bluuebunny/crossref_metadata_2025 huggingface dataset:
The nitric oxide synthase inhibitor, N-monomethyl-L-arginine blocks induction of a long-term potentiation-like phenomenon in rat medial frontal cortical neurons in vitro
Authors: Nowicky A. V. , Bindman L. J.
Published: December 2017

1. Nitric oxide has been implicated in the production of long-term depression (LTD) in the cerebellum and in the production of long-term potentiation (LTP) and LTD in the hippocampus. We now provide evidence of its involvement in the induction of long-term synaptic potentiation in in vitro slices in the cerebral cortex of the rat. 2. Intracellular recordings were made from layer V neurons in the medial frontal cortex, and excitatory synaptic potentials (EPSPs) were evoked by electrical stimulation of layers II/III. Tetanic stimulation of this pathway may induce LTD or LTP or no change at these synapses. First we established experimental conditions under which a long lasting potentiation could be induced with a high incidence (> 60%), namely perfusion of slices with 1 microM bicuculline methiodide, second the use of increased shock duration in the tetanic conditioning stimuli, third and most important the addition of QX-314 to the microelectrode to reduce potassium conductances. Because the potentiation of the mean EPSP slope was significantly greater than the control at 40-min postconditioning, but was declining throughout this period, we refer to it for brevity as LTP, but strictly class it as an LTP-like phenomenon. 3. The nitric oxide (NO) synthase inhibitor interfered with the production of LTP. In the control group of neurons (n = 13) the mean depolarizing slope of the EPSP at 30-min post-conditioning was 142.7 +/- 2% (mean +/- SE) of the prestimulation control.(ABSTRACT TRUNCATED AT 250 WORDS)
Monkey hippocampal neurons related to spatial and nonspatial functions
Authors: Ono T. , Nakamura K. , Nishijo H. , Eifuku S.
Published: December 2017

1. Neural activity in the monkey hippocampal formation (HF) was analyzed during a spatial moving task in which the monkey was guided by auditory and visual cues and when stimuli were presented from various directions. The monkey could control a motorized, movable device (cab) and its route to a target location by pressing the proper one of five available bars in an appropriate sequence (spatial moving task). In any of several locations in the field, neural responses were evident in relation to the presentation of various objects or human movement in some relative direction (left, anterior, right) as a directional stimulus test. 2. Of 238 hippocampal neurons analyzed, 172 (72.3%, 238-66) responded in either the spatial moving task, or to the direction from which stimulation was presented, or to the location of the monkey in the field, or to some combination of these. 3. The activity of 79 (33.2%) neurons was higher when the monkey was in some specific location in the field during the spatial moving task, regardless of the approach route or other task parameters (place related neurons). 4. Responses to the task cues in the spatial moving task were evident in 110 (46.3%) neurons (task related neurons). Of these, 77 (32.4%) neurons were not place related. The remaining 33 (13.9%) neurons were both task related and place related. These neurons responded to task cues in only that part of the field in which place related responses occurred. The neural response to the task cues disappeared when the monkey moved out of the place response region. The place related and task related neural responses disappeared when the room light was switched off. Thus information from the environment outside of the cab contributed to the place related and task related responses. 5. Stimuli presented from certain specific directions induced responses, selectively, in 41 (17.2%) of the neurons (direction related neurons). The dependence of the preferred direction was described in one of three ways--egocentric, allocentric, or place-direction specific. Nineteen egocentric neurons responded to a stimulus only when it was presented from a certain direction relative to the orientation of the monkey, regardless of the location of the monkey. Eleven allocentric neurons responded to a stimulus only when it was presented at a particular position in the room, regardless of the location or orientation of the monkey.(ABSTRACT TRUNCATED AT 400 WORDS)
Protein kinase C blocks somatostatin-induced modulation of calcium current in chick sympathetic neurons
Authors: Golard A. , Role L. W. , Siegelbaum S. A.
Published: December 2017

1. Somatostatin produces a voltage-dependent inhibition of N-type Ca2+ current in chick sympathetic neurons. Pretreatment of chick sympathetic ganglion neurons with protein kinase C (PKC) activators has no effect on calcium current (ICa) but reduces the inhibition of ICa by somatostatin. 2. The effects of the alkaloid PKC activator (-)-indolactam V were indistinguishable from those of 4 beta-phorbol-12-myristate-13-acetate (4 beta-PMA). The inactive isomers (+)-indolactam V and 4 alpha-PMA did not alter the modulation of ICa by somatostatin. 3. Modulation of ICa by somatostatin desensitizes, with a time for half desensitization of approximately 3 min. PKC activation mimics the normal desensitization process in that responses to 30 nM somatostatin are inhibited to a greater extent than are responses to 1 microM somatostatin. 4. PKC appears to act at the level of the somatostatin receptor or receptor-G protein interaction because PKC activation does not alter Ca2+ current inhibition in response to a nonhydrolyzable analog of GTP, GTP-gamma-S, which directly activates G proteins. 5. The specific PKC inhibitor calphostin C largely reverses the effects of phorbol esters, but does not slow the normal rate of desensitization of somatostatin responses. This indicates that PKC is not involved in the homologous desensitization of the somatostatin receptor. 6. Neither substance P, which activates PKC in these cells, nor arachidonic acid, another PKC activator, altered the action of somatostatin on ICa.
Light-evoked modulation of basolateral membrane Cl- conductance in chick retinal pigment epithelium: the light peak and fast oscillation
Authors: Gallemore R. P. , Steinberg R. H.
Published: December 2017

1. We studied the ionic mechanism of the light-peak voltage of the DC electroretinogram (DC ERG) in an in vitro preparation of chick neural retina-retinal pigment epithelium (RPE)-choroid. The light peak originates from a depolarization of the RPE basolateral (basal) membrane, associated with an increase in its conductance. Using conventional and Cl(-)-selective microelectrodes, we tested the hypothesis that the light-peak voltage is generated by an increase in Cl- conductance (gCl) of the basolateral (basal) membrane. 2. Perfusion of the RPE basal membrane with 4,4'-diisothiocyanostilbene-2,2'-disulfonate (DIDS), a known blocker of gCl in chick RPE, suppressed both the light-peak depolarization and the accompanying conductance increase of the basal membrane. 3. Using sustained transepithelial current to clamp the basal membrane potential at different levels, we estimated the reversal potential of the light peak. At membrane potentials above the equilibrium potential for Cl- (ECl = -40 +/- 10 mV mean +/- SE), light-peak polarity was reversed. Current-voltage (I-V) curves measured in the dark and at the peak of the light peak also gave a reversal potential in the same range as ECl. In addition, shifting ECl by changing intracellular Cl- (aCli) via passage of transepithelial current or perfusing the apical side of the RPE with the Cl- uptake blocker, furosemide, shifted the light-peak reversal potential in the same direction as the change in ECl. 4. The transference number for Cl-, TCl, was estimated from step decreases in basal Cl- and increased from 0.20 +/- 0.01 in the dark to 0.31 +/- 0.01 during the light peak. These results indicate an average increase of 55% in the relative conductance of the basal membrane for Cl-. 5. Light-evoked changes in aCli, measured with Cl(-)-selective microelectrodes, were too small to account for the change in basal membrane potential during the light peak. These data strongly support the hypothesis that the light peak originates from an increase in RPE basal membrane permeability to Cl-. 6. We also obtained support for the model of Joseph and Miller that the fast-oscillation trough of the DC ERG, generated by a delayed basal membrane hyperpolarization of the RPE, originates from light-evoked modulation of the Cl- transport pathway. Perfusing either the apical side of the RPE with furosemide or the basal side with DIDS suppressed the fast oscillation. The delayed basal hyperpolarization reversed polarity at membrane potentials positive to ECl.(ABSTRACT TRUNCATED AT 400 WORDS)
Dopaminergic modulation of rod pathway signals does not affect the scotopic ERG of cat at dark-adapted threshold
Authors: Naarendorp F. , Hitchock P. F. , Sieving P. A.
Published: December 2017

1. Two rod-driven electroretinogram (ERG) components were recorded to monitor scotopic retinal signals during experimental manipulation of dopamine and gamma-aminobutyric acid (GABA) in normal cat eyes and in eyes pretreated with 6-hydroxydopamine (6-OHDA). The scotopic threshold response (STR) was elicited near absolute threshold to monitor signals traversing the rod pathway near quantal threshold; scotopic PII, which normally begins approximately 2 log units higher, was also monitored. Responses were evaluated by V-log I curves and criterion amplitudes after intravitreal drug injections into intact eyes in vivo. The depletion of dopaminergic cells by pretreating with 6-OHDA was confirmed histologically by immunocytochemical methods. 2. Dopamine abolished the STR and markedly decreased PII in the normal eye. Both 6-OHDA pretreatment and application of the dopamine antagonist, haloperidol, increased the STR amplitudes, but only for stimuli beginning 2 log units above threshold; PII amplitude also was increased. However, neither 6-OHDA pretreatment nor haloperidol affected the STR near absolute threshold. 3. Both GABA and bicuculline suppressed the STR in the normal eye. However, when applied to eyes pretreated with 6-OHDA or concurrent with haloperidol, bicuculline enhanced the STR. GABA enhanced the PII amplitude in the normal eye but had no effect in eyes pretreated with 6-OHDA or in the presence of haloperidol. 4. These results suggest that 1) dopaminergic activity modulates signals in the rod pathway at higher stimulus intensities but not near absolute threshold and 2) GABA can affect the scotopic PII component by acting through dopaminergic cells in the dark-adapted retina.
Role of the caudal fastigial nucleus in saccade generation. I. Neuronal discharge pattern
Authors: Fuchs A. F. , Robinson F. R. , Straube A.
Published: December 2017

1. The effects of lesions in both human and nonhuman primates have implicated the cerebellum in the control of rapid eye movements, i.e., saccades. To examine the neural substrate of this control, we recorded the discharge patterns of cerebellar output cells in the fastigial nucleus while monkeys tracked a small, jumping spot of light. 2. In the caudal fastigial nucleus, neurons discharged for saccades in one or several directions. All exhibited a burst. Some also exhibited a saccade-related pause in firing either before or after saccades greater than approximately 3-5 degrees. Thirty-seven percent discharged only a burst, 44% also exhibited a pause before bursts in certain directions, and 19% also paused after the saccade-related burst in certain directions. Although many cells discharged steadily during intersaccadic intervals, few exhibited a robust relation between firing rate and eye position. 3. As a measure of directional selectivity, we plotted the burst lead time as a function of saccade direction for saccades of similar (10 degrees) radial amplitudes. Of 20 neurons tested, 17 burst earliest for contralateral saccades and 1 for upward saccades; 2 others showed little dependence on direction. Of 19 additional units tested only in the horizontal direction, 18 burst earlier for contralateral saccades. 4. For contralateral saccades the burst preceded saccades of all sizes by at least 7.7 ms on average. For ipsilateral saccades, the burst preceded small saccades by an average of 10.3 ms. However, as ipsilateral saccade size increased, the burst began later and later relative to saccade onset so that, on average, it always occurred after the onset of 20 degrees saccades but well before the saccade ended. 5. Many fastigial saccade-related units showed increases in the number of spikes with saccade size and in burst duration with saccade duration in one or more directions. For either relation the highest average correlation coefficients ranged from 0.6 to 0.65. In general, the average correlation coefficients and slopes for either relation were slightly larger for contralateral saccades. Pure burst neurons did not display better average correlations than neurons that also paused. For neurons that also paused either before or after saccades, there was a weak tendency for pause duration to increase with the duration of larger saccades. 6. We tested the effect of eye position on unit discharge in 13 cells by requiring the monkey to make 10 degrees ipsilateral and contralateral saccades from a variety of starting positions.(ABSTRACT TRUNCATED AT 400 WORDS)
A selective LTP of NMDA receptor-mediated currents induced by anoxia in CA1 hippocampal neurons
Authors: Crepel V. , Hammond C. , Chinestra P. , Diabira D. , Ben-Ari Y.
Published: December 2017

1. The possibility of long-lasting modifications of glutamatergic responses after anoxic-aglycemic (AA) episodes was investigated in CA1 hippocampal neurons of adult slices. Bicuculline (10 microM) was continuously bath applied to block GABAA receptor-mediated currents. AA episodes were induced by brief (1.30-3 min) perfusions with a glucose free artificial-cerebro-spinal-fluid (ACSF) saturated with 95% N2-5% CO2. 2. In presence of (0.6 mM) Mg2+ and a low concentration of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 1 microM), the Schaffer collateral field EPSPs consisted of an early AMPA receptor-mediated component and a late N-methyl-D-aspartate (NMDA) receptor-mediated component. The former was blocked by (10 microM) CNQX and the latter by (50) microM D-2-amino-5-phosphonovalerate (D-APV). The AA episode induced a selective long-term potentiation (LTP) of the NMDA receptor-mediated component [+70 +/- 13% (mean +/- SE), P < or = 0.008, n = 9] without affecting significantly the AMPA receptor-mediated component (+2 +/- 4, P < or = 0.86 n = 9). This selective LTP is due to an enhanced efficacy of synaptic transmission and will be referred to as anoxic LTP. 3. In slices perfused with an ACSF containing a physiological concentration of (1.3 mM) Mg2+ and no CNQX, the intracellularly recorded excitatory postsynaptic potential (EPSP) was mixed (AMPA/NMDA) at -65 mV and exclusively mediated by AMPA receptors at -100 mV. At -65 mV, the AA episode induced a persistent potentiation of the EPSP (peak amplitude potentiated by 43 +/- 6%, P < or = 0.008, n = 9, 1 h after return to control ACSF). This potentiated component of the EPSP was fully sensitive to (50 microM) D-APV. The CNQX-sensitive AMPA receptor-mediated component was not affected by the AA episode (-5.7 +/- 6%, P < or = 0.123, n = 9). Furthermore, at -100 mV a large APV-sensitive component appeared after the AA episode (+58 +/- 18% of the peak amplitude, P < or = 0.018, n = 9). Therefore, the AA episode induced a selective LTP of the NMDA receptor-mediated component of the EPSP. 4. A robust LTP (+50.0 +/- 7.5%, P < or = 0.008, n = 12) of the NMDA receptor-mediated intracellular EPSP was also observed when AMPA receptors were fully and continuously blocked by (15 microM) CNQX.(ABSTRACT TRUNCATED AT 400 WORDS)
Hyperpolarization-activated currents in neurons of the rat basolateral amygdala
Authors: Womble M. D. , Moises H. C.
Published: December 2017

1. A single microelectrode was used to obtain current-clamp or voltage-clamp recordings from two neuronal cell types (pyramidal and late-firing neurons) in the basolateral nucleus of the amygdala (BLA) in slices of the rat ventral forebrain. Conductances activated by hyperpolarizing voltage steps from a holding potential of -70 mV were identified and their sensitivity to muscarinic modulation was determined using bath superfusion of carbachol. 2. Unclamped pyramidal neurons exhibited anomalous rectification, seen as a slowly developing depolarizing sag in the electronic potential in response to a hyperpolarizing current pulse. 3. Stepping voltage-clamped pyramidal neurons to command potentials of between -70 and -100 mV activated a slowly developing inward current (ISlow) that followed a single exponential time course. Larger hyperpolarizing voltage steps evoked a rapidly developing inward current (IFast) that preceded the development of ISlow. 4. The ISlow component reversed at a level positive to the -70 mV holding potential. Its rate of activation accelerated as the hyperpolarizing voltage step was made more negative. The threshold for activation of the conductance underlying ISlow was approximately -60 mV, with half-activation occurring at -90 mV. 5. Extracellular Cs+ (2 mM) blocked ISlow and eliminated anomalous rectification in unclamped pyramidal neurons. The inhibition of ISlow by Cs+ was also associated with membrane hyperpolarization and reduction of the medium afterhyperpolarization. ISlow was unaffected by extracellular Ba2+ (100 microM). The properties of this current appeared similar to that of the mixed cationic H-current previously identified in other neurons. 6. In comparison with pyramidal cells, unclamped late-firing neurons displayed a lesser but more rapidly developing anomalous rectification in response to large hyperpolarizations from rest. In voltage clamp, hyperpolarizing steps to command potentials more negative than -100 mV elicited IFast. Late-firing neurons expressed little or no ISlow. 7. The properties of IFast were identical in both pyramidal and late-firing neurons. This current reversed at a potential negative to -70 mV. Its rate of current activation increased with the magnitude of the hyperpolarizing voltage step. This rate was approximately sevenfold faster than ISlow activation recorded at the same membrane potential. IFast was blocked by 2 mM extracellular Cs+ and reduced by 100 microM extracellular Ba2+. The threshold for activation of the underlying conductance was approximately -85 mV, with half-activation occurring at -112 mV. The properties of IFast were similar to those of the inward rectifier current previously identified in other central neurons. 8. Carbachol (40 microM) largely blocked IFast without affecting its rate of activation.(ABSTRACT TRUNCATED AT 400 WORDS)
Neuronal specification of direction and distance during reaching movements in the superior precentral premotor area and primary motor cortex of monkeys
Authors: Fu Q. G. , Suarez J. I. , Ebner T. J.
Published: December 2017

1. Single-unit neuronal activity was recorded in the primary motor and superior precentral premotor areas of two rhesus monkeys during an arm reaching task. The task involved moving a cursor displayed on a video terminal using a draftsman's arm-type manipulandum. From a centrally located start box the animal was required to move to 1 of 48 target boxes at eight different directions (0-360 degrees in 45 degrees intervals) and six distances (1.4-5.4 cm in 0.8-cm increments). Both direction and distance for the upcoming movement were unpredictable. 2. The activity of 197 arm movement-related cells was recorded and evaluated for each of the 48 targets. Histological examination showed the cells to be primarily in the primary motor cortex or in the premotor area around the superior precentral sulcus. Each cell's discharge was aligned on movement onset and averaged over five trials for each target. Movement kinematics including hand path velocity were also determined. The task time was divided into three epochs, a premovement period (PT), a movement period (MT), and total time (TT = PT+MT). For each epoch the average firing was correlated with the direction and distance of the movement using various regression procedures. 3. An analysis of variance (ANOVA) showed that the majority of neurons were modulated significantly by movement direction in each of the three time periods, PT (73.7%), MT (68.3%), and TT (78.5%). The relationship of the firing to direction was fit to a cosine tuning function for each significantly modulated cell. In 86.3% of the cells the firing was correlated significantly with a cosine function of movement direction in TT. A cell's preferred direction varied little for different movement distances. The mean difference in preferred direction for the smallest possible change in distance (0.8 cm) was 12.8 +/- 11.4 degrees (SD) and 17.1 +/- 14.7 degrees for the largest change in distance (4.0 cm). 4. Correlation analysis revealed that the activity of the majority of cells was modulated significantly by distance along at least one direction in each of the three time periods, PT (46.8%), MT (68.8%), and TT (67.7%). Subsequently, a univariate linear regression model was used to quantify a cell's discharge as a function of distance. For the regressions of firing with distance with a statistically significant correlation (r > 0.8), the mean slope was 3.59 +/- 0.17 spikes.s-1.cm-1 for the total time. The existence of a significant distance modulation was not invariably correlated with a cell's preferred movement direction.(ABSTRACT TRUNCATED AT 400 WORDS)
Coding of odor molecules by mitral/tufted cells in rabbit olfactory bulb. II. Aromatic compounds
Authors: Katoh K. , Koshimoto H. , Tani A. , Mori K.
Published: December 2017

1. Recordings of extracellular spike responses were made from single mitral/tufted cells in the ventromedial region of the main olfactory bulb of urethan-chloralose-anesthetized rabbits. Using periodic artificial inhalations, the olfactory epithelium was stimulated with series of aromatic and aliphatic compounds systematically varying in molecular conformation. 2. Analysis of response specificity of single mitral/tufted cells for alkylbenzenes indicated that the length of the hydrocarbon side chain attached to the benzene ring plays a role in determining the specificity of excitatory spike responses. 3. For a panel of isomeric (ortho-, meta-, and para-positions) disubstituted benzenes, single mitral/tufted cells tended to be activated selectively by one or two specific structural isomer(s). For a panel that contained both alkylbenzenes and disubstituted benzenes, single mitral/tufted cells were activated by subsets of odor molecules having similar conformations. These observations suggest that the overall conformation of the aromatic compounds plays an important role in determining tuning specificity of individual mitral/tufted cells. 4. For a panel of monosubstituted benzenes with various functional groups, single mitral/tufted cells in the ventromedial region tended to be activated not only by molecules having a hydrocarbon side chain (alkylbenzenes), but also by those having a methoxy group (--O--CH3), a bromine (--Br), or a chlorine (--Cl). However, most of the neurons were not activated by those having an amino group (--NH2), a hydroxy group (--OH), nor a carboxyl group (--COOH). 5. Examination with an expanded panel of stimulus odor molecules that included both aromatic and aliphatic compounds indicated that single mitral/tufted cells show excitatory spike responses to a range of odor molecules (molecular receptive range) having similar conformations. Different mitral/tufted cells in the ventromedial region typically showed different molecular receptive ranges. 6. In mitral/tufted cells with relatively high spontaneous discharges, single neurons in the ventromedial region showed inhibitory responses to subsets of odor molecules in addition to the excitatory response to other subsets of odor molecules. The odor molecules that caused inhibitory responses in single mitral/tufted cells showed molecular conformations resembling each other. 7. The present results together with previous studies indicate that determination of the molecular receptive range properties (both excitatory extent and inhibitory extent) of single mitral/tufted cells is a useful method for characterizing individual bulbar neurons. These results further support the hypothesis that conformational parameters of ligand odor molecules play a key role in sensory processing in the main olfactory bulb.
Block of GABA-transaminase modifies GABAergic transmission at the crayfish synapses
Authors: Golan H. , Grossman Y.
Published: December 2017

1. The cytosolic concentration of a neurotransmitter is believed to be an important factor determining its release. The effects of ethanolamine-O-sulfate (EOS), a gamma-aminobutyric acid (GABA)-transaminase blocker, on GABAergic postsynaptic and presynaptic inhibitory neurotransmission were examined in the crayfish opener neuromuscular synapses. 2. Intracellular recordings of evoked excitatory (EPSPs) and inhibitory postsynaptic potentials (IPSPs) as well as loose macropatch clamp measurements of excitatory (EPSCs) and inhibitory postsynaptic currents (IPSCs) were used to evaluate the effects of the drug, which was applied exclusively to the nerve bundle. 3. Under normal conditions, a stimulus train to the inhibitor before the excitor stimulation elicited two phases of inhibition: 1) a large reduction in EPSP amplitude associated with a decrease in its time constant of decay (tau D) at time intervals of 0–15 ms and 2) a moderate decrease in EPSP amplitude with a small change in EPSP tau D at intervals of 15–90 ms. EOS treatment selectively increased the inhibition of phase 2. 4. The muscle membrane electrical parameters and the existing postsynaptic tonic release of GABA were not affected by the drug. 5. EOS did not alter the IPSP's parameters such as amplitude, reversal potential, and conductance. 6. Quantal analysis of single IPSCs revealed no significant changes in the statistical parameters such as quantum size (q), quantal content (m), number of active zones (n), or probability of release (p). 7. Quantal analysis of EPSCs, released after interaction with the inhibitor, did exhibit a large reduction in m without any effect on q. 8. These results demonstrate that EOS has a specific and differential effect on neural transmission in two synapses of the same axon: it increases presynaptic inhibition without significant effect on the postsynaptic inhibitory mechanism.
Enhancement of neural synchronization in the anteroventral cochlear nucleus. I. Responses to tones at the characteristic frequency
Authors: Joris P. X. , Carney L. H. , Smith P. H. , Yin T. C.
Published: December 2017

1. Encoding temporal features of the acoustic waveform is an important attribute of the auditory system. Auditory nerve (AN) fibers synchronize or phase-lock to low-frequency tones and transmit this temporal information to cells in the anteroventral cochlear nucleus (AVCN). Phase-locking in the AVCN is usually reported to be similar to or weaker than in the AN. We studied phase-locking in axons of the trapezoid body (TB), which is the output tract of the AVCN, and found, to our surprise, that most TB axons exhibited enhanced synchronization compared with AN fibers. 2. Responses from axons in the TB of the cat were obtained with horseradish peroxidase (HRP)- or Neurobiotin-filled micropipettes or metal microelectrodes. A series of short tone bursts at increasing sound pressure level (SPL) was presented at the characteristic frequency (CF) of the fiber and phase-locking was quantified with the vector strength R at each SPL. For each fiber the maximum R value (Rmax) was then determined. 3. Low-frequency fibers in the TB showed very precise phase-locking: Rmax values could approach 0.99. For the majority of fibers (33/44, 75%) with CF < 700 Hz, Rmax was > or = 0.9 and therefore higher than is ever observed in the AN. We define such fibers as "high-sync." Most of these fibers also entrained to the stimulus, i.e., they fired a precisely timed action potential to almost every stimulus cycle. Some fibers showed perfect entrainment, with maximum discharge rates equaling the stimulus frequency. 4. To exclude the possibility that stimulus paradigms or acoustic and recording equipment were the source of this enhancement, we obtained additional data on low-frequency AN fibers using the same experimental protocol as in our TB experiments. These AN data agree well with published reports. 5. The morphological class of some of the cells studied was identified on the basis of anatomic features revealed by intra-axonal injection of HRP or Neurobiotin. Labeled low-CF axons (N = 7), which were all high-sync, originated from AVCN bushy cells: five were globular and two were spherical bushy cell axons. 6. Spontaneous rate of high-sync fibers covered a range from 0 to 176 spikes/s but were biased toward low values (mean 16 spikes/s). Responses to broadband clicks and sinusoidally amplitude-modulated signals provided additional evidence of improved timing properties.(ABSTRACT TRUNCATED AT 400 WORDS)
Spontaneous and transmitter-induced rhythmic activity in neonatal rat sympathetic preganglionic neurons in vitro
Authors: Shen E. , Wu S. Y. , Dun N. J.
Published: December 2017

1. Intracellular recordings were made from sympathetic preganglionic neurons (SPNs) in transverse thoracolumbar spinal cord slices of 12- to 16-day-old rats. 2. A population of SPNs exhibited spontaneous, rhythmic activities that can be grouped into regular firing, bursting, or tonic oscillatory mode; the spikes were interspersed with subthreshold afterdepolarizing potentials (ADPs). 3. Spontaneous activities were not abolished by the excitatory amino acid antagonists 6-cyano-7-nitroquinoxoline-2,3-dione (CNQX, 10-20 microM) and D-2-amino-5-phosphonovaleric acid (APV, 10-20 microM) nor by the inhibitory amino acid antagonists bicuculline (10-30 microM) and strychnine (1 microM). 4. Stimulation of lateral funiculus elicited a CNQX-sensitive excitatory postsynaptic potential (EPSP) in the majority of spontaneously active SPNs tested. Moreover, rhythmic activities could be triggered by stimulation of lateral funiculus in 8 of the 80 otherwise quiescent SPNs tested. 5. Spontaneous spikes and ADPs were abolished by either Na(+)-free or tetrodotoxin (TTX, 0.5 microM)-containing Krebs solution. 6. The spontaneous spike afterhyperpolarization (AH) consisted of two components: a fast AHf and a slower AHS with a mean half decay time of 74.5 +/- 10.2 and 153.8 +/- 15.4 (SD) ms, respectively. 7. Superfusing the slices with a Ca(2+)-free Krebs solution or Krebs solution containing tetraethylammonium (TEA, 10-30 mM) preferentially blocked the AHS, thereby increasing the spontaneous discharge frequency. 8. Caffeine (3 mM) initially prolonged the AHS, thereby slowing the discharge frequency; the spontaneous discharges were eventually obliterated in the continuous presence of caffeine.(ABSTRACT TRUNCATED AT 250 WORDS)
In vivo measurement of human wrist extensor muscle sarcomere length changes
Authors: Lieber R. L. , Loren G. J. , Friden J.
Published: December 2017

1. Human extensor carpi radialis brevis (ECRB) sarcomere length was measured intraoperatively in five subjects using laser diffraction. 2. In a separate cadaveric study, ECRB tendons were loaded to the muscle's predicted maximum tetanic tension, and tendon strain was measured to estimate active sarcomere shortening at the expense of tendon lengthening. 3. As the wrist joint was passively flexed from full extension to full flexion, ECRB sarcomere length increased from 2.6 to 3.4 microns at a rate of 7.6 nm/deg joint angle rotation. Correcting for tendon elongation during muscle activation yielded an active sarcomere length range of 2.44 to 3.33 microns. Maximal predicted sarcomere shortening accompanying muscle activation was dependent on initial sarcomere length and was always < 0.15 microns, suggesting a minimal effect of tendon compliance. 4. Thin filament lengths measured from electron micrographs of muscle biopsies obtained from the same region of the ECRB muscles were 1.30 +/- .027 (SE) microns whereas thick filaments were 1.66 +/- .027 microns long, suggesting an optimal sarcomere length of 2.80 microns and a maximum sarcomere length for active force generation of 4.26 microns. 5. These experiments demonstrate that human skeletal muscles can function on the descending limb of their sarcomere length-tension relationship under physiological conditions. Thus, muscle force changes during joint rotation are an important component of the motor control system.
The role of GABA-mediated inhibition in the rat ventral posterior medial thalamus. I. Assessment of receptive field changes following thalamic reticular nucleus lesions
Authors: Lee S. M. , Friedberg M. H. , Ebner F. F.
Published: December 2017

1. Changes in the receptive field (RF) properties of thalamic VPM neurons were assessed quantitatively using single-unit recording techniques following a selective excitotoxic lesion of the ipsilateral thalamic reticular nucleus (TRN). The response profiles to controlled deflections of the contralateral vibrissae were obtained from 97 VPM neurons in normal and 102 VPM neurons in TRN-lesioned animals. 2. Histological signs of TRN lesions were detectable in Nissl-stained sections as early as 20 h after the release of kainic acid into TRN. 3. The average RF size of VPM neurons in normal animals was 2.39 +/- 0.18 whiskers (mean +/- SE). Immediately after the lesion of TRN, the average RF size in VPM was enlarged significantly and remained expanded for as long as 1 mo after the destruction of TRN (7.64 +/- 0.47 whiskers, P < 0.001). 4. Subsequent lesions of trigeminal subnucleus interpolaris (SpVi) in TRN-lesioned animals produced a marked reduction in the RF size of VPM neurons. The average VPM RF size for TRN/SpVi lesioned animals was 2.14 +/- 0.64 whiskers. 5. The loss of inhibition from TRN increased the average response probability and magnitude to the center RF whisker by 38 and 34%, respectively. The response probability and magnitude of the surround RF whiskers increased by 64 and 69%, respectively. The average response latencies to the center and surround RF whiskers were significantly longer after the lesion of TRN; subsequent lesions of SpVi in TRN-lesioned cases reduced the average response latencies of VPM neurons to those seen in normal animals. 6. The RF of VPM neurons in both normal and TRN lesioned cases displayed a strong anterior-posterior (“row”) preference. Immediately adjacent anterior-posterior whiskers were twice as likely to elicit a response in VPM than immediately adjacent dorsal-ventral whiskers. 7. VPM units were tested for a preferential response to whisker movement in one of four directions (up, down, backward, and forward). The majority of the neurons in both normal and TRN-lesioned cases showed direction-selective responses, mostly in the up direction. Thus gamma-aminobutyric acid (GABA)-mediated inhibition in rat VPM does not appear to be responsible for direction selectivity of VPM neurons. 8. Virtually all neurons in rat VPM after TRN lesions displayed responses that were sustained for the duration of the stimulus (25.5% in normal vs. 88.2% in TRN-lesioned cases). VPM units showing sustained (tonic) responses maintained a high rate of spontaneous activity and, on average, responded to 2-3 times more whiskers than phasically responding units.(ABSTRACT TRUNCATED AT 400 WORDS)
Encoding of amplitude modulation in the cochlear nucleus of the cat
Authors: Rhode W. S. , Greenberg S.
Published: December 2017

1. Amplitude modulation (AM) is a pervasive property of acoustic communication systems. In the present study we investigate neural temporal mechanisms in the auditory nerve and cochlear nuclei of the pentobarbital sodium-anesthesized cat associated with the neural coding of 100% AM tones, both in quiet and in the presence of wideband, quasi-flat-spectrum noise. The AM carrier frequency was set to the neuron's characteristic frequency (CF) and the sound pressure level (SPL) of acoustic stimuli was varied over a wide dynamic range of intensities (< or = 40 dB). The temporal AM-encoding capability of auditory neurons was measured by computing the synchronization coefficient (SC) of the neural response to the signal's modulation and carrier frequency. The temporal modulation transfer function (tMTF) of a neuron was then computed by measuring the SC of the response to signals of variable fmod (50-2550 Hz). 2. Neurons in the cochlear nuclei synchronize on average more highly to the modulation frequency than fibers of comparable CF, threshold, and spontaneous rate in the auditory nerve. The disparity in performance is greatest at high SPLs and low signal-to-noise ratios. However, there is a significant degree of diversity in AM-encoding capability among neurons in both the cochlear nuclei and auditory nerve. Among auditory nerve fibers (ANFs), low- and medium-spontaneous-rate (SR) units (SR < 18 spike/s) phase-lock with greater precision than comparable high-SR units at any given frequency, particularly at moderate to high SPLs, consistent with previous studies. 3. The phase-locking capabilities of neurons in the cochlear nucleus are considerably more variable than in the auditory nerve. Moreover, the variability itself depends on two distinct measures of phase-locking performance. Most ANFs are capable of phase-locking to frequencies as high as 3–4 kHz. In the cochlear nucleus many unit types do not phase-lock to modulation frequencies > 1 kHz. As a result, phase-locking performance is measured on the basis of two parameters, maximum synchronization, irrespective of stimulus frequency, and the upper frequency limit for significant phase-locking. 4. Cochlear nucleus neurons may be divided into three distinct groups on the basis of maximum synchronization capability. In group 1 are the primary-like (PL) units of the anteroventral division, whose phase-locking capabilities are comparable with those of high-SR ANFs.(ABSTRACT TRUNCATED AT 400 WORDS)
Characterization of the membrane ion currents of a model molluscan muscle, the accessory radula closer muscle of Aplysia california. I. Hyperpolarization-activated currents
Authors: Brezina V. , Evans C. G. , Weiss K. R.
Published: December 2017

1. The simple neuromuscular circuit consisting of the accessory radula closer (ARC) muscle of the mollus Aplysia californica together with its innervating motor and modulatory neurons has been extensively studied as a model preparation in which it might be possible to reach an integrated understanding of the neural and cellular mechanisms of behavioral plasticity, in this case of a component of Aplysia feeding behavior. Previous work has suggested that much of the plasticity of this behavior is implemented by appropriate release of modulatory neurotransmitters and peptide cotransmitters that modulate several parameters of the contractions of the ARC muscle. However, little is as yet known about the underlying cellular mechanisms. 2. We have begun to study single, functionally intact fibers dissociated from the ARC muscle to assess to what extent the modulation of its contraction might be mediated by one candidate mechanism, modulation of its membrane ion currents. First, however, it was necessary to gain a thorough understanding of the unmodulated currents and their likely roles in normal contraction. Using voltage-clamp techniques, we have therefore identified and characterized the major currents present in the ARC muscle fibers. We describe these currents in this and the following two papers. These results constitute the first detailed description of ion currents in a molluscan muscle and lay the foundation for further study, to be presented in subsequent papers, of the roles of two currents that we have indeed found to be modulated in ways likely to contribute to the modulation of contraction. 3. In this paper we first describe the general electrophysiological characteristics of the dissociated fibers and present evidence that the fibers can be adequately space clamped. 4. The physiological operating voltage range of the nonspiking ARC muscle most likely extends from about -80 to about -25 mV. The steady-state current-voltage (I–V) relation of total membrane current rectifies inwardly in the negative and outwardly in the positive portion of this voltage range, with a plateau region of high or even negative slope resistance separating the two regions of rectification. 5. The current responsible for the inward rectification at negative voltages is a classical inwardly rectifying K current. It is activated by hyperpolarization with quasi-instantaneous kinetics; its whole I–V relation shifts along the voltage axis in a Nernstian manner with altered extracellular K+ concentration; it is blocked by low extracellular Ba2+ and Cs+, and the block is promoted by hyperpolarization.(ABSTRACT TRUNCATED AT 400 WORDS)
Neural ensemble coding in inferior temporal cortex
Authors: Gochin P. M. , Colombo M. , Dorfman G. A. , Gerstein G. L. , Gross C. G.
Published: December 2017

1. Isolated, single-neuron extracellular potentials were recorded sequentially in area TE of the inferior temporal cortex (IT) of two macaque monkeys (n = 58 and n = 41 neurons). Data were obtained while the animals were performing a paired-associate task. The task utilized five stimuli and eight stimulus pairings (4 correct and 4 incorrect). Data were evaluated as average spike rate during experimental epochs of 100 or 400 ms. Single-unit and population characteristics were measured using a form of linear discriminant analysis and information theoretic measures. To evaluate the significance of covariance on population code measures, additional data consisting of simultaneous recordings from < or = 8 isolated neurons (n = 37) were obtained from a third macaque monkey that was passively viewing visual stimuli. 2. On average, 43% of IT neurons were activated by any of the stimuli used (60% if those inhibited also are included). Yet the neurons were rather unique in the relative magnitude of their responses to each stimulus in the test set. These results suggest that information may be represented in IT by the pattern of activity across neurons and that the representation is not sparsely coded. It is further suggested that the representation scheme may have similarities to DNA or computer codes wherein a coding element is not a local parametric descriptor. This is a departure from the V1 representation, which appears to be both local and parametric. It is also different from theories of IT representation that suggest a constructive basis set or “alphabet”. From this view, determination of stimulus discrimination capacity in IT should be evaluated by measures of population activity patterns. 3. Evaluation of small groups of simultaneously recorded neurons obtained during a fixation task suggests that little information about visual stimuli is conveyed by covariance of activity in IT when a 100-ms time scale is used as in this study. This finding is consistent with a prior report, by Gochin et al., which used a 1-ms time scale and failed to find neural activity coherence or oscillations dependent on stimuli. 4. Population-stimulus-discrimination capacity measures were influenced by the number of neurons and to some extent the number and type of stimuli. 5. Information conveyed by individual neurons (mutual information) averaged 0.26 bits. The distribution of information values was unimodal and is therefore more consistent with a distributed than a local coding scheme.(ABSTRACT TRUNCATED AT 400 WORDS)
Kinetics of AP5 dissociation from NMDA receptors: evidence for two identical cooperative binding sites
Authors: Clements J. D. , Westbrook G. L.
Published: December 2017

s1. N-methyl-D-aspartate (NMDA) channels have two agonist binding sites that have similar binding rates for glutamate. However, it is not known whether the dissociation rates at these two sites, and hence their affinities, are similar. The competitive antagonist, D-2-amino-5-phosphonopentanoic acid (AP5), was used to study dissociation kinetics from NMDA receptors in outside-out patches from cultured hippocampal neurons. 2. Rapid steps from AP5 into NMDA produced currents with a sigmoidal activation time course that was limited by AP5 dissociation. Ensemble average currents were well fitted using kinetic models with two identical, cooperative antagonist binding sites per channel. The results suggest that the two NMDA binding sites have similar affinities, but that occupation of one site reduces the affinity of the other. 3. The agonist and antagonist binding kinetics are consistent with an approximately homogeneous population of NMDA channels in cultured hippocampal neurons.
Caudal ventrolateral medullary neurons are elements of the network responsible for the 10-Hz rhythm in sympathetic nerve discharge
Authors: Barman S. M. , Orer H. S. , Gebber G. L.
Published: December 2017

1. This is the first study to show that caudal ventrolateral medullary (CVLM) neurons play an important role in governing the 10-Hz rhythm in sympathetic nerve discharge (SND). Spike-triggered averaging showed that the naturally occurring discharges of 66 of 246 CVLM neurons located 0–2.5 mm rostral to the obex, 4–4.25 mm lateral to the midline, and within 2 mm of the ventral surface were correlated to the 10-Hz rhythm in inferior cardiac SND of 17 urethan-anesthetized cats. 2. Frequency domain analysis was used to characterize further the relationships between SND and the discharges of 45 CVLM neurons with activity correlated to the 10-Hz rhythm in inferior cardiac nerve activity. The autospectra of the discharges of 22 of these neurons contained a sharp peak near 10 Hz (corresponding to the peak in the autospectra of SND), although the mean firing rate of these neurons was only 5.9 +/- 0.5 (SE) spikes/s. The peak coherence value relating the 10-Hz discharges of these CVLM neurons and the inferior cardiac nerve was 0.42 +/- 0.03. The autospectra for the other 23 CVLM neurons did not contain a peak near 10 Hz. Their mean firing rate was 2.3 +/- 0.5 spikes/s, and the peak coherence value relating their discharges to the 10-Hz rhythm in SND was 0.08 +/- 0.01. The coherence value was significantly different than zero in all but three cases. 3. Importantly, spike-triggered averaging and coherence analysis demonstrated that CVLM neurons with activity correlated to the 10-Hz rhythm did not have activity correlated 1:1 to the cardiac-related rhythm in SND of baroreceptor-innervated cats. Also, their discharges were not correlated to the irregular 2- to 6-Hz oscillations in SND of baroreceptor-denervated cats. These data support the hypothesis that different pools of brain stem neurons generate the 10-Hz rhythm and the 2- to 6-Hz oscillations (or cardiac-related rhythm) in SND. 4. Despite the fact that CVLM neurons with activity correlated to the 10-Hz rhythm did not have activity correlated 1:1 to the cardiac-related rhythm in SND, these neurons were influenced by baroreceptor afferent nerve activity. First, their firing rates could be decreased (n = 12) or increased (n = 2) during the pressor response induced by inflating a balloon in the aorta (aortic obstruction). Second, on occasion, the discharges of CVLM neurons and the 10-Hz rhythm in SND were entrained to a harmonic of the heart rate.(ABSTRACT TRUNCATED AT 400 WORDS)