Physiology and in situ identification of putative aminergic neurotransmitters in the nervous system of Gyrocotyle fimbriata, a parasitic flatworm

The longitudinal nerve cords (LNC) in Gyrocotyle fimbriata do not change their activity in response to catecholamines but are excited by the amino acids glutamate and aspartate at concentrations less than 10(-5)M. This activity can be blocked by application of 2-amino-4-phosphonobutyrate (APB), an aminergic blocking agent. In situ measurements of fluorescent spectra from LNC neurites have a lambdamax at 513.6 nm. Treatment with HCI shifts the peak to 510 nm. Both glutamate and aspartate fluoresce and behave similarly with peak emissions of 512.5 nm before HCI treatment and 511 nm and 509 nm, respectively, after treatment. Dopamine and norepinephrine both fluoresce at 512.2 nm but the peaks shifts to 516.5 and 528, respectively, following acid treatment. These experiments indicate that the fluorescing substance in the neurones is not a known catecholamine and could be an amino acid.