bluuebunny/crossref_metadata_2025 huggingface dataset:
The activity of cerebellar neurones of the decerebrate dogfish Scyliorhinus during spontaneous swimming movements.
Authors: Paul D H , Roberts B L
Published: December 2014

Patterns of activity of cerebellar neurones in response to cutaneous stimulation and during spontaneous, swimming‐like movements were examined, using microelectrodes, in decerebrate dogfish (Scyliorhinus canicula). Continuous swimming movements, lasting for several hours, were obtained in fish in which the medial longitudinal fasciculus (m.l.f.) was lesioned in the rhombencephalon. Purkinje cells (P cells) and some stellate cells (S cells) were observed to discharge rhythmically, in phase with swimming movements. These units were distributed throughout the cerebellum, but with no apparent somatotopic distribution. After curarization, rhythmic motor discharges could still be recorded from ventral roots and phase locked P cell discharges were recorded from the cerebellum. P cells that discharged rhythmically during active swimming movements, did not do so when the body was oscillated passively during quiescent periods. Cutaneous stimulation evoked burst discharges in many P cells at long latency (ca. 100 ms) both before and after curarization and whether or not a rhythmic motor output was being generated. In rhythmically discharging units, a similar response was obtained when cutaneous stimulation was applied during that part of a cycle when the unit was most or least active. It was concluded that cerebellar neurones discharged in phase with the output of the spinal locomotory rhythm generators and independently of peripheral sensory feed‐back.
Influence of circulating catecholamines on protein secretion into rat parotid saliva during parasympathetic stimulation.
Authors: Anderson L C , Garrett J R , Johnson D A , Kauffman D L , Keller P J , Thulin A
Published: December 2014

Secretion of proteins by rat parotid glands in response to parasympathetic nerve stimulation was studied in vivo during pentobarbitone anaesthesia. Parasympathetic stimulation (3‐10 Hz) via the auriculotemporal nerve resulted in a copious flow of saliva low in protein. In contrast, sympathetic stimulation (5 Hz) via the cervical sympathetic trunk evoked saliva low in volume but high in protein. Nevertheless, the specific concentrations of amylase and peroxidase (mg/mg protein) and the ratio of amylase to peroxidase remained constant. Sodium dodecyl sulphate (SDS) polyacrylamide gel electrophoresis revealed a single, rapidly migrating protein band of unknown identity in proportionately greater amounts in parasympathetic saliva than in sympathetic saliva. Bilateral adrenalectomy led to reduced amylase and peroxidase secretion in response to parasympathetic stimulation both on a mg/ml and a mg/mg protein basis. SDS gel electrophoresis also demonstrated the decrease in specific amylase concentration following adrenalectomy. The ratio of amylase to peroxidase, however, was not significantly affected. Administration of 6‐hydroxydopamine 17‐72 h prior to adrenalectomy caused no further reduction in the secretion of amylase and peroxidase. Chronic sympathectomy of 2.5‐4 months duration resulted in an increased protein secretion (mg/ml) by the parotid gland in response to parasympathetic stimulation. This increase was only slightly reduced by bilateral adrenalectomy. However, as observed in non‐sympathectomized rats, adrenalectomy caused a significant reduction in the specific concentrations of both amylase and peroxidase, but did not affect the amylase to peroxidase ratios. We conclude that parasympathetic nerve stimulation of rat parotid glands after overnight starvation causes secretion of proteins in proportions similar to, but in significantly lower concentrations than those found in sympathetic saliva. Circulating catecholamines, however, influence the amount of amylase and peroxidase secreted by the rat parotid gland in response to parasympathetic nerve stimulation and account for most of the increased secretion of these enzymes following chronic sympathectomy.
Cat ventricular muscle treated with D600: effects on calcium and potassium currents.
Authors: McDonald T F , Pelzer D , Trautwein W
Published: December 2014

In single sucrose‐gap experiments on cat ventricular muscle strands stimulated with 300 ms pulses at 0.33 Hz, 2 microM‐D600 reduced the Ca‐dependent slow inward current (ICa) by 50% within 5 min and more than 90% in 90‐120 min. The late outward current was reduced by up to 30%. During the exposure to D600, Ca channels could be unblocked by hyperpolarizing pulses and blocked again by stimulation with depolarizing pulses. Since the degree of unblocking depended on voltage, and the degree of blocking depended on stimulation pattern, ICa amplitude could be rapidly manipulated to probe the dependence of K conductance on ICa. Under control conditions, an increase in stimulation rate from 0.02 to 1 Hz reduced ICa by 15% and increased the late outward current by a smaller amount. During exposure to D600, a similar intervention provoked a 60% reduction in ICa, but a control‐like increase in the late outward current. Two other series of experiments failed to disclose a link between ICa and K conductance: when a block of Ca channels was reimposed following their unblocking, the outward currents were independent of ICa amplitude. Unblock‐block experiments also provided information on the extent of steady‐state ICa at 0 mV. The fraction of Ca channels not undergoing inactivation appears to be very small. During full D600 block, the inward peak of the current wave form is broad and very much delayed in comparison with pre‐drug currents or currents on the first pulse following unblocking. A similar wave form was recorded in D600‐treated ventricular myocytes from cat but not guinea‐pig. The likely explanation is that D600 unmasks a small transient outward current in cat ventricle.
Adenosine‐5'‐triphosphate‐sensitive single potassium channel in the atrioventricular node cell of the rabbit heart.
Authors: Kakei M , Noma A
Published: December 2014

The patch‐clamp method was applied to single atrioventricular (a.v.) node cells of the rabbit heart to study the characteristics of the K+ channel. When the electrode contained 5.4 mM‐K+, depolarizations of the cell‐attached patch membrane induced outward single channel currents characterized by burst‐like openings; the open‐state probability increased from 0.005‐0.01 at ‐40 mV to 0.07‐0.1 at +20 mV of membrane potential. The reversal potentials of the current at K+ concentrations of 5.4, 20 and 130 mM in the electrode agreed with those given by the Nernst equation, indicating that this channel is selective for K+ ions. The slope conductance of the channel decreased beyond 60‐90 mV positive to the reversal potential (inward‐going rectification). The conductance near the reversal potential increased with increasing K+ concentrations on either side of the membrane: from 31‐32 pS at 5.4 mM‐K+ to 41‐42 pS at 20 mM‐K+ on the outside, and from 19 pS at 90 mM‐K+ to 29.3 pS at 130 mM‐K+ on the inside. Superfusion of the cell with 5.4 mM‐CN‐, glucose‐free Tyrode markedly increased the number of channel openings in the cell‐attached patch. In the inside‐out patch, application of 1 mM‐adenosine‐5'‐triphosphate (ATP) at the inner surface of the patch membrane blocked reversibly the channel activity, while 1 mM‐adenosine‐5'‐diphosphate (ADP) failed to block it. The conductance and kinetics of the channel were not modified by increasing the Ca2+ concentration from 10(‐8) M to 5 X 10(‐6) M on the inner side of the membrane, while a further increase in Ca2+ to 10(‐4) M decreased the open‐state probability. The probability density for the open time fitted well with an exponential distribution (time constant of 5.4 ms at 60 mV positive to the resting potential), while that for the closed time was separated into a fast and a slow component (time constants of 4.0 and 132.0 ms, respectively). The time constant of the slow component decreased significantly with depolarization in some preparations. However, neither the time constant of the fast component of the closed‐time histogram nor that of the open‐time histogram was voltage‐dependent.
The effects of neural crest deletions on the development of sensory innervation patterns in embryonic chick hind limb.
Authors: Scott S A
Published: December 2014

Selected lumbosacral dorsal root ganglia (d.r.g.s) were eliminated from chick embryos by removing the parent neural crest, and the dermatomes and axonal projection patterns established in the hind limb by the remaining intact d.r.g.s were studied physiologically and/or anatomically. Dermatomes of intact d.r.g.s expanded into denervated skin regions, partially but never completely replacing the lost innervation; some skin regions consistently remained without apparent innervation. Dermatome expansion was detected in young embryos, soon after skin innervation was established, suggesting that skin sensory axons in operated embryos ignored their usual dermatome borders. The axonal pathways (nerve trunks) normally supplied by axons from the deleted d.r.g.s were missing, and axons from intact d.r.g.s were only rarely found in aberrant pathways. In contrast, the relative distribution of axons from intact d.r.g.s within their usual complement of pathways was altered, with axonal projections shifting toward, but not into the deleted pathways. Shifts in axonal projection patterns were observed in embryos prior to the onset of sensory cell death. Thus, d.r.g. deletions appeared to affect the initial growth of axons into the limb. Together these results suggest that during normal development competitive interactions among axons from neighbouring d.r.g.s play an important role in establishing the borders between dermatomes and in determining the distribution of axons within projection pathways in the limb.
Spatial summation in subregions of simple‐cell receptive fields in cat striate cortex as a function of slit length.
Authors: Heggelund P , Krekling S , Skottun B C
Published: December 2014

Spatial summation along the optimum stimulus orientation in subregions of simple‐cell receptive fields in cat striate cortex was studied quantitatively by measuring the response to stationary light slits of variable length. Before summation analysis, the cell's discharge field was mapped by flashing a test slit on and off in a sequence of positions through the receptive field. A static activation procedure was used to determine the extension of subregions of the receptive field where light stimulation increased (enhancement) or decreased (suppression) the firing rate. An activation slit in the optimum orientation was positioned in the most responsive position of the discharge field and the effects of a parallel test slit, in a series of broadside positions, were assessed from the changes induced in the discharge elicited by the activation slit. Length‐response curves for on and off responses were made by positioning a test slit in the respective subregions of the discharge field. The activation procedure was used to make length‐response curves for suppression. A test slit of variable length was positioned in a suppression region defined by the activation profiles and an activation slit of fixed length was centred in the most responsive discharge field position. Length summation was found for all cells, both with respect to on and off responses, and suppression. The curves for on and off responses had a maximum value beyond which the response declined or levelled off, but some cells had a secondary, more shallow increase beyond an initial, steeply rising part. Similar properties were found for summation of suppression except that the effects were opposite in sign. Curves made for both on and off regions in the same cell often differed in shape. Such differences were also found when length‐response curves made in different suppression regions of the same cell were compared. The various length‐summation functions were explained by a model presuming that simple‐cell receptive fields consist of partially overlapping non‐concentric excitatory and inhibitory fields. This arrangement would also explain why length‐response curves in various subregions often had different shapes.
A quantitative analysis of interactions between photoreceptors in the salamander (Ambystoma) retina.
Authors: Attwell D , Wilson M , Wu S M
Published: December 2014

A quantitative description of the electrical properties of the photoreceptor layer in the salamander retina was obtained from earlier data on the characteristics of isolated rods and cones and on rod‐rod coupling, and from new data on rod‐cone and cone‐cone coupling and on the rod photocurrent. Injecting ‐1 nA current into a rod elicits hyperpolarizations of about 20 mV in an adjacent rod and 4 mV in an adjacent cone. Responses of more distant receptors are smaller. Injecting ‐1 nA into a cone elicits hyperpolarizations of about 4 mV in an adjacent rod and 0.4 mV in a nearby cone. Depolarizing current evokes smaller responses. Assuming, in agreement with anatomical evidence, that each rod is electrically coupled to four rods and to four cones around it, and that there is no direct electrical coupling between cones, we found these results could be predicted from the properties of isolated rods and cones if adjacent rods are coupled by a resistance of 300 M omega and adjacent rods and cones are coupled by a resistance of 5000 M omega. The small cone‐cone coupling seen is due to coupling via intervening rods. The two halves of double cones are not electrically coupled. The spectral sensitivity of both halves is a maximum around 620 nm wave‐length. The rod photocurrent has been characterized by voltage‐clamping rods isolated from the retina. In agreement with Bader, MacLeish & Schwartz (1979) we found the time course of the photocurrent to be approximately independent of voltage between ‐35 and ‐85 mV. The voltage responses of rods, single cones and double cones isolated from the retina obey the principle of univariance. Responses of receptors in the retina do not obey univariance. The main deviations from univariance observed can be explained if adjacent rods and cones are coupled by a resistance of 5000 M omega. Our data demonstrate that rod‐cone coupling is relatively weak. We simplified our description of the photoreceptor network, by omitting cones, to investigate the spatiotemporal processing that the rod network is capable of. Computer simulations predict, as is found experimentally, that the rod voltage response to a large spot of bright light should show a much more pronounced initial transient hyperpolarization than the response to a small spot of light of the same intensity. This difference is produced by the combination of electrical coupling of the rods with the existence of a voltage‐gated current, IA, in the rod membrane.(ABSTRACT TRUNCATED AT 400 WORDS)
The appearance and development of neurotransmitter sensitivity in Xenopus embryonic spinal neurones in vitro.
Authors: Bixby J L , Spitzer N C
Published: December 2014

We have determined the time of onset and examined some of the properties of neurotransmitter sensitivity in Xenopus spinal neurones developing in dissociated cell culture. These cells are initially insensitive, but acquire responses to several agonists over a period of 6 h. Nearly one‐third of the neurones were depolarized by gamma‐aminobutyric acid (GABA) or by both GABA and glycine; these cells were not affected by glutamate. The reversal potential of the ionophoretic GABA response is ‐35 mV. These neurones are likely to be Rohon‐Beard neurones. Roughly two‐thirds of the neurones were depolarized by glutamate and hyperpolarized by GABA and by glycine. The reversal potential of the ionophoretic GABA response is ‐58 mV. These neurones are likely to include motoneurones. A quantitative measure of the sensitivity to a given GABA dose was obtained at early and intermediate stages of development. The mean 'sensitivity index' (ionophoretic sensitivity/input resistance) for both classes of neurones in vitro was initially the same as that seen in Rohon‐Beard neurones in vivo. This sensitivity index did not increase with time in culture to attain the value at intermediate stages in vivo. The development of chemosensitivity in Rohon‐Beard‐like neurones in these cultures resembles that of Rohon‐Beard neurones in the spinal cord with respect to the time of onset of responses to GABA, the reversal potential, pharmacology and desensitization of these responses, and the spectrum of agonists to which they are sensitive. It differs in the absence of a developmental increase in sensitivity to GABA. The development of chemosensitivity in motoneurone‐like neurones in these cultures parallels that of Rohon‐Beard‐like neurones, with respect to the time of onset and level of sensitivity, as well as susceptibility to pharmacological blockers. Several features of normal neurotransmitter sensitivity, like features of the action potential, differentiate in culture in the absence of normal cellular interactions.
Co‐release of enkephalins and precursors with catecholamines from the perfused cat adrenal gland in situ.
Authors: Chaminade M , Foutz A S , Rossier J
Published: December 2014

We have compared the nature of the enkephalin‐like material derived from proenkephalin present in the intact cat adrenal gland with the material co‐released with catecholamines from the perfused adrenal in response to splanchnic nerve stimulation and to perfusions with solutions containing acetylcholine (ACh) or high potassium chloride (KCl). In cat adrenals most of the enkephalin‐like material was in the form of large enkephalin‐containing peptides. Free (met)enkephalin immunoreactivity represented only 25% of the total (met)enkephalin immunoreactivity as determined by enzymatic digestion of large enkephalin‐containing fragments. Electrical stimulation (15 Hz) of the splanchnic nerve or perfusion of the gland with ACh (0.1 mM) or KCl (50 mM), applied for 10 min, induced an immediate release of free (met)enkephalin immunoreactivity, (met)enkephalyl‐arg‐phe immunoreactivity, and of large (met)enkephalin‐containing peptides. The release by all three modes of stimulation followed a pattern that paralleled the output of catecholamines. A rapid fatigue of all secretory processes developed during the stimulation periods, similar to that observed for catecholamines. During splanchnic nerve stimulation, each nanomole of catecholamine output was accompanied by the output of 0.4 pmol free (met)enkephalin immunoreactivity, of 1.1 pmol total (met)enkephalin immunoreactivity and of 0.1 pmol (met)enkephalyl‐arg‐phe immunoreactivity. Analysis of the perfusate by high‐pressure liquid chromatography revealed that (met)enkephalin, (met)enkephalyl‐arg‐phe and (met)enkephalyl‐arg‐gly‐leu were released in molar ratios of 4 to 1 to 1 which is similar to the ratio found in the precursor, proenkephalin. The ratio of total (met)enkephalin immunoreactivity to free (met)enkephalin immunoreactivity in the perfusate was the same (approximately 2.7) during two successive periods of splanchnic nerve stimulation separated by 10 min. When release was evoked by increasing the K+ concentration to 50 mM‐KCl, this ratio was increased more than twofold compared with that obtained by electrical stimulation of the splanchnic nerve. Analysis of the perfusate by gel filtration showed that, during splanchnic nerve stimulation, 47% of the total (met)enkephalin immunoreactivity eluted in fractions containing fragments of low molecular weight. When KCl was used as stimulus only 12% of total (met)enkephalin immunoreactivity eluted in these fractions. The results indicate that the nature of the released peptides depends on the type of stimulus used to evoke release.(ABSTRACT TRUNCATED AT 400 WORDS)
Slowly inactivating potassium channels induced in Xenopus oocytes by messenger ribonucleic acid from Torpedo brain.
Authors: Gundersen C B , Miledi R , Parker I
Published: December 2014

Poly(A+) messenger RNA was extracted from the electric lobe and medulla of Torpedo and injected into oocytes of Xenopus laevis. The synthesis and processing of proteins coded by the injected messenger RNA led to the incorporation of voltage‐activated channels in the oocyte membrane. A large, well maintained outward current was recorded from injected oocytes in response to depolarization. Non‐injected oocytes did not show this current. The reversal potential of the current varied according to the Nernst equation with external potassium concentration, indicating that it was largely carried by potassium ions. The maintained potassium current was not reduced by manganese (5 mM) or lanthanum ions (0.1 mM). Tetraethylammonium and aminopyridines blocked the potassium current. The block produced by 3,4‐diaminopyridine was enhanced by previous activation, but diminished by strong depolarization. The amplitude of the potassium current increased over the approximate voltage range ‐30 to +50 mV, but reduced at more positive potentials. The decline of the current during maintained depolarization became slower as the membrane potential was made more positive, and the rate of onset of the current became faster. Estimates from noise analysis indicated that the slow potassium current passes through channels with a mean lifetime of about 14 ms and conductance of 14 pS (at ‐10 mV and room temperature). Injection of the messenger RNA also induced the formation of fast sodium and potassium channels activated by voltage, and channels activated by kainate.
Observations on the time course of the electromyographic response reflexly elicited by muscle vibration in man.
Authors: Matthews P B
Published: December 2014

Surface electromyography has been used to study the initial reflex response of various muscles to vibration, applied to their tendons, when the subject was already contracting them voluntarily. The response at the onset of vibration was of a latency appropriate for Ia monosynaptic action and was always highly phasic with an initial wave rising far above any maintained increase in electromyogram (e.m.g.) activity; its duration was typically well below 20 ms in the rectified average. Thus, there is nothing peculiar, in this respect, about flexor pollicis longus for which such behaviour has already been described, and used to draw certain wide‐ranging conclusions about the stretch reflex. Theoretical considerations, developed in an Appendix, show that quite apart from the operation of any inhibitory mechanisms such a phasic response is to be expected from a population of tonically discharging motoneurones when there is a step increase in the level of their excitatory drive.
Involvement of the renin‐angiotensin system in captopril‐induced sodium appetite in the rat.
Authors: Elfont R M , Epstein A N , Fitzsimons J T
Published: December 2014

The angiotensin converting enzyme inhibitor, captopril, given to rats in their drinking water (about 40 mg/day) for 6 days caused an increase in intake of hypertonic NaCl solution which began 1‐2 days after the captopril was started and reached a plateau after 4‐5 days. Twice‐daily subcutaneous injections of captopril (15 mg per injection) elicited a sodium appetite similar in pattern to that seen with oral administration. The rats remained in sodium and fluid balance during oral captopril treatment and the haematocrit did not alter. Captopril infused directly into the ventricles (12 micrograms/h), or captopril reaching the brain from the periphery across a leaky blood‐brain barrier, suppressed the sodium appetite which normally follows oral captopril. Continuous intravenous infusion of captopril at rates high enough to block angiotensin converting enzyme in the brain (25, 50 or 500 mg/day) did not cause sodium appetite. As soon as the rate was reduced to a low value (5 mg/day), NaCl intake increased. In conclusion, moderate levels of circulating captopril which do not cross the blood‐brain barrier in sufficient amounts to block cerebral angiotensin converting enzyme, result in an increase in circulating angiotensin I which stimulates sodium appetite when it is converted to angiotension II in the brain.
A novel membrane sodium current induced by injection of cyclic nucleotides into gastropod neurones.
Authors: Connor J A , Hockberger P
Published: December 2014

Injection of cyclic AMP (cAMP) or cyclic GMP into identifiable neurones from several different gastropod species immediately depolarized the cell membranes in a dose‐dependent manner. Doses were monitored photometrically and evidence is presented for depolarizing effects following nucleotide injections of as little as 30‐35 mumol. The depolarizing effect was reversible and was demonstrated under voltage clamp to be primarily the result of a nucleotide‐induced, transient increase in a membrane Na current, INa (cAMP). The charge‐carrying species was identified by using ion‐substituted salines, reversal potential in low‐Na saline, and intracellular ion‐sensitive electrode measurements. The current was resistant to tetrodotoxin, ouabain and amiloride. Substituting Trisma, tetramethylammonium or bis‐tris propane for Na prevented the induced current, whereas Li substitution did not. Duration of the induced current was greatly prolonged in neurones bathed in the phosphodiesterase inhibitor isobutylmethylxanthine, or following injection of any of several cAMP analogues, indicating that the reversible nature of the current stems primarily from in situ hydrolysis of the injected dose and not current inactivation. Amplitude of the induced current either remained constant or decreased over the voltage range where it could be easily measured, i.e. ‐30 greater than Vm greater than ‐100 mV, reflecting a voltage as well as a chemical sensitivity of INa (cAMP).
Respiratory rhythm generation in the in vitro brain stem‐spinal cord preparation of the neonatal rat.
Authors: Suzue T
Published: December 2014

An in vitro preparation was described for studying electrical activity of mammalian brain stem and spinal cord. The brain stem and the spinal cord were isolated from 0‐4‐day‐old rats, placed in a bath and perfused with modified Krebs solution. Various reflex responses could be recorded from cranial nerves by stimulation of other cranial nerves. The preparation was viable for more than 7 h. Spontaneous periodic neural activity could be recorded from phrenic, hypoglossal and other spinal nerves. The periodic discharges of phrenic nerves are synchronized with those of ventral roots C4 and the upward movements of the thorax which was isolated together with the spinal cord. The rhythm of periodic activity seems to be generated in the brain stem. The periodic activity was enhanced by perfusion with low pH solution and depressed by high pH solution. It was markedly depressed by opioid compounds such as enkephalin. It is suggested that this periodic activity corresponds to the respiratory rhythm generated in the brain stem of intact animals. The present preparation may be valuable for elucidating cellular mechanisms of generation and control of respiratory rhythm in the mammalian central nervous system.
Strychnine blocks transient but not sustained inhibition in mudpuppy retinal ganglion cells.
Authors: Belgum J H , Dvorak D R , McReynolds J S
Published: December 2014

Transient and sustained inhibitory synaptic inputs to on‐centre, off‐centre, and on‐off ganglion cells in the mudpuppy retina were studied using intracellular recording in the superfused eye‐cup preparation. When chemical transmission was blocked with 4 mM‐Co2+, application of either glycine or gamma‐aminobutyric acid (GABA) caused a hyperpolarization and conductance increase in all ganglion cells. For both amino acids, the responses were dose dependent in the range 0.05‐10 mM, with a half‐maximal response at about 0.7 mM. Glycine and GABA sensitivities were very similar in all three types of ganglion cells. The response to applied glycine was selectively antagonized by 10(‐5) M‐strychnine and the response to applied GABA was selectively antagonized by 10(‐5) M‐picrotoxin. In all ganglion cells, 10(‐5) M‐strychnine eliminated the transient inhibitory events which occur at the onset and termination of a light stimulus. The block of transient inhibition was associated with a relative depolarization of membrane potential and decrease in conductance at these times. Strychnine had no effect on membrane potential or conductance in darkness or during sustained inhibitory responses to light. Picrotoxin (10(‐5) M) did not block transient inhibitory events in any ganglion cells, but did affect other components of their responses. The results suggest that in all three classes of ganglion cells transient inhibition, but not sustained inhibition, may be mediated by glycine or a closely related substance.
Mucosal enteroceptors with vagal afferent fibres in the proximal duodenum of sheep.
Authors: Cottrell D F , Iggo A
Published: December 2014

Single‐unit afferent activity was recorded from the hepatic‐duodenal nerve of chloralose‐anaesthetized sheep using electrophysiological techniques. Impulse activity was examined while the duodenal mucosa was irrigated with different chemical solutions and explored mechanically. Sixty‐one mucosal mechanoreceptors were studied and these were divided into three classes of afferent response. (i) Thirty‐four units had no background activity. These 'silent' units had a mechanical threshold of 132 mg and had a slowly adapting response to maintained probing. They had non‐myelinated axons (mean conduction velocity 0.93 m s‐1). (ii) Five units adapted rapidly to mucosal probing. (iii) Twenty‐one units had spontaneous background activity. These 'spontaneous' units had a threshold to probing of 750 mg, and a characteristic sustained 'after‐discharge' and periods of mechanical insensitivity; 75% of them were non‐myelinated (mean conduction velocity 0.73 m s‐1). The other units had a mean conduction velocity of 3.3 m s‐1. The behaviour of most sensory units remained within these classes with the exception of ten otherwise silent units whose activity became spontaneous after the application of prostaglandin F2 alpha or sodium hydroxide solutions. Eighty per cent of all units were sensitive to a variety of chemical solutions. Five silent units and four spontaneous units were insensitive to the chemical solution applied. The responses to chemical solutions were sustained for up to 90 s but units became refractory to repetitive treatments, often becoming insensitive after the second application. A chemically specific population was subdivided into two groups: subgroup 1, thirty‐two units were excited by potassium chloride solutions (five rapid adapting, twenty silent, seven spontaneous); subgroup 2, twelve units were excited by volatile fatty acid solutions (eight silent units, four spontaneous). Three units were excited by both potassium chloride and volatile fatty acid solutions (two silent, one spontaneous). None of the units tested was sensitive to the osmolality of the solutions applied. Units were not excited by thermal changes over the range 10‐45 degrees C and all were mechanically sensitive. Thus no chemoreceptor or thermoreceptor with absolute specificity was found. The conclusions of this study are as follows. With five exceptions, all duodenal mucosal units had sustained responses to probing the mucosa. They therefore appear to differ from gastric mucosal units described as 'rapidly adapting mechanoreceptors with chemical sensitivity' (Iggo, 1957).(ABSTRACT TRUNCATED AT 400 WORDS)
Excitation of the cardiac vagus by vasopressin in mammals.
Authors: Courtice G P , Kwong T E , Lumbers E R , Potter E K
Published: December 2014

In unanaesthetized sheep, the sensitivity of the baroreceptor‐cardio‐inhibitory reflex was greater when intravenous vasopressin was used to raise blood pressure, than when intravenous phenylephrine was used to raise blood pressure. This difference was still evident in animals in which beta‐adrenergic blockade had been carried out using propranolol. In the presence of combined beta‐adrenergic and muscarinic blockade, a direct negative chronotropic effect of intravenous vasopressin could not be demonstrated. It was concluded, therefore, that intravenous vasopressin enhanced cardiac vagal tone. This effect of vasopressin on efferent cardiac vagal tone was confirmed directly in anaesthetized dogs by recording from single cardiac vagal efferent fibres. Furthermore, recordings from single carotid sinus baroreceptor fibres did not demonstrate a direct action of vasopressin on the sensitivity of the baroreceptors. However, the pressor effect of vasopressin is associated with a greater increase in efferent cardiac vagal discharge than that seen when equipressor doses of phenylephrine are given, or when blood pressure is raised by a similar amount by inflation of an intra‐aortic balloon. Studies in isolated guinea‐pig atrial preparations and in anaesthetized rabbits and dogs, revealed no consistent peripheral action of vasopressin on the action of the vagus at the heart.
Relaxation of rabbit psoas muscle fibres from rigor by photochemical generation of adenosine‐5'‐triphosphate.
Authors: Goldman Y E , Hibberd M G , Trentham D R
Published: December 2014

Correlations have been made between the mechanical and biochemical descriptions of muscle relaxation. Skinned muscle fibres in the rigor state were incubated in a solution containing P3‐1‐(2‐nitro)phenylethyladenosine‐5'‐triphosphate, 'caged ATP', an inert photolabile precursor of ATP, and free Ca2+ concentration less than 10(‐8) M. The mechanical response of the fibre was monitored during relaxation initiated by liberating ATP with a pulse of 347 nm light from a frequency‐doubled ruby laser. Tension first dropped and then rose briefly, before finally declining to the relaxed level. Stiffness, in phase with a sinusoidal length change, declined monotonically after the laser pulse. Out‐of‐phase stiffness increased briefly after a delay, then returned to the base line during the final relaxation. The development of the out‐of‐phase stiffness signal was taken as evidence that during the relaxation some cross‐bridges were present with properties similar to those in an active contraction. The tension rise and slower phase of relaxation can be explained by a mechanism in which some of the cross‐bridges reattach, generate force and finally detach in the absence of Ca2+ ions. In this model cross‐bridge attachment is facilitated by protein co‐operativity within the myofilaments. Detailed analysis of the mechanical transients makes other possible models for the initial tension rise unlikely. Stretching or releasing fibres prior to photolysis changed the time course of the early parts of the tension transient without significant effect on the later phases or on stiffness. The tension records from stretch, release and isometric trials converged to a final common time course of relaxation. Analysis of the convergence of tension records provided a means for measuring the cross‐bridge detachment rate from the thin filament as a function of ATP concentration. The apparent second‐order rate constant for detachment was at least 5 X 10(5) M‐1 S‐1 at 20‐22 degrees C. The final relaxation rate was less dependent on ATP concentration than the early convergence. The results indicate that ATP binding and cross‐bridge detachment from the nucleotide‐free intermediate of the cross‐bridge cycle are rapid compared to the cross‐bridge cycling rate.
Temperature dependence of isometric contractions of cat fast and slow skeletal muscles.
Authors: Buller A J , Kean C J , Ranatunga K W , Smith J M
Published: December 2014

The influence of temperature (range 38‐20 degrees C) on the isometric contractions of flexor digitorum longus (fast‐twitch) and soleus (slow‐twitch) muscles of the cat hind leg was examined in situ and with supramaximal nerve stimulation. The maximum tetanic tension decreased by 5‐7% on cooling from 38 to 27 degrees C and by about 17% on further cooling to 20 degrees C. The results were similar between the two muscles. The twitch tension increased by 100% in flexor digitorum longus and decreased by about 40% in soleus when the temperature was lowered from 38 to 20‐24 degrees C. The results are compared with those reported for fast‐ and slow‐twitch muscles of the rat.
Vagal control of gall‐bladder contraction.
Authors: Magee D F , Naruse S , Pap A
Published: December 2014

The role of the vagi in gall‐bladder contraction was studied in conscious dogs with chronic biliary fistulae. The interdigestive periodic contraction of this organ was abolished by bilateral cervical vagal blockade, atropine or pentolinium, but neither methacholine nor carbachol initiated contraction when the duodenum was kept alkaline. The orthodox view that gall‐bladder evacuation is primarily controlled by humoral mechanisms needs re‐evaluation. Vagal blockade prevented the usual gall‐bladder contraction in response to duodenal acidification.
Respiratory effects of carbon dioxide‐induced changes of medullary extracellular fluid pH in cats.
Authors: Eldridge F L , Kiley J P , Millhorn D E
Published: December 2014

Acute and steady‐state responses to hypercapnia of respiratory output, measured as integrated phrenic nerve activity, and medullary extracellular fluid (e.c.f.) pH, measured directly, were determined in paralysed, vagotomized and glomectomized cats. Medullary e.c.f. pH responds within seconds to an acute change of alveolar and arterial PCO2. The respiratory response closely and inversely matches the e.c.f. pH change, but not the cerebrospinal fluid pH change. The medullary e.c.f. pH change following a rapid step‐change in end‐tidal PCO2 requires at least 5 min for a new steady state to be achieved. Steady‐state studies in twenty‐six cats show: (a) that the respiratory response to progressive hypercapnic stimulation of the central chemoreceptors is curvilinear (Eldridge, Gill‐Kumar & Millhorn, 1981), (b) that the relationship between increasing end‐tidal PCO2 and medullary hydrogen ion concentration [(H+]) or changes of pH is linear (r = 0.995); a doubling of PCO2 causes 0.260 units pH change, (c) there is a curvilinear relationship between e.c.f. [H+] and the respiratory response that is the same as that found with CO2. We conclude that medullary e.c.f. pH measured by means of a surface electrode accurately reflects the CO2‐induced [H+] stimulus to respiration. The decreasing respiratory responses to identical changes of central chemoreceptor input are due to progressive neuronal saturation of a central pathway between the chemoreceptors and the respiratory controller.
Velocity of sarcomere shortening in rat cardiac muscle: relationship to force, sarcomere length, calcium and time.
Authors: Daniels M , Noble M I , ter Keurs H E , Wohlfart B
Published: December 2014

The relation between force and velocity was determined in sixteen trabeculae of rat right ventricle as a function of time during a twitch, of sarcomere length and of external Ca2+ concentration, [Ca2+]o. The trabeculae were studied in modified Krebs‐Henseleit solution at 25 degrees C. Force was measured with a semiconductor strain gauge. Sarcomere length was measured with a laser diffraction system. A servomotor system was used in which control could be switched between sarcomere length, muscle length and force. Force‐velocity relations were derived from load clamps and from contractions in which sarcomere length was initially held constant followed by a quick release and slower release of the sarcomeres at controlled velocity. Force‐velocity relations were fitted by Hill's equation (Hill, 1938), (Po‐P) b = (P+a) V, where P = force, V = velocity, Po = isometric force in mN/mm2 and a and b are constants. For [Ca2+]o = 2.5 mM, with both interventions the values (mean +/‐ S.D.) were: b = 1.00 +/‐ 0.45 micron/s; a = 9.52 +/‐ 5.60 mN/mm2; Vo measured = 13.6 +/‐ 3.0 micron/s; Vo calculated = 13.4 +/‐ 3.4 micron/s; Po measured = 96.5 +/‐ 25.0 mN/mm2; Po calculated = 119.3 +/‐ 34.5 mN/mm2. Vo rose with [Ca2+]o to a maximum at [Ca2+]o = 1.2 mM when Po was about 50% of maximum, while Po rose with [Ca2+]o to a maximum at above 2.5 mM. Vo rose with time during the twitch to a maximum at 25 ms following onset of contraction; Po was then about 50% of the maximum that was obtained at 120 ms. Vo increased with sarcomere length from zero at a sarcomere length of 1.6 micron to a maximum at 1.85 micron. Between 1.85 micron and 2.3 micron, Vo was constant. At 1.85 micron, Po was about 60% of maximum Po. These results are compatible with the hypothesis that Vo is more sensitive than Po to the amount of Ca2+ bound to the contractile proteins, and that Vo reaches a maximal value with an amount of Ca2+ bound to the contractile proteins at which Po has obtained only about 50% of its maximal value.
Effects of denervating brown adipose tissue on the responses to cold, hyperphagia and noradrenaline treatment in the rat.
Authors: Rothwell N J , Stock M J
Published: December 2014

Surgical denervation of the five sympathetic nerves supplying one lobe of the interscapular brown fat of control rats caused small reductions in mass, protein content and the activity of the thermogenic mitochondrial proton conductance pathway (assessed from guanosine‐5'‐diphosphate (GDP) binding) when compared to the intact lobe. Denervation did not affect the acute 100% increase in mitochondrial GDP binding capacity seen after a single injection of noradrenaline. Cold‐adaptation (4 degrees C for 7 days) or over‐feeding (cafeteria diet for 10 days) caused marked increases in the mass, protein content and specific mitochondrial GDP binding in intact brown adipose tissue, but these changes were totally prevented by surgical denervation. These data indicate that the hypertrophy and the increased thermogenic capacity of brown fat induced by cold‐adaptation or hyperphagia depend entirely upon the sympathetic innervation of the tissue.
Chloride conductance and extracellular potassium concentration interact to modify the excitability of rat optic nerve fibres.
Authors: Connors B W , Ransom B R
Published: December 2014

The excitability of developing rat optic nerves has been studied under conditions in which extracellular Cl‐ was replaced with other anions. In nerves younger than 3 days old, replacing Cl‐ with propionate or SO4(2‐) usually led to spontaneous and repetitive cycling of extracellular K+ concentration ([K+]o). [K+]o reached peaks of 8‐12 mM and then fell transiently below the base‐line level of 5 mM before increasing again. This cycling behaviour continued, with a wave‐length of 1‐2 min, for as long as 2 h. Nerves older than 5 days either did not cycle or did so only transiently. Substitution of ten different anions for Cl‐ indicated that a minimum hydrated radius, between that of BrO3‐ and HCO3‐, was necessary to induce cycling behaviour. Cycling behaviour was abolished by the Na+‐channel blocker tetrodotoxin. Reduction of the bath [K+] to 2.5 mM slowed the frequency of spontaneous cycles; a bath [K+] of 1 mM abolished them. When the temperature was lowered, cycle frequency slowed. Substitution of large anions for Cl‐ enhanced axonal excitability. This was inferred from the prevalence of spontaneous action potentials during cycling behaviour, and from the generation of relatively large evoked increases of [K+]o. Cycling behaviour is hypothesized to result from a repetition of the following three processes: (i) spontaneous axonal firing elicits a gradual increase in [K+]o which increases axonal excitability and facilitates further K+ release, (ii) axonal firing and K+ release are eventually halted by a combination of depolarization block, intracellular Na+ accumulation and hyperpolarization from electrogenic pumping, (iii) recovery of [K+]o to its minimal value depends on active K+ reuptake mediated by a highly stimulated axonal Na+‐K+‐ATPase. We conclude that a large proportion of the resting membrane conductance of optic nerve fibres is Cl‐ specific. A high Cl‐ conductance may stabilize fine central axons against the depolarizing effects of [K+]o increases.
An intracellular study of descending and non‐cutaneous afferent input to spinocervical tract neurones in the cat.
Authors: Harrison P J , Jankowska E
Published: December 2014

Previous studies of input on to spinocervical tract neurones have been extended by investigating the post‐synaptic actions of non‐cutaneous afferent fibres and of descending tracts on to these neurones, using intracellular recording. In particular, actions of group II muscle, joint and Pacinian afferent fibres and rubro‐ and corticospinal tract fibres were investigated. Group II muscle afferent fibres evoked excitation and inhibition at a minimal latency compatible with a disynaptic linkage. Increasing the stimulus strength to include group III afferent fibres enhanced these post‐synaptic actions only modestly. Inhibition was evoked less frequently and/or required trains of stimuli. Weak stimulation of the interosseous nerve evoked short latency (disynaptic) inhibition or excitation, the latter less frequently. Post‐synaptic potentials evoked below threshold for group III afferent fibres of the interosseous nerve are attributed to the actions of Pacinian corpuscles. Low threshold joint afferent fibres evoked excitation at short latency. Higher threshold joint afferent fibres usually evoked inhibition at longer latency, although high threshold excitation was sometimes observed. Stimulation of the pyramidal tract evoked constant latency, unitary e.p.s.p.s which followed high frequencies. The evidence suggests that such e.p.s.p.s are evoked monosynaptically. Polysynaptic excitation and inhibition were also observed. No convincing evidence could be found of actions evoked directly by the rubrospinal tract, although actions mediated via other descending systems could be induced from the red nucleus. A large degree of convergence was seen from different peripheral and descending systems on to individual neurones.
The relationship of receptive field properties to the dendritic shape of neurones in the cat striate cortex.
Authors: Martin K A , Whitteridge D
Published: December 2014

In this study, we examined the hypothesis that some features of the receptive fields of cortical neurones are determined by the extent to which their dendrites can sample from different parts of the visual field representation on the cortex. In particular, the orientation selectivity and size of the receptive fields of cortical neurones were examined for their relationship to the tangential organization of the dendrites of cortical neurones. Single neurones in the visual cortex of anaesthetized and paralysed cats were physiologically characterized and injected intracellularly with horseradish peroxidase (HRP). In some cases it was possible to identify whether the neurones received direct (monosynaptic) or indirect (polysynaptic) input from afferents of the lateral geniculate nucleus. The dendritic arborizations of the HRP‐filled cells, sampled from all layers, were reconstructed in three dimensions with computer assistance, and rotated to give the tangential or surface view. The bias in the tangential arrangement of the dendrites was determined by calculating the mean vector angle for the distribution of the dendrites of each cell. This bias was related to the orientation selectivity of the neurones. There was no consistent relationship between orientation selectivity and the tangential bias of the dendritic tree. The width of the receptive fields was compared to the equivalent 'width' of the tangential extent of the dendrites. There was no significant relationship between the two widths. The tangential arrangement of the dendritic field does not appear to be important in determining the orientation selectivity or the size of the receptive fields of neurones in the cat visual cortex. The former feature of the receptive fields may be determined by inhibitory processes, while the extent and number of the afferents providing input to a single neurone may determine the latter property.