bluuebunny/crossref_metadata_2025 huggingface dataset:
Epithelial solute permeability, ion transport and tight junction morphology in the developing lung of the fetal lamb
Authors: Olver R. E. , Schneeberger E. E. , Walters D. V.
Published: December 2014

1. Experiments were performed on exteriorized fetal lambs of between 69 days' gestation and term (147 days) in order to observe changes in lung volume and lung liquid secretion rate, and to delineate any alterations in solute permeability, ion transport and tight junction morphology in the maturing lung epithelium. Whilst it was technically possible to measure solute permeability as early as 69 days it was not feasible to apply the Ussing flux ratio technique before 84 days.

2. Fetal lung liquid volume and secretion rate, when normalized for body weight, increase linearly with gestation, whereas tracheal volume expressed in the same manner remains constant.

3. When expressed in terms of pore theory, epithelial permeability to small polar non‐electrolytes does not change between 69 days and term (equivalent pore radius 0.66 nm and 0.64 nm respectively).

4. In the immature fetus of 69‐76 days, mean epithelial tight junction strand number is 8.3, whereas by the end of gestation it has fallen to 4.6.

5. The transfer constants (min−1) for sodium and chloride movement in the direction lung liquid to plasma are, respectively, some 6 and 4 times greater at 84‐87 days than at term.

6. As in the mature fetus, the lung epithelium at 84‐87 days actively transports chloride from plasma to lung lumen, albeit with a slightly reduced transport e.m.f. Sodium movement does not, at any gestational age, differ from the predictions for passive transfer.

7. In lung liquid the concentrations of chloride and potassium increase and that of bicarbonate decreases during gestation, whilst that of sodium does not change. The rises in lung liquid chloride and potassium concentrations follow those in plasma, maintaining plasma/lung liquid ratios of 0.7 and 0.95 respectively. However, plasma bicarbonate remains constant and the plasma/lung liquid ratio for bicarbonate rises from 3 at 69‐76 days to 20 near term as the lung liquid bicarbonate falls from 9.8 to under 2 m‐mole kg−1 H2O.

8. Whereas lung liquid protein concentration remains constant and low at about 0.35 g l.−1, plasma protein concentration rises from 23 g l.−1 at 69‐76 days to 43 g l.−1 near term. During the same period arterial blood pressure doubles.
Free calcium ions in neurones of Helix aspersa measured with ion‐selective micro‐electrodes.
Authors: Alvarez‐Leefmans F J , Rink T J , Tsien R Y
Published: December 2014

1. Intracellular free calcium concentration, [Ca2+]i, was measured in giant neurones of the sub‐oesophageal ganglia of Helix aspersa, using Ca‐selective micro‐electrodes containing a PVC‐gelled, neutral‐ligand sensor. 2. In calibration solutions the electrodes had a virtually ideal, Nernstian, response down to 1 microM‐Ca2+ in the presence of 0.125 M‐K+, 18‐24 mV from 1 to 0.1 microM‐Ca2+ and 8‐14 mV from 0.1 to 0.01 microM‐Ca2+. Interference from H+ and Mg2+ was negligible. The small response to Na+ at sub‐micromolar Ca2+ was taken into account, when necessary, in measurement of [Ca2+]i. 3. Measurements of basal [Ca2+]i were made in ganglia from animals kept only a few weeks in captivity, in a bathing solution equilibrated with air and containing 2 mM‐Ca2+. In thirteen measurements from impalements which met stringent criteria for electrode performance and cell viability, the mean basal pCa (‐‐log10[Ca2+]) was 6.77 +/‐ 0.07 (S.E.), corresponding to a mean free Ca2+ concentration of 0.17 microM. 4. The basal [Ca2+]i in neurones from a group of snails kept hibernating for several months was higher, mean pCa 6.15, for ganglia handled in 2 mM‐Ca2+ solution. 5. Intracellular injections of Ca2+ or EGTA raised and lowered, respectively, the indicated basal [Ca2+]i, showing that the electrodes responded appropriately inside the cells and that unknown or untested components of cytoplasm were not significantly interfering with the Ca‐sensor. 6. Altering the external Ca2+ concentration between 0.1 and 10 mM usually produced only small, +/‐ 0.1 pCa units, changes in basal [Ca2+]i of satisfactorily impaled, quiescent cells. 7. In cell 1F, which has repetitive spikes with a substantial Ca current, changes in Ca gradient or blockade of voltage‐dependent Ca channels sometimes markedly altered [Ca2+]i, showing that Ca entry with the spikes was elevating [Ca2+]i. 8. Replacing external Na+ with Li+ or bis(2‐hydroxyethyl)dimethylammonium had little effect on [Ca2+]i. 9. Elevating CO2 to 5% or 79% lowered [Ca2+]i by an average of 0.16 and 0.26 pCa units respectively.
Morphological and electrophysiological characteristics of rat cerebellar slices maintained in vitro.
Authors: Crepel F , Dhanjal S S , Garthwaite J
Published: December 2014

1. The morphological and electrophysiological characteristics of sagittal cerebellar slices of adult rat cerebellum maintained in vitro were studied. 2. The ultrastructural preservation of the different neuronal cell types in many areas of these slices after 2‐3 h incubation was very similar to that observed in material fixed in situ. A limited degree of glial swelling was observed in some regions. 3. The conduction velocity of parallel fibres was within the normal in vivo range and the fibres retained their ability to activate Purkinje cells and inhibitory interneurones. 4. Purkinje cells, recorded intrasomatically, responded to white matter stimulation with characteristic antidromic activation and climbing fibre responses, and typical parallel fibre responses were evoked following parallel fibre stimulation. 5. Climbing fibre excitatory post‐synaptic potentials (e.p.s.p.s) were very similar whether recorded in the dendrites or somata of Purkinje cells. By contrast, marked differences in the associated spike potentials were evident, the initial fast, low‐threshold somatic spike appearing in the dendrites as a slow, high‐threshold spike. The secondary spikes, both in the soma and dendrites, were of the latter type. 6. The initial somatic spike was readily inactivated by cell depolarization but resisted moderate hyperpolarization, whereas the converse was true for the slow, high‐threshold spikes recorded in the dendrites. These differences suggest that these responses are generated in the soma and in the dendrites respectively. 7. Climbing fibre and parallel fibre e.p.s.p.s recorded in Purkinje cell somata were reversed under depolarizing current injected through the recording micro‐electrode. As in vivo, the parallel fibre e.p.s.p.s was more sensitive to injected current than the climbing fibre e.p.s.p. in several instances, despite the more proximal location of the synapses involved.
Effects of external calcium reduction on the kinetics of potassium contractures in frog twitch muscle fibres.
Authors: Cota G , Stefani E
Published: December 2014

1. The amplitude and time course of K contractures (Cl‐ constant) of single twitch muscle fibres of the frog have been analysed in three external Ca2+ concentrations. 2. The resting potential, effective resistance, threshold for the Na current and K‐induced depolarizations were not modified by replacing 1.8 mM‐Ca2+ by 3 mM‐Mg2+ in absence (low‐Ca saline: 3‐6 micro M‐Ca2+) or in the presence of 5 mM‐EGTA (Ca‐free saline: less than or equal to 10(‐9) M‐Ca2+). 3. The tension development during the initial phase of K contractures was independent of external Ca2+ while the amplitude, the duration and the time constant of spontaneous relaxation decreased progressively as Ca2+ concentration was diminished. 4. When the concentration of Mg2+ was increased to 5 mM in Ca‐free saline K contractures were slower and smaller than those in 3 mM‐Mg2+. 5. In Ca‐free saline the activation curve (peak tension vs. logarithm of external K+ concentration) shifted by 3‐5 mV towards more positive potentials while the inactivation curve (peak tension of the test contracture vs. logarithm of external K+ concentration during the conditioning period) shifted by 16‐18 mV towards more negative potentials. Both curves became steeper in Ca‐free saline. 6. The effects of external Ca2+ reduction were not modified by replacing all chloride for methanesulphonate. 7. Direct effects of external Ca2+ on excitation‐contraction coupling during K contractures could involve the inward Ca current and/or specific interactions between external Ca2+ ions and the coupling mechanism.
Single photon signals in fly photoreceptors and first order interneurones at behavioral threshold.
Authors: Dubs A , Laughlin S B , Srinivasan M V
Published: December 2014

1. The contrast sensitivity of the optomotor response of the fly Musca domestica was measured using a moving sinusoidal grating as the stimulus. In parallel experiments intracellular recordings were made from photoreceptors and first order visual interneurones to to determine their responses to the same threshold stimuli. Measurements of the spatial modulation transfer function for photoreceptors confirm that the optics of the eye were intact during recordings. 2. At the lowest intensity at which one can obtain an optomotor response, the photoreceptor signal is a train of discrete depolarizations, or bumps. With constant intensity stimuli, the temporal distribution of bumps followed the Poisson distribution with a mean rate of proportional to luminance. The mean bump rate at the threshold intensity for a behavioural response is 1.7 +/‐ 0.7 s‐1 (mean +/‐ S.D., n = 25). 3. Calibrations and the statistical properties of the bump train indicate that a bump represents one effective photon, implying that the bump : photon ratios are quantum capture efficiencies. 4. At low intensities the first order interneurones (the large monopolar cells or LMCs) show hyperpolarizing bumps each triggered by a receptor bump. Using a point source stimulus, centred in the field of view, the LMC bump rate is six times that in a single receptor viewing the same stimulus, as expected from the known projection of six receptor axons to each LMC. When using an extended stimulus (the grating), the bump rate is 18‐20 times that in receptors. Comparison with earlier work suggests that this increased lateral summation of receptor inputs to LMCs only occurs at very low intensities. 5. In both receptor and LMCs the amplitudes and wave forms of bumps depend upon the position of a point source stimulus within the field of view. With the light in the periphery of the field the bumps are smaller and slower than when the light is in the centre. This difference in response suggests that spatial stimulation is brought about by lateral interactions, possibly between receptors. 6. At higher mean intensities the signal‐to‐noise ratios in receptors responding to the appropriate threshold stimuli increase with intensity. This is suggestive of a decrease in the extent of spatial and/or temporal summation in the optomotor pathway.
Electrotonic coupling in internally perfused crayfish segmented axons.
Authors: Johnston M F , Ramón F
Published: December 2014

We have developed a technique for cannulation and internal perfusion of crayfish segmented lateral axons. Experiments on perfused and non‐perfused axons lead to the following conclusions: 1. Internally perfused segmented axons behave very similarly to non‐perfused axons. 2. The axial electrical resistance of the junctional region is almost as low as a comparable segment of axon. 3. Neither intracellular Ca2+ nor H+ is effective in disrupting the intercellular communication pathway in perfused axons. On the basis of these findings we have formulated a hypothesis for cellular control of intercellular coupling based on the existence of a soluble intermediate for Ca2+ or H+‐induced uncoupling. This hypothesis is consistent with data from both internally perfused and non‐perfused axons.
Sodium dependency of active chloride transport across isolated fish skin (Gillichthys mirabilis).
Authors: Marshall W S
Published: December 2014

1. The effects of thiocyanate, ouabain, ion‐substituted Ringer solution and electrochemical gradients on Na+ and Cl‐ transport were examined using the isolated skin of the marine teleost, Gillichthys mirabilis. 2. Bilateral replacement of Na+ with choline in the bathing solutions reduces net Cl‐ flux by 93%, indicating that active Cl‐ transport by the skin is Na‐dependent. 3. Thiocyanate inhibits short‐circuit current with an ED50 of 6.4 x 10(‐4)M, and, at 10(‐2)M, decreases Cl‐efflux, influx, net flux and short‐circuit current by 68, 33, 74 and 81%, respectively. 4. Ouabain (10(‐5)M) reduces Cl‐ efflux and net flux by 56 and 86%, respectively, indicating that the Cl‐ transport requires Na,K‐ATPase. 5. Subsequent addition of thiocyanate to ouabain‐treated skin reduces Cl‐ efflux, net flux and short‐circuit current, suggesting that the two agents operate at different sites involved in Cl‐ transport. 6. Unilateral substitution of gluconate for Cl‐ on the serosal side does not affect Cl‐ influx, indicating that Cl‐ passive transport is via Fickean diffusion, not Cl‐Cl exchange diffusion. 7. The addition of NaCl to the mucosal side, which mimics the in vivo sea‐water condition, increases Cl‐ influx and transepithelial potential and decreases tissue resistance. The net flux (secretion) of Cl‐ with hypertonic saline on the mucosal side (0.51 +/‐ 0.06 muequiv/cm2 . hr) demonstrates that the skin could secrete Cl‐ in vivo. 8. Na+ fluxes across the skin are passive, as the observed flux ration (efflux/influx) is similar to that predicted by the Ussing‐Teorell equation under both closed‐ and open‐circuit conditions. 9. The permeability ratio (PNa:PCl) in approximately 5.4:1.0, indicating that the skin is more permeable to Na+, and that at least part of the serosa‐positive transepithelial potential may be a Na+ diffusion potential. 10. The results suggest that Cl‐ secretion by Gillichthys skin is secondary active transport involving Na,K‐ATPase and serosal Na+.
Cellular distribution of neutral and basic amino acid transport systems in rabbit ileal mucosa.
Authors: King I S , Sepúlveda F V , Smith M W
Published: December 2014

1. An autoradiographic technique is described whereby the cellular location of tritiated amino acids can be determined following uptake by rabbit ileal mucosa. 2. Stirring solutions in contact with the intestinal mucosa during measurement of rapid influx changes the quantity, but not the distribution, of alanine taken up by the tissue. 3. Conditions predicted to favour either a high affinity system (Ly1) or a low affinity system (Ly2) were used to measure lysine distribution following uptake. Maximal uptake for both transport systems occurred in fully differentiated enterocytes at the tips of villi. Initial maturation of the Ly1 system, which was slow, was followed by a rapid phase of development. The Ly2 system lacked this rapid phase of late development. 4. The cellular distribution of alanine entering on a low affinity Na‐independent neutral amino acid carrier closely resembles that determine for Ly1 system for lysine entry. 5. Arginine is a potent inhibitor of lysine uptake through the Ly2 system. Little or no diffusion of lysine appears to take place into rabbit ileal enterocytes. 6. The different distribution of the high and low affinity systems for lysine transport provides further support for their independent existence. It also suggests that more than one message exists fo the switching on of amino acid transport function in differentiating enterocytes.
Modulatory influences of moving textured backgrounds on responsiveness of simple cells in feline striate cortex
Authors: Hammond P. , MacKay D. M.
Published: December 2014

1. The modulatory influences of synchronously moving textured backgrounds on responsiveness to optimally oriented moving bar stimuli were investigated in 107 simple cells, with incidental observations on four complex cells, recorded in the lightly anaesthetized feline striate cortex.

2. Background motion depressed bar responsiveness in 74% of simple cells, facilitated bar responsiveness in 4%, and was without influence in 22%. These results confirm our earlier observations (Hammond & MacKay, 1977).

3. Moving chequerboard patterns typically elicited stronger effects than moving visual noise.

4. Occluding a moving background by a mask of stationary texture of variable width and length indicated that the zone of background influence extended well beyond the excitatory receptive field along its axis, but not transverse to it. This was confirmed by a converse experiment using a window of moving texture in an otherwise stationary background.

5. The influence of background motion varied markedly with location relative to the cell's receptive field. A small stationary rectangular window of moving texture at different locations along the receptive field axis typically suppressed bar response when over the receptive field, but facilitated it at either end. Conversely, with the background moving and the masking texture stationary, suppression was minimal when the masking patch was centred over the receptive field.

6. Systematically varying the phase relationship between bar and background motion showed the interaction in simple cells to be greatest for in‐phase motion and least for motion in antiphase. The opposite is true for complex cells.

7. All the above effects showed non‐linearities and could be enhanced by making texture velocity greater than bar velocity or by selecting the polarity of contrast and length of a bar stimulus of optimal orientation and width so as to elicit relatively weak (submaximal) criterion responses.

8. Since textured backgrounds themselves evoke no response from simple cells, and since all specific afferents are known to be excitatory, it seems likely that textural influences upon simple cells are mediated only through complex cells.
Spatial spread of activation and background desensitization in toad rod outer segments
Authors: Lamb T. D. , McNaughton P. A. , Yau K.-W.
Published: December 2014

1. The spread of activation and background desensitization in rods was studied by recording membrane current from single outer segments in pieces of isolated toad retina.

2. Flash sensitivity changed slightly along the outer segment, falling by about 30% from base to tip.

3. When only the distal half of an outer segment was in the recording pipette, illumination of the unrecorded part elicited little or no photocurrent at the recorded part, indicating that a photoisomerization does not cause activation of the entire outer segment.

4. With diffuse illumination of an outer segment fully drawn into the pipette, the intensity—response relations at fixed times were invariant in form for most of the rising phase of the flash response and were considerably steeper than the Michaelis relation. The observed relation was consistent with a model in which a photoisomerization blocks all channels over a short region of the outer segment.

5. With illumination restricted to a narrow transverse slit, the intensity—response relations at fixed times were much less steep, as would be expected for a very limited longitudinal spread of activation. An upper limit for the effective longitudinal diffusion coefficient of the internal transmitter was estimated to be about 3 × 10−7 cm2 sec−1. This corresponds to a space constant for longitudinal spread of transmitter of about 3 μm at the time of the dim response peak.

6. The time course of flash responses elicited with light positioned either on the edge or on the centre of the outer segment was very similar.

7. Desensitization resulting from steady illumination by a transverse slit was also localized longitudinally. A linear desensitization parameter T, defined in Results, decayed approximately exponentially along the outer segment, on either side of the site of photoisomerization, with a space constant of about 6 μm.

8. Transverse spread of desensitization was more effective than longitudinal spread.

9. After turning off a dim diffuse background light, the decay of T was roughly exponential with a time constant of several seconds. From this, and the steady state space constant of 6 μm, it is estimated that the effective longitudinal diffusion coefficient for a ‘desensitizing substance’ would also be about 10−7 cm2 sec−1.

10. The restricted longitudinal spread of activation and desensitization may be explained by the barrier to diffusion presented by the stacked membranous disks in the outer segment. This baffling reduces the effective longitudinal diffusion coefficient to about 1/50 that of ordinary aqueous diffusion, but it does not significantly affect transverse spread.
The location of carbonic anhydrase in relation to the blood‐brain barrier at the medullary chemoreceptors of the cat.
Authors: Hanson M A , Nye P C , Torrance R W
Published: December 2014

1. The role of carbonic anhydrase near the medullary chemoreceptors has been investigated in the cat. Vertebral artery injections have been used to cause abrupt changes in respiration as a result of changes in the activity of medullary chemoreceptors. 2. Injections of 100% CO2‐saline were used to stimulate respiration and of Tris or alkalinized albumin solution to cause a reduction in respiration. 3. The injections gave rapid effects. We studied the effect on these of benzolamide (1‐4 mg/kg i.v.) a carbonic anhydrase inhibitor which does not easily cross the blood‐brain barrier and acetazolamide (50 mg/kg i.v.) an inhibitor which crosses the barrier more easily. 4. The effects of Tris were much reduced after benzolamide. Even addition of benzolamide to the injected Tris or albumin was sufficient to reduce their effects. 5. The effects of CO2‐saline were reduced only after acetazolamide i.v. Whereas addition of carbonic anhydrase to injected Tris potentiated the effects on respiration, after acetazolamide this potentiation was much less marked. 6. It is concluded that carbonic anhydrase acts in the region of the medullary chemoreceptors at two sites: (a) outside the blood‐brain barrier, probably at the luminal surface of the capillary endothelium, where it may act on plasma buffers, and (b) inside the barrier, in association with the chemoreceptors, where it may accelerate CO2/pH equilibration.
Mediators of slow synaptic potentials in the myenteric plexus of the guinea‐pig ileum
Authors: Johnson S. M. , Katayama Y. , Morita K. , North R. A.
Published: December 2014

1. Intracellular recordings were made from neurones in the myenteric plexus of the ileum isolated from adult guinea‐pigs.

2. Three synaptic potentials were evoked in different myenteric neurones by focal stimulation of the ganglion surface at a distance of up to 100 μm from the cell body from which the recording was made. These were the fast cholinergic excitatory post‐synaptic potential (e.p.s.p.), the slow e.p.s.p. and the slow inhibitory post‐synaptic potential (i.p.s.p.).

3. 5‐hydroxytryptamine and substance P were applied to the neurones by superfusion (10 n
m‐1 μ
m) or by electrophoresis within 5 μm of the neurone cell body. 5‐HT depolarized, hyperpolarized or had no effect on approximately equal numbers of neurones, whereas substance P depolarized 90% of neurones.

4. Many neurones with a depolarizing slow e.p.s.p. were hyperpolarized by superfusion or electrophoretic application of 5‐HT.

5. Superfusion with 5‐HT reversibly depressed the fast e.p.s.p., slow e.p.s.p. and slow i.p.s.p. Superfusion with substance P depressed the slow e.p.s.p.

6. Methysergide (10‐30 μ
m) reduced the amplitude of the fast e.p.s.p., the slow e.p.s.p. and the slow i.p.s.p.

7. Chymotrypsin (200 μg/ml.) reversibly reduced the amplitude of the slow e.p.s.p., but had no effect on membrane potential, the action potential or the fast e.p.s.p. Chymotrypsin reduced or abolished the depolarization caused by electrophoretic application of substance P, but had no effect on the depolarization or hyperpolarization caused by 5HT.

8. The results provide evidence that 5‐HT is not the transmitter which mediates the slow e.p.s.p. in myenteric neurones. The slow e.p.s.p. may be caused by substance P or another similar peptide.
Gaba‐antagonists alter spatial summation in receptive field centres of rod‐ but not cone‐drive cat retinal ganglion Y‐cells.
Authors: Kirby A W , Schweitzer‐Tong D E
Published: December 2014

1. When Y‐type cat retinal ganglion cells were driven by cones, the i.v. administration of the GABA‐antagonist picrotoxin failed to alter receptive field centre size. 2. This result is in marked contrast to our previous finding that when Y‐cells were driven by rods, GABA‐antagonists led to specific and reversible changes in centre size. 3. These results taken together suggest that for centre signals of Y‐cells, the rod and cone pathways are pharmacologically distinct.
Ion diffusion modified by tortuosity and volume fraction in the extracellular microenvironment of the rat cerebellum.
Authors: Nicholson C , Phillips J M
Published: December 2014

1. The validity of the macroscopic laws of ion diffusion was critically examined within the microenvironment of the extracellular space in the rat cerebellum using ion‐selective micropipettes and ionophoretic point sources. 2. The concepts of volume averaging, volume fraction (alpha) and tortuosity (lambda) were defined and shown to be theoretically appropriate for quantifying diffusion in a complex medium such as the brain. 3. Diffusion studies were made with the cations tetramethylammonium and tetraethylammonium and the anions alpha‐naphthalene sulphonate and hexafluoro‐arsenate, all of which remained essentially extracellular during the measurements. Diffusion parameters were measured for a period of 50s and over distances of the order of 0.1 mm. 4. Measurements of the diffusion coefficients of the ions in agar gel gave values that were very close to those derivable from the literature, thus confirming the validity of the method. 5. Measurements in the cerebellum did not reveal any systematic influences of ionophoretic current strength, electrode separation, anisotropy, inhomogeneity, charge discrimination or uptake, within the limits tested. 6. The pooled data from measurements with all the ions gave alpha = 0.21 +/‐ 0.02 (mean +/‐ S.E. of mean) and lambda = 1.55 +/‐ 0.05 (mean +/‐ S.E. of mean). 7. These results show that the extracellular space occupies about 20% of the rat cerebellum and that the diffusion coefficient for small monovalent extracellular ions is reduced by a factor of 2.4 (i.e. lambda 2) without regard to charge sign. The over‐all effect of this is to increase the apparent strength of any ionic source in the cerebellum by a factor of lambda 2/alpha, about 12‐fold in the present case, and to modify the time course of diffusion. 8. These conclusions confirm that the laws of macroscopic diffusion are closely obeyed in the cerebellum for small ions in the extracellular space, provided that volume fraction and tortuosity are explicitly taken into account. It is likely that these conclusions are generally applicable to other brain regions and other diffusing substances.
A study of renal‐efferent neurones and their neural connexions within cat renal ganglia using intracellular electrodes.
Authors: Decktor D L , Weems W A
Published: December 2014

1. Intracellular recordings were made, in vitro, fron neurones located within left renal ganglia and left coeliac ganglia of cat solar plexus. 2. Forty‐three percent of the neurones of the renal ganglia tested were identified by antidromic activation as renal‐efferent neurones. 3. Electrical stimulation of all nerve trunks emanating from renal ganglia, other than the renal nerves, did not antidromically activate renal ganglia neurones. Neurones not antidromically activated were designated as non‐efferent neurones. 4. Neurones within the renal ganglia were also characterized as phasic or tonic neurones depending on their pattern of discharge. 5. Electrical stimulation of renal nerves produced excitatory synaptic potentials (e.p.s.p.s) in 18% of the renal‐efferent neurones. 6. Compounded e.p.s.p.s were produced in 50% of the renal ganglia neurones tested by stimulation of the ipsilateral splanchnic nerves and in 84% of the neurones upon stimulation of the vertebral nerve. 7. Synaptic responses demonstrating characteristics typical of those induced by activation of multisynaptic neural pathways were produced upon stimulation of renal and coeliac nerves. 8. The results of this study indicate that the electrophysiological properties of renal‐efferent neurones vary considerably from neurone to neurone and that these neurones receive synaptic inputs from a variety of preganglionic fibres and possibly from other neurones having their soma located within the solar plexus.
Two groups of spinal interneurones that respond to stimulation of the abdominal viscera of the cat
Authors: McMahon S. B. , Morrison J. F. B.
Published: December 2014

1. Recordings have been made from sixty‐three spinal interneurones that received inputs from the abdominal viscera. These were divided into two groups: group A were sacral interneurones without either significant ascending projections or afferent input from the lumbar splanchnic nerves and group B were neurones with short ascending axons and afferent inputs from the lumbar splanchnic nerves, and often also from the pelvic and pudendal nerves.

2. Somato‐visceral convergence was common in both groups, and the somatic receptive fields of group A interneurones were in muscle and joints and less commonly skin innervated by sacral segments, whereas those of group B were innervated by lumbar and sacral segments.

3. Within both groups of neurones there was a proportion that showed no response to distension or contractions of the viscera, (despite the fact that they responded to visceral nerve stimulation), and those which did respond showed graded changes in discharge rate as intravesical pressure was raised. Some cells received inputs from only one viscus: the receptive fields of these cells are described as simple and the effect of raising the pressure in that viscus was either to excite or to inhibit the central neurone. Other cells received convergent inputs from two viscera: their receptive fields are described as compound and the effect of raising intraluminal pressures in the viscera allowed a further subdivision of these cells into two types. Type I cells were either excited or inhibited by distension or contractions of either viscus. Type II cells were excited by natural stimulation of one of the innervated viscera but inhibited by similar changes in the other. The static pressure thresholds of these cells were 9±5 mmHg intravesical pressure, and 24±11 mmHg intracolonic pressure (means±
s.d.).

4. It is proposed that within the population of neurones described there are cells (group A interneurones) that either mediate the vesico‐ and colono‐sphincteric reflexes or the colono‐vesical interactions that can be seen in the micturition reflex pathway.

5. It is proposed that the group B interneurones with short ascending projections mediate the vesico‐ and colono‐sympathetic reflexes because their patterns of convergence, position in the spinal cord, latencies, and static pressure thresholds are consistent with those reflexes.
Mediation of compensatory renal growth in the rat: cell culture demonstration of a serum factor.
Authors: Hansen P A
Published: December 2014

1. The participation of a circulating growth factor in the mediation of compensatory renal growth has been hypothesized but not proven. Theoretical considerations predict that in vitro methods could be profitably used to resolve this question, since such methods would allow dissociation of the growth effects of the postulated factor from the complex physiological changes which accompany compensatory renal growth in vivo. 2. A culture system using epithelial cells obtained from the rat kidney is described which is suitable for testing serum from previously unilaterally nephrectomized or sham‐operated rats for the presence of a factor mediating compensatory renal growth. The morphology of the cultured cells is compatible with that of proximal tubule epithelium, this being the cell type stimulated to divide in vivo after unilateral nephrectomy. 3. Treatment with serum from rats unilaterally nephrectomized 48 h previously results in consistent increase in uptake of tritiated thymidine by cultures, when compared with control serum from sham‐operated rats. Serum from rats unilaterally nephrectomized 18‐‐36 h previously is not consistently stimulatory. 4. There are indications that the differential effect of sera from unilaterally nephrectomized and control animals is due to the presence of a stimulatory factor in the former rather than an inhibitor in the latter. 5. Use of this culture system has confirmed the existence of a serum factor involved in compensatory renal growth.
The absence of position response in spindle afferent units from human finger muscles during accurate position holding.
Authors: Hulliger M , Nordh E , Vallbo A B
Published: December 2014

1. Single unit activity of muscle spindle afferents from finger extensor muscles was recorded in the radial nerve of waking human subjects. The mean discharge rate of the afferent units was determined while the receptor related finger was held at fixed angular positions of the metacarpo‐phalangeal joint. 2. During a visual tracking task the subjects had to maintain specified angular positions against a load of constant torque which opposed finger extension. For each unit a comparison was made between the mean discharge rates at two angular positions which differed by 20 deg. Under such isotonic conditions the rates of afferent discharge at the two joint positions did not significantly differ, neither for the whole sample of primary, nor for that of secondary units. This was true, no matter whether the load was small or intermediate. Large loads were not tested. 3. For comparison, the passive position responses of a sample of spindle afferent units from the same muscles were studied when the finger was held in fixed positions while the muscles were voluntarily relaxed. Under these conditions a significant position sensitivity was found for both primary and secondary afferents. The mean values were 0.28 impulses/sec. deg (primaries), and 0.21 impulses/sec. deg (secondaries). 4. The absence of position response during active position holding was interpreted as a manifestation of changes in fusimotor outflow which depended on joint position and were large enough to compensate for changes in muscle length.
Identification and brain‐stem projections of aortic baroreceptor afferent neurones in nodose ganglia of cats and rabbits.
Authors: Donoghue S , Garcia M , Jordan D , Spyer K M
Published: December 2014

1. The retrograde transport of horseradish peroxidase (HRP) was used to locate cell bodies of afferent neurones with axons in the aortic nerves within the nodose ganglia of cats and rabbits. 2. In the rabbit HRP‐labelled cells were localized to the medial aspect of the ganglion in the vicinity of the entry of the superior laryngeal and aortic nerves. 3. A similar grouping of labelled cells in rostro‐medial aspects of the ganglion was seen in the cat, though there were many other labelled cells distributed throughout the ganglion. It is suggested that the former cells may be barosensory and the latter chemosensory. 4. Extracellular recordings were made from baroreceptor afferents in the nodose ganglia of rabbits and cats using glass micro‐electrodes. Recordings sites were confined to rostral regions of the ganglia. 5. The projections of single baroreceptor afferents were studied by antidromic activation from the medulla oblongata using electrical stimulation applied through tungsten‐‐glass micro‐electrodes. Evidence is presented on the basis of depth‐‐threshold contours and antidromic latency which indicates that stimulation of the main axons can be distinguished from stimulation in areas of branching and presumed termination. 6. In cats aortic baroreceptor afferents gave branches to either medial (three out of six) or lateral (three out of six) subnuclei of the nucleus tractus solitarius (n.t.s.). One neurone had additional projections to the contralateral medial subnuclei of the n.t.s. 7. In rabbits the afferents have branches mainly to lateral subnuclei of the n.t.s. (seven out of eight neurones) with only one giving branches to the medial subnucleus of the n.t.s. and additionally to the nucleus alaris. 8. Projections to the medulla extending beyond the immediate vicinity of the n.t.s. were found in either species.
Stimulation by injected guanosine triphosphate of the sodium efflux in barnacle muscle fibres.
Authors: Bittar E E , Nwoga J
Published: December 2014

1. A study has been made of the mechanism by which injected disodium GTP stimulates the ouabain‐insensitive Na efflux in single muscle fibres from the barnacle, Balanus nubilus. 2. Injection of GTPNa2 causes a stimulatory response which is usually transitory and almost completely reversed by injecting MgCl2 (but not KCl). 3. Injected 5'‐guanylylimidodiphosphate, Gpp(NH)p, mimics this action of GTP but the reversal seen with injected Mg2+ is less pronounced. 4. (i) Pre‐treatment of these fibres with verapamil reduces the size of the stimulatory response to GTP and Gpp(NH)p. (ii) Pre‐injection of protein kinase inhibitor (PKI) or regulatory subunits reduces the response as well. (iii) Pre‐treatment with imipramine or trifluoperazine reduces the response to injected GTP; in combination with verapamil, a greater reduction in response is seen. 5. Injection of EDTA leads to a stimulatory response which is transitory. This response is largely abolished by verapamil. 6. Injection of cholera toxin leads to a sustained stimulatory rather than a transitory response. GTP or Gpp(NH)p when injected following peak stimulation by cholera toxin leads to a moderate sustained stimulation. 7. These results support the view that the stimulatory response to injected GTPNa2 is the result of activation of Ca2+ channels and of increased availability of GTPMg and that these two conditions bring about activation of adenylate cyclase and hence activation of cyclic AMP‐protein kinase by newly formed cyclic AMP.
Paracellular non‐electrolyte permeation during fluid transport across rabbit gall‐bladder epithelium
Authors: Steward Martin C.
Published: December 2014

1. Mucosa‐to‐serosa fluxes of seven polar non‐electrolytes were determined during isotonic fluid transport across the unilateral rabbit gall‐bladder preparation in an attempt to estimate the contribution of the paracellular pathway to the total transepithelial water flow.

2. 3H‐ and 14C‐labelled non‐electrolyte tracers appeared in the transported fluid at fractions (fn) of their mucosal concentration which were inversely related to molecular size: ethanediol, 0·80; thiourea, 0·55; glycerol, 0·16; erythritol, 0·11; mannitol, 0·05; sucrose, 0·05; inulin, 0·02. The mean volume flow rate was 78 μl. cm−2 hr−1.

3. While the fluxes of the larger molecules were probably due to diffusion through a small but unrestricted paracellular ‘shunt’ permeability, the high fn values obtained for the smaller molecules indicate the existence of a substantial paracellular permeability restricted to molecules smaller than erythritol.

4. Upper limits to the transcellular ethanediol and thiourea permeabilities, estimated from the time constants of tracer efflux from preloaded epithelial cells, were too low to account for more than a very small fraction of the transepithelial fluxes observed in the unilateral preparation.

5. Comparison of the fn values with the predictions of a hydrodynamic model of paracellular permeation suggests that in order to account for the large fluxes of ethanediol and thiourea, considerably more than one half of the transepithelial water flow must follow the paracellular pathway.

6. Following a reduction of the mucosal osmolality to 110 m‐osmole kg−1, the apparent non‐electrolyte permeability of the epithelium increased steadily over a period of 4 hr. This seems to reflect an increase in the shunt permeability rather than a change in the selectivity of the restricted permeability.

7. It is concluded that during isotonic fluid transport the bulk of the transepithelial water flow crossing the epithelium passes through paracellular channels of approximately 3 Å radius which are probably located in the intercellular junction.
Effect of dehydration on hypothalamic control of evaporation in the cat.
Authors: Baker M A , Doris P A
Published: December 2014

1. Cats were surgically prepared with intracranial thermodes for heating of the hypothalamic thermosensitive area or with venous cannulae for measurement of blood volume and plasma osmolality. They were kept in an environmental chamber in which the ambient temperature was cycled between 25 and 38 degrees C on an 18:6 hr diurnal schedule. 2. Measurements of blood volume and plasma osmolality and of the evaporative response to hypothalamic heating were made during the 38 degrees C phase of the diurnal temperature cycle in animals when they were hydrated ad lib and in the same animals after 72‐‐96 hr of water deprivation. 3. Water deprivation produced a loss of 10% of the body weight, a significant rise in plasma osmolality and a significant fall in blood volume. 4. Hypothalamic heating in hydrated animals generated a highly significant, positive, linear relationship between hypothalamic temperature and evaporative heat loss in every case. 5. In dehydrated animals, the evaporative response to hypothalamic heating was reduced. Rates of evaporation at a given hypothalamic temperature were lower and the slopes of the lines relating evaporative heat loss to hypothalamic temperature were significantly reduced. 6. It is concluded that dehydration reduces the thermal responsiveness of central neural structures controlling evaporation in the cat.
Post‐tetanic depolarization in sympathetic neurones of the guinea‐pig
Authors: Dun N. J. , Minota S.
Published: December 2014

1. Repetitive intracellular stimulation at a frequency of 5‐30 Hz for 1‐10 s evoked in neurones of the isolated inferior mesenteric and superior cervical ganglia of the guinea‐pig three types of post‐spike membrane potential changes: (i) hyperpolarization, (ii) hyperpolarization followed by a slow depolarization, and (iii) a second hyperpolarization following the initial two responses.

2. The initial post‐spike hyperpolarization had a mean duration of 2·0 s and was often associated with a fall in membrane resistance; it could be elicited in every sympathetic neurone studied. This response was termed the post‐tetanic hyperpolarization (PTH).

3. The slow depolarization which could be induced only in a portion of neurones had a mean amplitude and duration of 2·2 mV and 27·5 s, respectively; it was termed the post‐tetanic depolarization (PTD).

4. PTD was associated with a fall in membrane resistance, augmented by membrane hyperpolarization, and reduced by depolarization; its mean extrapolated equilibrium potential was ‐38 mV.

5. PTD was not blocked by nicotinic and muscarinic antagonists, or α‐and β‐adrenergic receptor antagonists, whereas it was suppressed by adrenaline, noradrenaline, Co2+ and a low Ca2+ solution.

6. The amplitude of the single spike after‐hyperpolarization in normal Krebs solution as well as in high K+ solution was increased during PTD; furthermore, conditioning hyperpolarization to the level of EK increased the amplitude of PTD in normal Krebs as well as in high K+ solution.

7. PTD with similar amplitude, time course and membrane characteristics could be evoked in a portion of neurones of the rabbit superior cervical ganglia; however, PTD was not detected in neurones of the rat superior cervical ganglia.

8. Decentralization of the guinea‐pig and rabbit superior cervical ganglia for 14 d did not alter the number of neurones in which PTD could be elicited, its amplitude, or its time course.

9. Our results suggest that a chemical substance(s) is responsible for the generation of PTD; it may be released from the soma and/or dendrites and acts in an auto‐receptive manner on the cells in question. The nature and origin of the second hyperpolarization remain to be clarified.
A transcortical loop demonstrated by stimulation of low‐threshold muscle afferents in the awake monkey
Authors: Chofflon M. , Lachat J.-M. , Rüegg D. G.
Published: December 2014

1. The hypothesis that a transcortical loop can be activated by electrical stimulation of low‐threshold muscle afferents was tested. The effect of these afferents on the excitability of motoneurones was measured with the monosynaptic spinal reflex (H‐reflex).

2. Four monkeys were trained to maintain a constant tonic activity in the soleus muscle so that the amplitude of evoked H‐reflexes was constant. The intensity of conditioning stimuli was just subthreshold for direct or reflex electromyographic responses. The intensity of the test stimuli was adjusted to evoke an H‐reflex of maximal amplitude. The amplitude of the H‐reflex was recorded for different intervals between conditioning and test stimuli (10‐1000 msec).

3. The excitability curve obtained showed three components: (1) an early excitatory process, F1, at intervals of 10‐20 msec, (2) a late excitatory process, F2, at intervals of 40‐80 msec and (3) a short latency depression of about 400 msec duration, on which F1 and F2 were superimposed.

4. F2 was selectively abolished during cooling of the contralateral motor cortex, after an irreversible lesion of the motor cortex, and after pyramidotomy; however, F1 and the inhibition remained unchanged.

5. The conduction time from the tibial nerve to the somatosensory cortex (SI), the cortical delay between SI and motor cortex, and the conduction time from motor cortex to the soleus muscle were measured in an anaesthetized animal. The sum of these values as an estimate of the transcortical loop time was 5 msec shorter than the latency of F2.

6. It is concluded that a transcortical loop can be activated by electrical stimulation of low‐threshold muscle afferents and, by analogy, also by mechanical perturbations applied during a motor task.
Effects of adenosine and its analogues on the perfused hind limb artery and vein of anaesthetized dogs
Authors: Cotterrell D. , Karim F.
Published: December 2014

1. The effects of infusion of adenosine and its analogues on arterial and venous resistance have been studied in the vascularly and sympathetically isolated hind limb of chloralose‐anaesthetized dogs. Resistance changes have been assessed by monitoring changes in perfusion pressures at constant flow through the femoral artery and metatarsal vein.

2. With sympathetic stimulation (10 V, 2 msec, 0·5‐2 Hz applied to the cut peripheral end of the lumbar sympathetic trunk), continuous infusion of adenosine, to produce a concentration of approximately 2 × 10−5
m, resulted in a near maximal sustained decrease in arterial perfusion pressure of 35·3±3·6%, and a decrease of about half this in venous perfusion pressure.

3. Bolus injections of adenosine into the artery, to produce a concentration of about 7 × 10−5
m, caused a transient decrease in resistance similar to that observed with continuous infusion. However, the venous response was smaller than that induced by continuous infusion.

4. Withdrawal of sympathetic stimulation to the limb had little effect on adenosine‐induced vasodilatation in the artery, but abolished the small response of the vein.

5. Less than 5% vasodilatation was produced in the artery and vein by 2‐deoxyadenosine, inosine, guanosine, xanthosine, cytidine or uridine when infused in amounts up to ten times, or by sodium phosphate (pH 7·4) in amounts one hundred times the maximal amounts of adenosine given.

6. These results suggest that adenosine caused vasodilatation, at least in arterioles, largely by acting directly on vascular muscle rather than via presynaptic inhibition of noradrenaline release.