REGIONAL DISTRIBUTION OF SUBSTANCE-P BINDING-SITES IN THE BRAIN-STEM OF THE HUMAN NEWBORN

The distribution of [H-3]substance P ([H-3]SP) binding sites in the br ainstem of the human newborn was investigated in eleven cases (aged 1 h to 6 months) by in vitro quantitative receptor autoradiography. The binding of [H-3]SP to newborn brainstem tissue was found to be saturab le (for the eight cases examined, K-d and B-max (M+/-S.E.M.) were 0.29 +/-0.03 nM and 206+/-21 fmol/mg tissue, respectively). Competition stu dies showed unlabeled SP to be the most potent peptide for displacing [3H]SP binding from tissue sections. The desaturating effect of GTP on the specific binding of [H-3]SP was also investigated, but was not fo und to be significant. Autoradiographic analysis showed that the neuro kinin-1 (NK-1)/SP binding sites were widely but unevenly distributed, and that they varied with age. The highest densities of (NK-1)/SP bind ing sites were observed in the locus coeruleus, olivaris inferior nucl ei, raphe magnus and obscurus nuclei, while low to moderate densities were observed in other brainstem structures. These findings support th e idea that SP is involved in cardiovascular regulation, and that it m ay interact with the catecholaminergic and/or serotonergic system.