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BACKGROUNDANDAIMS: The locus coeruleus complex (LCx), subdivided into nucleus coeruleus proper (LC) and subcoeruleus (LCα) is the major noradrenergic nucleus of the brain. Only a few data concern LCx-cerebellar projection. The aim of study was to identify LCx neurons projecting to the caudal vermis and determine their immunohistochemical characteristics. METHODS: The retrograde axonal transport method of fluorescent tracers Fast Blue (FB) and Diamidino Yellow injected respectively into lobules VIII and IX was used. In addition, double labeling immunofluorescence was applied to investigate the expression and coexistence of dopamine-β-hydroxylase (DBH) and choline acetyltransferase as well as neuropeptides including neuropeptide Y (NPY), somatostatin (SOM), leu-enkephalin (LENK) and substance P in LCx-cerebellar projecting neurons. RESULTS: It was shown that only lobules VIII was supplied by afferents from LCx. The FB-labeled neurons were distributed bilaterally with ipsilateral predominance in both LC and LCα, and were much more frequent in LC. They occupied the lateral region of LC and dorsolateral region of LCα. These neurons were the most numerous in the caudal part of LC, but in LCα they clustered in its rostral part. Nearly all FB-labeled neurons displayed immunoreactivity to DBH and only the single cells stained simultaneously for DBH and SOM, and for DBH and NPY. However, the FB-labeled perikarya did not contain immunoreactivities to the remaining substances investigated. Moreover, some FB- or FB/DBH-positive somata were closely apposed by SOM-, NPY- or LENK-immunoreactive fibers. CONCLUSIONS: This study has provided new data on the distribution of neurons projecting from LCx to the lobule VIII, and has revealed that they are noradrenergic (and non-cholinergic) in nature and that their activity can be modulated by some neuropeptides. The findings seem to be important considering the role of the lobule VIII in innervation of axial and proximal forelimb muscles.