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Two endocrine cell types, PbH + and PAS + cells, were recognized in the pars intermedia (PI) of the roach. Leuciscus rutilus, by light and electron microscopy. They can be distinguished by the appearance of their secretory granules. The PAS + cells stain with toluidine blue in semithin sections as opposed to the PbH + cells. After 5 days' treatment with metopirone the PhH + cells are highly activated whereas the PAS + cells show no response. The PbH + cells are assumed to produce MSH. In roaches adapted to diluted sea water (10 ‰) the transfer to fresh water for 1- -1 ½ hours or reset-pine injections for the same period had no notable effect on neither cell type. Three kinds of axons innervate the P1. Two of these, which have granules averaging 111 nm arid 151 nm in diameter. originate in the nucleus preopticus (NPO). The third type of axons has granules of an average Size of 74 nm and is probably aminergic. The glia cells in this part of the neurohypophysis (NH) are granular pituicytes, which are innervated by all three axon types. The border between the NH and the PT is composed of a double basement membrane from which a network extends into the NH. This network, the basement membrane and the capillaries are the main sites for the terminations of the axons although nerve fibers also invade the endocrine tissue. Only axon type 3 was observed to synapse frequently with the PbH + cells. [ABSTRACT FROM AUTHOR]

Three different endocrine cell types were identified by electron microscopy in the rostral pars distalis (RPD) of the roach, Leuciscus rutilus. The cells which are characterized by the morphology and sizes of their secretory granules are assumed to secrete prolactin. ACTH and TSH Prolactin cells occur in two forms which could be separated on account of the sizes of their granules. Intra-peritoneal injections of reserpine had a strong arid persistent effect 24 hours after the treatment. The prolactin cells with small granules reacted with a marked release of secretion. The border of the RPD is composed of a so-called double basement membrane in contact with the perivascular spaces and forms extensive ramifications into the rostral neurohypophysis (RNH). Nerve fibers of different categories terminate at the border and its network in the RNH. Substances released from these terminals may influence the endocrine cells of the RPD. The ACTII cells and the Prolactin cells are innervated by axons with granules less than 100 nm. The nomenclature of type `A' fibers and `B' fibers is discussed because it was difficult to make a reliable discrimination of the fibers and their nature by the sizes of their granules. However, four types of nerve fibers were distinguished in connection with the RPD although the presence of more types was indicated, in all four types the size variations of the granules are great and overlapping. The average sizes of the granules in these fibers are 157, 114, 119 and 81 nm. The origin of the nerve fibers innervating the RPD is discussed. All morphological data indicate a complex hypothalamic control of the RPD of the roach. [ABSTRACT FROM AUTHOR]