Ascending projections from the gigantocellular reticular and dorsal paragigantocellular nuclei of the medulla oblongata in the rat: an anterograde PHA-L tracing study

Abstract

Ascending projections from the gigantocellular reticular (NGc) and dorsal paragigantocellular (DPG) nuclei of the medulla oblongata were examined in the rat by utilizing anterograde axonal transport of Phaseolus vulgaris leucoagglutinin (PHA-L). New observations of fiber connections could be made by the merits of the PHA-L. PHA-L-labeled axon terminals were observed in the dorsal part of the nucleus of the solitary tract, the rostrolateral subnucleus of the interpeduncular nucleus, bed nucleus of the stria terminalis, lateral septal nucleus and subfornical organ, in which no previous authors had found projections from the NGc or DPG. The strongest projections were observed in the motor nucleus of the trigeminal nerve, lateral and dorsolateral subnuclei of the facial nucleus, and prepositus hypoglossal nucleus, which suggested that both NGc and DPG had some relation to the movements around the mouth and to the eyeball movements. The projections to the dorsal part of the nucleus of the solitary tract and to the subfornical organ from the NGc and DPG are considered to reveal certain roles in cardiovascular regulation. Mainly, the facial nucleus received projections from the NGc, the subfornical organ from caudal NGc, the red nucleus from the DPG, and the rostrolateral subnucleus of the interpeduncular nucleus from the rostral DPG, respectively. The NGc and DPG would have partially different roles with regard to the ascending innervation. The present PHA-L study was partially confirmed using wheat germ agglutinin conjugated to horseradish peroxidase which was injected into the bed nucleus of the stria terminalis and subfornical organ.