Immunohistochemical studies on the development of tyrosine hydroxylase- and serotonin-immunoreactive neurons in fetal dorsal raphe tissue transplanted into the anterior eye chamber of adult rats.

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Abstract
Pieces of tissue containing dorsal raphe nuclei of fetal rat brains were transplanted into the anterior eye chambers of adult rats. The differences between the developmental patterns of catecholaminergic and serotonergic neurons.sbd.especially the extension of their axonal processes.sbd.in the grafts were immunohistochemically examined using tyrosine hydroxylase (TH) and serotonin antisera. At an early stage after transplantation (3 days), TH-positive neurons appeared in grafts that had and had not been pretreated with a monoamine oxidase inhibitor (MAOI, Nialamide), while serotonin-positive neurons were demonstrated only in the grafts that had undergone MAOI pretreatment. Morphological differences in the growth pattern in the experimental milieu between the TH and serotonin neurons were also demonstrated: at this early stage, the somata of the TH neurons were multipolar and stellate shaped and possessed several distinct processes, while the serotonin neurons were ovoid shaped and lacked such processes. One week to 1 month after transplantation, the number of TH-positive fibers gradually increased, but their distribution was restricted to the area surrounding the cell bodies of the TH neurons in the graft. However, the processes of the serotonin neurons formed a dense plexus in the graft, and a small number of these fibers extended into the host iris 1 week after transplantation. By one month after the operation, the density of the serotonin fibers had gradually increased throughout the graft, and protruding serotonin fibers formed a network of varicose fibers in the host uveal tissue. The present results suggest that the regrowth pattern of the dopaminergic and serotonergic neurons in the grafts of the raphe nuclei show characteristic structural differences at various stages after transplantation.

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