EFFECT OF SENSORY DENERVATION ON THE STRUCTURE AND PHYSIOLOGICAL RESPONSIVENESS OF RABBIT LACRIMAL GLAND

Purpose. This work was conducted to determine the effects of unilatera l trigeminal ganglion ablation on lacrimal gland structure and secreto ry activity. Methods. Adult male New Zealand rabbits underwent unilate ral thermocoagulation of the ophthalmic division of the trigeminal gan glion. Sensory denervation was affirmed by anatomic inspection of the lesion and transmission electron microscopy (TEM) of the lacrimal glan d innervation, Eight to 10 days after the procedure, the intraorbital lacrimal glands were removed from both sides. To compare the physiolog ic competence of the intact and denervated glands, freshly isolated gl and fragments from the paired intact and denervated glands were stimul ated with carbachol (100 mu M), isoproterenol (10 mu M), phorbol-12, 1 3-dibutyrate (PDBu, 10 mu M), forskolin (40 mu M), or vehicle. Total s ecreted protein was measured at 30 or 60 min after the establishment o f baseline values. Intact and denervated glands also were examined by light and TEM, and the morphologic appearance of the acinar structures as well as the appearance of nerves innervating the aland after dener vation were assessed. Similar experiments were conducted with animals that underwent unilateral superior cervical ganglionectomy. Results. T issues from sensory denervated glands released significantly more prot ein than did tissues from innervated glands in response to in vitro st imulation by carbachol or isoproterenol but not in response to PDBu or forskolin. Microscopy showed that the acinar cells that had undergone sensory denervation showed a massive accumulation of secretory granul es. The secretory granules filled the entire cytoplasmic space and dis placed the ellipsoidal nuclei to the extreme periphery. Examination of segments of nerves revealed numerous unmyelinated axons, a few small- diameter myelinated axons, and a large amount of nerve degeneration af ter sensory denervation. In contrast to the effects of sensory denerva tion, sympathetic denervation did not alter either the acinar appearan ce or secretory responsiveness of the gland. Conclusion. Loss of the c onsiderable sensory innervation from the trigeminal ganglion has prono unced effects on the pharmacologic responsiveness and the structure of the lacrimal gland. The effects of sensory innervation on the gland m ay be mediated through two possible pathways: direct input to the glan d or control of the preganglionic parasympathetic pathway.