bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of synaptically mediated fast and slow inhibitory processes in piriform cortex in an in vitro slice preparation
Authors: Tseng G. F. , Haberly L. B.
Published: December 2017

1. Intracellular recordings were obtained from anatomically verified layer II pyramidal cells in slices from rat piriform cortex cut perpendicular to the surface. 2. Responses to afferent and association fiber stimulation at resting membrane potential consisted of a depolarizing potential followed by a late hyperpolarizing potential (LHP). Membrane polarization by current injection revealed two components in the depolarizing potential: an initial excitatory postsynaptic potential (EPSP) followed at brief latency by an inhibitory postsynaptic potential (IPSP) that inverted with membrane depolarization and truncated the duration of the EPSP. 3. The early IPSP displayed the following characteristics suggesting mediation by gamma-aminobutyric acid (GABA) receptors linked to Cl- channels: associated conductance increase, sensitivity to increases in internal Cl- concentration, blockage by picrotoxin and bicuculline, and potentiation by pentobarbital sodium. The reversal potential was in the depolarizing direction with respect to resting membrane potential so that the inhibitory effect was exclusively via current shunting. 4. The LHP had an associated conductance increase and a reversal potential of -90 mV in normal bathing medium that shifted according to Nernst predictions for a K+ potential with changes in external K+ over the range 4.5-8 mM indicating mediation by the opening of K+ channels and ruling out an electrogenic pump origin. 5. Lack of effect of bath-applied 8-bromoadenosine 3',5'-cyclic monophosphate (8-Br-cAMP) or internally applied ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) on the LHP and failure of high amplitude, direct membrane depolarization to evoke a comparable potential, argue against endogenous mediation of the LHP by a Ca2+ activated K+ conductance [gK(Ca)]. However, an apparent endogenously mediated gK(Ca) with a duration much greater than the LHP was observed in a low percent of layer II pyramidal cells. Lack of effect of 8-Br-cAMP also indicates a lack of dependence of the LHP on cAMP. 6. Other characteristics of the LHP that were demonstrated include: a lack of blockage by GABAA receptor antagonists, a probable voltage sensitivity (decrease in amplitude in the depolarizing direction), and an apparent brief onset latency (less than 10 ms) when the early IPSP was blocked by picrotoxin. The LHP was unaffected by pentobarbital sodium when the early IPSP was blocked by picrotoxin. 7. Both the LHP and early IPSP were blocked by low Ca2+/high Mg2+, consistent with disynaptic mediation.(ABSTRACT TRUNCATED AT 400 WORDS)
Contrast-sensitivity functions of W-, X-, and Y-like relay cells in the lateral geniculate nucleus of bush baby, Galago crassicaudatus
Authors: Norton T. T. , Casagrande V. A. , Irvin G. E. , Sesma M. A. , Petry H. M.
Published: December 2017

1. This paper represents a continuation of our effort to examine the relationship between the physiology of distinct classes of primate lateral geniculate nucleus (LGN) cells and spatial vision. The present study focuses on modeling the contrast-sensitivity functions (CSFs) of separate LGN cell classes, examining differences in the CSFs of different classes of LGN cells and comparing the results with behaviorally defined CSFs. 2. CSFs to drifting sinusoidal gratings were obtained from single LGN relay cells in the nocturnal primate, Galago crassicaudatus. The CSFs of 14 X-like, 27 Y-like, and 6 W-like cells with standard center-surround organization were well fit by a difference of Gaussians (DOG) model with small residual errors (mean error per data point +/- SEM = 0.008 +/- 0.002). The larger residual errors shown by a few of the Y-like cells were not due to nonlinearity of spatial summation. 3. The CSFs of eight cells that appeared to have nonstandard center-surround organization (primarily, a silent, suppressive surround) were also well fit by the DOG model. 4. The DOG curves that best fitted the data differed considerably between the three groups. As a group, X-like cells had a small center mechanism (Rc = 0.19 degrees) with high sensitivity (Kc = 76.53) and a small, sensitive surround (Rs = 0.71 degrees; Ks = 5.50). These parameters produced CSFs with high cutoff frequencies (Vcutoff = 2.5 c/deg) and low peak sensitivities (CSpk = 6.1) that occurred at 0.8 c/deg. 5. Y-like cells had a large center mechanism (Rc = 0.46 degrees) with low sensitivity (Kc = 21.16) and a large, insensitive surround (Rs = 2.38 degrees; Ks = 0.81). These parameters produced CSFs with lower cutoff frequencies (Vcutoff = 1.2 c/deg) and higher peak sensitivities (CSpk = 12.5) that occurred at 0.2 c/deg. 6. The few W-like cells that responded to gratings well enough to determine a CSF were quite variable. As a group they had a large center mechanism (Rc = 0.38 degrees) with intermediate sensitivity (Kc = 34.55) and a surround with intermediate size and sensitivity (Rs = 1.59 degrees; Ks = 1.59). These produced CSFs with intermediate cutoffs (Vcutoff = 1.6 c/deg) and low peak sensitivities (CSpk = 5.0) occurring at 0.4 c/deg.(ABSTRACT TRUNCATED AT 400 WORDS)
Neuronal activity in cortical motor areas related to ipsilateral, contralateral, and bilateral digit movements of the monkey
Authors: Tanji J. , Okano K. , Sato K. C.
Published: December 2017

1. Single cell activity was studied in the precentral (PCM), premotor (PM), and supplementary (SMA) motor cortex of the monkey to compare magnitudes of activity changes in relation to ipsilateral, contralateral, and bilateral digit movements. 2. Three Japanese monkeys were trained to press a small key with the right or left hand, or with both hands, in accordance with visual instruction signals given 2.6-5.4 s before a visual movement-trigger signal. Great care was taken to train the animal to use only the required part of the limb. As a result of extensive training, electromyographic (EMG) studies revealed that muscle activities before the key press were limited to the digit and hand muscles of the limb instructed to move. No overt increase or decrease in activity was detectable in the proximal limb or body muscles in relation to the key-press movements or instructions. 3. Even though the movement was thus limited to distal forelimb, distinct ipsilateral relationships were observed in 8.2% of the task-related PCM neurons. They changed their activity before ipsilateral and bilateral (but not before contralateral) key press. 4. A majority of the neurons recorded from the digit area of PCM (mostly limited to the anterior bank of the central sulcus) exhibited a contralateral relationship; namely the activity increased or decreased before the onset of the contralateral and bilateral key-press movements. In most of them, the magnitudes of the activity changes before the contralateral and bilateral movements were similar. 5. In proximal limb and trunk areas of PCM and also in the somatosensory cortex, no neurons were found to exhibit distinct relations to any of the key-press movements. 6. In both SMA and PM, a number of neurons exhibited relationships of the type never or only rarely observed in the primary motor cortex. Thirty-seven percent of SMA and 62% of PM neurons exhibited premovement activity changes before all of the key-press movements. The movement-specific type of activity was observed in 28% of SMA and 16% of PM neurons. In these neurons, the activity changes were observed in relation to only one of the right or left key-press movements or exclusively in relation to the bilateral key press. Neuronal activity resembling the majority of the PCM neurons (contralateral type) was observed in 31% of SMA and 13% of PM neurons. 7. Instruction-induced changes in activity were more often found in the secondary than in the primary motor area.(ABSTRACT TRUNCATED AT 400 WORDS)
Relation of cortical areas MT and MST to pursuit eye movements. III. Interaction with full-field visual stimulation
Authors: Komatsu H. , Wurtz R. H.
Published: December 2017

1. Pursuit eye movements are usually made against a visual background that is moved across the retina by the pursuit movement. We have investigated the effect of this visual stimulation on the response of pursuit cells that lie within the superior temporal sulcus (STS) of the monkey. 2. We assigned these pursuit cells to one of two groups depending on the nature of their preferred visual stimulus. One group of cells, comprising all cells located in the dorsal-medial region of the medial superior temporal area (MSTd) and some cells in lateral-anterior MST (MST1), responded to the motion of a large patterned field but showed little or no response to small spots or slits. The other group, consisting of all foveal middle temporal area (MTf) cells and many MST1 cells, responded preferentially to small spot motion or equally well to small spot motion or large field. 3. For many pursuit cells that preferred large-field stimuli, the visual response showed a reversal of the preferred direction of motion as the size of the stimulus field increased. The reversal usually occurred as the size of the moving random-dot field used as a stimulus increased in size from 20 x 20 degrees to 30 x 30 degrees for motion at approximately 10 degrees/s. The size of the filed stimulus leading to reversal of preferred direction depended on the speed of stimulus motion. Higher speeds of motion required larger stimulus fields to produce a reversal of preferred direction. This reversal (of preferred direction) did not reflect a center-surround organization of the receptive field but seemed to reflect the spatial summation properties of these cells. 4. For three-quarters of the cells that preferred large-field stimulation, the preferred direction of motion for the large field was opposite to the preferred direction of the pursuit response. The remaining cells showed either the same preferred directions for large-field visual stimulation and the pursuit response or had bidirectional visual responses. If we consider only the cells that show a reversal of preferred direction for large- and small-field stimuli, the preferred direction for the large field was always the opposite to that of pursuit, and the preferred direction for the small field was always the same. 5. During pursuit against a lighted background, the cells that showed opposite preferred directions for large-field stimulation and pursuit had synergistic responses--a facilitation of the pursuit response over the response during pursuit in the dark. Slow pursuit speeds (less than 20 degrees/s) produced the greatest facilitation.(ABSTRACT TRUNCATED AT 400 WORDS)
Electrophysiology of mammalian tectal neurons in vitro. I. Transient ionic conductances
Authors: Lopez-Barneo J. , Llinas R.
Published: December 2017

1. The electrophysiologic properties and ionic conductances of neurons located in the stratum griseum medium (SGM) of the guinea pig superior colliculus (SC) were studied by intracellular techniques in an in vitro mesencephalic slice preparation. 2. Cells were stained with Lucifer yellow and demonstrated a uniform appearance. They had an ovoid soma with dendrites directed toward the dorsal surface. These dendrites crossed the stratum opticum, and their fine ramifications reached the stratum zonale. 3. SGM cells had a mean resting potential of 59.4 +/- 5.1 (SE) mV (n = 30), a mean slope input resistance of 26.6 +/- 10 M omega (n = 30), and a mean time constant of 4.13 +/- 1.3 ms (n = 27). 4. Direct depolarization of SC neurons produced tonic repetitive firing. These Na+-dependent action potentials showed spike-frequency adaptation. After addition of tetrodotoxin (TTX) and replacement of Ca2+ by Ba2+, slow, high-threshold spikes were also generated. The trains of Ba2+ spikes did not show adaptation. 5. In about half of the cells direct hyperpolarization elicited a slow return of the membrane potential to base line at the termination of the pulse (probably due to activation of an A-type conductance) and no anomalous rectification. The remaining cells did not have an A-type conductance but demonstrated anomolous rectification which was reversibly abolished by Cs+ but unaffected by Ba2+. 6. Some cells could be anti- and/or orthodromically activated by a stimulating electrode placed at the intercollicular commissure. These, and action potentials elicited by direct activation, had a shoulder on their falling phase. The shoulder disappeared after removal of external Ca2+ or addition of Cd2+ to the bath. 7. During repetitive firing in those cells that demonstrated an A-type conductance, the shoulder became progressively more accentuated during the train of spikes, due to inactivation of this A-type conductance. This resulted in an increase in spike duration. 8. The electrophysiological properties of these cells and their morphological characteristics suggest that they may serve as the element integrating visual and nonvisual information at the superior colliculus.
Hearing in the ferret (Mustela putorius): effects of primary auditory cortical lesions on thresholds for pure tone detection
Authors: Kavanagh G. L. , Kelly J. B.
Published: December 2017

1. Pure tone thresholds were determined for five adult male ferrets before and after bilateral ablation of primary auditory cortex. Complete audiograms ranging from 0.016 to 48 kHz were obtained for two animals. The remaining three animals were tested at five frequencies selected to assess hearing throughout the audible range (0.125, 0.5, 2.0, 8.0, and 32.0 kHz). 2. Shortly after surgery one animal had elevated thresholds across the entire frequency range with the most pronounced hearing loss above 12.0 kHz. Four other animals had no elevation of thresholds at low and midrange frequencies but suffered a hearing loss at very high frequencies (32 kHz). 3. Repeated testing over a period of several months revealed substantial recovery of sensitivity. There was complete recovery of sensitivity in the low- and middle-frequency range of the audiogram. Some hearing loss persisted at the extreme upper end of the audiogram (32 kHz), but in two cases there was evidence of recovery at this frequency as well. 4. Following determination of absolute thresholds all animals were assessed for their ability to localize sound in space. Minimum audible angles were obtained on midline as well as within both left and right hemifields, i.e., around 0, -60 and +60 degrees azimuth. All animals had severe and persistent deficits in their ability to localize brief sounds within the lateral fields, but were still capable of midline localization.
Local superfusion modifies the inward rectifying potassium conductance of isolated retinal horizontal cells
Authors: Perlman I. , Knapp A. G. , Dowling J. E.
Published: December 2017

1. Horizontal cells were enzymatically and mechanically dissociated from the white perch (Roccus americana) retina and voltage clamped using patch electrodes. Steady-state current-voltage (I-V) relationships of solitary horizontal cells were determined by changing the membrane potential in a rampwise fashion. 2. The I-V curve of cells bathed in normal Ringer solution exhibited a large conductance increase at negative membrane potentials. This conductance activated near the K+ equilibrium potential, had no clear reversal potential, was enhanced by raising the extracellular concentration of K+, and was suppressed by external Cs+. These properties identify the conductance as the inward (anomalous) rectifier. 3. Continuous superfusion of the cells' local environment with drug-free Ringer reduced the magnitude of the inward rectifier current and shifted its activation point to more negative potentials. This effect developed over approximately 30 s, lasted as long as superfusion continued and was reversible upon cessation of superfusion. 4. Pressure ejection of drug-free Ringer solution onto cells bathed in the identical solution also reduced the magnitude of the inward rectifier current, although the effects were more rapid and more transient than those exerted by superfusion. Pressure ejection had little effect when cells were simultaneously superfused with Ringer, suggesting a common mode of action on the inward rectifier. 5. In the absence of superfusion, pressure ejection of Ringer containing 200 microM L-glutamate had a biphasic effect on membrane conductance. At potentials above -60 mV, glutamate caused a conductance increase with a reversal potential near +10 mV. At potentials below -60 mV, glutamate caused a conductance decrease whose reversal potential could not reliably be determined. The latter effect was similar to the suppression of the inward rectifier by application of Ringer alone, suggesting that it may represent an artifact of pressure ejection rather than a direct effect of glutamate. 6. In support of this interpretation, we found that pressure ejection of glutamate in the presence of external Cs+ (which blocks the inward rectifier) or during local superfusion with Ringer (which prevents attenuation of the inward rectifier by pressure ejection) did not cause a conductance decrease at negative potentials. Under these conditions, glutamate caused primarily a conductance increase with a reversal potential near +10 mV.(ABSTRACT TRUNCATED AT 400 WORDS)
The accessory optic system of rabbit. II. Spatial organization of direction selectivity
Authors: Simpson J. I. , Leonard C. S. , Soodak R. E.
Published: December 2017

1. To compare the spatial organization of the direction selectivity of neurons in the medial terminal nucleus (MTN) of the accessory optic system with that of neurons in the adjacent ventral tegmentum, extracellular single-unit recordings were made in the anesthetized rabbit. The ventral tegmental neurons were located in a region called the visual tegmental relay zone (VTRZ), which is defined by the ventral tegmental terminal field of contralaterally projecting MTN neurons. 2. Some of the present sample of MTN neurons (5 of 34) had monocular receptive fields composed of two parts distinguished by a marked difference in the orientation of their respective direction-selective tuning curves. For one part of the receptive field the preferred excitatory direction was "up," while for the other part it was "down." Such receptive fields for one eye were called bipartite, whereas the more usually encountered MTN receptive fields, which could be characterized by a single direction-selective tuning curve, were called uniform. 3. Of the 16 neurons recorded from the VTRZ, all but one were binocular. For these neurons, both uniform and bipartite receptive fields were found for each eye alone. The only monocular neuron encountered in the VTRZ had a contralateral, bipartite receptive field. 4. The spatial organization of the direction selectivity of bipartite receptive fields strongly suggests that they are suited to represent rotation of the visual field about a horizontal axis located in the vertical plane that divides the receptive field into two parts. 5. The boundary between the two parts of the bipartite receptive fields was found using handheld visual stimuli at one of two azimuthal locations, either close to 45 degrees or between 95 and 125 degrees (the 0 degree reference was rostral in the midsagittal plane). This particular structure of the bipartite receptive fields suggests that their preferred rotation axes have a close spatial relation to the best-response axes of the semicircular canals. 6. Seven VTRZ neurons were antidromically activated by electrical stimulation of the ipsilateral dorsal cap of the inferior olive. Since the receptive fields of VTRZ neurons have many of the structural features characteristic of the receptive fields of rostral dorsal cap neurons we conclude that the spatial organization of the receptive fields of dorsal cap neurons is, for the most part, synthesized prior to the inferior olive.(ABSTRACT TRUNCATED AT 400 WORDS)
Spinocervical tract neurons responsive to light mechanical stimulation of the raccoon forepaw
Authors: Hirata H. , Pubols B. H.
Published: December 2017

1. The extracellular activity of 45 antidromically identified spinocervical tract (SCT) neurons responsive to light mechanical stimulation of the glabrous surfaces of the forepaw was examined in raccoons anesthetized with pentobarbital sodium. An additional seven neurons had peripheral receptive fields (RFs) located on hairy skin of the forelimb, and three had deep RFs. 2. All recording sites were histologically verified as falling within Rexed's laminae III and IV in spinal cord segments C6-T1. Antidromic conduction velocities of the 55 neurons ranged between 8.3 and 64.2 m/s. 3. Units with glabrous skin RFs were classified according to their response to a maintained mechanical stimulus as either rapidly adapting (n = 39) or slowly adapting (n = 6). Of 11 cells tested, 2 displayed enhanced responses to noxious stimuli and were classed as multireceptive. 4. RF areas were significantly smaller on digits (range = 0.4-45.0 mm2) than on palm pads (range = 5.6-76.0 mm2), and comparable in size to RF areas previously reported in raccoon cuneate nuclear cells (32). 5. RA neurons fell into three distinct categories with respect to the relationship between instantaneous spike frequency during displacement ramp stimulation, and ramp velocity, steep functions (as defined by the value of power function exponents), flat functions, and discontinuous functions; SA neurons fell into two categories, continuous, and discontinuous. 6. The results, in conjunction with those of previous studies, lead to two major conclusions: 1) raccoon and primate spinocervicothalamic systems are more similar to each other than either is to that of the cat and 2) the ability of the raccoon SCT to convey information from the glabrous skin of the forepaw regarding characteristics of light mechanical stimuli is at least as precise as that of neurons of the dorsal column-medial lemniscal system.
Activity-dependent disinhibition. III. Desensitization and GABAB receptor-mediated presynaptic inhibition in the hippocampus in vitro
Authors: Thompson S. M. , Gahwiler B. H.
Published: December 2017

1. Single-electrode voltage-clamp recordings were made from CA3 pyramidal cells in organotypic hippocampal slice cultures for measurement of membrane currents underlying both the gamma-aminobutyric acid (GABA)-mediated, Cl- -dependent inhibitory postsynaptic potential (IPSC), evoked in response to stimulation of the mossy fiber pathway, and responses to iontophoretically applied GABA. Pre- and postsynaptic mechanisms mediating activity-dependent reductions in the conductance underlying the IPSC (gIPSC) were investigated. 2. During 99-s applications of GABA, the mean evoked conductance (gGABA) decreased 43% with an initial time constant of 51 s. Desensitization was never complete. 3. Ca2+-influx, activated with depolarizing voltage commands of 100-ms to 15-s duration in the presence of intracellular Cs+, had no effect on GABA responses. 4. Iontophoretic application of the GABAA-receptor agonist muscimol caused a rapid decrease of 80-100% in the amplitude of IPSCs evoked at depolarized membrane potentials (Vm). Recovery was 80% complete in 30 s. The second of two paired applications of muscimol, delivered at the same iontophoretic intensity, was reduced in amplitude 35%. This was shown to result from a decrease in driving force rather than from desensitization. We conclude that muscimol decreases IPSCs by causing an increase in the intracellular Cl- concentration. 5. Iontophoretic application of the GABAB-receptor agonist (+/-)-baclofen caused a decrease of only 30% in the amplitude of IPSCs evoked at depolarized Vms. This effect outlasted the post-synaptic effects of baclofen; recovery was 80% complete between 60 and 90 s. 6. Bath application of (-)-baclofen was found to decrease gIPSC without affecting the IPSC reversal potential. This effect was rapid in onset, could be observed at concentrations as low as 1 X 10(-7) M, and recovered quickly. The EC50 was roughly 5 X 10(-7) M and appeared similar to that for the baclofen-activated increase in postsynaptic conductance. No effect on responses to iontophoretically applied GABA was observed, demonstrating that baclofen decreases gIPSC by reducing presynaptic release via GABAB receptors. 7. Iontophoretic application of GABA reduced IPSCs in a dose-dependent manner. At low iontophoretic intensities, IPSCs were reduced only 30% and recovered slowly, as with baclofen iontophoresis. At higher iontophoretic intensities, IPSCs were more completely blocked. Recovery was initially fast, but took 60-90 s to be complete.(ABSTRACT TRUNCATED AT 400 WORDS)
Hypoxic changes in hippocampal neurons
Authors: Leblond J. , Krnjevic K.
Published: December 2017

1. Reversible effects of brief periods of anoxia (replacing 95% O2-5% CO2 with 95% N2-5% CO2 for 2-4 min) were studied in CA1 neurons in hippocampal slices (from Sprague-Dawley rats), kept in an interface-type chamber at 33.5 degree. 2. The predominant voltage change during anoxia (N2) was a hyperpolarization, accompanied by a marked fall in resistance and excitability; synaptic potentials were also depressed, especially inhibitory postsynaptic potentials (IPSPs). 3. In voltage-current (V-I) plots, the N2-evoked hypolarization had a reversal potential below -90mV, even when recording with 2 M KCl electrodes and after substituting 90% of medium Cl- with isethionate. The accompanying fall in input resistance (RN) is therefore probably caused by an increase in K conductance (in agreement with previous reports). There was evidence that anomalous rectification enhances the fall in RN but limits the hyperpolarization. 4. These effects of anoxia were not fully blocked by any of the K-channel antagonists tested, including Cs, TEA, 4-AP, quinine and apamin. 5. Intracellular injections of Ca chelators caused a variable depression of N2-evoked reductions in RN. 6. It is unlikely that N2 activates ATP-sensitive K channels as tolbutamide enhanced rather than depressed the hyperpolarization and fall in RN. 7. When early depletion of cellular ATP was prevented by incubation in creatine (25 mM for greater than 1 h), even longer anoxic periods produced only minor changes in potential, RN, and synaptic transmission. 8. It was concluded that activation of K conductance by a rise in cytosolic-free Ca2+ is the most plausible of several possible underlying mechanisms.
Effects of preventing reinnervation on axotomized spinal motoneurons in the cat. I. Motoneuron electrical properties
Authors: Pinter M. J. , Vanden Noven S.
Published: December 2017

1. The intent of this study was to determine the effect on the electrical properties of axotomized spinal motoneurons when motor axons are allowed to regenerate but are denied the opportunity to reinnervate muscle. 2. The nerve supplying the medial gastrocnemius (MG) muscle in cats was served close to its entry into the muscle and sutured onto the surface of the lateral gastrocnemius (LG) muscle. The MG muscle was excised to prevent availability of vacant end-plates to the regenerating MG axons. The electrical properties of antidromically identified MG motoneurons were studied using intracellular recording at various postoperative intervals. 3. In 9 of 12 experimental animals, no sign of functional innervation by MG axons of the LG muscle could be detected. In three experimental animals, electrical and contraction activity in the LG muscle was observed following electrical stimulation of the transplanted MG nerve. The observed electrical and contraction activity was, however, negligible compared to the effects of electrical stimulation of the intact LG-soleus nerve. 4. At the earliest postoperative interval studied (20 days), MG motoneuron electrical properties [input resistance, afterhyperpolarization (AHP) duration, conduction velocity, time constant, rheobase current, and sag] exhibited significant changes that were nearly identical to those described for spinal motoneurons following section of ventral roots or motor nerves or in the earliest stages of reinnervation. 5. At the 44-60 day postoperative (DPO) intervals, several motoneuron electrical properties showed signs of recovery to control levels. At 44 DPO, average values of input resistance, time constant, and AHP duration declined from the significant increases observed at 20 DPO and could not be distinguished statistically from control mean values. 6. These indications of an early recovery of normal electrical properties were not sustained. At subsequent postoperative intervals (90, 120, and 150-180 DPO), average values of motoneuron electrical properties tended to be similar to those observed at 20 DPO. 7. Correlations observed among control motoneuron electrical properties were weakened and the pattern of correlation was disrupted at all postoperative intervals. 8. In conjunction with previous results demonstrating recovery of normal electrical properties following reinnervation (Foehring et al. 1986b), our findings suggest that functional contact with muscle is required for the full expression of the normal range of motoneuron electrical properties.(ABSTRACT TRUNCATED AT 400 WORDS)
Kainate receptor-mediated synaptic currents in mudpuppy inner retinal neurons reduced by D-O-phosphoserine
Authors: Coleman P. A. , Miller R. F.
Published: December 2017

1. The effects of D-O-phosphoserine (DOS) were examined on proximal neurons in the superfused mudpuppy retinal-eyecup preparation by measuring their synaptically evoked whole-cell currents with the use of patch-clamp electrodes. 2. DOS reduced the light-evoked excitatory postsynaptic potentials (EPSPs) of amacrine and ganglion cells. This suppression was present even though the center responses of both ON- and OFF-bipolar cells were unaffected by DOS. 3. When recordings were done under voltage-clamp conditions. DOS diminished the magnitude of light-evoked synaptic currents associated with a reduction in synaptic conductance. 4. To determine which acidic amino acid receptor mediated the network-selective action of DOS, various glutamate agonists were tested against this excitatory amino acid receptor (EAAR) antagonist. DOS blocked the depolarizing effects of kainate (KA), but not those of N-methyl-D-aspartate (NMDA) or quisqualate (QQ). Thus DOS was a selective KA antagonist, and KA receptors appear to be the dominant EAAR subtype that mediates synaptic inputs into the inner retina of the mudpuppy.
Serotonergic/cholinergic muscle receptor cells in the crab stomatogastric nervous system. II. Rapid nicotinic and prolonged modulatory effects on neurons in the stomatogastric ganglion
Authors: Katz P. S. , Harris-Warrick R. M.
Published: December 2017

1. The gastropyloric receptor (GPR) cells, which are described in the preceding paper, are a set of proprioceptive cells in the crabs Cancer borealis and Cancer irroratus that contain serotonin (5-hydroxytryptamine, 5-HT) and choline acetyltransferase. These cells have a variety of synaptic effects on cells in the stomatogastric ganglion (STG). We used pharmacologic methods to distinguish the effects that were due to acetylcholine (ACh) from those that could be due to serotonin. 2. The GPR cells evoke excitatory postsynaptic potentials (EPSPs) in two gastric mill motor neurons [lateral and dorsal gastric (LG and DG)] in the stomatogastric ganglion. The EPSPs exhibit nicotinic pharmacology, indicating that they may be due to the release of ACh from the GPR cells. 3. A train of GPR action potentials induces plateau potential properties in the DG motor neuron. This plateau potential induction is not blocked by nicotinic or muscarinic antagonists, suggesting it might be due to serotonin released from the GPR cells. Bath-applied serotonin induces a tonic depolarization of DG with high-intensity spiking. 4. In the accompanying paper, it is shown that DG-evoked muscle contraction leads to the excitation of GPR2 through mechanical coupling of the muscles. Because GPR2 also excites DG, a positive feedback loop exists between GPR2 and DG. This reflex loop may be involved in the control of the medial tooth of the gastric mill. 5. GPR stimulation initiates or enhances rhythmic pyloric cycling. This is due at least in part to a direct enhancement of bursting in the pyloric dilator/anterior burster (PD/AB) pacemaker cell group and can outlast the period of GPR stimulation by up to 1 min. GPR-induced PD burst enhancement continues in the presence of nicotinic and muscarinic antagonists, indicating that the effect is probably not due to the release of ACh. Bath application of serotonin mimicks the neuromodulatory effect of GPR stimulation on the PD/AB group by inducing or enhancing bursting. 6. Thus the GPR cells elicit at least three different synaptic actions in the stomatogastric ganglion: 1) classical, fast nicotinic cholinergic EPSPs that may be important for reflex functions in the gastric mill; 2) noncholinergic, cycle-by-cycle plateau potential induction that might be critical for the timing and operation of the gastric mill, and 3) prolonged, noncholinergic burst enhancement in pyloric neurons that is mimicked by serotonin, lasts many cycles, and may act to assure that the pyloric central pattern generator (CPG) is activated and cycling strongly.
Consequences of 4-aminopyridine applications to trigeminal root ganglion neurons
Authors: Puil E. , Miura R. M. , Spigelman I.
Published: December 2017

1. The effects of 4-aminopyridine (4-AP) on the electrical properties of 30 trigeminal root ganglion (TRG) neurons were determined from the membrane voltage responses to step and sinusoidal current injections using intracellular microelectrode techniques in in vitro slice preparations (guinea pigs). 2. Comparisons of results from 4-AP applications (0.05-5 mM) with those from tetraethylammonium (TEA) applications (0.1-10 mM) revealed very different actions of these agents. Both agents produced an increase in input resistance and a decrease in threshold for spike generation. Applications of 4-AP increased subthreshold oscillations of the membrane potential and enhanced the repetitive spike firing evoked by intracellular injections of current pulses. However, TEA applications blocked the potential oscillations and did not exaggerate repetitive spike discharges. Spontaneous spike activity or bursts were observed in four neurons that received 4-AP applications. 3. Membrane properties were determined in 20 of the 30 neurons by fitting impedance data in the frequency domain with a four-parameter membrane model by the use of computer-intensive techniques. In the majority of neurons, the time-invariant and time-dependent membrane conductances decreased during 4-AP application. The time constant for the time-dependent conductance also decreased, suggesting that the closing of K+-channels was facilitated in the membrane. 4. Applications of 4-AP in a dose range of 50 microM-5 mM produced rapid (approximately tens of seconds) responses of the neurons, resulting in a dose-dependent increase of the impedance magnitude functions and in a leftward shift of the resonant "humps" to lower frequencies. This shift indicates that the TRG neuronal membrane is capable of producing large voltage responses to current inputs at low frequencies. Recovery from the effects of 4-AP was slow (usually greater than 30 min). 5. Applications of 4-AP at high doses (greater than or equal to 1 mM) and at various imposed membrane potentials in four neurons resulted in poorly reversible unspecific changes in certain membrane parameters (increased input capacitance and conductance) and an insensitivity of the input conductance to the imposed membrane potential. These effects could be interpreted as membrane breakdown. 6. The tendencies of TRG neurons to fire repetitively and in bursts of spikes during 4-AP application result from the increased oscillatory behavior of their membrane potentials and changes in membrane resonance induced by presumed blockade of K+ channels.(ABSTRACT TRUNCATED AT 400 WORDS)
Anoxia on slow inward currents of immature hippocampal neurons
Authors: Krnjevic K. , Cherubini E. , Ben-Ari Y.
Published: December 2017

1. The effects of brief anoxia (2-4 min) on membrane currents--especially the tetrodotoxin (TTX)-insensitive, Cd2+-sensitive slow inward currents, presumed to be Ca2+ currents--were studied by single-electrode voltage clamp in CA1 and CA3 neurons in submerged hippocampal slices from adult and newborn Wistar rats (PN1-13). 2. In mature neurons, anoxia had no effect on Q-type inward relaxations, but slowly activating C-type outward currents were depressed. The most striking change was the suppression of Ca inward currents (especially the slowly inactivating L-type, by greater than 95%). This effect of anoxia was not sensitive to the N-methyl-D-aspartate (NMDA) receptor blocker, D-aminophosphonovalerate. Anoxia also reversibly abolished the NMDA-evoked inward current. 3. In neurons from newborn animals (PN1-6), Q-type inward relaxations and postanoxic outward currents were very small or undetectable. The slow inward (Ca) currents were smaller than in mature cells, but they showed a clearer separation between low-threshold, fast-inactivating and high-threshold, slowly inactivating currents. Both types of current were more resistant to anoxia (mean depression of L-type was by only 53.3 +/- 5.6%, mean +/- SE). 4. In such immature neurons, the NMDA-evoked inward currents were also more resistant to anoxia. 5. By PN7-13, increasing maturation was reflected in 1) larger voltage-dependent inward currents, 2) increasingly evident Q-type relaxations and postanoxic outward currents, and 3) near-complete blockade of inward currents by anoxia (at PN11-13, mean depression of L-type currents was by 98.5 +/- 1.5%).
Studies of solitary semicircular canal hair cells in the adult pigeon. I. Frequency- and time-domain analysis of active and passive membrane properties
Authors: Correia M. J. , Christensen B. N. , Moore L. E. , Lang D. G.
Published: December 2017

1. Hair cells were enzymatically dissociated from the neuroepithelium (cristae ampullares) of the semicircular canals of white king pigeons (Columba livia). Those hair cells determined to be type II by an anatomic criterion, the ratio of the minimum width of the neck to the width of the cuticular plate, were studied with the use of the whole cell patch-clamp technique. 2. The mean +/- SD zero-current membrane potential, Vz, was found to be -54 +/- 12 mV for anterior crista hair cells (n = 71), -62 +/- 14 mV for posterior crista hair cells (n = 14), and -55 +/- 12 mV for lateral (horizontal) crista hair cells (n = 18). The mean +/- SD value of Vz for hair cells from all cristae (n = 103) was -56 +/- 13 mV. 3. Active and passive membrane properties were calculated in the time domain, in voltage- or current-clamp mode, from responses to voltage or current pulses and, in the frequency domain, by fitting a membrane model to admittance magnitude and phase data resulting from current responses to sum-of-sines voltages at different d.c. levels of voltage-clamp membrane potential. 4. The average value +/- SE of input resistance (Rin), over the range from -100 to -60 mV, was found to 1.5 +/- 0.3 G omega from a mean-voltage-as-a-function-of-current plot, V-I, (n = 7) and a mean of 1.4 +/- 0.3 G omega from individual (n = 15) current-as-a-function-of-voltage plots, I-V. A lower mean value 0.8 +/- 0.4 G omega was obtained for the input resistance from frequency-domain calculations for a different set of cells (n = 21). Also, in two different sets of cells, average input capacitance (Cin) was determined to be 12 +/- 3 pF (n = 7) from time-domain estimates and 14 +/- 3 pF (n = 21) from frequency-domain estimates. The (Rin)(Cin) product was 11 ms based on frequency-domain estimates and 17 ms from time-domain estimates. 5. I-V curves for hair cells voltage clamped at -60 mV showed some anomalous rectification for hyperpolarizations between -60 and -120 mV but no detectable N-shape for depolarizations between -50 and 90 mV. The I-V relation showed increasing slope with depolarization through the resting potential (Vz) and increased linearly between -40 and 80 mV; the best-fit straight-line maximum slope conductance for six cells over this range was 17.4 +/- 0.3 nS.(ABSTRACT TRUNCATED AT 400 WORDS)
Membrane current underlying muscarinic cholinergic excitation of motoneurons in lobster cardiac ganglion
Authors: Freschi J. E. , Livengood D. R.
Published: December 2017

1. We studied the effect of cholinergic agonists on motoneurons of the lobster cardiac ganglion under voltage clamp. 2. In unclamped neurons, acetylcholine (ACh) caused a depolarization and increase in burst potential frequency. By the use of nicotinic and muscarinic agonists, we determined that both types of receptors are present on the neurons. We therefore used specific muscarinic agonists to further study ionic mechanisms underlying the muscarinic cholinergic current (Imch). 3. Muscarinic agonists produced detectable inward current at doses above 10(-6) M, and maximum effect was seen at doses above 10(-3) M. 4. Imch was voltage-dependent. When the membrane holding potential was shifted to levels negative to the resting potential, the response declined, nulling but not reversing at -80 to -100 mV. The response enlarged with membrane depolarization, reaching a maximum at between -30 and -10 mV. With further depolarization, the response declined and then reversed at potentials around +20 mV. 5. The muscarinic response varied as a function of extracellular Na+ concentration and was completely blocked in Na+-free solutions. The relationship between response amplitude and external Na+ was well described by the electrodiffusion equation for Na+ driving force. 6. Imch amplitude also varied as a function of extracellular potassium concentration, becoming larger with low external K+ and smaller at higher concentrations. Shifting the Cl- equilibrium potential did not affect the properties of the Imch. 7. Tetrodotoxin (TTX) had no effect on Imch. In concentrations of 1-10 mM, such K+-channel blocking agents as Ba2+, Cs+, 4-aminopyridine (4-AP), or tetraethylammonium (TEA), and such Ca2+-channel blockers as Co2+ or Mn2+, when applied externally, did not suppress Imch. Above 30 mM, TEA did inhibit the response, and combinations of K+-channel blocking agents, each at concentrations insufficient alone to block the current, also inhibited Imch. 8. Current-voltage (I-V) curves obtained during muscarinic agonist perfusion consistently crossed the control I-V curves at a mean membrane potential of +24 mV. The reversal potential shifted to a more negative value in low extracellular Na+. 9. Although no reversal of Imch was seen when agonists were applied to cells clamped at negative holding potentials, the averaged curve of Imch, obtained by subtracting control ramp I-V curves from those obtained in the presence of agonist, did show a small net outward current at membrane potentials negative to -100 mV.(ABSTRACT TRUNCATED AT 400 WORDS)
Monosynaptic excitatory amino acid transmission from the posterior rhombencephalic reticular nucleus to spinal neurons involved in the control of locomotion in lamprey
Authors: Ohta Y. , Grillner S.
Published: December 2017

1. The reticulospinal neurons in the lamprey posterior rhombencephalic reticular nucleus (PRRN) and their projections to different types of spinal neurons have been investigated by the use of simultaneous paired intracellular recordings from one pre- and one postsynaptic cell. PRRN is of particular importance for the initiation of locomotion. 2. Intracellular stimulation of single PRRN neurons produced monosynaptic excitatory postsynaptic potentials (EPSPs) in simultaneously recorded motoneurons and spinal premotor interneurons of both the excitatory and inhibitory type. Individual PRRN neurons produced EPSPs in several different types of target cells, as revealed by signal averaging. Each single PRRN neuron had extensive monosynaptic connections to approximately 73% of the motoneuronal population. Conversely, several PRRN neurons converge on individual spinal neurons. The average amplitude of the EPSPs was 0.43 +/- 0.40 (SD) mV. The EPSPs varied in time course (time to peak = 7.5 +/- 2.8 ms; duration at one-half peak amplitude = 21.9 +/- 18.1 ms). 3. The EPSPs produced by reticulospinal cells were composed of either exclusively chemical, exclusively electrical, or mixed chemical and electrical components. The electrical EPSPs remained when the ordinary physiological solution was substituted for one without Ca2+ but with Mn2+. The chemical component of the EPSPs was always depressed when a broad-spectrum excitatory amino acid (EAA) antagonist, such as kynurenic acid, was applied, suggesting that the chemical component was because of EAA transmission. The chemical EPSP could have two components, one late, suppressed by N-methyl-D-aspartate (NMDA) antagonists, and one early because of activation of kainate/quisqualate receptors. 4. Three-dimensional reconstructions of Lucifer yellow-filled PRRN neurons were performed with a confocal laser scanning microscope. PRRN neurons producing monosynaptic excitatory amino acid EPSPs were found to have a fusiform cell body located near the surface of the fourth ventricle and an extensive fanlike dendritic tree extending to the ventral and lateral margin of the brain stem within the basal plate. The axons descend in the lateral funiculi of the spinal cord. 5. PRRN neurons utilizing EAA transmission are active during fictive locomotion. They presumably initiate and reinforce ongoing spinal locomotor activity by monosynaptically increasing the general excitability of the spinal premotor interneurons of the spinal locomotor networks by means of their extensive divergent and convergent monosynaptic connections.
Mechanics of stretch in activated crustacean slow muscle. I. Factors affecting peak force
Authors: Chapple W. D.
Published: December 2017

1. The active stiffness of ventral superficial abdominal muscle (VSM) of the hermit crab, Pagurus pollicarus, was measured with ramp stretches of different amplitudes and velocities. Active stiffness was calculated by subtracting the peak force produced by passive stretch and the isometric force just before stretch from the peak force produced by stretching active muscle. The result was then divided by stretch length to give stiffness. 2. The relationship between force just before stretch (the level of activation) and active stiffness was curvilinear and was found to apply under a variety of experiment conditions. For pooled data from eight experiments, active stiffness (GN.m-2.m-1) = 3.2*stress (MN/m2)-7.6*stress2. Decreasing the number of motor units or activating the inhibitor did not alter this relationship nor did the addition of proctolin, octopamine, or 5-HT to the bath. The relationship also applied during the rising phase of isometric tension. However, stiffness declined more rapidly than predicted by this relationship after the end of tetanus. 3. Active stiffness varied inversely with stretch amplitude for fast stretches, and the slope of this relationship increased with increasing muscle activation. At lower stretch velocities, the slope was much less than at rapid stretch velocities, so at low levels of activation and stretch velocity, active stiffness was essentially independent of stretch length. 4. Active stiffness covaried with muscle force as both were sampled at shorter and shorter lengths on the ascending limb of the length-tension curve.(ABSTRACT TRUNCATED AT 250 WORDS)