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  • Title: Corticospinal collaterals to medullary cardiovascular nuclei in the rat: an anterograde and a retrograde double-labeling study.
    Author: Ba-M'Hamed S, Roy JC, Bennis M, Poulain P, Sequeira H.
    Journal: J Hirnforsch; 1996; 37(3):367-75. PubMed ID: 8872559.
    Abstract:
    There is little evidence allowing the hypothesis of the existence of direct pathways from the sensorimotor cortex (SMC) to main cardiovascular medullary nuclei: the dorsal motor nucleus of the vagus (DMV), the nucleus of the solitary tract (NTS) and the rostral ventrolateral medulla (RVLM). The purpose of this study was to identify in the rat direct SMC-NTS/DMV and-RVLM projections descending through the pyramidal tract (PT) and corticospinal neurones projecting to spinal somatic centers and sending collaterals to the NTS/DMV and the RVLM. The first group of animals (N = 15) received injections of anterograde tracers into the SMC: wheat germ agglutinin conjugated to horseradish peroxydase (WGA-HRP) or rhodamine-conjugated dextran (DR). In the second group (n = 35), retrograde tracers were injected: fluorogold (FG) into the NTS/DMV or into the RVLM and DR into the lateral thoracic cord (Th2-Th4). Anterograde transport of WGA-HRP and DR allowed corticofugal fibers to be followed inside the PT ipsilaterally to the site of cortical injection and showed bilateral labeled projections to the NTS/DMV and RVLM. After retrograde transport, bilateral FG or DR labeled cells were distributed in the SMC, mainly in the medial (AGm) and lateral (AGl) agranular cortex. After spinal and bulbar injections, double-labeled cells were distributed in same cortical areas. After injections in RVLM, 49% of labeled cells showed a double-labeling in the frontal cortex (rostral AGm and premotor cortex) while only 24% were observed in the posterior SMC (caudal AGl). On the contrary, when injections were done in NTS/DMV, double-labeled neurons were respectively of 11% in the frontal cortex and 4% in the posterior SMC. In the present work it was shown that the SMC sent direct projections to bulbar cardiovascular nuclei by means of fibers descending through the PT and corticospinal collaterals. The hypothesis which may be drawn from this study is that cortical motor areas probably program cardiovascular adjustments, preparatory or concomitant to the control of striate muscles.
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