An electrophysiological study of pterygopalatine ganglion neurons in the rabbit

Neural regulation of lacrimal gland secretory processes: relevance in dry eye diseases

The lacrimal gland is the major contributor to the aqueous layer of the tear film which consists of water, electrolytes and proteins. The amount and composition of this layer is critical for the health, maintenance, and protection of the cells of the cornea and conjunctiva (the ocular surface). Small changes in the concentration of tear electrolytes have been correlated with dry eye syndrome. While the mechanisms of secretion of water, electrolytes and proteins from the lacrimal gland differ, all three are under tight neural control. This allows for a rapid response to meet the needs of the cells of the ocular surface in response to environmental conditions. The neural response consists of the activation of the afferent sensory nerves in the cornea and conjunctiva to stimulate efferent parasympathetic and sympathetic nerves that innervate the lacrimal gland. Neurotransmitters are released from the stimulated parasympathetic and sympathetic nerves that cause secretion of water, electrolytes, and proteins from the lacrimal gland and onto the ocular surface. This review focuses on the neural regulation of lacrimal gland secretion under normal and dry eye conditions.

Evaluation of novel dry eye model: preganglionic parasympathetic denervation in rabbit

PURPOSE

To evaluate ocular surface status after interruption of preganglionic, parasympathetic neural control after surgical removal of the greater superficial petrosal nerve (GSPN).

METHODS

New Zealand White rabbits underwent unilateral section and removal of a 5-mm portion of the GSPN by a route through the inner ear; no ocular or orbital tissue was involved. Before and 7 days after surgery, all animals underwent preliminary examination, including fluorescein staining, rose bengal instillation, blink rate, tear breakup time (BUT), tear flow, and impression cytology. Total tarsorrhaphy was carried out in four additional rabbits, and another four animals underwent unilateral sham procedures. The GSPN, pterygopalatine ganglion, lacrimal gland, and conjunctiva were evaluated by light and transmission electron microscopy (TEM).

RESULTS

GSPN sectioning resulted in significant changes of the ocular surface after 7 days: intense rose bengal staining of the conjunctiva, fluorescein staining of the cornea, increased blink rate (P < 0.05), decreased BUT (P < 0.005), decreased tear flow by 26% (P < 0.005), and decreased goblet cell density (P < 0.01). TEM revealed massive accumulation of secretory granules in lacrimal acinar cells. The changes were also seen after tarsorrhaphy. Neither the contralateral control nor the sham eyes were affected.

CONCLUSIONS

The effects of GSPN nerve section led to the rapid onset of a dry eye condition in the rabbits that continued for at least 1 week. The authors suggest that continuous neural drive of the pterygopalatine ganglion is necessary to maintain adequate tear flow and mucin secretion. It is likely the trigeminal system is the afferent origin of this continuous neural tone.