A new and more detailed picture of a key receptor in the brain that influences the effectiveness of serotonin-related antidepressants such as Prozac could lead to more targeted depression medication with fewer side effects.
Depressive disorders change a person’s mood, emotions and physical well-being and can co-occur with anxiety disorders and substance abuse. A study in January found half of Americans with severe depression don't get treatment.
“There are big drawbacks in the current therapies for depression,” says senior author John Traynor, professor of pharmacology at the University of Michigan Medical School. “Therapeutic benefits are delayed, there are unwanted side effects, and it’s not unusual for depressive symptoms to return.”
The high relapse rate indicates a need for additional treatment options for the estimated 20.9 million Americans with depression, Traynor and colleages write this week in the journal Proceedings of the National Academy of Sciences.
The best current treatments for depression are selective serotonin reuptake inhibitors, or SSRIs. These drugs work by flooding the brain’s synapses with serotonin, a neurotransmitter linked with mood, and increasing serotonin signaling through the more than 20 serotonin receptors in the brain.
However, the team of researchers showed one particular pathway, the serotonin 5HT1a receptor is linked with antidepressive and antianxiety behavior in mice.
“Rather than activating all serotonin receptors as SSRIs do, one could increase signaling through the one critical serotonin receptor that our research shows is important for antidepressant behavior,” says co-author Richard R. Neubig, M.D., Ph.D., co-director of the U-M Center for Chemical Genomics and professor of pharmacology at the U-M Medical School.
The new research details the complex actions of a family of proteins, known as RGS proteins, that act as brakes on neurotransmitter signaling.
Researchers created a mutant mouse to boost serotonin signaling at the 5HT1a receptor. This was done by genetically inhibiting the activity of braking proteins. Without the normal brake on serotonin signaling, these mutant mice showed antidepressive behavior even without being given antidepressant drugs. The mice were also more responsive to SSRIs.
Further research could lead to drugs capable of inhibiting the RGS proteins and which would target the antidepressant signal where it is required on critical 5HT1a receptors, the researcher said.
The study was funded by the National Institute of General Medical Sciences and the National Institute on Drug Abuse.