Introduction
Biogenic amines are important modulators of the nervous system. For
instance, most antidepressants act on norepinephrine, dopamine, and
serotonin production or reuptake \cite{COPPEN_1967}\cite{Muscat_1990}. In invertebrates, octopamine (OA), structurally related to
norepinephrine \cite{David_1985} , and its precursor tyramine
(TA) act as neurotransmitters, -hormones, and -modulators on many, if
not all, physiological processes (reviews: \cite{Roeder_2005} \cite{Farooqui_2012}, among others on locomotion regulation (Saraswati et al.,
2004; Brembs et al., 2007), aggression (Baier et al., 2002; Hoyer
et al., 2008; Zhou et al., 2008), feeding behavior (Long and
Murdock, 1983; Nisimura et al., 2005), mobilization of energy
metabolites (Mentel et al., 2003) and, upstream of dopamine, on
appetitive olfactory learning (Hammer, 1997;
Schwaerzel et al., 2003; Burke et al., 2012; Liu et al., 2012).
Different stressors can modify the OA/TA-system by enhancing tßh expression (Châtel et al., 2013), subsequently increasing OA
levels (Kononenko et al., 2009), which, in turn, releases
triglycerides and carbohydrates into the hemolymph (Woodring et al.,
1989).
Upon starvation, behavior and metabolism are modified. General
activity and arousal is enhanced (Connolly, 1966; Bell et al., 1985;
Lee and Park, 2004) as well as food sensitivity (Moss and Dethier,
1983; Simpson et al., 1991; Colomb et al., 2009) correlated with an
increase in sugar receptor neuron sensitivity and gene expression
(Amakawa, 2001; Meunier et al., 2007; Nishimura et al., 2012).
Several neuropeptides have been already identified to play a role
(review: Nässel and Winther, 2010): NPF and dopamine as motivation
signals (Krashes et al., 2009; Root et al., 2011), and dopamine as
modulator of starvation-induced sugar response for short starvation
periods (Inagaki et al., 2012).
Here, we investigated the involvement of the OA/TA-system on
starvation-dependent modulation of sugar responsiveness and
metabolism. We measured the proboscis extension response and recorded
sensillar response before and after starvation. Metabolism changes
were quantified by carbohydrate measurements in fed and starved flies
and by survival under starvation conditions.