In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: Upregulation of the expression of vasopressin gene in the paraventricular and supraoptic nuclei of the lithium - induced diabetes insipidus rat .
### Output Text:
Upregulation of the expression of <span class="chemical">vasopressin</span> gene in the paraventricular and supraoptic nuclei of the <span class="chemical">lithium</span> - induced diabetes insipidus rat . 