Age-related changes in oxytocin-, arginine vasopressin- and nitric oxide synthase-expressing neurons in the supraoptic nucleus of the rat

Many histochemical investigations indicated that the oxytocin (OXY), the arginine vasopressin (AVP) and the nitric oxide synthase (NOS) have been synthesized in the supraoptic nucleus (SON) neurons. The objective of this study was to examine the age-related expression of the OXY, the AVP and the NOS in the SON of the young adult (2-month-old) and the aged (24-month-old) rats. The histochemistry for reduced nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d; marker for the NOS) and the double labeling histochemistry for the OXY/NADPH-d or the AVP/NADPH-d were employed, and the quantitative analysis was performed with a computer-assisted image processing system. In comparison of the young adult and the aged group, the cell number, the cell size and the reactive density of the NOS-expressing neurons showed a significant increase along with age, and these evidences suggested the age-related increase of the nitric oxide (NO) production. The age-related significant increase was not detected in the number of the OXY/NOS-expressing neurons in the dorsal part, but was detected in the number of the AVP/NOS-expressing neurons in the ventral part. Based on our histochemical findings and reports demonstrated by other authors, we attempted to discuss the physiological role of NOS for the secretion of posterior pituitary hormones along with age.