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Biomedical subjects

R L Moss

Publications and source records attributed to R L Moss.

At least 253 records · Page 14Linked to original sources
PubMed1977

Elastic and viscous properties of resting frog skeletal muscle.

The mechanical properties of the resting, whole semitendinosus muscle of the frog have been characterized as functions of both muscle length and temperature. Measurements were made of pseudorandom white noise (PRWN) displacements (less than 10 A/half-sarcomere) applied to the muscle and the force responses to these movements. Signal correlation techniques were then used to obtain the dynamic modulus function for the muscle in the frequency range 2.44-320 Hz. This function was represented by a series combination of a Voigt element and a time delay element for tension propagation along the muscle. A dynamic elastic modulus (E), coefficient of damping (B), and tension transmission velocity (V) were measured for resting muscle on the basis of this model. For each of these parameters, a marked variation with sarcomere length (s) was found. The mean values for E and B at LO (s=2.25 mum) were 1.84+/-0.24 X 10(5) N/m2 and 2.33+/-0.25 X 10(2) Ns/m2, respectively. Further, B demonstrated a negative temperature dependence, Q10=0.78 (P less than 0.05), in the range s=2.6-3.0 mum, while E was not significantly temperature dependent. The length-dependent variations of E and B are interpreted as deriving from both passive muscle elements and attached crossbridges. Velocity was calculated at a single displacing frequency for every experiment; the mean value at LO and all temperatures was v=11.7+/-0.6 m/s. Velocity was also calculated as a function of frequency within several experiments: the results indicate considerable variation of v with frequency.

Animals↗
PubMed1977

Coitus-induced release of luteinizing hormone in the proestrous rat: fantasy or fact?

The influences of mating on serum luteinizing hormone (LH) and follicle stimulating hormone (FSH) levels were evaluated in 4-day cyclic proestrous rats of the Wistar strain. Blood samples were collected via guillotine from mated and unmated controls at 1900-2000 h or 2100--2200 h. Serum LH levels were determined by two independent radioimmunoassays. There were no significant differences in LH measurement between assays. At 1900--2000 h, LH levels were high, but not significantly different, in both the mated and unmated control animals. By 2100-2200 h, serum LH concentration had dropped in unmated controls but was significantly elevated in mated animals. There was no significant elevation in FSH either 1900-2000 h or 2100--2200 h on the evening of proestrus. The data indicate that when LH levels are normally high, coitus cannot further potentiate LH release. However, when LH levels are declining, coitus is an effective and adequate stimulus to initiate elevations in serum LH.

Animals↗
PubMed1976

Elastic modulus and stress relationships in stretched and shortened frog sartorii.

The longitudinal dynamic elastic modulus (delta stress/delta strain) of 11 sartorius muscles (Rana pipiens; 3 degrees C) was measured at static strains, 0.57 less than L/Lo less than 1.53. Pseudorandom white-noise displacements less than +/-0.031% Lo (mean, peak to peak) were imposed on tetanically stimulated and resting muscles to obtain the isometric moduli. The active elastic modulus at each length was determined as the difference between the low-frequency (15-80 Hz) asymptotes of the tetanic and resting modulus functions. Resting moduli were found to increase with stretch at a declining rate, suggesting that some resting elasticity is attributable to active crossbridges. For isometric, tetanically stimulated muscles above L/Lo = 1.0, the ratio dynamic elastic modulus/active stress was nearly constant (65.4); the data predict zero modulus at a stretched length corresponding to zero active stress. Hence, the modulus per crossbridge exhibits sarcomere length invariance. On the other hand, active muscles below L/Lo = 0.77 manifest a significant (P less than or equal to 0.05) additional modulus beyond that found at the same active stress in the stretched muscle. Sarcomeric structural rearrangements are suggested as a possible source of this additional modulus.

Animals↗
PubMed1976

Potentiation of lordosis behavior by intrahypothalamic infusion of synthetic luteinizing hormone-releasing hormone.

Saline and luteinizing hormone-releasing hormone (LRH) were infused into the medial preoptic area (MPOA), arcuate nucleus (ARC), lateral hypothalamic area (LHA) and the cerebral cortex (CC), and the effects on sexual behavior were studied in estrone- (E-) primed ovariectomized (OVX) female rats. Each cannulated, OVX female known to be sexually active was primed with E in doses too low to initiate consistent mating behavior. LRH infusion in either the MPOA or ARC faciliated sexual behavior as measured by the lordosis-to-mount (L/M) ratio; LRH infusion in the LHA or CC, as well as saline infusion in all neural sites, was ineffective in initiating comparable behavior patterns. The results concur with findings utilizing systemic LRH injections and support the notion that LRH may act directly on neural tissue to potentiate lordosis behavior in the female rat.

Animals↗
PubMed1975

Tuberoinfundibular neurons: dopaminergic and norepinephrinergic sensitivity.

The techniques of microelectrophoresis and antidromic identification have been utilized in the female rat anesthetized with urethane to localize the tuberoinfundibular neurons and to determine their pharmacological sensitivity to dopamine (DA), norepinephrine (NE) and glutamate (GLUT). Extracellular recordings were made of 149 single units in the arcuate (ARC) nucleus; 79 of which were antidromically identified (43 were spontaneously active and 36 were silent) and the remaining 70 cells were determined to be spontaneously active but could not be antidromically identified (unidentified ARC neurons). The mean latency of the antidromically activated potentials was 9,5 msec, which gave a conduction velocity of 0.05 mm/msec. The spontaneous firing rate of antidromically identified ARC neurons varied from less than 1/sec to 8/sec while unidentified cells discharged at rates from less than 3/sec to 10/sec. These data indicate that ARC neurons exist which are capable of conducting impulses and send their axons into the external layer of the ME. Successful drug applications were made on 104 ARC neurons; of the 43 antidromically identified units, 37 were spontaneously active and 6 were silent. There were 61 spontaneously active, unidentified neurons. Two distinct pools of antidromically identified ARC neurons were found based on their sensitivity to NE and DA. Neurons displaying excitation to NE(N = 23) were either inhibited (N = 10) or non-responsive (N = 13) to DA applied electrophoretically; no NE-sensitive ARC neurons were excited by DA. The second pool of neurons (N = 14) was excited by DA. These neurons when tested with NE were either reproducibly inhibited (N = 3) or nonresponsive (N = 11); no DA-sensitive neurons were excited by NE. In the unidentified ARC neurons, iontophoretically applied NE and DA gave reproducible effects on individual neurons, so that some neurons were excited by both NE and DA, some were inhibited by both, and still others were excited by one and inhibited by the other chemical. Glutamate (GLUT) had a powerful excitant action on nearly all the neurons tested, increasing the electrical activity of the spontaneously active neurons as well as initiating activity in quiescent ARC neurons. These data are suggestive of a tuberoinfundibular neuronal system whose activity is modulated by either DA or NE. This evidence is certainly compatible with a functional role for both DA and NE in regulating pituitary function by altering the activity of presumed neurosecretory neurons which release hypophysiotropic hormones.

Action Potentials↗
PubMed1975

Action of luteinizing hormone-releasing factor (lrf) in the initiation of lordosis behavior in the estrone-primed ovariectomized female rat.

In order to evaluate the precise role of luteinizing hormone-releasing factor (LRF) in mediating the onset of sexual behavior, the specificity, time-course, and dose-response relationship of LRF-facilitated lordosis behavior were determined. Ovariectomized female rats, pretreated with estrone and LRF, displayed a pattern of lordosis behavior which differed little from that produced by estrone-progesterone. Little if any lordosis behavior was observed in response to LRF alone, estrone alone, or estrone in combination with luteinizing hormone (LH), follicle-stimulating hormone (FSH), or thyrotropin-releasing factor (TRF). Furthermore, LRF-induced lordosis behavior occurred in the absence of the adrenals, thus eliminating adrenal progesterone as a factor in facilitating the appearnce of lordosis behavior. The LRF-facilitated lordosis behavior was seen 2 h after the injection of LRF and was maintained for a total of 8 h. A minimal dose of 150 ng LRF was required to initiate the first consistent appearance of lordosis behavior; the maximum response was obtained with 500 ng. It is thus suggested that LRF is not only responsible for the ovulatory discharge of LH and subsequent ovulation, but may also play a role in the initiation of the onset of mating behavior in the female rat.

Adrenal Glands↗