bluuebunny/crossref_metadata_2025_split huggingface dataset:
Atropine‐resistant depolarization in the guinea‐pig small intestine
Authors: Bywater R. A. R. , Holman M. E. , Taylor G. S. 
Published: December 2014

1. Junction potentials were recorded from the circular muscle cells of the guinea‐pig ileum following transmural stimulation in the presence of atropine at 30 °C.2. Single stimuli produced a transient hyperpolarization, the inhibitory junction potential (i.j.p.). At high stimulus strengths the i.j.p. was followed by a post‐stimulus depolarization (PSD).3. During repetitive stimulation the magnitude of the hyperpolarization decreased; however, at the end of the stimulus period the PSD was enhanced and often reached threshold for the generation of action potentials. Thus, the size of the PSD was not directly related to the degree of the preceding hyperpolarization.4. Hyperpolarization of the circular muscle cells was produced by the application of anodal current using large external electrodes. Rapid cessation of the applied current produced a transient after‐depolarization which was shorter in time course than the PSD following the i.j.p. If the applied anodal current was reduced slowly (at a rate which mimicked the decrease in the hyperpolarization during repetitive nerve stimulation) no after‐depolarization was observed.5. Conditioning hyperpolarization of the circular muscle cells reduced the amplitude of the i.j.p. The i.j.p. was reversed at membrane potentials greater than approximately ‐90 mV.6. The PSD did not appear to be due to the extracellular accumulation of potassium ions following the i.j.p. since the PSD persisted even when the i.j.p. was reversed.7. The neurotoxin apamin reversibly abolished the i.j.p. and unmasked a transient excitatory junction potential (e.j.p.) with a variable latency (350‐900 ms).
Oligosynaptic excitation of motoneurones by impulses in group Ia muscle spindle afferents in the cat
Authors: Jankowska Elżbieta , McCrea David , Mackel Robert 
Published: December 2014

1. Intracellular recording from hind‐limb motoneurones was used to investigate whether di‐ and trisynaptic (oligosynaptic) excitatory post‐synaptic potentials (e.p.s.p.s) are evoked from group Ia muscle spindle afferents in those motoneurones in which such potentials are evoked from Ib tendon organ afferents or entire group I afferents. Ia afferents of triceps surae and plantaris were activated either selectively by single brief stretches of these muscles, or together with Ib afferents by electrical stimuli applied to the nerves.2. Muscle stretches below threshold for Ib afferents (10‐35 μm) evoked e.p.s.p.s which appeared with latencies compatible with disynaptic and trisynaptic coupling between the afferents and the motoneurones. The latencies of a majority of these e.p.s.p.s were too short to allow their mediation by group II afferents, if any were activated by the applied stretches. They were also too short to be compatible with effects attributable to dorsal root reflexes. These e.p.s.p.s are thus attributed to oligosynaptic actions of Ia afferents.3. Stretch‐evoked di‐ and trisynaptic Ia e.p.s.p.s were found in 83% of motoneurones in which e.p.s.p.s were evoked by stimuli which activated both Ia and Ib afferents; in five motoneurone species they were found in more than 90%. These observations lead to the conclusion that group Ia muscle spindle afferents evoke not only inhibitory but also excitatory actions in parallel with group Ib tendon organ afferents.4. The distribution of Ia oligosynaptic stretch‐evoked excitation from ankle and toe extensor muscles was compared with the distribution of Ia non‐reciprocal inhibition as described by Jankowska, McCrea & Mackel (1981b). Excitation pre‐dominated in posterior biceps—semitendinosus motoneurones and inhibition in other species of motoneurones investigated, except those of intrinsic foot muscles (tibial motoneurones); similar proportions of the latter showed excitation and inhibition.5. Occurrence of oligosynaptic e.p.s.p.s as well as inhibitory post‐synaptic potentials (i.p.s.p.s) of Ia origin in some motoneurone species, and in particular in individual motoneurones, is indicative of a number of reflex pathways between group I afferents and these motoneurones. Furthermore, the disappearance of some of the e.p.s.p.s evoked by near‐threshold electrical stimulation following stronger stimuli indicates interactions between various functional groups of interneurones mediating group I actions.
Evidence that histamine and carbachol may open the same ion channels in longitudinal smooth muscle of guinea‐pig ileum
Authors: Bolton T. B. , Clark J. P. , Kitamura K. , Lang R. J. 
Published: December 2014

1. Membrane potential was recorded intracellularly by micro‐electrode in separated longitudinal muscle of guinea‐pig ileum. Electrotonic potentials were evoked in longitudinal strips by passing current between large external electrodes in the partition chamber.2. Histamine increased the frequency of action potential discharge at low concentrations and depolarized the membrane. At higher concentrations it caused substantial depolarization and action potential discharge was abolished. Carbachol had similar actions but the maximal depolarization by carbachol (using 10−4
m) was some 4‐5 mV greater than maximal depolarization by histamine (using 10−4
m).3. The change in size of evoked electrotonic potentials was used to estimate the effects of carbachol and histamine on the conductance of the smooth muscle membrane. The equilibrium potentials for histamine and carbachol depolarizations were estimated from their relative effects on potential and conductance and were found to be not significantly different; measurements of the effects on conductance showed that 10−4
m‐histamine increased conductance about 8‐fold whilst 10−4
m‐carbachol had a much greater effect on conductance. This difference could explain the differing maximal depolarizing effects of these agents if both were assumed to open channels having the same ionic selectivity (i.e. equilibrium potential).4. The efflux of 42K was studied in separated strips of longitudinal ileal muscle from guinea‐pig. In the presence of a concentration of carbachol (2 × 10−5
m or 10−4
m) having a maximal effect on 42K efflux rate, histamine (10−4
m) did not increase efflux further although 120 m
m‐potassium did so. Experiments with the irreversible muscarinic receptor blocker, propylbenzilylcholine mustard, indicated that the number of muscarinic receptors did not limit the 42K efflux response to carbachol and it was suggested that the response was limited by the availability of ion channels which could be opened by activated muscarinic receptors.5. Contractions to histamine and carbachol in 120 m
m‐potassium depolarizing solution were followed upon washing by a relaxation below basal tension. Carbachol, but not histamine, showed a pronounced and long lasting secondary contraction following this relaxation.6. These results are consistent with the idea that activated histamine and activated muscarinic receptors open the same ion channels in the smooth muscle membrane to produce depolarization, increased action potential discharge and contraction, although muscarinic receptors can open more of these. However, there was evidence that the opening of these channels is not the only pathway between receptor activation and contraction.
Functional maturation of motor nerve terminals in the avian iris: ultrastructure, transmitter metabolism and synaptic reliability
Authors: Pilar Guillermo , Tuttle Jeremy , Vaca Ken 
Published: December 2014

1. The transformation of easily fatigued embryonic neuromuscular junctions into highly reliable mature terminals was examined by studying functional and morphological changes during development of the avian iris. The mature ability to follow repetitive electrical nerve stimulation was correlated with the rate of acetylcholine (ACh) synthesis and choline uptake, and with the fine structure of the nerve terminals and the post‐synaptic elements.2. The terminals of the ciliary nerve of the chick initially form functional synaptic contacts with the iris muscle at embryonic St. 34‐40. At the onset of this period, no Na+‐dependent high affinity choline uptake can be demonstrated, and the low level of ACh synthesis present is sensitive to Na+ removal. At St. 36 [3H]ACh synthesis begins to increase, the increment being Na+‐dependent.3. ACh synthesis in the embryonic iris was insensitive to a conditioning [K+]o depolarization even as late as St. 43. Just before hatching, depolarization elicits some augmentation in synthesis, but by 2 days ex ovo this release‐induced response has increased by an order of magnitude.4. Concurrently with the acquisition of the ability to respond to depolarization with accelerated synthesis, neuromuscular transmission in the iris becomes reliable and secure during stimulation at 20 Hz. Embryonic junctions rapidly block during such stimulation, and the failure is shown to be presynaptic in origin, resulting most probably from failure to sustain adequate levels of transmitter release.5. Ultrastructural examination of the developing ciliary terminals revealed few synaptic vesicles at early stages, and a dearth of other specializations. The sequence of development from these small structurally undistinguished endings to large en plaque junctions completely filled with vesicles was reconstructed and compared to other neuromuscular junctions. Morphological maturation appears progressive with little evidence of discontinuity signalling functional status, but it is only after the terminals enlarge and become closely packed with vesicles that mature synaptic reliability is found.6. The temporal correlation between responsiveness of transmitter synthesis to depolarization and reliable neuromuscular transmission suggests that modulation of neurotransmitter metabolism in response to demand signals the achievement of junctional maturity.
Effects of endogenous and exogenous noradrenaline on the smooth muscle of guinea‐pig mesenteric vein
Authors: Suzuki Hikaru 
Published: December 2014

Membrane responses of smooth muscles of the guinea‐pig mesenteric vein to noradrenaline released from perivascular nerves or applied exogenously were investigated.1. Exogenously applied noradrenaline depolarized the muscle membrane at concentrations of over 10−6
m, and generated slow waves or action potentials. Application of phentolamine but not propranolol suppressed the depolarization.2. The depolarization induced by exogenous noradrenaline was associated with increase in the membrane resistance. The level of the membrane depolarization was modified by changing [K]o, but not by [Na]o or [Cl]o.3. Repetitive but not single stimulation of the nerves produced slow depolarization of the membrane. The amplitude of the slow depolarization was dependent on the frequency or number of stimuli within a certain range, but beyond this an increased frequency or an increased number of stimulating pulses produced no further increase in amplitude of the slow depolarization.4. The slow depolarization induced by nerve stimulation was analysed in relation to the diffusion of transmitter. The rising phase of the slow depolarization fitted well with the theoretically predicted one, while the falling phase did not.5. Stimulation of nerves with a high frequency and a large number of pulses produced slow waves or action potentials superimposed on the slow depolarization of the membrane.6. Membrane responses induced by nerve stimulation did not appear in the presence of TTX or phentolamine. TEA enhanced the nerve‐induced responses.7. Myogenic electrical activities insensitive to TTX and phentolamine were recorded from the mesenteric vein. These activities were induced by nerve stimulation only in the fresh tissues, were usually irregular in shape, size and frequency, and lasted for 5‐20 min.8. It was concluded that alpha‐adrenergic receptors on the muscle membrane reacted in a similar manner to noradrenaline either released from the nerves or applied exogenously. Noradrenaline depolarized the muscle membrane by the decrease in potassium conductance of the membrane.
Interactions between three slow potassium responses controlled by three distinct receptors in Aplysia neurones
Authors: Ascher Philippe , Chesnoy‐Marchais Dominique 
Published: December 2014

1. A voltage clamp study was made of the K+ permeability increases produced in certain identifiable neurones of the cerebral ganglion of Aplysia by any one of three distinct agonists (carbachol, histamine and dopamine).2. The three K+ responses involve three distinct receptors, as shown by the selective effects of reversible antagonists (Gruol & Weinreich, 1979a) as well as by the differential, irreversible effects of trimethyloxonium (TMO) ions.3. Prolonged exposure of the neurones to one of the agonists reduces the response to the same agonist (desensitization) and, over the low concentration range, doubling the concentration of an agonist leads to supra‐linear summation (potentiation).4. Prolonged exposure of the neurones to one of the agonists also reduces the response to the other agonists (cross‐desensitization) and combined application of two agonists reveals cross‐potentiation.5. The time course of desensitization (onset and decay) was the same for the histamine and carbachol responses and, except at very high concentration, was indistinguishable from that of cross‐desensitization. Likewise, potentiation was similar in the two agonist systems and did not differ significantly from cross‐potentiation.6. The results can be interpreted by assuming that the responses to the three agonists involve specific steps followed by common reaction steps, and that some of the common reaction steps control both potentiation and desensitization.7. The responses to carbachol and histamine differ in their voltage sensitivity. This suggests that one or more of the specific steps are voltage‐sensitive.8. Although an increase of the intracellular Ca2+ concentration can itself open K+ channels, and also inhibit the responses to the three agonists, an increase of internal Ca2+ does not appear to play an important role either in the development of the response or in the desensitization process.
Central gating of developmental plasticity in kitten visual cortex
Authors: Singer W. , Tretter F. , Yinon U. 
Published: December 2014

1. In nine 4‐week‐old, dark‐reared kittens we sutured one eye closed and rotated the other surgically. The kittens then grew up in a normally lighted animal colony with adequate room to play.2. For about two weeks after surgery their visual‐motor co‐ordination did not differ from that of kittens with conventional monocular deprivation; then severe disturbance of visually guided behaviour became progressively more apparent until, after another two to three weeks, all the kittens stopped responding to most visual stimuli entirely. At that point their behaviour in an unfamiliar environment closely resembled that of binocularly deprived cats exposed to light for the first time.3. Four weeks (n = 3) and 6 months (n = 6) after surgery, we examined the visual cortex with single‐unit recordings, and with evoked potentials elicited by electrical stimuli and patterned lights. We obtained the single‐unit recordings from 586 neurones of the striate cortex in both hemispheres, both ipsi‐ and contralateral to the deprived eye.4. The single‐unit recordings and the evoked potentials showed a clear relation between the kitten's abnormal visual behaviour and the functioning of the striate cortex. Only about half the normal percentage of cells responded to light, and most of those which did react had abnormal receptive field properties: they responded only sluggishly even when the light stimuli were aligned optimally.5. We also evoked cortical potentials with phase alternating square wave gratings of variable contrast and spatial frequency. The amplitude of the potentials indicated that contrast‐sensitivity was reduced at all spatial frequencies.6. In the kittens tested 4 weeks after surgery, ocular dominance had shifted toward the open rotated eye but this shift was considerably less pronounced than in control kittens monocularly deprived for a comparable period of time.7. In the kittens tested 6 months after surgery fewer cells than normal were binocular; ocular dominance had not shifted towards the open eye.8. Numerous control experiments indicated that these abnormalities did not result from transitory immobilization of the eye alone nor from lesions of the retina or of the optic nerve.We infer that a central mechanism prevents the inappropriate signals from the rotated eye from influencing the consolidation of central pathways.
Voltage‐clamp studies of transient inward current and mechanical oscillations induced by ouabain in ferret papillary muscle
Authors: Karagueuzian Hrayr S. , Katzung Bertram G. 
Published: December 2014

1. We studied the effects of a toxic concentration of ouabain on transmembrane electrical activity and on mechanical behaviour of right ventricular papillary muscles from ferrets in a single sucrose‐gap using current clamp and voltage clamp.2. Ouabain (1·4‐1·8 μM) induced oscillatory after‐potentials and after‐concentrations in current‐clamp experiments. Voltage clamp showed that the oscillatory after‐potential was caused by a transient inward current, similar to that in Purkinje fibres.3. The transient current had a sigmoidal dependence on the preceding (activating) voltage step V1, with a treshold around ‐13 mV and a plateau between +10 and 20 mV. There was a decline in current amplitude for more positive clamps. When activated by a fixed V1 voltage step, and measured at different repolarization levels V2, the transient current manifested an inverse dependence on V2 between ‐50 and ‐10 mV. No outward transient current could be detected. Total replacement of Na in the bathing medium by Tris or by sucrose abolished the transient current.4. Ouabain caused an increase of phasic (twitch) tension responses to voltage steps at all potentials without shifting the curve relating these variables on the voltage axis. The drug evoked an even greater increase in the tonic tension responses.5. After prolonged exposure, oscillatory mechanical responses were frequently recorded during positive voltage steps. Unlike the after‐contraction, these mechanical fluctuations were not consistently damped and were not accompanied by detectable synchronous current fluctuations. Catecholamines and dibutyryl cyclic AMP markedly reduced the amplitude of the tonic contraction and the mechanical oscillations but increased their frequency. Caffeine had no effect on the tonic contraction amplitude but abolished the fluctuations.6. These results support the proposal that Ca is transiently released from the overloaded sarcoplasmic reticulum in ouabain‐intoxicated muscle and may evoke oscillatory responses in nearby contractile fibrils. When these transient increases of sarcoplasmic free Ca are large enough, they may induce the transient transmembrane current described above.
Rapid restoration of functional input to the visual cortex of the cat after brief monocular deprivation
Authors: Blakemore Colin , Hawken M. J. 
Published: December 2014

1. We recorded extracellularly from 1045 neurones in area 17 of seven monocularly deprived kittens and we employed careful sampling techniques to examine the effects of removing the signals from the non‐deprived eye on the proportion of cells responding to stimulation of the deprived eye.2. Monocular deprivation itself produced a pronounced over‐all change in the ocular dominance of neurones in favour of the experienced eye, but both between animals and even between different samples of cells in individual animals there were marked variations in the magnitude of the effect.3. Monocular deprivation starting immediately at the time of natural eye opening and lasting for several weeks reduced to about 10% the proportion of cortical neurones influenced through the deprived eye. Enucleation of the experienced eye did not then produce a significant increase in the proportion of cells responsive to the deprived eye.4. Monocular deprivation lasting 3 days or more and beginning at 5 weeks of age, after normal binocular vision, also shifted ocular dominance substantially: 11‐27% of neurones responded through the deprived eye. Enucleation of the experienced eye or topical anaesthesia of the optic nerve resulted in a substantial recovery of input from the deprived eye: up to 78% of the cells responded.5. In such animals the majority of neurones that recovered input from the deprived eye had receptive field properties qualitatively similar to those of normal cortical cells. Recording in a single penetration both before and after enucleation (or optic nerve block) suggested that the orientation preferences of cells with recovered input followed the same sequence as was originally present for the non‐deprived eye.6. Recovery of input occurred in all cortical laminae in which cells were recorded, even in layer IV, and mainly took the form of an expansion of already existing clusters of cells driven by the deprived eye.7. Spontaneous activity tended to increase after enucleation.8. The results indicate that monocular deprivation after a period of normal binocular vision leaves subthreshold but functionally organized synaptic input from the deprived eye on cortical cells, which is revealed when activity arising in the retina of the non‐deprived eye is abolished.
Brief monocular deprivation leaves subthreshold synaptic input on neurones of the cat's visual cortex
Authors: Blakemore Colin , Hawken M. J. , Mark R. F. 
Published: December 2014

1. We have examined neurones in area 17 of monocularly deprived kittens for subthreshold input in response to visual stimulation through the deprived eye during reversible abolition of activity from the non‐deprived eye and during increased excitability of cortical neurones induced by ionophoresis of DL‐homocysteic acid (DL‐H).2. After two or three days of monocular deprivation, beginning five weeks post‐natally, most cortical neurones were dominated by the non‐deprived eye. From a sample of forty‐three neurones, from three kittens, driven exclusively by the non‐deprived eye, only 16% developed responses to stimulation through the deprived eye as a result of reversible pressure blinding of the non‐deprived eye. The responses through the deprived eye during pressure blinding usually developed over a period of several minutes and were always transitory: in no cases did the response persist for more than a few minutes after the return of the normal response through the non‐deprived eye. Occasionally cells became responsive through the deprived eye during a short period of heightened general excitability after the release of pressure.3. Ionophoretic application of DL‐H usually increased the spontaneous activity of cortical neurones. From two kittens monocularly deprived for three days during the fourth or fifth week of life, out of a sample of sixteen cortical neurones initially responsive only through the non‐deprived eye, 63% showed responses to visual stimulation through the deprived eye during DL‐H application. From a kitten monocularly deprived for 12 d from post‐natal day 38, 28% of eighteen initially monocular neurones developed responses through the deprived eye during DL‐H application.4. Preliminary results from intracellular recording showed apparently monocular neurones with excitatory input from the deprived eye producing subthreshold synaptic activity in response to moving bars of the same orientation that gave a suprathreshold response through the non‐deprived eye.