Histamine may act through cyclic AMP on hippocampal neurones.

Bath applied histamine and 8-bromo-cyclic AMP and intracellularly injected cyclic AMP block-long-lasting after-hyperpolarizations and the accommodation of firing in CA1 pyramidal cells recorded in rat hippocampal slices. This action is due to reduction of a calcium-activated potassium conductance (gK(Ca] and leads to potentiation of excitatory signals including epileptiform discharges. The effects are further potentiated and prolonged by a phosphodiesterase inhibitor (Ro 20-1724).