Norepinephrine content of discrete brain nuclei in acutely and chronically stressed borderline hypertensive rats

Forty-three male borderline hypertensive rats were subjected to either 3 days, or 4, 10, or 16 weeks of daily stress. An additional 43 animals served as unstressed, age-matched controls. At the end of study, animals were sacrificed, brains were removed, and cardiovascularly-important nuclei in the brainstem and hypothalamus were removed by micropunch. Assays revealed that norepinephrine (NE) levels were initially elevated in the brainstem in animals stressed for 3 days. As stress continued, NE levels were significantly lower in the brainstem, and eventually in the hypothalamus, of stressed animals. The relationship of these observations to environmentally-induced hypertension is discussed.