Dopaminergic mushroom body neurons in Drosophila: Flexibility of neuron identity in a model organism?

In classical neuroscience, Dale´s principle postulates that neuronal identity is conferred by the specific neurotransmitter that it releases. However, the brain might be more tractable to specific situations regardless of specific specialisation which may contradict this principle. Hence, this constrained approach of how we perceive and study the nervous system must be revisited and revised, specifically by studying the dopaminergic system. We presume a relatively flexible change in the dopaminergic system due to neuronal activity or environmental changes. While the parallel between the reward system of mammals and insects is generally well accepted, herein, we extend the idea that the insect nervous system might also possess incredible plasticity, similar to the mammalian system. In this review, we critically evaluate the available information about the reward system in vertebrates and invertebrates, emphasising the dopaminergic neuronal plasticity, a challenge to the classical Dale's principle. Thus, neurotransmitter switching significantly disrupts the static idea of neural network organisation and suggests greater possibilities for a dynamic response to the current life context of organisms.

Expression of Drosophila Matrix Metalloproteinases in Cultured Cell Lines Alters Neural and Glial Cell Morphology.

Matrix metalloproteinases (MMPs) are zinc- and calcium- dependent endopeptidases that play pivotal roles in many biological processes. The expression of several MMPs in the central nervous system (CNS) have been shown to change in response to injury and various neurological/neurodegenerative disorders. While extracellular MMPs degrade the extracellular matrix (ECM) and regulate cell surface receptor signaling, the intracellular functions of MMPs or their roles in CNS disorders is unclear. Around 23 different MMPs are found in the human genome with overlapping function, making analysis of the intracellular role of human MMPs a daunting task. However, the fruit fly Drosophila melanogaster genome encodes only two MMPs: dMMP1 and dMMP2. To better understand the intracellular role of MMPs in the CNS, we expressed Green Fluorescent Protein (GFP)- tagged dMMPs in SH-SY5Y neuroblastoma cells and C6 glioblastoma cell lines. Lipofection of GFP-dMMPs in SH-SY5Y cells enhanced nuclear rupture and reduced cell viability (coupled with increased apoptosis) as compared to GFP alone. In non-liposomal transfection experiments, dMMP1 localizes to both the cytoplasm and the nucleus whereas dMMP2 had predominantly cytoplasmic localization in both neural and glial cell lines. Cytoplasmic localization demonstrated co-localization of dMMPs with cytoskeleton proteins which suggests a possible role of dMMPs in cell morphology. This was further supported by transient dMMP expression experiments that showed that dMMPs significantly increased neurite formation and length in neuronal cell lines. Inhibition of endogenous MMPs decreased neurite formation, length and ßIII Tubulin protein levels in differentiated SH-SY5Y cells. Further, transient expression experiments showed similar changes in glial cell morphology, wherein dMMP expression increased glial process formation and process length. Interestingly, C6 cells expressing dMMPs had a glia-like appearance, suggesting MMPs may be involved in intracellular glial differentiation. Inhibition or suppression of endogenous MMPs in C6 cells increased process formation, increased process length, modulated GFAP protein expression, and induced distinct glial-like phenotypes. Taken together, our results strongly support the intracellular role that dMMPs can play in apoptosis, cytoskeleton remodeling, and cell differentiation. Our studies further reinforce the use of Drosophila MMPs to dissect out the precise mechanisms whereby they exert their intracellular roles in CNS disorders.

Exposure to Spectracide® causes behavioral deficits in Drosophila melanogaster: Insights from locomotor analysis and molecular modeling.

This study was focused on gaining insights into the mechanism by which the herbicide- Spectracide®, induces oxidative stress and alters behavior in Drosophila melanogaster. Exposure to Spectracide® (50%) significantly (p < 0.05) reduced the negative geotaxis response, jumping behavior and dampened locomotor activity rhythm in adult flies compared to non-exposed flies. Protein carbonyl levels indicative of oxidative damage increased significantly coupled with down-regulation of Sniffer gene expression encoding carbonyl reductase (CR) and its activity in Spectracide®-exposed flies. In silico modeling analysis revealed that the active ingredients of Spectracide® (atrazine, diquat dibromide, fluazifop-p-butyl, and dicamba) have significant binding affinity to the active site of CR enzyme, with atrazine having comparatively greater affinity. Our results suggest a mechanism by which ingredients in Spectracide® induce oxidative damage by competitive binding to the active site of a protective enzyme and impair its ability to prevent damage to proteins thereby leading to deficits in locomotor behavior in Drosophila.

The surfactant polyethoxylated tallowamine (POEA) reduces lifespan and inhibits fecundity in Drosophila melanogaster- In vivo and in vitro study.

In order to develop an understanding of the role of adjuvants in a popular glyphosate-based herbicide - Roundup® Concentrate Plus (RCP), on non-target organisms, the effects of pure glyphosate [N-(phosphonomethyl)-glycine], RCP and a non-ionic surfactant - polyethoxylated tallowamine (POEA) were studied in the fruit fly Drosophila melanogaster. Acute exposure to sub-lethal concentrations of RCP (15 µg/mL) and POEA (45 µg/mL) reduced (p < 0.001) lifespan of female flies compared to untreated controls or glyphosate (100 µg/mL). Negative geotaxis responses in female flies were reduced (p < 0.05) following acute exposure to sub-lethal concentrations of RCP and POEA whereas glyphosate did not significantly affect this response compared to untreated flies. Acute exposure to sub-lethal concentrations of RCP and POEA elevated (p < 0.05) protein carbonyl levels while markedly (p < 0.01) inhibiting carbonyl reductase activity whereas glyphosate treatment did not significantly affect protein carbonyl levels or carbonyl reductase activity. Fecundity was reduced (p < 0.05) following exposure to sub-lethal concentrations of RCP and POEA whereas glyphosate did not affect fecundity. In vitro treatment of ovarian stem sheath (OSS) cells with sub-lethal concentrations of RCP and POEA revealed decreased cell viability and enhanced caspase activity indicative of pro-apoptotic processes after 48 h compared to untreated controls. Glyphosate however was non-toxic at the concentration used. The results suggest that RCP and the surfactant POEA are more toxic than pure glyphosate and inhibit fecundity in Drosophila by impairing cell viability through enhanced apoptosis.

Changes in vitellogenin expression caused by nematodal and fungal infections in insects.

This study examined the expression and role of vitellogenin (Vg) in the body of the firebug Pyrrhocoris apterus (Heteroptera, Insecta) during infection elicited by two entomopathogenic organisms, the nematode Steinernema carpocapsae and the fungus Isaria fumosorosea Infection by S. carpocapsae significantly upregulated Vg mRNA expression in the male body. The corresponding increase in Vg protein expression was also confirmed by electrophoretic and immunoblotting analyses. Remarkably, in females, the opposite tendency was noted. Nematodal infection significantly reduced both Vg mRNA and Vg protein expression levels in fat body and hemolymph, respectively. We speculate that infection of reproductive females reduces Vg expression to a level that is still sufficient for defense, but is insufficient for reproduction. This circumstance reduces energy expenditure and helps the individual to cope with the infection. Importantly, purified Vg significantly inhibited growth of Xenorhabdus spp., an entomotoxic bacteria isolated from S. carpocapsae. However, the effect of Vg against I. fumosorosea was not so obvious. The fungus significantly stimulated Vg gene expression in males; however, a similar increase was not recapitulated at the protein level. Nevertheless, in females, both mRNA and protein Vg levels were significantly reduced after the fungal infection. The obtained data demonstrate that Vg is probably an important defense protein, possibly with a specific activity. This considerably expands the known spectrum of Vg functions, as its primary role was thought to be limited to regulating egg development in the female body.

Disruption of Adipokinetic Hormone Mediated Energy Homeostasis Has Subtle Effects on Physiology, Behavior and Lipid Status During Aging in Drosophila.

The impact of disruption of adipokinetic hormone (AKH) signaling was studied during aging in Drosophila in a sexually dimorphic manner. A mutant (Akh1) producing a non-functional AKH peptide was compared with isogenized wild-type controls (w1118), and Akh-rescue line where AKH was ectopically expressed in the mutant background (EE-Akh). Longevity, fecundity, and locomotor activity rhythms remained unaffected by lack of AKH signaling. While the strength of rhythms declined in general with age across all fly lines tested this was more so in case of Akh1 flies. Negative geotaxis was significantly impaired in Akh1 flies. Only young Akh1 flies of both sexes and old Akh1 females showed significantly higher body weight compared to age-matched iso-control flies (except in case of EE-Akh). Expression of genes involved in energy homeostasis and aging indicated that dTOR and Akt expression were elevated in Akh1 flies compared to other genotypes, whereas AMPK and dFoxO expression levels were significantly reduced. Multivariate analysis of the distribution of lipid species revealed a significant accumulation of specific diglyceride (DG) and triglyceride (TG) lipid species, irrespective of sex, attributable in part due to lack of AKH. Moreover, irrespective of lack of AKH, older flies of all genotypes accumulated TGs. Taken together, the results strongly suggest that disruption of AKH has very subtle effects on physiology, behavior and lipid status during aging.

Morphometric Analysis of Adult Dermacentor parumapertus Neumann (Acari: Ixodidae) From Various Locations Within its Geographical Range.

Dermacentor parumapertus Neumann (Acari: Ixodidae), a tick primarily associated with rabbits which occurs over much of the western United States, has a fairly large north-to-south distribution, being found from central Idaho southward into northern Mexico. This mostly obscure tick species has recently been the focus of attention due to the discovery of a unique strain of Rickettsia parkeri associated with it which appears closely related to a Rickettsia sp. found in the Atlantic rainforest of Brazil. Historically, a morphological variety of this species was reported in the literature based on significant variation in ornamentation of the tick throughout its range. This study examines several key morphological characters to determine if there are indeed more than one distinct population of this species throughout its range.

Lost in Translation: Defects in Transfer RNA Modifications and Neurological Disorders.

Transfer RNAs (tRNAs) are key molecules participating in protein synthesis. To augment their functionality they undergo extensive post-transcriptional modifications and, as such, are subject to regulation at multiple levels including transcription, transcript processing, localization and ribonucleoside base modification. Post-transcriptional enzyme-catalyzed modification of tRNA occurs at a number of base and sugar positions and influences specific anticodon-codon interactions and regulates translation, its efficiency and fidelity. This phenomenon of nucleoside modification is most remarkable and results in a rich structural diversity of tRNA of which over 100 modified nucleosides have been characterized. Most often these hypermodified nucleosides are found in the wobble position of tRNAs, where they play a direct role in codon recognition as well as in maintaining translational efficiency and fidelity, etc. Several recent studies have pointed to a link between defects in tRNA modifications and human diseases including neurological disorders. Therefore, defects in tRNA modifications in humans need intensive characterization at the enzymatic and mechanistic level in order to pave the way to understand how lack of such modifications are associated with neurological disorders with the ultimate goal of gaining insights into therapeutic interventions.

Disruption of dopamine homeostasis has sexually dimorphic effects on senescence characteristics of Drosophila melanogaster.

The neurotransmitter dopamine (DA) is known to be involved in a multitude of physiological processes. We investigated sexually dimorphic effects of disruptions in DA homeostasis and its relationship to senescence using three different Drosophila melanogaster mutants namely Catsup (Catsup26 ) with elevated DA levels, and pale (ple2 ), Punch (PuZ22 ) with depleted DA levels. In all genotypes including controls, DA levels were significantly lower in old (45-50-day-old) flies compared with young (3-5-day-old) in both sexes. Interestingly, females had lower DA content than males at young age whereas this difference was not observed in old age, suggesting that males had a larger decline in DA levels with age. Females, in general, were longer lived compared with males in all genotypes except ple2 mutants with depleted DA levels. This phenotype was abolished in the ple2 rescue flies. Interestingly, females also demonstrated marked age-related decline in circadian locomotor activity compared with males. Old Catsup26 males with elevated DA levels accumulated significantly lower levels of lipid peroxidation product 4-hydroxy 2-nonenal (4-HNE) compared with age-matched wild type, ple2 and PuZ22 mutant males. In Catsup26 revertant lines this phenomenon was absent. We also observed a sexually dimorphic response in the expression levels of key stress and aging associated and/or related transcription factor genes across genotypes with elevated or depleted DA levels which was reverted to wild type levels in specific rescue lines. Taken together, our results reveal a novel sexually dimorphic involvement of DA in senescence characteristics of D. melanogaster.

Insight into the Salivary Gland Transcriptome of Lygus lineolaris (Palisot de Beauvois).

The tarnished plant bug (TPB), Lygus lineolaris (Palisot de Beauvois) is a polyphagous, phytophagous insect that has emerged as a major pest of cotton, alfalfa, fruits, and vegetable crops in the eastern United States and Canada. Using its piercing-sucking mouthparts, TPB employs a "lacerate and flush" feeding strategy in which saliva injected into plant tissue degrades cell wall components and lyses cells whose contents are subsequently imbibed by the TPB. It is known that a major component of TPB saliva is the polygalacturonase enzymes that degrade the pectin in the cell walls. However, not much is known about the other components of the saliva of this important pest. In this study, we explored the salivary gland transcriptome of TPB using Illumina sequencing. After in silico conversion of RNA sequences into corresponding polypeptides, 25,767 putative proteins were discovered. Of these, 19,540 (78.83%) showed significant similarity to known proteins in the either the NCBI nr or Uniprot databases. Gene ontology (GO) terms were assigned to 7,512 proteins, and 791 proteins in the sialotranscriptome of TPB were found to collectively map to 107 Kyoto Encyclopedia of Genes and Genomes (KEGG) database pathways. A total of 3,653 Pfam domains were identified in 10,421 sialotranscriptome predicted proteins resulting in 12,814 Pfam annotations; some proteins had more than one Pfam domain. Functional annotation revealed a number of salivary gland proteins that potentially facilitate degradation of host plant tissues and mitigation of the host plant defense response. These transcripts/proteins and their potential roles in TPB establishment are described.

Hormonal Regulation of Response to Oxidative Stress in Insects-An Update.

Insects, like other organisms, must deal with a wide variety of potentially challenging environmental factors during the course of their life. An important example of such a challenge is the phenomenon of oxidative stress. This review summarizes the current knowledge on the role of adipokinetic hormones (AKH) as principal stress responsive hormones in insects involved in activation of anti-oxidative stress response pathways. Emphasis is placed on an analysis of oxidative stress experimentally induced by various stressors and monitored by suitable biomarkers, and on detailed characterization of AKH's role in the anti-stress reactions. These reactions are characterized by a significant increase of AKH levels in the insect body, and by effective reversal of the markers-disturbed by the stressors-after co-application of the stressor with AKH. A plausible mechanism of AKH action in the anti-oxidative stress response is discussed as well: this probably involves simultaneous employment of both protein kinase C and cyclic adenosine 3',5'-monophosphate pathways in the presence of extra and intra-cellular Ca(2+) stores, with the possible involvement of the FoxO transcription factors. The role of other insect hormones in the anti-oxidative defense reactions is also discussed.

Knockdown of adipokinetic hormone synthesis increases susceptibility to oxidative stress in Drosophila--a role for dFoxO?

Insect adipokinetic hormones (AKHs) are pleiotropic hormones known to play a protective role in response to oxidative stress (OS). However, the precise signaling pathways are unclear. We present evidence that AKH may primarily employ the Forkhead box class O transcription factor (FoxO) to exert this effect. The impact of knocking down AKH synthesis or its over-expression in its response to OS was studied in Drosophila melanogaster. AKH knockdown (AKH-RNAi) as well as AKH overexpression (AKH-oex) was achieved using the Gal-4/UAS system and controls were w(1118) (+/+), AKH-Gal4/+, UAS-AKH/+ and UAS-AKH-RNAi/+. Exposure to 80 µM hydrogen peroxide (HP) revealed that AKH-RNAi flies showed significantly higher mortality than AKH-oex or the respective control lines. This susceptibility was evidenced by significantly enhanced levels of protein carbonyls - a biomarker of OS, in AKH-RNAi flies compared to controls and AKH-oex flies. Interestingly, AKH-oex flies had the least amount of protein carbonyls. AKH-RNAi flies had significantly less dFoxO transcript and translated protein compared to control and AKH-oex flies in un-challenged condition as well as when challenged with HP. Sestrin - a major antioxidant defense protein and one of the targets of dFoxO - was also significantly down-regulated (both at mRNA and protein level) in AKH-RNAi flies (both unchallenged and challenged with HP) compared to control flies and flies with over-expressed AKH. These findings imply that dFoxO may act downstream of AKH as a transcription factor to mediate response to OS in D. melanogaster.

Perturbations in dopamine synthesis lead to discrete physiological effects and impact oxidative stress response in Drosophila.

The impact of mutations in four essential genes involved in dopamine (DA) synthesis and transport on longevity, motor behavior, and resistance to oxidative stress was monitored in Drosophila melanogaster. The fly lines used for this study were: (i) a loss of function mutation in Catecholamines up (Catsup(26)), which is a negative regulator of the rate limiting enzyme for DA synthesis, (ii) a mutant for the gene pale (ple(2)) that encodes for the rate limiting enzyme tyrosine hydroxylase (TH), (iii) a mutant for the gene Punch (Pu(Z22)) that encodes guanosine triphosphate cyclohydrolase, required for TH activity, and (iv) a mutant in the vesicular monoamine transporter (VMAT(Δ14)), which is required for packaging of DA as vesicles inside DA neurons. Median lifespans of ple(2), Pu(Z22) and VMAT(Δ14) mutants were significantly decreased compared to Catsup(26) and wild type controls that did not significantly differ between each other. Catsup(26) flies survived longer when exposed to hydrogen peroxide (80 µM) or paraquat (10mM) compared to ple(2), Pu(Z22) or VMAT(Δ14) and controls. These flies also exhibited significantly higher negative geotaxis activity compared to ple(2), Pu(Z22), VMAT(Δ14) and controls. All mutant flies demonstrated rhythmic circadian locomotor activity in general, albeit Catsup(26) and VMAT(Δ14) flies had slightly weaker rhythms. Expression analysis of some key antioxidant genes revealed that glutathione S-transferase Omega-1 (GSTO1) expression was significantly up-regulated in all DA synthesis pathway mutants and especially in Catsup(26) and VMAT(Δ14) flies at both mRNA and protein levels. Taken together, we hypothesize that DA could directly influence GSTO1 transcription and thus play a significant role in the regulation of response to oxidative stress. Additionally, perturbations in DA synthesis do not appear to have a significant impact on circadian locomotor activity rhythms per se, but do have an influence on general locomotor activity levels.

Role of adipokinetic hormone in stimulation of salivary gland activities: the fire bug Pyrrhocoris apterus L. (Heteroptera) as a model species.

The effect of adipokinetic hormone (Pyrap-AKH) in stimulating the function of insect salivary glands (SGs) in extra-oral digestive processes was studied in the firebug, Pyrrhocoris apterus L. (Heteroptera). The analyses were performed on samples of SGs and extracts of linden seeds, a natural source of the bug's food. The SGs from 3-day old P. apterus females (when the food ingestion culminates), primarily contained polygalacturonase (PG) enzyme activity, whereas the level of lipase, peptidase, amylase and α-glucosidase was negligible. The transcription of PG mRNA and enzymatic activity were significantly increased in SGs after Pyrap-AKH treatment. The piercing and sucking of linden seeds by the bugs stimulated the intrinsic enzymatic cocktail of seeds (lipase, peptidase, amylase, glucosidase), and moreover the activity of these enzymes was significantly enhanced when the seeds were fed on by the Pyrap-AKH treated bugs. Similarly, a significant increase in PG activity was recorded in linden seeds fed on by hormonally-treated bugs or when injected by SG extract from hormonally treated ones as compared to untreated controls. The mechanism of AKH action in SGs is unknown, but likely involves cAMP (and excludes cGMP) as a second messenger, since the content of this compound doubled in SGs after Pyrap-AKH treatment. This new and as yet undescribed function of AKH in SGs is compared with the effect of this hormone on digestive processes in the midgut elucidated earlier.

Auxin increases the hydrogen peroxide (H2O2) concentration in tomato (Solanum lycopersicum) root tips while inhibiting root growth.

BACKGROUND AND AIMS: The hormone auxin and reactive oxygen species (ROS) regulate root elongation, but the interactions between the two pathways are not well understood. The aim of this study was to investigate how auxin interacts with ROS in regulating root elongation in tomato, Solanum lycopersicum. METHODS: Wild-type and auxin-resistant mutant, diageotropica (dgt), of tomato (S. lycopersicum 'Ailsa Craig') were characterized in terms of root apical meristem and elongation zone histology, expression of the cell-cycle marker gene Sl-CycB1;1, accumulation of ROS, response to auxin and hydrogen peroxide (H2O2), and expression of ROS-related mRNAs. KEY RESULTS: The dgt mutant exhibited histological defects in the root apical meristem and elongation zone and displayed a constitutively increased level of hydrogen peroxide (H2O2) in the root tip, part of which was detected in the apoplast. Treatments of wild-type with auxin increased the H2O2 concentration in the root tip in a dose-dependent manner. Auxin and H2O2 elicited similar inhibition of cell elongation while bringing forth differential responses in terms of meristem length and number of cells in the elongation zone. Auxin treatments affected the expression of mRNAs of ROS-scavenging enzymes and less significantly mRNAs related to antioxidant level. The dgt mutation resulted in resistance to both auxin and H2O2 and affected profoundly the expression of mRNAs related to antioxidant level. CONCLUSIONS: The results indicate that auxin regulates the level of H2O2 in the root tip, so increasing the auxin level triggers accumulation of H2O2 leading to inhibition of root cell elongation and root growth. The dgt mutation affects this pathway by reducing the auxin responsiveness of tissues and by disrupting the H2O2 homeostasis in the root tip.

Adipokinetic hormone exerts its anti-oxidative effects using a conserved signal-transduction mechanism involving both PKC and cAMP by mobilizing extra- and intracellular Ca2+ stores.

The involvement of members of the adipokinetic hormone (AKH) family in regulation of response to oxidative stress (OS) has been reported recently. However, despite these neuropeptides being the best studied family of insect hormones, their precise signaling pathways in their OS responsive role remain to be elucidated. In this study, we have used an in vitro assay to determine the importance of extra and intra-cellular Ca(2+) stores as well as the involvement of protein kinase C (PKC) and cyclic adenosine 3',5'-monophosphate (cAMP) pathways by which AKH exerts its anti-oxidative effects. Lipid peroxidation product (4-HNE) was significantly enhanced and membrane fluidity reduced in microsomal fractions of isolated brains (CNS) of Pyrrhocoris apterus when treated with hydrogen peroxide (H2O2), whereas these biomarkers of OS were reduced to control levels when H2O2 was co-treated with Pyrap-AKH. The effects of mitigation of OS in isolated CNS by AKH were negated when these treatments were conducted in the presence of Ca(2+) channel inhibitors (CdCl2 and thapsigargin). Presence of either bisindolylmaliemide or chelyrythrine chloride (inhibitors of PKC) in the incubating medium also compromised the anti-oxidative function of AKH. However, supplementing the medium with either phorbol myristate acetate (PMA, an activator of PKC) or forskolin (an activator of cAMP) restored the protective effects of exogenous AKH treatment by reducing 4-HNE levels and increasing membrane fluidity to control levels. Taken together, our results strongly implicate the importance of both PKC and cAMP pathways in AKHs' anti-oxidative action by mobilizing both extra and intra-cellular stores of Ca(2+).

Nature's Timepiece-Molecular Coordination of Metabolism and Its Impact on Aging.

Circadian rhythms are found in almost all organisms from cyanobacteria to humans, where most behavioral and physiological processes occur over a period of approximately 24 h in tandem with the day/night cycles. In general, these rhythmic processes are under regulation of circadian clocks. The role of circadian clocks in regulating metabolism and consequently cellular and metabolic homeostasis is an intensively investigated area of research. However, the links between circadian clocks and aging are correlative and only recently being investigated. A physiological decline in most processes is associated with advancing age, and occurs at the onset of maturity and in some instances is the result of accumulation of cellular damage beyond a critical level. A fully functional circadian clock would be vital to timing events in general metabolism, thus contributing to metabolic health and to ensure an increased "health-span" during the process of aging. Here, we present recent evidence of links between clocks, cellular metabolism, aging and oxidative stress (one of the causative factors of aging). In the light of these data, we arrive at conceptual generalizations of this relationship across the spectrum of model organisms from fruit flies to mammals.

Unique roles of glucagon and glucagon-like peptides: Parallels in understanding the functions of adipokinetic hormones in stress responses in insects.

Glucagon is conventionally regarded as a hormone, counter regulatory in function to insulin and plays a critical anti-hypoglycemic role by maintaining glucose homeostasis in both animals and humans. Glucagon performs this function by increasing hepatic glucose output to the blood by stimulating glycogenolysis and gluconeogenesis in response to starvation. Additionally it plays a homeostatic role by decreasing glycogenesis and glycolysis in tandem to try and maintain optimal glucose levels. To perform this action, it also increases energy expenditure which is contrary to what one would expect and has actions which are unique and not entirely in agreement with its role in protection from hypoglycemia. Interestingly, glucagon-like peptides (GLP-1 and GLP-2) from the major fragment of proglucagon (in non-mammalian vertebrates, as well as in mammals) may also modulate response to stress in addition to their other physiological actions. These unique modes of action occur in response to psychological, metabolic and other stress situations and mirror the role of adipokinetic hormones (AKHs) in insects which perform a similar function. The findings on the anti-stress roles of glucagon and glucagon-like peptides in mammalian and non-mammalian vertebrates may throw light on the multiple stress responsive mechanisms which operate in a concerted manner under regulation by AKH in insects thus functioning as a stress responsive hormone while also maintaining organismal homeostasis.