show a specific recruitment pattern during MLR-induced locomotion. RS cells in the MRRN are primarily involved in initiation and maintenance of low-intensity swimming. At higher frequency locomotor rhythm, RS cells in both the MRRN and the PRRN are recruited.
γ-Frequency Excitatory Input to Granule Cells Facilitates Dendrodendritic Inhibition in the Rat Olfactory Bulb
Authors: Halabisky Brian , Strowbridge Ben W.
Published: May 2006

Recurrent and lateral inhibition play a prominent role in patterning the odor-evoked discharges in mitral cells, the output neurons of the olfactory bulb. Inhibitory responses in this brain region are mediated through reciprocal synaptic connections made between the dendrites of mitral cells and GABAergic interneurons. Previous studies have demonstrated that N-methyl-d-aspartate (NMDA) receptors on interneurons play a critical role in eliciting GABA release at reciprocal dendrodendritic synapses. In acute olfactory bulb slices, these receptors are tonically blocked by extracellular Mg2+, and recurrent inhibition is disabled. In the present study, we examined the mechanisms by which this tonic blockade could be reversed. We demonstrate that near-coincident activation of an excitatory pathway to the proximal dendrites of GABAergic interneurons relieves the Mg2+ blockade of NMDA receptors at reciprocal dendrodendritic synapses and greatly facilitates recurrent inhibition onto mitral cells. Gating of recurrent and lateral inhibition in the presence of extracellular Mg2+ requires γ-frequency stimulation of glutamatergic axons in the granule cell layer. Long-range excitatory axon connections from mitral cells innervated by different subpopulations of olfactory receptor neurons may provide a gating input to granule cells, thereby facilitating the mitral cell lateral inhibition that contributes to odorant encoding.
Low-Calcium Epileptiform Activity in the Hippocampus In Vivo
Authors: Feng Zhouyan , Durand Dominique M.
Published: May 2006

It has been clearly established that nonsynaptic interactions are sufficient for generating epileptiform activity in brain slices. However, it is not known whether this type of epilepsy model can be generated in vivo. In this paper we investigate low-calcium nonsynaptic epileptiform activity in an intact hippocampus. The calcium chelator EGTA was used to lower [Ca2+]o in the hippocampus of urethane anesthetized rats. Spontaneous and evoked field potentials in CA1 pyramidal stratum and in CA1 stratum radiatum were recorded using four-channel silicon recording probes. Three different types of epileptic activity were observed while synaptic transmission was gradually blocked by a decline in hippocampal [Ca2+]o. A short latency burst, named early-burst, occurred during the early period of EGTA application. Periodic slow-waves and a long latency high-frequency burst, named late-burst, were seen after synaptic transmission was mostly blocked. Therefore these activities appear to be associated with nonsynaptic mechanisms. Moreover, the slow-waves were similar in appearance to the depolarization potential shifts in vitro with low calcium. In addition, excitatory postsynaptic amino acid antagonists could not eliminate the development of slow-waves and late-bursts. The slow-waves and late-bursts were morphologically similar to electrographic seizure activity seen in patients with temporal lobe epilepsy. These results clearly show that epileptic activity can be generated in vivo in the absence of synaptic transmission. This type of low-calcium nonsynaptic epilepsy model in an intact hippocampus could play an important role in revealing additional mechanisms of epilepsy disorders and in developing novel anti-convulsant drugs.
Temporal Pattern Recognition Based on Instantaneous Spike Rate Coding in a Simple Auditory System
Authors: Nabatiyan A. , Poulet J.F.A. , de Polavieja G. G. , Hedwig B.
Published: May 2006

Auditory pattern recognition by the CNS is a fundamental process in acoustic communication. Because crickets communicate with stereotyped patterns of constant frequency syllables, they are established models to investigate the neuronal mechanisms of auditory pattern recognition. Here we provide evidence that for the neural processing of amplitude-modulated sounds, the instantaneous spike rate rather than the time-averaged neural activity is the appropriate coding principle by comparing both coding parameters in a thoracic interneuron (Omega neuron ON1) of the cricket ( Gryllus bimaculatus) auditory system. When stimulated with different temporal sound patterns, the analysis of the instantaneous spike rate demonstrates that the neuron acts as a low-pass filter for syllable patterns. The instantaneous spike rate is low at high syllable rates, but prominent peaks in the instantaneous spike rate are generated as the syllable rate resembles that of the species-specific pattern. The occurrence and repetition rate of these peaks in the neuronal discharge are sufficient to explain temporal filtering in the cricket auditory pathway as they closely match the tuning of phonotactic behavior to different sound patterns. Thus temporal filtering or “pattern recognition” occurs at an early stage in the auditory pathway.
Electrophysiological Differences in the CPG Aerial Respiratory Behavior Between Juvenile and AdultLymnaea
Authors: McComb Chlöe , Meems Ryanne , Syed Naweed , Lukowiak Ken
Published: May 2006

Intact, freely moving juvenile Lymnaea perform aerial respiration significantly less often than do adults. We therefore hypothesized that RPeD1, the central pattern generator (CPG) neuron that initiates rhythmogenesis, would be less active in juveniles than adults. Using both isolated and semi-intact preparations to directly test this hypothesis, we found the opposite; juvenile RPeD1s were significantly smaller and more excitable than RPeD1s from adults. Significant age-related differences were found in the membrane resistance (greater in juveniles), time constant (smaller in juveniles), and rheobase current (lower in juveniles), all of which would tend to make juvenile cells significantly more excitable. However, there were significant age-related differences in the synaptic connectivity within the CPG and in peripheral input to the CPG, all which favor more rhythmic activity in the adult CPG. As was the case for intact Lymnaea, juvenile semi-intact preparations perform aerial respiration less often than do adults. The difference in excitability between juvenile and adult RPeD1s is therefore not sufficient to cause increased rhythmogenesis. Age-related changes in synaptic connectivity within the respiratory CPG and in peripheral modulation allow respiratory rhythmogenesis to be more easily expressed in adults which may compensate for their decreased dependence on cutaneous respiration as their surface to volume ratio changes as the grow in size.
Effects of Amplitude Modulation on the Coding of Interaural Time Differences of Low-Frequency Sounds in the Inferior Colliculus. I. Response Properties
Authors: Sterbing S. J. , D'Angelo W. R. , Ostapoff E.-M. , Kuwada S.
Published: May 2006

Most sounds in the natural environment are amplitude-modulated (AM). To determine if AM alters the neuronal sensitivity to interaural time differences (ITDs) in low-frequency sounds, we tested neuronal responses to a binaural beat stimulus with and without modulation. We recorded from single units in the inferior colliculus of the unanesthetized rabbit. We primarily used low frequency (∼25 Hz) modulation that was identical at both ears. We found that modulation could enhance, suppress, or not affect the discharge rate. In extreme cases, a neuron that showed no response to the unmodulated binaural beat did so when modulation was added to both ears. At the other extreme, a neuron that showed sensitivity to the unmodulated binaural beat ceased firing with modulation. Modulation could also affect the frequency range of ITD sensitivity, best ITD, and ITD tuning width. Despite these changes in individual neurons, averaging across all neurons, the peak and width of the population ITD function remained unchanged. Because ITD-sensitive neurons also time-locked to the modulation frequency, the location and sound attributes are processed simultaneously by these neurons.
Reduced Endplate Currents Underlie Motor Unit Dysfunction in Canine Motor Neuron Disease
Authors: Rich Mark M. , Waldeck Robert. F. , Cork Linda C. , Balice-Gordon Rita J. , Fyffe Robert E. W. , Wang Xueyong , Cope Timothy C. , Pinter Martin J.
Published: May 2006

Hereditary canine spinal muscular atrophy (HCSMA) is an autosomal dominant degenerative disorder of motor neurons. In homozygous animals, motor units produce decreased force output and fail during repetitive activity. Previous studies suggest that decreased efficacy of neuromuscular transmission underlies these abnormalities. To examine this, we recorded muscle fiber endplate currents (EPCs) and found reduced amplitudes and increased failures during nerve stimulation in homozygotes compared with wild-type controls. Comparison of EPC amplitudes with muscle fiber current thresholds indicate that many EPCs from homozygotes fall below threshold for activating muscle fibers but can be raised above threshold following potentiation. To determine whether axonal abnormalities might play a role in causing motor unit dysfunction, we examined the postnatal maturation of axonal conduction velocity in relation to the appearance of tetanic failure. We also examined intracellularly labeled motor neurons for evidence of axonal neurofilament accumulations, which are found in many instances of motor neuron disease including HCSMA. Despite the appearance of tetanic failure between 90 and 120 days, average motor axon conduction velocity increased with age in homozygotes and achieved adult levels. Normal correlations between motor neuron properties (including conduction velocity) and motor unit properties were also observed. Labeled proximal motor axons of several motor neurons that supplied failing motor units exhibited little or no evidence of axonal swellings. We conclude that decreased release of transmitter from motor terminals underlies motor unit dysfunction in HCSMA and that the mechanisms determining the maturation of axonal conduction velocity and the pattern of correlation between motor neuron and motor unit properties do not contribute to the appearance or evolution of motor unit dysfunction.
Motion Adaptation in Area MT
Authors: Van Wezel Richard J. A. , Britten Kenneth H.
Published: May 2006

In many sensory systems, exposure to a prolonged stimulus causes adaptation, which tends to reduce neural responses to subsequent stimuli. Such effects are usually stimulus-specific, making adaptation a powerful probe into information processing. We used dynamic random dot kinematograms to test the magnitude and selectivity of adaptation effects in the middle temporal area (MT) and to compare them to effects on human motion discrimination. After 3 s of adaptation to a random dot pattern moving in the preferred direction, MT neuronal responses to subsequent test patterns were reduced by 26% on average compared with adaptation to a static pattern. This reduction in response magnitude was largely independent of what test stimulus was presented. However, adaptation in the opposite direction changed responses less often and very inconsistently. Therefore motion adaptation systematically and profoundly affects the neurons in MT representing the adapted direction, but much less those representing the opposite direction. In human psychophysical experiments, such adapting stimuli affected direction discrimination, biasing choices away from the adaptation direction. The magnitude of this perceptual shift was consistent with the magnitude of the changes seen in area MT, if one assumes that a motion comparison step occurs after MT.
Movement Rate Effect on Activation and Functional Coupling of Motor Cortical Areas
Authors: Toma Keiichiro , Mima Tatsuya , Matsuoka Takahiro , Gerloff Christian , Ohnishi Tatsuhito , Koshy Benjamin , Andres Frank , Hallett Mark
Published: May 2006

We investigated changes in the activation and functional coupling of bilateral primary sensorimotor (SM1) and supplementary motor (SMA) areas with different movement rates in eight normal volunteers. An auditory-cued repetitive right-thumb movement was performed at rates of 0.5, 0.75, 1, 2, 3, and 4 Hz. As a control condition, subjects listened to pacing tones with no movements. Electroencephalogram (EEG) was recorded from 28 scalp electrodes and electromyogram was obtained from the hand muscles. The event-related changes in EEG band-power (ERpow: activation of each area) and correlation (ERcor: functional coupling between each pair of cortical areas) were computed every 32 ms. Modulations of ERpow and ERcor were inspected in alpha (8–12 Hz) and beta (16–20 Hz) bands. Motor cortical activation and coupling was greater for faster movements. With increasing movement rate, the timing relationship between movement and tone switched from synchronization (for 0.5–1 Hz) to syncopation (for 3–4 Hz). The results suggested that for slow repetitive movements (0.5–1 Hz), each individual movement is separately controlled, and EEG activation and coupling of the motor cortical areas were immediately followed by transient deactivation and decoupling, having clear temporal modulation locked to each movement. In contrast, for fast repetitive movements (3–4 Hz), it appears that the rhythm is controlled and the motor cortices showed sustained EEG activation and continuous coupling.
Differential Thermosensitivity of Sensory Neurons in the Guinea Pig Trigeminal Ganglion
Authors: Cabanes C. , Viana F. , Belmonte C.
Published: May 2006

Intracellular recordings were employed to study the effects of temperature on membrane properties and excitability in sensory neurons of the intact guinea pig trigeminal ganglion (TG) maintained in vitro. Neurons were classified according to the shape and duration of the action potential into F (short-duration, fast spike) and S (long duration, slow spike with a “hump”) types. Most type F (33/34) neurons had axons with conduction velocities >1.5 m/s, while only 30% (6/23) of type S neurons reached these conduction speeds suggesting differences in myelination. Cooling reduced axonal conduction velocity and prolonged spike duration in both neuronal types. In F-type neurons with strong inward rectification. cooling also increased the excitability, augmenting the input resistance and reducing the current firing threshold. These effects were not observed in S-type neurons lacking inward rectification. In striking contrast to results obtained in cultured TG neurons, cooling or menthol did not induce firing in recordings from the acutely isolated ganglion. However, after application of submillimolar concentrations (100 μM) of the potassium channel blocker 4-aminopyridine (4-AP), 29% previously unresponsive neurons developed cold sensitivity. An additional 31% developed ongoing activity that was sensitive to temperature. Only neurons with strong inward rectification (mostly F-type) became thermosensitive. Cooling- and 4-AP–evoked firing were insensitive to intracellular application of 4-AP or somatic membrane hyperpolarization, suggesting that their action was most prominent at the level of the axon. The lack of excitatory actions of low temperature in the excised intact ganglion contrasts with the impulse discharges induced by cooling in trigeminal nerve terminals of the same species, suggesting a critical difference between cold-transduction mechanisms at the level of the nerve terminals and the soma.
Neuronal Responses in Cat Primary Auditory Cortex to Electrical Cochlear Stimulation: IV. Activation Pattern for Sinusoidal Stimulation
Authors: Raggio Marcia W. , Schreiner Christoph E.
Published: May 2006

Patterns of threshold distributions for single-cycle sinusoidal electrical stimulation and single pulse electrical stimulation were compared in primary auditory cortex of the adult cat. Furthermore, the effects of auditory deprivation on these distributions were evaluated and compared across three groups of adult cats. Threshold distributions for single and multiple unit responses from the middle cortical layers were obtained on the ectosylvian gyrus in an acutely implanted animal; 2 wk after deafening and implantation (short-term group); and neonatally deafened animals implanted following 2–5 yr of deafness (long-term group). For all three cases, we observed similar patterns of circumscribed regions of low response thresholds in the region of primary auditory cortex (AI). A dorsal and a ventral region of low response thresholds were found separated by a narrow, anterior-posterior strip of elevated thresholds. The ventral low-threshold regions in the short-term group were cochleotopically arranged. By contrast, the dorsal region in the short-term animals and both low-threshold regions in long-term deafened animals maintained only weak cochleotopicity. Analysis of the spatial extent of the low-threshold regions revealed that the activated area for sinusoidal stimulation was smaller and more circumscribed than for pulsatile stimulation for both dorsal and ventral AI. The width of the high-threshold ridge that separated the dorsal and ventral low-threshold regions was greater for sinusoidal stimulation. Sinusoidal and pulsatile threshold behavior differed significantly for electrode configurations with low and high minimum thresholds. Differences in threshold behavior and cortical response distributions between the sinusoidal and pulsatile stimulation suggest that stimulus shape plays a significant role in the activation of cortical activity. Differences in the activation pattern for short-term and long-term deafness reflect deafness-induced reorganizational changes based on factors such as differences in excitatory and inhibitory balance that are affected by the stimulation parameters.
Spatial Tuning to Virtual Sounds in the Inferior Colliculus of the Guinea Pig
Authors: Sterbing Susanne J. , Hartung Klaus , Hoffmann Klaus-Peter
Published: May 2006

How do neurons in the inferior colliculus (IC) encode the spatial location of sound? We have addressed this question using a virtual auditory environment. For this purpose, the individual head-related transfer functions (HRTFs) of 18 guinea pigs were measured under free-field conditions for 122 locations covering the upper hemisphere. From 257 neurons, 94% responded to the short (50-ms) white noise stimulus at 70 dB sound pressure level (SPL). Out of these neurons, 80% were spatially tuned with a receptive field that is smaller than a hemifield (at 70 dB). The remainder responded omnidirectionally or showed fractured receptive fields. The majority of the neurons preferred directions in the contralateral hemisphere. However, preference for front or rear positions and high elevations occurred frequently. For stimulation at 70 dB SPL, the average diameter of the receptive fields, based on half-maximal response, was less than a quarter of the upper hemisphere. Neurons that preferred frontal directions responded weakly or showed no response to posterior directions and vice versa. Hence, front/back discrimination is present at the single-neuron level in the IC. When nonindividual HRTFs were used to create the stimuli, the spatial receptive fields of most neurons became larger, split into several parts, changed position, or the response became omnidirectional. Variation of absolute sound intensity had little effect on the preferred directions of the neurons over a range of 20 to 40 dB above threshold. With increasing intensity, most receptive fields remained constant or expanded. Furthermore, we tested the influence of binaural decorrelation and stimulus bandwidth on spatial tuning. The vast majority of neurons with a low characteristic frequency (<2.5 kHz) lost spatial tuning under stimulation with binaurally uncorrelated noise, whereas high-frequency units were mostly unaffected. Most neurons that showed spatial tuning under broadband stimulation (white noise and 1 octave wide noise) turned omnidirectional when stimulated with 1/3 octave wide noise.
Differential Response Properties of IB4-Positive and -Negative Unmyelinated Sensory Neurons to Protons and Capsaicin
Authors: Dirajlal Sahera , Pauers Laura E. , Stucky Cheryl L.
Published: May 2006

Activation of unmyelinated (C-fiber) nociceptors by noxious chemicals plays a critical role in the initiation and maintenance of injury-induced pain. C-fiber nociceptors can be divided into two groups in which one class depends on nerve growth factor during postnatal development and contains neuropeptides, and the second class depends on glial cell line-derived neurotrophic factor during postnatal development and contains few neuropeptides but binds isolectin B4 (IB4). We determined the sensitivity of these two populations to protons and capsaicin using whole cell recordings of dorsal root ganglion neurons from adult mouse. IB4-negative unmyelinated neurons were significantly more responsive to protons than IB4-positive neurons in a concentration-dependent manner. Approximately 86% of IB4-negative neurons responded to pH 5.0 with an inward current compared with only 33% of IB4-positive neurons. The subtypes of proton-evoked currents in IB4-negative unmyelinated neurons were also more diverse. Many IB4-negative neurons exhibited transient, rapidly inactivating proton currents as well as sustained proton currents. In contrast, IB4-positive neurons never displayed transient proton currents and responded to protons only with sustained, slowly inactivating inward currents. The two classes of neurons also responded differently to capsaicin. Twice as many naı̈ve IB4-negative unmyelinated neurons responded to 1 μM capsaicin as IB4-positive neurons, and the capsaicin-evoked currents in IB4-negative neurons were approximately fourfold larger than those in IB4-positive neurons. Interestingly, proton exposure altered the capsaicin responsiveness of the two classes of neurons in opposite ways. Brief preexposure to protons increased the number of capsaicin-responsive IB4-positive neurons by twofold and increased the capsaicin-evoked currents by threefold. Conversely, proton exposure decreased the number of capsaicin-responsive IB4-negative neurons by 50%. These data suggest that IB4-negative unmyelinated nociceptors are initially the primary responders to both protons and capsaicin, but IB4-positive nociceptors have a unique capacity to be sensitized by protons to capsaicin-receptor agonists.
Modulation of Transmission in the Corticospinal and Group Ia Afferent Pathways to Soleus Motoneurons During Bicycling
Authors: Pyndt H. S. , Nielsen J. B.
Published: May 2006

Transmission in the corticospinal and Ia pathways to soleus motoneurons was investigated in healthy human subjects during bicycling. Soleus H reflexes and motor evoked potentials (MEPs) after transcranial magnetic stimulation (TMS) were modulated similarly during the crank cycle being large during downstroke [concomitant with soleus background electromyographic (EMG) activity] and small during upstroke. Tibialis anterior MEPs were in contrast large during upstroke and small during downstroke. The soleus H reflexes and MEPs were also recorded during tonic plantarflexion at a similar ankle joint position, corresponding ankle angle, and matched background EMG activity as during the different phases of bicycling. Relative to their size during tonic plantarflexion, the MEPs were found to be facilitated in the early part of downstroke during bicycling, whereas the H reflexes were depressed in the late part of downstroke. The intensity of TMS was decreased below MEP threshold and used to condition the soleus H reflex. At short intervals (conditioning-test intervals of −3 to −1 ms), TMS produced a facilitation of the H reflex that is in all likelihood caused by activation of the fast monosynaptic corticospinal pathway. This facilitation was significantly larger in the early part of downstroke during bicycling than during tonic plantarflexion. This suggests that the increased MEP during downstroke was caused by changes in transmission in the fast monosynaptic corticospinal pathway. To investigate whether the depression of H reflexes in the late part of downstroke was caused by increased presynaptic inhibition of Ia afferents, the soleus H reflex was conditioned by stimulation of the femoral nerve. At a short interval (conditioning-test interval: −7 to −5 ms), the femoral nerve stimulation produced a facilitation of the H reflex that is mediated by the heteronymous monosynaptic Ia pathway from the femoral nerve to soleus motoneurons. Within the initial 0.5 ms after its onset, the size of this facilitation depends on the level of presynaptic inhibition of the Ia afferents, which mediate the facilitation. The size of the facilitation was strongly depressed in the late part of downstroke, compared with the early part of downstroke, suggesting that increased presynaptic inhibition was indeed responsible for the depression of the H reflex. These findings suggest that there is a selectively increased transmission in the fast monosynaptic corticospinal pathway to soleus motoneurons in early downstroke during bicycling. It would seem likely that one cause of this is increased excitability of the involved cortical neurons. The increased presynaptic inhibition of Ia afferents in late downstroke may be of importance for depression of stretch reflex activity before and during upstroke.
NO Enhances Presynaptic Currents During Cerebellar Mossy Fiber—Granule Cell LTP
Authors: Maffei Arianna , Prestori Francesca , Shibuki Katsuei , Rossi Paola , Taglietti Vanni , D'Angelo Egidio
Published: May 2006

Nitric oxide (NO) is a candidate retrograde messenger in long-term potentiation (LTP). The NO metabolic pathway is expressed in the cerebellar granule cell layer but its physiological role remained unknown. In this paper we have investigated the role of NO in cerebellar mossy fiber–granule cell LTP, which has postsynaptic N-methyl-d-aspartate (NMDA) receptor-dependent induction. Pre- and postsynaptic current changes were simultaneously measured by using extracellular focal recordings, and NO release was monitored with an electrochemical probe in P21 rat cerebellar slices. High-frequency mossy fiber stimulation induced LTP and caused a significant NO release (6.2 ± 2.8 nM; n = 5) in the granular layer that was dependent on NMDA receptor as well as on nitric oxide synthase (NOS) activation. Preventing NO production by perfusing the NOS inhibitor 100 μM NG-nitro-l-arginine (L-NNA), blocking extracellular NO diffusion by 10 μM MbO2, or inhibiting the NO target guanylyl cyclase (sGC) with 10 μM 1 H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-dione (ODQ) prevented LTP. Moreover, the NO donor 10 μM 2-( N,N-diethylamino)-diazenolate-2-oxide·Na (DEA-NO) induced LTP, which was mutually occlusive with LTP generated by high-frequency stimulation, prevented by ODQ, and insensitive to NMDA channel blockade (50 μM APV + 25 μM 7-Cl-kyn) or interruption of mossy fiber stimulation. Thus NO is critical for LTP induction at the cerebellar mossy fiber–granule cell relay. Interestingly, LTP manipulations were accompanied by consensual changes in the presynaptic current, suggesting that NO acts as a retrograde signal-enhancing presynaptic terminal excitability.
Beta and Gamma Oscillations in the Olfactory System of the Urethane-Anesthetized Rat
Authors: Neville Kevin R. , Haberly Lewis B.
Published: May 2006

Fast oscillations in the beta (15–40 Hz in awake rats) and gamma (50–100 Hz) frequency ranges are prominent in field potentials induced by odorants in the mammalian olfactory bulb (OB) and piriform cortex (PC). Whereas the gamma oscillation has been studied for >50 yr, the beta oscillation has attracted attention only recently, and its origin, mechanism, and relationship to gamma are unknown. To address these questions, we have examined responses induced by odorants in the urethane-anesthetized rat—a preparation well-suited for the analysis of mechanisms. We found that both oscillations could be induced by odorants in a concentration-dependent manner. Analysis with a concentration series and spectral methods revealed that the beta and gamma oscillations were distinct and not harmonically related, indicating generation by independent mechanisms. The beta oscillation was synchronous at sites ≤4 mm apart in the OB, the greatest distance tested. In contrast, the gamma oscillation was synchronous in some experiments and asynchronous in others (frequency differed slightly at different sites, resulting in progressive phase shifts). Current source-density analysis indicated that, for both oscillations, the field potentials in the OB were generated by synaptic currents in granule cells. The two oscillations were differently affected by surgical interruption of the lateral olfactory tract. This lesion abolished the beta oscillation, whereas the gamma oscillation was still induced in the OB. Our results confirm previous reports that the gamma oscillation is generated within the OB but indicate that the beta oscillation requires the participation of PC.
Coordinated Interlimb Compensatory Responses to Electrical Stimulation of Cutaneous Nerves in the Hand and Foot During Walking
Authors: Haridas Carlos , Zehr E. Paul
Published: May 2006

It has been shown that stimulation of cutaneous nerves innervating the hand (superficial radial, SR) and foot (superficial peroneal, SP) elicit widespread reflex responses in many muscles across the body. These interlimb reflex responses were suggested to be functionally relevant to assist in motor coordination between the arms and legs during motor tasks such as walking. The experiments described in this paper were conducted to test the hypothesis that interlimb reflexes were phase-dependently modulated and produced functional kinematic changes during locomotion. Subjects walked on a treadmill while electromyographic (EMG) activity was collected continuously from all four limbs, and kinematic recordings were made of angular changes across the ankle, knee, elbow, and shoulder joints. Cutaneous reflexes were evoked by delivering trains of electrical stimulation pseudorandomly to the SP nerve or SR nerves in separate trials. Reflexes were phase-averaged according to the time of occurrence in the step cycle, and phasic amplitudes and latencies were calculated. For both nerves, significant phase-dependent modulation (including reflex reversals) of interlimb cutaneous reflex responses was seen in most muscles studied. Both SR and SP nerve stimulation resulted in significant alteration in ankle joint kinematics. The results suggest coordinated and functionally relevant reflex pathways from the SP and SR nerves onto motoneurons innervating muscles in nonstimulated limbs during walking, thus extending observations from the cat to that of the bipedal human.
Fast Rhythmic Bursting Can Be Induced in Layer 2/3 Cortical Neurons by Enhancing Persistent Na+Conductance or by Blocking BK Channels
Authors: Traub Roger D. , Buhl Eberhard H. , Gloveli Tengis , Whittington Miles A.
Published: May 2006

Fast rhythmic bursting (or “chattering”) is a firing pattern exhibited by selected neocortical neurons in cats in vivo and in slices of adult ferret and cat brain. Fast rhythmic bursting (FRB) has been recorded in certain superficial and deep principal neurons and in aspiny presumed local circuit neurons; it can be evoked by depolarizing currents or by sensory stimulation and has been proposed to depend on a persistent gNathat causes spike depolarizing afterpotentials. We constructed a multicompartment 11-conductance model of a layer 2/3 pyramidal neuron, containing apical dendritic calcium-mediated electrogenesis; the model can switch between rhythmic spiking (RS) and FRB modes of firing, with various parameter changes. FRB in this model is favored by enhancing persistent gNaand also by measures that reduce [Ca2+]ior that reduce the conductance of gK(C)(a fast voltage- and Ca2+-dependent conductance). Axonal excitability plays a critical role in generating fast bursts in the model. In vitro experiments in rat layer 2/3 neurons confirmed (as shown previously by others) that RS firing could be switched to fast rhythmic bursting, either by buffering [Ca2+]ior by enhancing persistent gNa. In addition, our experiments confirmed the model prediction that reducing gKC(with iberiotoxin) would favor FRB. During the bursts, fast prepotentials (spikelets) could occur that did not originate in apical dendrites and that appear to derive from the axon. We suggest that modulator-induced regulation of [Ca2+] dynamics or of BK channel conductance, for example via protein kinase A, could play a role in determining the firing pattern of neocortical neurons; specifically, such modulation could play a role in regulating whether neurons respond to strong stimulation with fast rhythmic bursts.
Hippocampus Retains the Periodicity of Gamma Stimulation In Vivo
Authors: Mikkonen J. E. , Grönfors T. , Chrobak J. J. , Penttonen M.
Published: May 2006

Several behavioral state dependent oscillatory rhythms have been identified in the brain. Of these neuronal rhythms, gamma (20–70 Hz) oscillations are prominent in the activated brain and are associated with various behavioral functions ranging from sensory binding to memory. Hippocampal gamma oscillations represent a widely studied band of frequencies co-occurring with information acquisition. However, induction of specific gamma frequencies within the hippocampal neuronal network has not been satisfactorily established. Using both in vivo intracellular and extracellular recordings from anesthetized rats, we show that hippocampal CA1 pyramidal cells can discharge at frequencies determined by the preceding gamma stimulation, provided that the gamma is introduced in theta cycles, as occurs in vivo. The dynamic short-term alterations in the oscillatory discharge described in this paper may serve as a coding mechanism in cortical neuronal networks.
Stimulation-Evoked Eye Movements With and Without the Lateral Rectus Muscle Pulley
Authors: Dimitrova Diana M. , Shall Mary S. , Goldberg Stephen J.
Published: May 2006

Recent studies have suggested that extraocular muscle (EOM) pulleys, composed of collagen, elastin, and smooth muscle, are among the tissues surrounding the eye. High-resolution magnetic-resonance imaging appears to indicate that the pulleys serve to both constrain and alter the pulling paths of the EOMs. The active pulley hypothesis suggests that the orbital layer of the EOMs inserts on the pulley and serves to control it. Based on anatomical data, the active pulley hypothesis also suggests that the orbital layer does not rotate the eye within the orbit; this is done by the global layer of the muscle. However, no physiological data exist to confirm this hypothesis. Here we used stimulation-evoked eye movements in anesthetized monkeys and cats before and after destruction of the lateral rectus muscle pulley by removal of the lateral bony orbit and adjacent orbital tissue. The absence of these structures resulted in increased lateral, in the primate, and medial, in the cat, eye-movement amplitude and velocity. Vertical eye movements in the cat were not significantly affected. The results indicate that these increases, confined to horizontal eye-movement amplitude and velocity, may be attributed to passive properties within the orbit. In relation to the active pulley hypothesis, we could discern no clear impact (in terms of amplitude or velocity profile of the movements) of lateral eye exposure that could be directly attributable to the active lateral pulley system.
Representation of the Temporal Order of Visual Objects in the Primate Lateral Prefrontal Cortex
Authors: Ninokura Yoshihisa , Mushiake Hajime , Tanji Jun
Published: May 2006

Recollecting a past episode involves remembering the temporal order of events. We studied cellular activity in the lateral prefrontal cortex (PFC) of two monkeys that were required to remember the temporal order in which visual objects appeared and to reach for each object in the same order after a delay. Here, we report the cellular activity in the lateral PFC, focusing on the delay period. We found that 43% of the delay-period activity was selective for the sequence in which the visual objects were presented during the cue period. While the majority of cellular activity was selective for multiple sequences, some cells (31%) were selective for only one of six sequences. Our findings show that PFC cells are involved in holding temporal order information when that information is necessary for planning forthcoming motor behavior.
Nitrergic Prejunctional Inhibition of Purinergic Neuromuscular Transmission in the Hamster Proximal Colon
Authors: Matsuyama Hayato , El-Mahmoudy AbuBakr , Shimizu Yasutake , Takewaki Tadashi
Published: May 2006

Neurogenic ATP and nitric oxide (NO) may play important roles in the physiological control of gastrointestinal motility. However, the interplay between purinergic and nitrergic neurons in mediating the inhibitory neurotransmission remains uncertain. This study investigated whether neurogenic NO modulates the purinergic transmission to circular smooth muscles of the hamster proximal colon. Electrical activity was recorded from circular muscle cells of the hamster proximal colon by using the microelectrode technique. Intramural nerve stimulation with a single pulse evoked a fast purinergic inhibitory junction potential (IJP) followed by a slow nitrergic IJP. The purinergic component of the second IJP evoked by paired stimulus pulses at pulse intervals between 1 and 3 s became smaller than that of the first IJP. This purinergic IJP depression could be observed at pulse intervals <3 s, but not at longer ones, and failed to occur in the presence of NO synthase inhibitor. Exogenous NO (0.3–1 μM), at which no hyperpolarization is produced, inhibited purinergic IJPs, without altering the nitrergic IJP and exogenously applied ATP-induced hyperpolarization. In the presence of both purinoceptor antagonist and nitric oxide synthase (NOS) inhibitor, intramural nerve stimulation with 5 pulses at 20 Hz evoked vasoactive intestinal peptide (VIP)-associated IJPs, suggesting that VIP component may be masked in the IJPs of the hamster proximal colon. Our results suggest that neurogenic NO may modulate the purinergic transmission to circular smooth muscles of the hamster proximal colon via a prejunctional mechanism. In addition, VIP may be involved in the neurotransmitter in the hamster proximal colon.
GABAAReceptor β3 Subunit Deletion Decreases α2/3 Subunits and IPSC Duration
Authors: Ramadan Epolia , Fu Zhanyan , Losi Gabriele , Homanics Gregg E. , Neale Joseph H. , Vicini Stefano
Published: May 2006

Deletion of the β3 subunit of the GABAAreceptor produces severe behavioral deficits and epilepsy. GABAAreceptor-mediated miniature inhibitory postsynaptic currents (mIPSCs) in cortical neurons in cultures from β3 −/− mice were significantly faster than those in β3 +/+ mice and were more prolonged by zolpidem. Surface staining revealed that the number of β2/3, α2, and α3 (but not of α1) subunit-expressing neurons and the intensity of subunit clusters were significantly reduced in β3 −/− mice. Transfection of β3 −/− neurons with β3 cDNA restored β2/3, α2, and α3 subunits immunostaining and slowed mIPSCs decay. We show that the deletion of the β3 subunit causes the loss of a subset of GABAAreceptors with α2 and α3 subunits while leaving a receptor population containing predominantly α1 subunit with fast spontaneous IPSC decay and increased zolpidem sensitivity.
Dendritic Ca2+Transients Evoked by Action Potentials in Rat Dorsal Cochlear Nucleus Pyramidal and Cartwheel Neurons
Authors: Molitor Scott C. , Manis Paul B.
Published: May 2006

Simultaneous fluorescence imaging and electrophysiologic recordings were used to investigate the Ca2+influx initiated by action potentials (APs) into dorsal cochlear nucleus (DCN) pyramidal cell (PC) and cartwheel cell (CWC) dendrites. Local application of Cd2+blocked Ca2+transients in PC and CWC dendrites, demonstrating that the Ca2+influx was initiated by dendritic Ca2+channels. In PCs, TTX eliminated the dendritic Ca2+transients when APs were completely blocked. However, the Ca2+influx could be partially recovered during an incomplete block of APs or when a large depolarization was substituted for the blocked APs. In CWCs, dendritic Ca2+transients evoked by individual APs, or simple spikes, were blocked by TTX and could be recovered during an incomplete block of APs or by a large depolarization. In contrast, dendritic Ca2+transients evoked by complex spikes, a burst of APs superimposed on a slow depolarization, were not blocked by TTX, despite eliminating the APs superimposed on the slow depolarization. These results suggest two different mechanisms for the retrograde activation of dendritic Ca2+channels: the first requires fast Na+channel-mediated APs or a large somatic depolarization, whereas the second is independent of Na+channel activation, requiring only the slow depolarization underlying complex spikes.