The mucosal epithelium of the toad urinary bladder reabsorbs sodium, acidifies the urine, and is responsive to neurohypophyseal hormnones. Mucosal epithelial cells, consisting of two major morphologic cell types, "mitochondria-rich" and "granular," were removed from the bladder and separated by density gradient centrifugation. The mitochondria-rich cells contained three times as much carbonic anhydrase activity as the granular cells. Oxytocin caused a 235 percent increase in the adenosine 3',5'-monophosphate content of mitochondria-rich cells but had no effect on the granular cells. The evidence indicates that the mitochondria-rich cell, which accounts for only 15 percent of the mucosal cells, plays a major role in the mediation of sodium ion and hydrogen ion transport in the toad bladder and is a specific site of action of neurohypophyseal hormones.

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Embryonic neurons were cultured from transgenic Drosophila melanogaster expressing a highly specific pseudosubstrate inhibitor of protein kinase C (PKC). Flies homozygous for this transgene, which is under the control of the yeast UAS promoter, were crossed to flies homozygous for the yeast heat shock inducible transcription factor GAL 4. Following heat shock, the progeny express the pseudosubstrate inhibitor at high levels. This strategy, which has the advantage of avoiding the non-specific effects of drugs, was used to study the role of PKC in process growth of cultured, differentiating neuroblasts. An external gold particle labeling procedure using a cell surface antigen expressed by mature neurons and processes was used to visualize neuronal processes directly in the scanning electron microscope. We observed that cell cultures expressing a low concentration of the pseudosubstrate inhibitor showed a significant decrease in the number of type I and II processes as compared to control cultures, while the proportions of neuroblasts, ganglion mother cells (GMCs), and mature neurons in the clusters were little affected.

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A light and transmission electron microscopic study was performed on 67 ductus arteriosus (DA) specimens from rabbits (31 days normal gestation period) ranging in age from 21 days of gestation to 4 da.ys after birth. Some fetuses were permitted to breath before sampling, while others were not. The aorta and pulmonary trunk served as controls. The objectives of the study were t o identify the earliest cellular alterations leading t o closure of the DA, to study in detail the sequence of cellular changes in closure of the DA, and to correlate these observations with what is known about the physiological factors involved in closure of the DA. Changes in the architecture of the DA wall were seen as early as on the twenty-sixth day of gestation and involved the appearance of increased numbers of radially or longitudinally reoriented smooth muscle cells in the intima and fragmentation of the internal elastic lamina. The progress of these changes continued and intensified until the end of gestation.At that stage the inner one-half of the medial smooth muscle cells was reoriented, and the lumen was significantly reduced by a greatly expanded intima which often contained many intercellular "ghost bodies." Very few mitoses were seen during DA closure, especially during 29 to 31 days of gestation. It is concluded that cellular changes involved in closure of the DA of the rabbit fetus begin far in advance of birth and breathing. These cellular changes are highly analogous to those which occur in the early pathogenesis of arterial intimal fibromuscular lesions. Closure of the DA, therefore, seems to afford an excellent, natural model for study of key cellular events involved in the production of arterial fibromuscular lesions.Since the work of Kennedy and Clark ('41) most investigators have agreed that closure of the ductus arteriosus (DA) found in mammals is related in some way to the sudden increase in blood oxygen level which occurs when breathing first begins. Although some marked species differences have been noted in the rate a t which DA closure occurs (Heyman and Rudolph, '75; Sharpe et al., '75), it has been generally believed that closure does not even begin until after birth and initial breathing have occurred (Sciacca and Condorelli, '60; Hornblad, '69; Brocolli and Carinci, '73). Ductus arteriosus closure is thought to proceed initially by a combination of physiological contraction and anatomical obliteration of the lumen involving proliferation of cells in the DA wall. However, the details of the cellular mechanisms involved in the anatomical obliteration of the lumen are poorly understood.In fact, some more recent investigations have provided evidence that a reorganization of the cellular architecture of the rat DA wall associated with subsequent closure begins long in advance of birth and breathing (Mato and Aikawa, '68; Jones et al., '69). This information prompted the present study which was an attempt to identify through histological and ultrastructural examination the earliest cellular alteration...

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Transgenic Drosophila strains expressing an inhibitory peptide of Ca2+/calmodulin dependent protein kinase II (CaM kinase), or a constitutively activated CaM kinase, show altered neuronal process morphology compared to wild type in scanning electron microscopy (SEM) of cultured mature neurons from embryonic neuroblasts. We observed significantly enhanced process growth in cells with inhibited enzyme, and reduced process growth in cells with activated enzyme, suggesting that active CaM kinase is involved in the inhibition of neurite growth during development. The subcellular distribution of CaM kinase in wild type neuronal cultures was determined using a gold particle labeling procedure which allowed the mapping of the enzyme directly in the scanning electron microscope (SEM). Before neuronal contact there was little labeling of processes, but after connections had been made the processes were heavily labeled. Our results suggest that the major transport of CaM kinase to the terminals does not occur until after or during the formation of neuronal connections when a functional synapse might be formed. Taken together, these results suggest a target-dependent transport of the enzyme along processes and an inhibitory role for CaM kinase on neurite branching.