bluuebunny/crossref_metadata_2025 huggingface dataset:
Control of intrinsic reticulo‐ruminal motility in the vagotomized sheep.
Authors: Gregory P C
Published: December 2014

The intrinsic motility of the reticulo‐rumen was studied by electromyography in nineteen sheep subjected to bilateral thoracic vagotomy and maintained by intragastric infusion of a complete liquid diet. The influences of distension, temperature and tactile and chemical stimuli on the intrinsic reticulo‐ruminal motility were investigated. The level of electrical discharge in the reticulum and rumen in the first 3 days after vagotomy was increased progressively with distension without giving rise to the large group discharges characteristic of the long‐term vagotomized sheep, and was reduced by atropine (0.1‐1 mg kg‐1) but not by hexamethonium (2 mg kg‐1). In the long‐term vagotomized animals, the frequency of the large group discharges over the reticulo‐rumen varied with the degree of reticulo‐ruminal distension. The discharges were absent below a threshold rumen volume; above the threshold they increased progressively with volume until a maximal rate of six to seven regular discharges per minute was established at large ruminal volumes. The discharges were abolished by atropine (0.1‐1 mg kg‐1) or hexamethonium (2 mg kg‐1). With the rumen volume below the threshold, in all areas of the reticulo‐rumen localized distension stimulated local discharge only and did not induce large group discharge. Replacement of rumen contents with an equal volume of 0.2 M‐acetic, ‐propionic or ‐butyric acid buffered to pH 4.0 rapidly abolished the large group discharges over the entire reticulo‐rumen. Replacement of rumen contents by an equal volume of 0.9% NaCl at 30 degrees C immediately abolished the large group discharges; at temperatures between 35 and 43 degrees C this had no effect. Gentle tactile stimulation increased local discharge in the reticulum and cranial dorsal sac but not in other areas of the rumen and did not affect large group discharge in any region. It is concluded that the intrinsic reticulo‐ruminal motility of chronically vagotomized sheep is principally regulated by the degree of reticulo‐ruminal distension. Like the C.N.S.‐controlled motility of the vagus‐intact sheep it is inhibited by high concentrations of volatile fatty acids. Local control mechanisms therefore may interact with central control in the over‐all regulation of motility in vagus‐intact sheep.
Discharges of pyramidal tract and other motor cortical neurones during locomotion in the cat.
Authors: Armstrong D M , Drew T
Published: December 2014

A method is described for chronically implanting fine flexible microwires into cat motor cortex, which permitted extracellular recordings to be made from 165 single neurones. Most units were recordable for 12 h and some for up to 2 days. Of the neurones tested, 57% were shown to project to the medullary pyramid (pyramidal tract neurones, p.t.n.s). Antidromic latencies corresponded to a range of conduction velocities from 63 to 9 m/s. In the animal at rest neurones discharged at rates from 0.5 to 44 impulses/s. During locomotion at 0.5 m/s (a slow walk) 56% of cells discharged faster than at rest and 80% showed frequency modulations time‐locked to the step cycle. Most fired one discrete burst of impulses per step or one peak period superimposed on a maintained discharge. In different cells peak activity occurred at widely different times during the step cycle. A few cells peaked twice per step. Peak rates (averaged over twenty steps) ranged from 10 to over 120 impulses/s, the values for most slow‐axon p.t.n.s (conduction velocity less than 21 m/s) being lower than for any of the fast‐axon p.t.n.s. For locomotion at speeds between 0.37 and 1.43 m/s a roughly linear relationship existed between discharge rate and speed in 14% of cells. However, the changes were modest and in most cells both mean rate and peak rate were unrelated to speed. In some cells discharge phasing was fixed (relative to the step cycle in the contralateral forelimb); in others there were progressive phase shifts (or more complex changes) as speed increased. During locomotion up a 10 degrees incline discharge phasings were the same as on the flat in all of the twenty‐seven neurones studied and most showed no substantial change in mean rate or peak rate (although there were substantial increases in limb muscle electromyogram amplitudes).
Characteristics of the neuroendocrine responses to stimulation of the splanchnic nerves in bursts in the conscious calf.
Authors: Bloom S R , Edwards A V
Published: December 2014

Neuroendocrine responses to splanchnic nerve stimulation in bursts (at 40 Hz for 1 s at 10 s intervals for 10 min) have been investigated in conscious adrenalectomized calves, 3‐6 weeks after birth, in the presence of various pharmacological blocking agents. Preganglionic blockade with hexamethonium abolished all the neuroendocrine responses that were monitored. Pre‐treatment with phentolamine significantly reduced, but failed to eliminate, the release of both pancreatic glucagon and pancreatic polypeptide. In the presence of phentolamine splanchnic nerve stimulation produced a massive rise in arterial plasma insulin concentration. None of these pancreatic neuroendocrine responses was significantly affected by additional pre‐treatment with propranolol. The rise in mean plasma insulin concentration which occurred in calves pre‐treated with both phentolamine and propranolol was significantly reduced by atropine. Release of bombesin‐like immunoreactivity (BLI) was unaffected by total post‐ganglionic adrenergic and cholinergic blockade. The results indicate that pancreatic endocrine responses to splanchnic nerve stimulation may be attributable, at least in part, to release of BLI in this species.
Activity of lingual, laryngeal and oesophageal receptors in conscious sheep.
Authors: Falempin M , Rousseau J P
Published: December 2014

Vagal afferent impulse traffic has been studied in conscious sheep by electromyographic recording from the motor units of the sterno‐cleido‐mastoid (s.c.m.) muscle reinnervated by sensory vagal axons. Units which responded during movements of the tongue and during the pharyngolaryngeal and oesophageal stages of swallowing were chosen for this study. Lingual units showed a phasic discharge bearing a temporal relation to movements of the tongue during licking of the lips or chewing of a bolus before swallowing. Laryngeal units had no spontaneous activity. A discharge occurred with the ascending movement of the larynx during swallowing. Oesophageal units did not exhibit any tonic activity. They fired only at the time of primary or secondary oesophageal peristalsis. The oesophageal units showed a bimodal distribution. The oesophageal receptors are more concentrated at the beginning and the end of the thoracic oesophagus. During primary peristalsis, the afferent discharge was reinforced in only 57% of the cases when sheep swallowed a bolus (pellets or inflated balloons). When the discharge was reinforced, its increase ceased as volumes of the bolus were increased from 20 to 40 ml. During local oesophageal contractions, the afferent discharge was only present when the inflated balloon was located at the site of the receptor. It was enhanced at the time the primary peristaltic wave passed over the balloon. Inflation of a second balloon cranially in the oesophagus led to abolition of the activity of the unit at the caudal site though the distension there was maintained.
The activation patterns of embryonic chick motoneurones projecting to inappropriate muscles.
Authors: Landmesser L T , O'Donovan M J
Published: December 2014

Chick lumbosacral motoneurones were caused to innervate foreign muscles by surgically rotating or shifting the limb bud about the anterior‐posterior axis in stage 17‐18 embryos. The activation pattern of such wrongly projecting motoneurones was assessed at stages 35‐38 by recording electromyographic activity from muscles in an isolated spinal cord/hind limb preparation. Muscle activity was classed as flexor‐ or extensor‐like according to the characteristics of the patterned sequence of bursts elicited by a single shock to the thoracic cord. Wrongly projecting motoneurones did not have their activation pattern altered to one appropriate for the muscle innervated; therefore in some cases a particular muscle was activated with a pattern similar to its original one, and in other cases in an opposite manner. Mixed flexor‐extensor‐like activation of a single muscle was, however, rare. The identity of motoneurones projecting to a muscle was determined by their cord location following retrograde labelling with horseradish peroxidase. This allowed us to conclude that motoneurones could develop their normal pattern of activation even when projecting to foreign muscles. It is concluded that the cord circuits (presumably composed of local interneurones responsible for the activation of motoneurones in the isolated cord preparation are not altered by retrograde influences from the muscle. Wrongly projecting motoneurones, which were maintained throughout the normal cell death period, were activated during spontaneous embryonic movements, and in many cases were found to have a behaviourally inappropriate activation pattern. These observations are discussed in relation to proposed mechanisms by which developmental errors in connectivity are corrected.
Cardiovascular responses evoked from the nicotine‐sensitive area on the ventral surface of the medulla oblongata in the cat.
Authors: Guertzenstein P G , Lopes O U
Published: December 2014

Experiments were carried out in cats anaesthetized with chloralose, (a) to examine the effect on blood pressure, heart rate and respiratory frequency produced by topical application of leptazol, nicotine and sodium pentobarbitone to the ventral surface of the medulla at an area around the rootlets of the XII cranial nerve, and (b) to study the role of this area in some cardiovascular reflexes. Leptazol applied uni‐ or bilaterally to this area produced hypotension, bradycardia and bradypnoea. The area from which leptazol produced these effects was localized 3‐6 mm lateral to the mid line and 5‐9 mm caudal to the lower border of the trapezoid bodies. When comparing the effects of leptazol and nicotine applied to this area it was found that in concentrations that produced similar falls in arterial blood pressure and heart rate leptazol produced a much stronger bradypnoea than nicotine. The hypotension produced by leptazol was mainly due to inhibition of sympathetic vasomotor tone since it was little affected by section of the vagi and by atropine given intravenously. Bilateral application of sodium pentobarbitone produced a small hypertension, tachycardia and pronounced tachypnoea. Unilateral application of sodium pentobarbitone had no effect by itself but inhibited the effects of leptazol applied to the same site. Cardiovascular reflexes produced by sinus nerve stimulation, by increased sinus pressure or by injections of veratridine into a vein or into the left ventricle of the heart were potentiated by topical application of leptazol to the ventral surface and depressed by the topical application of sodium pentobarbitone. The chemoreceptor reflex, produced by retrograde injections of lobeline into the lingual artery, was partially affected by topical application of sodium pentobarbitone: the evoked bradycardia was attenuated but the tachypnoea and hypertension were not affected. These results suggest that this medullary area on the ventral surface of the medulla plays an important role in normal cardiovascular regulation.
Effects of changes of blood pressure, respiratory acidosis and hypoxia on blood flow in the sciatic nerve of the rat.
Authors: Low P A , Tuck R R
Published: December 2014

Using the hydrogen clearance technique, we have measured blood flow in the sciatic nerves of healthy, anaesthetized rats at rest, at various arterial blood pressures, and during respiratory acidosis and hypoxia. The majority of hydrogen clearance curves were bi‐exponential. The slower component appears to reflect nerve blood flow more accurately than either the fast component or the composite value obtained from both components. Mean nerve blood flow estimated from the slow component of the seventeen bi‐exponential hydrogen clearance curves and from the seven mono‐exponential curves was 15.8 +/‐ 1.1 ml min‐1 100 g‐1 (+/‐ S.E. of the mean). The mean value of the fast component of the bi‐exponential curves was 118 +/‐ 6 ml min‐1 100 g‐1 and that obtained from both components was 25.9 +/‐ 2.6 ml min‐1 100 g‐1. Sciatic nerve blood flow was measured over a range of arterial blood pressures of 60‐160 mmHG. There is a curvilinear relationship between pressure and flow suggesting that the nerve vascular bed responds passively to changes in perfusion pressure. Respiratory acidosis resulted in no significant change in nerve blood flow. The mean flow was 15.5 +/‐ 1.9 ml min‐1 100 g‐1. During hypoxia, nerve blood flow decreased to 7.5 +/‐ 1.4 ml min‐1 100 g‐1 as a result of a reduction in arterial blood pressure and an increase in vascular resistance. These findings suggest that normal nerve blood flow is high in relation to metabolic activity, especially when compared with the brain.
Voltage‐dependent inactivation of inward‐rectifying single‐channel currents in the guinea‐pig heart cell membrane.
Authors: Sakmann B , Trube G
Published: December 2014

Inward currents through single K+ channels in isolated ventricular heart cells of the guinea‐pig were recorded using the patch‐clamp technique (Hamill, Marty, Neher, Sakmann & Sigworth, 1981). The voltage‐dependent gating properties of the channels were examined in the potential range between 0 and ‐120 mV with 145 mM‐KCl on the extracellular side of the membrane patch, i.e. with approximately symmetrical transmembrane K+ concentrations. When voltage pulses from 0 mV to negative test potentials were applied to patches containing several channels, more channels were open at the beginning of the pulses than in the steady state. Averages of many current responses showed inactivation of the mean current in response to the hyperpolarizing voltage pulses. The inactivation was stronger and faster at larger hyperpolarization. The lifetimes of the open and closed states of the channel and the probability of the open state p were estimated from records of the elementary currents at various constant potentials. As indicated by the inactivation of the averaged currents, the value of p was smaller at more negative potentials, approximately 0.15 at ‐50 mV and 0.02 at ‐110 mV. This caused a negative slope in the current‐voltage relation of the time‐averaged current at potentials more negative than ‐50 mV. The channel openings were grouped in complex bursts. At least three exponentials were needed to fit the frequency histogram of the lifetimes of all closed states (time constants at ‐50 mV: 1.1 ms, 16 ms and 3.2 s). The lifetimes of the individual openings were exponentially distributed (time constant: 70 ms). The kinetics of the channel were interpreted by two different models involving three states of a channel (closed‐closed‐open or closed‐open‐closed). The rate constants and their voltage dependence were estimated for both models. Both models describe the data equally well; the reason for this ambiguity is discussed. The channels are blocked by Cs+ or Ba2+. Cs+ (0.1 mM) caused frequent and short interruptions of the individual channel openings. Ba2+ (0.5 mM) also shortened the openings and in addition decreased the number of openings per burst. The results suggest that the inward‐rectifying current IK1 in heart ventricular cells is partially inactivated by hyperpolarization. The inactivation could account for part of the time‐dependent decrease in the whole‐cell current previously ascribed to depletion of K+.
Rearrangement of synapses on guinea‐pig sympathetic ganglion cells after partial interruption of the preganglionic nerve.
Authors: Maehlen J , Njå A
Published: December 2014

The rearrangement of synaptic connexions maintained by the intact preganglionic axons was examined with intracellular recording after partial denervation of the guinea‐pig superior cervical ganglion. After sprouting, the number of superior cervical ganglion cells innervated by each residual preganglionic axon was increased by a factor of about three. These new synaptic connexions were stable in the absence of reinnervation of the ganglion by the injured axons. The intact preganglionic axons that sprouted in the superior cervical ganglion abandoned most of the synaptic connexions they normally maintain with neurones in the stellate ganglion. Several months after the partial denervation some of the injured preganglionic axons had usually re‐established synaptic connexions with neurones in the superior cervical ganglion. However, both the rate and final degree of reinnervation were poor compared to reinnervation after complete denervation. During reinnervation of the superior cervical ganglion by the injured axons, there was a reduction in the degree of innervation of this ganglion by the sprouting axons. These results support the idea of an ongoing competition between preganglionic axons, and indicate some of the factors that probably determine the synaptic balance under normal and experimental conditions.
Visual cortical input alters spatial tuning in monkey lateral geniculate nucleus cells.
Authors: McClurkin J W , Marrocco R T
Published: December 2014

The response of monkey lateral geniculate nucleus (l.g.n.) cells to flashing spots, annuli, and drifting sine‐wave gratings were recorded with tungsten micro‐electrodes. These stimuli were presented (a) monocularly, through an aperture in the centre of a radial grating, or (b) dichoptically, in which the spots or drifting gratings were presented to the dominant eye's receptive field, while the centre of the radial grating was positioned on the corresponding retinal location of the other eye. Movement of the radial grating produced changes in the l.g.n. cell responses evoked by the spots and sine‐wave gratings. These changes were reversed by cryogenic blockade of the striate cortex. Therefore, radial grating movement altered the responses of l.g.n. cells by activating the corticogeniculate (c.g.) pathway. In about half of all cells, radial grating‐induced alterations of centre, or surround, or both responses to spots and annuli were produced. By adopting a simple spatial filtering model of the centre and surround mechanisms, it was possible to predict how these alterations in centre/surround balance would affect the cell's responses to sine‐wave gratings. Alterations were observed in the peak and band width of the spatial and/or temporal tuning curves. The radial gratings did not alter the spatial summation properties of cells. Minor alterations in the spectral neutral points of chromatically opponent neurones were occasionally found. These results are interpreted as support for the view that spatial and temporal tuning are dynamic properties of some l.g.n. neurones by virtue of descending input from the visual cortex.
Early post‐natal development of neuronal function in the kitten's visual cortex: a laminar analysis.
Authors: Albus K , Wolf W
Published: December 2014

The normal post‐natal development of visual cortical functions was studied by recording extracellularly from 612 single neurones in the striate and parastriate cortex of anaesthetized and paralysed kittens, ranging in age from 6 to 24 days. Analyses have been made of laminar differences in the developmental trends of receptive field properties such as orientation specificity and spatial organization of 'on' and 'off' zones. At the beginning of the second post‐natal week the majority of neurones (76%) only respond to light 'off' (unimodal 'off' neurones). Only later does the frequency of occurrence of unimodal 'on' neurones and of bimodal or multimodal neurones (with spatially segregated 'on' and 'off' zones arranged side by side) increase so that, by the middle of the fourth week, about equal numbers of these three receptive field types are found. The proportion of 'on‐off' neurones (with spatially coincident 'on' and 'off' zones) remains low (between 9% and 12%) during the early post‐natal period. In layers 4 and 6 of areas 17 and 18 the frequency of occurrence of visual neurones is quite normal even in the youngest kittens, whereas the probability of recording neurones in layers 2/3 and 5 in kittens less than 14 days old is remarkably low and only gradually improves up to the middle of the fourth week. A very rudimentary order in the spatial arrangement of orientation‐specific neurones and ocular dominance distribution is observed even in very young kittens. This order improves rapidly and reaches adult levels during the fourth post‐natal week. In visually inexperienced kittens, on average 11% of all responsive neurones are selective for the orientation of elongated visual stimuli, and 58% are biased. The proportion of orientation‐selective cells begins to increase rapidly about two days after lid opening, and proportions of orientation‐selective cells similar to that in the adult are reached by the end of the fourth post‐natal week. Orientation‐selective neurones in kittens less than 10 days old are only found in layers 4 and 6 and the lower part of layer 3. In layers 2/3 and 5 they are first seen in larger proportions by the beginning of the third post‐natal week. Our results show that, during the first post‐natal month, the time course of the functional development of visual cortical neurones depends on receptive field type and on intracortical location.(ABSTRACT TRUNCATED AT 400 WORDS)
Effect of sodium on transport of weak electrolytes across rat jejunum in vitro.
Authors: Jackson M J
Published: December 2014

The effects of ion substitution and inhibitors on the transport of two representative weak electrolytes, benzoic acid and amphetamine, across short‐circuited rat jejunum in vitro have been studied. The spontaneous asymmetries in the transport of the weak electrolytes were not dependent on the presence of either bicarbonate or chloride in the incubation medium. Net transport of the weak electrolytes was abolished when choline was substituted for sodium in the fluid bathing the mucosal surface of the tissue, but weak electrolyte transport was independent of the presence of sodium on the serosal side. Weak electrolyte transport was inhibited by ouabain and by orthovanadate. The effect of ouabain was abolished when potassium was substituted for sodium in the serosal fluid, and the effect of orthovanadate was potentiated in this condition. It was shown that the ability of the intestinal epithelium to discriminate between the ionized and non‐ionized forms of weak electrolytes was not altered when choline was substituted for sodium in the incubation medium, indicating that the effect of sodium was associated with the driving force for weak electrolyte transport. Weak electrolyte transport was not abolished by raising the serosal potassium concentration, suggesting that the transport process was directly related with the function of the sodium pump, rather than correlated with gradients of electrical or chemical potential established as a consequence of pump activity.
Responses of upper airway, intercostal and diaphragm muscle activity to stimulation of oesophageal afferents in dogs.
Authors: Cherniack N S , Haxhiu M A , Mitra J , Strohl K , Van Lunteren E
Published: December 2014

The effects of oesophageal distension on respiratory patterns and the moving average electromyogram (e.m.g.) activity of three upper airway muscles‐‐the alae nasi, the genioglossus, and the posterior cricoarytenoid‐‐and four chest wall muscles‐‐the costal and crural diaphragm and the inspiratory and expiratory intercostals‐‐were examined in ten anaesthetized, tracheostomized, spontaneously breathing dogs. Distension was produced by inflations of a balloon placed in the middle part of the thoracic oesophagus with volumes of air ranging from 50 to 200 ml. Oesophageal distension increased respiratory frequency, mainly due to a significant shortening of the expiratory time. Activity of both the costal and crural parts of the diaphragm was inhibited with oesophageal distension, whereas that of the inspiratory intercostal muscles increased, tending to maintain a near‐normal tidal volume and end‐tidal CO2. Phasic inspiratory activity of all three upper airway muscles increased in response to oesophageal distension, as did the activity of the expiratory intercostal muscles. The changes in the breathing pattern and the electrical activity of all muscles in response to oesophageal distension were immediate, occurring during the first breath after the balloon was inflated. The responses were graded, so that increases in the volume of the oesophageal balloon progressively increased the activity of the upper airway and intercostal muscles, and decreased diaphragm activity. Bilateral vagotomy abolished the effects of oesophageal distension on upper airway and chest wall muscle activity, suggesting that vagal afferents constitute the major pathway for the reflex.
The influence of blood pressure on trans‐synovial flow in the rabbit.
Authors: Knight A D , Levick J R
Published: December 2014

Fluid exchange across the synovium lining the cavity of extended knees was studied in twenty rabbit hindquarters. The isolated hindquarters were perfused with blood from an extracorporeal pump‐oxygenator system at controlled arterial pressure (PA) and venous pressure (PV). Intra‐articular pressure (PJ) was set at 18 cmH2O in most experiments. The rate of trans‐synovial absorption of Krebs solution (QS), measured by a drop‐counter, was a negative linear function of PA (70‐160 mmHg) and of PV (2‐42 cmH2O). The sensitivity of exchange to venous pressure ( dQS / dPV , mean ‐0.25 +/‐ 0.03 microliter min‐1 mmHg‐1) was greater than its sensitivity to arterial pressure ( dQS /dPA, mean ‐0.17 +/‐ 0.02 microliter min‐1 mmHg‐1). The ratio of the slopes, ( dQS / dPV )/( dQS /dPA), indicated the pre‐ to post‐capillary vascular resistance ratio. From this ratio and PA, PV, synovial capillary pressures PC were calculated by the equation of Pappenheimer & Soto ‐ Rivera (1948). Trans‐synovial absorption rate was a negative linear function of PC. This observation supports the application to the synovial cavity of Starling's hypothesis for fluid exchange between interstitial spaces and plasma (Starling, 1896). The slope dQS /dPC equalled the net hydraulic conductance of the blood‐joint barrier (synovium plus capillary endothelium), and averaged ‐0.425 +/‐ 0.025 microliter min‐1 mmHg‐1 at PJ = 18 cmH2O. When PJ was subatmospheric, as is common in extended normal joints, fluid exchange (measured indirectly as dPJ /dt) was only approximately 1/4 as sensitive to blood pressure as at PJ = 18 cmH2O. This observation supported the view that the conductance of the blood‐joint barrier depends on PJ.
Role of right atrial receptors in the control of drinking in the rat.
Authors: Kaufman S
Published: December 2014

Balloons were implanted at the junction of the superior vena cava and right atrium of the rat. Inflation of the balloon stretched the vein‐atrial junction but did not cause a change in either arterial or central venous blood pressure. Inflating the balloon attenuated spontaneous night‐time water intake and the drinking responses to 24 h water deprivation and subcutaneous (s.c.) isoprenaline (10 micrograms/kg body wt.). Water intake after I.P. hyperoncotic colloid (polyethylene glycol 20 M) was virtually abolished when the balloon was inflated immediately before giving access to water (4 h after injection). Inflating the balloon had no effect on drinking following I.V. hypertonic saline (5 ml 2M‐NaCl/kg body wt.). These results support the hypothesis that volume receptors on the right side of the heart are involved in controlling water intake.
Prostaglandin‐induced inhibition of acetylcholine release from neuronal elements of dog tracheal tissue.
Authors: Inoue T , Ito Y , Takeda K
Published: December 2014

In an attempt to elucidate the possible roles of endogenous prostaglandins on the neuro‐effector transmission in the dog trachea, effects of a prostaglandin antagonist (1‐acetyl‐2‐[8‐chloro‐10, 11‐ dihydrobenz (b.f) (1.4) oxazepine‐10‐carbonyl]hydrazine (SC‐19220] on the electrical and mechanical properties of smooth muscle cells and on neuro‐effector transmission in the smooth muscle layer were studied by means of micro‐electrode, double sucrose‐gap, and tension recording methods. The levels of prostaglandins in the perfusate from the dog tracheal tissue were also determined using radioimmunoassay. Excitatory junction potentials (e.j.p.s) and twitch tension evoked by electrical field stimulation with short pulse duration (50‐100 microseconds), which were abolished by tetrodotoxin (10(‐7) M) or atropine (5 X 10(‐6) M), showed gradual and continuous reduction in amplitude during superfusion with normal Krebs solution. Reduction in the amplitude of e.j.p.s occurred with no change in the membrane potential or membrane input resistance. SC‐19220 (3.1 X 10(‐5) M) did not modify the membrane potential, membrane input resistance or the sensitivity to acetylcholine of the smooth muscle cells. Yet, with application of SC‐19220 (3.1 X 10(‐6) M), gradual and continuous reductions in the amplitude of e.j.p.s and twitch contractions were no longer observed. With an increased concentration (3.1 X 10(‐5) M), e.j.p.s and twitch contractions with a constant amplitude were obtained after the initial increase in the amplitude. When the amplitude of twitch contractions was stabilized by treatment with indomethacin (10(‐5) M), low concentrations (10(‐12) to 10(‐10) M) of prostaglandin E2 (PGE2) or prostaglandin F2 alpha (10(‐8) to 10(‐6) M) markedly suppressed the amplitude of the twitch contractions. In some muscle preparations (ten out of twenty‐two preparations examined), SC‐19220 (3.1 X 10(‐6) to 3.1 X 10(‐5) M) produced a sustained contraction of the muscle, which was suppressed by atropine (5 X 10(‐6) M) or PGE2 (10(‐8) M). Following pre‐treatment of the tissue with atropine (5 X 10(‐6) M), SC‐19220 did not evoke contracture. In the resting condition, 10‐40 ng g‐1 wet wt. tissue min‐1 PGE or PGF was released into the perfusate from the tracheal muscle tissue of the control dog.(ABSTRACT TRUNCATED AT 400 WORDS)
Direct measurement of intracellular pH and buffering power in smooth muscle cells of guinea‐pig vas deferens.
Authors: Aickin C C
Published: December 2014

A double‐barrelled, pH‐sensitive micro‐electrode suitable for use in mammalian smooth muscle has been developed. It was shown to be unaffected by alteration of Na, K, Ca, Mg, Cl or CO2, and yielded the same results in mouse soleus muscle as had been obtained previously with the recessed‐tip pH‐sensitive glass electrode ( Aickin & Thomas, 1977 a). Intracellular pH (pHi) of the surface cells of guinea‐pig vas deferens was 7.06 +/‐ 0.09 (n = 52, S.D. of an observation) in Krebs solution equilibrated with 3% CO2 at pH 7.35. The membrane potential (Em) was ‐65.5 +/‐ 6.7 mV. Thus pHi is about 0.8 units more alkaline than that predicted if H+ ions were passively distributed across the cell membrane. Alteration of extracellular pH (pHo) at constant CO2 caused a smaller change in pHi, by about 40% of that in pHo. The change was complete in 6‐12 min and was of a similar magnitude whether the alteration was made in the continual presence or absence of CO2. Alteration of the CO2 level at constant pHo caused a rapid change in pHi followed by a slower, complete recovery. Thus the same stabilized pHi was recorded in different CO2‐containing solutions. When CO2 was removed, the expected intracellular alkalinization was reduced or even obscured by a considerable acidification. pHi then stabilized at a mean value of 6.81 +/‐ 0.11 (n = 18) with an Em of ‐60.8 +/‐ 8.2 mV. The acidification expected on readmission of CO2 was minimized or obscured by a rapid recovery of pHi to the value previously recorded in CO2‐containing solutions. A simultaneous increase in CO2 and decrease in pHo caused a rapid fall in pHi which increased in magnitude with decreasing pHo. This fall was followed by an incomplete recovery when pHo was above about 6.8 (but below 7.35), by no further change in pHi when pHo was about 6.7 and by a slow, continued fall in pHi when pHo was below 6.7. The intrinsic buffering power was calculated from the pHi changes observed on alteration of CO2. The values obtained increased in parallel with the extent to which pHi recovered following the imposed change, probably explained by an inseparable contribution to the minimization of the change by transport processes.(ABSTRACT TRUNCATED AT 400 WORDS)
White noise analysis of pace‐maker‐response interactions and non‐linearities in slowly adapting crayfish stretch receptor.
Authors: Buño W , Bustamante J , Fuentes J
Published: December 2014

Input‐output relations were investigated in the slowly adapting stretch receptor organ of crayfish using a Gaussian white noise length input with a 0.03‐12.5 Hz band width and the resulting action potential output. The noise input was presented to the de‐efferented receptor in situ, at three mean elongations and at four different amplitudes. The three mean elongations were set within the normal range in vivo, two at the extremes close to the minimum and maximum physiological lengths and the other in the mid‐range. With white noise inputs there is a finite probability that the system will be tested in all possible conditions within the chosen band width because white noise has the advantage that it contains, with a finite probability, all possible stimulus wave forms at random. The analysis indicated similarities between the effects of the input variables, namely white noise amplitude and mean elongation. With low input variables the activity was periodic. With larger inputs, impulse rates were higher and irregular. The average length trajectories leading to a spike (i.e. the average stimulus) were either biphasic with high inputs or multiphasic and periodic with lower input variables. The frequency of periodicity increased with mean elongation. Although for a given length and noise amplitude a variety of individual length trajectories preceded spikes, the final biphasic shortening‐lengthening average stimulus sequence before a spike was similar in all cases irrespective of the input variables. The number of possible trajectories decreased with increments in the input variables. The standard deviation of length values for each average stimulus was computed and displayed as a function of time relative to the spike. It was first constant, and decreased gradually to a minimum value at the spike reference. Standard deviation values were lower for higher white noise amplitudes and mean elongation. Simple, short‐lasting stimulus wave forms in the white noise were isolated and the corresponding responses were computed. Responses were periodic at low input variables and aperiodic with larger inputs and also asymmetric, being larger and briefer for lengthenings than for shortenings. Asymmetries augmented with input increments. Investigation of the interactions between the pace‐maker and the white noise effects showed that lengthenings were more effective when they occurred just after a spike while the effectiveness of shortenings was greater just before a spike.(ABSTRACT TRUNCATED AT 400 WORDS)
Programmed electromyographic activity and negative incremental muscle stiffness in monkeys jumping downward.
Authors: Dyhre-Poulsen P , Laursen A M
Published: December 2014

We trained monkeys to jump down from different heights, and recorded electromyograms (e.m.g.s) in arm muscles, and ground reaction forces. The landing movements were also recorded by high‐speed cinematography. The e.m.g. of the triceps began about 80 ms before landing. The initial burst lasted until about 20 ms after ground contact and was succeeded by bursts of gradually declining amplitude. These discharges were not of reflex origin, because when the monkey was deceived by a collapsible platform, they were time‐locked to the expected, not to the true landing. The amplitude of the e.m.g. in the triceps increased with the height of the jump, indicating adaptive control. The timing of the e.m.g. pattern was assumed to be programmed before take off, because it was unaffected by extinction of the light during the fall. The vertical ground reaction force produced by the arms had an inflexion on its rising phase which arose from the very rapid stretch of the muscles which control the wrist. Then came a sharp peak produced mainly by stretch of the triceps. The inflexion and the sharp peak were probably produced by short‐range stiffness of the muscles of the upper arm. The torque acting on the elbow joint, and the elbow joint stiffness were calculated from the ground reaction forces and the movement of the arm. The torque was high at impact and gradually declined during the landing. The force produced by the triceps increased sharply, then decreased while it continued to lengthen. Thus, the elbow joint showed high initial stiffness, which then decreased, and finally became negative. This dynamic relation between length and tension was very different from the static length‐tension characteristic of skeletal muscles. The observed behaviour of the muscles presumably takes advantage of the resistance of the musculo‐skeletal system to transient forces. The observed negative stiffness occurs only during submaximal contractions. We propose that the segmented pattern in the e.m.g. produces submaximal contractions in both slow and fast fibres in spite of a high excitatory drive.
The relationship between energy expenditure and environmental temperature in congenitally obese and non‐obese Zucker rats.
Authors: Armitage G , Harris R B , Hervey G R , Tobin G
Published: December 2014

The energy expenditure of normal and congenitally obese adult female Zucker rats has been measured by continuous indirect calorimetry for periods of 3‐10 days at ambient temperatures varied from 30 to 5 degrees C. Rectal temperatures were also recorded. Exposure to cold caused no ill‐effects in normal or obese rats. The rectal temperatures of obese rats were about 1 degree C lower than those of normal rats. The rectal temperatures of normal rats did not change measurably with ambient temperature; in obese rats rectal temperature rose slightly as ambient temperature fell. In normal and obese rats, energy expenditure showed a smooth, steeply sloping, negative relationship to ambient temperature. Energy expenditure per rat was higher in obese than in normal rats at all temperatures. The two slightly curvilinear regressions were nearly 'parallel', with a separation of about 40 kJ/day per rat at the mid‐point. This study therefore does not confirm suggestions that obese Zucker rats suffer from a defect in the level of energy expenditure, or in their capacity to increase it when exposed to cold. It is suggested that in both normal and obese rats the level of energy expenditure was determined by thermoregulatory control. The greater heat production of obese rats may have been a response to their lower core temperature. A steady state in which greater heat production is associated with lower core temperature implies lower insulation between body core and surface. This could be due to greater blood flow.
Post‐tetanic hyperpolarization evoked by depolarizing pulses in crayfish stretch receptor neurones in tetrodotoxin.
Authors: Holloway S F , Poppele R E
Published: December 2014

A post‐tetanic hyperpolarization (p.t.h.) that is quantitatively identical to that evoked by a train of action potentials in stretch receptor neurones of crayfish Procambarus clarki and Pacifastacus leniculus is evoked when the normal Na+ influx is blocked with tetrodotoxin (TTX) and a train of depolarizing pulses is used to simulate a train of action potentials. The p.t.h. evoked by depolarizing pulses in the presence of TTX is attributable to an electrogenic Na‐K pump, because it (a) is abolished by strophanthidin, (b) is abolished by removal of external K+, (c) depends in magnitude on internal Na+ concentration, (d) is not associated with a change in membrane conductance and (e) does not exhibit a reversal potential. When each action potential in the stimulus train is followed by a hyperpolarizing pulse, generation of the p.t.h. is prevented even though the action potentials are unchanged. The time constant for build‐up of the p.t.h. is longer than the time constant of decay. Increasing the magnitude of depolarizing pulses increases the magnitude of the p.t.h. response in the presence of TTX and also increases the time constant for its build‐up. The suppression of the p.t.h. occurring in low external Na+ appears to represent a response to a change in internal Na+ concentration, characterized by a time constant much longer than the decay of the p.t.h. The activity of the pump appears to be regulated by two mechanisms: a Na+‐sensitive mechanism with a time constant of the order of a minute and an apparently voltage‐sensitive mechanism with a time constant of about 5 s. The hypothesis is proposed that changes in the transmembrane electric field influence the enzymatic systems of the pump and disrupt the steady‐state distribution of conformation states. The decay of the p.t.h. represents a relaxation back to the resting distribution.
Direct observations of muscle arterioles and venules following contraction of skeletal muscle fibres in the rat.
Authors: Marshall J M , Tandon H C
Published: December 2014

Direct observations have been made of responses of individual arterioles and venules of rat spinotrapezius muscle to contraction of the skeletal muscle fibres. Stimuli of 4‐6 V intensity, 0.1 ms duration, delivered via a micro‐electrode inserted into the spinotrapezius, evoked contraction of a small bundle of skeletal muscle fibres, followed by vasodilatation which was limited to all those arterioles and venules which crossed or ran alongside activated muscle fibres. Since venules outside the region of contraction, but supplied by dilating arterioles, were not passively distended by the attendant rise in intravascular pressure, it is concluded that both the arterioles and venules dilated actively in response to muscle contraction. All arterioles responded to a single twitch contraction, the terminal arterioles (7‐13 micron i.d.) showing the largest increase in diameter. Collecting venules (9‐18 micron i.d.) responded to just two twitches in 1 s and larger venules to five twitches in 1 s. When twitch contractions were continuously evoked for 10 s, the responses in individual arterioles and venules were graded with twitch frequency, the fastest and largest response occurring at 6‐8 Hz. Tetanic contraction, at 40 Hz for 1 s, produced faster responses in all vessels, a maximum 55% increase from resting internal diameter being attained in only 8 s in some terminal arterioles. In all vessels the responses to tetanic contraction were equal to the maximal dilatation induced by papaverine. These results, in contrast with conclusions drawn from indirect estimates of venous responses, show that venules, like arterioles, dilate actively in response to muscle contraction. Venule dilatation may reduce the rise in capillary hydrostatic pressure, thereby limiting the outward filtration of fluid.
Axonal projections from the rostral expiratory neurones of the Bötzinger complex to medulla and spinal cord in the cat.
Authors: Fedorko L , Merrill E G
Published: December 2014

Axonal projections of eighty‐four rostral medullary expiratory neurones of the Bötzinger complex were tested using antidromic mapping techniques in anaesthetized cats. A projection to the ventral respiratory neurones of the medulla (n.r.a.) was shown in eleven out of twelve tested neurones. Also a spinal projection to the C5‐C6 cervical segments was evident in more than 72% of tested neurones; probably near 100% project to cervical cord. These axonal projections were found bilaterally in both brain stem and spinal cord. The majority of Bötzinger complex expiratory neurones were seen to have two to four axonal collaterals to the ventro‐lateral (v.l.) nucleus of the solitary tract (n.t.s.) and/or the n.r.a. and/or the spinal cord. In eight out of twelve of the tested neurones, electrophysiological evidence of axonal arborization in more than one of n.r.a. inspiratory, n.r.a. expiratory or v.l. n.t.s. regions was obtained. Similar evidence for the terminal arborization was found for 26% of tested neurones in the phrenic motor nucleus. The descending spinal expiratory axons of the Bötzinger complex neurones are located in the dorsal and medial parts of the lateral funiculus in C4 and C5 segments. Conduction velocity measurements indicate that these are large myelinated axons. We propose that the Bötzinger complex expiratory neurones are a source of synaptic inhibition for n.r.a. inspiratory neurones and phrenic motoneurones.
The response to hypoxia of arterial chemoreceptors in fetal sheep and new‐born lambs.
Authors: Blanco C E , Dawes G S , Hanson M A , McCooke H B
Published: December 2014

Carotid chemoreceptor activity was detected in each of fourteen halothane or pentobarbitone anaesthetized exteriorized fetal lambs of 90‐143 days gestational age. Activity was about 5 Hz at a Pa,O2 of 25 mmHg and it increased as Pa,O2 was reduced, either by compressing the umbilical cord or by reducing the (FIO2) oxygen fraction of the gas used to ventilate the ewe. Activity increased briskly when 1‐2 ml CO2‐saturated saline was injected retrogradely into the lingual artery, but not when saline of pH 7.4 or fetal arterial blood was injected. In two fetuses near‐term chemoreceptor activity was recorded continuously whilst the umbilical cord was ligated and ventilation with air started. Activity increased 200‐500% as Pa,O2 fell, but then fell to below control as Pa,O2 rose. We suggest that these changes in activity reflect those occurring naturally at birth. No spontaneous chemoreceptor activity could be detected on the day of birth in twelve pentobarbitone anaesthetized lambs delivered vaginally or by Caesarean section at 135‐146 days. Single baroreceptor activity could however be recorded in these lambs, and chemoreceptor activity could be elicited by hypercapnia. Spontaneous chemoreceptor activity was detected in six of seven lambs more than 2 days old. In eight conscious lambs the steady‐state respiratory response to isocapnic hypoxia was variable on the day of birth. In six of these lambs the response was significantly greater by the third day. We conclude that the arterial chemoreceptors are active and responsive in the fetus, but quiescent in the lamb on the day of birth when Pa,O2 has risen. The hypoxic sensitivity of the chemoreceptors is reset from the fetal to the adult range over the next few days.