The ascending fiber projections from the principal sensory trigeminal nucleus in the rat

Abstract

Persisting reports of uncrossed secondary trigeminothalamic pathways originating from the principal sensory trigeminal nucleus (PrV) are based mainly on data obtained from surgically induced lesions analyzed by methods other than reduced silver impregnation techniques. After complete stereotaxic or direct surgical lesions of PrV, degenerating fibers proceed ventrally and rostrally from the nucleus and cross the midline in the rostral pons, completing their decussation caudal to nucleus interpeduncularis. These fibers form a large trigeminal lemniscus that ascends through the midbrain dorsomedial to the smaller medial lemniscus. PrV fibers terminate in the posterior thalamic nucleus and throughout the medial two-thirds of the ventrobasal thalamic complex (VBm) contralateral to the side of the lesion. Connections with the ventral part of zona incerta were also found similar to those reported for the medial lemniscus.Another fiber system proceeds dorsad from the parvicellular reticular formation in the PrV region and terminates on cells of the ipsi-and contralateral motor trigeminal nuclei and the adjacent contralateral parvicellular reticular formation. Differential lesions indicate that these "intertrigeminal" commissural connections arise chiefly from the parvicellular reticular formation that lies between PrV and the motor trigeminal nucleus.These experiments, which also included selective lesions of dorsal and rostral portions of PrV, failed to produce any evidence supporting the existence of an uncrossed principal sensory trigeminothalamic pathway in the rat. While selective, ventral zona incerta PrV connections can be demonstrated, no PrV intralaminar projections appear to exist. Initial findings show that comparable fully decussated PrV-VBm connections also exist in the guinea pig but that some ipsilaterally ascending fibers occur in monkeys (Smith, '72). These and other recent data demonstrate that phyletic neural variations exist in the PrV-thalamic projections in various mammalian species.Although many techniques have been used to investigate secondary trigeminal sensory connections in a variety of animal species, differing and sometimes contradictory results have produced controversies concerning the course and sidedness of principal sensory nuclear projections in various species (Wallenberg, 1896, '05; von Economo, '11; Papez and Rundles, '37; Russell, '54; Carpenter, '57; Torvik, '57; Emmers, '65; '66; Karamanlidis and Voogd, '70; Mizuno, '70 neurophysiological activities have sometimes been inconclusive, and some authors disagree as to the course of secondary trigeminal fiber projections in the same species. In the cat, for example, a dorsal ipsilateral ascending component, in addition to the ventral contralateral lemniscal pathway, has been both reported and later denied (Russell, '54 '71). Viewed collectively these reports suggest that some species differences might exist and that interspeies generalizations should therefore be approached with caution.The aim of this investigation was t...

Modeling early cortical serotonergic deficits in autism

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Bilateral Integration of Whisker Information in the Primary Somatosensory Cortex of Rats

“…Because the whisker-to-barrel pathway is completely crossed subcortically (Waite, 1969;Smith, 1973;Erzurumlu and K illackey, 1980), bilateral whisker stimulation can be used to explore spatiotemporal aspects of interaction between these initially separate streams of input to the SI (Fig. 1 A).…”

Invited Review Anatomical loops and their electrical dynamics in relation to whisking by rat

“…All connections terminate in the intermediate and deep layers, and tend to occur in the lateral and rostral aspects of the colliculus (Huerta et al, 1983 Miyashita et al, 1994;Miyashita and Shigemi, 1995). cerebellum ) The trigeminal nuclei provide vibrissa sensory input to the cerebellum via two paths: interpolaris and caudalis project via the inferior olive climbing fibers (Huerta et al, 1983;Jacquin et al, 1989) and principalis, interpolaris and caudalis project via pontine mossy fibers (Smith, 1973;Watson and Switzer, 1978;Huerta et al, 1983;Swenson et al, 1984;Steindler, 1985;Mantle-St. John and Tracey, 1987). Projections from the trigeminal nuclei to the inferior olive overlap those from the olive to the cerebellum (Huerta et al, 1983); the target areas in the cerebellum include crura I and II (Watson and Switzer, 1978;Huerta et al, 1983) and the paramedian lobule and uvula (Watson and Switzer, 1978), all areas with facial receptive fields.…”