bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of sodium‐hydrogen exchange on intracellular pH, sodium and tension in sheep cardiac Purkinje fibres.
Authors: Kaila K , Vaughan-Jones R D
Published: December 2014

1. The influence of sarcolemmal Na+‐H+ exchange upon intracellular Na+ activity (aiNa), intracellular pH (pHi), extracellular surface pH (pHs) and tonic tension was investigated in sheep cardiac Purkinje fibres. Intracellular ion activities were measured with liquid sensor ion‐selective micro‐electrodes. A two‐micro‐electrode voltage‐clamp was also used to control membrane potential while simultaneously recording tonic tension. 2. Inhibition of the sarcolemmal Na+‐K+ pump by strophanthidin (10 mumol/l) produced a rise in aiNa, an increase in [Ca2+]i as evidenced by a rise in tonic tension, and a fall in pHi of 0.1‐0.3 units. The intracellular acidosis has been shown previously to be linked to the rise in [Ca2+]i (Vaughan‐Jones, Lederer & Eisner, 1983). 3. Amiloride (1‐2 mmol/l), an inhibitor of Na+‐H+ exchange, produced a small reversible decrease in pHi and aiNa. Both effects became more pronounced in strophanthidin‐exposed fibres. In addition, pHi decreased during application of strophanthidin and this decrease was reversibly inhibited by amiloride. It is concluded that sarcolemmal Na+‐H+ exchange is stimulated following inhibition of the Na+‐K+ pump. 4. In strophanthidin‐exposed fibres, a rise in [Ca2+]i resulted in an intracellular acidosis which could still be observed in the presence of amiloride (1 mmol/l). This suggests that the fall in pHi was not caused by a modulatory effect of [Ca2+]i on sarcolemmal Na+‐H+ exchange. 5. Tetrodotoxin (TTX) produced a small fall in aiNa (ca. 0.5 mmol/l) which was not augmented in the presence of strophanthidin. Furthermore, the effects on aiNa of TTX and amiloride were additive. Thus the influence of amiloride on aiNa does not involve blockade of voltage‐gated Na+ channels. 6. The stoicheiometry of Na+‐H+ exchange, estimated from the rates of change of pHi and aiNa in amiloride, appeared to be electroneutral (1:1). The stoicheiometry was unaffected by changes in pHi. 7. In strophanthidin‐exposed fibres (i.e. aiNa is elevated), the recovery of pHi from an intracellular acidosis (brought about by brief exposure to NH4Cl) was slowed greatly by amiloride (1‐2 mmol/l). The rise in aiNa that occurred during pHi recovery was also reduced by amiloride. It is concluded that Na+‐H+ exchange can be stimulated by a fall in pHi under conditions where aiNa is elevated. However, at a given pHi, its rate of recovery was slower in the presence than in the absence of strophanthidin.(ABSTRACT TRUNCATED AT 400 WORDS)
Factors influencing the ascending limb of the sarcomere length‐tension relationship in rabbit skinned muscle fibres.
Authors: Allen J D , Moss R L
Published: December 2014

1. The length dependence of Ca2+‐activated tension within the ascending limb of the length‐tension relationship, corresponding to sarcomere lengths below about 2.25 micron, was investigated in skinned fibres from rabbit psoas muscle. At high [Ca2+] a shallow phase and then a steep phase of tension decline were observed as sarcomere length was reduced, while at low [Ca2+] tension decreased monotonically with decreases in sarcomere length. The sarcomere length at which the ascending limb intersected zero tension was greater for lower concentrations of Ca2+. 2. The length tension relationship from maximally activated fibres changed when filament lattice spacing was reduced by osmotic compression. Relationships obtained in the presence of 5% (w/v) dextran T500 more distinctly demonstrated both the shallow and steep portions of the ascending limb than did relationships from untreated fibres. 3. As striation spacing was decreased a progressive decline in the Ca2+ sensitivity of tension development was observed. Tension‐pCa relationships from both control and dextran‐treated fibres underwent a rightward shift (i.e. to a higher [Ca2+]) by 0.23 pCa units as sarcomere length was reduced between 2.46 and 1.54 microns. 4. Fibre stiffness was studied by applying a 3.3 kHz sinusoidal length change at one end of the fibre and measuring the resultant tension change. At submaximal activation (pCa 5.8), stiffness increased relative to tension as sarcomere length was decreased below approximately 2.4 microns, suggesting that there is an activation‐related internal load at low [Ca2+]. At maximal activation, a significant increase in this ratio occurred only at sarcomere lengths less than approximately 1.8 microns, and presumably involved collision of the thick filaments with the Z‐lines. 5. Length‐dependent changes in the Ca2+ sensitivity of tension development do not appear to be the result of shortening‐induced dissociation of Ca2+ from troponin‐C, the Ca2+ binding subunit of troponin. Fibres activated in the absence of Ca2+, by the partial removal of whole troponin complexes, produced length‐tension relationships similar to those observed in the same fibres before troponin removal at a submaximal [Ca2+] yielding similar active tensions.
Changes in renal sympathetic nerve activity, heart rate and arterial blood pressure associated with eating in cats.
Authors: Matsukawa K , Ninomiya I
Published: December 2014

1. Renal sympathetic nerve activity, heart rate and arterial blood pressure were simultaneously measured in thirteen awake cats before, during and after eating which was evoked by presenting food for a period of 10‐15 s. 2. With food presentation, eating behaviour occurred in 93% (191) of 205 trials, and renal sympathetic nerve activity significantly increased in 65% of the 191 trials. On the other hand, in many of food presentation trials when no eating occurred, or with presentation of an empty food box, renal sympathetic nerve activity did not change significantly. 3. Eating started 1‐8 s after the food presentation. The increase in renal sympathetic nerve activity was closely related to the beginning of eating but not to the onset of food presentation. Renal sympathetic nerve activity and heart rate increased with a slight time lag of 0.5‐1.5 s from the onset of eating, whereas an increase in arterial blood pressure followed the onset of eating by 5.5 s. After the beginning of eating, renal sympathetic nerve activity, heart rate and arterial blood pressure increased at a maximum of 61 +/‐ 18% (mean +/‐ S.E. of mean), 26 +/‐ 4.0 beats/min, and 17 +/‐ 4.9 mmHg from the control values at 1.0, 5.5 and 11.5 s, respectively. 4. Cardiac‐related grouped discharges of renal sympathetic nerve activity, which were observed at rest, increased during eating. 5. When arterial blood pressure was elevated by noradrenaline (2‐5 micrograms/kg I.V.), renal sympathetic nerve activity during resting was almost completely inhibited and the increase in renal sympathetic nerve activity during eating was not induced. 6. We conclude that renal sympathetic nerve activity increases in association with eating behaviour but not as firmly with the food presentation, and that the increase in renal sympathetic nerve activity is initiated by descending input from the higher central nervous system rather than either by the viscero‐autonomic reflex due to food intake or by the baroreflex due to a decrease in arterial blood pressure.
The temperature dependence of isometric contractions of single, intact fibres dissected from a mouse foot muscle.
Authors: Lännergren J , Westerblad H
Published: December 2014

1. Isometric tension responses to electrical stimulation have been studied at 7.5 37.5 degrees C in single, intact fibres of the flexor digitorum brevis muscle of the mouse. A large number of reproducible tetani could be obtained at temperatures less than or equal to 35 degrees C. 2. The tetanic force per cross‐sectional area generated at 25.0 degrees C was 375 +/‐ 56 kPa (mean +/‐ S.D., n = 16). 3. The curve relating maximum tetanic tension to temperature exhibited a transition between a level of almost unaltered force (25.0‐32.5 degrees C) and a marked force decline (less than or equal to 20.0 degrees C). At temperatures higher than 35.0 degrees C force production was markedly depressed and this reduction was in some cases irreversible. 4. Twitch tension showed less regular dependence on temperature; it was reduced less than tetanic tension at low temperatures. Thus, the twitch/tetanus tension ratio was higher at low temperatures. 5. The times for twitch contraction and for twitch half‐relaxation (i) ranged from 7 to 14 ms and from 6 to 15 ms at 35.0 degrees C and (ii) exhibited Q10 values of 3.2 +/‐ 0.4 and 4.0 +/‐ 0.6, respectively. 6. It is concluded that it is possible to use intact, single fibres dissected from mammalian skeletal muscle in physiological studies. Our results are close to previous results obtained from mammalian muscles except that the tetanic tension per cross‐sectional area was found to be higher than commonly reported.
Some properties of a system for sodium‐dependent outward movement of magnesium from metabolizing human red blood cells.
Authors: Lüdi H , Schatzmann H J
Published: December 2014

1. In agreement with the report by Féray & Garay (1986) it is shown that Mg2+ leaves human red cells mainly by a saturable pathway at a maximal rate of some 200 mumol 1(‐1) cells h(‐1) only if the medium contains Na+.Mg2+0.5 (i.e. the free Mg2+ concentration for half‐maximal rate) at the internal membrane surface is 1.3 mM and the dissociation constant for Na+, KNa, at the external surface is 16‐17 mM. Mg2+ shows co‐operative behaviour. The Na+o‐stimulated Mg2+ outflow is sensitive to millimolar amiloride concentrations. Implication of the Na+ or Ca+ pump can be ruled out. 2. Na+i is inhibitory by simple competition with Na+o. The affinity for Na+ inside is the same as outside. There is no detectable competition between Na+i and Mg2+i. 3. At approximately 1 mM‐[Mg2+]i the outward Mg2+ movement stimulated by Na+o still proceeds when [Mg2+]o is increased up to 20 mM. Thus the Mg2+ movement is uphill and the apparent Mg2+0.5 at the external surface is larger than 20 mM. 4. Reversing the Na+ gradient (making [Na+]i greater than [Na+]o) does not elicit an inward Mg2+ movement, even if [Mg2+]o is simultaneously made larger than [Mg2+]i. 5. The Na+o‐dependent Mg2+ outflow ceases nearly completely (falling to 5% of the control) in metabolically depleted cells. 6. The behaviour observed is compatible with the assumptions that (1) the system possesses distinct binding sites for Na+ and for Mg2+, (2) the ionophoric moiety is passively mobile when loaded with Na+, (3) the movement of the Na+ form is rate limiting, and (4) the Mg2+ form preferentially moves in the outward direction owing to an input of metabolic energy (ATP hydrolysis) and is immobile in starved cells. 7. Mg2+ may be required at a further site(s) not involved in the actual Mg2+ translocation but in the energy input. The simple kinetics suggesting translocation of one Na+ ion in exchange for one Mg2+ ion were found in selected cells of average maximum transport rate (Vmax) and may not hold for all cell specimens. 8. The conclusion is that the system is a Mg2+ extrusion pump driven by metabolic energy directly and not by the inward Na+ gradient, although net inward Na+ movement is necessary to bring the ionophoric part of the system back to the in‐position. It appears that in intact cells the system operates far below saturation by Mg2+i and, by compensating for an inward leak of less than 5 mumol,1(‐1) cells h(‐1), sets the internal free Mg2+ concentration at about 0.5 of the equilibrium value.
Calcium current and calcium‐activated inward current in the oocyte of the starfish Leptasterias hexactis.
Authors: Lansman J B
Published: December 2014

1. Inward currents in the immature oocyte of the starfish Leptasterias hexactis were studied with a two‐micro‐electrode voltage clamp. Experiments investigated the role of Ca2+ in the Na+‐dependent plateau of the action potential. 2. Voltage steps more positive than ‐55 mV produced inward currents in normal sea water that activated and then decayed to a non‐zero level with a double‐exponential time course. Returning the voltage to the resting potential produced an inward tail current that relaxed slowly to zero with a time course of seconds. 3. Replacing Na+ with choline abolished the slowly decaying component as well as the slow tail current which followed the end of the voltage pulse. This suggested that inward current in Na+‐containing sea water consisted of a rapidly decaying component that flowed through Ca2+ channels and a more slowly decaying component carried by Na+. 4. Ca2+ current was isolated in Na+‐free sea water. Activation followed a sigmoidal time course that could be described with m2 kinetics. Inactivation during a maintained depolarization followed first‐order kinetics and was voltage dependent. 5. When Ba2+ was substituted for Ca2+ as the divalent ion charge carrier, inward currents in Na+‐containing sea water decayed along a single‐exponential time course. The absence of a slowly decaying Na+ current in Ba2+‐containing sea water suggested that Na+ current depended on Ca2+ influx. 6. The effects of altering Ca2+ influx on the time course of Na+ current were investigated. Na+ current decayed more rapidly as the test pulse potential was made more positive, while raising [Ca2+]o slowed the decaying phase without altering its dependence on membrane potential. 7. Tail currents measured after rapidly stepping the membrane potential back to the resting level consisted of a fast component associated with the closing of Ca2+ channels and a slow component that was abolished by removing Na+. 8. The variation of the amplitude of the slow component of tail current with the duration of the voltage‐clamp pulse indicated that Na+ current is associated with a time‐dependent component of membrane conductance. 9. Possible mechanisms for the slowly decaying Na+ current are considered. The results are discussed in relation to the idea that the conductance change to Na+ follows the time course of Ca2+ accumulation and removal from the cytoplasm.
Excitatory amino acid receptors and synaptic transmission in the rat ventrobasal thalamus.
Authors: Salt T E
Published: December 2014

1. Extracellular single‐neurone recordings were made in the ventrobasal thalamus (v.b.t.) of urethane‐anaesthetized rats with multi‐barrel ionophoretic electrodes in order to test the hypothesis that excitatory amino acid receptors are involved in the responses of these neurones to stimulation of sensory afferents. 2. Responses of neurones to either physiological stimulation of hair and vibrissa follicle sensory afferents and to ionophoretically applied excitatory amino acids were challenged with the antagonists D‐2‐amino‐5‐phosphonovalerate (APV), kynurenate and gamma‐D‐glutamylaminomethyl sulphonate (GAMS). 3. In agreement with previous findings in other brain areas, ionophoretically applied APV was found to selectively antagonize responses of v.b.t. neurones to N‐methylaspartate (NMA), whereas GAMS was found to be moderately kainate selective. Kynurenate was found to be relatively non‐selective. 4. Responses of neurones to short‐duration (10‐20 ms) physiological stimulation of afferents were resistant to APV when this antagonist was applied with NMA‐selective ionophoretic currents. In contrast, these APV currents were adequate to antagonize responses to maintained physiological stimulation. 5. The broad spectrum excitatory amino acid antagonist kynurenate was found to block synaptic responses of v.b.t. neurones to both short‐duration and maintained stimuli when it was applied with currents which were sufficient to reduce responses to ionophoretic quisqualate. 6. GAMS was found to selectively block kainate responses in a proportion of the neurones tested. In such cases, there was little effect of the antagonist on the responses evoked by either short‐duration or maintained sensory stimuli. 7. It is concluded that excitatory amino acid receptors of both the NMDA and non‐NMDA type are involved in the synaptic responses of v.b.t. neurones to sensory afferent stimulation, and that the apparent synaptic pharmacology depends on the mode of stimulation of the afferent pathway.
Maturation of the respiratory response to acute hypoxia in the newborn rat.
Authors: Eden G J , Hanson M A
Published: December 2014

1. We used a non‐invasive method to measure the breathing of conscious newborn rat pups continuously and studied the maturation of the respiratory response to reductions in inspired O2 fraction (FI,O2) from 0.21 to 0.15, 0.12 or 0.08 for 6 min. Newborn rats, like many other species, showed a "biphasic" respiratory response, ventilation (VE) increasing during the first 1‐2 min of hypoxia (phase 1) and then falling towards control, or below it, over the next 4 min (phase 2). 2. The secondary fall in VE decreased with age up to 14 days. The presence of a significant fall in VE in phase 2 depended on the FI,O2 to which the pups were exposed acutely; the lower the FI,O2 the greater the age at which a biphasic VE response was observed. 3. Our results are discussed in terms of two opposing components which determine VE during acute hypoxia in the neonate: (a) a fast arterial chemoreceptor‐mediated stimulation of VE and (b) a slower central nervous component which inhibits VE, possibly a persistence of a suprapontine mechanism which inhibits fetal breathing movements during hypoxia in utero. Both of these components undergo maturation after birth.
The effects of axotomy on bullfrog sympathetic neurones.
Authors: Gordon T , Kelly M E , Sanders E J , Shapiro J , Smith P A
Published: December 2014

1. The effects of axotomy on the electrical properties of B cells in paravertebral sympathetic ganglia were studied using standard intracellular recording techniques. The effects were apparent after 1 week and persisted throughout the 47 days of study. 2. Action potential duration (spike width) and amplitude (spike height) were significantly increased in axotomized neurones. 3. The duration of the after‐hyperpolarization which followed the action potential showed considerable scatter in control neurones (mean +/‐ S.E. of mean, 159.0 +/‐ 5.8 ms for 100 cells). Following axotomy, the duration was significantly reduced (50.9 +/‐ 2.3 ms for 97 cells). The amplitude of the after‐hyperpolarization was also significantly smaller in axotomized neurones. 4. Changes in the characteristics of the action potential and the after‐hyperpolarization in axotomized neurones were not due to alteration in resting membrane potential or input resistance which were unchanged after axotomy. Rheobase current was significantly increased. 5. There was neither a significant depression of the rate of rise or the amplitude of orthodromically evoked nicotinic e.p.s.p.s nor any obvious ultrastructural alteration following axotomy. 6. Despite the decrease in the duration of the after‐hyperpolarization, the rate of discharge in response to constant current injection was little changed in axotomized neurones. 7. Although axotomy produces significant changes in several measurable electrophysiological parameters in bullfrog sympathetic ganglion cells, the present results imply that mature neurones are able to maintain relatively normal electrical activity despite injury.
Calcium current activation kinetics in isolated pyramidal neurones of the Ca1 region of the mature guinea‐pig hippocampus.
Authors: Kay A R , Wong R K
Published: December 2014

1. Neurones were isolated from the CA1 region of the guinea‐pig hippocampus and subjected to the whole‐cell mode of voltage clamping, to determine the kinetics of voltage‐gated Ca2+ channel activation. 2. Isolated neurones had an abbreviated morphology, having lost most of the distal dendritic tree during the isolation procedure. The electrical compactness of the cells facilitates voltage clamp analysis. 3. Block of sodium and potassium currents revealed a persistent current activated on depolarization above ‐40 mV, which inactivated slowly when the intracellular medium contained EGTA. The current was blocked by Co2+ and Cd2+, augmented by increases in Ca2+ and could be carried by Ba2+, suggesting that the current is borne by Ca2+. 4. Steady‐state activation of the Ca2+ current was found to be well described by the Boltzman equation raised to the second power. 5. The open channel's current‐voltage (I‐V) relationship rectified in the inward direction and was consistent with the constant‐field equation. 6. The kinetics of Ca2+ current onset followed m2 kinetics throughout the range of its activation. Tail current kinetics were in accord with this model. A detailed Hodgkin‐Huxley model was derived, defining the activation of this current. 7. The kinetics of the currents observed in this regionally and morphologically defined class of neurones were consistent with the existence of a single kinetic class of channels.
A convergent input from nasal receptors and the larynx to the rostral sensory trigeminal nuclei of the cat.
Authors: Jordan D , Wood L M
Published: December 2014

1. Extracellular recordings were made from ninety‐one neurones in the vicinity of the rostral trigeminal nucleus in chloralose‐anaesthetized cats. 2. Sixty‐two neurones within this area were activated by electrical stimulation of the ipsilateral superior laryngeal nerve (s.l.n.). Only two of the twenty‐one neurones tested had an additional input from the contralateral s.l.n. 3. Fifty of these sixty‐two neurones were also activated synaptically by light mechanical stimulation of the ipsilateral nasal cavity and in the eight neurones tested electrical stimulation of the ipsilateral nostril evoked activity. All these neurones exhibited characteristics of postsynaptic responses to s.l.n. and nasal stimulation, showing a variable latency to onset to either stimulus, summation and facilitation of more than one stimulus. 4. None of those neurones receiving an s.l.n. input, or those with convergent inputs from the s.l.n. and nose, could be affected by mechanical stimulation of any part of the face. 5. The activity of a further twenty‐nine neurones was also recorded within this same general region. Sixteen responded to movement of the whiskers, five to touching the skin of the lower jaw, two to touching the skin of the upper jaw, three to touch around the eyebrows and three to touching other parts of the face. None of these neurones were activated by s.l.n. stimulation. 6. The location of seventeen of these neurones showing a convergent s.l.n. and nasal input was determined histologically. They were closely grouped together in a region 3.5‐4.5 mm rostral to obex in and around the main trigeminal sensory nucleus, dorsolateral to the retrofacial nucleus corresponding to the parvocellular division of the alaminar spinal trigeminal nucleus. 7. The lack of somatosensory input to those neurones receiving a convergent input from the nose and s.l.n. is discussed in relation to previous studies describing somatosensory‐visceral convergence to neurones within trigeminal nuclei.
Repriming and reversal of the isometric unexplained enthalpy in frog skeletal muscle.
Authors: Homsher E , Lacktis J , Yamada T , Zohman G
Published: December 2014

1. heat production and high‐energy phosphate hydrolysis by frog sartorius muscles in 6 s isometric tetani were measured to test the hypothesis that the isometric unexplained enthalpy (u.e.) and labile maintenance heat (l.m.h.) were of similar origin. Muscles were first given a conditioning tetanus to deplete the u.e. and l.m.h. A second (test) 6 s tetanus was given 6‐300 s later to ascertain the extent to which l.m.h. and u.e. had recovered (reprimed). 2. The labile maintenance heat repriming was biphasic: 42% of the conditioning l.m.h. reprimed with a time constant of 10 s, the remainder with a time constant of 500 s. 3. The u.e. produced in the test tetanus 6 s after the conditioning tetanus was reduced to 18% of its conditioning value. By 30 s, u.e. had returned to conditioning values even though the amount of high‐energy phosphate splitting was 17% less than that in the conditioning tetanus. 4. This observation is supported by measurements revealing that during the 30 s following a 6 s tetanus an amount of enthalpy was absorbed (less heat produced than expected from the measured metabolic changes) whose absolute value (after correction for oxygen consumption) was not different from the amount of unexplained enthalpy liberated during the tetanus. 5. The difference in repriming time course shows that l.m.h. and u.e. are not produced by the same reactions. The data are consistent with the hypothesis that calcium binding to troponin and parvalbumin produce u.e. while calcium binding to troponin and a non‐linear time course of ATP hydrolysis produce l.m.h.
The fade of the response to acetylcholine at the rabbit isolated sino‐atrial node.
Authors: Boyett M R , Roberts A
Published: December 2014

1. The effect of acetylcholine (ACh) on the frequency of spontaneous action potentials, recorded with glass microelectrodes from small preparations of the sino‐atrial node of the rabbit, has been investigated. 2. On application of ACh there was a rapid increase in cycle length (the interval between successive action potentials) but then, despite the continued presence of the ACh, cycle length decreased once again; i.e. the response to ACh 'faded' in the presence of ACh. This fade of the chronotropic response to ACh has been characterized. 3. To observe fade it was found to be important to use a fast flow bath in order to increase the ACh concentration at the preparation abruptly. In other words, the response to ACh was sensitive to the rate of increase in the ACh concentration at the tissue. This may explain why in one study of the sino‐atrial node of the guinea‐pig the authors failed to observe fade. 4. The concentration dependence of fade was studied in two ways: either as the fade in the response with different doses of ACh, or as the decrease in the response to a fixed test dose applied after a variable conditioning dose. Both methods indicated that fade increased with concentration over the range of roughly 10(‐7) to 10(‐5) M‐ACh. 5. The onset of fade, i.e. the decline in cycle length during an exposure to ACh, was monophasic with low doses of ACh and biphasic (with fast and slow phases) with higher doses. The mean half‐times of the fast and slow phases of fade were 10 +/‐ 2 s and 240 +/‐ 30 s (mean +/‐ S.E.M.; n = 5). However, in some preparations, rather than a smooth decrease in cycle length, there were discontinuities and cycle length could decrease in a stepwise fashion or even transiently alternate between two distinct states. 6. Time was required for recovery from fade because a response to a test dose applied soon after a conditioning dose was depressed. Recovery was studied by applying test doses at different times after conditioning doses. Recovery occurred with a half‐time of 40 +/‐ 8 s (mean +/‐ S.D.; n = 8) after a short exposure (30 s) to ACh, but was slower (half‐time, 250 +/‐ 20 s; n = 6) after a longer exposure (5 min). 7. Immediately after washing off ACh, cycle length decreased below its original value, although it then returned to this value over several minutes.(ABSTRACT TRUNCATED AT 400 WORDS)
Susceptibility of the developing rat gustatory system to the physiological effects of dietary sodium deprivation.
Authors: Hill D L
Published: December 2014

1. Multifibre responses were recorded from the chorda tympani nerve in rats fed either a NaCl‐deficient diet or a NaCl‐replete diet from 3 days post‐conception to at least 28 days post‐natal. Responses were also recorded in rats fed the NaCl‐deficient diet during early development and then fed the NaCl‐replete diet for 1‐20 days beginning at 28 days post‐natal, and in rats fed the NaCl‐deficient diet only as adults. The epithelial sodium transport blocker, amiloride, was used to study the physiological effects of the diet on taste receptor membrane function and to characterize the events involved in recovery of function. 2. Responses to lingual application of sodium salts increased with increasing stimulus concentration; however, response magnitudes were reduced in rats fed the NaCl‐deficient diet during early development compared to controls. Responses to non‐sodium salts and non‐salt stimuli were similar to controls. Amiloride was ineffective in suppressing taste responses to NaCl in deprived rats but effectively suppressed responses in controls by at least 50%. After early‐deprived rats were fed a NaCl‐replete diet, responses to sodium salts recovered to control levels within 15 days. There was a concomitant decrease in amiloride sensitivity during this period. 3. Rats fed the NaCl‐deficient diet from early gestation through adulthood had responses similar to younger deprived rats in that sodium responses were lower than controls. However, rats deprived only as adults were similar to controls. 4. The peripheral gustatory system in developing rats is susceptible to the sodium content of the diet and is 'plastic' in that early effects can be reversed by restricting dietary sodium. Once dietary manipulations are instituted past a sensitive period, however, functional taste responses seem unaffected.
Atrial receptor discharge in dogs with chronically induced difference in blood volume.
Authors: Hicks M N , Mary D A , Walters G E
Published: December 2014

1. Urinary responses to stimulation of atrial receptors have been found to be greater in dogs with a high blood volume than in dogs with a low blood volume. Two groups of dogs with different blood volume were examined by distending a large balloon in the left atrium, to stimulate atrial receptors and find out whether the increase in atrial receptor discharge was different in the two groups of dogs. 2. The relationship between atrial receptor discharge and left atrial pressure was determined in twenty‐six fibres studied in four dogs with a high blood volume and sixteen fibres studied in three dogs with a low blood volume. 3. The slope of the relationship representing the increase in atrial receptor activity during increases in left atrial pressure, and the activity at each left atrial pressure, were significantly greater in dogs with a high blood volume than in dogs with a low blood volume. 4. This study has shown that the atrial receptor discharge and their responses to increases in left atrial pressure are greater in dogs with a high blood volume than in those with a low blood volume.
Pressure changes in canine gall‐bladder associated with emptying.
Authors: Mathie R T , Plail R O , Stubbs R S
Published: December 2014

1. For decades it has been supposed that emptying of the gall‐bladder follows a rise in gall‐bladder pressure of some 10‐15 mmHg and relaxation of the sphincter of Oddi. 2. This subject has been re‐examined in dogs chronically fitted with fistulas, using a model which does not entail interference with either the bile duct or sphincter of Oddi. 3. The pressure in the gall‐bladder was recorded continuously under fasting conditions, after feeding and after intravenous infusion of the octapeptide of cholecystokinin (CCK‐OP) in six dogs. 4. Gall‐bladder pressure showed a modest sustained rise of 2‐3 mmHg following ingestion of food and intravenous infusions of CCK‐OP (125 ng kg‐1 h‐1). 5. During half of the experiments a transient rise of 3‐10 mmHg lasting 2‐3 min was observed after feeding and following infusion of I.V. CCK‐OP (125 ng kg‐1 h‐1). Emptying of the gall‐bladder, measured by bilirubin output from the biliary fistula, started shortly before the peak rise in pressure occurred. 6. We conclude that a significant rise in gall‐bladder pressure is not a prerequisite for emptying and that the pressure changes occurring physiologically are smaller than have been reported previously. 7. We believe that the larger pressure changes recorded in the past may have been produced because of resistance to bile flow introduced by the models employed. 8. Emptying of the gall‐bladder, in the dog, appears to have occurred within 40 min of the ingestion of food, suggesting that the cephalic and gastric phases of this process are quantitatively more important than has been thought previously.
Post‐natal development of electrophysiological properties of rat cerebral cortical pyramidal neurones.
Authors: McCormick D A , Prince D A
Published: December 2014

1. The post‐natal development of the electrophysiological properties of cortical layer V pyramidal neurons was investigated with intracellular recordings from rat sensorimotor cortical slices, in vitro. 2. At all ages post‐natally (post‐natal day 1 to day 36; P1‐P36) neurons were capable of generating a train of Na+‐dependent action potentials in response to intracellular injection of sufficient depolarizing current. During the second and third week post‐natally, these action potentials changed substantially, becoming faster in both their rising and falling phases, shorter in duration, and larger in amplitude. 3. Both mature (greater than P21) and immature (P2‐P4) cortical neurones could generate Ca2+‐dependent action potentials only if a substantial portion of K+ conductances were blocked. The maximum rate of rise of Ca2+ spikes also increased with age. 4. The apparent input resistance, specific membrane resistance, and membrane time constant all decreased with age from P1 to P30. Immature neurones had I‐V relationships that were substantially more linear than those of adult cells, although rectification was often present in both the hyperpolarizing and depolarizing range. Inward rectification in the depolarizing range was Na+ dependent and was substantially larger in mature versus immature neurones. 5. Single, or trains of, action potentials in immature neurones were followed by short duration (10‐50 ms) and long duration (1‐5 s) after‐hyperpolarizations (a.h.p.s) respectively. The duration of the latter appeared to decrease with age. The presence of large a.h.p.s indicates that Ca2+ entry occurs during the action potential of immature, as well as mature, neurones. 6. Responses to intracellular injection of depolarizing current pulses indicated that immature neurones have frequency versus injected current (f‐I) relationships which are in general less steep than those for adult neurones and more limited in terms of the range of firing frequencies. 7. Our results are consistent with the hypothesis that there is a considerable increase in the density of voltage‐dependent ionic channels underlying the electro‐responsiveness of cortical pyramidal neurones during post‐natal development.
Feeding‐ and chemical‐related activity of ventromedial hypothalamic neurones in freely behaving rats.
Authors: Ono T , Sasaki K , Shibata R
Published: December 2014

1. The activity of seventy‐eight single neurones in the ventromedial hypothalamus (v.m.h.) was recorded in sixty‐three freely behaving rats, and the effects of feeding, intraventricular (I.C.V.) administrations of noradrenaline, glucose, NaCl and ambient temperature on neuronal activity were analysed. If I.C.V. NaCl had an effect, intraperitoneal (I.P.) NaCl, mannitol and polyethylene glycol were also tested. 2. Neurones in the v.m.h. were classified into three groups according to diurnal variations and their relations to electroencephalogram (e.e.g.) and responses to feeding: diurnal‐e.e.g. related (57/78, 73.1%); diurnal‐e.e.g. independent (17/78, 21.8%); non‐diurnal‐e.e.g. independent (4/78, 5.1%). Of fifty‐seven e.e.g.‐related neurones, twenty‐six decreased activity during feeding episodes. Of seventeen e.e.g.‐independent neurones, eight increased activity gradually during feeding and sustained the increase after the feeding episode. The response magnitude of two e.e.g.‐independent neurones depended on the kind of food available. 3. Of twenty‐five e.e.g.‐related neurones tested, twelve responded to I.C.V. noradrenaline, but not to I.C.V. glucose or NaCl. Neurones independent of e.e.g. responded variously to I.C.V. noradrenaline, glucose and NaCl. When I.C.V. NaCl had an effect, I.P. NaCl, mannitol and polyethylene glycol had the same effect. The activity of three neurones was increased by I.C.V. glucose and decreased by I.C.V. noradrenaline, but was not changed by I.C.V. NaCl. The activity of three was increased by I.C.V. glucose and decreased by I.C.V. NaCl and by I.C.V. noradrenaline. The activity of five was increased, and that of three was decreased by I.C.V. glucose, NaCl and noradrenaline. Collectively, fourteen of twenty‐four tested neurones responded to I.C.V. glucose, twenty‐six of forty‐one tested neurones responded to I.C.V. noradrenaline and eleven of twenty‐six tested neurones responded to I.C.V. NaCl. 4. Increase of ambient temperature changed the activity of five e.e.g.‐independent neurones. Directions of these activity changes were the same as directions of responses to NaCl; two up, three down. 5. The results suggest two main neuronal groups in the v.m.h.: the e.e.g.‐related group is involved in the processing of information about sleep‐arousal. The e.e.g.‐independent group contributes to the long‐term processing of information concerned with the regulation of the internal environment such as glucose level, osmotic pressure, NaCl level, the trigger mechanism for feeding, ambient temperature, food preference, etc.
Disabling of the oculomotor neural integrator by kainic acid injections in the prepositus‐vestibular complex of the cat.
Authors: Cheron G , Godaux E
Published: December 2014

1. This study was intended to test the candidature of the prepositus‐vestibular nuclear complex for being the location of the oculomotor neural integrator (Robinson's integrator). 2. Microinjections of kainic acid (2 micrograms dissolved in 1 microliter) were made in awake cats. Injection sites were located either in the prepositus hypoglossi nucleus (p.h.), the medial vestibular nucleus (m.v.n.), the medial longitudinal fasciculus (m.l.f.) or in the magnocellular tegmental field of the reticular formation. 3. Theory predicts that a complete disabling of the neural integrator will cause (a) an exponential post‐saccadic drift whose time constant will be 0.16 s in the dark (b) a phase lead of +93 deg as the vestibulo‐ocular reflex is tested at 0.10 Hz in the dark and (c) a nearly complete abolition of the optokinetic nystagmus (o.k.n.). 4. About 1 h after a unilateral kainic acid injection in the p.h., we observed (a) a large bilateral post‐saccadic drift (time constant sometimes as low as 0.2 s) (b) a large phase lead at 0.10 Hz (range: from +69 to +98 deg) (c) an abolition of the o.k.n. control injection of phosphate buffer in the p.h. did not produce any deficit. 5. A unilateral kainic acid injection in the m.v.n. induced a nystagmus followed by signs of bilateral failure of the neural integrator similar to those observed after kainic acid injection in the p.h. 6. Injection near the mid‐line, between the two p.h. nuclei, induced a defect of the neural integrator less than that observed after kainic acid injection in either the p.h. or the m.v.n. Injection of kainic acid in the magnocellular tegmental field of the reticular formation did not produce any sign of failure of the neural integrator. No post‐saccadic drift was observed. 7. We have concluded that (a) the p.h. nucleus is involved in the integration processing, and that (b) the m.v.n. is involved either in the integration processing or in the relaying of the output of the neural integrator to the oculomotoneurones.
Cerebellar neuronal activity related to arm movements in trained rhesus monkeys.
Authors: Marple-Horvat D E , Stein J F
Published: December 2014

1. The role of the paravermal cerebellum in controlling arm movements in monkeys trained to perform visually guided movements was investigated. Discharge patterns of extracellularly recorded Purkinje, Golgi, nuclear and unidentified cells were correlated with arm position, velocity and acceleration. 2. The discharge of thirty‐seven out of fifty‐two movement‐related Purkinje cells and that of thirty‐three out of forty‐five other movement‐related cerebellar neurones was more highly correlated with limb velocity (0.95 greater than r greater than 0.4) than with position or acceleration. Twelve out of fifty‐two Purkinje cells and twelve out of forty‐five other cells were related to both limb velocity and limb position. Three Purkinje cells were related to limb acceleration and position and no cell was related to position or acceleration alone. 3. Modulation of discharge of these cells usually preceded movement (range ‐240 ms, unit leading movement, to +180 ms, unit lagging; mode ‐36 ms; mean ‐15 ms). 4. Each movement‐related neurone was tested for four directions of movement. All showed a preferred direction in which the correlation with arm movement velocity was highest. However, 43% (30/70) correlated at r greater than 0.4 with movements in a second direction, usually that opposite to their preferred direction. Sixty‐three per cent of these neurones fired earlier during movements in the preferred than in the opposite direction. 5. It is concluded that the paravermal cerebellum may be involved in computing the velocity vectors required for achieving properly directed and co‐ordinated movements of the whole arm.
Excitatory amino acid receptor‐mediated transmission of somatosensory evoked potentials in the rat thalamus.
Authors: Klockgether T
Published: December 2014

1. To examine the role of excitatory amino acid receptors in the rat ventrobasal thalamic nucleus (v.b.t.n.) for the transmission of cortical somatosensory evoked potentials (s.e.p.s), potentials were recorded from the somatosensory cortex of barbiturate‐anaesthetized and of unanaesthetized awake rats. The effects of microapplications of the selective N‐methyl‐D‐aspartate (NMDA) antagonist (‐)‐2‐amino‐7‐phosphono‐heptanoate ((‐)AP7) and the broad‐spectrum excitatory amino acid antagonist 1‐(p‐chlorobenzoyl)‐piperazine‐2,3‐dicarboxylate (pCB‐PzDA) into the thalamus on the amplitudes and latencies of cortical potentials were measured. 2. To define the receptor specificity of local microinjections of (‐)AP7 and pCB‐PzDA electroencephalogram (e.e.g.) recordings were made from the immediate vicinity of the injection cannula within the thalamus. (‐)AP7 selectively antagonized epileptic discharges induced by NMDA, but not those by kainate, whereas pCB‐PzDA antagonized epileptic discharges induced by both. 3. In both anaesthetized and unanaesthetized rats, microapplications of pCB‐PzDA into the thalamus suppressed transmission of cortical potentials as indicated by a decrease of their amplitudes and an increase of their peak latencies. Further experiments in anaesthetized rats showed that pCB‐PzDA exerted its effects in a dose‐dependent and site‐specific way. 4. In both anaesthetized and unanaesthetized rats, microapplications of (‐)AP7 into the ventrobasal thalamus did not affect cortical potentials. 5. These results are consistent with the assumption that an excitatory amino acid serves as transmitter at thalamic synapses mediating transmission of cortical potentials, and that this transmitter interacts preferentially with non‐NMDA receptors.
Synaptic modification of parallel fibre‐Purkinje cell transmission in in vitro guinea‐pig cerebellar slices.
Authors: Sakurai M
Published: December 2014

1. Synaptic transmission from parallel fibres to Purkinje cells and its modification by paired stimulation of parallel fibres and climbing fibres were studied in in vitro slices of the cerebellum obtained from guinea‐pigs. 2. Intracellular recordings were made from Purkinje cells, mainly from dendrites in the middle third of the molecular layer, but also, in a few cases, from somata. Climbing fibres were activated by stimulation of the white matter, while parallel fibres were stimulated with an electrode placed near the pial surface of the molecular layer. 3. Stimulation of the white matter elicited antidromic spikes, all‐or‐none climbing fibre responses, disynaptic responses through mossy fibres and parallel fibres, and trisynaptic responses through inhibitory interneurones. Climbing fibre responses were often followed by a small plateau potential, usually less than 2‐3 mV in amplitude and less than 100 ms in duration, followed by a slow hyperpolarization which reached its peak in several seconds. Inhibitory inputs to Purkinje cells were blocked with picrotoxin for the experiments described below. 4. Stimulation of the superficial molecular layer with currents less than 50 microA produced graded parallel fibre‐mediated excitatory postsynaptic potentials (e.p.s.p.s) ranging from 4 to 8 mV in peak amplitude. 5. Conjunctive stimulation of climbing fibres and parallel fibres at 4 Hz for 25 s induced depression of parallel fibre‐mediated e.p.s.p.s in Purkinje cells, both in the peak amplitudes and in the slopes. The depression was about 30% on average and lasted for more than 50 min. 6. No such depression occurred when the intensity of the white matter stimulation was set just subthreshold for the climbing fibre innervating the Purkinje cell under study. Instead, the parallel fibre‐mediated e.p.s.p.s were moderately potentiated for a period ranging from 10 to 50 min. Repetitive stimulation of the climbing fibre alone did not affect parallel fibre‐mediated e.p.s.p.s. 7. Immediately after the conjunctive stimulation or the repetitive stimulation of climbing fibres alone, a transient hyperpolarization which lasted for several minutes was seen. Its time course was similar to that of the hyperpolarization following a climbing fibre response. Except for this, there were no associated changes in the membrane potential, the input resistance, or the magnitudes of climbing fibre responses in any of the cases mentioned in 5 and 6 above.
Characteristics of transmural potential changes associated with the proton‐peptide co‐transport in toad small intestine.
Authors: Abe M , Hoshi T , Tajima A
Published: December 2014

1. Ionic dependence and kinetic properties of the peptide‐evoked potentials across everted toad intestine were investigated with eighteen dipeptides and four tripeptides. All peptides evoked saturable increases in the mucosal negativity regardless of the presence of Na+. 2. The peptide‐evoked potentials recorded in the absence of Na+ were sensitive to external pH (pHo); lowering pHo from 7.4 to 6.5 and 5.5 caused stepwise increases in their amplitude. 3. Loading epithelial cells with 9‐aminoacridine or acetate caused a significant increase or decrease in amplitude of the Gly‐Gly‐evoked potential, suggesting intracellular alkalinization or acidification also has a great influence on the peptide‐evoked potential. 4. Kinetically, Na+‐independent peptide‐evoked potentials conformed to simple Michaelis‐Menten kinetics, and lowering pHo caused a decrease of the half‐saturation concentration (Kt) for Gly‐Gly without changing the maximum potential difference increase. Similar affinity‐type kinetic effect was also seen for Gly‐Gly influx. 5. Simultaneous measurements of Gly‐Gly‐induced increase in short‐circuit current and Gly‐Gly influx revealed that the coupling ratio of H+ and Gly‐Gly flows was 1.78 +/‐ 0.12, suggesting the stoichiometry of the H+‐peptide co‐transport being 2:1. 6. Kinetic analyses of the peptide‐evoked potentials indicated that all glycyl‐dipeptides tested (Gly‐Gly, Gly‐Pro, Gly‐Sar, Gly‐Leu, Gly‐Phe) and other dipeptides (Ala‐Ala, Ala‐Phe, Phe‐Ala) shared a common carrier. Gly‐Gly‐Gly and Ala‐Ala‐Ala were also found to share the same carrier, while Phe‐Phe, Leu‐Leu and Phe‐Leu appeared to be transported by a different carrier. 7. Kt values for di‐ and tripeptides, which apparently shared a common carrier, fell in a narrow range (0.5‐2.2 mM). There was no clear correlation between 1/Kt value and molecular weight.