Monday, May 24, 2010

Growth Hormone and Sleep Deprivation By Jerry Brainum

As we age, memory lapses, also known as "senior moments" become more common. It most cases, these lapses aren't considered pathological, although they could be early warning signs of more severe problems up the road, such as forms of dementia. Such age-related memory blips could also be related to sleep disorders. After age 40, the restorative sleep stages, known as deep sleep cycles, gets shorter, and may even disappear completely after a while. In relation to memory, this is a problem because the neurons or brain cells in the portion of the brain most involved in memory and learning, the hippocampus, undergo restoration during the deep sleep stages. The deep sleep stages, particularly stage four, which is the last deep sleep stage before the dream stage (REM) occurs is also when growth hormone release peaks, usually about 90 minutes after falling asleep. Could there be a connection between the fact that GH secretion begins to decline around age 40, about the same time as deep sleep cycles become disrupted?
     There are receptors in the hippocampus called NMDA receptors, which are vital for the hippocampal function of learning and memory retention. But these receptors are only activated during deep sleep. This implies that unless you get enough sleep in the deep sleep stages, the restorative function of sleep in relation to hippocampal function won't occur.  In a new study, it was found that supplying growth hormone can rescue the loss of activation of NMDA receptors in the hippocampus during sleep deprivation. GH also prevented the loss of NMDA receptors, which would adversely affect memory and learning. The problem with all this is that GH secretion begins to drop at about age 40, when sleep problems also begin. As such, a lack of sufficient GH may be partially responsible for the increasing memory lapses seen after age 40 in many people.

Kim, E, et al. Growth hormone rescues hippocampal synaptic function after sleep deprivation.Am J Physiol Regul Integr Comp Physiol 2010;298:R1588-R1596.

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