bluuebunny/crossref_metadata_2025 huggingface dataset:
Changes in the response properties of neurons in the ventroposterior lateral thalamic nucleus of the raccoon after peripheral deafferentation
Authors: Rasmusson D. D.
Published: December 2017

1. Single neurons in the ventroposterior lateral thalamic nucleus were studied in 10 anesthetized raccoons, 4 of which had undergone amputation of the fourth digit 4-5 mo before recording. Neurons with receptive fields on the glabrous skin of a forepaw digit were examined in response to electrical stimulation of the “on-focus” digit that contained the neuron's receptive field and stimulation of an adjacent, “off-focus” digit. 2. In normal raccoons all neurons responded to on-focus stimulation with an excitation at a short latency (mean 13 ms), whereas only 63% of the neurons responded to off-focus digit stimulation. The off-focus responses had a longer latency (mean 27.2 ms) and a higher threshold than the on-focus responses (800 and 452 microA, respectively). Only 3 of 32 neurons tested with off-focus stimulation had both a latency and a threshold within the range of on-focus values. Inhibition following the excitation was seen in the majority of neurons with both types of stimulation. 3. In the raccoons with digit removal, the region of the thalamus that had lost its major peripheral input (the “deafferented” region) was distinguished from the normal third and fifth digit regions on the basis of the sequence of neuronal receptive fields within a penetration and receptive field size as described previously. 4. Almost all of the neurons in the deafferented region (91%) were excited by stimulation of one or both adjacent digits. The average latency for these responses was shorter (15.3 ms) and the threshold was lower than was the case with off-focus stimulation in control animals. These values were not significantly different from the responses to on-focus stimulation in the animals with digit amputation. 5. These results confirm that reorganization of sensory pathways can be observed at the thalamic level. In addition to the changes in the somatotopic map that have been shown previously with the use of mechanical stimuli, the present paper demonstrates an improvement in several quantitative measures of single-unit responses. Many of these changes suggest that this reorganization could be explained by an increased effectiveness of preexisting, weak connections from the off-focus digits; however, the increase in the proportion of neurons responding to stimulation of adjacent digits may indicate that sprouting of new connections also occurs.
Monosynaptic activation of medium-lead burst neurons from the superior colliculus in the alert cat
Authors: Chimoto S. , Iwamoto Y. , Shimazu H. , Yoshida K.
Published: December 2017

1. Extracellular recordings were made from medium-lead burst neurons (MLBNs) in the paramedian pontomedullary reticular formation rostral and caudal to the abducens nucleus in the alert cat. 2. Single-pulse stimulation of the contralateral superior colliculus during intersaccadic intervals evoked no response in most MLBNs. When collicular stimulation was applied at the beginning of saccades, spikes of MLBNs were consistently evoked with short latencies. The shortest latency was 0.8 ms, indicating monosynaptic activation of MLBNs from the superior colliculus. 3. Results suggest that monosynaptic excitatory effects from the colliculus are concealed by inhibitory input from omnipause neurons (OPNs) during intersaccadic intervals and that the monosynaptic collicular activation is disclosed when this inhibition is removed by a pause in OPN activity at the beginning of saccades.
Selective disruption by protein kinases of G-protein-mediated Ca2+ channel modulation
Authors: Shapiro M. S. , Zhou J. , Hille B.
Published: December 2017

1. We studied the effects of phorbol-12-myristate, 13-acetate (PMA) on G-protein-mediated inhibition of Ca2+ channels by several neurotransmitters in rat superior cervical ganglion (SCG) sympathetic neurons, with the use of the whole cell patch clamp. PMA attenuated membrane-delimited inhibition of calcium currents (ICa) by norepinephrine (NE) and somatostatin by more than half, but did not attenuate inhibition by M1 muscarinic receptors, which use a diffusible cytoplasmic messenger. Inhibition of ICa by NE through pertussis-toxin-sensitive and -insensitive G proteins was equally attenuated by PMA. PMA enhanced ICa in about half the neurons (enhancement of 10 +/- 1%, mean +/- SE) and strongly reduced the holding current in 44 of 61 cells. 2. The M-type K+ current (IM) was not suppressed by PMA, and PMA did not attenuate inhibition of IM by muscarinic agonists, which is also via a diffusible cytoplasmic messenger. 3. Attenuation of NE and somatostatin inhibition by PMA was blocked by 1 microM staurosporine, a broad-spectrum protein kinase inhibitor. Tests with three inhibitors selective for distinct isoforms of protein kinase C (PKC) gave mixed results. PMA's actions were unaffected by 1 microM calphostin C, blocked by 500 nM bisindolylmaleimide, and unaffected by the pseudosubstrate inhibitor PKC19-36. 4. Thus we find that two membrane-delimited signaling pathways that inhibit ion channels in rat SCG neurons are strongly attenuated by PMA, but signaling pathway(s) that use a diffusible cytoplasmic messenger are not. We speculate that a nonstandard PKC isoform, perhaps PKC mu, mediates PMA actions.
Inter- and intra-hemispheric spatiotemporal organization of spontaneous electrocortical oscillations
Authors: MacDonald K. D. , Brett B. , Barth D. S.
Published: December 2017

1. Two 64-channel epipial electrode arrays were positioned on homologous locations of the right and left hemisphere, covering most of primary and secondary auditory and somatosensory cortex in eight lightly anesthetized rats. Array placement was verified with the use of cytochrome oxidase histochemistry. 2. Middle-latency auditory and somatosensory evoked potentials (MAEPs and MSEPs, respectively) and spontaneous oscillations in the frequency range of 20-40 Hz (gamma oscillations) were recorded and found to be spatially constrained to regions of granular cortex, suggesting that both phenomena are closely associated with sensory information processing. 3. The MAEP and MSEP consisted of an initial biphasic sharp wave in primary auditory and somatosensory cortex, respectively, and a similar biphasic sharp wave occurred approximately 4-8 ms later in secondary sensory cortex of the given modality. Averaged gamma oscillations also revealed asynchronous activation of sensory cortex, but with a shorter 2-ms delay between oscillations in primary and secondary regions. Although the long latency shift of the MAEP and MSEP may be due in part to asynchronous activation of parallel thalamocortical projections to primary and secondary sensory cortex, the much shorter shift of gamma oscillations in a given modality is consistent with intracortical coupling of these regions. 4. Gamma oscillations occurred independently in auditory and somatosensory cortex within a given hemisphere. Furthermore, time series averaging revealed that there was no phase-locking of oscillations between the sensory modalities. 5. Gamma oscillations were loosely coupled between hemispheres; oscillations occurring in auditory or somatosensory cortex of one hemisphere were often associated with lower-amplitude oscillations in homologous contralateral sensory cortex. Yet, the fact that time series averaging revealed no interhemispheric phase-locking suggests that the corpus callosum may not coordinate the bilateral gamma oscillations, and that a thalamic modulatory influence may be involved.
Properties of spontaneous inhibitory synaptic currents in cultured rat spinal cord and medullary neurons
Authors: Lewis C. A. , Faber D. S.
Published: December 2017

1. To identify the type(s) and properties of inhibitory postsynaptic receptor(s) involved in synaptic transmission in cultured rat embryonic spinal cord and medullary neurons, we have used whole cell patch-clamp techniques to record miniature inhibitory postsynaptic currents (mIPSCs) in the presence of tetrodotoxin, DL-2-amino-5-phosphonovaleric acid, and 6-cyano-7-nitroquinoxaline-2,3-dione. 2. The mIPSCs recorded from both spinal cord and medullary neurons had skewed amplitude distributions. 3. The glycinergic antagonist strychnine and the GABAergic antagonist bicuculline each decreased both the frequency and mean peak amplitudes of mIPSCs. We conclude that both glycine and gamma-aminobutyric acid (GABA) are neurotransmitters at inhibitory synapses in our cultured cells. 4. Most (approximately 96-97%) mIPSCs decay with single-exponential time constants, and decay time distributions were consistently best fitted by the sum of four Gaussians with decay constants as follows: D1 = 5.8 +/- 0.1 (SE) ms (n = 63), D2 = 12.2 +/- 0.2 ms (n = 61), D3 = 23.2 +/- 0.4 ms (n = 54), and D4 = 44.7 +/- 1.0 ms (n = 57). We conclude that the four classes of decay times represent kinetically different inhibitory postsynaptic receptor populations. 5. Strychnine and bicuculline usually had one of two different effects on the mIPSC decay time constant distributions; either selective decreases in the frequency of mIPSCs with decay times in certain classes (i.e., the D1 class was reduced by bicuculline, the D2 class by strychnine, and the D3 and D4 classes by both antagonists) or a nonselective depression in the frequency of mIPSCs with decay times in all four classes. The particular effect observed in a given neuron was correlated with the presence or absence of ATP and guanosine 5'-triphosphate (GTP) in the patch pipette. Namely, in 71% of the antagonist applications where the pipette contained ATP and GTP, the result was a nonselective decrease in mIPSCs in all decay time constant classes. Conversely, in 54% of the antagonist applications in their absence, the result was a selective decrease in the frequency of mIPSCs in specific decay time constant classes. 6. In some experiments, mIPSCs reappeared in antagonist solution after an essentially complete block. Recovery from block in the continued presence of antagonist was never observed in the absence of ATP and GTP (8 neurons), and, at the same time, 5 of 9 neurons patched with ATP and GTP in the pipette did show recovery (56%).
Ca2+ release from intracellular stores induced by afferent stimulation of CA3 pyramidal neurons in hippocampal slices
Authors: Miller L. D. , Petrozzino J. J. , Golarai G. , Connor J. A.
Published: December 2017

1. Ca2+ imaging and simultaneous intracellular recording were performed on CA3 pyramidal neurons in hippocampal slice cultures and standard acute slices. Both fura-2 and a dextran conjugate of fura-2 (MW = 10,000) were used in the Ca2+ measurements to control for compartmentalization artifacts. Experiments were performed under conditions giving minimal ligand- and voltagegated Ca2+ influx, with the use of competitive and noncompetitive antagonists of ionotropic glutamate receptors and steady-state depolarization, respectively. 2. Tetanic stimulation of stratum lucidum evoked dendritic Ca2+ transients with rapid onset that were blocked by the noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist, MK-801 (2-5 microM), but not by the competitive alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) (10-50 microM). Zn(2+)-containing mossy fiber terminals (assessed by Timm's staining) and postsynaptic structures (thorny excrescences) are preserved in s. lucidum of hippocampal slice cultures. 3. A Ca2+ store loading protocol, consisting of brief repolarizations followed by steady depolarization, primed most of the neurons so that a subsequent tetanus gave a Ca2+ increase in the presence of MK-801 that was reported by both fura-2 and the dextran conjugate. The onset of the Ca2+ increase was significantly delayed (by 2-3 s) with respect to the MK-801-sensitive increase, and often had a different spatial pattern within the neuron. Response characteristics were similar in slice cultures and acute slices. 4. The delayed Ca2+ increase showed a steep rundown with subsequent stimuli, but was restored by further priming by the Ca2+ store loading paradigm. Postsynaptic currents evoked by the tetani under these conditions were not correlated with the magnitude of the delayed Ca2+ transients. 5. Delayed Ca2+ increases were observed in 44% of the neurons dialyzed with normal intracellular solution at room temperature. The success rate of observing delayed Ca2+ transients was increased to 86% in neurons maintained at 30 degrees C, and dialyzed with an inhibitor of the inositol-triphosphate-3-kinase. 6. The delayed Ca2+ transients could not be initiated after inhibition of endosomal Ca(2+)-ATPase-mediated uptake by thapsigargin. 7. Both fura-2 and the dextran conjugate reported increases in resting Ca2+ levels after the loading protocols, that were absent after priming in thapsigargin, and decreases in resting Ca2+ levels after successive tetani in MK-801, suggesting that the Ca2+ changes were largely cytosolic. 8. The present results support the hypothesis that these synaptically mediated, delayed Ca2+ transients represent release from intracellular Ca2+ stores that can be loaded and depleted repeatedly, and are evoked by presynaptic release of endogenous neurotransmitter.
Differential responsiveness of neocortical areas in the parieto-occipital region to low-intensity stimulation in vitro
Authors: Neumann-Haefelin T. , Hagemann G. , Witte O. W.
Published: December 2017

1. Extracellular recording techniques were used to map the responses to low-intensity stimuli across rat neocortical slices prepared from the parieto-occipital region. Intracellular recordings were obtained in regions of particular interest. After electrophysiological recording, slices were fixed in paraformaldehyde (4%) and Nissl-stained to allow identification of cytoarchitectonically discrete areas. 2. In most neocortical areas of the parieto-occipital region (Par1, HL, Fr1, Fr2), low-intensity stimuli applied to layer V evoked only short monophasic field excitatory postsynaptic potentials (fEPSPs) in layer II/III. In Oc2 (secondary visual cortex, rostral part), however, a long-lasting potential (up to 450 ms) consistently followed the short monophasic response seen in the other areas. 3. The late response observed in Oc2 was characterized by its inter-stimulus variability, polyphasic appearance and N-methyl-D-aspartate (NMDA)-receptor dependence. Intracellular recordings obtained from layer II/III pyramidal neurons located in Oc2 revealed short-latency, monophasic early excitatory postsynaptic potentials (eEPSPs) followed by long-lasting excitatory postsynaptic potentials (eEPSPs) followed by long-lasting excitatory postsynaptic potentials (EPSPs), which often triggered several action potentials 4. Recordings with two extracellular electrodes, one positioned directly above the stimulation electrode and the other at a variable distance (but also in layer II/III), suggested that the corresponding excitation spreads across the slice, but does not cross the cytoarchitectonic borders of Oc2. 5. Our data indicate that the electrophysiological responses to low-intensity stimuli differ within the parieto-occipital region of the rat neocortex. The type of response elicited depends on the cytoarchitectonic area in which the stimulus is applied. The results raise the question of whether further differences between neocortical subregions, with respect to basic electrophysiological properties, exist.
Astrocytic inwardly rectifying potassium currents are dependent on external sodium ions
Authors: Ransom C. B. , Sontheimer H. , Janigro D.
Published: December 2017

1. Two subtypes of astrocytes that expressed distinctly different ion channel complements were identified in primary cultures from rat spinal cord and hippocampus using whole cell patch-clamp techniques. One population of cells expressed voltage-activated Na+ currents and displayed outwardly rectifying I-V relationships; the other group of cells had no detectable Na+ currents and pronounced inwardly rectifying I-V curves. 2. Astrocytes expressing Na+ currents were hyperpolarized (by approximately 7 mV) upon removal of external sodium, suggesting a resting Na+ conductance in these cells. In contrast, cells expressing primarily inwardly rectifying K+ currents, Kir, depolarized (by approximately 4-6 mV) in low-sodium solutions. 3. Removal of external Na+ ions increased the input resistance (189% of control) and reduced the whole cell current amplitude (60% of control at -120 mV) of cells with Kir. The reduction in current amplitude was dose-dependent and became apparent after a 10% reduction of [Na+]0 in 7/7 cells tested. At -120 mV, the effect was near maximal in response to a 50% reduction of [Na+]0. 4. The outward potassium currents of cells expressing Na(+)-currents were unaffected by removal of bath Na+. 5. We conclude that the conductance of glial inwardly rectifying K+ channels is dependent on external sodium ions via a mechanism that does not involve sodium ion permeation or blockade of these channels.
Local mechanisms of phase-dependent postsynaptic modifications of NMDA-induced oscillations in the abducens motoneurons: a simulation study
Authors: Kopysova I. L. , Korogod S. M. , Durand J. , Tyc-Dumont S.
Published: December 2017

1. In vivo experiments have shown that extracellular microelectrophoretic application of N-methyl-D-aspartate (NMDA) induced oscillatory plateau potentials with bursts of action potentials in rat abducens motoneurons. The period of these slow NMDA oscillations could be altered by single trigeminal non-NMDA excitatory input delivered at low frequency during the NMDA oscillations. 2. A resetting of the oscillations was observed depending on the phase of slow oscillatory cycle during which the trigeminal excitation occurred. 3. We investigated local mechanisms responsible for the phase-dependent modifications of NMDA oscillations, including contributions of voltage and concentration transients, in the mathematical model of the isopotential membrane compartment equipped with voltage-gated Na+, K+, and Ca2+ channels, with Ca2+-dependent K+ channels, and with ligand-gated NMDA and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor channels. The faithful model was constructed with the use of models described earlier, which were modified by increasing time constants of kinetic variables of all voltage-gated conductances and by including coupled dynamics of voltages and ion concentrations. The changes in ion concentrations were produced near the membrane by transmembrane currents and removal mechanisms (pumps, diffusion). 4. This work focuses on local arrangement of voltage- and ligand-gated conductances and on local ion concentration changes in two separate pools: the postsynaptic pool of AMPA receptors and the extrasynaptic pool. In terms of the electrotonic and diffusional length constants, these pools were electrotonically close but diffusionally remote. 5. It was found that the effect of resetting can be produced by a local interaction between plateau and spike-generating conductances and glutamate receptors. 6. In vivo phase-dependent interactions between NMDA oscillations and AMPA synaptic input were reproduced by the local model only when changes in intracellular sodium and extracellular potassium concentrations were taken into account and the mechanisms of ion removal from postsynaptic pools had slower kinetics than the fast pump system operating in the extracellular pool. 7. Postsynaptic changes in ion concentrations of Na+ and K+ in intra- and extracellular layers near the membrane shift of Nernst equilibrium potentials for these ions depending on the phase of activation of synaptic input. Thus Na+ and k+ components of all transmembrane currents involved in the pattern generation are differently affected by synaptic action during the oscillations. We conclude that slow postsynaptic changes in ion concentrations near the membrane play a key role in the resetting of the NMDA oscillations.
Nature and precision of temporal coding in visual cortex: a metric-space analysis
Authors: Victor J. D. , Purpura K. P.
Published: December 2017

1. We recorded single-unit and multi-unit activity in response to transient presentation of texture and grating patterns at 25 sites within the parafoveal representation of V1, V2, and V3 of two awake monkeys trained to perform a fixation task. In grating experiments, stimuli varied in orientation, spatial frequency, or both. In texture experiments, stimuli varied in contrast, check size, texture type, or pairs of these attributes. 2. To examine the nature and precision of temporal coding, we compared individual responses elicited by each set of stimuli in terms of two families of metrics. One family of metrics, D(spike), was sensitive to the absolute spike time (following stimulus onset). The second family of metrics, D(interval), was sensitive to the pattern of interspike intervals. In each family, the metrics depend on a parameter q, which expresses the precision of temporal coding. For q = 0, both metrics collapse into the "spike count" metric D(Count), which is sensitive to the number of impulses but insensitive to their position in time. 3. Each of these metrics, with values of q ranging from 0 to 512/s, was used to calculate the distance between all pairs of spike trains within each dataset. The extent of stimulus-specific clustering manifest in these pairwise distances was quantified by an information measure. Chance clustering was estimated by applying the same procedure to synthetic data sets in which responses were assigned randomly to the input stimuli. 4. Of the 352 data sets, 170 showed evidence of tuning via the spike count (q = 0) metric, 294 showed evidence of tuning via the spike time metric, 272 showed evidence of tuning via the spike interval metric to the stimulus attribute (contrast, check size, orientation, spatial frequency, or texture type) under study. Across the entire dataset, the information not attributable to chance clustering averaged 0.042 bits for the spike count metric, 0.171 bits for the optimal spike time metric, and 0.107 bits for the optimal spike interval metric. 5. The reciprocal of the optimal cost q serves as a measure of the temporal precision of temporal coding. In V1 and V2, with both metrics, temporal precision was highest for contrast (ca. 10-30 ms) and lowest for texture type (ca. 100 ms). This systematic dependence of q on stimulus attribute provides a possible mechanism for the simultaneous representation of multiple stimulus attributes in one spike train. 6. Our findings are inconsistent with Poisson models of spike trains. Synthetic data sets in which firing rate was governed by a time-dependent Poisson process matched to the observed poststimulus time histogram (PSTH) overestimated clustering induced by D(count) and, for low values of q, D(spike)[q] and D(intervals)[q]. Synthetic data sets constructed from a modified Poisson process, which preserved not only the PSTH but also spike count statistics accounted for the clustering induced by D(count) but underestimated the clustering induced by D(spike)[q] and D(interval)[q].
Inhibition of transient potassium current in cultured and acutely dissociated mouse hippocampal neurons by GABAA receptor activation
Authors: Wu R. L. , Barish M. E.
Published: December 2017

1. The regulation of A-current, one of several transient voltage-gated potassium currents, was studied using whole cell gigaohm seal voltage-clamp techniques on hippocampal pyramidal neurons that were either acutely dissociated from postnatal mouse brain or isolated from embryonic mouse brain and grown in dissociated culture. These neurons also express gamma-aminobutyric acid-A (GABAA) receptors, the activation of which can, under some circumstances, depolarize immature neurons and the dendrites of more mature neurons. 2. Application of GABA (50 microM) reduced the amplitude of A-current when potassium current amplitude was measured during a period of slow and incomplete desensitization of IGABA. A-current was reduced to 67 +/- 9% of control (mean +/- SD, n - 14) in acutely dissociated neurons, and to 64 +/- 11% of control (n = 15) in cultured neurons. Similar A-current reductions were seen in large outside-out membrane patches pulled from somata of cultured neurons, an observation suggesting that imperfect control of membrane voltage was not responsible for A-current inhibition. 3. A-current inhibition exhibited the sensitivity expected of a GABAA-sensitive process. It was mimicked by muscimol and blocked by bicuculline, picrotoxin, and reduction of [Cl-] in the external solution. Baclophen and phaclophen, effective as agonist and antagonist on GABAB receptors, did not affect A-currents or their inhibition. Reduction in extracellular osmolarity (to increase cell swelling as might occur with Cl- entry), or removal of external HCO3- (which might flow inward through GABAA channels and cause local external acidification), did not affect A-current or its inhibition. The mechanisms of inhibition is not clear at present. 4. We suggest that reduced A-current may favor GABA-induced depolarization and consequent activation of voltage-gated calcium channels.
Calcium-induced long-term depression in the visual cortex of the rat in vitro
Authors: Artola A. , Hensch T. , Singer W.
Published: December 2017

1. In many brain areas, including neocortex and hippocampus, excitatory synapses can undergo both long-term potentiation (LTP) and long-term depression (LTD). It is established that a change in the postsynaptic calcium concentration ([Ca2+]i) is critical for the induction of both LTP and LTD. Protocols that induce these long-term synaptic modifications typically involve afferent stimulation. But, in hippocampus, LTP can also be induced by a transient increase of the extracellular calcium concentration ([Ca2+]o). The purpose of the present study was to determine whether raising [Ca2+]o also induces long-term modifications of excitatory synaptic transmission in the neocortex. 2. Intracellular recordings were obtained from regular spiking cells in layers II-III of slices of the rat visual cortex. Test stimuli were evoked with stimulation electrodes located in the white matter (w.m.) below the recorded cell and intracortically (i.c.) adjacent to the cell. Both the depolarizing slope and the amplitude of excitatory postsynaptic potentials (EPSPs) were measured. For exposure to elevated [Ca2+]o, the normal medium ([Ca2+]o = 2 mM) was exchanged for a period of 10 min against a medium containing 4 mM [Ca2+]o. 3. Elevated [Ca2+]o leads, after return to normal medium, to a long-lasting decrease of intracellularly recorded synaptic responses to both w.m. and i.c. stimulation even if activation of these two pathways is discontinued or N-methyl-D-aspartate (NMDA) receptors are blocked during elevated [Ca2+]o. This decrease is due to reduced efficacy of excitatory transmission because it is observed in the presence of the gamma-aminobutyric acid-A (GABAA) receptor antagonist, bicuculline. 4. Induction of LTD by raising [Ca2+]o is voltage dependent. First, elevated [Ca2+]o elicits LTD only in cells whose resting membrane potential (Vmr) is less polarized than -79 mV (and more polarized than -70 mV, which is the Vmr of the least polarized cell). Second, hyperpolarizing cells whose Vmr is in this susceptible range by 20 mV below Vmr during exposure to high [Ca2+]o prevents Ca2+-induced LTD. Third, when elevated [Ca2+]o is associated with postsynaptic depolarizing pulses, LTD is readily induced in cells whose Vmr is more polarized than -79 mV. This voltage dependence implies that the depression is induced by a postsynaptic process and hence that it occurs at synapses formed by excitatory terminals on the recorded neuron. 5. Assuming that a transient elevation of [Ca2+]o leads to an increase of [Ca2+]i, the results of this study suggest that a transient increase of [Ca2+]i is sufficient to elicit LTD. This may provide a mechanism for the induction of heterosynaptic LTD, a depression that occurs in afferents that are silent while the postsynaptic neuron is activated by other inputs.
Threshold for detecting temperature changes in a spider thermoreceptor
Authors: Ehn R. , Tichy H.
Published: December 2017

1. The threshold for detecting a change in temperature of a warm receptor in the wandering spider Cupiennius salei was determined by means of its frequency-dependent noise. To accomplish this, the warm receptor was regarded as a linear system consisting of two components, an amplifier (gain of the frequency response) and noise at its input added to the temperature stimulus (input noise density). 2. The frequency response was investigated with sinusoidal temperature modulations at frequencies between 0.05 and 12.8 Hz. The gain increased by 3.5 dB/octave in the frequency range between 0.05 and 6.4 Hz, from 0.19 to 3.1 degrees C-1. However, at the highest frequency, 12.8 Hz, the gain was reduced. 3. The noise density of the warm receptor was measured by the root-mean-square noise amplitude of the gain. The output noise density of the warm receptor, which describes the noise density of the gain, was constant at approximately 0.2 Hz-0.5 in the 0.05 to 6.4 Hz range, and increased at higher frequencies. The input noise density, given by the ratio of output noise density to gain, decreased by -2.7 dB/octave between 0.05 and 6.4 Hz, from 1.1 to 0.12 degrees C*Hz-0.5. 4. To define the threshold for detection of temperature changes from the input noise density, the energy of the threshold was equated to the energy of the noise. Assuming a signal-to-noise ratio of 1 and an upper limiting frequency of 10 Hz, the threshold estimated for the wandering spider Cupiennius ranges from 0.6 to 0.08 degrees C, depending on whether the inputs from only 1 or all 70 warm receptors of the 10 tarsal organs are combined.
Simultaneous encoding of carotid sinus pressure and dP/dt by NTS target neurons of myelinated baroreceptors
Authors: Rogers R. F. , Rose W. C. , Schwaber J. S.
Published: December 2017

1. We seek to understand the baroreceptor signal processing that occurs centrally, beginning with the transformation of the signal at the first stage of processing. Because quantitative descriptions of the encoding of mean arterial pressure and its derivative with respect to time by baroreceptive second-order neurons have been unavailable, we characterized the responses of nucleus tractus solitarius (NTS) neurons that receive direct myelinated baroreceptor inputs to combinations of these two stimulus variables. 2. In anesthetized, paralyzed, artificially ventilated rabbits, the carotid sinus was vascularly isolated and the carotid sinus nerve was dissected free from surrounding tissue. Single-unit extracellular recordings were made from NTS neurons that received direct (with the use of physiological criteria) synaptic inputs from carotid sinus baroreceptors with myelinated axons. The vast majority of these neurons did not receive ipsilateral aortic nerve convergent inputs. With the use of a computer-controlled linear motor, a piecewise linear pressure waveform containing 32 combinations of pressure and its rate of change with respect to time (dP/dt) was delivered to the ipsilateral carotid sinus. 3. The average NTS firing frequency during the different stimulus combinations of pressure and dP/dt was a nonlinear and interdependent function of both variables. Most notable was the "extinctive" encoding of carotid sinus pressure by these neurons. This was characterized by an increase in firing frequency going from low to medium mean pressures (analyzed at certain positive dP/dt values) followed by a decrease in activity during high-pressure stimuli. All second-order neurons analyzed had their maximal firing rates when dP/dt was positive. 4. All neurons had their maximal firing frequency locations ("receptive field centers") at just 3 of 32 possible pressure-dP/dt coordinates. The responses of a small population of neurons were used to generate a composite description of the encoding of pressure and dP/dt. When combined as a composite of individually normalized values, the encoding of carotid sinus pressure and dP/dt may be approximated with the use of two-dimensional Gaussian functions. 5. We conclude that the population of NTS neurons recorded most faithfully encodes the rate and direction of (mean) pressure change, as opposed to providing the CNS with an unambiguous encoding of absolute pressure. Instead, the activity of these neurons, individually or as a population, serves as an estimate for the first derivative of the myelinated baroreceptor signal's encoding of mean pressure. We therefore speculate that the output of these individual neurons is useful in dynamic, rather than static, arterial pressure control.
Corticocortical input to the smooth and saccadic eye movement subregions of the frontal eye field in Cebus monkeys
Authors: Tian J. R. , Lynch J. C.
Published: December 2017

1. The locations and connections of the smooth and saccadic eye movement subregions of the frontal eye field (FEFsem and FEFsac, respectively) were investigated in seven hemispheres of five Cebus monkeys. The supplementary eye field was also mapped in seven hemispheres and the hand/arm regions of the dorsal and ventral premotor areas were localized in five hemispheres. Monkeys were immobilized during experiments with Telazol, a dissociative anesthetic agent that has no significant effect on microstimulation-induced eye movement parameters (threshold, velocity, and duration). The functional subregions were defined with the use of low threshold intracortical microstimulation (current < or = 50 microA). Then different retrogradely transported fluorescent tracers were placed into these functionally defined regions. 2. The FEFsac in Cebus monkey is in the same location as the one in macaque monkeys, which is in Walker's areas 8a and 45. The FEFsem is located in the posterior shoulder of the superior arcuate sulcus near its medial tip and is therefore more accessible for tracer injections than the one in macaque monkeys. This subregion is within cytoarchitectural area 6a beta, which is distinct from the adjacent area 6a alpha (dorsal premotor area). This smooth eye movement subregion may be comparable with the one in macaque monkeys. 3. Cortical connection patterns of the FEFsac and FEFsem are similar and parallel to each other. The predominant neural input to these two subregions originates in other cortical eye fields, including the supplementary eye field, the parietal eye field, the middle superior temporal area, and the principal sulcus region. These cortical eye fields each contain two separate, almost non-overlapping, distributions of labeled neurons that project to the corresponding frontal eye field (FEF) subregions. These results suggest that there may be similar, but relatively independent, parallel corticocortical networks to control pursuit and saccadic eye movements. The weak connections between the middle temporal area (MT) and FEF suggest that the MT may not provide the major source of visuomotion inputs to the FEF, but that it rather plays a role in mediating visual information that is relayed from the striate and extrastriate cortices via MT to the parietal cortex and then to the FEF. In addition to the well-known neural connections between the lateral intraparietal area and the FEF, additional parietal projections have been demonstrated from the dorsomedial visual area area specifically to the FEFsac and from area 7m specifically to the FEFsem.
Inhibition of bradykinin-induced synovial plasma extravasation produced by intrathecal nicotine is mediated by the hypothalamopituitary adrenal axis
Authors: Miao F. J. , Janig W. , Green P. G. , Levine J. D.
Published: December 2017

1. Bradykinin (BK)-induced plasma extravasation (PE) in the rat knee joint, which is dependent to a large extent on the sympathetic innervation of the synovium, is powerfully inhibited, dose dependently, by intrathecal administration of nicotine, especially after interruption of the impulse traffic in afferents of the abdominal vagus nerve. In this study we investigated in vagotomized animals possible efferent pathways that might mediate the inhibition produced by the intrathecally applied nicotine. We studied the role of the sympathetic supply to the knee joint, of the sympathoadrenal system, and of the hypothalamopituitary-adrenal (HPA) axis in the ability of intrathecal nicotine to inhibit BK-induced PE in the knee joint. The experimental interventions performed were as follows: recording activity in the lumbar sympathetic trunk; antagonizing the effect of epinephrine, released from the adrenal medulla; acute interruption of the lumbar sympathetic trunks; hypophysectomy; and blockade of the glucocorticoid receptors. We employed acutely vagotomized animals because in these animals nicotine-induced inhibition is enhanced. 2. We found that hypophysectomy or blockade of the glucocorticoid receptors markedly attenuated the inhibition of BK-induced PE produced by intrathecal nicotine. 3. Intrathecal nicotine did not affect activity in the sympathetic chain. 4. Acute interruption of the lumbar sympathetic chain, which leaves the sympathetic terminals in the synovium intact but abolishes activity in the sympathetic postganglionic neurons, did not change the inhibition of BK-induced PE produced by intrathecal nicotine. 5. Blockade of the beta 2 adrenoceptors in the knee joint, preventing in this way potential effects of epinephrine released by the adrenal medulla, did not affect the inhibition of BK-induced PE produced by intrathecal nicotine. 6. The results of the present experiments strongly support the hypothesis that the powerful suppression of BK-induced PE in the knee joint generated by intrathecal nicotine is mediated via the HPA axis and not via activity in sympathetic neurons innervating the knee joint or the adrenal medulla. Future studies are needed to determine in which functional contexts this pathway is active in the control of PE in the synovia and of other aspects of inflammation.
Visual, presaccadic, and cognitive activation of single neurons in monkey lateral intraparietal area
Authors: Colby C. L. , Duhamel J. R. , Goldberg M. E.
Published: December 2017

1. Posterior parietal cortex contains neurons that are visually responsive and active in relation to saccadic eye movements. We recorded from single neurons in a subregion of parietal cortex, the lateral intraparietal area (LIP), in alert rhesus monkeys. To characterize more completely the circumstances under which LIP neurons are responsive, we used five tasks designed to test the impact of sensory, motor, and cognitive factors. We obtained quantitative data in multiple tasks in 91 neurons. We measured neural activity during central fixation and in relation to stimulus onset and saccade onset. 2. LIP neurons have visual responses to the onset of a stationary stimulus in the receptive field. These visual responses occurred both in tasks that require a subsequent eye movement toward the stimulus and in tasks in which eye movements are not permitted, indicating that this activity is sensory rather than presaccadic. 3. Visual responses were enhanced when the monkey had to use information provided by the stimulus to guide its behavior. The amplitude of the sensory response to a given stimulus was increased in a task in which the monkey would subsequently make a saccade to the location signaled by the stimulus, as compared with the amplitude of the visual response in a simple fixation task. 4. The visual response was also enhanced when the monkey attended to the stimulus without looking at it. This result shows that enhancement does not reflect saccade preparation because the response is enhanced even when the monkey is not permitted to make a saccade. Instead, enhancement reflects the allocation of attention to the spatial locus of the receptive field. 5. Many LIP neurons had saccade-related activity in addition to their visual responses. The visual response for most neurons was stronger than the saccade-related activation. 6. Saccade-related activity was independent of visual activity. Similar presaccadic activity was observed in trials that included a recent visual stimulus (memory-guided saccade task) and in trials with no visual stimulus (learned saccade task). 7. We observed increases in activity during fixation in tasks in which the monkey could anticipate the onset of a behaviorally significant stimulus. LIP neurons usually showed low levels of background firing in the fixation task during the period before stimulus onset. This background activity was increased in the peripheral attention and memory-guided saccade tasks during the period when the monkey was waiting for a behaviorally relevant stimulus to appear. 8. The results from these several tasks indicate that LIP neurons are activated in a variety of circumstances and are not involved exclusively in sensory processing or motor planning. The modulation of sensory responses by attention and anticipation suggests that cognitive factors play a major role in parietal function.
IPSPs modulate spike backpropagation and associated [Ca2+]i changes in the dendrites of hippocampal CA1 pyramidal neurons
Authors: Tsubokawa H. , Ross W. N.
Published: December 2017

1. We studied the effects of synaptic inhibition on backpropagating Na+ spikes in the apical dendrites of CA1 pyramidal neurons in transverse slices from the rat hippocampus. Action potentials were evoked synaptically by stimulation in the stratum radiatum or antidromically by stimulation in the alveus. 2. Inhibitory postsynaptic potentials, evoked by stimulation in the stratum lacunosum moleculare, reduced the amplitude of single spikes in the distal dendrites but did not change the amplitudes in the somatic or proximal regions. Inhibition also reduced the spike-associated [Ca2+]i changes in the distal dendrites but had little effect on the changes in the proximal part of the cell. Both of these results are consistent with inhibition converting actively backpropagating spikes into passively spreading potentials at some point in the arbor. 3. In most cells, the spike amplitude reduction in the distal dendrites was blocked by bicuculline methiodide (10 microM) and inhibition was most effective when evoked in a time window < 10 ms preceding the action potential. This suggests that the amplitude reduction was due to a conductance shunt activated by gamma-aminobuturic acid-A (GABAA) receptors. Synaptically evoked GABAB responses were detected but usually did not block spike propagation. 4. Direct hyperpolarization in the distal dendrites was also effective in blocking antidromically evoked spike backpropagation but probably does not contribute when the action potentials are evoked synaptically. 5. This effect of inhibition is different from its usual function in synaptic integration because spike generation and propagation down the axon are not significantly affected. This kind of inhibition might be important in regulating transient [Ca2+]i changes in the dendrites including individual dendritic branches.
In vitro characterization of a peripheral afferent pathway of the rat after chronic sciatic nerve section
Authors: Babbedge R. C. , Soper A. J. , Gentry C. T. , Hood V. C. , Campbell E. A. , Urban L.
Published: December 2017

1. We have studied the characteristics of the abnormal properties of damaged myelinated fibers (conduction velocity > 2.0 m/ s) after peripheral nerve injury in a novel in vitro model of the rat sciatic nerve/dorsal root ganglion/dorsal root (L4-5) preparation removed from control naive or sham-operated rats and animals that had received sciatic neurectomy 12-24 days before the in vitro study. A total of 122-245 filaments were recorded in each dorsal root. The proportion of A alpha, beta and A delta fibers were not significantly different between control, sham-operated, and axotomized nerves. Spontaneous activity was recorded in 3.4% (A alpha, beta) and 4.6% (A delta) of fibers in comparison with 0.4% (A alpha, beta) and 0.3% (A delta) in naive controls. 2. A sporadic, irregular, low-frequency (< 1 Hz) firing was seen in 26% of the fibers with spontaneous activity. Periodical (irregular) bursting pattern was observed in 43% of spontaneously active fibers, whereas a relatively stable, ongoing firing pattern (median frequency: 7.1 Hz) was displayed by 31% of active fibers. 3. Mechanosensitivity of the neuroma/peripheral nerve was displayed in preparations from lesioned [axotomized: 18.2% (A alpha, beta) and 14.1% (A delta), sham operated: 2% (A alpha, beta) and 0% (A delta)], but not control naive animals. There was no correlation between the presence of spontaneous activity and mechanosensitivity in single fibers. 4. The principal site of spontaneous activity generation was the dorsal root ganglion. Transection of the peripheral nerve (or removal of the neuroma), while recording from dorsal root filaments, produced a cessation of firing in 21% of fibers firing with ongoing discharge. The remaining active fibers continued firing until the DRG was removed. A sustained injury discharge was observed in damaged fibers but not control, undamaged fibers from naive animals after acute peripheral nerve transection. 5. We present an in vitro model for the study of abnormal primary sensory activity in peripheral neuropathy. Although our data are consistent with in vivo electrophysiological findings in published reports, the proportion of damaged afferent fibers displaying spontaneous activity was significantly lower under in vitro conditions. This model may serve as a valuable tool for further physiological and pharmacological studies of peripheral neuropathy.