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: It increases the behaviour stimulation evoked by phenylephrine ( given intraventricularly ) in rats , evaluated in the open field test as well as the aggressiveness evoked by clonidine in mice , both these effects being mediated by an alpha1 - adrenergic receptor .
### Output Text:
It increases the behaviour stimulation evoked by <span class="chemical">phenylephrine</span> ( given intraventricularly ) in rats , evaluated in the open field test as well as the aggressiveness evoked by <span class="chemical">clonidine</span> in mice , both these effects being mediated by an alpha1 - adrenergic receptor . 