ABSTRACT
Recent studies have explored certain changes of neurons containing neuropeptides that are involved in the cerebral microcirculation with aging. However, the degree of loss of vasoactive intestinal polypeptide (VIP)- and neuropeptide Y (NPY)-containing neurons in the aged CNS has not yet been established with certainty. Nitric oxide (NO) from the neuronal NO synthase (nNOS) appears to play the principal role in the cerebral flow response to functional activation. Several findings suggest that NO production may be decreased in the aged rat. Therefore, changes with aging of VIP-, NPY- and NOS-containing neurons were demonstrated by immunohistochemistry in this study. A major loss of VIP-immunoreactive (IR) neurons in the aged rat brain was observed in the frontal cortex area 3, parietal cortex area 1, hindlimb area, temporal cortex area 1 & 2, monocular part of occipital cortex area 1, occipital cortex area 2, and retrosplenial cortex. The axis of VIP neurons in the aged group showed an irregular orientation tendency, especially in layers II and III. Major loss of NPY-IR neurons in the aged rat brain were observed in the retrosplenial cortex, frontal cortex areas 1 and 2, parietal cortex areas 1 and 2, occipital cortex areas 1 and 2, the temporal cortex, hippocampus proper and cingulate cortex. Loss of NPY-IR neurons was observed mostly in layers V and VI. The number of NOS-IR cells was significantly decreased in the aged rat, but the extent of changes was variable in each area.Morphologically, the number of dendritic branches seemed to be decreased in the aged group and the length of dendrites of VIP-, NPY- and NOS-IR neurons showed a tendency to shorten. These results indicate the involvement of VIP-, NPY- and NOS-IR neurons in the aging process in relation to the increased incidence to cerebrovascular disorders in the elderly, and provide the first morphological evidence for the loss of VIP-, NPY- and NOS-IR neurons in each area of cerebral cortex and the hippocampus of the aged rat by immunohistochemistry.