Cerebellar and spinal projections of the coeruleus complex in the duck: A fluorescent retrograde double-labeling study

Abstract

The double fluorescent retrograde tracing technique was used to identify, within the coeruleus complex (Co complex) of the duck, the nerve cells projecting to the cerebellar cortex and to the spinal cord. This technique was also used to investigate the possibility that the cerebellar and spinal projections of the Co complex are collaterals of the same axons.In the same animal, nuclear Diamidino yellow dihydrochloride (DY) fluorescent tracer was placed into the cerebellar cortex of folia V-VII, and cytoplasmic fluorescent Fast blue (FB) dye was injected into C 3 -C 4 spinal cord segments.FB labeled multipolar somata and DY fluorescent nuclei were intermingled within the dorsal caudal region of the locus coeruleus (LCo) and within the dorsal division of the nucleus subcoeruleus (dSCo). Moreover, in the LCo, a low proportion of double-labeled neurons (about 3-4% of labelings) was evidenced among single-labeled neurons. In the ventral division of the nucleus subcoeruleus (vSCo), occasional DY labeled nuclei were found, whereas FB-labeled cells were frequently present.The present findings reveal the location of the coeruleocerebellar and coeruleospinal projecting neurons within the Co complex of the duck. They are intermingled in the caudal portion of the LCo and along the rostrocaudal extent of the subjacent dSco. The LCo and the dSCo are the major source of the projections to the folia V-VII, whereas the vSCo contributes very slightly to the innervation of the cerebellar injected areas. Moreover, the doublelabeling study demonstrates that in the duck a low percentage of neurons within the ventrolateral portion of the caudal region of the LCo projects both to the cerebellar cortex of folia V-VII and to C 3 -C 4 spinal cord segments via collaterals. Therefore, these neurons simultaneously influence the cerebellar cortex and spinal cord. The possibility that the projections studied are noradrenergic and that they play a role in feeding is discussed. Anat. Rec. 251:392-397, 1998. 1998 Key words: locus coeruleus; nucleus subcoeruleus; coeruleocerebellar fibers; coeruleospinal fibers; birds; fluorescent tracersIn mammals, neurons of the locus coeruleus (LCo) and nucleus subcoeruleus (SCo) (ϭ coeruleus (Co) complex) give rise to noradrenergic axons which project to the spinal cord, the cerebral and cerebellar cortices, subcortical telencephalic structures, the diencephalon, the midbrain, and various brainstem nuclei (Olson and Fuxe, 1972;Chu and

Locus Coeruleus in Non-Mammalian Vertebrates

“…In all the vertebrates, the LC substantially projects to the spinal cord [ 20 , 30 , 37 , 45 , 46 , 47 ]. In mammals, LC projections inhibit sensory neurons in the dorsal horn [ 52 , 53 ] and activate motor neurons in the ventral horn by acting on different types of NE receptors [ 2 , 39 , 44 , 54 ].…”

“…The above studies show conserved projections of the LC among vertebrates. However, these projections have been mapped at the populational level by anterograde/retrograde dye tracing [ 32 , 37 , 41 , 44 , 45 , 59 , 60 , 61 ], or immunostaining [ 13 , 62 , 63 , 64 ]. Next, a single-cell level wiring diagram will be important.…”

“…In amphibians and reptiles, LC axons project to TEC, DCm, Hyp, SN, OT, C, SC [ 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 ]. In birds, LC axons project to TEC, W, NCM, Th, SN, OT, C, SC [ 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 ]. In mammals, LC axons project to NeoC, BF, Hyp, T, Amy, Hipp, SN, VTA, C, SC [ 12 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 ].…”