Glutamate – A Forgotten Target for Interval Timing

immunohistochemical analysis against Arc protein was used to test whether a change in the CS–US interval (resulting in a new memory formation for duration) triggers plasticity in the dorsal striatum. In a similar fashion, the “time-shift paradigm” provides a powerful tool for isolating the role of Glu in the formation of memory for target durations. Recently, we examined the effect of intraperitoneal injection of a non-competitive NMDA receptor antagonist, MK-801, on the formation of the memory for the target duration in a “time-shift paradigm” version of peak-interval procedure. Contrary to our expectations, the peak time in MK-801 group was immediately shifted in the earliest sessions of the second phase (unpublished observation). A previous study (Miller et al., 2006) reported that systemic injection of MK-801 immediately increased the peak time, which can mask the possible effects of MK-801 on memory formation in our study. The effect of intra-dorsal striatum injection of drugs should be examined in the “time-shift paradigm” in future studies. Taken together, the role of Glu in interval timing will be clarified more precisely by considering the above three points: injection routes, receptor subtypes, and learning phases.