The medial forebrain bundle (MFB) and ascending monoaminergic pathways in the cat

Abstract

Unilateral lesions of the caudal hypothalamus involving the area of Tsaï result in a decreased concentration of both dopamine and serotonin (5-HT) in the ipsilateral striatum. Lesions of the rostromedial hypothalamus (medial to the fornix) and of the subthalamus do not interfere with the concentration of either amine in the corresponding striatum. Lesions of the rostrolateral hypothalamus involving the area of the medial forebrain bundle (MFB) are associated with an almost complete depletion of dopamine without any change of the 5-HT concentration in the corresponding striatum. Caudal and laterorostral hypothalamic lesions are associated with a cell loss in the ipsilateral substantia nigra, nucleus parabrachialis pigmentosus, and nucleus linearis. These results confirm previous findings suggesting that the dopamine and 5-HT ascending pathways course in the ventromedial tegmental area of the brainstem from the level of the upper pons to that of the caudal hypothalamus. Moreover they indicate that at the level of the lateral hypothalamus, the MFB contains the dopamine but not the 5-HT fibers ending in the striatum. 5-HT fibers derived from the nucleus linearis and ending in basomedial telencephalic structures apparently travel within the MFB.