LEARNED HELPLESSNESS AND IN-VIVO HIPPOCAMPAL NOREPINEPHRINE RELEASE

Hippocampal norepinephrine release was measured using in vivo microdia lysis in rats before and after exposure to inescapable tail shock stre ss and after testing for learned helplessness. Rats that did not devel op learned helplessness after stress had higher basal norepinephrine r elease after stress than rats developing learned helplessness or than control rats. After the shuttlebox test for learned helplessness, K+-s timulated 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 re sponses to stress.