Search PubMed⌕ Search

Biomedical subjects

R L Moss

Publications and source records attributed to R L Moss.

At least 181 records · Page 10Linked to original sources
PubMed1987

A1 noradrenergic input to medial preoptic-medial septal area: an electrophysiological study.

The effects of electrical stimulation of the A1 noradrenergic cell group on the extracellular activity of medial preoptic-medial septal (MPO-S) neurons were studied in ovariectomized (OVX) female rats under different hormonal conditions [estrogen and progesterone (E-P)-primed or unprimed] via conventional electrophysiological techniques. In addition, MPO-S neurons responding to the A1 noradrenergic cell group stimulation were characterized by examining their connections with the arcuate nucleus/median eminence (ARC/ME). With respect to stimulation of the A1 noradrenergic cell group, a large proportion of MPO-S neurons exhibited one of the following three types of orthodromic responses: orthodromic excitation (OD+), orthodromic inhibition (OD-), or complex orthodromic response (OD comp). The predominant type of response was OD+. Although E-P-priming did not change the relative proportion of neurons displaying a specific type of orthodromic response, it did increase the overall percentage of MPO-S neurons orthodromically responding to A1 stimulation (39% of MPO-S neurons responded to A1 stimulation in the E-P-primed group whereas only 25% of the neurons did so in the unprimed group). Neurons responsive to A1 stimulation were more likely to respond orthodromically to ARC/ME stimulation than were those neurons which were unresponsive to A1 stimulation. About one fifth of MPO-S neurons identified as projecting to the ARC/ME [putative luteinizing hormone-releasing hormone (LHRH) neurons] orthodromically responded to A1 stimulation. The predominant type of response was OD+. The present study indicates that A1 noradrenergic input to MPO-S neurons is predominantly excitatory.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Estrogen priming affects the sensitivity of midbrain central gray neurons to microiontophoretically applied LHRH but not beta-endorphin.

In vivo single-unit extracellular recording was used to assess neuronal membrane sensitivity at the level of the midbrain central gray (MCG) to the iontophoresis of luteinizing hormone releasing hormone (LHRH) and beta-endorphin (beta-END). The percentage of change in firing rate was evaluated to determine the effect of exogenously administered estradiol benzoate (EB) and EB plus progesterone (EB + P) on the membrane sensitivity of these MCG neurons to LHRH and beta-END. Ovariectomized adult female rats were primed with EB or EB + P, or nonprimed, 24-48 h prior to recording. EB priming significantly altered the membrane sensitivity of neurons in the MCG to LHRH by increasing the number of cells excited compared to the EB + P group and the nonprimed controls (p less than 0.005). The addition of P appeared to negate this effect. Hormonal priming did not alter the response profile for beta-END iontophoresis. The results suggest an estrogen-dependent sensitivity to LHRH at the MCG which translates into an increased electrical output, ultimately facilitating lordosis behavior. P treatment dampens this excitation. beta-END's effect on neuronal membrane excitability at the MCG was not distinctly characterized under the hormonal conditions our study evaluated and may reflect a regulatory role under physiological extremes.

Action Potentials↗
PubMed1986

Effects of human pancreatic growth hormone-releasing hormone and fragments of rat hypothalamic growth hormone-releasing hormone on the activity of rat brain neurons.

The effect of human pancreatic growth hormone-releasing factor (hpGRF), rat hypothalamic GRF1-29 (rhGRF1-29) and rhGRF3-40 on spontaneous extracellular activity was studied in urethane anesthetized, male rats. The results show that these peptides similarly depress the firing rate of responsive neurons in the amygdala, caudate-putamen and globus pallidus. A single neuron was excited by hpGRF and it was localized to the medial amygdala. These findings are in line with the hypothesis that GRF has effects on the central nervous system in addition to regulating pituitary growth hormone secretion.

Action Potentials↗
PubMed1986

Altered Ca2+ dependence of tension development in skinned skeletal muscle fibers following modification of troponin by partial substitution with cardiac troponin C.

Binding of Ca2+ to the troponin C (TnC) subunit of troponin is necessary for tension development in skeletal and cardiac muscles. Tension was measured in skinned fibers from rabbit skeletal muscle at various [Ca2+] before and after partial substitution of skeletal TnC with cardiac TnC. Following substitution, the tension-pCa relationship was altered in a manner consistent with the differences in the number of low-affinity Ca2+-binding sites on the two types of TnC and their affinities for Ca2+. The alterations in the tension-pCa relationship were for the most part reversed by reextraction of cardiac TnC and readdition of skeletal TnC into the fiber segments. These findings indicate that the type of TnC present plays an important role in determining the Ca2+ dependence of tension development in striated muscle.

Animals↗
PubMed1986

Behavioral specificity of beta-endorphin suppression of sexual behavior: differential receptor antagonism.

Open field behavior was observed in conjunction with mating behavior to discern whether the effect of intraventricular (ICV) beta-endorphin (beta-END) on sexual behavior may be secondary to akinesia. Three groups of ovariectomized, estrogen-progesterone-primed rats each received counterbalanced treatments of saline ICV, 2 micrograms beta-END ICV, or 2 micrograms beta-END ICV in combination with a selective opioid receptor antagonist. Receptive behavior (lordosis) and proceptive behaviors (presentation and ear wiggling) were consistently suppressed by beta-END, while ambulation was unaffected. Rearing and grooming were generally decreased, although this effect was statistically significant in only one experiment. Pretreatment with the mu-1 antagonist naloxazone (50 mg/kg intravenously) reversed the effects of beta-END on all behaviors tested. The delta receptor antagonist ICI-154,129 (12.5 and 50 micrograms ICV) only partially reversed the sexual effects of beta-END but completely reversed the open field effects. It is concluded that the suppressive effect of beta-END on sexual behavior, while not behaviorally specific, is not secondary to opioid-induced akinesia.

Animals↗
PubMed1986

Effect of beta-endorphin on sociosexual proclivity in a choice paradigm.

Intraventricularly-administered beta-endorphin (beta-END) suppresses receptive and proceptive behaviors of the ovariectomized, estrogen-progesterone-primed rat. This rat model was used in a four-way choice paradigm to investigate the behavioral specificity and motivational aspects of sexual suppression by beta-END. The experimental females showed a preference to associate with a sexually active 'stud' male over the other incentive animals as shown by significantly more approaches to and nose pokes into the stud male compartment. beta-END did not alter that choice preference. Rather, there was a decrease in overall social interaction after beta-END treatment, as shown by decreased total nose pokes. This overall decrease in social motivation, which was blocked by subcutaneous naloxone injection, was not specific to the stud male. It was not a result of akinesia, since total movement among the inner alleys was significantly higher after beta-END treatment, an effect also reversed by naloxone. These data suggest that intraventricular beta-END may act to suppress sociosexual motivation as a whole rather than sexual activity specifically.

Animals↗
PubMed1986

Effects of partial extraction of troponin complex upon the tension-pCa relation in rabbit skeletal muscle. Further evidence that tension development involves cooperative effects within the thin filament.

Partial extraction of troponin C (TnC) decreases the Ca2+ sensitivity of tension development in mammalian skinned muscle fibers (Moss, R. L., G. G. Giulian, and M. L. Greaser. 1985. Journal of General Physiology. 86:585), which suggests that Ca2+-activated tension development involves molecular cooperativity within the thin filament. This idea has been investigated further in the present study, in which Ca2+-insensitive activation of skinned fibers from rabbit psoas muscles was achieved by removing a small proportion of total troponin (Tn) complexes. Ca2+-activated isometric tension was measured at pCa values (i.e., -log[Ca2+]) between 6.7 and 4.5: (a) in control fiber segments, (b) in the same fibers after partial removal of Tn, and (c) after recombination of Tn. Tn removal was accomplished using contaminant protease activity found in preparations of LC2 from rabbit soleus muscle, and was quantitated using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and scanning densitometry. Partial Tn removal resulted in the development of a Ca2+-insensitive active tension, which varied in amount depending on the duration of the extraction, and concomitant decreases in maximal Ca2+-activated tensions. In addition, the tension-pCa relation was shifted to higher pCa values by as much as 0.3 pCa unit after Tn extraction. Readdition of Tn to the fiber segments resulted in the reduction of tension in the relaxing solution to control values and in the return of the tension-pCa relation to its original position. Thus, continuous Ca2+-insensitive activation of randomly spaced functional groups increased the Ca2+ sensitivity of tension development in the remaining functional groups along the thin filament. In addition, the variation in Ca2+-insensitive active tension as a function of Tn content after extraction suggests that only one-third to one-half of the functional groups within a thin filament need to be activated for complete disinhibition of that filament to be achieved.

Animals↗
PubMed1986

Effects on shortening velocity of rabbit skeletal muscle due to variations in the level of thin-filament activation.

The effect of Ca2+ upon maximum shortening velocity (Vmax) has been investigated in skinned single fibres from rabbit psoas muscles. Vmax was obtained at 15 degrees C by measuring the amounts of time (delta t) required to take up various amounts of slack (delta l) imposed at one end of the fibre. During maximal activation with Ca2+, plots of delta l vs. delta t were well fitted by a single straight line. Calculation of Vmax from the slopes of the fitted lines yielded a Vmax of 4.44 +/- 0.15 (S.E. of mean) muscle lengths per second (m.l./s). However, at lower levels of Ca2+ activation, plots of delta l vs. delta t were biphasic, containing an initial phase of steady high-velocity shortening and a subsequent phase of steady low-velocity shortening. The transition between these two phases occurred following active shortening equivalent to 60-80 nm/half-sarcomere. Vmax during the high-velocity phase was relatively insensitive to Ca2+ concentration between pCas (i.e. -log [Ca2+]) of 4.5 and 6.0; however, Vmax fell to 3.58 +/- 0.40 m.l./s at pCa 6.1 and further to 1.02 +/- 0.30 m.l./s at pCa 6.2. Vmax during the low-velocity phase decreased as Ca2+ was lowered within the entire range of pCas studied to a minimum value of 0.35 +/- 0.09 m.l./s at pCa 6.2. The degree of thin-filament activation at a particular pCa was varied by partial extraction of troponin-C, which resulted in a permanent though reversible inactivation of parts of the thin filaments. Partial extraction of troponin-C altered the plots of delta l vs. delta t obtained at pCa 4.5 to a biphasic form. In addition, Vmax during the high- and low-velocity phases of shortening was reduced at each pCa greater than 4.5. Vmax values obtained in control fibres at low Ca2+ concentrations and extracted fibres were in good agreement when generated isometric tensions were equivalent. This was the case for both the high- and low-velocity phases of shortening. Fibres were also activated in the absence of Ca2+ by partial removal of total troponin complexes. These fibres developed steady tensions less than 30% of maximum and underwent biphasic shortening, indicating that this phenomenon cannot be the result of shortening-induced dissociation of Ca2+ from troponin-C.(ABSTRACT TRUNCATED AT 400 WORDS)

Actin Cytoskeleton↗
PubMed1986

Mechanical and histochemical characterization of skeletal muscles from senescent rats.

Maximal shortening velocity (Vmax) and isometric tension (Po) were measured in living fiber bundles and skinned fibers from extensor digitorum longus (EDL) and soleus (SOL) muscles of young adult (9 mo) and senescent (30 mo) Fisher 344 rats. The fiber type composition of each muscle preparation was determined using myosin (M)-ATPase histochemistry. Vmax, determined by the slack test method, was unchanged in the EDL but was increased in the SOL muscles of young adult vs. senescent rats. Velocities determined at intermediate loads using the load-stepping technique were slower for EDL bundles but were nearly identical for SOL bundles from senescent vs. young adult rats. Po was greater in SOL and was unchanged in EDL bundles and skinned fibers from senescent vs. young adult rats. M-ATPase histochemistry and Vmax were in agreement for fast and slow muscle bundles and fibers. The relationship between tension and pCa (i.e.,--log[Ca2+]) in skinned fibers from each muscle was similar in both age groups. Sodium dodecyl sulfate-polyacrylamide gels of the skinned fibers consistently showed fast light chains (LCs) in the EDL fibers and slow LCs in the SOL fibers, with no apparent age-related differences.

Adenosine Triphosphatases↗
PubMed1986

Suppression of receptive and proceptive behavior in ovariectomized, estrogen-progesterone-primed rats by intraventricular beta-endorphin: studies of behavioral specificity.

Intraventricular (i.c.v.) administration of beta-endorphin (beta-END) has been shown to suppress lordosis behavior in ovariectomized (OVX) estrogen-progesterone (EP) primed rats, but the behavioral specificity of this effect is not known. Using OVX EP-primed rats, the present study assessed the effect of i.c.v. beta-END on proceptive behavior as well as on lordosis (receptive) behavior, and attempted to discern whether the sexual effects were secondary to generalized nonspecific behavioral effects. Doses of 0.5-4 micrograms beta-END (human) significantly suppressed lordosis behavior. Doses of 1 and 4 micrograms were used in experiments which measured proceptive behaviors (presentations and ear wiggling), and both doses abolished or nearly abolished the display of these behaviors. Administration of inactive peptide (a protein digest) had no effect on sexual behavior. Neither 1 nor 4 micrograms beta-END elicited measurable catalepsy. In a series of tests for responsiveness to general somatosensory stimuli, 1 microgram had no effect on responsiveness while 4 micrograms had minor effects, even though sexual activity was severely diminished after both doses. Blood pressure was unaltered by infusion of beta-END (1 microgram), although there was a significant reduction in heart rate. When open field behavior was tested in conjunction with sexual behavior, ambulation and rearing were significantly decreased after beta-END treatment as compared with saline treatment. However, simple linear correlation tests showed a lack of correlation between the changes in open field behavior and the changes in sexual behavior, indicating that the effects of beta-END on the two types of behavior may be unrelated.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Direct, neuronal action of atrial natriuretic factor in the rat brain.

The present investigation assessed the ability of atrial natriuretic factor (ANF) to affect hypothalamic neuronal excitability. Single neurons in the rostral septal-preoptic area of the female rat brain were recorded extracellularly and tested for responsiveness to iontophoretically applied and/or pressure-ejected ANF. Neurons responsive to ANF were detected in the lateral septal nucleus, the lateral paraolfactory area, the bed nucleus of the anterior commissure, and the medial preoptic area. The majority of neurons influenced by ANF (16 out of 18) exhibited a decrease in spontaneous firing rate during application of the peptide. In some cases, the inhibitory response outlasted the period of ANF application. When both iontophoretic and pressure ejection techniques were used to apply ANF to an individual neuron, the responses were similar. The results indicate that ANF is capable of modulating the membrane excitability of rat forebrain neurons and suggest that the peptide acts as a neuromodulator/neurotransmitter within the central nervous system.

Action Potentials↗
PubMed1985

Shortening velocity and myosin heavy chains of developing rabbit muscle fibers.

The regulation of vertebrate muscle contraction with respect to the role of the different subunits of myosin remains somewhat uncertain. One approach to gaining a better understanding of the molecular basis of contraction is to study developing muscle which undergoes changes in myosin isozyme composition and contractile properties during the normal course of maturation. The present study utilizes single fibers from psoas muscles of rabbits at several ages as a model system for fast-twitch muscle development. This approach eliminates the inherent problems of interpreting results from studies on whole muscles which usually contain heterogeneous fiber types with respect to contractile properties and isoenzyme composition. Maximum velocity of shortening and tension-generating ability of individual fibers were measured and the myosin heavy chain composition of the same fibers was examined using an ultrasensitive sodium dodecyl sulfate-polyacrylamide gel system. The results indicate that 1) with regard to contractile properties, there is a transitional period from slow to fast shortening velocities within the first postnatal month; 2) a strong, positive correlation exists between the speed of shortening and tension-generating ability of individual postnatal day 7 fibers, suggesting that as more myosin is incorporated in these developing fibers it is of the fast type; and 3) there is a wide variation in maximum velocity of shortening among postnatal day 7 psoas fibers which is also a time when a mixture of heavy chain isoforms characterizes the myosin composition of single muscle fibers.

Aging↗
PubMed1985

Hyperprolactinemia: its electrophysiologic and pharmacologic effect on neurons of the ventromedial nucleus of the hypothalamus.

Extracellular action potentials were recorded from 691 neurons in the ventromedial hypothalamus (VMH) of urethane anesthetized female rats under acute and chronic sham-operated and hyperprolactinemic conditions. Hyperprolactinemia was produced by transplanting pituitaries under the kidney capsules. Neuronal excitability was recorded and analyzed during spontaneous, baseline activity and following the iontophoretic application of prolactin, dopamine (DA) and luteinizing hormone-releasing hormone (LH-RH). No statistically significant changes were observed in the spontaneous electrical activity of VMH neurons under the conditions tested. Of the responsive neurons, approximately 90% of the neurons recorded and tested with prolactin displayed an increase in firing activity while DA produced a decrease, independent of the endogenous plasma prolactin levels (basal or elevated). However, the response to LH-RH was modified in the chronic hyperprolactinemic animal. The predominant response of VMH neurons to LH-RH in acute sham-operated and hyperprolactinemic as well as in chronic sham-operated animals was one of inhibition, while in the chronic hyperprolactinemic animal, the application of LH-RH initiated excitation rather than inhibition. These results provide evidence that chronic (long-term) exposure to elevated prolactin levels is a sufficient stimulus to modify the neuronal response pattern of VMH nerve cells to iontophoretically applied LH-RH but not to prolactin nor to DA.

Action Potentials↗
PubMed1985

Shortening velocity in single fibers from adult rabbit soleus muscles is correlated with myosin heavy chain composition.

Extensive variations exist in the heavy and light chain components of myosin in vertebrate striated muscles. In the present study, we have characterized a specific contractile property, velocity of shortening, and protein subunit composition of single fibers from adult rabbit soleus muscles. Maximum velocity of shortening (Vmax) was measured using the slack test method, and the myosin composition of these same fibers was determined using an ultrasensitive sodium dodecyl sulfate-polyacrylamide gel electrophoresis system. While most fibers were found to have velocities between 0.5 and 1.0 muscle length/s, several had velocities distributed between 1.33 and 2.99 muscle length/s. The fibers in the slower group had myosin subunits that were solely of the slow type; however, those in the faster group contained both fast and slow heavy chains and light chains. The velocity of shortening measured in fibers having both myosin types was highly correlated with the myosin heavy chain composition, with velocity increasing as the proportion of fast-type heavy chain increased. Variations in light chain composition, particularly fast and slow myosin light chain 1, appeared to occur independently of the variations in heavy chain composition, suggesting that some myosin molecules consist of mixtures of slow- and fast-type subunits.

Animals↗
PubMed1985

Myosin-ATPase fibre typing of chemically skinned muscle fibres.

The efficacy of myosin (M)-ATPase fibre typing to differentiate fibre types in chemically (EGTA) skinned muscle fibres was investigated. Cryosections or single fibres from isolated bundles of chemically skinned rat extensor digitorum longus (EDL) and soleus (SOL) muscles were stained for M-ATPase activity. The results indicate that two major fibre types (type I and II, Brooke & Kaiser, 1970) can be identified, as well as subgrouping of the type II fibres into types IIa and IIb. Thus, chemically skinning muscle fibres appears to have no detrimental effects on subsequent M-ATPase fibre typing.

Adenosine Triphosphatases↗
PubMed1985

LHRH and mating behavior: sexual receptivity versus sexual preference.

Sexual behavior and sexual preference measurements were obtained from ovariectomized female rats treated with estrogen, estrogen and progesterone, or estrogen followed by third ventricular infusion of luteinizing hormone releasing hormone (LHRH) or saline. The lordosis-to-mount ratio and the occurrence of receptive and proceptive behaviors were scored to assess total sexual receptivity. Sexual preference was determined by placing the test female in the center of a four-winged choice box apparatus in which each of the outer wings contained one of the following incentive animals: a sexually active male (SM), a castrate male (CM), a female in proestrus (PF), and an ovariectomized female (OF). Time spent in close proximity to the incentive animals was measured as an index of sexual preference. Estrogen and progesterone treatment resulted in high sexual receptivity and a marked preference for SM. Estrogen alone or in combination with saline also produced a significant preference for SM. Animals treated with estrogen and LHRH exhibited high levels of sexual receptivity compared to estrogen saline treated controls, but no enhancement of preference for SM was detected. The results indicate that fractionation of sexual receptivity and sexual motivation occurs following estrogen-LHRH treatment.

Animals↗
PubMed1985

The effects of partial extraction of TnC upon the tension-pCa relationship in rabbit skinned skeletal muscle fibers.

The activation of contraction in vertebrate skeletal muscle involves the binding of Ca2+ to low-affinity binding sites on the troponin C (TnC) subunit of the regulatory protein troponin. The present study is an investigation of possible cooperative interactions between adjacent functional groups, composed of seven actin monomers, one tropomyosin, and one troponin, along the same thin filament. Single skinned fibers were obtained from rabbit psoas muscles and were then placed in an experimental chamber containing relaxing solution maintained at 15 degrees C. Isometric tension was measured in solutions containing maximally and submaximally activating levels of free Ca2+ (a) in control fiber segments, (b) in the same segments after partial extraction of TnC, and finally (c) after recombination of TnC into the segments. The extraction was done at 11-13 degrees C in 20 mM Tris, 5 mM EDTA, pH 7.85 or 8.3, a procedure derived from that of Cox et al. (1981. Biochem. J. 195:205). Extraction of TnC was quantitated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the control and experimental samples. Partial extraction of TnC resulted in reductions in tension during maximal Ca activation and in a shift of the relative tension-pCa (i.e., -log[Ca2+]) relationship to lower pCa's. The readdition of TnC to the extracted fiber segments resulted in a recovery of tension to near-control levels and in the return of the tension-pCa relation to its original position. On the basis of these findings, we conclude that the sensitivity to Ca2+ of a functional group within the thin filament may vary depending upon the state of activation of immediately adjacent groups.

Animals↗