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

• Published in: Journal of comparative neurology (1911) 2021-07, Vol.529 (10), p.2706-2726, Article cne.25119
• Main Authors: Mehlman, Max L., Marcroft, Jennifer L., Taube, Jeffrey S.
• Format: Article
• Language: English
• Subjects: abducens nucleus; Animals; Brain - cytology; Brain architecture; Brain stem; Cerebral hemispheres; Cerebrospinal fluid; Dorsal raphe nucleus; Dorsal tegmental nucleus; Female; head direction cell; Information processing; navigation; Navigation behavior; Neural networks; Neural Pathways - cytology; Neuroanatomical Tract-Tracing Techniques; Neurons; Neurons - cytology; Raphe nuclei; Rats; Rats, Long-Evans; spatial orientation; Vestibular nuclei; Vestibular system
• ISSN: 0021-9967; 1096-9861
• DOI: 10.1002/cne.25119

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. Retrograde tracers were utilized to examine projections to the dorsal tegmental nucleus (DTN), a critical component of the head direction cell circuitry, and the abducens nucleus, an oculomotor structure. We found that the medial vestibular nucleus contains individual neurons that project to both the DTN and abducens nucleus. In contrast, neurons in the nucleus prepositus hypoglossi project to either the DTN or abducens nucleus, but rarely to both structures simultaneously. Additionally, we describe interhemispheric connections between the left and right DTN, and projections from the supragenual nucleus, interpeduncular nucleus, and retrosplenial cortex to the DTN.