Oogenesis in the Apogamous Fern Pteris cretica

The events that characterize egg formation and maturation inPteris cretica were investigated using transmission electronmicroscopy and electron microscope microprobe analysis. Theydid not differ significantly from those described for sexuallyreproducing ferns. The significance of these findings is discussedin relation to current theories concerning phase change in ferns. Pteris cretica, fern, apogamy, agamospory, transmission electron microscopy, oogenesis     

The resting release of acetylcholine by a retinal neuron

The cholinergic amacrine cells of the rabbit retina secrete acetylcholine by two mechanisms. One is activated by stimulation of the retina by light or depolarization of the amacrine cells by K+ ions. It requires the presence of extracellular Ca2+. The second is independent of extracellular Ca2+ and is unaffected by large depolarizations of the cells. It bears some similarity to the acetylcholine 'leakage' described at the neuromuscular junction. Although the Ca2+-independent mechanism accounts for about two thirds of the total acetylcholine release in the dark, the amount of acetylcholine released in this way is small compared with the release of acetylcholine triggered by stimulation of the retina with light. Its biological significance is unclear.     

Reflex cardiovascular responses caused by stimulation of pulmonary C-fibers with capsaicin in dogs

The purpose of these studies was to determine quantitatively the reflex cardiovascular responses to stimulation of the pulmonary C-fibers in dogs. We used a preparation in which the airway, pulmonary artery, and the pulmonary veins to the left lung were cannulated in situ. Ventilation and perfusion of the right lung maintained the animal in relatively normal homeostasis. Capsaicin, a decylenic acid amide of vanillylamine that selectively stimulates nerve endings of unmyelinated fibers (C-fibers), was injected into the left pulmonary artery in 5-ml boluses. Maximal reflex responses were obtained with concentrations as low as 0.8-1.6 X micrograms-1 X kg-1. Heart rate, hindlimb resistance, and left ventricular contractility were lowered transiently (the maximal responses showing declines of 40, 13, and 15.2%, respectively). As a result of these changes, combined with vasodilation in other resistance vessels, cardiac output fell 28% and blood pressure fell 35%. Interrupting the afferent neural pathway by severing the ipsilateral cervical vagus nerve eliminated these responses, confirming the distribution of their reflex origin. Although the role of these reflexes in homeostasis has not been decided, the results of this study suggest that the lungs of dogs, if appropriately stimulated, potentially can exert a major inhibitory influence on the neural regulation of cardiovascular function.     

Changes in left ventricular geometry during spontaneous breathing

The purpose of these experiments was to determine the effects of a spontaneously generated inspiration on the size and shape of the left ventricle (LV) in anesthetized supine dogs. We implanted markers in the LV to establish three perpendicular axes and recorded the motion of these markers using biplane cinefluoroscopy at 60 Hz. The primary changes in LV size that accompanied inspiration occurred at end diastole (ED). The largest change in LVED dimension was a 2.46-mm narrowing of the septal-lateral wall dimension, but the apex-base dimension decreased also, by 0.74 mm. The anteroposterior dimension actually widened by 1.07 mm. The septal-lateral narrowing was caused by both a 1.0-mm narrowing of the distance between the septal marker and the apex-base axis, as well as by a 1.4-mm narrowing between the apex-base axis and the lateral wall marker. Narrowing of the septal portion seemed expected because of presumed enhanced right ventricular filling during inspiration. Narrowing of the lateral portion of the LV, while the anteroposterior dimension widened, was surprising because a change in LVEDV shape is implied. Assuming ventricular homogeneity, this change in LVED shape implies that the forces applied to the epicardial surface were not uniform. There must have been a retraction on the anterior and posterior surface that was not experienced by the lateral LV wall. The net effect of these dimensional changes of the LV at end diastole (estimated from the product of the three ED axes) was a 3.5-cm3 reduction in LVED volume.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of cyclic salt in a maritime environment

Summary A previous paper (Part I)⁴ has shown that when vegetation and land slope are favourable to the capture of aerosol, the salinity of rainfall provides no measure of rate of acquisition of cyclic salt by a given land area.This is confirmed by the high level of chloride in Fiji foliage.The chloride content of experimental rice plants was found to be much higher than could be accounted for by all the chlorides introduced into the growth medium.Rice plants in the field, affected by the punctures of leaf hoppers, were shown to have a higher level of leaf chloride than unaffected plants.Chloride absorbed through the leaves was distributed in the plant differently from chloride taken up by the roots.Measurements on stomata and specific leaf area suggest that the aerosol particles enter through the stomata rather than through the rest of the leaf surface.