RECOGNITION AND NEURAL PLASTICITY RESPONDING TO DEFICIENT NUTRIENT INTAKE SCANNED BY A FUNCTIONAL MRI IN THE BRAIN OF RATS WITH L-LYSINE DEFICIENCY

Each L-amino acid (AA) in plasma and brain remains unchanged while nor mal diet is available. Once L-lysine (Lys) deficient diet was offered to rats, Lys in plasma and brain declined, and anorexia occurred. When solutions of AAs were offered, they selected the Lys solution, and th eir food intake and growth normalized. The single neuron activity in t he lateral hypothalamic area of these rats suggested that neural plast icity occurred, specifically responding to Lys, both by iontophoretic application and during ingestion of AA. The recognition site for defic ient nutrient intake in the brain of rats with Lys deficiency was iden tified by non-invasive magnetic resonance imaging (MRI 4.7 tesla, 40 c m bore in diameter) developed to monitor changes in cerebral blood flo w and oxygenation in rat brain. Wistar strain young male rats fed with Lys deficient diet for 4 days, were adapted to be settled in the cent er of the bore. When they received a Lys injection intraperitoneally ( 0.2 M, 10 mL/kg), a signal intensity decrease in the medial and latera l hypothalamus appeared 30 minutes later in T2 weighted images, refle cting increased oxygenation which lasted for 30 minutes, and then grad ually recovered. These changes never occurred in any other areas of th e brain of rats with Lys deficiency, i.e., the thalamus, the cortex, t he hippocampus, etc. There were no changes in the signal intensity wit h control injection of saline. In addition, oxygen comsumption in the brain of rats without Lys deficiency was not altered by intraperitonea l Lys injection. The present results suggest that in essential AA defi ciency, the medial and lateral hypothalamus may play important roles i n recognition responses to particular deficient nutrients in order to maintain homeostasis.