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: However , the diazepam enhancement of adrenaline - induced reflex bradycardia was antagonized by pretreatment of rats with an intravenous dose of picrotoxin ( an agent blocks chloride channels by binding to sites associated with the benzodiazepine - GABA - chloride channel macromolecular complex ) .
### Output Text:
However , the <span class="chemical">diazepam</span> enhancement of <span class="chemical">adrenaline</span> - induced reflex bradycardia was antagonized by pretreatment of rats with an intravenous dose of <span class="chemical">picrotoxin</span> ( an agent blocks <span class="chemical">chloride</span> channels by binding to sites associated with the <span class="chemical">benzodiazepine</span> - <span class="chemical">GABA</span> - <span class="chemical">chloride</span> channel macromolecular complex ) . 