Keywords: drosophila; octopamine; tyramine; oenocyte
Among four different octopamine (OA) receptors and three different tyramine (TA) receptors, TyrRIII is the only one expressed in oenocytes (El-Kholy et al., 2015).
A review by Roeder (2020) dicussed the role of OA/TA in regulating metabolic rates. Surely, OA and TA have been shown to regulate energy expenditure in invertebrates. However, the current literature features two issues: poor differentiation between the effects of the two monoamines in general and no evidence that the metabolic-rate-modulating effects of OA/TA are direct (that is, by being mediated by OA/TA receptors present on the fat body or oenocytes).
Perhaps it is also worth mentioning that OA/TA actions may have opposing effects, such as in locomotion (Saraswati et al., 2003). May similar things happen with regard to OA/TA modulation of metabolic traits? It seems that most studies using Drosopihla in the current literature looked at the effects of OA but not TA. I'd like to put forward that an investigation of the role of TyrRIII in Drosophila oenocytes may help differentiate the metabolic modulating effects of OA/TA, because we can look at the effects of TA in absence of any likely direct effects of OA, since there are no OA receptors on Drosophila oenocytes.
Note to myself:
Here is a nice review on insect tyramine receptors.