Sagittal cerebellar microbands of taurine neurons: Immunocytochemical demonstration by using antibodies against the taurine-synthesizing enzyme cysteine sulfinic acid decarboxylase

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Abstract
Taurine neurons in the cerebellum of rabbit, rat and mouse were localized at the light microscope level by using polyclonal antibodies against cysteine sulfinic acid decarboxylase (CSADCase; EC 4.1.1.29), the enzyme responsible for the conversion of cysteine sulfinic acid to hypotaurine and of cysteic acid to taurine. The indirect peroxidase-antiperoxidase method was used on Vibratome sections and on serial sections of paraffin-embedded tissue. Intensification of CSADCase immunoreactivity was achieved by pretreatment of the animal with L-cysteine or L-cysteic acid i.v. 1-2 h prior to perfusion. A combination of L-cysteic acid and demecolcine, which retards axoplasmic flow, was most effective in maximizing CSADCase immunoreactivity. Although these treatments intensified immunoreactivity in neurons, no more cells were reactive than in untreated controls. L-Glutamic acid did not increase CSADCase immunoreactivity but did increase immunoreactivity with antibodies against L-glutamic acid decarboxylase (GAD; EC 4.1.1.15), the synthetic enzyme for GABA. Specificity was established by negative results obtained with various control incubations including the use of CSADCase antiserum preabsorbed with the antigen. Taurine neurons of the cerebellar cortex are arranged in sagittal microbands, defined by intensely CSADCase-reactive Purkinje neurons and their axons and dendrites, together with stellate, basket and Golgi cells and their processes. In the vermis there is a narrow midline band, flanked laterally by 3 wider bands on either side, each separated from the next by an unreactive zone. Although the zonal borders are sharp, the interzonal areas contain some CSADCase-immunoreactive axons but no cell bodies. The 7 vermal bands are best observed in the anterior lobe. Others exist in the lateral hemispheres. The paraflocculus and flocculus contain numerous intensely immunoreactive neurons, and banding is difficult to discern. Lobule X of the vermis is also heavily endowed with taurine neurons. Numerous large and medium-sized deep cerebellar and vestibular nuclei are also immunoreactive. These observations indicate that cerebellar neurons are chemically heterogeneous but that neurons of similar chemical signature in the cerebellar cortex are organized into sagittal microbands. This corroborates earlier evidence that Purkinje cells containing motilin and those containing both motilin and GABA are also arranged in vermal sagittal microbands. The midline vermal band contains Purkinje neurons with multiple neuroactive substances-taurine, GABA and motilin. It remains to be determined how this chemical zonation in the cerebellar cortex relates to the banded afferent innervation from spinal, vestibular, reticular and olivary sources.