Clonidine‐induced cardiovascular effects after stereotaxic application in the hypothalamus of rats

Clonidine, a closely related analogue of the sympathomimetic imidazolines reduces heart rate and lowers blood pressure in animals as well as in patients with hypertension (Hoefke & Kobinger, 1966; Michel, Zimmerman & others, 1966). There is evidence that clonidine acts in the central nervous system (Sherman, Greca & others, 1968; Shaw, Hunyor & Korner, 1971) by activation of noradrenaline receptors (Schmitt & Schmitt, 1969, 1970; Kobinger & Walland, 1971). Although the findings indicate a central site of action in bulbar or diencephalic structures (Schmitt & Schmitt, 1969; Shaw & others, 1971), clonidine has not been studied after intracerebral application. We have injected clonidine via stereotaxically implanted cannulas directly into various areas of the hypothalamus in anaesthesized rats while blood pressure and heart rate were recorded simultaneously on a Grass polygraph. Most of the injections were made 2.5-3.5 mm anterior and 2.42.8 mm below the interaural line and 0.5-0.7 mm lateral acording to the atlas of Konig & Klippel (1963). Details of the experimental procedure will be published elsewhere.