Afferent projections to the mammillary complex of the rat, with special reference to those from surrounding hypothalamic regions

Abstract

To better understand the functional organization of the mammillary nuclei, we investigated the afferents to this nuclear complex in the rat with iontophoretically injected wheat germ agglutinin conjugated to horseradish peroxidase. Particular attention was paid to tracing local hypothalamic afferents to these nuclei. Injections into the medial mammillary nucleus (MMN) revealed strong projections from the subicular region, and weaker projections from the prefrontal cortex, medial septum, and the nucleus of the diagonal band of Broca. Other descending subcortical projections to the MMN arise from the anterior and the lateral hypothalamic area, the medial preoptic area, and the bed nucleus of the stria terminalis. Ascending afferents to the MMN were found to originate in the raphe and various tegmental nuclei. Following all injections into the MMN, labelled neurons were found in nuclei surrounding the mammillary body. The lateral and posterior subdivisions of the tuberomammillary nucleus projected mainly to the pars medianus and pars medialis of the MMN. The dorsal and ventral premammillary nuclei projected to the pars lateralis of the MMN. The supramammillary nucleus at rostral level had a small projection to the pars medialis and lateralis of the MMN. However, the most obvious projection from this nucleus was to the pars posterior of the MMN, chiefly from the lateral part of the caudal supramammillary nucleus. Injections into the lateral mammillary nucleus revealed inputs from the presubiculum, parasubiculum, septal region, dorsal tegmental nucleus, dorsal raphe nucleus, and periaqueductal gray. In addition, the lateral mammillary nucleus was found to receive a moderate projection from the medial part of the supramammillary nucleus and stronger projections from the lateral part of the caudal supramammillary nucleus. A very light projection was also seen from the lateral and posterior subdivisions of the tuberomammillary nucleus. These findings add to our knowledge of the extensive and complex connectivity of the mammillary nuclei. In particular, the local connections we have demonstrated with the supramammillary and tuberomammillary nuclei indicate the existence of significant local circuits as well as circuits involving more distant brain regions such as the septal nuclei, subiculum, prefrontal cortex, and brain stem tegmentum.

Projections from bed nuclei of the stria terminalis, anteromedial area: Cerebral hemisphere integration of neuroendocrine, autonomic, and behavioral aspects of energy balance

“…A projection to the arcuate nucleus was reported by Zaborsky (1982). (3) We confirmed previous retrograde tracer reports of BSTam projections to the medial preoptic nucleus (Simerly and Swanson, 1986), dorsomedial hypothalamic nucleus (Thompson and Swanson, 1998), "perifornical region" of the lateral hypothalamic area at tuberal levels (Allen and Cechetto, 1993), and lateral supramammillary nucleus (Gonzalo-Ruiz et al, 1992). (4) Retrograde labeling in the BSTam region has been reported after thalamic injections involving the paraventricular nucleus and the adjacent medial part of the mediodorsal nucleus (Groenewegen and Russchen, 1984;Groenewegen, 1988;Chen and Su, 1990) and lateral habenula (Li et al, 1993).…”

Mechanisms of distribution of mouse β-galactosidase in the adult GM1-gangliosidosis brain

“…This nucleus receives afferents from and sends projections to the subicular region of the hippocampal formation that travels along the postcommissural fornix. 25,26 Although most in vivo studies to date have indicated that lysosomal enzymes are retrogradely transported in axons, 12,13,27 our data strongly suggests that anterograde transport of bgal is an important component of axonal distribution of this enzyme in the adult GM1-gangliosidosis brain. This notion is supported by a recent study showing identical frequency of anterograde and retrograde movement of GFP-labeled a-L-iduronidase in neurites of primary rat neurons.…”

Evidence for Differential Control of Posterior Hypothalamic, Supramammillary, and Medial Mammillary Theta-Related Cellular Discharge by Ascending and Descending Pathways

“…It is also possible that the MM (in receipt of descending influences from the septo-hippocampal system, see below) mediates activity in PH and SuM. MM has been shown to project to surrounding hypothalamic regions including SuM and PH (Gonzalo-Ruiz et al, 1991). Clearly, more work is needed to distinguish between these possibilities.…”