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: Sprague - Dawley rats were injected intraperitoneally with pilocarpine , and the hippocampal formation was studied histologically at 1 , 2 , 4 , and 8 week intervals after pilocarpine - induced seizures .
### Output Text:
Sprague - Dawley rats were injected intraperitoneally with <span class="chemical">pilocarpine</span> , and the hippocampal formation was studied histologically at 1 , 2 , 4 , and 8 week intervals after <span class="chemical">pilocarpine</span> - induced seizures . 