bluuebunny/crossref_metadata_2025 huggingface dataset:
The ‘late’ reflex responses to muscle stretch: the ‘resonance hypothesis’ versus the ‘long‐loop hypothesis’
Authors: Eklund G. , Hagbarth K.-E. , Hägglund J. V. , Wallin E. U.
Published: December 2014

1. Experiments were performed to check the validity of previous claims concerning the ‘long‐loop’ aetiology of ‘late’ reflex electromyogram (e.m.g.) responses to muscle stretch in man. The primary aim was to investigate whether observations previously presented in favour of the ‘long‐loop hypothesis’ are explicable also in terms of the ‘resonance hypothesis’, according to which the ‘late’ reflex components represent spinal, short‐latency responses to intramuscular oscillations initiated by the impact.

2. The contracting wrist flexors of healthy subjects were exposed to trains of recurrent 25‐50 Hz stretch stimuli (wrist torque pulses). Each of the initial two or three pulses in the train was followed by e.m.g. peaks with a latency of 20‐25 msec. The e.m.g. peaks driven in this way had the following characteristics in common with the successive two or three e.m.g. peaks which were induced by single ramp stretches or tendon taps. (a) Changes in stimulus parameters which altered the strength of the initial e.m.g. peak often had an opposite effect on the strength of the succeeding peak(s). Muscle vibration which attenuated the initial peak often enchanced the succeeding one(s). (b) The initial e.m.g. peak was less affected than the succeeding peak(s) by the subjects’ attempts to respond with rapid ‘resist’ or ‘let go’ reactions.

3. Intramuscular oscillations (monitored by a needle accelerometer) and e.m.g. responses evoked by single ramp stretches and/or tendon taps were also studied in the long thumb flexor, the calf muscles and the masseter muscle. In the thumb flexor, the initial accelerometer deflexion was only rarely succeeded by a short latency e.m.g. peak, but the succeeding wave in the needle accelerogram was followed by such a peak, appearing about 40 msec after stimulus application. By contrast, the calf muscles and the jaw elevators exhibited a high amplitude, short‐latency e.m.g. response to the first but only rarely to the second intramuscular oscillation wave.

4. The interval between initial and second e.m.g. peaks following tendon taps was longer for calf muscles than for wrist flexors and longer for wrist flexors than for jaw elevators. Similar differences were observed with respect to the intervals between the damped intramuscular oscillations initiated by the impacts.

5. Without denying the existence of ‘long‐loop reflexes’ it is concluded that the characteristics of the ‘late’ reflex responses to muscle stretch in man are explicable also in terms of the ‘resonance hypothesis’.
Physiological responses, receptive fields and terminal arborizations of nociceptive cells in the leech.
Authors: Blackshaw S E , Nicholls J G , Parnas I
Published: December 2014

The physiological responses, receptive fields and morphology of individual nociceptor (N) neurones have been studied in the leech. In each of the midbody ganglia there are four N cells (two on either side). Each N cell has a distinctive territory that it supplies in the periphery, on the surface or internally. 1. Both N cells respond selectively to noxious mechanical stimuli applied to the skin but not to touch, light, pressure or stretch. The receptive field of each cell is well defined and covers roughly the same area, extending from the dorsal midline to the ventral midline, with considerable overlap. 2. One of the N cells, situated more medially in the ganglion, also fires at high frequencies in response to mechanical stimulation, such as pinching or squeezing, of the connective tissue lining the viscera. In contrast, the other N cell (situated laterally in the ganglion) is activated by pressure or pinches applied to the opening of the excretory duct but not the gut. 3. Following injection of horseradish peroxidase into the soma, axons of N cells appear as unspecialized fine processes about 1 micrometer in diameter, in the dermis of the leech, deep to the layer of epidermal cells. In addition, at specific sites in the skin, the N cell situated laterally in the ganglion makes distinctive coiled terminals in association with the expanded dendrites of large neurones in the periphery, the functions of which are unknown. This finding raises the possibility that lateral N cells may perform some additional role as yet not understood.
Selective reinnervation of skeletal muscle in the newt Triturus cristatus.
Authors: Holder N , Mills J , Tonge D A
Published: December 2014

1. A study was made of the effectiveness of synapses formed by foreign and original nerves during reinnervation of skeletal muscle of the newt Triturus cristatus. The extensor cranialis nerve (e.c.n.) of the forelimb was implanted into the humeroantebrachialis muscle (biceps) which was denervated by cutting or crushing the forelimb flexor nerve (f.f.n.). 2. Although biceps became innervated by the implanted nerve, neuromuscular transmission was abnormal. The ratio of the tensions developed by biceps during single and repetitive (50 Hz) stimulation of e.c.n. was lower than either that obtained in normal biceps or during stimulation of f.f.n. after it had regenerated. Similarly, the mean quantal content of e.p.p.s evoked in biceps during stimulation of e.c.n. were lower (m = 17.1) than those evoked in normal muscles (m = 74.6) or during stimulation of the regenerated f.f.n. (m = 40.4). 3. Although the implanted e.c.n. had innervated biceps, after 2‐3 months a sprout had grown out of the side of the nerve to reinnervate the extensor digitorum communis muscle (e.d.c.) of the forearm. The mean quantal content of e.p.p.s evoked in this muscle by stimulation of e.c.n. (m = 32.2) was higher than that of those e.p.p.s evoked by stimulation of e.c.n. (m = 32.2) was higher than that of those e.p.p.s evoked by stimulation of the same nerve in biceps (m = 17.1). 4. The results suggest that the synapses formed when a muscle is innervated by an inappropriate nerve are less effective than those formed when reinnervation by the correct nerve occurs. This may account for the tendency of the inappropriate synapses to regress following reinnervation by the correct nerve. In addition however, in the newt there seem to exist mechanisms which ensure that regenerating nerves reinnervate their correct muscles.
Power spectral analysis of electromyogram and compound muscle action potential during muscle fatigue and recovery.
Authors: Mills K R
Published: December 2014

1. The power spectral changes of the voluntary electromyogram (e.m.g.) and of the compound muscle action potential (c.m.a.p.) evoked by supramaximal nerve stimulation have been compared in fatigue and recovery of human voluntary muscle contraction. 2. The mean power frequency (m.p.f.) of the voluntary e.m.g. and that of the c.m.a.p. are similar during fatigue. Power spectral shift can be largely accounted for by change in shape of muscle action potentials. 3. The recovery rates of force and action potential amplitude are similar, being half complete at 30 s. M.p.f. and relaxation rate recover more slowly, being half complete at 3 min. 4. It is suggested that the recovery of power spectral changes is dependent on the metabolic state of the muscle.
Comparison of effects of denervation and botulinum toxin paralysis on muscle properties in mice
Authors: Brown M. C. , Hopkins W. G. , Keynes R. J.
Published: December 2014

1. The properties of denervated and fully innervated but paralysed soleus and extensor digitorum longus (e.d.l.) muscles were compared in mice.

2. Muscles were paralysed by single or repeated injections of botulinum toxin into the right lower leg. Contralateral muscles were denervated at the same time by sciatic nerve section. Muscles were excised 3‐20 days later and direct and indirect isometric twitch and tetanic tensions measured in vitro. ACh sensitivity was assessed from isometric contractions to various concentrations of bath‐applied ACh perchlorate.

3. Denervated muscles as expected from the work of others developed sensitivity to ACh earlier and more rapidly than paralysed muscles. A transient peak of sensitivity was reached after 7 days of denervation in soleus and after 8 days in e.d.l. However 2 days later the sensitivity of muscles fully paralysed to nerve twitch and tetanic stimuli was not significantly different from that of denervated muscles.

4. In both e.d.l. and soleus the direct tetanus/twitch ratios declined in paralysed and denervated muscles. The decline was initially more rapid in denervated than paralysed soleus, but the ratios for paralysed and denervated muscles were not significantly different after 10 days in either muscle. By this time there were no differences in the absolute strengths of the paralysed and denervated muscles.

5. It is concluded that the ACh sensitivity and dynamic properties of fully paralysed mouse muscles become equal to those of denervated muscles once the acute effects associated with nerve degeneration are past. This result is consistent with the idea that normal neuronal control of extrajunctional mammalian skeletal muscle properties is mediated solely by means of activity.
Circadian rhythms of urinary excretion: the relationship between the amount excreted and the circadian changes.
Authors: Minors D S , Waterhouse J M
Published: December 2014

1. The circadian rhythms of urinary excretion of water, sodium, chloride, potassium, urate, calcium and phosphate have been studied in several groups of volunteers. 2. These rhythms have been measured: under nychthemeral and constant routine regimens; while subjects were in an Isolation Unit or allowed free egress into society; with spontaneous changes in dietary intake; or after potassium‐loading. 3. A direct relationship between 24 h mean rate of excretion and range of excretion was found in all circumstances and for all variables; this relationship was found also when the mesor and amplitude of the cosine curve best describing each 24 h of data were considered. 4. These relationships derive from the observation that, with increases in 24 h mean rates of excretion, nocturnal rates increased less than diurnal rates. 5. This differential sensitivity as between the night and day times has both endogenous and exogenous components. 6. It is suggested that circadian rhythms of urinary excretion result at least partially from this differential sensitivity of the kidney to homeostatic control mechanisms.
The effects of muscle length on intracellular calcium transients in mammalian cardiac muscle.
Authors: Allen D G , Kurihara S
Published: December 2014

1. The calcium‐sensitive photoprotein aequorin was micro‐injected into cells of rat and cat ventricular muscles. The resulting light emission is a function of intracellular free calcium concentration ([Ca2+]i). The transient increases in [Ca2+]i that accompany contraction were monitored. 2. After an increase in muscle length, the developed tension increased immediately and then showed a slow increase over a period of minutes. The peak [Ca2+]i in each contraction was initially unchanged after an increase in muscle length but then showed a slow increase with a time course similar to that of the slow tension change. 3. As a consequence of these slow changes, the shape of the tension‐length relation depends on the procedure used to determine it and this change in shape can be attributed to changes in activation. 4. Immediately after an increase in muscle length the calcium transient was abbreviated. 5. When a quick release was performed during a contraction, a short‐lived increase in the [Ca2+]i was observed following the release. 6. The two previous observations can both be explained if the binding constant of troponin for calcium is a function of developed tension.
The role of mechanical and hormonal stimuli on uterine involution in the rat.
Authors: Wray S
Published: December 2014

1. Distension of part of the uterus of the rat after parturition by an inert material (‘Silgel’) prevented involution, as measured by change in collagen content and weight in the distended part. The other parts of the uterus, those emptied at parturition, involuted at the normal rate. 2. Removal of the distending material four days after parturition was followed by involution (measured in the same way) in this part of the uterus. 3. Removal of all fetal material from one horn before the end of pregnancy (at day 19) was followed by involution, but at a slower rate than after normal term. Bilateral ovariectomy at the same time as removal of fetuses increased the rate of this involution, but it was still slower than at normal term. 4. Ovariectomy alone on day 19 had no effect on subsequent changes in the uterus; weight and collagen content then followed the normal course to term. 5. It is concluded that mechanical factors associated with the presence of material within the uterine cavity play a preponderant role in maintaining the uterine wall, though hormonal factors can affect its reaction to a lesser extent.
Inverse effects of dansylation of red blood cell membrane on band 3 protein‐mediated transport of sulphate and chloride
Authors: Lepke Sigrid , Passow Hermann
Published: December 2014

1. Dansylation of the red cell membrane produces inverse effects on SO42- and Cl− equilibrium exchange. The former is enhanced by several orders of magnitude (Legrum, Fasold & Passow, 1980), the latter is inhibited. Both effects are potentiated after dansylation in the presence of 2‐(4‐amino‐3‐sulphophenyl)‐6‐methyl‐7‐benzothiazol sulphonic acid (APMB), a disulphonic acid that combines non‐covalently with the 4,4′‐diisothiocyanate dihydrostilbene‐2,2′‐disulphonic acid (H2DIDS) binding site of the anion transport protein.

2. After dansylation the maximum of the pH dependence of SO42- exchange near pH 6·3 is replaced by a plateau. When dansylation is performed in the presence of APMB, the plateau is reached at a much higher level at around pH 7·0 and resembles that observed by Funder & Wieth (1976) for Cl−.

3. The mutual interactions between the transfer site, the H2DIDS binding site, and the as yet unidentified danysl chloride binding sites were studied in detail. Occupation of the H2DIDS binding site by the non‐covalently binding agents 4,4′‐dinitrostilbene‐2,2′‐disulphonate (DNDS), 4,4′‐bis(acetamido) stilbene‐2,2′‐disulphonate (DAS) or APMB inhibit the enhanced SO42- exchange across the previously dansylated membrane. The apparent KI value remains the same as in untreated membranes for DNDS, is reduced to 1/3 for DAS, and to 1/60 for APMB. Conversely, when dansylation is carried out while the H2DIDS binding site is occupied by DNDS, APMB or DAS, the enhancement of SO42- exchange (as measured after removal of excess dansyl chloride and the additional agent) is prevented by DNDS, augmented by APMB and not affected by DAS. This suggests that the agents stabilize different conformations of the H2DIDS binding site that are associated with different accessibilities of the dansyl chloride binding sites.

4. The SO42- equilibrium exchange as measured at a fixed Cl− concentration is enhanced when the Cl− concentration at which dansylation is carried out is increased, indicating allosteric interactions between anion binding and the exposure of the dansyl chloride binding sites.

5. The enhanced K+ efflux from dansylated red cells is independent of the described modifications of the dansylation reaction by APMB, DAS or DNDS, demonstrating that there exists no simple correlation between the changes of anion and cation movements that are induced by dansylation.
Local effects of bleaching in retinal rods of the toad.
Authors: Baylor D A , Lamb T D
Published: December 2014

1. Suction electrode recordings were used to study the recovery of responsiveness in single toad rods after bleaching a small fraction (less than 5%) of the rhodopsin. 2. After a spatially uniform bleach that initially abolished the dark current over the entire length of the outer segment, the more proximal regions recovered faster than the more distal regions. For a time the most basal region was almost fully recovered while the tip remained fully saturated. 3. Such a gradient of responsiveness did not occur during uniform steady background illumination of dark‐adapted cells. 4. The entire outer segment recovered uniformly after a longitudinally graded bleach that simulated the pattern produced by self‐screening in the intact eye. 5. The recovery of the distal end of the outer segment was not affected by a bleach at the proximal end. This suggests that the differences in recovery rate reflect intrinsic local properties of the outer segment rather than longitudinal diffusion of a substance from the inner segment. 6. For at least the first 3 min after bleaching with a narrow transverse slit the reduction of responsiveness remained most pronounced in the bleached region, suggesting that this effect of bleaching does not spread extensively. 7. The increased noise induced by bleaching is shown to originate locally in the bleached region of outer segment. 8. When the tip was locally saturated after a bleach or during steady light, the current recorded from the tip was predominantly capacitive, resulting from intracellular voltage change. This indicates that when the dark current is abolished the outer segment plasma membrane has negligible leakage conductance.
Combined effects of ATP and phosphate on rubidium exchange mediated by Na‐K‐ATPase reconstituted into phospholipid vesicles
Authors: Karlish S. J. D. , Lieb W. R. , Stein W. D.
Published: December 2014

1. Phospholipid vesicles reconstituted with Na—K‐ATPase show an (ATP+phosphate)‐stimulated Rb—Rb exchange, with properties similar to the K—K exchange of human red cells. This includes a rate 15‐20% of the rate of active ATP‐dependent Na—K exchange.

2. We have studied activation of this Rb—Rb exchange by ATP at fixed phosphate concentrations and by phosphate at fixed ATP concentrations. It is found for both ATP and phosphate that with low concentrations of the fixed ligand an increase in concentration of the complementary ligand produces first stimulation and then inhibition of Rb—Rb exchange. At high concentrations of the fixed ligand the complementary ligand shows only saturation behaviour.

3. The pattern of activation and of inhibition by ATP and by phosphate is affected by the Rb0 concentration in the exterior medium, in that higher concentrations of Rb0 counteract inhibitory effects of high concentrations of ATP and phosphate.

4. (ATP+phosphate)‐stimulated Rb—Rb exchange is activated by Rb0 in the exterior medium along a sigmoid curve. An increase of Rbi within the vesicles, which raises the maximal velocity of Rb—Rb exchange, is accompanied by a smaller increase in the Rb0 concentration required for half‐maximal stimulation of the Rb—Rb exchange.

5. The data are interpreted in terms of a model similar to those proposed by Karlish & Stein (1982a,b), but extended to include simultaneous effects of ATP and phosphate. Inhibitions by high concentration of ATP or phosphate arise as a result of stabilization of E1 ATP or E2‐P forms respectively, in the presence of low concentrations of the complementary ligand. With high concentrations of the fixed ligand, saturation behaviour of the varying ligand is observed because the occluded Rb forms become the dominant transport intermediates. The occluded Rb forms bind both ATP and phosphate weakly and independently. The effects of ATP together with phosphate are accounted for by a simple combination of their separate effects on the Rb—Rb exchange.

6. We suggest that the functional role of the occluded Rb form E2 (Rb)occ in active transport is to minimize passive cation leaks through the system and allow control of the direction of cation movements by binding of physiological ligands such as ATP or phosphate.
A study of the motion of organelles which undergo retrograde and anterograde rapid axonal transport in Xenopus
Authors: Koles Z. J. , McLeod K. D. , Smith R. S.
Published: December 2014

1. Axonally transported organelles were detected optically in myelinated axons from Xenopus laevis at room temperature (21‐23 °C). Details of the motion of organelles which were transported in the retrograde and anterograde directions were studied using filmed records.

2. A group of 133 organelles with a mean retrograde velocity of 0·91 μm/sec was compared with a group of thirty‐nine organelles with a mean anterograde velocity of 0·93 μm/sec.

3. Averaged power spectra of the positional deviations about the mean positional change through time were constructed for organelles which travelled in the retrograde and anterograde directions. Most of the power in the two spectra was at frequencies below 0·2 Hz and each contained a single peak at 0·02‐0·04 Hz. The power spectrum for retrograde organelle motion had a magnitude about twice that for anterograde organelle motion.

4. Estimates of the instantaneous velocity of organelles which travelled in either direction varied smoothly with time. Instantaneous velocity was not a smooth function of organelle position, (i.e. was ‘saltatory’).

5. Histograms of the estimates for the groups of organelles whose major motion was retrograde or anterograde were broad, covering a range of about 3 μm/sec, were unimodal, and passed through zero to include a small group of values which indicated motion in the opposite (minor) direction.

6. Organelles spent, on average, more time moving in the minor direction the lower their mean velocity.

7. The variation in instantaneous velocity was greater for organelles which travelled in the retrograde direction than for those which travelled in the anterograde direction. No correlation was found between the variation of instantaneous velocity and the mean velocity of the organelles.

8. Images of organelles occasionally appeared to rotate while the organelle continued to move in the major direction of travel.

9. Evidence is presented that spatially related properties of the axon influence organelle velocity and that this influence is common to organelles which travel in the two major directions.

10. A hypothesis is presented to account for the findings. This supposes that each organelle travels through a stationary axoplasm and is propelled by the resultant of two opposing driving forces whose relative magnitude fluctuates with time. Spatially dependent properties of the axoplasm modify the postulated time‐related cycle of motion.
Interstitial space of mouse skeletal muscle
Authors: Sheff Michael F. , Zacks Sumner I.
Published: December 2014

1. A new preparation of mouse skeletal muscle, prepared from pectoral muscles, is described.

2. The sorbitol space of this muscle, both in vivo and in vitro, has been measured with dynamic loading of the muscle in vitro as an experimental variable.

3. The Na+ and K+ contents of the muscle have been determined and the apparent intracellular concentration for these ions calculated both in vivo and after incubation in vitro.

4. Histological studies on the incubated muscle have been made so as to permit comparison of the changes in the chemical measurements with changes in the ultrastructure of the muscle.

5. The results of these experiments show that there is an increase in the apparent extracellular space of the muscle following incubation. This increase is constant, and independent of the load, with the important exception that unloaded muscles do not reach an equilibrium during the period of incubation and have a much greater apparent extracellular space.

6. Intracellular Na+ and K+ concentrations are consistent with the sorbitol being restricted to an extracellular phase in the loaded muscle; but the evidence implies that sorbitol in the unloaded muscle penetrates into a space from which Na+ is excluded.

7. The total water content of the muscle per unit weight is unchanged by incubation, indicating that the apparent change in sorbitol space is in the ratio of intracellular space to extracellular space rather than by addition of water to the extracellular space.

The significance of these results is discussed with reference to the use of such preparations for in vitro studies.
Quantitative measurements of centrally and retinally generated saccadic suppression in a locust movement detector neurone.
Authors: Zaretsky M
Published: December 2014

1. Chronic recordings from tethered but otherwise freely moving locusts demonstrate that the response of the descending contralateral movement detector (d.c.m.d.) neurone, an identified visual interneurone of the brain, is greatly reduced during the performance of saccades. 2. The reduction in the response of the d.c.m.d. is effected by both a centrally generated corollary discharge and the changing contrast of the image of the visual background on the retina. 3. The corollary discharge that is concomitant with a saccade reduces the d.c.m.d. response by 0 . 94 log units, and this reduction is independent of contrast frequency. 4. Changing contrast produced by relative motion of eye and background reduces the sensitivity of the d.c.m.d. neurone by 0 . 16 log units for each 10‐fold increase in contrast frequency. This retinally generated reduction in sensitivity is not significantly different whether the locust performs saccades or is fixating with the visual background passively moved. The maximal reduction in the d.c.m.d. response by retinal sources is 0 . 45 log units. 5. Proprioceptive reafference does not contribute significantly to saccadic suppression of the response of the d.c.m.d. neurone.
Sodium currents and sodium‐current fluctuations in rat myelinated nerve fibres
Authors: Neumcke B. , Stämpfli R.
Published: December 2014

1. Sodium currents and fluctuations of sodium currents were measured in myelinated fibres of rat sciatic nerve under voltage clamp at 20 °C.

2. Relaxations of sodium currents during various test potentials were recorded in the presence of 6 nM‐TTX in the extracellular solution. The activation of sodium currents at low depolarizations could be described with the m2 formulation. At increasing potentials higher powers of m up to 4 were required. The mid‐point of the PNa (E) curve was located near E = ‐32 mV. Sodium inactivation during various depolarizations developed in two phases.

3. The resistance in series with the nodal membrane was calculated from peak sodium currents without and with 6 nM‐TTX in the extracellular solution. The resistance varied between different fibres and ranged between 190 and 620 kΩ.

4. From peak sodium currents at the same mambrane potential without and in the presence of TTX an apparent equilibrium dissociation constant of 1·6 nM was calculated for TTX binding to sodium channels.

5. The conductance γ and the number N0 (corrected for series‐resistance effects) of sodium channels were evaluated from ensemble average values of the mean sodium current and the variance of sodium‐current fluctuations at the beginning of a test pulse. The mean values were γ = 14·5 pS, N0 = 21,000 per node.

6. The spectral density of stationary sodium‐current fluctuations exhibited two relaxation components whose time constants were comparable to those of sodium activation and inactivation. At low depolarizations the variance produced by inactivation fluctuations was larger than predicted by the m3. h formulation.

7. It is concluded that individual sodium channels of rat and frog nerve have similar gating properties. In mammalian nodes the number of sodium channels is lower and the single‐channel conductance higher than in amphibian nodes.
Anion blockers inhibit impulse‐evoked quantal transmitter release at the crayfish neuromuscular junction
Authors: Niles Walter D. , Smith Dean O.
Published: December 2014

1. The effects of the anion‐transport blocking reagents Probenecid, 4,4′diisothiocyanostilbene‐2,2′‐disulphonate (DIDS), and pyridoxal phosphate on the number of quanta released (m) and the time course of the probability of quantal release, α(t), following an action potential were studied at single synaptic sites on the opener muscle in the crayfish leg.

2. Low concentrations (10‐50 μM) of DIDS or Probenecid produced decreases in m to about 30‐50% of the initial value; at higher concentrations (100 μM or greater), evoked release failed. Much greater concentrations (500 μM) of pyridoxal phosphate were necessary to produce decreases in m.

3. Synaptic depression in 50 μM‐Probenecid was reversible by removing the agent; after treatment with 50 μM‐DIDS, however, m partially regained the initial value upon removal of the drug.

4. The time course of α(t) after an action potential was unaffected by any of the reagents.

5. It is concluded that the reagents decrease the number of quanta evoked by a nerve impulse by decreasing the magnitude, but not the time course, of the average rate of quantal release following an action potential; it is suggested that nerves and other secretory cells may share a common mechanism during exocytosis that is subject to modification by these agents.
Effects of sympathetic nerve stimulation on intra‐oral mechanoreceptor activity in the cat
Authors: Cash R. M. , Linden R. W. A.
Published: December 2014

1. Micro‐electrode recordings were made from intra‐oral mechanoreceptor neurones in the trigeminal ganglion and mesencephalic nucleus of the fifth nerve in the cat.

2. The effect of cervical sympathetic trunk stimulation on the discharge of the mechanoreceptors to a controlled force was observed.

3. Almost half of the mechanoreceptor neurones studied were modulated by sympathetic stimulation. Sympathetic stimulation both decreased the impulse frequency to a controlled force application and raised the threshold in these receptors. The remainder were unaffected by sympathetic stimulation.

4. In previous studies involving recordings from either the trigeminal ganglion or mesencephalic nucleus no spontaneously active slowly adapting intra‐oral mechanoreceptors have been observed, yet in peripheral alveolar nerve studies many workers have reported spontaneously discharging neurones. In the present study spontaneous activity has been recorded from intra‐oral mechanoreceptors both in the trigeminal ganglion and in the mesencephalic nucleus after cutting the cervical sympathetic trunk. The spontaneous activity could be abolished in all cases but one, by sympathetic stimulation. It is suggested that reported spontaneous activity from intra‐oral mechanoreceptors could be due to cutting the peripheral nerve and therefore the sympathetic supply, thus removing an inhibitory influence from the sensory unit. The means by which the sympathetic supply inhibits the sensory unit has not been resolved.
Muscle receptors in the cross‐reinnervated soleus muscle of the cat
Authors: Gregory J. E. , Luff A. R. , Proske U.
Published: December 2014

1. Discharges have been recorded from afferents of the soleus muscle following reinnervation by the nerve of a fast twitch muscle, extensor digitorum longus. Recordings were made 227‐449 d post‐operatively.

2. The gross afferent discharge from the cross‐reinnervated soleus suggested the presence of fewer mechanosensitive receptors than in normal muscles, as judged by discharges seen during a maximal muscle twitch.

3. A comparison of receptors in the cross‐reinnervated muscle with afferents from a self‐reinnervated muscle showed that many of the responses in the self‐reinnervated muscle were also abnormal. It was concluded that much of the disruption resulted from the surgical interference and that rather less could be attributed to the foreign nerve.

4. A detailed analysis of response characteristics of receptors in cross‐reinnervated soleus muscles of five cats showed that afferent conduction velocities of identified spindles and tendon organs were generally lower than normal and responses to muscle stretch or vibration were often atypical. A large number of afferents which could not be classified as muscle spindles or tendon organs included a group called contraction receptors. These responded generally only during maximal muscle contractions and with a rather feeble discharge. A second group consisted of afferents in which impulses could be elicited by electrical stimulation of the nerve but not by any mechanical activity in the muscle.

5. In a further five animals a detailed study was made of the motor supply of muscle spindles. A fusimotor innervation was common, but invariably stimulation of the γ fibre had a static action on the spindle. No purely dynamic fusimotor fibres were encountered. There were many static β fibres (skeletofusimotor) no dynamic βs and three axons conducting in the α range, which developed no tension, yet produced specific intrafusal effects. Two of these had a mixed static—dynamic action while the third was purely static.

6. It was concluded that in the cross‐reinnervated soleus muscle the majority of afferents were abnormal in one or other respect. The central action of such abnormal receptors would have to be taken into account when seeking explanations of the transformation of a muscle's mechanical properties following reinnervation by a foreign nerve.
Effects of β‐adrenergic stimulation on calcium movements in rabbit aortic smooth muscle: relationship with cyclic AMP
Authors: Meisher Kaushik D. , van Breemen Cornelis
Published: December 2014

1. The effects of isoprenaline (10−6 M) on relaxation, unidirectional as well as net Ca2+ fluxes, and cyclic AMP levels were investigated in rabbit aorta under the condition of high‐K+ depolarization in the presence of phentolamine (10−5 M).

2. Isoprenaline (10−6 M) caused significant inhibition of Ca2+ influx stimulated by 145 mM‐K+ (0 Na+) solution. The time courses of Ca2+ influx inhibition and relaxation by isoprenaline were parallel. Isoprenaline also caused a significant inhibition of high‐K+‐induced gain in net Ca2+ content.

3. Ro 20‐1724 (1 mM), a phosphodiesterase inhibitor, also caused relaxation and Ca2+ influx inhibition in high‐K+‐depolarized rabbit aorta. Pre‐treatment with Ro 20‐1724 potentiated isoprenaline‐induced Ca2+ influx inhibition and relaxation.

4. Isoprenaline and Ro 20‐1724 each alone increased cyclic AMP levels. Furthermore pre‐treatment with Ro 20‐1724 caused potentiation of isoprenaline‐induced increases in cyclic AMP levels.

5. At submaximal concentration, D600 (10−7 M) caused partial inhibition of high‐K+‐stimulated Ca2+ influx and produced relaxation. However, unlike Ro 20‐1724, it did not potentiate isoprenaline‐induced Ca2+ influx inhibition and relaxation. D600 does not increase cyclic AMP levels in smooth muscle.

6. Dibutyryl cyclic AMP (1 mM), a lipid‐soluble analogue of cyclic AMP, caused relaxation and inhibited high‐K+‐stimulated Ca2+ influx.

7. Isoprenaline failed to cause stimulation of Ca2+ efflux in high‐K+‐depolarized rabbit aorta.

8. It is concluded that the inhibition of Ca2+ influx may be one of the mechanisms by which β‐receptor stimulation can reduce intracellular free Ca2+ to promote relaxation of smooth muscle. The data support the involvement of cyclic AMP in this action of the β‐agonist.

9. Since the experiments were conducted in 145 mM‐K+ (0 Na+) depolarizing conditions, the role of hyperpolarization or of a Na+—Ca2+ exchange mechanism in isoprenaline‐induced Ca2+ influx inhibition and/or relaxation can be excluded.
Renal excretion of sodium after bilateral renal sympathectomy in the anaesthetized and conscious rat.
Authors: Bencsáth P , Fekete M I , Kanyicska B , Szénási G , Takács L
Published: December 2014

1. The effect of bilateral renal denervation on sodium excretion was studied in conscious rats on normal, low and high sodium diet, and in rats recovering from anaesthesia, as well as in anaesthetized rats fed a normal sodium diet. 2. Sodium excretion of bilaterally denervated conscious rats on normal sodium intake and during either 2 weeks of sodium depletion or 6 days of sodium loading was not different from that of controls, despite changes in sodium supply of more than two orders of magnitude. Cortical noradrenaline concentration of control kidneys was 138 +/‐ 12 ng/g, but was only 7 +/‐ 3 ng/g (P less than 0 . 001) 6 weeks after denervation. 3. In rats recovering from anaesthesia urine flow, sodium excretion and glomerular filtration rate (G.F.R.) were not affected by denervation. 4. In anaesthetized non‐diuretic rats on normal sodium diet chronic bilateral renal denervation increased urine flow and sodium excretion four and five times, respectively, with no changes in G.F.R. 5. Mean arterial blood pressure in bilaterally denervated anaesthetized rats and in those recovering from anaesthesia was decreased by 2 . 7 kPa, P less than 0 . 001 and 1 . 2 kPa, P less than 0 . 05, respectively. 6. The participation of renal nerves in the regulation of sodium excretion in conscious rats seems improbable. The denervation natriuresis in anaesthetized rats can be related to higher pre‐denervation renal sympathetic nervous activity due to narcosis and surgical stress.
Effects of meal temperature and volume on the emptying of liquid from the human stomach.
Authors: Bateman D N
Published: December 2014

1. The effects of meal temperature and volume on the emptying of liquid meals have been studied in eight normal volunteers. Four drinks were investigated: (i) 200 ml, 12 degrees C, (ii) 200 ml, 37 degrees C, (iii) 500 ml, 12 degrees C, (iv) 500 ml, 37 degrees C. Gastric emptying was measured by real‐time ultrasound. 2. After an initial rapid phase of emptying, measured by the volume retained in the stomach at 5 min, emptying was mono‐exponential and measured as a half‐life. 3. The 5 min gastric volume was significantly reduced by giving a cold drink of 500 ml (12 degrees C: 250 +/‐ 33.1 ml. 37 degrees C: 307 +/‐ 25.8 ml, P less than 0.05). Temperature had no significant effect on the subsequent half‐life of emptying. 4. The half‐life was longer for meals of larger volume; at 37 degrees C this was statistically significant: 200 ml: t 1/2 7.6 +/‐ 2.1 min; 500 ml: t 1/2 15.3 +/‐ 2.8 min; P less than 0.01. 5. There was a significant positive correlation between the 5 min volume and the subsequent half‐life of emptying for all meals except 200 ml at 12 degrees C, suggesting that resting gastric muscle tone affects both phases of gastric emptying. 6. Significant correlations within subjects for 5 min volume measurements for meals of different volume and temperature and half‐lives of meals at 37 degrees C suggests that individuals have their own characteristics of gastric emptying for liquid meals.
The effect of low external pH on properties of the paracellular pathway and junctional structure in isolated frog skin.
Authors: Ferreira K T , Hill B S
Published: December 2014

1. Undirectional and net fluxes of Na, Cl and mannitol were measured across the isolated short‐circuited frog skin when the mucosal surface was bathed with Ringer solution at normal (7.4) or low (2.5) pH. When this solution was changed from normal to low pH, there was a marked increase in both influx and backflux of Cl and mannitol. Na backflux increased markedly but Na influx did not, resulting in a substantial decrease in net flux. 2. In open‐circuit conditions at low pH both undirectional fluxes of Na increased and the potential across the skin dropped by a third. 3. The total conductance, Gt and the short‐circuit current, Isc increased when the mucosal solution was changed from normal to low pH. The structural integrity of the ‘tight junctions’ in the epithelium was disrupted by the low pH treatment and at least 50% of the junctions examined showed a separation of the two, previously apposed, membranes. 4. It has been shown previously that when a low pH solution bathes the mucosal surface the total and shunt conductance increase; the present results demonstrate that under these conditions the short‐circuit current no longer provides a good estimate of the net Na flux. We present calculations to show that protons can be the carriers for the extra charge transfer. 5. Using our values for net Na flux in open circuit and published values for the solute‐linked volume flow, Jv, it could be shown that the osmolarity of the absorbate decreased at low pH.
Influence of sarcomere length, tonicity, and external sodium concentration on conduction velocity in frog muscle fibres.
Authors: Oetliker H , Schümperli R A
Published: December 2014

1. Using an optical technique, conduction velocity in isolated frog muscle fibres has been measured at different sarcomere lengths and in solutions of altered tonicity and Na content. 2. Conduction velocity (in m/s) in normal Ringer solution is found to be independent of sarcomere length in the range of 2‐5 microns. 3. Fibre cross‐section appears to become circular with stretch to sarcomere lengths exceeding 4 microns. The data on fibre diameter and length are in agreement with the assumption that constant fibre volume is maintained during passive length changes. 4. In Na‐deficient solutions, conduction velocity is reduced, in agreement with predictions based on action potential parameters. 5. In solutions of half or twice the normal tonicity, the conduction velocity is proportional to the square root of the measured fibre diameter. After correcting the bias involved in estimating fibre cross‐section from only one measurement of fibre diameter, the data suggest an increase in specific internal resistance (Ri) by about 8% in twice hypertonic solution and a decrease by about 5% in half normal tonicity. 6. Releasing and stretching a fibre in hypertonic solution has no effect on conduction velocity as long as the initial sarcomere length is not exceeded. Stretching the fibre beyond the sarcomere length at which it was transferred to hypertonic solution reversibly increases conduction velocity.
Role of membrane potential in the response of rat small mesenteric arteries to exogenous noradrenaline stimulation.
Authors: Mulvany M J , Nilsson H , Flatman J A
Published: December 2014

1. We have made simultaneous measurements of membrane potential and wall tension in rat 200 microns mesenteric arteries. 2. The resting membrane potential was ‐59.2 +/‐ 0.4 mV and stable (218 measurements, fifty‐two vessels). 3. With maximal exogenous noradrenaline stimulation (10 microM) the membrane depolarized to about ‐34 mV. During the onset of tension development oscillations (period about 6 sec) in both tension and membrane potential were often seen; the membrane potential changes led the tension changes by about 1.2 sec. 4. In the presence of increased K+ (e.g. 40 mM), vessels had an increased noradrenaline sensitivity, and here noradrenaline stimulation produced little change in membrane potential. 5. With maximal K+ stimulation (85 mM), in the presence of phentolamine (1 microM), the membrane depolarized to about ‐17 mV, the tension being about 70% of the maximal noradrenaline response. 6. In the presence of phentolamine (1 microM), noradrenaline caused hyperpolarization without tension development. The hyperpolarization was inhibited by propranolol and mimicked by isoprenaline. 7. The results suggest that in these small vessels membrane potential variations are not essential to, but have an important modulating influence on, the tension response to exogenous noradrenaline.
The action of puromycin and cycloheximide on the initiation of rapid axonal transport in amphibian dorsal root neurones
Authors: Nichols T. R. , Smith R. S. , Snyder R. E.
Published: December 2014

1. Amphibian dorsal root ganglia—sciatic nerve preparations were incubated in vitro and the rapid axonal transport of radioactive labels was studied with a position‐sensitive detector and by conventional liquid scintillation analysis. Protein was labelled by exposure of the ganglia to [35S]methionine or [3H]leucine and lipid was labelled using [32P]orthophosphoric acid.

2. Protein synthesis was interrupted by exposure of the ganglia to either cycloheximide or puromycin. When ganglia were exposed to either inhibitor prior to or simultaneously with a label, the somal export of both protein and lipid to the axon was reduced by two to three orders of magnitude.

3. Using the position‐sensitive detector, [35S]methionine was observed to be exported from the ninth dorsal root ganglia of Rana catesbiana 3·49±1·56 h (± S.D.) after exposure, and [32P]phosphate 4·46±1·85 h after exposure.

4. Export of [35S]methionine or [32P]phosphate was disrupted 3·32±1·21 h (± S.D.) or 1·93±1·04 h respectively after exposure of the ganglia to cycloheximide or puromycin.

5. For a given preparation the time required for [35S]methionine to be exported was statistically equal to the time required for cycloheximide or puromycin to disrupt export. No such correlation was found to exist for the export of [32P]phosphate.

6. Analysis revealed that materials labelled with either [35S]methionine or [32P]phosphate continue to be exported from the ganglia for several hours after the initial disruption in outflow caused by the inhibitors.

7. The results do not provide support for the hypothesis of Ambron, Goldman & Schwartz (1975) that a ‘key’ newly synthesized, and non‐storable, polypeptide is added to an already assembled structure to allow rapid axonal transport to be initiated.
Cholinergic transmission in cat parasympathetic ganglia.
Authors: Gallagher J P , Griffith W H , Shinnick‐Gallagher P
Published: December 2014

1. Intracellular electrical recording techniques were used to study the ionic mechanisms of cholinergic synaptic transmission in cat vesical pelvic ganglia (v.p.g.). 2. Orthodromic nerve stimulation as well as ionophoretic application of acetylcholine (ACh) resulted in, first, a fast excitatory post‐synaptic potential (f.e.p.s.p.) and secondly, a slow inhibitory post‐synaptic potential (s.i.p.s.p). These distinct post‐synaptic responses were direct actions of ACh and not mediated through an interneurone. In addition, a slow excitatory post‐synaptic potential (s.e.p.s.p.) was observed in 44% of the cells. 3. The f.e.p.s.p., mediated via nicotinic receptors, had a reversal potential of ‐10 mV and resembled the conventional rapid depolarization in other ganglia. The s.i.p.s.p., mediated by muscarinic receptors, had a reversal potential of about ‐100 mV and resulted from an increase in potassium conductance. 4. The slow muscarinic hyperpolarization could be observed in the absence of antagonists and it was elicited at stimulus frequencies in the physiological range (2‐10 Hz). the s.i.p.s.p. induced orthodromically or ionophoretically inhibited firing in spontaneously active neurones. These observations suggest that the muscarinic hyperpolarization may occur under physiological conditions and has sufficient magnitude to be inhibitory to neuronal activity.
GABA‐mediated changes in excitability of the rat lateral olfactory tract in vitro.
Authors: Cain C R , Simmonds M A
Published: December 2014

1. Conditioning stimulation of the lateral olfactory tract (l.o.t.) in the rat olfactory cortex slice evoked a slow depolarization of the terminal regions of the l.o.t. The depolarization lasted about 150 ms and was abolished by the gamma‐aminobutyric acid (GABA) antagonist bicuculline. 2. Excitability testing of the terminal regions of the l.o.t. showed an increase in excitability which lasted for about 150 ms following a conditioning stimulus. This increase in excitability was abolished by the calcium antagonist cadmium and by the GABA antagonists bicuculline and penicillin. 3. Superfused GABA caused a consistent decrease in the excitability of the terminal regions of the l.o.t. within the cortex but an increase in excitability of the axons within the tract itself. These effects were antagonized by bicuculline. K+ caused similar changes in excitability which were not antagonized by bicuculline. 4. The difference between the effects of superfused GABA and the effects of orthodromic conditioning can be explained if a more restricted location of action is assumed for the GABA released by conditioning stimulation. It is suggested that GABA causes a decrease in excitability at its locus of action and that the observed increases in excitability occur in adjacent areas of neuronal membrane.