Cytoplasmic syncytial connections between neuron bodies in the CNS of adult animals.

Studies of neurons in the dentate gyrus and hippocampal fields CA1 and CA2 and cerebellar granule cells were performed to test the hypothesis that there are syncytial connections between the bodies of neurons in adult higher vertebrates. Electron microscopic investigations showed that these cells were densely packed and had incomplete glial coatings. The outer cell membranes of these cells were found to be in contact, and membrane contacts in the form of tight junctions and gap junctions were seen. These areas showed membrane perforation and the establishment of syncytial connections between neurons, with all the expected ultrastructural characteristics. These connections could form between several contacting neurons, resulting in a unified functional cell cluster. These studies support the hypothesis that cytoplasmic syncytial interneuronal connections, along with synaptic and contact-type electrical connections, form not only in tissue cultures and the autonomic nervous system during early postnatal ontogenesis, but also in the CNS in adult vertebrates.