Afferent and efferent connections of the cerebellum of the chondrostean Acipenser baeri: A carbocyanine dye (DiI) tracing study

Abstract

The afferent and efferent connections of the cerebellum of the primitive bony fish Acipenser baeri were studied in fixed brains with a fluorescent lipophylic carbocyanine (DiI). The three regions of the cerebellum (the auricles, valvula, and corpus) showed similar afferents, mostly originated from extensive precerebellar populations of the midbrain tegmentum and from the inferior olive. A pretectal nucleus was also labeled after DiI application to the three regions of the cerebellum. However, DiI application to the pretectal region revealed that the pretectocerebellar projection mainly targeted to the caudal region of the corpus cerebelli. Some precerebellar cells were observed in the torus semicircularis, isthmic central gray, and rhombencephalic reticular formation. Primary fibers of the anterior lateral line nerve and neurons of the octavolateral area also project to the auricle. After DiI application to the auricles, most ascending efferents coursed to the region of the nucleus of the medial longitudinal fascicle and thalamus, mostly contralaterally. Ipsilateral descending fibers were also labeled in the medullary octavolateral area. Application of DiI to the nucleus of the medial longitudinal fascicle revealed three clusters of cerebellar projection neurons located in the granular layers of the auricles, valvula, and corpus cerebelli, mostly contralateral to the application site. These cerebellar projection neurons did not exhibit a number of characteristics of teleost eurydendroid cells (i.e., the cerebellar efferent cells of teleosts), such as the presence of spiny dendrites ascending to the molecular layer. Comparison of the afferent and efferent projections of the sturgeon cerebellum with those reported in teleosts supports the hypothesis that some traits observed in the teleost cerebellar system represent recent evolutionary developments.

Distribution of glycine immunoreactivity in the brain of the Siberian sturgeon (Acipenser baeri): Comparison with γ-aminobutyric acid

“…This nuclear organization is similar to that reported for lampreys (Ronan and Northcutt, 1987;González and Anadón, 1992), but the DON and MON of the paddlefish Polyodon spathula and the Siberian sturgeon exhibit a conspicuous cerebellar crest that receives parallel fibers from granule cells located in the cerebellar auricles (Hofmann et al, 2002;Huesa et al, 2003). No such cerebellar molecular-like structure or cells similar to crest cells are observed in the octavolateral area of lampreys (González and Anadón, 1992;González et al, 1997;Villar-Cerviño et al, 2008a).…”

“…The only Gly-ir fibers observed in the Siberian sturgeon cerebellum were those crossing the intracerebellar commissure between the secondary gustatory/visceral nuclei of both sides, but apparently these Gly-ir fibers do not form part of Figure 8 cerebellar circuits. The absence of afferent Gly-ir fibers contacting cerebellar neurons appears to be consistent with the absence of Gly-ir cells in the precerebellar nuclei of the Siberian sturgeon (paracommissural pretectum, midbrain tegmentum, inferior olive; see Huesa et al, 2003). Studies in other groups of jawed fishes appear to be necessary to understand the early evolution of glycinergic cerebellar circuits (because agnathans lack a true cerebellum).…”

“…The cerebellar nucleus homologue consists of intracerebellar efferent neurons, which is similar to the eurydendroid cell system found in teleosts (Huesa et al, 2003). In mammals, both the cerebellar cortex and the cerebellar nuclei contain glycinergic populations (see Bäurle and Grüsser-Cornehls, 1997;Tanaka and Ezure, 2004;Zeilhofer et al, 2005;Crook et al, 2006), and some Gly-ir cells have also been observed in the cerebellum of the frog Rana temporaria (Reichenberger et al, 1993).…”

“…The Siberian sturgeon cerebellum is well developed and contains the same regions as the teleostean cerebellum (Huesa et al, 2003). The cerebellar nucleus homologue consists of intracerebellar efferent neurons, which is similar to the eurydendroid cell system found in teleosts (Huesa et al, 2003).…”

Integración sensório-motora y plasticidad sináptica en la corteza cerebelar

“…Ellas constituyen el principal sistema de input del circuito cerebelar en virtud de la gran diversidad de informaciones que conducen (Takacs & Metzger, 2002). A su vez, las fi bras trepaderas se originan en el núcleo olivar inferior (Huesa, 2003;Houk et al, 1996;Lang, 2001). La oliva inferior también emite una proyección colateral para los núcleos cerebelares (Ruigrok & Voogd, 2000).…”