Caffeine is a mild stimulant of the central nervous system capable of improving cognitive and intellectual functions such as alertness and sense of well-being (J R Soc Med. 88:437,1995). In addition, it has been shown to reduce the reaction time and improve memory (Psychopharmacol. 122:158,1995), particularly at low doses (Proc Natl Acad Sci U S A. 78:3260, 1981). Caffeine can improve cognitive function through antagonism of adenosine receptors, which induces the release of acetylcholine, or even the induction of synaptic changes, due to prolonged use (Nature. 361:31,1993; Ann Rev Neurosci. 21:149,1998). It has been suggested also that the consumption of caffeine have neuroprotective effects, improving memory deficits in dementia patients (Psychopharmacol. 122:158, 1995). On the other hand, caffeine is also capable of inducing anxiety, and an interaction between the anxiogenic and mnemonic effects of this drug has been demonstrated (J Neurosci Met. 102: 117, 2000). Our aim is to verify the effects of acute or chronic caffeine administration on scopolamine (a classical muscarinic antagonist) - induced amnesia in rats tested in the plus-maze discriminative avoidance task, for concomitant evaluation of aversive memory and anxiety levels.

Male Wistar rats were divided in 4 groups (saline-saline, saline-scopolamine, caffeine-saline and caffeine-scopolamine). For the acute treatment, animals received acute caffeine (10mg/kg, i.p) or saline (i.p.), 30 min before training and scopolamine (1mg/kg i.p.) or saline, 20min before training. The test was realized 24h after training and all animals received saline 20min before trial. For the chronic treatment, caffeine (10mg/kg, i.p.) or saline were administered for 28 days and on 29^th day the same acute treatment protocol was applied. Before the test, performed 24h after training, the groups received caffeine or saline 30min before and saline 20min before the session. The apparatus used a modified elevated plus-maze, consisting of 2 open and 2 enclosed arms (one of these aversive, with sound and light during the time the animal remains in it within the training session). The test session consists in allowing the animal to explore apparatus without stimuli.