The crinoid echinoderm Antedon mediterranea autotomises its arms at specialised skeletal joints known as syzygies that occur at regular intervals along the length of each arm. Detachment is achieved through the nervously mediated destabilisation of ligament fibres at a particular syzygy. The aim of this investigation was to identify neurotransmitters that are involved in the autotomy response. Physiological experiments were conducted on isolated preparations of syzygial joints, which can be induced to undergo autotomy-like fracture by applying stimulatory agents such as elevated [K+]o. Initial experiments with elevated [K+]o showed that the autotomy threshold (the minimum amount of stimulation required to provoke autotomy) is lowest in syzygies at the arm base and rises distally. Of a range of neurotransmitter agonists tested, only L-glutamate invoked syzygial destabilisation, as did its analogues L-aspartate, -amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) and kainate, but not L-(+)-2-amino-4-phosphonobutyrate (L-AP4) or N-methyl-D-aspartate (NMDA).
- juxtaligamental cells