bluuebunny/crossref_metadata_2025 huggingface dataset:
Transient length-related mechanical states in smooth muscle
Authors: Meiss Richard A.
Published: April 2011

The isotonic shortening of electrically stimulated ovarian ligament smooth muscle strips from rabbits was studied by briefly applying sudden increases in afterload (force steps, 0.6 to 3.0 s long) just sufficient to halt the shortening. Upon removal of the extra afterload, the isotonic shortening velocity significantly increased compared with prestep velocities measured at the same muscle lengths. The degree of potentiation depended upon the duration of the force step. Muscles yielded initially when the step was applied, and their stiffness decreased. During the zero-velocity portion of the force step there was a steady increase in stiffness back to levels appropriate to that force. Complete force–velocity curves were made following short (0.6 s) and long (3.0 s) force steps. The values for Vmax (and all intermediate velocities) were significantly greater following a long force step. In a final experimental series, muscles were held isometric immediately after removal of the force step. Force rose monotonically, with a more rapid redevelopment following a long force step. A mathematical model is presented, according to which the effect of the duration of the force step on the poststep mechanical properties may be due to either the alteration of an internal resistance to shortening or a change in the kinetic properties of the cross-bridge array. A hypothesis is proposed relating the steady decline in isotonic shortening velocity to a partial local depletion of energy-yielding substrates.Key words: smooth muscle, isotonic contractions, mechanics, models.
Cross-bridge kinetics and shortening in smooth muscle
Authors: Hellstrand Per
Published: April 2011

Stiffness measurements were performed on smooth muscle preparations from guinea-pig taenia coli to obtain information on the number of attached cross bridges under varying contractile conditions. The normalized stiffness of the cross-bridge system in smooth muscle may be of a magnitude similar to that assumed in skeletal muscle. Transition from isometric contraction to unloaded shortening was associated with a decrease in stiffness to 50% or less of the isometric value, slightly higher than that found in skeletal muscle fibers. Comparison of phasic (5 s) and tonic (5 min) contractions showed lower Vmax, intracellular [Ca2+], and myosin 20 kDa light chain phosphorylation at 5 min, indicating development of a latch state. Isometric force and stiffness were identical in the two types of contraction. However, stiffness during unloaded shortening was greater in the latch state, which may be the result of the presence of a population of cross bridges with a low rate constant for detachment.Key words: smooth muscle mechanics, cross bridges, latch, myosin phosphorylation.
Characterization of isoform diversity in smooth muscle myosin heavy chains
Authors: Kelley Christine A. , Adelstein Robert S.
Published: April 2011

In this paper we review some of our recent work on the structural and biochemical characterization of isoforms of the heavy chain of vertebrate smooth muscle myosin II. There exist both amino-terminal and carboxyl-terminal alternatively spliced isoforms of the smooth muscle myosin heavy chain (MHC). mRNA splicing at the 3′ end generates two MHCs, which differ in length and amino acid sequence in the carboxyl terminus. We will refer to the longer, 204-kDa isoform as MHC204 and the shorter, 200-kDa isoform as MHC200. We found that MHC204, but not MHC200, can be phosphorylated by casein kinase II on a serine near the carboxyl terminus, suggesting that these isoforms may be differentially regulated. The physiological significance of this phosphorylation is not known. However, as demonstrated in this paper, phosphorylation does not appear to affect filament formation, velocity of movement of actin filaments by myosin in an in vitro motility assay, actin-activated Mg2+ ATPase activity, or myosin conformation. Our results also show that MHC204 and MHC200 form homodimers, but not heterodimers. Purified MHC204 and MHC200 homodimers are not enzymatically different, at least as measured using an in vitro motility assay. The amino-terminal spliced MHC204 and MHC200 isoforms are the result of the specific insertion or deletion of seven amino acids near the ATP-binding region in the myosin head. We refer to these isoforms as inserted (MHC204-I; MHC200-I) or noninserted (MHC204; MHC200), respectively. In contrast to the carboxyl-terminal spliced isoforms, the amino-terminal spliced inserted and noninserted myosin heavy chain isoforms are enzymatically different. The inserted isoform, which is expressed in intestinal, phasic-type smooth muscle, has a higher actin-activated Mg ATPase activity and moves actin filaments at a greater velocity in an in vitro motility assay than the noninserted MHC isoform, which is expressed in tonic-type vascular smooth muscle. The results presented in this review suggest that the alternative splicing of smooth muscle mRNA results in at least four different isoforms of the myosin heavy chain molecule. The potential relevance of these molecular isoforms to smooth muscle function is discussed.Key words: myosin, heavy chain isoforms.
Endothelin receptor antagonists: a brief review
Authors: Moreland Suzanne
Published: April 2011

The endothelins are a family of potent vasoconstrictors, some of which also have vasodilatory activity. In many diseases associated with tissue hypoxia or ischemia and in diseases in which vasoconstriction plays a role, the circulating levels of endothelin are higher than in healthy, control subjects. These findings stimulated research aimed at discovering endothelin receptor antagonists. This review focuses on the binding potency and vascular activity of these new peptide and nonpeptide endothelin receptor antagonists.Key words: endothelin, endothelin receptor subtypes, vascular smooth muscle, endothelin receptor antagonist.
Noradrenergic, noncholinergic inhibitory junction potentials in rat proximal colon: role of nitric oxide
Authors: Serio Rosa , Mulé Flavia , Postorino Alessandra
Published: April 2011

Using a single sucrose gap apparatus, experiments were performed to determine the involvement of nitric oxide (NO) in the generation of noradrenergic, noncholinergic (NANC) inhibitory junction potentials in circular muscle of rat proximal colon. Inhibitors of NO synthase, Nω-nitro-L-arginine and its methyl ester, reduced the amplitude of the electrically evoked inhibitory junction potentials, without affecting membrane resting potential. Such an effect was stereospecific and it was prevented by L-arginine but not by D-arginine. Sodium nitroprusside induced a tetrodotoxin-resistant hyperpolarization, which was not affected by NO synthase inhibitors. Aparnin reduced sodium nitroprusside induced hyperpolarization, as well as NANC inhibitory junction potentials, and α-chymotrypsin decreased the amplitude of electrical field stimulation evoked responses. Residual responses after NO synthase inhibitors or after α-chymotrypsin were further reduced by pretreatment with α-chymotrypsin or NO synthase inhibitors, respectively. These results suggest that, in rat colonic circular muscle, NO plays an important role in NANC inhibitory junction potential generation. However, another mechanism, peptidergic in nature, is also involved.Key words: nonadrenergic noncholinergic nerves, inhibitory junction potential, nitric oxide, rat colon.
Isolation and characterization of a new bradykinin potentiating octapeptide from γ-casein
Authors: Lebrun Ivo , Henriques Olga B. , Lebrun Fabiana L. A. S. , Carmona Adriana K. , Juliano Luiz , Camargo Antonio C. M.
Published: April 2011

Peptides that display bradykinin-potentiating activity have been obtained from a number of distinct sources, such as snake venoms, fibrinogen, and casein. This paper describes the isolation and sequencing of a novel bradykinin-potentiating peptide, generated by tryptic hydrolysis of the γ-casein chain. No homology was found to other known vasoactive or vasopotentiating peptides. The octapeptide Tyr-Pro-Val-Gln-Pro-Phe-Thr-Glu, corresponding to the γ-casein(114–121) sequence, was isolated from the tryptic hydrolysis of γ-casein and also synthesized by solid-phase peptide synthesis. Both natural and synthetic peptides had the same retention time in HPLC and displayed a selective potentiating activity on isolated guinea-pig ileum for bradykinin and Lys-bradykinin but were not able to potentiate the effects of Met-Lys-bradykinin, Ile-Ser-bradykinin, angiotensin II, acetylcholine, or histamine. Intravenous injections of bradykinin and of bradykinin-potentiating octapeptide produced a persistent hypotension in conscious rats, a pattern that was not obtained when the octapeptide was replaced by captopril. This bradykinin-potentiating octapeptide is a strong competitive inhibitor of endo-oligopeptidase A (EC 3.4.24.15, formerly EC 3.4.22.19), but it has low inhibitory potency towards angiotensin-converting enzyme (EC 3.4.15.1). Thus, our results suggest that other peptidases in addition to angiotensin-converting enzyme, such as endo-oligopeptidase A, may contribute to the reduction of the effective concentration of bradykinin in the circulation.Key words: bradykinin, potentiating peptides, casein, endo-oligopeptidase A, angiotensin-converting enzyme, smooth muscle, rat arterial blood pressure.
Nonlinear behaviour of human motoneurons
Authors: Smith Louise , Zhong Tao , Bawa Parveen
Published: April 2011

When ramp-and-hold currents are injected into a motoneuron of an anesthetized cat, the motoneuron responds with a high initial firing rate (dynamic phase), which then adapts to a lower steady-state firing rate. The firing rates during the dynamic and the steady-state phases are linearly related to the rate of change and the magnitude of the injected current, respectively. In human subjects, where inputs to the motoneurons are not accessible, force parameters are used to describe motoneuron behaviour. Population responses of human motoneurons, measured in terms of gross electromyographic (EMG) activity, increase linearly with the magnitude and the rate of change of force. No study has attempted to examine the question of linearity of single motor units during the dynamic as well as the steady-state phases. The following study recorded single motor unit and EMG activities simultaneously from the flexor carpi radialis muscle in human subjects completing ramp-and-hold force trajectories. Although the results confirmed the linear relationship between EMG activities and the rate and magnitude of the force, a nonlinear activity pattern was observed between the single motor unit firing and the force parameters, suggesting that recruitment must be responsible for the linear behaviour of EMG activity. Comparisons of different background activity levels on the firing patterns of a given motor unit, as well as comparisons of two simultaneously recorded units, further supported nonlinear response patterns of single motor units.Key words: human, motoneurons, motor units, nonlinearity, force trajectory, repetitive firing.
Effects of intravenous infusions of noradrenaline into the pregnant ewe on uterine blood flow, fetal renal function, and lung liquid flow
Authors: Stevens A. D. , Lumbers E. R.
Published: April 2011

To determine the effects on the fetus of high maternal levels of noradrenaline, experiments were carried out in 17 pregnant ewes (123–137 days gestation). Intravenous infusion of 40 mg/min of norepinephrine to the ewe for 1.5 h increased maternal arterial pressure and significantly decreased maternal placental blood flow (p < 0.05). Fetal arterial pressure did not change, but fetal arterial [Formula: see text] fell (p < 0.01) and [Formula: see text] rose (p < 0.01). Fetal urine flow fell and osmolality rose (p < 0.01), fetal lung liquid flow and osmolar excretion fell (p < 0.01, p < 0.05, respectively), and the lung sodium:potassium ratio changed. These effects of high levels of maternal noradrenaline were transient, i.e., 2.5 h after the infusion of noradrenaline had finished, fetal urine flow and lung liquid flow had both returned to control values and fetal [Formula: see text] was significantly depressed relative to control values (p < 0.01). It is concluded that high levels of maternal catecholamines reduce placental blood flow and cause small changes in fetal oxygenation. These changes are sufficient to transiently affect fetal water excretion and to reduce lung liquid flow.Key words: maternal noradrenaline, uterine blood flow, fetal oxygen, lung liquid, blood volume, fetal, renal.
Proprioceptive coordination of discrete movement sequences: mechanism and generality
Authors: Cordo Paul , Bevan Leslie , Gurfinkel Victor , Carlton Les , Carlton Mary , Kerr Graham
Published: April 2011

A "discrete" movement sequence is defined as a movement with a single goal that involves a series of overlapping joint rotations. Reaching-and-grasping and throwing are examples of discrete movement sequences. The central nervous system (CNS) can use reafferent proprioceptive information from one joint rotation in a sequence to coordinate subsequent rotations at other joints. The experiments reported in this paper demonstrate how the human CNS uses proprioceptive information to coordinate discrete movement sequences. We examined the mechanism (at an information processing level) underlying proprioceptive coordination and the generality (i.e., the boundary conditions) of these mechanisms as they apply to everyday movement sequences. Adult human subjects performed a discrete movement sequence that resembles backhand throwing: elbow extension followed by hand opening. The task was to open the hand as the elbow passed through a prescribed "target" angle. We eliminated visual information and made the arrival time at the target angle unpredictable so that the available kinematic information was provided exclusively by proprioception. The subjects were capable of performing this motor task with a high degree of precision, thereby demonstrating that the nervous system can use proprioceptive input to coordinate discrete movement sequences. Our data indicate that precise coordination is achieved by extracting kinematic information related to both the velocity of elbow rotation as well as the elbow position during movement (i.e., "dynamic position"). Dynamic position information appears to be encoded as both absolute joint angle and angular distance, although more precisely as angular distance. Although our experiments were conducted under rather restrictive laboratory conditions, this mechanism of motor coordination might also apply to everyday movement. Our results suggest that this mechanism could be employed for passive as well as active movement sequences, with and without opposing loads; it could exert its influence in discrete movement sequences as brief as 210 ms or as long as 1.5 s; and it does not involve any significant degree of learning (this proprioceptive mechanism appears to be readily available for use on the first attempt of a novel motor task).Key words: proprioception, movement, kinesthesia, arm, human.
Pharmacogenetics in clinical pharmacology and toxicology
Authors: Inaba T. , Nebert D. W. , Burehell B. , Watkins P. B. , Goldstein J. A. , Bertilsson L. , Tucker G. T.
Published: April 2011

An international symposium entitled Pharmacogenetics in clinical pharmacology and toxicology: a tribute to Werner Kalow was held in Toronto, Ontario, July 20, 1994. This subject was particularly important to discuss in the presence of Werner Kalow, 77 years young, who is considered as one of the grandfathers of this unique combination of medical research fields. It has become increasingly appreciated that dozens of human drug metabolism polymorphisms exist. The interindividual variabilities in drug metabolism discussed at this symposium do not represent small differences such as 50% or 3-fold but, rather, represent 10- to greater than 1000-fold differences. When attributed to a single gene, dramatic differences can be seen among family members, just as blue and brown eyes can occur in siblings. These differences can result in acute drug toxicity. In addition, there are chronic effects: over one's lifetime, striking differences in the metabolism of drugs, occupationally hazardous chemicals, and other environmental pollutants can lead to interindividual differences in the buildup of DNA damage (e.g., mutations, chromosomal breaks, rearrangements) leading to toxicity and tumor initiation, as well as leading to a buildup in nongenotoxic signals (signal transduction pathways without DNA damage) important for toxicity, tumor promotion, and tumor progression. The human UDP glucuronosyltransferase (UGT superfamily is known to comprise more than 10 genes in humans, and probably in other mammalian species. Breakthroughs in UGT gene mutations responsible for the Crigler-Najjar syndrome and Gilbert's disease have recently been reported. The human cytochrome P450 termed CYP3A4 is a major P450 enzyme in the liver and gastrointestinal tract, and the full impact of the CYP3A4 polymorphism has yet to be fully appreciated. CYP3A4 metabolism of cyclosporin A, commonly prescribed to organ transplant recipients, the induction of CYP3A4 by rifampicin, and inhibition of CYP3A4 metabolism by erythromycin or ketoconazole are now quite well understood. The field of ethnopharmacology, or pharmacoanthropology, has recently emerged, pioneered at least in part by Kalow. Differences in debrisoquine–sparteine metabolism, S-mephenytoin hydroxylation, diazepam clearance, and omeprazole clearance in various Caucasian and Oriental subpopulations in a number of countries have been extensively reported. After a number of inconclusive studies, it has now been shown unequivocally that the human S-mephenytoin 4′-hydroxylase polymorphism represents at least two distinct mutations (one involving a splice site) in the CYP2C19 gene. Finally, the implications and clinical significance of a number of human polymorphisms (CYP2D6, CYP2C19, N-acetylation (NAT2), S-methylation by thiopurine methyltransferase (TPMT), and ester hydrolysis by plasma cholinesterase) were carefully reviewed at this symposium.Key words: pharmacology, toxicology, drug metabolism, pharmacogenetic polymorphism.
Myocardial lipoprotein lipase activity: regulation by diabetes and fructose-induced hypertriglyceridemia
Authors: Liu Limin , Severson David L.
Published: April 2011

The decrease in myocardial lipoprotein lipase (LPL) activity observed previously in acute, severe models of insulin-deficient diabetes may be a compensatory response to hypertriglyceridemia and a sustained increase in fatty acid delivery to cardiomyocytes. The administration of fructose (10% solution in the drinking water for 4 days) to rats produced hypertriglyceridemia, but heparin-releasable LPL activity from perfused hearts and total and heparin-releasable LPL activities in isolated cardiomyocytes were not reduced. The acute (4 day) induction of a mild diabetic state (60 mg/kg streptozotocin) resulted in modest hypertriglyceridemia, and a selective decrease in heparin-releasable LPL activity in perfused hearts; LPL activity in cardiomyocytes from diabetic rat hearts was not reduced. Therefore, the diabetes-induced fall in myocardial LPL activity is not secondary to hypertriglyceridemia, since fructose treatment did not change LPL activity. Perfusion of rat hearts with 100 μM lysophosphatidylcholine (LPC) released a small amount of LPL activity into the perfusate, but only if albumin was omitted from the perfusion solution. Thus, the selective reduction in heparin-releasable LPL activity in perfused diabetic hearts is probably not the consequence of displacement by LPC, a lipolytic product of the LPL-catalyzed degradation of triacylglycerol-rich lipoproteins. Circulating LPL activity in the plasma of diabetic rats was not decreased relative to control plasma enzyme activity; therefore, the reduction in heparin-releasable LPL activity is not because circulating LPL was less available for uptake by the endothelium in diabetic hearts.Key words: diabetes, lipoprotein lipase, perfused hearts, cardiomyocytes.
L-Propionylcarnitine effects on cardiac carnitine content and function in secondary carnitine deficiency
Authors: Broderick Tom L. , DiDomenico Denise , Paulson Dennis J. , Shug Austin L.
Published: April 2011

Long-term treatment with sodium pivalate, a compound conjugated to carnitine and excreted in the urine, results in carnitine deficiency and cardiac dysfunction. Since L-propionylcarnitine (LPC) is generally of benefit to cardiac function, it was of interest to determine whether it is effective in preventing the reductions in both heart carnitine content and function from occurring in carnitine deficiency. Secondary carnitine deficiency was induced in male Sprague–Dawley rats by supplementing the drinking water with 20 mM sodium pivalate for 26 weeks. Control animals received an equimolar concentration of sodium bicarbonate. At 13 weeks into treatment, a subgroup of control and sodium pivalate animals were given 80 mg/kg of LPC in their drinking water. Following treatment, isolated working hearts were perfused with buffer containing 11 mM glucose and 0.4 mM palmitate. Hearts from sodium pivalate treated animals demonstrated a severe reduction in tissue carnitine. When mechanical function was measured in these hearts, heart rate, rate–pressure product, and aortic flow were significantly depressed. Treatment with LPC, however, prevented the depletion in cardiac carnitine content and improved these cardiac parameters. Our results demonstrate that LPC treatment is beneficial in preventing the depression in cardiac function from occurring in this model of secondary carnitine deficiency.Key words: L-propionylcarnitine, cardiac function, carnitine deficiency.
Relationship among sensitivity to adrenaline, plasma corticosterone level; and estrous cycle in rats
Authors: Rodrigues M. L. V. , Marcondes F. K. , Spadari-Bratfisch R. C.
Published: April 2011

The dose–response curves to the chronotropic effect of adrenaline obtained in right atria isolated from female rats indicated an order of increasing sensitivity to adrenaline, at the pD2 level, according to the estrous cycle, as follows: estrus ≤ metestrus ≤ diestrus ≤ proestrus. Inhibition of neuronal and extraneuronal uptake shifted the dose–response curves to adrenaline to the left only in right atria isolated from rats during estrus or metestrus. Moreover, under these experimental conditions, right atria were subsensitive to adrenaline during proestrus, in contrast to metestrus. Plasma corticosterone levels were lower during estrus and higher at proestrus. There was a positive correlation between right atria sensitivity to adrenaline and plasma corticosterone levels and estrous cycle phases. Our results also suggest that in the rat right atria during proestrus, as opposed to the other phases of the estrous cycle, there was an endogenous inhibition of extraneuronal uptake together with some alteration at the adrenoceptor level and (or) at intracellular mechanisms beyond receptors.Key words: adrenergic response, female, adrenaline, chronotropism, right atria.
Differential effect of desipramine and 2-hydroxydesipramine on depolarization-induced calcium uptake in synaptosomes from rat limbic sites
Authors: Beauchamp G. , Lavoie P.-A. , Elie R.
Published: April 2011

This study was conducted to investigate the inhibition of synaptosomal45Ca uptake by desipramine and its major metabolite 2-hydroxydesipramine in the rat hippocampus and cingulate cortex, areas associated with emotional control. A concentration-dependent inhibition of net depolarization-induced45Ca uptake was observed for desipramine (20–200 μM) in synaptosomes from both sites. However, 20 μM 2-hydroxydesipramine failed to inhibit calcium channel function in either of the two limbic sites; higher concentrations (60 or 200 μM) did produce a minor degree of inhibition in hippocampus synaptosomes. Others have shown that the clinically encountered plasma concentrations of 2-hydroxydesipramine are lower than those of desipramine, and the brain concentration of 2-hydroxydesipramine is therefore not expected to surpass or even reach 20 μM. In view of the previously observed clinical activity of 2-hydroxydesipramine, the present results indicate that calcium channel antagonism may not be the basis for the therapeutic effect of tricyclic antidepressants.Key words: voltage-dependent calcium channels,45Ca uptake, hippocampus, cingulate cortex, tricyclic antidepressants.
Inhibition of neurons in the rat medial amygdaloid nucleus in vitro by somatostatin
Authors: Lu Yun-Fei , Hattori Yykio , Moriwaki Akiyoshi , Hayashi Yasushi , Hori Yasuo
Published: April 2011

Effects of somatostatin (SRIF) on neurons in the medial amygdaloid nucleus were investigated in rat brain slice preparations, using extracellular recordings. Following bath application of SRIF at 10−7–10−6 M, 63 of 81 (78%) medial amygdala neurons showed an inhibitory response. The inhibitory effect of SRIF was dose dependent, and the threshold concentration was approximately 10−9 M. The inhibitory response to SRIF persisted during synaptic blockade in two-thirds of neurons tested. The inhibitory effect of SRIF was reduced by picrotoxin, a GABAA receptor antagonist, in one-third of neurons. These results suggest that SRIF exerts an inhibitory effect on medial amygdala neurons through either a direct action on SRIF receptors or a GABAergic synaptic involvement.Key words: somatostatin, amygdala, brain slice, neuron activity, picrotoxin.
Effects of propofol and thiopentone on picrotoxin convulsive threshold in the rabbit
Authors: Hasan Zyheir , Khatib Said , Abu-Laban Ayman
Published: April 2011

The purpose of the present study was to examine the effect of intravenous administration of propofol and thiopentone on picrotoxin-induced seizures using the picrotoxin convulsive threshold test in the rabbit. Neither propofol nor thiopentone at a dose of 1.25 mg/kg had any significant effect on picrotoxin seizure threshold. However, at higher doses (2.5, 5, 10 mg/kg) both propofol and thiopentone produced a significant and dose-dependent increase in the picrotoxin convulsive threshold. These findings suggest that propofol is an effective anticonvulsant against picrotoxin-induced seizures in the rabbit.Key words: convulsions, intravenous anesthetics, picrotoxin, propofol, thiopentone.
Endothelial cell products alter mammalian skeletal muscle function in vitro
Authors: Murrant C. L. , Barclay J. K.
Published: April 2011

We tested the hypothesis that endothelin and nitric oxide (NO) alter the force developed by fast-twitch and slow-twitch mammalian skeletal muscle, using a mouse skeletal muscle preparation trimmed to approximately 50% of the original diameter to decrease diffusion distances. We suspended trimmed soleus (SOL) and extensor digitorum longus (EDL) muscles in Krebs–Henseleit buffer (27 °C; pH 7.4) gassed with 95% O2 – 5% CO2. Muscles were stimulated once every 90 s for 500 ms at 50 Hz for SOL and 100 Hz for EDL. The force developed by trimmed SOL was 223.8 ± 9.1 mN/mm2 and by EDL was 247.3 ± 9.4 mN/mm2. Endothelin 1 (ET-1) had no effect on EDL but significantly accelerated the rate of decrease of developed force of SOL at concentrations of 10−10 mol/L and higher within 10 contractions. When ET-1 was removed, force returned toward control value. Endothelin 3 (ET-3) had no effect on either muscle. S-Nitroso-N-acetylpenicillamine (SNAP), a source of NO, increased developed force over time in both muscles, with a threshold of 10−6 mol/L. The effect was evident within 5 contractions in both muscles. Force remained elevated above control values after the removal of SNAP. Thus ET-1 attenuated and NO amplified mammalian skeletal muscle function.Key words: soleus, extensor digitorum longus, tetanic contractions, endothelin 1, endothelin 3, S-nitroso-N-acetylpenicillamine.
Targeted disruption of the mouse B2bradykinin receptor in embryonic stem cells
Authors: Borkowski Joseph A. , Hess J. Fred
Published: April 2011

Two mammalian genes encoding bradykinin (BK) receptors termed B1and B2have been identified by molecular cloning techniques. Some pharmacological data suggest the existence of further subtypes of the B2receptor. To unambiguously determine whether additional genes encoding B2BK receptors might exist in mammals, steps have been taken toward the generation of mice with a "knockout" of the BK B2receptor. A genomic clone of the mouse B2BK receptor was isolated and its coding sequence determined by DNA sequence analysis. A physical map of the DNA flanking this coding sequence was generated. A vector, pBS-KO-1, was constructed for targeted disruption of the mouse B2receptor gene. This vector contains 1 kb (kilobase) of DNA upstream of the mouse B2receptor coding sequence, a neomycin resistance gene (neo), and 5.4 kb of DNA downstream of the B2receptor coding sequence. Thus, the correct homologous recombination event will result in a chromosome in which the coding sequence for the mouse B2BK receptor is replaced with the neomycin resistance gene. pBS-KO-1 was transfected into embryonic stem cells, and clones containing a targeted disruption of the mouse B2BK receptor were identified.Key words: bradykinin, G-protein-coupled receptor, embryonic stem cells, gene targeting, homologous recombination.
Central tachykinins: mediators of defence reaction and stress reactions
Authors: Culman Juraj , Unger Thomas
Published: April 2011

The tachykinins substance P, neurokinin A, and neurokinin B are natural agonists for NK1, NK2, and NK3receptors, respectively. Evidence from biochemical, neurophysiological, pharmacological, and molecular biology studies indicates that the tachykinin-containing pathways within the brain contribute to central cardiovascular and endocrine regulation and to the control of motor activity. The hypothalamus, which represents a site for the integration of central neuroendocrine and autonomic processes, is rich in tachykinin nerve endings and tachykinin receptors. Stimulation of periventricular or hypothalamic NK1receptors in conscious rats induces an integrated cardiovascular, behavioural, and endocrine response. The cardiovascular response is associated with increased sympathoadrenal activity and comprises an increase in blood pressure and heart rate, mesenteric and renal vasoconstriction, and hind-limb vasodilatation. The behavioural response consists of increased locomotion and grooming behaviour. This response pattern is consistent with an integrated stress response to nociceptive stimuli and pain in rodents. Several studies have demonstrated rapid changes in substance P levels and its receptors in distinct brain areas following acute stress. These data indicate that substance P and other tachykinins, in addition to serving as nociceptive and pain transmitters in the spinal cord, may act in the brain as neurotransmitters–neuromodulators within the neuronal circuits mediating central stress responses.Key words: tachykinins, substance P, central nervous system, defence reaction, stress.
Tachykinins, sensory nerves, and asthma—an overview
Authors: Lundberg Jan M.
Published: April 2011

Tachykinin peptides, substance P (SP) and neurokinin A (NKA), are released from airway sensory nerves upon exposure to irritant chemicals and endogenous agents including bradykinin, prostaglandins, histamine, and protons. The released neuropeptides are potent inducers of a cascade of responses, including vasodilatation, mucus secretion, plasma protein extravasation, leukocyte adhesion–activation, and bronchoconstriction. Neurokinin 1 receptors (preferably activated by SP) seem to be most important for inflammatory actions, while neurokinin 2 receptors (preferably activated by NKA) mediate bronchoconstriction. Species differences exist whereby rat and guinea-pig have a more developed neurogenic inflammation response than normal human airways. However, disease states such as inflammation or viral infections lead to enhanced peptide synthesis and (or) increased sensory nerve excitability. Together with increased neurokinin 1 receptor synthesis and loss of major tachykinin-degrading enzymes such as neutral endopeptidase in airway inflammation, this suggests that recently developed, orally active nonpeptide neurokinin receptor antagonists could have a therapeutic potential in asthmatic patients.Key words: neurokinins, sensory nerves, inflammation, bronchoconstriction, receptors.
Interleukin 1β, but not tumor necrosis factor, enhances neurogenic vasodilatation in the rat skin: involvement of nitric oxide
Authors: Herbert M. K. , Hering S. , Holzer P.
Published: April 2011

In phenobarbitone-anesthetized rats the effects of interleukin 1β (IL-1β) and tumor necrosis factors (TNFs) were examined on die capsaicin-induced increase of plantar cutaneous blood flow in the rat hind paw as measured by laser Doppler flowmetry. IL-1β (0.5–500 pg) or TNFα or TNFβ (50–5000 pg) was injected subcutaneously into the left paws, while the right paws received vehicle (10 μL) only. IL-1β was without effect on blood flow by its own but dose dependency enhanced the hyperemia due to capsaicin (0.3 μg). TNFs failed to enhance the capsaicin-induced vasodilatation, although 5000 pg TNFα produced a transient increase of local blood flow. Indomethacin (10 mg/kg, i.p.) did not alter the capsaicin-induced vasodilatation but prevented IL-1β (50 pg) from augmenting the hyperemic response to capsaicin. Likewise, blockade of nitric oxide formation by NG-nitro-L-arginine methyl ester (L-NAME) failed to affect the capsaicin-evoked vasodilatation but abolished its amplification by IL-1β. Systemic pretreatment with a neurotoxic dose of capsaicin reduced the capsaicin-induced hyperemia and prevented the facilitatory effect of IL-1β. The hyperemia evoked by intraplantar calcitonin gene related peptide (0.038–3.8 ng) was not altered by IL-1β (50 pg). These data indicate that IL-1β but not TNF enhances the cutaneous hyperemic response to capsaicin. This proinflammatory action arises from sensitization of afferent nerve endings and depends on nitric oxide and cyclooxygenase products as essential intermediates.Key words: interleukin 1β, tumor necrosis factor, capsaicin, neurogenic inflammation, nitric oxide.
Brain tissue hydrolysate acts on presynaptic adenosine receptors in the rat hippocampus
Authors: Xiong H. , WoJtwics J.M. , Baskys A.
Published: April 2011

Adenosine is a potent inhibitory modulator in the brain. It suppresses glutarnatergic synaptic transmission and possibly acts as a brain endogenous neuroprotective agent. In this study we have examined the effects of a clinically used porcine brain tissue hydrolysate, Cerebrolysin™, on synaptic transmission in the CA1 area of rat hippocampal slices. A major effect of the drug at doses approximating those administered clinically to demented patients was a depression of synaptic transmission at the Schaffer collateral–commissural pathway in CA1. Detailed analysis showed that the inhibition is presynaptic and can be reduced by low doses of a specific blocker of adenosine A1 receptors, 8-cyclopentyltheophylline. Because Cerebrolysin™ does not contain a detectable amount of adenosine, the effect on adenosine A1 receptors must be indirect, perhaps by release of the endogenous agonist. This action of Cerebrolysin™ is consistent with a putative neuroprotective action underlying its clinical usage.Key words: adenosine, Cerebrolysin™, hippocampus, brain slices, synaptic transmission.
Quantification of the hemolysis associated with use of T-61Ras a euthanasia agent in rabbits–a comparison with EuthanylR(pentobarbital sodium) and the impact on serum hexosaminidase measurements
Authors: Doyghty Michael J. , Stuart Darrin
Published: April 2011

Albino rabbits (2–2.3 kg) were euthanized with T-61R(N-[2-(m-methoxyphenyl)-2-ethylbutyl-(1)-]-γ-hydroxybutyramide, 200 mg/mL; 4,4′-methylene-bis-(cyclohexyltrimethylammonium iodide), 50 mg/mL; tetracaine hydrochloride, 5 mg/mL; 0.2–1.0 mL/kg, iv) or EuthanylR(pentobarbital sodium, 100–240 mg/kg, iv) at 15:00 h, and samples of arteriovenous blood or venous blood were collected. The time to loss of consciousness was dose dependent for T-61, ranging from 7 to 1 s or less. Serum obtained after T-61 euthanasia, but not after Euthanyl, was routinely contaminated with measurable hemoglobin levels (up to an estimated 3 mg/mL). The extent of hemolysis increased with increasing T-61 doses. The activity of hexosaminidase in the serum (determined by hydrolysis of a methylumbelliferyl substrate at pH 4.6) was up to 80% lower in sera obtained after the use of T-61 compared with sera obtained after the use of Euthanyl or without euthanasia drugs. The reduction in measurable activity appears to be due to interference, by hemoglobin, in the fluorescence measurements of the methylumbeiliferol reaction product (with threshold effects being detected at 0.1 mg/mL). Standardization of serum volumes used in these types of enzyme assays and reporting on hemoglobin levels is thus recommended.Key words: euthanasia, rabbits, T-61R, N-[2-(m-methoxyphenyl)-2-ethylbutyl-(1)-]-γ-hydroxybutyramide, 4,4′-methylene-bis-(cyclohexyltrimethylammonium iodide), tetracaine hydrochloride, EuthanylR, pentobarbital sodium, serum, hemoglobin, hexosaminidase.
Effect of sympathectomy on inotropic responsiveness to α-adrenoceptor stimulation in developing mouse myocardia
Authors: Tanaka Hikaru , Matsuda Tomoyuki , Adachi Mika , Shigenobu Koki
Published: April 2011

Effects of postnatal sympathectomy on inotropic responsiveness to α-adrenoceptor stimulation were examined in mouse myocardia to determine whether the developmental conversion of α-adrenoceptor-mediated inotropic responses from positive to negative is triggered by sympathetic innervation. Sympathectomy was performed chemically by consecutively administering 6-hydroxydopamine for 14 days after birth and confirmed by the absence of inotropic responses to tyramine. In newborn myocardia, phenylephrine, in the presence of propranolol, produced concentration-dependent positive inotropic responses. Three weeks after birth, phenylephrine, in the presence of propranolol, produced concentration-dependent negative inotropic responses, both in control and in sympathectomized myocardia; no difference was observed between the two groups of mice in the maximum decrease in contractile force produced by phenylephrine. The sensitivity (pD2 value) to phenylephrine was significantly higher in sympathectomized myocardia. In conclusion, sympathetic innervation of the mouse ventricular myocardium is not required for the developmental conversion of the α-adrenoceptor-mediated inotropic response from positive to negative.Key words: inotropism, α-adrenoceptor, supersensitivity, sympathetic innervation, development.
Adult plasticity in the visual system
Authors: Chino Yuzo M.
Published: April 2011

When visual cortical neurons in adult mammals are deprived of their normal afferent input from retinae, they are capable of acquiring new receptive fields by modifying the effectiveness of existing intrinsic connections, a basis for topographic map reorganization. To gain insights into the underlying mechanisms and functional significance of this adult plasticity, we measured the spatial limits and time course of retinotopic map reorganization. We also determined whether reactivated neurons exhibit normal receptive field properties. We found that virtually all units in the denervated zone of cortex acquired new receptive fields (i.e., there were no silent areas in the cortex) and map reorganization can take place within hours of deafferentation provided that retinal lesions are relatively small (<5°). Furthermore, after long periods of recovery, reactivated units exhibited strikingly normal selectivity to stimulus orientation, direction of movement, and spatial frequency if relatively high contrast stimuli were used. However, responsiveness of these neurons, measured in terms of the maximum response amplitude and the contrast threshold, was clearly reduced. Thus, contrary to traditional belief, the adult visual cortex is capable of exhibiting considerable plasticity, and reactivated neurons are capable of contributing to an analysis of a visual scene.Key words: adult plasticity, visual cortex, retinal lesions, map reorganization, cat.
Evolution off spontaneous activity in the developing rat superior colliculus
Authors: Itaya Stephen K. , Fortin Stephane , Molotchnikoff Stephane
Published: April 2011

During the first 10 days after birth in the rat there are a succession of major developmental stages in the retinotectal pathway. During most of this time, the only recordable event in the superior colliculus is spontaneous activity. We studied and characterized this spontaneous activity, hypothesizing that it could play an important role in pathway development. The spontaneous discharges are detectable on postnatal day 5 (P5). After P5, the number of spontaneously active cells per penetration increases up to P10, after which they decrease to adult-like levels by P14–P15. Between P5 and P10, the spontaneous discharges exhibit several patterns of activity, from constant firing to intermittent bursts with periods of quiescence, without any bearing to age. We isolated the retina and superior colliculus by injecting xylocaine onto the optic nerve and found no change in collicular activity. While this suggests that the spontaneous activity in the colliculus is independent of the retina at the ages studied, the opposite experiment, i.e., electrically stimulating the optic nerve, resulted in increased firing by collicular neurons, perhaps via nonclassical synaptic transmission. Finally, we compared interval histograms for spontaneously active cells between P5 and P15. The histograms suggest that at certain ages, spontaneous firing is more regular; moreover, these ages precede major functional advances, e.g., onset of numerous spontaneously firing cells at P6, the first response to optic nerve stimulation at P10, and the first light-evoked response at P12–P13. Our results support the hypothesis that spontaneous activity in the neonatal superior colliculus has a role in development of the retinotectal pathway, but the data also indicate that classical synaptic transmission is not involved.Key words: superior colliculus, spontaneous activity, development, rat.
Baclofen attenuates cardiorespiratory effects of vagal C fiber stimulation in rats
Authors: Seifert Erin , Trippenbach Teresa
Published: April 2011

We tested the hypothesis that γ-aminobutyric acid (GABA) acting on GABAB receptors modulates vagal C fiber mediated reflexes. The effects of a GABAB receptor agonist, (−)-baclofen, injected bilaterally into the nucleus tractus solitarius (NTS), on the cardiorespiratory response to C fiber stimulation with phenyldiguanide (PDG) introduced into the right atrium were evaluated in urethane-anesthetized Wistar rats. We recorded integrated diaphragmatic EMG (Di) and mean arterial blood pressure (ABP). Before injections of baclofen into the NTS, PDG caused bradycardia, hypotension, and apnea, followed by a decrease in Di amplitude and variable changes in respiratory timing. Only injections of baclofen at 0.6 mm caudal to the obex reduced or prevented the PDG-evoked apnea. In contrast, independent of site of injection baclofen diminished bradycardia and the decrease in Di in postapnea breaths. The ABP response to PDG was never affected by baclofen. A GABAB receptor antagonist, CGP 35348, fully restored the responses to PDG, but CGP 35348 alone did not affect the responses to PDG. Our results suggest that GABAB receptors are present on neurons in the medullary pathway of vagal C fibers. In the caudal NTS, GABAB receptors modulate the PDG-evoked apnea, and within the larger area of the NTS these receptors modulate bradycardia and postapnea patterns of breathing. The absence of effects of CGP 35348 alone implies that GABAB receptors on the vagal C fiber pathway are not tonically active in rats.Key words: control of breathing, phenyldiguanide, CGP 35348, GABAB receptors, pulmonary chemoreflex.
Effect of denervation of the rat superior mesenteric arterial bed on the distribution of resistance among the first four orders of branching
Authors: Scott T. M. , Chafe L. L. , Vliet B. N. Van
Published: April 2011

The rat superior mesenteric artery with its first four orders of branching has been examined as an isolated perfused preparation. Lumen diameter and proportional resistance at each level have been determined and compared under conditions of constant pressure following methoxamine-induced constriction and acetylcholine-induced relaxation in intact and denervated preparations. A comparison was also made between intact preparations under conditions of constant pressure and constant flow. Lumen diameter and segment length were measured by analysis of video-taped images. The distribution of resistance among the first four orders of branching was estimated from the measured values using the Poiseuille formula. Intact first and fourth order branches had a proportionately low resistance, with the remaining resistance being fairly evenly distributed between the second and third order branches. No change in the pattern occurred as a result of either methoxamine or acetylcholine treatment. The pattern of distribution of resistance changed following denervation, so that proportional resistance was high in the first order branches and fell off from the second to fourth order branches. With methoxamine, the first order branches of denervates had a significantly higher resistance than in intact tissues, with the distribution of resistance in the second to fourth order branches following the basal resistance pattern. Reduction in the proportion of resistance with acetylcholine was similar in both intact and denervated preparations. Distribution of resistance did not differ between constant flow and constant pressure intact preparations.Key words: proportional resistance, denervation, mesenteric artery, video microscopy.
Effect of neural blockades, gastrointestinal regulatory peptides, and diversion of gastroduodenal contents on periodic pancreatic secretion in the preruminant calf
Authors: Zabielski R. , Kiela P. , Onaga T. , Mineo H. , Kato S. , Gregory P. C.
Published: April 2011

The role of nerves, gastrointestinal peptides, and gastroduodenal contents in the regulation of pancreatic periodic function were studied in preruminant calves. Nine male, Friesian calves were surgically fitted with pancreatic and duodenal catheters, abomasal and duodenal cannulae, and duodenal electrodes. Pancreatic secretion oscillated in phase with the duodenal migrating myoelectric complex. Pancreatic secretion and duodenal motility were abolished by intravenous atropine (5 μg∙kg−1∙min−1). The frequency of pancreatic and duodenal cycles was similarly increased by motilin and decreased by pituitary adenylate cyclase activating polypeptide-27; secretin lengthened duodenal but not pancreatic cycles, resulting in loss of synchronization; cholecystokinin-8 and secretin increased pancreatic secretion (all infusions at 120 pmol∙kg−1∙h−1); intraduodenal lidocaine (2%) or diversion of gastroduodenal contents reduced pancreatic secretion without altering periodicity. In conclusion, generation of pancreatic as well as of duodenal periodicity in the calf depends upon cholinergic neural efferent input. Secretin, cholecystokinin-8, pituitary adenylate cyclase activating polypeptide, duodenal contents, and mucosal afferent receptors seem to have relatively minor regulatory roles but can modulate the level of pancreatic secretion. The importance of enteric neural influence from the duodenum and the role of motilin in the regulation of pancreatic periodicity and its synchronization with the duodenal motility cycle remain to be determined.Key words: pancreatic juice, duodenal migrating myoelectric complex, secretin, motilin, pituitary adenylate cyclase activating polypeptide, atropine, lidocaine, calf.