Tachykinergic afferents to the rat arcuate nucleus. A combined immunohistochemical and retrograde tracing study.

The location of the cells giving rise to the tachykinergic innervation of the rat arcuate nucleus was studied by combining immunohistochemistry and retrograde axonal transport of a protein-gold complex (WGA-ApoHRP-gold). Small volumes (20 nl) of this marker were injected into the arcuate nucleus of the rat. Twenty-four to 30 h later, rats were injected with colchicine. After 24-h survival time, the paraformaldehyde-fixed brains were investigated for silver intensification of the gold particles and for tachykinin immunohistochemistry. Doubly immuno-silver-labeled cells were observed mainly in brainstem structures such as raphe nuclei, central gray pontine, and laterodorsal tegmental nucleus. Intranuclear and intrahypothalamic (ventromedial, dorsomedial, premamillary, and supramamillary) cell bodies were also doubly labeled, principally ipsilateral to the injection site. Minor afferent projections arise from the medial preoptic area. This anatomohistochemical study demonstrates that the arcuate nucleus receives intra- and extrahypothalamic tachykinergic inputs and shows that infundibular neurons undergo convergent tachykinergic influences.