A method for assessing relative changes in local cerebral blood flow by recording pulsatile electricM impedance fluctuations has been developed (BI~ZlS and TAC~I~A~A 1962) and used to study cerebral circulatory events associated with natural states of alertness in cats (BIRZlS and TACmBA~A 1964). Consistent localized patterns in the impedance pulsations were observed during arousal, characterized chiefly by a selective and quantitative increase in amplitude in a specific area of the posterior hypothalamus. During sleep, the amplitude in most areas increased slowly and progressively, except during the "paradoxical" stage of sleep associated with low voltage electrocortical activity. At that time the impedance pulsations resumed a site-specific pattern similar to that of alertness. Evidence was presented for concluding that the observed changes were related primarily to relative changes in blood flow under the electrodes.
In the present study, local cerebral impedance patterns of unanesthetized cats receiving stimulant or depressant drugs are compared with those of natural states of alertness, and the alterations obtained are interpreted in terms of local blood flow changes.
Methods
Eleven cats were prepared with permanently implanted bipolar electrodes in association cortex, midbrain reticular formation (RF), posterior hypothalamus, and dorsal hippocampus, and, in some cats, in medial thalamus. All placements were verified histologically from frozen, thionine-stained sections.