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: In brain membranes from spontaneously hypertensive rats clonidine , 10 ( - 8 ) to 10 ( - 5 ) M , did not influence stereoselective binding of [ 3H ] - naloxone ( 8 nM ) , and naloxone , 10 ( - 8 ) to 10 ( - 4 ) M , did not influence clonidine - suppressible binding of [ 3H ] - dihydroergocryptine ( 1 nM ) .
### Output Text:
In brain membranes from spontaneously hypertensive rats <span class="chemical">clonidine</span> , 10 ( - 8 ) to 10 ( - 5 ) M , did not influence stereoselective binding of <span class="chemical">[ 3H ] - naloxone</span> ( 8 nM ) , and <span class="chemical">naloxone</span> , 10 ( - 8 ) to 10 ( - 4 ) M , did not influence <span class="chemical">clonidine</span> - suppressible binding of <span class="chemical">[ 3H ] - dihydroergocryptine</span> ( 1 nM ) . 