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Corticotropin releasing factor (CRF)-containing afferents to the rat lateral septum (LS) have been determined by means of cobalt-enhanced immunohistochemistry, tracing of retrograde transport of horseradish peroxidase (HRP), and by lesioning experiments. When unilateral lesions included the rostral part of the hypothalamus, CRF-like immunoreactive (CRFI) ipsilateral fibers in the LS decreased in number. Lesions in other brain regions did not cause alterations in the septal CRFI fibers. These findings suggest that the septal CRFI fibers originate in the rostral part of the hypothalamus. Furthermore, combined HRP and immunohistochemical staining on the same sections demonstrated double-labeled cells in two discrete areas within the rostral hypothalamus: one was the perifornical hypothalamic area (PeF) at the level of the paraventricular hypothalamic nucleus, and the other was the most caudal part of the anterior hypothalamic nucleus (AHc). These findings show that a large proportion of the CRFI projections to the LS have their origins in the PeF and AHc.

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The subpopulations of lymphocytes and non-lymphoid cells in high endothelial venules (HEV) and in lymphatic capillaries surrounding lymphoid follicles in bronchus-associated lymphoid tissue (BALT) were examined by electron microscopy after preembedding the tissue and staining with an immunoperoxidase technique. The results were compared with those obtained in gut-associated lymphoid tissue (GALT) reported previously. Monoclonal mouse-anti-rat T cell, IgG, IgM, IgA, and Ia antisera were used. Plasma cells that were reactive to anti-IgG, anti-IgM, and anti-IgA were detected as cells in which the 3',3'-diaminobenzidine tetrahydroxychloride reaction product was localized in rough endoplasmic reticulum and perinuclear spaces but not on plasma membranes. These plasma cells did not occur in either lymphatic capillaries or HEV in BALT as they did in GALT. Cells with surface Ig (sIg cells), T-cell antigen (T cells), and Ia antigen (Ia cells) were present in BALT. T cells were located predominantly in the follicular area opposite the bronchial epithelium; IgM- and IgG-reactive cells were found in the follicular area adjacent to the bronchial epithelium; and IgA-positive cells were found in the lateral part of the area where the T cells were localized (T-cell area). Ia cells were abundant throughout BALT and in moderate numbers in the epithelium. A striking observation was the presence of "nurse-cell"-like structures in the periphery of BALT. The percentages of T, sIgG, sIgM, and sIgA cells in the HEV were 54.7%, 2.4%, 28.9%, and 27.3%, respectively, and in the lymphatic capillaries, 41.2%, 3.8%, 38.2%, and 21.2%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

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