OBJECTIVE: This study aims to determine the effect of age on the function of rostral C1 (rC1) neurons in mediating feeding response.
METHOD: Male Sprague Dawley rats at 3-months (n = 22) and 24-months (n = 22) old were used and further divided into two subgroups; 1) treatment group with 2-deoxy-d-glucose (2DG) and 2) vehicle group. Feeding hormones such as cholecystokinin (CCK), ghrelin and leptin were analysed using enzyme-linked immunosorbent assay (ELISA). Rat brain was carefully dissected to obtain the brainstem RVLM region. Further analysis was carried out to determine the level of proteins and genes in RVLM that were associated with feeding pathway. Protein expression of tyrosine hydroxylase (TH), phosphorylated TH at Serine40 (pSer40TH), AMP-activated protein kinase (AMPK), phosphorylated AMPK (phospho AMPK) and neuropeptide Y Y5 receptor (NPY5R) were determined by western blot. Expression of TH, AMPK and NPY genes were determined by real-time PCR.
RESULTS: This study showed that blood glucose level was elevated in young and old rats following 2DG administration. Plasma CCK-8 concentration was higher in the aged rats at basal and increased with 2DG administration in young rats, but the leptin and ghrelin showed no changes. Old rats showed higher TH and lower AMPK mRNA levels. Glucoprivation decreased AMPK mRNA level in young rats and decreased TH mRNA in old rats. Aged rC1 neurons showed higher NPY5R protein level. Following glucoprivation, rC1 neurons produced distinct molecular changes across age in which, in young rats, AMPK phosphorylation level was increased and in old rats, TH phosphorylation level was increased.
CONCLUSION: These findings suggest that glucose-counterregulatory responses by rC1 neurons at least, contribute to the ability of young and old rats in coping glucoprivation. Age-induced molecular changes within rC1 neurons may attenuate the glucoprivic responses. This situation may explain the impairment of feeding response in the elderly.
METHODS: Adrenal medulla from male Sprague Dawley rats at the age of 3-months (n=12) and 24-months (n=12) were further divided into two groups: 1) treatment group with 2DG to create glucoprivation condition and 2) the vehicle group which received normal saline as control.
RESULTS: The results showed that the level of glucose, adrenaline and noradrenaline were increased in response to acute glucoprivation conditions in both young and old rats. No age-related differences were found in the basal gene expression of the enzymes that involved in the catecholamines biosynthesis pathway. Interestingly the expressions of TH and DBH protein as well as the level of TH phosphorylation at Ser40, PKA, PKC and ERK1/2 substrates were higher in basal condition of the aged rats. However, contradicted findings were obtained in glucoprivic condition, which the protein expressions of DBH, pERK1/2 and substrates for pPKC were increased in young rats. Only substrate for pCDK was highly expressed in the old rats in the glucoprivic condition, while pPKC and pERK1/2 were decreased significantly. The results demonstrate that adrenal medulla of young and old rats are responsive to glucose deficit and capable to restore the blood glucose level by increasing the levels of blood catecholamines.
CONCLUSION: The present findings also suggest that, at least in rats, aging alters the protein expression of the biosynthetic catecholamine enzymes as well as protein kinase substrates that may attenuate the response to glucoprivation.