An ipsilateral olivocerebellar pathway in the normal neonatal rat demonstrated by the retrograde transport of True blue

Neonatal rats, aged less than 24 h, were anaesthetised and 25 nl of 2% True blue was injected into the lateral part of the left cerebellar hemisphere. After 48–60 h, the brains were fixed by perfusion and 30 μm thick frozen sections were prepared of the brainstem and cerebellum. Only animals in which the injection sites were clearly unilateral were studied. In the contralateral inferior olive numerous True blue-labelled neurones were seen. In addition, the ipsilateral olive in all animals contained True blue-labelled neurones. This demonstrates that in these neonatal animals there is an ipsilateral olivocerebellar pathway.