KAINIC ACID ADMINISTRATION IN THE FASTIGIAL NUCLEUS PRODUCES DIFFERENTIAL CARDIOVASCULAR EFFECTS IN AWAKE AND ANESTHETIZED RATS

Kainic acid was microinjected or microdialyzed into the rostral medial aspect of the fastigial nucleus to determine its effect on mean arter ial pressure and heart rate. This was carried out in both the awake an d the anesthetized (alpha-chloralose) rat. In awake animals, kainic ac id elicited an initial phasic presser response which was followed by a long-term elevation of mean arterial pressure that lasted for the dur ation of the experiment (2 h). Rats anesthetized with alpha-chloralose exhibited only a tonic depressor response. This converted to a presse r response as the rats began to emerge from anesthesia after 2 h. Both the awake and the anesthetized rats exhibited regular phasic changes in mean arterial pressure that was superimposed on the longer term cha nges in the mean arterial pressure. Similar results were obtained in b oth the microinjected and the microdialyzed animals. Thus, stimulation of the intrinsic fastigial neurons by kainic acid evokes an elevation of the mean arterial pressure in the awake rat. This is manifested as a decrease in pressure in the anesthetized animal. Thus, stimulation of the cardiovascular region of the fastigial nucleus can increase or decrease mean arterial pressure. It is possible that the direction of the change in mean arterial pressure is dependent on the level of intr insic fastigial neural activity.