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R L Moss

Publications and source records attributed to R L Moss.

At least 217 records · Page 12Linked to original sources
PubMed1983

Action of estrogen and mechanical vaginocervical stimulation on the membrane excitability of hypothalamic and midbrain neurons.

The effect of vaginocervical stimulation (VCS) and estrogen iontophoresis on the electrical activity recorded in urethane-anesthetized female rats from medial preoptic-septal (MPO-S) and midbrain central gray (MCG) neurons was studied during two phases of the estrous cycle, namely metestrus (M) and late proestrus-estrus (LP-E). The spontaneous discharge rate of both MPO-S and MCG neurons varied over the two stages of the estrous cycle. The spontaneous electrical activity of the MPO-S neurons was higher during M than during LP-E whereas MCG unit activity was low during M and higher during LP-E. The VCS-evoked changes in unit activity were specific, in that they were observed in response to mechanical genital stimulation and not in response to painful stimuli and/or nonspecific arousal. These responses were not dependent on the stage of estrous cycle. Finally, the iontophoresis of 17 beta-estradiol hemisuccinate evoked electrophysiological responses from MPO-S and MCG neurons. More MPO-S neurons were responsive to estrogen in LP-E than in M, while fewer MCG neurons were responsive to estrogen in LP-E than in M. The results clearly show that ongoing electrical activity of hypothalamic and midbrain nerve cells can fluctuate between M and LP-E phases of the estrous cycle and change with vaginocervical probing as well as iontophoretically applied estrogen. Furthermore, the results suggest the existence of a reciprocal relationship between the membrane activity of MPO-S and MCG neurons which may be related CNS control of reproductive activities.

Animals↗
PubMed1983

Alterations in the Ca2+ sensitivity of tension development by single skeletal muscle fibers at stretched lengths.

The apparent length dependence in the calcium sensitivity of tension development in skeletal muscle has been investigated in the present study. At sarcomere lengths of 2.46-2.62 micron, the Hill plot of tension-pCa data is well fit by not one but two straight lines, suggesting the possible involvement of more than a single class of Ca2+-binding site in tension development. On the other hand, increasing the sarcomere length to 3.00-3.25 micron yielded Hill plots that were described by a single straight line, which indicates that at long lengths tension might be regulated by the binding of Ca2+ to a single class of Ca2+-binding sites, presumably the low affinity sites of TnC. This length-dependent transformation of the tension pCa relation occurred at free Mg2+ concentrations of both 0.05 and 3.2 mM. Although the mechanism of this effect is uncertain, plausible explanations for the biphasic Hill plot at the shorter lengths include the possible involvement of Ca2+ activation of the thick filaments and/or myosin LC2 phosphorylation in the process of tension development.

Animals↗
PubMed1983

Effects of EDTA treatment upon the protein subunit composition and mechanical properties of mammalian single skeletal muscle fibers.

Considerable interest has been focused on the role of myosin light chain LC(2) in the contraction of vertebrate striated muscle. A study was undertaken to further our investigations (Moss, R.L., G.G. Giulian, and M.L. Greaser, 1981, J. Biol. Chem., 257:8588-8591) of the effects of LC(2) removal upon contraction in skinned fibers from rabbit psoas muscles. Isometric tension and maximum velocity of shortening, V(max), were measured in fiber segments prior to LC(2) removal. The segments were then bathed at 30 degrees C for up to 240 min in a buffer solution containing 20 mM EDTA in order to extract up to 60 percent of the LC(2). Troponin C (TnC) was also partially removed by this procedure. Mechanical measurements were done following the EDTA extraction and the readditions of first TnC and then LC(2) to the segments. The protein subunit compositions of the same fiber segments were determined following each of these procedures by SDS PAGE of small pieces of the fiber. V(max) was found to decrease as the LC(2) content of the fiber segments was reduced by increasing the duration of extraction. EDTA treatment also resulted in substantial reductions in tension due mainly to the loss of TnC, though smaller reductions due to the extraction of LC(2) were also observed. Reversal of the order of recombination of LC(2) and TnC indicated that the reduction in V(max) following EDTA treatment was a specific effect of LC(2) removal. These results strongly suggest that LC(2) may have roles in determining the kinetics and extent of interaction between myosin and actin.

Animals↗
PubMed1983

Action of prolactin, dopamine and LHRH on ventromedial hypothalamic neurons as a function of ovarian hormones.

The effect of iontophoretically-applied prolactin, dopamine, LHRH and LHRH-antagonist analog on the electrical activity of neurons (n = 192) located in the ventromedial nucleus of the hypothalamus (VMH) was studied in untreated and hormone-treated ovariectomized female rats (n = 63). The spontaneous electrical activity of VMH neurons was unaffected by the presence or absence of the ovarian hormones. Neuropharmacological studies indicate that the iontophoretic deposition of prolactin and dopamine produced opposing results, in that prolactin increased the electrical activity of the majority of the VMH neurons tested while dopamine decreased their activity. Finally, the application of LHRH and LHRH-antagonist analog to VMH neurons resulted in a marked suppression of their electrical activity that was even more pronounced in the presence of ovarian hormones. The present work provides evidence at the electrophysiological level of hormonal influences on the responsiveness of VMH neurons to LHRH and its antagonist analog, and demonstrates a relationship between the responsiveness of VMH neurons to prolactin and dopamine.

Animals↗
PubMed1983

Facilitation of sexual receptivity in the female rat by a fragment of the LHRH decapeptide, Ac-LHRH.

The following fragments of LHRH were administered intraventricularly and tested for their ability to enhance sexual receptivity in ovariectomized, estrogen-primed female rats: LHRH1-6 NH2, Ac-LHRH5-10, des-Tyr5-LHRH and des-Gly10-LHRH. LHRH1-6 NH2 had no effect on sexual behavior compared to saline-infused controls. Ac-LHRH5-10, des-Tyr5 LHRH and des-Gly10-LHRH significantly elevated lordotic responding compared to saline-infused controls. The results suggest that the elements contained in the LHRH structure may be functionally differentiated and indicate that the active sequence for facilitation of mating behavior is contained in the last half of the LHRH molecule.

Animals↗
PubMed1983

Metabolic cost of the stimulated beating of isolated adult rat heart cells in suspension.

Heart cells from adult rats were induced to beat in suspension by electric field stimulation. We have gained evidence that all the rod-shaped cells in suspension were indeed beating, and that the beat had dynamic characteristics similar to those of intact heart muscle contracting under zero load. The cells were undamaged in the process, as judged by maintenance of ATP levels, morphology, and ability to beat. In gaining such evidence, we also measured the metabolic cost to the cells of beating under zero load. In cells with oxidative phosphorylation inhibited by rotenone plus oligomycin (termed anaerobic), the rate of beat-dependent lactate production suggested an equivalent rate of ATP utilization of 0.126 +/- 0.013 nmol ATP/beat per mg protein (plus isoproterenol), and 0.058 +/- 0.005 nmol ATP/beat per mg protein (minus isoproterenol). In respiring cells, the rate of beat-dependent oligomycin-sensitive oxygen consumption gave an equivalent rate of ATP utilization of 0.198 +/- 0.009 nmol ATP/beat per mg protein (plus isoproterenol), and 0.126 +/- 0.013 nmol ATP/beat per mg protein (minus isoproterenol). The cells beat with the same approximate maximum velocity whether isoproterenol was present or not. We calculate that--in the case of anaerobic cells without isoproterenol--this rate of ATP utilization can account for only about a 15% degree of activation of the contractile proteins. In addition, we have found an oligomycin-insensitive beat-dependent mitochondrial respiration of 0.023 +/- 0.006 nanoatom O/beat per mg. The cause of this respiration is not known. The total rate of oxygen consumption of cells and also the rate per beat was comparable to that measured in nonworking whole hearts.

Adenosine Triphosphate↗
PubMed1982

Physiological effects accompanying the removal of myosin LC2 from skinned skeletal muscle fibers.

The possible role of the LC2 light chain of myosin in the contraction of vertebrate striated muscle has long been a subject of interest. This problem has been addressed in the present study in which the mechanical effects of partial removal of LC2 from skinned fibers of rabbit psoas muscle have been investigated. Each fiber was divided into three segments, thus allowing determinations of the LC2 content of the fiber 1) prior to extraction of the LC2 subunit, i.e. control, 2) following extraction of LC2, and 3) following readdition of LC2 to the fiber. Measurements of isometric tension and the maximum velocity of shortening were made in these fiber segments at each of the above stages of the extraction protocol. LC2 was partially removed from the fiber segments by treatment with a solution containing 20 mM EDTA, 50 mM KCl, 5 mM phosphate buffer, pH 7.0, for 120 min at 30 degrees C, a procedure modified from Chantler and Szent-Gyorgyi (Chantler, P. D., and Szent-Gyorgyi, A. G. (1980) J. Mol. Biol. 138, 473-492). LC2 content was determined using sodium dodecyl sulfate-polyacrylamide gel electrophoretic techniques. The results indicate that removal of about one-third of the total LC2 within a fiber segment reduced Vmax by nearly 50%, with very little effect upon isometric tension. Readdition of LC2 to these fiber segments resulted in recovery of Vmax to near control values. These findings suggest that LC2 may modulate the kinetics of interaction of myosin with actin in mammalian skeletal muscle.

Animals↗
PubMed1982

The effect of calcium on the maximum velocity of shortening in skinned skeletal muscle fibres of the rabbit.

The relationship between maximum shortening velocity (Vmax) and free calcium concentration has been studied in skinned single fibres from rabbit psoas and soleus muscles. At both 10 and 15 degrees C, Vmax measured in the psoas fibres was found to decrease by 40% when the pCa(-log[Ca2+]) was increased from 5.49 (maximally activating) to 6.21. Further decreases in Vmax were observed when the pCa was increased to 6.32. Vmax measured in soleus fibres at 15 degrees C also decreased when the Ca2+ concentration was lowered, though the magnitude of this effect was slightly less than in the psoas fibres. Thus, a distinct effect of Ca2+ upon Vmax has been shown to occur in mammalian skeletal muscle. The occurrence of this effect in both fast and slow muscle types may indicate that the underlying mechanism in the two cases is similar.

Adenosine Triphosphatases↗
PubMed1982

Evidence for vasoactive intestinal polypeptide (VIP) altering the firing rate of preoptic, septal and midbrain central gray neurons.

The effect of the iontophoretic application of vasoactive intestinal polypeptide (VIP) on the extracellular electrical activity (neuronal firing rate) of 91 neurons localized in the preoptic (PO), septal (S) region and midbrain central gray (MCG) was studied in urethane-anesthetized female rats. When applied in minute quantities, VIP induced both excitatory (N = 14) and inhibitory (N = 8) changes in the membrane excitability of PO and S neurons (total N = 58), while only inhibitory (N = 9) changes were observed in the MCG neurons (total N = 33; thus 24 MCG neurons were found to be unresponsive to VIP). The latency and duration of the VIP-induced response was, for the most part, characterized by a rapid onset and persisted for the duration of the ejecting pulse. However, five out of the 58 PO and S neurons and one out of the 33 MCG neurons did show responses that were longer and more variable in latency and duration. Of 26 PO neurons recorded and tested with VIP, only five neurons were determined to be antidromically identified (AI) as having their axons in the median eminence. The application of VIP increased the neuronal firing rate in two AI PO neurons, decreased the activity in one, and was ineffective in altering the activity in two other AI PO neurons. The VIP-induced changes in the neuronal firing rate appear to be specific and reproducible, and not related to the ejecting current nor pH of the solution. The results suggest that VIP, a gastrointestinal hormone that is also localized in the brain, can alter the neuronal firing rate of hypothalamic and midbrain neurons, thus providing additional evidence of its possible influence on brain and neuroendocrine function.

Animals↗
PubMed1982

Inhibition of lordosis behavior in the female rat by intraventricular infusion of prolactin and by chronic hyperprolactinemia.

The role of prolactin (PRL) in the control of the lordosis reflex of female rats was investigated. In the initial series of experiments, the normal high level of sexual receptivity observed in the ovariectomized, estrogen-progesterone (E-P) primed female rat was suppressed by intraventricular infusion of 100 ng PRL. Mating behavior remained suppressed 2, 3, and 5 hours following a single infusion of PRL into the third ventricle. In contrast, infusions of either an equal volume of the solvent vehicle (saline) or 100 ng of adrenocorticotropic hormone (ACTH) were ineffective in modulating the level of mating behavior in hormone-primed female rats. In a second series of experiments, chronic hyperprolactinemia was induced by pituitary transplants under the renal capsule in intact, normal cycle diestrus rats (N=12). A significant decrement in E-P induced mating behavior was observed at 12 and 14 weeks posttransplantation but not at 4 weeks. Sham-operated animals (N=12) displayed the characteristic pattern of behavior normally observed under exogenous E-P therapy. In summary, transient exposure as well as chronic exposure to high levels of PRL can suppress mating behavior, thus suggesting a possible role for PRL in the mediation of reproductive behavior in the female rat.

Adrenocorticotropic Hormone↗
PubMed1981

Initial report on combined in vivo single cell recording and intracellular staining.

This paper reports preliminary data obtained from the combination of extracellular single unit recording, microiontophoretic testing and intracellular staining of single neurons in the diencephalon of the anesthetized rat. Sixty neurons were recorded extracellularly and iontophoretically tested with glass multibarrelled micropipettes. Thirty-four of these neurons were identified by antidromic invasion from median eminence stimulation. Seventeen of these antidromically identified neurons were subsequently impaled with the micropipette and intracellularly stained with the fluorescent dye lucifer yellow-CH. The average diameter of the antidromically identified neuronal cell bodies was 7.4 microns. The iontophoretic response profiles of these stained neurons were similar to the profiles of non-stained antidromically identified neurons. Four of the remaining 26 neurons were synaptically activated from median eminence stimulation and were successfully marked with lucifer yellow. Average soma diameters of these neurons was 12.8 microns. Twenty-two neurons were not antidromically or orthodromically identified from median eminence stimulation. Three of these neurons were intracellularly stained with lucifer yellow and their soma diameters averaged 6.9 microns. Approximately 50% of all staining attempts, subsequent to extracellular recording and iontophoretic testing, were successful. The combination of these techniques is therefore a feasible approach to the in vivo study of the physiologic, pharmacologic and morphologic properties of single neurons.

Animals↗
PubMed1981

The effect of LHRH antagonist analogs and an antibody to LHRH on mating behavior in female rats.

The action of two antagonist analogs and an antibody to luteinizing hormone-releasing hormone (LHRH) on sexual receptivity was studied in avariectomized, estrogen-progesterone primed female rats. Small amounts of each LHRH substance or saline was infused through a cannula positioned in either the third ventricle or arcuate-ventromedial (ARC-VMH) area of the hypothalamus. Infusions were carried out at the time of progesterone priming, which was 42 hrs post-estrogen treatment, and sexual receptivity, as denoted by the lordosis-to-mount ratio, was measured six hrs later. One antagonist analog, [D-pGlu1, D-Phe2, D-Trp3,6]-LHRH[1], had little or no effect on sexual receptivity when tested in either site. Similarly, an antibody to LHRH, tested only in the ARC-VMH, had no observable effect on lordotic behavior. However, the second and the most potent antagonist analog, [Ac-dehydro-Pro1, pCl-D-Phe2, D-Trp3,6]-LHRH[2], produced a marked and significant decrement in lordotic behavior when infused into either the third ventricle or ARC-VMH. These results suggest that this potent and long-acting, competitive antagonist analog of LHRH prevented endogenous LHRH from exerting its normal role in the induction of sexual receptivity and provide evidence to support the contention that the role of LHRH in mediating receptivity in the female rat is physiologically relevant.

Animals↗
PubMed1981

Effects of calcium and ionic strength on shortening velocity and tension development in frog skinned muscle fibres.

1. The influence of Ca2+ concentration and ionic strength on the maximum velocity of shortening (Vmax) and the tension generating capability of frog skinned muscle fibres has been studied at temperatures between 1 and 10 degrees C. 2. Fibre segments were mounted between a force transducer and servo motor, where they could be viewed and photographed through a microscope. Segments in which the striations became non-uniform during activation were discarded. 3. Velocity was obtained as a function of load by stepping the tension to values less than the steady isometric tension. Vmax was then determined by an extrapolation technique. Vmax was also obtained using a second, independent method by measuring the times required to take up various amounts of slack imposed on the segments. 4. Vmax was significantly influenced by the Ca2+ concentration, decreasing by about one half when the Ca2+ concentration was reduced to give steady tensions less than half-maximal. 5. Vmax was not influenced by changes in ionic strength, in the range 0.09-0.18 M. Steady tension was found to increase as ionic strength was decreased in the same range. 6. These results indicate that the effect of changes in ionic strength is to alter the numbers or stiffness of attached cross-bridges, while there is no apparent influence of ionic strength on the steady-state kinetics of the actin-myosin interaction during unloaded shortening. The mechanism responsible for the influence of Ca2+ on Vmax is unknown, though possible sites of action for Ca2+ are discussed.

Animals↗
PubMed1981

Mechanical properties and myosin light chain composition of skinned muscle fibres from adult and new-born rabbits.

1. The maximum velocity of shortening, Vmax, and stiffness were measured in skinned single fibre segments from psoas and soleus muscles of adult rabbits and psoas muscles of new-born rabbits, and the myosin light chain composition was also determined in the same segments used in the mechanical studies. 2. Vmax was obtained at 15 degrees C during maximal activation at pCa 5.49 using a method involving measurement of the time required to take up various amounts of slack imposed on the segments. Stiffness was measured during activation at 10 degrees C by application of length steps complete in 0.6 msec. The myosin light chain composition of the segments was then determined by SDS-polyacrylamide gel electrophoresis. 3. Only fast type light chains were found to be present in the psoas fibre segments, though the relative amounts of myosin LC1f, LC2f and LC3f in these segments was somewhat variable. In most instances, the sum of the amounts of LC1f and LC3f present was equivalent to the amount of LC2f. Only slow type light chains were found in the soleus segments and the sum of the amounts of LC1as and LC1bs was about equal to the amount of LC2s. 4. The results indicate that there are no consistent relationships between Vmax, tension development or stiffness and LC1f/LC2f in the segments from adult and new-born psoas muscles, or between these mechanical parameters and LC1as/LC2s or LC1bs/LC2s in the adult soleus segments. However, the psoas segments, which had light chains of the fast type, had Vmax values that were consistently higher than those of the soleus segments, which had light chains of the slow type. 5. The stiffness values obtained in each of the three kinds of muscle were similar, suggesting that cross-bridge stiffness is similar in rabbit skeletal muscles of different type and age. Moreover, the results indicate that the amount of end compliance introduced by the connections to the fibre segments has a marked influence on the stiffness that is measured.

Animals↗
PubMed1981

Myocyte growth without physiological impairment in gradually induced rat cardiac hypertrophy.

A surgical technique was developed to place sutures around the pulmonary arteries of young rats (about 1 month old and 100 g body weight). As the operated rats grew, the pulmonary arteries were gradually constricted, leading after 4-6 weeks to the development of severe right ventricular hypertrophy with free wall weights about twice those from control rats. There were no signs of heart failure or cardiac decompensation. Collagen concentrations were the same in operated and control rats. Myocytes were isolated from right ventricles by enzymatic digestion. Autoradiographic studies showed considerable uptake in non-myocyte nuclei. Myocyte sarcomere lengths were unchanged. However, myocyte lengths and areas increased sufficiently to account for the increase in free wall weights observed. Physiological studies were done on isolated papillary muscles and ventricular strands, which were subsequently fixed. The force-generating capability at optimum length, magnitude of active compliance, and maximum speed of shortening (using four different techniques) were measured in each isolated muscle. There were no significant changes observed between operated and control rats. Microscopic examination of the muscle cross-sections confirmed that average myocyte area in the muscles obtained from operated rats was significantly increased. The results show that it is possible to obtain considerable increases in average myocyte size (by about a factor of 2) while still maintaining normal physiological function.

Animals↗
PubMed1981

Iontophoresis of morphine into the arcuate nucleus: effects on dopamine concentrations in hypophysial portal plasma and serum prolactin concentrations.

The effects of morphine on the release of dopamine from tuberoinfundibular neurons and the release of PRL from the anterior pituitary gland were studied in diestrous female rats. Morphine ions ejected iontophoretically in minute quantities into the arcuate nuclei (using one electrode per nucleus) were found to reduce markedly the concentration of dopamine in hypophysial portal plasma. Thirty minutes after the iontophoretic ejection of morphine using charges of 3.6 and 6.6 millicoulombs/electrode, the concentrations of dopamine in hypophysial portal plasma were reduced 70% and 83%, respectively, relative to the preiontophoretic values. When morphine was iontophoresed into each arcuate nucleus using a charge of 1.5 millicoulombs/electrode, there was no change in the concentration of dopamine in hypophysial portal plasma. The suppressive effect of morphine on dopamine release was prevented by pretreatment of the animals with naloxone (5 mg/kg, ip). In addition to the reduction of the concentration of dopamine in hypophysial portal plasma, the iontophoresis of morphine into the arcuate nuclei enhanced the serum concentration of PRL. On the basis of the present observations, it is suggested that morphine acts on an opiate receptor within the arcuate nucleus to suppress the secretion of dopamine from tuberoinfundibular neurons into hypophysial portal blood, thereby enhancing pituitary gland secretion of PRL.

Animals↗