Effects of caffeine injection in paradoxical sleep window on memory in rat

Some investigators believe that the amount of REM sleep is increased after learning of some tasks, and learning processing and memory consolidation occur during some of these periods. These specific periods are called Paradoxical Sleep Windows (PSW). The neurochemical nature of PSW and its active neurotransmitter are unknown. NMRI rats were trained in a two-way shuttle avoidance task (100 trials per one session) and memory retention was tested one week later. Those animals that reached to 70% learning criterion were divided into 8 groups. In drug section, the animals of each group were administrated saline, caffeine (25mg/kg), adenosine (7mg/kg), adenosine (50mg/kg), physostigmine (0.1mg/kg) or Scopolamine (5mg/kg i.p.), after learning. In drug-deprivation section, the first group was deprived from REM sleep for 1-4hr after learning with platform technique. Animals in second group were administrated caffeine (25mg/kg) in addition to REM sleep deprivation for 1-4 hr after learning. Injection of caffeine caused a significant increase in memory (P<0.05). Deprived animals showed a significant memory deficit (P<0.05) and caffeine attenuated memory impairment which was induced by paradoxical sleep deprivation. Other drugs had no significant effect on memory. Caffeine can enhance memory and attenuate paradoxical sleep deprivation-induced memory impairment. Effects of caffeine on memory involve systems other than cholinergic and adenosine systems. Memory processing which occurs in PSW can not be attributed to one neurotransmitter system.