Previous studies observed that CMS protocols impaired (Alfarez et al., 2003) or had no effect on LTP (Holderbach et al., 2007). Differences in LTP induction protocols could account for the discrepancy between those studies and the current one. Although Alfarez et al. used a primed-burst-stimulation protocol and Holderbach et al. used a paired-Theta-Burst protocol, both groups reported >150% LTP in control animals, which is larger than the magnitude of LTP (~135%) observed in the present study. We tested if a stronger TBS protocol (sTBS; 10 bursts of 5 stimuli, 100 Hz within burst, 200 ms interburst interval, repeated 4 times) would also result in enhanced LTP in CMS-exposed animals. As seen in Figure 7, sTBS produced robust LTP in non-stress animals that was significantly greater than LTP produced in stress animals. This finding is consistent with Alvarez et al. and several other studies in the literature that show stress (acute or chronic) is capable of impairing LTP. In our hands, this impairment is only observed during intense LTP-inducing stimulation.
