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 cogn itive and neurochemical alterations caused by diet restriction (DR) in mice, as a possible model for some of the behavioral symptoms of pati ents 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 showe d significantly improved maze performance while this was impaired in a nimals on DR to 40%. However, in these animals, injections of tyrosine (100 mg/kg/day) restored performance. Improved maze performance in th e 60% DR and 40% DR + tyrosine animals was related to increased beta:a lpha tone in the hippocampus - an area, together with the septum, resp onsible for spatial learning. This was associated with changes in alph a- and beta-receptor density (B-max), without affecting affinity( K-d) ; and increased norepinephrine (NE) in the 40% DR + tyrosine group. an d methoxyhydroxyphenylglycol (MHPG) in both groups. In the hypothalamu s, the brain area responsible for energy metabolism, there was a progr essive increase in alpha:beta tone with increasing DR associated with changes in B-max. Tyrosine treatment reversed these alterations. Tyros ine improves some of the neurobiological disturbances of DR without ca using an increase in body weight. Such a strategy might have important implications for the possible treatment of patients with anorexia ner vosa.