Syncytial Cytoplasmic Anastomoses between Neurites in Caudal Mesenteric Ganglion Cells in Adult Cats

Abstract

The fact that most published data on syncytial cytoplasmic anastomoses are based on the autonomic nervous system in the early postnatal period of development, when many nerve fibers are poorly ensheathed by glia or have no glial sheaths at all, has led to the assumption that these anastomoses do not exist in adults because of the significant development of the glia and glial insulation of individual neurites from each other. We tested this assumption using electron microscopic studies of the caudal mesenteric ganglion in adult cats. A high level of glial ensheathing of neurites was observed. However, syncytial pores were seen between contacting neurites lacking glial sheaths in almost every specimen. This is the first report describing axodendritic synapses with perforations in the presynaptic zone outside the synaptic specializations in the autonomic nervous system. It is suggested that although syncytial cytoplasmic connections are seen in adult animals, they do not contradict the neuron theory.

Neuropeptide repertoire and 3D anatomy of the ctenophore nervous system

“…51 Loops created by neurites of the same neuron are known in mammalian brains, although they occur through self-synapses. 52 Fusion of neurite membranes between different neurons has been described in cnidarians 53 and bilaterians 54 and is a common mechanism of giant fiber formation. 55,56 Self-fusion in contrast appears to be relatively rare, predominantly representing a developmental or repair mechanism.…”

The unique neuronal structure and neuropeptide repertoire in the ctenophore Mnemiopsis leidyi shed light on the evolution of animal nervous systems

“…Loops created by neurites of the same neuron are known in mammalian brains however they occur through self-synapses 53 . Fusion of neurite membranes between different neurons has been described in cnidarians 54 and bilaterians 55 and is a common mechanism of giant fibre formation 56,57 . Self-fusion in contrast appears to be relatively rare representing a developmental or repair mechanism 52 .…”