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: The present study was designed to investigate whether nociceptin / orphanin FQ and nocistatin could modulate impairment of learning and memory induced by scopolamine , a muscarinic cholinergic receptor antagonist , using spontaneous alternation of Y - maze and step - down type passive avoidance tasks in mice .
### Output Text:
The present study was designed to investigate whether <span class="chemical">nociceptin</span> / <span class="chemical">orphanin FQ</span> and <span class="chemical">nocistatin</span> could modulate impairment of learning and memory induced by <span class="chemical">scopolamine</span> , a muscarinic cholinergic receptor antagonist , using spontaneous alternation of Y - maze and step - down type passive avoidance tasks in mice . 