Retrograde HRP study of neurons in the cervical enlargement projecting to the cerebellum in the cat.

After cerebellar HRP injections in kittens labeled neurons were found in laminae V-VIII in the cervical enlargement. Most of the labeled neurons were localized in two groups, one in laminae V-VI, the other centrally in lamina VII. Labeled neurons were also observed in the medial part of lamina VII of C5 and T1 and a few in lamina VIII. Neurons in the cervical enlargement seem to terminate largely in cerebellar lobules IV-V of the anterior lobe. Some neurons in laminae V-VI terminated in the ipsilateral paramedian lobule. Neurons in laminae V-VI and central lamina VII of C5-T1 had uncrossed axons. Neurons in medial lamina VII of C5, in lamina VIII and neighbouring parts of lamina VII of C6-T1 had crossed axons. The ramifications of proximal dendrites and axons of the labeled neurons are described using the tetramethylbenzidine (TMB) method for HRP histochemistry. The neurons in the various laminae differed in their characteristic morphology. In conclusion, the findings of Matsushita et al. (1979) concerning the localization and axonal course of cerebellar projecting neurons in the cervical enlargement are confirmed. In addition new data concerning the morphology of the labeled neurons are presented.