Distribution of substance P-like immunoreactive fibres and terminals in the medulla oblongata of the human infant.

This study provides a detailed report of the distribution and density of substance P-like immunoreactive fibres and terminals within the human infant medulla. Seven brains with no signs of macroscopic alteration fixed usually within 24-48 h after death were used. Free floating transverse sections (50-60 microns) were then immunostained with a monoclonal antibody against substance P using the avidin-biotin-peroxidase technique. Morphologically three types of substance P-like immunoreactive fibres were observed: those with small varicosities of less than 1 micron, those with medium varicosities of 1-2 microns and those with large varicosities of 2-4 microns. Very dense substance P-like immunoreactivity was present within the spinal trigeminal nucleus, parts of the gracile and cuneate fasciculi and the paracommissural subnucleus of the solitary nucleus; dense substance P-like immunoreactivity was present within the dorsal nucleus of the vagus nerve, commissural, medial, dorsal, dorsolateral ventral and ventrolateral subnuclei of the solitary nuclear complex, parasolitary nucleus, raphe obscurus, inferior olivary complex (medial, dorsal, dorsomedial nuclei) and ventrolateral part of the dorsal reticular nucleus; moderate substance P-like immunoreactivity was present within the gelatinosus nucleus of the solitary tract, lateral reticular nucleus proper, intermediate reticular zone and parvocellular reticular nucleus; sparse substance P-like immunoreactivity was present within the hypoglossal nucleus, retroambigual nucleus and much of the reticular formation (dorsal, parvocellular, ventral gigantocellular, dorsal paragigantocellular nuclei): and very sparse substance P-like immunoreactivity was present within the nucleus ambiguus, medial vestibular nucleus and parts of the reticular formation (ventral, medial, gigantocellular, ventral gigantocellular, dorsal paragigantocellular nuclei). Substance P-like immunoreactivity was absent in the area postrema, intercalated nucleus, gracile and cuneate nuclei, in the epiolivary, subtrigeminal and parvocellular divisions of the lateral reticular nucleus, spinal vestibular nucleus, and in the solitary and pyramidal tracts. In several regions the substance P-like immunoreactive fibres formed distinct pericellular arrays around the somata and dendrites of neurons (hypoglossal nucleus, dorsal nucleus of the vagus nerve, retroambigual nucleus, intermediate reticular zone). The results indicate the high specificity of the localization of substance P in various structures of the brainstem and underline the presumed significance of this peptide in autonomic and sensorimotor functions of the brain.