Effects of histamine precursor and (R)-alpha-methylhistamine on the avoidance response in rats

The aim of this work is to clarify the role of histamine in learning and me mory processes. In order to do this, the effect of administration of the hi stamine precursor, L-histidine (HIS) and of the agonist of the H-3 receptor . (R)-alpha -methylhistamine (RAMH), on active avoidance response in rats i s studied. Treatment with RAMH (10 mg/kg i.p.) increased the number of avoi dance responses produced during acquisition and retention of the learning. In contrast, administration of L-his (500 mg/kg i.p.) impairs performance i n the shuttle-box. These results are consistent with a role for histamine i n cognitive processes and suggest that a increase in cerebral histamine lev els impair the acquisition of avoidance response, whereas reduced levels fa cilitate this acquisition. (C) 2001 Elsevier Science B.V. All rights reserv ed.