Increased locomotor activity in mice lacking the low-density lipoprotein receptor

While the low-density lipoprotein receptor (LDLR) is best known for its role in regulating serum cholesterol, LDLR is expressed in brain, suggesting that it may play a role in CNS function as well. Here, using mice with a null mutation in LDLR (LDLR-/-), we investigated whether the absence of LDLR affects a series of behavioral functions. We also utilized the fact that plasma cholesterol levels can be regulated in LDLR-/- mice by manipulating dietary cholesterol to investigate whether elevated plasma cholesterol might independently affect behavioral performance. LDLR-/- mice showed no major deficits in general sensory or motor function. However, LDLR-/- mice exhibited increased locomotor activity in an open field test without evidence of altered anxiety in either an open field or a light/dark emergence test. By contrast, modulating dietary cholesterol produced only isolated effects. While both C57BL/6J and LDLR-/- mice fed a high cholesterol diet showed increased anxiety in a light/dark task, and LDLR-/- mice fed a high cholesterol diet exhibited longer target latencies in the probe trial of the Morris water maze, no other findings supported a general effect of cholesterol on anxiety or spatial memory. Collectively these studies suggest that while LDLR-/- mice exhibit no major developmental defects, LDLR nevertheless plays a significant role in modulating locomotor behavior in the adult.