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: Intracerebroventricular injection of ethacrynic acid ( 50 % convulsive dose ; 50 micrograms / mouse ) accelerated the synthesis / turnover of 5 - hydroxytryptamine ( 5 - HT ) but suppressed the synthesis of gamma - aminobutyric acid and acetylcholine in mouse brain .
### Output Text:
Intracerebroventricular injection of <span class="chemical">ethacrynic acid</span> ( 50 % convulsive dose ; 50 micrograms / mouse ) accelerated the synthesis / turnover of <span class="chemical">5 - hydroxytryptamine</span> ( <span class="chemical">5 - HT</span> ) but suppressed the synthesis of <span class="chemical">gamma - aminobutyric acid</span> and <span class="chemical">acetylcholine</span> in mouse brain . 