bluuebunny/crossref_metadata_2025 huggingface dataset:
Restoration of lung liquid volume following its acute alteration in fetal sheep.
Authors: Dickson K A , Harding R
Published: December 2014

1. The experiments were aimed at determining the means by which lung liquid volume is controlled in fetal sheep. Six unanaesthetized chronically catheterized fetuses between 121 and 144 days of gestation were used in experiments in which lung liquid volume was acutely reduced or increased. 2. The effects on lung liquid volume, secretion and flow in the trachea were continuously monitored until the original volume was restored. Tracheal pressure, breathing activity, electrocortical activity and laryngeal adductor muscle activity were also monitored. 3. Following a mean reduction in lung liquid volume of 54.1% (40.0 +/‐ 4.3 ml) there was a reduction in tracheal pressure of 1.91 +/‐ 0.26 mmHg. There was no change in the rate of lung liquid secretion and there was a near cessation in its rate of efflux from the trachea. Influx of liquid from the upper airway was rarely seen. 4. 5 h after its reduction, lung liquid volume had returned to control values. Tracheal pressure and the rate of liquid flow in the trachea returned to control values over 7‐8 h. 5. In the hour following the reduction in lung liquid volume the incidence and amplitude of fetal inspiratory muscle electromyogram (e.m.g.) activity were reduced by 19% and 28% respectively. There was no change in laryngeal adductor muscle activity or in the duration of fetal sleep states. 6. When lung liquid volume was increased by 25.4 +/‐ 3.1 ml tracheal pressure increased by 2.01 +/‐ 0.17 mmHg. Although there was no change in the rate of liquid secretion there was a rapid efflux of liquid from the trachea principally during epochs of fetal breathing activity thus returning lung liquid volume to its control value. 7. Following the increase in lung liquid volume there were no changes in the incidence or amplitude of fetal inspiratory muscle activity, the activity of laryngeal adductor muscles or in the duration of sleep states. 8. It is concluded that following its alteration in fetal sheep lung liquid volume is restored by passive means. There was no evidence of volume‐receptive neural reflexes being activated in defence of lung liquid volume.
Maintenance of constant arm position or force: reflex and volitional components in man.
Authors: Colebatch J G , McCloskey D I
Published: December 2014

1. Normal subjects, with closed eyes, attempted to keep constant either the force exerted at the wrist or the position of the wrist against an elastic load. The load was attached to the wrist 275 mm from the axis of rotation of the elbow joint. During recording, the far end of the elastic load was displaced slowly enough that it was not immediately perceived but far enough for perception to occur before its completion. 2. The over‐all relation between wrist force and position for the two conditions was approximately linear and could be described in terms of effective stiffness. The effective stiffness for the constant‐position task averaged 2.8 N/mm (210 N m/rad), while for the constant‐force task the mean effective stiffness was ‐0.028 N/mm (‐2.1 N m/rad), indicative of slight over‐compensation. 3. Averaging the performance at the onset of the imposed disturbance indicated that the subjects' behaviour consisted of two parts: an initial, small‐range response followed by a second phase over the remainder of the displacement. The transition corresponded to the subjects' threshold for detection of the disturbance. 4. The stiffness measured for the response prior to perception was taken as a measure which included the tonic stretch reflex. The stiffness was altered appropriately for the two tasks, being lower when the subjects tried to maintain the force exerted constant (average 1.1 N/mm, 83 N m/rad) than when they attempted to keep the position constant (average 2.3 N/mm, 170 N m/rad). A small degree of co‐contraction occurred but could be dissociated from the stiffness changes. 5. Scaling the results allowed comparison of the initial stiffness with values for the decerebrate cat. When analysed in this way, the values recorded in man during the constant‐position task were similar to those reported for short‐range stiffness in the decerebrate cat. 6. The thresholds for detection of the disturbance were much lower than those reported for subjects with relaxed muscles. 7. The stretch reflex in man has a direct role in compensating for small disturbances during motor tasks. It may also function to improve detection of applied disturbances by magnifying the corresponding force change. Once the stimulus is perceived and voluntary intervention is possible, a greater contrast is seen between the subjects' performance of the two tasks.
Climbing fibres projecting to cat cerebellar anterior lobe activated by cutaneous A and C fibres.
Authors: Ekerot C F , Gustavsson P , Oscarsson O , Schouenborg J
Published: December 2014

1. Climbing fibre responses evoked on stimulation of the ipsilateral superficial radial nerve were examined in the forelimb area of the C3 zone in the barbiturate‐anaesthetized cat. Climbing fibre responses were recorded in sixty‐five Purkinje cells and as field potentials from the surface of the cerebellum. 2. In addition to the previously described A beta‐fibre‐evoked climbing fibre response, late climbing fibre responses were consistently evoked in all Purkinje cells studied when C fibres were stimulated. The latencies of the A beta‐ and C‐fibre‐evoked climbing fibre responses were 11‐20 ms and 110‐220 ms, respectively. In most experiments climbing fibre responses with an intermediate latency (20‐30 ms) were evoked. It was demonstrated that this response depended on A delta fibres. 3. The long‐latency climbing fibre response generated by electrical stimulation at C‐fibre strength was evoked also during selective anodal block of conduction in A fibres (Brown & Hamman, 1972). Hence, impulses in C fibres were sufficient for generation of climbing fibre responses. 4. The distribution within the forelimb area of the C3 zone of the A beta‐ and C‐fibre‐evoked climbing fibre field potential was similar. No climbing fibre response was evoked in this area of the C3 zone by stimulation of A and C fibres in the contralateral superficial radial nerve or in the plantar nerves of the hind limbs. 5. It can be concluded that climbing fibres projecting to the forelimb area of the C3 zone in the cerebellum receive a somatotopically organized input from both A beta and C fibres.
The role of external compression and movement in lymph propulsion in the sheep hind limb.
Authors: McGeown J G , McHale N G , Thornbury K D
Published: December 2014

1. Pressure fluctuations and lymph flow were measured in metatarsal lymphatics in anaesthetized sheep. 2. Intermittent compression significantly increased lymph flow when this was applied over the hoof but did not increase flow significantly when applied over the metatarsal region. 3. In a second preparation a 15 cm length of metatarsal lymphatic was cannulated at both ends and measurements were made of the ability of the duct to pump saline from an inflow reservoir through an outflow at the same height. 4. In the absence of external forces fluid was propelled by the lymphatic's intrinsic contractions but when intermittent compression was applied over the metatarsal region flow increased almost fourfold. 5. When animals with the doubly cannulated duct were allowed to recover, the effect of normal limb movements on fluid propulsion was examined. Under these conditions flow only occurred in response to intrinsic lymphatic contractions and appeared to be unaffected by the animal moving round the cage. 6. These results suggest that the effects of external forces on lymph flow are more dependent on compression of tissues in the lymphatic drainage area than on compression of the main lymphatic ducts. External compression can increase fluid propulsion by these vessels but, since forces of adequate magnitude appear not to be encountered in normal hind‐limb movements, lymph propulsion in this region must depend on intrinsic lymphatic pumping.
Cyclic guanosine 3',5'‐monophosphate regulates the calcium current in single cells from frog ventricle.
Authors: Fischmeister R , Hartzell H C
Published: December 2014

1. The effect of intracellular perfusion with cyclic AMP and cyclic GMP on Ca2+ current (ICa) was studied in single cells isolated from frog ventricle using the whole‐cell patch‐clamp technique and a perfused pipette. 2. Intracellular perfusion with cyclic GMP (0.1‐20 microM) had no effect on the basal ICa. However, when ICa was increased by isoprenaline or by intracellular perfusion with cyclic AMP, perfusion with cyclic GMP (20 microM) reduced ICa by an average of 67%. The effect of cyclic GMP on ICa elevated by cyclic AMP was reversible. A half‐maximal effect of cyclic GMP was observed at 0.6 microM. Cyclic GMP had no significant effect on the shape of the ICa current‐voltage relationship. 3. The effect of cyclic GMP was specific to the 3',5' form; 2',3'‐cyclic GMP had no effect. 4. The effect of cyclic GMP was apparently not mediated by stimulation of cyclic‐GMP‐dependent protein kinase because 8‐bromo‐cyclic GMP, a very potent activator of the protein kinase, was without effect. 5. Cyclic GMP had no effect on ICa elevated by the non‐hydrolysable 8‐bromo‐cyclic AMP. The effect of cyclic GMP on cyclic‐AMP‐elevated ICa was partially blocked by the phosphodiesterase inhibitor, methylisobutylxanthine. Thus, it was hypothesized that the effect of cyclic GMP was mediated by hydrolysis of cyclic AMP as a result of a stimulation of a cyclic nucleotide phosphodiesterase by cyclic GMP. 6. The dose‐response curve for cyclic AMP on ICa was well fitted by the Michaelis equation with a K50 (i.e. concentration of cyclic AMP at which response is 50% of the maximum) of 0.7 microM and a maximal 11‐fold stimulation of ICa. Cyclic GMP shifted the curve one log unit to the right and decreased the maximal stimulation to 8.6‐fold. Thus, the effect of cyclic GMP appeared uncompetitive. 7. The products of cyclic AMP and cyclic GMP hydrolysis, 5'‐AMP and 5'‐GMP, had no effect on ICa. Furthermore, strong buffering of intracellular pH did not reduce the effect of cyclic GMP. 8. It is proposed that cyclic‐GMP‐stimulation of a cyclic nucleotide phosphodiesterase may be one of several mechanisms by which acetylcholine regulates ICa.
The effect of treadmill speed on ventilation at the start of exercise in man.
Authors: Casey K , Duffin J , Kelsey C J , McAvoy G V
Published: December 2014

1. The change in ventilation at the start of exercise was determined during both hyperoxic rebreathing and air breathing in four volunteers. 2. In order to differentiate between the effects of limb‐movement frequency and exercise load in terms of oxygen uptake, three treadmill exercises were tested: E1, at an oxygen uptake of 1 l/min on a level treadmill; E2, at 2 l/min on an inclined treadmill at the same speed as E1; E3, at 2 l/min on a level treadmill at a higher speed. All of the exercises were performed at a walking pace. 3. Prior to rebreathing, hyperventilation for 5 min to 20 mmHg was used to reduce carbon dioxide to below the central chemoreceptor threshold. From eleven to fourteen rebreathing experiments were done on each volunteer for each of the three exercises, with the treadmill started at carbon dioxide levels which ranged from 36 (below threshold) to 58 mmHg (above threshold). 4. Ten experiments were performed on each volunteer for each of the three exercises during air breathing, with the treadmill started after 5 min of rest. 5. In both the rebreathing experiments and the air breathing experiments it was found that the change in ventilation at the start of exercise was the same for exercises E1 and E2, and significantly greater for exercise E3. 6. It was concluded that the frequency of limb movement, rather than exercise load (oxygen consumption) is a determinant of the change in ventilation at the start of exercise.
Cold stimulation of teeth: a comparison between the responses of cat intradental A delta and C fibres and human sensation.
Authors: Jyväsjärvi E , Kniffki K D
Published: December 2014

1. In nembutal‐anaesthetized cats, the responses of intradental A delta and C fibres to rapid cooling of the crown of canine teeth were studied. 2. Single‐unit recordings were obtained from a total of eighty‐six intradental A delta and C fibres. The mean conduction velocity of A delta fibres was 13.9 m/s (n = 43; range: 3.6‐26.0 m/s), that of C fibres was 1.3 m/s (n = 43; range: 0.5‐2.2 m/s). 3. In the intact tooth none of the identified A delta or C fibres showed any ongoing activity in the absence of intentional stimulation. 4. 84% of the A delta fibres (thirty‐six out of forty‐three) and 88% of the C fibres thirty‐eight out of forty‐three) were excited by cold stimulation of the canine tooth they were innervating. 5. For all cold‐sensitive A delta fibres the responses to rapid lowering of the tooth temperature were rather uniform. After an initial high‐frequency discharge during the most rapid change in temperature, the discharge rate fell as the rate of change of temperature became smaller, and firing stopped completely when the temperature had reached a steady level. No firing occurred as the tooth temperature returned to its initial value. 6. A good linear correlation (r = 0.89) was found between the initial dynamic discharge of responding A delta fibres and the maximum rate of change of temperature achieved in a particular experiment. 7. The response behaviour of C fibres to rapid cooling of the tooth was also rather uniform but different from that of A delta fibres. For C fibres no initial dynamic response phase was observed. After a mean latency of 7.3 s the fibres began to discharge regularly at a low rate at a time when the change of tooth temperature was already small. 8. The firing rate of the C fibres had a weak linear correlation (r = 0.6) with the static tooth temperature achieved. No discharge was observed as the temperature returned to its initial value. 9. For eleven cold‐sensitive A delta and C fibres the receptive fields were determined by mechanical stimulation of the exposed pulp tissue. For A delta fibres the receptive fields were located at the pulp‐dentine border, those for C fibres were located much deeper in the pulp and tended to have higher mechanical thresholds.(ABSTRACT TRUNCATED AT 400 WORDS)
Factors affecting the microclimate pH in rat jejunum.
Authors: Shimada T
Published: December 2014

1. Single‐barrelled pH‐sensitive microelectrodes filled with liquid ion exchanger were used to study the layer of microclimate pH in the vicinity of the surface of rat jejunum in vitro. 2. During perfusion with a Na+‐containing solution of pH 7.30, a layer having a pH gradient ranging from 7.30 (pH of the luminal bulk phase) to 6.05 +/‐ 0.03 (pH of the deepest region) was detected in eighteen different animals. The thickness of the layer was estimated to be 600‐700 microns. No regional difference was seen along the height of the villus. 3. The addition of D‐glucose to the perfusion solution significantly augmented the acidity of the deepest region without changing the thickness of the layer. On the other hand, the elimination of Na+ from the perfusion solution caused a significant reduction of the pH gradient. The lowest pH changed from a control value of 6.18 +/‐ 0.15 (n = 13 measurements from three animals) to 6.46 +/‐ 0.06 (n = 13). The gradient was sensitive to amiloride in the presence of Na+, K+, Ca2+ and Cl‐ had no significant effect on the microclimate pH. 4. Depletion of the surface mucus by treatment with dithiothreitol significantly raised the pH of the deepest region. 5. Glycylglycine and L‐carnosine were found to reduce the microclimate pH gradient significantly, while glycine did not. 6. These results indicate that H+ secretion by the Na+‐H+ antiport and the formation of mucus layer are important factors for maintaining the microclimate pH layer, and that H+‐coupled co‐transport, such as H+‐dipeptide co‐transport, causes a significant diminution of the microclimate pH gradient.
Actions of acetylcholine in the guinea‐pig and cat medial and lateral geniculate nuclei, in vitro.
Authors: McCormick D A , Prince D A
Published: December 2014

1. The mechanisms of action of acetylcholine (ACh) in the medial (m.g.n.) and dorsal lateral geniculate (l.g.n.d.) nuclei were investigated using intracellular recordings techniques in guinea‐pig and cat in vitro thalamic slices. 2. Application of ACh to neurones in guinea‐pig geniculate nuclei resulted in a hyperpolarization in all neurones followed by a slow depolarization in 52% of l.g.n.d. and 46% of m.g.n. neurones. Neither the hyperpolarization nor the slow depolarization were eliminated by blockade of synaptic transmission and both were activated by acetyl‐beta‐methylcholine and DL‐muscarine and blocked by scopolamine, indicating that these responses are mediated by direct activation of muscarinic receptors on the cells studied. 3. The ACh‐induced hyperpolarization was associated with an increase in apparent input conductance (Gi) of 4‐13 nS. The reversal potential of the ACh‐induced hyperpolarization varied in a Nernstian manner with changes in extracellular [K+] and was greatly reduced by bath application of the K+ antagonist Ba2+ or intracellular injection of Cs+. These findings show that the muscarinic hyperpolarization is mediated by an increase in K+ conductance. 4. The ACh‐induced slow depolarization was associated with a decrease in Gi of 2‐15 nS, had an extrapolated reversal potential near EK, and was sensitive to [K+]o, indicating that this response is due to a decrease in K+ conductance. 5. In contrast to effects on guinea‐pig geniculate neurones, applications of ACh to cat l.g.n.d. and m.g.n. cells resulted in a rapid depolarization in nearly all cells, followed in some neurones by a hyperpolarization and/or a slow depolarization. The rapid excitatory response was associated with an increase in membrane conductance, had an estimated reversal potential of ‐49 to ‐4 mV and may be mediated by nicotinic receptors. The hyperpolarization and slow depolarization were similar to those of the guinea‐pig in that they were associated with an increase and decrease, respectively, of Gi, and were mediated by muscarinic receptors. 6. The muscarinic hyperpolarization interacted with the intrinsic properties of the thalamic neurones to inhibit single‐spike activity while promoting the occurrence of burst discharges. The muscarinic slow depolarization had the opposite effect; it brought the membrane potential into the range where burst firing was blocked and single‐spike firing predominated. Depending upon the membrane potential, the rapid excitatory response of cat geniculate neurones could activate either a burst or a train of action potentials.(ABSTRACT TRUNCATED AT 400 WORDS)
The effects of noradrenaline on neurones in the rat dorsal motor nucleus of the vagus, in vitro.
Authors: Fukuda A , Minami T , Nabekura J , Oomura Y
Published: December 2014

1. Intracellular recordings were made from vagal motoneurones identified by antidromic stimulation in the dorsal motor nucleus of the vagus (d.m.v.) in slice preparations of rat medulla oblongata. 2. Noradrenaline (NA) applied by perfusion (0.01 microM to 1 mM) depolarized 55%, hyperpolarized 32% and produced a biphasic response (hyperpolarization followed by depolarization) in 9% of the d.m.v. neurones tested. 3. The NA effects persisted after complete elimination of synaptic inputs during perfusion with Ca2+‐free high‐Mg2+ solution, and therefore probably resulted from a direct action on the postsynaptic membranes. 4. The NA depolarization was blocked by prazosin and the NA hyperpolarization by yohimbine, but neither was blocked by propranolol or timolol. Phenoxybenzamine blocked both responses. The results indicate that NA depolarization is mediated by alpha 1‐adrenoceptors and hyperpolarization by alpha 2‐adrenoceptors. 5. The neurones which were depolarized by NA were also hyperpolarized by NA when the alpha 1‐adrenoceptors were blocked by prazosin (all of seven neurones tested). This result suggests that most vagal motoneurones in the d.m.v. have both alpha 1‐and alpha 2‐adrenoceptors. 6. The NA depolarization was accompanied by a decrease in membrane conductance and the hyperpolarization by an increase in membrane conductance, both of which were measured under manual‐clamp conditions. 7. The reversal potentials for the NA responses were around ‐85 mV in normal Ringer solution, and shifted as predicted by the Nernst equation when the extracellular K+ concentration was changed. 8. The inhibitory postsynaptic potentials evoked by focal electrical stimulation on the slice surface of the commissural part of the nucleus of the tractus solitarius (n.t.s.), which contains an A2 catecholaminergic cell group, were abolished by yohimbine. 9. The results suggest that NA modulates vagal output by decreasing or increasing the K+ conductance of d.m.v. neurones through alpha 1‐ or alpha 2‐adrenoceptors. In addition, the A2 noradrenergic cell group within the n.t.s. may send inhibitory inputs to the d.m.v.
Outward currents of single hippocampal cells obtained from the adult guinea‐pig.
Authors: Numann R E , Wadman W J , Wong R K
Published: December 2014

1. Neurones were isolated from the hippocampus of adult guinea‐pigs by enzymatic and mechanical treatment. The electrophysiological properties of these cells were examined immediately after dissociation by intracellular recordings using low‐resistance electrodes (2‐5 M omega). 2. Pyramidal‐shaped cells were identified visually. Intracellular recordings showed that these cells have input resistances ranging from 200 to 1300 M omega. Passive voltage responses to hyperpolarizing current injection were fitted by single exponentials decaying with time constants ranging from 15 to 60 ms. This suggests that the electrotonic structure of these cells is compact such that injected current elicited isopotential intracellular responses. 3. Outward currents activated by depolarization were examined in these cells using voltage‐clamp techniques. The amplitude and the time course of the outward currents were profoundly affected by the holding potential. For cells held at ‐50 mV or more positive, depolarizing steps produced a slowly rising outward current. At holding potentials negative to ‐55 mV depolarizing pulses produced an additional early transient outward current followed by a slowly rising component which decayed gradually during sustained depolarizations. 4. The outward currents were separated by their kinetic properties and their sensitivity to cobalt (Co2+), tetraethylammonium (TEA) and 4‐aminopyridine (4‐AP). 5. The transient current peaked within 6 ms of the onset of depolarizing pulses. It decayed exponentially with a time constant of 20‐40 ms. The amplitude of the current activated by a fixed depolarization increased gradually as the duration or the amplitude of the hyperpolarizing pre‐pulse increased. The current activated by a fixed depolarization reached its half‐maximal level when the hyperpolarizing pre‐pulse was at ‐83 mV. 6. 4‐AP exerted two actions on the transient current. Firstly, the time constant of the falling phase decreased by about a factor of two. Secondly, the current was blocked in a time‐ and voltage‐dependent manner: the block increased when the hyperpolarizing pre‐pulse lengthened. TEA, up to 10 mM, did not affect the amplitude of the transient current. Co2+ suppressed this current. The effects of Co2+ consisted of a shift to the positive direction of the voltage dependence of the current. 7. The delayed currents can be divided into Ca2+‐dependent and Ca2+‐independent components. The component persistent in the Co2+ solution (K‐current) decayed slowly with maintained depolarization (time constant greater than 3 s).(ABSTRACT TRUNCATED AT 400 WORDS)
The effects of frusemide, saralasin and hypotension on fetal plasma renin activity and on fetal renal function.
Authors: Lumbers E R , Stevens A D
Published: December 2014

1. In eleven chronically catheterized fetal sheep aged 124‐142 days, hypotension caused by infusion of sodium nitroprusside (1.6‐3.3 mg/h) and competitive antagonism of angiotensin II by saralasin (3.3 mg/h) both caused a fall in fetal urine flow (P less than 0.02 and P less than 0.05, respectively), and in sodium excretion (P less than 0.05 and P less than 0.01) because they both caused a fall in glomerular filtration rate (G.F.R., P less than 0.02 and P less than 0.01). Neither hypotension nor saralasin had any significant effect on fractional sodium reabsorption. Saralasin only caused a significant fall in systolic pressure (P = 0.05) while infusion of sodium nitroprusside caused a fall in both systolic and diastolic pressure (P less than 0.005 and P less than 0.02). 2. Frusemide (6 mg I.V) caused a marked natriuresis and diuresis (F = 24.9, P less than 0.005 and F = 30.5, P less than 0.005). This effect was maximal within 30 min. There was no change in fetal G.F.R. and there was a significant decrease in the fraction of the filtered sodium load that was reabsorbed (F = 10.44, P less than 0.0025). Fetal mean plasma renin activity (p.r.a.) rose progressively throughout (F = 9.3, P less than 0.005). When frusemide was given to fetal sheep which were hypotensive because they were infused with sodium nitroprusside, it still caused a diuresis (F = 5.73, P less than 0.025) and the fraction of the filtered sodium load that was reabsorbed decreased (F = 4.06, P less than 0.05) to a similar extent to that seen in animals given frusemide alone. On the other hand, frusemide was ineffective as a diuretic i.e. it had no effect on fractional sodium reabsorption, when given to fetal sheep which were infused with saralasin. 3. Injection of frusemide was associated with a significant rise in the diastolic pressures of hypotensive fetuses (P less than 0.05). Furthermore, when the infusion of saralasin was terminated 1.5 h after frusemide injection, blood pressure rose significantly (F = 11.19, P less than 0.0005 for systolic pressure and F = 7.15, P less than 0.005 for diastolic pressure) and p.r.a. fell (F = 4.78, P less than 0.025). 4. It is concluded that the fetal renin‐angiotensin system can play a significant role in regulation of fetal blood pressure.(ABSTRACT TRUNCATED AT 400 WORDS)
Pharmacologically distinct actions of serotonin on single pyramidal neurones of the rat hippocampus recorded in vitro.
Authors: Andrade R , Nicoll R A
Published: December 2014

1. The actions of serotonin (5‐HT) on pyramidal cells of the CA1 region of the rat hippocampus were characterized using intracellular recording in in vitro brain slices. 2. 5‐HT typically evokes a biphasic response consisting of a hyperpolarization which is followed by a longer‐lasting depolarization. These effects on membrane potential are accompanied by a decrease in the calcium‐activated after‐hyperpolarization (a.h.p). 3. Detailed analysis using 5‐HT antagonists and agonists indicates that the hyperpolarization is mediated by a 5‐HT1A receptor. Spiperone is the most effective antagonist of the response and the selective 5‐HT1A agonist, 8‐OHDPAT, behaves as a partial agonist at this receptor. In agreement with the distribution of 5‐HT1A binding sites, responses to 5‐HT were most prominent in the stratum radiatum. 4. The hyperpolarizing response is associated with a decrease in input resistance, is blocked by extracellular barium and intracellular caesium, is unaffected by the chloride gradient, and its reversal potential shifts with the extracellular concentration of potassium as predicted for a response mediated by a selective increase in potassium permeability. 5. The depolarizing response and reduction in the a.h.p. could be studied in isolation by blocking the hyperpolarizing response with either pertussis toxin or spiperone. The pharmacology of these responses did not correspond to that of any of the 5‐HT binding sites reported in C.N.S. tissue. Although the depolarization and blockade of the a.h.p. have the same time course it is unclear if they are mediated by the same or different receptors. 6. The depolarization most likely results from a decrease in resting potassium conductance. However, neither a blockade of the M current nor the a.h.p. current can account for the depolarization. 7. Blockade of phosphodiesterase activity by 3‐isobutyl‐1‐methylxanthine (IBMX) did not enhance the depressant action of 5‐HT on the a.h.p., making it unlikely that this action is mediated by cyclic AMP. 8. Blockade of the a.h.p. by 5‐HT reduces spike frequency adaptation and counteracts the inhibitory action of 5‐HT on 5‐HT1A receptors. This excitatory action outlasts the hyperpolarizing action. 9. In summary 5‐HT acts on at least two distinct receptors on hippocampal pyramidal cells, one coupled to the opening of potassium channels and a second coupled to a decrease in a resting potassium conductance and a decrease in the a.h.p.
Single‐channel recordings of three types of calcium channels in chick sensory neurones.
Authors: Fox A P , Nowycky M C , Tsien R W
Published: December 2014

1. T‐, and L‐type Ca2+ channels were studied in cell‐attached patch recordings from the cell bodies of chick dorsal root ganglion neurones. All experiments were performed with isotonic BaCl2 (110 mM) in the recording pipette and with isotonic potassium aspartate in the bathing solution to zero the cell membrane potential. 2. L‐type channels are distinguished by a unitary slope conductance of 25 pS, activation over the range of membrane potentials between 0 and +40 mV, little inactivation over the course of a 136 ms depolarization, and availability for opening even at depolarized holding potentials (h.p. greater than ‐40 mV). L channels show a predominant mode of gating (mode 1) characterized by brief openings (approximately 1 ms), occasionally interspersed with another pattern of gating characterized by much longer openings (mode 2). 3. The dihydropyridine (DHP) Ca2+ agonist Bay K 8644 promotes mode 2 activity and shifts the voltage dependence of L‐type channel activation towards more negative potentials. It leaves the unitary current‐voltage relation unchanged. 4. Nifedipine, a DHP Ca2+ antagonist, strongly inhibits L‐type channel activity through an increase in the proportion of blank sweeps. 5. T‐type Ca2+ channels are distinguished by a much smaller unitary slope conductance (8 pS) and by activation and inactivation over relatively negative ranges of potential. Inactivation is complete by the end of 136 ms pulses to test potentials beyond ‐20 mV. 6. N‐type Ca2+ channels are distinguished by an intermediate unitary slope conductance (13 pS), and by activation over a range of potentials between those of T‐ and L‐type channels. Inactivation of N‐type channels takes place over an exceptionally broad range of holding potentials (‐80 to ‐20 mV). 7. Cell‐attached patch data on the voltage dependence of activation and inactivation of T‐ and N‐type channels are in excellent agreement with results from whole‐cell recordings (Fox, Nowycky & Tsien, 1987) if allowances are made for variations in external surface potential. 8. Patches containing one or two channels of a single type were used for analysis of gating kinetics. The predominant pattern of activity for each of the channel types is an exponential distribution of relatively brief (approximately 1 ms) openings, and a bi‐exponential distribution of short and long closings. 9. Patches containing all possible combinations of channel types were observed. However, preliminary evidence suggests that channels are distributed unevenly over the cell body; clustering of N‐type channels is particularly prominent.(ABSTRACT TRUNCATED AT 400 WORDS)
Responses mediated by excitatory amino acid receptors in solitary retinal ganglion cells from rat.
Authors: Aizenman E , Frosch M P , Lipton S A
Published: December 2014

1. The pharmacological properties of excitatory amino acid responses on ganglion cells dissociated from the rat retina were examined with the use of the whole‐cell voltage‐clamp technique. 2. L‐Glutamate at a concentration of 50 microM produced inward non‐desensitizing currents at negative holding potentials in nearly every cell tested (83%, n = 18) In physiological solutions, L‐glutamate responses reversed at approximately ‐9 mV, and higher concentrations of this agonist introduced a desensitizing component to the response. 3. At negative holding potentials, kainate (25‐125 microM) produced inward currents in all of the cells tested (n = 37). These currents never desensitized, even at high agonist concentrations, and reversed near ‐6 mV. Currents induced by 50 microM‐kainate were reversibly antagonized by kynurenate (100‐300 microM) but not by 100 microM‐2‐amino‐5‐phosphonovalerate (APV). 4. Quisqualate generated smaller, non‐desensitizing currents in only 50% of the cells tested (n = 38). Quisqualate responses reversed in polarity near ‐4 mV and were maximal at an agonist dose of 25 microM, with higher concentrations introducing a rapidly desensitizing component without a detectable increase in amplitude. Currents produced by quisqualate at a concentration of 50 microM were not antagonized by either 750 microM‐kynurenate or 100 microM‐APV. 5. N‐Methyl‐D‐aspartate (NMDA) produced inward currents at negative holding potentials in 68% of the cells tested (n = 31), but only when magnesium was excluded from the extracellular medium. NMDA currents were non‐desensitizing at agonist concentrations of up to 200 microM, with higher concentrations introducing a rapidly desensitizing component. NMDA (200 microM) responses were blocked by APV (100 microM) and kynurenate (300 microM) and reversed near ‐1 mV. 6. Responses generated by kainate (50‐125 microM) were antagonized by quisqualate (30‐250 microM). This antagonism occurred even in cells having no measurable response to quisqualate alone, suggesting the possibility that quisqualate may be acting both as an agonist, in the 50% of the cells that have the quisqualate‐specific receptor, and as an antagonist, at the kainate‐specific site on all cells.(ABSTRACT TRUNCATED AT 400 WORDS)
The responsiveness of neurones in the frontal opercular gustatory cortex of the macaque monkey is independent of hunger.
Authors: Rolls E T , Scott T R , Sienkiewicz Z J , Yaxley S
Published: December 2014

1. In order to determine whether the responsiveness of neurones in the primary gustatory cortex is influenced by hunger, the activity of neurones in the gustatory cortex in the frontal operculum was recorded while macaque monkeys (Macaca fascicularis) were fed to satiety. The responses of single neurones in the gustatory cortex to the prototypical taste stimuli glucose, NaCl, HCl and quinine hydrochloride, and to fruit juice, were measured before, while, and after the monkey was fed to satiety with glucose or fruit juice. 2. While behaviour turned from avid acceptance to active rejection upon repletion, the responsiveness of the neurones to the stimulus array, including the satiating solution, was unmodified. 3. It is concluded that in the gustatory cortex in the frontal operculum, neuronal responses to gustatory stimuli are not influenced by the normal transition from hunger to satiety. This is in contrast to the responses of a population of neurones recorded in the hypothalamus, which only occur to the taste of food when the monkey is hungry. Thus the neurones in the primary gustatory cortex are involved in a motivation‐independent analysis of gustatory stimuli, whereas the hypothalamic neurones may be more closely related to the influence of motivational state on behavioural responsiveness to gustatory stimuli.
Open‐state substructure of inwardly rectifying potassium channels revealed by magnesium block in guinea‐pig heart cells.
Authors: Matsuda H
Published: December 2014

1. Outward single‐channel currents through inwardly rectifying K+ channels of cardiac myocytes were studied in the open cell‐attached configuration to clarify the mechanism of the rectification. The outward currents, which were not recorded in the cell‐attached configuration, appeared after the inner surface of the patch was exposed to low‐Mg2+ solution by rupturing a part of the cell membrane. 2. The single‐channel current‐voltage (I‐V) relation was linear in the absence of Mg2+ and crossed the voltage axis near the equilibrium potential for K+ (EK). The channel conductance was 22 and 16 pS (15‐16 degrees C) at external K+ concentrations of 150 and 40 mM, respectively. 3. The channel rapidly closed on stepping the membrane potential of the patch to values more positive than EK. Decay of the average current during depolarization was fitted with a single‐exponential function. The time constant appeared voltage dependent, but also tended to increase slowly with time after opening the cell to the bath solution. 4. Mg2+ on the cytoplasmic side blocked the outward currents without affecting the inward currents. The half‐saturation concentration of the Mg2+ block was 1.7 microM as examined by measuring the mean patch current at +70 mV. 5. In the presence of internal Mg2+ at a micromolar level (2‐10 microM), the outward single‐channel current fluctuated between four levels including two intermediate levels (sublevels) in addition to the fully open channel current and the zero‐current levels. The I‐V relations of each sublevel were equally spaced with an interval of about 7 pS. Corresponding sublevels were found spontaneously in the inward direction. 6. Occupancy at each level was estimated from reconstructed traces at various Mg2+ concentrations and voltages, and compared with the value predicted from the binomial theorem. At different probabilities for the blocked state, the distribution of the current levels showed reasonable agreement with the binomial theorem. These findings suggest that the inwardly rectifying K+ channel of cardiac cells is composed of three identical conducting subunits and each subunit is blocked by Mg2+ independently. 7. Dwell times in each substate were distributed exponentially. On the assumption of the above model, the blocking (mu) and unblocking (lambda) rates were calculated. The value of mu increased with higher Mg2+ concentrations or larger depolarizations, while lambda ranged between 50 and 90 s‐1 and seemed independent of Mg2+. 8. Owing to the voltage‐dependent block by Mg2+, the average current decayed exponentially on depolarization beyond EK.(ABSTRACT TRUNCATED AT 400 WORDS)
Effects of varying patterns of external compression on lymph flow in the hindlimb of the anaesthetized sheep.
Authors: McGeown J G , McHale N G , Thornbury K D
Published: December 2014

1. Lymphatics draining the region distal to the fetlock were cannulated in anaesthetized sheep. A pneumatic cuff was used to intermittently compress the drainage area. 2. Intermittent inflation of the cuff accelerated lymph flow. This effect increased dramatically as the frequency of inflation was increased. 3. With a constant inflation time, increasing the time between inflations increased the additional volume of lymph expelled per external compression threefold over the range of 0.5‐8 s. Longer intervals produced little further change. 4. There was no significant difference between the effects on lymph volume per compression of intermittent cuff inflations lasting from 1 to 18 s with a constant time between inflations. 5. A cuff pressure of 20 mmHg produced a significant rise in lymph flow. Increasing the pressure applied during cuff inflation increased the effect up to the maximum pressure used (320 mmHg). 6. These studies demonstrate that the promotion of lymph formation by tissue compression is related to the number of compressions applied and the period of time between them. Increasing the pressure exaggerates the effect but increasing the length of each compression does not. This suggests that compression empties the terminal lymphatics centripetally. These vessels refill after compression is released and in our preparation this is complete in about 8 s.
Effects of okadaic acid on isometric tension and myosin phosphorylation of chemically skinned guinea‐pig taenia coli.
Authors: Bialojan C , Rüegg J C , Takai A
Published: December 2014

1. In guinea‐pig taenia coli skinned with Triton X‐100, the marine sponge toxin okadaic acid (OA; 0.1‐10 microM) produced a dose‐dependent enhancement of isometric tension in the presence of low concentrations (0.1‐1 microM) of Ca2+. 2. The Ca2+‐tension relation of the skinned taenia showed a high co‐operativity (Hill coefficient, h = 5) in the presence of 0.2 microM‐calmodulin. The concentration of Ca2+ required to obtain half‐maximal tension (ED50) was 1.8 microM. OA (5 microM) reduced the co‐operativity (h = 2.3) and increased the Ca2+ sensitivity (ED50 = 0.92 microM‐Ca2+). OA further increased the tension produced with 30 microM‐Ca2+, while it failed to produce any mechanical effect in Ca2+‐free solution. When the calmodulin concentration was increased the Ca2+ sensitivity increased as well, but the co‐operativity was not affected both in the absence and in the presence of OA. 3. The level of myosin phosphorylation was analysed by two‐dimensional gel electrophoresis. OA produced an increase in phosphorylated light chains and a concomitant decrease in unphosphorylated light chains. The effect was completely reversed when OA was washed out. 4. In solutions containing more than 1 microM‐Ca2+, a third protein band appeared on the gels next to the bands of light chains. OA markedly increased the third band which disappeared when OA and Ca2+ were simultaneously removed. 5. OA reversibly slowed down both relaxation and dephosphorylation induced by Ca2+ removal following activation with 30 microM‐Ca2+. Complete relaxation did not occur in the presence of more than 1 microM‐OA. The concentration of OA required to produce a 50% reduction (ID50) of the relaxation rate was 78 nM. 6. The phosphatase activity in the taenia extract was inhibited by OA (1‐10 microM) in a dose‐dependent manner. The inhibition was well described as a mixed noncompetitive inhibition, and the dose‐inhibition relation was shifted to the right when the concentration of substrate (phosphorylated light chains) was increased. The lower and upper limits of the change of ID50 produced by changing the substrate concentration were estimated to be 10 and 165 nM‐OA, respectively. 7. These results strongly suggest that the tension enhancement and the slow‐down of relaxation are both causally related to inhibition of myosin phosphatase activity by OA.
Response properties of motoneurones in a slice preparation of the turtle spinal cord.
Authors: Hounsgaard J , Kiehn O , Mintz I
Published: December 2014

1. Motoneurones in transverse sections of the turtle spinal cord were investigated in vitro with intracellular recording techniques. 2. Turtle motoneurones had a resting membrane potential of ‐60 to ‐80 mV, spike height of 90‐110 mV and were able to maintain rhythmic firing during depolarization. In agreement with the size variation of the cells the input resistance and time constant ranged from 18 M omega and 12 ms to 55 M omega and 61 ms. 3. The active response properties of motoneurones included time‐dependent inward rectification in response to hyperpolarizing current pulses. The action potential had an initial segment (IS) and a soma‐dendritic (SD) component and was followed by a fast and a slow after‐hyperpolarization (AHP) with different sensitivity to membrane potential. 4. The relation between firing rate and injected current was sigmoid when determined for the first few interspike intervals during depolarizing current pulses. Adaptation was biphasic with an early phase lasting 0.5‐1 s and a late phase lasting 10‐20 s. 5. The ionic conductances responsible for the active membrane properties included a tetrodotoxin (TTX)‐sensitive Na+ conductance generating the action potential and a Ca2+ conductance transiently activated during the action potential. A tetraethylamonium (TEA)‐sensitive K+ conductance was responsible for spike repolarization and the fast AHP. A Ca2+‐dependent K+ conductance, blocked by Mn2+ and apamin, accounted for only part of the slow AHP. The time‐dependent inward rectification was selectively blocked by extracellular Cs+ at concentrations below 1 mM. 6. The results show that the response properties of spinal motoneurones of the turtle are closely similar to those known from mammals in vivo. The experiments confirm and extend the identification of the ionic conductances underlying the active response properties of spinal motoneurones.
Noise and single channels activated by excitatory amino acids in rat cerebellar granule neurones.
Authors: Cull-Candy S G , Howe J R , Ogden D C
Published: December 2014

1. Glutamate‐receptor ion channels in rat cerebellar granule cells maintained in explant cultures have been investigated with patch‐clamp methods. Properties of these channels were determined from noise analysis of whole‐cell currents and from noise and single‐channel currents recorded in outside‐out membrane patches. 2. Glutamate (10‐20 microM) evoked two types of response. Some granule cells gave small inward currents accompanied by clear increases in current noise ('large noise' responses), whereas other cells gave larger inward currents and small noise increases ('small noise' responses). 3. A mean single‐channel conductance (gamma) of 46.6 pS was estimated for glutamate from four 'large noise' cells. A mean gamma value of 8.4 pS was estimated for seven other 'large noise' cells. The results suggest that in these latter cells glutamate activated both large (approximately equal to 50 pS) and small conductance (approximately equal to 140 fS) channels. 4. Applications of aspartate (10‐30 microM) or N‐methyl‐D‐aspartate (NMDA, 10‐30 microM) produced small inward currents and large increases in noise; gamma noise = 48.5 pS (aspartate) and 46.7 pS (NMDA). 5. Large single‐channel currents were evoked by glutamate, aspartate and NMDA in outside‐out patches. The mean conductance values obtained for the largest amplitude openings were: gamma(glutamate) = 49.5 pS, gamma(aspartate) = 51.5 pS, and gamma(NMDA) = 53.0 pS. For each agonist, these 50 pS openings comprised 75‐85% of the completely resolved currents in each patch. Openings to 40 and 30 pS conductance levels accounted for 10‐15% and 3‐7% of the total, and the presence of apparently direct transitions between these levels and the 50 pS level suggests they are sublevels of the same multi‐conductance channels. 6. A mean channel conductance of 22.9 pS was estimated from noise evoked by quisqualate (10‐30 microM). Single‐channel currents were examined in four patches. In two, quisqualate evoked predominantly small currents of two amplitudes, gamma = 8.4 pS and 16.5 pS; some 50 pS openings were also present. In the other two patches, most openings were 50 pS events. 7. Granule cells gave inward currents to kainate (10‐30 microM), and a mean conductance of 3.1 pS was estimated from kainate noise. In patches in which aspartate or NMDA produced mainly 50 pS openings, more than 74% of the single‐channel currents evoked by kainate were of smaller amplitude, with mean conductances of gamma = 8.1 and 15.1 pS.(ABSTRACT TRUNCATED AT 400 WORDS)