de la salut. Crta. Valldemossa, Km 7.5 Mallorca, Spain

Cholinergic system plays a role generating EEG and regulating vigilance states. An important indicator variable of behavioural states is the theta rhythm. Hippocampus is the main theta rhythm generator. The aim of this study was to analyse the effects of pilocarpine (a muscarinic agonist) on the power of cortical and hippocampal theta band. Six male Wistar rats (350-375 g) maintained in standard conditions have been used. The animals were implanted with a chronic tripolar EEG electrode in frontal cortex and hippocampus (CA4), with cerebellar reference. A cannula was also placed in the lateral ventricle (AP –0.8, ML –2.0, DV –3.3). EEGs, EMG (obtained over the neck muscles) and behavioural states were digitised and computed stored along 2 hours during dark period (6 hours after lights off, when theta rhythm has been shown to be lower). Two pilocarpine doses (120 and 360 |mu|g/|mu|l, i.c.v.) have been compared to saline. EEG corresponding to passive and active behavioural states was submitted to FFT. The variations in theta power (4-8 Hz) for each state have been compared with and without pilocarpine. In the cortex, an increase in the theta band was observed in both passive and active behavioural states after pilocarpine treatment. In the hippocampus, the increase was only observed in active states. No significant differences between doses were found. In conclusion and agreeing with previous results, pilocarpine increases theta power band and probably the information flow between hippocampus and cortex.