Distribution of nitrergic nerves in the rat adrenal gland: Plasticity in aging and disease

This thesis presents the localization and characterization of the recently discovered nitric oxide (NO)-synthesizing nerves in the adrenal glands of rats, and their changes in various conditions which cause alteration in adrenal nerve and/or glandular activities. The study was conducted mainly by qualitative analysis of the NO-synthesizing enzyme, nitric oxide synthase (NOS) immunohistochemically and/or by the use of reduced nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase histochemistry which also marks the site of neuronal NOS immunoreactivity. In parts of the study, where quantification of the levels of NOS was required, computer assisted image analysis and biochemical assay for measuring the activity of NOS were also used. In the adult rat adrenal glands NOS immunoreactivity occurred in a population of nerve cell bodies and fibres, where NADPH-diaphorase staining also colocalized. In the adrenal cortical cells NADPH-diaphorase staining alone was observed without NOS immunoreactivity. As found from surgical extrinsic and intrinsic adrenal denervation studies, the NOS-immunoreactive nerve fibres in the gland have both extrinsic and intrinsic origins. The extrinsic nitrergic nerve fibres innervate adrenal chromaffin and ganglion cells. The intrinsic nitrergic nerve fibres which arise from the local neurons innervate adrenal blood vessels and the zona glomerulosa of cortex. Colocalization studies revealed that a population of NADPH-diaphorase stained NO-synthesizing adrenal intrinsic neuronal cell bodies contained vasoactive intestinal peptide and neuropeptide Y, but not calcitonin gene-related peptide, substance P, tyrosine hydroxylase or calretinin. Developmental studies showed that NOS-immunoreactive nerve fibres were present in adrenal glands of rats at all ages examined from the 16th day of gestation up to 2 years of age. A considerable degree of variation in the distribution of the immunoreactive nerve fibres in both medulla and the zona glomerulosa of cortex was observed at different ages. The NOS-containing neuronal cell bodies within the adrenal gland were found from the 20th day of gestation onwards, and increased in their number to reach to that of adult levels by the 4th day after birth. In the glands from the aging rats their number was increased by 28.6 % above the adult levels. NOS immunoreactivity in the chromaffin cells was observed only in the glands of the aging rats. Guanethidine, 6-hydroxydopamine or capsaicin treatments did not cause any change in the adrenal NOS immunoreactivity and NADPH-diaphorase staining. In contrast, reserpine treatment for 7 days caused a significant decrease in the NOS immunoreactivity in the nerve fibres that innervate the chromaffin and ganglion cells. Hypophysectomy did not cause any change in the NOS immunoreactivity, although it eliminated most of the NADPH-diaphorase staining adrenal cortical cells. Streptozotocin-induced diabetes of 8 weeks duration caused an increase in the NOS-immunoreactive nerve fibres and induced NOS immunoreactivity in a small number of adrenal cortical cells. It also caused an increase in the intensity of NADPH-diaphorase staining in the adrenal cortical cells. A significant degree of prevention of such diabetic-induced increase in both NOS and NADPH-diaphorase was found with ganglioside treatment. At a later stage (12 weeks of diabetes duration) the effect of streptozotocin-induced diabetes was a decrease in the NOS-immunoreactive nerve fibres but an increase in the occurrence of NOS-immunoreactive adrenal cortical cells. The intensity of NADPH-diaphorase staining in the cortical cells was still increased