Pretrigeminal preparation.

The pretrigeminal preparation (pretrigeminal animal) is obtained by transection the pons in front of roots of the trigeminal nerves. The rostral part of the preparation (isolated cerebrum) has olfactory, visual and humoral inputs and controls vertical position of eye and their pupillary diameter and accommodation. The pretrigeminal preparation was described in the cat and rat. During the acute stage the isolated cerebrum is continuously awake, alternatively alert and drowsy. In the chronic stage a sleep-waking cycle recovers, but paradoxical sleep remains absent and synchronized sleep is reduced. Thus the cerebrum can largely compensate for the withdrawal of influences from the deactivating structures of the lower brain stem. Olfactory and visual stimuli produce a virtually normal arousal response. Its major components are: dilatation of pupils, desynchronization of cortical EEG activity, appearance of theta activity in the hippocampal EEG, and an increase of the cerebral blood flow. If the stimulus is repeated, the arousal response habituates with a normal rate. In the pretrigeminal cat there are two ocular targeting reflexes: vertical fixation and accommodation. The fixation reflex has a normal general course and shows normal habituation, but it is less precise than in the intact cat. The accommodation reflex is normal. Classical and instrumental ocular conditioned reflexes can be elaborated in the pretrigeminal cat. The conditioned pupillary dilatation appears at a normal rate. On the other hand, the elaboration of the conditioned vertical eye movement is slower than in the intact cat, possibly as a result of the lack of the proprioceptive feedback from the extraocular muscles. In conclusion, excitability, integrity and plasticity of the isolated cerebrum of the pretrigeminal preparation seem to be virtually normal. In contrast to the pretrigeminal preparation, the "cerveau isolé" is comatose during the acute stage. In the chronic stage, however, the sleep-waking cycle recovers and with time it becomes similar to that in the pretrigeminal preparation. However, the vertical fixation reflex remains impaired in the low "cerveau isolé" and is obviously absent in the high "cerveau isolé". The caudal part of the preparation has a normal contact with the outside world, but it cannot largely make use of it. However, it satisfactorily controls the circulation and respiration. Rats are superior than cats: pretrigeminal cat cannot turn over from one side to the other and is fed by stomach tube, whereas pretrigeminal rat can crawl and eat food introduced into the mouth.(ABSTRACT TRUNCATED AT 400 WORDS)