DISTRIBUTION AND ORIGIN OF PEPTIDE-CONTAINING NERVE-FIBERS IN THE RATAND HUMAN MAMMARY-GLAND

The structures in the mammary gland involved in milk ejection have bee n investigated with regard to their relation to different types of pep tidergic nerve fibres and their origin. Lactating rats were studied wi th immunohistochemistry focusing on the nipple, the parenchyma, the ma mmary blood vessels and the mammary nerve. The human mammary gland was also analysed. In the mammary gland from rat and human, nerve endings in the subepidermis, around smooth muscle cells in the nipple, in the connective tissue surrounding lactiferous ducts and alveoli in the ni pple and in the parenchyma of the mammary gland showed immunoreactivit y for calcitonin gene-related peptide, substance P, vasoactive intesti nal polypeptide, peptide histidine isoleucine, neuropeptide Y, galanin and tyrosine hydroxylase, whereas dynorphin-positive nerve fibres cou ld not be detected. The mammary nerve contained calcitonin gene-relate d peptide, vasoactive intestinal polypeptide, neuropeptide Y and tyros ine hydroxylase immunoreactivities; the adventitia of the mammary arte ry contained nerve fibres immunoreactive for neuropeptide Y and tyrosi ne hydroxylase, while vasoactive intestinal polypeptide-, peptide hist idine isoleucine-, calcitonin gene-related peptide- and substance P-po sitive fibres were found in the tissue surrounding the artery. The wal l of the mammary vein had nerve terminals immunoreactive or neuropepti de Y, tyrosine hydroxylase, calcitonin gene-related peptide and substa nce P. With the help of retrograde tracing using wheat germ agglutinin in combination with immunohistochemistry, projections of calcitonin g ene-related peptide-immunoreactive cells in the dorsal root ganglia to the nipple were established. Neurons in the sympathetic stellate gang lion containing neuropeptide Y and tyrosine hydroxylase also projected to the mammary gland. Moreover retrogradely-labelled cells were found in the nodose ganglion, and they were vasoactive intestinal polypepti de-immunoreactive. These results demonstrate a rich distribution of di fferent types of nerve fibres in structures of the mammary gland relat ed to milk ejection. These nerve fibres and. their peptides may be inv olved in the local control of milk ejection.