Comparison of the distribution of oxytocin and vasopressin in the rat brain.

While immunohistochemistry has been used extensively to map both oxytocin (OT) and vasopressin (VP) pathways in the brain, little information is available concerning the quantitative distribution of these hormones--particularly oxytocin. We have isolated oxytocin from extrahypothalamic regions of the rat brain and shown it to behave identically with standard oxytocin in radioimmunoassay (RIA) and on high-performance liquid chromatography. Using sensitive RIA we have measured and compared levels of both oxytocin and vasopressin in the rat brain. Both hormones are widely distributed, with the largest amounts outside the hypothalamus being found in the locus coeruleus. Considerable quantities of both peptides (but particularly oxytocin) are found in mesencephalic, pontine and medullary nuclei. This distribution is similar to that of the catecholamines, and the possible interaction of oxytocin and vasopressin with catecholaminergic pathways in the central control of various functions is discussed.