This study was supported by Guangdong Provincial High-level Clinical Key Specialties (SZGSP014) and Shenzhen Natural Science Foundation (JCYJ20210324125805012).

All animal experiments performed following this protocol are performed under the approval of the Institutional Animal Care and Use Committee (IACUC).
1. Animal preparation
<ol>
	<li>Prepare 12 healthy 6-week-old SPF Wistar female rats weighing 160 g &#177; 20 g.</li>
	<li>Use a slit lamp and ophthalmoscope to examine the eye conditions of all rats, ensuring that there are no anterior segment or retinal diseases.</li>
	<li>Raise all the rats for 1 week with sufficient food an...

Scopolamine-Induced Lacrimal Gland Dysfunction in Rats

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Aqueous-deficient dry eye (ADDE) is an important type of dry eye, accounting for about 1/3 of the total dry eye population17, and the main cause of ADDE is lacrimal gland pathological damage and inflammation13. For this type of dry eye, the most common clinical treatment methods are artificial tears to alleviate symptoms or topical application of steroids or cyclosporine18, while there are few treatment options for damage to the lacrimal gland. There...

By 2021, approximately 12% of people are significantly affected by dry eyes1, making it one of the most common chronic eye diseases. Dry eye can be divided into two types: aqueous-deficient dry eye (ADDE) and evaporative dry eye (EDE)2, depending on the different factors that affect the disease. ADDE is further divided into Sj&#246;gren&#39;s syndrome (SS) and non-SS, but the majority of dry eye patients are non-SS patients in clinical3. Chronic dry eye symptoms seriously affect the visual quality of patients. Currently, the conventional treatment of DED involves the application of artificial tears to lubricate the ocular surface and physical therapy of the eyelids. However, dry eye syndrome may not offer a complete cure in many cases. Therefore, studying the pathogenesis of dry eye disease is crucial for the development of new therapies and drugs. Animal models of dry eye syndrome provide a foundation for further research.
There are many ways to construct animal models of dry eye syndrome4, including changing tear secretion levels by altering hormone levels. For example, removing the testes of rats can reduce androgen secretion, increase tear secretion, and decrease the concentration of free secretory component (SC) and IgA in tears5,6. Another method is to indicate autoimmune reactions in the lacrimal gland by removing the eye surface nerves that control the gland. Additionally, directly reducing tear secretion can be achieved by surgically removing the lacrimal gland7. Changing environmental conditions can also accelerate tear evaporation. For example, culturing animals in low humidity and dry ventilation conditions can establish a model of excessive evaporative dry eye8, which can be combined with other methods to increase the severity of dry eye. The main drugs used to induce dry eye experimental models are atropine and scopolamine9. As parasympathetic inhibitors, both can induce pharmacological blockade of cholinergic (muscarinic) receptors in the lacrimal gland and inhibit tear secretion. Compared with dry eyes caused by atropine muscle injection10, scopolamine has a stronger inhibitory effect on secretion glands, a longer duration of drug action, and weaker effects on cardiac, small intestinal, and bronchial smooth muscles. It is one of the most mature drugs for dry-eye animal models.
Different methods can be used to induce dry eye with scopolamine, such as subcutaneous injection, drug pump, or patch application4,11,12. In order to reduce the frequency of drug administration to experimental animals, many researchers apply transdermal patches to the tails of mice or use drug pumps. However, both of these methods have limitations. For example, the absorption of transdermal patches needs to take into account the individual absorption of mice, which can lead to inconsistent drug dosage. Although drug pumps can accurately control the dosage of each administration, they are not always compatible with the drug being delivered or the concentration being used. They also need to be placed surgically &#8211; which is more invasive to the animal, requiring an anesthetic event, and there is potential for post-surgical complications such as dehiscence. Subcutaneous injection, although more cumbersome, can ensure accurate dosage for each administration and maintain consistency in drug administration among different rats. At the same time, it has a lower cost and is suitable for conducting a large number of animal experiments.
This study applies repeated subcutaneous injection of scopolamine to establish a dry eye rat model. We analyze dry eye indicators such as corneal defects, tear secretion levels, and pathological morphology of the cornea, conjunctiva, and lacrimal gland. By combining drug concentration, pathological manifestations, and dry eye symptoms, we further elaborate on the dry eye rat model in detail, providing more accurate experimental data for the study of dry eye treatment and pathological mechanisms. We also describe the modeling process in detail for future researchers.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>0.9% sodium chloride solution</td>
			<td>SJZ No.4 Pharmaceutical</td>
			<td>H13023201</td>
			<td></td>
		</tr>
		<tr>
			<td>4% paraformaldehyde</td>
			<td>Wuhan Servicebio Technology Co., Ltd</td>
			<td>G1113</td>
			<td></td>
		</tr>
		<tr>
			<td>Absolute ethanol</td>
			<td>Sinopharm Chemical Reagent Co., Ltd.</td>
			<td>10009218</td>
			<td></td>
		</tr>
		<tr>
			<td>Fluorescein sodium ophthalmic strips</td>
			<td>Tianjin Yinuoxinkang Medical Device Tech Co., Ltd</td>
			<td>YN-YG-I</td>
			<td></td>
		</tr>
		<tr>
			<td>Hematoxylin and eosin</td>
			<td>Nanjing Jiancheng Bioengineering Institute</td>
			<td>D006</td>
			<td></td>
		</tr>
		<tr>
			<td>Neutral balsam</td>
			<td>Beijing Solarbio Science &#38; Technology Co., Ltd.&#160;</td>
			<td>G8590</td>
			<td></td>
		</tr>
		<tr>
			<td>Paraffin</td>
			<td>Beijing Solarbio Science &#38; Technology Co., Ltd.</td>
			<td>YA0012</td>
			<td></td>
		</tr>
		<tr>
			<td>Periodic Acid-Schiff Staining Kit</td>
			<td>Beyotime Biotechnology</td>
			<td>C0142S</td>
			<td></td>
		</tr>
		<tr>
			<td>Schirmer tear test strips</td>
			<td>Tianjin Yinuoxinkang Medical Device Tech Co., Ltd</td>
			<td>YN-LZ-I</td>
			<td></td>
		</tr>
		<tr>
			<td>Scopolamine hydrobromide</td>
			<td>Shanghai Macklin Biochemical Co., Ltd</td>
			<td>S860151</td>
			<td></td>
		</tr>
		<tr>
			<td>Small animal microscope</td>
			<td>Head Biotechnology Co,. Ltd</td>
			<td>ZM191</td>
			<td></td>
		</tr>
		<tr>
			<td>Xylene</td>
			<td>Sinopharm Chemical Reagent Co., Ltd.</td>
			<td>10023418</td>
			<td></td>
		</tr>
	</tbody>
</table>

a rat dry eye model with lacrimal gland dysfunction induced by scopolamine

Aqueous-deficient dry eye (ADDE) is a type of dry eye disease that can result in the reduction of tear secretion quantity and quality. Prolonged abnormal tear production can lead to a disturbance in the ocular surface environment, including corneal damage and inflammation. In severe cases, ADDE can cause vision loss or even blindness. Currently, dry eye treatment is limited to eye drops or physical therapy, which can only alleviate eye discomfort symptoms and cannot fundamentally cure dry eye syndrome. To restore the function of the lacrimal gland in dry eye, we have created an animal model of lacrimal gland dysfunction in rats induced by scopolamine. Through the comprehensive evaluation of the lacrimal gland, corneas, conjunctivas, and other factors, we aim to provide a full understanding of the pathological changes of ADDE. Compared with the current dry eye mouse model, this ADDE animal model includes a functional evaluation of the lacrimal gland, providing a better platform for studying lacrimal gland dysfunction in ADDE.

Author Spotlight: Challenges in Developing Dry Eye Animal Models and Future Research Directions

A Rat Dry Eye Model with Lacrimal Gland Dysfunction Induced by Scopolamine

The process of developing a dry eye animal model is a long one. It requires continuous subcutaneous injection of scopolamine in the hind legs of rice to suppress the secretion of the lacrymal gland in rice. So, experimenters need to have enough patience to administer the medication regularly over a long period of time.Our protocol is a very useful method that can created different degrees of dry eye models based on different drug concentrations. It can make it easiest for the future researchers to study the treatment of dry eye disease. Our team will continue to explore the field of lacrimal gland regeneration, very excited to work on reconstructing 3D and conducting transplantation experiments.Our ultimate goal is to develop more advanced and efficient treatment options for individuals suffering from dry eye syndrome.

Schirmer I test, SIT I 
The tear volume of the rats was measured on days 0, 3, 5, 7, 11, 15, and 19 after the start of the experiment. The experimental results showed that the tear secretion of the scopolamine group (2.5 group, 5 group, 7.5 group), compared with the control group (0 group), was significantly decreased, and the difference was statistically significant (P &#60; 0.01). There was no statistical significance between the 2.5 group, 5 group, and 7.5 group (P &#62; 0.05). There was no signi...

Watch this Scientific Journal Video about A Rat Dry Eye Model with Lacrimal Gland Dysfunction Induced by Scopolamine at JoVE.com

Here, we establish a rat model of lacrimal gland dysfunction to provide a basis for the study of aqueous-deficient dry eye.

Aqueous-deficient dry eye (ADDE) is a type of dry eye disease that can result in the reduction of tear secretion quantity and quality. Prolonged abnormal ...