Temperature-induced stress response in Lymantria dispar neurosecretory neurons

Larisa Ilijin,Vesna Perić Mataruga,Milena Vlahović,Dragana Matić,Ivana Kmetič,Marija Mrdaković,Anja Gavrilović

doi:10.3906/biy-1306-75

Larisa Ilijin, Vesna Perić Mataruga + Show 5 more

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https://doi.org/10.3906/biy-1306-75

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Abstract

The release of neurosecretory material from A2 neurosecretory neurons (NSNs) was stimulated in Lymantria dispar fourth instar caterpillars exposed to a temperature of 35 °C for 1, 12, and 24 h, as well as those allowed recover after exposure (12 h at 35 °C, then 12 h at 23 °C). The levels of 2 protein forms with the same molecular mass as bombyxin (3-4 and 4-5 kDa) increased with prolonged exposure to 35 °C. The second band was present only in the groups exposed to this stressor. There was intensified synthetic activity and a low level of secretion in L2' NSNs after exposure to 35 °C. We previously found these NSNs to be immunopositive for prothoracicotropic neurohormone. After this stress, densitometric analysis revealed a decreased amount of the 11-12 kDa isoform (present in the control group). The new isoform (13-15 kDa), expressed after exposure of the insects to a high temperature, increased in amount with prolonged exposure and after recovery at 23 °C. Short-term exposure of caterpillars to high temperatures (35 °C) is a stressor and activates carbohydrate metabolism, while PTTH immunopositive NSNs are secretory-inactive during acute thermal stress regimes.

Highlights

Insects are the largest group of invertebrates and very diverse; only a few neurohormones regulate all of their living processes
We examined the morphometric characteristics of neurosecretory neurons (NSNs), which synthesize the large and small form of PTTH, and differences in the intensity of brain protein bands in the region of their molecular masses in fourth instar caterpillars of gypsy moths exposed to 35 °C for 1, 12, or 24 h, as well as in caterpillars allowed to recover after exposure (12 h at 35 °C and 1 h at 23 °C)
After acute exposure to a temperature of 35 °C for 1, 12, and 24 h, the cytoplasm of A2 NSNs was filled with a considerable amount of large granulated neurosecretory material

Summary

Introduction

Insects are the largest group of invertebrates and very diverse; only a few neurohormones regulate all of their living processes. Neurohormones are synthesized mainly in neurosecretory neurons (NSNs) of the insect brain, and several peripheral neurons make up less than 1% of all neurons in the nervous system. The type of NSNs can be distinguished by greatest diameter, staining affinities, neurosecretory granule size, and protocerebral location (Raab, 1982). In the Lymantria dispar brain the majority of NSNs are located in the medial and dorsolateral part of the protocerebrum. Based on morphological characteristics and protocerebral location, we divided the medial group of NSNs into groups A1, A1’, and A2 and the dorsolateral group into L1, L2, and L2’ (Perić Mataruga et al, 2001; Perić Mataruga and Lazarević, 2003). The synthesis of ecdysone, a major morphogenetic hormone, is regulated by prothoracicotropic

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