bluuebunny/crossref_metadata_2025_split huggingface dataset:
The electrogenic potential in rat C nerve fibres: some effects of lithium and thallium
Authors: Smith I. C. H. 
Published: December 2014

1. Subsequent to bathing a desheathed vagus nerve in a K‐free medium Li (5‐50 m
M) generates a hyperpolarizing response in the same manner as does K except that Li is 23 times less potent than K. Preincubation with small concentrations of either Li or K inhibits a subsequent K response.2. The Li response is less phasic than the K response. In the presence of a cardiac glycoside Li has no effect whereas K depolarizes the preparation. Thus Li is presumed to generate a relatively pure ouabain‐sensitive electrogenic response.3. If a Li response is always terminated with 50 m
M‐Li, but various concentrations are used during the first half, the total response has a constant area despite the wide range of activation during the first half. This implies that the electrogenic pump ratio is constant over this range of activation.4. Thallium (1 m
M) also generates a ouabain‐sensitive response, but even short exposures (5 min) produces a strong and lasting inhibition of subsequent potassium responses. On a slower time scale Tl also inhibits the electrogenic post‐tetanic hyperpolarization. After exposure to Tl a test action potential shows that the afterpotential is also decreased.5. If action potentials are produced during an electrogenic response the hyperpolarizing afterpotential reverses polarity. It is supposed that this is due to a short‐circuiting of the electrogenic potential during this time.
Further evidence for a physiological role for hypothalamic dopamine in thermoregulation in the rat
Authors: Cox B. , Lee T. F. 
Published: December 2014

1. Intrahypothalamic injection of either dopamine or noradrenaline in a dose volume of 1 μl. caused a fall in core temperature in lightly restrained rats maintained at an ambient temperature of 17 ± 1 °C.2. The hypothermic effects of dopamine (10 μg) and noradrenaline (2 μg) were selectively antagonized by systemic pre‐treatment with pimozide (0·5 mg/kg) and phentolamine (1 mg/kg) respectively.3. The location of the dopamine‐ and noradrenaline‐sensitive sites were defined more accurately by reducing the dose volume to 0·5 μl. and making injections at different points throughout the preoptic region.4. Both the dopamine‐ and the noradrenaline‐sensitive sites were located within the preoptic region, but they did not have identical locations being separated by a distance of 0·4 mm.5. Unilateral intrahypothalamic injection of 6‐hydroxydopamine (10 μg in 2 μl.) caused a significant fall in core temperature, which was antagonized by systemic injection of either pimozide or phentolamine.6. Rats placed 0·65 m below a 250 W infra‐red lamp responded to the imposed heat load by vasodilation of tail skin blood vessels, indicated by an increased tail skin temperature.7. Rats were tested two weeks after bilateral intrahypothalamic injection of 6‐hydroxydopamine (10 μg in 2 μl.). This pre‐treatment significantly reduced the increase in tail skin temperature so that the rats were less able to withstand the imposed heat load. Rats receiving similar 6‐hydroxydopamine pre‐treatment following injection of desipramine (25 mg/kg,
I.P.) were also less able to cope with a heat load.8. Three serial sections (0·8 mm thick) were prepared from the preoptic area of the rat brain, one anterior, one posterior and one corresponding to the dopamine‐sensitive site.9. Pre‐treatment with 6‐hydroxydopamine reduced both the dopamine and the noradrenaline concentration in the dopamine‐sensitive site. Pre‐treatment with desipramine and 6‐hydroxydopamine selectively reduced dopamine.10. These results indicate that there are receptors for both dopamine and noradrenaline in the preoptic anterior hypothalamus, which mediate a fall in core temperature in rats, but the evidence suggests that it is endogenous dopamine which is more likely to play an important physiological role.
Transformation of signals by interneurones in the barnacle's visual pathway
Authors: Oertel Donata , Stuart Ann E. 
Published: December 2014

1. The photoreceptors of the median eye of the giant barnacle drive decrementally‐conducting neurones in the supraoesophageal ganglion termed ‘inverting cells’ (I‐cells) which in turn drive impulse‐producing neurones termed ‘amplifying cells’ (A‐cells). Using intracellular recording techniques we have studied the role of I‐cells in visual processing.2. Horseradish peroxidase injections show that I‐cells are interneurones whose processes are confined to the regions of the photoreceptor terminals on both sides of the bilaterally symmetrical ganglion.3. In the dark, I‐cell membrane potentials (‐45 mV) are considerably less negative than those of other ganglion cells (‐60 to ‐70 mV). At the onset of a maintained light, I‐cells undergo a transient peak hyperpolarization which declines to a steady‐state response. Both response components are graded with light intensity.4. The reversal potential of the peak of the I‐cell light response depends on the external K+ concentration more strongly than does the dark resting potential (3‐30 m
m‐K+). This evidence indicates that the hyperpolarization results from an increase in the cell's permeability to K+ ions.5. At the offset of light an I‐cell undergoes a transient depolarization that overshoots the dark membrane potential. Dimming of a background light can also cause the I‐cell membrane potential to overshoot its dark resting value. This overshoot is associated with a large depolarizing synaptic potential in A‐cells.6. An overshoot of the dark resting potential can also be elicited by the break of a hyperpolarizing pulse of current injected into an I‐cell. The amplitude of this overshoot increases with pulse duration over a time course of seconds.7. In the presence of external tetraethylammonium ion (TEA) and tetrodotoxin, (TTX), the break of a hyperpolarizing pulse or the onset of a depolarizing pulse can evoke in an I‐cell an action potential whose rate of rise and amplitude depend on the external Ca concentration. This action potential can be maintained by replacement of external Ca with Ba, or blocked by addition of 15 m
m‐Co to the saline. These observation's indicate that depolarizing potential changes in this cell activate a voltage‐sensitive Ca conductance.8. When hyperpolarizing current pulses are injected into an I‐cell, the voltage during the pulse sags back slowly towards the dark resting potential. Thus, during hyperpolarization with light or current an I‐cell's membrane properties change over a time course of seconds.9. The onset of a depolarizing pulse or the offset of a hyperpolarizing pulse of current injected into an I‐cell leads to a transient depolarization of a simultaneously impaled A‐cell. Synaptic transmission occurs when the I‐cell is depolarized to the vicinity of the dark resting potential. The amplitude of the response in an A‐cell depends on the rate of change of the I‐cell voltage.
The fatigue and voluntary discharge properties of single motor units in man
Authors: Grimby Lennart , Hannerz Jan , Hedman Björn 
Published: December 2014

1. The discharge properties of single motor units during prolonged maximal voluntary effort have been studied using electromyographic recordings, mainly in the short big toe extensor muscle but also in the anterior tibial muscle.2. The required selectivity of the e.m.g. recordings was achieved in the short big toe extensor muscle after previous mechanical lesions to the terminal nerve twigs and muscle fibres and consequent collateral sprouting, and in the anterior tibial muscle with the use of a high impedance wire electrode.3. During the first few hundred milliseconds of sustained maximal effort the motor units fired at rates ranging from about 30‐60 Hz, and the tension was the same as that obtained on electrical tetanization of the nerve to the toe extensor muscles above 50 Hz.4. During prolonged maximal effort the firing rates and the proportion of motor units firing successively decreased. Motor units initially firing at 30 Hz continued to fire tonically but at 15‐20 Hz. Motor units initially firing at 60 Hz ceased to fire tonically but could still be made to discharge phasically. The period of time during which all motor units responded tonically could be increased from some seconds up to 20 sec by long‐term training.5. Motor units with a limited endurance fired at a lower tension in the early than in the late stages of maintained contraction.6. It is suggested that motoneurones innervating slow twitch muscle fibres respond continuously to prolonged voluntary drive at rates sufficient for full fusion but that the threshold of motoneurones innervating fast twitch muscle fibres increases so that they finally mainly fire phasically thus protecting the peripheral excitation and contractile mechanisms from excessive exhaustion.
Intestinal control of gastric function in the calf: the relationship of neural and endocrine factors
Authors: Bell F. R. , Green A. R. , Wass J. A. H. , Webber D. E. 
Published: December 2014

1. Gastric emptying and secretion were measured in conscious calves during alkaline or acid perfusion of the duodenum with simultaneous assessment of endogenous plasma somatostatin, gastrin and blood 5‐hydroxytryptamine (5‐HT).2. Alkaline duodenal perfusion (isotonic NaHCO3) caused rapid gastric emptying and increased gastric acid secretion without any affect on basal levels of somatostatin, 5‐HT or gastrin.3. Duodenal perfusion of 60 m
m‐HCl caused complete inhibition of gastric emptying, reduced gastric acid secretion considerably, and an associated elevation of somatostatin basal levels from 123.8 ± 11.2 to 281.9 ± 23.0 pg/ml. (P < 0.01) occurred.4. These effects of duodenal perfusion were unimpaired by bilateral lumbar splanchnectomy.5. On bilateral cervical vagotomy of the splanchnectomized calves, the inhibition of gastric function evoked by duodenal acidification persisted, and plasma somatostatin showed a further significant elevation to 506.9 ± 49.9 pg/ml. (P < 0.01) but gastrin and 5‐HT remained unchanged. The increased gastric function caused by alkaline duodenal function was significantly reduced following vagotomy but basal somatostatin, gastrin and 5‐HT in the blood remained unaffected.6. These results suggest that the stimulatory effect on gastric emptying and acid secretion of isotonic NaHCO3 in the duodenum may be mediated, partially at least, through the vagal nerves but not the splanchnics.7. The complete inhibition of gastric function which ensued on acidification of the duodenum and which continues after splanchnovagotomy, is not mediated by the autonomic nervous system. This inhibitory process appears to involve the endocrine system only, with somatostatin (but not gastrin or 5‐HT) fulfilling a main enterogastrone role.
The effects of single afferent impulses on the probability of firing of external intercostal motoneurones in the cat
Authors: Kirkwood P. A. , Sears T. A. 
Published: December 2014

1. Recordings of afferent discharges from external intercostal muscle spindles were made from in‐continuity dorsal roots of anaesthetized, paralysed cats and the afferents were characterized as described in the preceding paper (Kirkwood & Sears, 1982).2. The strengths and time courses of the raised probabilities of firing of external intercostal motoneurones evoked by the synaptic actions of impulses in the afferents were measured by constructing cross‐correlation histograms from the discharges of the individual afferents and the discharges of the motoneurones, which were simultaneously recorded from the cut central ends of intercostal nerve filaments. Other dorsal roots, apart from the rootlet containing the afferent fibre, were cut to prevent afferent synchronization from affecting the results.3. Cross‐correlation histograms involving single efferent discharges showed narrow peaks (mean half‐width 0·99 msec) at monosynaptic latencies.4. This mean half‐width is slightly longer than the mean rise‐time of the e.p.s.p.s described in the preceding paper, but much shorter than the mean half‐width of those e.p.s.p.s. These measurements, together with the shapes of individual histogram peaks thus confirm the prediction of Kirkwood & Sears (1978) that the shape of such a peak should be approximated by the time differential of the underlying e.p.s.p. plus the e.p.s.p. time course itself. Amplitudes of the peaks were also consistent with the predictions of Kirkwood & Sears (1978).5. The cross‐correlation histograms involving multi‐unit efferent discharges were entirely consistent with those involving single efferent discharges and were used to demonstrate the patterns of projections of individual afferents to different groups of intercostal motoneurones.6. Individual afferents excited α motoneurones of all spike sizes in the intercostal filament recordings but excitation of γ motoneurones was not detected.7. Individual afferents excited motoneurones of the same segment and both adjacent segments, but no projection beyond these was detected.8. The amplitude of the multi‐unit cross‐correlation peak was taken as a measure of the over‐all strength of the connexions to a given segment. When this amplitude was measured for motoneurones of the same segment as the afferent, for sixteen out of nineteen afferents there was a highly significant positive correlation with the conduction velocity of the afferent. The remaining three afferents gave a strength of connexion which appeared to be much stronger than would be expected from the rest of the population of afferents.9. The strength of connexion to adjacent segments was generally lower than to the same segment.
Pharmacological separation of charge movement components in frog skeletal muscle
Authors: Huang C. L.-H. 
Published: December 2014

1. Charge movements to small 10 mV steps superimposed upon a wide range of closely spaced depolarizing voltage‐clamp pulses were studied in frog skeletal muscles under different pharmacological conditions in hypertonic solutions.2. In control fibres, capacitance was strongly voltage‐dependent, especially between potentials of ‐60 and ‐20 mV, confirming earlier work. There was a sharp increase in capacitance at around ‐50 mV. The dependence of non‐linear charge on potential was asymmetrical and saturated at around 25 nC/μF.3. The presence of tetracaine abolished the ‘hump’ in the non‐linear transients, which became simple monotonic decays. The dependence of capacitance upon potential was reduced. The maximum available amount of non‐linear charge fell to 10 nC/μF.4. The presence of lidocaine abolished both the ‘hump’ as well as the monotonic part of the non‐linear transients. This resulted in capacitance falling with depolarization from ‐85 mV.5. Comparing the steady‐state properties of the non‐linear charge under the different pharmacological conditions made it possible to deduce empirically the following components:(i) A lidocaine‐resistant component (qα), which was responsible for the fall in observed capacitance with depolarization from the control voltage.(ii) A component resistant to tetracaine yet abolished by lidocaine (qβ). This possesses quasi‐exponential kinetics, and a maximum charge of about 20 nC/μF.(iii) A component abolished by both lidocaine and tetracaine (qγ), which possesses a maximum charge of 15 nC/μF. This has complex kinetics, and its steep dependence upon voltage resembles the potential‐dependence of the development of tension in skeletal muscle.
The effect of lesions in the neural crest on the formation of synaptic connexions in the embryonic chick spinal cord
Authors: Eide Anne‐Lill , Jansen Jan K. S. , Ribchester Richard R. 
Published: December 2014

1. The pattern of synaptic activity in lateral gastrocnemius (l.g.) motoneurones in the lumbar spinal cord of chick embryos (Stage 44‐45, 19‐21 d of incubation) has been examined using intracellular recording. In the motoneurones of normal chick embryos, stimulation of different peripheral, sciatic nerve branches gave rise to characteristic synaptic responses. Stimulation of the lateral gastrocnemius nerve caused a monosynaptic e.p.s.p. which was graded by the intensity of nerve stimulation. Stimulation of synergistic muscle afferents also caused a brief latency e.p.s.p., followed by longer latency excitatory and inhibitory synaptic potentials. Stimulation of antagonistic muscle afferents or cutaneous afferents gave rise to longer latency inhibitory and excitatory synaptic potentials respectively.2. The synaptic activity of l.g. motoneurones was also recorded in embryos in which short segments of the lumbar neural crest had been destroyed by microcautery at 3 d of incubation (Stage 18). The embryos developed without sensory ganglia and dorsal roots in the corresponding region.3. At 19‐21 d of incubation, the amplitude of the l.g. e.p.s.p. of l.g. motoneurones in deafferented segments was on the average only a half to a third of the amplitude seen in motoneurones of intact spinal segments. However, both the l.g. and synergist e.p.s.p.s were larger than those seen in acutely deafferented segments of normal embryos.4. In spite of the weak monosynaptic input from l.g. and synergistic afferents, the pattern of synaptic activity evoked by antagonistic muscle afferent or cutaneous afferent stimulation was not different from normal. This was even the case for gastrocnemius motoneurones in which no early e.p.s.p. could be evoked by stimulating the l.g. or synergistic muscle nerves.5. No muscle spindles could be seen in sections of l.g. muscles from embryos with extensive lesions of the lumbosacral neural crest. Incomplete lesions of l.g. segments reduced the number of spindles in the muscle.6. These results suggest that when motoneurones are deprived of part of their normal synaptic input before the formation of peripheral connexions, the identity of the motoneurones (in terms of the origin of their synaptic input) is preserved. Missing synaptic inputs are either replaced by appropriate afferent fibres, if they are available, or not at all. The chick sensory ganglion cells with monosynaptic connexions to motoneurones appear to be unable to compensate significantly for peripheral or central defects in the innervation of the hind limb. They behave as if their developmental possibilities were quite rigidly determined at an early embryonic stage.
A comparison of the structures of α‐ and γ‐spinal motoneurones of the cat
Authors: Westbury D. R. 
Published: December 2014

1. The structures of seven γ‐motoneurones (axonal conduction velocities of 15‐48 m/sec) were compared with those of nine α‐motoneurones (axonal conduction velocities of 71‐91 m/sec) by using histochemical methods to reveal horseradish peroxidase which had previously been injected intracellularly into indentified motoneurones in the cat lumbosacral spinal cord.2. The size of the cell bodies of the motoneurones, and the diameters of their intramedullary axons, were related to their axonal conduction velocities over the whole range studied.3. Despite the smaller size of the cell bodies of the γ‐motoneurones, their dendritic trees extended as far as those of the α‐motoneurones. However, γ‐motoneurones had fewer main dendrites than the α‐motoneurones and these branched much less, so that the dendritic trees of the γ‐motoneurones were much simpler than those of α‐motoneurones. Although the extents of the dendritic trees were not related to axonal conduction velocity, the complexity of the dendritic trees was clearly related to axonal conduction velocity and to cell body size.4. The total surface area of each cell, taken as an indication of the area available for synaptic contact, was much smaller for γ‐ than for α‐motoneurones, and was related to axonal conduction velocity.5. Only one of the seven γ‐motoneurones studied had axon collaterals whereas five of the nine α‐motoneurones had well developed collaterals. This finding is consistent with the relative contribution that each group of motoneurone axons makes to recurrent inhibition.6. One of the γ‐motoneurones had two axons, of different diameter, which emerged from the spinal cord at the same level but in different ventral rootlets.7. These features of motoneurone structure are related to aspects of their physiological properties.
An enquiry into the mechanism by which substance P facilitates the phasic longitudinal contractions of the rabbit ileum
Authors: Holzer Peter 
Published: December 2014

1. The effect of substance P on the phasic longitudinal contractions of the isolated rabbit ileum has been investigated. The contractions were recorded isotonically. Substance P in concentrations below those which cause tonic contraction (0·2‐2 nM) increased the height of the phasic contractions in a concentration‐dependent fashion without affecting their frequency (8‐12/min).2. The effect of substance P was inhibited by verapamil, ouabain, noradrenaline, and isoprenaline, but was unaffected by tetrodotoxin, atropine, D‐2‐ala,5‐metenkephalin, somatostatin, and vasoactive intestinal polypeptide.3. Tetraethylammonium, which blocks voltage‐dependent K+ channels, enhanced the phasic contractile activity of the rabbit ileum in a manner quite similar to substance P, but the maximal response to tetraethylammonium was larger than that to substance P.4. The effect of matched concentrations of substance P and tetraethylammonium, which enhanced the phasic contractions to a similar extent, was investigated at various concentrations of K+, Na+, Ca2+ and Cl− in the bathing medium. Both substance P and tetraethylammonium lost their ability to enhance the phasic contractions when K+ was omitted from the medium or when its concentration therein was increased by a factor of 4, or when the NaCl concentration was reduced to less than 10%. The relative increase in phasic contractile activity evoked by substance P was smaller than that evoked by tetraethylammonium when more than 90% of the Cl− was replaced with propionate.5. Noradrenaline, in a concentration which just abolished the spontaneous phasic contractions (200‐300 nM), reduced the enhancing effect of substance P on the phasic activity by 40‐50%, but did not influence the effect of tetraethylammonium.6. These results indicate that substance P enhances the phasic longitudinal contractions of the isolated rabbit ileum by a direct action on the smooth muscle cells and that this effect is brought about by facilitation of the myogenically controlled action potential discharges in the ileum. Circumstantial evidence suggests that the underlying ionic mechanism of action of substance P is a decrease in K+ and Cl− conductances.