From the previous findings, we predicted that oxytocin would dampen brain circuits in all ways, quieting both background noise and wanted signals, Dr. Tsien explains. Instead, we found that oxytocin increased the reliability of stimulated impulses good for brain function, but quite unexpected.
To resolve this paradox, Dr. Tsien and his Stanford graduate student Scott Owen collaborated with Gord Fishell, PhD, the Julius Raynes Professor of Neuroscience and Physiology at NYU Langone Medical Center, and NYU graduate student Sebnem Tuncdemir. They identified the particular type of inhibitory interneurons responsible for the effects of oxytocin: fast-spiking inhibitory interneurons.
The mystery of how oxytocin drives these fast-spiking inhibitory cells to fire, yet also increases signaling to pyramidal neurons, was solved through studies with rodent models. The researchers found that continually activating the fast-spiking inhibitory neurons good for lowering background noise also causes their GABA-releasing synapses to fatigue. Accordingly, when a stimulus arrives, the tired synapses release less GABA and excitation of the pyramidal neuron is not dampened as much, so that excitation drives the pyramidal neurons firing more reliably.
The stronger signal and muffled background noise arise from the same fundamental action of oxytocin and give two benefits for the price of one, Dr. Fishell explains. Its too early to say how the lack of oxytocin signaling is involved in the wide diversity of autism-spectrum disorders, and the jury is still out about its possible therapeutic effects. But it is encouraging to find that a naturally occurring neurohormone can enhance brain circuits by dialing up wanted signals while quieting background noise.
|Contact: Craig Andrews|
NYU Langone Medical Center / New York University School of Medicine