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F. Schroedl, M.E. De Stefano, F. Minvielle, K. Stuebinger, A. Brehmer, W.L. Neuhuber; Somatostatin in the Avian Pterygopalatine Ganglion and Choroid . Invest. Ophthalmol. Vis. Sci. 2005;46(13):3345.
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Purpose: In the ciliary ganglion of chicken and quail, somatostatin (SOM) is an exclusive marker for parasympathetic postganglionic neurons innervating the choroid. A second parasympathetic pathway projecting to the choroid originates from the pterygopalatine ganglion (PTY). Aim of this study was to investigate SOM immunoreactivity in the avian PTY and its colocalization with other neuroactive substances in the choroid, with special respect to the intrinsic choroidal neurons (ICN). Methods: PTY and choroids of chicken and quail were processed for assessing the expression and localization of the following markers by means of histochemistry and immunocytochemistry: neuronal nitric oxide synthase (nNOS), NADPH–diaphorase, galanin (GAL), vasoactive intestinal polypeptide (VIP), choline acetyl transferase (ChAT), and SOM. For documentation, light–, confocal laser scanning– and electron microscopy were used. Results: PTY neurons showed immunopositivity to nNOS– and to NADPH–diaphorase histochemistry. SOM immunoreactivity was absent in perikarya, but neurons were densely surrounded by SOM–positive nerve fibres, which formed contacts with membrane specializations on PTY neurons, as revealed by electron microscopy. In the choroid, nNOS /GAL–immunoreactive ICN were likewise closely apposed by SOM–immunopositive nerve fibres, as revealed by confocal microscopy. A colocalization of both markers was not detectable. ChAT immunoreactive nerve fibres highly colocalize for SOM, but not for VIP, and were likewise approaching ICN, whereas ChAT immunoreactivity was absent in ICN. At the electron microscope, GAL– immunoreactive nerve fibres contacted ICN. GAL was also found to a high degree in PTY perikarya and ICN. Conclusions: SOM immunoreactivity in PTY may originate from either preganglionic fibres of the superior salivatory nucleus, and/or postganglionic fibres from the ciliary ganglion, and/or fibres from the brainstem via yet unknown pathways. It may regulate the production of NO in PTY neurons and ICN. SOM/ChAT/GAL–immunoreactive appositions on ICN indicate, besides known sympathetic and primary afferent contacts, parasympathetic influence on ICN, or, in case of GAL also intrinsic connections. This would highlight the role of ICN as local choroidal integrators, being involved in neuronal circuits regulating ocular homeostasis.
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