Abstract
Purpose: :
To investigate the presence of nitric oxide synthase- (NOS-) positive nerve fibers in rat Meibomian glands (MG) at various stages of development. Considerable evidence suggests that nicotinamide adenine dinucleotide diaphorase (NADPH-d) is a neuronal nitric oxide synthase (NOS).
Methods: :
Sections of the central, upper eyelids of Wistar rats were processed histochemically for NADPH-d to investigate the presence and distribution of NOS-positive nerve fibers at the following time points: day 1 and weeks 1, 2 and 3 post partum, and in adult controls.
Results: :
Day 1: MGs acini were lightly stained and located at a distance from the mucosal border. The submucous layer was relatively wide and heavily vascularized by tortuous, branching blood vessels which entered the septa between the acini. Vessels were accompanied by intensely stained NOS- positive nerve fibers.Week1: Both the vessels and NOS-positive fibers were still present, but less numerous. MGs were now closer to the mucosa, so that the submucoa was thinner. The acini were mostly pale but ocassionally dark.Week 2: There were fewer blood vessels in both the submucosa and within the septa. Darker acini were more common than lightly stained acini and this acinar staining was more intense peripherally than centrally. NADPH-d positive dots were observed in the vicinity of the MGs.Week 3: MGs were adjacent to the mucosal border and stained more intensely than at earlier times; almost all acini were stained. The microscopic appearances were almost identital with those of adult palpebra. Submucosal and septal blood vessels and NADPH-d positive nerve fibers were less numerous.
Conclusions: :
NADPH-d histochemical staining confirmed differences in the density of stained nerve fibers at different developmental stages. The greatest density of NOS-positive nerve fibers occurred in 1-day-old rats whereas they were less numerous in adult rat eyelids. We conclude that MGs utilize NO as a neurotransmitter mostly in early developmental stages and this need thereafter decreases and stabilizes at 3 weeks post-natally.
Keywords: development • eyelid • neurotransmitters/neurotransmitter systems