Effects of the intra-arterial injection of bradykinin into the limbs, upon the activity of mesencephalic reticular units.

The changes in firing rate of mesencephalic reticular units after intra-arterial injection into the limbs of a potent nociceptive agent, bradykinin, were studied in cats (unanesthetized, immobilized with flaxedil and hyperventilated). 30 per cent of the d35 studied cells were affected, 56 per cent were excited, 23 per cent inhibited and 5 per cent had mixed effects. Among the 75 excited cells, the activation of 16 of them seemed to related to the arousa- processes (group A); for 56 cells the increase seemed dire-tly dependent on the nociceptive stimulation itself (group B). The changes of firing rate were repruducible; their latencies and durations were of the same order as the latencies and duration of the nociceptive reactions and painful sensation s, which have been obtained in animals and men after bradykinin injections. The modifications induced by bradykinin administration were suppressed by Ketamin and Thiopental.