Anatomical connections of the nucleus prepositus of the cat

Abstract

The afferent and efferent connections of the nucleus prepositus hypoglossi with brainstem nuclei were studied using anterograde and retrograde axonal transport techniques, and by intracellular recordings and injections of horseradish peroxidase into prepositus hypoglossi neurons. The results of experiments in which horseradish peroxidase was injected into the prepositus hypoglossi suggest that the major inputs to the prepositus hypoglossi arise from the ipsi- and contralateral perihypoglossal nuclei (particularly the prepositus hypoglossi and intercalatus), vestibular nuclei (particularly the medial, inferior, and ventrolateral nuclei), the paramedian medullary and pontine reticular formation, and from the cerebellar cortex (flocculus, paraflocculus, and crus I; the nodulus was not available for study). Regions containing fewer labeled cells included the interstitial n. of Cajal, the rostral interstitial n. of the medial longitudinal fasciculus, the n. of the posterior commissure, the superior colliculus, the n. of the optic tract, the extraocular motor nuclei, the spinal trigeminal n., and the central cervical n. The efferent connections of the prepositus hypoglossi were studied by injecting 3H-leucine into the prepositus hypoglossi, and by following the axons of intracellularly injected prepositus hypoglossi neurons. The results suggest that in addition to the cerebellar cortex, the most important extrinsic targets of prepositus hypoglossi efferents are the vestibular nuclei (particularly the medial, inferior, and ventrolateral nuclei, and the area X), the inferior olive (contralateral dorsal cap of Kooy and ipsilateral subnucleus b of the medial accessory olive), the paramedian medullary and pontine reticular formation, the reticular formation surrounding the parabigeminal n., the contralateral superior colliculus and pretectum, the extraocular motor nuclei (particularly the contralateral abducens nucleus and the ipsilateral medial rectus subdivision of the oculomotor nucleus), the ventral lateral geniculate n., and the central lateral thalamic nucleus. Other areas which were lightly labeled in the autoradiographic experiments were the contralateral spinal trigeminal n., the n. raphe pontis, the Edinger Westphal n., the zona incerta, and the paracentral thalamic n. Many of the efferent connections of the prepositus hypoglossi appear to arise from principal prepositus hypoglossi neurons whose axons collateralize extensively in the brainstem. On the other hand, small prepositus hypoglossi neurons project to the inferior olive, and multidendritic neurons project to the cerebellar flocculus, apparently without collateralizing in the brainstem.(ABSTRACT TRUNCATED AT 400 WORDS)

A Cholinergic Synaptically Triggered Event Participates in the Generation of Persistent Activity Necessary for Eye Fixation

“…The prepositus hypoglossi (PH) nucleus, a neuronal structure involved in the maintenance of eye position after horizontal eye movements, has been suggested to play an important role in the integration of the horizontal gaze (Moschovakis, 1997;DelgadoGarcia, 2000). In support, it has been found that neurons in this nucleus project monosynaptically on extraocular motoneurons located in the abducens and oculomotor nuclei, as well as on many other structures involved in eye movement control (McCrea and Baker, 1985b). Extracellular recordings of PH neuronal activity during spontaneous and vestibularly and visually evoked eye movements in monkeys and cats have shown the presence of cells encoding pure eye position (Ló pez- Barneo et al, 1982;Delgado-García et al, 1989) or related position velocity and velocity position signals (Ló pez- Barneo et al, 1982;DelgadoGarcía et al, 1989;McFarland and Fuchs, 1992).…”

Neural Correlates of Forward and Inverse Models for Eye Movements: Evidence from Three-Dimensional Kinematics

“…Because motoneurons are restricted to innervating the extraocular muscles, the output of the inverse model is also represented in BT cells, which like motoneurons discharge during both saccades and slow eye movements. BT neurons also receive similar neuroanatomical projections as motoneurons (McCrea and Baker, 1985;Belknap and McCrea, 1988), making it possible that they construct a replica of the motoneuron signal. In addition, BT cells project to multiple targets, including motoneurons, the cerebellum, and the thalamus (Langer et al, 1985;McCrea and Baker, 1985).…”

Differential Sensorimotor Processing of Vestibulo-Ocular Signals during Rotation and Translation

“…Specifically, to incorporate motor projections from the PH (Fig. 10 A, dashed line) (McCrea and Baker, 1985;Langer et al, 1986;Escudero and Delgado-Garcia, 1988;Spencer et al, 1989;Escudero et al, 1992;McFarland and Fuchs, 1992), a collateral PH output projection to the EM I cell type was included in the model of Figure 10 B to maintain the appropriate dynamic processing of canal signals in the RVOR. In addition, projections to and from visuomotor areas have been included (for details, see Green andGaliana, 1998, 1999;Green, 2000).…”

“…The dotted line indicates an assumed weak projection from EM I cells to the ipsilateral abducens to account for the disynaptic utriculo-ocular pathways (Uchino et al, 1994(Uchino et al, , 1996. The dashed line indicates an inhibitory projection from PH neurons [i.e., at the output of F( s)] to the contralateral abducens (McCrea and Baker, 1985;Langer et al, 1986;Escudero and Delgado-Garcia, 1988) that may account for the inhibitory polysynaptic utriculoabducens pathway (Uchino et al, 1997). B, Actual model structure based on the schematic in A that was used to examine the predicted responses of the EM C and EM I cell types under different visual-vestibular interaction conditions.…”