Ultrasound and the developing brain – lessons from manipulation of mouse neurons

There’s a bit of wing-nuttery on the net about a possible relationship between the widespread use of obstetric ultrasound and an increase in the percentage of children diagnoses with autism (though there’s also been a simultaneous decrease in the percent of children diagnosed with mental retardation).

Sometimes the discussions have even had humorous consequences.

Still, there’s some reason for interest.

Which brings us the use of intermediate intensity ultrasound for altering the brain …

Sound and no fury | The Economist

… William Tyler and his colleagues at Arizona State University..

… knew from experiments done by other groups of researchers that ultrasound can have a physical effect on tissue. Unfortunately, that effect is generally a harmful one. When nerve cells were exposed to it at close range, for example, they heated up and died. Dr Tyler, however, realised that all of the studies he had examined used high-intensity ultrasound. He guessed that lowering the intensity might allow nerve cells to be manipulated without damage.

To test this idea, he and his colleagues placed slices of living mouse brain into an artificial version of cerebrospinal fluid, the liquid that cushions the brain. They then beamed different frequencies of low-intensity ultrasound at the slices and monitored the results using dye molecules that give off light in response to the activity of proteins called ion channels. (An ion channel is a molecule that allows the passage of electrically charged atoms of sodium, potassium, calcium and so on through the outer membrane of a cell.)

The purpose of all this was to coax the cells to release neurotransmitters. These are molecules that carry information from one nerve cell to another. When they arrive, they cause ion channels to open and thus trigger the electrical impulses that pass messages along nerve fibres. When those pulses arrive at the other end of a fibre they, in turn, trigger the release of more neurotransmitters.

Disruption of this system of communication is characteristic of several medical conditions, including Alzheimer’s disease, Parkinson’s disease, depression and epilepsy. Ways of boosting the release of neurotransmitters may thus have therapeutic value. And the ultrasound did indeed boost their release.

How that came about is not absolutely certain, but Dr Tyler thinks the shaking that his ultrasound gave to the cells in question opened up some of their ion channels. The cells were thus fooled into acting as though an impulse had arrived, and released neurotransmitters as a consequence…

So the obvious question is how does the intensity and duration of the ultrasound used in these experiments compare with the intensity of ultrasound used in obstetric scans? After all, “disruption of this system of communication” is also a characteristic of autism.

It feels like it would be wise to do further animal model studies, and to discourage obstetric ultrasound done largely for entertainment purposes rather than to truly guide and manage pregnancy.