Development of a quantitative method for evaluation of the electroencephalogram of rats by using radiotelemetry

The objective of this study was to develop a method for recording the electroencephalogram (EEG) of rats by using radiotelemetry followed by automated analysis of the raw tracing by fast Fourier transformation (FFT). We surgically implanted four 4- to 5-month-old Wistar (Crl:(WI)BR) rats each with two epidural electrodes and an attached radiotransmitter (Physiotel Implant, model TA11CTA, Data Sciences International, Inc., St. Paul, Minn.). Raw EEG signals were routed to a digital storage oscilloscope (DataSys 7200, Gould Instrument Systems, Valley View, Ohio) with FFT and averaging capabilities. FFTs of raw signals were generated at baseline (predose) and after intraperitoneal dosing of the rats with atropine (30 min postdose; 6 mg/kg), caffeine (90 and 150 min postdose; 30 mg/kg), ketamine (15 and 30 min postdose; 50 mg/kg), and pentobarbarbital (60 and 90 min postdose; 40 mg/kg). For atropine, caffeine, and pentobarbital, the overall direction of the change in power across the spectrum (0 to 40 Hz) was the same as that reported previously. Relative peaks in power were consistent with those previous reports for atropine at < or =5 Hz and caffeine at approximately 7.5 Hz. Ketamine caused a shift in peak power from 5 to 10 Hz to < 5 Hz, as shown by other investigators. FFT analysis of EEG signals captured by radiotelemetry may provide a meaningful method for studying the CNS effect of novel compounds.