Learned helplessness and in vivo hippocampal norepinephrine release.

Hippocampal norepinephrine release was measured using in vivo microdialysis in rats before and after exposure to inescapable tail shock stress and after testing for learned helplessness. Rats that did not develop learned helplessness after stress had higher basal norepinephrine release after stress than rats developing learned helplessness or than control rats. After the shuttlebox test for learned helplessness, K(+)-stimulated norepinephrine release was lower in learned helpless than in nonhelpless or control rats. These results confirm an important role for the hippocampal noradrenergic system in differential behavioral responses to stress.