DENDRITIC REGRESSION DISSOCIATED FROM NEURONAL DEATH BUT ASSOCIATED WITH PARTIAL DEAFFERENTATION IN AGING RAT SUPRAOPTIC NUCLEUS

As neurons are lost in normal aging, the dendrites of surviving neighb or neurons may proliferate, regress, or remain unchanged. In the case of age-related dendritic regression, it has been difficult to distingu ish whether the regression precedes neuronal death or whether it is a consequence of loss of afferent supply. The rat supraoptic nucleus (SO N) represents a model system in which there is no age-related loss of neurons, but in which there is an age-related loss of afferents. The m agnocellular neurosecretory neurons of the SON, that produce vasopress in and oxytocin for release in the posterior pituitary, were studied i n male Fischer 344 rats at 3, 12, 20, 27, 30, and 32 months of age. Co unts in Nissl-stained sections showed no neuronal loss with age, and c onfirmed similar findings in other strains of rat and in mouse and hum an. Nucleolar size increased between 3 and 12 months of age, due, in p art, to nucleolar fusion, and was unchanged between 12 and 32 months o f age, indicating maintenance of general cellular function in old age. Dendritic extent quantified in Golgi-stained tissue increased between 3 and 12 months of age, was stable between 12 and 20 months, and decr eased between 20 and 27 months. We interpret the increase between 3 an d 12 months as a late maturational change. Dendritic regression betwee n 20 and 27 months was probably the result of deafferentation due to t he preceding age-related loss of the noradrenergic input to the SON fr om the ventral medulla.