Abstract
Background: Learning and memory are among the higher functions of the brain. State-dependent memory (STM) is a type of memory in which the recall of a learned behavior is happend only in the same sensory and physiologic condition in which the behavior is encoded. The STM is seen with some drugs, e.g. the morphine. The pentylenetetrazol (PTZ) is a durg which is used for the induction of seizure in experimental models. Some studies have been revealed different effects of the PTZ on brain higher function (learning, memory …). The aim of present study was to explore the effect of PTZ on morphine-induced STM.
Materials and Methods: In this study, male adult Wistar rats (190-220 g) were used. Animals in 3 groups (n=8) during 3 sessions (learning/memory, STM and interaction) were studied. During 48 hour (training and test) the learning and memory of animals were studied in inhibitory avoidance apparatus. The step-through latency in the test day was used as a criterion for memory. Post-training injection of saline or morphine (2.5, 5 and 7.5 mg/kg-ip) in different groups was carried out. In addition, the pre-test injection of morphine at the same doses was made to study the STM. Moreover, the interaction of pre-test single-dose PTZ (60 mg/kg-ip) on STM was studied. The locomotion of the animals was measured using the open field.
Results: The post-training injection of morphine (2.5, 5 and 7.5 mg/kg-ip) impaired the inhibitory memory of rats compared to control group (p<0.001). The post-training and pre-test injections of the same dose of morphine (7.5 mg/kg-ip) reversed the impaired memory compared to morphine (2.5 and 5 mg/kg-ip), (p<0.001). The pre-test PTZ (60 mg/kg-ip) maintained the morphine (7.5 mg/kg-ip) STM (p<0.001).
Conclusion: The present study revealed that the post-training ip injection of different doses of morphine results in the impairment of inhibitory avoidance memory in rat. In addition, the pre-test injection of the same doses of morphine reverses the impaired memory. This process is called STM. Consequently, the pre-test injection of PTZ maintains the morphine STM.
