Metrazol potentiated after-discharges: dose-response relationships and effects of selective lesions

In Experiment 1 the dose-response effects of pentylentetrazol (Metrazol) on photically evoked after-discharge (PhAD) parameters were examined. Metrazol potentiated PhAD activity by affecting all measured parameters - PhAD frequency, amplitude, burst duration and spindle composition - in particular PhAD burt duration and spindle composition. A mimimum effective dose of 10 mg/Kg of Metrazol was required for some statistically reliable potentiation. Metrazol dosage levels of 20 and 25 mg/Kg induced lengthy bouts of EEG spindling and spiking as well as near maximized PhAD component augmentation. In Experiment 2 stereotaxically oriented knife-cuts isolated the thalamus from cortical and/or midbrain and brainstem input. Such lesions did not block the capacity of Metrazol to potentiate PhADs, although the lesions altered evoked activity. These findings are discussed in terms of the current thought of Metrazol action and thalamic mechanisms in the control of after-discharge activity.