bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of contrast on the transfer properties of cat retinal ganglion cells.
Authors: Shapley R M , Victor J D
Published: December 2014

1. Variation in stimulus contrast produces a marked effect on the dynamics of the cat retina. This contrast effect was investigated by measurement of the responses of X and Y ganglion cells. The stimuli were sine gratings or rectangular spots modulated by a temporal signal which was a sum of sinusoids. Fourier analysis of the neural response to such a stimulus allowed us to calculate first order and second order frequency kernels. 2. The first order frequency kernel of both X and Y ganglion cells became more sharply tuned at higher contrasts. The peak amplitude also shifted to higher temporal frequency at higher contrasts. Responses to low frequencies of modulation (less than 1 Hz) grew less than proportionally with contrast. However, response amplitudes at higher modulation frequencies (greater than 4 Hz) scaled approximately proportionally with contrast. Also, there was a marked phase advance in these latter components as contrast increased. 3. The contrast effect was significantly larger for Y cells than for X cells. 4. The first order frequency kernel was measured with single sine waves as well as with the sum of sinusoids as a modulation signal. The transfer function measured in this way was much less affected by increases in contrast. This implied that stimulus energy at one temporal frequency could affect the response amplitude and phase shift at another temporal frequency. 5. Direct proof was found that modulation at one frequency modifies the response at other frequencies. This was demonstrated by perturbation experiments in which the modulation stimulus was the sum of one strong perturbing sinusoid and seven weak test sinusoids. 6. The shape of the graph of the amplitude of the first order frequency kernel vs. temporal frequency did not depend on the amplitudes of the first order components, but rather on local retinal contrast. This was shown in an experiment with a sine grating placed at different positions in the visual field. The shape of the first order kernel did not vary with spatial phase, while the magnitudes of the first order responses varied greatly with spatial phase. 7. Models for the contrast gain control mechanism are considered in the Discussion.
Changes in total and quantal release of acetylcholine in the mouse diaphragm during activation and inhibition of membrane ATPase.
Authors: Vizi E S , Vyskocil F
Published: December 2014

1. Acetylcholine (ACh) released from mouse diaphragm was gel filtrated and estimated by bio‐assay and compared with electrophysiologically measured quantal release, expressed either as frequency of miniature end‐plate potentials or quantum content of end‐plate potentials. 2. Activation of Na+‐K+‐dependent membrane ATPase (membrane ATPase) in Na+‐loaded muscles lowered the total amount of ACh released at rest to one tenth of the control value, but quantal release remained unchanged. 3. Inhibition of membrane ATPase by 2 X 10(‐5) M‐ouabain or by K‐free solution led to an increase in total release and to a delayed progressive increase in quantal release. When Ca2+ was removed only the total release was enhanced. 4. Depolarization of the diaphragm by 8, 11 and 14 mM‐K increased both total and quantal release only in the presence of Ca2+ in the perfusion medium. When Ca2+ was removed, no significant increase in release was observed. 5. The total and quantal release in response to 2 Hz stimulation of the preparation was increased 1.4 and 45 times, respectively. It is concluded that the total amount of ACh released at rest consists of two fractions, quantal and non‐quantal, the former representing about 1% of the total release.
Calcium current in molluscan neurones: measurement under conditions which maximize its visibility.
Authors: Connor J A
Published: December 2014

1. Membrane currents were studied in isolated somata of molluscan neurones from Archidoris monteryensis and Anisodoris nobilis. Under voltage clamp, inward current displayed a two phase time course, and in some cases a clear reversal potential difference could be shown for the fast and slow phases. The slower phase was carried predominantly by calcium ions. 2. The apparent magnitude of the slower phase was greatly influenced by conditions which altered potassium current flow. Blocking voltage‐dependent potassium conductances, either by appropriate conditioning polarizations or by tetraethyl‐ammonium (TEA) ion, enhanced the magnitude, while conditions which augmented potassium current made the slow phase disappear. 3. A fraction of the membrane potassium conductance was TEA insensitive. This fraction could be blocked by procedures which prevented internal levels of calcium from increasing during the voltage clamp pulse. Three such procedures were demonstrated; replacement of external calcium by magnesium, internal buffering by EGTA, and replacement of calcium by permeant barium. 4. Internal EGTA buffering or external barium in combination with external TEA produced an extreme change in membrane current as compared with the normal time course. Membrane current, when activated by pulses up to +50 mV, was net inward and showed only fractional inactivation over time courses running to several seconds. Pulses to voltages greater than +60 mV resulted in outward current. 5. It is concluded that under normal conditions the calcium conductance has the extended time course clearly evident under the modified conditions of paragraph 4 but that the calcium flux component is easily missed. 6. In agreement with several prior studies it is also concluded that a rise in internal calcium is causally related to a rise in potassium conductance. A transmembrane flux of calcium can be uncoupled from the gK increase by appropriate buffering of internal calcium. 7. The transient potassium current, IA, which bears a resemblance to calcium‐dependent potassium transients in some muscle cells did not depend upon internal calcium but instead is a voltage‐activated mechanism.
Effect of antrum exclusion on endocrine cells of rat stomach.
Authors: Alumets J , El Munshid H A , Håkanson R , Liedberg G , Oscarson J , Rehfeld J F , Sundler F
Published: December 2014

1. Following antrum exclusion the serum gastrin concentration was raised and independent of the prandial state. The antral gastrin concentration and number of gastrin cells were greatly lowered. 2. The histamine content and the number of histamine‐storing endocrine ('entero‐chromaffin‐like') cells in the oxyntic mucosa was almost doubled and the mucosal histidine decarboxylase activity was greatly elevated following antrum exclusion. 3. At the ultrastructural level both types of histamine‐storing endocrine cells (ECL and A‐like) were found to be enlarged and to have a reduced number of granules per unit cytoplasm. These changes are compatible with an increased secretory activity. The G (gastrin) cells were not increased in size but their granule volume density was lowered. 4. We propose that antrum exclusion results in uninhibited gastrin release causing profound changes in the histamine‐storing endocrine cells of the oxyntic mucosa. The cells respond to the hypergastrinemia by an increase in functional activity (activation of histidine decarboxylase and reduction of granule volume density) as well as by an increase in number and size.
Natural selective cooling of the human brain: evidence of its occurrence and magnitude.
Authors: Cabanac M , Caputa M
Published: December 2014

1. The technique of perceptual rating of thermal stimuli was used, in eight human subjects immersed in warm water, in order to appreciate whether they were hypo‐, normo‐ or hyperthermic. Oesophageal, tympanic and forehead skin temperatures were recorded, as also was the temperature of the skin above the angularis oculi vein. Once the subjects gave clearly hyperthermic ratings, one arm was exposed to a 6 m/s wind. After 5‐‐10 min the arm was re‐immersed and the face was fanned. 2. Fanning of the arm resulted in lowering of body core temperature. However ratings of thermal stimuli remained hyperthermic. 3. Face fanning decreased forehead skin, angularis oculi vein and tympanic temperatures. Hyperthermic ratings were replaced by normothermic ratings, although oesophageal temperature continued to rise. 4. The upper limit of oesophageal temperature for normothermic ratings was 37.o6 +/‐ 0.09 degrees C during the control period without fanning. This temperature rose to 37.91 +/‐ 0.09 degrees C during facial ventilation. 5. These results suggest a selective cerebral cooling due to venous blood returning from facial skin via the ophthalmic vein to the cavernous sinus, where a cooling of arterial blood ascending to the brain can take place.
Muscle spindle discharge in normal and obstructed movements.
Authors: Prochazka A , Stephens J A , Wand P
Published: December 2014

1. The discharge activity of muscle spindle endings located in tail and hind limb muscles was recorded during voluntary movements in the cat. 2. During active shortening of the receptor‐bearing muscles, both primary and secondary endings tended to fall silent. This was more pronounced, the higher the rate of muscle shortening. We suggest that in unobstructed movements in which muscle velocities exceed 0.2 resting lengths per second (lr/sec), the firing patterns of spindle afferents are dominated by their responses to the length variations. At velocities lower than 0.2 lr/sec, fusimotor action may predominate. 3. When active muscle shortening was unexpectedly halted, both primary and secondary endings resumed firing, but the increases in discharge rate were not as abrupt as might have been expected had there been strong co‐activation of fusimotor and skeletomotor neurones. Rather, for the types of movements studied, fusimotor action appears to have been quite modest.
Relationship between spatial frequency selectivity and receptive field profile of simple cells.
Authors: Andrews B W , Pollen D A
Published: December 2014

1. Receptive fields of simple cells in area 17 of the cat were mapped with stationary stimuli. Spatial frequency selectivities of the same cells were measured with drifting sinusoidal gratings. 2. The reconstructed field profile (inverse Fourier transform of selectivity curve) shows qualitative agreement with the mapped profile, and suggests the existence of additional side‐lobes in the field. The side‐lobes may correspond to the 'unresponsive regions' investigated by Maffei & Fiorentini (1976). 3. Our data suggest that the simple cell may perform approximately linear spatial summation of inputs to the visual system. However, the output of the simple cell is generally non‐linear as reflected in its truncated responses to gratings.
Histochemical reactions of fibres in a fast twitch muscle of the cat
Authors: Edjtehadi Guiti D. , Lewis D. M.
Published: December 2014

1. Serial sections of flexor digitorum longus muscle (f.d.l.) of the cat were examined histochemically for four enzyme systems: adenosine triphosphatase (ATPase) with alkaline and acid pre‐incubation, phosphorylase and succinic dehydrogenase (SDHase).

2. The number of types into which fibres should be divided was assessed by estimating enzyme reaction intensity from measurements of light transmission through photomicrographs. It was concluded that in general the enzyme reaction intensities of fibres were distributed continuously. However, the distribution histograms showed two (phosphorylase and SDHase) or three (acid and alkaline ATPase) clear peaks. Eighteen combinations of reaction intensities (profiles) were seen of which eight were very rare. The distribution of profiles differed between individuals but were similar in right and left muscles.

3. Areas of fibres were measured from muscles which had been fixed at the length at which twitch tension was maximal. The variance in fibre area with any one profile was significantly less than the variance in fibre area of all fibres within a muscle. There were significant differences between the mean areas of fibres with different profiles.

4. If only three enzyme reactions are considered (acid and alkaline ATPase and phosphorylase) the majority of fibres fall into one of the three classes commonly accepted for other muscles. The remainder would fit into this classification with the minimal assumption of only one error of fibre typing resulting from the continuous distributions of enzyme reaction intensities. The SDHase reaction was not strongly correlated with the three classes and could be used to divide the fibres further into six groups. Differences between means of fibre areas were significant for all pairs out of these six groups except one.

5. The grouping may be considered to reflect a dual system of enzymes, the two systems being (a) ATPases and phosphorylase, (b) SDHase. A possible role of nervous activity in determining this dual system is discussed. The hypothesis involves two partly independent characteristics of motoneuronal activity: (a) the frequency of impulses, and (b) the total number of impulses.

6. The measurements are correlated with other physiological variables in the individual animals. The mean areas of fibres in all groups increased with body weight. There were changes in the proportions of light and dark SDHase fibres related to weight. The total area contributed by dark alkaline ATPase fibres decreased and that by intermediate alkaline ATPase fibres increased with increasing twitch time to peak.

7. Specific tension of the group of slower muscle fibres in f.d.l. was estimated to be 0·29 N.mm−2 compared with 0·39 N.mm−2 for the faster fibres.
Activity patterns of cerebellar cortical neurones and climbing fibre afferents in the awake cat.
Authors: Armstrong D M , Rawson J A
Published: December 2014

1. Glass‐insulated tungsten micro‐electrodes were used to record from single neurones in the intermediate zone of the cerebellar cortex of cats in a state of quiet wakefulness. 2. Two hundred and seventy Purkinje (P) cells were recorded extracellularly, 95% of which displayed an irregular tonic discharge at rates between 19 and 95/s (over‐all mean 44/s), including complex spikes (c.s.) which occurred at 1.0‐‐2.5/s )over‐all mean 1.5/s). The remaining cells discharged c.s. at the usual rate but only one or two simple spikes (s.s.) per minute. C.s. of spike plus wavelet and of multi‐spiked type were present in approximately equal numbers of cells. 3. Presumed climbing fibre‐e.p.s.p.s were recorded from fifty‐six P cells and occurred both singly and in groups of two to six e.p.s.p.s at an intra‐group frequency of about 500/s. The cells giving rise to the c.f.s therefore discharge propagated impulses both singly and in short bursts as previously reported for anesthetized animals. A single e.p.s.p. can give rise to more than one spike in the multi‐spiked type of c.s., and probably to a complete c.s. event. 4. Following spontaneous c.s. the interval to the next s.s. varied from 8 to 600 ms. There was an inverse correlation between duration of the post‐c.s. interval and the rate at which s.s. were discharged in the preceding 100 ms. The duration exceeded the mean s.s. interval provided s.s. rate was less than 40‐‐50/s, and the post‐c.s. interval would then constitute a real interruption of s.s. discharge. 5. When the superficial radial (s.r.) nerves were stimulated with single shocks too weak to produce a behavioural response changes in discharge pattern were detected in eighty‐eight of 151 P cells tested. The initial responses were almost always excitatory and consisted in seventy‐two cells of a c.s., in eleven of a c.s. preceded by a brief increase in s.s. and in two cases of a s.s. discharge alone. The spino‐olivo‐cerebellar paths responsible for the c.s. showed transmission characteristics similar to those reported for animals anaesthetized with barbiturates. 6. C.s. were readily evoked by tapping or squeezing the forepaws. 7. Excitatory responses to nerve stimulation were usually followed by a depression of the tonic s.s. discharge. Its duration ranged widely in different cells (from 10 to 500 ms) and it would coincide with equally variable periods of facilitation previously seen in neurones of nucleus interpositus. It is therefore likely that such facilitations of the cerebellar nuclear cells result at least in part from reductions in the tonic inhibitory input from the P cells. 8. Thirty‐six units were classes as 'probable cortical interneurones'. They discharged more regularly, at rates between 9 and 28/s. Twenty such units (56%) responded to s.r. stimulation with a brief excitation not usually followed by any pronounced depression.
The effect of temperature on the asymmetrical charge movement in squid giant axons.
Authors: Kimura J E , Meves H
Published: December 2014

1. Asymmetrical displacement currents ('gating currents') have been recorded in intracellularly perfused squid giant axons by averaging the currents associated with depolarizing and hyperpolarizing voltage pulses. The effect of temperature on 'gating currents' was studied and compared with the effect of temperature on Na currents. 2. Increasing the temperature in seven steps from 0 to 15 degrees C increased the area under the on‐ and off‐response (Qon, Qoff). The average Q10 values for Qon and Qoff (measured with depolarizing pulses to 0 to 20 mV) were 1.41 and 1.62, respectively. 3. The on‐ and the off‐response were described mathematically by the sum of two exponentials. The first component of the on‐response, Qon 1, represented 80% or more of the total charge movement associated with 2.5 msec pulses; the Q10 of Qon 1 was similar to that of total Qon. The first component of the off‐response, Qoff 1, represented 50‐‐70% of total Qoff; its Q10 was smaller than that of total Qoff. 4. The temperature dependence of the rate constants (tauon 1)‐1 and (tauoff 1)‐1 was stronger at temperatures below 6‐‐8 degrees C (Q10 = 3.1‐‐6.4) than at higher temperatures (Q10 = 2.0‐‐3.3). In an Arrhenius plot two lines of different slope were required to fit the data. 5. The effect of increasing the temperature on the Q vs. V curve can be described as an increase of Qmax or, alternatively, as a shift of the curve to more negative potentials. 6. Increasing the temperature from 0 to 15 degrees C increased the peak of the Na current (recorded in sea water with a fifth of the normal Na concentration), increased the rate constants taum‐1 and tauh‐1 and shifted the m3infinity and hinfinity curves to more positive potentials. 7. The Q10 of the rate constant taum‐1 varied between 2.04 and 2.61 and was independent of temperature. In an Arrhenius plot the values for taum‐1 could be fitted by a single line. 8. The results support the view that 'gating current' does not simply reflect changes of the Na activation variable m. The increase of Qon, Qoff with increasing temperature may be attributed to an increase in membrane fluidity. The possibility that those charges which become mobile at higher temperatures may not be related to gating is considered.
Electrophysiological and sensory properties of the thalamic reticular neurones related to somatic sensation in rats.
Authors: Sugitani M
Published: December 2014

1. In urethane‐anaesthetized rats, studies were made on unit discharges of neurones of the thalamic reticular nucleus (tr) receiving the somatosensory input. Such units were found distributed in a part of the tr (s‐tr) surrounding the anterior and anterolateral borders of the ventrobasal nuclear complex (vb). 2. A series of five to ten bursts of grouped discharges were elicited in the s‐tr neurones as orthodromic responses to single shock stimulation of the medial lemniscus (ml) or the somatosensory cortex (smc). In contrast to this, the vb relay cells were fired by ml impulses only once at short latencies, though later there occurred a series of two to three bursts of grouped discharges. The same response pattern was seen by stimulating the smc, except that the initial response to smc shocks was of antidromic origin. 3. The mean response latency of the s‐tr neurones to ml shocks was about 0.6 msec longer than that of the vb relay cells. Ml fibres connected to the s‐tr neurones had the same distribution of conduction velocity as those connected to the vb relay cells. It is suggested that most, if not all, of the s‐tr neurones are innervated by axon collaterals of the vb relay cells. 4. About half the s‐tr units were activated from vibrissae. For most of the remaining half either movements of hairs or touch to the skin were effective. In the vb, the units discharged by movements of hairs were most numerous and those activated from vibrissae were less frequent. While responses of the s‐tr neurones to adequate stimuli were almost exclusively of phasic type, 30% of the responses of the vb relay cells were tonic and the remainder were phasic. 5. By exploring the tr extensively, the s‐tr was found to be contiguous caudally to the perigeniculate reticular nucleus which is immediately adjacent to the dorsal lateral geniculate nucleus and contains reticular neurones activated by visual stimuli. Though few in number, units were found in the tr which received a convergence of somatosensory and visual inputs or of somatosensory and auditory inputs.
The effects of theophylline and choleragen on sodium and chloride ion movements within isolated rabbit ileum.
Authors: Naftalin R J , Simmons N L
Published: December 2014

1. Theophylline (10 mM) and choleragen change the direction of net Cl‐ movements across rabbit ileum, in the short‐circuit current condition, from absorption to secretion. The specific activity ratio R of Cl‐ tracers within the tissue coming from mucosal and serosal solutions respectively is increased, which is consistent with an increase in Cl‐ exchange flux across the mucosal border. 2. Net Na+ movement is also changed from net absorption to secretion by theophylline and choleragen; the specific activity ratio R of Na+ tracers is raised by theophylline. Because of the large paracellular component to transepithelial Na+ movements, an increase in Na+ exchange flux across the mucosal border is not detected. 3. 2,4,6‐Triaminopyrimidine (20 mM) which has been previously shown to block paracellular Na+ movements, blocks both the theophylline and choleragen‐dependent reversal of net Na+ movement by preventing the decrease in m‐s Na flux. The theophylline‐dependent increase in the ratio R of Na+ is still present, and is consistent with an increase in Na+ exchange flux across the mucosal border‐‐unmasked by removal of the paracellular flux components. 4. Ouabain (0.1 mM) abolishes net absorption of Na+ and Cl‐ in control and net secretion of Na+ and Cl‐ in theophylline‐treated tissue. Ouabain does not affect the theophylline‐dependent increase in Cl‐ exchange across the mucosal border. 5. Replacement of Ringer Cl‐ with SO24‐ or Na+ by choline prevents the effects of theophylline and choleragen on Na+ and Cl‐ fluxes respectively. 6. Ethacrynate (0.1 mM) prevents the theophylline‐dependent effects on net Na+ movement. Raising ethacrynate to 0.2 mM abolishes the effects of theophylline on Cl‐ exchange. An interpretation of these results is that theophylline and choleragen raise the Cl‐ permeability of the brush border. This increases NaCl leakage from the hypertonic lateral intercellular space into the mucosal solution thereby causing secretion. The selective action of triaminopyrimidine and ethacrynate (0.1 mM) on Na+ flux indicates that Na+ and Cl‐ move via separate transport pathways across the mucosal border.
Effect of acetylcholine stimulation on calcium and sodium uptake by the isolated rat pancreas.
Authors: Bobinski H , Kelly J A
Published: December 2014

1. The role of Ca2+ and Na+ ions in 'stimulus‐secretion' coupling in the isolated uncinate pancreas of 4‐week‐old rats has been examined using radioisotope tracer techniques. The amount of 45Ca2+ and 22Na+ (mumole/g wet wt.) taken up by unstimulated glands was compared to that of glands in which amylase release was stimulated by ACh(10(‐5) M) at various incubation times. 2. The amount of 45Ca taken up by the glands within 60 min of incubation was not found to be increased by the presence of ACh(10(‐5) M). In fact, during short incubation periods the 45Ca uptake was significantly less in the stimulated glands than the unstimulated glands. 3. Presence of ACh(10(‐5) M) did cause a significant initial increase in 22Na uptake lasting up to 20 min from onset of stimulation. 4. These results indicate that the rise in intracellular Ca2+ concentration which is suggested by an increase in 45Ca efflux during the action of pancreatic secretagogues, is not a consequence of increased 45Ca uptake by the pancreas; but they indicate that an initial action of ACh could be to elicit an increase in Na+ influx and that Na+ ions are likely to be involved in the action of ACh on pancreatic acinar cells.
Phasic firing enhances vasopressin release from the rat neurohypophysis
Authors: Dutton A. , Dyball R. E. J.
Published: December 2014

1. Isolated rat neural lobes were incubated in vitro and electrically stimulated to release vasopressin. The released vasopressin was assayed using a radioimmunoassay and there was a reasonably good correlation (r = 0.81) between results obtained with this assay and those obtained by bioassay with the rat blood pressure method.

2. Regular stimulation at frequencies of 5, 10 and 20 Hz released progressively more vasopressin and the release could be blocked by addition of tetrodotoxin to the incubation medium.

3. Stimulation with pulse patterns derived from tape recordings of phasically firing units in the supraoptic nucleus of dehydrated rats released more vasopressin than the same number of pulses regularly spaced in time. In the range 2‐8 pulses/sec vasopressin release was related to the pulse frequency within the bursts (r = 0.90) and the number of short (< 100 msec) interpulse intervals (r = 0.92). Vasopressin released per pulse increased over the frequency range 3‐6 pulses/sec, but above 6 pulses/sec vasopressin release per pulse tended to diminish.

4. We conclude that phasic firing of vasopressin neurosecretory cells may enhance vasopressin release in vivo and that an important factor in determining release is the number of short interspike intervals.
Electrophysiological identification of two types of fibres in rat extraocular muscles.
Authors: Chiarandini D J , Stefani E
Published: December 2014

1. The synaptic potentials and electrical properties of rat inferior rectus muscles were examined in vitro. 2. In most fibres the spontaneous synaptic activity consisted of typical miniature end‐plate potentials which had a normal distribution of amplitudes and rather uniform time courses. Suprathreshold and maximal nerve stimulation evoked unitary end‐plate potentials (e.p.p.s). The synaptic activity of these fibres could be recorded only in the innervation zone of the muscle. These fibres were identified as being focally innervated. 3. Focally innervated fibres gave action potentials upon direct and indirect stimulation. They had an effective resistance (Reff) of 1.62 +/‐ 0.22 M omega (mean +/‐ S.E., twenty‐two fibres) and a time constant (tau m) of 3.8 +/‐ 0.4 msec (twenty‐one fibres). Voltage‐current curves in control saline were linear between membrane potentials of ‐50 to ‐140 mV. 4. In a small number of fibres the spontaneous synaptic activity consisted of miniature small‐nerve junction potentials which had a skewed distribution of amplitudes with predominance of smaller voltages and time courses with a wide range of variation. Nerve stimulation evoked composite small‐nerve junction potentials (s.j.p.s) which could be resolved into unitary components by varying the strength of stimulation. S.j.p.s had a higher threshold than e.p.p.s. Synaptic potentials could be recorded outside the innervation zone, at various sites along the muscle length. These fibres were recognized as being multiply innervated with polyneuronal innervation. 5. Multiply innervated fibres lacked action potentials had a large Reff of 6.0 +/‐ 1.1 M omega (six fibres) and a prolonged tau m of 29.8 +/‐ 4.8 msec. Reff show a moderate decrease to hyperpolarization and a rather large decrease to depolarization which denote, respectively, the presence of anomalous and delayed reactification. 6. It is concluded that rat extraocular muscles contain at least two populations of muscle fibres that in terms of synaptic activity and electrical properties are comparable to twitch fibres of other mammalian muscles and to slow or tonic fibres of amphibians.
Change of statistical parameters of transmitter release during various kinetic tests in unparalysed voltage‐clamped rat diaphragm.
Authors: Glavinović M I
Published: December 2014

1. The statistical nature of transmitter release was studied in unparalysed cut rat diaphragm using a voltage clamp technique at room temperature (23 degrees C). 2. While the binomial distribution described observed amplitude histograms well, the Poisson distribution was clearly inadequate. Values of m ranged from 40 to 45, while values for n varied from 45 to 53 and p was between 0.82 and 0.90. 3. Estimation of the probability of release from the transient decay of e.p.c.s in short tetanic trains (11 pulses, 150 Hz) gave values of p from 0.031 to 0.054, which are more than one order of magnitude lower than statistical estimates. 4. As a result of the short tetanic stimulation (5 pulses, 20, 50 and 100 Hz) there is an initial transient facilitation which afterwards becomes masked by depression. Statistical analysis suggests that the changes in the average numbers of quanta released (m) could be attributed to the change in the immediately available store (n). 5. During long tetanic stimulation (4000 pulses, 10‐100 Hz) statistical analysis suggests that the decrease in the average number of quanta released (m) could be attributed almost entirely to the decrease in the immediately available store (n). The probability of release (p) decreased only slightly. The extent of the post‐tetanic potentiation indicates that it cannot be explained on the grounds of increased probability of release (p) only. There should be an increase as well in the immediately available store (n). 6. It is suggested that while depression is most likely caused by the depletion of the immediately available store due to insufficient replenishment, the facilitation is probably caused by the increase in the capacity of the immediately available store to contain transmitter.
Potassium activity in photoreceptors, glial cells and extracellular space in the drone retina: changes during photostimulation.
Authors: Coles J A , Tsacopoulos M
Published: December 2014

1. A double‐barrelled potassium‐sensitive micro‐electrode was developed that was fine enough to record intracellular electrical potentials and potassium activities (aK) in the drone retina. 2. aK was measured in the photoreceptor cells, in the pigment (glial) cells, and in the extracellular space, in the superfused, cut, retina. The effect of photostimulation was studied: 20 msec light flashes, intense enough to evoke receptor potentials of maximum amplitude were presented, 1/sec, in a train lasting about 2 min. 3. In photoreceptors with membrane potentials greater than or equal to 50 mV aK in the dark was 79 mM, S.D. = 27 mM, n = 11. During photostimulation aK fell by 21.5 +/‐ 9.5 mM with a half‐time of 30 +/‐ 22 sec. (A tentative conversion from activities to free concentrations can be made by taking the activity coefficient as 0.70 its value in the Ringer solution). 4. In pigment cells with membrane potentials greater than or equal to 50 mV, aK in the dark was 52 mM, S.D. = 13 mM, n = 11. During photostimulation aK increased by 14 +/‐ 5 mM. 5. In the extracellular space aK increased during photostimulation with a mean half‐time of less than 1.3 sec to a maximum (mean value 14 mM, S.D. = 8.4 mM, n = 22), and then fell to a plateau. 6. It is estimated from the anatomy that the photoreceptors occupy approximately 38% of the total volume of the retina, the pigment cells 57%, and extracellular space 5%. Hence, it seems possible that during photostimulation nearly all the net loss of potassium from the photoreceptors is temporarily stored in the pigment cells. 7. Recordings were made in the extracellular space of the intact animal by passing the electrode through a hole in the cornea. The mean aK in the dark was 7.7 mM, S.E. = 0.4 mM, n = 22. In the superfused retina, aK in the dark was 6.3 mM, S.E. = 0.7 mM, n = 22, even though aK in the Ringer solution was 2.2 mM. Increasing the aK of the Ringer solution to 7.0 mM had no apparent effect on aK in the extracellular space at depths greater than 20 micron. 8. In the intact animal the amplitude and time course of the change in extracellular aK evoked by the standard pattern of photostimulation were within the range observed in the superfused preparation.
The importance of flow pulsatility for the rate of transvascular fluid filtration in lungs.
Authors: Hauge A , Nicolaysen G
Published: December 2014

1. The rate of transvascular fluid filtration has been studied with a gravimetric technique in isolated perfused rabbit lungs during periods of elevated left atrial pressure (PLA). 2. Fluid filtration was expressed as the filtration coefficient, Kf (g/min x 100 g bloodless lung x mmHg PLA) and determined during alternately pulsatile and non‐pulsatile perfusion in six zone III and three zone II/I lung preparations. Perfusion pattern was changed without interruption of flow. Mean in‐ and outflow pressures were kept constant. 3. In all the lungs it was found that Kf was higher during pulsatile than during non‐pulsatile flow (P less than 0.01). Mean Kf (+/‐ S.E. of mean) for the zone III preparations was 0.42 (+/‐ 0.089) and 0.27 (+/‐ 0.057) for pulsatile and non‐pulsatile perfusion, respectively. The corresponding figures for the zone II/I preparations were 0.11 (+/‐ 0.035) and 0.04 (+/‐ 0.030). 4. We suggest that the difference is due to a larger filtration area and/or a higher mean microvascular hydrostatic pressure during pulsatile than during non‐pulsatile flow and not to a rise in hydraulic conductivity due to pressure pulsations ('stretched pores'). 5. When the water‐exchange function of the lung is considered, flow pattern should be taken into account as an entity in its own right in addition to the steady state or the mean component of blood flow.
Transmitter release: ruthenium red used to demonstrate a possible role of sialic acid containing substrates.
Authors: Baux G , Simonneau M , Tauc L
Published: December 2014

1. The possible function of sialic acid‐containing substrates (SACS) in synaptic terminals of Aplysia was studied by intracellular injection of ruthenium red and of neuraminidase. 2. Ruthenium red, a dye known to have sialic acid as a molecular target, blocked transmission irreversibly in both cholinergic (buccal ganglion) and non‐cholinergic (cerebral ganglion) synapses. 3. An intracellular site of action is likely because much less ruthenium red was necessary to block transmission when it was injected intracellularly than when it was presented by bath perfusion. 4. Ca2+ spikes recorded in the presence of tetrodotoxin or in Na+‐free solution were not modified by ruthenium red or neuraminidase injections or perfusions. It is therefore improbable that these substances blocked transmission by blocking voltage‐dependent Ca2+ influx. 5. Strong electrotonic depolarization of a pre‐synaptic interneurone in the presence of 10(‐4) M‐tetrodotoxin caused a sustained post‐synaptic response, which was abolished by ruthenium red. This result eliminates axonal conduction block as the principal mechanism of ruthenium red action. 6. Post‐synaptic responses to ionophoretically applied acetylcholine (ACh) were not modified by bath perfusion of 2 x 10(‐2) M‐ruthenium red. 7. Biochemical analysis of pools of [3H]ACh was performed after injection of a precursor, [3H]acetate, into an identified interneurone. Ruthenium red appeared to increase significantly the ‘free’ (cytoplasmic) ACh pool without any change of ‘bound’ (vesicular) [3H]ACh‐pool. 8. A model is proposed in which SACS act as intracellular Ca2+ receptors involved in transmitter release.
Chloride, sodium, potassium and hydrogen ion transport in isolated canine gastric mucosa.
Authors: Kuo Y J , Shanbour L L
Published: December 2014

1. The fluxes of isotopically labelled Na+, Cl‐ and K+ in each direction and H+ secretion across isolated dog gastric mucosa were measured under short‐circuit conditions. 2. In the non‐stimulated state, the net flux of Na+ was 6.61 micronequiv/cm2.hr from mucosal (luminal, secretory) to serosal (nutrient, blood) side, whereas the net flux of Cl‐ was only 0.79 micronequiv/cm2.hr, and the direction was from serosal to mucosal side. 3. There was a positive correlation between the net flux of Cl‐ and acid secretion, however, net flux of Na+ was not correlated with acid secretion initiated by secretagogue treatment. 4. With ion substitution studies, only replacement of mucosal Na+ with choline produced a highly significant decrease in potential difference (p.d.). This indicates that active transport of Na+ from the mucosal to the serosal side is the most important source for the generation of the gastric p.d. in dog gastric mucosa. 5. From ion substitution studies, it was also observed that Cl‐ in either mucosal or serosal solution is necessary for maintaining acid secretion; whereas only serosal Na+ and K+ are essential for acid secretion. Removal of either Na+ or K+ from the mucosal solution had no effect on acid secretion. 6. Substitution of SO2‐(4) for Cl‐ had no effect on active transport of Na+, but choline substitution for Na+ diminished active transport of Cl‐.
The nature of the atrial receptors responsible for a reflex increase in heart rate in the dog.
Authors: Kappagoda C T , Linden R J , Sivananthan N
Published: December 2014

1. In dogs anaesthetized with chloralose, small latex balloons were positioned at the left pulmonary vein‐atrial junctions so as to stretch this region. By recording action potentials from slips of the cervical vagi it was established that distension of these balloons stimulated receptor endings in the atrial endocardium which discharged into the myelinated branches of the vagi i.e. Paintal type A, type B and Intermediate type receptors. 2. In other dogs, cooling the cervical vagus in steps of 2 degrees C reduced this response in vagal myelinated fibres. With twelve receptors the response to distension was reduced by 30% when the vagus was cooled to 16 degrees C, by 70% when cooled to 12 degrees C and abolished at 8‐‐12 degrees C. 3. In a third group of dogs, distension of balloons at the pulmonary vein‐atrial junctions resulted in a reflex increase in heart rate. Cooling the cervical vagi in these dogs in stages to 8 degrees C reduced this increase in heart rate. In nine dogs the response was reduced by 20% when the vagi was cooled to 16 degrees C, by 70% when cooled to 12 degrees C and abolished between 12 and 8 degrees C. 4. In a fourth group of dogs, distension of balloons at the pulmonary vein‐atrial junctions was shown also to activate receptor endings in the atria which discharged into non‐myelinated branches of the Vagi. In twelve receptors, cooling the cervical vagus in steps of 2 degrees C reduced this evoked increase in activity in non‐myelinated fibres. These responses were abolished over a wide range of temperature unlike the responses observed above. 5. It is concluded that the increase in heart rate which follows distension of balloons at the pulmonary vein‐atrial junctions is mediated solely by the Paintal‐type receptors which discharge into the myelinated fibres in the vagi.
Inactivation of delayed outward current in molluscan neurone somata.
Authors: Aldrich R W , Getting P A , Thompson S H
Published: December 2014

1. Inactivation of delayed outward current was studied by voltage clamp of isolated neurone somata of the molluscs Archidoris and Anisodoris. During prolonged voltage clamp steps in normal artificial sea water delayed outward current rises to a peak and then declines to a non‐zero steady‐state. During repetitive clamp pulses at repetition rates slower than 2/sec, the amplitude of peak outward current in the second pulse is commonly less than the amplitude at the end of the preceding pulse, giving the impression of continued inactivation during the repolarized interval. We have termed this property cumulative inactivation. 2. Two components of delayed outward current were separated using tetraethyl ammonium ions (TEA) and cobalt ions (Co). External TEA blocks 90% of a voltage and time dependent outward current termed K current (IK). External Co blocks 85% of a Ca activated delayed outward current termed Ca current (ICa does not inactivate during prolonged or repetitive voltage clamp pulses. IK, however, inactivates during prolonged voltage clamp steps and shows cumulative inactivation during repetitive voltage clamp pulses. 3. Inactivation of IK is voltage and time dependent and does not require influx of Ca ions. 4. As measured by a prepulse method, the onset of inactivation is characterized by a two time constant process. Fast inactivation occurs with a time course comparable to the rate of rise of outward current and can account for 90% of total inactivation. 5. Recovery from inactivation is slow with a time constant approximately an order of magnitude slower than the onset of inactivation. 6. The current‐voltage (I‐V) curve for peak IK can be N‐shaped, with a region of negative slope resistance in the range of +30 to +80 mV. The I‐V curve for steady‐state IK, however, shows little or no tendency to form a local maximum. 7. The pattern of delayed outward current varies considerably between cells. A major contributing factor to this variability appears to be the relative contributions of ICa and IK to delayed outward current.
On the purpose of selective innervation of guinea‐pig superior cervical ganglion cells.
Authors: Lichtman J W , Purves D , Yip J W
Published: December 2014

Preganglionic axons arising from different levels of the mammalian spinal cord make preferential connexions with different classes of superior cervical ganglion cells (Langley, 1892, 1900; Njå & Purves, 1977a). For example, preganglionic axons from the first thoracic segment (T1) make relatively strong connexions with ganglion cells activating end‐organs of the eye; conversely, axons arising from T4 selectively innervate ganglion cells projecting to the ear. In the present work we have asked whether this selectivity reflects the function of the pre‐ and post‐synaptic cells, and aspect of their respective positions, or some other criterion. 1. End‐organs with different functions at the same locus (the eye) respond to stimulation of the same ventral roots; end‐organs of a single modality (hairs or blood vessels) at different positions, however, tend to be activated by different spinal segments. Thus the segmental innervation of ganglion cells is correlated with the position rather than the function of post‐ganglionic targets. 2. The role of target position in ganglion cell innervation was examined directly by recording from neurones sending axons to different destinations. Superior cervical ganglion cells running dorso‐medially in a spinal nerve receive, on average, innervation from more caudal segments than cells projecting ventro‐laterally. 3. These selective connexions do not depend on intraganglionic cell position: neurones located at different points along the major axes of the superior cervical ganglion receive, on average, the same segmental innervation. In accord with this observation, retrogradely labelled neurones innervating a particular target such as the eye or ear are widely and randomly distributed within a large portion of the ganglion. Thus the importance of post‐ganglionic target position in ganglion cell innervation is not simply a reflexion of ganglionic topography. 4. We conclude that one purpose of the selective connexions in the superior cervical ganglion is to bring together preganglionic axons arising from different levels of the spinal cord and ganglion cells whose axons innervate particular regions of the superior cervical territory.
Pancreotone, an inhibitor of pancreatic secretion in extracts of ileal and colonic mucosa.
Authors: Harper A A , Hood A J , Mushens J , Smy J R
Published: December 2014

1. Pancreotone is a polypeptide material obtained from ileal and colonic mucosa by extraction with alcohol and subsequent precipitation by bile salts. 2. In anaesthetized cats in inhibits the actions of secretin on the pancreas, and of pancreozymin on the pancreas and gall‐bladder. 3. Pancreotone has a less powerful inhibitory action on pentagastrin‐stimulated gastric secretion. 4. The actions of pancreotone resemble the inhibitory effects on the pancreas and stomach of intraileal and intracolonic infusions of oleic acid and other substances in cats with the vagal and splanchnic nerves cut. Pancreotone may be the humoral mediator of these inhibitory effects. 5. A possible relationship between the actions of pancreotone and somatostatin on the stomach, and of pancreotone and pancreatic polypeptide on the pancreas, is discussed.
Air humidity and carotid rete function in thermo‐regulation of the goat
Authors: Jessen Claus , Pongratz Hans
Published: December 2014

1. The effects of air humidity on respiratory rate have been studied in conscious goats exposed to an air temperature of + 33 °C. Before the experiments the animals had been chronically implanted with hypothalamic thermodes and intravascular heat exchangers to manipulate hypothalamic and general body core temperatures.

2. Raising air humidity from 37 to 96% at constant air temperature resulted in a rise of respiratory rate, an immediate increase in hypothalamic temperature and a delayed smaller increase in general body core temperature.

3. The rise of respiratory rate was smaller when general body core temperature was clamped at its control level and was absent when hypothalamic and general body core temperatures were clamped at their control levels during the humid air phase.

4. It is concluded that the effect of high air humidity on respiratory rate in goats is predominantly the result of a rise in hypothalamic temperature acting on local thermosensitive structures. The carotid rete heat exchanger is thought to provide the thermal link between the evaporating surfaces of the upper respiratory tract and the hypothalamus.

5. This function of the carotid rete heat exchanger is restricted to heat stressed animals. In animals subject to central cooling no local effects on hypothalamic temperature could be observed when the temperature of the inspired air was altered from + 33 to ‐ 17 °C.