Differential Effects of Aging on NADPH-diaphroase and Tyrosine Hydroxylase-Positive Neurons in Rat Brain Stem

Huh, Young Buhm; Ahn, Hee Kyung

Abstract

Nitric oxide is synthesized by neurons containing the nitric oxide synthase (NOS), and the nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) is a selective histochemical marker for the brain. Although, many reports have been published describing in detail the distribution of NADPH-d and tyrosine hydroxylase (TH), little information is available on possible morphological changes of NADPH-d and TH containing neurons during aging of the brain stem. Therefore, in this study, we assessed the effects of aging on the somal area and staining intensity of NADPH-d-positive and TH-immunoreactive (TH-IR) neurons in rat brain stem. In previous studies, enzyme activities of nitric oxide synthase (NOS) and NADPH-d were shown to be in an almost perfect correlation in the brain. Therefore, we evaluated the change of NADPH-d-positive neurons using a microdensitometrical method as a way of measuring changes in NOS activity. By using a double-labelling technique, we have shown that these two enzymes are located in separate neurons in most brain stem nuclei. In the aged group, the size of NADPH-d-positive neurons was not significantly changed in most nuclei of the brain stem compared to the control group. Staining intensity of NADPH-d-positive neurons was significantly changed in periaqueductal gray, superior colliculus and inferior colliculus in the aged group. In the aged rats, the size of TH-IR neurons was significantly changed in locus ceruleus and lateral paragigantocellular nucleus. Staining intensity of TH-IR neurons was significantly decreased in principal trigeminal nucleus, locus ceruleus and lateral paragigantocellular nucleus of the aged group. These results demonstrate that the NADPH-d-positive and TH-IR neurons are differently influenced by aging than the control group in the brain stem of rats. Difference in the changes of NADPH-d-positive neurons in brain stem nuclei suggest that neuronal NOS is regulated by different mechanims in the regions of the brain stem during aging.