SENSORY AND AUTONOMIC INNERVATION OF THE RAT EYELID - NEURONAL ORIGINS AND PEPTIDE PHENOTYPES

Neuronal origins, peptide phenotypes and target distributions were det ermined for sensory and autonomic nerves projecting to the eyelid. The retrograde tracer, Fluoro-Ruby, was injected into the superior tarsal muscle and meibomian gland of Sprague-Dawley rats. Labelled neurons w ere observed within the pterygopalatine (31 +/- 6 of a total of 8238 /- 1610 ganglion neurons), trigeminal (173 +/- 43 of 62 082 +/- 5869) and superior cervical ganglia (184 +/- 35 of 21 900 +/- 1741). Immunos taining revealed vasoactive intestinal polypeptide immunoreactivity (V IP-ir) in nearly all Fluoro-Ruby-labelled pterygopalatine ganglion neu rons (86 +/- 5%) but only rarely in trigeminal (0.3 +/- 0.3%) or super ior cervical (1.4 +/- 1.4%) ganglion neurons. Calcitonin gene-related peptide (CGRP)-ir was not observed in pterygopalatine or superior cerv ical ganglion somata, but was present in 24 +/- 4% of trigeminal neuro ns. Bright dopamine beta-hydroxylase (DBH) immunofluorescence was obse rved in the majority of eyelid-projecting neurons within the superior cervical ganglia (65 +/- 5%) and lighter staining was detected in pter ygopalatine neurons (63 +/- 3%), but no DBH-ir was observed in trigemi nal neurons. Examination of eyelid sections revealed dense VIP-ir inne rvation of meibomian gland acini and vasculature and modest distributi on within tarsal muscle. CGRP-ir fibers surrounded ductal and vascular elements of the meibomian gland and the perimeter of tarsal muscle. D BH-ir fibers were associated with meibomian gland blood vessels and ac ini, and were more densely distributed within tarsal muscle. This stud y provides evidence for prominent meibomian gland innervation by paras ympathetic pterygopalatine ganglion VIP-ir neurons, with more restrict ed innervation by sensory trigeminal CGRP-ir and sympathetic neurons. Tarsal muscle receives abundant sympathetic innervation, as well as mo derate parasympathetic and sensory CGRP-ir projections. The eyelid con tains substantial non-CGRP-ir sensory innervation, the targets of whic h remain undetermined. The distribution of identified autonomic and se nsory fibers is consistent with the idea that meibomian gland function , as well as that of the tarsal muscle, is regulated by peripheral inn ervation.