NIMH · Study Reveals New Clues to How Depression May Develop

Science Update • April 20, 2011

Study Reveals New Clues to How Depression May Develop

Activating neurons in a brain structure linked to disappointment increased depression-like behaviors in rats, while suppressing the neurons' activity reduced the behaviors, according to an NIMH-funded study. The findings help to explain previous research linking this brain structure to depression in humans and highlight a cellular process that hadn't been previously explored in mood disorders research. The study was published in the February 24, 2011, issue of Nature.

Background

Depression is one of the most studied mental disorders, with research honing in on brain structures, circuits, and biochemical processes critical to the development of the disorder. Yet many questions remain about how changes in the brain result in the observable symptoms and behaviors associated with depression.

To advance the science in this area, Bo Li, Ph.D., of Cold Spring Harbor Laboratory in New York, and colleagues, explored the role and connectivity of neurons in the lateral habenula (LHb) in rats that showed learned helplessness, a set of behaviors similar to symptoms of depression in people. The LHb is associated with how humans and animals experience disappointment or anticipate negative outcomes.

Results of the Study

The researchers found that LHb neurons receive input from many different brain regions involved in responding to stress. LHb neurons also connect out to many brain regions, such as the ventral tegmental area (VTA). The VTA helps to control reward-seeking behavior and may have a role in depression and other mood disorders.

LHb neurons in helpless rats were more responsive, such that communication signals to the VTA were more likely to be transmitted in the helpless rats than in control rats. In an attempt to moderate this phenomenon, the researchers tested the effects of deep brain stimulation (DBS), a surgical procedure currently being tested in humans for treatment-resistant depression. Applying continuous electrical stimulation directly to the LHb resulted in greatly reduced transmission to the VTA and a marked reduction in helpless behavior. The effects on transmission lasted only as long as the stimulation lasted. More intense stimulation resulted in stronger behavioral effects.

Significance

Although LHb activity was previously unstudied in the context of mood disorders, these findings suggest that this brain structure may actually play a central role in the development of depression.

What's Next

Further studies focusing on the molecular processes and signals underlying LHb activity in depression may reveal new targets for treatment development, according to the researchers. Such new treatments also may be able to reverse some forms of depressive disorders.

This study was supported in part by a Biobehavioral Research Award for Innovative New Scientists (BRAINS) from NIMH. Dr. Li was one of 12 researchers to receive this award in 2010.

Lateral habenula neuron labeled with green fluorescent protein. The area marked by a white box is shown at greater magnification in the image on the right.

Source: Bo Li, Ph.D., Cold Spring Harbor Laboratory

Reference
Li B, Piriz J, Mirrione M, Chung C, Proulx CD, Schulz D, Henn F, Malinow R. Synaptic potentiation onto habenula neurons in the learned helplessness model of depression. Nature. 2011 Feb 24;470(7335):535-9. PubMed PMID: 21350486.


full-text:
NIMH · Study Reveals New Clues to How Depression May Develop



Nature. 2011 Feb 24;470(7335):535-9.
Synaptic potentiation onto habenula neurons in the learned helplessness model of depression.
Li B, Piriz J, Mirrione M, Chung C, Proulx CD, Schulz D, Henn F, Malinow R.
SourceCenter for Neural Circuits and Behavior, Department of Neuroscience, University of California at San Diego, La Jolla, California 92093, USA. bli@cshl.edu


Abstract
The cellular basis of depressive disorders is poorly understood. Recent studies in monkeys indicate that neurons in the lateral habenula (LHb), a nucleus that mediates communication between forebrain and midbrain structures, can increase their activity when an animal fails to receive an expected positive reward or receives a stimulus that predicts aversive conditions (that is, disappointment or anticipation of a negative outcome). LHb neurons project to, and modulate, dopamine-rich regions, such as the ventral tegmental area (VTA), that control reward-seeking behaviour and participate in depressive disorders. Here we show that in two learned helplessness models of depression, excitatory synapses onto LHb neurons projecting to the VTA are potentiated. Synaptic potentiation correlates with an animal's helplessness behaviour and is due to an enhanced presynaptic release probability. Depleting transmitter release by repeated electrical stimulation of LHb afferents, using a protocol that can be effective for patients who are depressed, markedly suppresses synaptic drive onto VTA-projecting LHb neurons in brain slices and can significantly reduce learned helplessness behaviour in rats. Our results indicate that increased presynaptic action onto LHb neurons contributes to the rodent learned helplessness model of depression.

PMID:21350486[PubMed - indexed for MEDLINE]
Synaptic potentiation onto habenula neurons in the... [Nature. 2011] - PubMed result