Abstract
Gypsy moth caterpillars were exposed to an increased rearing temperature of 35?C and diet, supplemented with Cd, a heavy metal pollutant, and tannic acid, a plant secondary metabolite. After 3 days? exposure to stressors, changes in the number, morphometric parameters of L1 neurosecretory neurons (nsn) (sizes of the nsn and their nuclei), and the quantity of neurosecretory material in the cytoplasm of the neurons were estimated. Acute exposure to the high temperature of 35?C induced increases in the number of L1 nsn, their size and the size of their nuclei with prolonged exposure time. After acute exposure to different Cd concentrations, the number of L1 nsn was reduced, their size increased and the size of their nuclei decreased. Together with the enhanced relative density of the cytoplasm, our results point to an intensive synthesis and retention of neurosecretory material in the neurons. The relative density of the neurosecretory material in the cytoplasm increased at the thermal treatment, suggesting intensive synthesis and secretory activity in L1 nsn. Caterpillars reared on an artificial substrate with the addition of high concentrations of tannic acid (TA) showed a decreased number of nsn, increased cell size and decreased size of their nuclei. The reduction in the relative density of the cytoplasm led us to conclude that this treatment induced a high synthetic activity of L1 nsn.
Highlights
Insect hormones, such as Lepidopteran brain neurohormones and allatostatins have dominant roles in stress response mechanisms. (Homberg et al, 1991; Stay and Tobe, 2007)
The effects of acute exposure to Cd on L1 nsn In Fig. 1, L1 nsn in 4th instar gypsy moth caterpillars after a 3-day feeding with various Cd concentrations are presented
The relative density of neurosecretory material present in L1 nsn cytoplasm was enhanced in all Cd-treated groups (Fig. 2D)
Summary
Insect hormones, such as Lepidopteran brain neurohormones and allatostatins have dominant roles in stress response mechanisms. (Homberg et al, 1991; Stay and Tobe, 2007). Insect hormones, such as Lepidopteran brain neurohormones and allatostatins have dominant roles in stress response mechanisms. (Homberg et al, 1991; Stay and Tobe, 2007). Allatostatins are neuropeptides that rapidly and reversibly inhibit the synthesis of juvenile hormones in the corpora allata (secretory and neurochaemal structure). Juvenile hormones (JH) play an important role in all insect life processes – development, physiology, behavior, etc. Allatostatins largely determine the rate at which the corpora allata synthesizes JH (Hoffmann et al, 1999). Acute and chronic exposure of gypsy moth caterpillars to Cd produces toxic effects on their life processes (Ilijin et al, 2010; 2011; 2012; Vlahović et al, 2012; 2013). Cd appears to inhibit ecdysone secretion and interfere with other insect hormones that regulate stress response, development, reproduction, etc. Cd appears to inhibit ecdysone secretion and interfere with other insect hormones that regulate stress response, development, reproduction, etc. (Rodrigez et al, 2007)
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