bluuebunny/crossref_metadata_2025 huggingface dataset:
Intracellular characterization of neurons in the locust brain signaling impending collision
Authors: Rind F. C.
Published: December 2017

1. In response to a rapidly approaching object, intracellular recordings show that excitation in the locust lobula giant movement detecting (LGMD) neuron builds up exponentially, particularly during the final stages of object approach. After the cessation of object motion, inhibitory potentials in the LGMD then help to terminate this excitation. Excitation in the LGMD follows object recession with a short, constant latency but is cut back rapidly by hyperpolarizing potentials. The timing of these hyperpolarizing potentials in the LGMD is variable, and their latency following object recession is shortest with the highest velocities of motion simulated. The hyperpolarizing potentials last from 50-300 ms and are often followed by re-excitation. The observed hyperpolarizations of the LGMD can occur without any preceding excitation and are accompanied by a measurable conductance increase. The hyperpolarizations are likely to be inhibitory postsynaptic potentials (PSPs). The behavior of the intracellularly recorded inhibitory PSPs (IPSPs) closely parallels that of the feed forward inhibitory loop in the neural network described by Rind and Bramwell. 2. The preference of the LGMD for approaching versus receding objects remains over a wide range of starting and finishing distances. The response to object approach, measured both as membrane potential and spike rate, remains single peaked with starting distances of between 200 and 2,100 mm, and approach speeds of 0.5-2 m/s. These results confirm the behavior predicted by the neural network described by Rind and Bramwell but contradicts the findings of Rind and Simmons, forcing a re-evaluation of the suitability of some of the mechanical visual stimuli used in that study. 3. For depolarization of the LGMD neuron to be maintained or increased throughout the motion of image edges, the edges must move with increasing velocity over the eye. Membrane potential declines before the end of edge motion with constant velocities of edge motion. 4. A second identified neuron, the LGMD2 also is shown to respond directionally to approaching objects. In both the LGMD and LGMD2 neurons, postsynaptic inhibition shapes the directional response to object motion.
Plasticity of dorsal horn cell receptive fields after peripheral nerve regeneration
Authors: Koerber H. R. , Mirnics K.
Published: December 2017

1. The tibial and sural nerves were transected and repaired in nine adult cats. The receptive field (RF) properties of dorsal horn neurons were examined at three different intervals (5-6, 9, or 12 mo) after axotomy. The properties examined included RF location, area, and modality convergence. In some cases, discrete areas of the cell's RF were stimulated electrically while the evoked cord dorsum potentials (CDPs) and any intracellularly recorded responses were simultaneously recorded. 2. At the shortest interval following reinnervation, the somatotopic organization in the affected areas of the dorsal horn was lost. Dorsal horn cells that received input primarily from regenerated fibers had large, low-threshold excitatory RFs that contained much of the reinnervated skin. Those cells with RFs restricted to a fraction of the reinnervated skin had significant components of their RFs on the foot dorsum supplied by intact fibers (i.e., superficial peroneal nerve). 3. At longer intervals the somatotopic organization remained scrambled. Dorsal horn cell low-threshold RFs were significantly reduced in size. Many cells exhibited large areas of excitatory subliminal fringe and concise inhibitory RFs. In addition, those cells that responded to peripheral stimuli across a wide range of stimulus intensities (wide-dynamic-range cells) also exhibited plasticity in the relative sizes of their low- and high-threshold RFs. 4. At the shortest recovery time, focal electrical stimulation of the skin within the RF of an impaled cell and simultaneous recordings of the evoked CDPs and postsynaptic potentials revealed that at numerous locations within the initial large RFs, single fibers or small groups of fibers could be electrically activated that were not connected to the dorsal horn cell. At the longer recovery times there was a much higher incidence of connectivity. 5. These results suggest that mechanisms affecting both synaptic efficacy of afferent fiber connections and/or the establishment of afferent-driven inhibitory inputs may effect the reshaping of dorsal horn cell RFs after reinnervation. These results are discussed in relation to their potential contribution to previously observed cortical plasticity and functional recovery following similar lesions.
Visual motion processing in the anterior ectosylvian sulcus of the cat
Authors: Scannell J. W. , Sengpiel F. , Tovee M. J. , Benson P. J. , Blakemore C. , Young M. P.
Published: December 2017

1. Neurons that are selectively sensitive to the direction of motion of elongated contours have been found in several cortical areas in many species. However, in the striate cortex of the cat and monkey, and the extrastriate posteromedial lateral suprasylvian visual area of the cat, such cells are generally component motion selective, signaling only the direction of movement orthogonal to the preferred orientation; a direction that is not necessarily the same as the motion of the entire pattern or texture of which the cell's preferred contour is part. The primate extrastriate middle temporal area is the only cortical region currently known to contain a substantial population of pattern-motion-selective cells that respond to the shared vector of motion of mixtures of contours. 2. From analyzing published data on the connectivity of the cat's cortex, we predicted that the anterior ectosylvian visual area (AEV), situated within the anterior ectosylvian sulcus, might be a higher-order motion processing area and thus likely to contain pattern-motion-selective neurons. This paper presents the results of a study on neuronal responses in AEV. 3. Ninety percent of AEV cells that responded strongly to drifting grating and/or plaid stimuli were directionally selective (directionality index > 0.5). For this group, the mean directionality index was 0.75. Moreover, 55% of these cells were unequivocally classified as pattern motion selective and only one neuron was classified as definitely component motion selective. Thus high-level pattern motion coding occurs in the cat extrastriate cortex and is not limited to the primate middle temporal area. 4. AEV contains a heterogeneous population of directionally selective cells. There was no clear relation between the degree of directional selectivity for plaids or gratings and the degree of selectivity for pattern motion or component motion. Nevertheless, 28% of the highly responsive cells were both more strongly modulated by plaids than gratings and more pattern motion selective than component motion selective. Such cells could correspond to a population of "selection units" signaling the salience of local motion information. 5. AEV lacks global retinotopic order but the preferred direction of motion of neurons (rather than axis of motion, as in the middle temporal area and the posteromedial lateral suprasylvian visual area) is mapped systematically across the cortex. Our data are compatible with AEV being a nonretinotopic, feature-mapped area in which cells representing similar parts of "motion space" are brought together on the cortical sheet.
Pharmacological dissection of high-voltage-activated Ca2+ current types in acutely dissociated rat supraoptic magnocellular neurons
Authors: Foehring R. C. , Armstrong W. E.
Published: December 2017

1. We used pharmacological blockers and whole cell voltage-clamp recordings from acutely dissociated magnocellular neurons from the rat supraoptic nucleus to test for the presence of L-, N-, P-, Q-, and R-type calcium currents. 2. We found clear evidence for L-type (dihydropyridine sensitive), N-type (blocked by omega-conotoxin (GVIA), and P-type (blocked by omega-agatoxin IVA) currents. Nifedipine blocked 28 +/- 2% (mean +/- SE) of the current, omega-conotoxin GVIA blocked 26 +/- 4%, and omega-agatoxin IVA (25-30 nM) blocked 17 +/- 4%. In addition, omega-conotoxin MVIIC blocked about half (54 +/- 2%) of the current remaining after L-, N-, and P-type currents were blocked, suggesting the presence of Q-type currents. 3. About 20% of the whole cell current was unblocked by the combination of all four blockers, suggesting the presence of a fifth current type. This residual current inactivated slowly at -10 mV.
Functional organization of thalamocortical relays
Authors: Sherman S. M. , Guillery R. W.
Published: December 2017

The thalamus has long been seen as responsible for relaying information on the way to the cerebral cortex, but it has not been until the last decade or so that the functional nature of this relay has attracted significant attention. Whereas earlier views tended to relegate thalamic function to a simple, machine-like relay process, recent research, reviewed in this article, demonstrates complicated circuitry and a rich array of membrane properties underlying the thalamic relay. It is now clear that the thalamic relay does not have merely a trivial function. Suggestions that the thalamic circuits and cell properties only come into play during certain phases of sleep to effectively disconnect the relay are correct as far as they go, but they are incomplete, because they fail to take into account interesting and variable properties of the relay that, we argue, occur during normal waking behavior. Although the specific function of the circuits and cellular properties of the thalamic relay for waking behavior is far from clear, we offer two related hypotheses based on recent experimental evidence. One is that the thalamus is not used just to relay peripheral information from, for example, visual, auditory, or cerebellar inputs, but that some thalamic nuclei are arranged instead to relay information from one cortical area to another. The second is that the thalamus is not a simple, passive relay of information to cortex but instead is involved in many dynamic processes that significantly alter the nature of the information relayed to cortex.
High-frequency oscillations in membrane potentials of medullary inspiratory and expiratory neurons (including laryngeal motoneurons)
Authors: Huang W. X. , Cohen M. I. , Yu Q. , See W. R. , He Q.
Published: December 2017

1. In midcollicular decerebrate, unanesthetized, paralyzed cats ventilated with a cycle-triggered pump system, the properties of high-frequency oscillations (HFOs, 50-100 Hz) in membrane potentials (MPs) of medullary inspiratory (I) and expiratory (E) cells were studied. Simultaneous recordings were taken from bilateral phrenic and recurrent laryngeal (RL) nerves and from cells in the intermediate ventral respiratory group (intVRG, 0-1 mm rostral to the obex) or the caudal ventral respiratory group (cVRG, 2-4 mm caudal to the obex). 2. Spectral coherence analyses were used to detect the presence of HFOs during I in I and E cell MPs. Cross-correlation histograms (CCHs) between the cell and phrenic signals were used to ascertain cell-nerve HFO phase relations and to identify cells as RL motoneurons. Of the 103 cells that had significant HFOs (cell-phrenic coherences > or = 0.1), measurable HFO peak lags in the CCH were seen in 53 cells: 1) RL cells (9 I cells and 7 E cells); and 2) other types of cell (8 intVRG I cells, 18 intVRG E cells, and 11 cVRG E cells). These cells had high HFO correlations; the cell-phrenic coherence range was 0.35-0.94, with a mean HFO frequency of 58 Hz. 3. The cell-phrenic HFO lag (in ms) was measured in the CCH as the lag of the primary peak (peak located nearest to 0 lag). The phase lag was defined as (lag of primary peak in ms)/(HFO period in ms). The phase lags differed markedly between two subsets of cells: 1) RL I cells had HFO depolarization peaks that lagged the phrenic HFO peaks (average cell-phrenic phase lag = -0.18); and 2) the non-RL cells, regardless of location (intVRG or cVRG) and type (I or E), had HFO depolarization peaks leading (preceding) the phrenic HFO peaks (average cell-phrenic phase lag = 0.28). In addition, the cVRG E cells had significantly shorter cell-phrenic phase lags than the intVRG E cells (0.23 vs. 0.31, respectively). 4. These lags can be compared with the (I unit)-phrenic phase lags (average approximately 0.3) found in earlier extracellular studies. 1) There is a transmission delay of about one half HFO cycle from excitatory I cells to RL I cells. 2) Because a depolarization peak in the MP of an E cell corresponds to the start of a hyperpolarizing wave, the excitatory bulbospinal pathways from I cells have transmission times comparable with those of the inhibitory intramedullary pathways from I cells to E cells. 5. These results indicate that study of HFO phase relations can furnish useful information on functional connectivity of medullary respiratory neurons during the I phase.
Sodium-dependent plateau potentials in cultured Retzius cells of the medicinal leech
Authors: Angstadt J. D. , Choo J. J.
Published: December 2017

1. Individual leech Retzius (Rz) cells were removed from mid-body ganglia and plated in cell culture on concanavalin A or polylysine. Experiments on the majority of cells were performed after 6-11 days in culture. Isolated Rz cells were superfused with normal leech saline (NS), cobalt saline (Ca2+ replaced with Co2+), or one of a variety of other modified salines. 2. Prolonged plateau potentials (PPs) with durations ranging from several seconds to nearly 2 min were evoked in isolated Rz cells in response to 1-s depolarizing current pulses delivered under discontinuous current clamp. Some PPs terminated spontaneously while others were terminated with hyperpolarizing current pulses. PPs were associated with a dramatic increase in the input conductance of the neuron. The PP decayed slightly over time, and this decay was accompanied by a small decrease in the input conductance. 3. PP duration was enhanced by penetrating cells with electrodes containing tetraethylammonium (TEA) and by bathing cells in Co2+ saline, but PPs were evoked also in NS and using electrodes without TEA. The effects of TEA and Co2+ saline suggest that voltage-dependent and especially calcium-dependent outward currents normally suppress plateau formation. 4. PPs occurred most reliably in neurons with extensive neurite sprouting. Isolated somata with few or no neurites usually failed to express PP, although there were several exceptions to this trend. 5. PPs persisted when Ca2+ was replaced with either of the calcium channel blockers Co2+, Ni2+, or Mn2+, when 200 microM Cd2+ was added to normal saline, or when Na+ was replaced with Li+. In contrast, PPs were eliminated rapidly when Na+ was replaced with N-methyl-D-glucamine. 6. Isolated Rz cells also expressed repetitive PPs either spontaneously or in response to injection of sustained depolarizing current. Spontaneous repetitive PPs were suppressed by hyperpolarizing current. Repetitive PPs in isolated Rz cells are similar in many respects to the bursting electrical activity induced by Co2+ saline in Rz and other neurons in intact ganglia. 7. The ionic dependence and prolonged duration of PPs suggest that these responses are generated by a persistent voltage-dependent Na+ current. A quantitative computer simulation of PPs was achieved using a depolarization-activated Na+ conductance with very slow inactivation. Repetitive PPs were simulated by addition of a slow outward current in the form of an electrogenic pump.
Force dependent response reversal mediated by low- and high-threshold afferents from the same mechanoreceptor in a crayfish leg
Authors: Leibrock C. S. , Marchand A. R. , Barnes W. J.
Published: December 2017

1. The reflex responses initiated by cuticular stress detector one (CSD1) afferents in anterior levator motor neurnons in the fifth walking leg of crayfish were studied in an in vitro preparation by means of intracellular recordings. 2. The response in the anterior levator reversed with strong mechanical stimulation. Inhibitory responses were correlated with the activation of low-threshold CSD1 units, excitatory responses with the activation of high-threshold CSD1 units. Two opposing reflexes thus originate from the same sense organ at different levels of stimulation. 3. Some low-threshold units were inactive at stimulus strengths that activated the high-threshold units. Other low-threshold units remained active. Their reflex effects were reduced by either pre- or postsynaptic mechanisms. 4. Functionally, this force dependent response reversal could be important in switching from postural/locomotor responses to defensive responses such as limb autotomy.
Compression injury of mammalian spinal cord in vitro and the dynamics of action potential conduction failure
Authors: Shi R. , Blight A. R.
Published: December 2017

1. White matter strips from the ventral spinal cord of adult guinea pigs were isolated in vitro, and their electrophysiological characteristics and response to controlled focal compression injury were examined. A double sucrose gap technique was used for stimulation and recording at opposite ends of a 12.5 mm-diam central well superfused with oxygenated Krebs solution. 2. The compound action potential recorded with the sucrose gap was similar in form to single fiber potentials recorded with intra-axonal electrodes, including the presence of a prolonged depolarizing afterpotential. 3. Three types of conduction block resulting from compression were identified: an immediate, spontaneously reversible component, which may result from a transient increase in membrane permeability and consequent disturbance of ionic distribution; a second component that was irreversible within 1-2 h of recording, perhaps resulting from complete axolemmal disruption; and a third component, which may have been due to disruption of the myelin sheath, that appeared to be reversible with application of 10-100 microM of the potassium channel blocker 4-aminopyridine. 4. Conduction deficits--decreased amplitude and increased latency of the compound potential--were stable between 5 and 60 min postinjury, and their intensity corellated with the extent of initial compression over a full range of severity. 5. Stimulus-response data indicate that mechanical damage to axons in compression was evenly distributed across the caliber spectrum, suggesting that the susceptibility of large caliber axons seen histopathologically after injury in vivo may be based on delayed, secondary processes. 6. The model provides the ability to monitor changes in the properties of central myelinated axons after compression injury in the absence of pathological variables related to vascular damage. This initial investigation found no evidence of secondary deterioration of axons in the 1st h after injury, although there was evidence of both transient and lasting mechanical damage to axons and their myelin sheaths.
D2 dopamine receptor-mediated inhibition of a hyperpolarization-activated current in rod photoreceptors
Authors: Akopian A. , Witkovsky P.
Published: December 2017

1. Using the whole cell patch clamp method, we investigated the effect of dopamine on a hyperpolarization-activated current (Ih) in the inner segments of rod photoreceptors of the Xenopus retina. 2. Ih was elicited by hyperpolarizing voltage steps to -120 mV from a holding potential of -40 mV. Dopamine reversibly reduced Ih in a dose-dependent manner. Dopamine-mediated inhibition of Ih was blocked by the D2 dopamine antagonist sulpiride. 3. The D2 dopamine agonist quinpirole (0.1-20 microM) inhibited Ih whereas the D1 agonist SKF-38393 (100 microM) had no effect on Ih. Quinpirole-induced inhibition of Ih was blocked by sulpiride, but not by the D4 antagonist, clozapine. The D3 agonists (+/-)-7-hydroxy-2-dipropylaminotetralin hydrochloride and trans-7-hydroxy-2[N-propyl-N-(3'-iodo-2'-propenyl)amino]-tetralin maleate were, respectively, 5 and 100 times less effective than quinpirole in inhibiting Ih. 4. Quinpirole failed to reduce Ih when the internal solution contained GDP beta S (500 microM). Internal application GTP gamma S (300 microM) progressively and irreversibly reduced Ih and blocked a further reduction by quinpirole, indicating that the inhibition of Ih by quinpirole involves a G protein. 5. The inhibition of Ih by quinpirole was not affected by intracellularly applied adenosine 3',5'-cyclic monophosphate (cAMP) or by the protein kinase inhibitor H-7, indicating that a cAMP-mediated second messenger cascade does not participate in the dopamine-mediated inhibition. 6. Ih was not altered when the patch pipette contained a nominally Ca(2+)-free internal solution, but the inhibition of Ih by quinpirole was abolished, suggesting an involvement of Ca(2+) in the quinpirole-induced effect. 7. We conclude that a D2 dopamine receptor modulates Ih through the activation of a G protein and that intracellular Ca2+, but not cAMP, plays a key role in this process. 8. The reduction of Ih by dopamine may reduce the ability of rods to signal time-modulated light stimuli.
Electrotonic architecture of hippocampal CA1 pyramidal neurons based on three-dimensional reconstructions
Authors: Mainen Z. F. , Carnevale N. T. , Zador A. M. , Claiborne B. J. , Brown T. H.
Published: December 2017

1. The spread of electrical signals in pyramidal neurons from the CA1 field of rat hippocampus was investigated through multicompartmental modeling based on three-dimensional morphometric reconstructions of four of these cells. These models were used to dissect the electrotonic architecture of these neurons, and to evaluate the equivalent cylinder approach that this laboratory and others have previously applied to them. Robustness of results was verified by the use of wide ranges of values of specific membrane resistance (Rm) and cytoplasmic resistivity. 2. The anatomy exhibited extreme departures from a key assumption of the equivalent cylinder model, the so-called "3/2 power law." 3. The compartmental models showed that the frequency distribution of steady-state electrotonic distances between the soma and the dendritic terminations was multimodal, with a large range and a sizeable coefficient of variation. This violated another central assumption of the equivalent cylinder model, namely, that all terminations are electronically equidistant from the soma. This finding, which was observed both for "centrifugal" (away from the soma) and "centripetal" (toward the soma) spread of electrical signals, indicates that the concept of an equivalent electrotonic length for the whole dendritic tree is not appropriate for these neurons. 4. The multiple peaks in the electrotonic distance distributions, whether for centrifugal or centripetal voltage transfer, were clearly related to the laminar organization of synaptic afferents in the CA1 region. 5. The results in the three preceding paragraphs reveal how little of the electrotonic architecture of these neurons is captured by a simple equivalent cylinder model. The multicompartmental model is more appropriate for exploring synaptic signaling and transient events in CA1 pyramidal neurons. 6. There was significant attenuation of synaptic potential, current, and charge as they spread from the dendritic tree to the soma. Charge suffered the least and voltage suffered the most attenuation. Attenuation depended weakly on Rm and strongly on synaptic location. Delay of time to peak was more distorted for voltage than for current and was more affected by Rm. 7. Adequate space clamp is not possible for most of the synapses on these cells. Application of a somatic voltage clamp had no significant effect on voltage transients in the subsynaptic membrane. 8. The possible existence of steep voltage gradients within the dendritic tree is consistent with the idea that there can be some degree of local processing and that different regions of the neuron may function semiautonomously. These spatial gradients are potentially relevant to synaptic plasticity in the hippocampus, and they also suggest caution in interpreting some neurophysiological results.
Dynamic, spatially nonuniform calcium regulation in frog rods exposed to light
Authors: McCarthy S. T. , Younger J. P. , Owen W. G.
Published: December 2017

1. In intact rods of the bullfrog, Rana Catesbeiana, that were loaded with Fura-2 by incubation, we made high-resolution measurements of Na:Ca,K exchange currents and measured cytosolic free calcium concentrations during exposure to steps of illumination. The calcium dynamics we observed are indicative of unmanipulated rods because Fura-2 had little effect on calcium buffering within the outer segment. 2. In the dark, the total concentration of calcium within the outer segment, determined by integrating the exchange current, was near 50 microM. The free calcium concentration in darkness was 200-400 nM, indicating that > of = 99% of the internal calcium was bound to buffer molecules or equivalently sequestered. 3. During saturating illumination, the concentration of free calcium near the membrane (assayed by the exchange current) fell more rapidly than the space-averaged free calcium concentration (measured with Fura-2), but both had time courses that were best described by a sum of three exponential terms. The time constants were the same for each assay, but the weighting factors were different. 4. The relationship between the exchange current and space-averaged calcium concentration is consistent with significant concentration gradients within the outer segment resulting from high buffering power, diffusional restrictions, and the fact that all net gain and loss of calcium occurs at the membrane. The data further indicate that effective buffering, and hence calcium mobility, is not uniform within the outer segment. 5. Calcium kinetics were independent of the calcium concentration, indicating that the dominant buffers effectively have a low affinity for calcium (KD >> [Ca2+]dark free). 6. The dynamics of calcium changes and of exchange currents evoked by saturating and nonsaturating illumination are completely predictable from changes in the circulating current. Calcium and current are related by a linear transformation, indicating that calcium fluxes within the outer segment are passive and that buffers equilibrate rapidly. 7. Although calcium concentrations change slowly with respect to changes in the circulating current, both measured and calculated calcium dynamics are well correlated with changes in light adaptation. Responses to test flashes depended weakly on the detailed time course of the adapting stimulus but strongly on the free cytosolic calcium concentration at the time the test flash was delivered.
Eye-centered, head-centered, and intermediate coding of remembered sound locations in area LIP
Authors: Stricanne B. , Andersen R. A. , Mazzoni P.
Published: December 2017

1. The lateral intraparietal area (LIP) of the posterior parietal cortex lies within the dorsal cortical stream for spatial vision and processes visual information to plan saccadic eye movements. We investigated how LIP neurons respond when a monkey makes saccades to the remembered location of sound sources in the absence of visual stimulation. 2. Forty-three (36%) of the 118 neurons sampled showed significant auditory triggered activity during the memory period. This figure is similar to the proportion of cells showing visually triggered memory activity. 3. Of the cells showing auditory memory activity, 44% discharged in an eye-centered manner, similar to the way in which LIP cells discharge for visually initiated saccades. Another 33% responded in head-centered coordinates, and the remaining 23% had responses intermediate between the two reference frames. 4. For a substantial number of cells in all three categories, the magnitude of the response was modulated by eye position. Similar orbital "gain fields" had been shown previously for visual saccades. 5. We propose that area LIP is either at the origin of, or participates in, the transformation of auditory signals for oculomotor purposes, and that orbital gains on the discharge are part of this process. 6. Finally, we suggest that, by the level of area LIP, cells are concerned with the abstract quality of where a stimulus is in space, independent of the exact nature of the stimulus.
Long-term depression of Aplysia sensorimotor synapses in cell culture: inductive role of a rise in postsynaptic calcium
Authors: Lin X. Y. , Glanzman D. L.
Published: December 2017

1. Activation of sensory neurons at 2 Hz for 15 min induces long-term depression (LTD) of isolated Aplysia sensorimotor synapses in cell culture. 2. Prior infusion of the Ca2+ chelator 1,2-bis-(2-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid (BAPTA) into the postsynaptic motor neuron blocks the induction of LTD, but not short-term synaptic depression. 3. Invertebrate central synapses possess the capacity for LTD. This form of long-term synaptic plasticity may play an important role in learning in Aplysia.
Intracellular QX-314 inhibits calcium currents in hippocampal CA1 pyramidal neurons
Authors: Talbot M. J. , Sayer R. J.
Published: December 2017

1. The effects of intracellular QX-314 on Ca2+ currents were examined in CA1 pyramidal cells acutely isolated from rat hippocampus. In neurons dialyzed with 10 mM QX-314 (bromide salt), the amplitude of the high-threshold Ca2+ current was on average 20% of that in control cells and the current-voltage relationships (I-Vs) were shifted in the positive voltage direction. 2. The positive shift in the I-Vs was due to the presence of intracellular Br-, because it was reproduced by 10 mM NaBr and was not present when the chloride salt of QX-314 was used. 3. Low-threshold (T-type) Ca2+ currents, at test voltages of -50 and -40 mV, were on average < 45% of control amplitude in cells containing 10 mM QX-314 (chloride salt) and < 10% of control amplitude in cells with 10 mM QX-314 (bromide salt). 4. In neurons dialyzed with 1 mM QX-314, high-threshold Ca2+ currents were still significantly different from control and Na+ currents were not completely blocked. 5. The proportions of high-threshold Ca2+ current blocked by omega-conotoxin GVIA, omega-agatoxin IVA, and nimodipine were similar in cells dialyzed with 10 mM QX-314 and control cells, indicating that the drug does not selectively inhibit any of the Ca2+ channel subtypes distinguished by these antagonists.
Two forms of long-term potentiation in area CA1 activate different signal transduction cascades
Authors: Cavus I. , Teyler T.
Published: December 2017

1. The effects of protein kinase inhibitors on N-methyl-D-aspartate (NMDA)-receptor-mediated, voltage-dependent calcium channel (VDCC)-mediated, and 100-Hz long-term potentiation (LTP) were studied in area CA1 of rat hippocampal slices. 2. A 25-Hz tetanus induced a quickly developing potentiation that was blocked by the NMDA antagonist D,L-2-amino-5-phosphonovaleric acid (APV) and was not affected by the L-type VDCC inhibitor nifedipine, suggesting that it was mediated by NMDA receptors (NMDA-LTP). 3. Application of a 200-Hz tetanus in APV induced a slowly developing NMDA-receptor-independent potentiation that was blocked by nifedipine and thus named VDCC-LTP. NMDA- and VDCC-LTP reached comparable magnitudes despite their different induction parameters and developmental kinetics. 4. Bath perfusion of the broad-spectrum serine/threonine kinase inhibitor 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7) blocked NMDA-LTP but not VDCC-LTP, whereas the tyrosine kinase inhibitors genistein and lavendustin A blocked VDCC-LTP but not NMDA-LTP. These results suggest a differential involvement of H-7-sensitive serine/threonine kinases and tyrosine kinases in the two forms of LTP. 5. Tetanization of 200 Hz in control media resulted in a compound potentiation twice as large as NMDA- or VDCC-LTP, implying that the two forms of LTP did not facilitate or reduce each other's expression. The often-used 100-Hz tetanus (1 s twice) induced a potentiation that was comparable in size with the 200-Hz compound LTP. Nifedipine, genistein, and lavendustin A reduced the 100-Hz LTP by approximately 50%, suggesting that this LTP is also a compound potentiation consisting of NMDA- and VDCC-mediated components and their corresponding signal transduction pathways.
Proton potentiation of ATP-gated ion channel responses to ATP and Zn2+ in rat nodose ganglion neurons
Authors: Li C. , Peoples R. W. , Weight F. F.
Published: December 2017

1. The modulation by protons of ATP-gated ion channel responses to ATP and Zn2+ was studied in freshly isolated rat nodose ganglion neurons using the whole cell patch-clamp technique. 2. Reduced external pH enhanced, whereas elevated external pH suppressed, current activated by 10 microM ATP. The pH producing the half-maximal effect (EC50) at this ATP concentration was 7.1. 3. Acidification shifted the ATP concentration-response curve to the left, decreasing the EC50 for ATP, and alkalinization shifted the ATP concentration-response curve to the right, increasing the EC50 for ATP. Fitting the data to a single-site pH model yielded an apparent pKa of the site on the ATP-gated ion channel of 7.6. Between pH 6.8 and 7.8, a change of 0.1 pH unit was calculated to change the ATP EC50 by 4.03 microM. Changing pH did not alter the maximal response to ATP. 4. The potentiating effect of protons appeared to be due to a direct action on the ATP-gated channel, as it could not be explained by an increase in the concentration of one or more species of ATP. 5. Lowering pH also increased the potency of Zn2+ for enhancement of ATP-activated current without altering its maximal response. Changing the pH from 7.3 to 6.8 changed the Zn2+ EC50 from 12 to 1.7 microM. 6. The potentiation of ATP-activated current by protons could not be attributed solely to an increase in the affinity of the receptor for Zn2+, as the Zn2+ chelator N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine did not alter the effect of protons. 7. Protons and Zn2+ do not appear to act at the same site on ATP-gated channels, as responses to maximally effective concentrations of Zn2+ were enhanced further by protons and vice versa. 8. These results suggest that protons regulate the function of P2X purinoceptors in rat nodose ganglion neurons by modulating the affinity of the binding sites for ATP and Zn2+ on these receptor channels.
Glycine regulation of synaptic NMDA receptors in hippocampal neurons
Authors: Wilcox K. S. , Fitzsimonds R. M. , Johnson B. , Dichter M. A.
Published: December 2017

1. Although glycine has been identified as a required coagonist with glutamate at N-methyl-D-aspartate (NMDA) receptors, the understanding of glycine's role in excitatory synaptic neurotransmission is quite limited. In the present study, we used the whole cell patch-clamp technique to examine the ability of glycine to regulate current flow through synaptic NMDA receptors at excitatory synapses between cultured hippocampal neurons and in acutely isolated hippocampal slices. 2. These studies demonstrate that the glycine modulatory site on the synaptic NMDA receptor is not saturated under baseline conditions and that increased glycine concentrations can markedly increased NMDA-receptor-mediated excitatory postsynaptic currents (EPSCs) in hippocampal neurons in both dissociated cell culture and in slice. Saturation of the maximal effect of glycine takes place at different concentrations for different cells in culture, suggesting the presence of heterogenous NMDA receptor subunit compositions. 3. Bath-applied glycine had no effect on the time course of EPSCs in either brain slice or culture, indicating that desensitization of the NMDA receptor is not prevented by glycine over the time course of an EPSC. 4. When extracellular glycine concentration is high, all miniature EPSCs recorded in the cultured hippocampal neurons contained NMDA components, indicating that segregation of non-NMDA receptors at individual synaptic boutons does not occur.
Differential activation of two distinct mechanisms for presynaptic inhibition by a single inhibitory axon
Authors: Fischer Y. , Parnas I.
Published: December 2017

1. Presynaptic inhibition of excitatory transmitter release evoked by inhibitory axon stimulation was studied at individual release boutons of the crayfish opener neuromuscular junction. 2. Presynaptic inhibition was maximal (approximately 30%) when a single inhibitory action potential preceded the excitatory test action potential by 1–2 ms. This inhibition lasted at most 5 ms. It was blocked by 50 microM picrotoxin, and is probably mediated mainly by gamma-aminobutyric acid-A (GABAA) receptors. 3. Presynaptic inhibition produced by a brief train of inhibitory action potentials (5 pulses at 100 Hz) was maximal (approximately 60%) when the last inhibitory action potential (of the train) preceded the excitatory test action potential by 10 ms. This inhibition lasted up to 50 ms. It seems that in this case GABAB receptors were activated as well, because the combined action of picrotoxin (50 microM) and 20H-Saclofen (100 microM) was required to block the inhibition. 4. We thus show that one and the same inhibitory release bouton can differentially activate two distinct mechanisms for presynaptic inhibition by activating GABAA and GABAB receptors.
Neurons in the ventral intraparietal area of awake macaque monkey closely resemble neurons in the dorsal part of the medial superior temporal area in their responses to optic flow patterns
Authors: Schaafsma S. J. , Duysens J.
Published: December 2017

1. Neurons in the ventral intraparietal area (VIP) are known to respond to translating random dot patterns. Such responses can be explained on the basis of the input of the middle temporal area (MT) to this area. Anatomic evidence has shown that VIP receives input from the dorsal part of the medial superior temporal area (MSTd) also. Neurons in the latter area are though to be involved in egomotion because they are sensitive to first-order optic flow components such as divergence and rotation. Because of their MT and MSTd input, neurons in VIP may be expected to show sensitivity to such first-order optic flow as well. 2. The question of whether VIP neurons are selective to translation and/or first-order optic flow was investigated quantitatively in two awake monkeys by recording the responses of 52 visually responsive units and by fitting their tuning curves. The responses after presentation of random dot patterns exhibiting either expansion, contraction, clockwise rotation, or anticlockwise rotation were compared with the responses to translation stimuli tested in eight directions. 3. Most VIP neurons showed clear direction-selective responses, particularly to expansion but sometimes also to a combination of components (spiral stimuli). 4. A typical feature of VIP neurons is that their responses to these optic flow components remain when different parts of the receptive field are stimulated separately (“scale invariance”). For the most responsive subfield the response was on average 93% of the whole field response. For all subfields the mean response was on average 64% of the whole field response. 5. To test whether the scale invariance arose from convergence of translation-sensitive subfields with radial or circular direction preferences (“mosaic hypothesis”), the direction selectivity for translating stimuli was tested over these subfields. Basically the direction selectivity for translation was unchanged in the various subfields, thereby excluding the direction mosaic hypothesis. 6. It is concluded that the receptive field characteristics of VIP are very similar to those of MSTd neurons.
Pharmacological Block of the Electrogenic Sodium Pump Disrupts Rhythmic Bursting Induced by Strychnine and Bicuculline in the Neonatal Rat Spinal Cord
Authors: Ballerini Laura , Bracci Enrico , Nistri Andrea
Published: December 2017

Ballerini, Laura, Enrico Bracci, and Andrea Nistri. Pharmacological block of the electrogenic sodium pump disrupts rhythmic bursting induced by strychnine and bicuculline in the neonatal rat spinal cord. J. Neurophysiol. 77: 17–23, 1997. The cellular mechanisms underlying rhythmic bursts induced in the isolated neonatal rat spinal cord by bath application of strychnine and bicuculline (which block glycine- and γ-aminobutyric acid-A-receptor-mediated inhibition, respectively) were probed with pharmacological tools. Such spontaneous bursts were recorded either intracellularly from lumbar motoneurons or extracellularly from ventral roots. As previously described, these network-driven events consisted of large-amplitude depolarizations arising abruptly from baseline with a highly regular period (on average 28 s). Burst episodes (lasting on average 7 s) comprised several oscillations and appeared synchronously on flexor and extensor motoneuron pools of both sides of the spinal cord. Their diffuse location made convenient to use bath-applied substances in the attempt to selectively block distinct membrane processes operating through the network. Application of apamin (0.4 μM) shortened both cycle period and burst duration without changing their regular rhythmicity. Similar results were obtained with carbachol (10 μM). Cs+ (4 mM) reversibly hyperpolarized the motoneuron membrane potential and largely increased burst duration, which was characterized by a long series of repetitive oscillatory waves. Cycle period and rhythmicity remained unaltered. Ouabain (10 μM), strophanthidin (4 μM), or K+-free solutions disrupted rhythmic bursting, which was fragmented into irregularly occurring paroxysmal activity mixed with short depolarizing events, still developing simultaneously on both sides of the spinal cord. Bursting activity eventually ceased after ∼30–40 min of application of ouabain or strophanthidin. Prolonged washout of strophanthidin or K+-free solutions reestablished regular bursting patterns, whereas no recovery from ouabain was observed. At the time of strong depression of bursting, it was still possible to evoke bursts by single electrical pulses applied to the segmental dorsal root. Antidromic spikes of motoneurons could still be evoked by ventral root stimulation. These results demonstrate that, in a spinal bursting network mainly made up by excitatory processes, blockers of slow Ca2+-dependent K+ currents, such as apamin or carbachol, or of the slow inward rectifier, such as Cs+, did not suppress rhythmicity, suggesting that these conductances simply contributed to control cycle period and/or burst duration. Conversely, pharmacological blockers of the electrogenic Na+ pump such as ouabain, strophanthidin, or K+-free solutions severely disrupted all characteristics of rhythmic bursting. It is proposed that the operation of the electrogenic Na+ pump of premotoneurons was a crucial element for rhythmic bursting.
Ca2+ Channel Antagonist U-92032 Inhibits Both T-Type Ca2+ Channels and Na+ Channels in Hippocampal CA1 Pyramidal Neurons
Authors: Avery Robert B. , Johnston Daniel
Published: December 2017

Avery, Robert B. and Daniel Johnston. Ca2+ channel antagonist U-92032 inhibits both T-type Ca2+ channels and Na+ channels in hippocampal CA1 pyramidal neurons. J. Neurophysiol. 77: 1023–1028, 1997. The effects of 7-[[4-[bis(4-fluoropheny l ) - m e t h y l ] - 1 - p i p e r a z i n y l ] m e t h y l ] - 2 - [ ( 2 - h y d r o x y e t h y l ) a m i n o ]4 -( 1 - m e t h y l e t h y l ) - 2 , 4 , 6 - c y c l o h e p t a t r i e n - 1 - o n e  ( U - 9 2 0 3 2 ) ,  anewly described Ca2+ channel blocker, on voltage-gated ionic currents were measured. Whole cell voltage-clamp records were obtained from acutely isolated CA1 hippocampal pyramidal neurons from 7- to 14-day-old rats. Dimethyl sulfoxide, at either 0.01% or 0.1%, partially inhibited T-type Ca2+ currents (∼20% inhibition) but not high-voltage-activated (HVA) Ca2+ currents. Ethanol (0.2%) did not affect Ca2+ currents. U-92032 selectively inhibited T-type Ca2+ currents (median inhibiting concentration ∼ 500 nM). HVA Ca2+ currents were less sensitive, with ∼75% of the current resistant at 10 μM. Inhibition of Ca2+ currents was reversible. U-92032 inhibited Na+ currents at concentrations similar to those required for T-type currents (>33% block at 1 μM). Block of Na+ currents took several minutes to develop and was irreversible. Voltage-gated K+ currents were insensitive to U-92032 (1 or 10 μM). These results indicate that U-92032 inhibits both T-type Ca2+ channels and Na+ channels, constraining its utility in certain studies. Among Ca2+ channels, however, U-92032 should prove a useful tool for distinguishing physiological contributions of T-type channels.
Distinct Muscarinic Receptor Subtypes Suppress Excitatory and Inhibitory Synaptic Responses in Cortical Neurons
Authors: Kimura Fumitaka , Baughman Robert W.
Published: December 2017

Kimura, Fumitaka and Robert W. Baughman. Distinct muscarinic receptor subtypes suppress excitatory and inhibitory synaptic responses in cortical neurons. J. Neurophysiol. 77: 709–716, 1997. Simultaneous whole cell recordings from monosynaptically connected cortical cells were performed with the use of two patch pipettes to determine the effect of acetylcholine (ACh) on both excitatory and inhibitory postsynaptic potentials (EPSPs and IPSPs, respectively) in cultured neurons from rat visual cortex. For 96% of EPSPs and 73% of IPSPs, ACh potently suppressed postsynaptic potentials in a dose-dependent manner. The estimated effective concentrations to produce half maximal response (EC50s) were 30 and 210 nM for EPSPs and IPSPs, respectively. To identify what subtypes of ACh receptors are involved in the suppression of postsynaptic potentials, three different, partially selective muscarinic receptor antagonists were used. According to the comparison of estimated Schild coefficients for each of the three antagonists against the suppression by ACh, EPSPs are most likely mediated by m4 receptors, and IPSPs by m1 receptors. When cells were treated with pertussis toxin, which inactivates m2 and m4 receptors while leaving m1, m3, and m5 receptors intact, 7 of 8 EPSPs were resistant to ACh whereas 8 of 12 IPSPs were still suppressed by ACh. This result supports the interpretation that the suppression of EPSPs was mediated by m4 receptors and that of IPSPs by m1 receptors. To obtain an indication as to whether ACh works presynaptically or postsynaptically, 1/CV2 analysis was carried out. The resultant diagonal alignment of the ratio of 1/CV2 plotted against the ratio of the amplitude of postsynaptic potentials suggests a presynaptic mechanism for the suppression of both EPSPs and IPSPs. In addition, in many cases a large synaptic suppression was observed without an obvious change in the input resistance. Furthermore, in one case where a single inhibitory driver cell was recorded with three different follower cells sequentially, none of the three IPSPs was suppressed by ACh, providing additional support for the presynaptic localization of ACh action. These results suggest that in cerebral cortex ACh has, in addition to its direct facilitatory effect via m3 pharmacology, a suppressive effect on EPSPs and IPSPs via m1 and m4 muscarinic receptors, respectively, probably with a presynaptic site of action. Separation of the actions of ACh into different receptor–second messenger pathways with potential for independent interactions with other neuromodulatory systems may be an important aspect of the mechanism of cholinergic regulation of functional state in cortex. Separation of cholinergic effects at different receptors might also offer a means for selective pharmacological intervention in disorders of sleep or memory.