Effects of unilateral climbing fibre deafferentation on cytochrome oxidase activity in the developing rat cerebellum

Abstract

In a previous study, we found a relationship between climbing fibre synaptogenesis and cytochrome oxidase activity in Purkinje cells during normal development of the rat cerebellum. To determine whether removal of a major depolarizing afferent would alter the level of cytochrome oxidase activity in a post-synaptic neuron, climbing fibre input to Purkinje cells in the right hemicerebellum was interrupted by unilateral pedunculotomy in postnatal day 1 rat pups. After survival to postnatal day 5 (P5) or postnatal day 10 (P10), the cytochrome oxidase reactivity of mitochondria, packing density of mitochondria and perikaryal area of Purkinje cell somata were quantified at the electron microscopic level and compared with the same parameters in both sham-operated animals and normal controls. We found that the areal and numerical densities of darkly reactive mitochondria were lower in deafferented cells than those in the sham-operated animals. Cells of sham-operated animals, however, had higher densities of darkly reactive mitochondria than those in normal animals of the same age group, indicating that cell shrinkage or retarded growth had an effect on the levels of cytochrome oxidase activity in the operated animals. In addition, both operated groups had higher numerical densities of mitochondria than cells of normal animals, reflecting the decreased cell size of the sham and deafferented groups. From these data, we concluded that neonatal destruction of climbing fibres leads to lower levels of cytochrome oxidase activity in Purkinje cell somata that survived to both P5 and P10. The data from the P5 animals was more striking than that from P10, perhaps reflecting the increased number of synaptic interactions of Purkinje cells at P10. We also concluded that destruction of excitatory input did not lead to changes in the total area or number of mitochondria in a post-synaptic neuron, indicating that there was a conversion from darkly to lightly reactive mitochondria in the partially deafferented neurons; however, this may also reflect the smaller cell size of the deafferented group. Thus, our results further substantiate the close relationship between the levels of cytochrome oxidase activity in Purkinje cell somata and the type of input that they receive or fail to receive.