Recognition of deficient nutrient intake in the brain of rat with L-lysine deficiency monitored by functional magnetic resonance imaging, electrophysiologically and behaviorally

Each L-amino acid (AA) in plasma and brain remains unchanged all day long while normal diet is available. But once restriction of L-lysine (Lys) was introduced, strong anorexia happened. When Lys deficient diet was offered to rats, their growth were decreased depending upon dietary Lys intake, and they ingested Lys solution in choice quantitatively and both appetite and growth normalized. The recognition site for the deficit in rat's brain was identified by brain oxygenation using a functional MRI that higher signals in the ventromedial hypothalamus and lateral hypothalamic area (LHA) appeared, at 30-50 minutes after Lys injection i.p. and then recovered. Degree of Lys hunger, assayed by bar-pressing (50mg pellet of normal diet/30 presses), was suppressed by Lys micro-injection into the LHA, similar to free Lys ingestion but any other AA never did, suggesting the LHA as recognition site for Lys deficit in rats with Lys deficiency due to AA homeostasis.