Fusion of Brain Neurons in Rat Embryos

Abstract

Syncytial interneuronal connections in the sensorimotor cortex and caudate nucleus were studied in 20 rats of 14–22 days of intrauterine development. While the development of glial processes was extremely weak, many neuron bodies and their processes were in direct contact with each other. Contacting membranes formed extended and punctate contacts reminiscent of gap and tight junctions. As a result, intercellular clefts showed varicose-type deformation. Hardly detectable membrane pores were seen around contacts, which increased in size to large perforations. The margins of perforations formed a rounded structure consisting of the fused plasmalemmas of adjacent cells. Areas of paired membranes between perforations were fragmented, increasing the number of residual bodies until the neurons fused completely, forming a neuroplasm common to the contacting cells. These results lead to the conclusion that neuron fusion in the cerebral cortex and brainstem nuclei of vertebrates can occur not only in pathology, but also in normal animals at the intrauterine stage of development.