Three cases representative of WGA-HRP injections into the SON are illustrated diagrammatically in Fig. 1. Injections aimed at the SON can be placed into two general groups. In the first group, representing approximately one-third of the injections (6 animals BR773, not shown BR774,778,779,785,789,790), WGA-HRP was largely confined to the SON unilaterally and extended throughout the rostrocaudal length of the nucleus (Fig. 1, BR773; Table 1, BR770, 773). Although the SON was heavily labeled with WGA-HRP the adjoining lateral hypothalamic region dorsal to the SON was also labeled to varying extents. The WGA-HRP staining found in the lateral hypothalamic area, however, often represented the most diffuse portion of the WGA-HRP injection site. The distribution of WGA-HRP-positive neurons resulting from an injection limited mainly to the SON is detailed in Fig. 2 BR770) and Table 1 (BR770 and 773) and is representative of all similar WGA-HRP injections.

In animal BR826, the injection site involved the caudal two-thirds of the SON (Fig. 4, C-E). The rostra1 third of the SON in this animal, however, was largely unstained. The injection site in animal BR8 18 was similar to BR826 except that the FB stainingnot only involved the complete rostrocaudal extent of the SON but had spread dorsal to the SON (Fig. 3) and as well involved the neuropil immediately caudal to the nucleus.

In animal BR826, the injection site involved the caudal two-thirds of the SON (Fig. 4, C-E). The rostra1 third of the SON in this animal, however, was largely unstained. The injection site in animal BR8 18 was similar to BR826 except that the FB stainingnot only involved the complete rostrocaudal extent of the SON but had spread dorsal to the SON (Fig. 3) and as well involved the neuropil immediately caudal to the nucleus.