bluuebunny/crossref_metadata_2025 huggingface dataset:
Synaptically evoked prolonged depolarizations in the developing auditory system
Authors: Kotak V. C. , Sanes D. H.
Published: December 2017

1. Although synaptic transmission is known to influence many aspects of neuronal development, activity rates are quite low at early ages. The present study describes a long-lasting postsynaptic response to brief periods of synaptic stimulation that may underlie such an influence. Whole-cell patch clamp recordings were made from the lateral superior olive (LSO) in a brain slice preparation from early postnatal gerbils. 2. Stimulation of the excitatory afferent pathway from the cochlear nucleus elicited a prolonged depolarization (PD) in approximately 60% of the LSO neurons tested. Low frequency stimulation (1 Hz) was as effective as tetanic stimulation in producing PDs. These synaptically evoked depolarizations ranged in amplitude from 3 to 32 mV and recovered spontaneously after 0.5-35 min. 3. The LSO neuron input resistance declined during every PD episode and remained significantly lower even after the membrane potential had recovered. These PDs were partially reversed by 2 mM Ni(+2), but 1 microM tetrodotoxin and 10 microM 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) were ineffective. The metabotropic glutamate receptor agonist, trans-1-aminocyclopentane-1,3-dicarboxylic acid (40 microM), produced depolarizations that outlasted the exposure period by an average of 20 min and were also partially repolarized by 2 mM Ni(+2). In contrast, the depolarizations produced by alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid or N-methyl-D-aspartate decayed within a much shorter period of time. 4. To test whether in vivo discharge rates are, in fact, very low during development, spontaneous activity was recorded from neurons of the auditory midbrain in gerbils before and during the onset of sound-evoked responses. The average discharge rate of auditory neurons was quite low (X = 0.4 spikes/s), although many cells displayed brief periods of rapid discharge rate (X = 37 spikes/ s). Together, these results demonstrate a novel form of developmental plasticity elicited by low rates of glutamatergic transmission that may involve a metabotropic pathway and prolonged calcium influx.
Human fetal central neurons in culture: voltage- and ligand-gated currents
Authors: Sah D. W.
Published: December 2017

1. The functional properties of sodium, potassium, calcium, N-methyl-D-aspartate (NMDA), kainate, and gamma-aminobutyric acid (GABA) currents were studied in dissociated monolayer cultures of fetal human brain neurons, using the whole cell patch-clamp technique. 2. Sodium currents were characterized with respect to the following properties: current density, voltage dependence of activation, voltage dependence of inactivation, and sensitivity to tetrodotoxin (TTX). All sodium currents exhibited voltage dependencies of activation and inactivation, and sensitivities to TTX that are characteristic of the neuronal form of the sodium current. 3. At least two types of potassium current were present, resembling the delayed rectifier and fast-inactivating potassium current. These two types of potassium current were distinguishable by their different kinetics, voltage dependencies of activation and inactivation, and sensitivities to 4-aminopyridine and tetraethylammonium. 4. High-voltage-activated calcium channel currents were present and were characterized with respect to current density, voltage dependencies of activation and inactivation, and sensitivity to cadmium. Low-voltage-activated calcium channel currents were also present. 5. NMDA- and kainate-gated currents were studied with respect to current density, time course, and current-voltage relationship. Kainate currents were also characterized with respect to inhibition by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). In addition, NMDA and kainate responses were compared for cortical versus cerebellar neurons. NMDA responses, which are only found in neurons, were present, confirming the neuronal phenotype suggested by the presence of the neuronal form of the sodium current. Nondesensitizing kainate currents were also present, with a half-maximally effective concentration (EC50) of approximately 200 microM for kainate; CNQX inhibited the kainate current with a half-inactivating concentration of 0.55 microM. 6. GABA-gated currents were characterized with respect to current density, time course, receptor subtype, desensitization, dose response, current-voltage relationship, ionic selectivity, pharmacology, and potentiation by the neurosteroid 5 alpha-pregnan-3 alpha-ol-11,20-dione (alfaxalone). Desensitizing GABAA currents were selective for chloride, inhibited by bicuculline and tert-butyl-bicyclophosphorothionate, and potentiated by diazepam, pentobarbital sodium, and alfaxalone. The EC50 for GABA was 15 microM.
Calcium-dependent plateau potentials in a crab stomatogastric ganglion motor neuron. II. Calcium-activated slow inward current
Authors: Zhang B. , Wootton J. F. , Harris-Warrick R. M.
Published: December 2017

1. Using intracellular recording and voltage-clamp techniques, we examined the biophysical properties of a Ca(2+)-activated slow inward current and its physiological role in plateau potential generation in the dorsal gastric (DG) motor neuron of the stomatogastric ganglion in the crab, Cancer borealis. 2. As shown in the accompanying paper, a brief puff of serotonin (5-HT) evoked a plateau potential in the DG neuron. Intracellular loading of the Ca2+ chelator ethylene glycol-bis (beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) prevented 5-HT from evoking a plateau potential. On the contrary, rapid increase of intracellular Ca2+ by photolysis of caged-Ca2+ (bound to DM-nitrophen) evoked a plateau response in DG bathed in normal saline. 3. Extracellular tetrodotoxin (TTX), tetraethylammonium (TEA), 4-aminopyridine (4-AP), and Cs+ and intracellular iontophoresis of Cs+ were used to block voltage-dependent INa, IK, and Ih. Under these conditions we voltage clamped DG using two electrodes and isolated a long-lasting tail current after a short depolarization of the cell. 4. The reversal potential of the slow tail current was extrapolated to be -27 +/- 3.5 (SE) mV. Na+ substitutions with choline+, tris(hydroxymethyl)aminomethane+ (Tris+) or n-methyl-glucamine+ (NMG+) did not significantly affect the reversal potential or the amplitude. 5. The slow tail current was Ca2+ dependent. It was reduced or abolished by the Ca2+ channel blocker Co2+, intracellular injection of EGTA, and by Ba2+ replacement of Ca2+ as the charge carrier. The activation and deactivation of this current do not show an apparent dependence on voltage. 6. When the voltage-dependent Na+, K+, and Ca2+ channels were blocked, a brief puff of caffeine evoked a slow depolarization. In voltage clamp, caffeine evoked a slow inward current with an apparent conductance increase. This current was reduced by intracellular EGTA. The current-voltage (I-V) relationship of the caffeine-evoked current was linear with a reversal potential of -25 +/- 4.8 mV. This was not statistically different from the reversal potential of the depolarization-evoked tail current. 7. 5-HT enhanced the depolarization-evoked slow tail current but had no effect on the caffeine-evoked slow inward current. 8. We conclude that the slow tail current is a Ca(2+)-activated nonselective current, similar to the Ca(2+)-activated nonspecific cation currents described in other preparations. This current appears to play an important role in plateau generation and maintenance in DG. 5-HT has no direct effect on the properties of this current, but it indirectly enhances the current through an increase of voltage-dependent Ca2+ current.
Calcium and potassium currents in the fast coxal depressor motor neuron of the cockroach Periplaneta americana
Authors: David J. A. , Pitman R. M.
Published: December 2017

1. Membrane currents have been examined in the cell body of the fast coxal depressor motor neuron (Df) of the cockroach Periplaneta americana with the use of two-electrode voltage clamp. 2. Most of the outward current induced by membrane depolarizations to between -40 and +80 mV was carried by K+ because it was blocked by external tetraethylammonium+ (TEA+; 20 mM) and internal Cs+. 3. Over the potential range -20 to +80 mV, a large proportion of this TEA+/Cs(+)-sensitive K+ current consisted of two temporal components, a transient outward current (IKtrans) and a sustained outward current (IKsus). IKtrans and a large proportion of IKsus appeared to be calcium-activated potassium currents (IK,Ca,trans and IK,Ca,sus, respectively) because these were suppressed by injecting ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA), removing Ca2+ from the saline or replacing Ca2+ with Ba2+. After suppression of IK,Ca by internal EGTA or Ca(2+)-free saline, membrane depolarizations positive to -40 mV induced voltage-dependent outward currents (IK,V), which consisted of single-component outward relaxations. 4. When outward currents were blocked by external TEA+/internal Cs+, a voltage-dependent inward current consisting of a transient and a sustained component was observed over the potential range -40 to +40 mV. Both components of this inward current appeared to be carried by Ca2+ because they were blocked by external Cd2+ (1 mM), verapamil (0.1 mM), nifedipine (0.1 mM), or diltiazem (0.1 mM). 5. Both the transient component of the calcium current (ICa,trans) and the sustained component (ICa,sus) were maximal at 0 mV and present when Ca2+ in the saline were replaced by Ba2+. The inactivation of ICa,trans is voltage dependent, the rate of inactivation increasing with membrane depolarization. 6. The current-voltage relationships of Ca2+ currents differed from those of calcium-activated K+ currents. It is proposed that the discrepancy between these current-voltage relationships arises from the rapidity with which IK,Ca is saturated by Ca2+ entering through voltage-dependent channels and because the apparent reversal potential for ICa is not at ECa. 7. Although the similarity in the shape of IK,Ca and ICa might suggest that the time course of IK,Ca is determined by the kinetics of ICa, this appears unlikely in view of the rapid saturation of IK,Ca by Ca2+, which considerably outlasts the period of Ca2+ influx.
Self-reinnervated cat medial gastrocnemius muscles. II. analysis of the mechanisms and significance of fiber type grouping in reinnervated muscles
Authors: Rafuse V. F. , Gordon T.
Published: December 2017

1. The technique of glycogen depletion was used to determine whether regenerating motor axons reestablish the normal regionalization of motor units (MUs) in the cat medial gastrocnemius (MG) muscle, 2) whether the extent of clumping between MU fibers and/or type grouping of muscle fibers progressively increases with a decrease in reinnervated MU numbers, and 3) whether the pattern of innervation can explain why MUs fail to increase significantly in size when the cut nerve is sutured directly to the muscle, even when few axons make functional connections. 2. Distributions of MU fibers were analyzed in 5 normal and 14 reinnervated cat MG muscles 4.5-16 mo after sectioning of its nerve and suturing of the proximal end to the distal nerve sheaths (N-N suture) or directly to the muscle fascia (N-M suture). Muscle unit distributions were quantified according to location, territory size, density, and extent of clumping between fibers from the same MU. 3. Normal MU fibers were regionalized within five regions along the muscle's longitudinal and transverse axes. Reinnervated MUs were located within similar regions, indicating that regenerating axons follow the major proximal nerve branches to restore normal compartmentalization. 4. Muscle unit fibers were diffusely scattered within discrete MU territories in normal muscles. Territory size tended to increase with MU size, whereas density of muscle unit fibers within the territory decreased. 5. Territories increased with MU size after N-N suture but were smaller and showed little size variation after N-M suture. The extent of muscle unit fiber clumping was inversely related to the number of reinnervated MUs. On average, the extent of clumping was substantially higher in muscles reinnervated after N-M suture. These results indicate that distal nerve sheaths facilitate proximal axon branching, which establishes MU territory size. Once the territory is established, motor axons branch distally to increase MU size, which in turn compensates for reduced MU numbers. 6. Muscles reinnervated by < 80% of the MUs exhibited fiber type grouping of type I fibers, and on average the extent of clumping was substantially higher in muscles reinnervated after N-M suture. With less innervation, type grouping increased inversely with the number of reinnervated MUs. However, for a similar number of MUs, type I fiber type grouping was substantially higher in muscle reinnervated after N-M suture. Type grouping therefore reflects muscle unit fiber clumping under conditions where MU size increased (N-N suture) or MU territory size decreased (N-M suture).
Whole cell and single-channel properties of a unique voltage-activated sustained calcium current identified in teleost retinal horizontal cells
Authors: Pfeiffer-Linn C. L. , Lasater E. M.
Published: December 2017

1. A voltage-activated, sustained calcium current in white bass retinal cone horizontal cells was characterized on the basis of electrophysiological and pharmacological criteria. Studies were performed with the use of a combination of whole cell and single-channel analysis of outside-out excised patches from isolated, cultured retinal horizontal cells. 2. We found that the white bass sustained calcium channel represents a unique type of calcium channel. On the basis of our analysis, it does not fall into any current classification scheme. The horizontal cell channel shares some biophysical and pharmacological properties with the typical high-voltage-activated L-type channel, but it also has features in common with the P-type channel. 3. The biophysical characteristics of the channel were most typical of an L-type channel. It activated above -30 mV membrane potential and only very slowly inactivated. It had a single-channel conductance of 25 pS. 4. Like the typical L-type current, the horizontal cell current was sensitive to the dihydropyridine agonist Bay K 8644. It prolonged the channel open time, which resulted in a large increase in macroscopic current flow into the cell. However, unlike the typical L current, dihydropyridine antagonists (nifedipine, nimodipine, etc.) as well as the specific L-channel inhibitor diltiazem were only moderately effective at best. 5. In a previous study, we found the current was antagonized by a factor found in funnel-web spider toxin. Here we show that the current is completely blocked by low doses of omega-agatoxin IVA. These are characteristics of the P-type calcium channel. But unlike the P current, the horizontal cell current is relatively insensitive to low or high doses of omega-conotoxin MVIIC. 6. The overall combination of calcium channel characteristics sets apart the calcium channel in bass horizontal cells from previously described channels. It appears to be a unique, tissue-specific ion channel, which we have labeled the PL channel.
Activation of NMDA receptors produces dopamine-mediated changes in fish retinal horizontal cell light responses
Authors: Harsanyi K. , Wang Y. , Mangel S. C.
Published: December 2017

1. The action of N-methyl-D-aspartate (NMDA) on cone horizontal cells was studied in in vitro goldfish retinas superfused with a bicarbonate-based Ringer solution that contained D-serine (0.5 microM), a glycine analogue, but no added Mg2+. Horizontal cell light responses and electrical coupling were assessed by monitoring responses to full-field stimuli and to small, centered (0.4 mm diam) spots of light, respectively. 2. NMDA uncoupled horizontal cells, reduced their light responsiveness, and acted in a dose-dependent manner, with threshold at 10 microM and maximum effect at 100 microM. 3. Application of the NMDA antagonists DL-2-amino-7-phosphonoheptanoic acid-AP-5) or D-2-amino-5-phosphonopentanoic acid-AP-5) (50 microM) blocked the uncoupling action of NMDA (100 microM), as did prior application of SCH23390, a dopamine D1 antagonist, or prior treatment of the retinas with 6-hydroxydopamine, a procedure that destroys dopaminergic neurons. 4. Addition of Mg2+ (1 mM) partially blocked the effects of NMDA at 100 microM and completely blocked the effects of 50 microM NMDA. The effects of NMDA (50 or 100 microM) were also reduced if it was applied without D-serine. 5. Both flickering (5 Hz) and sustained light stimulation uncoupled horizontal cells and reduced their light responsiveness. Application of AP-7 blocked the effects of flickering light stimulation, but did not block the effects of sustained light. 6. These results suggest that activation of NMDA receptors in the fish retina uncouples cone horizontal cells and decreases their light responsiveness by increasing dopamine release. The results further suggest that flickering light, but not sustained light, increases the release of dopamine through activation of NMDA receptors.
Bistability and its regulation by serotonin in the endogenously bursting neuron R15 in Aplysia
Authors: Lechner H. A. , Baxter D. A. , Clark J. W. , Byrne J. H.
Published: December 2017

1. Previous computational studies of models of neuron R15 in Aplysia have indicated that several distinct modes of electrical activity may coexist at a given set of parameters, that this multistability can be modulated by transmitters such as serotonin (5-HT) and that brief perturbations of the membrane potential can induce persistent changes in the mode of electrical activity. To test these predictions, the responses of R15 neurons to injections of brief (1.5 s) current pulses were recorded intracellularly in the absence and presence of 5-HT. 2. In the absence of 5-HT, brief perturbations induced abrupt transitions in the electrical activity from bursting to beating. Such transitions were observed in approximately 20% of the cases. The duration of beating activity varied from several seconds to tens of minutes. In the presence of low concentrations (1 microM) of 5-HT, both the probability of mode transitions and the duration of induced beating activity increased significantly. 3. These results indicate that at least two stable modes of electrical activity can coexist in R15 neurons and that this bistability can be regulated by 5-HT. In general, these conclusions agree with the results from analyses of mathematical models of R15. Although the function of these dynamic properties in R15 is speculative, our results, interpreted on the background of the model, support the notion that nonlinear dynamical properties of individual neurons can endow them with richer forms of information processing than has generally been appreciated.
Tilt responses of neurons in the caudal descending nucleus of the decerebrate cat: influence of the caudal cerebellar vermis and of neck receptors
Authors: Wilson V. J. , Ikegami H. , Schor R. H. , Thomson D. B.
Published: December 2017

1. In decerebrate cats with intact cerebellums, we studied the responses of neurons in the caudal areas of the vestibular nuclei to natural vestibular stimulation in vertical planes and to neck rotation. The activity of most neurons was recorded in the caudal half of the descending nucleus. 2. One goal of our experiments was to compare the dynamic and spatial properties of responses to sinusoidal vestibular stimulation with those seen in previous experiments in which the caudal cerebellar vermis, including the nodulus and uvula, was removed. This part of the cerebellum receives vestibular input and projects to the caudal areas of the vestibular nuclei, suggesting that it could influence responses to stimulation of the labyrinth. 3. As in our previous experiments, most neurons could be classified as receiving predominant input either from the otoliths or from one vertical semicircular canal. When mean gain and phase and response vector orientations were compared, there were no obvious differences between the behavior of neurons in the partially decerebellate preparation and the one with the cerebellum intact, demonstrating that in the decerebrate cat the nodulus and uvula have little or no influence on the processing of vertical vestibular input in this region of the vestibular nuclei. 4. Only 23 of 74 (31%) of neurons tested responded to neck rotation. This contrasts with the much larger fractions that respond to this stimulus in Deiters' nucleus and in the rostral descending nucleus. We also recorded from neurons near the vestibular nuclei, mainly in the external cuneate nucleus. All of them (9 of 9) responded to neck rotation. 5. Responses to neck rotation also differed in their dynamics from those found more rostrally in the vestibular nuclei. Dynamics of more rostral neurons resemble those of neck muscle spindles, as do those of external cuneate neurons. The dynamics of caudal vestibular neurons, on the other hand, have a steeper gain slope and more advanced phases than do those of neurons in the more rostral vestibular nuclei. This suggests the possibility of involvement of additional receptors in the production of these responses. 6. In the more rostral vestibular nuclei, responses to vestibular and neck rotation are most often antagonistic, so that head rotation results in little or no response. This is not the case in the caudal areas of the vestibular nuclei, where less than half the neurons tested displayed antagonistic behavior. Further experiments are required to put the neck projection to the caudal vestibular nuclei in a functional context.
Motor-unit behavior in humans during fatiguing arm movements
Authors: Miller K. J. , Garland S. J. , Ivanova T. , Ohtsuki T.
Published: December 2017

1. The activity of 40 triceps brachii motor units was recorded from the dominant arms of 9 healthy adult volunteers (age 27.8 +/- 4.4 yr, mean +/- SD) during a fatigue task that included both isometric and anisometric contractions. The fatigue task lasted 8.3 min and consisted of 50 extension and 50 flexion movements of the elbow. Each movement (40 degrees in 0.8s) was separated by an isometric contraction. A constant load resisting extension of 17.7 +/- 3.0% of maximal voluntary contractions (MVC) was applied throughout the task. This paradigm enabled the direct contrast of motor-unit discharge behavior during the different types of fatiguing contractions. 2. Motor-unit behavior was examined to determine the relative contribution of two mechanisms for optimizing force production under fatiguing conditions: recruitment of motor units and modulation of motor-unit discharge following recruitment. Threshold torques for motor-unit recruitment thresholds were determined by ramp-and-hold isometric contractions. Motor-unit discharge was evaluated during the fatigue task by contrasting the number of motor-unit potentials (spikes) per contraction for concentric eccentric, and isometric contractions. 3. The fatigue task resulted in a 30 +/- 12% decline in the mean MVC of elbow extension. Recruitment of nine new motor units (23%) was evident during the fatiguing extension movements, often within five to seven movements (i.e., within 25-35 s). Each newly recruited motor unit had the largest recruitment threshold torque in that experiment. 4. Analysis of the motor units that were active from the beginning of the fatigue task revealed that the mean number of motor-unit spikes per contraction increased, or remained constant as fatigue ensued, yet for the majority of motor units it increased or remained constant. None of the newly recruited motor units demonstrated decreased number of mean spikes per contraction after recruitment. Further, concurrently active motor units displayed different discharge behavior in two-thirds of the subjects. It is proposed that if the neural drive to the muscle is distributed uniformly upon the motoneuron pool, peripheral feedback from the exercising muscle may modulate specific motoneuron discharge levels during fatigue.
Membrane properties and cell ultrastructure of taste receptor cells in Necturus lingual slices
Authors: Bigiani A. , Kim D. J. , Roper S. D.
Published: December 2017

1. Whole cell patch-clamp recordings and electron micrographs were obtained from cells in Necturus taste buds in lingual slices to study their membrane properties and to correlate these properties with cell ultrastructure. 2. Two different populations of taste receptor cells could be identified: one type possessed voltage-gated Na+ and K+ (noninactivating) currents (group 1 cells); the other type possessed only K+ (inactivating) currents (group 2 cells). 3. The zero-current ("resting") potential (Vo) and whole cell resistance (Ro) of these two types of taste cells differed significantly. For group 1 cells, on average, Vo = -75 mV and Ro = 24.6 G omega, and for group 2 cells, Vo = -49 mV and Ro = 48.9 G omega. The difference in Ro was not explained completely by differences in cell sizes, suggesting that intrinsic membrane properties differed between the populations. 4. Cells injected with biocytin were the electron microscope after tissues were reacted with majority (14 of 16) of cells with voltage-gated Na+ and K+ currents (group 1 cells) were characterized by abundant rough endoplasmic reticulum and dense granular packets in the apical process. These are features of dark cells. All the cells that only possessed K+ currents (group 2 cells) were characterize by well-developed smooth endoplasmic reticulum and an absence granular packets. These features characterize light cells. 5. These findings indicate that there is a good, although not exact, correlation between electrophysiological properties and cell morphotype in Necturus taste bud cells. All dark cells possessed Na+ and K+ currents and thus would be expected to be capable of generating action potentials. Most light cells only possessed outward K+ currents and thus would be incapable of generating action potentials.
Local effects of glycinergic inhibition in the spinal cord motor systems for swimming in amphibian embryos
Authors: Perrins R. , Soffe S. R.
Published: December 2017

1. We have studied the effects of locally applying the glycinergic antagonist strychnine to rhythmically active spinal neurons in amphibian embryos during fictive swimming. Intracellular recordings were made from motoneurons and premotor interneurons in Xenopus laevis, a well-studied model system, and from motoneurons in three other species (Rana temporaria, Bufo bufo, and Triturus vulgaris). Overall, these embryos cover a range of swimming patterns from the short-cycle-period, brief-motor-root bursts of Xenopus, to the long-cycle-period, long-motor-root bursts of Rana, which are more typical of adult patterns. 2. Local strychnine application had no significant effect on the gross pattern of swimming; episode duration and the burst duration in rostral ventral roots away from the application site were unaltered, and left-right alternation was preserved. We have therefore been able to examine the effects of inhibition on individual neurons, uninfluenced by overall changes in the operation of the swimming neural circuitry. 3. In all cases strychnine blocked midcycle inhibition and significantly increased the peak on-cycle depolarization during swimming. In Rana, Bufo, and Triturus motoneurons, and in Xenopus interneurons, strychnine significantly increased the reliability of firing during swimming. In Xenopus motoneurons, where spiking was 100% reliable anyway, the timing of the spikes was advanced relative to rostral ventral root activity. These results do not provide support for postinhibitory rebound as a factor in the spike-generating process during swimming. In addition to midcycle inhibition, Xenopus motoneurons can also show a smaller, additional on-cycle inhibition that is blocked by strychnine. 4. In both Rana and Bufo the duration of caudal ventral root bursts close to the site of drug application was increased by strychnine, showing that the increased motoneuron reliability not only leads to more intense, but also more extensive, ventral root activity. 5. At the level of single neurons, glycinergic inhibition effectively reduces on-cycle excitation and in turn controls the reliability, extent, and precise timing of motoneuron firing. These changes may be the individual components underlying broader effects of inhibition described previously, such as locomotor frequency control. They also show how any modulation of inhibition in localized regions of the spinal cord could produce localized control of neuronal firing properties.
Basolateral amiloride-sensitive Na+ transport pathway in rat tongue epithelium
Authors: Mierson S. , Olson M. M. , Tietz A. E.
Published: December 2017

1. Experiments were conducted to test for the presence of basolateral Na+ channels in the rat lingual epithelium. Researchers have proposed a model in which some lingual taste cells have Na+ channels in the basolateral membrane. That model is designed to account for the portion of the neural taste response and the portion of the transepithelial short-circuit current (Isc) in vitro that are insensitive to mucosal amiloride; some Na+ would diffuse across the tight junction into the cell via this lateral pathway, and would be transported out of the cell by Na+ pumps in the basal membrane. The model could also account for the differential effect of mucosal amiloride on Na+ salts of various anions, in which the neural taste responses to Na+ salts with anions larger than Cl- are more sensitive to mucosal amiloride than is the taste response to NaCl. 2. Voltage-clamp data were obtained from an in vitro preparation of the anterior-dorsal rat tongue epithelium in which the connective tissue was removed by enzyme digestion. Isc in a modified Ussing chamber was reduced by amiloride in the submucosal solution. 3. The pattern of sensitivity to submucosal amiloride differed in several respects from the pattern for mucosal amiloride. The inhibition constant (Ki) was 52 microM amiloride concentration, higher than for the apical amiloride-sensitive Na+ channel. The selectivity for Na+ over K+ was much less than for the response to mucosal amiloride; with 0.5 M NaCl or KCl on the mucosal side, the ratio of inhibition for the NaCl response to inhibition for the KCl response varied between 1 and 3. 4. As the concentration of NaCl in the mucosal solution was varied, submucosal amiloride caused little inhibition of Isc for mucosal NaCl below isosmotic concentration, with the percent inhibition increasing as mucosal salt concentration increased. With 0.5 M sodium gluconate in the mucosal solution, there was very little inhibition due to submucosal amiloride. 5. The results support the presence of amiloride-sensitive Na+ channels in the basolateral membranes of the dorsal tongue epithelium in rat, and are consistent with the proposed model in which these channels are present in taste cells.
Presynaptic inhibition of glutamatergic synaptic transmission to rat motoneurons by serotonin
Authors: Singer J. H. , Bellingham M. C. , Berger A. J.
Published: December 2017

1. In a brain stem slice preparation, we recorded glutamatergic excitatory postsynaptic currents (EPSCs) in hypoglossal motoneurons (HMs) evoked by extracellular stimulation in the reticular formation just ipsilateral to the hypoglossal motor nucleus (n. XII). Serotonin (5-HT) inhibited glutamatergic synaptic transmission in a dose-dependent fashion as indicated by a reduction in the evoked EPSC (eEPSC) peak amplitude to 46 +/- 2% (mean +/- SE, n = 26) of control (5-HT 10 microM). This effect was not voltage dependent, as the eEPSC reversal potential was not altered (n = 5). Additionally, 5-HT decreased the rate of rise of the eEPSC to 41 +/- 2% of control (n = 14). Blockade of N-methyl-D-aspartate-receptor-channels by D(-)-2-amino-5-phosphonopentanoic acid (50 microM) or of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid/kainate receptor-channels by 6,7-dinitro-quinoxaline (20 microM) did not alter the relative reduction of the eEPSC amplitude by 5-HT (n = 7 and 3, respectively). 2. In the presence of tetrodotoxin (1 microM), bath application of 5-HT did not reduce postsynaptic glutamate currents elicited by pressure ejection of L-glutamate (1 mM) onto HMs (n = 5), and it increased the median interevent interval of spontaneous miniature EPSCs (mEPSCs) to 178 +/- 12% of control (n = 4), suggesting that 5-HT acts presynaptically to reduce the probability of vesicle release. mEPSC amplitude was decreased slightly in three of four cells (median amplitude = 92 +/- 3% of control). 3. The specific 5-HT1B receptor agonist [3-(1,2,5,6-tetrahydropyrid-4-yl)pyrrolo[3,2-b]pyrid-5-one] (1 microM) mimicked 5-HT in its effect on eEPSCs (eEPSC amplitude reduced to 31 +/- 5% of control; rate of rise reduced to 40 +/- 4% of control, n = 10 and 5, respectively) and mEPSCs (median interevent interval increased to 231 +/- 36% of control; median mEPSC amplitude = 102 +/- 3% of control, n = 5). Additionally, 5-HT-mediated inhibition was not blocked by coapplication of 1-(2-methoxyphenyl)-4-[4-(2-phthalimido) butyl] piperazine hydrobromide (1 microM), a 5-HT1A antagonist, and 3-[2-[4-(4-flurobenzoyl)-1-piperdinyl]ethyl]-2,4(1H,3H)-quin azolinedione tartrate (1 microM), a 5-HT2A/2C antagonist (n = 4). These data indicate that the 5-HT effect is primarily 5-HT1B receptor mediated. 4. We conclude that 5-HT, acting through presynaptic 5-HT1B receptors, inhibits glutamatergic synaptic transmission by reducing the probability of vesicle release.
Properties of a slow nonselective cation conductance modulated by neurotensin and other neurotransmitters in midbrain dopaminergic neurons
Authors: Farkas R. H. , Chien P. Y. , Nakajima S. , Nakajima Y.
Published: December 2017

1. A widespread mechanism of slow excitation throughout the nervous system involves overlapping changes in nonselective ion conductance and K+ conductance. We used whole cell patch-clamp recording to characterize such a nonselective conductance induced by neurotensin (NT) and other neurotransmitters in immunocytochemically identified dopaminergic neurons cultured from the rat ventral tegmental area (VTA). 2. The NT-induced inward current consisted of an initial peak and later "hump." The response was blocked reversibly by the nonpeptide NT-receptor antagonist SR48692, suggesting that it resulted from activation of NT receptors. 3. The channel was almost equally permeable to Na+ and K+, as determined from the reversal potential shift upon switching from Na+- to K(+)-containing external solution. The permeability of Cs+ was similar to that of Na+, as determined from the zero-current equation and average reversal potential in the 75 mM Na+ solution. Cl- was not significantly permeable. 4. In Ca(2+)-free external solution, the NT-induced current showed a fourfold increase in amplitude, and in high Mg2+ (20 mM) external solution, the NT-induced current showed an 80% decrease in amplitude, suggesting that external Ca2+ and Mg2+ could block the nonselective conductance. 5. The NT response was unaffected by loading the neurons with either the Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid or with 1 mM ca2+. The nonselective conductance was therefore not Ca2+ activated. 6. Loading the neurons with cyclic GMP or cyclic AMP (each with the phosphodiesterase inhibitor isobutyl-methylxanthine) did not affect the NT response. The NT-induced nonselective conductance was therefore not cyclic nucleotide-activated. 7. The latency of the NT response was long (> or = 185 ms, average 406 ms, 30 degrees C), indicating that NT did not induce the conductance through ligand-gated channels. Thus, NT activated a slow nonselective cation conductance. 8. Neurokinin B, a metabotropic glutamate agonist, and muscarine elicited responses similar to the NT response. The NT response could be elicited after desensitizing the responses to these other neurotransmitters, indicating receptor specificity in the activation of the nonselective conductance.
Calcium-independent actions of alpha-latrotoxin on spontaneous and evoked synaptic transmission in the hippocampus
Authors: Capogna M. , Gahwiler B. H. , Thompson S. M.
Published: December 2017

1. The black widow spider venom component, alpha-latrotoxin (alpha-LTx) (< 0.5 nM), increased the frequency of miniature excitatory postsynaptic currents (mEPSCs) in hippocampal CA3 pyramidal cells 14-fold, without changing their amplitude. 2. This action of alpha-LTx was not affected by application of Ca(2+)-free/ethylene glycol-bis(b-aminoethyl ether)-N,N,N',N'-tetraacetic acid-containing saline, 100 microM Cd2+, or 50 microM Gd3+. The increase in mEPSC frequency was thus not due to an influx of Ca2+ into the axon terminal via voltage-dependent Ca2+ channels or alpha-LTx-induced pores. 3. alpha-LTx did not increase spontaneous release when synaptic transmission had been impaired by botulinum toxin/F. 4. alpha-LTx reduced the amplitude of EPSCs, elicited with stimulation of mossy fibers, without affecting paired-pulse facilitation. 5. The Ca2+ ionophore ionomycin (2–2.5 microM) also enhanced the frequency of mEPSCs, but unlike alpha-LTx, potentiated evoked EPSCs and reduced paired-pulse facilitation. Application of N-methyl-D-aspartate elicited a high frequency of Ca(2+)-dependent, tetrodotoxin-sensitive spontaneous EPSCs, but did not affect evoked EPSC amplitude. Agents that stimulate vesicular release by increasing presynaptic Ca2+ influx thus do not mimic the alpha-LTx-induced depression of evoked EPSCs. 6. We conclude that entry of Ca2+ into presynaptic axon terminals is not responsible for the effects of low concentrations of alpha-LTx on either spontaneous or evoked transmitter release in the hippocampus. 7. Potential presynaptic mechanisms that could mediate the opposing actions of alpha-LTx on spontaneous and evoked transmitter release in the hippocampus (i.e., alpha-LTx-induced ionic pores, depletion of synaptic vesicles, actions on exocytotic proteins) are discussed.
White noise approach for estimating the passive electrical properties of neurons
Authors: Wright W. N. , Bardakjian B. L. , Valiante T. A. , Perez-Velazquez J. L. , Carlen P. L.
Published: December 2017

1. The passive electrical properties of whole cell patched dentate granule cells were studied with the use of zero-mean Gaussian white noise current stimuli. Transmembrane voltage responses were used to compute the first-order Wiener kernels describing the current-voltage relationship at the soma for six cells. Frequency domain optimization techniques using a gradient method for function minimization were then employed to identify the optimal electrical parameter values. Low-power white noise stimuli are presented as a favorable alternative to the use of short-pulse current inputs for investigating neuronal passive electrical properties. 2. The optimization results demonstrated that the lumped resistive and capacitive properties of the recording electrode must be included in the analytic input impedance expression to optimally fit the measured cellular responses. The addition of the electrode resistance (Re) and capacitance (Ce) to the original parameters (somatic conductance, somatic capacitance, axial resistance, dendritic conductance, and dendritic capacitance) results in a seven-parameter model. The mean Ce value from the six cells was 5.4 +/- 0.3 (SE) pF, whereas Re following formation of the patch was found to be 20 +/- 2 M omega. 3. The six dentate granule cells were found to have an input resistance of 600 +/- 20 M omega and a dendritic to somatic conductance ratio of 6.3 +/- 1.1. The electronic length of the equivalent dendritic cylinder was found to be 0.42 +/- 0.03. The membrane time constant in the soma was found to be 13 +/- 3 ms, whereas the membrane time constant of the dendrites was 58 +/- 5 ms. Incorporation of morphological estimations led to the following distributed electrical parameters: somatic membrane resistance = 25 +/- 4 k omega cm2, somatic membrane capacitance = 0.48 +/- 0.05 microF/cm2, Ri (input resistance) = 72 +/- 5 omega cm, dendritic membrane resistance = 59 +/- 4 k omega cm2, and dendritic membrane capacitance = 0.97 +/- 0.06 microF/cm2. On the basis of capacitive measurements, the ratio of dendritic surface area to somatic surface area was found to be 34 +/- 2. 4. For comparative purposes, hyperpolarizing short pulses were also injected into each cell. The short-pulse input impedance measurements were found to underestimate the input resistance of the cell and to overestimate both the somatic conductance and the membrane time constants relative to the white noise input impedance measurements.
Pharmacologically novel GABA receptor in human dorsal root ganglion neurons
Authors: Valeyev A. Y. , Hackman J. C. , Wood P. M. , Davidoff R. A.
Published: December 2017

1. Whole cell voltage-clamp studies of gamma-aminobutyric acid (GABA) receptors were performed on large (> 80 microns) cultured human dorsal root ganglion (DRG) neurons. 2. GABA and pentobarbital sodium when applied in micromolar concentrations evoked inward Cl- currents in DRG neurons voltage clamped at negative membrane potentials. 3. Diazepam (10 microM) and pentobarbital (10 microM) upmodulated the GABA current by approximately 149 and 168%, respectively. 4. The GABA currents in human DRG cells were unaffected by the classical GABA antagonists picrotoxin and bicuclline (100 microM). In contrast, the GABA responses evoked in adult rat DRG cells cultured in an identical manner were inhibited by both antagonists. The glycine receptor antagonist strychnine (100 microM) did not alter GABA currents in human DRG cells. 5. Human DRG cells did not respond to glycine (10–100 microM) or taurine (10–100 microM). The GABAB agonist baclofen had no effect on the holding current when patch pipettes were filled with 130 mM KCl. The GABAB antagonists saclofen applied either alone or with GABA was without effect. 6. The differences between the GABA receptors described here and GABA receptors in other species may reflect the presence of receptor subunits unique to human DRG cells.
Three distinct G protein pathways mediate inhibition of neuronal calcium current by bradykinin
Authors: Wilk-Blaszczak M. A. , Singer W. D. , Belardetti F.
Published: December 2017

1. In NG108-15 cells dialyzed with 10 mM ethylene glycolbis (beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) or bis (o-aminophenoxy)-N,N,N',N'-tetraacetic acid (BAPTA), bradykinin (BK) selectively inhibited the N-type calcium current. This effect of BK was blocked by an antibody directed against the G protein G13. Thus under these conditions G13 mediates the inhibition of voltage-dependent calcium current (ICa, V) by BK. In contrast, activation of K+ currents by BK is mediated by Gq/11. BK also couples to Gi2. 2. We now examine the involvement of G proteins in the inhibition of ICa, V by BK when NG108-15 cells are dialyzed with 1 mM BAPTA. Under these conditions, BK inhibited both the N- and L-type, but not the T-type, calcium currents. Intracellular application of anti-G13 antibody did not suppress the response to BK. Applications of either anti-Gq/11 antibody or pertussis toxin (PTX, to block Gi2) were similarly ineffective. Even combined application of anti-Gq/11 and -G13 antibodies, or PTX together with either antibody, did not block inhibition of ICa, V by BK. However, the combination of both antibodies with PTX blocked the response to BK in low BAPTA. In conclusion, both Gq/11 and a PTX-sensitive G protein (presumably Gi2), together with G13, are involved in the inhibition of ICa, V by BK. 3. Gq/11 inhibited only the L-type calcium current, whereas the PTX-sensitive G protein inhibited both the N- and L-type calcium currents. 4. The BAPTA dependence of the Gq/11 and PTX-sensitive inhibitions may reflect a Ca2+ requirement of the pathway(s) acting on the L current and/or a direct suppressive effect of BAPTA.
Ionic basis of the postsynaptic depolarizing GABA response in hippocampal pyramidal cells
Authors: Perkins K. L. , Wong R. K.
Published: December 2017

1. Whole cell voltage-clamp recording with recording pipette solutions of differing ionic composition was used to determine the ionic basis of the depolarizing gamma-aminobutyric acid (GABA) response. In the presence of 4-aminopyridine and excitatory amino acid receptor blockers, giant GABA-mediated postsynaptic currents (GPSCs) were recorded from CA3 pyramidal neurons in hippocampal slices from adult guinea pigs. With the GABAB component blocked, the GPSC was composed of an initial outward current (GABAA component) that peaked at 115 ms followed by a late inward current (GABAD component) that peaked at 400-600 ms. 2. Reduction of the intracellular concentration of potassium ([K+]i)resulted in no significant change in the reversal potential of the GABAD component of the GPSC, indicating that it is not a nonspecific cation current. 3. The HCO3- permeability of the channel mediating the GABAD response was assessed by using recording pipette solutions containing three different concentrations of bicarbonate ([HCO3-], 19, 49, and 102 mM). The reversal potential of the GABAD response shifted in the depolarizing direction as the HCO3- equilibrium potential was shifted in the depolarizing direction, indicating that the channel mediating the GABAD response is permeable to HCO3-. The reversal potential of the GABAD response was more sensitive to changes in recording pipette [HCO3-] than the reversal potential of the GABAA response, indicating that the GABAD response is carried by HCO3- to a greater extent than the GABAA response. 4. The outward current-inward current sequence of the biphasic GPSC was reversed to an inward current-outward current sequence by using a high [Cl-]/low [HCO3-] recording pipette solution (40 mM Cl-/6 mM HCO3-), indicating that the GABAA component is more sensitive to changes in [Cl-]i, and the GABAD component is more sensitive to changes in [HCO3-]i. 5. These data indicate that the GABAD component of the GPSC is predominantly carried by HCO3-. While this result supports the recently propsed chloride accumulation model, the model in its present form cannot explain the inward current-outward current polarity sequence of the GPSC recorded with the high [Cl-]/low [HCO3-] intracellular solution. The data obtained using that solution reveal the need for a more expansive chloride accumulation/ depletion model or for a model utilizing two distinct ionotropic GABA channels with different anion permeability ratios to account for the biphasic nature of the GPSC.