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: Microinjections of gamma - vinyl - GABA , 5 micrograms , into the dorsal striatum , bilaterally , failed to prevent the development of convulsions produced by pilocarpine , 380 mg / kg .
### Output Text:
Microinjections of <span class="chemical">gamma - vinyl - GABA</span> , 5 micrograms , into the dorsal striatum , bilaterally , failed to prevent the development of convulsions produced by <span class="chemical">pilocarpine</span> , 380 mg / kg . 