Autoradiographic study of descending pathways from the pontine reticular formation and the mesencephalic trigeminal nucleus in the rat

Abstract

Descending projections were studied in autoradiographically prepared material after injections of tritiated leucine in the pontine tegmentum of rats. Injections involving the medial pontine reticular formation resulted not only in labeling commissural fibers, the medial reticulospinal tract, and the dorsal cap of the inferior olive, but also, in two cases, in labeling a cerebellar projection that originated from a region near the midline and clearly dorsal to the nucleus reticularis tegmenti pontis. The labeled fibers passed ventral in the midline to the pontine gray, then laterally through the gray and into the middle cerebellar peduncle to terminate as mossy fibers primarily in the flocculus, lobulus simplex, and Crus I of the ansiform lobule. Injections involving the mesencephalic nucleus of the trigeminal nerve (Vmes), resulted in labeling of Probst's tract, which descends in the dorsolateral reticular formation. Probst's tract gave off extensive terminal branches to the lateral medullary reticular formation and weaker projections to restricted portions of the descending trigeminal nucleus, the solitary nucleus, and the hypoglossal nucleus. In one case, fibers could be traced into the dorsal horn of the upper cervical cord.

Projections from the brain to the spinal cord in the mouse

“…The magnocellular nuclei of the reticular formation have been shown to give rise to major projections to the spinal cord in a wide variety of vertebrate species (Crutcher et al 1978;Kneisley et al 1978;Basbaum and Fields 1979;Zemlan and Pfaff 1979;Goode et al 1980;Hayes and Rustioni 1981;Martin et al 1982;Leong et al 1984;Carlton et al 1985;Oka et al 1986;Sirkin and Feng 1987;Michaloudi et al 1988;Nudo and Masterton 1988;Shen et al 1990;Holstege 1991;Kausz 1991;Masson et al 1991;Hobbelen et al 1992;Kudo et al 1993;Wada et al 1993;Aicher et al 1995;Cruce et al 1999;de Boer-van Huizen and ten Donkelaar 1999;Carretta et al 2001;Sanchez-Camacho et al 2001a, b;Stockx et al 2007;Reed et al 2008). While nomenclatural inconsistencies abound, we consider that the magnocellular reticular nuclei should be taken to include PnO, PnC, PnV, Gi (including GiA, GiV), DPGi, and LPGi.…”

“…The origin of these pathways has been studied in a wide variety of mammals. The best known centers that give origin to these pathways are the cerebral cortex (Miller 1987;Masterton 1988, 1990;Galea and Darian-Smith 1994), the red nucleus (Pompeiano and Brodal 1957;Nyberg-Hansen and Brodal 1964;Carlton et al 1985;Xu and Martin 1989;Kuchler et al 2002), the brainstem reticular formation (Torvik and Brodal 1957;Nyberg-Hansen 1965;Peterson et al 1975;Basbaum and Fields 1979;Nordlander et al 1985;Sirkin and Feng 1987;Cruce et al 1999;Satoda et al 2002), and the vestibular nuclei (Peterson and Coulter 1977;Hayes and Rustioni 1981;Kimmel et al 1982;Leong et al 1984;Nudo and Masterton 1988;Masson et al 1991;Wada et al 1993;Lakke 1997). Apart from these well-known centers of origin of the descending tracts, there are a large number of other nuclei that are labeled in retrograde tracing studies following spinal cord injections.…”

Projections from the oral pontine reticular nucleus to the spinal cord of the mouse

“…Therefore, PnO must have a role in muscle relaxation during REM sleep. PnO has been shown to have spinal projections in many species [6][7][8][9][10][11] and its fiber termination in the spinal cord has also been reported in the rat [12,13] and cat [9,[14][15][16][17]. However, controversies in the projecting pattern also exist.…”

“…In the rat, fibers from PnC were observed in the ipsilateral ventral funiculus especially the medial portion of it and terminated predominantly in laminae 7 to 9 [13]. In addition, it was reported that some contralateral fibers were found in the dorsal part of the lateral funiculus after injections of radioactive leucine into the rostral pontine reticular nucleus.…”

Pacifier Use May Decrease the Risk of SIDS

“…When they descend through the Varolio's bridge as the "stretch of Probst," they cross the dorsolateral bulb at the level of the dorsal nucleus of the vagus nerve, pass into the lateral tegmental field, and terminate in the spinal cord at the level of the caudate trigeminal nucleus up to C1/C3 [23]. Passing through the large neurons of the nucleus Probst, located ventrally to the solitary tract, they reach the hypoglossal nucleus, trigeminal main sensory and caudate nucleus, solitary nucleus, and eventually the supra-trigeminal nucleus [24][25][26]. The nerve cells of the midbrain's RF, in particular those of the DRN and LDT, both directly and through the thalamus, send widespread aspecific projections to the entire cortex and form part of the ascending reticular activator system (ARAS).…”