bluuebunny/crossref_metadata_2025 huggingface dataset:
Partial uncoupling of salt gland blood flow and secretion in the Pekin duck (Anas platyrhynchos).
Authors: Gerstberger R
Published: December 2014

1. The aim of this study was to investigate the relationship between the blood flow through and the secretion by the salt glands of conscious, salt‐water‐adapted Pekin ducks. 2. Intravenous loading with hypertonic saline induced a steady‐state secretion from the salt glands with a concomitant increase in whole‐organ blood flow. The distribution of elevated local glandular blood flow was, however, uneven and in addition demonstrated vasomotor patterns that ranged from constant to rhythmic. 3. During on‐going salt gland secretion, the infusion of three vasoactive agents, 5Val‐angiotensin II (ANG II), 8Arg‐vasotocin (AVT) and noradrenaline, via the carotid artery had differential effects on salt gland blood flow and secretion. 4. ANG II (80 pmol min‐1 (kg body wt)‐1) had no effect on mean arterial blood pressure (MABP), produced a transient 30% decrease in glandular blood flow and strongly diminished salt gland secretion (retention of 6.4 mosmol NaCl). 5. AVT (20 pmol min‐1 (kg body wt)‐1) had no effect on MABP and did not alter salt gland secretion despite a 35% reduction in blood flow. 6. Noradrenaline (20 nmol min‐1 (kg body wt)‐1) elevated MABP by 15 mmHg, reduced salt gland blood flow by more than 50%, but diminished salt gland secretion only slightly (retention of 2.7 mosmol NaCl). 7. Using ANG II, AVT and noradrenaline as hormonal tools, integrated changes in blood flow rate did not correspond with integrated changes in salt gland excretion. The partial dissociation between both parameters shows that control of secretion by the salt gland is more complex than simply being linearly dependent upon blood flow through it.
Chemiosmotic control of renin release from isolated renin granules of rat kidneys.
Authors: Sigmon D H , Fray J C
Published: December 2014

1. Renin‐containing granules were isolated, characterized, and used to gain insight into a possible chemiosmotic mechanism of renin secretion. 2. Renin granules were obtained by a modification of the sucrose gradient method, which yielded a 67‐fold purification of renin granules as assessed by marker enzymes, or a modification of the Percoll gradient, which yielded a 230‐fold enrichment of renin granules. 3. Granular renin content was increased by chronic sodium deprivation and hypophysectomy. 4. Renin release from granules was inversely related to osmotic strength (150‐900 mosmol l‐1). pH had a biphasic effect on renin release, with greater stimulation at both acidic (pH 5) and alkaline (pH 8 and 9) pH. The pH effect was dependent on Cl‐; raising Cl‐ stimulated release. This effect was abolished by‐oligomycin and N,N'‐dicyclohexylcarbodiimide (DCCD) at pH 5, but not at pH 8; the effect was enhanced by NH4+. 5. Either valinomycin or carbonyl cyanide m‐chlorophenylhydrazone (CCCP) alone was without effect; but in combination they caused a potent stimulation at all pHs. Nigericin stimulated renin release at all pHs, but its effect required K+. 6. Raising K+ stimulated renin release from granules, whereas raising Na+ was without effect. Lowering Ca2+ below 10(‐6) M significantly stimulated renin release. 7. Taken together, the evidence is consistent with the chemiosmotic hypothesis for the control of renin release from granules and may have some implications for the regulation of renin secretion from juxtaglomerular cells.
Plasticity of sympathetic reflex organization following cross‐union of inappropriate nerves in the adult cat.
Authors: Jänig W , Koltzenburg M
Published: December 2014

1. The present study has investigated the reflex organization of sympathetic neurones and its control of autonomic effector organs following nerve injury and repair. A well‐defined population of vasoconstrictor neurones supplying blood vessels of the hairy skin was forced to innervate a territory that contained some appropriate, but mainly inappropriate autonomic effector organs. For this purpose the central stump of the cut sural nerve was sutured to the peripheral stump of the cut tibial nerve 11‐12 months prior to the terminal experiment. 2. The activity of postganglionic sympathetic neurones was recorded from fine strands of the sural nerve proximal to the nerve lesion. Using a laser‐Doppler device cutaneous blood flow was measured in the hairless skin of the hindpaw that was now reinnervated by the sural nerve. The results show a qualitative change of the reflex organization of sympathetic neurones following cross‐union of these nerves. 3. Stimulation of arterial chemoreceptors by ventilating the animals with a hypoxic gas mixture (8% O2 in N2 for 3‐8 min) increased the activity in twelve out of thirteen strands containing postganglionic sympathetic fibres. The increase of sympathetic activity contrasts with results from normal animals where systemic hypoxia causes a reflex decrease of activity in postganglionic fibres of the sural nerve. 4. Reflex changes of sympathetic activity were closely followed by corresponding changes of cutaneous blood flow. Systemic hypoxia produced vasoconstriction in operated animals in contrast to the vasodilatation observed in normal animals. 5. We conclude that the reflex organization of sympathetic neurones can change qualitatively following nerve lesion when sympathetic neurones regenerate and supply inappropriate target tissues. This long‐lasting change reflects the plasticity of the autonomic nervous system and can produce a sustained abnormal control of reinnervated autonomic effector organs.
Changes in the baroreceptor reflex at the start of muscle contraction in the decerebrate cat.
Authors: McWilliam P N , Yang T , Chen L X
Published: December 2014

1. The action of muscle contraction on the sensitivity of the cardiac vagal component of the baroreceptor reflex was examined in decerebrate cats. 2. The sensitivity of the baroreceptor reflex was expressed as the difference between the maximum prolongation of the R‐R interval in response to carotid sinus baroreceptor stimulation and the mean of ten R‐R intervals immediately before carotid sinus pressure elevation. 3. Muscle contraction elicited by electrical stimulation of L7 ventral roots (50 Hz) significantly reduced the sensitivity of the baroreceptor reflex by reducing the prolongation of the R‐R interval from 269 +/‐ 31 to 159 +/‐ 22 ms. 4. Inhibition of the cardiac vagal component of the baroreceptor reflex was seen just 1 s after the onset of contraction and with stimulation frequencies as low as 10 Hz. 5. These results show for the first time that changes in the sensitivity of the baroreceptor reflex during exercise result in part from afferent information originating in the contracting muscles.
Effect of frusemide on lithium clearance and proximal tubular reabsorption in anaesthetized rats.
Authors: Walter S J , Shirley D G
Published: December 2014

1. In order to investigate the lithiuretic effect of frusemide, simultaneous measurements of fractional lithium excretion (FELi) and fractional fluid delivery to the end of the proximal convoluted tubules were made in Inactin‐anaesthetized rats, first during a control period, then during intravenous infusion of frusemide at either 0.8 or 8.0 mg kg‐1 h‐1. Fluid balance was maintained by infusion of NaCl‐KCl solution adjusted to match urinary excretion rates; measurements were made after urine flow had stabilized. 2. In time‐control animals, which did not receive frusemide, no significant changes were observed in either FELi or fractional fluid delivery to the end of the proximal convoluted tubules (determined as the plasma/tubular fluid inulin concentration ratio, P/TFIn). 3. In animals given the high dose of frusemide, FELi increased from 0.22 +/‐ 0.02 (mean +/‐ S.E.M.) during the control period to 0.45 +/‐ 0.03 during frusemide infusion (P less than 0.001); this was accompanied by a modest increase in P/TFIn, from 0.43 +/‐ 0.02 to 0.51 +/‐ 0.02 (P less than 0.01). 4. In animals given the lower dose of frusemide, FELi increased from 0.21 +/‐ 0.01 to 0.37 +/‐ 0.01 (P less than 0.001). In this group, however, there was no discernible change in P/TFIn (0.43 +/‐ 0.02 vs. 0.44 +/‐ 0.01, not significant). 5. These results suggest that under control conditions a significant component of lithium reabsorption may occur beyond the proximal tubule, most likely in the loop of Henle.
Dynamic control of muscle stiffness and H reflex modulation during hopping and jumping in man.
Authors: Dyhre‐Poulsen P , Simonsen E B , Voigt M
Published: December 2014

1. The objective of the study was to evaluate the functional effects of reflexes on muscle mechanics during natural voluntary movements. The excitability of the H (Hoffmann) reflex was used as a measure of the excitability of the central component of the stretch reflex. 2. We recorded EMG, ground reaction forces and the H reflex in the soleus muscle in humans while landing from a downward jump, during drop jumping and during hopping. The movements were also recorded by high‐speed cinematography. 3. The EMG pattern was adapted to the motor task. When landing the EMG in the soleus muscle and in the anterior tibial muscle showed preinnervation and alternating activity after touch down. When hopping there was little preinnervation in the soleus muscle, and the activity was initiated about 45 ms after touch down by a peak and continued unbroken until lift off. In the drop jumps the EMG pattern depended on the jumping style used by the subject. 4. The H reflex in the soleus muscle was strongly modulated in a manner appropriate to the requirements of the motor task. During landing from a downward jump the H reflex was low at touch down whereas while hopping it was high at touch down. During drop jumping it was variable and influenced by the jumping technique. 5. Muscle stiffness in the ankle joint was negative after touch down when landing, but always positive when hopping. 6. It is suggested that during landing the alternating EMG pattern after touch down was programmed and little influenced by reflexes. During hopping reflexes could contribute to the initial peak and the EMG during lift off. 7. The programmed EMG activity and the suppression of the H reflex while landing probably contribute to the development of the negative stiffness and change the muscles from a spring to a damping unit.
Species‐specific transfer of plasma albumin from blood into different cerebrospinal fluid compartments in the fetal sheep.
Authors: Dziegielewska K M , Habgood M D , Møllgård K , Stagaard M , Saunders N R
Published: December 2014

1. The blood‐cerebrospinal fluid (CSF) transfer of endogenous sheep albumin and several exogenous species of albumin has been investigated in different CSF compartments of the immature fetal sheep brain, at an early stage of development (60 days gestation, term is 150 days) when the CSF concentration of total protein is high. 2. There were marked differences in the steady‐state CSF/plasma ratios for all species of albumin (including endogenous sheep albumin) between different CSF compartments. Ratios measured in the cisterna magna were significantly higher than those in the dorsal subarachnoid space, which in turn were higher than those in the lateral ventricles. The ratios for endogenous sheep albumin were (%; mean +/‐ S.E.M.): lateral ventricle (LV), 4.0 +/‐ 0.03; dorsal subarachnoid (DSA), 6.1 +/‐ 1.0; cisterna magna (CM), 13.7 +/‐ 0.8. 3. Three hours after I.V. injection, the CSF/plasma ratios for bovine albumin (LV, 2.0 +/‐ 0.2; DSA, 2.4 +/‐ 0.1; CM, 7.2 +/‐ 0.7%) were significantly lower than the ratio for endogenous sheep albumin in all three compartments. The ratios for human albumin (LV, 0.7 +/‐ 0.2; DSA, 1.0 +/‐ 0.2; CM, 3.9 +/‐ 0.4%) were significantly lower than those for bovine albumin. 4. In all three CSF compartments, the endogenous sheep albumin ratios were higher than would be expected on the basis of transfer by passive mechanisms. Conversely, steady‐state CSF/plasma ratios for [3H]sucrose and [14C]inulin were consistent with passive transfer, and there were no differences between the ratios for these markers measured in each of the three CSF regions. 5. Goat albumin and [35S]sheep albumin ratios were not significantly different, 5 h after injection, from the endogenous sheep albumin levels in each of the three CSF compartments. 6. It is concluded that in the 60‐day‐old fetal sheep, all of the endogenous albumin in CSF is derived from the plasma by a specific transfer mechanism that can distinguish between different species of the same protein. There is also some evidence of a small passive component of blood‐CSF albumin transfer. 7. Immunocytochemical evidence suggests that the route of transfer from blood to CSF is transcellular, through the choroid plexus epithelial cells. 8. Regional variations in albumin ratios are probably due to differences in specific transfer into each CSF compartment. This is reflected in a differential immunocytochemical staining for albumin in choroid plexus epithelial cells from different regions of the brain. 9. The results are discussed in terms of differences in albumin amino acid sequences, structural homologies, and transfer by a specific transcellular mechanism.
Uneven distribution of excitatory amino acid receptors on ventral horn neurones of newborn rat spinal cord.
Authors: Onodera K , Takeuchi A
Published: December 2014

1. The distribution of excitatory amino acid receptors on ventral horn neurones was investigated using slices of newborn rat spinal cord. 2. The neurone and the tip of the pipette used to inject amino acids were visualized using Lucifer Yellow under a fluorescent microscope. The pipette was precisely located on the soma and dendrite of the neurone under visual control, and L‐glutamate (Glu), L‐aspartate (Asp), N‐methyl‐D‐aspartate (NMDA), kainate (KA) and quisqualate (Quis) were ionophoretically applied with a short pulse. The potential changes were intracellularly recorded from the soma. 3. Sensitivity to Glu as tested with short pulses (1‐2 ms) was almost the same at the soma and along dendrites. 4. The amplitude of the responses to NMDA produced at the soma and the proximal part of the dendrite was about the same as that of Glu, but smaller than that of Glu at the distal part of the dendrite. Suppression of the Glu potential by an NMDA receptor antagonist, 2‐amino‐5‐phosphonovaleric acid (APV), was greater at the soma than at the dendrite, suggesting that the contribution of NMDA receptors to the Glu potential was greater at the soma. 5. Sensitivity to Asp was about one‐half that to Glu sensitivity on the soma and even less on the dendrite. Sensitivity to KA was high at the soma and low at the dendrite. However, Quis responses were produced throughout the neurone. 6. The Quis response induced by the application of a short pulse showed two phases: a fast response followed by a very slow depolarization that lasted more than 10 s. 7. The fast Quis response was easily desensitized and insensitive to APV. The time course of the fast Quis potential was shorter than that of Glu. 8. The slow Quis response was more pronounced at the dendrites than at the soma and was reduced by the intracellular injection of EGTA, suggesting the contribution of Ca2+ in the cell, possibly mediated by a second messenger system. 9. Experimental results suggest that the distribution of excitatory amino acid receptors differs between the soma and the dendrites of spinal neurones.
The dependence of the response of cat spindle Ia afferents to sinusoidal stretch on the velocity of concomitant movement.
Authors: Baumann T K , Hulliger M
Published: December 2014

1. The responses of de‐efferented soleus muscle spindle primary afferents to 1 Hz sinusoidal stretches, which were superimposed on triangular background movements of intermediate amplitude (1.2 mm, half peak‐to‐peak) and widely varying speed, were recorded in anaesthetized cats. 2. Compared with control responses to the same sinusoids applied at fixed mean muscle length, the sensitivity to small (50 and 100 microns, half peak‐to‐peak), but not to large (1000 microns), sinusoidal movements was dramatically reduced during concomitant stretching, unless the background movements were extremely slow (well below 0.005 resting lengths per second). 3. For small stretches (50 and 100 microns) the reduction of sensitivity caused by background movement depended on the speed of this movement. For the highest velocity studied (1.6 mm s‐1, corresponding to about 0.03 resting lengths per second) sensitivity dropped to below 10% of the control values. 4. The functional implication is that the sensitivity of spindle Ia afferents to small irregularities of voluntary movements (of any but the slowest speeds) may well be very much lower than it has hitherto been inferred from the striking sensitivity to minute disturbances at fixed mean muscle length. The present finding clearly puts extra demands on the gain of any spinal or central reflex actions of the sensory feedback from spindle afferents. 5. The effect is interpreted in terms of the widely accepted cross‐bridge hypothesis of spindle small‐movement sensitivity. The result suggests that in de‐efferented intrafusal muscle fibres, which are subjected to imposed stretches, connected cross‐bridges (conveying a friction‐like property to the contractile fibre poles) may exist not only in a state of permanent attachment, but also in a dynamic equilibrium between stretch‐induced detachment and reattachment. Indirect evidence further suggests that the duration of this disruption and reattachment cycle is of the order of 1 s.
Membrane properties of external urethral and external anal sphincter motoneurones in the cat.
Authors: Sasaki M
Published: December 2014

1. Intracellular recordings were made from external urethral sphincter (EUS) and external anal sphincter (EAS) motoneurones in the cat spinal cord under pentobarbitone anaesthesia. EUS and EAS motoneurones were located in segments S1 and S2 in the lateral part of the ventral horn corresponding to column Y of Romanes in the cat or group X of Onuf in man. 2. The axonal conduction velocity of sphincter motoneurones, calculated from the latency of the antidromic action potential and the conduction distance, ranged from 16 to 80 ms‐1, much slower than that of hindlimb motoneurones. The duration of the spike after‐hyperpolarization (AHP) was in a similar range to that of hindlimb motoneurones. The antidromic latency, the duration of the action potential and the duration of the AHP were positively correlated with one another. 3. The input resistance ranged from 2.6 to 9.0 M omega and was positively correlated with the latency of the antidromic spike. The plots of input resistance versus conduction velocity in sphincter motoneurones were distributed around the extrapolated regression line determined for hindlimb motoneurones, indicating that there is a common correlation amongst conduction velocity, input resistance, and size of motoneurones regardless of the muscle type innervated by a motoneurone. 4. The regression line relating AHP duration and input resistance in sphincter motoneurones was quite different from that in hindlimb motoneurones in its slope, indicating that the AHP duration does not depend solely on the size of the motoneurone. 5. The voltage responses to injection of steps of hyperpolarizing current developed a time‐dependent depolarizing 'sag' at higher current levels. The delay in onset and the time constant of decay of this depolarizing sag depended upon the peak amplitude of the hyperpolarizing response. The slope resistance in the I‐V curve decreased in the hyperpolarizing direction in all neurones examined, indicating the existence of anomalous rectification analogous to the Q current IQ. In some sphincter motoneurones, an increase of slope resistance in the I‐V curve was observed when the membrane was further hyperpolarized. 6. The membrane time constant was positively correlated with input resistance, suggesting that motoneurones with high input resistance have high specific membrane resistivity. The dendritic‐to‐soma conductance ratio (p) and electrotonic length of dendrite (L) were estimated according to Rall's model. p was smaller than that of hindlimb motoneurones, suggesting less developed dendritic arborization. L was similar to that of hindlimb motoneurones. 7. No differences were observed, in any of the above characteristics of motoneurones, between EUS and EAS.
Cross‐bridge movement in fast and slow skeletal muscles of the chick.
Authors: Matsubara I , Yagi N , Saeki Y , Kurihara S
Published: December 2014

1. Fast (posterior latissimus dorsi, PLD) and slow (anterior latissimus dorsi, ALD) muscles of the chick were studied by time‐resolved X‐ray diffraction using a synchrotron radiation source. 2. In both muscles and at both 20 and 30 degrees C, intensities of the X‐ray equatorial reflections changed faster than tension at the beginning of tetanus. When the intensity change was converted into the mass transfer from the thick to the thin filament, the difference between the half‐rise times of the transfer and tension development at 20 degrees C was 140 ms in ALD and 37 ms in PLD. At 30 degrees C it was 110 ms and 10‐20 ms for ALD and PLD respectively. 3. These results indicate that in the early stage of contraction, some of the myosin heads in the vicinity of the thin filament are developing little or no tension, and suggest that the fast and slow muscles differ in the transition rate of myosin heads from the state of attachment with low tension to that with high tension.
Topography and nociceptive receptive fields of climbing fibres projecting to the cerebellar anterior lobe in the cat.
Authors: Ekerot C F , Garwicz M , Schouenborg J
Published: December 2014

1. The cutaneous receptive fields of 225 climbing fibres projecting to the forelimb area of the C3 zone in the cerebellar anterior lobe were mapped in the pentobarbitone‐anaesthetized cat. Responses in climbing fibres were recorded as complex spikes in Purkinje cells. 2. A detailed topographical organization of the nociceptive climbing fibre input to the C3 zone was found. In the medial C3 zone climbing fibres with receptive fields covering proximal and/or lateral parts of the forelimb projected most medially. Climbing fibres with receptive fields located more medially on the forelimb projected successively more laterally. The sequence of receptive fields found in the lateral C3 zone was roughly the reverse of that in the medial C3 zone. Climbing fibres with receptive fields restricted to the digits projected preferentially to the caudal part of the forelimb area, whereas those with receptive fields covering both proximal and ventral areas of the forearm projected to more rostral parts. 3. The representation of the forelimb was uneven. Receptive fields with a focus on the digits or along the lateral side of the forearm dominated. 4. The proximal borders of the receptive fields were located close to joints. The area from which maximal responses were evoked was usually located eccentrically within the receptive field. Based on spatial characteristics the receptive fields could be divided into eight classes, which in turn were tentatively divided into subclasses. Similar subclasses of receptive fields were found in different cats. This classification was further supported by the results of a quantitative analysis of eighty‐nine climbing fibres. The receptive fields of these climbing fibres were mapped with standardized noxious stimulation. 5. Climbing fibres terminating within sagittal strips (width, 100‐300 microns; length, greater than 1 mm) had receptive fields which belonged to the same subclass. There were commonly abrupt changes in receptive fields between such microzones. Most classes of receptive fields were found in both the medial and the lateral parts of the C3 zone. However, receptive fields with a focus on the ventral side of either the metacarpals, the wrist or the forearm were found only in the medial part of the C3 zone. Furthermore, the class of receptive fields restricted to the lateral side of the upper arm and shoulder was only found in the lateral part of the C3 zone. 6. In the discussion, it is proposed that climbing fibres projecting to each microzone carry information from spinal multireceptive reflex arcs acting on a single muscle or a group of synergistic muscles.(ABSTRACT TRUNCATED AT 400 WORDS)
Inhibitory modulation by FMRFamide of the voltage‐gated sodium current in identified neurones in Lymnaea stagnalis.
Authors: Brussaard A B , Lodder J C , ter Maat A , de Vlieger T A , Kits K S
Published: December 2014

1. The putative neurotransmitter FMRFa (Phe‐Met‐Arg‐Phe‐amide) caused an inhibitory modulation of the voltage‐gated sodium current (INa) in central neurones, the peptidergic caudo dorsal cells (CDCs) of the mollusc Lymnaea stagnalis. FMRFa reduced INa at all command potentials tested (ranging from ‐35 to +20 mV), but the amplitude of the effect of FMRFa was voltage dependent, inhibition being stronger at more negative potentials (50 +/‐ 5% reduction at half‐maximal INa activation versus 25 +/‐ 8% at the peak of the I‐V curve). 2. INa current traces were well fitted by a Hodgkin & Huxley based model, using m3 activation kinetics and two time constants for inactivation. 3. The steady‐state inactivation curve of INa was characterized by half‐maximal inactivation at ‐42.5 +/‐ 1.81 mV and a slope factor of 4.6 +/‐ 0.28 mV. The fastest time constant of inactivation ran from 100 +/‐ 5 to 0.8 +/‐ 0.32 ms and the slower time constant from 505 +/‐ 45 to 4.8 +/‐ 1.40 ms in the range ‐40 to ‐5 mV. 4. FMRFa had no significant effect on either component of inactivation, nor on the voltage dependence of steady‐state inactivation, nor on the maximal conductance. 5. FMRFa affected the activation of INa. The activation time constant was increased, ranging from 0.75 +/‐ 0.050 to 0.22 +/‐ 0.017 ms under control and from 0.91 +/‐ 0.043 to 0.31 +/‐ 0.038 ms with FMRFa in the voltage range ‐25 to +5 mV. The steady‐state activation curve was shifted to less negative potentials: half‐maximal activation occurred at ‐26.5 +/‐ 1.2 mV under control and at 23.6 +/‐ 1.4 mV with FMRFa; the slope factor (4.6 +/‐ 1.4 mV in control experiments) was not affected. The combination of slower activation kinetics and a shift in the voltage dependence of activation in the Hodgkin & Huxley based model, adequately explained the reduction of INa by FMRFa. 6. The physiological consequence is that the spiking threshold is increased, causing an arrest of on‐going firing activity and a decrease in excitability.
The modulation of rat hippocampal synaptic conductances by baclofen and gamma‐aminobutyric acid.
Authors: Yoon K W , Rothman S M
Published: December 2014

1. We examined the effects of gamma‐aminobutyric acid (GABA) and baclofen on pre‐ and postsynaptic membrane conductances in dissociated rat hippocampal cells. Both GABA (5 microM with 10 microM‐bicuculline) and baclofen (50 microM) caused small but significant increases in membrane conductance that were blocked by 2‐hydroxysaclofen (100 microM), a GABAB receptor antagonist. This increase in membrane conductance seems to be mediated by GABAB receptors. 2. At a low concentration of GABA (1 microM) which has a very small direct postsynaptic effect on GABAA receptors, no postsynaptic GABAB effect was detected. However, at this concentration, GABA near maximally attenuated both excitatory and inhibitory synaptic currents. This GABA effect on transmitter release was significantly attenuated by 2‐hydroxysaclofen. 3. Baclofen was also more potent in attenuating the inhibitory synaptic conductance than increasing postsynaptic conductance. Concentrations below 1 microM diminished synaptic currents by greater than 50%. At these low baclofen concentrations 2‐hydroxysaclofen significantly attenuated baclofen's reduction of synaptic currents. 4. The effects of GABA and baclofen on synaptic conductances were blocked by pretreating the cultures with pertussis toxin, suggesting that a GTP‐associated protein, Gi or Go is responsible for reducing transmitter release. 5. Despite the ability of GABA to diminish inhibitory synaptic currents through GABAB receptor activation, we observed no effect of 2‐hydroxysaclofen on paired‐pulse depression. Therefore, these presynaptic GABAB receptors may not be true ‘autoreceptors’. 6. Our findings indicate that in culture, at least, the presynaptic GABAB effect responsible for synaptic modulation has a pharmacological profile similar to the postsynaptic GABAB effect. At present, it is unnecessary to postulate two different types of GABAB receptors.
Effects of different lighting regimes on daily hormonal and behavioural rhythms in the pregnant ewe and sheep fetus.
Authors: McMillen I C , Walker D W
Published: December 2014

1. We have studied the effect of altering the time of darkness during a 12 h photoperiod on the diurnal rhythms of maternal and fetal plasma melatonin and prolactin concentrations and fetal breathing movements (FBMs) in the late pregnant sheep. 2. Four ewes were exposed to a ‘normal’ 12 h light‐12 h dark regime with lights off at 19.00 h. Eight ewes were exposed to an ‘altered’ 12 h light‐12 h dark regime with lights off at 11.00 h. FBMs were recorded continuously and 2 hourly maternal and fetal blood samples taken during 24 h experiments between 120 and 138 days gestation. 3. Plasma melatonin concentrations were higher during the hours of darkness in the ewes and fetuses in both the normal and altered groups; i.e. altering the time of darkness was associated with a shift in the timing of the daily increase in melatonin concentrations in the mother and fetus. 4. In the fetuses, the mean 24 h plasma prolactin concentration was higher in the altered lighting group (28.8 +/‐ 6.1 micrograms/l) compared to the normal lighting group (13.0 +/‐ 3.9 micrograms/l). There was no difference, however, between groups in the daily variation of fetal plasma prolactin concentrations, which were higher at 17.00‐01.00 h than at 05.00‐19.00 h. Thus, altering the time of darkness did not change the timing of the daily plasma prolactin rhythm in the fetus. 5. Under the normal lighting regime maternal plasma prolactin concentrations were higher at 17.00‐19.00 h (i.e. from 2 h before lights off) than at 09.00‐11.00 h. In contrast, under altered lighting, plasma prolactin concentrations were higher at 01.00‐07.00 h (i.e. 2‐8 h after lights on) than at 09.00 h. 6. In the normal lighting group the incidence (min/h) of FBMs were highest at 16.00‐21.00 h and reached a minimum at 05.00‐06.00 h. In contrast, in the altered lighting group the incidence of FBMs was lowest at 19.00‐20.00 h and reached a maximum at 11.00‐12.00 h. 7. The results suggest that the light‐dark cycle influences the diurnal modulation of FBMs, but not the daily variation of fetal plasma prolactin concentrations. The role of plasma melatonin concentrations, and evidence for a photo‐inducible phase of increased prolactin secretion in the fetus, is discussed.
Identification of neurons receiving input from pulmonary rapidly adapting receptors in the cat.
Authors: Lipski J , Ezure K , Wong She R B
Published: December 2014

1. Extracellular and intracellular recordings were made in the caudal subdivisions of the nucleus tractus solitarii (NTS) to locate and characterize neurons excited by afferents from pulmonary rapidly adapting receptors (RARs) in Nembutal‐anaesthetized cats. 2. Neurons identified as second‐order cells activated by RARs (RAR‐cells) were activated by electrical stimulation of myelinated afferents in the cervical portion of the vagus nerve(s) and by at least two of the following ‘physiological’ stimuli: (a) collapse of the lungs to atmospheric pressure; (b) hyperinflation of the lungs by either increasing tidal volume or maintained lung inflations; and (c) brief inhalation of ammonia vapour. 3. Of the ninety‐nine RAR‐cells identified and studied extracellularly, eighty‐four were localized within the commissural nucleus of the NTS. Seventy‐four cells responded monosynaptically to electrical stimulation of both ipsi‐ and contralateral vagal stimulation. The remaining ten RAR‐cells located in the commissural nucleus and the fifteen located in the caudal portion of the medial subnucleus of the NTS rostral to the obex, responded to the ipsilateral vagus only. 4. Under control ventilatory conditions (bilateral pneumothorax, positive end‐expiratory pressure of approx. 2 cmH2O), forty‐eight of the ninety‐nine RAR‐cells showed spontaneous ventilator‐related activity, occurring primarily during ventilator‐induced deflations (thirty of forty‐eight). ‘Reversal’ of this ventilator‐related modulation, from firing predominantly during lung deflations to lung inflations, and vice versa, could be induced in eleven of the RAR‐cells by changing the lung volume or by the inhalation of ammonia vapour. 5. Modulation of firing in synchrony with the central respiratory rhythm was observed in the activity of fourteen of the ninety‐nine RAR‐cells. 6. Intracellular recordings were made from twenty‐two NTS neurons caudal to the obex that received monosynaptic excitatory postsynaptic potentials (EPSPs) from both ipsi‐ and contralateral vagus nerves. Two were positively identified as RAR‐cells. 7. It is concluded that the commissural nucleus of the NTS is the major location of RAR‐cells, and that the response characteristics of these neurons largely, but not entirely, correspond to the known properties of RARs.
Regional cerebral blood flow during volitional breathing in man.
Authors: Colebatch J G , Adams L , Murphy K , Martin A J , Lammertsma A A , Tochon‐Danguy H J , Clark J C , Friston K J , Guz A
Published: December 2014

1. Positron emission tomographic imaging of brain blood flow was used to identify areas of motor activation associated with volitional inspiration in six normal male subjects. 2. Scans were performed using intravenous infusion of H2(15)O during voluntary targeted breathing and positive pressure passive ventilation at the same level. 3. Regional increases in brain blood flow, due to active inspiration, were derived using a pixel by pixel comparison of images obtained during the voluntary and passive ventilation phases. 4. Pooling data from all subjects revealed statistically significant increases in blood flow bilaterally in the primary motor cortex (left, 5.4%; right, 4.3%), in the right pre‐motor cortex (7.6%), in the supplementary motor area (SMA; 3.1%) and in the cerebellum (4.9%). 5. The site of increased neural activation in the motor cortex, associated with volitional inspiration, is consistent with an area which when stimulated, either directly during neurosurgery or transcranially with a magnetic stimulus, results in activation of the diaphragm. 6. The presence of additional sites of neural activation in the pre‐motor cortex and SMA appears analogous to the results of studies on voluntary limb movement. The site of the increase in the SMA was posterior to that previously reported for arm movements. These areas are believed to have a role ‘upstream’ of the motor cortex in the planning and organization of movement. 7. This technique provides a means of studying the volitional motor control of respiratory related tasks in man.
Capsaicin‐sensitive nerves mediate inhibitory junction potentials and dilatation in guinea‐pig mesenteric artery.
Authors: Meehan A G , Hottenstein O D , Kreulen D L
Published: December 2014

1. The present study examined the effects of repetitive nerve stimulation on membrane potential and on contractile responses to noradrenaline in the guinea‐pig inferior mesenteric artery and its distal branches. 2. Repetitive stimulation of perivascular nerves evoked slow inhibitory junction potentials (IJPs) and dilator responses. Individual nerve shocks elicited excitatory junction potentials (EJP)s. 3. Stimulation‐evoked IJPs were abolished in the presence of tetrodotoxin (0.3 microM) or a low‐Ca2+ (0.5 mM) superfusion solution. 4. The amplitudes and durations of IJPs were dependent on the frequency and duration of repetitive nerve stimulation. Nerve stimulation delivered at 5 Hz for 5 s induced IJPs which had an average amplitude of 2 mV and an average duration of 130 s. When the time interval between successive stimulation periods was less than 4 min, the amplitudes of IJPs were reduced in a time‐dependent manner. 5. Stimulation‐evoked IJPs were unaffected following endothelium removal. Furthermore, stimulation‐evoked IJPs were not affected by atropine (1 microM), indomethacin (20 microM), prazosin (0.5 microM), phentolamine (10 microM), propranolol (0.5 microM) or alpha,beta‐methylene ATP (0.2 microM). 6. Pre‐treatment of arteries with guanethidine (30 microM) or 6‐hydroxydopamine (0.4 mM) abolished stimulation‐evoked EJPs but had no effect on stimulation‐evoked IJPs. 7. In a similar manner to repetitive nerve stimulation, capsaicin (10 microM) itself induced membrane hyperpolarization and dilatation in mesenteric arteries. Moreover, following application of capsaicin (10 microM), stimulation‐evoked IJPs and dilator responses were abolished. 8. EJPs evoked during stimulation‐induced IJPs were reduced in amplitude, compared to EJPs evoked under resting conditions. 9. These findings suggest that, in addition to an excitatory sympathetic innervation, mesenteric arteries receive an inhibitory, capsaicin‐sensitive innervation which is activated by low‐frequency repetitive stimulation.
Impulse conduction in CA1 apical dendrites of rabbit hippocampus: its possible implication in normal and abnormal activities.
Authors: Fujita Y
Published: December 2014

1. Impulse conduction in CA1 apical dendrites was studied by stimulating afferent fibres to the distal portion of the dendrites (Schaffer stimulation) and recording intracellularly from the pyramidal cell body in the hippocampus of the rabbit anaesthetized with sodium pentobarbitone and immobilized with d‐tubocurarine. 2. The stimulation, when strong enough, produced a full spike in all the pyramidal cells (n = 48) which were capable of producing spikes of 51‐67 mV in amplitude. A single‐shock Schaffer stimulation produced a single spike in forty‐six cells and a two‐spike burst in two cells. All the single spikes and the first spike of the two‐spike burst arose directly from the baseline. 3. By reducing the stimulus strength, three categories of small spikes (alpha, beta and gamma) could be distinguished in twenty‐two pyramidal cells. alpha was of the lowest threshold with an amplitude of less than 7.5 mV and the time from the foot of the spike to its peak (peak time) was more than 0.40 ms. beta was of the next lowest threshold with an amplitude of 8.7‐13.5 mV and had a peak time of 0.26‐0.36 ms (n = 3242). gamma was of the highest threshold with an amplitude of 6.6‐9.7 mV and had a peak time of 0.20‐0.27 ms (n = 1783). The duration of alpha was 1.5‐4.0 ms, whereas that of beta and gamma was 1.2‐1.5 ms. 4. Within a given pyramidal cell, the waveform of beta and gamma was remarkably constant, being independent of stimulus strength. They were therefore regarded as units and referred to as unitary D‐spikes. The unitary D‐spikes tended to summate forming a larger, longer‐lasting potential which was referred to as the D‐spike. alpha was probably a D‐spike produced at a greater distance away from the recording microelectrode, as compared with beta and gamma. 5. Within a given pyramidal cell unitary D‐spikes beta and gamma could be further subdivided into two subclasses, respectively, according to the differences in amplitude. Furthermore alpha contained at least one unitary D‐spike. Thus, at least five different unitary D‐spikes could be distinguished in the same cell. They were thought to be dendritic in origin, because only the dendrites could possibly give rise to so many small spikes which could be seen with the intrasomatically placed microelectrode. 6. In most cases a full spike consisted of the A‐, B‐ and D‐spikes.(ABSTRACT TRUNCATED AT 400 WORDS)
Electrical activation and c‐fos mRNA expression in rat neurosecretory neurones after systemic administration of cholecystokinin.
Authors: Hamamura M , Leng G , Emson P C , Kiyama H
Published: December 2014

1. The expression of c‐fos mRNA in the rat hypothalamus was examined by in situ hybridization following systemic administration of cholecystokinin (CCK), a procedure known to activate magnocellular oxytocin neurons but not magnocellular vasopressin neurones. 2. Conscious male rats were given a single I.P. injection of 50 micrograms/kg CCK, c‐fos mRNA signal was apparent in the supraoptic and paraventricular nuclei in rats killed 10 min after injection but not in uninjected or saline‐(vehicle) injected rats. The density of c‐fos mRNA at both sites was further elevated in rats killed 30 min or 60 min following injection, and was absent in rats killed 4 h after injection. 3. In the paraventricular nucleus the most dense expression of c‐fos mRNA following CCK administration was in the medial, mainly parvocellular portion of the nucleus, in an area corresponding to the distribution of corticotrophin‐releasing factor mRNA determined by in situ hybridization in adjacent sections. 4. The I.P. injection of CCK increased plasma oxytocin concentrations, measured by specific radioimmunoassay from 13 +/‐ 5 pg/ml in control rats to 107 +/‐ 9 pg/ml in the rats killed 10 min after injection, a similar response to that observed previously in urethane‐anaesthetized rats. 5. In each of six urethane‐anaesthetized rats, recordings were made from single neurones in the supraoptic nucleus, identified antidronomically as projecting to the posterior pituitary and identified electrophysiologically as putative oxytocin neurones. Following I.P. injection of 50 micrograms/kg CCK, the neurones increased their firing rate by a mean of 1.3 +/‐ 0.2 spikes/s averaged over the 10 min following injection. 6. From the appearance of c‐fos mRNA in supraoptic neurones following CCK administration we conclude that this message is expressed in magnocellular oxytocin neurones, since vasopressin neuronal activity and vasopressin release is known to be unaffected by this stimulus, and since the supraoptic nucleus contains essentially only oxytocin neurones and vasopressin neurones. 7. We conclude that c‐fos mRNA expression can be induced in supraoptic oxytocin neurones following brief and modest episodes of electrical activation, suggesting that c‐fos may be involved in the gene regulation of these neurones under physiological conditions.
Acetylcholine recycling and release at rat motor nerve terminals studied using (‐)‐vesamicol and troxpyrrolium.
Authors: Searl T , Prior C , Marshall I G
Published: December 2014

1. The presynaptic mechanisms governing the release and recycling of synaptic vesicles have been studied by examining the effects of nerve stimulation, (‐)‐vesamicol (an inhibitor of acetylcholine transport into synaptic vesicles) and troxypyrrolium (an inhibitor of the high‐affinity, sodium‐dependent, choline uptake system) on endplate currents (EPCs) and miniature endplate currents (MECPs) recorded from motor endplates in cut rat hemidiaphragm preparations. 2. In control experiments, 5 min of 10 Hz nerve stimulation had no effect on either the mean or the distribution of MEPC amplitudes. 3. Nerve stimulation in the presence of (‐)‐vesamicol (25 nM‐10 microM) revealed a population of MEPCs that was unaffected by the compound and a population of MEPCs whose mean amplitude was selectively reduced by the compound. 4. Nerve stimulation in the presence of troxypyrrolium (20 microM) produced a uniform reduction in the amplitude of all MEPCs with no change in the coefficient of variance of MEPC amplitudes. 5. The concentration‐dependent effects of (‐)‐vesamicol on the amplitude of the evoked EPCs paralleled the concentration‐dependent effects of the compound on MEPC amplitudes. 6. The results are consistent with the hypothesis that both recycled and performed synaptic vesicles are heterogeneously released from rat motor nerve terminals and that (‐)‐vesamicol acts selectively on recycling vesicles. In addition, a model of vascular loading that accounts for the different effects of nerve stimulation on MEPC amplitudes in the presence of (‐)‐vesamicol and troxypyrrolium is described.
Three types of bovine chromaffin cell Ca2+ channels: facilitation increases the opening probability of a 27 pS channel.
Authors: Artalejo C R , Mogul D J , Perlman R L , Fox A P
Published: December 2014

1. Cell‐attached patch recordings from bovine chromaffin cells were performed with 90 mM‐Ba2+ in the patch pipette and with isotonic potassium aspartate in the bathing solution to zero the membrane potential. Three different types of unitary Ca2+ channel activity could be distinguished in these recordings. 2. A 27 pS Ca2+ channel was distinguished by constructing amplitude histograms and measuring slope conductance. This channel activated over a broad range of potentials (depolarizations greater than ‐10 mV). 3. A second Ca2+ channel with a slope conductance of 14 pS could also be detected with amplitude histograms. This channel activated with depolarizations greater than ‐20 mV. 4. An 18 pS Ca2+ channel was observed infrequently indicating that this channel may carry only a small amount of the whole‐cell current. This 18 pS channel was sensitive to changes in holding potential. Depolarizing the patch to +10 mV from a holding potential of ‐80 mV elicited robust unitary activity. Changing the patch holding potential to ‐40 mV while maintaining test depolarizations to +10 mV completely inactivated the 18 pS channel. Neither the 25 pS nor the 14 pS Ca2+ channels were affected by changes in holding potential in the range from ‐80 mV to ‐40 mV, indicating the 18 pS channel was a different type of channel. As the 18 pS channel was observed so infrequently, no detailed studies of it were possible. 5. Chromaffin cell Ca2+ currents exhibited facilitation. Large pre‐depolarizations greatly augmented whole‐cell currents observed in these cells. Whole‐cell currents could double or triple after recruiting facilitation. The application of large pre‐depolarizations altered the gating behaviour of the 27 pS Ca2+ channel manifested as dramatically increased channel opening probabilities measured during subsequent test pulses. Large pre‐depolarizations induced unitary activity in the 27 pS Ca2+ channel similar to the long‐lived openings exhibited by L‐type Ca2+ channels in the presence of Bay K 8644. Large pre‐depolarizations did not change the gating behaviour of the 14 pS Ca2+ channel. 6. Repetitive depolarizations in the physiological range could also induce facilitation. At the single‐channel level facilitation was manifested as a striking increase in opening probability of the 27 pS Ca2+ channel. No effect of repetitive activity was observed on 14 pS channel gating. At the whole‐cell level, repetitive depolarizations dramatically increased the current observed. 7. Facilitation of 27 pS Ca2+ channel activity could be induced by changing the holding potential to a depolarized level (greater than or equal to ‐10 mV).(ABSTRACT TRUNCATED AT 400 WORDS)