Cardiorespiratory and electroencephalographic responses to stimulation of the mesencephalic tegmentum in toads, lizards, and rats.

Rectangular pulses delivered to the mesencephalic tegmentum were used as central step-like stimuli, and their effects on blood pressure, heart and respiratory rates, and brain waves were tested in toads, lizards, and rats under urethane anesthesia. The delay response was much shorter and the rate of change was faster in rats than in toads or lizards. Response duration was longer in toads and lizards than in rats. Long-lasting error and poststimulus oscillations were observed in toads and lizards but not in rats. Eighty percent of responses in rats, 53.337 D in toads, and only 2.22% in lizards showed adaptation to the stimulus. In toads and lizards the whole variables were systematically affected, whereas in rats 42% of responses were discriminative. Tegmental stimulation induced desynchronization in rats, synchronization in lizards, and had no effect in toads. These results suggest that whereas the cardiovascular control in the rat may act as proportional, derivative, or integrative and in the toad only as proportional, a derivative component becomes apparent in the lizard.