Studies on the effect of lesions of the ventral noradrenergic tract on the antinociceptive action of morphine.

In rats, lesions were placed in the ventral tegmental noradrenergic tract (VT). In some animals lesions also involved the dorsal tegmental noradrenergic tract (DT). Morphine (Mf) analgesia was examined by the tail compression method 8-9 days after lesions. VT lesions produced no changes in Mf activity, while lesions involving VT + DT produced a partial attenuation of the antinoceptive action of Mf. These results suggest that the ascending NA fibres forming the VT are not essential for the antinoceptive effect of Mf.