COMPARISONS BETWEEN BRAIN DOPAMINERGIC-NEURONS OF JUVENILE AND AGED RATS - SEX-RELATED DIFFERENCES

It is known that several aspects of dopaminergic neurotransmission det eriorate with advanced age. In the present report, we have studied the possible existence of sexual differences in these aging-induced chang es. Thus, we measured several pre- and postsynaptic biochemical parame ters, indicative of the activity of dopaminergic neurons, in striatum, limbic forebrain and hypothalamic-anterior pituitary area of aged (24 -26 months) and young (2 months) rats of both sexes. Tyrosine hydroxyl ase (TH) activity, as well as the number of D2-dopaminergic receptors, decreased in the striatum of aged rats, especially in the males in wh ich the decrease in the number of receptors was associated with an inc rease in their affinity. In addition, the ratio between dopamine (DA) and its intraneuronal metabolite, L-3,4-dihydroxyphenylacetic acid (DO PAC), which can be used as an index of neurotransmitter turnover, was increased in aged females in parallel with a decreased DA content. In the limbic forebrain, TH activity was also decreased during aging, but only in males, whereas the DOPAC/DA ratio was increased in females, a lthough in parallel with an increased DOPAC production. Finally, in th e hypothalamic-anterior pituitary area, aging only affected the female s, in which increased plasma prolactin levels were observed. This effe ct might be the result of a low responsiveness of pituitary lactotroph s to DA released from hypothalamic neurons, in spite of high prolactin levels producing a constant, although ineffective, stimulation of the activity of these neurons, as reflected by the high DOPAC content and DOPAC/DA ratio observed in the medial basal hypothalamus. In summary, these data allow us to suggest that the activity of brain dopaminergi c neurons is modified with aging and there are significant differences as a function of sex and brain area.