Localization of NADPH-diaphorase in the rat pineal gland: an experimental enzyme histochemical study

We have used the NADPH-diaphorase enzyme histochemical technique to localize the enzyme nitric oxide synthase in the rat pineal gland. Some scattered NADPH-diaphorase positive pineal cells were present, mostly in the rostral part of the gland close to the pineal stalk. In addition, NADPH-diaphorase positive nerve fibers were located in the pineal capsule, in the connective tissue septae of the gland, and also intraparenchymally between the pinealocytes. Most nerve fibers were endowed with boutons en passage. These nerve fibers remained in the gland after bilateral removal of the superior cervical ganglia verifying a non-sympathetic nature of the NADPH-diaphorase positive nerve fibers. Pineal blood vessels also exhibited NADPH-diaphorase activity. The number and distribution of NADPH-diaphorase containing cells and nerve fibers were not affected by bilateral superior cervical ganglionectomy. Furthermore, animals sacrificed during day or night exhibited the same NADPH-diaphorase pattern. The present investigation provides the first morphological evidence for the presence of NADPH-diaphorase activity in rat pineal cells, suggesting an influence of nitric oxide on pineal metabolism. Furthermore, the presence of NADPH-diaphorase activity in the pineal blood vessels as well as in the perivascular nerve fiber suggests an influence of nitric oxide on the blood flow to the gland and/or the metabolism of the pineal cells adjacent to the blood vessels.