The anatomy of the nervous system of the hydrozoan jellyfish, Polyorchis penicillatus, as revealed by a monoclonal antibody.

Dissociated cells from the margin and tentacles of the hydromedusa Polyorchis penicillatus were centrifuged in a Percoll gradient to remove cnidocytes. The resulting formaldehyde-fixed cells were used to inoculate mice to produce monoclonal antibodies. One of the hybridomas, which secreted antibodies against all neurons, was cloned and designated as mAb 5C6. Immunohistochemical labelling with mAb 5C6 of whole-mount preparations and paraffin sections provided a far more complete picture of the organisation of the hydromedusan nervous system than was previously available when using neuronal labelling techniques that restrict labelling to certain neuronal types. Besides confirming anatomical features described in earlier studies these techniques allowed us to discover a number of new structures and to determine connections that were only suspected. Such findings included:1. The discovery of an arch-like connection between the swimming motor neuron network at the apices of the subumbrellar muscle sheets 2. An orthogonal network connecting each pair of radial nerves in each radius 3. Continuity of a central branch of the radial nerve with the radial innervation of the manubrium 4. Details of the sensory neuronal contribution to the microanatomy of the ocelli and cnidocyte batteries 5. Presence of specialised receptor cells in the margin at the bases of tentacles 6. Neurons apparently innervating the radial muscles of the velum 7. Isolated neurons in the peduncle and gonads