AGING ALTERS THE RHYTHMIC EXPRESSION OF VASOACTIVE INTESTINAL POLYPEPTIDE MESSENGER-RNA BUT NOT ARGININE-VASOPRESSIN MESSENGER-RNA IN THE SUPRACHIASMATIC NUCLEI OF FEMALE RATS

Our laboratory has shown that the ability of the suprachiasmatic nucle i (SCN) to regulate a number of rhythmic processes may be compromised by the time females reach middle age. Therefore, we examined the effec ts of aging on the rhythmic expression of two neuropeptides synthesize d in the SCN, vasoactive intestinal polypeptide (VIP) and arginine vas opressin (AVP), using in situ hybridization. Because both VIP and AVP are outputs of the SCN, we hypothesized that age-related changes in rh ythmicity are associated with alterations in the patterns of expressio n of these peptides. We found that VIP mRNA levels exhibited a 24 hr r hythm in young females, but by the time animals were middle-aged, this rhythm was gone. The attenuation of rhythmicity was associated with a decline in the level of mRNA per cell and in the number of cells in t he SCN producing detectable VIP mRNA. AVP mRNA also showed a robust 24 hr rhythm in young females. However, in contrast to VIP, the AVP rhyt hm was not altered in the aging animals. The amount of mRNA per cell a nd the number of cells expressing AVP mRNA also was not affected with age. Based on these results we conclude that (1) various components of the SCN are differentially affected by aging; and (2) age-related cha nges in various rhythms may be attributable to changes in the ability of the SCN to transmit timing information to target sites. This may ex plain why the deterioration of various rhythmic processes occurs at di fferent rates and at different times during the aging process.