HISTAMINERGIC DRUGS IN THE RAT CAUDATE-NUCLEUS - EFFECTS ON LEARNED HELPLESSNESS

The effect of pharmacological manipulation of histaminergic receptors in the caudate nucleus (CN) has been examined in rats previously submi tted to inescapable electric shock to produce learned helplessness (LH ). Histamine H-1 agonist 2-tiazolylethyl amine (TEA) microinjection pr oduced protective effects, preventing the activity and cognitive loss typical in LH. Injection of the H-1 antagonist astemizole (AZ) produce d effects symmetrical to those produced by TEA, further reducing activ ity and impairing cognitive functions. The histamine H-2 agonist 4-met hyl-histamine (4MH) produced a shift on the side preference for rotati on that interfered in the learning tests and obscured the effects of t his drug on LH. Injection of the H-2 antagonist cymetidine (CYM) cause d LH-like effects in control animals. Thus, brain histamine seems to p lay a relevant role in the control of motor and cognitive functions of the CN.