Extravascular circulation in the pituitary of Mugil cephalus (Teleostei)

Summary Extravascular circulation in the pituitary of Mugil cephalus was investigated by injecting live fish with horseradish peroxidase and studying the distribution of the enzyme in the gland. The principal components of the extravascular circulatory system are the pericapillary spaces, and, arising from them, the interlobular and circumhypophyseal spaces. Extensions of these spaces penetrate the glandular parenchyma of the pars distalis, where they merge with pericellular spaces. In the neurohypophysis, pericapillary spaces are connected to the periaxonal spaces.Capillaries penetrating from the proximal neurohypophysis into the pars distalis are accompanied by neurosecretory axons. These axons form a mass of tissue which is limited near the capillaries by the pericapillary spaces and near the adenohypophysis by the interlobular spaces. Toward the interior of the adenohypophysis the amount of nervous tissue accompanying the capillaries progressively diminishes, thus reducing the distance between pericapillary and interlobular spaces. Within the pars distalis, the neurosecretory axons accompanying the capillaries are sparse, and the secretory and stellate cells are mostly located directly adjacent to the pericapillary spaces. In the neuro-intermediate lobe, interlobular spaces outline the neuro-adenohypophyseal boundary.The relationship between extravascular spaces and hormone-secreting cells varies in the different regions of the adenohypophysis depending upon the type of neurosecretory innervation in the respective region. In the regions of prolactin and gonadotropin cells, where neurosecretory axons are in direct contact with the secretory cells, the hormone-secreting and stellate cells are adjacent to the pericapillary spaces. In the regions of ACTH and STH cells, secretory and stellate cells are found adjacent to the interlobular spaces, which are interposed between the cells and the neurosecretory axons.Abbreviations AH adenohypophysis - CH circumhypophyseal - DNH distal neurohypophysis - HRP horseradish peroxidase - NH neurohypophysis - NS neurosecretory - PD pars distalis - PI pars intermedia - PPD proximal pars distalis - RNH rostral neurohypophysis - RPD rostral pars distalis This research was supported by a grant from the National Council for Research and Development, Israel, and the GKSS Geesthacht-Tesperhude, Federal Republic of Germany     

Development of muscarinic cholinergic receptor binding in the visual system of monocularly deprived and dark reared rats

In 25 day old rats monocularly deprived by unilateral eyelid suture on postnatal day 10 (MD), [³H]quinuclidinyl benzylate (³H-QNB) binding was significantly reduced in the visual cortex (VC) of both sides, but elevated in both superior colliculi (SC). Muscarinic receptor binding in the frontal cortex (FC), a non-visual brain area, in the lateral geniculate nucleus (LGN), and in the retina was not affected. In 25 day old rats raised in complete darkness from birth (DR) similar changes in³H-QNB binding were found in VC and SC. However, binding levels were also decreased in the FC and significantly increased in the retina. In adult (6 month old) MD and DR rats the differences in³H-QNB binding as compared to age-matched controls had disappeared completely in all visual brain areas studied. Detailed Scatchard analyses indicate that the alterations in the³H-QNB binding were due to changes in receptor number only.This paper is dedicated to Dr. Derek Richter on his seventy-fifth birthday.     

Fine structure of the coelomic epithelium of Sagitta elegans (Chaetognatha)

Summary The coelomic space in the trunk of the arrow worm Sagitta elegans is lined by a thin epithelium, which may be termed coelomic epithelium. The visceral part of this epithelium is composed of flat cells characterized by thin and thick myofilaments, which constitute the circular musculature of the gut. In addition mitochondria, rough ER, and smooth walled cisterns, as well as vesicular and granular inclusions occur; the apical and basal plasma membranes exhibit no particular specializations. The parietal epithelium is exceedingly thin and covers the muscle cells of the body wall. In the lateral fields columnar ciliated cells are to be found which are rich in rough ER cisterns and which apparently are also coelomic epithelial cells.     

Transdifferentiation and regeneration in vitro

Striated muscle tissue and endoderm can be isolated from the anthomedusa Podocoryne carnea. The isolates are uncontaminated by other cell types and can be cultivated in artificial seawater for months without undergoing autonomous regeneration. However, if the endoderm is combined with collagenase-treated striated muscle, a regeneration process is initiated which leads to the formation of the sexual and feeding organ (manubrium) of the medusa. The original endoderm and striated muscle are replaced in the regenerate by at least seven new cell types, including gametes. Labeling experiments with [³H]thymidine and experiments in which mitosis is inhibited in either the striated muscle or the endoderm with mitomycin C demonstrate that the striated muscle is able to transdifferentiate into all the cell types found in the regenerate. With the possible exception of ectodermal smooth muscle this statement is also valid for the endoderm.