Neurons in the trigeminal sensory nuclei (TSN) were indicated to project simultaneously to the cerebellar paramedian lobule (PML) of both sides by way of axon collaterals in the rabbit. Injections of Fast Blue and Diamidino Yellow made in twelve rabbits into the regions of the left and right PML cortex, respectively, resulted in retrograde double labeling of neurons in the principal trigeminal (Vp) and spinal trigeminal nuclei including subnucleus oralis (Vo), and rostral (Vir) and caudal (Vic) subnucleus interpolaris. Sparse labeling was seen among the root fibers of the facial nerve immediately adjacent to Vp. The data indicated that out of the total population of ipsilateral and contralateral single labeled neurons in TSN subdivisions, double labeled neurons constituted about 11% in Vo, 2% in Vp and Vir, and 1% in Vic. Thus, it seems that out of TSN neurons sending collateral projections to PML of both hemispheres, those in Vo project more frequently than those in Vp, Vir and Vic. The homotopic (corresponding) middle (c and d) PML sublobules receive collateral projections from neurons of all these TSN subdivisions, whereas the caudal (a and b) and rostral (e and f) sublobules seem to be targets of the projection from Vp and Vir. The findings suggest that some TSN neurons may exert simultaneous bilateral modulatory influences upon the regions in various sublobules of both PML.
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In this study, we utilized a double retrograde axonal tracing technique to investigate the possible existence of collateralized axonal projections from the pontine nuclei (PN) to the rostral (rPML) and caudal (cPML) parts of cerebellar paramedian lobule in the rabbit, known to be the forelimb and hindlimb regions, respectively. Following injections of fluorescent tracers Fast Blue (FB) and Diamidino Yellow (DY) within rPML and cPML, respectively, substantial numbers of FB and DY single labeled neurons were found in the dorsolateral, paramedian, lateral and peduncular pontine nuclei bilaterally with a very clearcut contralateral preponderance. No labeling was observed in the ventral pontine nucleus. Extensive areas of overlap of FB or DY labeled neurons indicated that no somatotopical relationship existed in projection from PN to the two functionally different PML target regions. In addition, a small number of double FB + DY labeled neurons was detected in the common areas of FB and DY single labeling in PN. These neurons give rise to pontocerebellar projections to rPML and cPML simultaneously by way of axonal collaterals and thus they may play a role in the coordination of unilateral forelimb and hindlimb movements.
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To study projections of the trigeminal sensory nuclei (TSN) to the rostral parts of the paramedian lobule (PML) and of the uvula of the rabbit cerebellar cortex, the retrograde double fluorescent labeling method was used. Injections of Fast Blue (FB) into PML and Diamidino Yellow (DY) into the uvula, resulted in prominent labeling neurons with FB bilaterally and with DY ipsilaterally, in the principal trigeminal nucleus, subnucleus oralis, and rostral and caudal subnucleus interpolaris. We observed topographical arrangement of neurons in such a fashion that FB labeled cells were localized in the medial and DY labeled cells in the lateral regions of TSN. Apart from this small number of double FB+DY labeled neurons (n=138) were found in the narrow common region of single labeling. This implies that PML and the uvula receive independent trigeminal sensory information from neurons in separate regions of TSN. However, some trigeminal neurons may also exert simultaneous influences upon these hemispheral and vermal components by way of axonal branchings.
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