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Abstract
The efferent and intranuclear connections of the nuclei of the descending trigeminal
tract of the mallard have been studied with lesion methods, and by axonal transport
techniques following injections of tritiated leucine, and of horseradish peroxidase.
The large subnucleus oralis neurons, including those belonging to the nucleus of the
ascending glossopharyngeal tract, have proven to be the sole origin of trigeminocerebellar
connections. The cerebellar afferents are of the mossy fiber type, and terminate predominantly
in lobules V, VI and VII, and possibly, lobule IV. Trigeminocerebellar projections
are ipsilateral except for the vermal area. Subnucleus interpolaris is the main source
of intratrigeminal fibers that terminate in subnucleus oralis and the ventral part
of the main sensory nucleus. These intranuclear connections are bilateral, but the
medium-celled caudal part of subnucleus interpolaris in particular contains the majority
of bi- and/or contralaterally projecting neurons. Additionally, the small cells in
the rostral part of subnucleus interpolaris project ipsilaterally upon the parabrachial
region, and upon the lateral reticular formation. Projections upon the parabrachial
region furthermore emanate bilaterally from layer I of the rostral subnucleus caudalis.
A minor part of layer I neurons sends its axons contralaterally along with those of
the dorsal column nuclei toward the thalamic nucleus dorsolateralis posterior. Associated
with the medial lemniscus, contralateral termination is also present in the lateral
part of the ventral lamella of oliva caudalis, in the marginal zone of nucleus mesencephalicus
lateralis, pars dorsalis and immediately surrounding intercollicular grey and, finally,
in the nucleus intercalatus thalami. Furthermore, a bilaterally descending projection
from subnucleus caudalis upon layers I and II of the rostral cervical cord was observed.
Close to their origin subnucleus caudalis neurons project upon the adjoining caudal
part of the lateral reticular formation.