Adjustment of L1 neurosecretory neuron activity in response to different stressors in gypsy moth caterpillars

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.