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Recovery of the Sense of Taste Depends on Age
Age slows down recovery of the
sense of taste; © cressida/SXC
Age dramatically delays the time it takes to recover the sense of taste following a significant nerve injury, Medical College of Georgia (MCG) researchers said.
When old rats received nerve injuries similar to ones that can occur in ear or dental surgery, their taste buds took essentially twice as long to recover function as their younger counterparts, Lynnette McCluskey, neuroscientist in the MCG Schools of Graduate Studies and Medicine reported.
"This is probably something that has a huge quality-of-life impact," said McCluskey, who uses taste buds to study regeneration of sensory nerves that enable touch, vision and hearing as well as taste. Similar studies have shown that age only slightly delays recovery time for neurons that enable movement.
In younger rats, injury to the chorda tympani nerve, which innervates the front of the tongue, typically prompts an infusion of immune cells called neutrophils to the injury site as well as surrounding tissue. Short-term, the neutrophils, which are like a front-line demolition crew pulverizing tissue for removal, can actually hinder the function of nearby nerves. But soon a similar number of white blood cells called macrophages move in to call off the neutrophils and start cleaning things up. Within 45 days, the witherd taste bud is regenerated, the nerve has recovered and taste is intact. "The nerve grows back, stimulates those cells to regenerate and it hooks up perfectly," McCluskey said.
But older rats experience a much bigger invasion of neutrophils although McCluskey notes it doesn't seem to impact nearby nerve function as with younger rats. "That was better than we expected," she said. They also have proportionately fewer subsequent macrophages moving in which she suspects may be part of the reason for the significantly delayed recovery.
She and colleagues suggest that a balanced response between neutrophils and macrophages enhance recovery. In adult rats, they documented the usual, rapid neutrophil response at the immediate site of a taste system injury and in nearby tissue. When they blocked the neutrophil response, nearby nerve function was unaffected and when they increased neutrophils, it decreased function – at least initially – in injured and nearby uninjured nerves.
Most old rats eventually recovered their sense of taste but not until at least 85 days after injury. Interestingly taste buds and nerves were present much earlier but apparently not functioning. "That was the really surprising part," McCluskey said. "We don't know if the nerve is completely normal in terms of morphology but it's there."
REHACARE.de; Source: Medical College of Georgia
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( Source: REHACARE.de )