Late emergence of Thy-1 on climbing fibres demonstrates a gradient of maturation from the fissures to the folial convexities in developing rat cerebellum.

In the third week of postnatal life, Thy-1 staining of Purkinje cells starts to decrease, first in the depths of the fissures and then progressively, over the next 10 weeks, up the walls of the fissures to the convexities of the folia. This is accompanied by a far more striking appearance of high levels of Thy-1 on a network of fibres whose distribution strongly suggests they are climbing fibres. They acquire the antigen in the same topographical gradient of maturation, and at the same time, as Purkinje cells lose it. That these are climbing fibres was confirmed by destroying the inferior olive with 3-acetylpyridine, which also eliminated the intense Thy-1 staining in the cerebellum. At a stage (18 days) when only some climbing fibres in the molecular layer are seen to be Thy-1-positive, only a proportion of inferior olivary neurons are Thy-1-positive with intense antigen labelling over the Nissl substance. The possibility that Thy-1 also appears on mossy fibres, and at relatively low levels on parallel fibres, is discussed.