Role of MAP kinase in signaling indispensable amino acid deficiency in the brain

Deficiencies of indispensable amino acids (IAAs) appear to be sensed in the anterior piriform cortex (APC) where neurons are activated and potentiated, however, the mediating intracellular signaling mechanisms are largely unexplored. It is postulated that signaling of amino acid deficiency may share many of the same pathways seen with long-term potentiation (LTP). Phosphorylation of mitogen-activated protein kinase (pMAP kinase) has been shown to be a necessary signaling event for the genesis and maintenance of LTP. Immunoperoxidase immunohistochemistry was used to determine the number of neurons showing activation of the MAP kinase signal transduction system. Relative to rats eating a corrected diet, rats consuming threonine-devoid diet showed significantly greater pMAP kinase labeling in the APC, dorsomedial hypothalamus, and the paraventricular hypothalamic nucleus. These are areas previously associated with control of food intake. However, since the dorsomedial hypothalamus and the paraventricular hypothalamic nucleus have not previously been implicated as chemosensory areas for IAAs, phosphorylated MAP kinase expression in these areas may reflect secondary activation.