AsianScientist (Feb. 14, 2017) – Noradrenaline, a hormone best known for its effects on heart rate and blood flow, also regulates vision through binding β-adrenergic receptors. These findings have been published in PLOS ONE.
Understanding how noradrenaline functions in the brain is expected to give new insights on how the brain processes spatial information, which has important implications on patient care and machine learning.
Noradrenaline exerts its effects by binding to adrenergic receptors. Drugs called beta blockers target β-adrenergic receptors, but there are also exist α-adrenergic receptors, for which there exists alpha blockers. Although noradrenaline is also known to affect vision, studies on different animals have been inconclusive about which receptors are primarily responsible for this effect.
“Noradrenaline administration modulates the primary visual cortex (V1),” said Osaka University Associate Professor Satoshi Shimegi. “It changes the spatial sensitivity of this region.”
In a new set of experiments, the Shimegi lab observed the effects of noradrenaline on the vision of free-moving rats.
“We wanted to observe behaving animals, because this is a better representation of nature,” explained graduate student Mr. Ryo Mizuyama, first author of the study.
The rats were subjected to one of two different inhibitors of β-adrenergic receptors or one inhibitor of β-adrenergic receptors. Of the three, only the β-adrenergic receptor inhibitor, propranolol hydrochloride, had an effect on vision performance.
“Contrast sensitivity was suppressed,” said Mizuyama, who further added that, “contrast sensitivity defines one’s ability to distinguish objects at different light and dark contrasts.”
Interestingly, however, the effect on contrast sensitivity was found only for a specific range of spatial frequencies.
“The contrast sensitivity at optimal spatial frequencies was suppressed by propranolol hydrochloride,” observed Shimegi. “This result suggests that only neurons sensitive to specific spatial frequencies are affected by the inhibitor. Therefore, noradrenaline could improve vision by targeting a very small subgroup of neurons or neural circuits.”
The article can be found at: Mizuyama et al. (2016) Noradrenaline Improves Behavioral Contrast Sensitivity via the β-Adrenergic Receptor.
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Source: Osaka University.
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