bluuebunny/crossref_metadata_2025 huggingface dataset:
Left ventricular response in healthy young men during heavy-intensity weight-lifting exercise
Authors: Lentini A. C. , McKelvie R. S. , McCartney N. , Tomlinson C. W. , MacDougall J. D.
Published: December 2017

We examined cardiac volumes (using echocardiography), intra-arterial blood pressure (BP), and intrathoracic pressure (ITP) in healthy males performing leg press exercise to failure at 95% of their maximum dynamic strength. Compared with preexercise, during the lifting phase of exercise, end-diastolic volume (EDV; 147 +/- 8 to 103 +/- 7 ml) and end-systolic volume (ESV; 54 +/- 5 to 27 +/- 4 ml) decreased (P < 0.05); heart rate (82 +/- 6 to 143 +/- 5 beats/min), systolic BP (160 +/- 6 to 270 +/- 21 Torr), diastolic BP (91 +/- 2 to 183 +/- 18 Torr), ITP (0.8 +/- 0.8 to 57.8 +/- 24 Torr), and peak systolic BP/ESV (SBP/ESV; 3.0 +/- 0.3 to 11.0 +/- 1.5 Torr/ml) increased (P < 0.05); and stroke volume decreased (94 +/- 3 to 77 +/- 4 ml; P > 0.05). Full knee extension was associated with most values returning to preexercise levels except for ESV (38 +/- 7 ml), heart rate (130 +/- 9 beats/min), and ITP (-12.5 +/- 2.1 Torr). During the lowering phase, significant decreases in EDV to 105 +/- 14 ml and ESV to 27 +/- 7 ml were observed with increases in systolic BP to 207 +/- 23 Torr, diastolic BP to 116 +/- 8 Torr, and SBP/ESV to 10.0 +/- 2.5 Torr/ml. Stroke volume decreased to 78 +/- 9 ml (P > 0.05). Thus rapid changes in cardiac volumes, contractility, and pressure occur during weight lifting that are related to different phases of the lift.
Distribution of surfactant and ventilation in surfactant-treated preterm lambs
Authors: Ueda T. , Ikegami M. , Rider E. D. , Jobe A. H.
Published: December 2017

Surfactant-deficient ventilated preterm lambs were treated with 100 mg/kg of surfactant radiolabeled with microspheres at 30 min and 2.5 h of age to evaluate the effect of treatment technique on surfactant distribution. The treatments were four positions with four boluses (bolus 4), two lateral positions with two boluses (bolus 2), or a 30-min infusion (infusion). The bolus groups had uniform surfactant distributions to the > 100 pieces analyzed for each lung. Infusion resulted in a very nonuniform surfactant distribution (P < 0.01). Surfactant was recovered equivalently in all lobes of the bolus groups, whereas infusion lungs contained surfactant preferentially in upper lobes (P < 0.01). The second dose of surfactant localized into the same lung doses as the first dose (P < 0.001). Blood flow increased proportionately to surfactant content in the bolus groups. With infusion, blood flow decreased and ventilation measured with 99Tc-labeled aerosol increased to pieces of lung receiving large amounts of the infusion surfactant, suggesting that localized overinflation was likely. Physiological measurements indicated better responses to bolus treatments, although the infusion lambs did improve. These results indicate that different treatment techniques can have large effects on surfactant distributions.
Response to rest and exercise in the cold: effects of age and aerobic fitness
Authors: Falk B. , Bar-Or O. , Smolander J. , Frost G.
Published: December 2017

The aim of this study was to determine whether age-related differences in the response to cold exposure are due to aging per se or are caused by a reduced maximal oxygen uptake (VO2max) often observed with aging. Three groups of men, 8 young adults (YA), 8 well-trained seniors (TS), and 11 untrained seniors (US), were tested on a cycle ergometer in thermoneutral (22 degrees C) and cold (5 degrees C) conditions during rest and then during exercise (approximately 50 W). In the thermoneutral conditions, 10 min of rest were followed by 10 min of exercise. After 60 min of rest, subjects entered the cold where 30 min of rest were followed by 30 min exercise. The subjects of the three groups had similar body surface area and subcutaneous fat thickness. It was found that rectal temperature (Tre) decreased during rest in the cold and continued to decrease at a higher rate during exercise in TS and US but not in YA. The mean skin temperature was similar in all the groups, except for the thigh temperature, which was lower in YA than in TS and US. Oxygen uptake (VO2) increased during cold, significantly more so at rest than during exercise. YA displayed the highest VO2 during the first 10 min of rest in the cold, whereas TS displayed the highest VO2 during exercise in the cold. Neither aging nor VO2max appeared to affect thermal comfort or cold sensation.(ABSTRACT TRUNCATED AT 250 WORDS)
Effect of hydration on lung interstitial permeability response to albumin and hyaluronidase
Authors: Tajaddini A. , Brown L. V. , Lai-Fook S. J.
Published: December 2017

Previous studies showed that the flows of albumin and hyaluronidase solutions increased relative to that of saline in isolated segments of rabbit lung interstitium (Lai-Fook et al. J. Appl. Physiol. 67:606–613, 1989). We questioned whether these effects were hydration dependent. In interstitial segments the flows of lactated Ringer, albumin (5 and 10 g/dl), and hyaluronidase (0.02%) solutions were measured at mean interstitial pressures (Pm) between -5 and 15 cmH2O with a constant driving pressure of 5 cmH2O. The albumin-to-Ringer flow ratio increased monotonically from near the viscosity-dependent value (0.75–0.77) at -5 cmH2O Pm to values of 1.6–2.1 at 15 cmH2O Pm. A similar behavior was observed for the flow of the hyaluronidase solution relative to that of Ringer solution. The increased permeability response to albumin was independent of the albumin concentration used. By contrast, the response to hyaluronidase was lower when the interstitium was perfused with the higher concentration albumin solution (10 g/dl) before the flow of hyaluronidase, indicating an inhibitory effect of albumin on the hyaluronidase response. Estimates of interstitial hydration from Pm indicated an increased interstitial permeability (conductivity) to the flows of albumin and hyaluronidase solutions only after interstitial volume had doubled, whereas interstitial permeability was viscosity dependent at normal interstitial hydration.
Seizure-Like Events in Disinhibited Ventral Slices of Adult Rat Hippocampus
Authors: Borck Cornelius , Jefferys John G. R.
Published: December 2017

Epileptic discharges lasting 2–90 s, were studied in vitro in slices from the ventral hippocampus of adult rats, in which inhibition was blocked acutely with bicuculline methiodide (BMI, 5–30 μM) and potassium ([K+]o) raised to 5 mM. These seizure-like events (SLEs) comprised three distinct phases, called here primary, secondary, and tertiary bursts. Primary bursts lasted 90–150 ms. Secondary bursts lasted a further 70–250 ms, comprising a short series of afterdischarges riding on the same depolarization as the primary burst. Finally a train of tertiary bursts started with a peak frequency of 5–10 Hz and could last >1 min. Slices from the ventral hippocampus showed significantly higher susceptibility to SLEs than did dorsal slices. SLEs proved sensitive to α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonists. They were insensitive to N-methyl-d-aspartate (NMDA) receptor antagonists; 50 μl d-2-amino-5-phosphonopentanoic acid (d-AP5) did block the transient secondary bursts selectively. SLEs were restricted to the hippocampus proper even if the entorhinal cortex was present. Entorhinal bursts could last <2 s and were only coupled with hippocampal bursts in a minority of slices. Reentry of epileptic bursts occasionally occurred during interictal discharges, but not during the later stages of SLEs. Full-length SLEs always started in CA3 region and could be recorded in minislices containing CA3 plus dentate hilus. Ion-sensitive microelectrodes revealed that interictal discharges were followed by short (2–3 s) [K+]o waves, peaking at ∼7.5 mM. SLEs were always accompanied by increases in [K+]oreaching ∼8.5 mM at the start of tertiary bursts; [K+]o then increased more slowly to a ceiling of 11–12 mM. After the end of each SLE, [K+]o fell back to baseline within 10–15 s. SLEs were accompanied by significant increase in synaptic activity, compared with baseline and/or interictal activity, estimated by the variance of the intracellular signal in the absence of epileptic bursts and action potentials (0.38 mV2, compared with 0.13 mV2, and 0.1 mV2, respectively). No significant increases were observed in the interval preceding spontaneous interictal activity. These studies show that focal assemblies of hippocampal neurons, without long reentrant loops, are sufficient for the generation of SLEs. We propose that a key factor in the transition from interictal activity to SLEs is an increase in axonal and terminal excitability, resulting, at least in part, from elevations in [K+]o.
ω-AgaIVA–Sensitive (P/Q-type) and –Resistant (R-type) High-Voltage–Activated Ba2+Currents in Embryonic Cockroach Brain Neurons
Authors: Benquet Pascal , Guen Janine Le , Dayanithi Govindan , Pichon Yves , Tiaho François
Published: December 2017

By means of the whole cell patch-clamp technique, the biophysical and pharmacological properties of voltage-dependent Ba2+currents ( IBa) were characterized in embryonic cockroach brain neurons in primary culture. IBawas characterized by a threshold of approximately −30 mV, a maximum at ∼0 mV, and a reversal potential near +40 mV. Varying the holding potential from −100 to −40 mV did not modify these properties. The steady-state, voltage-dependent activation and inactivation properties of the current were determined by fitting the corresponding curves with the Boltzmann equation and yielded V0.5of −10 ± 2 (SE) mV and −30 ± 1 mV, respectively. IBawas insensitive to the dihydropyridine (DHP) agonist BayK8644 (1 μM) and antagonist isradipine (10 μM) but was efficiently and reversibly blocked by the phenylalkylamine verapamil in a dose-dependent manner ( IC50= 170 μM). The toxin ω-CgTxGVIA (1 μM) had no significant effect on IBa. Micromolar doses of ω-CmTxMVIIC were needed to reduce the current amplitude significantly, and the effect was slow. At 1 μM, 38% of the peak current was blocked after 1 h. In contrast, IBawas potently and irreversibly blocked by nanomolar concentrations of ω-AgaTxIVA in ∼81% of the neurons. Approximately 20% of the current was unaffected after treatment of the neurons with high concentrations of the toxin (0.4–1 μM). The steady-state dose-response relationship was fitted with a Hill equation and yielded an IC50of 17 nM and a Hill coefficient ( n) of 0.6. A better fit was obtained with a combination of two Hill equations corresponding to specific ( IC50= 9 nM; n = 1) and nonspecific ( IC50= 900 nM; n = 1) ω-AgaTxIVA–sensitive components. In the remaining 19% of the neurons, concentrations ≥100 nM ω-AgaTxIVA had no visible effect on IBa. On the basis of these results, it is concluded that embryonic cockroach brain neurons in primary culture express at least two types of voltage-dependent, high-voltage–activated (HVA) calcium channels: a specific ω-AgaTxIVA–sensitive component and DHP-, ω-CgTxGVIA–, and ω-AgaTxIVA–resistant component related respectively to the P/Q- and R-type voltage-dependent calcium channels.
Effects of Altering Spectral Cues in Infancy on Horizontal and Vertical Sound Localization by Adult Ferrets
Authors: Parsons Carl H. , Lanyon Richard G. , Schnupp Jan W. H. , King Andrew J.
Published: December 2017

We investigated the behavioral consequences of removing the pinna and concha of the external ear bilaterally in infancy on the sound localization ability of adult ferrets. Altering spectral cues in this manner has previously been shown to disrupt the development of the neural representation of auditory space in the superior colliculus. Using broadband noise stimuli, we tested pinnae-removed ferrets and normal ferrets in three sound localization tasks. In each case, we found that both groups of animals performed significantly better when longer duration noise bursts were used. In a relative localization task, we measured the acuity with which the ferrets could discriminate between two speakers in the horizontal plane. The speakers were placed symmetrically either around the anterior midline or around a position 45° lateral to the midline. In this task, the pinnae-removed ferrets achieved very similar scores to the normal ferrets. By contrast, in another relative localization task that measured localization ability in the midsagittal plane, pinnae-removed ferrets performed less well than normals. In an absolute localization task, 12 speakers were spaced at 30° intervals in the horizontal plane at the level of the ferrets' ears. Overall, the pinnae-removed ferrets also performed poorly in this task compared with normal ferrets: they made significantly fewer correct responses, larger localization errors and more front-back errors. Both normal and pinnae-removed animals showed an improvement in performance with practice, although the pattern of improvement differed for each group. The largest improvements in localization accuracy were achieved by the pinnae-removed ferrets, particularly at the frontal positions, and their performance eventually approached that of the normal animals. Nevertheless, some intergroup differences were still present. In particular, the pinnae-removed ferrets continued to make significantly more front-back errors than the normals. These deficits can be attributed to differences in the spectral localization cues available to the animals. Acoustical measurements showed that, compared with normal animals, the head-related transfer functions in the horizontal plane were largely ambiguous around the interaural axis and also contained fewer location-dependent features in the midsagittal plane.
Organization of Inhibitory Frequency Receptive Fields in Cat Primary Auditory Cortex
Authors: Sutter M. L. , Schreiner C. E. , McLean M. , O'connor K. N. , Loftus W. C.
Published: December 2017

Based on properties of excitatory frequency (spectral) receptive fields (esRFs), previous studies have indicated that cat primary auditory cortex (A1) is composed of functionally distinct dorsal and ventral subdivisions. Dorsal A1 (A1d) has been suggested to be involved in analyzing complex spectral patterns, whereas ventral A1 (A1v) appears better suited for analyzing narrowband sounds. However, these studies were based on single-tone stimuli and did not consider how neuronal responses to tones are modulated when the tones are part of a more complex acoustic environment. In the visual and peripheral auditory systems, stimulus components outside of the esRF can exert strong modulatory effects on responses. We investigated the organization of inhibitory frequency regions outside of the pure-tone esRF in single neurons in cat A1. We found a high incidence of inhibitory response areas (in 95% of sampled neurons) and a wide variety in the structure of inhibitory bands ranging from a single band to more than four distinct inhibitory regions. Unlike the auditory nerve where most fibers possess two surrounding “lateral” suppression bands, only 38% of A1 cells had this simple structure. The word lateral is defined in this sense to be inhibition or suppression that extends beyond the low- and high-frequency borders of the esRF. Regional differences in the distribution of inhibitory RF structure across A1 were evident. In A1d, only 16% of the cells had simple two-banded lateral RF organization, whereas 50% of A1v cells had this organization. This nonhomogeneous topographic distribution of inhibitory properties is consistent with the hypothesis that A1 is composed of at least two functionally distinct subdivisions that may be part of different auditory cortical processing streams.
Behavior of Jaw Muscle Spindle Afferents During Cortically Induced Rhythmic Jaw Movements in the Anesthetized Rabbit
Authors: Hidaka O. , Morimoto T. , Kato T. , Masuda Y. , Inoue T. , Takada K.
Published: December 2017

The regulation by muscle spindles of jaw-closing muscle activity during mastication was evaluated in anesthetized rabbits. Simultaneous records were made of the discharges of muscle spindle units in the mesencephalic trigeminal nucleus, masseter and digastric muscle activity (electromyogram [EMG]), and jaw-movement parameters during cortically induced rhythmic jaw movements. One of three test strips of polyurethane foam, each of a different hardness, was inserted between the opposing molars during the jaw movements. The induced rhythmic jaw movements were crescent shaped and were divided into three phases: jaw-opening, jaw-closing, and power. The firing rate of muscle spindle units during each phase increased after strip application, with a tendency for the spindle discharge to be continuous throughout the entire chewing cycle. However, although the firing rate did not change during the jaw-opening and jaw-closing phases when the strip hardness was altered, the firing rate during the power phase increased in a hardness-dependent manner. In addition, the integrated EMG activity, the duration of the masseteric bursts, and the minimum gape increased with strip hardness. Spindle discharge during the power phase correlated with jaw-closing muscle activity, implying that the change in jaw-closing muscle activity associated with strip hardness was caused by increased spindle discharge produced through insertion of a test strip. The increased firing rate during the other two phases may be involved in a long-latency spindle feedback. This could contribute to matching the spatiotemporal pattern of the central pattern generator to that of the moving jaw.
Sevoflurane Induced Suppression of Inhibitory Synaptic Transmission Between Soma-Soma PairedLymnaeaNeurons
Authors: Hamakawa Toshiro , Feng Zhong-Ping , Grigoriv Nikita , Inoue Takuya , Takasaki Mayumi , Roth Sheldon , Lukowiak Ken , Hasan Shabih U. , Syed Naweed I.
Published: December 2017

The cellular and synaptic mechanisms by which general anesthetics affect cell-cell communications in the nervous system remain poorly defined. In this study, we sought to determine how clinically relevant concentrations of sevoflurane affected inhibitory synaptic transmission between identified Lymnaea neurons in vitro. Inhibitory synapses were reconstructed in cell culture, between the somata of two functionally well-characterized neurons, right pedal dorsal 1 (RPeD1, the giant dopaminergic neuron) and visceral dorsal 4 (VD4). Clinically relevant concentrations of sevoflurane (1–4%) were tested for their effects on synaptic transmission and the intrinsic membrane properties of soma-soma paired cells. RPeD1- induced inhibitory postsynaptic potentials (IPSPs) in VD4 were completely and reversibly blocked by sevoflurane (4%). Sevoflurane also suppressed action potentials in both RPeD1 and VD4 cells. To determine whether the anesthetic-induced synaptic depression involved postsynaptic transmitter receptors, dopamine was pressure applied to VD4, either in the presence or absence of sevoflurane. Dopamine (10−]5M) activated a voltage-insensitive K+current in VD4. The same K+current was also altered by sevoflurane; however, the effects of two compounds were nonadditive. Because transmitter release from RPeD1 requires Ca2+influx through voltage-gated Ca2+channels, we next tested whether the anesthetic-induced synaptic depression involved these channels. Individually isolated RPeD1 somata were whole cell voltage clamped, and Ca2+currents were analyzed in control and various anesthetic conditions. Clinically relevant concentrations of sevoflurane did not significantly affect voltage-activated Ca2+channels in RPeD1. Taken together, this study provides the first direct evidence that sevoflurane-induced synaptic depression involves both pre- and postsynaptic ion channels.
Donders' Law in Torticollis
Authors: Medendorp W. P. , van Gisbergen J.A.M. , Horstink M.W.I.M. , Gielen C.C.A.M.
Published: December 2017

We investigated head movements of patients with spasmodic torticollis toward targets in various directions. These patients, whose severe dystonia was reflected in an abnormal resting head position, appeared to retain a Donders'-type strategy for the control of the rotational degrees of freedom of the head. As in normals, rotation vectors, representing head orientation, were confined to a curved surface, which specifies how head torsion depends on gaze direction. The orientation of the surface in body coordinates, which was very stereotyped in normals, was different for patients. The same Donders surface was found for head movements and for stationary head postures, indicating that the same neural mechanism governs its implementation in both tasks. To interpret our results, we propose a conceptual scheme incorporating the basal ganglia, which are thought to be involved in the etiology of torticollis, and an implementation stage for Donders' law.
Temporal Properties of Chronic Cochlear Electrical Stimulation Determine Temporal Resolution of Neurons in Cat Inferior Colliculus
Authors: Vollmer Maike , Snyder Russell L. , Leake Patricia A. , Beitel Ralph E. , Moore Charlotte M. , Rebscher Stephen J.
Published: December 2017

As cochlear implants have become increasingly successful in the rehabilitation of adults with profound hearing impairment, the number of pediatric implant subjects has increased. We have developed an animal model of congenital deafness and investigated the effect of electrical stimulus frequency on the temporal resolution of central neurons in the developing auditory system of deaf cats. Maximum following frequencies (Fmax) and response latencies of isolated single neurons to intracochlear electrical pulse trains (charge balanced, constant current biphasic pulses) were recorded in the contralateral inferior colliculus (IC) of two groups of neonatally deafened, barbiturate-anesthetized cats: animals chronically stimulated with low-frequency signals (≤80 Hz) and animals receiving chronic high-frequency stimulation (≥300 pps). The results were compared with data from unstimulated, acutely deafened and implanted adult cats with previously normal hearing (controls). Characteristic differences were seen between the temporal response properties of neurons in the external nucleus (ICX; ∼16% of the recordings) and neurons in the central nucleus (ICC; ∼81% of all recordings) of the IC: 1) in all three experimental groups, neurons in the ICX had significantly lower Fmax and longer response latencies than those in the ICC. 2) Chronic electrical stimulation in neonatally deafened cats altered the temporal resolution of neurons exclusively in the ICC but not in the ICX. The magnitude of this effect was dependent on the frequency of the chronic stimulation. Specifically, low-frequency signals (30 pps, 80 pps) maintained the temporal resolution of ICC neurons, whereas higher-frequency stimuli significantly improved temporal resolution of ICC neurons (i.e., higher Fmax and shorter response latencies) compared with neurons in control cats. Furthermore, Fmax and latencies to electrical stimuli were not correlated with the tonotopic gradient of the ICC, and changes in temporal resolution following chronic electrical stimulation occurred uniformly throughout the entire ICC. In all three experimental groups, increasing Fmax was correlated with shorter response latencies. The results indicate that the temporal features of the chronically applied electrical signals critically influence temporal processing of neurons in the cochleotopically organized ICC. We suggest that such plastic changes in temporal processing of central auditory neurons may contribute to the intersubject variability and gradual improvements in speech recognition performance observed in clinical studies of deaf children using cochlear implants.
Adenosine A1 and Class II Metabotropic Glutamate Receptors Mediate Shared Presynaptic Inhibition of Retinotectal Transmission
Authors: Zhang Chunyi , Schmidt John T.
Published: December 2017

Presynaptic inhibition is one of the major control mechanisms in the CNS. Previously we reported that adenosine A1 receptors mediate presynaptic inhibition at the retinotectal synapse of goldfish. Here we extend these findings to metabotropic glutamate receptors (mGluRs) and report that presynaptic inhibition produced by both A1 adenosine receptors and group II mGluRs is due to Giprotein coupling to inhibition of N-type calcium channels in the retinal ganglion cells. Adenosine (100 μM) and an A1 (but not A2) receptor agonist reduced calcium current ( ICa2+) by 16–19% in cultured retinal ganglion cells, consistent with their inhibition of retinotectal synaptic transmission (−30% amplitude of field potentials). The general metabotropic glutamate receptor (mGluR) agonist 1S,3R-1-amino-cyclopentane-1,3-dicarboxylic acid (1S,3R-ACPD, 50 μM) and the selective group II mGluR receptor agonist (2S,2′R,3′R)-2-(2′,3′-dicarboxy-cyclopropyl)glycine (DCG-IV, 300 nM) inhibited both synaptic transmission and ICa2+, whereas the group III mGluR agonistl-2-amino-4-phosphono-butyrate (l-AP4) inhibited neither synaptic transmission nor ICa2+. When the N-type calcium channels were blocked with ω-conotoxin GVIA, both adenosine and DCG-IV had much smaller percentage effects on the residual 20% of ICa2+, suggesting effects mainly on the N-type calcium channels. The inhibitory effects of A1 adenosine receptors and mGluRs were both blocked by pertussis toxin, indicating that they are mediated by either Gior Go. They were also inhibited by activation of protein kinase C (PKC), which is known to phosphorylate and inhibit Gi. Finally, when applied sequentially, inhibition by adenosine and DCG-IV were not additive but occluded each other. Together these results suggest that adenosine A1 receptors and group II mGluRs mediate presynaptic inhibition of retinotectal synaptic transmission by sharing a pertussis toxin (PTX)–sensitive, PKC-regulated Giprotein coupled to N-type calcium channels.
Selective Modulation of Excitatory Transmission by μ-Opioid Receptor Activation in Rat Supraoptic Neurons
Authors: Liu Qing-Song , Han Sheng , Jia You-Sheng , Ju Gong
Published: December 2017

Opioid peptides have profound inhibitory effects on the production of oxytocin and vasopressin, but their direct effects on magnocellular neuroendocrine neurons appear to be relatively weak. We tested whether a presynaptic mechanism is involved in this inhibition. The effects of μ-opioid receptor agonist d-Ala2, N-CH3-Phe4, Gly5-ol-enkephalin (DAGO) on excitatory and inhibitory transmission were studied in supraoptic nucleus (SON) neurons from rat hypothalamic slices using whole cell recording. DAGO reduced the amplitude of evoked glutamatergic excitatory postsynaptic currents (EPSCs) in a dose-dependent manner. In the presence of tetrodotoxin (TTX) to block spike activity, DAGO also reduced the frequency of spontaneous miniature EPSCs without altering their amplitude distribution, rising time, or decaying time constant. The above effects of DAGO were reversed by wash out, or by addition of opioid receptor antagonist naloxone or selective μ-antagonist Cys2-Tyr3-Orn5-Pen7-NH2(CTOP). In contrast, DAGO had no significant effect on the evoked and spontaneous miniature GABAergic inhibitory postsynaptic currents (IPSCs) in most SON neurons. A direct membrane hyperpolarization of SON neurons was not detected in the presence of DAGO. These results indicate that μ-opioid receptor activation selectively inhibits excitatory activity in SON neurons via a presynaptic mechanism.
Weight Support and Balance During Perturbed Stance in the Chronic Spinal Cat
Authors: Macpherson Jane M. , Fung Joyce
Published: December 2017

The intact cat maintains balance during unexpected disturbances of stance through automatic postural responses that are stereotyped and rapid. The extent to which the chronic spinal cat can maintain balance during stance is unclear, and there have been no quantitative studies that examined this question directly. This study examined whether the isolated lumbosacral cord of the chronic spinal cat can generate automatic postural responses in the hindlimbs during translation of the support surface. Responses to 16 directions of linear translation in the horizontal plane were quantified before and after spinalization at the T6 level in terms of forces exerted by each paw against the support, motion of the body segments (kinematics), and electromyographic (EMG) activity. After spinalization, the cats were trained on a daily basis to stand on the force platform, and all four cats were able to support their full body weight. The cats usually required assistance for balance or stability in the horizontal plane, which was provided by an experimenter exerting gentle lateral force at the level of the hips. Three of the four animals could maintain independent stance for a brief period (10 s) after the experimenter stabilized them. The fourth cat maintained weight support but always required assistance with balance. Perturbations were delivered during the periods of independent stance in three cats and during assisted stance in the fourth. A response to translation in the spinal cats was observed only in those muscles that were tonically active to maintain stance and never in the flexors. Moreover, latencies were increased and amplitudes of activation were diminished compared with control. Nevertheless, flexors and extensors were recruited easily during behaviors such as paw shake and stepping. It is concluded that centers above the lumbosacral cord are required for the full elaboration of automatic postural responses. Although the spinal cat can achieve good weight support, it cannot maintain balance during stance except for brief periods and within narrow limits. This limited stability is probably achieved through spinal reflex mechanisms and the stiffness characteristics of the tonically active extensors.
Long-Lasting Increase in Cellular Excitability Associated With the Priming of LTP Induction in Rat Hippocampus
Authors: Cohen Akiva S. , Coussens Christine M. , Raymond Clarke R. , Abraham Wickliffe C.
Published: December 2017

The mechanisms underlying the facilitation (priming) of long-term potentiation (LTP) by prior activation of metabotropic glutamate receptors (mGluRs) were investigated in area CA1 of rat hippocampal slices. In particular, we focused on whether a long-lasting increase in postsynaptic excitability could account for the facilitated LTP. Administration of the mGluR agonist 1S,3R-aminocyclopentanedicarboxylic acid (ACPD) produced rapid decreases in the amplitude of both the slow spike afterhyperpolarization (AHPslow) and spike frequency adaptation recorded intracellularly from CA1 pyramidal cells. These changes persisted after drug washout, showing only a slow decay over 20 min. ACPD also caused a leftward shift of the field EPSP-population spike relation and an overall increase in population spike amplitude, but this effect was not as persistent as the intracellularly measured alterations in cell excitability. ACPD-treated cells showed increased spike discharges during LTP-inducing tetanic stimulation, and the amplitude of the AHPslow was negatively correlated with the degree of initial LTP induction. The β-adrenergic agonist isoproterenol also caused excitability changes as recorded intracellularly, whereas in extracellular experiments it weakly primed the induction but not the persistence of LTP. ACPD primed both LTP measures. Isoproterenol administration during the tetanus occluded the priming effect of ACPD on initial LTP induction but not its effect on LTP persistence. We conclude that the persistent excitability changes elicited by ACPD contributes to the priming of LTP induction but that other ACPD-triggered mechanisms must account for the facilitated persistence of LTP in the priming paradigm.
Physiological Evidence for the Discrimination ofl-Arginine From Structural Analogues by the Zebrafish Olfactory System
Authors: Lipschitz D. L. , Michel W. C.
Published: December 2017

Although it is generally assumed that fish are capable of discriminating amino acid odorants on the basis of differences in side-chain structure, less is known about their ability to discriminate amino acids with modifications to α-carboxyl and α-amino groups. In this study, the ability of the zebrafish olfactory system to detect and presumably discriminate analogues of the basic amino acid Arg was assessed, by using cross-adaptation and activity-dependent labeling techniques. Electrophysiological recordings established that esterification (l-arginine methyl ester; AME) or deletion (agmatine or amino-4-guanidobutane; AGB) of the α-carboxyl group yielded odorants more potent than Arg, whereas deletion of the α-amino group (l-argininic acid; AA) yielded a less potent analogue. In cross-adaptation experiments, no test-competitor odorant combination yielded complete cross-adaptation, suggesting the detection of these Arg analogues by multiple odorant receptors (ORs) with partially nonoverlapping specificities. Activity-dependent immunocytochemical labeling of olfactory receptor neurons supported this conclusion. AGB, an ion-channel–permeant probe (and odorant), labeled 4.9 ± 0.4% ( n = 24) of sensory epithelium, whereas the addition of Arg, 1-ethylguanidine sulfate, l-α-amino-β-guanidinopropionate, or AME to AGB resulted in a significant elevation of labeling (8–14%). This study provides evidence that the olfactory system has the potential to discriminate among amino acid odorants with modified α-carboxyl and α-amino groups.
Pattern of Pulses That Maximize Force Output From Single Human Thenar Motor Units
Authors: Thomas C. K. , Johansson R. S. , Bigland-Ritchie B.
Published: December 2017

We assessed the sequence of nerve impulses that maximize force output from individual human thenar motor units. When these motor units were stimulated intraneurally by a variable sequence of seven pulses, the pattern of pulses that elicited maximum force always started with a short (5–15 ms) interpulse interval termed a “doublet.” The twitch force summation caused by this “doublet” elicited, on average, 48 ± 13% (SD) of the maximum tetanic force. The peak amplitude of “doublet” forces was 3.5 times that of the initial twitches, and twitch potentiation appeared to have little influence on twitch force summation elicited by the “doublets.” For some units, the second optimal interpulse interval was also short. Peak forces elicited by the third to sixth interpulse intervals did not change substantially when the last interpulse interval was varied between 5 to 55 ms, so maximum force could not be attributed to any unique interpulse interval. Each successive pulse contributed a smaller force increment. When five to seven pulses were delivered in an optimal sequence, the evoked force was close to that recorded during maximal tetanic stimulation. In contrast, maximal force-time integral was evoked with one short interpulse interval (5–15 ms) then substantially longer interpulse intervals (>100 ms). Maximum force and force-time integrals were therefore elicited by different patterns of stimuli. We conclude that a brief initial interpulse interval (5–15 ms) is required to elicit maximum “doublet” force from human thenar motor units and that near-maximal tetanic forces can be elicited by only five or six additional post-“doublet” pulses if appropriately spaced in time. However, the rate at which these post-“doublet” stimuli must be provided is fairly uncritical. In contrast, maximum post-“doublet” force-time integrals were obtained at intervals corresponding to motoneuronal firing rates of ∼7 Hz, rates close to that typically used to recruit motor units and to maintain weak voluntary contractions.
Reorganization in the Cutaneous Core of the Human Thalamic Principal Somatic Sensory Nucleus (Ventral Caudal) in Patients With Dystonia
Authors: Lenz Fred A. , Byl Nancy N.
Published: December 2017

A wide range of observations suggest that sensory inputs play a significant role in dystonia. For example, the map of the hand representation in the primary sensory cortex (area 3b) is altered in monkeys with dystonia-like movements resulting from overtraining in a gripping task. We investigated whether similar reorganization occurs in the somatic sensory thalamus of patients with dystonia (dystonia patients). We studied recordings of neuronal activity and microstimulation-evoked responses from the cutaneous core of the human principal somatic sensory nucleus (ventral caudal, Vc) of 11 dystonia patients who underwent stereotactic thalamotomy. Fifteen patients with essential tremor who underwent similar procedures were used as controls. The cutaneous core of Vc was defined as the part of the cellular thalamic region where the majority of cells had receptive fields (RFs) to innocuous cutaneous stimuli. The proportion of RFs including multiple parts of the body was greater in dystonia patients (29%) than in patients with essential tremor (11%). Similarly, the percentage of projected fields (PFs) including multiple body parts was higher in dystonia patients (71%) than in patients with essential tremor (41%). A match at a thalamic site was said to occur if the RF and PF at that site included a body part in common. Such matches were significantly less prevalent in dystonia patients (33%) than in patients with essential tremor (58%). The average length of the trajectory where the PF included a consistent, cutaneous RF was significantly longer in patients with dystonia than in control patients with essential tremor. The findings of sensory reorganization in Vc thalamus are congruent with those reported in the somatic sensory cortex of monkeys with dystonia-like movements resulting from overtraining in a gripping task.
Role of L-Type Ca2+Channels in Transmitter Release From Mammalian Inner Hair Cells I. Gross Sound-Evoked Potentials
Authors: Zhang Si Yi , Robertson Donald , Yates Graeme , Everett Alan
Published: December 2017

Intracochlear perfusion and gross potential recording of sound-evoked neural and hair cell responses were used to study the site of action of the L-type Ca2+channel blocker nimodipine in the guinea pig inner ear. In agreement with previous work nimodipine (1–10 μM) caused changes in both the compound auditory nerve action potential (CAP) and the DC component of the hair cell receptor potential (summating potential, or SP) in normal cochleae. For 20-kHz stimulation, the effect of nimodipine on the CAP threshold was markedly greater than the effect on the threshold of the negative SP. This latter result was consistent with a dominant action of nimodipine at the final output stage of cochlear transduction: either the release of transmitter from inner hair cells (IHCs) or the postsynaptic spike generation process. In animals in which the outer hair cells (OHCs) had been destroyed by prior administration of kanamycin, nimodipine still caused a large change in the 20-kHz CAP threshold, but even less change was observed in the negative SP threshold than in normal cochleae. When any neural contamination of the SP recording in kanamycin-treated animals was removed by prior intracochlear perfusion with TTX, nimodipine caused no significant change in SP threshold. Some features of the data also suggest a separate involvement of nimodipine-sensitive channels in OHC function. Perfusion of the cochlea with solutions containing Ni2+(100 μM) caused no measurable change in either CAP or SP. These results are consistent with, but do not prove, the notion that L-type channels are directly involved in controlling transmitter release from the IHCs and that T-type Ca2+channels are not involved at any stage of cochlear transduction.
Acoustic and Current-Pulse Responses of Identified Neurons in the Dorsal Cochlear Nucleus of Unanesthetized, Decerebrate Gerbils
Authors: Ding Jiang , Benson Thane E. , Voigt Herbert F.
Published: December 2017

In an effort to establish relationships between cell physiology and morphology in the dorsal cochlear nucleus (DCN), intracellular single-unit recording and marking experiments were conducted on decerebrate gerbils using horseradish peroxidase (HRP)- or neurobiotin-filled micropipettes. Intracellular responses to acoustic (tone and broadband noise bursts) and electric current-pulse stimuli were recorded and associated with cell morphology. Units were classified according to the response map scheme (type I to type V). Results from 19 identified neurons, including 13 fusiform cells, 2 giant cells, and 4 cartwheel cells, reveal correlations between cell morphology of these neurons and their acoustic responses. Most fusiform cells (8/13) are associated with type III unit response properties. A subset of fusiform cells was type I/III units (2), type III-i units (2), and a type IV-T unit. The giant cells were associated with type IV-i unit response properties. Cartwheel cells all had weak acoustic responses that were difficult to classify. Some measures of membrane properties also were correlated with cell morphology but to a lesser degree. Giant cells and all but one fusiform cell fired only simple action potentials (APs), whereas all cartwheel cells discharged complex APs. Giant and fusiform cells all had monotonic rate versus current level curves, whereas cartwheel cells had nonmonotonic curves. This implies that inhibitory acoustic responses, resulting in nonmonotonic rate versus sound level curves, are due to local inhibitory interactions rather than strictly to membrane properties. A complex-spiking fusiform cell with type III unit properties suggests that cartwheel cells are not the only complex-spiking cells in DCN. The diverse response properties of the DCN′s fusiform cells suggests that they are very sensitive to the specific complement of excitatory and inhibitory inputs they receive.
Disynaptic Pyramidal Excitation in Forelimb Motoneurons Mediated Via C3–C4 Propriospinal Neurons in theMacaca fuscata
Authors: Alstermark B. , Isa T. , Ohki Y. , Saito Y.
Published: December 2017

In contrast to findings in the cat, it recently has been shown that disynaptic pyramidal EPSPs only rarely are observed in forelimb motoneurons of the macaque monkey in the intact spinal cord or after a corticospinal transection in C5. This finding has been taken to indicate that the disynaptic pyramidal excitatory pathway via C3–C4 propriospinal neurons (PNs) is weakened through phylogeny when the monosynaptic cortico-motoneuronal connection has been strengthened. We reinvestigate this issue with special focus on the possibility that the inhibitory control of the C3–C4 PNs may be stronger in the macaque monkey than in the cat. The effect in forelimb motoneurons of electrical stimulation in the contralateral pyramid was investigated in anesthetized macaque monkeys ( Macaca fuscata). We confirmed the low frequency of disynaptic pyramidal EPSPs in forelimb motoneurons. However, after intravenous injection of strychnine, disynaptic EPSPs could be evoked in 39 of 41 forelimb motoneurons recorded after lesion of the corticospinal fibers in C5. After a corresponding lesion in C2, disynaptic pyramidal EPSPs were observed in 2 of 25 motoneurons. In contrast to previous reports, we conclude that C3–C4 PNs can mediate disynaptic pyramidal excitation in high frequency of occurrence to forelimb motoneurons in the C6–C8 segments and that this transmission is under a stronger inhibitory control than in the cat. Thus, the hypothesis that the disynaptic excitatory cortico-motoneuronal pathway via the C3–C4 PNs is weakened in parallel with the strengthened monosynaptic connection through phylogeny is not supported by the present findings.
Antagonistic Effects of Phentolamine and Octopamine on Rhythmic Motor Output of Crayfish Thoracic Ganglia
Authors: Gill Mark D. , Skorupski Peter
Published: December 2017

Spontaneous rhythmic motor output of crayfish thoracic ganglia consists of bursts of activity in antagonistic leg motor neurons (MNs), alternating with a rather slow cycle period (typically ≥20 s). The most common pattern (77% of preparations) consists of long coxal promotor bursts, the duration of which was correlated strongly with cycle period, and relatively short remotor bursts independent of cycle period. Octopamine, at a concentration of 2–30 μM reversibly retarded this rhythm, increasing both cycle period and promotor burst duration. Higher concentrations of octopamine inhibited promotor nerve activity and abolished rhythmic bursting. Phentolamine (10–50 μM) had the opposite effect of decreasing cycle period, mainly by decreasing promotor burst duration. Whereas in the presence of octopamine promotor bursts were lengthened and became even more strongly related to cycle period, phentolamine promoted a more symmetrical rhythm with shorter promotor bursts that were less dependent on cycle period. When octopamine was applied in the presence of phentolamine, there was no significant increase in cycle period or burst duration, although high octopamine concentrations (100 μM) were still capable of inhibiting promotor nerve activity. To our knowledge, pharmacological modulation of a spontaneous locomotor rhythm by an amine antagonist (applied by itself) has not been reported previously. The results raise the testable possibility that phentolamine exerts its modulatory effects by acting as an octopamine antagonist in crayfish thoracic ganglia.
Calcium Release From Internal Stores Is Required for the Generation of Spontaneous Hyperpolarizations in Dopaminergic Neurons of Neonatal Rats
Authors: Seutin Vincent , Mkahli Fatiha , Massotte Laurent , Dresse Albert
Published: December 2017

We recently have demonstrated the existence of spontaneous hyperpolarizations in midbrain dopaminergic neurons of neonatal but not adult rats. These events are mediated by the opening of apamin-sensitive K+channels after a rise in the intracellular concentration of Ca2+. They are resistant to tetrodotoxin in most cases and are probably endogenous (i.e., not synaptically activated). Here their mechanism was investigated. Cyclopiazonic acid (10 μM), a specific inhibitor of endoplasmic reticulum Ca2+ATPases, reversibly abolished the events. Caffeine, which promotes Ca2+release from intracellular stores, had concentration-dependent effects. At 1 mM, it markedly and steadily increased the frequency and the amplitude of the hyperpolarizations. At 10 mM, it induced a transient increase in their frequency followed by their cessation. All these effects were quickly reversible. Ryanodine (10 μM), which decreases the conductance of Ca2+release channels, irreversibly blocked the spontaneous hyperpolarizations. Dantrolene (100 μM), a blocker of Ca2+release from sarcoplasmic reticulum of striated muscle, did not affect the events. On the other hand, Cd2+(100–300 μM), a broad antagonist of membrane voltage-gated Ca2+channels, significantly reduced the amplitude and the frequency of the hyperpolarizations. However, when the frequency of the events was increased by 1 mM caffeine, Cd2+affected them to a smaller extent, whereas cyclopiazonic acid still abolished them. We conclude that internal stores are the major source of Ca2+ions that induce the K+channel openings underlying the spontaneous hyperpolarizations of these neurons.