bluuebunny/crossref_metadata_2025 huggingface dataset:
Calcium‐dependent responses in neurons of the isolated respiratory network of newborn rats.
Authors: Onimaru H , Ballanyi K , Richter D W
Published: December 2014

1. Membrane potentials (Em) and currents (Im) were measured using whole‐cell patch clamp techniques in inspiratory (Insp, types I‐III), preinspiratory (Pre‐I) and tonic expiratory (Exp) neurons of the ventral respiratory group (VRG) in the isolated brainstem‐spinal cord preparation of 0‐ to 4‐day‐old rats. 2. After blocking on‐going synaptic activity with 0.2‐0.5 microM tetrodotoxin (TTX), Ca(2+)‐dependent responses were analysed using patch pipettes containing 120 mM Cs+ and 20 mM tetraethylammonium (TEA) to block K+ conductances. 3. In all cells studied, all‐or‐none high voltage‐activated (HVA) Ca2+ spikes with an activation threshold of ‐33 +/‐ 6.9 mV (n = 37) were evoked by depolarizing current pulses. 4. In less than 15% of Insp and Pre‐I cells and in 20% of Exp neurons, termination of hyperpolarizing pulses led to low voltage‐activated (LVA) Ca2+ spikes with a threshold potential of between ‐70 and ‐60 mV (n = 7). 5. In more than 50% of Insp III and Pre‐I neurons, depolarizing pulses evoked graded ‘plateau’ potentials with an amplitude of 5‐20 mV. Slow voltage ramp commands revealed that this type of Ca2+ response was due to an inward current with a mean activation threshold of ‐42 +/‐ 2.1 mV (n = 5). These intermediate voltage‐activated (IVA) plateau potentials persisted for several seconds after termination of depolarizing current pulses and decreased in amplitude at more negative holding potentials. 6. The HVA and LVA Ca2+ spikes as well as the IVA plateau potentials and the underlying inward current were potentiated after extracellular addition of 2 mM Ba2+ whereas 1‐2 mM Co2+ led to blockade of these responses. 7. Nifedipine (10 microM) selectively suppressed HVA Ca2+ potentials whereas 0.2‐0.4 microM omega‐agatoxin‐IVA reduced the IVA response without major effects on HVA Ca2+ spikes. omega‐Conotoxin‐GVIA (2 microM) led to a partial blockade of both IVA and HVA potentials. 8. After extracellular application of TTX, Ba2+ and/or TEA, HVA and LVA Ca2+ spikes as well as IVA plateau potentials were also revealed using patch pipettes containing K+ instead of Cs+ and TEA. 9. The results indicate that neonatal respiratory neurons have a complex set of Ca(2+)‐dependent membrane conductances. The relevance of these conductances for initiation and maintenance of respiratory bursts is discussed.
Effects of hypernatraemia in the central nervous system and its therapy in rats and rabbits.
Authors: Ayus J C , Armstrong D L , Arieff A I
Published: December 2014

1. We studied the effects of acute (1 or 4 h) and chronic (1 week) hypernatraemia (plasma [Na+], 170‐190 mM) on brain histology, and brain water and solute contents in rats and rabbits. 2. In rabbits with acute hypernatraemia, there was significant loss of intracellular brain water, with increases in brain [Na+ + K+], amino acid concentration, and undetermined solute (idiogenic osmole). After 1 week of recovery, brain intracellular water content had returned to normal. 3. In hypernatraemic rats there was myelinolysis of brain white matter, with karyorrhexis and necrosis of neurons. 4. Hypernatraemic rabbits were treated with 77 mM NaCl (i.v.) to normalize plasma [Na+] over 4‐24 h intervals. Therapy of either acute or chronic hypernatraemia resulted in significant brain oedema because brain osmolality failed to decrease at the same rate as plasma osmolality. 5. It is concluded that: (a) untreated hypernatraemia results in brain lesions demonstrating myelinolysis and cellular necrosis; (b) normalization of hypernatraemia over 4‐24 h results in cerebral oedema, due primarily to failure of brain amino acids and idiogenic osmoles to dissipate as plasma [Na+] is decreased to normal.
Interaction of training and diet on metabolism and endurance during exercise in man.
Authors: Helge J W , Richter E A , Kiens B
Published: December 2014

1. Ten untrained young men ingested a carbohydrate‐rich diet (65 energy percent (E%) carbohydrate, T‐CHO) and ten similar subjects a fat‐rich diet (62 E% fat, T‐FAT) while endurance training was performed 3‐4 times a week for 7 weeks. For another 8th week of training both groups ingested the carbohydrate‐rich diet (T‐CHO and T‐FAT/CHO). 2. Maximal oxygen uptake increased by 11% (P < 0.05) in both groups after 7 and 8 weeks. Time to exhaustion at 81% of pre‐training maximal oxygen uptake increased significantly from a mean (+/‐ S.E.M.) of 35 +/‐ 4 min to 102 +/‐ 5 and 65 +/‐ 7 min in T‐CHO and T‐FAT, respectively, after 7 weeks (P < 0.05, T‐CHO vs. T‐FAT). After 8 weeks, endurance remained unchanged in T‐CHO but increased (P < 0.05) to 77 +/‐ 9 min in T‐FAT/CHO which, however, was still less (P < 0.05) than in T‐CHO. 3. Muscle glycogen breakdown rate during exercise was halved by endurance training equally in both T‐CHO and T‐FAT after 7 and 8 weeks, and muscle glycogen stores at exhaustion were not depleted in any group. 4. During exercise after 7 weeks, the respiratory exchange ratio (RER) was unchanged in T‐CHO (0.88 +/‐ 0.01) compared with pre‐training but decreased (P < 0.05) to 0.82 +/‐ 0.02 in T‐FAT. After 8 weeks, RER in both T‐CHO and T‐FAT/CHO was approximately 0.87. 5. During exercise, plasma noradrenaline concentration and heart rate were higher in T‐FAT than in T‐CHO both at 7 and at 8 weeks. 6. It is concluded that ingesting a fat‐rich diet during an endurance training programme is detrimental to improvement in endurance. This is not due to a simple lack of carbohydrate fuel, but rather to suboptimal adaptations that are not remedied by short‐term increased carbohydrate availability. Furthermore, the study suggests that the decrease in RER usually seen after training when exercising at the same absolute intensity as before training can be prevented by a carbohydrate‐rich diet.
Excitatory amino acid‐mediated chemoreflex excitation of respiratory neurones in rostral ventrolateral medulla in rats.
Authors: Sun M K , Reis D J
Published: December 2014

1. In anaesthetized rats, extracellular and intracellular recordings were made from 119 respiratory neurones in the rostroventrolateral reticular nucleus (RVL) of the medulla oblongata. 2. Two types of active respiratory neurones were detected in RVL: expiratory (E) and pre‐inspiratory (Pre‐I), based on the relationship between their discharge and that of the phrenic nerve. Some Pre‐I but none of the E neurones could be antidromically excited from the C(3)‐C(4) level of the spinal cord. 3. E and Pre‐I neurones of RVL were excited by stimulation of the arterial chemoreceptors by a close arterial injection of sodium cyanide. The reflex excitation of RVL E neurones was preceded by increased phrenic nerve activity, while the excitation of RVL Pre‐I neurones preceded the increases in phrenic nerve activity. 4. The chemoreflex excitation of the two types of RVL respiratory neurones as well as their resting discharge was abolished or significantly depressed by microionophoresis of kynurenate, a wide‐spectrum antagonist of excitatory amino acid receptors, while xanthurenate, an inactive analogue of kynurenate, was without effect. 5. In ventilated rats, bilateral microinjection into RVL of kynurenate, but not xanthurenate, abolished resting activity and chemoreflex excitation of phrenic nerve activity, whilst in spontaneously breathing rats, kynurenate microinjection into RVL produced apnea and silenced phrenic nerves. 6. We conclude: (a) chemoreflex excitation of the phrenic nerves is mediated by stimulating Pre‐I neurones of RVL by excitatory amino acidergic inputs and (b) RVL Pre‐I neurones may directly and/or indirectly excite spinal phrenic motor neurones and hence are involved in inspiratory rhythmogenesis.
Synchronous release of ATP and neurotransmitter within milliseconds of a motor nerve impulse in the frog.
Authors: Silinsky E M , Redman R S
Published: December 2014

1. It has been suggested that ATP is released together with the neurotransmitter acetylcholine (ACh) and, after hydrolysis to adenosine, is the primary physiological mediator of prejunctional neuromuscular depression. To evaluate whether ATP is released with sufficient rapidity to mediate prejunctional depression, outside‐out patches containing both ATP‐gated and ACh‐gated ion channels were made from acutely dissociated guinea‐pig sympathetic neurons and used to detect the co‐release of nucleotide and neurotransmitter in frog cutaneous pectoris nerve‐muscle preparations. 2. In a normal bathing solution in which muscle nicotinic receptors were blocked, a single stimulus to the motor nerve produced channel openings in the detector patch characteristic of both ATP and ACh. 3. In the remaining experiments, preparations were treated with sufficient hexamethonium (200 microM) to block nicotinic responses in the detector patch. In these experiments, a single temporally isolated nerve impulse caused the synchronous opening of ATP‐gated channels in the detector patch with a latency of < 5 ms when patches were placed within 10 microns of the motor nerve ending. This multichannel phasic response was followed by trail of discrete channel openings characteristic of ATP‐gated channels. 4. The selective ATP antagonist suramin (50 microM) reversibly eliminated the response to nerve stimulation. 5. The results suggest that ATP is released synchronously together with the neurotransmitter ACh in response to an individual nerve impulse and with a brief latency characteristic of quantal release from synaptic vesicles.
Long‐lasting synaptic facilitation induced by serotonin in superficial dorsal horn neurones of the rat spinal cord.
Authors: Hori Y , Endo K , Takahashi T
Published: December 2014

1. Modulatory actions of serotonin (5‐hydroxytryptamine, 5‐HT) on excitatory postsynaptic currents (EPSCs) were studied with whole‐cell recordings from superficial dorsal horn (SDH) neurones in neonatal rat spinal cord slices. In one‐third of SDH neurones, 5‐HT induced a sustained potentiation of evoked EPSCs lasting for more than 30 min after wash‐out. This potentiation was often preceded by a transient suppression of EPSCs. 2. Serotonin differentially modulated the frequency of miniature EPSCs recorded in the presence of tetrodotoxin (TTX) according to the SDH neurones, producing a transient suppression, a transient facilitation or a long‐lasting facilitation. 3. The 5‐HT1A‐receptor agonist 8‐hydroxy‐2‐(di‐n‐propylamino)tetralin (8‐OH‐DPAT) suppressed the amplitude of evoked EPSCs and frequency of miniature EPSCs in a reversible manner. In contrast, the 5‐HT2‐receptor agonists 1‐(2,5‐dimethoxy‐4‐iodophenyl)‐2‐aminopropane (DOI) and alpha‐methyl‐5‐HT induced long‐lasting potentiations of EPSC amplitude and miniature EPSC frequency. 4. Neither the mean amplitude nor the kinetics of miniature EPSCs were affected by 5‐HT during the sustained facilitation of miniature EPSC frequency, suggesting that the facilitatory effect of 5‐HT was presynaptically mediated. The 5‐HT‐induced long‐lasting facilitation of miniature EPSC frequency was observed also in Ca(2+)‐free, Mg2+ solution. 5. The long‐lasting facilitation of evoked EPSC amplitude and miniature EPSC frequency by 5‐HT was mimicked by the phorbol ester, phorbol 12,13‐dibutyrate (PDBu), and blocked reversibly by the protein kinase C (PKC) inhibitor, calphostin C. Forskolin applied together with 3‐isobutyl‐1‐methylxanthine (IBMX) had no effect on the evoked EPSCs. 6. We conclude that serotonin can induce a long‐lasting facilitation of evoked EPSCs and spontaneous release of excitatory transmitter at SDH synapses of rat spinal cord. Our results suggest that intracellular PKC linked to the 5‐HT2 receptor may mediate this effect by directly activating the exocytotic machinery.
Plateau‐generating neurones in the dorsal horn in an in vitro preparation of the turtle spinal cord.
Authors: Russo R E , Hounsgaard J
Published: December 2014

1. In transverse slices of the spinal cord of the turtle, intracellular recordings were used to characterize and analyse the responses to injected current and activation of primary afferents in dorsal horn neurones. 2. A subpopulation of neurones, with cell bodies located laterally in the deep dorsal horn and dendrites radiating towards the pial surface, was distinguished by the ability to generate plateau potentials. Activation of the plateau potential by a suprathreshold depolarizing current pulse produced an increasing firing frequency during the first few seconds and a sustained after‐discharge. 3. The plateau potential was assumed to be mediated by L‐type Ca2+ channels since it was blocked by Co2+ (3 mM) and nifedipine (10 microM) and enhanced by Bay K 8644 (0.5‐2 microM). 4. The threshold for activating the plateau potential declined during the first few seconds of depolarization. The decline in threshold gradually subsided over 3‐10 s after repolarization. 5. Frequency potentiation of the plateau potential contributed to wind‐up of the response to depolarizing current pulses and primary afferent stimuli repeated at frequencies higher than 0.1‐0.3 Hz. 6. The sustained after‐discharge mediated by the plateau potential was curtailed by a slow after‐hyperpolarization (sAHP) evoked by strong depolarizations. The relative strength of the plateau potential and sAHP varied among cells. In some cells the plateau potential and sAHP interacted to produce damped oscillations upon depolarization. The sAHP was mediated by both apamin and tetraethylammonium (TEA)‐sensitive K+ channels. 7. Our findings suggest that basic properties of sensory integration may reside with the specialized intrinsic response properties of particular subtypes of neurones in the dorsal horn.
Myofibrillar ATPase activity in skinned human skeletal muscle fibres: fibre type and temperature dependence.
Authors: Stienen G J , Kiers J L , Bottinelli R , Reggiani C
Published: December 2014

1. Myofibrillar ATP consumption and isometric tension (P0) were determined in chemically skinned skeletal muscle fibres from human rectus abdominis and vastus lateralis muscle. Fibres were classified in four groups (I, IIA, IIB, IIA/B or mixed) based on myosin heavy chain composition. 2. ATP consumption (+/‐ S.E.M.) at 20 degrees C varied from 0.41 +/‐ 0.06 mmol l‐1 s‐1 in type IIB fibres (n = 5) to 0.10 +/‐ 0.01 mmol l‐1 s‐1 in type I fibres (n = 13). 3. The ratio between ATPase activity and P0 (tension cost) differed significantly between fast type II and slow type I fibres. At 12 degrees C tension cost was lower than the values found previously in corresponding fibre types in the rat. 4. The relative increase in ATPase activity for a 10 degrees C temperature change (Q10), determined in the range from 12 to 30 degrees C, was temperature independent and amounted to 2.60 +/‐ 0.06. The increase in P0 with temperature was smaller and declined when the temperature increased. 5. From these measurements, estimates were obtained for the maximum rate of isometric ATP consumption and force development at muscle temperature in vivo (35 degrees C).
The role of Na(+)‐Ca2+ exchange in activation of excitation‐contraction coupling in rat ventricular myocytes.
Authors: Wasserstrom J A , Vites A M
Published: December 2014

1. The purpose of this study was to determine whether mechanisms other than Ca2+ influx via L‐type Ca2+ current (ICa) might contribute to activation of contraction in rat ventricular myocytes. The whole‐cell voltage‐clamp technique was used with normal transmembrane K+ and Na+ gradients at 34 degrees C. The sarcoplasmic reticulum (SR) was conditioned with one to three prepulses to +100 mV for 100 ms. 2. Cell shortening (delta L) increased with test voltage up to a plateau level at about +20 mV, beyond which cell shortening remained fairly constant, thus describing a sigmoidal voltage dependence. This relationship was obtained when holding potential (Vh) was either ‐40 or ‐70 mV; however, greater shortening was obtained at the more negative Vh. 3. The sigmoidal V‐delta L relationship was converted to a bell shape following the magnitude of ICa when internal Cs+ was substituted for K+ and when the temperature was reduced to 22 degrees C. 4. At 34 degrees C, block of ICa with nifedipine (10 microM) decreased shortening by about 50% but did not alter the voltage dependence of delta L when Vh was either ‐40 or ‐70 mV. Addition of Ni2+ (4‐5 mM) blocked all remaining contractions. 5. When cell shortening was triggered by an action potential voltage clamp, there was again about 50% of the contraction that was insensitive to nifedipine but was blocked by Ni2+. 6. Our results demonstrate that there is a significant contribution of a nifedipine‐insensitive mechanism to the activation of contraction. This mechanism is likely to be reverse mode Na(+)‐Ca2+ exchange since it appears to be sensitive to both voltage and Ni2+. We conclude that a contribution of reverse Na(+)‐Ca2+ exchange to activation of excitation‐contraction coupling occurs in rat heart at near‐physiological conditions which include warm temperatures, normal transmembrane Na+ and K+ gradients and activation in response to an action potential.
Ontogeny of bipedal locomotion: walking and running in the chick.
Authors: Muir G D , Gosline J M , Steeves J D
Published: December 2014

1. The purpose of this study was to determine whether the production of an energy‐efficient bipedal walk is an innate attribute of a precocial bird. 2. The locomotor characteristics of hatchling chicks were quantified using kinetic (ground reaction forces) and kinematic (stride length, leg support duration) measurements as the animals moved overground unrestrained. All measurements were made over a range of velocities and at regular intervals throughout the first 2 weeks of life. 3. Ground reaction force records showed that, like all terrestrial walking vertebrates, chicks undergo cyclical increases and decreases in the body's potential and kinetic energy with each step. The out‐of‐phase exchange of potential with kinetic energy is an efficient mechanism for the conservation of energy during walking. However, comparisons between chicks at posthatching (P) days 1‐2 and P14 revealed that P1‐2 chicks are unable to conserve energy because they walk with disproportionately small potential energy oscillations. During running, however, the oscillations between potential and kinetic energy are similar for both P1‐2 and P14 animals. 4. P1‐2 chicks also walk with a shorter stride length than P14 chicks. Examination of limb support durations shows that younger animals (P1‐2, P3) spend less time in single limb support than P14 animals during walking but not running. 5. The results show that even highly precocial bipeds need to acquire the ability to walk in a controlled and energy efficient manner, although they can innately run as well as an adult. This disparity could be due to the distinct actions of the legs in these two behaviours, and the requirement for longer durations of single leg support during walking. These differences relate to constraints inherent to bipedal locomotion and many of the locomotor changes occurring in the first weeks after hatching may therefore be analogous to similar changes seen during human locomotor development.
The role of a single aspartate residue in ionic selectivity and block of a murine inward rectifier K+ channel Kir2.1.
Authors: Abrams C J , Davies N W , Shelton P A , Stanfield P R
Published: December 2014

1. The effects of Rb+ and Cs+ as blocking ions were investigated on wild‐type and mutant forms of the inward rectifier K+ channel, IRK1 (Kir2.1). 2. In wild‐type channels, Rb+ blockage was voltage dependent, increasing and then falling with increasing hyperpolarization. 3. Rb+ blockage was abolished by replacing Asp172 in the M2 domain of the pore‐forming subunit by Asn, but was re‐established by a change to Gln, narrowing the pore. Blocking affinity was reduced in D172Q, and was also reduced by replacing Gly168 in M2 by Ala. 4. Cs+ blockage was also abolished in D172N but was re‐established in D172Q. 5. There appears to be a balance between charge and pore size in determining whether ions block or permeate. A major part of the selectivity of Kir2.1 is associated with Asp172 in the M2 domain.
The possible role of nitric oxide in relaxations and excitatory neuroeffector transmission in the cat airway.
Authors: Tanaka H , Jing L , Takahashi S , Ito Y
Published: December 2014

1. To study the possible role of nitric oxide (NO free radical; NO) or NO‐containing compounds in the non‐adrenergic, non‐cholinergic (NANC) relaxations, we observed the effects of carboxy‐2‐phenyl‐4, 4, 5, 5‐tetramethyl‐imidazoline‐1‐oxyl‐3‐oxide (C‐PTIO; a newly synthesized NO scavenger) on NANC relaxations in the cat airway. In addition, we also observed the effects of C‐PTIO on excitatory junction potentials (EJPs), since NO has a prejunctional action on transmitter release. 2. Nitrosocystine (Cys‐NO) (10(‐7)‐10(‐3) M) dose‐dependently relaxed the bronchial tissue in the presence of 5‐HT, atropine and guanethidine and C‐PTIO (10(‐4) M) shifted the concentration‐response curve of the Cys‐NO to the right. 3. Electrical field stimulation (EFS) evoked biphasic NANC relaxations in the small bronchi of the cat. In general, C‐PTIO suppressed non‐selectively both the first and second components of the NANC relaxations to a similar extent. However, in some bronchial preparations C‐PTIO (10(‐4) M) selectively suppressed the first component of the NANC relaxation to approximately 50% of the initial value, enhancing the amplitude of the second component of the NANC relaxations. 4. After pretreatment of the bronchial tissues with alpha‐chymotrypsin (1 unit ml‐1) for 30 min in order to inhibit any response to peptides, EFS evoked monophasic NANC relaxation. C‐PTIO (10(‐5) ‐ 10(‐4) M) dose‐dependently suppressed, and at a concentration of 10(‐4) M almost halved, the amplitude of NANC relaxation. Additional application of L‐NAME further reduced the C‐PTIO‐resistant NANC relaxation to 20‐30% of the initial value. 5. C‐PTIO (10(‐4) M) enhanced the EJP amplitude evoked by single EFS in the trachea but not in the bronchi. However, C‐PTIO enhanced the summation of the EJPs to repeated stimulation to a similar extent in the tracheal and bronchial tissues. Simultaneous application of C‐PTIO and L‐NAME did not further enhance the summation. 6. These results indicate that NO. and NO‐containing compounds are involved in the L‐NAME‐sensitive NANC relaxation in the cat airway, and that only NO. has a prejunctional action which inhibits excitatory neuroeffector transmission.
Novel glial‐neuronal signalling by coactivation of metabotropic glutamate and beta‐adrenergic receptors in rat hippocampus.
Authors: Winder D G , Ritch P S , Gereau R W , Conn P J
Published: December 2014

1. We have previously reported that activation of group II‐like metabotropic glutamate receptors (mGluRs) in rat hippocampus results in a potentiation of the accumulation of cAMP elicited by activation of G‐protein Gs‐coupled receptors. This large increase in cAMP levels results in release of cAMP or a cAMP metabolite and depression of synaptic transmission at the Schaffer collateral‐CA1 pyramidal cell synapse through activation of A1 adenosine receptors. 2. Consistent with these studies, we report that antagonists of group II mGluRs block both the potentiation of cAMP accumulation elicited by activation of mGluRs and the depression of synaptic transmission induced by coactivation of mGluRs and beta‐adrenergic receptors. 3. In situ hybridization studies suggest that of the cloned group II mGluRs only mGluR‐3 mRNA is present in area CA1. Interestingly, mGluR‐3 appears to be present predominantly in glia in this region. Thus, we tested the hypothesis that mGluRs coupled to potentiation of cAMP accumulation were present on glia rather than neurons in area CA1. 4. The selective group II mGluR agonist 2S,1'R,2'R,3'R‐2(2,3‐dicarboxycyclo‐propyl)glycine (DCG‐IV) failed to enhance cAMP‐mediated electrophysiological responses to the beta‐adrenergic receptor agonist isoprenaline (Iso) in CA1 pyramidal cells, suggesting that mGluRs coupled to potentiation of cAMP accumulation may not be present in these cells. 5. Pre‐incubation of hippocampal slices with either of the selective glial toxins L‐alpha‐aminoadipic acid (L‐AA) or fluorocitrate (FC) blocked mGluR‐mediated potentiation of cAMP accumulation. However, L‐AA and FC had no discernible effects on viability of CA1 pyramidal cells, or cAMP‐mediated electrophysiological effects in these neurons. 6. Pre‐incubation of hippocampal slices with the neurotoxin kainate resulted in disruption of neuronal transmission and degeneration of neurons in area CA1, but had no effect on mGluR‐mediated potentiation of cAMP accumulation. 7. Pre‐incubation of hippocampal slices with the cAMP/cAMP metabolite transport blocker probenicid blocked the depression of synaptic transmission elicited by coapplication of Iso and DCG‐IV, while having no significant effect on cAMP accumulation elicited by these agonists. 8. Taken together, these data suggest that mGluRs coupled to potentiation of cAMP accumulation are present on glia rather than neurons in area CA1 of hippocampus. This suggests that a novel form of glial‐neuronal communication may exist, since activation of these mGluRs in concert with beta‐adrenergic receptors results in depression of synaptic transmission.
Reversible inactivations of the cerebellum prevent the extinction of conditioned nictitating membrane responses in rabbits.
Authors: Ramnani N , Yeo C H
Published: December 2014

1. Studies show that reversible inactivation of the anterior interpositus nucleus (AIP) of the cerebellum with muscimol (a GABAA agonist) prevents acquisition of the classically conditioned nictitating membrane response (NMR) in the rabbit. Here, we have used reversible inactivations of the AIP with muscimol to investigate the role of the cerebellum in the extinction of this response. 2. Experimental subjects were implanted with cannulae targeted to the AIP, through which muscimol could be infused via an injector cannula. This experiment was divided into three phases lasting 4 days, separated by 3 day intervals. Experimental and unoperated control subjects received acquisition training in phase 1; in phases 2 and 3 they received extinction training. 3. Presentation of the conditioned stimulus (CS) alone in phase 2 produced normal extinction in control subjects. Muscimol inactivation of the AIP in experimental subjects during phase 2 prevented extinction of conditioned responses (CRs), shown by initial high CR frequency in the first post‐drug session of phase 3, which then extinguished in a manner indistinguishable from controls in phase 2. 4. Our findings support the suggestion that similar cerebellar circuitry is engaged in acquisition and extinction of NMR conditioning.
A novel physiological function for platelet‐derived growth factor‐BB in rat dermis.
Authors: Rodt S A , Ahlén K , Berg A , Rubin K , Reed R K
Published: December 2014

1. The present experiments describe a role for platelet‐derived growth factor‐BB and cellular adhesion receptors towards extracellular matrix molecules (beta 1‐integrins) in control of interstitial fluid pressure (Pif). 2. Pif was measured in rat skin with sharpened glass capillaries (3‐7 microns) connected to a servocontrolled counter‐pressure system. 3. The collagen and laminin‐binding alpha 2 beta 1‐integrin is involved in the control of Pif since subdermal injection (5 microliters) of monoclonal hamster anti‐rat alpha 2 beta 1‐integrin IgG (anti‐alpha 2 beta 1) resulted in increased negativity of Pif. Control Pif averaged ‐0.88 +/‐ 0.23 mmHg (+/‐ S.D.) and decreased to ‐2.50 +/‐ 0.35 mmHg (P < 0.05) and ‐3.88 +/‐ 1.45 mmHg (P < 0.05) at anti‐alpha 2 beta 1 concentrations of 0.56 and 1.12 mg ml‐1, respectively. 4. The effect of anti‐alpha 2 beta 1 was abolished when platelet‐derived growth factor‐BB (PDGF‐BB) (200 ng ml‐1) was injected together with anti‐alpha 2 beta 1. 5. The time‐ and dose‐responses of PDGF‐BB to counteract increased negativity of Pif were studied further using dextran anaphylaxis as an experimental model inducing increased negativity of Pif in skin. Control Pif averaged ‐0.33 +/‐ 0.43 mmHg and fell to ‐4.10 +/‐ 1.47 mmHg within 10 min after dextran (P < 0.01). Subsequent subdermal injection of PDGF‐BB at 200 ng ml‐1 normalized Pif in 10‐20 min which became ‐1.37 +/‐ 1.23 mmHg (P < 0.01 versus dextran, P > 0.05 versus control). PDGF‐BB had little or no effect at 50 ng ml‐1. PDGF‐AA and basic fibroblast growth factor had no effect on Pif. 6. The in vivo function reported for PDGF‐BB has not been described previously and provides further evidence for active participation of connective tissue cells in control of Pif by altering tension on extracellular matrix structures.
Studies on the roles of ATP, adenosine and nitric oxide in mediating muscle vasodilatation induced in the rat by acute systemic hypoxia.
Authors: Skinner M R , Marshall J M
Published: December 2014

1. In Saffan‐anaesthetized rats, we have further investigated the mechanisms underlying the vasodilatation induced by adenosine in skeletal muscle by acute systemic hypoxia (breathing 8% O2 for 5 min). 2. In eleven rats the nitric oxide (NO) synthesis inhibitor nitro‐L‐arginine methyl ester (L‐NAME, 10 mg kg‐1, i.v.) reduced the increase in femoral vascular conductance (FVC) induced by hypoxia by approximately 50%. L‐NAME had similar effects on the increase in FVC induced by intra‐arterial (I.A.) infusion of adenosine (at 1.2 mg kg‐1 min‐1 for 5 min via the tail artery) and by ATP (I.A., 1 mg kg‐1 min‐1 for 5 min). Subsequent administration of the adenosine receptor antagonist 8‐sulphophenyl theophylline (8‐SPT, 20 mg kg‐1, i.v.) virtually abolished the adenosine‐ and ATP‐induced increase in FVC. 3. In a further nine rats, 8‐SPT reduced the increase in FVC induced by hypoxia by approximately 50%. This remaining increase in FVC was substantially reduced by L‐NAME. 4. In an additional nine rats, alpha,beta‐methyleneADP (160 micrograms kg‐1, i.v.) which inhibits the 5'‐ectonucleotidase that degrades AMP to adenosine, reduced the peripheral vasodilatation (fall in arterial blood pressure, ABP) induced by ATP infusion, but had no effect on the increase in FVC or decrease in ABP evoked by systemic hypoxia. 5. These results provide the first evidence that the muscle vasodilatation induced by adenosine during systemic hypoxia is mainly dependent on NO synthesis. They also suggest that adenosine is released as such rather than being formed extracellularly from AMP. Given evidence that extraluminal adenosine acts in an NO‐independent fashion we propose that hypoxia releases adenosine from the endothelium. Our results also indicate that hypoxia induces muscle vasodilatation that is adenosine independent but NO dependent: they allow the possibility that this is partly mediated by ATP released from the endothelium.
Membrane potentials and microenvironment of rat dorsal vagal cells in vitro during energy depletion.
Authors: Ballanyi K , Doutheil J , Brockhaus J
Published: December 2014

1. Brainstem slices were taken from mature rats. In the dorsal vagal nucleus (DVNX), membrane potentials (Em) of neurons (DVNs) and glia, as well as extracellular oxygen, K+ and pH (Po2, aKo, pHo), were analysed during metabolic disturbances. 2. Postsynaptic potentials of DVNs, elicited by repetitive electrical stimulation of the solitary tract (TS), led to a secondary glial depolarization of up to 25 mV, a fall in Po2 of up to 150 mmHg, a rise in extracellular aKo of up to 9 mM, and a fall in pHo of about 0.2 pH units. 3. Hypoxic superfusates produced tissue anoxia, leading to an aKo increase of less than 2 mM and a pHo fall of 0.24 +/‐ 0.04 pH units (mean +/‐ S.D.). Glucose‐free solution evoked, after a delay of more than 8 min, a slow rise in aKo of 1.9 +/‐ 0.8 mM, accompanied by a mean increase in pHo of 0.24 +/‐ 0.13 pH units. After pre‐incubation in glucose‐free solution, anoxia elevated aKo by up to 15 mM, whereas the anoxia‐induced pHo decrease was completely blocked. 4. In 45 of 118 DVNs, anoxia elicited a persistent hyperpolarization of 15.6 +/‐ 5.0 mV. In the remaining DVNs, anoxic exposure either did not produce a change in Em (37%) or led to a depolarization of less than 10 mV (25%). A stable depolarization of 9 +/‐ 3.8 mV was detected in glial cells during anoxia. Similar responses were revealed in oxygenated glucose‐free solution after a delay of 12‐60 min. 5. The metabolism‐related hyperpolarizations were blocked by 100‐500 microM tolbutamide or 20‐100 microM glibenclamide, leading to recovery of spontaneous (0.5‐6 Hz) spike discharge. In these cells, 400‐500 microM diazoxide evoked hyperpolarizations and blockade of spontaneous activity. 6. In DVNs and glial cells, a progressive depolarization of up to 40 mV in amplitude developed during anoxic exposure after pre‐incubation in glucose‐free solution. 7. The results show that oxygen or glucose depletion does not impair the viability of DVNX cells. The contribution of neuronal ATP‐sensitive K+ (KATP) channels to this tolerance is discussed.
Properties of the cAMP‐activated C1‐ current in choroid plexus epithelial cells isolated from the rat.
Authors: Kibble J D , Trezise A E , Brown P D
Published: December 2014

1. This study used whole‐cell patch clamp and RNA in situ hybridization experiments to determine whether the cAMP‐activated C1‐ current expressed in choroid plexus epithelial cells was carried by the cystic fibrosis transmembrane conductance regulator (CFTR) channel. 2. In patch clamp experiments, inclusion of 0.25 mM cAMP and 375 protein kinase A catalytic subunit (PKA) in the electrode solution caused activation of an inwardly rectifying current (21/23 cells). This current was C1‐ selective, since the current reversal potential (Erev) was ‐31 +/‐ 3 mV with equilibrium potential values for C1‐ (EC1) and Na+ (ENa) of ‐44 and 0 mV, respectively. 3. In anion substitution experiments, the relative anion permeability sequence for the inward rectifier was: I‐ (3.5) > HCO3‐(1.5) = C1‐(1.0) > Br‐(0.6) > aspartate (0.2). 4. The inward rectifier was sensitive to inhibition by a range of known channel inhibitors, including: glibenclamide (100 microns), DIDS (100 and 500 microns), NPPB (100 microns) and Ba2+ (1 mM). 5. In RNA in situ hybridization experiments, using two independent rat CFTR cRNA probes, expression of CFTR could not be detected in epithelial cells from the rat choroid plexus. 6. In conclusion, the cAMP‐dependent whole‐cell C1‐ current present in choroid plexus epithelial cells from the rat has properties which are distinctly different from those of CFTR.
In vivo human gastrocnemius architecture with changing joint angle at rest and during graded isometric contraction.
Authors: Narici M V , Binzoni T , Hiltbrand E , Fasel J , Terrier F , Cerretelli P
Published: December 2014

1. Human gastrocnemius medialis architecture was analysed in vivo, by ultrasonography, as a function of joint angle at rest and during voluntary isometric contractions up to the maximum force (MCV). maximum force (MVC). 2. At rest, as ankle joint angle increased from 90 to 150 deg, pennation increased from 15.8 to 27.7 deg, fibre length decreased from 57.0 to 34.0 mm and the physiological cross‐sectional area (PCSA) increased from 42.1 to 63.5 cm2. 3. From rest to MVC, at a fixed ankle joint angle of 110 deg, pennation angle increased from 15.5 to 33.6 deg and fibre length decreased from 50.8 to 32.9 mm, with no significant change in the distance between the aponeuroses. As a result of these changes the PCSA increased by 34.8%. 4. Measurements of pennation angle, fibre length and distance between the aponeuroses of the gastrocnemius medialis were also performed by ultrasound on a cadaver leg and found to be in good agreement with direct anatomical measurements. 5. It is concluded that human gastrocnemius medialis architecture is significantly affected both by changes of joint angle at rest and by isometric contraction intensity. The remarkable shortening observed during isometric contraction suggests that, at rest, the gastrocnemius muscle and tendon are considerably slack. The extrapolation of muscle architectural data obtained from cadavers to in vivo conditions should be made only for matching muscle lengths.
Role of Rho proteins in carbachol‐induced contractions in intact and permeabilized guinea‐pig intestinal smooth muscle.
Authors: Otto B , Steusloff A , Just I , Aktories K , Pfitzer G
Published: December 2014

1. The aim of this study was to determine whether the low molecular mass GTPase RhoA or related proteins are involved in carbachol‐ and high‐K(+)‐induced contractions in intact intestinal smooth muscle as well as the carbachol‐induced increase in Ca2+ sensitivity of the myofilaments in permeabilized preparations. 2. The carbachol‐induced increase in the Ca2+ sensitivity of force production in beta‐escin‐permeabilized intestinal smooth muscle was enhanced in preparations that were loaded with the constitutively active mutant of RhoA, Val14RhoA, and was inhibited by exoenzyme C3 from Clostridium botulinum, which ADP‐ribosylates and inactivates small GTPases of the Rho family. The effect of C3 on Ca2+ sensitivity in the absence of the agonist was negligible, while the maximal Ca(2+)‐activated force was inhibited by about 20%. 3. Inhibition of carbachol‐induced force was associated with an increase in ADP‐ribosylation of a protein band with a molecular mass of approximately 22 kDa, corresponding to Rho, and was partially reversed in the presence of Ile41RhoA, which is not a substrate for C3. Val14RhoA did not restore carbachol‐induced Ca2+ sensitization in C3‐treated smooth muscle. 4. In intact intestinal smooth muscle, toxin B from Clostridium difficile, which monoglucosylates members of the Rho family, inhibited high‐K(+)‐induced contractions and the initial phasic response to carbachol by about 30%. The delayed contractile response to carbachol was completely inhibited. 5. In smooth muscle preparations that were permeabilized with beta‐escin after treatment with toxin B, carbachol‐and GTP gamma S‐induced Ca2+ sensitization was significantly inhibited. 6. These findings are consistent with a role for Rho or Rho‐like proteins in agonist‐induced increase in Ca2+ sensitivity of force production in intact and permeabilized intestinal smooth muscle.
The magnitude of the initial injury induced by stretches of maximally activated muscle fibres of mice and rats increases in old age.
Authors: Brooks S V , Faulkner J A
Published: December 2014

1. Our purpose was to compare the susceptibilities of muscles in animals of different ages to the injuries induced by stretching the contracting muscle. Single stretches provide an effective method for studying the factors that contribute to the initiation of contraction‐induced injury. We hypothesized that, for maximally activated muscles in old compared with young or adult mice, the work input during a single stretch of any given strain is not different, but for a given work input the magnitude of the injury is greater. 2. The force deficit resulting from each single stretch was calculated as the decrease in the maximum isometric force expressed as a percentage of the maximum force prior to the stretch. Force deficits were compared 1 min after single stretches of in situ extensor digitorum longus (EDL) muscles of young, adult and old mice. In addition, measurements of force deficits immediately following single stretches of single permeabilized fibre segments from EDL muscles of young and old rats permitted investigation of the initial injury at the level of the contractile apparatus. 3. For maximally activated EDL muscles in young, adult and old mice, no differences were observed for the work input during stretches of any given strain. Furthermore, the relationships between the work and the resultant force deficit were not different for muscles in young and adult mice. In contrast, compared with the work‐force deficit relationships for muscles in either young or adult mice, the relationship was significantly steeper for muscles in old mice. For single permeabilized fibres from muscles of old rats, the force deficits immediately after single stretches were greater than those observed for fibres from muscles of young rats. We conclude that the increased susceptibility of muscles in old animals to contraction‐induced injury resides at least in part within the myofibrils.
A novel mechanism of activity‐dependent NMDA receptor antagonism describes the effect of ifenprodil in rat cultured cortical neurones.
Authors: Kew J N , Trube G , Kemp J A
Published: December 2014

1. Ifenprodil is a selective, atypical non‐competitive antagonist of NMDA receptors that contain the NR2B subunit with an undefined mechanism of action. Ifenprodil is neuroprotective in in vivo models of cerebral ischaemia but lacks many of the undesirable side‐effects associated with NMDA antagonist. 2. Using whole‐cell voltage‐clamp recordings, we have studied the mechanism of inhibition of NMDA‐evoked currents by ifenprodil in rat cultured cortical neurones in the presence of saturating concentrations of glycine. 3. Ifenprodil antagonized NMDA receptors in an activity‐dependent manner, whilst also increasing the receptor affinity for glutamate recognition‐site agonists. Ifenprodil inhibition curves against 10 and 100 microM NMDA‐evoked currents yielded IC50 values of 0.88 and 0.17 microM, respectively. Thus, the apparent affinity of ifenprodil for the NMDA receptor is increased in an NMDA concentration‐dependent manner. 4. Currents evoked by 0.3 and 1 microM NMDA were potentiated to approximately 200% of control levels in the presence of 3 microM ifenprodil. Thus, with increasing concentration of NMDA the effect of ifenprodil on NMDA‐evoked currents changed from one of potentiation to one of increasing inhibition. 5. These results are predicted by a reaction scheme in which ifenprodil exhibits a 39‐ and 50‐fold higher affinity for the agonist‐bound activated and desensitized states of the NMDA receptor, respectively, relative to the resting, agonist‐unbound state. Furthermore, ifenprodil binding to the NMDA receptor results in a 6‐fold higher affinity for glutamate site agonists. 6. This represents a novel mechanism of NMDA receptor antagonism that, together with the subunit selectivity, probably contributes to the attractive neuropharmacological profile of this and related compounds.
Mechanical efficiency and fatigue of fast and slow muscles of the mouse.
Authors: Barclay C J
Published: December 2014

1. In this study, the efficiency of energy conversion in skeletal muscles from the mouse was determined before and after a series of contractions that produced a moderate level of fatigue. 2. Initial mechanical efficiency was defined as the ratio of mechanical power output to the rate of initial enthalpy output. The rate of initial enthalpy output was the sum of the power output and rate of initial heat output. Heat output was measured using a thermopile with high temporal resolution. 3. Experiments were performed in vitro (25 degrees C) using bundles of fibres from fast‐twitch extensor digitorum longus (EDL) and slow‐twitch soleus muscles from mice. Muscles were fatigued using a series of thirty isometric tetani. Initial mechanical efficiency was determined before and again immediately after the fatigue protocol using a series of isovelocity contractions at shortening velocities between 0 and the maximum shortening velocity (Vmax). Efficiency was determined over the second half of the shortening at each velocity. 4. The fatigue protocol significantly reduced maximum isometric force Vmax, maximum power output and flattened the force‐velocity curve. The magnitude of these effects was greater in EDL muscle than soleus muscle. In unfatigued muscle, the maximum mechanical efficiency was 0.333 for EDL muscles and 0.425 for soleus muscles. In both muscle types, the fatiguing contractions caused maximum efficiency to decrease. The magnitude of the decrease was 15% of the pre‐fatigue value in EDL and 9% in soleus. 5. In a separate series of experiments, the effect of the fatigue protocol on the partitioning of energy expenditure between crossbridge and non‐crossbridge sources was determined. Data from these experiments enabled the efficiency of energy conversion by the crossbridges to be estimated. It was concluded that the decrease in initial mechanical efficiency reflected a decrease in the efficiency of energy conversion by the crossbridges.
Activation of midlumbar neurones by afferents from anterior hindlimb muscles in the cat.
Authors: Aggelopoulos N C , Bawa P , Edgley S A
Published: December 2014

1. It has been suggested that a group of interneurones located in the midlumbar segments of the spinal cord might play a role in switching from the stance to swing phases of the step cycle during locomotion. We have further examined the input to these neurones from proprioceptive afferents to test whether the connections to these cells are consistent with this role. 2. Electrical stimulation of group I and group II afferents in branches of the femoral nerve which supply iliopsoas, the major hip flexor muscle, excited a large majority of intermediate zone midlumbar interneurones which receive input from quadriceps group II afferents. The central latencies and properties of the EPSPs indicate that both group I and group II afferents from iliopsoas make monosynaptic connections with many midlumbar interneurones. 3. Group II afferents from both the ankle flexor tibialis anterior and the digit dorsiflexor extensor digitorum longus excited midlumbar interneurones. Similarly, they were also excited by group II afferents from both of the two main anatomical divisions of the sartorius muscle. 4. The frequent and potent excitation of midlumbar neurones from group I and II afferents in iliopsoas suggests that they may be excited at the end of the stance phase of the step when these muscles are stretched. This possibility is discussed in relation to recent work on the functional control of the step cycle.
cGMP‐mediated effects on the physiology of bovine and human retinal Müller (glial) cells.
Authors: Kusaka S , Dabin I , Barnstable C J , Puro D G
Published: December 2014

1. Whole‐cell currents of freshly dissociated or cultured Müller cells from human and bovine retinas were studied using the perforated‐patch and standard whole‐cell recording techniques. 2. We found that internal perfusion of cGMP or external exposure to 8‐bromo‐cGMP activated a calcium permeable, non‐selective cation current in Müller cells, the principal glial cells of the retina. In addition, the activity of calcium‐activated potassium channels increased markedly. These currents were minimally affected by cAMP. 3. Molecular studies using the reverse transcription‐polymerase chain reaction demonstrated that human müller cells in culture contain transcripts closely related to the rod cyclic nucleotide‐gated (CNG) channel. 4. Since guanylate cyclase is a known target for nitric oxide (NO), we tested the effect of NO donors on Müller cell currents. These agents induced currents that were qualitatively similar to those activated by cGMP. 5. Our experiments support the idea that the NO‐cGMP pathway regulates the physiology of Müller cells and may play a role in integrating neuron‐glia interactions in the retina.