Stories about: Takao Hensch

How the antidepressant ketamine rapidly awakens the brain, and why its effects vary more in women

(CREDIT: NATHALIE PICARD / BOSTON CHILDREN’S HOSPITAL)

In small doses, the anesthetic ketamine is a mildly hallucinogenic party drug known as “Special K.” In even smaller doses, ketamine relieves depression — abruptly and sometimes dramatically, steering some people away from suicidal thoughts. Studies indicate that ketamine works in 60 to 70 percent of people not helped by slower-acting SSRIs, the usual drugs for depression.

Two ketamine-like drugs are in the clinical pipeline, and, as of this week, one appears close to FDA approval. With no significant new antidepressant in more than 30 years, anticipation is high. Yet no one has pinned down how low-dose ketamine works. Studies have implicated various brain neurotransmitters and their receptors — serotonin, dopamine, glutamate, GABA receptors, opioid receptors — but findings have been contradictory.

“We felt it was time to figure this out once and for all,” says neuroscientist Takao Hensch, PhD.

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Opening up brain critical periods: Lynx1 and where sensory information meets context

auditory critical periods involve neurons in levels 1 and 4 of the auditory cortex
Interneurons (white) from layer 1 (L1) of the auditory cortex descend to contact parvalbumin cells (red) in layer 4. (Images courtesy Hensch Lab).

Babies’ brains are like sponges — highly tuned to incoming sensory information and readily rewiring their circuits. But when so-called critical periods close, our brains lose much of this plasticity. Classic experiments reveal this in the visual system: when kittens and mice had one eye covered shortly after birth, that eye was blind for life, even after the covering was removed. The brain never learned to interpret the visual inputs.

In 2010, a study led by Takao Hensch, PhD, of the F.M. Kirby Neurobiology Center at Boston Children’s Hospital, showed that levels of a protein called Lynx1 rise just as the critical period for visual acuity closes. When the researchers deleted the Lynx1 gene in mice, the critical period reopened and mice recovered vision in the blind eye.

A new study this week in Nature Neuroscience extends Lynx1’s role to the auditory system.

“If we remove Lynx1, the auditory critical period stays open longer,” says Hensch.

Equally important, the study pinpoints the location in the brain where sensory inputs combine with another essential ingredient: what neuroscientists call context.

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