Neuronal death and the development of the pontine nuclei and inferior olive in the chick

Abstract

The cerebellar inputs from the chick's inferior olive and medial pontine nucleus are largely or entirely crossed, and those from the lateral pontine nucleus are partly (probably more than 50%) crossed. The neurons of these cell groups leave their last generation cycle between stages 20–25 (inferior olive); stages 24–29 (medial pontine nucleus); and stages 25–30 (lateral pontine nucleus). During normal development, about one-third of the cells in the inferior olive are lost, presumably through their death, over the 4 days before hatching; this corresponds to the previously demonstrated time of induced cell loss in the olive following cerebellar lesions. There is normally no cell loss, however, in the developing pontine nuclei. The absence of cell death in the pontine nuclei is of special interest, since this is the first report of such an absence for a brain nucleus. It may be due to the great abundance of potential synaptic sites available to the mossy fibres from the pons. All this lends weight to the view that for a neuron to survive during normal development it is more critically important for its axon to make synapses than for its dendrites and soma to receive synapses.