The effect of heat stress on the activity of A1 and A2 neurosecretory neurons of Morimus funereus (Coleoptera: Cerambycidae) larvae

Snežana Leković,Vera Nenadović,Jelica Lazarević,Jelisaveta Ivanović

doi:10.14411/eje.2001.002

Abstract

A study on the effect of heat stress on the activity of the medial A1 and A2 neurosecretory neurons (NSN), and the activity of midgut a-amylase and protease was performed on the fifth larval instar of Morimus funereus. Exposure of the larvae to 35Â°C led to a decrease in the activity of both A1 and A2 NSN, the former being more marked than the latter. These neurons responded differently to heat stress in terms of neurosecretory material synthesis and release. The changes in the size of both A1 NSN and their nuclei and protease activity in the larvae exposed to elevated temperature were significantly correlated, which suggests that A1 NSN play a role in the regulation of the activity of this enzyme during heat stress. The significant correlations between the size of A2 NSN and protease activity in the controls, and the size of both A2 NSN and their nuclei and amylase activity in larvae exposed to heat stress, similarly may mean that A2 NSN regulate both digestive enzyme activities depending on environmental temperature.

Highlights

Temperature is one of the most important environ mental factors affecting the performance and ecological distribution of organisms
In the heat stressed larvae there were significant posi tive correlations between the size of both A2 neurosecretory neurons (NSN) and their nuclei, and amylase activity (AA). Such correlations were not recorded in the control group, which showed a significant positive correlation between SPA and the size of A2 NSN (Table 1). This comparative study on the NSN and the activity of the digestive enzymes in xylophagous M. funereus larvae demonstrates that heat stress (35°C) results in changes in both NSN activity and activity of the mesenteric proteases and amylase
Our earlier study showed that heat stress adversely affected the survival and moulting of fifth instar M. funereus larvae (Ivanovic et al, 1992)

Summary

Introduction

Temperature is one of the most important environ mental factors affecting the performance and ecological distribution of organisms. Studies on acclimatization and acclimation in Morimus funereus larvae revealed seasonal changes in the activity of some digestive enzymes (protease and amylase), ther moresistance, haemolymph ion and trehalose concentra tion, qualitative and quantitative free amino acid composition and the level of glycogen in the fat body (Ivanovic, 1969; Ivanovic et al, 1975a; Ivanovic & Jankovic-Hladni, 1991; Jankovic-Hladni et al, 1992). These studies included investigations of the changes in proto cerebral NSN activity based on cytological parameters, and showed an interrelationship between the changes in some NSN of the medial group and in the proteolytic and amylolytic activity in the midgut of the larvae

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