SUMMARY1. The relationship between active force and velocity of shortening was studied during tetanic contraction of isolated semitendinosus muscle fibres of the frog (0.5-2.0o C). Measurements were carried out with the fibre immersed in isotonic (1 OOR) Ringer solution and in solutions that were made hypotonic by reduction of NaCl (osmolality 0-62 and 0 81 of normal Ringer) and hypertonic by addition of sucrose (osmolality 1 22 and 1-44 of normal Ringer).2. The force-velocity relation was hyperbolic at loads lower than 80 % of measured isometric force (PO) but exhibited a reversed curvature between 0-8P0 and PO. The maximum velocity of shortening was determined in two different ways: (i) by extrapolation to zero load from forcevelocity data truncated at 0-8P0 (computer fitting of hyperbola, leastsquares method) and (ii) by recording the time required to take up the slack of the fibre after a quick release during tetanus. 3. Isometric force and maximum speed of shortening both changed inversely with the tonicity of the extracellular medium. Immersion of the fibre in 0-81R hypotonic solution caused active tension and shortening velocity to increase by 10± 1 % (mean + S.E. ofmean, n = 14) and 12 + 1 %, respectively. Conversely, force and shortening velocity decreased by 12+1 % (n = 13) and 22+2 % when normal Ringer was replaced by 1-22R hypertonic solution. These changes doubled when the tonicity was altered from normal Ringer to 0-62R and 1-44R, respectively.4. Changes in fibre cross-sectional area equivalent to those obtained in the 0-81R and 1.22R solutions (+11 % and -13%, respectively) were produced by varying the sarcomere length within the range 2-0-2-5 Asm in the normal Ringer solution. Maximum
The response of 835 click-sensitive neurons in the inferior colliculus (IC) to ramp frequency modulated (FM) tones was studied in the anaesthetized rat. More than 70% of the cells were sensitive to the FM sound, and over 25% were "FM specialized". Systematic variations of the stimulus parameters showed that sweep velocity, sweep range, and intensity of the FM signal were the 3 basic determinants for the unit response. For an "FM specialized" cell, the response pattern to each of the parameters was either monotonic or bell-shaped. The population statistics of response patterns to the FM parameters, including the tuning factors, were generated. A stimulus domain was proposed to represent the "receptive space" of the FM cells.
A search in ancient Chinese medicinal literature and modern phytochemical reference indicates that the therapeutic value of Leonurus artemisia (I-mu ts'ao, the Chinese motherwort) might reside in a uterotonic principle present in leaves. Leonurine (4-guanidino-n-butyl syringate) was isolated from fresh and dry leaves of Leonurus artemisia. The uterotonic effect of leonurine was demonstrated in rat uterus in vitro. Results from this study suggest that functional phytochemistry based on ethnobotanical experience could lead to development of new and effective drugs from Chinese medicine.
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