CONTROL OF CONJUNCTIVAL GOBLET CELL MUCOUS PRODUCTION

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The mucous layer constitutes a physical and chemical barrier that protects the ocular surface from bacterial and environmental insults. One of the most important sources of the mucous layer is conjunctival goblet cells. Goblet cell mucous secretion can be stimulated by a neural stimulus to the cornea via parasympathetic and sympathetic nerves near goblet cells. This suggests that goblet cells are able to respond rapidly to external challenges to the ocular surface by secreting mucus to protect the eye surface. Under normal conditions, minor stimuli to the ocular surface would ensure a constant low level secretion. A more significant stimulus, such as ocular trauma, would cause a greater protective secretory response. A mucin-deficiency disease such as anesthetic cornea, vitamin A deficiency, late keratoconjunctivitis sicca, Sjogrens syndrome, thermal and alkali burns would occur with a breakdown of reflex secretion. Breakdown could occur because of a dysfunction of the stimulating neural pathways, leading to a decreased mucous secretion, loss of the protective coat and deterioration of the ocular surface. In diseases of mucous overproduction, a constant irritative stimulus to the ocular surface would increase neural stimulation, and thus increase goblet cell secretion. These diseases include vernal conjunctivitis, giant papillary conjunctivitis, early keratoconjunctivitis sicca, mucous fishing syndrome, and atopy. Thus, the overall goal of the project is to determine the components of the different neural pathways that stimulate mucous secretion by investigating which nerves, neurotransmitters, receptors, second messengers and cell types are involved. First, the role of sensory, parasympathetic, and sympathetic nerves in stimulating conjunctival goblet cell mucous secretion will be investigated. Second, the identity and relationship of nerve fibers to conjunctival goblet cells will be determined. Third, the role of the prostaglandin PGE2 in neural stimulation of goblet cell secretion will be explored. For in vivo secretion experiments, rat conjunctival goblet cell secretion will be stimulated by a corneal wound or by topical application of agonists. Goblet cell mucin, in buttons of conjunctiva, will be stained histochemically and the number of goblet cells per area counted. A decrease in this number indicates an increase in mucous secretion. For in vitro secretion experiments, conjunctival tissue will be removed and incubated with or without agonists. Mucous secretion will be measured by an enzyme-linked lectin assay using Helix pomatia agglutinin, which preferentially recognizes goblet cell secretory product. The neural innervation of goblet cells will be determined by confocal microscopy with immunofluorescence labelling and by immunoelectron microscopy. Receptors on goblet cells will be localized by immunohistochemistry or autoradiography. Knowledge of the normal mechanism of neural regulation of goblet cell mucous secretion will provide a scientific basis to develop therapeutic treatments for diseases of the mucous layer.