Behavioral and neurochemical alterations caused by diet restriction - The effect of tyrosine administration in mice

We have investigated the effect of tyrosine administration on the cognitive and neurochemical alterations caused by diet restriction (DR) in mice, as a possible model for some of the behavioral symptoms of patients with anorexia nervosa. Young female mice were fed to 100, 60, and 40% of the calculated daily nutritional requirements for a period of up to 18 days. Cognitive function was evaluated using a modified eight-arm maze with water as a reward. Animals fed to 60% of controls showed significantly improved maze performance while this was impaired in animals on DR to 40%. However, in these animals, injections of tyrosine (100 mg/kg/day) restored performance. Improved maze performance in the 60% DR and 40% DR + tyrosine animals was related to increased beta:alpha tone in the hippocampus - an area, together with the septum, responsible for spatial learning. This was associated with changes in alpha- and beta-receptor density (B-max), without affecting affinity( K-d); and increased norepinephrine (NE) in the 40% DR + tyrosine group. and methoxyhydroxyphenylglycol (MHPG) in both groups. In the hypothalamus, the brain area responsible for energy metabolism, there was a progressive increase in alpha:beta tone with increasing DR associated with changes in B-max. Tyrosine treatment reversed these alterations. Tyrosine improves some of the neurobiological disturbances of DR without causing an increase in body weight. Such a strategy might have important implications for the possible treatment of patients with anorexia nervosa.