Abstract
Since it is generally thought that ketamine hydrochloride has no depressive effect on the reticular formation, we expected that the acoustical stapedial reflex has not been affected by this medicine. On the contrary, ketamine hydrochloride supressed the acoustical stapedial reflex in the guinea pig, that is, mainly changed the slope of the stimulus-response curve without appreciablly raising its threshold.
Since ketamine hydrochloride has a depressant effect on thalamic and cortical activity, we thought that ketamine hydrochloride did not supress the direct route which was located in the lower brain stem but supressed the indirect route which would facilitate the acoustical stapedial reflex. As a conclusion, there seems to be neuro-anatomical links to the final common pathway of the acoustical stapedial reflex which would have to descent from at least the mid-brain level.
