RESUMO
BACKGROUND: Several studies have been shown that antidepressant drugs have contradictory effects on cognitive processes. Therefore, the aim of this study was to investigate the effects of amitriptyline and fluoxetine on synaptic plasticity in the dentate gyrus (DG) of the hippocampal formation in rat. MATERIALS AND METHODS: Experimental groups were the control, the fluoxetine, and amitriptyline. The rats were treated for 21 days and then, paired pulse facilitation/inhibition (PPF/I) and long-term potentiation (LTP) in perforant path-DG synapses were assessed (by 400 Hz tetanization). Field excitatory post-synaptic potential (fEPSP) slope and population spike (PS) amplitude were measured. RESULTS: The results of PPF/I showed that PS amplitude ratios were increased in 10-70 ms inter-stimulus intervals in the amitriptyline group compared to the control group. In the fluoxetine group, EPSP slope ratios were decreased in intervals 30, 40, and 50 ms inter-stimulus intervals compared to the control group. The PS-LTP was significantly lower in the fluoxetine and the amitriptyline groups with respect to the control group. CONCLUSION: The results showed that fluoxetine and amitriptyline affect synaptic plasticity in the hippocampus and these effects is probably due to the impact on the number of active neurons.
RESUMO
BACKGROUND: One of the serious problems that opioid addicted people are facing is repeated withdrawal syndrome that is accompanying with a significant stress load for addicts. Therefore, the aim of this study was to evaluate the effects of repeated withdrawal on spatial learning, memory and serum cortisol levels in morphine-dependent mice. MATERIALS AND METHODS: Male NMRI mice received morphine as daily increasing doses for 3 days. After that, the mice underwent one time or repeated spontaneous or pharmacologic (naloxone-precipitated) withdrawal. Then spatial learning and memory were investigated by morris water maze test, and at the end trunk blood samples were collected for measurement of serum cortisol levels. RESULTS: The results showed that only repeated spontaneous withdrawal significantly increases escape latency (P < 0.05), and in other models of withdrawal, spatial learning and memory were intact. The results of probe trial were intact in all groups. Radioimmunoassay showed that serum cortisol levels were increased significantly in all models of withdrawal (P < 0.05 and P < 0.01) except the repeated spontaneous withdrawal. CONCLUSION: The results showed that short periods of withdrawal syndrome can increase serum cortisol levels; however they do not affect spatial learning and memory. Nevertheless, repeated spontaneous withdrawal can make learning slow.
