DEVELOPMENTAL PATTERNS OF HISTAMINE-LIKE IMMUNOREACTIVITY IN THE MOUSE

We studied the appearance and distribution of histamine (HA) during mo use embryogenesis, neonatal period, and adulthood using a specific rab bit HA antiserum and indirect immunofluorescence. HA first appeared on the Embryonic Day 13 (E13) in scattered mast cells in the gastrointes tinal (GI) muscularis externa and liver, The splenic primordium contai ned a dense population of intensely HA-immunoreactive (HA-ir) cells fr om E13 on, From E15 to the birth, HA was detected in many embryonic ce ll types. On E15, the first HA-ir epithelial endocrine cells appeared in the oxyntic mucosa, In addition to the HA-ir cells in GI tract and liver, some nerve cells in ganglia of the peripheral nervous system (P NS), some fibers in spinal and cranial nerves, nerve fibers in mesente rium, and nerve plexuses of the gastrointestinal muscularis externa we re HA-ir from E15 on. Occasional HA-ir nerve fibers were detected with in the glandular epithelium of the oxyntic mucosa, pancreas, and saliv ary glands during late embryogenesis. During the same period, bright f luorescence was observed in cells of the kidney convoluted tubules and pancreatic islet cells. From E14 on, mast cells exhibiting bright flu orescence were scattered throughout the connective tissue of the fetus , and their number increased rapidly with age. Their density was espec ially high in subcutaneous connective tissue, Embryonic epidermal ails showed faint HA immunoreactivity. In musculoskeletal tissues, develop ing bone and occasional striated muscle cells exhibited HA immunoreact ivity. Interestingly, most cells in liver showed transiently weak HA i mmunoreactivity during embryogenesis. In adult mouse, HA was stored on ly by scattered mast cells, oxyntic epithelial cells, and neurons in t he tuberomamillary nucleus of the brain, The other HA-containing embry onic cells were negative for HA in adult mouse, In conclusion, HA immu noreactivity is widely distributed in epithelial, neuronal, and mast c ells in various organs during mouse embryogenesis.