Neuroanatomical regions of the chick brain involved in monitoring amino acid deficient diets.

Chicks fed a diet deficient in tryptophan will reduce food intake dramatically. Chicks will select a balanced diet over one that is deficient in tryptophan (trp). The amygdala and prepiriform cortex have been implicated in monitoring amino acid (AA) balance, and hence food intake in rats. Therefore, comparable regions of the chick brain were studied to determine if they were involved in monitoring AA deficient diets. In each of four experiments, 48 chicks were used (24 experimentally-operated and 24 sham-operated controls). After starting on a commercial diet, chicks were fed semipurified diets: balanced (bal) or trp deficient (def). The following dietary regimen was followed in all experiments in both pre- and postoperatively; 1) bal diet for an adjustment period; 2) bal diet for 1-2 days; 3) def diet for 2-3 days; 4) choice of both diets presented simultaneously. This was followed by ablation of a brain region and then a repetition of the dietary regimen. Brain regions ablated or isolated include the nucleus taeniae (Tn), piriform cortex (CPi), frontal archistriatum (FA) and ventral archistriatum (AV). No differences in selection were observed when lesions ablating the FA, AV or Tn were performed. A significant decrease in selection of the bal diet was observed after knife cuts which isolated the piriform cortex from medial connections. It is suggested that this brain region may be involved in monitoring AA profiles in the plasma.