Retrograde double‐labeling study of the marnmillothalamic and the mammillotegmental projections in the rat

Abstract

Collateral axonal branching from the medial or lateral mammillary nuclei to the anterior thalamus, Gudden's tegmental nuclei, the nucleus reticularis tegmenti pontis, and the medial pontine nucleus was studied using the fluores- cent retrograde double-labeling method. One day after injection of Fast Blue into the anterior thalamic nuclei or Gudden's tegmental nuclei, Nuclear Yel- low was injected into Gudden's tegmental nuclei or the nucleus reticularis teg- menti pontis and the medial pontine nucleus. Following 1day survival, single- and double-labeled neurons were examined in the mammillary nuclei. The lateral mammillary nucleus contains neurons whose collateral fibers project to both the dorsal tegmental nucleus of Gudden and the ipsilateral or contralateral anterodorsal thalamic nucleus, to both the medial pontine nucleus and the anterodorsal thalamic nucleus, and to both the dorsal tegmen- tal nucleus of Gudden and the medial pontine nucleus. The pars medianus and pars medialis of the medial mammillary nucleus contain neurons whose collat- eral fibers project to both the anteromedial thalamic nucleus and the ventral tegmental nucleus of Gudden, to both the anteromedial thalamic nucleus and the medial part of the nucleus reticularis tegmenti pontis, and to both the ven- tral tegmental nucleus of Gudden and the medial part of the nucleus reticu- laris tegmenti pontis. The dorsal half of the pars posterior of the medial mam- millary nucleus contains a few neurons whose collateral fibers project to both the anteromedial thalamic nucleus and the rostral part of the ventral tegmen- tal nucleus of Gudden, and to both the caudal part of the anteroventral thal- amic nucleus and the rostral part of the ventral tegmental nucleus of Gudden, while the pars lateralis of the medial mammillary nucleus contains no double- labeled neurons and projects only to the anteroventral thalamic nucleus.