MECHANISM OF CHANGES IN BRAIN NOREPINEPHRINE LEVELS FOLLOWING OLFACTORY BULB LESIONS

Rats killed 27 days after an olfactory bulb is transected show characteristic alterations in the quantities of norepinephrine in certain brain regions (1,2). In the ipsilateral telencephalon, the locus of most of the axons which leave the olfactory bulb (3), norepeniphrine levels decrease. This effect probably reflects a loss of noradrenergic nerve endings, since the ability of the telencephalon to take up and retain 3H-norepinephrine placed in the lateral cerebral ventricles also declines. In the brain stem, norepinephrine levels increase. This region is not known to receive a significant number of nerve fibers originating in the olfactory bulb (3); hence the elevation in its norepinephrine content must result from a trans-synaptic mechanism. This communication provides information on the time-course of the changes in brain norepinephrine levels after olfactory bulb lesions and on the anatomic and biochemical mechanisms responsible for these changes. © 1969.