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Parasympathetic Mediated Pupillary Dilation Elicited by Lingual Nerve Stimulation in Cats

¹From the Department of Ophthalmology, Tohoku University School of Medicine, Miyagi, Japan; the ²Department of Neuroanatomy, Field of Neurology, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan; and the ³Department of Oral Physiology, School of Dentistry, Health Sciences University of Hokkaido, Hokkaido, Japan.

PURPOSE. To determine the autonomic efferent nerve pathways for the reflex pupillary dilation elicited by somatic stimulation in cats.

METHODS. Cats anesthetized with a mixture of -chloralose (50 mg/kg) and urethane (100 mg/kg) were intubated and paralyzed by intravenous injection of pancuronium bromide. The central cut end of the lingual nerve (LN) was stimulated electrically to simulate somatic stimulation, and 1 µL of lidocaine (2%) was microinjected into the Vsp or the EW nucleus to determine its effect on the pupillary dilation induced by LN stimulation. The effect of electrically stimulating the Vsp or sectioning the superior cervical sympathetic nerve (CSN) on the pupillary response was also examined.

RESULTS. Stimulation of the LN or the trigeminal spinal nucleus (Vsp) evoked pupillary dilation in a frequency- and intensity-dependent manner. These responses were not affected by sectioning the ipsilateral or both CSNs. The pupillary responses were markedly suppressed by microinjecting lidocaine into the ipsilateral Vsp or the Edinger-Westphal (EW) nucleus, but not by injection into the contralateral Vsp.

CONCLUSIONS. These results indicate that the Vsp and EW nucleus act as bulbar relay centers for pupillary dilation elicited by LN stimulation and suggest that the efferent arc of the response is a parasympathetic pathway. The contralateral pupillary dilation appears to be mediated, at least in part, by fibers projecting from the Vsp to the contralateral EW nucleus.