Anatomical organization of the limb premotor network in the turtle (Chrysemys picta) revealed by in vitro transport of biocytin and neurobiotin

Abstract

The in vitro turtle brainstem-cerebellum preparation has been a valuable tool in the study of central motor programs. In the present study, we investigate the anatomical organization of the turtle rubrocerebellar limb premotor network and its sensory connections in vitro by combining the rapid anterograde and retrograde transport of neurobiotin and biocytin with the extended viability of the isolated turtle brainstem-cerebellum. These compounds retrogradely labeled soma, dendrites, and axons, and orthogradely labeled axons and, to a lesser extent, terminals. The chelonian red nucleus receives a dense input from the contralateral lateral cerebellar nucleus and projects heavily to the contralateral spinal cord. Rubral axons sparsely innervate the lateral cerebellar nucleus and project heavily to the lateral reticular nucleus. Lateral reticular axons heavily innervate the lateral cerebellar nucleus before terminating in the pars lateralis of the cerebellar cortex as mossy fibers. These prominent, recurrent loops among the lateral cerebellar nucleus, red nucleus, and lateral reticular nucleus constitute the turtle rubrocerebellar limb premotor network. Sensory inputs to the red nucleus originate in the contralateral dorsal column nuclei, the principal trigeminal nucleus, and the spinothalamic system. These sites project bilaterally to the lateral reticular nucleus. The lateral cerebellar nucleus receives a contralateral input from the dorsal column nuclei. The red nucleus projects sparsely to the dorsal column nuclei. The red nucleus also receives an ipsilateral descending projection from the suprapeduncular nucleus, located in the diencephalon, and an ascending input from the rostral rhombencephalic reticular formation. An ipsilateral descending pathway originating in the red nucleus is likely to be the rubro-olivary tract.

Immunohistochemical and hodological characterization of calbindin‐D28k‐containing neurons in the spinal cord of the turtle, Pseudemys scripta elegans

“…Spinal Pathways The distribution of CBir neurons in the spinal cord of the turtle includes areas that possess cells with long ascending projections to supraspinal structures, supporting that CBir neurons might participate in these ascending pathways (Kunzle and Sarrafizadeh and Houk, 1994). This fact has been corroborated with double immunohistochemical and tracing experiments in mammals (Craig et al, 2002;Gamboa-Esteves et al, 2001;Li et al, 2000;Menétrey et al, 1992).…”

“…The spinothalamic projection observed would correspond, at least in part, to the ascending pathway to the so-called rostrolateral perirotundal complex nucleus ventrolateralis and intermediodorsalis (Hoogland, 1981;Kunzle and Woodson, 1982). The projections revealed following injections in the mesencephalic area would include spinal-mesodiencephalic and spinoparabrachial projections, whereas injections in the rhombencephalon would label spinoreticular cells (Kunzle and Sarrafizadeh and Houk, 1994). Notably, in a recent study in the anuran amphibian Xenopus laevis a largely comparable set of ascending pathways arising in CBir neurons has been demonstrated (Morona et al, 2006b).…”

Ascending spinal influences on rubrospinal cells in the cat

“…In the turtle as for the cat, somatic projections to the RNm have been established (Keifer and Houk 1994;Sarrafizadeh and Houk 1994). Similarly, the receptive fields are complex, wide, often bilateral, may include two or more limbs and are composed of excitatory and inhibitory regions.…”

Review : Evolution of the Motor System: Why the Elephant's Trunk Works Like a Human's Hand

“…There is, however, a functional similarity between the pNr and mNr in the aspect of digital movement. Although the first evidence for the rubro-olivary projection was found in quadrupedal reptiles, it was not found in amphibians (46,47). It would be of great interest to search for evidence for differences in the olivary projections of reptiles and amphibians.…”