Localization of motoneurons innervating the tensor tympani muscles: an horseradish peroxidase study in the guinea pig and cat

Motoneurons innervating the tensor tympani muscle were identified in the adult guinea pig and cat by the horseradish peroxidase (HRP) method. After HRP injection into the tensor tympani muscle, HRP-labeled neurons were seen in the regions outside the cytoarchitectonically-defined confines of the trigeminal motor nucleus; in the regions rostral to the rostral pole of the nucleus, as well as in the regions ventral and ventrolateral to the nucleus at the levels of the rostral half (guinea pig) or the rostral two-thirds (cat) of the nucleus. The tensor tympani motoneurons were generally smaller than the masticatory motoneurons.

Localization of masticatory motoneurons in the trigeminal motor nucleus of the guinea pig

The myotopical arrangement of masticatory motoneurons was examined in the guinea pig by the horseradish peroxidase method. The trigeminal motor nucleus was composed of dorsolateral and ventromedial divisions; the former was seen in the whole rostrocaudal extent of the nucleus, while the latter was present at levels of the caudal two thirds of the nucleus. The jaw-closer motoneurons were located in the dorsolateral division, and the jaw-opener motoneurons (mylohyoid and anterior digastric motoneurons) were seen in the ventromedial division.

Direct projections from the extrathalamic forebrain structures to the neocortex in the macaque monkey

Extrathalamic direct projections from the subcortical forebrain structures to the neocortex were examined in the macaque monkey by the horseradish peroxidase method. The enzyme, when injected into discrete regions in the neocortex, labeled cell bodies of extrathalamic forebrain neurons in the basal nucleus of Meynert, nucleus of the diagonal band, medial septal nucleus, hypothalamus, claustrum and dorsolateral part of the basal amygdaloid nucleus. Neurons in the basal nucleus of Meynert, lateral hypothalamus and claustrum appeared to send their axons widely, but not diffusely, to the neocortex.