Behavioral effects of GABA in the hippocampal formation: functional interaction with histamine

Some behavioral effects of GABA in the hippocampus and its probable interaction with histamine in adult male rats were studied. Four experiments were performed. In Expt. 1, rats were implanted unilaterally into the ventral hippocampus and they were microinjected with increasing doses of GABA. Five minutes later the following behavioral scores were measured in a holeboard: (1) locomotion, (2) head-dipping and (3) rearing. Results showed that GABA induced an increase in locomotion and a decrease in the frequency of long-lasting rears. In Expt. 2, the implanted rats were microinjected into the ventral hippocampus with Gamma-vinyl-GABA (GVG), an inhibitor of the metabolizing enzyme of GABA and picrotoxin and bicuculline, both antagonists of GABA. The following behaviors were measured later in the holeboard: (1) locomotion, (2) head-dipping frequency, (3) rearing activity and (4) grooming frequency. Results showed that GVG also increased the locomotor activity and this effect was antagonized by picrotoxin and bicuculline. In Expt. 3 the brain endogenous levels of GABA were measured in rats microinjected with GVG. Results showed that the GVG injection into the hippocampus augmented the endogenous levels of GABA. In Expt. 4 the implanted rats were microinjected into the hippocampus with GVG and histamine. Behavioral scores were measured later in the holeboard. Results showed that the increase in locomotion induced by GVG was blocked by the administration of histamine. Present results show that GABA may be involved in some hippocampal-mediated behaviors and suggest a histamine-GABA link in the final expression of these behaviors.