bluuebunny/crossref_metadata_2025 huggingface dataset:
Reflex actions of one proprioceptor on the motoneurones of a muscle receptor and their central modulation in the shore crab.
Authors: Head S I , Bush B M
Published: December 2014

1. Reflex efferent control of a muscle stretch receptor by a joint proprioceptor of the same limb was studied in an isolated CNS preparation from the shore crab. The influence of ‘fictive locomotor’ activity on this interjoint reflex was also examined. 2. The thoracic‐coxal muscle receptor organ (TCMRO) and the coxo‐basal chordotonal organ (CBCO), which monitor movement and position of the first and second joints of the posterior leg, were isolated together with the whole thoracic ganglion complex. The TCMRO, functionally analogous to a mammalian muscle spindle, has two receptor motoneurones. RM1 innervating the receptor muscle alone and RM2 which also supplies the ‘extrafusal’ promotor muscle. The CBCO is a typical arthropod elastic strand organ, with many sensory neurones but lacking an efferent supply. The TCMRO was fixed at its mid‐length, and stretch‐hold‐release stimuli were applied to the CBCO. Efferent activity was recorded from the cut nerve roots of the four basal limb muscles and intracellularly as excitatory junction potentials (EJPs) from the receptor muscle. 3. A dynamic increase in the frequency of action potentials in RM1 occurred on both stretch and release of the CBCO. During the hold phase the RM1 activity declined from the dynamic response but remained elevated compared to the resting tonic discharge. RM2, identified by EJPs occurring 1:1 with a unit in the promoter nerve, responded in a similar way. 4. One or more promotor motoneurones were usually co‐activated with the two receptor efferents in response to input from the CBCO. In a typical example the average spike frequency of RM1 rose from 0 to 27 Hz during the dynamic phases (stretch and release) of the CBCO stimulus, falling to 2.5 Hz during the hold phase, while the corresponding promotor spike frequencies were 25 and 7.5 Hz, respectively. The other three muscle nerves recorded from generally also showed reflex driving by the CBCO. 5. The totally isolated thoracic ganglion could produce a rhythmic, bursting motor output in the absence of any sensory input. During this centrally generated activity the receptor motor innervation was strongly co‐activated with the promotor bursts, and the reflex input from the CBCO was overridden or modulated in a phase‐dependent manner. 6. The proximally directed interjoint reflex to the receptor muscle probably functions to maintain the tension on the sensory endings of the TCMRO, and so enable them to respond effectively at all times to movements of the basal leg joint.(ABSTRACT TRUNCATED AT 400 WORDS)
Inhibition of Ca(2+)‐activated K+ currents by intracellular acidosis in isolated type I cells of the neonatal rat carotid body.
Authors: Peers C , Green F K
Published: December 2014

1. K+ and Ca2+ currents were recorded from enzymatically isolated type I cells of the neonatal rat carotid body, using the whole‐cell configuration of the patch‐clamp technique. The effects of intracellular acidosis, caused by bath application of anions of weak acids (propionate and acetate), were tested on these currents. 2. Bath application of propionate or acetate (10 or 20 mM) caused reversible reductions in K+ current amplitudes. These effects were maximal at low, positive test potentials where a shoulder in the current‐voltage relationship occurs due to the activation of Ca(2+)‐activated K+ currents. 3. Time‐course studies showed propionate to cause a rapid initial reduction of K+ currents which recovered partially during its continued application. Removal of propionate produced small, transient overshoots of K+ current amplitudes. In the absence of propionate or acetate, bath application of the Na(+)‐H+ exchange inhibitor amiloride caused slowly developing inhibition of K+ current amplitudes. 4. Changing extracellular pH from 7.4 to 8.0 increased K+ current amplitudes, but at this pHo propionate caused smaller reductions in K+ currents than at a pHo of 7.4. 5. In the presence of 0.1 mM‐Cd2+, or in high‐Mg2+ (6 mM), low‐Ca2+ (0.1 mM) solutions, the residual, Ca(2+)‐independent K+ currents were unaffected by 20 mM‐propionate or acetate. 6. Ca2+ channel currents were also recorded, using 10 mM‐Ba2+ as the charge carrier. These sustained currents were completely abolished by 0.1 mM‐Cd2+ and were enlarged in the presence of 5 microM‐Bay K 8644, suggesting that the currents passed through L‐type Ca2+ channels. 7. Ca2+ channel currents were not significantly affected by intracellular acidosis caused by bath application of 10 mM‐propionate or acetate. They were also unaffected by a reduction of the extracellular pH from 7.4 to 7.0. 8. It is concluded that intracellular acidosis selectively inhibits Ca(2+)‐activated K+ currents in type I carotid body cells. The possible significance of this effect on chemotransduction in the intact carotid body is discussed.
C‐protein limits shortening velocity of rabbit skeletal muscle fibres at low levels of Ca2+ activation.
Authors: Hofmann P A , Greaser M L , Moss R L
Published: December 2014

1. Effects on maximum shortening velocity (Vmax) due to partial extraction of C‐protein were investigated in skinned fibres from rabbit psoas muscles. Up to 80% of endogenous C‐protein was extracted, as assessed by sodium dodecyl sulphate‐polyacrylamide gel electrophoresis (SDS‐PAGE) of fibre segments obtained before and after the extraction protocol. Vmax was obtained at 15 degrees C by measuring the times required to take up various amounts of slack imposed at one end of the fibre. 2. During maximal activation with Ca2+, Vmax in control fibres was 4.26 +/‐ 0.16 (mean +/‐ S.E.M., n = 7) muscle lengths per second (ML/s). Following extraction of approximately 40% of endogenous C‐protein, Vmax in these same fibres was 4.41 +/‐ 0.24 ML/s. 3. At sufficiently low levels of submaximal activation, high‐ and low‐velocity phases of unloaded shortening were observed. Partial extraction of C‐protein significantly increased Vmax in the low‐velocity phase but had no effect on the high‐velocity phase. The effect on low‐velocity Vmax was fully reversed by re‐addition of purified C‐protein. 4. At low levels of activation, the amount of shortening to the break‐point between the high‐ and low‐velocity phases was not significantly affected by C‐protein extraction. Under control conditions the average break‐point was 85.6 +/‐ 3.1 nm/half‐sarcomere, while 84.1 +/‐ 3.1 nm/half‐sarcomere was obtained following partial extraction of C‐protein. 5. These results are considered in terms of a model in which an internal load slows Vmax at low levels of activation once a given amount of active shortening has occurred. C‐protein may contribute to this internal load either by binding to actin and myosin or by influencing mechanical properties of myosin cross‐bridges.
The influence of charge on the effects of n‐octyl derivatives on sodium current inactivation in rat sensory neurones.
Authors: Elliott A A , Elliott J R
Published: December 2014

1. The whole‐cell patch‐clamp technique was used to determine the actions of n‐octyl sulphate (OS‐) anions and n‐octyl trimethylammonium (OTMA+) cations on sodium current steady‐state inactivation and peak amplitude in cells isolated from dorsal root ganglia of neonatal rats and maintained in short‐term tissue culture. This paper concentrates on the effects of external addition but the actions of internal OS‐ and OTMA+ are briefly considered. 2. The main action of external OS‐ was to cause a hyperpolarizing shift in the voltage dependence of the steady‐state inactivation parameter, h infinity. At 1‐6 mM OS‐ caused a shift in the mid‐point of the h infinity curve of around ‐30 mV. The shape of the h infinity curve was altered in a concentration‐dependent manner. Internal OS‐ had no discernible effect on the shape or position of the h infinity curve. 3. External OS‐ produced a relatively small (less than 25%) reduction in the maximum current achieved following pre‐pulses sufficiently negative to remove resting steady‐state inactivation. 4. By contrast, external OTMA+ had little effect on the voltage dependence of h infinity and produced a small, but significant, increase in the maximum sodium current. 2 mM‐external OTMA+ moved the mid‐point of the h infinity curve (Vh) 5 mV in the depolarizing direction (relative to the mean of control and reversal curves) and increased the maximum current by 13%. One millimolar internal OTMA+ induced a frequency‐dependent current block. 5. Raising the external calcium concentration from 2 to 20 mM (in the presence of 2 mM‐magnesium and 5 mM‐cobalt) caused an 18 mV depolarizing shift in Vh, consistent with a reduction in the negativity of an external surface charge. The maximum current was reduced by 22%. 6. One millimolar OS‐ reduced the surface potential of egg phosphatidylcholine (EPC) monolayers (at an air‐0.5 M‐NaCl interface) by 35 mV but 1 or 2 mM‐OTMA+ produced only a 2‐3 mV increase. The quantitative agreement between the effects of OS‐, on Vh in the rat and on monolayer surface potential, decreased with increasing concentration.(ABSTRACT TRUNCATED AT 400 WORDS)
Mechanisms of inhibition in cat visual cortex.
Authors: Berman N J , Douglas R J , Martin K A , Whitteridge D
Published: December 2014

1. Neurones from layers 2‐6 of the cat primary visual cortex were studied using extracellular and intracellular recordings made in vivo. The aim was to identify inhibitory events and determine whether they were associated with small or large (shunting) changes in the input conductance of the neurones. 2. Visual stimulation of subfields of simple receptive fields produced depolarizing or hyperpolarizing potentials that were associated with increased or decreased firing rates respectively. Hyperpolarizing potentials were small, 5 mV or less. In the same neurones, brief electrical stimulation of cortical afferents produced a characteristic sequence of a brief depolarization followed by a long‐lasting (200‐400 ms) hyperpolarization. 3. During the response to a stationary flashed bar, the synaptic activation increased the input conductance of the neurone by about 5‐20%. Conductance changes of similar magnitude were obtained by electrically stimulating the neurone. Neurones stimulated with non‐optimal orientations or directions of motion showed little change in input conductance. 4. These data indicate that while visually or electrically induced inhibition can be readily demonstrated in visual cortex, the inhibition is not associated with large sustained conductance changes. Thus a shunting or multiplicative inhibitory mechanism is not the principal mechanism of inhibition.
Effects of alpha‐melanocyte stimulating hormone on fever caused by endotoxin in rabbits.
Authors: Goelst K , Mitchell D , Laburn H
Published: December 2014

1. We measured the effect of intravenous and intracerebroventricular injections of alpha‐melanocyte stimulating hormone (alpha‐MSH) on changes in body temperature and serum iron concentration following i.v. injection of endotoxin in rabbits. 2. Intravenous alpha‐MSH (2.5 micrograms) significantly reduced both phases of endotoxin fever and attenuated the fall in serum iron concentration which follows endotoxin injection. 3. Intracerebroventricular alpha‐MSH (200 ng) reduced only the second phase of the fever and had no effect on the fall in the serum iron concentrations. 4. We conclude that alpha‐MSH, in doses that are known to inhibit endogenous pyrogen fever, inhibits the fever induced by endotoxin in rabbits, probably by blocking the actions of endogenous pyrogens mediating the endotoxin fever.
Nucleus tractus solitarii lesions alter the metabolic and hyperthermic response to central prostaglandin E1 in the rat.
Authors: Fyda D M , Cooper K E , Veale W L
Published: December 2014

1. Given that the nucleus tractus solitarii (NTS) may regulate the ability of brown adipose tissue to evoke non‐shivering thermogenesis and that brown fat may mediate the rise in whole‐body metabolism observed following central pyrogen administration, we assessed whether interruption of baroreceptor afferents coursing though the NTS would interfere with the ability of prostaglandin E1 to evoke a normal fever response profile. 2. Infusion of 150‐600 ng of prostaglandin E1 (PGE1) into a lateral cerebral ventricle of the conscious rat resulted in a rise in core temperature, and also an increase in whole‐body metabolic rate, brown adipose tissue temperature, arterial blood pressure and heart rate. 3. Following bilateral electrolytic lesions to the NTS, resting core and brown fat temperatures, metabolic rates, blood pressures and heart rates in the NTS‐lesioned animals were comparable to control rats. However, the PGE1‐evoked increase in metabolic rate, along with the rise in core and brown adipose tissue temperatures and heart rate were attenuated. The pressor response was, however, enhanced, possibly due to the demonstrated interference by the lesions with normal baroreflex control. 4. The findings suggest that the nucleus tractus solitarii region of the rats' brain may be important in mediating the thermogenesis evoked by central PGE1.
Effect of external Cd2+ and other divalent cations on carbachol‐activated non‐selective cation channels in guinea‐pig ileum.
Authors: Inoue R
Published: December 2014

1. Inhibitory actions of the external divalent cations, Cd2+, Ni2+, Mn2+ and Co2+ on carbachol (CCh)‐induced inward current (Ins,ACh) were investigated in caesium aspartate‐loaded single longitudinal smooth muscle cells of guinea‐pig ileum, using a rapid solution‐switching device, under voltage‐clamped conditions. 2. Cd2+ (20‐1000 microM), when added to the external solution, reduced Ins,ACh rapidly and reversibly. This effect occurred dose dependently, the relationship being adequately described by a Michaelis‐Menten equation with a Hill coefficient (n) of 1.0 and a dissociation constant (Kd) of 98 microM. 3. The inhibitory action of Cd2+ was associated neither with agonist concentration (CCh) nor with changes in reversal potential, and was voltage independent. 4. The appearance and removal of the effect of Cd2+ were both rapid (a few hundred milliseconds), in sharp contrast with a relatively slow time course of atropine or CCh action (of the order of seconds). 5. Other divalent cations (Ni2+, Mn2+, Co2+, Mg2+) applied externally also suppressed Ins,ACh, but less potently. The sequence of apparent potency was Cd2+ (98 microM) greater than or equal to Ni2+ (131 microM) much greater than Co2+ (700 microM) greater than or equal to Mn2+ (1000 microM) much greater than Mg2+ (approximately 10 mM). 6. External Ca2+ increased Ins,ACh dose dependently and antagonized the inhibitory effect of Cd2+. However, this effect may not be a simple competition with Cd2+. 7. These results show that external divalent cations strongly modulate Ins,ACh channels, possibly through direct interaction with the channel protein.
Optical detection of postsynaptic potentials evoked by vagal stimulation in the early embryonic chick brain stem slice.
Authors: Komuro H , Sakai T , Momose‐Sato Y , Hirota A , Kamino K
Published: December 2014

1. A voltage‐sensitive dye and multiple‐site optical recording of changes in membrane potential were used to reveal the postsynaptic potentials in the early embryonic chick brain stem slice preparation. 2. Vagus‐brain stem preparations were isolated from 8‐day‐old chick embryos and then transverse slice preparations were prepared with both the right and left vagus nerve fibres intact. The slice preparations were stained with a voltage‐sensitive merocyanine‐rhodanine dye (NK2761). 3. Voltage‐related optical (absorbance) changes evoked by vagus nerve stimulation with positive square current pulses using a suction electrode were recorded simultaneously from 127 contiguous loci in the preparation, using a 12 x 12‐element photodiode array. Optical responses appeared in a limited area near the dorsal surface of the stimulated side. 4. When relatively large stimulating currents were applied, optical changes having two (or sometimes three) components were recorded. One component was the fast spike‐like signal and another the delayed, long‐lasting slow signal. 5. The size of the slow signal was decreased by continuous stimulation, reduced by low external calcium ion concentrations and eliminated in the presence of manganese or cadmium ions. 6. The slow signals were eliminated in the presence of kynurenic acid, and they were reduced by 2‐APV (DL‐2‐amino‐5‐phosphono‐valeric acid) and by CNQX (6‐cyano‐7‐nitroquinoxaline‐2,3‐dione). We conclude that the slow signals correspond to excitatory postsynaptic potentials which are glutamate mediated.
Electrophysiological and immunohistochemical analysis of muscle differentiation in a mouse mesodermal stem cell line.
Authors: Kubo Y
Published: December 2014

1. A mesodermal stem cell line C3H10T1/2 was induced to differentiate to muscle by adding 0.3 microM‐5‐aza‐2'‐deoxy‐cytidine to the medium for 24 h. The changes in membrane currents during differentiation were studied by whole‐cell recording and changes in the expression of fibronectin, Neural Cell Adhesion Molecule (NCAM), myosin and desmin were studied immunohistochemically. 2. The stem cells showed the morphology of fibroblastic cells. Most of the stem cells showed ATP‐induced slow K+ current. T‐type Ca2+ current and inward rectifier K+ current were observed in 19% of the stem cells. The stem cells expressed fibronectin, but not NCAM, myosin or desmin. 3. About 2 weeks after the addition of 5‐aza‐2'‐deoxy‐cytidine, large multinucleated skeletal muscle‐like cells appeared. Most of the induced muscles showed L‐type Ca2+ current, responses to acetylcholine, outward K+ current, inward rectifier K+ current and contraction upon depolarizing stimulation. They expressed NCAM, myosin and desmin, but not fibronectin, and showed no ATP response. 4. In some batches (2/14), the induced muscles showed spontaneous twitches, and possessed tetrodotoxin (TTX)‐sensitive Na+ current in addition to the currents described above. Furthermore clear striation was observed in some of the twitching muscles under Nomarski optics. 5. To ascertain the properties of cells at the initial step of muscle differentiation, whose differentiation is determined but not yet evident morphologically or electrophysiologically, subcloning was performed from the heterogeneous cells 10 days after induction. Three myogenic clones were obtained, which proliferated at low cell densities but differentiated to muscle with a high incidence at high cell densities, as well as ten non‐myogenic clones. 6. Most myogenic clones still showed ATP‐induced K+ current and fibronectin. In addition, most of them showed T‐type Ca2+ current and inward rectifier K+ current. They had already expressed NCAM. No other properties observed in muscles had yet been expressed. Most cells of the non‐myogenic clones showed ATP‐induced K+ current and fibronectin. T‐type Ca2+ current was also expressed, but not inward rectifier K+ current or NCAM. 7. The properties of the observed ionic currents were studied. The TTX‐sensitive Na+ current could be completely blocked by 0.1 microM‐TTX. It could be evoked by depolarizing steps to a level above ‐40 mV, while steady‐state inactivation was detectable around ‐75 mV and reached half by ‐52 mV. T‐type Ca2+ current could be evoked by a depolarizing pulse to a level above ‐45 mV, with a maximum amplitude around ‐15 mV.(ABSTRACT TRUNCATED AT 400 WORDS)
The effect of analogues of angiotensin II on drinking and cardiovascular responses to central angiotensin II in the rat.
Authors: Camargo L A , De Luca L A , Menani J V , Renzi A , Saad W A , Saad W A , Silveira J E
Published: December 2014

1. Intracerebroventricular (I.C.V.) infusion (60 ng h‐1) of Isoleu5‐angiotensin II (Isoleu5‐‐AngII) and des‐amine‐angiotensin II (des‐amine‐AngII) in rats caused increased drinking behaviour and an increase in arterial blood pressure. 2. Des‐amine‐AngII caused similar increases in heart rate and arterial blood pressure as AngII. 3. Previous I.C.V. injection of the antagonists [Leu8]‐AngII, des‐amine‐[Leu8]‐AngII and octanoyl‐[Leu8]‐AngII prevented the increases in heart rate and blood pressure produced by I.C.V. infusion of AngII and caused partial reduction of the dipsogenic response. 4. The three antagonists had no effect on the increase in arterial blood pressure and heart rate caused by des‐amine‐AngII. The drinking response was reduced by previous injection of [Leu8]‐AngII and des‐amine‐[Leu8]‐AngII but not by octanoyl‐[Leu8]‐AngII. 5. In conclusion, Isoleu5‐AngII and des‐amine‐AngII increase drinking behaviour, arterial blood pressure and heart rate when infused into the cerebral ventricle of rats. The study with the antagonists showed that des‐amine‐AngII probably binds more strongly to AngII‐receptors.
Renovascular effects of neuropeptide‐Y in the split hydronephrotic rat kidney: non‐uniform pattern of vascular reactivity.
Authors: Dietrich M S , Fretschner M , Nobiling R , Persson P B , Steinhausen M
Published: December 2014

1. The renovascular effects of neuropeptide‐Y (NPY) were examined in the split hydronephrotic rat kidney. 2. Systemic infusion of low non‐pressor doses of NPY (0.2 micrograms kg‐1 up to 5.0 micrograms kg‐1) produced a non‐uniform pattern of vascular reactivity. In general, a significant constriction of the proximal and distal arcuate artery was seen at all doses. No constriction was seen at the interlobular artery or the larger part of the afferent arteriole. These segments initially dilated during the lower dose infusions. The very distal part of the afferent arteriole adjacent to the glomerulus and the proximal efferent arteriole responded in a similar way to the arcuate arteries. 3. NPY, locally applied into the tissue bath at concentrations of 1 nmol l‐1 up to 25 nmol l‐1, produced non‐uniform vascular reactions similar to those of intravenously infused NPY. At the considerably higher local dosage of 1.14 mumol l‐1, all vascular segments revealed vasoconstriction. 4. NPY application did not attenuate effects of acetylcholine. This observation suggests that the mechanism of NPY‐induced vasoconstriction does not rely upon antagonism of endothelium‐derived vasodilatation. 5. The pattern of vascular reactivity to NPY was substantially different from that known for the vasoconstrictors noradrenaline and angiotensin II in our preparation.
Paroxysmal inhibitory potentials mediated by GABAB receptors in partially disinhibited rat hippocampal slice cultures.
Authors: Scanziani M , Gähwiler B H , Thompson S M
Published: December 2014

1. Intracellular recording techniques were used to study synaptic potentials in CA3 pyramidal cells elicited with mossy fibre stimulation in partially disinhibited hippocampal slice cultures. Two experimental protocols were used: (1) high concentrations (20‐40 microM) of the A‐type gamma‐aminobutyric acid (GABAA) receptor antagonist bicuculline plus low concentrations (2‐4 microM) of the glutamate receptor antagonist 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX), or (2) low concentrations (1‐2.5 microM) of bicuculline alone. 2. Under the first condition, stimulation of mossy fibre afferents evoked epileptic bursts alternating with a response consisting of an excitatory postsynaptic potential (EPSP) followed by an unusually large and long‐lasting hyperpolarizing potential with a maximal amplitude in the range of ‐30 mV from the resting membrane potential. 3. This paroxysmal inhibitory potential (PIP) had a reversal potential near that of potassium. The amplitude of the PIP was not dependent on action potentials superimposed on the preceding EPSP, and was present in cells recorded with microelectrodes containing the Ca2+ chelator EGTA. These data suggest that the PIP is not a Ca(2+)‐activated K+ potential. 4. The PIP was prolonged by the GABA‐uptake blocker nipecotic acid, was reduced by hyperpolarizing interneurons with the opioid agonist FK 33‐824, and was abolished by the GABAB‐receptor antagonist CGP 35 348. These data indicate that the PIP is mediated by the activation of GABAB receptors following GABA release from interneurons. 5. The NMDA‐receptor antagonist D‐2‐amino‐5‐phosphonovalerate (D‐APV) strongly reduced the amplitude of the PIP, but had no effect on the GABAB receptor‐mediated inhibitory postsynaptic potential (IPSP) under control conditions. 6. Under the first condition, regular stimulation elicited a cyclical pattern of evoked responses. There was either an alternation between an epileptic burst and a PIP or, at shorter interstimulus intervals, a sequence of gradually increasing PIPs followed by an epileptic burst, which then reset the cycle. 7. Under the second condition, in low concentrations of bicuculline alone, the early GABAA‐mediated IPSP was little affected, but the late GABAB‐mediated IPSP was greatly enhanced. These enhanced late IPSPs were comparable in amplitude and duration to the PIPs seen under the first conditions, could exhibit cyclical behaviour, and were reduced by D‐APV. 8. Application of CGP 35 348 abolished the late IPSP under control conditions, but had no effect on hippocampal excitability. In contrast, CGP 35 348 blocked the PIP elicited in low bicuculline, and consequently led to intense epileptic discharge.(ABSTRACT TRUNCATED AT 400 WORDS)
Pavlovian conditioning in the rabbit during inactivation of the interpositus nucleus.
Authors: Welsh J P , Harvey J A
Published: December 2014

1. We have examined the role of the anterior interpositus nucleus (AIP) of the cerebellum in Pavlovian conditioning of the nictitating membrane response (NMR) of the rabbit with the use of reversible brain lesions produced by the local anaesthetic lidocaine. Previous experiments have demonstrated that destructive lesions of the AIP prevent the performance of conditioned NMRs (CRs). Microinjections of lidocaine into the AIP were used in the present experiment to determine whether the deficit in the performance of CRs resulted from a deficit in learning or memory. 2. A 3‐phase procedure was employed to determine whether associative learning required the function of the AIP. In phase 1, rabbits were trained to make CRs to a flashing‐light conditioned stimulus (CS) that was paired with an air‐puff unconditioned stimulus (UCS) directed at the cornea. In phase 2, the AIP was anaesthetized during a session of conditioning in which a tone CS was paired with the UCS. Presentations of the light CS were interpolated throughout the tone conditioning in order to monitor the degree to which CRs were impaired by lidocaine. Phase 3 occurred after the effects of the lidocaine had dissipated and consisted of a test of retention to determine whether learning occurred during phase 2 but could not be expressed because of a performance deficit resulting from the inactivation of the AIP. 3. Infusion of lidocaine into the AIP abolished CRs to the light CS and prevented the performance of CRs to the tone CS in phase 2. The effect of the infusion was specifically due to a conduction block of neurons and/or fibres in the lateral aspect of the AIP. The infusion of lidocaine into regions surrounding the AIP did not affect CRs elicited by the light CS or prevent acquisition of CRs to the tone. Infusions of saline directly into the AIP did not impair the performance of CRs to either the tone or light CS. Quantitative analysis of diffusion revealed that the abolition of CRs was accompanied by anaesthetization of the AIP. 4. The retention test in phase 3 indicated that learning occurred normally during phase 2 when the AIP was inactivated and performance was abolished. When the function of the AIP was restored and performance had recovered, the subjects demonstrated a frequency of CRs to the tone CS that was indistinguishable from control subjects whose performance had never been impaired. 5. The CRs observed during the retention test provided an unequivocal measure of associative learning.(ABSTRACT TRUNCATED AT 400 WORDS)
Effects of extracellular pH, PCO2 and HCO3‐ on intracellular pH in isolated type‐I cells of the neonatal rat carotid body.
Authors: Buckler K J , Vaughan‐Jones R D , Peers C , Lagadic‐Gossmann D , Nye P C
Published: December 2014

1. The effects of changing PCO2 extracellular pH (pHo) and HCO3‐ on intracellular pH (pHi) were studied in isolated neonatal rat type‐I carotid body cells using the pH‐sensitive fluoroprobe, carboxy‐SNARF‐1. 2. Simulated respiratory acidosis and alkalosis (i.e. changes in PCO2 at constant HCO3‐) led to rapid (half‐time t0.5 = 3 s) monotonic changes in pHi. The relationship between pHi and pHo under these conditions was linear, steep (0.63 pHi/pHo) and remarkably similar to the response predicted from a passive cell model (i.e. a cell lacking pHi regulation). 3. In order to model the above pHi changes (point 2), it was necessary to determine beta i (intrinsic intracellular buffering power). By using small incremental acid loads in the cell (progressive [NH4+]o removal), beta i was determined as a function of pHi to be: beta i = 127.6‐16.04 pHi. 4. Changes in PCO2 at constant pHo (i.e. simultaneously changing HCO3‐) caused rapid transient changes in pHi but did not significantly affect steady‐state pHi over the range 1‐10% CO2. 5. When PCO2 was held constant (5%), changing HCO3‐ and thus pHo (i.e. a simulated metabolic acidosis/alkalosis) led to much slower changes in pHi (t0.5 approximately 1 min). Steady‐state pHi showed an almost identical dependence on pHo (slope 0.68) to that found for simulated respiratory acidosis/alkalosis. Therefore, over the range of pHo, PCO2 and [HCO3‐]o tested, steady‐state pHi appeared to be a unique function of pHo and independent of PCO2 and [HCO3‐]o. 6. The effects on pHi of respiratory acidosis, metabolic acidosis and increases of PCO2 at constant pHo (present work) were compared with previously published work on the ability of similar manoeuvres to increase the carotid sinus nerve (CSN) discharge rate. The two sets of data showed several striking similarities: (i) in both cases, the response to a respiratory acidosis was rapid in onset, maintained and reversible; (ii) in both cases, the speed of response to a metabolic acidosis was significantly slower than in (i) but, again, it was maintained and reversible; (iii) in both cases, increases in PCO2 at constant pHo elicited a rapid response but one which was only transient with no change in the steady‐state value. 7. The close correlation between the effects of changing pHo, PCO2 and [HCO3‐]o on pHi and on CSN discharge suggests that a change in type‐I cell pHi is the first step in the chemoreception of blood pH by the carotid body.(ABSTRACT TRUNCATED AT 400 WORDS)
Mechanism of extracellular ATP‐induced increase of cytosolic Ca2+ concentration in isolated rat ventricular myocytes.
Authors: Christie A , Sharma V K , Sheu S S
Published: December 2014

1. Changes in the cytosolic Ca2+ concentration ([Ca2+]i) of isolated rat ventricular myocytes in suspension were measured in response to extracellular ATP using the fluorescent Ca2+ indicators Quin‐2 and Fura‐2. 2. ATP produced a concentration‐, time‐ and Mg(2+)‐dependent, biphasic increase of [Ca2+]i whereas slowly hydrolysable ATP analogues produced a slow, monophasic increase of [Ca2+]i and the non‐hydrolysable ATP analogues were without effect. 3. Extracellular Ca2+ was required for the ATP‐induced increase of [Ca2+]i and pre‐treatment of the cells with caffeine, ryanodine, verapamil or nimodipine partially inhibited the [Ca2+]i increase. 4. Whole‐cell patch‐clamp experiments revealed that ATP activated an ionic current that had a linear current‐voltage relationship with a reversal potential near O mV. Quinidine, a putative P2 purinergic receptor blocker, abolished the ATP‐activated current. The ATP‐activated current was Mg2+ dependent. 5. Associated with the ATP‐activated current was cellular depolarization. In a physiological solution, ATP depolarized cells to the threshold for the firing of action potentials. In the presence of the voltage‐activated ion channel blockers tetrodotoxin, 4‐aminopyridine, caesium and nitrendipine, ATP depolarized cells to ‐44 +/‐ 6 mV from a resting potential of ‐66 +/‐ 4 mV (n = 11). 6. Sodium dodecyl sulphate (SDS) polyacrylamide gel electrophoresis and autoradiography demonstrated that extracellular ATP stimulated the phosphorylation of several extracellular membrane‐bound proteins. The phosphorylation of these proteins was concentration, time and Mg2+ dependent. Pre‐treatment of cells with the slowly hydrolysable ATP analogues inhibited the ATP‐induced phosphorylation. Adenosine 5'‐O‐3‐thiotriphosphate (ATP gamma S) thiophosphorylated proteins with the same apparent molecular weight as the proteins phosphorylated by ATP. 7. These results suggest that the ATP‐induced increase of [Ca2+]i is a result of the activation, possibly by protein phosphorylation, of a novel ion channel carrying inward current. The ATP‐activated channel may be permeable to Na+ and Ca2+ and causes [Ca2+]i to rise. More importantly, this inward current depolarizes the cell to the threshold of inducing spontaneous firing of action potentials. The firing of action potentials results in the influx of Ca2+ through L‐type Ca2+ channels which would trigger Ca2+ release from the sarcoplasmic reticulum and lead to the increase in [Ca2+]i.
The effect of intracellular pH on ATP‐dependent potassium channels of frog skeletal muscle.
Authors: Davies N W , Standen N B , Stanfield P R
Published: December 2014

1. We have used patch‐clamp methods to study the effects of pH at the cytoplasmic surface of the membrane on ATP‐dependent K+ channels (KATP channels) in patches excised from frog (Rana temporaria) skeletal muscle, and to study the kinetics of ATP binding. 2. In the absence of ATP, a reduction in pH led to a slight decrease in single‐channel current amplitude, an increase in the number of very brief closings, an increase in the apparent mean open time, and an increase in burst duration. After correction for missed closings, the change in mean open time was slight. Despite these changes in detailed kinetics, the channel open‐state probability, Popen, changed little with changes in pH in the absence of ATP. 3. In the presence of ATP, a decrease in internal pH (pHi) reduced the degree of channel inhibition by ATP, shifting the curve relating Popen and [ATP] to higher concentrations of ATP without altering its steepness. The ATP concentration for half‐inhibition of channel activity (Ki) was 17 microM at pH 7.2 and 260 microM at pH 6.3. 4. The effect of pH could be modelled by assuming that one or two protons bind to the channel and prevent ATP binding to exert its effect of causing channel closure. The predicted dissociation constants for ATP and H+ respectively were 5.4 and 0.11 microM. 5. The rate constants for binding and unbinding of ATP were estimated from the dependence of the mean open time on [ATP] and from the Ki. The apparent rate constants for ATP binding were 0.6 and 0.04 mM‐1 ms‐1 at pH 7.2 and 6.3 respectively, while the rate constant for unbinding was 0.01 ms‐1. In terms of our model the calculated true rate constant for ATP binding was 1.85 mM‐1 ms‐1. ATP binding also led to a reduction in burst duration. 6. The effect of pH described here differs from findings in cardiac muscle and pancreatic B‐cells. The results are discussed in relation to the possible function of KATP channels in skeletal muscle during exercise.
Fetal breathing, sleep state and cardiovascular adaptations to anaemia in sheep.
Authors: Matsuda K , Ducsay C , Koos B J
Published: December 2014

1. In unanaesthetized fetal sheep (greater than 0.8 term) prolonged anaemia initially reduced the incidences of low‐voltage electrocortical activity, rapid eye movements and breathing activity; but the incidence of each returned to normal within 4‐7 h. 2. Anaemia induced a persistent rise in fetal heart rate and plasma concentrations of adrenaline, noradrenaline and cortisol. 3. After 16 h the fetal haematocrit was returned to normal. Isocapnic hypoxia induced less than 1 h later also inhibited eye and breathing activity. 4. After 1 h fetal arterial PO2 (Pa,O2) was returned to normal. This rise in O2 tension was associated with an elevation in the incidence of low‐voltage electrocortical activity, eye movements and breathing. Breathing movements also occurred during high‐voltage electrocortical activity. 5. It is concluded that the brain PO2 set‐point for hypoxic inhibition adapts rapidly to alterations in O2‐carrying capacity and is probably due to changes in the concentration and/or receptor affinity of a central neuromodulator. Secondly, a rise in brain PO2 at birth may contribute to the onset of continuous breathing.
The stimulus interval‐tension relation in enzymatically isolated single myocytes of the frog heart.
Authors: Cecchi G , Colomo F , Poggesi C , Tesi C
Published: December 2014

1. Apparatus for recording the small tensions developed by electrically stimulated single intact myocytes of frog heart is described. A laser‐light optoelectronic transducer was used. The compliance of the force probes was 10‐20 nm/nN, with a frequency response of 600‐900 Hz in Ringer solution. The myocyte shortening during an ordinary twitch contraction was no greater than 1% of the slack length. The overall sensitivity of the transducer system was 5‐10 mV/nN, with a total noise of 0.5‐1 nN peak to peak. The experiments were performed at 20‐23 degrees C on either atrial or ventricular myocytes at 2.15‐2.2 microns sarcomere length, in 1 mM‐Ca2+ Ringer solution. 2. Isoprenaline (5 microM), increases in external Ca2+ concentration ([Ca2+]o), and shortening of stimulus interval potentiated the myocyte twitch tension. The dependence of twitch characteristics on these inotropic interventions for all the atrial and ventricular myocytes tested was comparable to that of multicellular preparations under similar experimental conditions. This implies that the enzymatic isolation procedure had not altered the physiological properties of the myocytes. 3. The stimulus interval‐tension relation for premature twitches of atrial and ventricular myocytes showed (i) a very steep rising phase in the region of intervals just longer than 0.52 and 0.66 s (the duration of the mechanical refractoriness in atrial or ventricular cells), (ii) a peak, at intervals of 0.7‐0.8 s, where the twitch tension was strongly potentiated compared to that of the controls, and (iii) as the stimulus interval was further increased, a progressive return to the control level. The stimulus interval‐tension relation for steady‐state conditions exhibited similar characteristics. 4. The degree of tension potentiation by isoprenaline was greater in the controls than in the earliest test twitches. The result was that the stimulus interval‐tension relations for isoprenaline‐treated myocytes showed a gentler rise and a lower peak than for untreated cells. 5. The stimulus interval‐tension relation of the heart is a basic property of its cells. It is related to changes in the activation level. The higher the activation level reached in control twitches, the lower the stimulus interval‐dependent potentiation capability.
Marked splenic hyperaemia during post‐haemorrhagic hypotension in the rat, rabbit and cat.
Authors: Iversen P O , Benestad H B , Nicolaysen G
Published: December 2014

1. The regulation of the splenic perfusion during normal and pathological conditions is incompletely understood. We studied the time course of splenic blood flow during the initial (0‐24 h) development of haemorrhagic anaemia in awake and anaesthetized rats, as well as in awake rabbits and cats. Another group of rats had either normovolaemic anaemia or beginning polycythaemia. 2. The microsphere method was used to measure splenic blood flow. The awake rats were rendered anaemic either by a heavy (1.5% of body weight) or a moderate (0.7% of body weight) bleeding (hypovolaemia), by haemolysis (normovolaemia) or by bleeding (1.5% of body weight) followed by transfusion of autologous plasma (normovolaemia). Polycythaemia was induced with injections of erythropoietin. The anaesthetized rats as well as the awake rabbits and cats were also bled heavily (1.5% of body weight). 3. In awake rats, splenic blood flow increased to 215% of control within the first 5 min after bleeding. The perfusion declined nearly to baseline over the next 24 h. A similar, but less prominent splenic hyperaemia was detected in the awake rabbits and cats. However, this hyperaemic response was not detected in the normovolaemic, the polycythaemic or the anaesthetized and bled rats. 4. Administration of the adrenergic beta‐blocking agent propranolol prior to bleeding significantly attenuated the splenic hyperaemia in the awake rats, while the alpha‐blocking agent phentolamine or the cholinergic blocking agent atropine had no effect. 5. Concomitant with the initial increase in splenic perfusion, cardiac output increased to 123% of control in the awake, heavily bled rats. In the bled, anaesthetized rats cardiac output decreased to 91% of control 5 min after bleeding. A decrease in cardiac output to 64 and 70% of control was observed in the awake rabbits and cats, respectively. 6. Immediately following the bleeding, we noticed a substantial release of platelets from the rat spleen. 7. It appears that a heavy acute blood loss in awake rats, rabbits and cats elicits a marked reduction in splenic vascular tone, perhaps mediated by beta‐adrenergic receptor activity. Anaesthesia abolished this response in rats. Possibly, the induced hypovolaemia triggered an accelerated release of platelets from the rat spleen, dependent on an augmented splenic blood flow.
Barium‐ or quinine‐induced depolarization activates K+, Na+ and cationic conductances in frog proximal tubular cells.
Authors: Discala F , Belachgar F , Planelles G , Hulin P , Anagnostopoulos T
Published: December 2014

1. Frog proximal tubular cells were fused into giant cells. We measured membrane potential (Vm), its changes (delta Vm), and current‐induced voltage changes (delta psi) in single cells, during control and experimental states. Each cell served as its own control. 2. In the presence of a physiological Ringer solution, the transference number for potassium (tK) was 0.50. Barium (3 mM) reduced membrane conductance (Gm) by 50%; low‐Cl‐ solutions and low‐Na+ solutions also diminished Gm, by 52 and 30%, respectively. The association of barium and low‐NaCl solutions decreased Gm to approximately 38% of control, indicating that the impermeant substitute of a physiological ion may interact with other pathways; alternatively, blockade of steady‐state conductances may activate physiologically silent processes. 3. In an attempt to enhance the contribution of the partial K+ conductance (GK) to Gm, fused cells were exposed to low‐Cl‐ solutions, containing in addition 0.1 mM‐methazolamide, to inhibit the rheogenic Na(+)‐HCO3‐symport, and 1 microM‐amiloride, to block Na+ conductance (GNa). tK went up to 0.83. 4. The high tK preparation was challenged with barium (3 mM) or quinine (Quin, 1 mM). These blockers produced large depolarizations (approximately 60 mV), however, although Gm decreased along early‐ and mid‐depolarization, Gm plateaued and eventually it increased with larger and larger depolarization. 5. Depolarization‐associated increase in Gm reflects activation of other conductances. These are Na+, cationic, and K+ conductance(s) poorly sensitive to quinine or barium. In the presence of Ba(2+)‐ or Quin‐induced depolarization, injection of depolarizing current produces delayed increase in conductance. 6. Depolarization‐induced activation of cationic conductance (Gcat) and GNa results in enlargement of the K+ electrochemical potential difference, to about 70 mV; this difference allows recycling of K+ ions outwards, since a GK is still detected and may contribute up to 38% of the total conductance.
Projections of group II‐activated midlumbar spinocerebellar tract neurones to the region of nucleus Z in the cat.
Authors: Asif M , Edgley S A
Published: December 2014

1. The possibility that dorsal horn spinocerebellar tract neurones in the midlumbar segments of the cat spinal cord which convey information from hindlimb group II muscle afferents to the cerebellum send collateral projections to medulla in the region of nucleus Z has been examined. 2. Dorsal horn spinocerebellar tract neurones (n = 25) were identified by antidromic activation from the cerebellum and by synaptic activation following stimulation of hindlimb group II afferents. A high proportion (21/25) were also antidromically activated by stimuli delivered to the region of nucleus Z. 3. The results of collision tests between antidromic spikes evoked from the cerebellum and the medulla and the fact that the latency for antidromic activation from nucleus Z at threshold was greater than from the cerebellum indicates that at least 11/25 (44%) of the neurones had collateral projections to the medulla. 4. Antidromic threshold mapping revealed that some of the neurones could be activated from parts of the dorsal medulla adjacent to, but not directly overlying, nucleus Z. The possible relevance of these data with regard to sensation of lower limb position and motion is discussed.
Convergence of descending and various peripheral inputs onto common propriospinal‐like neurones in man.
Authors: Burke D , Gracies J M , Mazevet D , Meunier S , Pierrot‐Deseilligny E
Published: December 2014

1. The patterns of excitation and convergence by peripheral afferents on propriospinal‐like neurones projecting to forearm flexor carpi radialis (FCR) motoneurones in human subjects were determined at rest and during various voluntary contractions, using H reflex testing. 2. At rest, the FCR H reflex could be facilitated by mixed nerve (ulnar, musculocutaneous) and cutaneous (afferents from both sides of the hand) inputs. The characteristics of this facilitation (low threshold, long central latency, short duration) were compatible with those of the propriospinal‐like system. Quantitatively this facilitation was rare and weak. 3. Voluntary contraction increased the extent of the propriospinal‐like facilitation of the FCR H reflex. It is shown in the companion paper (Burke, Gracies, Meunier & Pierrot‐Deseilligny, 1992) that this increase results not from a decrease in presynaptic inhibition of afferents to propriospinal‐like neurones, but from increased excitation of these neurones. It is argued that at the onset of contraction this excitation is purely descending in origin, whereas the contraction‐induced afferent discharge is probably the major factor during weak tonic contraction. 4. The distribution of the increased facilitation of the FCR H reflex depended on the muscles involved in the contraction: ulnar nerve‐evoked facilitation was increased much more at the onset of voluntary wrist flexion than voluntary elbow flexion, and vice versa for the musculo‐cutaneous‐induced facilitation. This finding is consistent with the view that there are subsets of propriospinal‐like neurones, specialized with regard to afferent input, and indicates that descending excitation is directed preferentially to the subset of neurones which receives excitatory feedback from the contracting muscle. 5. To investigate the convergence of different afferent inputs onto common neurones the spatial facilitation technique was used. When present the convergence had a threshold and time course compatible with those of the propriospinal‐like system. Convergence was found between the different mixed nerves and between ulnar and superficial radial nerves. 6. The wide convergence found between different inputs onto common neurones and the finding that, during contraction of a given muscle, descending excitation reaches subsets of neurones projecting to motor nuclei of muscles operating at other joints suggest that the propriospinal‐like system would be operative during complex multi‐joint movements.