Mamillary body in the rat: Topography and synaptology of projections from the subicular complex, prefrontal cortex, and midbrain tegmentum

Abstract

The retrograde and anterograde transport of horseradish peroxidase conjugated to wheat germ agglutinin (WGA-HRP) has been used to trace afferent connections of the rat mamillary body (MB) at the light and electron microscopic levels. Injections of WGA-HRP into different parts of the MB resulted in heavy retrograde labeling in the subicular complex, medial prefrontal cortex, and dorsal and ventral tegmental nuclei. Injections of WGA-HRP into each of these brain regions, respectively, resulted in anterograde labeling with specific distributions and characteristic synaptic organizations in the MB. Projections from the rostrodorsal and caudoventral subiculum terminated in a topographically organized laminar fashion in the medial mamillary nucleus bilaterally, whereas afferent projections from the presubiculum and parasubiculum terminated only in the lateral mamillary nucleus. Labeled axon terminals which originated from the subicular complex were characterized by round vesicles and formed asymmetric synaptic junctions with small-diameter dendrites and dendritic spines in the medial and lateral mamillary nuclei. Projections from the prefrontal cortex originated mainly in the infralimbic area and to a lesser degree in the prelimbic and anterior cingulate areas. Injections of tracer into these brain regions gave rise to dense labeling of axon terminals in the medial mamillary nucleus, pars medianus, and in the anterior dorsomedial portion of the pars medialis. The labeled terminals were characterized by round vesicles and formed asymmetric synaptic junctions with small-diameter dendrites and dendritic spines. Projections from the dorsal tegmental nucleus terminated in the ipsilateral lateral mamillary nucleus, whereas afferent projections from the anterior and posterior subnuclei of the ventral tegmental nucleus terminated topographically in the medial mamillary nucleus. The ventral tegmental nucleus, pars anterior projected to the midline region of the medial nucleus and the dorsolateral and ventromedial subdivisions of the pars posterior projected to medial and lateral parts of the medial nucleus, respectively. In contrast to the synaptic morphology of subicular complex and medial prefrontal cortex axon terminals in the MB, labeled axon terminals in the MB which originated from the midbrain tegmentum were characterized by pleomorphic vesicles and formed symmetric synaptic junctions with neuronal somata and proximal dendrites as well as distal dendrites and dendritic spines.(ABSTRACT TRUNCATED AT 400 WORDS)

Firing Properties of Head Direction Cells in the Rat Anterior Thalamic Nucleus: Dependence on Vestibular Input

“…The rat medial vestibular nuclei, which encode horizontal semicircular canal information, project directly to the dorsal tegmental nucleus (Liu et al, 1984). The dorsal tegmental nucleus innervates the lateral mammillary nuclei (Allen and Hopkins, 1989), which in turn send a major projection to the ATN (Shibata, 1992). The present data illustrate the critical involvement of vestibular input in the ATN neural coding of direction.…”

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

“…The loss of rhythmic discharge of MM cells after septal procaine supports the results of partial coherence analysis suggesting that rhythmical, -related MM discharge (but not that of SuM) is driven by descending inputs originating in the hippocampal formation (Kocsis and Vertes, 1994). As noted above, the MM is likely to receive descending input originating in the hippocampus and relayed via the subiculum Cowan, 1975, 1977;Allen and Hopkins, 1989). The MM projects heavily to the anterior thalamus (Veazy et al, 1982) and may be involved in relaying -frequency activity from the septohippocampal system to the anterior nucleus of the thalamus .…”

A Continuous Attractor Network Model Without Recurrent Excitation: Maintenance and Integration in the Head Direction Cell System

“…On the other hand, reciprocal connections between LMN and DTN have been demonstrated experimentally. Anatomical studies suggest that LMN receives ascending inhibitory (GABAergic) afferents from DTN (Shibata, 1987;Allen and Hopkins, 1989;Gonzalo-Ruiz et al, 1992;Wirtshafter and Stratford, 1993) and that, in turn, LMN sends descending excitatory efferents back to DTN Hopkins, 1989, 1990). Finally, electrophysiological data suggest that a large fraction of cells in DTN are selective for angular velocity in either clockwise or counterclockwise directions (Bassett and Taube, 2001b;).…”