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: Convulsant effect of lindane and regional brain concentration of GABA and dopamine .
### Output Text:
Convulsant effect of <span class="chemical">lindane</span> and regional brain concentration of <span class="chemical">GABA</span> and <span class="chemical">dopamine</span> . 