Catecholaminergic afferents to the cat median eminence as determined by double-labelling methods

The localization of dopaminergic and non-dopaminergic neuronal perikarya sending axons to the median eminence was investigated in the cat by using two colour double-immunostaining techniques. Unconjugated cholera toxin and wheat germ agglutinin were used as retrograde tracers and injected respectively into the median eminence and the neuro-intermediate pituitary of the same animal. As controls, cholera toxin was also injected into the arcuate (infundibular) nucleus or third ventricle. The retrograde labelling of one of the tracers was combined with tyrosine hydroxylase immunohistochemistry as a marker for dopaminergic neurons. The retrograde labelling studies of cholera toxin alone and the double-immunostaining of cholera toxin and wheat germ agglutinin on the same sections revealed that the cat median eminence receives major afferent projections originating in midline hypothalamic nuclear groups such as the anterior periventricular nucleus, the periventricular part of the paraventricular nucleus and the arcuate nucleus; minor afferent projections arise from the anterior hypothalamic area, the rostral part of the medial preoptic area around the organum vasculosum of the lamina terminalis and to a lesser extent from the posterior hypothalamic region. We further determine that the rostral part of the parvocellular arcuate neurons constitutes the main source of dopaminergic afferents to the median eminence in the cat brain.