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: Previous studies have indicated that the globus pallidus receives neurotensinergic innervation from the striatum , and systemic administration of a neurotensin analog could produce antiparkinsonian effects .
### Output Text:
Previous studies have indicated that the globus pallidus receives neurotensinergic innervation from the striatum , and systemic administration of a <span class="chemical">neurotensin</span> analog could produce antiparkinsonian effects . 