TRH and respiratory depression: Experimental drugs that have been tested previously for the reversal of opioid-induced respiratory depression include the 5HT4a receptor agonist BIMU-8 (Manzke et al., 2003), thyrotropin-releasing hormone (Horita et al., 1976), nicotinic acetylcholine receptor agonists (Ren et al., 2019), ampakines (Ren et al., 2006, 2009), microglia inhibitors (Hutchinson et al., 2008), and D1-receptor agonists (Lalley, 2004, 2005).