OK, so who out there thinks their child with PWS, despite having some learning difficulties, has a memory like an elephant? And is pretty good at spatial tasks?
Well, one possible explanation is provided by Dr. Horvathâ€™s study, link below. Dr. Horvath has done some very nice work on the brain/gut axis, and has an interest in PWS. We all know about ghrelin, which is a â€˜hunger hormoneâ€™ found at high levels in the circulation of individuals with PWS. Recently, ghrelin has been shown to be able to modulate some neuronal connections (ie, â€˜rewireâ€™) in the hypothalamus and brain stem, which is presumably how it influences energy balance. Here, Dr. Horvathâ€™s group shows that circulating ghrelin also enters the hippocampus of the brain and encourages neurons to form new interactions â€“ influencing memory and spatial learning. Overall, administering ghrelin improved learning in several tasks, with more ghrelin leading to better learning. Note that not all the data was completely straightforward (never is…); in some cases, at highest level of ghrelin administration, the positive effect was lost. Additional studies used mice are depleted of ghrelin (ghrelin knock-outs). These mice form less neuronal interactions in the hippocampus and do poorly on tests of spatial learning. This poor performance can be overcome if the ghrelin is provided to the mice. Thus, in addition to its role in the endocrine system (GH release) and the metabolic realm (hunger), ghrelin is now shown to have a role in higher brain function.
Clearly, there is still a lot left to understand about this new role for ghrelin â€“ but what an interesting study….
Ghrelin controls hippocampal spine synapse density and memory performance. Diano S, Farr SA, Benoit SC, McNay EC, da Silva I, Horvath B, Gaskin FS, Nonaka N, Jaeger LB, Banks WA, Morley JE, Pinto S, Sherwin RS, Xu L, Yamada KA, Sleeman MW, Tschop MH, Horvath TL. Nat Neurosci. 9(3):381-8, 2006.