Abstract
The linear nucleus (Li) was identified in 1978 from its projections to the cerebellum. However, there is no systematic study of its connections with other areas of the central nervous system possibly due to the challenge of injecting retrograde tracers into this nucleus. The present study examines its afferents from some nuclei involved in motor and cardiovascular control with anterograde tracer injections. BDA injections into the central amygdaloid nucleus result in labeled fibers to the ipsilateral Li. Bilateral projections with an ipsilateral dominance were observed after injections in a) jointly the paralemniscal nucleus, the noradrenergic group 7/ Köllike -Fuse nucleus/subcoeruleus nucleus, b) the gigantocellular reticular nucleus, c) and the solitary nucleus/the parvicellular/intermediate reticular nucleus. Retrogradely labeled neurons were observed in Li after BDA injections into all these nuclei except the central amygdaloid and the paralemniscal nuclei. Our results suggest that Li is involved in a variety of physiological functions apart from motor and balance control it may exert via its cerebellar projections.
Highlights
The linear nucleus (Li) is found in the medullary reticular formation surrounding the middle segment of the compact part of the ambiguus nucleus (AmbC) in dorsal, medial and/or lateral aspects
The present study found that hyperpolarization-activated cyclic nucleotide-gated channel 4 (HCN4) was diffusely located throughout the medulla and its expression in Li was more striking compared to the adjacent reticular formation (Fig. 1)
The present study reports that paralemniscal nucleus (PL), Köllike-Fuse nucleus (KF) and Su5, gigantocellular reticular nucleus (Gi), solitary nucleus (Sol) and adjacent parvicellular reticular nucleus (PCRt)/intermediate reticular nucleus (IRt) project to Li
Summary
The linear nucleus (Li) is found in the medullary reticular formation surrounding the middle segment of the compact part of the ambiguus nucleus (AmbC) in dorsal, medial and/or lateral aspects. It resembles an upside down L or a capital pi (Π) in Nissl stained or retrograde tracer labeled sections [37]. This part of the brain contains clusters of nuclei with diverse functions centered on speech, swallowing, cardiovascular and respiratory control and is expected to have different functional inputs from the rest of the brain.
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