Co-localization of ecdysteroid receptors and c-fos-like protein in the brain of Manduca sexta larvae

Peripheral regulation by ecdysteroids of olfactory responsiveness in male Egyptian cotton leaf worms, Spodoptera littoralis

Physiological and behavioral plasticity allows animals to adapt to changes in external (environmental) and internal (physiological) factors. In insects, the physiological state modulates adult behavior in response to different odorant stimuli. Hormones have the potential to play a major role in the plasticity of the olfactory responses. To explore if peripheral olfactory processing could be regulated by steroid hormones, we characterized the molecular, electrophysiological, and behavioral response to changes in endogenous hormone levels in adult male Spodoptera littoralis. The expression of the receptor complex (EcR/USP) was localized by in situ hybridization in the olfactory sensilla of antennae. Injections of 20-hydroxyecdysone (20E) induced an ecdysteroid signaling pathway in antennae and increased expression of the nuclear receptors EcR, USP and E75. Diacylglycerol kinase (DGK) and CaM expression were also up-regulated by 20E. Taken together, these molecular, electrophysiological, and behavioral results suggest a hormonal regulation of the peripheral olfactory processing in S. littoralis.

Agonistic behavior and electrical stimulation of the antennae induces Fos-like protein expression in the male cricket brain

Immediate early genes (IEG) such as c-Fos and Fos-related antigens (FRA) have been used as markers of neuronal activation. In this study, we determined whether the expression of c-Fos/FRAs is increased in the brains of adult male Acheta domesticus crickets following agonistic interactions. We looked for c-Fos/FRA proteins in the brain of un-fought, control male crickets and of dominant and subordinate male crickets sacrificed at different time periods following an agonistic interaction. Using immunoblot analysis, we found four different c-Fos/FRA-like proteins in the adult cricket brain. Continuous agonistic interaction increased c-Fos/FRA protein expression in the brains of subordinate males compared to control and dominant males. In addition, direct electrical stimulation of the male cricket antennae increased c-Fos/FRA-like protein in the brain. We identified the specific brain regions that exhibit c-Fos/FRA-like immunoreactivity in crickets. We detected c-Fos/FRA-like cellular immunoreactivity in different functional regions of the adult brain including the pars intercerebralis, protocerebrum, deutocerebrum, and the cortex of the mushroom bodies.

c-Fos-related antigens in the central nervous system of an insect, Acheta domesticus

Fos-related antigens (Fra) were detected in the nuclei of neurones in young adult Acheta domesticus female crickets by immunohistochemical analysis, using an antibody that recognizes the amino-acid sequence 127-152 of c-Fos protein. Specificity of Fra immunoreactivity was confirmed by Western blot analysis of nuclear extracts from neural tissues. A major immunoreactive doublet with an apparent molecular mass of 52,000/54,000 Da was detected in nuclear extracts. Immunostaining of the 52,000/54,000 Da doublet showed variations in intensity during the first 5 days following the imaginal molt. Staining was more intense between day 2 and day 4 when ecdysteroid titers were high. Expression of Fra was low in allatectomized (i.e., deprived of juvenile hormone and ecdysteroids) and ovariectomized (i.e., deprived of ecdysteroids) females as compared to control females. These results show the involvement of hormone-regulated process in expression of Fra. The effect of nociceptive stimulation on Fra expression was tested. Twenty minutes after removal of the ovipositor, a supplementary band with an apparent molecular mass of 70,000 Da appeared in the nuclear extracts, then decreased and disappeared totally after 45 min. Several other Fos-related antigens with different temporal patterns of expression were also detected.

Circadian regulation of Fos-like expression in the brain of the blow fly Calliphora vicina

Expression of Fos-like immunoreactivity (FOS-lir) was examined in the brains of the blow fly Calliphora vicina for evidence of circadian regulation by photic stimuli. Fos-lir in various parts of the brain was investigated as a function of light and time of day. Immunohistochemistry demonstrated that photic stimuli have an inductive effect on c-fos expression in the various parts of the brain, but only in the neurons of the pars intercerebralis did the clear photic induction of c-fos expression occur at times when light was capable of phase-shifting circadian locomotor activity rhythms. This suggests that the c-fos gene may play a role in the photic pathway for circadian entrainment and that these neurons may be involved in the transduction of photic signals. Whether changes in c-fos expression are essential components of this pathway remains to be determined.