High dietary cholesterol facilitates classical conditioning of the rabbit's nictitating membrane response

Abstract

Studies have shown that modifying dietary cholesterol may improve learning and that serum cholesterol levels can be positively correlated with cognitive performance. Rabbits fed a 0, 0.5, 1 or 2% cholesterol diet for eight weeks and 0.12 ppm copper added to their drinking water received trace and then delay classical conditioning pairing tone with corneal air puff during which movement of the nictitating membrane (NM) across the eye was monitored. We found that the level of classical conditioning and conditioning-specific reflex modification (CRM) as well as the number of beta amyloid-labeled neurons in the cortex and hippocampus were a function of the concentration of cholesterol in the diet. The data provide support for the idea that dietary cholesterol may facilitate learning and memory.

Cholesterol and Copper Affect Learning and Memory in the Rabbit

“…This is a finding we have seen in many of our subsequent experiments [48–50]. The facilitated conditioning was indexed by higher levels of responding to the CS [32, 48] and heightened responsivity to the US measured after conditioning, and known as a conditioning-specific reflex modification [32, 48–50]. When the levels of beta amyloid accumulation in our cholesterol-fed rabbits were examined by the Sparks laboratory, the immunoreactivity was relatively light although significantly higher than in the rabbits fed normal chow.…”

“…This is a finding we have seen in many of our subsequent experiments [48–50]. The facilitated conditioning was indexed by higher levels of responding to the CS [32, 48] and heightened responsivity to the US measured after conditioning, and known as a conditioning-specific reflex modification [32, 48–50].…”

Dietary cholesterol concentration affects synaptic plasticity and dendrite spine morphology of rabbit hippocampal neurons

“…However, statistical analysis of EPSP 2 /EPSP 1 revealed no group differences. This supports the contention that dietary concentrations may not significantly influence presynaptic function in hippocampus and thus pre-synaptic function may not be the major contributor to the altered behavioral performance induced by dietary cholesterol concentrations (Schreurs et al, 2003; Schreurs et al, 2007b; Schreurs et al, 2012; Schreurs, 2013). …”

The effects of cholesterol on learning and memory

“…Prompted by Sparks’ original observation that cholesterol-fed rabbits developed elevated levels of neuronal beta amyloid (Sparks et al ., 1994), we were surprised to find that rabbits fed cholesterol for eight weeks showed improved trace classical conditioning and reflex facilitation of the NMR (Schreurs et al ., 2003) and that these facilitating effects of cholesterol were a function of the concentration (Schreurs et al ., 2007b) and duration of the cholesterol diet (Schreurs et al ., 2007a). These facilitating effects were generalized beyond NMR conditioning because an eight-week, 2% cholesterol diet also facilitated rabbit heart rate conditioning – an index of conditioned fear (Schreurs et al ., 2007c).…”