An autoradiographic study of the descending connections of the mammillary nuclei of the rat

Abstract

The descending connections of the mammillary nuclei of the rat were studied using the autoradiographic technique to trace anterograde axonal connections. Injections of tritiated leucine or tritiated proline were stereotaxically aimed at either the medial or lateral mammillary nucleus. Label in the medial and lateral mammillary nuclei was rated as either high or low. With a rating of high in both medial and lateral mammillary nuclei (11 animals) three major projection sites were seen: the dorsal tegmental nucleus (DTN), the ventral tegmental nucleus (VTN) and a pontine region which included both the pontine grey and the tegmental reticular nucleus. In the nine animals in which the medial mammillary nucleus was rated high but the lateral mammillary nucleus was rated low, no label was present in DTN, although the other two regions were labeled. The one animal in which the lateral mammillary nucleus was high but the medial was low, had label in all three major projection sites; since fibers destined for the DTN pass through the VTN, it could not be determined whether or not lateral mammillary efferents were in synaptic contact with the VTN. Labeled fibers were present throughout a wide dorsal-ventral extenf of the mesencephalon; these fibers are components of the mammilotegmental system and not part of the mammillary peduncle.

Interruption of the connections of the mammillary bodies protects against generalized pentylenetetrazol seizures in guinea pigs

“…Most neurons in the medial mammillary bodies have bipolar axons that send processes rostrally to the anterior nucleus of the thalamus via the MT and caudally to the dorsal and ventral tegmental nuclei of the brain stem via the mammillotegmental tract (Cowan et al, 1964;Cruce, 1975Cruce, , 1977Van der Kooy et al, 1978;Veazey et al, 1982a, b). Reciprocal connections from the tegmental nuclei to the MB project anteriorly in the MP.…”

Lesions of the Tegmentomammillary Circuit in the Head Direction System Disrupt the Head Direction Signal in the Anterior Thalamus

“…Nonetheless, lesions of the DTN that also affected the mlf would have interrupted the reciprocating pathway from the LMN to DTN (Fig. 1), which is thought to intermingle with the mlf as it enters the DTN ventrally (Cruce, 1977). Frohardt et al (2006) described two cases in which the mlf was deliberately interrupted without damaging the DTN and found the animals to be unimpaired on a DTN-dependent spatial task, suggesting functional independence of the DTN and mlf.…”

Sim1andSim2are required for the correct targeting of mammillary body axons

“…The MBs participate in two pathways that are essential for processing spatial information (reviewed by Vann and Aggleton, 2004). First, the MBs link two brain regions that are crucial for episodic spatial memory, the hippocampus and the anterior thalamus, by receiving afferents from the former via the fornix, and by sending efferents to the latter via the mammillothalamic tract (MTT) (Van der Kooy et al, 1978;Cruce, 1977;Hayakawa and Zyo, 1989;Allen and Hopkins, 1990). Second, the lateral mammillary nucleus contains head direction cells that aid navigation by firing selectively when an animal is facing in a specific direction in the horizontal plane (Vann and Aggleton, 2003).…”

“…The MTEG is one of the earliest tracts to develop in the CNS, appearing at about E10.5 (Easter et al, 1993;Mastick and Easter, 1996). Much later, at about E17.5, each axon of the MTEG generates collateral that will contribute to the formation of the MTT (Van der Kooy et al, 1978;Cruce, 1977;Hayakawa and Zyo, 1989;Allen and Hopkins, 1990). A minority of MB neurons appear to contribute only to the MTT (Hayakawa and Zyo, 1989).…”