Systemic Administration of Docosahexaenoic Acid Suppresses Trigeminal Secondary Nociceptive Neuronal Activity in Rats

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have elegantly presented electrophysiological evidence of the reduction of noxious and non-noxious trigeminal sensory transmission after intravenous administration of docosahexaenoic acid (DHA; 10 mM) in otherwise healthy instrumented, anesthetized rats. The results are convincing and add support for the complementary use of DHA in the treatment of pain. One drawback of the manuscript, however, is the lack of discussion on the limitations of the study. These limitations should have included the selected route of administration (i.e., IV), the use of healthy animals rather than animals with a condition that causes pain, and the effect of DHA on both noxious and non-noxious transmission.

 

Specific minor comments

Lines 78-81. Consider removing these two sentences since results and conclusions are not typically presented in the introduction.

Line 92-93. Consider rephrasing 'mixture of anesthetics (0.3 mg/kg of medetomidine, 4.0 mg/kg of midazolam 92 and 5.0 mg/kg of butorphanol) at 2–3 mg/kg/h as required'. These are not anesthetics and the drugs should be provided as concentration in the final solution and then as volume per unit of time and unit of weight for the constant rate infusion.

Line 105. Reference [16] should read [26].

Line 147. If used, please provide details of the software used for the statistical analysis.

Line 174. Rephrase ‘following an intravenous injection of 10 mM DHA into the receptive field center’.

Line 309. Delete ‘without causing side effects’; this was not demonstrated in your study.

Line 349. Pages for reference 5 are missing.

Lines 352 and 404. Issue number may not be needed.

In some references (e.g., 16, 17, 20), et. al. is used but not in others. Please make sure that its use is required and if not, please amend as appropriate.

Author Response

Reviewer #1:

Comments and Suggestions for Authors

The authors have elegantly presented electrophysiological evidence of the reduction of noxious and non-noxious trigeminal sensory transmission after intravenous administration of docosahexaenoic acid (DHA; 10 mM) in otherwise healthy instrumented, anesthetized rats. The results are convincing and add support for the complementary use of DHA in the treatment of pain. One drawback of the manuscript, however, is the lack of discussion on the limitations of the study. These limitations should have included the selected route of administration (i.e., IV), the use of healthy animals rather than animals with a condition that causes pain, and the effect of DHA on both noxious and non-noxious transmission.

Answer:

We appreciate reviewer’s careful reviews on our manuscript. We have carefully checked the reviewer’s constructive and helpful comments and made necessary corrections to revised manuscript (marked by red font) We believe that your comments helped to improve our manuscript.

According to reviewer’s comment, we have added new sentences in the discussion section (page 9) as follows; Finally, the present study examines the effects of a single intravenous administration of DHA on nociceptive pain in naïve rats, whereas the effects on pathological pain, such as inflammatory or neuropathic pain, require further investigation. Therefore, future experiments should focus on investigating the effects on pathological pain. Furthermore, experiments on continuous intravenous administration of DHA are necessary to examine the duration of its analgesic effects.

Specific minor comments

Comment

Lines 78-81. Consider removing these two sentences since results and conclusions are not typically presented in the introduction.

Answer:

According to reviewer’s comment, we have removed following two sentences (page 2); As a result, we found that in the absence of inflammatory or neuropathic pain, acute intravenous DHA suppresses trigeminal sensory transmission, including nociception. Hence, DHA might be viewed as a potential CAM agent for managing trigeminal nociceptive pain without causing side effects. 

Comment

Line 92-93. Consider rephrasing 'mixture of anesthetics (0.3 mg/kg of medetomidine, 4.0 mg/kg of midazolam 92 and 5.0 mg/kg of butorphanol) at 2–3 mg/kg/h as required'. These are not anesthetics and the drugs should be provided as concentration in the final solution and then as volume per unit of time and unit of weight for the constant rate infusion.

Answer:

According to reviewer’s comment, we have revised as follows (page 3);…(0.3 mg/kg of medetomidine, 4.0 mg/kg of midazolam and 5.0 mg/kg of butorphanol) at 0.25-0.45mL/kg/h as required…

Comment

Line 105. Reference [16] should read [26].

Answer:

According to reviewer’s comment, we have revised as follows (page 3);…the rat brain atlas of Paxinos and Watson [26].

Comment

Line 147. If used, please provide details of the software used for the statistical analysis.

Answer:

According to reviewer’s comment, we have added the software used for the statistical analysis.as follows (page 4); A one-way repeated-measures analysis of variance was used for statistical evaluation, with Tukey–Kramer or Dunnett’s tests administered as post-hoc analyses and the Student’s t-test for electrophysiological data (Excel Statcel 4).

Comment

Line 174. Rephrase ‘following an intravenous injection of 10 mM DHA into the receptive field center’.

Answer:

According to reviewer’s comment, we have revised as follows (page ５);…an intravenous injection of 10 mM DHA, non-noxious (2-10 g) …

Comment

Line 309. Delete ‘without causing side effects’; this was not demonstrated in your study.

Answer:

According to reviewer’s comment, we have deleted ‘without causing side effects’;(Conclusion; page 9)

Comment

Line 349. Pages for reference 5 are missing.

Answer:

According to reviewer’s comment, we have added pages as follows;

Iwata, K.; Takeda, M.; Oh, S.; Shinoda, M. Neurophysiology of orofacial pain. In Contemporary Oral Medicine; Farah, C.S., Balasubramaniam, R., McCullough, M.J., Eds.; Springer International Publishing: New York, USA, 2017. pp.1-2

Comment

Lines 352 and 404. Issue number may not be needed.

Answer:

According to the reviewer’s comment, we have deleted Issue number (ref. No.6 and 34) as follows;

6. …Comp. Biochem. Physiol. 1976, 54, 395-401.
7. …Eur. J. Oral Sci. 2023, 131, e12917.

Comment

In some references (e.g., 16, 17, 20), et. al. is used but not in others. Please make sure that its use is required and if not, please amend as appropriate.

Answer:

According to reviewer’s comment, we have revised (pages10-11) for References. No. 2, 9,10,12 and 19.

For example, 2. Takeda, M.; Matsumoto, S.; Sessle, B.J.; et al.

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Editor,

After reviewing a manuscript, I find it suitable to be published in the IJTM after minor corrections and explanations. The manuscript is well structured and data presented are of interest to the readers. Methods used provide the results which are well explained in the discussion section. Here are the remarks that should be addressed:

1. The authors mention that they measured DHA concentration in blood, which I failed to see in the materials and methods and results section.
2. Limitations of the study should be mentioned at the end of the manuscript. One of them beaning a single dose od DHA used in the experiment.

 

 

 

 

Author Response

Reviewer #2:

Comments and Suggestions for Authors

Dear Editor,

After reviewing a manuscript, I find it suitable to be published in the IJTM after minor corrections and explanations. The manuscript is well structured and data presented are of interest to the readers. Methods used provide the results which are well explained in the discussion section. Here are the remarks that should be addressed:

Answer:

We appreciate reviewer’s careful reviews on our manuscript. We have carefully checked the reviewer’s constructive and helpful comments and made necessary corrections to revised manuscript (marked by red font) We believe that your comments helped to improve our manuscript.

Comment

The authors mention that they measured DHA concentration in blood, which I failed to see in the materials and methods and results section.

Answer:

We appreciate reviewer’s careful reviews on our manuscript. The blood concentration of DHA was not measured in this study. The concentration of DHA mentioned in the discussion section, 10 μM, is a theoretical value that would be diluted in the blood when administered systemically, and it is compared to the effects on neurons observed in previous in vitro experiments.

Comment

Limitations of the study should be mentioned at the end of the manuscript. One of them beaning a single dose od DHA used in the experiment.

Answer:

According to reviewer’s comment, we have added new sentences in the discussion (page 9) as follows; Finally, the present study examines the effects of a single intravenous administration of DHA on nociceptive pain in naïve rats, whereas the effects on pathological pain, such as inflammatory or neuropathic pain, require further investigation. Therefore, future experiments should focus on investigating the effects on pathological pain. Furthermore, experiments on continuous intravenous administration of DHA are necessary to examine the duration of its analgesic effects.