ISSN : 1226-9654
This study investigated the effects of chronic injection of benzodiazepine agonist, diazepam(2mg/kg) and inverse agonist, β-CCM(1mg/kg) on the conditioned freezing in Sparague-Dawley male rats, using 2-trial conditioned fear test. Each animal in chronic treatment groups was injected twice a day for 5 days. Each animal in acute treatment groups was injected only once before training. On the first training day, each rat was placed in the observation chamber, and 3 min later it recieved three shock (0.75s, 1mA) at a 20-s intershock interval. During the second testing day, the animal's behavior was observed according to a time-sampling procedure in the same preshocked chamber. Results showed that the conditioned freezing was significantly reduced in animals treated with single injection of diazepam, administered before the 1st training trial, but not in those treated with repeated injections of diazepam(exp 1). In constrast, both single and repeated injections of β-CCM caused an increasing in the conditioned freezing response(exp 2). The finding that the acute treatment of diazepam given before training attenuate the conditioned freezing was consistent with our previous study. It was also founded that the repeated administrations of diazepam induced tolerance effect and the effects of agonist and inverse agonist ligands of benzodiazepine receptor on conditioned freezing were contrary to each other. It is suggested that benzodiazepine receptors are involved in the control of the rat's species-specific defensive response.