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: Down - regulation of norepinephrine transporter function induced by chronic administration of desipramine linking to the alteration of sensitivity of local - anesthetics - induced convulsions and the counteraction by co - administration with local anesthetics .
### Output Text:
Down - regulation of <span class="chemical">norepinephrine</span> transporter function induced by chronic administration of <span class="chemical">desipramine</span> linking to the alteration of sensitivity of local - anesthetics - induced convulsions and the counteraction by co - administration with local anesthetics . 