gamma-Aminobutyric acid (GABA) and other amino acids in tissues of the tick, Amblyomma hebraeum (Acari: Ixodidae) throughout the feeding and reproductive periods

We assayed a variety of tick (Amblyomma hebraeum Koch; Acari, Ixodidae) tissues for a number of amino acids throughout the feeding and early reproductive periods. Our HPLC assay could detect as little as 2-5 pmol per sample of the following: GABA, glycine, serine, glutamine, alanine, taurine, glutamate and aspartate. All of these amino acids could be detected in the salivary gland, synganglion (= total CNS in acarines), haemolymph, Gene's organ, seminal receptacle and ovary. GABA reached high levels in the salivary gland of freshly engorged ticks (685 nmol g(-1)) and in the synganglion it exceeded 1000 nmol g(-1) throughout most of the feeding cycle and the first week post-engorgement. GABA also reached a peak titre in the haemolymph of 40 nmol ml(-1). Taurine levels peaked at 1065 nmol g(-1) in the salivary gland from large partially fed ticks. Glutamate and aspartate were likewise found in the salivary gland and synganglion at high concentrations. For most of the amino acids there is insufficient information to correlate these titres (and fluctuations of titres) to neuromodulatory functions. It is possible, however, that the high GABA titre in the salivary gland of engorged ticks is correlated with an augmented level of fluid secretion.