Author(s)

Rosana Alves, José Gilberto Barbosa de Carvalho, Marco Antonio Campana Venditti

Departamento de Psicobiologia, Escola Paulista de Medicina, Universidade Federal de S?o Paulo, Rua Botucatu, Brazil.

Rearing is an exploratory behavior induced by novelty, such as exposure to an open field. Stimulation of certain brain regions, including the hippocampus, induces both rearing and clonic convulsions. Brain excitability is controlled by gamma-aminobutyric acid (GABA) inhibitory neurotransmission through its ionotropic GABA_A/allosteric benzodiazepine site. Drugs that decrease GABA_A receptor fast inhibitory neurotransmission induce clonic convulsions and rearing when injected into the hippocampus. Therefore, individual differences in rearing behavior may be related to the susceptibility to clonic convulsions, which could involve differences in brain excitability controlled by GABA_A/allosteric benzodiazepine site receptors. Adult, male Wistar rats were divided into high- (HR) and low-rearing (LR) groups based on the number of rearings in the open field test. Groups of HR and LR rats were challenged with convulsant drugs that antagonize GABA neurotransmission via different mechanisms of action (3-mercaptopropionic acid, a glutamate decarboxilase inhibitor; bicuculline, a GABA_A receptor antagonist; pentylenetetrazol and picrotoxin, both GABA_A receptor chloride channel blockers and DMCM, a benzodiazepine inverse agonist). The convulsant doses that induced 50% of clonic convulsions were determined for each drug. The LR rats had a higher susceptibility (a lower convulsant dose 50%) to clonic convulsions induced by DMCM than the HR rats, but there were no differences between the groups in the susceptibility to tonic convulsions induced by the same drug. There were no significant differences in the convulsant dose 50% for clonic convulsions between the groups for all other drugs injected. In another experiment, additional HR and LR rats were injected with a sedative-hypnotic dose of diazepam, which caused a significantly higher hypnotic effect (sleeping-time) in the LR rats than in the HR rats. The LR group was also shown to have a significantly lower density of [³H]-Flunitrazepam bound to the GABA_A receptor in hippocampal membranes. Our data suggest that inter-individual differences in rearing are related, at least in part, to the GABA inhibitory neurotransmission controlled by the benzodiazepine allosteric site in the GABA_A receptor.

Open Field; Rearing Behavior; Clonic Convulsion; Diazepam; Sleep; Benzodiazepine; DMCM; GABA_A Receptor; [³H]-Flunitrazepam Binding; Hippocampus; Novelty; Stress

R. Alves, J. Carvalho and M. Venditti, "High- and Low-Rearing Rats Differ in the Brain Excitability Controlled by the Allosteric Benzodiazepine Site in the GABA_A Receptor," Journal of Behavioral and Brain Science, Vol. 2 No. 3, 2012, pp. 315-325. doi: 10.4236/jbbs.2012.23036.