bluuebunny/crossref_metadata_2025 huggingface dataset:
Respiratory periodicity following stimulation of vagal afferents
Authors: Iscoe Steve , Vanner Stephen
Published: April 2011

The effects on respiratory periodicity of electrical stimulation of the cut central end of a vagus nerve were studied in anaesthetized, vagotomized, paralyzed, and ventilated rabbits. Electrical activity of a phrenic nerve was used to determine inspiratory and expiratory durations (Ti and Te). The central cut end of one vagus nerve was electrically stimulated during the entire inspiratory phase of every 10th respiratory cycle and Ti and Te of that respiratory cycle and the following 8 were measured. When only the fastest conducting afferents (pulmonary stretch receptor afferents) were stimulated, reductions in Ti and Te were restricted to the stimulated cycle. When stimulus intensity was increased, activating higher threshold, more slowly conducting afferents (including those of irritant receptors), Te but not necessarily Ti decreased, increasing the frequency of phrenic bursts (respiratory frequency). The recovery of Te following stimulation was exponential, with a time constant of 3–7 s which varied inversely with control respiratory frequency. The effects on Ti and Te on higher intensity stimulation suggest either that coupling between inspiratory and expiratory neurones in the brainstem respiratory oscillator can be "looser" than currently hypothesized or a separate population of expiratory neurones, with a short-term memory (three time constants or [Formula: see text]), mediates the observed effects.
Parathyroid hormone responsiveness in the sheep fetus and newborn lamb
Authors: Kooh Sang Whay
Published: April 2011

Responsiveness of the sheep fetus to parathyroid hormone (PTH) infusion was studied in the unanesthetized fetus in situ and the results were compared with those obtained in the newborn lamb. PTH, 0.5 USP U/min per kilogram body weight was infused intravenously to four sheep fetuses in utero (gestational age 127–141 days) and 10 newborn lambs (1–20 days of age). PTH infusion increased plasma Ca in the fetus and the PTH-induced hypercalcemia increased plasma calcitonin although the maternal levels of Ca and calcitonin did not change. In the fetus, as well as in the newborn lamb, PTH decreased the percentage tubular reabsorption of phosphate (TRP) and increased urinary excretion of cAMP. These results indicate that the sheep fetus has developed the target organ responsiveness to PTH and a normal calcitonin secretory mechanism by the last trimester of gestation.
Development of radioimmunoassayable β-endorphin and methionine-enkephalin binding sites in regions of rat brain
Authors: Tsang D. , Ng S. C.
Published: April 2011

The development profiles of [3H]methionine-enkephalin ([3H]Met-enk) binding sites and radioimmunoassayable (RIA) β-endorphin in regions of rat brain were determined. The amount [3H]Met-enk bound reached its maximum in the 1st week after birth in the cerebellum, in the brainstem at the 2nd week, and in the whole forebrain at the 3rd week, that of RIA β-endorphin reached its highest level at day 2 postpartum (p.p.) in the cerebellum, at days 7–15 p.p. in the whole forebrain, and at days 17–21 p.p. in the brainstem. These findings suggest that both the development of RIA β-endorphin and [3H]Met-enk sites in rat brain follow a caudal to rostral sequence. Also, the close interrelationship between the elevation and decline in the amount of [3H]Met-enk bound and RIA β-endorphin levels in each brain region suggests that these two components are important entities of the central nervous system.
Ineffectiveness of protamine zinc somatostatin as a long-acting inhibitor of insulin and growth hormone secretion
Authors: Tannenbaum Gloria Shaffer , Colle Eleanor
Published: April 2011

The present studies examined the duration of inhibitory action of a preparation of cyclic somatostatin (SRIF) in suspension with protamine zinc (PZ) on (1) physiologic growth hormone (GH) and immunoreactive insulin (IRI) secretion during feeding in the rat and (2) plasma IRI levels in a 10-year-old boy with idiopathic hyperinsulinemic hypoglycemia. Chronically cannulated adult male rats were administered 250 μg PZ–SRIF subcutaneously twice daily at 12-h intervals for 7 days. Control animals received the PZ vehicle on the same schedule. On the test day, blood samples were obtained every 15 min for periods of 6 h following a single PZ–SRIF injection 1.5 h prior to sampling. Prominent GH secretory bursts were still evident in all PZ–SRIF-treated rats and these pulses occurred at the predictable time in relation to the light–dark cycle. Plasma IRI levels were typically elevated in response to feeding and no significant differences were observed in the mean 6-hGH, IRI, and glucose levels of PZ–SRIF-treated rats when compared with PZ-treated controls. In the boy with idiopathic hyperinsulinemic hypoglycemia, subcutaneous injection of 200 μg PZ–SRIF depressed plasma IRI levels for only 30 min. These results suggest that PZ is not the agent of choice for significant prolongation of the inhibitory action of SRIF on IRI and GH secretion.
A comparison of the porphyrin-inducing activity of barbiturates and benzodiazepines in chick embryo liver cells
Authors: Zimmer S. , Taub H. , Marks G. S.
Published: April 2011

Five benzodiazepines, flurazepam, nitrazepam, diazepam, oxazepam, and chlordiazepoxide, have been tested for porphyrin-inducing activity in chick embryo liver cell culture and for δ-aminolevulinic acid (ALA) synthetase inducing activity in the 17-day-old chick embryo. Flurazepam and nitrazepam were found to have considerably lower potency than secobarbital whereas diazepam, oxazepam, and chlordiazepoxide were less potent than phenobarbital in these test systems. The following conclusions were arrived at. (1) A hypnotic dose of flurazepam or nitrazepam would be less likely than a comparable dose of secobarbital to increase ALA synthetase activity in a patient with hereditary hepatic porphyria. (2) A sedative dose of diazepam, oxazepam, or chlordiazepoxide would be less likely than a comparable dose of phenobarbital to increase ALA synthetase activity in a patient with hereditary hepatic porphyria. (3) The benzodiazepines, although apparently less likely to precipitate an attack than barbiturates, should be used with great caution in porphyria patients.
Steroid anaesthetics: inhibition of depolarization–secretion coupling at the mouse motor nerve terminal
Authors: Pennefather P. , Puil E. , Quastel D. M. J.
Published: April 2011

The coupling between nerve terminal depolarization and quantal secretion of acetylcholine at the mouse neuromuscular junction was estimated by measuring the multiplication of the frequency of miniature end-plate potentials (m.e.p.p.s) produced by increasing the concentration of calcium in the medium from 0.1 to 1.0 mM in the presence of 15 mM potassium. Depolarization–secretion coupling was inhibited by the anaesthetic steroids progesterone, pregnanedione, and alphaxalone. The nonanaesthetic steroid Δ16-alphaxalone also inhibited depolarization–secretion coupling with the same potency as alphaxalone. This result indicates that inhibition of depolarization–secretion coupling in nerve terminals is unlikely to play a major role in the production of anaesthesia.
Changes in plasma motilin concentration in response to manipulation of intragastric and intraduodenal contents in man
Authors: Collins Stephen M. , Lewis Terence D. , Fox Jo-Ann E. T. , Track Norman S. , Meghji Mohamed M. , Daniel E. E.
Published: April 2011

Immunoreactive plasma motilin concentrations were studied following a variety of stimuli in 24 healthy fasting subjects. Plasma motilin was measured by a radioimmunoassay using antibody GP 71 (J. C. Brown) and natural porcine motilin as standard. Basal motilin levels ranged from undetectable to 365 pg/mL. Antral and intraduodenal infusion of 50 mL 0.1 N HCl (pH 1.2) at 5 mL/min failed to alter significantly plasma motilin levels but duodenal acid infusions at 17 mL/min caused a significant increase (70.8 ± 29.5 pg/mL, mean ± SEM; n = 6), maximal at 40 min. Duodenal alkalinization with 50 mL 0.3 M Tris buffer (pH 8.0) infused at 5 mL/min produced no change in plasma motilin. A mixed meal did not affect plasma motilin levels. Ingestion of 60 g fat significantly increased plasma motilin (n = 13; maximal increase 150.3 ± 43.3 pg/mL at 30 min) but duodenal infusions of fat failed to increase plasma motilin levels. These results suggest that motilin secretion induced by fat requires that the fat be present initially within the stomach for secretion to occur. We conclude that ingested fat is a potent stimulus of motilin release. As duodenal acidification (50 mL, 0.1 N HCl over 10 min) induces duodenal activity resembling migrating motor complexes but does not release motilin, our data argue against the release of motilin following duodenal acidification as a trigger for the initiation of these complexes in man.
Biochemical changes in progressive muscular dystrophy. XI. Cyclic nucleotides in the skeletal and cardiac muscle of normal and dystrophic mice
Authors: Srivastava Uma , Sebag Mikael , Thakur Manohar
Published: April 2011

cAMP and cGMP contents were determined in the skeletal and cardiac muscle of normal and dystrophic mice. cAMP content increased in the dystrophic muscle at every stage of the disease whereas cGMP content decreased in the preliminary stages and increased at the terminal stage of the disease. The content of both nucleotides per heart was not affected in murine dystrophy. Thus, levels of cyclic nucleotides appear to be selectively altered in dystrophic skeletal muscle.
BaCl2-induced contractions in the guinea pig ileum longitudinal muscle: role of presynaptic release of neurotransmitters and Ca2+ translocation in the postsynaptic membrane
Authors: Clement John G.
Published: April 2011

Early studies indicated that the BaCl2-induced contractions in the guinea pig ileum longitudinal muscle strip (GPI-LMS) were, in part, neuronal in origin. However, recent studies have suggested that BaCl2-induced contractions were produced by an action directly on the smooth muscle membrane. The purpose of this study was to investigate the mechanism of the BaCl2 contractions in the GPI-LMS. Botulinum toxin (5 × 105 MLD/mL), which blocks the electrically induced release of acetylcholine (ACh), hemicholinium-3 (HC-3; 110 μM), which blocks ACh synthesis, tetrodotoxin (TTX; 60 nM), which blocks Na+ channels, black widow spider venom, which depletes the presynaptic neuron of neurotransmitter, and atropine (2.9 μM), a potent muscarinic antagonist, had no effect on the BaCl2 contractions. Desensitization of the GPI-LMS to substance P did not affect the BaCl2 contraction. In Ca2+-free buffer the BaCl2 dose–response curve was shifted to the right. In Ca2+-free solution the time to 50% inhibition of the contractile response to ACh (73 nM) and BaCl2 (1.16 mM) was 3.7 and 125 min, respectively. The D 600 IC50 for ACh and BaCl2 contractions was 220 and 130 nM, respectively. In Ca2+-free buffer either EGTA (0.53 mM) or D 600 (1 μM) were potent inhibitors of BaCl2 contractions. These results suggest that in the GPI-LMS the BaCl2 response is not mediated by a release of ACh (or substance P) because inhibitors of ACh release, synthesis, and receptors do not affect the responses. Also, the BaCl2 contraction is not due to activation of Na+ channels because TTX is without effect. The BaCl2-induced contraction appears to be mainly due to the movement of membrane bound Ca2+ through D 600 sensitive Ca2+ channels with extracellular Ca2+ and possible passage of Ba2+ ions intracellularly playing relatively minor roles.
Somatostatin and gastrin release into the gastric lumen in rats
Authors: Koop H. , Simson G. , McIntosh C. , Bedell R. A. , Arnold R. , Creutzfeldt W.
Published: April 2011

Somatostatin and gastrin release into the gastric lumen was investigated in anaesthetized, vagally intact rats. The stomach was perfused at a flow rate of 0.5 mL∙min−1. During perfusion with 0.1 M HCl or buffers of varying pH the somatostatin and gastrin concentrations in the perfusate were <10 pg∙mL−1 and approximately 30 pg∙mL−1, respectively. Peptone caused a slight pH-independent increase in somatostatin release; gastrin release was unchanged despite an increase in serum gastrin from a basal of 15 ± 4 to 155 ± 34 pg∙mL−1 during peptone stimulation. Intravenous infusion of carbachol (1 μg∙kg−1∙min−1) strongly stimulated luminal somatostatin and gastrin release (from 5 ± 1 to 192 ± 52 pg∙mL−1 and from 27 ± 5 to 198 ± 41 pg∙mL−1, respectively) during perfusion with 0.1 M HCl. Phosphate buffer perfusion at pH 7.5 abolished the cholinergic-mediated somatostatin release but the gastrin response was unaffected. It is suggested that changes of luminal hormone concentrations in the rat stomach do not reflect the secretory activity of the endocrine cells in the gastric mucosa.
Effect of arachidonic acid and indomethacin on renal function of dogs with pericardial tamponade
Authors: Boudreau Robert J. , Mandin Henry
Published: April 2011

Previous studies revealed persistent sodium retention in dogs with chronic pericardial tamponade (induced by injection of Freund adjuvant into pericardial sacs) and pericardiocentesis, revealed in increased sodium excretion. Three groups of dogs were studied. Group 1 was treated with indomethacin (2.5 mg/kg, iv) prior to pericardiocentesis. Compared with experiments without indomethacin, sodium excretion did not increase following pericardiocentesis in animals treated with indomethacin despite similar changes in arterial pressure, venous pressure, hematocrit, plasma protein concentration, and renin activity. This effect of indomethacin was presumably mediated through prostaglandin (PG) synthesis inhibition. Group 2 dogs received an infusion of arachidonic acid (AA) (to increase PG synthesis) into the left renal artery (20 μg∙kg−1∙min−1). Sodium excretion increased after AA infusion during tamponade (11.2 to 30.9 mequiv∙min−1) with a further increase occurring after pericardiocentesis (84.4 mequiv.∙min−1). Animals in group 3 were infused with both 20 and 80 μg∙kg−1∙min−1 doses of AA. Although sodium excretion following 80 μg∙kg−1∙min−1 AA (21 mequiv.∙min−1) was higher than that seen during 20 μg∙kg−1∙min−1 (14.2 mequiv.∙min−1), a further increase in sodium excretion to 45.6 mequiv.∙min−1 followed pericardiocentesis. During tamponade, AA did not change any of the measured parameters other than sodium excretion, a result compatible with the proposed distal tubular site of action of PG. Absolute but not fractional cortical blood flow distribution increased during the time sodium excretion increased following pericardiocentesis in all experiments. It is proposed that increased PG synthesis may be one possible mechanism involved in the natriuresis seen following pericardiocentesis. One cannot exclude the possibility that increased absolute blood flow to the superficial cortex also contributes to the observed natriuresis. Changes in arterial pressure, venous pressure, hematocrit, plasma protein concentration, and renin activity appear to contribute to the observed natriuresis but only when PG synthesis is not blocked.
Erratum: Influence of temperature and external Ca2+ concentration upon dantrolene action on excitation–contraction coupling in frog skeletal muscle
Authors: Oba Toshiharu
Published: April 2011

Effects of dantrolene (DAN) on electrical and mechanical responses in frog skeletal muscle were studied at various Ca2+ concentrations and temperatures to elucidate the mechanism of action of DAN. The following results were obtained. (a) Twitch tension of a DAN-injected fiber, elicited by intracellular stimulation, increased transiently and then decreased whereas extracellular DAN always depressed the tension. (b) Lowering the external Ca2+ concentration resulted in the potentiation of twitch tension. The addition of DAN, however, reduced the tension significantly (p < 0.05). (c) Extracellular DAN caused a transient reduction and subsequent elevation of the threshold current; however intracellular DAN caused only elevation of threshold. (d) DAN prevented the slow depolarization of the membrane in low Ca2+ medium. (e) These effects of the drug were temperature dependent, the effect being more pronounced at higher temperatures. These findings suggest that DAN may manifest its effects by replacement of Ca2+ from its binding sites on the membrane and that this occupation of the Ca2+ sites by DAN is temperature dependent.
Somatosensory unit input to the spinal cord during normal walking
Authors: Loeb Gerald E.
Published: April 2011

Chronic recording techniques in freely walking cats have been used to sample unitary activity from most large myelinated afferent classes. Cutaneous mechanoreceptors are highly sensitive and generate regular activity patterns predictable from their modalities. Knee joint afferents can fire briskly during midrange locomotory movements but appear to be influenced by factors other than joint angle. Golgi tendon organs generate activity consistent with sensitivity to active muscle tension. Muscle spindle afferents do not appear to conform to any single functional pattern for all muscles. It is suggested that degree and rate of stretch are sensed by spindles (possibly under dynamic fusimotor bias) in extensor muscles which normally undergo isometric or lengthening contractions whereas rapidly modulated static fusimotor activity is employed to preserve spindle activity during the rapidly shortening contractions of flexor muscles. Both patterns may be represented in different spindles of bifunctional, biarticular muscles such as rectus femoris and sartorius.
Comment: Unresolved questions concerning muscle afferents
Authors: Abrahams V. C.
Published: April 2011

Some current questions regarding muscle afferent receptors are discussed. These include the significance of variable distribution patterns of muscle spindles in different muscles and of differences in intrinsic spindle morphology. The significance of the very large and variable population of small myelinated afferent fibres in muscle is also discussed.
Function of sensory input in Insect motor systems
Authors: Pearson K. G.
Published: April 2011

The organization and function of sensory input has been examined in three insect motor systems: locust jumping, cockroach walking, and locust flight. In these three systems sensory input is primarily involved in the production of the normal patterns of motor activity rather than in the compensation for sudden changes in the external environment. At least two general functions for sensory input in the normal patterning of motor activity can be identified: (1) compensation for changes in the peripheral elements of the motor system which occur as a result of use and maturation and (2) regulation of switching from one phase of a movement to another following the attainment of a specific state by peripheral structures. Reflex pathways may exist for compensating for sudden environmental disturbances but these have not yet been clearly demonstrated.
Stimulus–response relationships during locomotion
Authors: Rossignol S. , Julien C. , Gauthier L.
Published: April 2011

Crossed hind limb responses to high intensity stimulation of the superficial peroneal nerve in the cat were studied under various conditions. In precollicularly decerebrate cats walking on a treadmill, the same stimulus train evokes a crossed extension response during the contralateral stance phase and a crossed flexion response during the contralateral swing phase. In acute spinal cats (Th13) injected with clonidine, a similar stimulus train can evoke a crossed extension response when the limb is manually placed in flexion and a crossed flexion response when the limb is positioned in extension. During "fictive" locomotion, induced in spinal paralyzed cats by nialamide and L-DOPA, the same stimulus may increase the amplitude and (or) the duration of crossed flexor or crossed extensor activity (in-phase responses). In some instances in these preparations, the crossed responses may be out-of-phase with the central rhythm. It is concluded that crossed hind limb responses during locomotion are selected by both central and peripheral mechanisms.
Pulmonary afferent and central influences on respiratory phase-switching in the cat
Authors: Cohen Morton I.
Published: April 2011

A striking feature of the mammalian respiratory rhythm generator is the abruptness of the transitions between the inspiratory (I) and expiratory (E) phases ("phase-switching"). Although reciprocal inhibitory actions between I and E neurons are important for maintaining the alternation of respiratory phases, phase-switching actions are probably produced by recurrent inhibitory neuronal loops acting within each phase. The operation of such negative feedback circuits has been studied using two types of experimental input: (a) activation of pulmonary stretch receptors by lung inflation, which shortens the I phase and prolongs the E phase, and (b) electrical stimulation in the rostral pontine "pneumotaxic center" region, which can produce premature I → E or E → I switching, depending on stimulation site. These inputs produce diverse effects on discharges of various types of medullary respiratory neuron; analysis of such observations has led to hypotheses about the possible roles of different neuron populations in phase-switching.
Transcortical reflexes and servo control of movement
Authors: Evarts Edward V. , Fromm Christoph
Published: April 2011

Sherrington proposed that the major role of proprioceptors is in processing afferent inputs generated by the active movements of the animal itself, and noted that the reflex effects of proprioceptive inputs are "mild." Current experimental results are consistent with the view that the major role of both segmental and transcortical proprioceptive reflexes is in small active movements and active postural stability, with muscle afferent inputs reducing "… errors of muscle length produced by fluctuating levels of motor discharge …" as stated by Goodwin and coworkers in 1978.Exteroceptive reflexes generate intense muscular responses and are of critical importance in prompt reprogramming essential for effective responses to environmental stimuli. Within the motor cortex (MI) there is a caudal region (MI/c) which receives exteroceptive cutaneous inputs and a rostral region (MI/r) which receives proprioceptive inputs. Transcortical reflexes mediated via pyramidal tract neurons (PTNs) of MI/r have properties which are analogous to segmental proprioceptive reflexes: changes of muscle length elicit PTN discharges which oppose the length change and so act to maintain stability. Furthermore, MI/r PTNs which are recruited earliest for small active movements are most sensitive to proprioceptive inputs. Data are not yet available concerning transcortical reflexes via MI/c during voluntary movement, but it is speculated that the cutaneous reflexes via MI/c might be functionally analogous to segmental cutaneous reflexes.Short-latency reflex responses also occur in postcentral (PoC) PTNs, and in this report we present results concerning the properties of PoC PTNs during active and passive movement. Caudal (area 2–5) PoC PTNs were similar to MI PTNs in that they often discharged prior to electromyogram (EMG) activity with active movement, and had different discharge frequencies with different steady state loads, but were unlike most MI PTNs in having the same changes of discharge with active and passive movement. Our finding of PoC discharge prior to movement onset, confirming that of Soso and Fetz in 1980, is discussed in connection with the concept of corollary discharge.
Rapid vertical tube rotor gradient assay for binding of 2,3,7,8-tetrachIorodibenzo-p-dioxin to the Ah receptor
Authors: Tsui Hing Wo , Okey Allan B.
Published: April 2011

The Ah receptor, which regulates induction of aryl hydrocarbon hydroxylase (cytochrome P1-450), can be assayed using [3H]2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) as the radioligand. Sucrose density gradient (SDG) centrifligation is the most reliable method for detecting and quantitating Ah receptor; however, previous gradient assays in swinging bucket rotors (SBR) have required overnight centrifugation to achieve adequate separation of specific receptor peaks from nonspecific binding to other cytosolic components. These lengthy runs limit the number of assays which can be performed and could permit excessive dissociation of radioligand from the receptor. Thus, we tested brief (2-h) SDG centrifugation assays in a vertical tube rotor (VTR) as a possible alternative to prolonged SBR runs. Two-hour VTR runs yield gradient profiles very similar to those obtained with 16-h runs in an SBR and the calculated sedimentation coefficient (in low ionic strength buffer) is about 9.6 S for the Ah receptor assayed in either rotor. The concentration of Ah receptor in cytosols from liver, lung, kidney, and testis of C57BL/6J mice is the same by VTR analysis as when measured by SBR analysis. Thus, extensive dissociation of [3H]TCDD from the Ah receptor does not appear to occur in cystosols from a variety of tissues even with run times up to 16 h. Assays performed by rapid VTR centrifugation appear equally valid to those obtained by overnight SBR centrifugation.
Slow diffusion of Ca2+ in the rat's hippocampus
Authors: Morris M. E. , Krnjević K.
Published: April 2011

Ca2+-sensitive microelectrodes, attached to CaCl2-containing micropipettes, were inserted into the dorsal hippocampus of rats under urethane. When Ca2+ was released iontophoretically, the amplitude and time course of the resultant increase in extracellular Ca2+ concentration could be fitted to a simple diffusion model, but the apparent diffusion coefficient of Ca2+ was only about 1/100 of its value in water, possibly because of reversible Ca2+ binding to hippocampal tissue. A further anomaly was a very low transport number (<0.01) for the release of Ca2+ from microelectrodes in vivo.
Ibotenic acid: its excitatory and possibly sedative actions in cerebral cortex
Authors: Puil E.
Published: April 2011

A slowly developing excitation with afterdischarge is produced by microiontophoretic application of the racemate of ibotenic acid to pericruciate cortical neurons of cats which had been "decerebrated" by forebrain isolation during brief anesthesia. The extracellularly observed excitation tended to accumulate with repeated applications. In many instances the ibotenate excitation was blocked with local administrations of H2-receptor antagonists which also "antagonized" glutamate excitation. With intracellular recording, similar iontophoretic applications of ibotenate were observed to produce longlasting depolarizations and repetitive firing which was not maintained despite suprathreshoid depolarization. These actions were not accompanied by consistent changes in membrane resistance. A most striking feature of ibotenate action was to increase spontaneous synaptic activity and the amplitude of EPSP's evoked by electrical stimulation of the cortical surface or n. ventralis lateralis of the thalamus. These new data are strongly suggestive of presynaptic actions of ibotenate in the cerebral cortex although postsynaptic actions of this isoxazole presumably are also important to an understanding of how ibotenate produces its inebriating and hypnotic effects in animals and man.
Effects of crude oil ingestion on avian intestinal function
Authors: Eastin Jr. William C. , Murray Helen C.
Published: April 2011

Intestinal function in mallard ducklings (Anas platyrhynchos) on a freshwater regime was studied after a 7-day dietary ingestion of 0.25% and 2.5% Prudhoe Bay crude oil (PBCO) or a 2.5% paraffin mixture with an in vivo luminal perfusion technique. Dietary ingestion of 2.5% PBCO may have an effect on the integrity of the duckling intestine. There were no significant effects of PBCO on the absorption of Na, Cl, K, or H2O compared with control animals. The ducklings fed 2.5% paraffin had a significant depression in Na and H2O absorption compared with controls. However, this depression does not seem to be related to an effect on intestinal mucosa Na-K-ATPase activity.
Commissural potentiation of perforant path evoked responses in the dentate gyrus of the rat
Authors: Assaf S. Y. , Miller J. J.
Published: April 2011

The effects of conditioning stimuli applied to the commissural pathway on the perforant path (PP) evoked EPSP and population spike response were examined in urethane anaesthetized rats. Whereas conditioning stimuli applied to the PP resulted in a short-term potentiation of both the EPSP and population spike evoked by a test pulse to the same pathway (homosynaptic potentiation), only the population spike was potentiated when the PP test pulse was preceded by a conditioning volley to the commissural afferent. This form of heterosynaptic potentiation, which occurs in the absence of any significant change in the synaptic currents generated by the perforant path, suggests that alterations in postsynaptic excitability may underly the process of short-term potentiation rather than an augmented transmitter release.
Central and peripheral adaptations of the gas transport system to one-leg training
Authors: Thomas S. G. , Cunningham D. A. , Plyley M. J. , Boughner D. R. , Cook R. A.
Published: April 2011

The role of central and peripheral adaptations in the response to endurance training was examined. Changes in cardiac structure and function, oxygen extraction, and muscle enzyme activities following one-leg training were studied.Eleven subjects (eight females, three males) trained on a cycle ergometer 4 weeks with one leg (leg 1), then 4 weeks with the second leg (leg 2). Cardiovascular responses to exercise with both legs and each leg separately were evaluated at entry (T1), after 4 weeks of training (T2), and after a second 4 weeks of training (T3). Peak oxygen uptake ([Formula: see text] peak) during exercise with leg 1 (T1 to T2 increased 19.8% (P < 0.05) and during exercise with leg 2 (T2 to T3 increased 16.9% (P < 0.05). Maximal oxygen uptake with both legs increased 7.9% from T1 to T2 and 9.4% from T2 to T3 (P < 0.05). During exercise at 60% of [Formula: see text] peak, cardiac output [Formula: see text] was increased significantly only when the trained leg was exercised. [Formula: see text] increased 12.2% for leg 1 between T1 and T2 and 13.0% for leg 2 between T2 and T3 (P < 0.05). M-mode echocardiographic assessment of left ventricular internal diameter at diastole and peak velocity of circumferential fibre shortening at rest or during supine cycle ergometer exercise at T1 and T3 revealed no training induced changes in cardiac dimensions or function. Enzyme analysis of muscle biopsy samples from the vastus lateralis (At T1, T2, T3) revealed no consistent pattern of change in aerobic (malate dehydrogenase and 3-hydroxyacyl-CoA dehydrogenase) or anaerobic (phosphofructokinase, lactate dehydroginase, and creatine kinase) enzyme activities. Increases in cardiac output and maximal oxygen uptake which result from short duration endurance training can be achieved, therefore, without measurable central cardiac adaptation. The absence of echocardio-graphically determined changes in cardiac dimensions and contractility and the absence of an increase in cardiac output during exercise with the nontrained leg following training of the contralateral limb support this conclusion.
Vascular response of the chicken hindlimb to vasoactive agents, asphyxia, and exercise
Authors: Ploucha James M. , Ringer Robert K. , Scott Jerry B.
Published: April 2011

Previous studies in live chickens have measured heart rate, blood pressure, and cardiac output during drug administration or asphyxia and made assumptions concerning the peripheral vasculature. The present study employs a constant-flow, isolated hindlimb perfusion technique to measure directly changes in skeletal muscle vascular resistance induced either by local infra-arterial (i.a.) bolus, or continuous i.a. infusion, of various vasoactive substances. Prostaglandin E1 (0.5 μg, bolus) produced arteriolar vasodilation lasting 10 min, as indicated by a fall in perfusion pressure. Bolus injection of histamine (10 μg diphosphate) or adenosine (5 and 10 μg) produced vasodilation of less than 2-min duration. Theophylline infusion (5 mM infused at 1 mL/min, i.a.) blocked the effect of adenosine. Norepinephrine (1 μg) produced vasoconstriction which was reduced 60% by systemic alpha-adrenergic blockade with phenoxybenzamine (7.5–10 mg/kg). Tracheal occlusion produced intense vasoconstriction which was reduced 70% by alpha-adrenergic blockade. Electrical stimulation of the peripheral end of the cut sciatic nerve (6 Hz) produced an immediate vasodilation lasting several minutes.
Triazene metabolism. II Transportability and enzyme inhibitory characteristics of metabolites of antitumor dimethyltriazenes
Authors: Godin James R. P. , Llanos Gerard , Vaughan Keith , Renton Kenneth W.
Published: April 2011

A series of dimethyltriazenes (Ar∙N=N∙NMe2), monomethyltriazenes (Ar∙N=N∙NH∙Me), and triazene carbinolamines (Ar∙N=N∙NMe∙CH2OH) have been studied for their inhibitory effects on the enzyme, hog liver esterase (EC 3.1.1.1). p-Nitrophenyl acetate was used as the model substrate and the rate of hydrolysis was followed spectrophotometrically at 400 nm, the absorption maximum of the p-nitrophenylate ion. Only triazenes with an ester group in the aryl moiety exhibited significant inhibition. Preincubation of the enzyme with the monomethyltriazene (MeO2C∙C6H4∙N=N∙NHMe) or the methyloltriazene (MeO2C∙C6H4∙N=N∙NMe∙CH2OH) gave enhanced inhibition, which was not observed when the dimethyltriazene (MeO2C∙C6H4∙N=N∙NMe2) was preincubated with the enzyme. Inhibition of enzyme activity by the monomethyltriazene was shown to be essentially irreversible, whereas the model substrates, methyl benzoate and methyl p-aminobenzoate, gave reversible inhibition in the same assay. The inhibition by the N-methyloltriazene was only partially reversible. The results are discussed with relevance to the role of the monomethyltriazenes and N-methyloltriazenes as possible transportable metabolites of the antitumour dimethyltriazenes.
Internal cesium ions block various K conductances in spinal motoneurons
Authors: Puil E. , Werman R.
Published: April 2011

Conventional intracellular recording with low resistance electrodes was used to examine the effects of iontophoretic injections of Cs+ ions (30–200 nA for 30–500 s) into spinal motoneurons of cats anesthetized with pentobarbital and paralyzed with gallamine. The most striking effects of internal Cs+ were a great prolongation of the falling phase of action potentials, a large reduction in the amplitude of their afterhyperpolarizations, and a considerable increase in the size of delayed depolarizations. A reduction of resting membrane conductance (up to half of control values) and a small increase in membrane potential usually were evident. Although the rate of rise and amplitude of spikes sometimes were increased, the above effects on membrane properties usually were accompanied by block of antidromic invasion or synaptic spike generation, and inactivation of directly evoked spikes. Recovery of spike genesis was very rapid but the prolongation of spikes and other effects of Cs+ lasted 4–35 min, depending on the amount of Cs+ application. Larger injections of Cs+ resulted in greater depolarizations of up to 13 mV. It is concluded that internal Cs+ ions block voltage-dependent K+ conductance of spike repolarization, the Ca2+-activated K+ conductance responsible for the afterhyperpolarization, and some of the K+ conductance responsible for the resting potential. It is suggested that the enhanced delayed depolarization may result from a Cs+-blockade of an early outward K+ current which would unmask an inward current of Ca2+ ions.
A quantum mechanical Interaction of human erythrocytes
Authors: Rowlands S. , Sewchand L. S. , Enns E. G.
Published: April 2011

Theory predicts that the membrane potential will polarize membrane molecules and cause them to vibrate coherently at a frequency of ~ 1011 Hz. If the supply of metabolic energy exceeds a minimum value, membrane phonons may condense their momentum into a single "giant" vibrational mode. At 1011 Hz ionic screening is small up to distances of approximately a micrometre, so forces of a range several orders of magnitude longer than chemical forces can arise. These forces may be attractive or repulsive depending on frequency. They should occur in every metabolically active membrane and may control macromolecular transport and enzyme–substrate interactions. We find that normal human erythrocytes in plasma form rouleaux faster than Brownian motion predicts. When cells are fixed in glutaraldehyde or are metabolically depleted, or if the membrane potential is brought to zero, the rate of aggregation agrees with Brownian theory. When the metabolically depleted cells are revived or if the membrane potential is restored, then the interaction returns.
Distribution of 13N following intravenous injection of [l3N]ammonia in the rat
Authors: Freed Barry R. , Gelbard Alan S.
Published: April 2011

Ammonia labeled with cyclotron-produced 13N was injected intravenously in rats and the content of 13N in 14 major organs and tissues was determined at eight intervals ranging from 0.2 to 50 min after injection. The distribution of 13N at 12 s was employed to estimate the unidirectional tissue extraction for ammonia. The estimated fractional extraction for most of the tissues studied ranged from 70 to 100%. The 12-s 13N concentrations in a number of tissues (with lungs and brain the principal exceptions) were found to be quite similar to those reported for 42K+ and 86Rb+ in the rat, suggesting a similar mechanism of transcapillary extraction. Most of the injected dose was initially extracted by the musculature, kings, and kidneys. The lungs and kidneys released the bulk of their extracted ammonia-derived nitrogen within 10 min of injection. The gut, heart, and spleen also recirculated extracted nitrogen, but on a much smaller scale than the lungs and kidneys. The recirculated label was accumulated mainly by muscle, liver, and skin. The results suggest that the lungs and kidneys are important sources of systemically recirculated ammonia metabolites in the rat.
Cyclic adenosine monophosphate and cyclic guanosine monophosphate variations during isometric tetanus in frog sartorius muscle
Authors: Fang Giorgio , Menchetti Giovanni , Torre Giovannella Della , Volpi Lino , Secca Teresa , Orlacchio Aldo
Published: April 2011

Tetanic stimulation at different temperatures (5 and 20 °C) of the frog sartorius muscle results in an increase of cyclic guanosine monophosphate (cGMP) directly correlated to the tension developed. Cyclic adenosine monophosphate (cAMP) levels change differently for different temperature values. The variations could be explained by the interaction between Ca2+ and the enzymes which control cyclic nucleotide levels, namely, adenylate cyclase, guanylate cyclase, and phosphodiesterase.
2-Amino-7-phosphonoheptanoic acid as an amino acid antagonist
Authors: McLennan H.
Published: April 2011

The optical isomers of 2-amino-7-phosphoheptanoate (APH), the phosphonic acid analogue of α-aminosuberic acid, have been examined for their ability to block the excitation of rat spinal neurones induced by various acidic amino acids. Both isomers were active, although the D(−) form was approximately twice as potent. The pattern of action of APH indicated that it reacts with N-methyl-D-aspartate-preferring receptors.
In vitro metabolism of sparteine by human liver: competitive inhibition by debrisoquine
Authors: Otton S. V. , Inaba T. , Mahon W. A. , Kalow W.
Published: April 2011

Population data indicate that the genetic control is the same for the oxidation of sparteine and debrisoquine, although whether the level of control is regulatory or enzymatic is not clear. Therefore, the influence of debrisoquine on the rates of in vitro formation of the two dehydrogenated metabolites of sparteine in the 9000 × g supernatant fractions of human liver was examined. The interaction of these two drugs was competitive, indicating that the same form of cytochrome P450 is responsible for their biotransformation. Antipyrine at concentrations as high as 4 mM had no effect on sparteine oxidation.
Bromocriptine suppression of dispersed pituitary lactotrophs from estrogen-pretreated rats: a quantitative electron microscopic study
Authors: McComb D. J. , Kovacs K. , Croxford R. , Milligan J. V.
Published: April 2011

Dispersed rat lactotrophs were treated with bromocriptine (10−10 M) for either 30 min or 3 h to investigate its effect on cell morphology using light and electron microscopy and ultrastructural morphometry. After 30 min, lactotrophs treated with bromocriptine exhibited an increase in storage granule size (p < 0.05). Crinophagy was also evident and a significant increase in lysosome volume density was observed (p < 0.001). However, no significant change in prolactin content in the media was detected until 3 h of incubation in bromocriptine (p < 0.05). At this time a nonsignificant decrease in Golgi region volume density was also observed.
The effect of amitriptyline, mianserin, and viloxazine at pre- and post-junctional muscarinic receptors in guinea-pig ileal longitudinal muscle
Authors: Kwok Y. H. , Mitchelson F.
Published: April 2011

The antimuscarinic activity of amitriptyline, mianserin, and viloxazine was compared with atropine in guinea-pig ileal longitudinal muscle. The pA2 values obtained using carbachol (CCh) as agonist were as follows: atropine, 9.55; amitriptyline, 7.50; mianserin, 6.40; and viloxazine, 4.91. Responses to transmural electrical stimulation (1–50 Hz) were more resistant than those produced by CCh to inhibition by atropine and the antidepressants. This did not appear to be due to a selective inhibition of prejunctional inhibitory muscarinic receptors, as a pA2 of 8.73 was obtained with atropine for the depression of oxotremorine-induced inhibition of acetylcholine (ACh) output. Amitriptyline (10 μM) caused a 2.4-fold increase in ACh output and was 200-fold weaker than atropine at doubling ACh output in the longitudinal muscle stimulated at 0.3 Hz. Mianserin (10 μM) and viloxazine (1–10 μM) did not significantly affect ACh output. It is suggested that the antidepressants exhibit a greater affinity for the postjunctional muscarinic receptors in the guinea-pig ileal longitudinal muscle.
Lack of effect of barbiturate and ketamine anesthesia on renal blood flow in chronically instrumented rats prepared for micropuncture
Authors: Cupples W. A. , Veress A. T. , Sonnenberg H.
Published: April 2011

Fifteen-micrometer microspheres were used to study renal blood flow in rats which had been cannulated 3 or more days previously. Renal blood flow was assessed while the animals were conscious, after induction of anesthesia with inactin, pentobarbital, or ketamine, and after preparation for renal micropuncture. Blood pressure fell with anesthesia when barbiturates were used and was restored by tracheostomy. In conscious rats, right and left renal blood flows averaged 4.70 ± 0.24 and 4.64 ± 0.23 mL/min per gram kidney weight, respectively. These values were essentially unchanged following anesthesia with all agents used and they were also unaffected by surgery. We conclude that, in chronically prepared rats, renal blood flow is not affected by anesthesia or by micropuncture surgery.
Extracellular divalent cations in excitation–contraction coupling: hypertonic solution effects
Authors: Oota Isao , Kosaka Isao , Nagai Torao , Yabu Hideyo
Published: April 2011

It is the purpose of this article to point out that the membrane-bound Ca plays an important role in excitation–contraction (E–C) coupling of skeletal muscle fibers and that other divalent cations are unable to substitute for this role of membrane-bound Ca.
The role of calcium in excitation–contraction coupling in crustacean muscle fibers
Authors: Suarez-Kurtz G.
Published: April 2011

The evidence that calcium (Ca) plays an important role in electrical activity and an essential role in excitation–contraction (E–C) coupling in crustacean muscles is reviewed. These muscles produce graded electrical and mechanical responses to applied depolarizations. Removal of Ca from the bath solution eliminates both responses. Addition of Ba2+ or Sr2+ to Ca-free saline restores membrane electrogenesis, and all-or-none action potentials can be induced. With Sr2+ vigorous contractions are produced, whereas Ba action potentials evoke minimal or no tension, showing that rapid depolarization of the membrane potential is not sufficient per se for E–C coupling in crab and barnacle muscle. Several inorganic (e.g., multivalent cations) and organic (e.g., aminoglycoside antibiotics) which block membrane Ca channels block electrogenesis and contraction. However, the "Ca antagonists" verapamil and D600 also block Ca uptake at intracellular storage sites, resulting in spontaneous contractions and the delayed relaxation of small contractions associated with residual Ca currents. The evidence that the Ca which enters the fibres needs to release Ca from intracellular storage sites to produce contractions is detailed and discussed. Finally, a model for E–C coupling is discussed. This model includes the sites and mechanisms of action for several chemicals which modify E–C coupling in crustacean muscle fibres.
Calcium currents of frog and insect skeletal muscle fibres measured during voltage clamp
Authors: Stanfield P. R. , Ashcroft Frances M.
Published: April 2011

Both vertebrate and invertebrate skeletal muscle fibres have Ca2+ permeability mechanisms which are turned on by depolarization of the surface membrane. In frog muscle, Ca currents are extremely slow and will be scarcely activated during the action potential that normally elicits a twitch. This Ca permeability cannot therefore play any substantial, direct role in excitation–contraction coupling. In insect (Carausius morosus) muscle, Ca currents activate within milliseconds of depolarization, even at low temperature, and may well play at least a triggering role in excitation–contraction coupling. These Ca currents show saturation with increasing [Ca]o, while the instantaneous current–voltage relation rectifies inwards, as expected from a very low [Ca]i. The Ca channel is permeable to Sr2+ and Ba2+. Inactivation of Ca currents under a maintained depolarization depends on Ca2+ carrying inward current, however, rather than on the depolarization itself.