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. 2019 Dec;61(4):236-241.
doi: 10.1016/j.job.2019.08.002. Epub 2019 Sep 3.

Dynamic photoacoustic imaging of neurovascular coupling in salivary glands

Laurie J Rich  1 , Eftekhar Rajab Bolookat  2 , Mukund Seshadri  3
Affiliations

Dynamic photoacoustic imaging of neurovascular coupling in salivary glands

Laurie J Rich et al. J Oral Biosci. 2019 Dec.

Abstract

The purpose of this study was to apply photoacoustic imaging (PAI), a relatively new imaging method, to non-invasively map neurovascular dynamics in salivary glands. Dynamic PAI with co-registered ultrasound (US) was performed in mice to monitor salivary gland hemodynamics in response to exogenous muscarinic receptor stimulation (pilocarpine) and blockade (atropine). Pilocarpine increased salivary gland oxygen saturation (%sO2) within minutes after administration, which was abrogated by atropine. A significant correlation was observed between change in %sO2 measured by PAI and saliva secretion. PAI is a novel imaging method that can be used for functional assessment of neurovascular dynamics in salivary glands.

Keywords: Atropine; Pilocarpine; Salivary glands; Ultrasonography.

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Conflict of interest statement

Conflicts of interest

The authors declare no competing financial interests. The funding sponsors had no role in the design of the study, collection, analyses, or interpretation of data, writing of the manuscript, and in the decision to publish the results.

Figures

Figure 1.
Figure 1.. Dynamic photoacoustic imaging of neurovascular coupling in salivary glands.
(A) Schematic illustration of the dynamic PAI method developed for temporal mapping of neurovascular dynamics in murine salivary glands. The method involves acquisition of a series of PA images before and after parasympathetic stimulation using pilocarpine. Changes in %sO2 were correlated with saliva secretion. The effect of muscarinic blockade (Atropine) was studied to validate the method. Panel of images represent pseudo-colorized oxygen saturation map (B) of healthy murine salivary gland along with co-registered images of Masson’s Trichrome staining (C). Threshold image (D) of the immunostained section of the gland is shown to visualize large ducts and vessels (white arrows). Areas of high %sO2 signal corresponded with regions containing large ductal and vascular structures embedded within connective tissue inside the salivary gland.
Figure 2.
Figure 2.. Dynamic PAI of salivary gland hemodynamic response to pilocarpine.
(A) Panel of images represents dynamic series of PA oxygen saturation (%sO2) maps of salivary glands acquired before (pre-stimulation), and 1, 3, 5, and 7 min after pilocarpine or saline administration. Bar graphs of quantitative estimates of change in %sO2 levels (B) and salivary secretion (C) at different time points post-pilocarpine administration. (D) Correlation plot comparing temporal change in %sO2 levels with saliva volume measurements (Pearson r = 0.9009). Error bars represent standard error of the mean. **p < 0.01, ***p < 0.001.
Figure 3.
Figure 3.. Effect of atropine on pilocarpine-induced hemodynamic response in salivary glands.
(A) Pseudo-colorized %sO2 maps of salivary glands acquired before (Pre-Pilocarpine) and after pilocarpine (Post-Pilocarpine) administration with or without atropine. A visual loss in hemodynamic response to pilocarpine stimulation was observed after atropine treatment (+Atropine). (B) Quantitative measure of change in salivary gland %sO2 levels showed a significant reduction in animals pre-treated with atropine compared to animals treated with pilocarpine alone (No atropine). (C) Saliva volume measurements also showed significantly lower salivary secretion levels in atropine treated animals compared to animals treated only with pilocarpine. Error bars represent standard error of the mean. **p < 0.01, ***p < 0.001, ****p < 0.0001.
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