Is age-induced decline in immune response associated with hypothalamic glutamate receptor density and dietary protein?

Manipulation of dietary protein has been found to be the most useful dictator in the age-associated decline of neuroimmune activity in mammals. In the present study, we sought to clarify the effect of dietary protein on age-induced alterations of hypothalamic glutamatergic activity and immune response. The hypothalamic glutamatergic activity and immune response were found to increase and decrease, respectively, with the increase in age of rats from young (3 months) to old (18 months) maintained with normal (20%) protein diet. Intake of low (5%) protein diet (LPD) and high (40%) protein diet (HPD) under short-term period (7 days) failed to alter the age-associated loss of immune response and increase in hypothalamic glutamatergic activity. However, long-term (30 days) supplementation of LPD retarded the age-induced decline in immune response and increase in hypothalamic glutamatergic activity, whereas, HPD consumption under similar condition potentiated the age-related immunosuppression and increase in hypothalamic glutamatergic activity. These results suggest that (a) the age-associated immunosuppression may be inversely related to the hypothalamic glutamatergic activity and (b) consumption of diets having variable quantity of protein without variation of calorie content modulates immune response and hypothalamic glutamatergic activity depending upon age and duration of dietary supplementation.