QUANTIFICATION OF L-DOPA AND DOPAMINE IN SQUID INK - IMPLICATIONS FORCHEMORECEPTION

Squid ink is an alarm substance that both confuses predators and alert s conspecifics to the presence of danger. Although the ejection of ink is a powerful visual stimulus, studies also indicate a chemical compo nent to the signal. Squid ink is composed mainly of melanin pigments, but the nonpigmented portion of the ink contains the enzymes and precu rsors of melanin synthesis. Our previous behavioral studies showed tha t squid olfactory organs detect L-dopa, a key chemical in melanogenesi s. Squid olfactory neurons also respond to dopamine, a biogenic amine not previously described in squid ink. We performed HPLC on ink taken from the ink sacs of adult Loligo opalescens. The ink was conjugated w ith orthophthaldialdehyde (OPA) and injected into the HPLC, and amine- containing compounds were detected fluorometrically. Standard curves c onstructed for L-dopa and dopamine allowed quantitation from individua l ink sacs. We found that L-dopa was present in undiluted ink at a mea n concentration of 1.15 mM and was significantly greater than the mean dopamine concentration of 0.19 mM. These values are greater than thos e at which both compounds are effective in behavioral and electrophysi ological experiments. In addition we found that an unidentified antiox idant in the ink may prevent rapid oxidation of L-dopa and dopamine fo llowing dilution in seawater.