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