REGIONAL VASOCONSTRICTION AND EXCESSIVE GROOMING INDUCED BY L-ARGININE INJECTION INTO THE CISTERNA-MAGNA OF CONSCIOUS RATS

Hemodynamic and behavioral changes caused by intracisternally injected L-arginine which has a pressor effect were studied in conscious rats. One week or more after inserting a cannula into the cisterna magna, electromagnetic flow probes were implanted around the superior mesenteric artery, renal artery, or terminal aorta under anesthesia. A catheter for measurement of blood pressure was inserted into the terminal aorta via a femoral artery or into the common carotid. After recovery from surgery, blood flow, arterial blood pressure, heart rate, and behaviors were observed in the conscious state. Peripheral resistance, calculated as pressure divided by flow, increased an average of 80% in the superior mesenteric artery and 60% in the renal artery when the pressure was increased by 25% following intracisternal injection of 5 mumol of L-arginine. Hindquarter (terminal aortic) resistance showed an insignificant decrease of about 10%. The average heart rate showed no significant change. Grooming, moving, and eating all increased significantly after injection of L-arginine. Circulatory events and behaviors did not always synchronize after the injection. Intravenous chlorisondamine chloride, a ganglion blocker, significantly attenuated the pressor effect caused by intracisternal injection Of L-arginine. These findings indicate that centrally injected L-arginine not only specifically triggers vasoconstriction in the viscera presumably through excitation of the regional sympathetic vasoconstrictor fibers to raise blood pressure but also centrally induces excessive grooming. However, the relationship between circulation and behavior caused by intracisternal injection of L-arginine remains unknown.