Long‐term high‐intensity sound stimulation inhibits h current (Ih) in CA1 pyramidal neurons

Afferent neurotransmission to hippocampal pyramidal cells can lead to long‐term changes to their intrinsic membrane properties and affect many ion currents. One of the most plastic neuronal currents is the hyperpolarization‐activated cationic current (Ih), which changes in CA1 pyramidal cells in response to many types of physiological and pathological processes, including auditory stimulation. Recently, we demonstrated that long‐term potentiation (LTP) in rat hippocampal Schaffer‐CA1 synapses is depressed by high‐intensity sound stimulation. Here, we investigated whether a long‐term high‐intensity sound stimulation could affect intrinsic membrane properties of rat CA1 pyramidal neurons. Our results showed that Ih is depressed by long‐term high‐intensity sound exposure (1 min of 110 dB sound, applied two times per day for 10 days). This resulted in a decreased resting membrane potential, increased membrane input resistance and time constant, and decreased action potential threshold. In addition, CA1 pyramidal neurons from sound‐exposed animals fired more action potentials than neurons from control animals; however, this effect was not caused by a decreased Ih. On the other hand, a single episode (1 min) of 110 dB sound stimulation which also inhibits hippocampal LTP did not affect Ih and firing in pyramidal neurons, suggesting that effects on Ih are long‐term responses to high‐intensity sound exposure. Our results show that prolonged exposure to high‐intensity sound affects intrinsic membrane properties of hippocampal pyramidal neurons, mainly by decreasing the amplitude of Ih. High‐intensity sound exposure is able to induce physiological changes in nonauditory areas as the hippocampus, including inhibition of long‐term potentiation (LTP). Here, we show that long‐term high‐intensity sound exposure produces intrinsic changes in the electrophysiological properties of CA1 pyramidal neurons, mainly by reduction in the magnitude of the h current. These effects seen to be a homeostatic compensation for the reduced LTP observed in the hippocampus after long‐term sound exposure.