Intrinsic choroidal neurons in the duck eye receive sympathetic input: anatomical evidence for adrenergic modulation of nitrergic functions in the choroid

Abstract

Intrinsic choroidal neurons (ICN) in the duck eye form an intramural ganglionic plexus that may subserve complex integrative functions. A key feature of such ganglia is an innervation by sympathetic postganglionic neurons. The present study was thus aimed at determining the sympathetic postganglionic innervation of ICN. Choroids were processed for double immunofluorescence labelling with the following markers: tyrosine-hydroxylase (TH)/nitric oxide synthase (nNOS), TH/galanin (GAL), dopamine-beta-hydroxylase (DBH)/vasoactive intestinal polypeptide (VIP), TH/DBH and DBH/alpha-smooth-muscle actin (alphaSMA), and for triple immunofluorescence labelling with VIP/DBH/TH. Epifluorescence and confocal laser scanning microscopy were used for evaluation. Immunoperoxidase staining for TH or DBH in combination with NADPH-diaphorase histochemistry was applied for electron microscopy. ICN spread over the entire choroid but were concentrated in an equatorial zone passing obliquely from naso-cranial to temporocaudal. More than 80% of nNOS-positive ICN showed close appositions of TH/DBH-immunoreactive varicose nerve fibres at the light-microscopic level, as could be confirmed by confocal laser scanning microscopy. Ultrastructurally, these appositions could be defined as both synapses or close contacts without synaptic specialisation. Vascular and non-vascular smooth muscle fibres also received TH/DBH-immunopositive innervation. Our findings suggest that most ICN receive a sympathetic input that might modulate their nitrergic effects upon vascular and non-vascular smooth muscle fibres in the choroid and that they may have more complex functions than merely being a simple parasympathetic relay.

Intrinsic choroidal neurons in the chicken eye: chemical coding and synaptic input

“…It has been shown that in ducks ICNs are approached by sympathetic nerve fibers; this was confirmed at the ultra-structural level (Schrödl et al 2001b). We postulate that chicken ICNs are also part of the circuit of the sympathetic nervous system as indicated by the presence of TH- and VMAT2-positive boutons in close association.…”

“…Because this antibody did not show positive staining in the chicken choroid (although it did label fibers in prior bird experiments; Schrödl et al 2001b), VMAT2 was used as an alternative marker for catecholamines. Prior to that, the superior cervical ganglion was screened for VMAT2; VMAT2 was detected in numerous neurons and fibers of the respective ganglion (Fig.…”

Sensory collaterals, intramural ganglia and motor nerves in the guinea-pig bladder: evidence for intramural neural circuits

“…The function of these local networks has been found to depend on the organ. In the gut, the ganglia play a role in the generation and coordination of peristaltic activity and secretion (Furness et al 2004), whereas in the choroid of the eye, they influence blood flow and contraction in the smooth muscle (Schrodl et al 2001(Schrodl et al , 2003. Such peripheral neural networks also receive input from collaterals of extrinsic primary sensory fibres.…”

Intrinsic Choroidal Neurons in the Human Eye: Projections, Targets, and Basic Electrophysiological Data

“…ICNs may be suitable candidates for the neuronal control of these refractive changes. 12,40,41 Possible targets of ICNs other than those expressing smooth muscle actin are still to be determined.…”