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: The results demonstrate that the threshold for pilocarpine - induced seizures in rats is subjected to the regulation of the GABA - mediated synaptic inhibition within the substantia nigra .
### Output Text:
The results demonstrate that the threshold for <span class="chemical">pilocarpine</span> - induced seizures in rats is subjected to the regulation of the <span class="chemical">GABA</span> - mediated synaptic inhibition within the substantia nigra . 