bluuebunny/crossref_metadata_2025 huggingface dataset:
Lung congestion augments the responses of cells in the rapidly adapting receptor pathway to cigarette smoke in rabbit.
Authors: Zhang Z , Bonham A C
Published: December 2014

1. We examined the effects of cigarette smoke, inhaled alone and during mild pulmonary venous congestion, on the activity of fifty‐three neurones in the nucleus tractus solitarii (NTS) that were excited by input from pulmonary rapidly adapting receptors (RAR). Ten neurones excited by slowly adapting stretch receptors (SAR) were also studied. 2. Extracellular recordings of RAR‐activated neurones were recorded in alpha‐chloralose anaesthetized rabbits. Smoke from low‐ and high‐nicotine cigarettes was delivered through a ventilator. Mild pulmonary venous congestion was produced by inflating a balloon in the left atrium. 3. Inhalation of three breaths of smoke from low‐nicotine cigarettes increased the activity of fifty‐one out of fifty‐three RAR‐activated neurones from 5.9 +/‐ 1.0 to 14.4 +/‐ 2.1 spikes breath‐1 (P < 0.05). 4. The responses of fifteen neurones were compared with smoke inhaled alone or during mild pulmonary venous congestion. Smoke alone increased unit activity from 6.8 +/‐ 2.3 to 12.6 +/‐ 3.7 spikes breath‐1 (P < 0.05). Small increases in left atrial pressure (2.0 +/‐ 0.5 mmHg) had no effect on baseline unit activity (7.6 +/‐ 2.11 vs. 7.7 +/‐ 2.3 spikes breath‐1; P > 0.05), but enhanced the responses to smoke, increasing the activity from 7.6 +/‐ 2.1 to 17.1 +/‐ 4.8 spikes breath‐1 (P < 0.05). The response was greater than to smoke alone (P < 0.05). 5. Of ten SAR‐activated neurones, seven failed to respond to inhaled cigarette smoke, two were excited and one was inhibited. Pulmonary venous congestion had no effect on the unit activity before and after smoke (n = 4 neurones). 6. We conclude that smoke‐evoked excitation of RAR lower‐order neurones is augmented by pulmonary venous congestion.
Electrophysiological properties of P2X‐purinoceptors in rat superior cervical, nodose and guinea‐pig coeliac neurones.
Authors: Khakh B S , Humphrey P P , Surprenant A
Published: December 2014

1. Whole‐cell recordings were made from guinea‐pig coeliac, rat nodose and rat superior cervical (SCG) neurones in culture, and currents in response to fast‐flow (concentration clamp) application of ATP and other ATP analogues were measured. 2. At a holding potential of ‐70 mV, ATP evoked inward currents in all neurons. ATP‐induced currents reversed at approximately 0 mV and showed strong inward rectification. Halving the external sodium concentration shifted the reversal potential by ‐15 to ‐17 mV, while increasing external potassium from 2 to 20 mM produced a 6‐10 mV shift in reversal potential. Latency to onset of ATP current was < 1 ms; rise time was concentration dependent with maximum time to peak of 5‐20 ms in nodose and coeliac neurones but 80 ms in superior cervical neurones. 3. Threshold concentrations of ATP were 0.1 microM for nodose and coeliac neurones but 10 microM for superior cervical neurones; EC50 values were approximately 3 microM for both nodose and coeliac neurones and 43 microM for superior cervical ganglia. Hill slopes for ATP concentration‐response curves were not significantly different from unity in nodose and coeliac neurones whereas the Hill slope in superior cervical neurones was two. 4. 2‐MethylthioATP (2‐MeSATP) acted as a full agonist in all three neuronal preparations; EC50 values were 0.4, 2.8 and 46 microM for nodose, coeliac and superior cervical neurones, respectively. alpha,beta‐Methylene ATP (alpha,beta‐MeATP) was a full agonist in nodose and coeliac neurones with EC50 values of 9 and 13 microM, respectively. 5. In superior cervical neurones alpha,beta‐MeATP had little or no agonist action but produced a concentration‐dependent attenuation of the ATP current. Thus, alpha, beta‐MeATP appears to behave as a partial agonist at P2X‐purinoceptors in superior cervical neurones. 6. The non‐selective purinoceptor antagonists suramin (1‐100 microM) and pyridoxal‐5'‐phosphate (30 microM), as well as the putative P2Y‐selective antagonist, Cibacron Blue (30 microM), inhibited all agonist‐evoked responses to a similar degree in all three neuronal populations. 7. This study demonstrates that an agonist potency profile of 2‐MeSATP > or = ATP > or = alpha,beta‐MeATP is characteristic of ligand‐gated P2X‐purinoceptors in isolated peripheral neurones. We also suggest that the P2X‐receptor in superior cervical neurones may represent a distinct subtype of P2X‐purinoceptor from that present in nodose and coeliac neurones.
Regulation of spontaneous phasic firing of rat supraoptic vasopressin neurones in vivo by glutamate receptors.
Authors: Nissen R , Hu B , Renaud L P
Published: December 2014

1. Vasopressin‐secreting neurones in the rat hypothalamic supraoptic nucleus display patterned spontaneous phasic activity, which is apparently maintained in vivo through yet unidentified neurotransmitter system(s). The present investigation used extracellular recording techniques in anaesthetized Long‐Evans rats to evaluate whether the neurotransmitter mechanism underlying phasic firing is provided via a family of ionotropic glutamate receptors. 2. N‐Methyl‐D‐aspartate (NMDA) reliably evoked bursts of activity in twenty‐seven of twenty‐eight phasic neurones. Amino‐3‐hydroxy‐5‐methyl‐isoxazole‐4‐propionic acid (AMPA) and kainate also elicited pronounced excitations in twenty‐one of twenty‐one and and fourteen of fifteen phasic cells, respectively. 3. A rapid blockade of on‐going phasic activity was consistently induced following brief applications of both NMDA and non‐NMDA receptor antagonists; extended application of antagonists resulted in prolonged silent periods, during which phasic activity failed to recur for minutes. Neither saline nor a cholecystokinin receptor antagonist influenced cell firing. 4. In contrast to putative vasopressin cells, application of NMDA receptor ligands did not affect the spontaneous activity in most putative oxytocin‐secreting neurones, whereas kainate and AMPA potently excited seven of nine and four of five putative oxytocin cells, respectively. 5. These results imply that the maintenance of spontaneous phasic discharges in vivo in supraoptic vasopressin‐secreting neurones requires tonic synaptic activation involving both NMDA and non‐NMDA glutamate receptors. In putative oxytocin‐secreting neurones, spontaneous firing appears to be predominantly regulated by non‐NMDA receptors. Glutamatergic innervations may be in a unique position to influence the genesis of patterned electrical activity in supraoptic vasopressin neurones.
The antagonistic effect of K+o and dihydro‐ouabain on the Na+ pump current of single rat and guinea‐pig cardiac cells.
Authors: Hermans A N , Glitsch H G , Verdonck F
Published: December 2014

1. The antagonistic effect of extracellular potassium ions (K+o) and dihydro‐ouabain (DHO) on the Na(+)‐K+ pump current (Ip) was studied in isolated ventricular cells. 2. The myocytes were isolated from rats and guinea‐pigs, two species with different sensitivity towards cardiac glycosides. Ip measurements were performed at 32‐34 degrees C by means of whole‐cell recording. The membrane potential was held at ‐20 mV throughout. 3. The DHO concentration ([DHO]) required for half‐maximal Ip inhibition (apparent KD value, KD') amounted to 2.4 x 10(‐3) and 1.4 x 10(‐5) M for rat and guinea‐pig myocytes, respectively, at 5.4 mM K+o. 4. The data suggest one‐to‐one binding of DHO to the Na(+)‐K+ pump and a smaller association rate constant, as well as a larger dissociation rate constant, for binding of DHO in the rat cells. 5. Ip activation by K+o was nearly identical in myocytes of both species and was measured to be half‐maximal at approximately 1 mM K+o. Half‐maximal Ip activation by K+o remained essentially unchanged, but Ip decreased in media containing [DHO] near the respective KD' at 5.4 mM K+o. 6. The concentration‐response curve of Ip inhibition by DHO was shifted to higher [DHO] at higher [K+]o. KD' increased correspondingly. The slope of the curve was unaffected. 7. Ip and KD' displayed a similar dependence on [K+]o. 8. KD' was larger in Na(+)‐free than in Na(+)‐containing media under conditions in which the activation of Ip by K+o was nearly the same. 9. It is concluded that the antagonism between K+o and DHO, with regard to the activation of Ip, is non‐competitive. A possible mechanism of the antagonism is discussed. The mechanism implies binding of K+o and DHO to different conformational states of the Na(+)‐K+ pump which are temporarily exposed to the external face of the sarcolemma in the pump cycle. The DHO‐bound states do not participate in the generation of Ip.
Febrile responses induced in adrenalectomized rats by administration of interleukin‐1 beta or prostaglandin E2.
Authors: Watanabe T , Makisumi T , Macari M , Tan N , Nakamori T , Nakamura S , Murakami N
Published: December 2014

1. The present study was carried out to investigate the effect of bilateral adrenalectomy on fevers induced in rats by systemic injection of interleukin‐1 beta (IL‐1 beta) or by central injection of prostaglandin E2 (PGE2). 2. Intraperitoneal (I.P.) injections of two doses of IL‐1 beta (0.5 and 1.0 microgram kg‐1) induced biphasic fevers in normal control rats in a dose‐dependent manner. Adrenalectomized (ADX) rats showed higher fevers than sham‐ADX rats after I.P. injection of small doses of IL‐1 beta (0.5 micrograms kg‐1). This fever enhancement was inhibited by acute or chronic glucocorticoid, dexamethasone (DEX), treatment. In contrast, there was no significant difference between fevers induced in ADX and sham‐ADX rats by I.P. injection of large doses of IL‐1 beta (1.0 g kg‐1). 3. Dose‐dependent fevers were observed in normal control rats after injections of several doses of PGE2 (5, 25 and 100 ng) into the preoptic hypothalamic area (POA). The injection of a large dose of PGE2 (100 ng) into the POA led to a lower fever in ADX rats, compared with that in sham‐ADX rats. This fever in ADX rats was increased by acute or chronic treatment with DEX. On the other hand, adrenalectomy had no effect on fevers induced by the injections of small doses of PGE2 (5 and 25 ng) 4. The injections of PGE2 (100 ng) into the POA induced increases in oxygen consumptions in ADX rats that were significantly smaller than those in sham‐ADX rats, suggesting that the lower PGE2 fever was, at least in part, due to attenuated thermogenesis in ADX rats. 5. There was no significant difference in plasma osmolality between the ADX and the sham‐ADX rats. The ADX rats were given 0.9% salt water instead of tap water. 6. These results suggest that endogenous glucocorticoid is one of the important modulators of the IL‐1‐induced and the PGE2‐induced fevers in rats.
Altered Ca2+ sensitivity of tension in single skeletal muscle fibres from MyoD gene‐inactivated mice.
Authors: Metzger J M , Rudnicki M A , Westfall M V
Published: December 2014

1. Single, fast glycolytic skeletal muscle fibres were isolated from wild‐type (MyoD+/+) and MyoD mutant mice (MyoD‐/‐), which lack a functional copy of the MyoD gene. Fibres were chemically permeabilized to permit manipulation and control of the ionic environment of the otherwise intact myofilament apparatus. 2. Results show a fivefold greater variability in the [Ca2+] required for half‐maximum tension generation among individual MyoD‐/‐ fibres in comparison with controls (p < 0.05). 3. Consistent with this finding, Western blot analysis showed a sevenfold greater variability in the isoform expression pattern of the thin filament regulatory protein troponin T in Myod‐/‐ compared with control fibres (p < 0.05). 4. Electrophoretic analysis of single‐fibre segments indicated no apparent alteration in the isoform expression pattern of other regulatory and contractile proteins. In addition, other parameters of contractile function, including velocity of unloaded shortening, and maximum force production, were not significantly different between MyoD‐/‐ and MyoD ø fibres. 5. These findings indicate that the thin filament structure‐ function relationship is altered due to the MyoD mutation and suggest that MyoD plays a role in establishing and/or maintaining the differentiated phenotype of adult fast skeletal muscle fibres.
Reduced servo‐control of fatigued human finger extensor and flexor muscles.
Authors: Hagbarth K E , Bongiovanni L G , Nordin M
Published: December 2014

1. In healthy human subjects holding the index finger semi‐extended at the metacarpophalangeal joint against a moderate load, electromyographic (EMG) activity was recorded from the finger extensor and flexor muscles during different stages of muscle fatigue. The aim was to study the effect of muscle fatigue on the level of background EMG activity and on the reflex responses to torque pulses causing sudden extensor unloadings. Paired comparisons were made between the averaged EMG and finger deflection responses under two conditions: (1) at a stage of fatigue (following a sustained co‐contraction) when great effort was required to maintain the finger position, and (2) under non‐fatigue conditions while the subject tried to produce similar background EMG levels to those in the corresponding fatigue trials. 2. Both the unloading reflex in the extensor and the concurrent stretch reflex in the flexor were significantly less pronounced and had a longer latency in the fatigue trials. Consequently, the finger deflections had a larger amplitude and were arrested later in the fatigue trials. 3. It is concluded that‐‐with avoidance of ‘automatic gain compensation’, i.e. reflex modifications attributable to differences in background EMG levels‐‐the servo‐like action of the unloading and stretch reflexes is reduced in fatigued finger extensor and flexor muscles.
Chemical mediators of spinal inhibition of rat sympathetic neurones on stimulation in the nucleus tractus solitarii.
Authors: Lewis D I , Coote J H
Published: December 2014

1. This study was undertaken to gain more direct evidence of the pathways and neurochemical mediators of a spinally mediated baroreceptor inhibition of sympathetic preganglionic neurones (SPNs). 2. For this purpose, single‐pulse electrical stimulation within identified vasodepressor regions of the nucleus tractus solitarii (NTS) was used together with extracellular recordings of single antidromically identified SPNs in the T2 segment of the spinal cord of anaesthetized rats. 3. The actions of agonists and antagonists of inhibitory amino acids on the NTS‐induced inhibitions were determined, when they were iontophoretically applied in the vicinity of SPNs via a multibarrel micropipette assembly. 4. Extracellular recordings were made from sixty‐nine SPNs. In forty‐four SPNs, NTS stimulation elicited a period of inhibition of activity in both spontaneous and ‘D,L‐homocysteic acid‐driven’ SPNs with a latency to onset of 60 +/‐ 6 ms and a magnitude of 80 +/‐ 3%. 5. In six out of eight neurones, the NTS‐induced inhibition was reduced by 74 +/‐ 16% during the application of the glycine antagonist strychnine (0‐10 nA, 5‐10 min) with doses that selectively blocked the inhibitory effect of iontophoretically applied glycine. 6. In nine out of nine neurones, the NTS‐induced inhibition was reduced by 38 +/‐ 6% during the application of the GABAA antagonist bicuculline (5‐15 nA, 4‐14 min) with doses that selectively blocked the inhibitory effect of iontophoretically applied GABA. 7. In two SPNs, the actions of strychnine and bicuculline were shown to be additive in blocking the NTS inhibition. 8. The selective GABAB antagonists, CGP 35348 (20‐50 nA, 6‐25 min) and CGP 55845A (10 nA, 11 min) did not antagonize the NTS‐induced inhibition. 9. It is suggested that GABA and glycine interneurones are activated by a baroreceptor bulbospinal pathway to inhibit sympathetic preganglionic neurones in the spinal cord.
Target‐derived factors regulate the expression of Ca(2+)‐activated K+ currents in developing chick sympathetic neurones.
Authors: Raucher S , Dryer S E
Published: December 2014

1. The functional expression of Ca(2+)‐activated K+ currents (IK(Ca)) and voltage‐activated Ca2+ currents (ICa) was examined using whole‐cell recordings from chick lumbar sympathetic neurones developing in situ and under various conditions in vitro. 2. Macroscopic IK(Ca) was expressed at low current density (< 0.01 mA cm‐2) in neurones isolated at embryonic days 9‐16 (E9‐16). IK(Ca) was expressed at high densities (> 0.04 mA cm‐2) at E17‐19. By contrast, there was no significant difference in ICa density between sympathetic neurones isolated at E13 and E18. 3. When sympathetic neurones were isolated at E13 and maintained in vitro for 5 days, IK(Ca) was expressed at a significantly lower density (< 0.01 mA cm‐2) than in neurones isolated acutely at E18 (> 0.04 mA cm‐2). There was no difference in ICa density between neurones that developed in vitro and in situ. 4. When E13 sympathetic neurones were cultured for 5 days in the presence of a confluent layer of ventricular myocytes, they expressed IK(Ca) at a high density (> 0.04 mA cm‐2), similar to that of E18 neurones that developed entirely in situ. Cardiac cell‐conditioned medium produced similar effects. However, co‐culture of sympathetic neurones with spinal cord explants did not allow for normal IK(Ca) expression in vitro. 5. Culturing sympathetic neurones in the presence of 5 ng ml‐1 nerve growth factor (NGF) caused a significant increase in IK(Ca) density but this effect was only seen in 50% of cells examined. 6. The largest developmental changes in macroscopic IK(Ca) occur several days after other K+ currents and ICa are expressed at maximal density. The normal developmental expression of IK(Ca) is dependent upon extrinsic factors, including target‐derived differentiation factors.
Rhythm generation in the segmented hindbrain of chick embryos.
Authors: Fortin G , Kato F , Lumsden A , Champagnat J
Published: December 2014

1. The embryonic hindbrain of chick is segmented until stage 24, when it starts to generate rhythmic activities in cranial nerves. In order to recognize a possible influence of segmentation on the organization of neuronal systems generating motor rhythms, the activity of trigeminal, facial, glossopharyngeal, vagal and hypoglossal nerves was studied during embryonic stages 24‐36, by simultaneous recording of different cranial nerves in an isolated, superfused chick hindbrain preparation. 2. Highly correlated recurrent episodes of cyclical burst discharges occurred in all nerves studied (correlation coefficients, 0.8 +/‐ 0.1) throughout stages 24‐36. 3. Such coactivation is unlikely to be due to monosynaptic connections between widely divergent premotor neurons and motoneurons, or between motoneurons themselves, because no short‐term correlation was apparent in the millisecond range between activities of different motor nerves. 4. Complete transverse or midsagittal sectioning of the hindbrain disrupted coactivation of nerves located at distinct rostrocaudal levels or occupying an ipsi‐ or contralateral position, respectively, while sparing the ability of individual nerves to generate rhythmic activity. Each hindbrain segment thus contains bilaterally the motor nuclei together with their own rhythm generator. Coactivation of motor patterns appears to result from intersegmental and cross‐median connections between these rhythm generators. 5. The results are in keeping with the hypothesis of a segmental organization of the primordial hindbrain rhythm generator and give further support to the early determination of both the anatomical and the functional fate of neurons in this region of the vertebrate central nervous system.
The effects of systemic hypoxia on renal function in the anaesthetized rat.
Authors: Neylon M , Marshall J M , Johns E J
Published: December 2014

1. In rats anaesthetized with Saffan, renal function was monitored from the left kidney from the 5th minute of spontaneous breathing of 12% O2 for two 20 min periods and during air breathing before, between and after the hypoxic periods. Two groups of animals (I and II) were used, each group comprising two subgroups in which the left kidney was innervated or denervated, respectively; in Group II, renal perfusion pressure (RPP) was maintained during the 2nd hypoxic period by occl97uding the distal aorta. 2. In both subgroups of Group I, both hypoxic periods produced hyperventilation, arterial PO2 falling to approximately 50 mmHg. Concomitantly, mean arterial pressure (MABP) fell by similar extents (approximately 23%, from a baseline level of 140 mmHg during the 2nd hypoxic period). In the innervated subgroup, renal vascular conductance (RVC) increased, but glomerular filtration rate (GFR) fell (by 48 and 6%, respectively, during the 2nd hypoxic period), while urine flow, absolute sodium excretion (UNaV) and fractional sodium excretion (FENa) fell (by 52, 63 and 61%, respectively). Baseline urine flow, UNaV and FENa were higher in the denervated subgroup, but hypoxia produced similar percentage changes from baseline in all variables. 3. In Group II, both subgroups showed similar changes during the 1st hypoxic period as the corresponding subgroups of Group I. However, during the 2nd hypoxic period when the fall in MABP was reduced to approximately 7%, the increase in RVC persisted only in the denervated subgroup; there was no significant change in GFR, urine flow, UNaV or FENa in either subgroup. 4. These results indicate that, in the rat, moderate hypoxia produces antidiuresis and antinatriuresis that are not dependent on the renal nerves, but are dependent on the hypoxia‐induced fall in MABP. The fall in renal perfusion pressure (RPP) may directly determine renal function, but reflex influences upon the kidney initiated by, for example, arterial baroreceptor unloading, may play a role. The fall in GFR and increase in RVC, which persisted after denervation or when renal perfusion was controlled, implies a local dilatatory influence acting preferentially on the efferent arterioles.
Effects of vitamin E deficiency on autonomic neuroeffector mechanisms in the rat caecum, vas deferens and urinary bladder.
Authors: Hoyle C H , Ralevic V , Lincoln J , Knight G E , Goss-Sampson M A , Milla P J , Burnstock G
Published: December 2014

1. Modified sucrose‐gap, standard organ‐bath techniques and transmitter release studies were used to examine neuromuscular transmission in the caecum, vas deferens and urinary bladder in normal rats and in rats maintained for 12 months on a diet free of vitamin E. 2. In the caecum circular muscle, non‐adrenergic, non‐cholinergic inhibitory junction potentials were absent from 48 and 15% of preparations from vitamin E‐deficient and control animals, respectively. Cholinergic excitatory junction potentials were absent from 83 and 8% of vitamin E‐deficient and control preparations, respectively. Responses to applied noradrenaline (0.1‐30 microM), alpha,beta‐methylene ATP (3‐100 microM) and acetylcholine (0.1‐30 microM) were attenuated or absent in vitamin E‐deficient tissues. Responses to applied KCl were similar in both groups. Release of [3H]noradrenaline or endogenous acetylcholine could not be evoked from vitamin E‐deficient tissues. 3. In contrast, in isolated preparations of the vas deferens and urinary bladder, neuromuscular transmission by adrenergic, cholinergic and purinergic components were unaffected by long‐term vitamin E deficiency. 4. In conclusion, vitamin E deficiency causes dysfunction of autonomic neuroeffector mechanisms in the smooth muscle of the rat caecum, at both a pre‐ and postjunctional level. The lesions in autonomic transmission mechanisms brought about by long‐term vitamin E deficiency were found only in the caecum; no changes in sympathetic neuromuscular transmission were observed in the vas deferens, or in parasympathetic neuromuscular transmission in the urinary bladder.
Effects of hypothalamic thermal stimuli on sympathetic neurones innervating skin and skeletal muscle of the cat hindlimb.
Authors: Grewe W , Jänig W , Kümmel H
Published: December 2014

1. Postganglionic neurones supplying hairless and hairy skin of the cat hindlimb were analysed for their responses to thermal stimuli applied to the anterior hypothalamus and spinal cord in anaesthetized and artificially ventilated cats. Activity was recorded from multi‐ and single‐unit bundles which were isolated from peripheral nerves. The neurones were functionally identified as cutaneous vasoconstrictor (CVC) and muscle vasoconstrictor (MVC) neurones. Activity in sudomotor (SM) neurones was either monitored indirectly by recording the phasic negative deflections of the skin potential from the surface of the hairless skin, or in some experiments additionally by recording activity directly from the SM axons. 2. The activity in forty‐one out of forty‐four multi‐unit and six out of six single‐unit CVC bundles was inhibited, in a graded manner, by hypothalamic warming. An increase in the temperature of the surface of hairless skin followed the decrease in activity of the CVC neurones supplying it. Large changes in skin temperature only followed decreases in CVC activity of more than 40%. Cooling of the hypothalamus had only weak transient effects on CVC neurones. 3. Simultaneous warming of hypothalamus and spinal cord had multiplicative effects on the activity in CVC neurones. Subthreshold warming of one structure increased the response to warming of the other one and reduced the threshold temperature. 4. SM neurones were not affected by hypothalamic warming, but activated during hypothalamic cooling. 5. MVC neurones were weakly activated during hypothalamic warming only if arterial blood pressure decreased, otherwise they were unaffected. It is likely that this activation was due to secondary unloading of arterial baroreceptors. 6. Two silent postganglionic neurones projecting to skin were activated during hypothalamic warming. These neurones may have had a vasodilatory function. 7. Rhythmicity of the activity in CVC neurones, related to the cycle of artificial ventilation, increased during hypothalamic warming whereas that of MVC neurones was unchanged. 8. The functionally highly specific responses to hypothalamic warming in CVC neurones indicate a pathway from the hypothalamus that is specific for CVC neurones, in contrast to MVC and SM neurones. This central pathway is integrated with other spinal and supraspinal reflex pathways that determine the characteristic reflex pattern of CVC neurones to somatic and visceral stimuli and possibly with pathways that generate other physiological changes during hypothalamic warming (e.g. increase in respiratory drive).
Functional role of follicular cells in the generation of osmolarity‐dependent Cl‐ currents in Xenopus follicles.
Authors: Arellano R O , Miledi R
Published: December 2014

1. Osmolarity‐dependent (osmo‐dependent) ionic currents from follicle‐enclosed Xenopus oocytes (follicles) were studied using the two‐microelectrode voltage‐clamp technique, combined with intra‐oocyte pressure injection of sucrose or polyethylene glycols (PEGs). 2. Intra‐oocyte injections of sucrose or PEG (3‐25 nmol) generated inward membrane currents (follicles held at ‐60 mV) associated with an increase in membrane conductance. These currents were carried mainly by chloride ions (ICl(osm)), and were strongly attenuated by increasing the tonicity of the external medium, or by external application of La3+ (0.1‐1 mM). 3. The ability to generate ICl(osm) depended on the molecular weight of the injected PEG. Injections of PEG 200 or 300 generated ICl(osm) in 95% of the follicles tested, PEG 600 generated comparable currents in only 20% of the follicles, while similar injections of PEG 1000 did not elicit ICl(osm). 4. Octanol (1‐1.5 mM), a gap junction channel blocker, reversibly inhibited 50‐90% of the ICl(osm) generated by injections of sucrose or PEG 300. Moreover, sucrose or PEG injections did not elicit ICl(osm) in defolliculated oocytes. 5. It is concluded that an increase in the internal osmolarity of the follicular cells activates a mechanism, probably involving cellular swelling, which leads to the opening of ICl(osm) channels most probably located in the follicular cell membrane.
Motor co‐ordinates in primate red nucleus: preferential relation to muscle activation versus kinematic variables.
Authors: Miller L E , Houk J C
Published: December 2014

1. Magnocellular red nucleus (RNm) neurones (n = 158) were recorded from two macaque monkeys during a tracking task using one of six single‐degree‐of‐freedom manipulanda. This task allowed us to study discrete movements about most of the joints of the arm. Single‐unit, kinematic and electromyographic (EMG) signals from ten to twenty muscles of the upper limb were collected for approximately 2 min while the monkey used a given manipulandum. Movements about different joints were studied by switching among manipulanda. 2. Cross‐correlation functions were calculated between RNm discharge rate and the kinematic variables, position and velocity, and between RNm and each of the EMG signals. Statistically significant cross‐correlation peaks were found in 24% of the position correlations, 22% of the velocity correlations and 32% of the EMG correlations. The highest correlations were for EMG, reaching above 0.60. The peak correlation provided an effective means of identifying neurones with strong functional relations to one or more movements and/or muscles. These could then be analysed in detail, on a trial‐by‐trial basis. 3. The similarity between the dynamics of EMG and velocity signals of many highly practised movements makes it difficult to determine which might be the more likely target of RNm control. Therefore, we sought exceptions to this pattern, in order to distinguish between these two possible modes of control. For example, at the end of a movement, muscles occasionally remained active as velocity approached zero. Small corrective movements were often accompanied by a disproportionately large EMG. During these periods, RNm activity usually followed the time course of one or more of the EMG signals as opposed to the velocity signal. In the majority of cases, RNm responses were bidirectional, less frequently unidirectional and rarely reciprocal. These patterns were similar to the patterns of muscle activity. They did not resemble the velocity signals unless the latter were passed through a rectifier. 4. The results support the hypothesis that the red nucleus generates motor commands in a muscle‐based co‐ordinate system. Covariation between RNm discharge and velocity may result indirectly from correlations between muscle activation and movement. We discuss how the cerebellar cortex might convert the distributed representation of target position, known to be present in the posterior parietal cortex, directly into dynamic, muscle‐based commands in the rubro‐cortico‐cerebellar limb premotor network.
Focal [Ca2+]i increases detected by aequorin but not by fura‐2 in histamine‐ and caffeine‐stimulated swine carotid artery.
Authors: Rembold C M , Van Riper D A , Chen X L
Published: December 2014

1. We hypothesized that the homogeneity of intracellular [Ca2+] ([Ca2+]i) varies and is regulated in arterial smooth muscle. 2. We evaluated this hypothesis by exploiting the different characteristics of several [Ca2+]i indicators: (1) aequorin, which theoretically can measure focal increases in [Ca2+]i, (2) fura‐2, which is predominantly a measure of mean cytoplasmic [Ca2+], and (3) myosin light chain phosphorylation and force, which reflect increases in [Ca2+] near the contractile apparatus. 3. From the differences in the observed aequorin and fura‐2 signals, we developed an index of the relative degree of [Ca2+]i homogeneity as the ratio of the aequorin signal and fura‐2 signal. 4. Stimulation with intermediate concentrations of histamine (1 and 10 microM) or high [K+]o (25 and 40 mM) increased [Ca2+]i and contractile stress. Relative [Ca2+]i homogeneity, estimated from the aequorin/fura‐2 ratio, remained similar to levels observed in unstimulated tissues. 5. Higher concentrations of histamine (100 microM) also increased [Ca2+]i and stress, but the aequorin/fura 2 ratio declined , indicating increased [Ca2+]i homogeneity. Similarly, the aequorin/fura‐2 ratio decreased when extracellular Ca2+ was removed. 6. Stimulation with histamine in low extracellular [Ca2+] transiently increased [Ca2+]i and the aequorin/fura‐2 ratio. Similarly, in tissues treated with low extracellular [Ca2+], restoration of extracellular Ca2+ transiently increased both [Ca2+]i and the aequorin/fura‐2 ratio. Although both of these experiments demonstrated a transient decrease in [Ca2+]i homogeneity, only histamine stimulation led to increased myosin light chain phosphorylation and force. These results indicate that the focal increases in [Ca2+]i observed with histamine stimulation and Ca2+ restoration occurred in different cellular regions. 7. Addition of caffeine (20 mM) increased [Ca2+]i and [cAMP], but this was not accompanied by sustained increased myosin light chain phosphorylation or contraction. Phosphorylation of myosin light chain kinase did not appear to underlie the lack of increase in myosin light chain phosphorylation. Rather, caffeine induced a sustained increase in the aequorin/fura‐2 ratio, suggesting that caffeine inhibits smooth muscle contraction by localizing increases in [Ca2+]i to a region distant from the contractile apparatus. 8. These data suggest that there can be transient and sustained focal increases in [Ca2+]i. Aequorin detected increased [Ca2+]i in small regions of the cytoplasm during release from and refilling of the intracellular Ca2+ store and with caffeine stimulation. Dual use of aequorin and fura‐2 permits determination of relative [Ca2+]i homogeneity in smooth muscle.
Comparison of subsarcolemmal and bulk calcium concentration during spontaneous calcium release in rat ventricular myocytes.
Authors: Trafford A W , Díaz M E , O'Neill S C , Eisner D A
Published: December 2014

1. The aim of these experiments was to compare the time course of changes in intracellular Ca2+ concentration ([Ca2+]i) measured in the bulk cytoplasm with those estimated to occur near the sarcolemma. Sarcolemmal Na(+)‐Ca2+ exchange current and [Ca2+]i were measured in single, voltage‐clamped ventricular myocytes. 2. Spontaneous Ca2+ release from the sarcoplasmic reticulum (SR) resulted in a transient inward current. This current developed and decayed more quickly than the accompanying changes in [Ca2+]i (measured with indo‐1) resulting in a hysteresis between [Ca2+]i and current. A similar hysteresis was also observed if [Ca2+]i was elevated with caffeine and was removed if the current was low pass filtered with a time constant of 132 ms. 3. Digital video imaging (using fluo‐3 or calcium green‐1 to measure [Ca2+]i) allowed measurement of [Ca2+]i at all points in the cell during the wave of spontaneous Ca2+ release. The hysteresis between [Ca2+]i and current remained, even after allowing for the spatial and temporal properties of this wave. 4. The hysteresis can be accounted for if there is a barrier to diffusion of Ca2+ ions separating the bulk cytoplasm from the space under the sarcolemma (into which Ca2+ is released from the sarcoplasmic reticulum). The calculated subsarcolemmal [Ca2+] rises and falls more quickly (and reaches a higher peak) than does the bulk [Ca2+]. The delay introduced by this barrier is equivalent to a time constant of 133 ms. 5. The subsarcolemmal space described in this paper may be equivalent to the ‘fuzzy space’ previously suggested to be important in controlling SR Ca2+ release.
Influence of hypoxic duration and posthypoxic inspired O2 concentration on short term potentiation of breathing in humans.
Authors: Dahan A , Berkenbosch A , DeGoede J , van den Elsen M , Olievier I , van Kleef J
Published: December 2014

1. Short term potentiation (STP) of breathing refers to respiratory activity at a higher level than expected just from the dynamics of the peripheral and central chemoreceptors. In humans STP is activated by hypoxic stimulation. 2. To investigate the effects of the duration of hypoxia and the posthypoxic inspired O2 concentration on STP, the ventilatory responses to 30 s and 1, 3 and 5 min of hypoxia (end‐tidal PO2, P(ET.O2) approximately 6.5 kPa) followed by normoxia (P(ET.O2) approximately 14.5 kPa) and hyperoxia (P(ET.O2) approximately 70 kPa) were studied in ten healthy subjects. End‐tidal PCO2 (P(ET.CO2)) was clamped during hypoxic and recovery periods at 5.7 kPa. 3. Steady‐state ventilation (VE) was 13.7 +/‐ 0.6 l min‐1 during normoxia and increased to 15.5 +/‐ 0.3 l min‐1 during hyperoxia (P < 0.05) due to the reduced Haldane effect and some decrease in cerebral blood flow (CBF). 4. The mean responses following hypoxia reached normoxic baseline after 69, 54, 12 and 12 s when 30 s and 1, 3 and 5 min of hypoxia, respectively, were followed by normoxia. An undershoot of 10 and 20% below hyperoxic baseline was observed when 3 and 5 min of hypoxia, respectively, were followed by hyperoxia. Hyperoxic VE reached hyperoxic baseline after 9, 15, 12 and 9 s at the termination of 30 s and 1, 3 and 5 min of hypoxia, respectively. 5. Normoxic recovery from 30 s and 1 min of hypoxia displayed a fast and subsequent slow decrease towards normoxic baseline. The fast component was attributed to the loss of the hypoxic drive at the site of the peripheral chemoreceptors, and the slow component to the decay of the STP that had been activated centrally by the stimulus. A slow decrease at the termination of 30 s and 1 min of hypoxia by hyperoxia was not observed since this component was cancelled by the increase in ventilatory output due to the reduced Haldane effect and some decrease of CBF. 6. Decay of the STP was not apparent in the normoxic recovery from 3 and 5 min of hypoxia as a slow component since it cancelled against the slow ventilatory increase related to the increase of brain tissue PCO2 due to the reduction of CBF at the relief of hypoxia. The undershoot observed when hyperoxia followed 3 and 5 min of hypoxia reflects the stimulatory effects of hyperoxia on VE. 7. The manifestation of the STP as a slow ventilatory decrease depends on the duration of hypoxia and the subsequent inspired oxygen concentration. We argue that STP is not abolished by the central depressive effects of hypoxia, although the manifestation of the STP may be overridden or counteracted by other mechanisms.
Effects of low doses of caffeine on [Ca2+]i in voltage‐clamped snail (Helix aspersa) neurones.
Authors: Orkand R K , Thomas R C
Published: December 2014

1. We have measured cytosolic free Ca2+ concentrations ([Ca2+]i) in voltage‐clamped snail neurones using fura‐2. Transient increases in [Ca2+]i were induced by depolarizing voltage steps of 20‐60 mV for 0.1‐10 s from a holding potential of ‐50 or ‐60 mV. 2. Low doses of caffeine, 0.2‐1 mM, increased the size of the [Ca2+]i transients by both increasing the peak and producing an undershoot. 3. Ryanodine, an inhibitor of Ca2+ release from the intracellular Ca2+ stores, and cyclopiazonic acid (CPA), an inhibitor of the Ca(2+)‐ATPase of the intracellular Ca2+ stores, both reduced the size of the [Ca2+]i transients and blocked the effects of caffeine on the transients. 4. The effects of caffeine and CPA were greater on transients produced by long, small, rather than short, large depolarizations. This suggests that calcium‐induced calcium release (CICR) played a greater role in the [Ca2+]i increase resulting from longer, smaller depolarizations. 5. Increasing the extracellular pH from 7.5 to over 9, which inhibits the plasmalemmal Ca(2+)‐H(+)‐ATPase, increased the resting [Ca2+]i level. Depolarization‐induced [Ca2+]i transients became much larger while the two effects of caffeine remained. CPA was ineffective at high pH. 6. In some experiments the increase in basal [Ca2+]i caused by alkaline pH was reduced by 0.2 or 0.5 mM caffeine. The increase in basal [Ca2+]i caused by maintained depolarization was reduced, after a transient increase, by 0.5 mM caffeine. Both reduction and increase were blocked by CPA. 7. We conclude that low doses of caffeine can increase uptake by intracellular Ca2+ stores. Caffeine could also release Ca2+ from ryanodine‐insensitive Ca(2+)‐ATPase‐dependent stores as well as facilitating normal ryanodine‐sensitive CICR.
Excessive repolarization‐dependent calcium currents induced by strong depolarizations in rat skeletal myoballs.
Authors: Fleig A , Penner R
Published: December 2014

1. Whole‐cell patch‐clamp recordings were used to study voltage‐dependent Ca2+ currents in skeletal myoballs cultured from newborn rats. 2. Depolarizing voltage pulses evoked classical L‐type Ca2+ currents, whereas repolarization induced tail currents, whose properties deviated from the expected behaviour of the preceding Ca2+ currents in both voltage dependence and kinetics. 3. Depolarizations of up to +10 mV primarily recruited tail currents that correspond to the Ca2+ channels activated and conducting during the depolarizing pulse, but stronger depolarizations yielded an additional tail current component that exceeded the ‘normal’ tail current amplitude by several‐fold. 4. Activation kinetics of the tail currents were biexponential, with a fast time constant matching the activation time course of the pulse currents (tau approximately 40 ms) and an additional slower component with a voltage‐dependent time course that had no kinetic counterpart in the pulse currents (tau approximately 150‐600 ms). 5. Both pulse and tail currents were blocked by the dihydropyridine, PN200‐110, suggesting that they represent Ca2+ channels of the L‐type. 6. We suggest the presence of at least two subsets of dihydropyridine‐sensitive Ca2+ channels in skeletal muscle cells. One subset has classical L‐type channel characteristics and the other has anomalous gating behaviour that is ‘activated’ or ‘primed’ by strong and long‐lasting depolarizations without conducting significant Ca2+ current‐‐however, upon repolarization, this subset of channels generates large tail currents.
Cyclic AMP‐dependent modulation of giant depolarizing potentials by metabotropic glutamate receptors in the rat hippocampus.
Authors: Strata F , Sciancalepore M , Cherubini E
Published: December 2014

1. Intracellular recordings were used to study the role of metabotropic glutamate receptors (mGluRs) in modulating GABA‐mediated giant depolarizing potentials (GDPs) in immature rat hippocampal CA3 neurones. 2. The mGluR antagonist (RS)‐alpha‐methyl‐4‐carboxyphenylglycine (MCPG, 1 mM) reduced the frequency of GDPs. The broad‐spectrum ionotropic glutamate receptor antagonist kynurenic acid (1 mM) blocked GDPs. 3. In the presence of kynurenic acid, both tetanic stimulation of the hilus or bath application of quisqualic acid (1 microM) and trans‐1‐aminocyclopentane‐1,3‐dicarboxylic acid (t‐ACPD, 20 microM) induced the appearance of GDPs. These effects were antagonized by MCPG (1 mM) or L(+)‐2‐amino‐3‐phosphonopropionic acid (L‐AP3) and blocked by bicuculline (10 microM). 4. 8‐Bromo‐cAMP (8‐Br‐cAMP, 0.3 mM), 3‐isobutyl‐1‐methylxanthine (IBMX, 200 microM) or forskolin (30 microM) mimicked the effects of mGluR agonists on GDPs. The forskolin analogue 1,9‐dideoxyforskolin (30 microM), which does not activate adenylate cyclase, was ineffective. 5. Incubation of slices in the presence of the protein kinase A inhibitor Rp‐adenosine 3',5'‐cyclic monophosphothioate triethylamine (Rp‐cAMPS) (500 microM) or superfusion of Rp‐cAMPS (20 microM) prevented the effects of forskolin or t‐ACPD on GDPs. In the presence of kynurenic acid, the protein kinase C activator, phorbol 12,13‐diacetate (2 microM) induced the appearance of GDPs. This effect was prevented by staurosporine (1 microM). However, staurosporine (1‐3 microM) did not modify the effects of t‐ACPD on GDPs. 6. It is suggested that, during development, mGluRs enhance the synchronous release of GABA, responsible for GDPs, through cAMP‐dependent protein kinase.
Actions of vasodilator nerves on arteriolar smooth muscle and neurotransmitter release from sympathetic nerves in the guinea‐pig small intestine.
Authors: Kotecha N , Neild T O
Published: December 2014

1. Brief constrictions of arterioles of the isolated submucosa of the guinea‐pig small intestine were evoked by stimulation of the perivascular sympathetic nerves. Prior stimulation of vasodilator neurones in the submucosal nerve plexus greatly reduced the constrictor response to sympathetic stimulation. 2. Vasodilator nerve stimulation reduced both the amplitude and rate of decay of the excitatory junction potential (EJP) evoked in the arteriolar smooth muscle by sympathetic nerve stimulation. 3. Computer simulation of the effect of membrane resistance changes on the EJP amplitude indicated that the change in amplitude could not be explained by the fall in membrane resistance alone, suggesting that vasodilator nerve activity reduced neurotransmitter release from the sympathetic nerves.
Evidence that heterosynaptic depolarization underlies associativity of long‐term potentiation in rat hippocampus.
Authors: Clark K A , Collingridge G L
Published: December 2014

1. Whole‐cell patch‐clamp recording has been used to study the effect of heterosynaptic depolarization on pure N‐methyl‐D‐aspartate (NMDA) receptor‐mediated synaptic transmission in the CA1 region of rat hippocampal slices. 2. In neurones voltage clamped at ‐60 mV, paired‐pulse stimulation of one set of Schaffer collateral‐commissural fibres resulted in homosynaptic paired‐pulse facilitation of the NMDA receptor‐mediated excitatory postsynaptic current (EPSCN). In contrast, stimulation of one set of fibres prior to stimulation of a second set of fibres (i.e. heterosynaptic paired‐pulse stimulation) did not result in any heterosynaptic interactions. 3. However, under current‐clamp conditions, heterosynaptic paired‐pulse stimulation resulted in heterosynaptic ‘paired‐pulse facilitation’ of the NMDA receptor‐mediated excitatory postsynaptic potential (EPSPN). 4. In neurones held at ‐50 or ‐40 mV, perfusion of nominally Mg(2+)‐free medium converted the response to heterosynaptic paired‐pulse stimulation from ‘heterosynaptic facilitation’ to ‘heterosynaptic depression’ of EPSPN. 5. When neurones were held at potentials of between ‐30 and +40 mV then heterosynaptic paired‐pulse stimulation, in normal Mg(2+)‐containing medium, resulted in ‘paired‐pulse depression’ of EPSPN. Under voltage‐clamp conditions (tested at +40 mV) no heterosynaptic interactions were seen. 6. The time course of ‘heterosynaptic facilitation’ at ‐60 mV and of ‘heterosynaptic depression’ at +40 mV of EPSPN was similar to the time course of EPSCN. 7. We conclude, firstly, that the voltage clamp is able to prevent any voltage breakthrough associated with the synaptic activation of NMDA receptors from influencing neighbouring synapses. Secondly, when the neurone is not voltage clamped these same synapses are strongly influenced by the spreading depolarization generated by the synaptic activation of their neighbours. The time course and direction of this influence are compatible with the hypothesis that spreading synaptic depolarization, leading to a reduction of the voltage‐dependent Mg2+ block of synaptic NMDA receptor channels, underlies the property of associativity.