Aim: 

Excitatory and depressant effects and sleep alterations have been observed after pilocarpine administration. The cause of these anomalies is not well studied. The present work aims to verify whether pilocarpine central effects are related to alterations in hippocampus-cortex synchronization.

Methods: 

Rats (n=7) were submitted to different treatments: saline, pilocarpine 120 mg/ml and 360 mg/ml, i.c.v. Monopolar EEGs were recorded at the hippocampus (AP -4.0, ML +2.0, DV –3.0) and cortex (AP +2.0, ML +2.5) with cerebellar reference. EEGs, EMG (obtained over the neck muscles) and behavioural states were digitised at 512 Hz along 2 hours during the dark period. Hippocampus-cortex connectivity was assessed from EEG recordings using the "phase lag index" (PLI), a recently developed phase synchronization measure between two signals. Hippocampus-cortex PLI was estimated during active wakefulness, passive wakefulness, slow wave sleep and REM sleep for EEG delta (0.5-4 Hz) and theta (4-8 Hz) bands.

Results: 

During passive waking after saline treatment, a hippocampus-cortex coupling appeared in theta band with the hippocampus leading the cortical activity but the coupling was reversed after pilocarpine administration. During active waking, hippocampus-cortex coupling in theta band was reversed when compared to passive waking but the effect was cancelled with the high pilocarpine dose. During REM sleep, only the low pilocarpine dose was effective in coupling the hippocampal-cortical synchrony in theta band.

Conclusion: 

Pilocarpine alters hippocampus-cortex connectivity during passive and active wake in opposite ways. During REM sleep, only low doses of pilocarpine can induce a hippocampal-cortical coupling.