The organization of the bulbar fibre connections to the trigeminal, facial and hypoglossal motor nuclei. II. An autoradiographic tracing study in cat.

In 34 cats 3H-leucine was injected in the pontine and medullary tegmentum. The location of the labelled neurons and the distribution of the labelled fibres and terminals were studied autoradiographically. The findings indicate that the neurons in the bulbar lateral tegmental field (Berman, 1968) represent the main source of the propriobulbar projections to the hypoglossal, facial and motor V nuclei, while those in the medial tegmental field distribute their fibres mainly to the spinal cord. The neurons in the lateral part of the lateral tegmental field give rise to ascending and descending fibres which compose the lateral propriobulbar system, and distribute fibres mainly to ipsilateral bulbar motor nuclei. The neurons in the medial part of the lateral tegmental field compose the medial propriobulbar system, which is organized bilaterally and tends to distribute fibres to the motor nuclei bilaterally. The various neuronal cell groups which project through the medial propriobulbar system to the different motor nuclei bilaterally show relatively less spatial segregation than those which project through the lateral system to these motor nuclei.