Involvement of ACh in settlement process of Balanus amphitrite

The aim of the present study was to investigate the presence and distribution of cholinergic molecules in Balanus amphitrite cyprids and their possible involvement in the settlement adhesion process. Acetylcholinesterase (the lythic enzyme of acetylcholine) activity was detected, for the first time, by biochemical and histoenzymological methods, in the thoracic muscles, gut wall and cement gland. The immunodetection of ChAT-like molecules in the same area and in the neuropil of the central nervous system suggests the presence of a cholinergic innervation, and the involvement of acetylcholine in muscular contraction and cement gland exocytosis. The binding of FITC-conjugate alfa bungarotoxin in the cement gland cells confirms the latter hypothesised role. Furthermore by experimental laboratory tests, and using different logarithmic concentrations of cholinergic antagonists and agonists, the acetylcholine involvement in the barnacle settlement process was also investigated. An increase of acetylcholine available, due to the partial inhibition of AChE activity, produces an increase of percentage of the cyprid settlement. The data presented leads us to hypothesise that acetylcholine can play a neurotransmitter/neuromodulator role in barnacle cyprids and that is involved in the settlement adhesion processes.