This review article by Lewitus et al. provides a timely summary of the influence of estrogen on aspects of basal ganglia cells and function, as well as some related insight into the influence in hippocampus. The paper is well-written, and the tables summarizing the influence of sex, estrous stage, and estrogen (E2) on a variety of parameters from receptor binding to behavior will be a valuable resource for those tackling sex differences in cellular and behavioral experiments. One limitation of the paper, however, is the absence of figures to illustrate key points. It would be very helpful to include a diagram indicating E2 levels throughout the estrous cycle in mice and rats. The literature is not clear about this, so that summary figure showing the diurnal pattern of E2 (and perhaps progesterone) levels would be beneficial to the field. Also helpful would be a diagram of where specific estrogen receptor subtypes are located on the striatal cells discussed. The apparent absence of estrogen receptors on striatal dopamine axons is particularly important to emphasize, as this implies that changes in DAT activity with E2, for example, are necessarily indirect (as discussed further below). Illustrating the sources of sex hormones would also be helpful but less critical than the other two recommended diagrams. One final recommendation would be to add a brief discussion of the rationale for the focus on estrogen, rather than progesterone, in most studies (and in this review). Is there evidence to support the lack of a regulatory role for progesterone – or just a lack of evidence? Even without these recommended additions, the article would make a good contribution to the literature; but the impact would be enhanced by the changes.

1) p. 4. The authors state, “classic ERs are implicated in the induction of the expression of tyrosine hydroxylase (Küppers et al., 2001).” This presumably means induction by estrogen, but is ambiguous as written. Also, this needs clarification in light of later statements that dopamine axons (at least) do not express estrogen receptors.

2) p. 6. The authors cite Wang and Dey (2006) for their statement about when E2 levels re highest, but this review is mainly about conception and implantation, and how hormone levels affect that. It would be helpful to have a better reference, and ideally to show diagram of estrogen/E2 changes across the rodent estrous cycle. The cycle is roughly 4 days in mice; is it the same in rats?
p. 6, last line. Should be, “Hormone effects on plasticity”.

3) p. 8. Cited evidence for the presence of pre-synaptic GABA receptors on dopamine terminals by Lopes et al., 2019 and Roberts et al., 2021) is indirect. Direct localization on dopamine axons was recently reported by Patel JC et al. 2024, which should also be cited.

4) A general comment is that dopamine release sites are found along striatal dopamine axons, not a “terminals” per se. Use of “terminals” is not accurate, and should be replaced with “release sites” or similar.

5) p. 9. If there are no estrogen receptors on dopamine axons (p. 8), it is not clear how E2 might lead to increased DAT activity. The section on receptors modulation of DAT should reflect this seeming paradox. Given that increased dopamine release when E2 is high, it is possible that this is an indirect effect of increased dopamine release and activation of D2 autoreceptors, which increases DAT activity for autoregulation. Results of chronic E2 administration discussed on p. 10 showing increased D2 binding would be consistent with this, with the need to explain estrogen receptor dependence when these are not present in dopamine axons (e.g., perhaps E2 effects on nAChRs or on cholinergic interneurons).

6) p. 9. The authors speculate that, “If E2 indeed increases DAT expression, this may be yet another possible reason for greater stimulated dopamine release in the presence of E2, as there may be greater stores of readily releasable dopamine at axon terminals.” Usually, increased DAT expression or activity leads to decreased evoked extracellular dopamine concentration – and release and uptake compete to regulate extracellular levels. Consequently, this seems an unlikely explanation for elevated dopamine levels, especially as D2 autoreceptor activation will also decrease dopamine stores by decreasing the activity of tyrosine hydroxylase. Also arguing against increased dopamine stores with E2 is the finding discussed on p. 12 that the effect of amphetamine on locomotion is greater in males than females – as amphetamine reverses the DAT to release dopamine from stores, whereas cocaine only blocks uptake.

7) p. 12 and elsewhere. The authors might note that conflicting data about sex differences for a given behavior may reflect the estrous stage of the animals examined, and whether only one stage was examined or whether the results were simply averaged across the cycle. Time of day may also matter, which adding complexity, but also depth to evaluation of sex differences.

8) The review has focused on estrogen/E2. Detailed consideration of other sex hormones is clearly beyond the scope of the article. That said, it would be helpful for the authors to include a brief discussion of whether other hormones, particularly progesterone, have (or are expected to have) similarly regulatory influence over the processes discuss – or whether E2 is the primary influencer over the estrous cycle so that the focus of future work can remain on estrogen.

Minor
p. 4. Should superscript 2+ in Ca2+.

The authors have thoughtfully addressed the concerns of all five reviewers, and impressive feat! Most helpful is the addition of figures to support the narrative points. Overall, this is an outstanding report that will make a strong, timely, and well-cited addition to the literature!