The Projections of the Lateral Reticular Nucleus to the Deep Cerebellar Nuclei. An Experimental Analysis in the Rat

Abstract

The projections of the lateral reticular nucleus (LRN) to the cerebellar nuclei were studied using the retrograde axonal transport of tetramethyl rhodamine dextran amine (10% solution in 0.01 M neutral phosphate buffer) in 19 adult Wistar strain rats. The cerebellar nuclei receive topographically organized projections from the LRN. The projections are bilateral with an ipsilateral predominance and they are symmetrical. The contralateral component is progressively larger for projections to the nuclei interpositalis, to the nucleus lateralis and to the nucleus medialis. The projections to the various cerebellar nuclei arise from rostrocaudally oriented columns of neurons located in different (partly overlapping) areas of the magnocellular division of the LRN. The nucleus lateralis receives terminals from the dorsomedial area (mainly from the rostral level of the LRN), the nuclei interpositalis from the dorsolateral area (mainly from the central level) and the nucleus medialis from the intermedioventral area (mainly from the caudal level). Afferent fibres from the small subtrigeminal division were traced to the three cerebellar nuclei and from the parvocellular division to the nuclei interpositalis and medialis. The density of the projections from the LRN to the nuclei interpositalis increases progressively with the shift of the terminal field from the rostrolateral to the caudomedial part of the nucleus. The projections to the nucleus lateralis reach principally the dorsolateral hump, whereas only a few neurons project to the other divisions (parvo- and magnocellular). The projections to the various regions of the nucleus medialis show different densities. The highest density was found for projections to the caudal part, in particular to the dorsolateral protuberance and to the ventrolateral area of the middle division. Conversely, a low density of projections was found for the other areas of the middle division. The regions of the magnocellular division of the LRN which project to the nuclei lateralis (and are thus related to the cerebral cortex), interpositalis (related to the red nucleus) and medialis (related to the spinal cord) also receive afferent terminals from the cerebral cortex, the red nucleus and the spinal cord respectively, in addition to various afferent inputs. Thus, each of these areas is apparently concerned with integrating some spinal and supraspinal information in reverberating circuits.

Projection patterns of single mossy fibers originating from the lateral reticular nucleus in the rat cerebellar cortex and nuclei

“…This result is partly consistent with the retrograde labeling study by Parenti et al (1996). They showed that the DN received a projection from the dorsomedial part of the rostral LRN, into which we could not inject BDA, and distinguished the intermedioventral and caudal LRN and dorsolateral part of the middle LRN, with the former projecting to the FN and the latter to the IP.…”

“…Previous anterograde or retrograde studies did not identify whether nuclear projections of LRN neurons are by means of collaterals of mossy fibers or if there are specific nuclear-projecting neurons. Because most of the reconstructed LRN axons originated from the LRNm, we cannot discuss in detail the topographical relationship in LRN-nuclear projection as elaborated in a retrograde labeling study (Parenti et al, 1996). However, it is very clear that the topographical relationship in LRN-nuclear projection was much weaker and vaguer than that in the olivonuclear projection (Van der Want et al, 1989;Sugihara et al, 1996), in which neurons in a subdivision of the IO project to a relatively localized area in one of the cerebellar nuclei.…”

“…Now, it is generally accepted that the LRN projects to the bilateral cerebellar cortices with ipsilateral predominance Ikeda, 1976: Voogd, 1964), and to the ''classical spinal receiving area,'' i.e., the anterior lobe and paramedian lobule, rather than the whole Cx (Clendenin et al, 1974a;. Innervations from the LRN to the DCN (Parenti et al, 1996) and to the vestibular nuclei (VN) are also bilateral with ipsilateral predominance. The cerebellar cortical projection of the LRN shows a multiple longitudinal zonal pattern (Kü nzle, 1975;Chan-Palay et al, 1977) that is roughly related to zebrin-identified Purkinje cell zones .…”

Cerebellum and Cerebellar Connections

“…The lateral reticular nucleus of the rat has been reported to project to almost all lobules of the cerebellum, with an ipsilateral preponderance (Chan- Palay, 1977;Eisenman, 1982;Hrycyshyn et al, 1982;Payne, 1987;Parenti et al, 1996). In the anterograde axonal Chockkan, V., & Hawkes, R. (1994).…”

“…Projection patterns of single mossy fibers originating from the lateral reticular nucleus in the rat cerebellar cortex and nuclei. Journal of Comparative Neurology 411, 97-118 with permission, Copyright 1999, Wiley-Liss, Inc. collateral projections that terminate predominantly ipsilaterally Parenti et al, 1996;Wu et al, 1999).…”