bluuebunny/crossref_metadata_2025 huggingface dataset:
On the role of calcium in the electrical responses of cockroach salivary gland cells to dopamine.
Authors: Ginsborg B L , House C R , Mitchell M R
Published: December 2014

1. The calcium dependence of the intracellularly recorded hyperpolarizing responses of salivary gland acinar cells of Nauphoeta cinerea (Olivier) to ionophoretically applied dopamine has been examined. The results of withdrawing calcium from the bathing solution were essentially the same whether or not other divalent cations were present. The effects of calcium withdrawal were rapidly reversed on replacement of calcium. 2. Small responses to dopamine were reduced or abolished by calcium withdrawal but could be restored by an increase in the amount of ejected dopamine. Calcium withdrawal did not have any consistent effect on the input resistance: a reduction in input resistance is therefore not the main cause of the reduction in the amplitude of the responses to dopamine. 3. In very low calcium solutions responses elicited by repeated prolonged dopamine applications progressively declined. 4. It is suggested that the hyperpolarizing responses to dopamine depend on an influx of calcium into the cytosol from a store which can be replenished only from the exterior.
Tendon organ discharge during voluntary movements in cats.
Authors: Prochazka A , Wand P
Published: December 2014

1. The discharge activity of tendon organ afferents was recorded during voluntary movements in cats. 2. The eight tendon organ afferents in our sample all fired during isotonic movements involving active muscle shortening. 3. Firing rates usually exceeded 100 sec‐1, even up to the highest muscle shortening velocity observed, 1.8 resting lengths per second (lr/sec). 4. We suggest that during voluntary, isotonic movements involving muscle shortening at velocities exceeding 0.2 lr/sec, the net action of muscle afferents on homonymous motoneurones is often inhibition. 5. These observations on tendon organs, taken together with previous findings on muscle spindles, indicate that in normal fast movements the role of the large muscle afferents is to signal dynamic functions of muscle length and force.
Magnesium buffering in intact human red blood cells measured using the ionophore A23187.
Authors: Flatman P W , Lew V L
Published: December 2014

1. A method was developed for measuring the cytoplasmic magnesium buffering of intact red cells using the divalent cation selective ionophore A23187. Addition of A23187 to a suspension of red cells induces rapid equilibration of ionized magnesium across the cell membrane. 2. Entry of magnesium into red cells is associated with cell swelling and depolarization of the membrane potential. 3. At an external ionized magnesium concentration of about 0.15 mM corresponding to an internal ionized concentration of 0.4 mM the addition of A23187 did not produce a change in the magnesium content of the cells. This indicates that the normal ionized magnesium concentration inside the oxygenated red cell is about 0.4 mM. 4. The magnesium buffering curve for oxygenated, inosine‐fed human red blood cells is adequately described by the existence of three buffer systems of increasing capacity and decreasing affinity. These are 0.15 mM with a Km < 10(‐7) M, probably structural magnesium bound within the cell proteins; 1.6 mM with a Km approximately equal to 0.08 mM, mainly ATP and other nucleotides; and about 21‐25 mM with a Km approximately equal to 3.6 mM, a major portion of this being organic phosphates. It is suggested that the contribution of 2,3‐DPG to the low affinity site involves each phosphate group acting as an independent binding site for magnesium.
Morphology of spinal motoneurones mediating a cutaneous spinal reflex in the cat.
Authors: Egger M D , Freeman N C , Proshansky E
Published: December 2014

1. Intracellular injections of horseradish peroxidase were made in a functionally identified population of motoneurones in spinal cords of cats. These motoneurones were activated by tactile stimulation of the hind‐limb central foot pad. 2. Cell bodies of twenty‐two such motoneurones were located in the dorsolateral portion of the ventral horn in the first sacral segment. The mean diameter of the major axis of transverse sections through twelve of these cell bodies was 68 . 2 micrometer, the mean diameter of the minor axis was 48 . 7 micrometer. The major axis tended to be oriented dorsomedially‐ventrolaterally. 3. In the transverse plane, the dendrites had a characteristic configuration, with a prominent group of dendrites travelling from the cell body dorsomedially into the dorsal horn, entering Rexed's lamina VI. For seventeen motoneurones with well stained dendrites, the mean medial spread of the dendrites was 960 micrometer. Though the mean lateral spread was only 508 micrometer, all of these motoneurones sent dendritic projections into the lateral white matter. The mean dorsal spread of the dendrites was 693 micrometer, the mean ventral spread, 748 micrometer. In the rostrocaudal direction, the mean spread rostrally was 911 micrometer, the mean spread caudally was 998 micrometer. The maximum dendritic spread for a single motoneurone was 2,940 micrometer, in the rostro caudal direction. The sum of dendritic lengths over an entire dendritic tree for the best‐stained motoneurones exceeded 13,000 micrometer. 4. The mean diameter of the initial segment of axons of nineteen motoneurones was 4 . 3 micrometer. These axons were notable for the lack or paucity of axon collaterals. Only five of twenty‐one axons possessed collaterals; of these, only one possessed more than a single collateral system. This sparseness of the collateral system was reflected in a low level of recurrent inhibition. 5. A possible relationship is discussed between the prominent dorsomedially oriented dendritic bundles of the motoneurones and the axon collaterals of dorsal horn cells mediating cutaneous stimulation which can activate these motoneurones.
Effects of vagotomy on drinking in the rat.
Authors: Moore‐Gillon M J
Published: December 2014

1. Left or right cervical vagotomy caused elevated intakes of water after hypertonic saline, isoprenaline and polyethylene glycol compared with normal rats. In cervically vagotomized rats sodium nitrite caused a dose‐dependent water intake whereas in normal rats it produced a smaller, more variable response. The same procedure also reduced the extent to which drinking following overnight water deprivation was inhibited by plasma volume expansion. Drinking after diazoxide or in response to ligation of the abdominal inferior vena cava was not affected by cervical vagotomy. 2. The antidiuresis that followed isoprenaline treatment was greater in cervically vagotomized than normal rats; that which occurred after caval ligation was unaffected. 3. Subdiaphragmatic vagotomy did not alter water intake in response to hypertonic saline, isoprenaline or polyethylene glycol. 4. It is concluded that nerves within the supradiaphragmatic distribution of the vagi modify water intake in response to changes in the degree of vascular filling.
Innervation density of mechanoreceptive fibres supplying glabrous skin of the monkey's index finger.
Authors: Darian‐Smith I , Kenins P
Published: December 2014

1. The innervation densities of mechanoreceptive fibres supplying the ridged glabrous skin of the middle and terminal phalanges of the monkey's (Macaca nemestrina) index finger were estimated using a combination of histological and neurophysiological procedures. 2. This estimate was based on (a) a count of the total number of A beta myelinated fibres in the palmar digital nerve at the level of the proximal phalanx, (b) the demonstration that the majority of A beta fibres in the monkey's palmar digital nerve are mechanoreceptive afferents, (c) the estimation, based on a sample of 398 fibres, of the fractions of rapidly adapting, slowly adapting and Pacinian mechanoreceptive fibres in the palmar digital nerve, and (d) the estimation of the area of glabrous skin innervated by the palmar digital nerve. 3. The estimated innervation density of the finger pad and the skin of the middle phalanx were: rapidly adapting fibres, 178 and 80/cm2; slowly adapting fibres, 134 and 46/cm2; and Pacinian fibres, 13/cm2 for both phalanges.
The effect of lanthanum ions on acetylcholine in frog muscle.
Authors: Miledi R , Molenaar P C , Polak R L
Published: December 2014

1. Frog sartorius muscles were treated with an irreversible cholinesterase inhibitor and then incubated in Ringer with 2 mM‐LaCl3. The amounts of ACh in the tissue and medium were assayed by mass fragmentography, miniature end‐plate potentials (min. e.p.p.s) were recorded and the end‐plate was investigated by electron microscopy. 2. Addition of La3+ caused in normal, but not in denervated, muscles a discharge of both min. e.p.p.s and chemically detectable ACh. After 30 min both min. e.p.p.s and ACh release decreased. Between 4 and 5 hr after the addition of La3+ min. e.p.p.s had practically ceased and the rate of ACh release was almost back to that in the absence of La3+. 3. La3+ caused a 50% reduction in the ACh content of the tissue within the first 30 min; thereafter ACh gradually increased to 110% by 5 hr. At this time synaptic vesicles were practically absent in most terminals. The ACh was predominantly located in the end‐plate regions of the muscles, before as well as after the incubation with La3+. ACh in end‐plate free parts of the muscles was unchanged by La3+. 4. Hemicholinium‐3 inhibited the synthesis of ACh in the muscles, but it had almost no influence on La3+‐induced ACh release. 5. From these and other results, it is concluded that the ACh released by La3+ originates exclusively from the nerve terminals, that most likely this ACh is released via exocytosis from synaptic vesicles, and that the synthesis of ACh following the release of ACh takes place in the nerve terminals. The results further indicate that in freshly excised muscle the greater part (80‐90%) of the ACh contained in the nerve terminals is located in the vesicles.
Calcium component to action potentials in rat pars intermedia cells.
Authors: Douglas W W , Taraskevich P S
Published: December 2014

1. The ionic dependence of the action potential of rat pars intermedia cells was investigated by using intracellular recording techniques. 2. In the presence of tetrodotoxin (TTX, 5 x 10(‐6)M), the action potentials evoked by passing depolarizing current through the recording electrode were abolished, confirming that they are mainly dependent on Na; however, when tetraethylammonium (TEA, 10 mM) was added to the TTX‐containing solution the imposed depolarizations triggered all‐or‐none regenerative potentials indicative of involvement of another ion. 3. There TTX‐insensitive regenerative potentials persisted when the cells were perifused with Na‐free solution but were severely reduced or abolished by Ca‐free solution. This suggests that the ion producing these potentials is Ca. 4. These Ca action potentials were suppressed by Ni, Co and Mn in concentrations that did not suppress the "Na spikes' recorded in the absence of TTX and TEA. 5. Sr and Ba could substitute for Ca in maintaining the action potentials recorded in the presence of TTX. These ions also prolonged the duration of these action potentials. 6. The demonstration of a Ca component to the predominantly Na‐dependent action potentials of pars intermedia cells heightens the possibility that these action potentials participate in the regulation of secretion.
Neural mechanisms of spatial tactile discrimination: neural patterns evoked by braille‐like dot patterns in the monkey.
Authors: Johnson K O , Lamb G D
Published: December 2014

1. The experiments reported here were designed to investigate the responses of cutaneous mechanoreceptive afferents to spatially configured dot patterns scanned across the skin. Braille‐like patterns were selected because the discrimination of Braille characters must depend on spatial patterning rather than some other facet of the afferent discharge. 2. A multifactorial experimental design was used in which each afferent fibre was studied using every combination of six dot patterns, two dot sizes, two dot spacings, two contact forces and two scanning velocities. Two other factors, scanning direction relative to the skin ridges and intermittent versus continuous scanning, were studied. 3. Beside the general question concerning the response properties of the mechanoreceptive afferents, three major questions were addressed here. (i) What is the critical spatial dimension at which neural spatial patterning breaks down and below which tactual discrimination must depend on facets of the afferent discharge other than spatial neural patterning? (ii) Which mechanoreceptive population sets this critical dimension? (iii) Why is tactual discrimination enhanced by lateral scanning? 4. The results presented here suggest that the critical dimension, below which spatial neural patterning breaks down, is of the order of 1.0 mm and that the slowly adapting (SA) afferent fibres are responsible for this limit. 5. At dimensions above approximately 1.0 mm the spatial contrast between peaks and troughs in the SA discharge is markedly enhanced during scanning. When the skin is stationary the discharge rates in the SA population drop rapidly to low levels. A second possible reason for enhanced tactual discrimination during scanning is related to the increased spatiotemporal information in a coherent pattern of neural activity moving across a discrete population of afferent fibres. 6. The effects of variations in conduction velocity are analysed and it is shown that they place serious constraints on the transmission of spatiotemporal information.
Nervous control of the internal anal sphincter of the cat.
Authors: Bouvier M , Gonella J
Published: December 2014

1. The effects of sympathetic and parasympathetic efferent nerve stimulation on the activity of longitudinal and circular coats of th anal sphincteric area have been studied on acute animals using extracellular electrical recordings. In addition, the effect of intramural sympathetic nerves stimulation has been investigated on anal sphincteric circular muscle, with the sucrose gap technique. 2. Hypogastric nerve stimulation elicited in anal sphincteric circular muscle slow time course depolarization responses (latency 200‐400 msec) which were abolished by alpha‐adrenergic blockers (dihydroergotamine, phentolamine). 3. Stimulation of the parasympathetic outflow to the internal anal sphincter (second ventral sacral root: VS2) inhibited spontaneous electrical activity of the circular muscle. Pharmacological arguments lead to the conclusion that the inhibition induced by VS2 stimulation is mediated through intramural non‐adrenergic non‐cholinergic (purinergic) inhibitory neurones. 4. Rectal distension caused an inhibition of the anal sphincteric circular muscle activity which persisted in the presence of atropine, phentolamine and propranolol, indicating that this inhibition was produced by non‐adrenergic non‐cholinergic intramural neurones. 5. VS2 stimulation produced only an activation of the longitudinal muscle of the sphincteric area, which was abolished by hexamethonium and atropine; in contrast, hypogastric nerve stimulation gave rise to an inhibition which was blocked by propranolol. These results indicate that the longitudinal muscle receives (1) an excitatory innervation from preganglionic parasympathetic nerves connected with intramural cholinergic neurones, and (2) an inhibitory sympathetic innervation from noradrenergic axons running in the hypogastric nerves. No inhibitory no‐adrenergic non‐cholinergic innervation was observed in the longitudinal muscle in response to VS2 stimulation. 6. The results obtained from simultaneous stimulation of VS2 and hypogastric nerves indicate that in the anal sphincteric circular muscle the release of noradrenaline from sympathetic nerves is modulated by cholinergic receptors located on noradrenergic nerve endings, muscarinic receptors which can abolish the release of noradrenaline, and probably nicotinic receptors which increase the noradrenaline release. The eventual functional significance of the nicotinic receptors is discussed.
Response of soleus Ia afferents to vibration in the presence of the tonic vibration reflex in the decerebrate cat
Authors: Clark F. J. , Matthews P. B. C. , Muir R. B.
Published: December 2014

1. Micro‐electrode recordings were made from single Ia afferents in the intact nerve to the soleus muscle in the decerebrate cat while the muscle was developing a tonic vibration reflex. This was done in order to test how effectively the afferents were excited by the vibration, and to see if any insecurity in driving might be related to tremor.

2. When the amplitude of vibration was 50 μm, and the tonic vibration reflex was reasonably well developed (> 1 N of active tension) all but one of forty‐four Ia afferents were driven 1:1 by the vibration. Most were still driven by 30 μm vibration. The vibration, consisting of a train of discrete pulses at 150 Hz, was applied longitudinally in combination with a stretch of 1 mm to make the muscle taut.

3. If the reflex was poorly developed (active tension < 1 N) the driving was on average less secure. However, fourteen of eighteen afferents then studied were still driven 1:1 by 50 μm vibration. The lower level of excitation by vibration was thought to be due to a deficiency of spontaneous fusimotor activity, because stroking the cat's tail or other similar gentle manipulation led each of the three misbehaving afferents so tested to be driven securely by 50 μm vibration; at the same time the reflex tension increased.

4. Additional, indirect evidence favouring widespread security of Ia driving by 50 μm vibration in the presence of the reflex was obtained by modulating the amplitude of the 150 Hz vibration with a 7‐10 Hz square wave and detecting any tension fluctuations at that frequency by spectral analysis. Small degrees of modulation (e.g. < 10%) produced little if any effect, although larger depths of modulation had a powerful action.

5. When the amplitude of vibration was reduced to permit insecure driving but still to elicit a reflex response, the fluctuations in Ia firing pattern were unlike those previously seen in the de‐efferented muscle. Spectral analysis showed that these firing fluctuations bore a general similarity to the tremor in the same preparation, but measurement of coherence demonstrated that the tremor and Ia firing were not well related. This was probably because individual Ia afferents were primarily influenced by local factors, and provides further evidence against the tremor of this preparation being attributable to the action of the stretch reflex.
The relation between stiffness and filament overlap in stimulated frog muscle fibres.
Authors: Ford L E , Huxley A F , Simmons R M
Published: December 2014

1. Tension transients were recorded at sarcomere lengths from 2.0 to 3.2 mum in isolated fibres from the tibialis anterior muscle of frogs during tetanic stimulation at 0‐1 degrees C. 2. The length of a selected portion of the fibre was controlled by feed‐back from a spot‐follower device. The step was complete in 0.2 ms and the natural frequency of the force transducer was 10.8 kHz. 3. The transients were analysed by comparing the tension record with the output of an analogue circuit (delay line) which contained components representing (a) force transducer response, (b) fibre inertia, (c) viscosity and inertia of surrounding fluid, (d) passive stiffness and viscosity of the fibre, (e) tendon compliance and (f) stiffness and early tension recovery of the contractile apparatus. 4. In releases at different sarcomere lengths, the instantaneous stiffness and the early tension recovery attributed to the contractile apparatus varied almost exactly in proportion to the developed tension. In the later phases of the transient there were minor deviations from proportionality. 5. The results confirm that the entire transient represents events in the cross‐bridges. 6. At full overlap, the compliance attributable to the cross‐bridges is at least 80%, and probably well over 90% of the measured instantaneous compliance of the fibre. Stiffness can therefore be used as a measure of the number of attached cross‐bridges. 7. The amount of instantaneous sliding movement of thick relative to thin filaments required to bring tension in a cross‐bridge from the isometric value to zero is about 3.9 nm if filament and Z‐line compliance are negligible, as suggested by the results. It is not however excluded that filament compliance, though small, may be sufficient to reduce this figure to 3.5 nm or possibly 3.1 nm. 8. The responses to quick stretch, unlike those to release, could not be satisfactorily matched with the delay line. The deviations suggest that the instantaneous elasticity is non‐linear in stretches. 9. In resting fibres at all sarcomere lengths, the first peak of the tension response was determined chiefly by fibre inertia and viscosity, rather than elasticity.
A comparison of binocular depth mechanisms in areas 17 and 18 of the cat visual cortex
Authors: Ferster David
Published: December 2014

1. The retinal disparity sensitivity of neurones in areas 17 and 18 of the cat visual cortex was examined. The response of each cell to an optimally oriented slit was measured as disparity was varied orthogonally to the receptive field orientation. Eye movements were monitored with a binocular reference cell simultaneously recorded in area 17 (Hubel & Wiesel, 1970).

2. Two types of disparity‐sensitive cells were found, similar to those observed in the monkey by Poggio & Fischer (1977). The first type, tuned excitatory cells, were usually binocular and had a sharp peak in their disparity—response curve. They responded maximally at the disparity that brought their receptive fields into superposition on the tangent screen. This disparity closely coincided with the disparity at which the reference cell's receptive fields were also superimposed. By analogy with the monkey this point was taken to be the fixation point, or 0°. The second type, near and far cells, were most often monocular. They gave their weakest response (which was usually no response at all) at 0°. On one side of 0° the response grew linearly for up to 4° and then remained at the maximum. On the other side of zero, it remained at the minimum for up to several degrees before rising towards the maximum.

3. The receptive field organization of several disparity‐sensitive cells was examined using the activity profile method of Henry, Bishop & Coombs (1969). The size and strength of the discrete excitatory and inhibitory regions of the receptive fields of a cell could quantitatively account for the shape of its disparity—response curve.

4. The laminar distribution of disparity sensitivity as well as of several other receptive field properties in areas 17 and 18 was studied. The organization of the two areas was remarkably similar in many respects. There was a difference, however, in the proportions of the two types of disparity‐sensitive cells in the two areas. Area 17 contained many more tuned excitatory cells than near and far cells, while area 18 had the reverse distribution. In addition, the cells in area 18 were sensitive to a much broader range of disparities. While both areas contain disparity‐sensitive neurones, these differences suggest that they play different roles in depth vision.

5. Recent psychophysical and neurophysiological evidence has led to a new model of stereopsis in which depth is signalled by the pooled activity of large groups of cells (Richards, 1971). The current results are consistent with this model.
Slow calcium and potassium currents across frog muscle membrane: measurements with a vaseline‐gap technique.
Authors: Almers W , Palade P T
Published: December 2014

1. A vaseline‐gap voltage‐clamp technique was used to record slow Ca2+ and K+ currents from frog skeletal muscle fibres loaded with the Ca2+ chelator EGTA. 2. K+ currents were increased when Mg2+ replaced external Ca2+, and they were abolished when internal K+ was replaced by tetraethylammonium (TEA+). Ca2+ currents could be studied in isolation in fibres loaded with (TEA)2EGTA. 3. Under maintained depolarization, Ca2+ currents slowly increase (half‐time of 35 msec or more at 25 mV) and then decline to a steady value. Decline under repolarization is rapid (half‐time of 6‐7 msec) and complete. During an action potential, the Ca2+ influx through this system is probably less than the influx observed with tracers. 4. Ba2+, Sr2+, Ca2+, Mn2+ and Mg2+ can carry current across the membrane; Ni2+ and Co2+ cannot. Ca2+ currents are weakly blocked by external Mg2+.
Influence of agonists on desensitization of glutamate receptors on locust muscle.
Authors: Anis N A , Clark R B , Gration K A , Usherwood P N
Published: December 2014

1. The desensitization, by ionophoretically and bath‐applied L‐glutamate and agonists, of excitatory post‐junctional receptor populations on locust extensor tibiae muscle was investigated. 2. The kinetics of onset of and recovery from desensitization were determined ionophoretically either with trains of glutamate/agonist pulses of different frequencies ('conditioning trains') followed by a single ‘test’ pulse at different intervals after cessation of the conditioning train or with trains of constant frequency drug pulses superimposed upon steady ‘conditioning’ doses. Both methods gave quantitatively similar results. 3. For approximately equipotent doses, L‐glutamate and agonists produced different rates of desensitization onset. Qualitatively similar results were obtained when changes in input conductance of single muscle fibres were measured during bath application of the amino acids. 4. The time courses of recovery from desensitization for receptor populations activated by glutamate and agonists could be described adequately by single exponentials and were independent of the concentration of amino acid except when desensitization exceeded ca. 90%. 5. The rate of recovery from desensitization was different for each agonist.
Individual excitatory post‐synaptic potentials due to muscle spindle Ia afferents in cat triceps surae motoneurones.
Authors: Harrison P J , Taylor A
Published: December 2014

1. The monosynaptic projection of single Ia muscle spindle afferents to motoneurones of identified type has been examined by spike triggered averaging in barbiturate anaesthetized cats. 2. The amplitude of averaged individual monosynaptic e.p.s.p.s in medical gastrocnemius motoneurones from homonymous Ia afferents was clearly related to the motor unit mechanical properties. It was largest in type S units, intermediate in type FR and smallest in type FF. 3. The projection frequency of homonymous Ia afferents to medial gastrocnemius motoneurones followed the same order. 4. Similar trends were evident in both respects for the heteronymous projections of triceps surae. 5. The mechanical property of units which related most directly to e.p.s.p. size was muscle unit contraction strength, a single continuous relation existing throughout all three unit types. 6. On the basis of motor axon conduction velocity measurements, it appeared that motoneurone size could provide a simple explanation for e.p.s.p. size in type S and type FR units, but not in type FF. The latter had unduly small e.p.s.p.s relative to their axon conduction velocity, indicating a qualitatively different presynaptic organization for FF motoneurones from the others. 7. The data make it possible to predict that Ia afferent excitation alone would cause recruitment of units in order of increasing contraction strength and that this order would also obtain if a substantial part of the excitation came from other sources with uniform effect on all unit types. 8. It is shown that a consequence of the observed organization is that the gain of the Ia mediated stretch reflex would be approximately proportional to the developed force.
Re‐innervation of ganglia transplanted to the neck from different levels of the guinea‐pig sympathetic chain.
Authors: Purves D , Thompson W , Yip J W
Published: December 2014

Thoracic and lumbar sympathetic ganglia from donor guinea‐pigs were transplanted to the bed of an excised superior cervical ganglion in host animals. Homotopic transplants of superior cervical ganglia served as controls. In this way the same set of preganglionic axons (the cervical sympathetic trunk) was confronted with ganglia from different levels of the sympathetic chain. Re‐innervation of the transplants was studied after 3‐5 months. 1. Neurones in ganglia transplanted from different levels of the sympathetic chain were re‐innervated to about the same over‐all degree by the preganglionic axons of the host's cervical sympathetic trunk. Thus, the mean amplitude of post‐synaptic potentials, the estimated number of innervating axons, and the number of spinal segments providing innervation to each neurone were similar in transplanted thoracic, lumbar and superior cervical ganglion cells. 2. Neurones in transplanted mid‐thoracic ganglia, however, were re‐innervated more frequently, and more strongly, by axons arising from more caudal thoracic segments than neurones in transplanted superior cervical ganglia. Stimulation of axons arising from the fourth thoracic spinal segment (T4), for example, elicited post‐synaptic potentials that on average were twice as large in transplanted fifth thoracic ganglion cells as in transplanted superior cervical ganglion cells; conversely, axons arising from T1 re‐innervated neurones in the superior cervical ganglion about 2‐3 times more effectively than fifth thoracic ganglion cells. This difference in the re‐innervation of the fifth thoracic and the superior cervical ganglion is in the same direction as (although less pronounced than) the normal difference in the segmental innervation of these ganglia. 3. Transplanted lumbar ganglia were also re‐innervated more effectively by relatively caudal segments compared to re‐innervated cervical ganglia, but this difference was no greater than that observed for transplanted thoracic ganglia. 4. We conclude that preganglionic axons can distinguish (or be distinguished by) ganglia derived from different levels of the sympathetic chain. Our findings are consistent with the view that ganglion cells have some permanent property that biases the innervation they receive.
Direct observations on the contacts made between Ia afferent fibres and alpha‐motoneurones in the cat's lumbosacral spinal cord.
Authors: Brown A G , Fyffe R E
Published: December 2014

1. The enzyme horseradish peroxidase was injected into identified lumbosacral alpha‐motoneurones and Group Ia afferent fibres in cats anaesthetized with chloralose and paralysed with gallamine triethiodide. Subsequent histological examination allowed the determination of (a) the extent of the motoneuronal dendritic trees, (b) the number and location of Ia synapses upon the motoneurones. 2. alpha‐motoneurones had seven to eighteen primary dendrites and each produced daughter branches up to the fourth to the sixth order. At dendritic bifurcations Rall's 3/2 Power Law was obeyed. There was little or no dendritic tapering up to about 800 micrometers from the soma. Beyond this distance, however, there was considerable tapering. 3. Horseradish peroxidase injections revealed that motoneuronal dendrites are much longer than previously thought. Individual dendrites could be traced for up to 1600 micrometers from the soma and dendritic trees were usually 2‐3 mm from tip to tip. Nearly all the motoneurones had dendrites that entered the white matter of the cord. Dendrites could also reach as far dorsally as laminae V and VI. 4. Ia synapses upon motoneuronal somata were examined in cords counterstained with cresyl violet or methylene green. About 10% of Ia boutons in lamina IX were on somata and each Ia collateral terminated on 3.66 motoneuronal somata or the most proximal (30 micrometer) dendrites, with on average about two contacts per motoneurone. 5. Ten Ia afferent fibre‐motoneurone pairs were injected with horseradish peroxidase. The following conclusions were drawn: (i) only one collateral of any given Ia axon makes contact with a motoneurone even though other collaterals from the same axon might pass through the dendritic tree, (ii) usually all contacts made between a Ia fibre and a motoneurone are at about the same geometrical distance from the soma, even when on different dendrites, (iii) between two and five contacts are made upon the dendritic tree (average 3.4) at distances of between 20 and 820 micrometers from the soma. 6. The results are discussed in relation to previous anatomical and electrophysiological work.
The effects of heart rate on the action potential of guinea‐pig and human ventricular muscle.
Authors: Attwell D , Cohen I , Eisner D A
Published: December 2014

1. On increasing the stimulation frequency of isolated pieces of guinea‐pig ventricular muscle, the resting potential depolarizes, and the action potential duration and amplitude are reduced. On termination of the high frequency train of action potentials, these changes are reversed. 2. The resting potential changes are roughly exponential, with a time constant of the order of 10 sec, and are attributable to K+ accumulation in the extracellular space. They are not explicable in terms of known gating variables. 3. The action potential duration and amplitude recover much more slowly than the resting potential, after a high frequency train (half‐time approximately 5 min). The time course of these recoveries is not exponential, and is slower after trains which produce more shortening of the action potential. The slow time course suggests that K+ accumulation is not the main cause of the changes in action potential shape. Furthermore, when a certain depolarization of the resting potential is produced by a high frequency train, there is a greater reduction of the action potential duration than that which occurs when the bathing [K+] is raised to produce the same depolarization (Reiter & Stickel, 1968). This is so even when a gradient of extracellular [K+] is induced in the preparation, to mimic non‐uniform K+ accumulation. 4. Similarly, the shortening of the action potential produced by toxic doses or cardiotonic steroids is probably not the result of K+ accumulation. 5. The slow changes of the action potential shape produced by a high frequency train are not attributable to the effects of gating variables, nor (solely) to a rise in the intracellular Na concentration stimulating the electrogenic Na/K pump. The dye 3,3'‐diethylthiadicarbocyanine, which blocks the Ca2+‐activated K conductance in the erythrocyte, has no significant effect on the shape changes. 6. After a sudden change in heart rate, the QT interval of the human electrocardiogram (e.c.g.) changes slowly to a new equilibrium value. The time course of this change is similar to that of the action potential duration in guinea‐pig ventricle following a change in stimulation frequency. These changes of the e.c.g. are probably not due to slow alterations of neural or hormonal factors extrinsic to the heart. In the whole heart, the effects on the ventricular action potential duration of changes in sympathetic or vagal tone, or of circulating catecholamines, can be largely accounted for by the changes of atrial driving frequency they produce.
Neuromuscular junctions and alpha‐bungarotoxin‐binding sites in denervated and contralateral cat skeletal muscles.
Authors: Steinbach J H
Published: December 2014

1. The distributions of cholinesterase (ChE) activity and acetylcholine (ACh) receptors were studied in normal and denervated cat hind‐limb fast‐twitch skeletal muscles and in muscles contralateral to denervated muscles. 2. On normal muscle fibres almost all receptors were confined to the immediately post‐junctional membrane, although a perijunctional gradient of increased ACh receptor density was found on both fast‐ and slow‐twitch fibres. After denervation, the extrajunctional ACh receptor density increased greatly and remained high for at least 10 months. Ectopic regions staining for ChE activity and having a high density of ACh receptors appeared in denervated muscle. The number of junctional ACh receptors decreased slowly after denervation, with a half‐time of about 140 days. 3. Fast‐twitch muscles contralateral to denervated muscles also showed changes, including an increase in junctional size and a small but significant increase in extra‐junctional ACh receptor density.
Pancreatic endocrine responses to exogenous neurotensin in the conscious calf.
Authors: Blackburn A M , Bloom S R , Edwards A V
Published: December 2014

1. Responses to neurotensin have been investigated in conscious calves 2‐5 weeks after birth given continuous I.V. infusions of the peptide for 15 min (5 pmol. kg‐1 . min‐1). 2. In control calves the concentration of the peptide in the arterial plasma had risen by 160 +/‐ 10 pmol/l at the end of the infusion,. after which it fell exponentially (t1/2: 1.4 min). 3. This dose of neurotensin produced no significant change in mean heart rate, aortic blood pressure, plasma gastrin or glucose concentration. 4. It was found that neurotensin could produce a pronounced rise in the concentration of both insulin and pancreatic polypeptide (PP) in the arterial plasma, together with a much smaller rise in pancreatic glucagon concentration. 5. Each of these three pancreatic endocrine responses was found to be glucose‐sensitive within the range ca. 5.0‐9.0 mmol/l. Hyperglycaemia potentiated insulin release and inhibited release of PP and glucagon. 6. The results are discussed in relation to the findings of other workers in other species.
The effects of stimulation of autonomic nerves on carotid body blood flow in the cat.
Authors: Acker H , O'Regan R G
Published: December 2014

1. The effects of electrical stimulation of the distal ends of cut preganglionic cervical sympathetic trunks and cut sinus nerves on carotid body total blood flow, local blood flow and tissue PO2 (Pt,O2) were studied in anaesthetized cats. 2. Sympathetic stimulation caused reductions, often marked, of the total blood flow through the carotid body, yet did not influence local flow or Pt,O2 recorded by electrodes whose tips lay in deep locations within the carotid body. Intraglomeral electrodes did respond to reductions of perfusion pressure and to perfusions of the carotid body with saline solutions. 3. Values of Pt,O2 recorded from superficial tissues of the carotid body were higher than those from deeper locations and were increased by blowing oxygen over the surface of the organ. In these locations, sympathetic stimulation increased Pt,O2. 4. An increase in the frequency of sinus nerve chemosensory discharges during sympathetic stimulation was obtained in the presence of an unchanged Pt,O2 recorded from deep glomeral locations. 5. Stimulation of the distal end of the sinus nerve increased the total blood flow through the carotid body but did not affect local flow or Pt,O2 recorded from deep glomeral locations. 6. It is concluded that autonomic nerves supplying the carotid body mainly influence arteriovenous anastomotic and/or other shunt vessels, with little control being exerted on vessels regulating the flow through the capillary network of the specific tissue. This investigation also indicates that the flow in the capillary network of the specific tissue is a small proportion of the total flow. Support is given to the view that autonomic nerves can influence chemoreceptor activity by non‐vascular mechanisms.
Some physical and chemical properties of the smooth muscle inhibitory factor in extracts of the bovine retractor penis muscle.
Authors: Gillespie J S , Hunter J C , Martin W
Published: December 2014

1. A method of extracting and partially purifying a smooth muscle inhibitory factor from the bovine retractor penis is described. This consists of extraction in methanol followed by adsorption on an anion exchange resin, elution from the resin with 500 mM‐sodium chloride solution and, if necessary, removal of adenine nucleotides by adsorption on alumina. 2. The inhibitory factor exists in a stable pharmacologically inactive form and an unstable pharmacologically active form. Conversion to the active form is by a brief exposure to acid at pH 2.0. 3. The inhibitory factor is insoluble in ether or acetone but soluble in methanol. Anhydrous methanol, however, irreversibly destroys pharmacological activity especially if the inhibitory factor is in the active form. This effect of methanol is prevented by the presence of 20‐30‐% water. 4. The inhibitory factor binds to an anion exchange resin but not to a cation exchange resin. It can be eluted from the resin by 500 mM‐sodium chloride solution. 5. The molecular weight of the inhibitory factor, as judged by the ability to pass ultrafiltration membranes, is about 500. 6. Inhibitory activity is unaffected by the proteases trypsin, subtilisin or pepsin or by leucine aminopeptidase, pyroglutamate aminopeptidase or carboxypeptidase. The inhibitory effect of the extract and the inhibitory response to stimulation of the non‐adrenergic, non‐cholinergic nerves are also unaffected by the protease inhibitor, aprotinin. The active material, therefore, is unlikely to be a peptide. 7. Inhibitory activity is abolished by exposure of the extracts to periodic acid or sodium periodate. Acetic anhydride in pyridine also abolishes activity but the vehicle pyridine is also effective. 8. Sodium borohydride but not borate abolishes inhibitory activity when added to the acid‐activated material at pH 2.0 but has no effect or may even potentiate activity if added to the stable inactive form at pH 9.0. When added to the acid‐activated but neutralized material at pH 6.8 it usually abolishes inhibitory activity but occasionally has no effect. 9. These results suggest the smooth muscle inhibitory factor in these extracts is potent and probably novel. It does not appear to be a peptide or a lipid but may contain a carbohydrate as part of the molecule. Its possible physiological role is discussed.
Inspiratory inhibition of vagal responses to baroreceptor and chemoreceptor stimuli in the dog.
Authors: Potter E K
Published: December 2014

1. Single and few‐fibre cardiac efferent filaments were dissected from the cervical vagus nerve of dogs anaesthetized with chloralose and paralysed with pancuronium. 2. Brief selective baroreceptor or chemoreceptor stimuli, given during the expiratory phase of the central respiratory cycle and while the lungs were motionless, evoked trains of action potentials in cardiac vagal efferent fibres. These vagal responses outlasted the duration of the stimuli by 1‐3 s. 3. Brief selective baroreceptor or chemoreceptor stimuli given during the inspiratory phase of the central respiratory cycle (monitored as phrenic discharge) but while the lungs were motionless, failed to evoke reflex increases in discharge. Background vagal discharge was also inhibited during central inspiratory activity. 4. Brief baroreceptor or chemoreceptor stimuli given during lung inflation but in the expiratory phase of the central respiratory cycle (phrenic silence), also failed to evoke any reflex increase in discharge, but left resting vagal tone relatively unaffected. Only when vagal tone was high was it markedly inhibited by lung inflation, in the absence of central inspiratory activity. 5. A point of contrast between the inhibitory effects of lung inflation and of central inspiratory activity is that both tonic and reflexly evoked vagal discharge are inhibited during central inspiratory activity, but lung inflation more markedly inhibits reflexly evoked vagal discharge than tonic vagal discharge. 6. A model is suggested to explain the different mechanisms of inhibition by lung inflation and by central inspiratory activity.
Developmental changes in epithelial transport characteristics of preimplantation rabbit blastocysts.
Authors: Benos D J
Published: December 2014

1. Transepithelial sucrose and urea permeability coefficients were measured in different‐aged preimplantation rabbit blastocysts. Sucrose permeability remained constant from 4 to 6 days after fertilization (approximately 1 X 10(‐8) cm s‐1), but thereafter increased. Urea permeability was very low throughout this period (5 X 10(‐7) cm s‐1) but a phloretin‐sensitive component to urea influx appeared between day 6 and day 7 post coitum (p.c.). 2. Glucose uptake was small (0.2‐0.5 nmol cm‐2 s‐1 and independent of external sodium throughout the preimplantation period. 3. Methionine uptake was 10 times greater than glucose uptake, and was strongly dependent upon the presence of external sodium in 5 and 6 day p.c. blastocysts. The sodium dependence of methionine uptake was lost by the seventh day after fertilization. 4. The transepithelial electrical resistance was always less than 35 omega cm2 in 4 day p.c. blastocysts, and averaged 1758 omega cm2 in 6 day p.c. blastocysts. 5. The transepithelial influx of 140 La averaged 0.46 +/‐ 0.11 nmol cm‐2 h‐1 (n = 6) in 4 day p.c. blastocysts. The 5 day p.c. embryos, on the other hand were impermeable to lanthanum (n = 10). 6. These results indicate that the epithelium of the preimplantation rabbit blastocyst undergoes dramatic changes in transport characteristics with development. The blastocyst can be characterized as a ‘leaky’ transporting epithelium during the early blastocyst period, and as a ‘tight’ epithelium during the mid to late stages of the preimplantation period.
Calcium‐activated force responses in fast‐ and slow‐twitch skinned muscle fibres of the rat at different temperatures.
Authors: Stephenson D G , Williams D A
Published: December 2014

1. Force responses from mechanically skinned fibres of rat skeletal muscles (extensor digitorum longus and soleus) were measured at different temperatures in the range 3‐35 degrees C following sudden changes in Ca2+ concentration in the preparations. 2. At all temperatures there were characteristic differences between the slow‐ and fast‐twitch muscle fibres with respect to the relative steady‐state force‐[Ca2+] relation: such as a lower [Ca2+] threshold for activation and a less steep force‐pCa curve in slow‐twitch muscle fibres. 3. At 3‐5 degrees C the force changes in both types of muscle fibres lagged considerably behind the estimated changes in [Ca2+] within the preparations and this enabled us to perform a comparative analysis of the Ca2+ kinetics in the process of force development in both muscle fibre types. This analysis suggest that two and six Ca2+ ions are involved in the regulatory unit for contraction of slow‐ and fast‐twitch muscle fibres respectively. 4. The rate of relaxation following a sudden decrease in [Ca2+] was much lower in the slow‐twitch than in the fast‐twitch muscle at 5 degrees C, suggesting that properties of the contractile apparatus could play an essential role in determining the rate of relaxation in vivo. 5. There was substantial variation in Ca2+ sensitivity between muscle fibres of the same type from different animals at each temperature. However the steepness of the force‐[Ca2+] relation was essentially the same for all fibres of the same type. 6. A change in temperature from 5 to 25 degrees C had a statistically significant effect on the sensitivity of the fast‐twitch muscle fibres, rendering them less sensitive to Ca2+ by a factor of 2. However a further increase in temperature from 25 to 35 degrees C did not have any statistically significant effect on the force‐[Ca2+] relation in fast‐twitch muscle fibres. 7. The effect of temperature on the Ca2+ sensitivity of slow‐twitch muscle fibres was not statistically significant, mainly because of the large variation in sensitivity amongst these preparations at room temperature. 8. Two types of oscillatory processes not associated with intracellular membranes were observed in the force response of all slow‐twitch muscle fibres when submaximally activated (less than 60% maximum force) at 25 and 35 degrees C, but never at 3‐5 degrees C. The frequency of oscillations increased with temperature. 9. Maximum Ca2+‐activated force in both muscle fibre types was greatly dependent upon temperature over the range 0‐25 degrees C, but increased only slightly above 25 degrees C. 10. Experiments on the rigor state suggest that the number of possible actomyosin interacting sites diminishes considerably as temperature is decreased below 25 degrees C.