bluuebunny/crossref_metadata_2025 huggingface dataset:
Fusimotor reflexes in triceps surae muscle elicited by extension of the contralateral hind limb in the cat.
Authors: Appelberg B , Hulliger M , Johansson H , Sojka P
Published: December 2014

Experiments were performed in thirty‐two cats anaesthetized with chloralose. The aim of the study was to investigate the reflex effects of flexion or extension of the contralateral hind limb on ipsilateral fusimotor neurones, to compare these effects with the effects elicited by stretch of the ipsilateral posterior biceps and semitendinosus (p.b.s.t.) muscles (Appelberg, Hulliger, Johansson & Sojka, 1982) and to clarify the interactions between the reflexes elicited from the ipsilateral and the contralateral side. Activity in fusimotor neurones was studied indirectly by recording from primary and secondary muscle spindle afferents of the triceps surae muscle. The mean rate of firing and the modulation of the afferent response to sinusoidal extension of the triceps surae was determined. Control measurements were made with the ipsilateral p.b.s.t. muscles relaxed and the contralateral hind limb in resting position. Tests were made with stretch of the ipsilateral p.b.s.t. and/or extension/flexion of the contralateral hind limb. With extension of the contralateral hind limb 64 out of 210 primary afferents (30.5%) showed predominantly dynamic reflexes (41 out of 134 in spinalized preparations: 30.6%), 25 (11.9%) showed mixed or predominantly static effects (1 spinalized: 0.7%), 121 (57.6%) showed no effect (92 spinalized: 68.7%). Flexion of the limb gave, with only two exceptions, no observable effect. Thirty‐three secondary afferents were investigated. Five responded to extension of the contralateral hind limb with excitatory reflex effects. Flexion did not influence the secondary afferents. Mostly the reflex effects were not accompanied by detectable electromyogram (e.m.g.) activity in the ipsilateral triceps (surface recordings), indicating that the reflexes mainly involved gamma‐motoneurones. A comparison was made between the reflexes elicited by stretch of the ipsilateral p.b.s.t. and extension of the contralateral hind limb. The percentage of responsive units was higher for the contralateral stimulus. Spinalization almost abolished the statis reflex responses to both ipsi‐ and contralateral stimulation, and it increased the number of dynamic responses to ipsilateral stimulation. The ipsilaterally elicited reflexes also seemed more dependent upon background activity. Ipsilateral stimulus could facilitate or reduce a contralaterally evoked response, even when the ipsilateral stimulus alone gave no effect. The reflexes could also summate. Quite often combined stimuli changed the character of the reflex from dynamic to static or vice versa.(ABSTRACT TRUNCATED AT 400 WORDS)
Exercise‐induced arterial hypoxaemia in healthy human subjects at sea level.
Authors: Dempsey J A , Hanson P G , Henderson K S
Published: December 2014

We determined the incidence of exercise‐induced arterial hypoxaemia and its determinants in sixteen highly trained, healthy runners who were capable of achieving and sustaining very high metabolic rates (maximal O2 uptake = 72 +/‐ 2 ml kg‐1 min‐1 or 4.81 +/‐ 0.13 l min‐1). Arterial blood gases and acid‐base status were determined at each load of a progressive short‐term exercise test and repeatedly during constant‐load treadmill running while breathing air and during inhalation of mildly hypoxic, hyperoxic, and helium‐enriched gases. Three types of responses to heavy and maximum exercise were evident and highly reproducible within subjects. Four runners maintained arterial PO2 (Pa, O2) within 10 mmHg of resting values, another four showed 10‐15 mmHg reductions in Pa, O2, and the remaining eight showed reductions of 21‐35 mmHg, i.e. in all cases to a Pa, O2 of less than 75 mmHg and to less than 60 mmHg in two cases. During constant‐load exercise, Pa, O2 was often maintained during the initial 30 s when hyperventilation was greatest; then hypoxaemia occurred and in most cases was either maintained or worsened over the ensuing 3‐4 min. The most severe hypoxaemia during heavy exercise was associated with no or little alveolar hyperventilation (Pa, CO2 greater than 35 mmHg and PA, O2 less than 110 mmHg) and an alveolar to arterial PO2 difference [(A‐a)DO2] in excess of 40 mmHg. During 3‐4 min of heavy exercise alveolar PO2 (PA, O2) decreased by 20 mmHg in mild hypoxia (0.17 FI, O2; inspired % O2) and increased by 20 mmHg during mild hyperoxia (0.24 FI, O2) and 10 mmHg during the hyperventilation which accompanied normoxic helium breathing. In all cases Pa, O2 changed in proportion to PA, O2 with no consistent change in the alveolar to arterial PO2 difference [(A‐a)DO2]. In view of the correction of hypoxaemia with mild hyperoxia and the very high ratios of alveolar ventilation to pulmonary blood flow (VA/QC = 4‐6) achieved during heavy exercise, we think it unlikely that non‐uniformity of the VA/QC distribution or veno‐arterial shunt could explain the hypoxaemia observed in most of our subjects. By exclusion, we suggest that hypoxaemia may be attributed to a diffusion limitation secondary to very short red cell transit times in at least a portion of the pulmonary circulation.(ABSTRACT TRUNCATED AT 400 WORDS)
The passive electrical properties of spheroidal aggregates cultured from neonatal rat heart cells.
Authors: De Bruijne J , Jongsma H J , van Ginneken A C
Published: December 2014

Membrane specific resistance and capacitance of non‐spontaneously active spheroidal aggregates, cultured from collagenase‐dissociated neonatal rat heart cells, were calculated from changes in membrane potential due to intracellularly injected rectangular hyper‐ and depolarizing current pulses during diastole. The relation between steady‐state membrane voltage displacement and injected current is linear for current pulses between +10 and ‐10 nA. No significant fall‐off of electrotonic potential is measured in an aggregate at increasing distances from the site of current injection. The aggregate membrane resistance (input resistance) was best fitted by an inverse square function of the aggregate radius. This suggests selective current flow through the outer membranes of the spheroidal aggregate. Taking this into account the membrane specific resistance was calculated to be 753 +/‐ 38 omega cm2 (S.E. of mean; n = 39). The time course of the change in membrane potential is exponential with a time constant ranging from 5 to 26 ms, depending on the aggregate radius. The aggregate membrane capacitance is calculated from the exponential transients for each aggregate and appears to be a cubic function of the radius, indicating that the membrane area of all cells in the preparation equally contributes to the input capacitance. The membrane specific capacitance is calculated to be 0.97 +/‐ 0.02 microF/cm2 (S.E. of mean; n = 100). It is concluded that myocytes in aggregates are electrically well coupled and that a resistance in series with the inner membranes, if present, is negligible compared to the membrane resistance of the internal cells. In order to explain the finding that the membrane resistance was not inversely related to the cube of the aggregate radius, it is postulated that the membrane specific resistance might be a function of aggregate radius.
Hamster intestinal disaccharide absorption: extracellular hydrolysis precedes transport of the monosaccharide products.
Authors: Alvarado F , Lherminier M , Phan H H
Published: December 2014

Hydrolase‐related transport was re‐investigated in hamster small intestine by the tissue accumulation method. The Na+‐dependent, phlorizin‐sensitive monosaccharide transport system saturates with 30 mM‐D‐glucose. According to the hydrolase‐related transport hypothesis, additional glucose units will be taken up if they are given in the form of a disaccharide susceptible to hydrolysis. But in experiments with [14C]sucrose we found no evidence for any such surplus glucose uptake. The uptake of 14C label from sucrose was abolished by using Tris, a strong inhibitor of sucrase, by adding competitive inhibitors of the D‐glucose transport system (D‐glucose, beta‐methyl‐D‐glucopyranoside or phlorizin), and by substituting Li+ for the Na+ in the incubation medium. Glucose and fructose derived from sucrose did not enter the tissues in equimolar amounts: the glucose moiety was taken up much faster. We conclude that in hamster intestine there is no evidence for the existence of hydrolase‐related transport with sucrose as the monosaccharide donor. The enzymatic hydrolysis of sucrose and the transport of its products, glucose and fructose, are two distinct events, acting sequentially.
Effect of hyperglycaemia on sugar transport in the isolated mucosa of guinea‐pig small intestine.
Authors: Fischer E , Lauterbach F
Published: December 2014

The effect of hyperglycaemia on sugar transport was studied by comparing transepithelial permeation and tissue content of 3‐O‐methyl‐D‐glucose (3‐O‐MG), beta‐methyl‐D‐glucoside (beta‐MDG) and D‐glucose in isolated mucosae of guinea‐pig jejunum mounted in a flux chamber. Sugars were administered either to the luminal or the blood side of mucosae prepared either from normal animals or those maintained in a hyperglycaemic state by I.V. glucose infusion for 12 h. In control animals, absorptive sugar fluxes increased in the order glucose greater than beta‐MDG greater than 3‐O‐MG. Only beta‐MDG was accumulated in the tissue beyond the medium concentration. Permeation of 3‐O‐MG and beta‐MDG in the direction blood‐to‐lumen was mainly paracellular as indicated by the strict correlation with the simultaneous permeation of polyethylene glycol (mol. wt. 900). Luminal addition of 10(‐3) M‐phlorhizin increased permeation and decreased tissue content of beta‐MDG and D‐glucose when administered on the blood side, suggesting that these sugars are recaptured at the brush border even from vigorously mixed solutions. For flux coefficient calculation the preparation was regarded as a three‐compartment system. With all three sugars, the influx coefficient was higher at the luminal, but lower at the basolateral membrane than the corresponding efflux coefficient. 3‐O‐MG displayed the highest basolateral influx coefficient of all three sugars, being even higher than its luminal influx coefficient. The luminal influx coefficient of beta‐MDG was 22 times greater, and its basolateral efflux coefficient 2.5 times less than the corresponding values for 3‐O‐MG, resulting in cellular beta‐MDG accumulation. D‐Glucose was suited best for transepithelial transport, having a luminal influx coefficient only 1.6 times less, and a basolateral efflux coefficient almost 10 times greater than those for beta‐MDG. Prolonged hyperglycaemia increased the lumen‐to‐blood permeation of all three sugars 1.3‐2‐fold. No significant differences in tissue content to control values were observed after 45 min (3‐O‐MG, D‐glucose) or 90 min (beta‐MDG) incubation. Therefore, flux coefficients increased by the same factors in luminal and basolateral membranes, i.e. 1.7, 1.3 and 1.7 for 3‐O‐MG, beta‐MDG and D‐glucose, respectively. These results indicate that changes in both the luminal and basolateral membranes play a role in the increase of sugar transport in hyperglycaemia and that a regulatory mechanism might exist between the transport systems located in both membranes.(ABSTRACT TRUNCATED AT 400 WORDS)
Facilitation of soleus‐coupled Renshaw cells during voluntary contraction of pretibial flexor muscles in man.
Authors: Katz R , Pierrot-Deseilligny E
Published: December 2014

Recurrent inhibition to soleus motoneurones, brought about by a conditioning H‐reflex discharge, was estimated in human subjects by a subsequent test H reflex. Changes in recurrent inhibition during voluntary ankle dorsiflexion were evaluated by comparing the amplitude of the test H reflex to a reference H reflex: both reflexes were subjected to the same type of influences which modified soleus monosynaptic reflex excitability during pretibial flexor contraction, but only the test H reflex was subject to the recurrent inhibition evoked by the conditioning H‐reflex discharge. During tonic or phasic ramp contractions of the pretibial flexors the inhibition of the test H reflex, as compared to rest, was more marked than that of the reference H reflex. Evidence is presented that this may indicate a facilitation of soleus‐coupled Renshaw cells. Since this facilitation of soleus‐coupled Renshaw cells was also observed before ramp contraction, it is, at least in part, supraspinal in origin. Within the range of forces studied (8‐45% of maximum force) there was no evidence that the facilitation of soleus‐coupled Renshaw cells increased along with increased force of the pretibial flexor voluntary contraction. During voluntary phasic ankle dorsiflexion, facilitation of soleus‐coupled Renshaw cells was maximum at the moment when soleus motoneurones were most facilitated by the stretch‐induced soleus I a discharge. There was no evidence for changes in Renshaw cell excitability during ballistic contractions. It is suggested that this facilitation of soleus‐coupled Renshaw cells may be one of the mechanisms preventing the occurrence of a soleus stretch reflex during a voluntary ankle dorsiflexion. Such a mechanism could become important if reciprocal inhibition, via I a inhibitory interneurones, were not strong enough, e.g. because of a weak gamma‐drive to the contracting muscles.
Segmental analysis of renal glucose transport in young female rats.
Authors: McSherry N R , Wen S F
Published: December 2014

Free‐flow micropuncture studies were performed on twenty‐seven young female Sprague‐Dawley rats before and after 10% extracellular volume expansion to evaluate glucose reabsorption at the accessible sites of both surface and papillary nephrons. In the distal nephron segments no significant glucose reabsorption was observed for the distal tubule and papillary collecting duct but significant difference in fractional glucose delivery was demonstrated between the bend of the Henle's loop and early distal tubule and between the late distal tubule and the base of the collecting duct. Comparison of the fractional glucose delivery within the same nephron group for both superficial and juxtamedullary nephrons indicated that glucose reabsorption occurred at some sites beyond the bend of the Henle's loop. Volume expansion inhibited glucose reabsorption in the proximal convoluted tubule, enhanced it in the segment between the late proximal and early distal tubules, but had no effect on glucose transport at further distal sites. It is concluded that, in addition to the proximal tubule, the ascending loop of Henle or cortical collecting tubule may play a role in maintaining glucose‐free urine under physiological conditions.
Unitary inhibitory synaptic potentials in the guinea‐pig hippocampus in vitro.
Authors: Miles R , Wong R K
Published: December 2014

Mechanisms involved in the generation of synaptic inhibition have been investigated by making simultaneous intracellular recordings from pairs of neurones in the CA3 pyramidal cell field of guinea‐pig hippocampal slices. Inhibitory post‐synaptic potentials dependent on single presynaptic action potentials (i.p.s.p.s) and mediated through monosynaptic and disynaptic connexions have been identified. The recurrent nature of some hippocampal inhibition has been demonstrated by showing that activity in a single cell may initiate feed‐back i.p.s.p.s onto itself. The observation of synchronous i.p.s.p.s in recordings from two cells illustrates the divergence of synaptic contacts made by inhibitory neurones. The peak conductance change associated with an i.p.s.p. was in the range 5‐9 nS and it reversed uniformly throughout its time course at membrane potentials between ‐73 and ‐80 mV. The shortest time‐to‐peak of synaptic potentials was approximately 3 ms and in this case the i.p.s.p. decayed with a time constant comparable to the passive membrane time constant of the post‐synaptic neurone. The peak amplitude of i.p.s.p.s fluctuated in a way consistent with the quantal release of inhibitory neurotransmitter. Inhibitory neurones could fire bursts of action potentials not unlike those generated by pyramidal cells in this area. A comparison of the conductance change associated with identified i.p.s.p.s with that associated with the maximal inhibitory post‐synaptic potential resulting from electrical stimulation of fibre pathways suggested that, in the slice, a pyramidal cell is innervated by up to fifteen inhibitory neurones.
Properties of mechanoreceptive fibres serving skin grafts transferred to the hands of adult baboons (Papio anubis).
Authors: Dykes R W , Terzis J K , Turnbull B G
Published: December 2014

In nine adult baboons, full‐thickness skin grafts were reciprocally exchanged between three glabrous skin sites on one hand and glabrous skin sites on the contralateral hand or foot, and a hairy skin site on the dorsum of the ipsilateral hand. The grafts acquired some of the physical characteristics of the recipient site; glabrous skin became thinner and more pliable on the dorsum of the hand and hairy skin became thicker and displayed a more irregular surface contour when transferred to the palm. The electrophysiological properties of cutaneous mechanoreceptors serving these grafts were examined about 5 months after surgery and again after 1 year. Measurements of conduction velocity, receptive field size and shape, and responses to mechanical stimuli suggested that axons serving mechanoreceptors in glabrous grafts functioned at nearly normal levels by 5 months, while axons innervating hairy skin grafts, whether transferred to a glabrous skin site or to a hairy skin site, performed less well even after 1 year. These observations suggest that factors intrinsic to the graft are a major determinant of the quality of sensory function achieved following a skin graft procedure. These factors affect the relative proportions of rapidly and slowly adapting fibres, conduction velocities, thresholds and receptive field configurations. As a result, hairy skin is not the tissue choice for plastic surgical procedures requiring optimum sensory return.
Adrenal medullary responses to splanchnic nerve stimulation in new‐born calves.
Authors: Edwards A V
Published: December 2014

Right adrenal medullary and various cardiovascular responses to stimulation of the peripheral end of the right splanchnic nerve have been investigated in conscious calves 24‐48 h after birth and compared with those obtained previously in older conscious calves. The results show that splanchnic nerve stimulation produces a smaller rise in mean aortic blood pressure and haematocrit in new‐born calves than occurs in older animals. The fall in adrenal vascular resistance is also reduced, as is the amount of catecholamine released from the adrenal medulla, at 24‐48 h. Although the absolute amounts of adrenaline and noradrenaline released in response to splanchnic nerve stimulation were significantly less in 24‐48 h old calves, the ratio (3:2) was the same as that found in 2‐5 week old animals and that in which the two amines are stored in the gland. The results confirm the contention that the sympathetic innervation is relatively immature immediately after birth in this species and that functional maturation occurs gradually over a period of weeks. However, they also show that the ratio in which adrenaline and noradrenaline are released from the adrenal medullae provide no index of this process, as had previously been suggested.
Relation between red nucleus discharge and movement parameters in trained macaque monkeys.
Authors: Gibson A R , Houk J C , Kohlerman N J
Published: December 2014

Correlation and regression analyses were performed on thirty‐three of the magnocellular red nucleus cells described in the previous paper. We sought to test for reliable relations between the parameters of individual tracking movements and corresponding bursts of neural discharge. High correlations were found between the following burst and movement parameters: (i) burst latency versus movement latency; (ii) burst duration versus movement duration; (iii) burst frequency versus movement velocity and (iv) number of spikes in the burst versus movement amplitude. Cells were ranked according to the average of the duration, velocity and amplitude correlation coefficients. The top twenty cells had average correlation coefficients ranging from 0.69 to 0.88 for their preferred movement. These cases were judged most likely to reveal the control functions of the red nucleus, and the following points refer to this sample. Burst onset led movement onset by 118 +/‐ 23 ms, and burst offset led movement offset by 50 +/‐ 38 ms. Burst duration increased as the duration of the movement increased (r = 0.87 +/‐ 0.11). The duration of the burst was approximately equal to movement duration (slope of 0.99 +/‐ 0.16) plus a constant (72 +/‐ 34 ms) throughout a broad range. Average discharge rate during the burst increased with average movement velocity (r = 0.69 +/‐ 0.15). The slope of the relation was 0.36 +/‐ 0.21 (pulses/s)/(deg/s) of joint rotation. The regression lines had consistent upward offsets (56 +/‐ 15 pulses/s) that exceeded the spontaneous discharge rate (17 +/‐ 10 pulses/s). The number of spikes in the burst increased with movement amplitude independent of velocity (r = 0.72 +/‐ 0.11). The slope of the relation was 0.62 spikes/deg and the offset was 13 +/‐ 4 spikes. The preferred movement was co‐ordinated hand in fifteen cases, digit in three, elbow in one and shoulder in one. When these cells were tested with an alternate movement, the failure rate (cases in which a burst did not accompany a movement) increased from 1.4 to 20%, and the correlation coefficients generally were low and lacked significance. Cells in the top twenty had directionally specific responses, low variance in lead time, large depths of modulation (41‐118 pulses/s) and low failure rates. Cells that failed to show strong parametric correlations often had one or more of the former attributes. It appears that high parametric correlations with individual movements are particularly restrictive criteria of relatedness.(ABSTRACT TRUNCATED AT 400 WORDS)
Shortening velocity extrapolated to zero load and unloaded shortening velocity of whole rat skeletal muscle.
Authors: Claflin D R , Faulkner J A
Published: December 2014

The shortening velocity at zero load (Vmax) extrapolated from velocities measured during isotonic releases was compared with unloaded shortening velocity (V0) determined by the slack test. Experiments were performed in vitro at 20 degrees C on soleus muscles from rats. The Vmax was 3.2 +/‐ 0.1 (mean +/‐ S.E. of mean, n = 10) fibre lengths/s while the V0 determined for the same muscles was 5.0 +/‐ 0.1 fibre lengths/s. The ratio of V0/Vmax was 1.6 +/‐ 0.1. Soleus muscles of the rat are heterogeneous with respect to the intrinsic shortening velocities of their fibres. The results suggest that V0 is a measure of the unloaded shortening velocity of the fastest fibres whereas Vmax is a function of the force‐velocity characteristics of all the fibres within a skeletal muscle preparation.
The contrast sensitivity of human colour vision to red‐green and blue‐yellow chromatic gratings.
Authors: Mullen K T
Published: December 2014

A method of producing red‐green and blue‐yellow sinusoidal chromatic gratings is used which permits the correction of all chromatic aberrations. A quantitative criterion is adopted to choose the intensity match of the two colours in the stimulus: this is the intensity ratio at which contrast sensitivity for the chromatic grating differs most from the contrast sensitivity for a monochromatic luminance grating. Results show that this intensity match varies with spatial frequency and does not necessarily correspond to a luminance match between the colours. Contrast sensitivities to the chromatic gratings at the criterion intensity match are measured as a function of spatial frequency, using field sizes ranging from 2 to 23 deg. Both blue‐yellow and red‐green contrast sensitivity functions have similar low‐pass characteristics, with no low‐frequency attenuation even at low frequencies below 0.1 cycles/deg. These functions indicate that the limiting acuities based on red‐green and blue‐yellow colour discriminations are similar at 11 or 12 cycles/deg. Comparisons between contrast sensitivity functions for the chromatic and monochromatic gratings are made at the same mean luminances. Results show that, at low spatial frequencies below 0.5 cycles/deg, contrast sensitivity is greater to the chromatic gratings, consisting of two monochromatic gratings added in antiphase, than to either monochromatic grating alone. Above 0.5 cycles/deg, contrast sensitivity is greater to monochromatic than to chromatic gratings.
Localization of visually evoked cortical activity in humans.
Authors: Srebro R
Published: December 2014

The locations of cortical activity evoked by visual stimuli presented at different positions in the visual field are deduced from the scalp topography of visually evoked potentials in humans. To accomplish this, the Laplacian evoked potential is measured using a multi‐electrode array. It is shown that the Laplacian response has the following useful attributes for this purpose. It is reference‐free. Its spatial resolution is approximately 2 cm referred to the surface of the cortex. Its spatial sensitivity characteristic is that of a spatial band‐pass filter. It is relatively insensitive to source‐‐sink configurations that are oriented tangentially to the surface of the scalp. Only modest assumptions about the source‐‐sink configuration are required to obtain a unique inversion of the scalp topography. Stimuli consisting of checkerboard‐filled octant or annular octant segments are presented as appearance‐disappearance pulses at sixteen different positions in the visual field in randomized order. The locations of evoked cortical activity in the occipital, parietal and temporal lobes are represented on a Mercator projection map for each octant or octant segment stimulated. Lower hemifield stimuli activate cortex which lies mainly on the convexity of the occipital lobe contralateral to the side of stimulus presentation in the visual field. The more peripheral the stimulus is in the visual field, the more rostral is the location of the active cortex. The rostral‐to‐caudal location of the evoked activity varies from subject to subject by as much as 3 cm on the surface of the occipital cortex. Furthermore, in any single subject there is a substantial amount of hemispheric asymmetry. Upper hemifield stimuli activate cortex that lies on the extreme caudal pole of the occipital lobe. This activity is relatively weak, and in some subjects it is almost unmeasurable. It is suggested that the representation of the upper hemifield in the cortex lies mostly on the inferior and mesial walls of the occipital lobe and possibly within the calcarine fissures. Those locations are inaccessible to the Laplacian analysis because the current generators therein may be oriented tangentially to the surface of the overlying scalp. Posterior parietal lobe activity and/or inferior temporal lobe activity is frequently evoked. Different subjects have different patterns of evoked activity. Unilateral or bilateral posterior parietal lobe activity is the most common pattern. Unilateral inferior temporal lobe activity is a less common pattern.(ABSTRACT TRUNCATED AT 400 WORDS)
Respiratory effects of sectioning the carotid sinus glossopharyngeal and abdominal vagal nerves in the awake rat.
Authors: Martin-Body R L , Robson G J , Sinclair J D
Published: December 2014

Normoxic and hypoxic respiration has been measured in awake rats after denervation procedures designed to eliminate the regulatory input from the carotid bodies, from all chemosensory tissue supplied by the glossopharyngeal nerve (n. IX), and from abdominal chemoreceptors. Studies were made 1 day after section of the carotid sinus nerve (c.s.n.), n. IX (at a level including c.s.n.), the abdominal vagus (n. Xa) and combinations of these nerves. Results were compared with those found in normal controls. C.s.n. section led to hypoventilation in both normoxia and hypoxia, reductions in respiratory frequency being consistent and substantial, and reductions in tidal volume varying with the degree of hypoxia. By comparison, section of n. IX produced significantly greater reductions of both normoxic and hypoxic ventilation. Section of n. Xa produced no significant change in normoxic ventilation but in hypoxia produced a significant small reduction in ventilation, mostly from an effect on tidal volume. Denervation of all the associated chemosensory tissue by combined section of n. IX and n. Xa demonstrated a summation of effects but left two distinct residual responses, one to mild hypoxia, and one to severe hypoxia, both associated mainly with increases of tidal volume. The experiments demonstrate that glomus tissues at different sites in the rat produce significant and distinct contributions to respiratory regulation. Denervation of all known receptors shows that significant ventilatory responses to hypoxia are still produced, either by unrevealed peripheral chemoreceptors, or by central neural mechanisms.
The early time course of potassium‐stimulated calcium uptake in presynaptic nerve terminals isolated from rat brain.
Authors: Nachshen D A
Published: December 2014

K‐stimulated (voltage‐dependent) 45Ca uptake in rat brain synaptosomes was measured at times ranging from 0.1 to 10 s, in experiments that employed a rapid‐mixing device to initiate and terminate radiotracer uptake. The rapid mixing did not disrupt the functional integrity of the synaptosomes, as judged by their ability to take up Ca. In solutions containing a low (0.02 mM) concentration of Ca, the rate of K‐stimulated Ca uptake measured after 0‐0.12 s depolarization was 8 times greater than that measured after 5‐10 s of depolarization. The decline in rate of K‐stimulated Ca uptake was not due to tracer backflux from the synaptosomes, nor to Ca loading of the nerve terminals, since it also occurred after synaptosomes were depolarized in solutions without Ca. It is suggested that this decline in rate of Ca uptake after depolarization was due to inactivation of voltage‐dependent Ca channels in the nerve terminals. This inactivation appeared to be voltage rather than Ca dependent. The extent to which K‐stimulated Ca uptake declined after depolarization in high‐K solution depended on the K concentration that was used to depolarize the synaptosomes. Whereas pre‐incubation in solution with one‐half of the Na replaced by K significantly reduced subsequent K‐stimulated Ca uptake, pre‐incubation in non‐depolarizing solution, with one‐half of the Na replaced by choline, had no significant effect on subsequent K‐stimulated Ca uptake. In solutions containing a high (0.5‐2 mM) concentration of Ca, the rate of K‐stimulated Ca uptake measured after 0‐0.12 s was 40 times greater than that measured after 5‐10 s. High Ca accelerated the rate at which K‐stimulated Ca uptake declined with prolonged depolarization. The effect was mimicked by high (10 mM) concentrations of Sr, but not of Ba. The accelerated rate of decline observed with high Ca could be either a direct effect of Ca on the Ca channels or, more probably, an indirect effect of Ca loading on the nerve terminals. The apparent efficacy of several Ca‐channel blockers (Ni, La and verapamil) in reducing K‐stimulated Ca uptake was enhanced when the synaptosomes were depolarized in the presence of inhibitory agents for brief (less than 1 s) intervals before K‐stimulated Ca uptake was measured.
Capillarity, oxidative capacity and fibre composition of the soleus and gastrocnemius muscles of rats in hypothyroidism.
Authors: Sillau A H
Published: December 2014

Muscle capillarity, mean and maximal diffusion distances and muscle fibre composition were evaluated in frozen sections stained for myosin ATPase of the soleus and the white area of the gastrocnemius medial head (gastrocnemius) of rats made hypothyroid by the injection of propylthiouracil (PTU) (50 mg kg‐1) every day for 21 or 42 days. Oxygen consumption in the presence of excess ADP and Pi with pyruvate plus malate as substrates and the activity of cytochrome c oxidase were measured in muscle homogenates. Treatment with PTU decreased body oxygen consumption and the concentration of triiodothyronine in plasma. The capacity of the soleus and gastrocnemius muscles' homogenates to oxidize pyruvate plus malate and their cytochrome c oxidase activity were reduced after 21 or 42 days of treatment with PTU. Fibre composition in the soleus muscle was changed by treatment with PTU. There was a decrease in the proportion of type IIa or fast glycolytic oxidative fibres and an increase in type I or slow oxidative fibres. After 21 days of PTU administration there was also an increase in the proportion of fibres classified as IIc. The changes in fibre composition are believed to be the result of changes in the types of myosin synthesized by the fibres. Therefore, the fibres classified as IIc are, most probably, IIa fibres in the process of changing their myosin to that of the type I fibres. No changes in fibre composition were evident in the white area of the gastrocnemius medial head, an area made up of IIb or fast glycolytic fibres. The indices of capillarity: capillary density and capillary to fibre ratio, as well as mean and maximal diffusion distances from the capillaries, were not changed by the treatment with PTU in the muscles studied. The lack of changes in capillarity in spite of significant changes in oxidative capacity indicates that in skeletal muscle capillarity is not necessarily related to the oxidative capacity of the fibres.
Organization of input to the interneurones mediating group I non‐reciprocal inhibition of motoneurones in the cat.
Authors: Harrison P J , Jankowska E
Published: December 2014

Patterns of convergence of different presynaptic fibre types onto interneurones mediating non‐reciprocal inhibition of motoneurones have been studied in order to investigate to what extent the population of these interneurones is homogeneous or can be divided into subgroups on the basis of their input. In a sample of interneurones, all of which were interposed in pathways from the group I afferents of one group of muscles (triceps surae and plantaris), individual interneurones exhibited a wide variety of convergence patterns. Some interneurones were influenced by only a few types of afferent or descending fibre systems whereas others were influenced by many. Furthermore, various fibre systems excited and/or inhibited individual interneurones in different combinations. While there appeared to be too many patterns of convergence to allow any simple classification into a few distinct groups of interneurones, two possibilities were considered. One was that certain presynaptic fibre types influence individual interneurones in preferred combinations. The other was that they converge entirely at random. To investigate this, the frequencies of convergence of various pairs of fibre types were predicted assuming that each of them influences a proportion of the interneurones independently of other sources. Generally, there was close correspondence between such predicted and observed frequencies of occurrence of tested combinations of input. These findings are thus compatible with an organization whereby individual presynaptic fibres innervate a random sample of the population of interneurones. Deviations from the predicted incidence of convergence patterns were found primarily for synaptic actions mediated di‐ or oligosynaptically and are attributed to a consequence of convergence at the pre‐interneuronal level. A particular consequence of such an organization is that interneurones in pathways of non‐reciprocal inhibition are shared by afferents of different muscles in a continuum of combinations. The functional implications of this arrangement are discussed.
Effects of subdiaphragmatic vagotomy on energy balance and thermogenesis in the rat.
Authors: Andrews P L , Rothwell N J , Stock M J
Published: December 2014

Subdiaphragmatic vagotomy caused chronic gastric distension and hypertrophy, and a reduction in voluntary food intake in rats fed a pelleted stock diet. These effects were minimized by feeding a more digestible semisynthetic diet. Vagotomized rats fed the pelleted diet showed lower rates of oxygen consumption than pair‐fed controls, and the rise in metabolic rate (thermic response) following gastric intubation with a carbohydrate meal was diminished. This could be restored to normal by simultaneous injection of insulin. Thermic responses to fat and noradrenaline were normal in the vagotomized group. On the powdered semisynthetic diet, vagotomized rats gained more weight and showed greater efficiency of energy gain than pair‐fed controls. The thermic response to a single meal of the semisynthetic diet was depressed in these vagotomized rats, but restored to normal by acute insulin treatment. The activity of the thermogenic proton conductance pathway in brown adipose tissue mitochondria (assessed from purine nucleotide binding) was reduced by vagotomy in animals on both diets, but was restored to normal by chronic insulin treatment, which also slightly raised brown fat activity in sham‐operated rats. These results demonstrate that the reduced gastric activity and food intake following vagotomy is dependent on the digestibility and/or composition of the diet. When differences in food intake are abolished by pair feeding, vagotomy reduces thermogenic responses to carbohydrate, probably as a result of impaired insulin release. This may be responsible for the enhanced energetic efficiency and elevated weight and energy gains seen after vagotomy.
Urinary sodium excretion and the renin‐aldosterone system in new‐born calves.
Authors: Safwate A
Published: December 2014

Urinary Na+ and K+ excretion, plasma aldosterone levels (PAL) and plasma renin activity (PRA) were measured in three groups of four 3‐day‐old calves infused with aldosterone, ethacrynic acid and hydrochlorothiazide or with vehicle. Aldosterone infusion (16.7 micrograms/kg body wt. given by rapid injection, followed by the infusion of 33.3 micrograms/kg body wt. during 6 h) decreased urinary Na+ concentration and excretion during the 6 h period of infusion. This effect disappeared during the following 18 h. Ethacrynic acid (2 mg/kg body wt. by rapid injection, followed by the infusion of 1.5 mg/kg body wt..h during 6 h) and hydrochlorothiazide (8 mg/kg body wt. by rapid injection, followed by the infusion of 6 mg/kg body wt..h during 6 h) increased urinary volume and urinary excretion of Na+, but decreased urinary K+ concentration without affecting urinary K+ excretion during the 6 h period of infusion. During the same time, the plasma Na+ concentration decreased, PRA increased rapidly and was followed by a significant rise in PAL. These results demonstrate that in very young healthy calves, the renal tubules are able to respond to aldosterone. The renin‐aldosterone system is also operative in these animals since it responds to Na+ depletion induced by the combination of diuretics and inhibitors of tubular Na+ reabsorption.
Mechanotransducer ion channels in chick skeletal muscle: the effects of extracellular pH.
Authors: Guharay F , Sachs F
Published: December 2014

The membrane of tissue‐cultured chick pectoral muscle contains an ionic channel which is activated by membrane tension. With 150 mM‐external K+ and 150 mM‐internal Na+, the channel has a conductance of 70 pS and a reversal potential of +30 mV. With 150 mM‐external Na+ and 150 mM‐internal K+ (normal gradient) the channel has a conductance of 35 pS and a reversal potential of ‐30 mV. The ratio of K+ permeability to Na+ permeability, PK:PNa, is 4 based upon reversal potentials and is 2 based upon conductance. Kinetic analysis of single‐channel records indicates that there are one open (O) and three closed (C) states. When analysed according to a linear sequential model: C1‐C2‐C3‐O4, only the rate constant that governs the C1‐C2 transition (k1,2) is found to be affected by stretch or voltage. The effects of stretch and voltage on k1,2 can be summarized as k1,2 = k1,2(0) exp (alpha V + theta P2), where K1,2(0) is the voltage and stretch‐independent part of the rate constant, alpha is the voltage sensitivity, V is the transmembrane potential, theta is the stretch sensitivity and P is the applied suction. Increasing extracellular pH from 7.4 to 10.0 increases both alpha and theta in a manner suggesting titration of site(s) with a pK of 9.1. A single lysine of N‐terminal amino acid may be be responsible for modulating both the voltage and pressure responses. Extracellular pH does not affect k1,2(0), the voltage‐ and stretch‐independent part of k1,2, suggesting that pH in the range 7.4‐10 does not alter the local surface charge. The conductance and reversal potential of the s.a. channel are unaffected by pH, suggesting that the titrated site(s) is not close to the mouth of the channel.
Different types of slowly conducting afferent units in cat skeletal muscle and tendon.
Authors: Mense S , Meyer H
Published: December 2014

In chloralose‐anaesthetized cats, the impulse activity of single afferent units conducting at less than 30 m s‐1 and having receptive fields in the triceps surae muscle or the calcaneal tendon, was recorded from thin filaments of the dorsal roots L7 and S1. The receptive fields of the units were tested with a variety of graded natural stimuli (local pressure, stretch, contractions, temperature changes). In addition, the algesic agent bradykinin was injected into the receptive fields, but the sensitivity of the receptors to this substance was not used for classification purposes. Four types of receptors could be distinguished using the strongest response to innocuous natural stimulation as the criterion for characterizing a given ending: (a) nociceptors showing no response to innocuous forms of stimulation and requiring noxious (tissue‐threatening) stimuli to be clearly activated; (b) low‐threshold pressure‐sensitive receptors responding to innocuous indentation of the tissue but being relatively insensitive to stretch and contractions; (c) contraction‐sensitive receptors reaching high discharge frequencies during active contractions of moderate force and innocuous stretch, but being relatively insensitive to local pressure stimulation; (d) thermosensitive receptors responding strongly to small changes in temperature without reacting to innocuous mechanical stimulation. The possible involvement of the different receptor types in central nervous functions (nociception, mechanoreception, ergoreception, thermoregulation) is discussed.
Calcium‐dependent action potentials in rat supraoptic neurosecretory neurones recorded in vitro.
Authors: Bourque C W , Renaud L P
Published: December 2014

Intracellular recordings obtained from thirty‐nine supraoptic nucleus neurones in perfused hypothalamic explants displayed a mean resting membrane potential of ‐69 mV and spike amplitude of 79 mV. Voltage‐current plots were linear in the hyperpolarizing direction and revealed a mean slope resistance of 197 M omega. After Na+ channel blockade with tetrodotoxin (TTX; 0.3‐16 microM), the voltage‐current relationship did not change significantly for hyperpolarizing pulses. An increase in spike threshold in TTX permitted visualization of a reduction in slope resistance to depolarizing current pulses. This rectification was reduced by the addition of the Ca2+ channel blockers Cd2+, Co2+ or Mn2+. High threshold TTX‐resistant spikes with amplitudes ranging between 25 and 64 mV were evoked in an all‐or‐none manner by brief intracellular current pulses applied above 1.0 Hz. Current pulses presented at lower frequencies (less than or equal to 0.5 Hz) evoked graded responses. In seventeen of nineteen cells, prolonged depolarizing current pulses elicited repetitive firing of TTX‐resistant spikes with a progressive increase in their amplitude, rise and fall times and after‐hyperpolarizations. TTX‐resistant spikes were reversibly abolished when CaCl2 was replaced by equimolar amounts of EGTA or by the addition of either Cd2+, Co2+ or Mn2+ to the perfusion medium. In artificial medium containing EGTA, both the shoulder on the repolarization phase of the spike and the subsequent after‐hyperpolarization were reversibly abolished. Tetraethylammonium (TEA; 2‐5 mM) induced prolongation of mean action potential durations from 1.9 to 12.3 ms (nineteen cells); in TTX, TEA also prolonged the duration and increased the over‐all peak amplitude of the TTX‐resistant (Ca2+) spike. While TEA also enhanced the amplitude of the Na+ spike, no comparable prolongation in spike duration was observed. These data indicate that somatic action potentials of supraoptic nucleus cells arise from the co‐activation of a low threshold Na+ conductance and a higher threshold Ca2+ conductance; the latter is expressed as a shoulder on the repolarization phase of the action potential.
Membrane current through adenosine‐triphosphate‐regulated potassium channels in guinea‐pig ventricular cells.
Authors: Noma A , Shibasaki T
Published: December 2014

The question whether activation of the ATP‐regulated K channel is responsible for macroscopic anoxia‐induced outward currents was examined in ventricular cells isolated enzymatically from guinea‐pig heart. Gigaseal patch‐clamp electrodes were used for a whole‐cell voltage clamp. Membrane currents were compared in the same cell while the cell interior was dialysed by perfusing the electrode with different solutions. When the cell was dialysed with various ATP‐deficient (less than or equal to 2 mM) internal solutions, the Ca current decreased in a dose‐dependent manner to less than 10% of control at 0.5 mM‐ATP. A slight (ca. 25%) decrease of the slope conductance for hyperpolarizing current was observed. When a delayed rectification on depolarization followed by a marked outward current tail on repolarization was present under control conditions, this time‐dependent outward current was also depressed. An increase in a time‐independent outward current was observed accompanied by marked current fluctuations. The outward current showed a reversal potential near the K equilibrium potential, inward rectification, and no relaxation on voltage jumps. The power density spectrum of the current fluctuations showed a pattern similar to the spectrum calculated from the single‐channel currents of ATP‐regulated K channels. The amplitude of the single‐channel current, estimated from the fluctuations, was almost equal to that of the single‐channel current. The total number of channels within one cell was estimated as 2000‐3000. It is concluded that the ATP‐regulated K channels are responsible for the increase in the outward current and the shortening of the action potential duration under various anoxic conditions.