Oxytocin-immunoreactive nerve cells in the supraoptic nucleus of the hypothalamus after treatment with histamine.

Immunohistochemical, morphometric and statistical methods were used to study oxytocin immunoreactive elements in the supraoptic nucleus (SON) of the hypothalamus of 180 male rats. Untreated rats, rats that were given either an intraperitoneal (ip) or intracerebroventricular (icv) injection of histamine (HA) (n = 40 each group) and control animals that received ip or icv injections of saline were included in our study. Oxytocin immunoreactive neurons and oxytocin-labelled nerve tracts were found in the SON of untreated animals. Treatment with saline either intracerebroventricular or intraperitoneally did not modify the oxytocin immunoreaction described for untreated animals. I.c.v. treatment with HA increased the numbers of oxytocin labelled elements. On the contrary, oxytocin immunoreaction after intraperitoneal treatment with HA was similar to that described for control and untreated animals. The morphometric and statistical studies confirmed these findings. The importance and signification of these results are discussed in this paper.