Observations on the brainstem-spinal descending systems of normal and reeler mutant mice by the retrograde HRP method.

Brainstem neurons which project to the lumbar spinal level were identified in both reeler mutant mice and normal controls (Balb/c mice) by the retrograde horseradish peroxidase (HRP) technique. In normal controls after HRP injection into the lumbar cord, retrogradely labelled neurons were observed in (1) the lateral vestibular nucleus, (2) the pontine and medullary reticular formations including the nucleus centralis caudalis pontis, nucleus gigantocellularis, nucleus paragigantocellularis, nucleus raphe magnus et pallidus, and nucleus centralis medullae oblongatae pars ventralis et dorsalis, and (3) the dorsal column nuclei, i.e., the nucleus gracilis and nucleus cuneatus medialis. In reeler mutant mice, labelled neurons were again seen in the nuclei referred to above, and their cellular type and distribution patterns within the corresponding nuclei were similar to those of the normal controls. These observations suggest that (1) the brainstem nuclei of reeler mutant mice which project to the lumbar spinal cord are cytoarchitecturally normal, (2) the reeler genetic locus (rl) does not affect the nonlaminated structures in the brainstem, at least those referred to above, and (3) the motor dysfunctions observed in the reeler, such as action tremor, dystonic posture, and reeling ataxic gait, are not attributable to the brainstem-spinal descending systems.