THE RESPONSE OF MEDIAL NEUROSECRETORY NEURONS TO TEMPERATURE STRESS

The central nervous system and neurohormones are an important component of the process of adaptation to a changing environment (Ivan o vi c and Jank ovic-Hladni , 1991). Activity of neurosecretory neurons determines the content of ncurohormones which control the dynamics of metabolism and metamorphosis (l v an o v i c and Ja n kov ic i Hl a d n i , 1991). Neuropeptides synthesized in the medial part of the insect protocerebrum include tropic factors regulating the synthesis of ecdysteroids (prothoracicotropic factors PTTH, K a w aka m i et al., 1990) and juvenile hormones (allatotropic factors -ATTH, Bogus and Scheller, 1994), as well as a number ofneuropeptides modifying the rate and direction of metabolism (Raabe, 1982).


THE RESPONSE OF MEDIAL NEUROSECRETORY NEURONS TO TEMPERATURE STRESS IN MORIMUS FUNEREUS
The central nervous system and neurohormones are an important component of the process of adaptation to a changing environment (Ivan o vi c and Jank o vic -Hl adni , 1991).Activity of neurosecretory neurons determines the content of ncurohormones which control the dynamics of metabolism and metamorphosis (l v an o v i c and Ja n kov ic i Hl a d n i , 1991).Neuropeptides synthesized in the medial part of the insect protocerebrum include tropic factors regulating the synthesis of ecdysteroids (prothoracicotropic factors -PTTH, K a w aka m i et al., 1990) and juvenile hormones (allatotropic factors -ATTH, Bogus and Scheller, 1994), as well as a number ofneuropeptides modifying the rate and direction of metabolism (Raabe, 1982).
The cerarnbycid beetle Morimus funereus inhabits deciduous and coniferous trees in the forests of Southeastern Europe.As such, it is exposed to significant seasonal changes in temperature during development.The purpose of the present work was to examine the response of A, neurosecretory neurons to temperature stress in A1. funereus larvae.
The effects of different constant temperatures (23°C and 8°C) on activity of medial neurosecretory cells were investigated in Morimus funereus larvae (body weight 500-700mg) collected from nature on Fruska Gora Mountain during March (average daily temperature was 3-5°C).The control larvae were sacrificed immediately (natural control group -NC), and the othcr larvae were divided into four experimental groups.They were placed in separate test tubes with crumbled oak bark and exposed to 23°C and 8°C.Larvae were sacrificed after two and thirty days of e:;<posure to different constant temperatures.The histological procedure was carried out according to Pan 0 v's (1980) Alcian Blue phloxine and paraldehyde thionine phloxine techniques.The activity ofA, protocercbral neurosecretory neurons was determined by combined monitoring of the following cytological parameters: number of neurons; and size of the neurons and their nuclei, expressed using the formula V= 1I6n xa xb 2 (a representing the larger and b the smaller diameter of each neuron or its nuclei).The amount of neurosecretory material in the perikaryon was arbitrarily estimated as well expressed, expressed, poorly expressed, or empty (represented as % of the analyzed neurons).Similarly, the quality of neurosecretory material was described as powdery or fine-, medium-or coarsegrained.The size of neurons and their nuclei was determined using the Leica QWIN program, and the results were expressed in urn".Differences between experimental groups were tested by Student's t-test.
Our results showed that the number of A, neurosecretory neurons in larvae exposed to different constant temperatures for two and thirty days was higher than in NC (Tab.I).The size of A, neurosecretory neurons and their nuclei increased after two and thirty days exposure to different constant temperatures.This increase was significant in the group exposed to 23°C for two days (Tab.1).The cytoplasm of A j neurosecretory neurons in larvae exposed to 23°C and 8°C for two days contained medium-and coarse-grained neurosecretory materials.After thirty days of exposure to different constant temperatures, A j cells mostly contained powdery neurosecretion.The percentage of empty cells was higher in all groups than in NC (Fig. !).These results demonstrate that elevated temperatures increase the activity ofA j neurosecretory neurons in M'.funereus larvae.A similar result was obtained in Lymantria dispar larvae (A, neurons were active) under the influence of nutritional stress (Peric-Mataruga and Lazarev ic , 2001).The medial neurosecretory  neurons (to which Al neurons belong) of the protocerebrum synthesize allatotropic hormones (Bogus and Scheller, 1994;Veelaert et al., 1995).Kataoka et al. (1989) have described a 13-amino-acid structure of this hormone, whose Mr is 20 kD in Manduca sexta.Also, Ilij in et al. (2004) showed that many close bands appeared in the region of molecular masses from 14.2 to 24 kD in starved Mfunereus larvae refed with an artificial diet.The presence of allatotropic neurohormones from the medial part of the protocerebrum stimulates the corpora allata (CA) (Meng-Ping et al., 2001).Our previous investigation showed an increase ofCA activity in Mfunereus larvae exposed to 23°C (Mrdakovi6 et al., 2003).Increased secretion of allatotropic hormone and concommitant increase in secretion of JH from CA are common in insects under stressful conditions.Many experiments with M.jimereus larvae have shown that different environmental factors such as stressful temperature and nutritive substrates of different quality and quantity affect the activity of cerebral neurosecretory cells (I v an o v ic et al., 1992;Le ko vi c et al., 2001), which are probably the site of ATTH synthesis.

Table 1 .
Means and standard errors for size of A, protocerebral neurosecretory neurons (V NSN) and their nuclei (Vn NSN), and number of A, neurons (N) in Morimus [unereus larvae exposed to different constant temperatures.NC -