Fine structure of the lateral mammillary projection to the dorsal tegmental nucleus of gudden in the rat

Abstract

The synaptic organization of projections from the lateral mammillary neurons within the dorsal tegmental nucleus of Gudden is studied in the rat with the aid of anterograde transport of horseradish peroxidase conjugated with wheat germ agglutinin (WGA-HRP) and visualized with tetramethylbenzidine. The dorsal tegmental nucleus consists of the pars ventralis (TDV) and the pars dorsalis (TDD). The normal neuropil of the dorsal tegmental nucleus contains three classes of axodendritic terminals, that is, terminals containing round, flat, and pleomorphic vesicles. They make up 44%, 5%, and 51%, respectively, of all axodendritic terminals in the TDV, and 62%, 1%, and 37% in the TDD. Injection of WGA-HRP into the lateral mammillary nucleus permits ultrastructural recognition of many anterograde labeled terminals within both the TDV and TDD. In the TDV, 81% of the labeled terminals contain round synaptic vesicles and make asymmetric synaptic contacts. A few of the labeled terminals contain pleomorphic vesicles and make symmetric synaptic contacts. More than 50% of the labeled terminals contact intermediate dendrites (1-2 microns diameter). In the TDD, almost all labeled terminals are small, contain round vesicles, and make asymmetric synaptic contacts. These terminals mainly contact intermediate as well as distal (less than 1 micron diameter) dendrites. There are only a few labeled terminals with pleomorphic vesicles and no terminals with flat vesicles. The termination pattern of the lateral mammillary neurons in the TDV is similar to that in the TDD. Anterograde labeled axon terminals often contact retrograde labeled dendrites in the TDV. No reciprocal connections are present in the TDD. These results suggest that the TDV and the TDD receive mainly excitatory and a few inhibitory inputs from the lateral mammillary nucleus. The TDV neurons also have direct reciprocal connections with the lateral mammillary neurons.

Lesions of the dorsal tegmental nuclei disrupt control of navigation by distal landmarks in cued, directional, and place variants of the Morris water task.

“…The DTN sends a strong projection to the lateral mammillary nuclei, which reciprocates this input by sending large projections back to the DTN (Gonzalo-Ruiz, Sanz-Anquela, & Spencer, 1993; Hayakawa & Zyo, 1990; Wirtshafter & Stratford, 1993). The DTN receives additional input from the habenula, interpeduncular nuclei, and nucleus prepositus hypoglossi (reviewed in Taube (2007)), and lesion studies including the habenula (Lecourtier, Neijt, & Kelly, 2004) or interpeduncular nuclei (Clark & Taube, 2009) have reported impairments in hidden platform variants of the Morris water task, suggesting that damage to these areas also impairs landmark navigation.…”

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

“…Chronic recording electrode arrays with microdrives were built using (Hayakawa and Zyo, 1990). The DTN receives prominent projections from both the nucleus prepositus hypoglossi, ipsilaterally, and the supragenual nucleus, contralaterally (shown on left only).…”

Neural Correlates for Angular Head Velocity in the Rat Dorsal Tegmental Nucleus

“…Which cell types DTN AHV cells contact within the LMN is not known. However, because of the prominent reciprocal connections between the LMN and DTN (Hayakawa and Zyo, 1990) and between the DTN and nPH (Liu et al, 1984), it is possible that the neural integration of AHV to angular head displacement arises from the interaction between these three nuclei. The DTN is, in fact, characterized by reciprocal patterns of connections with the LMN, nPH, interpeduncular nucleus (Groenewegen et al, 1986), and medial habenular nucleus (Groenewegen and Wouterlood, 1988).…”