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Japanese Journal of Ophthalmology Vol.43 No.4

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Japanese Journal of Ophthalmology Vol.43 No.4 Autonomic Nerves Containing Substance P in the Aqueous Outflow Channels and Scleral Spur of the Guinea Pig Mariko Sasamoto, Hai-Bo Chen and Shigeo Tsukahara Department of Ophthalmology, Yamanashi Medical University, Tamaho, Yamanashi, Japan Purpose: To study the innervation of the aqueous outflow channels and scleral spur by auto- nomic nerves containing substance P. Methods: The experiments were conducted on guinea pigs. Immunohistochemical tech- niques and capsaicin-ablation of the sensory nerves were used to investigate nerves contain- ing substance P at the light and electron microscopic level. Results: Nerves containing substance P were observed in the aqueous outflow channels and scleral spur regions. The fine structures of these nerves had a similar pattern in those regions, and the labeled elements had abundant small vesicles, a few large vesicles, and numerous neurotubuli. Following capsaicin treatment, these nerves remained intact and no degener- ated substance P-like immunoreactive nerves were found. Conclusions: Nerves containing substance P are most likely of autonomic origin in view of their ultrastructural features. These nerves innervate the aqueous outflow channels and scleral spur, and are probably important for neurogenic influences on the intraocular pres- sure by the autonomic nervous system. Jpn J Ophthalmol 1999;43:272–278 © 1999 Japa- nese Ophthalmological Society Key Words: Aqueous outflow channels, capsaicin, guinea pig, immunohistochemistry, substance P. Introduction The scleral spur region should also be considered 4,5 Aqueous outflow channels and the scleral spur because it plays a part in outflow regulation. The human scleral spur contains elastic tissue, similar to play important roles in the regulation of intraocular sclera, so that changes in the IOP might affect these pressure (IOP), and are known to have varied pepti- 5 dergic innervation, which have received special at- tissues. tention.1 It is believed that the neuropeptides play an There has been recent interest in neuromodula- important role as neuroregulators of aqueous out- tion by substance P (SP) in the adrenal gland from 6 and Livett et al,7 who sug- flow regulation at these sites. the works of Neri et al gested that SP regulated stress-induced catechola- In the conventional outflow pathway, aqueous hu- mine secretion and the ACTH-stimulated release of mor from the anterior chamber passes through the aldosterone. trabecular meshwork, crosses the inner wall of Kondo8 classified autonomic efferent nerves into Schlemm’s canal, and passes into the collectors chan- two groups: “adrenopeptidergic” and “cholinopepti- nels, the intrascleral and episcleral venous plex- dergic.” From the results of an earlier study,9 we sug- uses.2,3 gested that SP of autonomic origin serves as a neu- rotransmitter or neuromodulator for the regulation of IOP in the guinea pig trabecular meshwork. Received: May 20, 1998 Because little information is available about the Correspondence and reprint requests to: Shigeo TSUKA- 10,11 HARA, MD, PhD, Department of Ophthalmology, Yamanashi neuronal regulation of IOP, such problems should Medical University, Tamaho, Yamanashi, 409-3898, Japan be studied in more detail. In the present study, we Jpn J Ophthalmol 43, 272–278 (1999) © 1999 Japanese Ophthalmological Society 0021-5155/99/$–see front matter Published by Elsevier Science Inc. PII S0021-5155(99)00024-6 M. SASAMOTO ET AL. 273 NERVES CONTAINING SUBSTANCE P have studied the innervation in a wider range of tis- The specimens were soaked in freshly prepared sues, and have determined the nonsensory origin of 0.02%, 3,39-diaminobenzidine tetrahydrochloride the substance P-like immunoreactive (SP-LI) nerves (DAB) in 0.05 mmol/L Tris-HCl buffer (pH 7.6) for inside the aqueous outflow channels and scleral spur 30 minutes. Then soaked in 0.02% DAB and 0.0025% using ultrastructural immunohistochemistry and cap- H2O2 in Tris-HCl buffer (pH 7.6) for 5 minutes at saicin treatment. room temperature, washed in 0.1 mmol/L PBS, and postfixed in 2% osmium tetroxide in 0.1 mmol/L Materials and Methods PBS for 1 hour at room temperature. The sections All animal experiments were performed in confor- were then dehydrated and finally embedded in ep- mity with the recommendations of the ARVO Reso- oxy resin and incubated. After incubation, the slides lution on the Use of Animals in Research. were separated from the sections embedded in ep- oxy resin by heating. Ultrathin sections and semithin m Tissue Preparation sections (1 m) were cut on a microtome (MT-2B; Ivan Sorvall, Norwalk, CT, USA). Ultrathin sections Five male Hartley guinea pigs weighing 300–400 g were stained with 1% uranyl acetate and lead citrate, were used for the study. Sodium pentobarbital (50 and examined under a transmission electron micro- mg/kg) and sodium heparin (1,000 units/kg) were in- scope (H-500; Hitachi, Tokyo). Semithin sections jected intraperitoneally to anesthetize the animals. were stained with Toluidine blue and examined un- Animals were perfused through the thoracic aorta der a light microscope (Nikon, Tokyo). with 0.1 mmol/L phosphate-buffered saline (PBS) (pH 7.4) followed by Zamboni’s fixative solution. Capsaicin Treatment The eyeballs were enucleated, the anterior segment of the eye was removed and further fixed in the same Chemical ablation of sensory nerves was performed solution for 6 hours at 48C. After immersion in 0.1 on seven male Hartley guinea pigs as described pre- 12 mmol/L PBS containing 20% sucrose overnight at viously. A total dose of 125 mg/kg capsaicin (Na- 48C, the specimens were frozen and cut into 20-mm sections in a cryostat (CM-1800, Leica, Heidelberg, Germany). The sections were mounted on albumin- coated slides and dried at room temperature. The immunostaining procedure was performed, not on free-floating sections, but on sections mounted on a slide. After immunostaining, a capsule contain- ing epoxy resin was inverted over the stained sec- tions mounted on the slides and a layer of epoxy resin was laid over, covering the capsule and section. Finally, the sections embedded in the epoxy resin were separated from the slides by heating the slides. After treatment with 1% hydrogen peroxide in methanol for 30 minutes, they were rinsed with 0.1 mmol/L PBS. Immunohistochemical Processing (Pre-embedding Method) For immunohistochemistry, the specimens were treated with 10% normal goat serum for 30 minutes at room temperature and incubated with rabbit anti- SP serum (1:500; Chemicon International, Temecula, Figure 1. Light micrograph of substance P-like immunore- CA, USA) for 48 hours at 48C. They were then incu- active (SP-LI) innervation in outflow channels and scleral bated in peroxidase-labeled affinity-purified anti- spur (SS). SP-LI nerves (arrowheads) are scattered 5 body to rabbit IgG serum (1:200; Kirkegaard & throughout these sites. Inset: high magnification (Bar 150 mm) of varicose axon (arrow). Asterisk: Schlemm’s ca- Perry Laboratories, Gaithersburg, MD, USA) for 12 nal, stars: episcleral vessels, S: sclera, ES: episclera, CT: hours at 48C and fixed in 1% glutaraldehyde in 0.1 cribiform layer in trabecular meshwork, CLM: ciliary lon- mmol/L PBS for 20 minutes at 48C. gitudinal muscle. 274 Jpn J Ophthalmol Vol 43: 272–278, 1999 calai Tesque, Kyoto) was injected subcutaneously over rabbit normal serum with the same dilution (5003) 2 days under sodium pentobarbital anesthesia 2 weeks as SP antiserum to check nonspecific reaction. before the immunohistochemical study. The elimina- tion of the blink reflex, tested by gentle stimulation Results of the cornea with gauze with the animals restrained, Light Microscopic was used to confirm the ablation of the sensory Findings After Capsaicin Treatment nerves by the capsaicin treatment. The tissues sur- rounding the Schlemm’s canal were used as control. In semithin sections, SP-LI nerves were observed To assess immunohistochemical specificity, an- as varicose or nonvaricose linear structures in the other section of 20 mm was incubated in 0.1 mmol/L aqueous outflow channels and scleral spur. These PBS to check intrinsic peroxidase, and was placed in varicosities had the typical appearance of autonomic nerves (Figure 1). Ultrastructural Findings in Aqueous Outflow Channels and Scleral Spur SP-LI nerves in and around the aqueous outflow channels and scleral spur regions are shown in Fig- ure 2. Most of the SP-LI nerves were filled with many labeled small vesicles (30–60 nm), a few large vesicles (100–200 nm), and numerous neurotubuli. Some of the neurotubuli were seen in close proxim- ity to the axolemma. SP-LI nerves were located very close to an epi- scleral vascular channel (Figure 2A) and were in close contact with networks of collagen fibers (Fig- ure 2B). Figure 2. Electron micrographs of substance P-like immu- noreactive (SP-LI) nerves. (A) SP-LI nerves (A1, A2, A3) are seen around episcleral vein (star). Inset: Higher magni- fication (Bar 5 0.1 mm) of axon (double arrows). SP-LI materials are confined to numerous small vesicles (small arrow) and neurotubuli (white arrow). SP-LI nerves sec- tioned longitudinally (A1, A2) and transversely (A3). E: Figure 3. Electron micrograph of substance P-like immu- endothelial cells of episcleral vein, SM: smooth muscle cell, noreactive (SP-LI) nerves following capsaicin treatment. R: red blood cell, N: nucleus. (B) SP-LI nerves (A4 and SP-LI nerves (A1, A2, and A3) are found in close proximity A5) are seen in close proximity to collagen fiber networks to collagen fiber networks (CF) around the external wall (CF) in scleral spur. A4 packed with numerous small vesi- (EW) of Schlemm’s canal (asterisk). Inset: High magnifica- cles (small arrow) and some neurotubuli (white arrow). A5 tion (Bar 5 0.1 mm) of axon (double arrows). SP-LI materi- contains numerous small vesicles (small arrow), several als confined to small vesicles (arrow), large vesicle (arrow- large vesicles (arrowhead), and numerous neurotubuli head), and numerous neurotubuli (small arrow).
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