eLife Assessment
This study presents important information about the role of mu opioid receptors in synaptic communication between the medial habenula and the interpeduncular nucleus. The authors provide solid evidence that mu opioid receptor activation has differential effects on glutamate release from substance P neurons and cholinergic neurons, with a canonical reduction in release from the former but a novel increase in release from the latter. They also show that blocking potassium channels can unmask a nicotinic cholinergic synaptic response that is also facilitated by mu opioid receptor activation. This work will be of interest to those studying the interpeduncular nucleus, as well as the larger neuroscience community studying opioids and motivated behavior.