Fear and anxiety behavior in rats

Abstract

Fear can be considered as a functional defense behavior to protect living beings against dangerous situation. In our studies we have investigated the fear behavior in rats in elevated plus maze .The increase in two parameters percent of open arm entries (%OAE) and percent of time spent in the open arms (% OAT) and decrease in the percent of time spent in closed arm (%CAT) was considered as fear and anxiety effects .In our previous study we measured these parameters in control and prenatal stressed male rats before and after treating by different doses of testosterone enantate .Our data showed that prenatal stress increased fear and anxiety behavior compared with control , and testosterone treatment decreased this behavior dose dependently which is probably due to the inhibitory effects of testosterone on HPA and on some brain nuclei . Several central sites have been implicated in the modulation of fear and anxiety. Some researchers suggested the probable effects of GABA receptors in this modulation. we studied the effects of ICV and IP injection of GABAA and GABAB receptor agonists and antagonists on fear and anxiety. ICV injection of different doses of muscimol, a GABAA receptor agonist, induces anxiety profile in rats. Neither ICV nor IP injection of GABAB receptor agonist baclofen altered the three parameters. ICV injection of GABAB receptor antagonist CGP 35348 increased % OAE and % OAT and decreased % CAT. The response induced by injection of muscimol (0.5 ?g/rat ICV) or administration of CGP35348 (10 ?g/rat ICV) was reduced by i.c.v. (1, 2, and 4 ?g/rat) or IP (0.25, 0.5, and 0.75 mg/kg) injection of the GABAA receptor antagonist bicuculline, but the effect of CGP35348 on %CAT was not significantly altered by IP administration of bicuculline.IP administration of bicuculline (but not ICV) by itself reduced both %OAE and %OAT, but did not alter %CAT. None of the drugs altered the locomotor activity of the animals The current findings support our hypothesis that the anxiolytic effects of GABAB antagonist are mediated by autoreceptor blockade-induced release of endogenous GABA, which in turn activates postsynaptic GABAA receptors. The effects of morphine on fear and anxiety behavior are being investigated now.