Antagonists are any chemicals that fit into receptor sites on the post-synaptic neuron, inhibiting the neuron from firing. Well-known antagonists for serotonin, which we looked at in the previous blog post, are anti-psychotic drugs like Clozapine, which acts on the HT2A serotonin receptors to decrease the effects of serotonin in the brain. Many ant-psychotic drugs also act as antagonists for dopamine, as an excess of both dopamine and serotonin has been associated with schizophrenia.
However, easy-to-understand studies referencing this effect of Clozapine are difficult to come by, so while this is useful knowledge for students on how anti-psychotic medication works, when teaching about antagonists there is more available research on the effects of scopolamine on acetylcholine, and hence on memory. (And incidentally on motion sickness, as scopolamine is excellent at preventing nausea and vomiting!)
Scopolamine acts by blocking the acetylcholine receptors, specifically the muscarinic receptors (see the link below). Atri et al (2004) reported how blocking the muscarinic acetylcholine receptors (mAChRs), by injecting scopolamine impairs learning of paired words.
As an age-related deterioration in cognitive function is thought to be predominantly related to a decline in cholinergic neurotransmission (relating to nerve cells in which acetylcholine acts as a neurotransmitter), scopolamine administration has often been used to model dementia. Scopolamine has therefore been extensively used for preclinical and clinical testing of treatments for cognitive impairment. For example, Tröster et al (2013) found that scopolamine negatively affected anterograde short-term memory and verbal and nonverbal learning in middle-aged men.