Biogenic amines modulate transepithelial potential (TEP) in labellar taste sensilla of the blowfly.

SOLLAI, GIORGIA;SOLARI, PAOLO;MASALA, CARLA;Corda V;CRNJAR, ROBERTO MASSIMO

2012-01-01

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Abstract

Biogenic amines act as important neuromodulators, neurohormones and neurotransmitters of many physiological processes in invertebrates (Brigaud et al, 2009). Their effects are observed at various levels of insect nervous systems, such as in modulating the sensitivity of sensory receptors and interneurons (Scheiner et al, 2002). Among biogenic amines, octopamine (OA), structurally related to noradrenaline (Roeder, 1999), tyramine (TA), the biosynthetic intermediate of OA (Brigaud et al, 2009) and dopamine (DA), are widespread in insect nervous tissues (Blenau et al, 2001). Biogenic amines are known to be involved in chemoreception mechanisms, by modulating the transepithelial potential (TEP), for which a major role has been proposed in the generation of the receptor potential (Dolzer et al, 2001; Grosmaitre et al, 2001; Pophof, 2000). Nonetheless, the effects of OA and particularly TA and DA on taste systems, are little understood. By means of electrophysiological techniques, we investigated whether OA, TA and DA affect the TEP in the labellar taste chemosensilla of the blowfly Protophormia terraenovae. Drugs dissolved in saline at 0.1 mM were injected (1 μl) near the labellum base, in order to reach the accessory cells where the K+-dependent TEP generation mechanism is located (Sollai et al, 2008). TEP values were monitored before and for 20 min (every 5 min) after drug injection. Results show that OA and TA increase the TEP values already 5 min after injection and throughout the 20 min interval. Conversely, the TEP value is reduced after 5 and 10 min from DA administration, but it rebounds to starting values after 15 and 20 min. Injection of saline (control) does not alter the TEP values. In conclusion, OA, TA and DA appear to modulate the TEP amplitude, possibly by affecting the electrogenic K+ transport, as described in other insect epithelia, such as Malpighian tubules in Drosophila (Blumenthal, 2005) or olfactory sensilla in Manduca (Dolzer et al, 2001).