5-Hydroxytryptamine metabolism in the damselfly, Ischnura graellsii, in relation to sex and larval-adult period

Bioconcentrations, depuration, shift in metabolome and a behavioural response in the nymphs of the dragonfly Aeshna cyanea (Müller, 1764) to environmentally relevant concentrations of methamphetamine

Methamphetamine (MEA) is commonly detected in municipal wastewater. It causes imbalances in the system of neurotransmitters as well as several other adverse effects on human health. The aim of this study was to investigate bioconcentration and depuration rates at an environmentally relevant concentration of 1 µg·L^-1 in Aeshna cyanea nymphs exposed to MEA for six days followed by three days of depuration. The metabolomes of nymphs sampled during exposure and depuration were compared using non-targeted screening. Concurrently, a behavioural experiment was run to evaluate the effect of MEA on movement. Since most samples were below the limits of quantification (LOQs) - MEA was quantified in only four out of the 87 samples and only during the first 24 h of exposure at concentrations at LOQ level - we estimated maximal possible bioconcentration factor (BCF) on 0.63 using the LOQ. An MEA metabolite - amphetamine - was not detected in any sample at levels above their LOQs. From 247 up to 1458 significant down- and up-regulated metabolite signals (p ≤ 0.05) were detected by non-targeted screening during initial times of exposure and depuration. Numbers of significant down- and/or up-regulated signals in metabolomes (p ≤ 0.05) calculated for particular sampling times possibly correlated with the size of the effect on movement recorded at the same times. In the MEA treatment, movement was not significantly greater during exposure (p > 0.05) but was significantly lower during depuration (p < 0.05). This study shows how MEA acts on dragonfly nymphs, an ecologically important group of aquatic insects with a high trophic level.

Melatonin synthesis in the optic lobes and midbrain of the grasshopper Oedipoda caerulescens

The pathways of insect melatonin (MEL) biosynthesis apparently follow the same routes as those identified in vertebrates but information on MEL synthesis variations related with serotonin (5-HT), 5-hydroxy-indole acetic acid (5HIAA), and N-acetylserotonin (NAS) levels, as well as 5-HT N-acetyltransferase (NAT) activity throughout the day, is very limited in the insect nervous system. In the present study, the levels of MEL, metabolites (5-HT, NAS, and 5-HIAA) and enzyme NAT were determined in the optic lobes and the midbrain of the grasshopper Oedipoda caerulescens, in conditions of light and darkness. In both tissues, a different pattern of MEL synthesis was observed over the light/dark cycle. Variations in the levels of 5-HT, NAS and NAT activity related to the synthesis of cerebral MEL follow a pattern very similar to that observed in the pineal of mammals, with a peak of synthesis in the first half of the scotophase. Also, we observed differences in the metabolism of 5-HT between the optic lobes and the midbrain light/dark-dependent.