Distribution of Adrenergic Nerves to Orbital Structures

Beta-adrenergic glaucoma drugs reduce lymphatic clearance from the eye: A sequential photoacoustic imaging study

Our study aims to determine whether the beta-adrenergic system is involved in the regulation of lymphatic drainage from the eye. For this purpose, we assessed the effect of 2 topical beta-adrenergic blockers, timolol and betaxolol, commonly used as glaucoma drugs, on lymphatic clearance of albumin from the aqueous humor to neck lymph nodes. Adult mice were treated with either topical timolol, a non-selective β-blocker, 0.5% (n = 8), or topical betaxolol, a selective β₁-adrenergic blocker, 0.5% (n = 6) twice daily for 14 days and compared to respective control groups (n = 5 and n = 7). Changes in lymphatic clearance from the eye were assessed using a quantitative in vivo photoacoustic imaging approach. In all subjects, right eye and neck lymph nodes were longitudinally assessed by sequential photoacoustic imaging just prior to near-infrared dye injection into the anterior chamber of the eye, and 20 min, 2 and 4 h after injection. Repeat measurements of mean pixel intensities (MPIs) of right eyes and nodes were performed at all timepoints. The areas under the curves (AUC) were calculated and the AUC of the treated-group was compared to that of controls using the Mann-Whitney U test. The slopes of MPI of each region of interest over time were compared using the linear mixed model after adjusting for IOP decrease after treatment and other parameters such as sex and body weight. In the timolol-treated group, right neck nodes showed significant decrease in AUC signal intensity compared with controls (P = 0.003), and significant decrease in slope of MPI compared with controls (P = 0.0025). In the betaxolol-treated group, right neck nodes showed significant decrease in AUC signal intensity compared with controls (P = 0.02), and significant decrease in slope of MPI compared with controls (P = 0.0069). Topical treatment with timolol and betaxolol reduced lymphatic clearance of albumin from the aqueous humor to the neck lymph nodes. This finding may be relevant for the management of secondary glaucomas and inflammatory eye disease in which the clearance of accumulated proteins and antigen from the eye is important to disease recovery and sight protection. This study suggests that the beta-adrenergic system plays a role in the regulation of lymphatic clearance from the eye.

Peptidergic and catecholaminergic fibers in the human corneal epithelium. An immunohistochemical and electron microscopic study

Innervation of the clinically normal human corneal epithelium was investigated utilizing immunohistochemical and electron microscopic techniques. All corneal epithelial sheets examined demonstrated neuron specific enolase (NSE: a non-specific marker for neural elements), calcitonin gene-related peptide (CGRP: a putative marker for sensory fibers), and tyrosine hydroxylase (TH: a marker for catecholaminergic nerves) immunoreactive fibers. NSE, CGRP, and TH fibers formed a dense basal epithelial plexus. The CGrp fibers tended to have beaded profiles, while TH fibers were smooth. Numerous free nerve endings originating from the basal epithelial plexus og NSE and CGRP fibers terminated throughout the thickness of epithelium. The densities of fibers in the basal epithelial nerve plexus were: NSE greater than CGRP greater than TH. Transmission electron microscopy demonstrated two types of epithelial nerve fibers, one containing large dense-core vesicles and another small dense-core vesicles. Both types contained clear vesicles. These large and small dense-core vesicle fibers appeared to correspond to the CGRP and TH immunoreactive fibers, respectively. These results provide morphological baseline data on the normal sensory and sympathetic corneal epithelial innervation.

Nerve fibers showing immunoreactivities for thyrosine hydroxylase and dopamine-beta-hydroxylase re-appear in the guinea pig uvea after sympathectomy

After sympathectomy we have studied the re-appearance of nerve fibers showing catecholaminergic characteristics in the uvea of the guinea pig. Immunoreactivities for two catecholamine symthetizing enzymes, tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (DBH), were used as markers. Both TH-like and DBH-like immunoreactive nerve fibers disappeared after the extirpation of ipsilateral superior cervical ganglion. In the choroid the TH-like and DBH-like immunoreactive nerve fibers re-appeared within 2 weeks. In the iris and the ciliary body both of these types of immunoreactive nerve fibers re-appeared 10 weeks after the denervation. The morphological appearance of these re-appearing nerve fibers was not similar to those in the non-denervated uvea.

The innervation of the rabbit's anterior eye segment: a retrograde tracing study

The differential innervation of the distinct elements of the anterior segment of the rabbit eye, i.e. cornea, conjunctiva, ciliary body, iris, and trabecular meshwork, was studied using horseradish peroxidase-wheatgerm agglutinin (HRP-WGA) as a tracer. HRP-WGA was injected into the anterior chamber, the conjunctiva, or the cornea, and the animals were killed after 6 to 96 hr. The HRP-WGA localization was studied at the light and electron microscopic level. Injection into the anterior chamber led to an ubiquitous spread of the tracer in all elements of the anterior segment, resulting in a consistent retrograde labelling of neurons in the trigeminal (sensory), superior cervical (sympathetic) and ciliary (parasympathetic) ganglion. Neurons in the proximal part of the pterygopalatine ganglion (parasympathetic) were labelled only when the injected tracer was present in the conjunctiva. Varying survival times after corneal injection were used to establish restricted corneal uptake. Up to 16 hr after corneal injection, HRP-WGA was limited to the cornea and led to the exclusive labelling of neurons in the trigeminal ganglion, indicating that the central cornea has an almost exclusive sensory innervation. The trigeminal sensory neurons projecting to the cornea were restricted to a small antero-medial part of the trigeminal ganglion. Electron microscopy revealed four different cell types in the trigeminal ganglion. However, distinct elements of the anterior segment did not project to specific cell types.

Sympathetic innervation of the rat cornea as demonstrated by the retrograde and anterograde transport of horseradish peroxidase-wheat germ agglutinin

The sympathetic innervation of the rat cornea was studied by using the method of intraaxonal transport of horseradish peroxidase-wheat germ agglutinin conjugate (HRP-WGA). In the first set of experiments, the relative number of superior cervical ganglion neurons that innervate the rat central cornea was estimated by the method of retrograde HRP-WGA transport. Following tracer application to the scarificed central corneal surface, 49-198 labeled neurons were observed in the ophthalmic region of the ipsilateral trigeminal ganglion and zero to four cells in the rostral pole of the ipsilateral superior cervical ganglion. In the second set of experiments, the three-dimensional distribution and termination sites of the corneal sympathetic nerve fibers were investigated by the technique of HRP-WGA anterograde transport from the superior cervical ganglion. HRP-WGA-labeled axons in corneal whole mounts were identified by the presence within their axoplasm of linear arrays of HRP-TMB reaction product, and their distribution was plotted faithfully onto line drawings made with a drawing tube attachment. Large numbers of HRP-labeled fibers were found in all animals within the corneoscleral limbus where the majority were associated with blood vessels. Fewer fibers (zero to 14 per animal) entered the cornea proper. The latter fibers entered the peripheral cornea in the deep to middle layers of the stroma and ascended into progressively more superficial layers as they coursed centrally. The majority of fibers branched infrequently in the peripheral cornea and increased in branching complexity near the central cornea. HRP-labeled axonal varicosities suggestive of terminal and preterminal expansions were located preferentially in the subepithelial layer of the corneal stroma and in the basal epithelium. Approximately 75% of the axonal varicosities were located in the central half of the cornea. The results of the current investigation reveal that the rat cornea is innervated sparsely by sympathetic nerve fibers derived from the superior cervical ganglion. These data provide additional support to current theories that corneal sympathetic nerve fibers may influence select aspects of corneal physiology, including ion transport and hydration, mitogenesis and wound healing, and sensitivity.

Evidence for sympathetic neural influence on human corneal epithelial function

Patients with unilateral Horner's syndrome were studied to determine the influence of sympathetic innervation on the structure and function of the human cornea. There was no difference in total corneal thickness, corneal oxygen uptake rate or corneal touch threshold between the normal and Horner's eyes of these patients. Epithelial thickness, however, was slightly but significantly greater in the Horner's eye than in the normal fellow eye (P less than 0.025). When subjected to a hypoxic "Stress Test", patients with post-ganglionic lesions showed significantly more epithelial greying and microcystic oedema (P less than 0.025 and P less than 0.01, respectively) and reported seeing smaller and brighter haloes in the Horner's eye. The cornea of the affected eye of these patients also showed a significantly shower rate of deswelling in the first hour following the "Stress Test" (P less than 0.05). These findings suggest that both in the resting state and when the cornea is physiologically challenged, the sympathetic nervous system and in particular, the terminal sympathetic neuron, has a small but significant influence on the human corneal epithelium.

Sensory supply of the anterior uvea: a light and electron microscope study

We have studied the ultrastructural features of sensory nerve fibers in the ciliary body and the iris and their parent trigeminal ganglion cells, using intra-axonally transported horseradish peroxidase as a tracer. Unmyelinated nerve fibers of ipsilateral trigeminal origin were found in stroma of both the ciliary body and the iris. Most appeared in bundles of nerve fibers; but some were found singly. Two distinct types of varicosities were found, one containing both a few irregularly shaped vesicles and mitochondria, the other containing mitochondria only. The thin profiles of the axons between these varicosities or endings contained neurotubules and filaments. The trigeminal ganglion cells supplying the anterior eye were of a relatively small size (15-50 micron in diameter) and confined to the anteromedial part of the ipsilateral ganglion. These cells could not be classified according to the arrangement of their subcellular organelles. The morphological characteristics of the sensory nerve fibers and ganglion cells supplying the anterior uvea are consistent with the view that pain may be the predominant sensation mediated by these neurons.

Sympathetic nerves to the rat cornea

The adrenergic innervation of the rat cornea was investigated by using the formaldehyde induced fluorescence (FIF) technique. The fluorescent nerves were observed mainly in the corneal stroma. Either cervical sympathectomy or pre-treatment with reserpine completely abolished the fluorescence of the adrenergic nerves of the cornea. After a stereotactic coagulation of the ophthalmic division of the trigeminal nerve, no adrenergic fibres were visible in the cornea and the number of the fluorescent iridic nerves was also reduced to a marked extent. On the other hand, ciliary ganglionectomy seemed to have no effect on the adrenergic fibres of the cornea. When the rats had been pre-treated with a monoamine oxidase inhibitors, nialamide, and noradrenaline, not only was there an increase in the intensity of the specific fluorescence, but also in the number of adrenergic nerves in the cornea. The epithelium was also shown to contain adrenergic nerves by administering high doses of nialamide combined with noradrenaline, both intravenously as well as topically on the cornea, under the protection of propranolol. It may be concluded that the rat cornea receives its adrenergic innervation along the posterior ciliary nerves. The short ciliary nerves do not appear to carry sympathetic nerves to the cornea.

The sphincter pupillae of the guinea-pig: structure of muscle cells, intercellular relations and density of innervation

Compared with those of visceral and vascular smooth muscles, the smooth muscle cells of the sphincter pupillae of the guinea-pig show remarkable structural features. They are small, irregular in shape, and have a surface to volume ratio of about 2.73 (i. e. for every cubic micrometre of cell volume there are on average 2.73µm2of cell surface). Mitochon­dria constitute about 12% of the cell volume. Smooth sarcoplasmic reticulum is extremely well developed, lying underneath wide areas of the cell surface, between and around caveolae, and around most mitochondria. Stacks of cisternae of sarcoplasmic reticulum are present in superficial and deep regions of muscle cells. In some muscle cells rough sarcoplasmic reticulum is predominant. Thick, thin and intermediate myofilaments are readily seen in all preparations. A few cells showed myofilaments with size and arrangement similar to those of striated muscle. Nexuses are frequently associated with sacs of sarcoplasmic reticulum and are more numerous than in smooth muscles previously studied. In montages of cross-sectioned sphincters about 24 nexuses for 100 muscle cells are counted. Frequently two parts of the same cell are connected by a nexus. Nexuses also occur between muscle cells which are in close relationship with the same nerve varicosity. The density of innervation is very high. In a montage from a full cross-section of the sphincter, there are 2791 profiles of muscle cells and 843 nerve fibres, of which 425 contain synaptic vesicles and 194 are separated from muscle cells by a gap of only about 20 nm. In a number of the closely apposed nerve endings junctional specializations are seen. Collagen fibrils have a diameter of about 50 nm. Some bundles of collagen lie between the muscle cell membrane and the basal lamina. Melanocytes and a few fibroblasts are seen. Blood vessels do not penetrate into the muscle but are numerous around it. No muscle cell is more than 20µm away from the nearest capillary. Endothelial cells contain abundant microfilaments 10 nm in diameter. Capillaries are not fenestrated.