Age-associated hypothalamic glutamate receptor density: effect of dietary protein.

An age-associated (3-18 months) increase in hypothalamic glutamate receptor (HgluR) binding due to increase in receptor density (Bmax) was observed in rats maintained with normal (20%) protein diet. Short-term supplementation of low (5%) protein diet (LPD) and high (40%) protein diet (HPD) produced no significant change in the HgluR binding and Bmax in young as well as aged rats. Consumption of LPD for long-term period (LTP) increased the HgluR binding by increasing Bmax in young rats; whereas, intake of the same diet by the aged rats under similar condition reduced the HgluR binding by reducing Bmax. Unlike LPD, HPD intake by the young rats for LTP decreased the HgluR binding by decreasing affinity (1/KD) without altering Bmax. However, the aged rats when supplemented with HPD for LTP, the HgluR binding was increased due to increase in Bmax. Further, no age-induced increase in HgluR binding and Bmax was observed following short-term supplementation of LPD; whereas, long-term intake of LPD decreased the HgluR binding and Bmax in 18 months old rats compared to 3 months old rats under similar condition. On the other hand, HPD under LTP potentiated the age-induced increase in HgluR binding and Bmax. These results, thus, suggest that dietary protein affects the hypothalamic glutamatergic activity by modulating its receptor population depending on the age of the subject, quantity of dietary protein and its duration of supplementation.