Synthesis
LME, anxiety
SECONDARY, EVENT
Reviewing Editor: Ifat Levy, Yale University School of MedicineDecisions are customarily a result of the Reviewing Editor and the peer reviewers coming together and discussing their recommendations until a consensus is reached. When revisions are invited, a fact-based synthesis statement explaining their decision and outlining what is needed to prepare a revision will be listed below. The following reviewer(s) agreed to reveal their identity: NONE. Note: If this manuscript was transferred from JNeurosci and a decision was made to accept the manuscript without peer review, a brief statement to this effect will instead be what is listed below.In this randomized-control study the matrix metalloproteinase (MMP)-9 inhibitor antibiotic doxycycline was used to test whether MMP-9 blockade reduces fear memory retention in Pavlovian trace fear conditioning. The study was pre-registered and all analyses were closed before unblinding groups relation. The main pre-registered outcome was fear potentiated startle (FPS) and secondary outcome were skin conductance response (SCR), pupil size (PSR), and respiratory amplitude in the interaction between drug and condition (CS+/CS-) during the retention phase. The main outcome was no drug by condition interaction or effect for drug on FPS. Secondary outcomes show no drug by condition interaction in any of the secondary measures and main effect for drug only in SCR. An analysis with trial showed an interaction between trial and group, taken together suggesting an overall lower response in the placebo group.Major comment:This study is well designed, pre-registered and according to the method section well powered. However, the main point does not seem justified. With all 4 measures (FPS, SCR, PSR, and respiration) failing to show a group by condition interaction during retention, the data suggest no evidence for MMP-9 reducing fear memory. As these were the pre-registered hypotheses, the authors should stick to them as the main story, and only after that enter into exploratory analysis of additional factors such as sex and anxiety.Minor comments:- Similarly to comments from the previous reviewers, the text still needs editing. There is misuse of tenses such as line 53 “we find”; missing parts of sentences, e.g. line 219 “During a 180-min metabolization interval”; Sentences over 40 words long; over- and misuse of acronyms (is SEBR different from FPS?) Line 194 “doxycycline is detectable in CSF, the cerebrospinal fluid (CSF)”. Titles of the physiological measures are acronyms such as the SEBR, or no new line for the SCR, which is written as SC.- The methods should be streamlined. Currently, some parts are introduced in an order that makes it hard to understand. For example, the CS+, CS- and US are introduced, but the reinforcement rate is in a completely different segment, which makes it hard to understand the flow of the experiment. The methods lack details about how the responses were quantified. As this is a trace fear conditioning, what was the event the analysis was locked to, in the FPS, to the sound, in the SCR to the CS, the CS onset, but for the trace? Did you look for a peak? Or measure tonic response? What units did you measure (microsiemens)?- The analysis plan is hard to follow. In all tests you started with a t-test and later moved to higher order analysis. Why is that? Start with ANOVA or LME and then go to the post hoc t-tests. In the current analysis there are dozens of results, if you try to correct the article for multiple tests you will likely find that most are nullified. Why are you using repeated measures ANOVA in the FPS and LME in the SCR? The r commands are mentioned (aov(), lme()) instead of the package you used (lme4; add citation).- As this substance is given 3 and a half hours before fear memory is created, what are the clinical implications? Using a reconsolidation paradigm might be more clinically relevant.