Effect of lesions of raphe nuclei on the activity of catecholaminergic and serotonergic neurones in various brain regions of the rat in vivo.

The dorsal raphe nucleus (DRN), the median raphe nucleus (MRN) and the B9 cell groups were lesioned separately. Then, the concentrations of 5-hydroxytryptamine (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), dopamine (DA), 5-hydroxytryptophan (5-HTP) and dopa were measured in various brain regions. The levels of the two latter compounds presumably reflect the activity of serotonergic and catecholaminergic neurones respectively under the experimental conditions. The findings suggest close functional interrelationships between the two types of neurones. Lesions of cell bodies in the DRN cause decreased activity of catecholaminergic neurones in the striatum, the brainstem, the hippocampus, and the hypothalamus. Lesions of the MRN cause increased activity of catecholaminergic mechanisms in the hypothalamus which may be explained by a functional disinhibition after destruction of the MRN. The other brain regions investigated are not affected. Lesions of the B9 cell group elicit increased activity of catecholaminergic neurones in the brainstem and hippocampus.