The role of serotonergic neurons in nucleus raphe magnus in opioid antinociception

It has been proposed that serotonergic neurons do not mediate opioid analgesia, based on the observation that the firing rates of serotonergic neurons are not modulated by antinociceptive treatments such as systemic opioids or periaqueductal gray (PAG) stimulation. However, several points need to be clarified regarding the data supporting this hypothesis. These include establishing whether anesthesia has influenced the results of these experiments, whether the serotonergic neurons recorded project to the dorsal horn, and whether presynaptic effects might allow opioids to change serotonin release without changing neuronal firing rate.