THE ROLE OF TYRAMINE IN MODULATION OF SPIDER, CUPIENNIUS SALEI, MECHANORECEPTORS

Abstract

Efferent neurons containing GABA, glutamate, acetylcholine and octopamine (OA) innervate spider, Cupiennius salei, mechanosensory neurons. The spider leg transcriptome library contains several putative transmitter receptors including G-protein coupled α- and β-adrenergic OA and tyramine (TA) receptors. I performed intracellular recordings from the strain detecting VS-3 neurons. TA caused a dose-dependent rise in action potential firing with an EC50 of 15.1 μM. VS-3 neuron sensitivity increased at all frequencies, but particularly in the high frequency range. Mianserin, an antagonist of β-adrenergic-like receptors, blocked the TA effect. Yohimbine, an antagonist of α-adrenergic-like receptors did not inhibit the TA effect, but reduced the baseline firing. These results indicate that the VS-3 neurons have at least two different adrenergic receptor types. The effects of TA and OA are similar, although OA is more potent. Thus, TA probably activates β-adrenergic OA receptors. The yohimbine effect indicates that α-adrenergic receptors maintain baseline sensitivity in VS-3 neurons.