After 'freezing' in fear, what part of the brain helps make fish swim again?
The brain is the body's mission control center, sending messages to the other organs about how to respond to various external and internal stimuli. Located in the forebrain, the habenular region is one such message-conducting system. Two new papers from Carnegie scientists explain how the habenulae develop and their unsuspected role in recovering from fear.
Found in all vertebrates, the bilaterally paired habenulae regulate the transmission of dopamine and serotonin, two important chemicals related to motor control, mood, and learning.
Previous research has shown that the habenular system is involved in modulating sleep cycles, anxiety, and pain and reward processing, among other things. It has also been associated with depression and addiction.
New work from Carnegie's Erik Duboué and Marnie Halpern, assisted by Kiara Eldred, a Johns Hopkins graduate student, and Elim Hong, now a group leader in Neuroscience at the Institut de Biologie Paris-Seine, focused on the action of the habenular region in regulating fear responses in larval zebrafish.
It turns out that the habenulae differ between the left and right sides of the fish brain, both in their structure and when it comes to experiencing and recovering from fear. A mild electric shock makes zebrafish larvae "freeze" in fear, just like a deer in headlights. After this occurs, neurons in the left habenula are needed for a rapid return to swimming activity, according to the team's findings, published by Current Biology.
Erik R. Duboué, Elim Hong, Kiara C. Eldred, Marnie E. Halpern. Left Habenular Activity Attenuates Fear Responses in Larval Zebrafish. Current Biology, 2017; DOI: 10.1016/j.cub.2017.06.017
A. Labeled habenular neurons in the forebrain of larval zebrafish connected to their midbrain target. B. Dorsal view of the left-right asymmetric habenular region in a normal larva and in C. one lacking chemokine signaling, where many neurons are misrouted and project in the wrong direction.Credit: Images courtesy of Courtney Akitake and Sara Roberson