bluuebunny/crossref_metadata_2025 huggingface dataset:
Two populations or granular vesicles in constricted post‐ganglionic sympathetic nerves.
Authors: Tomlinson D R
Published: December 2014

1. A comparative study has been made of the effects of different fixatives on the ultrastructural appearance of granular vesicles accumulated against a constriction in cat hypogastric nerves. 2. After fixation in either osmium tetroxide or in glutaraldehyde followed by post‐osmication accumulations of large granular vesicles (65–90 nm in diameter) were observed in profiles of swollen axons. 3. Fixation in acrolein and sodium dichromate revealed a second population of small granular vesicles (mostly 30–50 nm in diameter) in addition to the large vesicles seen after the other fixatives. 4. In reserpinized cats the small granular vesicles were absent. The large granular vesicles were much less numerous, irrespective of the fixative used. 5. It is suggested that either the small vesicles occur in normal noradrenergic axons but are only revealed by catecholamine‐sensitive fixatives or they occur as a result of constricting the nerve trunk. Evidence for and against these possibilities is discussed.
Action potential and non‐linear current‐voltage relation in starfish oocytes.
Authors: Miyazaki S I , Ohmori H , Sasaki S
Published: December 2014

1. The electrical properties of the oocyte membrane of the starfish, Asterina pectinifera, were investigated using an intracellular microelectrode. 2. The resting potential in artificial sea‐water ranged from −70 to −80 mV. 3. The starfish oocyte membrane was capable of generating an action potential as a result of permeability increases to both Ca and Na ions.4. The Ca component of the action potential was reversibly suppressed by Co or Mg ions, while the Na component was not affected by tetrodotoxin 5 times 10‐minus 6 g/ml. 5. The steady‐state relation of voltage vs. current was not linear but S‐shaped. The curve wascomposed of inward‐going rectification at the membrane potential more negative than −65 mV, outward‐going rectification at the potential more positive than OmV and the transitional region between them. These findings are compared with those obtained in the mature egg of the tunicate.
Potassium rectifications of the starfish oocyte membrane and their changes during oocyte maturation.
Authors: Miyazaki S I , Ohmori H , Sasaki S
Published: December 2014

1. The current‐voltage relations of the oocyte membrane of the starfish, Asterina pectinifera, and their changes during maturation were investigated using current‐clamp techniques. 2. The resting potential of the oocyte membrane in sea water was found to be determined by the diffusion potential of K ions. 3. In the absence of Na and Ca inward currents the steady‐state current‐voltage relation of the oocyte membrane had inward‐going K rectification at membrane potentials more negative than −65 mV and outward‐going K rectification at potentials more positive than −30 mV, forming a S‐shaped I–V curve. 4. A negative resistance region of the steady‐state I–V curve was revealed with voltage‐clamp technique in the potential range between −65 and −30 mV. 5.Transient K activation occurred when the membrane was brought from a resting potential of about −75 mV to potentials more positive than −20 mV, and this was immediately followed by K inactivation. Accordingly, the steady‐state I–V relation showed only slight outward‐going rectification. 6. At the beginning of meiosis, which is signalled by break‐down of the nucleus, the limiting slope conductance in the inward rectifying region of the I–V curve decreased sevenfold. The cell membrane lost its selective permeability to K ions and was depolarized from −70 to between −20 and OmV in standard artificial sea‐water. The depolarized resting potential was partly due to the relative increase in Na permeability. K conductance began to increase again within 30 min after breakdown of the nucleus. The resting potential became gradually larger and eventually attained −70 mV in the mature egg. 7. In the mature egg, K activation upon depolarization was no longer followed by inactivation. Accordingly, the slope conductance in the outward rectifying region of the I–V curve increased. 8. The action potential was augmented at the stage of nuclear breakdown. Thereafter the maximum rate of rise decreased and the duration of the action potential shortened. These changes were caused primarily by changes in K conductance during maturation. 9. Fertilization of the egg during the maturation process did not affect the changes in the I–V relation described above, except for a transient change of the membrane permeability upon fertilization.
Lithium ions and the release of transmitter at the frog neuromuscular junction.
Authors: Crawford A C
Published: December 2014

1. Transmitter release has been examined at the frog neuromuscular junction when all or part of the Na of the Ringer is replaced by Li ions. 2. No immediate change occurs in either the mean quantal content of the end‐plate potential or the miniature end‐plate potential frequency on changing to Li Ringer but over the following hour both these quantities increase by more than two orders of magnitude. 3. During thefirst 30–40 min of an exposure to Li‐Ringer the m.e.p.p. frequency rises exponentially with a time constant of 10 min, and the mean quantal content of the e.p.p. grows by addition of extra evoked quanta, the increment rising exponentially with a time constant the same as that of the m.e.p.p. frequency. 4. Following this initial period in Li‐Ringer the m. e.p.p. frequency accelerates to a peak of several hundred quanta per second and then declines slowly over the next few hours. Just before the m.e.p.p.frequency peak the conduction velocity of the presynaptic action potential declines and shortly afterwards synaptic transmission fails as the action potential no longer conducts into the terminals. 5. The rise in the m.e.p.p. frequency during the first 30–40 min is independent of the [Ca‐2+]o. At subsequent times before the peak external Cabecomes progressively more effective in accelerating the m.e.p.p. frequency and in the presence of 1mM‐EGTA spontaneous release stabilizes at 60–80 quanta/sec. 6. The [Li‐+]o strongly influences the rate of increases in both evoked and spontaneous release but not their extent; replacing only half the Na of the Ringer by Li increases the time constants of the increases to about 30 min. 7. Rises in the m.e.p.p. frequency can be irreversibly accelerated by tetanizing the nerve in a Li‐Ringer in which the Ca has been chelated by EGTA. The extent of the increases in the m.e.p.p. frequency is dependent on the number of pulses in the tetanus and is little affected by the frequency of stimulation. Accumulation of Li ions inside the presynaptic terminals probably underlies the changes in spontaneous release. 8. When only 10 percent of the Na of the Ringer is replaced by Li‐+ ions the magnitude of post‐tetanic potentiation of the e.p.p. and of the post‐tetanic rise in the m.e.p.p. frequency is increased. Under these conditions changes in facilitation of the e.p.p. are small. 9. Various mechanisms by which Li could alter transmitter release are discussed and it is suggested that intracellular Ca sequestering mechanisms of the presynaptic terminals are affected when an end‐plate is exposed to Li‐Ringer.
Active chloride secretion by in vitro guinea‐pig seminal vesicle and its possible relation to vesicular function in vivo.
Authors: Levine N , Rinaldo J E , Schultz S G
Published: December 2014

1. The guinea‐pig seminal vesicle in vivo is characterized by a transmural electrical potential difference of approximately 11 mV with the lumen electrically negative with respect to the interstitial fluid. The concentrations of Na, Cl and K in the vesicular fluid are 13, 15, and 0–4 mM, respectively. 2. When mounted as a flat sheet in a short‐circuit apparatus, guinea‐pig seminal vesicles initially undergo a decline in the transmural electrical potential difference and short‐circuit current (‘low phase’) followed by a spontaneous increase in these parameters (‘high phase’). 3. During the low phase, net C1 movements across the tissue do not differ significantly from zero, and there is a small ‘residual’ current that is unaccounted for. 4. During the high phase, there is a significant active C1 secretion into the mucosal solution, not detectable net movement of Na and an unaccounted for or ‘residual’ current that is equal to that found in the low phase. 5. Theophylline, dibutyryl‐3'‐5' cyclic adenosinemonophosphate, prostaglandin E1 and prostaglandin F2alpha markedly stimulate the transmural electrical potential difference and short‐circuit current during the low phase, but have no effect when added to the bathing solution during the high phase. 6. Diffusion potentials determined across in vitro seminal vesicles suggest that the spontaneous transmural electrical potential difference in vivo may be attributable to the large ionic asymmetries between the vesicular fluid and the plasma. 7. It is postulated that two phases are involved in the elaboration of seminal vesicular fluid. The initial phase, following emptying of the vesicle, is characterized by the secretion of electrolytes, organic molecules and water. Active C1 secretion presumably regulated by intracellular cyclic adenosinemonophosphate and/or prostaglandins may be the driving force for this initial secretion of electrolytes. Following this secretory phase, electrolytes and water are reabsorbed, thereby concentrating the organic components in the vesicular reservoir.
The interaction of lithium ions with the sodium‐potassium pump in frog skeletal muscle.
Authors: Beaugé L
Published: December 2014

1. The effects of external Li on Na and K efflux as well as those on K influx were studied in high Na muscles from Rana pipiens. 2. In the absence of external Ba, substitution of K‐free Li for K‐free Mg resulted in an increase of both Na and K efflux. The additional of ouabain produced an inhibition of Na efflux and at the same time a marked increase in the efflux of K. 3. K permeability was greatly reduced by adding 2 mM‐Ba to the incubation solutions. Under these conditions, Li gave rise to a ouabain sensitive Na efflux which was 57% of that in the absence of Ba. On the other hand, the efflux of K was only slightly increased and was not affected further by ouabain. 4. The activation curves of Na efflux against the stimulating cation concentration in Na‐free Mg‐Ba Ringer followed a more or less hyperbolic function for both K and Li. While half‐maximal activation was attained at higher concentrations of Li than of K, the maximal efflux in Li was smaller than in K. 5. The extra Na efflux produced by K was increased when Li was added to the media. This increment was not a simple additive effect and was independent of the Li concentration. In addition, at some concentrations Li increased the ouabain‐sensitive K influx, whereas at others it reduced it. 6. Reversible changes in membrane permeability to monovalent cations were accomplished by incubating the muscles in the presence of Nystatin, 50 mug/ml. When internal K was reduced to values around 1‐2 mumole/g (using Li as a replacement), thus minimizing the possibility of K leaking out of the cells, both Ko and Lio were able to promote a ouabain‐sensitive extra efflux of Na. 7. The residual Na efflux in (K+Na)‐free solutions was not affected by the removal of Ca from the media in either Mg or Li solutions, both in the absence and the presence of Ba. On the other hand, the values for the residual efflux were higher in Mg (0‐00228 min‐1) than in Li (0.00135 min‐1). 8. These results fully support the notion that Li ions have a K‐like activating action on the Na pump in muscles. In addition, they suggest that some other kind of interaction may exist between Li and the Na‐K pump.
Effects of post‐operative visual environments on reorganization of retinotectal projection in goldfish.
Authors: Yoon M G
Published: December 2014

1. Possible influence of different visual environments on the reorganization of retinotectal projection was studied with neurophysiological mapping methods following excision of the caudal half of the optic tectum in adult goldfish. 2. Post‐operative light‐deprivation showed no significant effects: in the absence of visual input, the visual projection from the whole retina because compressed on to the remaining rostral half‐tectum in correct retinotopic order within 4 months, regardless of whether the contralateral optic nerve was left intact, or severed and then allowed to regenerate. 3. When the operated goldfish were continually exposed to visual stimuli without any dark period (post‐operative dark‐deprivation), two different results were observed: if the optic nerve was sectioned, in addition to excision of the caudal tectum, an orderly field compression was observed within 70 days in the re‐established retinotectal projection; on the other hand, if the optic nerve was left intact, the dark‐deprived fish retained the original connexions between the remaining rostral half‐tectum and the temporal hemiretina without showing any sign of field compression for up to 253 days. 4. When the dark‐deprived fish was then transferred into darkness, the suppressive effect disappeared: a compression of the retinotectal projection was induced within 2 or 3 weeks after the transfer. 5. Histological preparations of the fish brains showed consistent morphologic changes in the laminar structure of the remaining half‐tectum. The stratum opticum and the stratum fibrosum et griseum superficiale merged together to form a new layer which contained an intricate network of thick fibre bundles.
Energy balance in DNFB‐treated and untreated frog muscle.
Authors: Curtin N A , Woledge R C
Published: December 2014

1. Heat production and chemical changes were measured in untreated and dinitrofluorobenzene (DNFB)‐treated muscles during isometric tetani. Levels of total creatine (Ct), free creatine, ATP, ADP, AMP, inorganic phosphate, glucose‐1‐phosphate, glucose‐6‐phosphate, fructose‐6‐phosphate, fructose‐1,6‐diphosphate, pyruvate, phosphoenolpyruvate, and lactate were measured. Changes in inosinic acid (IMP) were also measured. 2. DNFB effectively inhibited the creatine kinase reaction (Lohmann reaction). 3. Our major finding is that even after effective treatment with DNFB the observed heat plus work after 2 sec and 5 sec of stimulation is significantly greater than the enthalpy change produced by the measured chemical changes. This confirms that an unidentified exothermic process occurs during muscle contraction; this conclusion was reached previously from studies of untreated muscle. 4. The unexplained heat plus work is unlikely to be derived from glycolytic reactions since under anaerobic conditions no formation of lactate, pyruvate, phosphoenolpyruvate or fructose‐1,6‐diphosphate could be detected in either untreated or DNFB‐treated muscles even 34 sec after a series of three 5 sec isometric tetani. 5. In the first 2 sec of stimulation the unexplained heat plus work is less in DNFB‐treated muscles than in untreated muscles. However from 2 to 5 sec of stimulation the unexplained heat plus work is the same in treated and untreated muscles.
Spontaneous and synaptic excitation of paramedian reticular neurones in the decerebrate cat.
Authors: Duggan A W , Game C J
Published: December 2014

1. In decerebrate cats neurones in the region of the paramedian reticular nucleus were identified by responses to stimulation of implanted cerebellar electrodes. Approximately one half were antidromically activated and one half orthodromically. 2. Somatic stimulation and electrical stimulation of both hind limb and cranial nerves activated many of these cells. There was no correlation between the effects of these stimuli on cell firing and on blood pressure. 3. A number of rhythms in spontaneous firing were observed. One fifth of cells fired with the rhythm of efferent activity in the recurrent laryngeal nerve. In animals showing cycles of stability and instability in blood pressure corresponding phases of activity and inactivity in the firing of paramedian reticular neurones were observed. 4. Most paramedian reticular cells showed bursts of firing preceding abrupt rises in blood pressure but this was also observed with cells lateral to this area. 5. One third of cells studied showed changes in firing rate correlated with the changes in blood pressure which followed I.V. acetylcholine and noradrenaline. 6. Bilateral carotid artery occlusion, which always produced a rise in blood pressure, had little effect on cell firing.
An investigation into the site of termination of static gamma fibres within muscle spindles of the cat peroneus longus muscle.
Authors: Brown M C , Butler R G
Published: December 2014

1. The distribution of static fusimotor fibres to intrafusal muscle fibres of cat peroneus longus muscle spindles was investigated using the glycogen‐depletion technique of Edström & Kugelberg (1968). Single static gamma fibres were stimulation intermittently at high rates for 3 hr with the blood supply occluded for some of this time. Subsequently the portion of muscle containing the activated spindles was fixed, sectioned and stained for glycogen with the periodic acid‐Schiff (PAS) method. 2. Ten static axons caused depletion in eleven spindles. In five of these the only glycogen‐depleted fibres were nuclear chain fibres. In the other six spindles one nuclear bag fibre was depleted in addition to chain fibres and this was always the larger of the two within the spindle. 3. These results on a medium‐sized hind limb muscle are compared with findings concerning the distribution of static gamma fibre axons previously investigated only in very small muscles. The results agree in showing that nearly all static gamma fibres innervate nuclear chain fibres but that in 50–75% of the times in which static gamma fibres innervate spindles the distribution is to bag fibres as well as to chain fibres. The interpretation to be put upon this is uncertain. One possibility with which the results from peroneus longus are consistent is that the bag fibres which are usually innervated by static axons are the ‘intermediate’ bag fibres whose ultrastructure has recently been shown to resemble that of chain fibres.
Ionic mechanism of the efferent olivo‐cochlear inhibition studied by cochlear perfusion in the cat.
Authors: Desmedt J E , Robertson D
Published: December 2014

1. A method for perfusing the scala tympani of the cat's cochlea from basal turn to apex is described. The perfusion with modified Krebs solution did not interfere with the recording of cochlear microphonic (CM) and neural responses to sound, nor with the efferent inhibition elicited by stereotaxic stimulation of the crossed olivo‐cochlear bundle (COCB) in the medulla. 2. Cochlear perfusion with solutions in which most of the chloride was replaced by large anions (sulphate or gluconate) decreased or eliminated auditory nerve or the ventral cochlear nucleus. These effects were reversible. They were only observed if the rate of perfusion (2–20 mul/min) was adequate to reduce the chloride concentration in perilymph below about 80 mM, this being estimated, in different perfusion of the same cochlea, by a chloride‐selective electrode. 3. The COCB‐induced negative shift of the endocochlear potential recorded with a glass micro‐electrode inserted into the scala media was abolished by I.V. strychnine o.2 mg/kg. It was decreased when the perilymph chloride was reduced to 50–70 mM and could be abolished when the perilymph chloride dropped to about 5 mM. 4. The COCB‐induced potentiation of the cochlear microphonic potential was also reduced by chloride substitution but the pattern of this effect differed from that of neural inhibition. 5. Similar cochlear perfusions with a solution in which the small diameter bromide anion was substituted for chloride did not affect the COCB‐efferent effects. 6. The data indicate that the inhibitory transmitter released by COCB terminals elicits an increased conductance to small anions (normally to chloride) in the membrane of the auditory dendrite and of the outer hair cell. The significance of the COCB‐induced negative shift of endocochlear potential and of the potentiation of CM is discussed, as well as the pre‐ and post‐synaptic mechanisms involved in the efferent gating exerted on the auditory input. The latter would seem to involve primarily a post‐synaptic mechanism at efferent axo‐dendritic synapses.
The ionic dependence of action potentials induced by colchicine in an insect motoneurone cell body.
Authors: Pitman R M
Published: December 2014

1. The ionic requirements of the action potential recorded in the cell of an identified cockroach (Periplaneta americana) motoneurone following pre‐treatment of the animal with colchicine have been studied. 2. Small cubes of gelatin containing 1% colchicine were implanted into one metathoracic leg near to the nerve trunk containing the axon of the identified motoneurone. 3. Electrophysiological experiments were performed 4‐‐10 days after this treatment, when action potentials which frequently overshoot zero potential can be recorded from the cell body. Such action potentials are not normally seen in untreated animals. 4. Sodium‐free solution reversibly abolished the action potential within 5 min. 5. Tetrodotoxin (10(−8)M) reversibly depressed the action potential. It was totally abolished by 10(−7)M tetrodotoxin, but this effect was not reversible. 6. Saline solution containing 40 mM manganous chloride either had no effect on the action potential amplitude, or caused a slight increase. It also caused prolongation of the falling phase and loss of the after‐hyperpolarization. These effects were all reversible. 7. It is concluded that sodium carries a major proportion of the inward current of the action potential in this neurone. Some calcium probably enters also, and may, at least in part, be responsible for triggering the delayed rise in potassium conductance during the action potential.
Polyphasic synaptic potentials in the ganglion of the mollusc, Navanax.
Authors: Levitan H , Tauc L
Published: December 2014

1.Included in the ensemble of synaptic input received by identified neurones in the ganglion of the marine mollusc Navanax are biphasic synaptic potentials, consisting of a depolarization followed by a hyperpolarization. 2. Both phases are chemically mediated as judged by their susceptibility to a high magnesium medium and neither exhibits depression with repetition. 3. The hyperpolarizing phase has a reversal potential of about −50mV, which varies only with changes in the external chloride concentration. This phase is unaffected by cholinolytics. 4. The depolarizing phase reverses at a more positive potential, is probably the result of a change in sodium conductance and is blocked by hexamethonium and high concentrations of eserine. 5. The biphasic synaptic potentials are therefore similar in many respects to the biphasic response evoked by iontophoretic application of acetylcholine on to these cells, suggesting that the two types of cholinergic receptors previously characterized on these neurones are both functional.
Electrophysiological properties of spinal motoneurones of normal and dystrophic mice.
Authors: Huizar P , Kuno M , Miyata Y
Published: December 2014

1. The properties of spinal motoneurones of normal and dystrophic mice (129/ReJ) were examined with intracellular electrodes. 2. The following parameters of spinal motoneurones showed no significant differences between normal and dystrophic mice: resting and action potentials, the amplitude and duration of after‐hyperpolarization, rheobasic current for excitation, threshold for excitation of the somadendritic membrane (IS‐SD inflexion) and input resistance. 3. The changes in motoneurone properties observed 13–16 days after section of the sciatic nerve (axotomy) were similar in both normal and dystrophic mice. 4. The axonal conduction velocity of motoneurones in dystrophic mice was about ten times slower than that in normal mice. The conduction velocity of the sciatic nerve was only about 25% slower in dystrophic mice than in the normal animal. The estimated ventral root conduction velocity as well as the observed dorsal root conduction velocity in dystrophic mice was at least twenty times slower than that in normal mice. 5. In dystrophic mice, spinal motoneurones often showed multiple discharges in response to single, antidromic stimuli. The site of initiation of multiple discharge was located in the motor axon rather than in the motoneurone cell body. 6. In dystrophic mice, nerve impulses were transmitted from fibre to fibre (‘cross‐talk’). The site of impulse transmission among nerve fibres was near the distal portion of the spinal roots. 7. Synaptic potentials and peripheral reflex discharges evoked by stimulation of the dorsal roots showed a longer latency and were more prolonged in dystrophic mice than in the control mice. 8. The motoneurone properties of dystrophic mice showed no tendency of progressive changes with age ranging from 63 to 148 days. 9. It is concluded that the properties of motoneurone cell bodies examined in dystrophic mice are indistinguishable from those in normal mice and that the only abnormality in motoneurones of the former residues in the motor axon. 10. It is suggested that integrity of the discharge pattern of spinal motoneurones in dystrophic mice is interfered by anomalous impluse transmission in the motor axons and that the motoneurones in dystrophic mice are a homogeneous group rather than a mixture of "normal" and "abnormal" neurones.
Sensitivity of central chemoreceptors controlling blood glucose and body temperature during glucose deprivation.
Authors: Fiorentini A , Müller E E
Published: December 2014

1. The rise in blood glucose and the fall in body temperature which follows the injection of a glucose analogue, 2‐deoxy‐D‐glucose (2‐DG) into the lateral cerebral ventricle (I.C.V) of unanaesthetized rats were studied and found to be dose‐dependent. These 2‐DG induced responses are elicited by the impairment of glucose metabolism within central ‘glucoreceptors’. 2. 2DG induced hyperglycaemia and hypothermia were completely prevented and even the converse effects occurred when fivefold equimolar amounts of D‐fructose were simultaneously injected I.C.V.; fructose, at equimolar doses, did not modify the effects of 2‐DG. 3. D‐xylose and D‐ribose, even at high doses, did not influence 2‐DG hyperglycaemia, but increased slightly the 2‐DG induced hypothermia. This suggests that the pentose phosphate pathway is unable to support the metabolism within the glucoreceptors. 4. Pyruvate suppressed the 2‐DG induced hyperglycaemia with a marked delay, while acetate (as ethyl ester) and a mixture of malate plus oxaloacetate did not prevent 2‐DG induced effects. These results may be accounted for by the low dosage used. 5. Acetoacetate and 3‐hydroxybutyrate did not prevent 2‐DG hypothermia and hyperglycaemia. 6. An effective prevention of the 2‐DG induced hyperglycaemia and hypothermia was achieved with fumarate and glutamate, indicating that the stimulation of the Krebs cycle within ‘glucoreceptors’ removes the glucoprivic effects. 7. The results indicate that prevention of 2‐DG induced effects occurred only with alternate source of metabolic fuel which can support high respiratory rates in brain tissue. It is concluded that central chemoreceptors are not specifically responsive to glucose, or hexoses, but to the rate of oxidative metabolism.
Convergence in a thermal afferent pathway in the rat.
Authors: Hellon R F , Mitchell D
Published: December 2014

1. In anaesthetized rats, unit activity was recorded in the afferent somatosensory pathway leading from the scrotum. Recording sites were in the dorsal horn near the entry zone of the scrotal nerve, in the ventrobasal complex of the thalamus and in the somatosensory (SI) cortex. During recording, the temperatures of the left and right sides of the scrotum were varied independently. 2. Almost all (64/67) the units in dorsal horn, thalamus and cortex responding specifically to scrotal temperature were equally affected by temperature changes on either side of the scrotum. The receptive fields of these units were bilateral and large, implying a massive convergence of fibres from thermoreceptors on to each central unit. In contrast, mechanosensitive units responded only to unilateral stimulation. 3. As a consequence of the convergence in the thermal pathway, the firing rate of each central unit was a function of an additive combination, often simply the sum, of the temperatures of the two sides of the scrotum. 4. The relationship between firing rate and the temperature of one side of the scrotum was sigmoid, the position, but not the shape, of the curve depending on the temperature at which the opposite side was maintained. An increase in the maintained temperature shifted the sigmoid response curve towards lower temperatures and vice versa. 5. The convergence which this pathway exhibits would be well suited to integration of the temperature of the scrotal skin, but not to spatial discrimination.
Potassium activation in Helix aspersa neurones under voltage clamp: a component mediated by calcium influx.
Authors: Meech R W , Standen N B
Published: December 2014

1. Helix aspersa neurones under voltage clamp generate prolonged outward currents (potassium currents) in response to depolarizing command pulses. 2. The potassium currents recorded from cell A were reversibly reduced 25–50% by 10 mM cobalt ions in the bathing medium; 1 mM lanthanum, 10(−6) g/ml. D‐600 and 10(−6) g/ml. iproveratril had similar effects but were only partially reversible. 3. The relationship between the potassium currents and the membrane potential had an “n” shape in normal saline. In calcium‐free saline (containing 25 mM magnesium) the potassium currents were reduced and the “n” shape was abolished. The effect of calcium‐free saline was readily reversible. 4. The voltage‐dependence of the calcium‐sensitive potassium currents was similar to that of the “late” calcium channel in squid axons (Baker, Hodgkin & Ridgway, 1971). 5. When cell A was depolarents were made up of two exponentially declining components. The slower of the two components was reduced in calcium‐free saline. 6. When cell A was depolarized by 150 mV for 10 msec and then repolarized the “tail” currents were made up of a single rapidly declining component. The reversal potential of this component changed by 58 mV for a tenfold change in the external potassium concentration as predicted by the Nernst equation. 7. The reversal potential of “tail” currents having both components was less sensitive to changes in the external potassium concentration. 8. Tetraethylammonium (TEA) ions blocked both calcium dependent and voltage sensitive potassium currents. Each receptor was found to bind a single molecule of TEA. The dissociaton constant was about 10 mM in each case. 9. The intracellular concentration of ionized calcium was estimated from the potential at which there was no apparent calcium influx (the null point). It was between 3 x 10(−8) M and 8 x 10(−8) M with 10(−2) M calcium in the bathing medium. 10. The null point changed 30 mV for a tenfold change in the external calcium concentration as predicted by the Nernst equation. 11. It is concluded that depolarization of Helix neurones activates two typesof potassium channel. One channel is voltage dependent and highly selective for potassium. Activation of the other channel is dependent on the influx (or injection, see Meech, 1972, 1974a) of calcium. This calcium mediated potassium activation system saturates at high external calcium concentrations and is inhibited by external magnesium ions.
The movement of potassium ions during electrical activity, and the kinetics of the recovery process, in the non‐myelinated fibres of the garfish olfactory nerve.
Authors: Ritchie J M , Straub R W
Published: December 2014

1. An electrophysiological study was made with the sucrose gap of the compound action potential of the non‐myelinated fibres of the garfish olfactory nerve at temperatures between 8 and 22 degrees C. The efflux of 42K with stimulation, and the post‐tetanic hyperpolarization following a period of repetitive stimulation, were also studied. 2. At 22 degrees C the compound action potential (at zero conduction distance) reached its peak in about 5 msec and lasted about 12 msec; the conduction velocity was 19.4 cm/sec. The corresponding extrapolated values at 0 degrees C were: time to peak, 16 msec; duration, 37 msec; conduction velocity, 4.2 cm/sec. 3. The rate constant for resting potassium efflux (kr) was 0.0108 min‐1 at 22 degrees C and 0.00489 min‐1 at 0 degrees C. 4. The extra fractional loss of potassium with stimulation (ks) was 2.02 x 10(−4) impulse‐1 at 22 degrees C and 4.41 x 10(−4) impulse‐1 at 0 degrees C. 5. Raising the external potassium concentration, or addition of ouabain (1 mM), raised the resting rate of efflux of potassium. 6. The post‐tetanic hyperpolarization, which reflects the electrogenic extrusion of sodium ions, indicated a rate constant for active sodium efflux at 22 degrees C of 0.47 min=1. 7. The rate constant was decreased by a 10 degrees C fall in temperature by a factor of 1.73. 8. Increasing the external potassium concentration increased the rate constant, apparently by potassium combining with some site with an equilibrium dissociation constant of 1.2 mMM. 9. The rate constant was decreased slightly in acidic solutions and increased slightly in alkaline solutions. 10. 14C‐labelled ouabain was found to bind to the garfish olfactory nerve with an equilibrium dissociation constant of about 0.5 muM. The maximum saturable binding capacity, 22.3 p‐mole/mg dry, suggests that there are about 350 sodium pumping sites per square micron membrane.
The mode of activation of pyramidal tract cells by intracortical stimuli.
Authors: Jankowska E , Padel Y , Tanaka R
Published: December 2014

1. Direct and indirect effects of intracortical stimulattion on pyramidal tract cells were compared in the monkey and in the cat under barbiturate or chloralose anaesthesia. The hind‐limb motor areas were explored, that in the monkey only within the convex part of the precentral gyrus. The intracortical stimuli were applied in the nearest vicinity of pyramidal tract cells, where antidromic spike potentials of single cells were recorded. 2. Average records of descending volleys in corticospinal tract fibres were taken from the surface of the lateral funiculus or from its dissected fascicles. The sensitivity of the recording was sufficient to detect responses in single fibres. 3. The latencies of the earliest descending volleys evoked by weak intracortical stimuli were compared with the latencies of the antidromic spike potentials of pyramidal tract cells evoked by stimulation of the lateral funiculus at a low lumbar level (same conduction distance). Only in about one third of cases these latencies were similar and compatible with a direct activation of pyramidal tract cells. In the remaining cases they indicated mono‐ or polysynaptic activation of pyramidal tract cells. 4. Latencies of the later components of the descending volleys indicated that they were due to indirect activation of pyramidal tract cells in practically all cases. 5. The components of the descending volleys attributable to the indirect activation of pyramidal tract cells were greatly increased when repetitive intracortical stimuli were applied instead of single ones. 6. The investigation leads to the conclusion that a weak intracortical stimulation is relatively ineffective in a direct excitation of pyramidal tract cells and that the effects of such a stimulation are mainly indirect, especially when repetitive stimuli are used.
Uptake of 5‐methyltetrahydrofolic acid by the rat jejunum.
Authors: Blair J A , Matty A J , Razzaque A
Published: December 2014

1. Everted sacs of rat jejunum were used to study the transport of 5‐methyltetrahydrofolic acid at various concentrations and at different pHs. 2. The transport of 5‐methyltetrahydrofolic acid appeared to be linear with increasing incubation time at a 5‐methyltetrahydrofolic acid concentration of 10(−5) M in the incubating medium. Tissue uptake was much higher than serosal uptake. 3. At ‘zero’ concentration gradient of 5‐methyltetrahydrofolic acid, the transport from mucosal to serosal sides was negligible but tissue uptake was appreciable. 4. Reducing the incubation temperature from 37 to 27 degrees C gave a Q10 value of 1‐8. 5. The characteristics of 5‐methyltetrahydrofolic acid uptake suggested a non‐saturable transport mechanism. 6. Studies were also carried out with isolated mucosal epithelial cells at different incubation times and at different pH values. 7. The over‐all results suggest that 5‐methyltetrahydrofolic acid transport is most likely a passive diffusion of its zwitterion and also a solvent drag with water flow. 8. The 5‐methyltetrahydrofolic acid may be converted to its zwitterion in an acid microclimate at the surface of the intestinal absorbing cell.
The effectiveness of bicuculline as an antagonist of GABA and visually evoked inhibition in the cat's striate cortex.
Authors: Sillito A M
Published: December 2014

1. The iontophoretic application of the alkaloid bicuculline to neurones in area 17 of the cat's visual cortex effectively antagonized the inhibitory action of iontophoretically applied GABA in fifty‐four out of sixty‐two neurones examined. It had little or no effect on the inhibitory action of iontophoretically applied glycine. 2. At the stage that the iontophoretic application of bicuculline blocked the inhibitory action of GABA it also reduced or blocked visually evoked inhibitory influences acting on forty‐three of the fifty‐four cells. This effect on visually evoked inhibition was not reproduced by simply raising the neural spontaneous activity with iontophoretically applied glutamate. 3. For those seven neurones where the iontophoresis of bicuculline failed to block the inhibitory action of iontophoretically applied GABA it also failed to produce any change in visually evoked inhibition. 4. In all cases where a visually evoked inhibition of a cells resting discharge was reduced by the iontophoretic application of bicuculline, the inhibitory response was replaced by an excitatory response. The application of bicuculline also revealed excitatory responses to certain of the visual stimuli that previously appeared to exert neither inhibitory nor excitatory effects on a cell, and often where cells normally exhibited small excitatory responses it produced large increases in the magnitude of the evoked response. 5. These results indicate that the normal responses of the neurones examined in the present work, to the particular visual stimuli used, reflect an interaction between simultaneously evoked excitatory and inhibitory inputs. It is suggested that the iontophoretic application of bicuculline by blocking or reducing the inhibitory input moves the balance between the inputs in favour of the excitatory input. 6. The present results support the view that GABA is an inhibitory transmitter in the visual cortex.
The tendon organs of cat medial gastrocnemius: significance of motor unit type and size for the activation of Ib afferents.
Authors: Reinking R M , Stephens J A , Stuart D G
Published: December 2014

1. Histological and histochemical studies suggest that each tendon organ in a mixed mammalian muscle should be particularly responsive to the contraction of a discrete number of motor units (ca. ten to fifteen), each with differing mechanical properties. This report describes physiological experiments that demonstrate this arrangement for the tendon organs of cat medial gastrocnemius. 2. No correlations could be found between the intensity of discharge of a single tendon organ and the contraction strengths of motor units whose contraction excited the receptor. Tendon organs were found to be as responsive to contraction of small slow twitch units as they were to contraction of larger fast twitch units. Taking the data as a whole, the apparent sensitivity of the receptors during motor unit contractions (pps/force recorded at the tendon) was inversely related to the contraction strengths of the motor units. 3. These findings are discussed in relation to recent evidence on the territory of single motor units in medial gastrocnemius and the force producing capabilities of their individual muscle fibres. It is concluded that in general each motor unit, whose contraction excites a given receptor, contributes one muscle fibre to the receptor capsule. Further, it appears that the various excitatory effects of those muscle fibres inserting into a given receptor capsule are not simply related to their relative contraction strengths but also depend on the details of the mechanical coupling between each fibre and the Ib afferent receptor endings. 4. The results of an ensemble analysis show that despite the lack of correlation between the intensity of tendon organ discharge and the force developed at the tendon during contraction of different motor units, a correlation does appear when the responses of several tendon organs and the forces developed by the motor units which excite them are summed progressively. This finding has implications for the recruitment order of motor units in that the profile of the collective Ib response is shown to differ according to whether motor unit forces are summed randomly or in order of increasing contraction strengths.
Ion fluxes during the inhibitory junction potential in the guinea‐pig taenia coli.
Authors: den Hertog A , Jager L P
Published: December 2014

1. Contribution of different ions to the inhibitory junction potential (i.j.p.) in the guinea‐pig taenia coli was studied by measuring the 42K, 24Na and 36Cl fluxes, the membrane resistance and the influence of various external ion concentrations. 2. The membrane resistance, as measured by the electrotonic potential, decreased transiently during the i.j.p. A maximal reduction of the electrotonic potential of about 50% was found at the top of the i.j.p. 3. The i.j.p. amplitude could be reduced by raising the external potassium concentration. Extrapolation of the relationship observed shows that the inhibitory response would be abolished at 115 mM potassium. Similar experiments were made in chloride‐free medium, chloride being replaced by isethionate. Amplitude and time course of the response were not different in chloride containing Locke solution and chloride‐free medium. 4. The half‐times of 42K, 24Na and 36Cl effluxes during rest were 29, 10 and 9 min respectively. The 42K‐efflux from the preparation was markedly increased to about three times the resting efflux during field stimulation. In low‐chloride solution a similar effect on 42K‐efflux was observed during field stimulation. Only a slight increase in the chloride efflux was observed but the sodium efflux was not affected during field stimulation. 5. From the results presented it is concluded that the inhibitory junction potential is caused by a selective increase in potassium permeability of the smooth‐muscle cell membrane.
Responses of hair cells in the statocyst of Hermissenda.
Authors: Detwiler P B , Fuortes M G
Published: December 2014

Responses to mechanical stimulation were recorded from hair cells in the statocyst of Hermissenda crassicornis. The response to a brief stimulus is a depolarizing wave which reaches peak in about 25 msec and decays slowly. 2. Hyperpolarization by extrinsic currents increases the amplitude of the response; depolarization decreases it and eventually reverses its polarity. It is inferred from these results that the primary outcome of the transduction process is an increase of membrane conductance and that the voltage change (generator potential) follows as a secondary event. 3. The features of the conductance change were reconstructed from the time course of the generator potential and the passive properties of the membrane. It was found that the increase of membrane conductance develops slowly and is roughly proportional to the energy delivered by the stimulus. 4. The time course of the conductance change required to reproduce the generator potential is similar to the output of a model involving a sequence of transformations. 5. The generator potential is sensitive to temperature, becoming faster as temperature is raised. This effect is reproduced by the model if the transition rates are assumed to be temperature‐dependent, with a Q10 of about 2. 6. It is concluded that a chain of temperature‐sensitive processes is interposed between the stimulus and the increase of membrane conductance.
Concealed colour opponency in ganglion cells of the rhesus monkey retina.
Authors: De Monasterio F M , Gouras P , Tolhurst D J
Published: December 2014

Criteria for distinguishing colour‐opponent from spectrally non‐opponent cells and identifying colour‐opponent subtypes on the basis of the cone inputs they receive, have been examined in ganglion cells of the macaque retina using threshold and suprathreshold stimuli, with and without chromatic adaptation. 2. Criteria based on suprathreshold responses were found to be insufficient for distinguishing between opponent and non‐opponent cells in one‐third of the sample. Criteria based on a 560 nm neutral point were found to be insufficient for distinguishing between colour‐opponent subtypes in one‐half of the remaining cells. 3. The neutral point of colour‐opponent ganglion cells varies with the geometry and intensity of the stimulus, as well as with the amount of centre‐surround interaction and the receptive‐field location of a cell. As a result, the neutral point is often an ambiguous criterion for identifying colour‐opponent subtypes on the basis of their cone inputs. 4. About one third of the colour‐opponent ganglion cells did not show colour opponency in the presence of neutral backgrounds, and only revealed this behaviour in the presence of chromatic adaptation (concealed colour opponency). 5. The proportion of these concealed colour‐opponent cells increased towards the peripheral areas of the retina.
Localization and electrical characteristics of a giant synapse in the spinal cord of the lamprey.
Authors: Ringham G L
Published: December 2014

1. Physiological and morphological experiments were carried out to determine the characteristics of a giant synapse in the lamprey spinal cord. The presynaptic element is a Müller fibre, running the length of the spinal cord, and the post‐synaptic element is a lateral interneurone. 2. Injection of the interneurone with fluorescent dye revealed several dendritic processes extending into the region of the Müller fibres and spreading over a longitudinal distance of about 150 mum. Electron microscopic examination of the Müller fibres confirmed that they do not send out processes to form synapses. Thus, the synapse is between the cylindrical fibre and one or more dendritic branches of the interneurone. 3. Measurements with intracellular electrodes showed the Müller fibres to have input resistances of about 1 Momega and space constants of 1‐0‐1‐7 mm. The space constant was larger for hyperpolarizing pulses than for depolarizing pulses because of delayed recitification. The interneurones had input resistances of about 6 Momega. 4. The neurones were electrically as well as chemically coupled. When a current‐passing electrode was placed in the fibre and hyperpolarizing pulses applied, the amplitude of the electrical coupling potential recorded from the interneurone was maximal at one position of the current‐passing electrode and decreased as the electrode was moved away from the optimal position. The decrease in amplitude with electrode displacement indicated that the region of synaptic contact was very restricted. 5. The electrical synapse was highly rectifying, the forward resistance being about nine‐times smaller than the backward resistance.