Proceedings of The Physiological Society

Physiology 2016 (Dublin, Ireland) (2016) Proc Physiol Soc 37, PCB276

Poster Communications

Analysing the effect of body growth on epithelial nerve net structure in Pleurobrachia pileus

A. Courtney1, G. O. Merces1, M. Pickering1

1. School of Medicine, University College Dublin, Dublin 4, Ireland.

Genetic studies suggest that the marine invertebrate, the ctenophore, evolved a neuromuscular system independently to all other animals (1). They therefore represent an exciting opportunity as a new invertebrate model organism to study the evolution of the nervous system and basic principles of neurophysiology. In order to understand how a nervous system functions we must first understand how this system is organised structurally. The challenges associated with mapping network architecture are more tractable in small, simple nerve nets. In addition, Pleurobrachia pileus adult forms have significant variability in body size. This study therefore aims to investigate how nervous system architecture adapts to a changing body size. P. pileus were collected from Irish coastal sites, fixed in 4% paraformaldehyde and classified into large (>0.2g) and small (<0.2g) cohorts. An antibody against tyrosylated α-tubulin was used to visualise the epithelial nerve net. The polygonal shapes were manually traced and the average surface area at the aboral organ and body wall were calculated. The size of the nerve net polygons at the aboral organ was significantly increased in large animals (mean±SEM: 1477±76 µm2, n=5) compared to small animals (966±137 µm2, n=5; p=0.0129, t-test), which suggests the basic architecture of the network is persistent as the body size changes in this region. However, the polygons of the network in the body wall show no difference in size between large (1104±99 µm2, n=4) and small animals (820±140 µm2, n=3; p=0.1652), which suggests that this region of the network responds to increasing size by adding additional structural elements. Our findings suggest a previously unidentified functional distinction of sub regions of the nerve net in P. pileus. Nerve nets are often considered global through conducting pathways in which the same behaviour can be evoked by stimulating any part of the network. Previous electrophysiological studies have shown that this is not the case in ctenophores as ciliary and muscular responses are confined to specific sites and only interact with other pathways indirectly (2). This study provides structural evidence to support these claims. The larger polygonal surface area of the aboral organ (‘rudimentary brain') as the animal increases in size suggests that this structural difference is important in terms of relaying information to and from the body to a defined location. This contrasts a smaller and consistent polygonal size on the body wall as the animal grows which indicates an increase in the number of polygons. This might suggest the development of new sensory receptors through new polygonal formation.

Where applicable, experiments conform with Society ethical requirements