Anatomical projections to the dorsal tegmental nucleus and abducens nucleus arise from separate cell populations in the nucleus prepositus hypoglossi, but overlapping cell populations in the medial vestibular nucleus

Abstract

Specialized circuitry in the brain processes spatial information to provide a sense of direction used for navigation. The dorsal tegmental nucleus (DTN) is a core component of this circuitry and utilizes vestibular inputs to generate neural activity encoding the animal's directional heading. Projections arising from the nucleus prepositus hypoglossi (NPH) and the medial vestibular nucleus (MVe) are thought to transmit critical vestibular signals to the DTN and other brain areas, including the abducens nucleus (ABN), a component of eye movement circuitry. Here, we utilized a dual retrograde tracer approach in rats to investigate whether overlapping or distinct populations of neurons project from the NPH or MVe to the DTN and ABN. We report that individual MVe neurons project to both the DTN and ABN. In contrast, we observed individual NPH neurons that project to either the DTN or ABN, but rarely to both structures simultaneously. We also examined labeling patterns in other structures located in the brainstem and posterior cortex and observed (1) complex patterns of interhemispheric connectivity between the left and right DTN, (2) projections from the supragenual nucleus, interpeduncular nucleus, and retrosplenial cortex to the DTN, (3) projections from the lateral superior olive to the ABN, and (4) a unique population of cerebrospinal fluid‐contacting neurons in the dorsal raphe nucleus. Collectively, our experiments provide valuable new information that extends our understanding of the anatomical organization of the brain's spatial processing circuitry.

Angular head velocity cells within brainstem nuclei projecting to the head direction circuit

“…Although the SGN receives direct input from the vestibular nuclei, Nishilke et al (2000) in examining cortical projections to the vestibular nuclei, did not identify the visual cortex as among the areas projecting there. The SGN, however, is reciprocally connected with the DTN (Biazoli et al, 2006) and the DTN receives projections from both the LMN (Hayakawa and Zyo, 1990) and retrosplenial cortex (Mehlman et al, 2021), an area known to play a role in processing landmark information (Clark et al, 2010;Jacob et al, 2017). Therefore, it's possible that visual landmark information is conveyed to the SGN via these feedback pathways.…”

“…Collectively, these studies suggest that the hypothesized attractor network that generates the HD signal is present across the connections between the DTN and LMN. While both the NPH and SGN send projections to the DTN, the SGN  DTN projections are considerably denser than the NPH  DTN projections (Graham et al, 2021;Mehlman et al, 2021), suggesting that the SGN plays a more pivotal role in generating the HD signal.…”