Activation Of I_h Channel Mediates Short-Term Rhythmic Activities After Periodic Stimuli In Rat Visual Cortex

Processing of temporal information is fundamental for many brain functions, such as sensory perception, motor behavior and cognition. Rhythmic neuronal activities after periodic conditioning stimuli (CS) were observed in various brain regions, and are believed to contribute to the recollection of the time interval within a short period after episodic stimuli. However, the neuronal and circuitry mechanisms in generating such post-CS rhythmic activities are much less understood. Here we show that the short-term plasticity of after-hyperpolarization potentials (AHPs), mediated by hyperpolarization-activated (Ih) channels, induced by the repetitive visual or extracellular electric stimuli mediates the post-CS rhythmic activities in rat visual cortex. Postsynaptic membrane potentials of visual cortical neurons were measured by in vivo whole-cell recording in anaesthetized rats. Both the periodical light and intra-cortical electrical stimuli, ranging from 5 to 10 Hz, were efficient to entrain post-CS rhythmic activities at the stimulation frequency. Such post-CS activities were found to last up to 1 second with the dependence on the CS number and frequency presented. Dual whole-recording data revealed that the curve of AHP activation was gradually aligned during CS, with the increase in the similarity of curve shape between different V1 neurons. Intracellular blocking of Ih channel by 5mM Cs+ included in the recording pipette significantly abolished the alignment of AHP curve, but didn't change the post-CS rhythmic activities. However, extracellular application of ZD 7288 totally blocked both the alignment of AHP curve and the post-CS rhythmic activities. Thus, short-term plasticity of Ih channel activation after periodic conditioning stimuli contribute to the post-CS rhythmic activities, enabling the visual processing and short-term memory of the time interval of past episode.