Evidence of an incerto-hypothalamic dopamine neurone system in the rat.

With the recently introduced glyoxylic acid histochemical fluorescence method, a previously unknown catecholamine-containing fibre system has been revealed in the zona incerta, hypothalamus and the caudal septum. These fibres, designated the incerto-hypothalamic system, have a characteristic, very delicate, finely varicose appearance, and they have a weak fluorescence, indicating an unusually low intra-neuronal amine content. On the basis of their distribution a caudal and a rostral part can be discriminated: the caudal part extends from the area of the dopamine-containing cell bodies in the caudal thalamus, the posterior hypothalamic area and the medial zona incerta (the A11 and A13 cell groups) into the dorsal part of the dorso-medial nucleus and the dorsal and anterior hypothalamic areas; the rostral part extends from the area of the rostral periventricular dopaminergic cell system (the A14 cell group) into the medial preoptic area and the periventricular and suprachiasmatic preoptic nuclei. The system probably extends also into the most caudal portion of the lateral septal nucleus. From a series of lesions and in vitro uptake studies, evidence has been obtained that the incerto-hypothalamic fibres are the projections of short, intradiencephalic dopaminergic neurones whose cell bodies are located in the A11, A13 and A14 cell groups. The projection areas of these neurones signify an involvement of the system in the control of secretion of pituitary hormones.