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F. Schroedl, A. Brehmer, D. Nickla, W. L. Neuhuber; A Further Morphological Classification of the Pterygopalatine Ganglion in Chicken. Invest. Ophthalmol. Vis. Sci. 2009;50(13):3932.
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Blood vessels and non-vascular smooth muscle cells of the chicken choroid receive parasympathetic innervation from the ciliary ganglion and from the pterygopalatine ganglia (PPG). In birds, the PPG, unlike the ciliary ganglion, consists of a chain of interconnected microganglia in the medial part of the orbit, and hence has not been thoroughly investigated. The aim of this study was to further characterize the neurochemical characteristics of these neurons.
Chicken PPG were investigated by single, double and triple immunohistochemistry against choline acetyl transferase (ChAT), neuronal nitric oxide synthase (nNOS), vasoactive intestinal polypeptide (VIP), tyrosine hydroxilase TH, vesicular monoamine transporter 2 (VMAT2), calcitonin gene-related peptide (CGRP). Fluorescence and confocal laserscanning microscopy were used for documentation.
ChAT/nNOS/VIP positive neurons of the PPG can be divided into small (~12 µm diameter) and large (~25 µm diameter) neurons. Subpopulations of these neurons (~ 15%) co-stain for TH, but not for VMAT2. CGRP-positive nerve fibers form bouton-like endings in close association to PPG neurons. In addition, numerous VMAT2-positive boutons are found in close vicinity to PPG neurons.
Small and large neurons of the chicken PPG may correspond with the vasomotor and secretomotor neurons described for mammals (e.g., Kuchiiwa et al., Neurosci Lett 2000). TH-positive nerve fibres in the choroid are not only of sympathetic origin, but can also derive from the PPG, which is important for lesion studies. Multiple inputs to the PPG (CGRP/ VMAT2) reveal a much more complex organization in this relay structure.
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