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: We studied the effect of lindane ( 150 mg / kg ) on the GABAergic and dopaminergic systems by measuring the concentration of GABA , dopamine and its metabolites in 7 brain areas at the onset of seizures .
### Output Text:
We studied the effect of <span class="chemical">lindane</span> ( 150 mg / kg ) on the GABAergic and dopaminergic systems by measuring the concentration of <span class="chemical">GABA</span> , <span class="chemical">dopamine</span> and its metabolites in 7 brain areas at the onset of seizures . 