Immunohistochemical identification of oxytocin neurons in the suprachiasmatic nucleus of the male and female albino rats:A morphometrical study

Abstract

Background: The suprachiasmatic nucleus (SCN) is one of the nuclei in the anterior hypothalamus superior to the optic chiasma. It is well known that vasopressin and oxytocin neurons are located in the hypothalamic para-ventricular and the supraoptic nuclei. Extensive vasopressin neurons were observed in the rostral and middle regions of the suprachiasmatic nucleus. Aim of the work: Although the presence of oxytocin immunoreactive neurons within the SCN is unusual, this study was designed to clarify immunohistochemical localization of oxytocin neurons in the suprachiasmatic nucleus in the male and pregnant female adult albino rat and to investigate morphometrical differences in those neurons in relation to the gender. Material and Methods: Twenty adult rats (10male and 10 non pregnant female) were involved in this study. Rats were anaesthetized with ketamine, sacrificed and their brains were carefully dissected. The anterior portion of the hypothalmus containing the suprachiasmatic nucleus was taken. Coronal sections of the brain were prepared for histological stains (Hematoxylin and Eosin) and immunohistochemical stain (Oxytocin immunostaining). The diameters and number of oxytocin labelled neurons in the suprachiasmatic nucleus in each group were measured in a fixed field. The data will be used for morphometrical study. Results: The SCN in rat was formed mainly of 2 regions according to the change in the shape, rostral SCN (rSCN) and caudal SCN (cSCN).The rSCN appeared as a collection of neurons basal to the third ventricle and superior to the optic chiasma. It showed mixture of bipolar and multipolar cells. The cSCN was formed of mixture of large rounded and small bipolar neurons. The rostral part of the nucleus showed positive OT immune-reactive neurons throughout its structure in both male and female rats, the caudal part of the nucleus exhibited OT immune-reactive neurons in the lateral part only on both sides of the third ventricle, while its medial potion showed negative reaction for OT in both groups. Conclusion: The present findings proved immunehistochemical identification of OT neurons in the adult male and nonpregnant female rat SCN, and indicate clear sex differences in OT neurons morphometrical measurements which may be parallel to differences in the neuroendocrine and behavioral function in both sexes.