bluuebunny/crossref_metadata_2025 huggingface dataset:
The effects of vasoactive intestinal peptide on neuromuscular transmission in the frog
Authors: Gold Michael R.
Published: December 2014

1. The effects of vasoactive intestinal peptide (VIP) on cholinergic transmission were studied at the neuromuscular junction of the frog.

2. Bath application of VIP (10−8‐10−7 M) produced a dose‐dependent increase in quantal content of the end‐plate potential (e.p.p.), while having no effect on quantal size or on resting membrane potential of the muscle fibres.

3. The increases in e.p.p. amplitude observed at end‐plates blocked with Mg2+ or curare were comparable.

4. VIP increased miniature end‐plate potential frequency when the nerve terminal was depolarized with K+. This effect was abolished by removing Ca2+ from the bathing solution.

5. Ionophoretic application of VIP to the end‐plate also increased quantal content, while having no effect on quantal size or on the input resistance and resting membrane potential of the fibres.

6. Some possible mechanisms for the action of VIP are discussed, and it is proposed that it may act on some step involved in depolarization—secretion coupling.
Asynchronous respiratory activity of the diaphragm during spontaneous breathing in the lamb
Authors: Henderson‐Smart D. J. , Johnson P. , McClelland Mary E.
Published: December 2014

1. Direct simultaneous recordings from chronically implanted electrodes in different parts of the diaphragm were made in young lambs in which laryngeal adductor (thyroarytenoideus) and intercostal electromyograms, airflow, tracheal pressure and electrocorticogram and electro‐oculograms for behavioural state were also recorded.

2. An asynchrony of diaphragmatic contraction occurred which was dependent on sleep state. The vertebral portion showed maximal post‐inspiratory activity while the lateral paratendinous portion usually terminated abruptly with end‐inspiration, reciprocating closely with the onset of expiratory laryngeal adductor activity during quiet sleep. The contraction of the sternal portion was similar to the vertebral portion. In active (rapid eye movement) sleep there was no expiratory laryngeal constriction and post‐inspiratory activity occurred in all portions of the diaphragm. During the characteristic bursts of rapid breathing in active sleep all post‐inspiratory activity disappeared and the diaphragm contracted synchronously.

3. General anaesthesia (Halothane/N2O or Nembutal) abolished expiratory laryngeal adductor activity and the discharge pattern became similar in all parts of the diaphragm.

4. Intrathoracic vagotomy of Xylocaine blockade below the recurrent laryngeal nerves abolished post‐inspiratory activity in all parts of the diaphragm, in contrast to the effect on expiratory laryngeal adductor activity which increased.

5. Sustained ‘tonic’ electromyographic activity was often recorded from the costal and to a lesser extent the paratendinous portion of the diaphragm. This activity related to adjacent intercostal activity:ipsilateral intercostal blockade with local anaesthetic (Xylocaine 1%) abolished both the intercostal and the ‘tonic’ activity of the costal margins of the diaphragm. Conversely ipsilateral phrenic nerve blockade abolished all but the ‘tonic’ activity which related to intercostal activity.

6. Interpretation of the respiratory activity of the diaphragm could not be made adequately from conventionally placed electrodes (i.e. costal, sternal slip or surface) during spontaneous breathing in unanaesthetized lambs. Simultaneous recordings showed that while expiratory flow and duration were actively controlled by expiratory laryngeal adductor activity and the diaphragm, the latter performed asynchronously. While both laryngeal and diaphragmatic expiratory functions were substantially under vagal control, the former increased and the latter decreased with reduced vagal input.
Accurate repositioning of the human thumb against unpredictable dynamic loads is dependent upon peripheral feed‐back
Authors: Day B. L. , Marsden C. D.
Published: December 2014

1. The strategy of accurate movement of the human thumb has been studied in nine subjects. An open‐loop hypothesis, which states that a new final position is defined by re‐setting the agonist/antagonist spring constants, was tested

2. Subjects were trained to flex the top joint of the thumb rapidly through 20 deg in about a third of a second from a fixed starting position against a load. Occasionally, and unpredictably, the viscous friction of the load was altered prior to it's being moved. The spring hypothesis predicts that such a change in load should have no effect on final position accuracy.

3. Under normal conditions no final position error developed when the viscous friction was increased. A small overshoot occurred when the viscous friction was decreased.

4. The electromyogram recorded from surface electrodes over the belly of flexor pollicis longus in the forearm revealed an increase in activity in response to an increase in viscous friction and a decrease in activity when the viscous friction was reduced.

5. When the joint and cutaneous afferents from the thumb were anaesthetized, the e.m.g. response to a change in viscous friction was severely attenuated and consistent final position errors developed.

6. Even though the compensatory open‐loop muscle properties went some way towards maintaining accuracy, the change in final position error that occurred as a result of thumb anaesthesia correlated well (r = 0·84) with the amount of muscle e.m.g. response that was lost.

7. The latency of the e.m.g. response to a change in viscous friction was compared to that of a voluntary response by asking the subject to push down or let go upon perception of the load change. Approximately the first 100 ms of the e.m.g. response was unaffected by the voluntary intervention of the subject.

8. We conclude that the spring hypothesis does not explain human thumb movement. It is argued that the long‐latency stretch reflex machinery is responsible for some automatic compensation for unexpected interference with movement.
Difference in kinetics between the distal and proximal parts of the canine parietal cell mass in response to pentagastrin.
Authors: Larsson J O
Published: December 2014

1. Dogs were provided with one denervated gastric pouch in the distal and another of equal size in the proximal part of the corpus fundus. Dose‐response curves for pentagastrin were determined for acid output and mucosal blood flow, which was measured with the Neutral Red technique. 2. Maximum acid output was significantly higher for the distal (mean 165.4 mumol min‐1) than for the proximal pouch (53.8 mumol). ED50 for acid output was significantly higher for the proximal (5.10 micrograms kg‐1 h‐1 of pentagastrin) than for the distal pouch (1.98 micrograms). 3. ED50 for blood flow did not differ significantly between the distal (0.48 microgram) and the proximal pouch (1.23 micrograms). For both pouches ED50 for blood flow was significantly lower than that for simultaneous acid output. This indicated that the rise in blood flow precedes that of acid output. 4. Regression analysis indicated similar ratios between maximum mucosal blood flow and maximum acid output for the distal (0.17 ml mumol‐1) and the proximal (0.14 ml mumol‐1)pouch. 5. The difference in maximum acid output between the two pouches correlates well with the known difference between distal and proximal parts in volume fraction of the parietal cells, while there is no valid explanation for the difference in ED50 for acid output. It can be excluded that these differences in acid production depend on dissimilarities in mucosal blood flow.
Block of some non‐adrenergic inhibitory responses of smooth muscle by a substance from haemolysed erythrocytes
Authors: Bowman Anne , Gillespie J. S.
Published: December 2014

1. A preparation of haemolysed rat erythrocytes (the haemolysate) blocked the relaxations of both the bovine retractor penis and the rat anococcygeus muscles in response to field stimulation of their non‐adrenergic inhibitory nerves. The effective concentration range was 5‐20 μl./ml. of haemolysate, equivalent to 0·25‐1·0 μl./ml. of blood. The active principle in the haemolysate was a non‐dialysable, heat‐labile material of molecular weight between 50,000 and 100,000 daltons. If, as appeared probable, the active component of the haemolysate was oxyhaemoglobin, its effective blocking concentration was 0·5‐2 μM.

2. Haemolysate (5‐20 μl./ml.) also blocked the relaxation of both the bovine retractor penis and the rat anococcygeus to the inhibitory factor extracted from the bovine retractor penis, an observation supporting the possibility that this inhibitory factor may be the transmitter released by the inhibitory nerves in these tissues. In the bovine retractor penis, haemolysate was also effective in blocking relaxations in response to sodium nitroprusside, but relaxations produced by prostaglandin E1 or isobutylmethylxanthine were unchanged or only slightly reduced.

3. In contrast, in the taenia of the guinea‐pig caecum, haemolysate did not block the non‐adrenergic inhibitory response to field stimulation, nor the relaxation produced by ATP, although it did block the relaxation produced by the inhibitory factor.

4. In spiral strips of isolated rabbit aorta, haemolysate (10 μl./ml.) increased the contraction produced by noradrenaline and blocked the relaxation produced by the inhibitory factor. These were shown to be independent effects.

5. Apamin, which blocked the relaxation of the taenia of the guinea‐pig caecum elicited by either ATP or field stimulation of its non‐adrenergic nerves, was without effect on relaxations of the bovine retractor penis or rat anococcygeus muscles in response to field stimulation of inhibitory nerves or to inhibitory factor.

6. These differences in the blocking effects of apamin and haemolysate suggest either that the transmitter in the bovine retractor penis and rat anococcygeus differs from that in the guinea‐pig taenia, or, if the transmitter is the same, then its mechanism of action differs.
Neural encoding of input transients investigated by intracellular injection of ramp currents in cat α‐motoneurones
Authors: Baldissera F. , Campadelli Paola , Piccinelli L.
Published: December 2014

1. Input—output relations were analysed in spinal α‐motoneurones during current transients reaching a steady level after a linear growth of different slopes. The motoneurone output considered in the analysis was the instantaneous frequency of the cell discharge.

2. In all motoneurones firing frequency during the ramp exceeded that of the final steady level and it was related to the velocity of rise of the current. In the majority of motoneurones the instantaneous frequency grew during the ramp stimulus, as if it were dependent on current intensity as well as on its rate of rise. Only in a few cells was firing frequency constant over the first two interspike intervals during the ramp, as would be expected if this response depended solely on the rate of rise.

3. Frequency—velocity (f/v) plots for different rates of rise of the injected current showed a linear relation for each interspike interval. Presence or absence of an intensity component was revealed in these plots by divergence or, respectively, overlapping of the f/v relations for the first and second intervals. Divergence was eliminated by subtraction of the estimated intensity component. The slope of the f/v relation for the first interval did not change significantly after subtraction of the intensity component and was taken as an index of the dynamic sensitivity of the motoneurones. The slope of the f/v relation varied greatly (from 47 to 330 impulses s−1. (nA ms−1)−1) in the population examined and was higher in motoneurones with a long‐lasting afterhyperpolarization (a.h.p.) than in those where it was short‐lasting.

4. It is proposed that the ability of the motoneurones to encode both the steady level and the rate of change of input signals depends on the conductance changes responsible for the a.h.p. and their accumulation. A positive correlation was found between the size of the a.h.p. potassium current, estimated as a.h.p. peak voltage/cell input resistance, and the slope of the f/v relation for the first interval.
Activity‐induced potassium accumulation and its uptake in frog ventricular muscle.
Authors: Martin G , Morad M
Published: December 2014

1. Extracellular K+ activity in frog ventricular muscle was monitored with a K+‐selective micro‐electrode during and following periods of rapid stimulation. 2. During activity K+ accumulated in the paracellular space, declined with continued beating and became depleted below bathing K+ concentrations, [K+], when activity was terminated. 3. The re‐uptake and depletion of K+ was inhibited by ouabain, Li+ and lowering bathing [K+], and was enhanced by prolonged stimulation, raising bathing [K+], and by addition of adrenaline. These ionic and drug dependencies of the K+ re‐uptake process are similar to the ionic and drug dependencies of the Na+‐K+‐ATPase system. 4. Frequency‐induced K+ accumulation appears to result from a delay in the activation of the Na+ pump. 5. Possible changes in intracellular sodium concentration, [Na+]i, in the response to changes in frequency, appear to be a more powerful stimulant of the K+ re‐uptake process than changes in extracellular potassium concentration, [K+]o. 6. Frequency‐induced changes in [K+]o were also detected by measurements of resting potential. Alterations in membrane potential and action potential duration observed during and following electrical stimulation are suggestive of an electrogenic K+ re‐uptake process. 7. Aside from their direct effects on the action potential, Ca2+ and Mg2+ had little or no effect on Na+ pump activity. While Ni2+ suppressed pump activity, Ba2+ indirectly enhanced the K+ uptake process by blocking the resting K+ conductance. 8. K+ uptake rate was estimated to range between 3 and 8 p‐mole/cm2.sec. Since diffusion in and out of the paracellular space was a much slower process (t1/2 60‐90 sec), it contributes little to the beat‐to‐beat control of paracellular [K+].
Effects of ATP or phosphate on passive rubidium fluxes mediated by Na‐K‐ATPase reconstituted into phospholipid vesicles
Authors: Karlish S. J. D. , Stein W. D.
Published: December 2014

1. The passive Rb fluxes mediated by the Na—K pump in reconstituted vesicles, described by Karlish & Stein (1982), are affected by ATP or by phosphate acting separately.

2. Rb—Rb exchange through inside‐out pumps is stimulated by ATP at low concentrations and is inhibited at high concentrations. There are mutual effects of Rb at cytoplasmic sites and ATP. The higher is the Rb concentration, the greater is the degree of stimulation and the less is the inhibition of exchange by ATP, and the higher are the concentrations of ATP required to produce effects. ATP stimulates Rb—Rb exchange maximally by about 5‐fold.

3. There are similar effects of ATP on zero‐trans net Rb uptake through inside‐out pumps. However, much lower degrees of stimulation and greater inhibition of the net flux by ATP are observed, and much lower concentrations of ATP are required for these effects, by comparison with those on Rb—Rb exchange.

4. Rb uptake on inside‐out pumps in Na‐loaded vesicles shows only inhibition by ATP.

5. Phosphate effects require the presence of Mg0 ions. At low Mg0 concentrations (up to 100 μM) phosphate moderately stimulates Rb uptake into Rb‐free or Rb‐loaded vesicles (about 50%), but has no effect on Rb uptake into Na‐loaded vesicles. At millimolar concentrations of Mg0 ions, phosphate strongly inhibits the Rb uptake into Rb‐free or Na‐loaded vesicles but has no effect on Rb uptake into Rb‐loaded vesicles.

6. The separate effects of ATP and of phosphate are explained in terms of the model proposed by Karlish & Stein (1982), modified to take into account stimulation of the conformational transition E2(Rb)occ → E1 Rb by ATP, and stimulation of the conformational transition E2(Rb)occ → E2 Rb by phosphate due to phosphorylation of the protein.
Pressure‐volume relationships above and below atmospheric pressure in the synovial cavity of the rabbit knee.
Authors: Knight A D , Levick J R
Published: December 2014

1. The pressure‐volume relationship in the synovial cavity of the rabbit knee was investigated by the infusion of a non‐absorbable oil into the cavity. 2. The pressure (P)‐volume (V) curve was sigmoid. Its slope dP/dV (elastance) was steep at subatmospheric, physiological pressures, least steep at 5 cm H2O, and steepened progressively at higher, pathological pressures. 3. Elastance dP/dV was a good approximation to linear functions of P below atmospheric pressure and above 5 cm H2O. Each part of the pressure‐volume relationship could therefore be described by an exponential expression. 4. Flexion of the joint increased pressure at a given volume. This was mainly due to steepening of the pressure‐volume curve, and also partly due to a shift towards the pressure axis. 5. Pressure‐volume curves determined by the infusion of normal saline or Krebs solution were grossly distorted, because these fluids were absorbed across the permeable synovium. 6. The physiological significance of the synovial pressure‐volume curve is discussed, and mechanical explanations of the curve are suggested.
Spontaneous and evoked excitatory junction potentials in rat tail arteries.
Authors: Cheung D W
Published: December 2014

1. The frequency, amplitude and time course of spontaneous excitatory junction potentials (s.e.j.p.s) and their relationship to the time course and amplitude of evoked excitatory junction potentials (e.j.p.s) were examined. 2. The frequency and amplitude of s.e.j.p.s varied dramatically between cells. There was good correlation between their rise and decay times. 3. The amplitude and time course of e.j.p.s also varied between cells. E.j.p.s with large amplitudes and fast time courses were recorded in cells with high s.e.j.p. frequencies. 4. Active responses propagated only for very limited distances. 5. The frequency of s.e.j.p.s decreased after reserpine and 6‐hydroxydopamine (6‐OHDA) treatments, suggesting that s.e.j.p.s were related to spontaneous release of noradrenaline from nerve terminals.
On the nature of histamine‐mediated slow hyperpolarizing synaptic potentials in identified molluscan neurones
Authors: McCaman R. E. , Weinreich D.
Published: December 2014

1. Standard intracellular stimulating and recording techniques were used to test the correspondence between monosynaptic post‐synaptic potentials (p.s.p.s) evoked by histamine‐containing C‐2 neurones and responses to focally applied histamine recorded from two classes of identified post‐synaptic neurones in the cerebral ganglion of Aplysia californica.

2. Two types of p.s.p.s were examined: (1) a monophasic slow hyperpolarizing potential (Isp.s.p.) lasting 1‐2 sec; and (2) a biphasic p.s.p. consisting of a fast depolarizing component <0·5 sec in duration (Efp.s.p.) plus a slow hyperpolarizing potential (Isp.s.p.) designated the EfIsp.s.p.

3. Ionophoretic or pressure applied histamine mimicked both p.s.p.s and produced conductance increases in the post‐synaptic neurones similar to those associated with the evoked p.s.p.s.

4. The reversal potentials (Erev) for the Isp.s.p. and EfIsp.s.p., estimated by extrapolation, were ‐85±5·3, ‐35±5·5, and ‐83±8·1 mV (mean±S.D.), respectively. The Isp.s.p.s were produced by an increase in potassium conductance because their Erevs were shifted about 16 mV by doubling or halving the concentration of extracellular potassium and they could be eliminated by cooling or by intracellular injection of TEA ions.

5. The average Erev values for the slow hyperpolarizing histamine responses were similar to those for the Isp.s.p.s; about ‐83 and ‐86 mV in neurones receiving the monophasic Isp.s.p.s and biphasic EfIsp.s.p., respectively.

6. Cimetidine, an antihistamine drug that selectively blocks histamine receptors associated with potassium conductances in Aplysia, reversibly abolished the Isp.s.p.s and slow hyperpolarizing responses to focally applied histamine. In similar concentrations, cimetidine had no discernible effects on the Efp.s.p. and depolarizing response to histamine or on several different types of p.s.p.s mediated by the C‐2 neurones.

7. It is proposed that the Isp.s.p.s are mediated by histamine released from the C‐2 neurones.
Control of evaporative heat loss during changes in plasma osmolality in the cat
Authors: Baker M. A. , Doris P. A.
Published: December 2014

1. The effects of intravenous infusion of hypertonic saline and distilled water into normally hydrated and dehydrated cats have been examined at both high and neutral ambient temperatures.

2. In hydrated cats measurements of body temperature (Tb) and evaporative heat loss (e.h.l.) show that infusion of 30% saline (1·5 ml./kg) at an ambient temperature of 38 °C, lowers e.h.l. by an average of 0·21 W/kg (P < 0·001) and elevates Tb by 0·43 °C (P < 0·01).

3. At 25 °C alterations in these two parameters were in the same direction, though not statistically different from pre‐infusion levels (P > 0·05).

4. Infusion of distilled water (15 ml./kg) into dehydrated animals produced significant increases in e.h.l. (+0·35 W/kg, P < 0·001) and reductions in Tb (‐0·45°C, P < 0·001) at 38 °C. No significant effects were observed at 25 °C.

5. Infusion of water into normally hydrated animals at 38 °C also significantly increased e.h.l. (+0·13 W/kg, P < 0·05) and insignificantly lowered Tb (‐0·03 °C, P > 0·05).

6. Local heating of the preoptic hypothalamic area in four animals indicated that hypertonic saline infusion into normally hydrated animals caused a reduction in the slope and displacement to the right of the relationship between hypothalamic temperature and e.h.l.

7. Conversely, water infusion into dehydrated animals increased the slope and shifted this relationship to the left.

8. These experiments provide evidence for an osmotic interaction in body temperature regulation which acts to alter the responsiveness of the hypothalamus to increasing temperature. This osmotic component may be an important factor in the alterations in thermoregulation seen in dehydrated animals.
Effects of calcium and strontium in the process of acetylcholine release from motor nerve endings
Authors: Mellow A. M. , Perry B. D. , Silinsky E. M.
Published: December 2014

1. The effects of Ca and Sr ions on synchronous acetyleholine (ACh) secretion (the impulsive, physiologically functional form of secretion which produces an end‐plate potential in response to a single nerve impulse) and on asynchronous ACh secretion (the delayed, residual increase in miniature end‐plate potential frequency evoked by repetitive nerve impulses or by accumulation of intracellular divalent cations) were studied at frog neuromuscular junctions.

2. In a comparison of their extracellular effects, Ca was far more effective than Sr in supporting synchronous ACh secretion but less effective than Sr in mediating asynchronous release evoked by repetitive nerve impulses.

3. In studies of their intracellular effects, Sr and Ca were delivered to the nerve terminal cytoplasm using liposomes as a vehicle. Ca‐containing liposomes, although producing effects on asynchronous ACh secretion that were indistinguishable from those of equimolar Sr‐containing liposomes, were more effective than Sr‐containing liposomes in increasing synchronous release.

4. Extracellular Ca behaved as a potent competitve inhibitor of asynchronous, neurally evoked release mediated by Sr. In contrast, intracellular Ca (i.e. liposomal Ca), whilst increasing synchronous ACh release, failed to antagonize evoked asynchronous release.

5. The results demonstrate that synchronous and asynchronous secretion have different sensitivities to alterations in intracellular divalent cation concentrations. It is suggested that selectivity for Ca over Sr may occur at intraterminal sites responsible for synchronous ACh secretion but not at sites responsible for asynchronous ACh release. Furthermore, Ca appears to bind with high affinity as an antagonist at the external surface of the nerve ending. These results are discussed in conjunction with current theories of depolarization—secretion coupling.
The pH oscillations in arterial blood during exercise; a potential signal for the ventilatory response in the dog
Authors: Cross Brenda A. , Davey A. , Guz A. , Katona P. G. , Maclean M. , Murphy K. , Semple S. J. G. , Stidwill R.
Published: December 2014

1. The effect of electrically induced ‘exercise’ on the respiratory oscillation of arterial pH was studied in chloralose‐anaesthetized dogs with spinal cord transection at T8/9 (dermatome level T6/7).

2. Respiratory oscillations of arterial pH (presumed to be due to oscillations of arterial PCO2) were sensed with a fast‐responding electrode in one carotid artery. Breath‐by‐breath estimates of the maximum rate of change of pH of the downstroke of the pH oscillation (dpH/dt↓max) were obtained by differentiating the pH signal.

3. Consistent with the findings of the previous paper (Cross et al. 1982), the ventilatory response to exercise could not be explained on the basis of sensitivity to CO2; the ΔV̇I/ΔPa, CO2 was significantly greater for ‘exercise’ than for CO2 inhalation.

4. On average, the amplitude of the pH oscillations decreased during ‘exercise’. The change in the phase relationship (ϕ) between respiratory and pH cycles, although significant from the second breath onwards, was not thought to be responsible for the increased ventilation V̇I; the direction of the change was opposite to that previously found to increase V̇I.

5. Inspiratory duration (ti), expiratory duration (te), V̇I and the dpH/dt↓max changed significantly by the third breath of ‘exercise’. A significantly linear relationship was obtained between te and dpH/dt↓max during the on‐transient (first ten breaths) of ‘exercise’. This relationship was maintained throughout ‘exercise’. V̇I and dpH/dt↓max were also linearly related during the on‐transient, although the same relationship did not hold true throughout ‘exercise’.

6. The dpH/dt↓max was related to CO2 production (V̇CO2) lending support to the prediction that the slope of the downstroke of the pH oscillation is a function of V̇CO2.

7. It was concluded that the dpH/dt↓max (dpCO2/dt↑max) is a potential humoral signal in ‘exercise’ and could account totally for the shortening of te. Since there was a late rise in V̇I (due to an increase in tidal volume VT) in the absence of a change in dpH/dt↓max, it was considered unlikely that the dpH/dt↓max was the only humoral signal present during ‘exercise’.
Effects of hypertonic solutions on quantal transmitter release at the crayfish neuromuscular junction
Authors: Niles Walter D. , Smith Dean O.
Published: December 2014

1. The effects of a hypertonic bathing medium, containing either NaCl or melezitose, on the average number (m) and the time course of quantal release following an action potential were studied using focal extracellular recording methods at synaptic sites on the opener muscle of the crayfish leg.

2. After the application of hypertonic saline, the rate of spontaneous quantal release increased but m decreased to a new level within 1 min; the extent of depression depended on the magnitude of the increase in tonicity until the osmolarity was 50% greater than the normal value of 0·43 osmol/l (Osm), but greater increases in tonicity exerted little further effect.

3. The synaptic delays were increased and distributed over a longer range of time in hypertonic solutions; also, the latency between the first and second quantal releases in a multiple response to a single nerve impulse was also increased.

4. Hypertonicity had no significant effect on the conduction velocity of the action potential, the independence of successive quantal releases in the same response, or the uniformity of the rise and fall of the probability of quanta release following an action potential, α(t).

5. The time course of α(t) is prolonged in hypertonic solutions; this was manifested as an increase in the time constant of the exponential decline in α(t) from its peak value following the nerve impulse.

5. When the potentiating agent 5‐hydroxytryptamine (5‐HT) was added to the hypertonic saline, m was increased, and the time course of α(t) was prolonged further than in the hypertonic solution alone; 5‐HT produced no change in the time course of α(t) when it was added to normal saline, although m was increased.

6. It is concluded that in this preparation hypertonicity decreases the rate of release of each quantum from the nerve terminal following a nerve impulse.
Analysis of orientation bias in cat retina
Authors: Levick W. R. , Thibos L. N.
Published: December 2014

1. Responses of cat retinal ganglion cells to a drifting sinusoidal grating stimulus were measured as a function of the grating orientation and spatial frequency.

2. The response at fixed frequency and contrast varied with orientation in the manner of a cosine function. A new measure was introduced to quantify this orientation bias in the response domain on an absolute scale of 0‐100%. Under experimental conditions designed to maximize the effect, the mean bias for 250 cells was 16% and the range was 0‐46%. In 70% of cells there was significant bias.

3. Orientation bias varied with spatial frequency and was maximal near the high‐frequency limit. The majority of biassed cells preferred the same orientation at high and low frequencies but in some cells a reversal occurred: the orientation which gave maximum response at high frequencies gave minimum response at low frequencies. The greatest variation of cut‐off frequency with orientation was ⅔ octave.

4. Orientation bias was due to neural, not optical, factors. Nevertheless, the phenomenon could often be imitated by deliberately introduced optical astigmatism of up to 4 dioptres for brisk‐sustained units and over 10 dioptres for brisk‐transient units.

5. The grating orientation preferred by cells varied systematically with position in the visual field. The central tendency was for the grating which yielded maximum response to lie parallel to the line joining the cell to the area centralis. This generalization failed for units within 2° of the centre of the area centralis.

6. Analysis of orientation bias indicates a functional asymmetry of receptive fields such that the centre mechanism, and sometimes also the surround mechanism, is elongated along the line joining cell to area centralis.
The responses to somatic stimuli of deep spinothalamic tract cells in the lumbar spinal cord of the cat
Authors: Meyers D. E. R. , Snow P. J.
Published: December 2014

1. The responses to natural somatic stimuli of thirty‐seven antidromically identified spinothalamic tract (s.t.t.) cells in Rexed's laminae VII and VIII of the lumbar spinal cord of the cat have been studied. A further twenty‐eight s.t.t. cells were identified antidromically.

2. Cells were activated from sites in, or close to, one of the following locations: nucleus (n.) parafascicularis or n. centrum medianum, magnocellular part of the medial geniculate or the medial leminiscus, n. ventralis posterior medialis, n. lateralis posterior.

3. The majority (84%) of s.t.t. cells showed spontaneous discharge at 1‐67 Hz.

4. Somatic stimuli excited 81% of s.t.t. cells but gave rise to inhibition of spontaneous discharge in 54% of cells. Only 8·1% of cells gave only inhibitory responses while 35·1% gave only excitatory responses and 45·9% gave both inhibitory and excitatory responses. No response could be elicited in 10·8% of cells.

5. The proportion of s.t.t. cells giving inhibitory and excitatory responses to hair movement, light touch or tap, innocuous pinch, noxious pinch, joint movement, twisting of and intense pressure on joints, flicking, palpation or deflexion of large muscles, skin cooling and warming and noxious heat are documented. Of these stimuli, only skin cooling and warming failed to produce a response in any cell.

6. Many cells showed convergence from receptors in muscles, joint and skin although 29·7% responded exclusively to innocuous cutaneous stimuli.

7. Convergence from receptors on wide, and sometimes quite separate, areas of the hind quarters was common but exclusively contralateral receptive fields were not found and for none of the above stimuli was the contralateral side more effective than the ipsilateral side.
The morphology of physiologically identified deep spinothalamic tract cells in the lumbar spinal cord of the cat
Authors: Meyers D. E. R. , Snow P. J.
Published: December 2014

1. The morphology of eleven physiologically identified, deep, spinothalmic tract (s.t.t.) cells in the seventh lumbar segment of the cat were studied after being intracellularly injected with horseradish peroxidase (HRP).

2. Four of these cells, prepared for combined light and electron microscopy, did not appear to be as well filled with HRP as the other cells which were prepared solely for the light microscope. In these four cells the axons were not stained and significantly fewer distal dendrites were stained.

3. The axons of the other seven cells projected medially, crossed the mid line in the ventral white commissure and ascended in the contralateral ventral funiculus. No axon collaterals were found.

4. The dendrites of eight cells could be divided into three groups. The first group projected laterally across lamina VII, usually passing through the ventrolateral portion of lamina VI before entering the lateral funiculus. The second group projected ventrally, ventromedially and ventrolaterally through the ventral parts of laminae VII and VIII and into the ipsilateral ventral funiculus. The third group projected towards the central canal, the ventral border of the dorsal columns and the dorsal parts of the ipsilateral ventral funiculus. This group usually branched profusely and projected into lamina X.

5. Of the remaining three cells, one was located more deeply than any other cell, one was probably incompletely filled, and one was located more laterally. The first two cells had dendritic trees which bore strong similarities to the other eight cells described above.

6. In all, 12·3‐37·5% of dendritic tips were found in the white matter of the ventral or lateral funiculi.

7. Dendrites never entered the dorsal columns but they could often be traced to points very close to the dorsal columns before they turned abruptly and ran parallel to the grey‐white border.

8. These data are discussed in relation to the excitatory and inhibitory responses of s.t.t. cells to somatic stimuli and the axonal projections of physiologically identified primary afferents and spinal interneurones.
Effect of fusimotor stimulation on Ia discharge during shortening of cat soleus muscle at different speeds
Authors: Appenteng K. , Prochazka A. , Proske U. , Wand P.
Published: December 2014

1. In barbiturate‐anaesthetized cats, the L7 and S1 dorsal and ventral roots were dissected to isolate functionally single afferents identified as primary endings of soleus muscle spindles, and motor filaments which exerted a fusimotor action on the afferents with limited action on extrafusal muscle. Up to seven filaments, with an action on a given primary ending, could be isolated and each was classified as exerting either a predominantly dynamic or static action.

2. Combined stimulation of these filaments, at rates up to 200 impulses/s could maintain afferent firing during muscle shortenings at speeds up to 200 mm/s.

3. Fusimotor stimulation could also maintain afferent firing at a target frequency of 100 impulses/s during muscle shortenings up to 200 mm/s. The timing, in relation to the onset of shortening, and the rates of fusimotor stimulation were found to be critical in achieving the target frequency.

4. Sinusoidal modulation of the frequency of fusimotor stimulation was used to study the conditions required to achieve constant afferent firing in the face of imposed sinusoidal length changes.

5. For given depths of modulation, the phase advance of fusimotor stimulation needed to produce minimum modulation of afferent firing (best compensation) increased with increasing frequency of the sinusoids. The compensation deteriorated with an increase in the frequency of the sinusoids and a change in the mean muscle lengths, although in some cases it could be restored by adjustments to the depth of modulation of fusimotor rate. This suggests that for movements of varying speeds and amplitudes, settings which are appropriate for shortening at a given velocity and mean muscle length, do not apply if either of these two variables are altered.

6. These findings demonstrate that the fusimotor system is potentially capable of eliciting constant afferent firing as envisaged in the ‘servo‐assistance’ hypothesis (Matthews, 1964, 1972; Stein, 1974). This, and the fact that constant afferent firing is not seen during normal unobstructed shortenings at velocities greater than 0·2 resting length/s (Prochazka, 1981), are used to argue that it is by choice rather than necessity that ‘servo‐assistance’ (as defined above) is not employed during normal movements. However, servo‐assistance of a different form (involving modulated spindle afferent feed‐back from both agonists and antagonists) remains a viable alternative.
Differences between foreign and original innervation of skeletal muscle in the frog
Authors: Sayers Helen , Tonge D. A.
Published: December 2014

1. In order to investigate the characteristics of synapses formed by a foreign nerve in skeletal muscle of the frog, the hypoglossal nerve in Rana pipiens was implanted under the cutaneus pectoris (c.p.) muscle which was denervated 1 month later.

2. Within 1 week of crushing the c.p. nerve, hypoglossal nerve fibres could be seen extending towards the denervated end‐plates and the muscle contracted in response to stimulation of the implanted nerve.

3. The synapses formed by the foreign nerve differed from those of the original nerve in several ways. The mean quantal content (m) of end‐plate potentials (e.p.p.s) evoked by stimulation of the hypoglossal nerve in c.p. was lower than that of e.p.p.s evoked by stimulation of the regenerated original nerve. The mean latency between stimulation of the implanted nerve and the onset of e.p.p.s was longer than that for stimulation of the original nerve. Stimulation of the foreign nerve often evoked multiphasic e.p.p.s whereas these were only seen on original nerve stimulation during the first 3 months after regeneration. These abnormalities of the foreign innervation persisted for at least 6 months after crushing the original nerve.

4. The geniohyoid muscle (which is normally innervated by the hypoglossal nerve) and c.p. appear to contain similar types of muscle fibre. Furthermore, when the geniohyoid muscle became reinnervated by the hypoglossal nerve after it had been crushed, the synapses formed were more effective than those formed by the hypoglossal nerve in c.p.

5. Even if reinnervation of c.p. by its nerve was delayed by cutting the brachial nerve at its exit from the vertebral column, the synapses formed by the hypoglossal nerve in c.p. remained abnormal, suggesting that an incompatability exists between the c.p. muscle and the hypoglossal nerve.

6. In spite of the differences found between the synapses formed by the hypoglossal nerve and the original nerve in c.p., there was no evidence of regression of the hypoglossal innervation during the period of observation.
Evidence for non‐cholinergic, non‐adrenergic transmission in the guinea‐pig ileum
Authors: Bauer V. , Kuriyama H.
Published: December 2014

To elucidate further the innervation of the longitudinal and circular muscle cells of the guinea‐pig ileum, junction potentials elicited by field stimulation were recorded from both muscle layers in the presence and absence of atropine (1‐2 μM) with guanethidine (10 μM) at 36 °C.

1. In longitudinal muscle cells, a single stimulus elicited an atropine‐sensitive transient depolarization (cholinergic e.j.p.), whereas in circular muscle cells, a transient hyperpolarization (non‐cholinergic non‐adrenergic i.j.p.) was elicited. With stimulation of nerves in the presence of atropine and guanethidine, responses of circular muscle cells to nerve stimulation were preserved while the longitudinal muscle cells generated depolarization (non‐ch., non‐adr. e.j.p.), hyperpolarization (non‐ch., non‐adr. i.j.p.) or both depolarization and subsequent hyperpolarization. These potential changes ceased with application of TTX or excess Mg2+.

2. The latency for junction potentials recorded from longitudinal muscles after field stimulation was in the following order; non‐ch., non‐adr. e.j.p. < cholinergic e.j.p. < non‐ch., non‐adr. i.j.p. The cholinergic e.j.p.s had a lower, and non‐ch., non‐adr. i.j.p.s a higher threshold.

3. At low frequencies of stimulation (below 1 Hz) amplitudes of successively generated cholinergic e.j.p.s and non‐ch., non‐adr. i.j.p.s were gradually reduced, but at higher frequencies (2‐20 Hz) of stimulation they were summated. The amplitudes of non‐ch., non‐adr. e.j.p.s were, however, not affected at low frequencies of stimulation (up to 0·5 Hz) and were summated at higher frequencies (over 1 Hz) of stimulation.

4. Reversal potentials for non‐ch., non‐adr. e.j.p.s and i.j.p.s estimated from the amplitude of junction potentials and membrane potential were ‐27 and ‐80 mV, respectively. The reversal potential for non‐ch., non‐adr. e.j.p.s was higher (more negative) than that for cholinergic e.j.p.s

5. Generation of i.j.p.s in longitudinal muscle cells elicited by repetitive stimulation was followed by a rebound depolarization on which was superimposed a burst of spikes. During repetitive stimulation, the amplitude of hyperpolarization was gradually reduced but the rebound depolarization and spike discharge were enhanced. Thus, while the rebound depolarization was related to the amplitude of the preceding hyperpolarization it was more related to the duration of the stimulation.

6. Therefore longitudinal muscles of the guinea‐pig ileum show evidence of having in addition to cholinergic and adrenergic innervation, both excitatory and inhibitory non‐ch., non‐adr. innervation. In the longitudinal muscle layer of the ileum, the non‐ch., non‐adr. excitatory fibres are more densely distributed in the terminal rather than in the proximal region, while in the case of non‐ch., non‐adr. inhibitory fibres, the distribution is reversed. Circular muscle cells are, however, homogenously innervated by non‐ch., non‐adr. inhibitory nerves.
Light adaptation of invertebrate photoreceptors: influence of intracellular pH buffering capacity.
Authors: Bolsover S R , Brown J E
Published: December 2014

1. The possible role of pH changes in mediating light adaptation in Limulus ventral photoreceptor cells was studied by intracellular injection of zwitterionic pH buffers. The intracellular concentration of buffer was estimated by inclusion of a radioactive marker in the injection solution. 2. The light‐induced increase of intracellular Ca2+ concentration was monitored by intracellular aequorin. The light‐induced increase of Ca2+ concentration was not markedly altered by injection of pH buffer to an intracellular concentration of about 200 mM. 3. The progressive decrease in responsiveness during intracellular ionophoretic injection of Ca2+ was not markedly altered by injection of pH buffer to an intracellular concentration of about 200 mM. 4. Photoreceptors of both Limulus and Balanus were impaled with two micropipettes and voltage clamped. Membrane current induced by a prolonged steady illumination declined from an early transient to a plateau. This delayed decline of current indicates a light‐induced reduction of sensitivity (i.e. light adaptation). The wave forms were similar before and after injection of pH buffer to an intracellular concentration of about 200 mM. 5. We conclude that it is unlikely that a light‐induced change of cytosolic pH mediates light adaptation in Limulus (and Balanus) photoreceptors.
The effects of sodium replacement on the responses of toad rods
Authors: Bastian Bruce L. , Fain Gordon L.
Published: December 2014

1. We have investigated the effects of Na+ substitution on the membrane potential and light responses of rods in the superfused retina of the toad, Bufo marinus.

2. When all of the Na+ in the Ringer was replaced with Li+, the effects on the rods depended upon the external free Ca2+ concentration ([Ca2+]o). At [Ca2+]o ≥ 10−6 M, the membrane potential (Em) hyperpolarized and light responses were greatly diminished or abolished. At [Ca2+]o ≤ 10−7 M, Li+ replacement had little effect on Em or response amplitude.

3. We interpret these results as revealing a Na+—Ca+ counter‐transport in rods. At high [Ca2+]o, replacing Na+ with Li+ would have produced an increase in the rod cytosol free Ca2+ concentration ([Ca2+]i) and the blockage of the light‐dependent conductance, leading directly to the suppression of light responses. At [Ca2+]o ≤ 10−7 M, this presumably would not have occurred.

4. Since at these low Ca2+ concentrations we observed light responses of nearly normal amplitude in Li+, our results suggest that the light‐dependent conductance is permeable to Li+.

5. Substitution of Na+ with K+ in low Ca2+ produced a complete suppression of the responses. However, it was still possible to measure large light‐induced changes in rod input resistance.

6. Substitution of Na+ with tetramethylammonium, tetraethylammonium, Tris, or choline in low Ca2+ produced a large hyperpolarization of the membrane potential and a diminution of response amplitude. However, we were unable to observe a complete suppression of the responses for these cations.

7. Substitution of Na+ with tetrapropylammonium or with an uncharged substance (glucose or urea) in low Ca2+ produced a large hyperpolarization of membrane potential and a considerable decrease in the light responses. In about half our attempts, the responses were observed to decline reversibly to less than 20% of their peak amplitude in Na+.

8. Results with tetrapropylammonium were indistinguishable from those of glucose or urea, indicating that the light‐dependent conductance probably is not permeable to TPA. The resistance changes measured with K+ substitution and the responses observed in the presence of the organic ions TMA, TEA, Tris and choline suggest that these species may be permeable, but we are unable to discount alternative explanations.