Learned helplessness: effects on brain monoamines and the pituitary-gonadal axis

The effect of the learned helplessness paradigm, a model of depression, on biogenic amines in eight brain regions, and on the serum levels of luteinizing hormone, corticosterone, and testosterone in male rats was determined. Rats which were exposed to uncontrollable and unpredictable shocks (HY-rats) had hormone levels similar to those in appropriate control animals. However, HY-rats had higher levels of 5-HIAA in the pons/medulla oblongata and lower levels of 5-HT in the cortex than rats which could escape the shocks (HE-rats). Furthermore, striatal levels of NE were higher in HY-rats when compared to HE-rats and non-shocked controls (HC-rats). Shock treatment per se resulted in lower NE levels in the hippocampus. These data implicate the serotonergic and noradrenergic systems as possible mediators of the learned helplessness phenomenon, but do not support the view that this behavior is associated with impaired pituitary-gonadal function.