Oxytocinergic neurosecretory system in genetically selected rats differing in emotionality. A morphometric investigation.

The study was carried out on lines of rats selected for high (KHA) and low (KLA) rates of development of an active avoidance conditioned reflex in a shuttle box. The volume of nucleoli of oxytocinergic cells of the paraventricular and supraoptic nuclei of the hypothalamus, as well as the content of oxytocin-immunopositive material in the posterior lobe of the hypophysis, were measured. The volume of the nucleoli in the intact KHA rats was smaller, and the amount of oxytocin-immunopositive material in the posterior lobe of the hypophysis greater, than in the KLA rats. A stressor (unavoidable electrodermal stimulation) exerts an opposite effect on the oxytocinergic system of the hypothalamus in rats of the two lines: the volume of the nucleoli increases in the KHA rats, while the amount of oxytocin-immunopositive material in the posterior lobe of the hypophysis decreases; the changes are opposite in the KLA rats. These results suggests that the reactivity of the oxytocinergic system is closely associated with the specific features of the animal's adaptive behavior, in particular, with the capacity for learning.