Shown are some of the known (arrow = activation, blunt line = inhibition) and postulated (question marks) pathways and effectors through which 5-HT, SP and TRH receptor activation affect membrane excitability. Abbreviations: AA (arachidonic acid), DAG (diacylglycerol), GIRK (G-protein-gated inwardly rectifying potassium channel), IP3 (inositol trisphosphate), KV (voltage-gated potassium channel), PIP2 (phosphatidylinositol bisphosphate), PK (protein kinase), PL (phospholipase), SK (small conductance calcium-activated potassium channel), TASK (TWIK-related acid-sensitive potassium channel)