bluuebunny/crossref_metadata_2025 huggingface dataset:
Saccades to somatosensory targets. II. motor convergence in primate superior colliculus
Authors: Groh J. M. , Sparks D. L.
Published: December 2017

1. We examined cells with saccade-related activity in the superior colliculus (SC) of monkeys performing saccades to both somatosensory and visual targets. Our goals were 1) to determine whether signals from these separate sensory systems have converged onto a common motor pathway by the level of the SC; 2) to determine the frame of reference of somatosensory saccade signals in the SC; and 3) to relate collicular motor activity to the behavioral characteristics of somatosensory saccades. 2. Somatosensory targets consisted of vibrotactile stimuli delivered to the hands, which were held in fixed spatial positions. Saccades of different directions and amplitudes were elicited from different initial eye positions. Of 86 cells with motor-related activity, 85 (99%) discharged for saccades to both visual and somatosensory targets. The remaining cell was active only for visual saccades. 3. Cells with saccade-related activity had movement fields representing the direction and amplitude of saccades to both visual and somatosensory targets. We found no cells that discharged for saccades to a particular somatosensory target regardless of the vector of the saccade. 4. Small modality-dependent differences in the spatial tuning of the movement fields were observed, but these variations formed no clear pattern. Given the large population of cells active in conjunction with each saccade, these small tuning differences may have no net effect. Because the visual and somatosensory movement fields of individual cells were similar to each other, the inaccuracy of somatosensory saccades is likely to be the result of inaccurate signals reaching the SC, rather than an error signal added downstream. 5. The peak discharge frequency of collicular motor cells was lower for somatosensory saccades than for visual saccades, although the number of spikes in the discharge was about the same. 6. The latency of the onset of the prelude of motor activity following the cue to initiate a saccade was about the same for somatosensory and visual trials, even though somatosensory saccades have longer reaction times than visual saccades. However, the peak of the motor activity was delayed on somatosensory trials such that the timing of the peak was the same with respect to the movement on somatosensory and visual trials. 7. We conclude that the same population of saccade-related neurons in the SC that represents saccades to visual targets also represents saccades to somatosensory targets. Somatosensory saccades are encoded by these cells as the change in eye position necessary to bring the target onto the fovea, rather than the location of the stimulus on the body surface. Modality-dependent differences in the frequency and timing of collicular motor activity may contribute to velocity and reaction time differences.
B64, a newly identified central pattern generator element producing a phase switch from protraction to retraction in buccal motor programs of Aplysia californica
Authors: Hurwitz I. , Susswein A. J.
Published: December 2017

1. Buccal motor programs in Aplysia are characterized by two phases of activity, which represent protraction and retraction of the radula in intact animals. The shift from protraction to retraction is caused by synaptic activity inhibiting neurons that are active during protraction and exciting neurons that are active during retraction. 2. B64, a newly identified neuron present bilaterally in the buccal ganglia, is partially responsible for the phase shift. Stimulating a single B64 causes bilateral inhibition of neurons B31/B32 and other neurons active during protraction and cause bilateral excitation of neurons B4/B5 and other neurons active during retraction. B64 is active throughout retraction. The amplitude and waveforms of the synaptic potentials caused by firing B64 are similar, but not identical, to those seen during retraction. 3. Some of the effects of B64 on B31/B32 and on B4/B5 are monosynaptic, as shown by their maintained presence in high divalent cation seawater, which blocks polysynaptic activity. 4. A brief depolarization of B64 leads to a long-lasting depolarization and firing. The ability of B64 to respond in this way is at least partially caused by an endogenous plateau potential, as this property is still seen after synaptic transmission is blocked. 5. Hyperpolarization of B64 bilaterally and preventing the somata from firing unmasks a large excitatory postsynaptic potential in B64. This procedure does not block the shift from protraction to retraction, indicating that spiking in the B64 somata is not necessary for the phase shift. 6. The firing pattern and synaptic connections of B64 are consistent with the hypothesis that the neuron is part of a central pattern generator underlying buccal motor programs. B64 is monosynaptically inhibited by neurons that are active along with B31/B32, which are responsible for producing the protraction phase of a buccal motor program. During the later portion of the protraction phase B64 is excited. In addition, firing B64 can phase advance and phase delay buccal motor programs. 7. Regulating the firing of B64 can regulate the expression of buccal motor programs. Stimulation of B64 at frequencies of 0.5-1.0 Hz leads to complete inhibition of buccal motor programs, whereas steady-state depolarization of B64 can lead to repetitive bursts of activity.
Activation of GABAB receptors at individual release boutons of the crayfish opener neuromuscular junction produces presynaptic inhibition
Authors: Fischer Y. , Parnas I.
Published: December 2017

1. Presynaptic inhibition in crustaceans involves the activation of gamma-aminobutyric acid-A (GABAA) receptors that produce an increase in chloride conductance at excitatory axon terminals. Such inhibition produced by single inhibitory pulses is blocked by picrotoxin, a GABAA antagonist. 2. Presynaptic inhibition produced by bath application of GABA was not blocked by picrotoxin. Measurements of the membrane resistance of the excitatory axon terminals revealed that substantial presynaptic inhibition still persisted after 50 microM picrotoxin had completely blocked the increase in conductance produced by 10 microM GABA. 3. Baclofen, a GABAB agonist, reduced release from the excitatory nerve terminals, and 20H-Saclofen, a GABAB antagonist, blocked the effect of baclofen and the presynaptic inhibition produced by 10 microM GABA. 4. 20H-Saclofen alone did not block presynaptic inhibition produced by 100 microM GABA, and the combined action of both 20H-Saclofen and picrotoxin was required to block such effects. 5. The excitatory nerve terminals seem to contain GABAA and GABAB receptors. The GABAB receptors are preferentially activated at lower GABA concentrations (in the microM range), whereas both the GABAA and GABAB receptors are activated at high GABA concentrations.
Persistence of the olfactory receptor current in a wide variety of extracellular environments
Authors: Kleene S. J. , Pun R. Y.
Published: December 2017

We measured the current activated by cytoplasmic adenosine 3':5'-cyclic monophosphate (cAMP) in olfactory cilia from the frog Rana pipiens. The odorant-induced current in frog olfactory receptor neurons was also measured for comparison. In both cases, recordings were performed near the neuronal resting potential in a variety of extracellular bath solutions. 2. In Ca(2+)-free baths, cAMP activated an inward current in excised olfactory cilia that was carried entirely by cations. As extracellular Ca2+ was increased, the cationic current decreased while a second current, carried by C1-, increased. Total cAMP-activated current decreased with increasing extracellular CA2+. When external Na+ but not Ca2+ was eliminated, only the C1- component of the current persisted. When external Na+ and Ca2+ were both removed, there was no cAMP-activated current. 3. In receptor neurons, the total odorant-induced receptor current varied in a similar way with the extracellular ionic environment. Under conditions favoring the anionic receptor current, the response amplitude decreased and the latency increased. 4. It is known that olfactory receptor currents persist in a wide variety of extracellular environments. This persistence can be sufficiently explained by the balance between cationic and anionic currents demonstrated here.
Retinal slip neurons in the nucleus of the optic tract and dorsal terminal nucleus in cats with congenital strabismus
Authors: Distler C. , Hoffmann K. P.
Published: December 2017

1. Visual response properties of neurons in the nucleus of the optic tract (NOT) and dorsal terminal nucleus of the accessory optic tract (DTN) were electrophysiologically investigated in five congenitally strabismic cats and compared with normal adult cats and 3- to 4-wk-old kittens. 2. As in normal cats, NOT-DTN cells of strabismic cats preferred horizontal ipsiversive stimulus movement. However, NOT-DTN neurons in strabismic cats altered their activity to a lesser amount per degree change of stimulus direction than do normal adult cats. In addition, NOT-DTN cells in strabismic cats exhibited a broader directional tuning, i.e., they increase their activity to a broader range of directions than control NOT-DTN cells. 3. Spontaneous activity and activity difference between preferred and nonpreferred direction were significantly lower in NOT-DTN neurons of strabismic cats than in normal adult cats and resembled that found in 3-wk-old kittens. Maximal stimulus-related activity was lower than in normal adult cats but higher than in kittens. 4. Visual latencies to onset of movement in the preferred direction were indistinguishable in strabismic and in normal adult cats. Visual latencies to onset of movement in the nonpreferred direction, however, were shorter in strabismic cats than in normal adult cats. 5. The average velocity tuning curve of NOT-DTN cells in strabismic cats was very flat without a well-defined optimal stimulus velocity. Thus it closely resembled data from 3-wk-old kittens. 6. Binocular convergence was significantly altered to a stronger dominance of the contralateral eye in NOT-DTN of strabismic cats. This reduction of binocular neurons was less pronounced than in cats with artificially induced strabismus or in 3-wk-old kittens. 7. In conclusion, the data presented here for retinal slip neurons in the NOT-DTN of strabismic cats closely resemble those from 3-wk-old kittens where no functional cortical input to the NOT-DTN is present. However, the elevated stimulus-driven activity and the still relatively high degree of binocularity give a clear indication of a functional, albeit weak and abnormal, cortical input to the NOT-DTN in these naturally strabismic cats.
Capsaicin-induced currents with distinct desensitization and Ca2+ dependence in rat trigeminal ganglion cells
Authors: Liu L. , Simon S. A.
Published: December 2017

1. Whole cell patch-clamp records from cultured rat trigeminal ganglion cells having soma diameters ranging from 20 to 50 microM revealed that capsaicin activated two inward currents and an outward current. At -60 mV, the inward currents could be distinguished by their different peak times, which were 4.2 +/- 3.1 and 41.4 +/- 16.4 (SD) s. 2. Cells with the smallest soma diameters had the largest current densities. 3. The more rapidly activating current had a linear current-voltage relation and a reversal potential near 0 mV. 4. The more slowly activating current is not a Ca(2+)-activated Cl- current. 5. The peak of the rapid current (Ip)-capsaicin concentration (C) relationship was characterized by Ip/Ipmax = [1 + (C/Kd)n]-1, where n = 1.2 and the dissociation constant (Kd) = 0.68 microM. 6. The rapidly activating current was heterogeneous in regards to both its rate of activation and extent of desensitization. In cells bathed in buffer containing calcium and held at -60 mV, most of the capsaicin-activated currents desensitized. Removal of extracellular Ca2+ could reduce, eliminate, or have no effect on desensitization. 7. At positive holding potentials the currents very slowly desensitized, even in the presence of Ca2+. 8. Repeated 30-s applications of 1 microM capsaicin separated by 0.5, 2.5, and 5.5 min all induced tachyphylaxis. Tachyphylaxis decreased exponentially until the current remained approximately constant. Decreasing the time between capsaicin applications increased the extent of tachyphylaxis, whereas elimination of extracellular Ca2+ markedly reduced tachyphylaxis.
Single-domain/bound calcium hypothesis of transmitter release and facilitation
Authors: Bertram R. , Sherman A. , Stanley E. F.
Published: December 2017

1. We describe a model of transmitter release that is based on the finding that release can be gated during the opening of individual Ca2+ channels, suggesting that the release site can be activated by the Ca2+ domain under a single channel. In this model each release site contains four independent Ca2+ binding sites or gates with unbinding kinetics graded from slow to fast and affinities ranging from high to low. All four gates must be bound for release to occur. Thus synaptic dynamics are governed by the kinetics of Ca2+ binding and unbinding from release sites, not Ca2+ diffusion. 2. Fast facilitation occurs when an action potential invades a terminal with one or more ions remaining bound to the release sites. Residual free Ca2+ is not necessary for facilitation with this mechanism, but if present it would enhance facilitation by binding to high-affinity gates between pulses. 3. This model can account for key features of release. These include fourth-power cooperativity with regard to external Ca2+; a release time course that is virtually independent of an increase in quantal content; an inverse relation between external Ca2+ and the degree of facilitation; and a steplike increase in facilitation with increasing stimulus frequency, with each step corresponding to a unitary decline in the Ca2+ cooperativity. 4. Facilitation of single-channel-based secretion is shown to be robust even if channel opening is stochastic. Spontaneous release of transmitter, assumed to be due in part to spontaneous Ca2+ channel openings, is shown to be elevated during and after a train of impulses. 5. An extension of the model to include multiple Ca2+ channels per release site demonstrates that one role of overlapping Ca2+ domains may be to accentuate depolarization-evoked release relative to spontaneous release.
Orbitofrontal cortex neurons: role in olfactory and visual association learning
Authors: Rolls E. T. , Critchley H. D. , Mason R. , Wakeman E. A.
Published: December 2017

1. The orbitofrontal cortex is implicated in the rapid learning of new associations between visual stimuli and primary reinforcers such as taste. It is also the site of convergence of information from olfactory, gustatory, and visual modalities. To investigate the neuronal mechanisms underlying the formation of odor-taste associations, we made recordings from olfactory neurons in the orbitofrontal cortex during the performance of an olfactory discrimination task and its reversal in macaques. 2. It was found that 68% of odor-responsive neurons modified their responses after the changes in the taste reward associations of the odorants. Full reversal of the neuronal responses was seen in 25% of these neurons. Extinction of the differential neuronal responses after task reversal was seen in 43% of these neurons. 3. For comparison, visually responsive orbitofrontal neurons were tested during reversal of a visual discrimination task. Seventy-one percent of these visual cells showed rapid full reversal of the visual stimulus to which they responded, when the association of the visual with taste was reversed in the reversal task. 4. These demonstrate that of many orbitofrontal cortex olfactory neurons on the taste with which the odor is associated. 5. This modification is likely to be important for setting the motivational value of olfactory for feeding and other rewarded behavior. However, it is less complete, and much slower, than the modifications found or orbit frontal visual during visual-taste reversal. This relative inflexibility of olfactory responses is consistent with the need for some stability is odor-taste associations to facilitate the formation and perception of flavors.
Representation of olfactory information in the primate orbitofrontal cortex
Authors: Rolls E. T. , Critchley H. D. , Treves A.
Published: December 2017

1. To analyze the information represented about individual odor stimuli in the responses of single olfactory neurons in the primate orbitofrontal area, neuronal responses were measured to a set of seven to nine odorants in macaques performing an olfactory discrimination task. The population of neurons analyzed had responses that were significantly differential to the odorants. 2. Information theoretic analyses were applied to the responses of the neurons, and information measures were calculated from the firing rate of the responses and from the principal components of the responses. The information reflected by the firing rate of the response accounted for the majority of the information present (86%) when compared with the information derived from the first three principal components of the spike train. This indicated that temporal encoding had a very minor role in the encoding of olfactory information by single orbitofrontal olfactory cells. 3. The average information about which odorant was presented, averaged across the 38 neurons, was 0.09 bits, a figure that is low when compared with the information values previously published for the responses of temporal lobe face-selective neurons. 4. Application of information theoretic analyses to the responses of these neurons showed how much information about which stimulus was delivered was present in the responses of individual neurons. It was found that for the majority of the neurons significant amounts of information were reflected about one or two of the odorants presented. 5. For each neuron, the information reflected in the responses of that neuron about the reinforcement value and the information about the identity of the odorants were calculated. It is shown that many neurons carry information about which of the odorants was presented; in addition, some neurons reflect information only about the taste association of the stimuli and not about odorant identity. 6. Measurements of the sparseness of the representation indicated that a broadly distributed representation of the identity of odorants was present in this population of neurons.
Recruitment of triceps surae motor units in the decerebrate cat. I. Independence of type S units in soleus and medial gastrocnemius muscles
Authors: Dacko S. M. , Sokoloff A. J. , Cope T. C.
Published: December 2017

1. We tested the hypothesis that reflex inhibition of soleus motor units reflects selective inhibition of slow-twitch (type S) motor units throughout the triceps surae. Physiological properties including type, together with firing behavior, were measured from single motor units in the medial gastrocnemius (MG) muscle of decerebrate cats with the use of intra-axonal recording and stimulation. MG unit firing was contrasted during net inhibition or excitation of the slow-twitch soleus muscle produced by ramp-hold-release stretches of MG. 2. Stretch of the MG muscle increased the firing of type S motor units in the MG regardless of the reflex response of the soleus muscle. When stretch inhibited soleus, each of the 14 type S units sampled from MG either was newly recruited or exhibited increases in the rate of ongoing firing. Increased firing was observed in 320 of 321 stretch trials. For 8 of these 14 units, a total of 155 stretch trials evoked reflex excitation of soleus, and unit firing increased in all trials. 3. For the eight MG type S motor units studied during both reflex inhibition and excitation of soleus, firing rate tended to be higher during inhibition. The higher rates were also associated with the higher MG forces required to elicit soleus inhibition. For one MG type S unit it was possible to compare firing rates during soleus inhibition and excitation for trials of overlapping levels of MG force. For this unit, firing rate was similar, but still appreciably higher, during inhibition. 4. Soleus inhibition was also produced by stretch of the plantaris (PL) or lateral gastrocnemius (LG) muscles. Type S units in PL (n = 2) or in LG (n = 1) were recruited or increased firing rate even when stretch of these muscles produced soleus inhibition. 5. The firing behavior of 12 fast-twitch (type F) units was studied (11 from MG, 1 from PL). All type F units either were recruited or accelerated the rate of firing during soleus inhibition, as well as during soleus excitation. 6. These findings give evidence that reflex inhibition of type S motor units in the soleus muscle does not necessarily reflect an organizational scheme in which there is inactivation of type S units in other active muscles. In the DISCUSSION we point out the absence of direct evidence for selective inactivation of units on the basis of their type classification.
Block of glutamate decarboxylase decreases GABAergic inhibition at the crayfish synapses: possible role of presynaptic metabotropic mechanisms
Authors: Golan H. , Grossman Y.
Published: December 2017

1. The cytosolic concentration of a neurotransmitter is believed to be an important factor determining its release. The effects of 3-mercaptopropionic acid (MP) and aminooxyacetic acid (AOAA), glutamate decarboxylase (GAD) blockers, on GABAergic postsynaptic and presynaptic inhibitory neurotransmission were examined in the crayfish (Procambarus clarkii) opener neuromuscular synapses. 2. Intracellular recordings of evoked excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs) as well as loose macropatch clamp measurements of excitatory postsynaptic currents (EPSCs) and inhibitory postsynaptic currents (IPSCs) were used to evaluate the effects of the drugs, which were applied exclusively to the nerve bundle. 3. Under normal conditions, a stimulus train to the inhibitor preceding the excitor stimulation elicited a large reduction in EPSP amplitude in a time interval-dependent manner. This inhibition is effected by postsynaptic as well as presynaptic processes. 4. Treatment with MP or AOAA decreased the IPSP amplitude and its altered conductance but had no effect on the IPSP reversal potential or the resting potential of the cell. They did, however, slightly increase the Rin of the fiber. 5. Quantal analysis of single IPSCs revealed that GAD blockers increased the number of failures and thus reduced quantal content (m), diminished the probability of release (p), but did not affect the quantum current (q) or the statistical parameter (n), believed to be the number of available active zones. 6. Quantal analysis of EPSCs, released after interaction with the inhibitor, revealed a reduction in m without any effect on q. GAD blockers greatly reduced the efficacy of this inhibition without affecting the EPSC q. 7. GAD blockers increased the output of the excitor release sites by the following mechanisms: 1) increased EPSC, 2) increased EPSC facilitation, or 3) enhancement of spontaneous activity (miniature EPSCs). 8. Short time incubation with picrotoxin and CGP-35348 eliminated IPSCs and evoked inhibition. However, longer exposure (90 min) increased the excitor responses, similarly to the effects of GAD blockers. 9. Baclofen, a gamma-aminobutyric acid-B (GABAB) agonist, antagonized AOAA effects on evoked inhibition. 10. These results demonstrate that GAD blockers decrease postsynaptic and presynaptic inhibition by reducing both tonic and evoked release, most likely by diminishing p. 11. The reduction in GABA synthesis and release revealed a complex mechanism for GABAergic metabotropic regulation of inhibition efficacy and the release from the excitor glutamatergic terminals.
Sign stimulus activates a peptidergic neural system controlling reproductive behavior in Aplysia
Authors: Begnoche V. L. , Moore S. K. , Blum N. , Van Gils C. , Mayeri E.
Published: December 2017

1. In the marine mollusk Aplysia, egg laying is a complex behavior that lasts for up to several hours. We used behavioral and electrophysiological methods to determine how egg laying occurs in groups of animals and how it is related to other aspects of reproductive behavior. 2. Prolonged contact with an existing egg mass by the lips and tentacles of an animal is a sign stimulus for release of egg-laying behavior and two other fixed action patterns in the same individual, mating as a female during egg laying and mating as a male after egg laying. 3. Prolonged contact with the egg mass initiated repetitive spike activity in bag cell neurons, which are part of a peptidergic neural system that modulates neuronal activity in the CNS for up to several hours. The sign stimulus thus activates the neuromodulatory system, which may serve as an innate releasing mechanism, and an associated internal drive, for control of the behavioral sequence.
Distribution and functional properties of glutamate receptors in the leech central nervous system
Authors: Dierkes P. W. , Hochstrate P. , Schlue W. R.
Published: December 2017

1. The effect of kainate and other glutamatergic agonists on the membrane potential (Em), the intracellular Na+ activity (aNai), and the intracellular free Ca2+ concentration ([Ca2+]i) of identified leech neurons and neuropile glial cells was measured with conventional and ion-sensitive microelectrodes, as well as with the use of the iontophoretically injected fluorescent indicators sodium-binding benzofuran isophthalate and Fura-2. 2. In Retzius neurons, AE, L, 8, and 101 motoneurons, and in the unclassified 50 neurons (Leydig cells) and AP neurons, as well as in neuropile glial cells, bath application of 100 microM kainate evoked a marked membrane depolarization and an increase in aNai and [Ca2+]i. The kainate-induced aNai increase persisted in solutions with high Mg2+ concentration in which synaptic transmission is blocked. 3. A membrane depolarization as well as an increase in aNai and [Ca2+]i was also evoked by L-glutamate, quisqualate, and L-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA). The agonist-induced [Ca2+]i increase was inhibited by 6,7-dinitroquinoxaline-2,3-dione (DNQX). 4. In Ca(2+)-free solution, the kainate-induced [Ca2+]i increase was abolished in the neurons and in neuropile glial cells, whereas membrane depolarization and aNai increase were unchanged. In Na(+)-free solution, kainate had no effect on Em, aNai, or [Ca2+]i in the neurons. 5. In the mechanosensory T, P, and N neurons, kainate induced considerably smaller membrane depolarizations than in the other neurons or in neuropile glial cells, and it had no significant effect on aNai or [Ca2+]i. 6. It is concluded that in leech segmental ganglia the majority of the neurons and the neuropile glial cells, but probably not the mechanosensory neurons, possess glutamate receptors of the AMPA-kainate type. In the neurons, the [Ca2+]i increase caused by glutamatergic agonists is due to Ca2+ influx through voltage-dependent Ca2+ channels that are activated by the agonist-induced membrane depolarization.
Role of voltage-gated calcium channels in the generation of activity-induced extracellular pH transients in the rat hippocampal slice
Authors: Paalasmaa P. , Kaila K.
Published: December 2017

1. The role of voltage-gated calcium channels in the generation of activity-induced alkaline shifts in extracellular pH (pHo) was studied in rat hippocampal slices (area CAI) by means of Ca(2+)-and H(+)-selective microlectrodes inserted into the stratum pyramidale and/or stratum radiatum. 2. After complete pharmacological blockade of ionotropic glutamate receptors and gamma-aminobutyric acid-A (GABAA) receptors, trains (5-10 Hz, 5-10s) of antidromic spikes in pyramidal neurons were associated with a fast alkaline transient of up to 0.17 pH units and a fall in the extracellular Ca2+ concentration ([Ca2+]o). The alkaline shift was strongly enhanced upon inhibition of extracellular carbonic anhydrase. 3. Application of 100 microM Ni2+ plus 100 microM Cd2+ inhibited both the fall in [Ca2+]o and the alkaline transient triggered by antidromic spikes. The alkaline shift was abolished in the absence of extracellular Ca2+. 4. In the absence of postsynaptic receptor antagonists, alkaline transients linked to a given level of synaptic excitation in s. radiatum were strongly suppressed after blockade of somatic (and, consequently, of dendritic “backpropagating”) spikes by microdrop application of tetrodotoxin to the cell-body layer. 5. We have previously shown that activity-induced alkaline transients in the CAI region are due to an influx of Ca2+ into neurons, which triggers an influx of H+ ions probably caused by activation of a plasmalemmal Ca2+/H+ ATPase. The present results indicate that much (in s. pyramidale perhaps all) of the pH-changing influx of Ca2+ is mediated by voltage-gated Ca2+ channels.
Role of chloride-homeostasis in the inhibitory control of neuronal network oscillators
Authors: Jarolimek W. , Brunner H. , Lewen A. , Misgeld U.
Published: December 2017

1. Spontaneous synaptic activity in networks formed by dissociated neurons from embryonic rat midbrain was analyzed in tight seal whole cell recordings. 2. Application of furosemide (0.5 mM) to the cell and its surrounding area increased the frequency of spontaneous synaptic currents. Incubation of the culture with furosemide resulted in “rhythmic” burst activity. 3. Furosemide (0.1-0.5 mM) changed equilibrium potentials of inhibitory postsynaptic currents, gamma-aminobutyric acid-A (GABAA) or glycine receptor-mediated Cl- currents by a blockade of Cl(-)-outward transport. Furosemide did not alter the slope conductance of GABAA receptor-mediated currents. Membrane conductance and cell excitability were also unaffected. 4. We conclude that furosemide locked the activity of the network in “burst activity” mode through impairment of inhibition resulting from the disturbance of Cl- homeostasis.
Anterior parietal cortical response to tactile and skin-heating stimuli applied to the same skin site
Authors: Tommerdahl M. , Delemos K. A. , Vierck C. J. , Favorov O. V. , Whitsel B. L.
Published: December 2017

1. The response of anterior parietal cortex to skin stimuli was evaluated with optical intrinsic signal imaging and extracellular microelectrode recording methods in anesthetized squirrel monkeys. 2. Nonnoxious mechanical stimulation (vibrotactile or skin tapping) of the contralateral radial interdigital pad was accompanied by a decrease in reflectance (at 833 nm) in sectors of cytoarchitectonic areas 3b and 1. This intrinsic signal was in register with regions shown by previous receptive field mapping studies to receive low-threshold mechanoreceptor input from the radial interdigital pad. 3. A skin-heating stimulus applied to the contralateral radial interdigital pad with a stationary probe/thermode evoked no discernable intrinsic signal in areas 3b and 1, but evoked a signal within a circumscribed part of area 3a. The region of area 3a responsive to skin heating with the stationary probe/thermode was adjacent to the areas 3b and 1 regions that developed an intrinsic signal in response to vibrotactile stimulation of the same skin site. Skin heating with a stationary probe/thermode also evoked intrinsic signal in regions of areas 4 and 2 neighboring the area 3b/1 regions activated by vibrotactile stimulation of the contralateral radial interdigital pad. 4. The intrinsic signal evoked in area 3a by a series of heating stimuli to the contralateral radial interdigital pad (applied with a stationary probe/thermode) increased progressively in magnitude with repeated stimulation (exhibited slow temporal summation) and remained above prestimulus levels for a prolonged period after termination of repetitive stimulation. 5. Brief mechanical stimuli (,taps”) applied to the contralateral radial interdigital pad with a probe/thermode maintained either at 37 degrees C or at 52 degrees C were accompanied by the development of an intrinsic signal in both area 3a and areas 3b/1. For the 52 degrees C stimulus, the area 3a intrinsic signal was larger and the intrinsic signal in areas 3b/1 smaller than the corresponding signals evoked by the 37 degrees C stimulus. 6. Spike discharge activity was recorded from area 3a neurons during a repetitive heating stimulus applied with a stationary probe/ thermode to the contralateral radial interdigital pad. Like the area 3a intrinsic signal elicited by repetitive heating of the same skin site, the area 3a neuron spike discharge activity also exhibited slow temporal summation and poststimulus response persistence. 7. The experimental findings suggest 1) a leading role for area 3a in the anterior parietal cortical processing of skin-heating stimuli, and 2) the presence of inhibitory interactions between the anterior parietal responses to painful and vibrotactile stimuli consistent with those demonstrated in recent cortical imaging and psychophysical studies of human subjects.
Glycine current in rat septal cholinergic neuron in culture: monophasic positive modulation by Zn2+
Authors: Kumamoto E. , Murata Y.
Published: December 2017

1. Membrane currents induced by glycine (Iglys) were investigated in cholinergic neurons in primary culture, isolated from the septal region of fetal rat brains, by use of the whole cell voltage-clamp recording configuration. A glycine response was observed in 131 of 150 neurons examined. 2. Igly was accompanied by an increase in conductance and reversed the direction at the Cl- equilibrium potential. The Igly-voltage relation was a little outwardly rectifying in a range of -40 to +30 mV in a nearly symmetrical Cl- solution system. 3. Glycine applied by local perfusion produced an Igly, which increased in amplitude sigmoidally with increasing concentrations (EC50 = 110 microM; nH = 1.75) and desensitized at higher concentrations. There was no nondesensitizing component in Igly (100 microM). Strychnine inhibited Igly in a dose-dependent and competitive manner; it took at most 1 min for this action to be attained to a steady level. Schild analysis yielded the dissociation constant for strychnine to be 0.062 microM. Igly was depressed noncompetitively by a gamma-aminobutyric acid-A (GABAA) receptor-channel blocker, picrotoxin, in a dose-dependent manner (IC50 = 45 microM for peak Igly at 100 microM). On the contrary, another GABAA inhibitor, bicuculline (10 microM), did not affect Igly. 4. Igly was unaffected by spermine (1 mM), ethanol (1-100 mM), and diazepam (1 microM) and was depressed by 14% by pentobarbital (100 microM). On the other hand, Zn2+ potentiated Igly in a dose-dependent (EC50 = 9.1 microM; nH = 1.3; 38% increase for Igly at 50 microM by 100 microM Zn2+) and reversible manner. The facilitatory action was due to an increase in the apparent affinity for glycine (by 139% by 100 microM Zn2+), and did not depend on holding potentials. Pb2+ (100 microM) and La3+ (100 microM) also enhanced Igly (50 microM) by 23 and 14%, respectively; these actions were abolished in the presence of Zn2+ (100 microM). Igly was not affected by Ba2+, Sr2+, Co2+, Mn2+, Cd2+, and Al3+ (100 microM each). 5. Rat septal cholinergic neurons in culture were endowed with a Cl(-)-selective glycine receptor channel whose activation was sensitive to strychnine and picrotoxin. Zn2+ induced a positive modulation of the glycine response, possibly through an allosteric interaction with the glycine-binding site; this action was shared by Pb2+ and La3+ with a potency sequence of Zn2+ > Pb2+ > La3+. This metal-ion binding site could serve to enhance a glycine action.
Role of syringeal muscles in controlling the phonology of bird song
Authors: Goller F. , Suthers R. A.
Published: December 2017

1. The contribution of syringeal muscles to controlling the phonology of song was studied by recording bilateral airflow, subsyringeal air sac pressure, electromyograms (EMGs) of six syringeal muscles, and vocal output in spontaneously singing brown thrashers (Toxostoma rufum). 2. EMG activity in musculus syringealis ventralis (vS), the largest syringeal muscle, increases exponentially with the fundamental frequency of the ipsilaterally generated sound and closely parallels frequency modulation. 3. The EMG activity of other syringeal muscles is also positively correlated with sound frequency, but the amplitude of their EMGs changes only a small amount compared with variation in the amplitude of their EMGs correlated with changing syringeal resistance. The elevated activity in all syringeal muscles during high-frequency sounds may reflect an increased need for structural stability during the strong contractions of the largest syringeal muscle (vS). 4. Several syringeal mechanisms are used to generate amplitude modulation (AM). The most common of these involves modulating the rate of syringeal airflow, through activity by adductor (m. syringealis dorsalis and m. tracheobronchialis dorsalis) and abductor (m. tracheobronchialis ventralis) muscles, which change syringeal resistance, switch sound production from one side of the syrinx to the other, or produce rapid oscillatory flow changes. Variation in the phase relationship between AM and EMG bursts during oscillatory airflow suggests complex biomechanical interaction between antagonistic muscles. 5. AM can also arise from acoustic interactions of two independently generated sounds (beat notes) including cross talk signals between the two syringeal halves. In this latter mechanism, sound generated on one side radiates slightly out of phase with the source from the contralateral side, resulting in lateralized AM generation.
Brain-behavior relationships: evidence from practice effects in spatial stimulus-response compatibility
Authors: Iacoboni M. , Woods R. P. , Mazziotta J. C.
Published: December 2017

1. We measured relative cerebral blood flow (rCBF) changes with positron emission tomography and H(2) 15O in six normal subjects repeatedly performing a spatial stimulus-response compatibility task. Subjects had two motor response conditions. They were instructed to respond with the left hand to a left visual field light stimulus and with the right hand to a right visual field light stimulus (compatible condition), and with the right hand to a left visual field light stimulus and with the left hand to a right visual field light stimulus (incompatible condition). Six rCBF measurements per condition were performed in each subject. 2. Reaction times were faster (P < 0.0005) in the compatible (287 ms) than the incompatible (339 ms) condition (spatial stimulus-response compatibility effect). A bilateral increase (P < 0.05) in rCBF in the superior parietal lobule of the two hemispheres was observed during the incompatible condition when compared with the compatible one. No rCBF decreases were observed. Reaction times correlated (P < 0.0001) with the rCBF in the two activated superior parietal lobule areas. 3. Reaction times decreased with practice according to a linear trend (P < 0.05). Practice-related linear rCBF increases (P < 0.05) were observed in the dorsolateral prefrontal, premotor, and primary motor cortex of the left hemisphere. No significant rCBF decreases were observed. 4. Practice did not affect the spatial stimulus-response compatibility effect. A parallel shortening of reaction times was observed in both compatible and incompatible conditions, in both left and right hand responses, and in both left and right visual fields. Accordingly, when rCBF was analyzed, the spatial stimulus-response compatibility by practice interaction did not show any significant activated area. 5. These findings suggest that the two activated areas in the left and right superior parietal lobules subserve the mapping of the visual stimulus spatial attributes onto the motor response spatial attributes and that the rCBF increases in the incompatible response condition represent the more complex computational remapping required when stimuli and response do not match spatially. 6. The dorsolateral prefrontal, premotor, and motor rCBF linear increases in the left hemisphere seem to reflect the effect of practice on cortical processes common to both compatible and incompatible response conditions. These cortical processes presumably strengthen the links between stimuli and responses under different stimulus-response compatibility conditions. The lateralization of the rCBF increases suggests a left hemisphere superiority in these processes.
H2O2 sensitivity of afferent splanchnic C fiber units in vitro
Authors: Adelson D. W. , Wei J. Y. , Kruger L.
Published: December 2017

1. Single-unit impulse activity evoked by transient, focal application of hydrogen peroxide (H2O2) to identified visceral receptive fields has been characterized in an in vitro rat splanchnic nerve-mesentery preparation. In addition to H2O2 responsiveness, units were characterized in terms of sensitivity to mechanical stimuli, warming, and bradykinin. 2. Mesenteric receptive fields of single splanchnic afferent C fibers in vitro were located with the use of warm (approximately 45 degrees C saline) or mechanical search stimuli. After delimitation of the warm-sensitive and/or mechanosensitive receptive field, units were tested for responsiveness to transient, focal application of H2O2. Microliter volumes (usually 1 microliter) of H2O2 (88-880 mM) evoked responses in 25 of 42 (60%) units with identified warm-sensitive and/or mechanosensitive receptive fields, and in an additional 10 units for which H2O2 was the only effective stimulus. 3. Tachyphylaxis to repeated H2O2 stimulation was observed with interstimulus intervals <30 min, but did not indicate irreversible inactivation of the terminal, because 1) during this period warm and mechanical stimuli elicited responses equal to or greater than those before H2O2 treatment, and 2) H2O2 sensitivity was restored after units were allowed to recover. 4. Eight units unresponsive to an initial dose of H2O2 responded vigorously to a repeated application at the same site, suggesting a potentiating effect of prior H2O2 exposure. 5. Sixty-two percent (8 of 13) of H2O2-responsive units, but no (0 of 6) H2O2-unresponsive units responded to transient, focal bradykinin (9-90 nM) application. 6. An indirect mode of H2O2-evoked afferent excitation in some units was suggested by several observations, including the prolonged (up to 8 min) duration of the response of some units to transient H2O2 application, and the occasionally long (>2 min) response latencies to focal application of H2O2 to defined receptive fields. 7. Excitation of splanchnic neurons by H2O2 may be relevant to the modulation of reactive oxygen species production by immunocompetent cells, because sensory neuropeptides contained in these afferent fibers are known to influence the respiratory burst of macrophages and neutrophils.
Inhibitory synaptic transmission in isolated patches of membrane from cultured rat spinal cord and medullary neurons
Authors: Lewis C. A. , Faber D. S.
Published: December 2017

1. To quantify the variability in the characteristics of inhibitory glycinergic and GABAergic currents at single synaptic connections between cultured rat embryonic spinal cord or medullary neurons, we have used patch-clamp techniques to record miniature inhibitory postsynaptic currents (mIPSCs) in cell-attached patches. Experiments were performed with the patch pipette containing either a low-calcium internal saline to allow comparison with subsequent whole cell recordings or external saline with tetrodotoxin, DL-2-amino-5-phosphonovaleric acid, and 6-cyano-7-nitroquinoxaline-2,3-dione, a solution that is more appropriate for bathing a nerve terminal. 2. The mIPSCs recorded from the synapses restricted to the cell-attached patches were characterized by their times to peak, amplitudes, and time constants of decay. The degree of variability in these characteristics was quantified with the use of the following model-independent parameters: the coefficient of variation, skewness, and kurtosis. The distribution of time to peak values has a mean value of 5.6 +/- 0.5 (SE) ms, has the lowest coefficient of variation (0.33 +/- 0.01), is fairly symmetrical, and has a Gaussian shape with respect to peakedness. On the other hand, both the amplitude and decay time constant distributions are highly skewed and more peaked than Gaussian distributions. The mean amplitude is -6.6 +/- 0.6 pA with a coefficient of variation of 0.60 +/- 0.05, whereas the mean decay time constant is 22.8 +/- 1.0 ms with a coefficient of variation of 0.81 +/- 0.03. 3. The amplitude distributions for spontaneous inhibitory currents recorded from cell-attached patches are best fitted by the sum of multiple Gaussians. The coefficient of variation for the first Gaussian peak fitted to the amplitude distributions is 0.290 +/- 0.028. 4. Decay time distributions were consistently best fitted by the sum of four Gaussians with decay constants as follows: D1 = 5.7 +/- 0.2 ms (n = 12), D2 = 11.2 +/- 0.7 ms (n = 11), D3 = 20.6 +/- 0.8 ms (n = 12), and D4 = 43.8 +/- 2.3 ms (n = 16). These mean values are essentially identical to those reported in the preceding paper for mIPSCs recorded in the whole cell configuration. 5. In eight neurons we were able to record mIPSCs both in cell-attached patches and in subsequent whole cell configurations. The properties of mIPSCs recorded from single synapses (i.e., times to peak, amplitude, and time constants of decay) show as much variability as those of mIPSCs recorded subsequently in the whole cell mode; that is, there are no statistically significant differences in the coefficients of variation, skewness, or kurtosis for the three different distributions.
Postsynaptic mechanisms underlying long-term depression of GABAergic transmission in neurons of the deep cerebellar nuclei
Authors: Morishita W. , Sastry B. R.
Published: December 2017

1. The mechanisms underlying long-term depression (LTD) of gamma-aminobutyric acid-A (GABAA) receptor-mediated synaptic transmission induced by 10-Hz stimulation of the inhibitory afferents were investigated using perforated and whole cell voltage-clamp recordings from neurons of the deep cerebellar nuclei (DCN). 2. LTD of inhibitory postsynaptic currents (IPSCs) was reliably induced when the 10-Hz stimulation was delivered under current-clamp conditions where the postsynaptic neuronal membrane was allowed to depolarize. 3. Currents elicited by local applications of the GABAA receptor agonist, 4,5,6,7-tetrahydroisoxazolo [5,4-c]pyridin-3-ol hydrochloride (THIP) were also depressed during LTD. 4. LTD could be induced heterosynaptically and did not require the activation of GABAA receptors during the 10-Hz stimulation. 5. In cells loaded with QX-314 and superfused with media containing 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and 2-amino-5-phosphonovaleric acid (APV), a series of depolarizing pulses (50 mV, 200 ms) induced a sustained depression of the IPSC. However, this was not observed in cells recorded with high bis-(o-aminophenoxy)-N,N,N',N'-tetraacetic acid (BAPTA)-containing pipette solutions or when they were exposed to the L-type Ca2+ channel antagonist, nitrendipine. 6. The 10-Hz-induced LTD was also inhibited by BAPTA and was significantly reduced when DCN cells were loaded with microcystin LR or treated with okadaic acid, both inhibitors of protein phosphatases. 7. These results indicate that increases in postsynaptic [Ca2+] and phosphatase activity can reduce the efficacy of GABAA receptor-mediated synaptic transmission.