Effects of the acute administration of Imipramine on learned helplessness of male and female rats

Abstract

Learned helplessness is an animal model of depresion based on the difficulty to learn an escape response as a function of previous experience with uncontrolable shocks. The aim of this work was to evaluate the effects of the Imipramine on male and female rats submitted to unavoidable shocks. One hundred an sixty Wistar rats were divided into twenty groups (n=8), according to sex (male or female), treatment ( shock-CHI or non-shock –NCH) and dose of Imipramine (0,4,8,16 and 32 mg/kg). The groups were treated in pairs, as a function of the shock treatment. All animales were exposed to two sessions (training and test) with an interval of 24 hours between them. In the training session, CHI groups were exposed to 60 uncontrollable shocks (RI 60 (20-100 s) 1 mA, 10s). The subjects of the NCH groups were placed in the box, but did not receive shocks . about 24 hours later, the subjects received an i.p. injection of vehicle (0 mg/kg) or Imipramine (4,8,16 or 32 mg/kg), and 30 minutes later, they were exposed to a test session in a Shuttlebox, under an escape contingency. They were exposed to 30 shocks (1 mA, RI 60s). The shocks were automatically interrupted if the subject jumped out from one compartment to the other. When the escape response was absent, shock was automatically interrupted after 10s. The time elapsed from the beginning to the end of the shock was designed as the latency of response. The results showed that rats exposed to uncontrollable shocks failed more to escape and presented greater latencies in the test sessionif compared to those not previously exposed to the shocks. At doses of 4 and 8 mg/kg (males) and 8, 16 and 32 (females), learned helplessness; and 3 the effect of Imipramine seems to be realted to the gender in the fails.