Increased plasma d-lactic acid associated with impaired memory in rats.
OBJECTIVE
d-Lactic acidosis is associated with memory impairment in humans. Recent research indicates that d-lactic acid may inhibit the supply of energy from astrocytes to neurons involved with memory formation. However, little is known about the effects of increased hind-gut fermentation due to changes in diet on circulating lactic acid concentrations and memory.


METHODS
Thirty-six male Wistar rats were fed three dietary treatments: a commercial rat and mouse chow, a soluble carbohydrate based diet or a fermentable carbohydrate based diet. The parameters estimating memory were examined by employing the object recognition test. Physical parameters of fermentation including hind-gut and plasma lactic acid concentrations were examined after sacrifice, either 3 or 21h after feeding.


RESULTS
Increased fermentation in the hind-gut of rats, indicated by lower caecum pH, was associated with increased plasma l-lactic acid (r=-0.41, p=0.020) and d-lactic acid (r=-0.33, p=0.087). Memory, being able to discriminate between a familiar and a novel object during the object recognition test, was reduced with increasing plasma d-lactic acid (r=-0.51, p=0.021).


CONCLUSIONS
Memory impairment was associated with alterations in plasma d-lactic acid following the fermentation of carbohydrate in the hind-gut. Further work is still required to determine whether these effects are mediated centrally or via direct connections through the enteric nervous system.
Hanstock
T L
TL
School of Behavioural, Cognitive and Social Sciences, University of New England, Armidale, NSW 2351, Australia.
Mallet
P E
PE
Clayton
E H
EH
D000140:Acidosis, Lactic / Q000097:blood / Q000150:complications*; D000704:Analysis of Variance; D000818:Animals; D004032:Diet; D005285:Fermentation / Q000502:physiology*; D019344:Lactic Acid / Q000097:blood*; D008297:Male; D008569:Memory Disorders / Q000097:blood / Q000209:etiology*; D051381:Rats; D017208:Rats, Wistar; D021641:Recognition, Psychology / Q000502:physiology*; D012007:Rectum / Q000502:physiology
D019344:Lactic Acid