Effects of transection, local cooling and electrical stimulation in the mid-pontine region upon the hippocampal theta rhythm in the rabbit

1) Effects of cooling, electrical stimulation and transection at the pontine level upon hippocampal EEG activities were studied in rabbits anesthetized with Nembutal and immobilized with D-tubocurarine. 2) Following a mid-pontine pretrigeminal transection, the hippocampal theta rhythm became higher in frequency and larger in amplitude. 3) Exactly the same results were obtained by means of cooling the mid-pontine region. 4) Exactly the same results could be obtained simply by introducing the cooling needle into the mid-pontine region. This was presumably due to the destruction of a particular nervous tissue by the cooling needle. 5) Electrical stimulation of the mid-pontine region had dual effects on the theta rhythm. One was an amplitude-decreasing effect and the other was a frequency-increasing effect. The former was higher in threshold than the latter. 6) Taken all these results together, it is thought that there exist a theta rhythm-facilitatory system above the mid-pontine level and a theta rhythm-inhibiting system below the mid-pontine level.