Influence of chloralose on brain regional glucose utilization

Choralose, a widely used anesthetic in neurophysiology, produces a unique pattern of anesthesia characterized by both an excitant (myoclonic jerks and startle response) and depressant (sedation and anesthesia) action. We investigated the influence of chloralose on the rate of regional brain glucose metabolism to determine if chloralose produces anesthesia by hyperexciting certain brain regions. That is, does chloralose act as an 'epileptoid anesthetic'. Rats were anesthetized with either 60 or 120 mg/kg chloralose and regional brain glucose utilization rates quantitated by the 2-deoxyglucose method. In chloralose-anesthesized rats, glucose consumption rates decreased in the frontal and auditory cortex, reticular nucleus of thalamus, superior colliculus, medial geniculate body, midbrain reticular formation and hippocampus. Rates of glucose use were not decreased in the lateral lemniscus and a zone in the vicinity of the oculomotor nucleus, medial longitudinal fasciculus and surrounding reticular formation. Since chloralose did not induce any discernible focal points of high activity, chloralose appears not to be an epileptogen. Rather, chloralose appears to act as a general depressant except in certain gray areas of the midbrain and lower brain stem. Retained and possibly increased functional activity in the vicinity of the oculomotor nucleus and medial longitudinal fasciculus may represent active reflex pathways involved in mediating the paradoxical startle response and myoclonic activity observed in chloralose-anesthetized animals.