Markers of the sympathetic, parasympathetic and sensory nervous system are altered in the human diabetic choroid

BACKGROUND

We sought to evaluate alterations in markers of the autonomic nervous system in human diabetic choroid.

METHODS

Eighteen eyeballs from subjects with diabetes and 22 eyeballs from subjects without diabetes were evaluated in this study. Synaptophysin, tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DβH), neuronal nitric oxide synthase (nNOS), choline acetyltransferase (ChAT), vesicular monoamine transporter II (VMAT-2), vesicular acetylcholine transporter (VAChT), vasoactive intestinal peptide (VIP), neuropeptide Y (NPY), and calcitonin gene-related peptide (CGRP) levels were detected by western blot analysis and immunofluorescence was performed in some cases. Furthermore, differences in adrenergic (α1- and β2-subtypes) and cholinergic (M1 and M3) receptor levels between diabetic subjects and controls were noted.

RESULTS

Decreased synaptophysin levels were found in diabetic choroids by western blot analysis and a reduction of synaptophysin-immunoreactive nerves was also found by immunofluorescence. Furthermore, a decrease of the levels of the key enzyme (TH) and transporter (VMAT2) of norepinephrine was evident both by western blot analysis and immunofluorescence. Additionally, increased NPY, VAChT, nNOS, and CGRP levels were observed in diabetic choroids. The levels of adrenergic (β2 subtype) and acetylcholine (M1 subtype) receptors decreased in diabetic choroids, as shown by western blotting and although the differences in α1 and M3 were not significant, there was a downward trend.

CONCLUSIONS

In the diabetic choroid, the levels of neurotransmitters, enzymes, and receptors associated with choroidal blood flow regulation are altered. These changes may affect the regulation of choroidal blood flow and may be associated with impaired retinal function and retinal pathology.

Fluorescence Histochemical Demonstration of Adrenergic Terminations in the Human Choroid

With the existing literature on the aspects of anatomic and physiological ocular choroid membrane variables in mind, the authors verify the possibility of applying the methods of Axelsson et al and of Lindvall and Bjorklund, as simplified by Furness and Costa for fluorescent microscopy, to the study of human choroid nerve topographic distribution. The material for the study was obtained from three human eyeballs, two enucleated because of malignant melanoma of the choroid and one because of neoplasia of the ciliary body. A binocular dissecting microscope was used. A fluorescent microscope was used to observe the histological specimens and photographs were taken. The following results are presented and discussed: 1) the fluorescent paravascular nervous fibres and periarterial nervous plexuses divided into preterminal and terminal fibres; 2) in the suprachoroidal layer, there were small groups of polygonal nervous branches with or without this connection; 3) the most intervasal plexus development was in the posterior part of the vascular layer with preterminal and terminal fibres, 4) in the intervascular space, melanocytes and free adrenergic nervous terminations were observed; 5) adrenergic fibres were not observed in the choriocapillaris of the choroid membrane; 6) there were adrenergic neurons in the vascular layer.

Age-related decline in VIP-positive parasympathetic nerve fibers in the human submacular choroid

PURPOSE

An age-related decline in macular choroidal blood flow (ChBF) occurs in humans. Vasodilatory nerve fibers containing vasoactive intestinal polypeptide (VIP) innervate choroidal blood vessels. The current study was conducted to examine the possibility that an age-related loss of these fibers might occur in the submacular choroid in humans, and thus contribute to a decline in ChBF.

METHODS

Macular choroid punches were collected from 35 healthy human donors ranging from 21 to 93 years of age. Choroidal samples were immunolabeled using anti-VIP and the peroxidase-antiperoxidase

METHOD

VIP-positive nerve fiber abundance was quantified in up to 12 fields per punch. Fifty macular punches were analyzed, and results for eye pairs were averaged. Choroidal vessel diameter (ChVD) was measured for these same fields. The relationship between age and vessel diameter or VIP-positive fiber abundance was analyzed. Multivariate statistical models were generated correcting for gender, variables related to the tissue specimens, and potential procedural sources of variability.

RESULTS

The fully adjusted multivariate models showed a significant age-related reduction in both the VIP-positive fiber abundance (P = 0.0003, adjusted R(2) = 0.51) and ChVD (P < 0.0001, adjusted R(2) = 0.63), with slopes of -0.45 and -0.19, respectively. Adjusting for the same variables, VIP-positive fiber abundance showed a significant direct correlation with ChVD.

CONCLUSIONS

The results indicate a significant age-related decline in VIP-positive nerve fibers and vessel diameter in the submacular choroid in disease-free human donor eyes. These findings suggest that a decline in the neural control of ChBF and vessel diameter may explain the reductions in ChBF and its adaptive control observed clinically with aging.

Age-related changes in sympathetic neurotransmission in rat retina and choroid

While age-related night vision loss and age-related macular degeneration are well characterized, less is known about the normal aging process in the retina and choroid. The purpose of this study was to ascertain whether dopamine beta-hydroxylase (DBH), beta1- and beta2-adrenergic receptor gene and protein expression are altered in the retina and choroid with age. The retina and choroid were dissected from F344xBNF1 hybrid rats aged 8, 22, and 32 months. Real-time PCR and Western blot analysis were conducted to determine steady-state mRNA and protein expression. Immunohistochemistry (IHC) was conducted to localize DBH protein expression in the retina. DBH protein expression was substantially decreased with age in the retina, particularly in the outer nuclear layer, with no changes in DBH expression noted in the choroid. There was a significant increase in beta1-adrenergic receptor protein expression in retinal samples at 22 months, while beta2-adrenergic receptor protein expression was not affected by age. Decreased expression of DBH with age in the retina could lead to reduced production of norepinephrine, potentially resulting in an increase of beta1-adrenergic receptor expression due to denervation supersensitivity. Gene expression for DBH, beta1- and beta2-adrenergic receptors were observed to peak at 22 months and return to baseline levels by 32 months of age in the choroid. Our findings suggest that the retina may be more sensitive to age-related loss of sympathetic neurotransmission than the choroid, which may partially explain normal age-related vision loss in the elderly.

[A comparative study of choroidal innervation in the human and the rabbit (oryctolagus cuniculus)]

OBJECTIVE

To analyze morphological differences between the choroidal innervation of the human and the rabbit, the latter being a species frequently used as an experimental model of human ocular diseases.

METHODS

Twelve human and 12 rabbit choroidal whole mounts were processed using an indirect immunohistochemical technique, peroxidase-anti-peroxidase and antibodies against 200 kD neurofilament.

RESULTS

Choroidal nerve fibers were perivascular and intervascular. Perivascular fibers surrounded all arteries forming a network that was more developed in the rabbit. In humans, intervascular fibers were mainly concentrated at the posterior pole where they formed a denser and more highly organized plexus than in the rabbit, which did not exhibit a preferential location for these fibers. Human choroidal ganglion cells were far more numerous than in the rabbit and were concentrated in a circumferential area corresponding to the entrance of the short posterior ciliary arteries of the submacular area. In the rabbit, these cells were restricted to the peripheral choroid.

CONCLUSIONS

Some differences were observed between human and rabbit choroidal innervation. The abundance of ganglion cells and their preferential distribution could be necessary to maintain a constant blood flow in the central area of the human choroid. The lack of organization of rabbit choroidal innervation at the posterior pole could be associated with an absence of the macula. These differences, along with peculiarities of retinal vascularization, should be taken into consideration when using the rabbit as an experimental model to study human eye diseases in which regulation of choroidal blood flow is involved.

Sustained upregulation of glial fibrillary acidic protein in Müller cells in pigeon retina following disruption of the parasympathetic control of choroidal blood flow

Choroidal blood flow in pigeon eyes is light driven and controlled by a parasympathetic input from ciliary ganglion (CG) neurons that receive input from the medial subdivision of the ipsilateral nucleus of Edinger-Westphal (EWM). EWM lesions diminish basal ChBF and irreversibly prevent ipsilateral light-evoked increases in ChBF, presumably rendering the retina mildly ischemic. To characterize the location, severity, and time course of the retinal abnormality caused by an EWM lesion, we quantitatively analyzed the cellular and regional extent of Müller cell glial fibrillary acidic protein (GFAP) immunolabeling up to nearly a year after an EWM lesion. We found that unilateral EWM lesions greatly increased Müller cell GFAP throughout the entire retinal depth and topographic extent of the affected eye, up to nearly a year post lesion. By contrast, destruction of the pupilloconstrictive pretectum or of the pupilloconstrictive part of lateral EW (EWL) did not appreciably increase Müller cell GFAP. Thus, the large increase in Müller cell GFAP following an EW lesion is attributable to an ongoing defect in choroidal vasodilatory function rather than to chronic pupil dilation. The Müller cell GFAP increase was greater ipsilateral than contralateral to the EWM destruction for the retinal territory deep to the heavily CG-innervated superior and temporal choroid, but not for the retinal territory deep to the poorly CG-innervated inferior and nasal choroid. The GFAP increase was light-dependent, since it did not occur in EW-lesioned birds housed in dim illumination. Our results show that the chronic vascular insufficiency caused by the loss of the EWM-mediated parasympathetic control of choroidal blood flow leads to a significant and sustained increase in retinal Müller cell GFAP. This increase could be a sign of a disturbance in retinal homeostasis that eventually leads to retinal injury and impaired visual function.

Choroidal innervation and optic neuropathy in macacque monkeys with laser- or anterior chamber perfusion-induced short-term elevation of intraocular pressure

Long-term intraocular pressure (IOP) elevation leads to a significant reduction of the intrinsic choroidal innervation and axon loss in the optic nerve. In this study we investigated early changes in these tissues in order to clarify the putative sequence of events between choroidal ganglion cell loss and optic nerve axon loss in 19 monkeys with experimentally induced glaucoma. After 1 month of increased IOP, severe optic neuropathy but no reduction of choroidal ganglion cells (CGC) was detectable. Beginning at 2 months after treatment signs of degeneration in CGC morphology were observed. Laser treatment of the trabecular meshwork without IOP elevation caused no changes in choroidal innervation. Our results show that there is no apparent association between reduction of CGC and optic neuropathy in the early stages of IOP elevation.

Choroidal innervation in primate eyes

Arteries and arterioles of the choroid are surrounded by numerous nerve fibers staining for nitric oxide synthase (NOS) and vasoactive intestinal peptide (VIP). In most mammalian eyes these nerve fibers derive from the pterygopalatine ganglion via the facial nerve. Stimulation of the facial nerve causes vasodilation of the choroidal vasculature. In primates with a well developed fovea centralis there are ganglion cells in the choroidal stroma which in human eyes amount to around 2000. The postganglionic nerve fibers of these choroidal ganglion cells (CGC) join the perivascular nerve fiber plexus. The CGC stain for NOS and VIP like the nerve cells within the pterygopalatine ganglion. There are, however, differences between the two cell populations. Immunohistochemical and ultrastructural classification of the CGC show that in addition to NOS and VIP almost half of the cells stain for calretinin, single ones for neuropeptide Y (NPY) and galanin. A number of cells is in close contact with numerous boutons staining for nNOS, VIP, NPY, tyrosine hydroxylase (TH), vesicular monoaminergic transporter (VMAT)2, vesicular acetylcholine transporter (VACHT), calretinin, and NPY. These data indicate a more complex integrative function of CGCs e.g. volume regulation in parallel with ciliary muscle contraction during accommodation. Ultrastructural and immunohistochemical studies indicate, that CGCs in addition may have mechanosensory properties. Whether they are involved in volume-regulatory functions independent of accommodation is not yet known. In glaucoma disease the number of CGCs is significantly reduced. This holds true for eyes with primary open angle glaucoma, pseudoexfoliation glaucoma and experimentally induced monkey glaucoma indicating that elevated IOP is involved in the pathogenesis of glaucomatous CGC-degeneration.

Choroidal ganglion cells in prenatal, young, and middle-aged human donor eyes

PURPOSE

In the current study, the appearance and development of choroidal ganglion cells (CGCs) was investigated in eyes of 18 human donors between the 13th week of gestation (wog) and 42 years of age.

METHODS

The number and diameter of CGCs was evaluated in scleral and choroidal whole mounts stained for NADPH diaphorase. To demonstrate the synaptic input of the CGCs, sections were stained with antibodies against synaptophysin, vesicular acetylcholin transporter, tyrosin hydroxylase, and vesicular monoaminergic transporter 2.

RESULTS

Clusters of small CGCs were first seen in the 18th wog next to the nasal and temporal long ciliary nerves. Immunohistochemistry in the 25th wog revealed 3298 and 5429 nitric oxide synthase/NADPH diaphorase positive CGCs, surrounded by numerous cholinergic and aminergic boutons. The number of CGCs decreased to 1000-2500 after birth. During postnatal development, the CGCs spread into small groups, distributed all over the choroid. The size of CGCs increased markedly up to adulthood.

CONCLUSIONS

CGCs appear late during choroidal development, in parallel with the differentiation of the outer vascular layers. This coincidence might point to the primary role of the CGCs as specific vasoregulators in species with a well-developed fovea centralis.

NPY and TH innervation in human choroidal whole-mounts

To determine the distribution of NPY and TH human choroidal innervation, choroidal whole-mounts were processed for indirect immunofluorescence. An antibody to a component of the neuronal cytoskeleton, neurofilament 200 kDa (NF-200) was used to identify neurons and axons. A double immunostaining was performed, antibodies against NF-200 being combined with antibodies against neuropeptide Y (NPY) and tyroxine hydroxylase (TH). Fibers containing both NPY and TH were distributed in three plexuses, one in the suprachoroid large-sized vessel layer, and two in the medium-sized vessel layer. Intrinsic choroidal neurons (ICNs) containing NPY and TH were observed in the suprachoroid. The TH(+) ICNs were located in the medium-sized vessel layer. Overall, NPY(+) and TH(+) ICNs were more frequent in the central temporal area, both in isolation and forming microganglia. We also detected small spindle elements intensely immunoreactive to TH(+) and distributed mainly in the suprachoroid from the equator to the periphery. In conclusion, the human choroid contains abundant NPY and TH nerve fibers related to chroroidal vascular structures; it further possesses NPY(+) and TH(+) ICNs which contribute to the choroidal self-regulation persisting after sympathetic denervation. Additionally, these ICNs may at least partially explain why the choroidal blood flow does not respond to the factors that influence systemic vascular control. The preferential location of these cells in the submacular area suggests that dysfunction or degeneration of these cells may be a factor in vascular pathologies found in ocular disease, such as diabetic macular edema or age-related macular degeneration.

Cervical sympathectomy causes photoreceptor-specific cell death in the rat retina

Changes in the regulation of the vasculature of the eye may be related to some age-related ocular diseases. We have previously shown that loss of sympathetic innervation, as can normally occur with age, resulted in substantial vascular growth of the choroid. The current study was designed to determine whether changes induced by sympathetic denervation causes significant loss of photoreceptors and increased glial cell reactivity in the retina. Sympathetic denervation was performed followed by immunohistochemistry, TUNEL staining, and protein expression analysis to investigate photoreceptor loss. There was a significant reduction (30%) in photoreceptor numbers in the sympathectomized eye. This loss was due to apoptosis, as there was over a doubling in apoptotic cell numbers after sympathectomy. This loss of photoreceptors in the sympathectomized eye resulted in a significantly reduced width of the outer nuclear layer of the retina when compared to the contralateral eye. Increased glial fibrillary acidic protein (GFAP) staining was also noted after sympathectomy in the ganglion cell layer with streaking toward the bipolar cell layer. These results suggest that loss of sympathetic innervation may cause significant changes to the physiology of the choroid.

Anatomical and functional evidence for progressive age-related decline in parasympathetic control of choroidal blood flow in pigeons

The choroid receives extensive parasympathetic innervation, which in birds arises largely from the ciliary ganglion (CG). Since age-related changes in parasympathetic regulation of choroidal blood flow (ChBF) could contribute to age-related retinal decline, we used anatomical and functional methods to determine if ChBF control by the CG shows age-related decline in pigeons. The efficacy of the choroidal vasodilatory response to activation of the CG preganglionic input from the medial subdivision of the nucleus of Edinger-Westphal (EWM) was assessed using laser Doppler flowmetry (LDF). The EWM receives bisynaptic retinal input, and electrical stimulation of EWM or light stimulation of the retina in young animals produces dramatic choroidal vasodilation. Transcleral LDF was therefore used to measure both basal ChBF and the increases in ChBF elicited by electrical stimulation of EWM or by retinal illumination in 0.5-18 year old pigeons. Fixed cryostat sections of the eye from 0.5 to 22 year old pigeons were immunolabeled for the 3A10 neurofilament-associated antigen to determine if intrachoroidal nerve fibers arising from CG exhibited age-related loss. We focused on superior choroid, since it is the primary target for CG nerve fibers. There was a marked age-related loss in the ChBF vasodilatory response elicited by either EWM stimulation or retinal illumination, as was also true for basal ChBF. A progressive decrease in choroidal nerve fibers of CG origin, to 17% of youthful abundance by 22 years of age, was also observed. The evoked ChBF increase, and basal ChBF, achieved 50% of their age-related decline between the ages of 3 and 4 years, while half the loss in CG innervation of choroid was later, occurring by 10 years. Age-related loss of choroidal nerve fibers occurs in parallel with but more slowly than the reduction in basal ChBF and the choroidal vasodilation that can be elicited via natural (light) or electrical activation of the central neural input to CG choroidal neurons. The prominent age-related decline in parasympathetic control of ChBF early in the pigeon life span could contribute to the age-related retinal decline observed in pigeons.

Morphology of the long and short uveal nerves in the human eye

The aim of this study was to examine the architecture of the uveal nerves in the sclera and suprachoroid of human eyes. Eyes from 17 adult human donors were investigated. The uveal nerves in different regions (retrobulbar, intrascleral, suprachoroidal, pars plana) were prepared and studied by light and electron microscopy. In addition, immunohistochemistry was performed for various neuronal markers. The long uveal nerves showed a characteristic suprachoroidal location with no branches supplying the choroid. It was found that typically they are composed of myelinated (75%) and non-myelinated (25%) nerve fibres. They mainly contain aminergic and sensory nerve fibres. A separate set of cholinergic non-myelinated nerve fibre bundles runs parallel with these long uveal nerves. The short uveal nerves supply the suprachoroidal nerve plexus with approximately 13% of their nerve fibres. The nerves and the branches supplying the choroid appear as mixed nerves containing sympathetic, parasympathetic and sensory axons. This study therefore provides new information about the quantity, type and distribution of myelinated and non-myelinated nerve fibres in the posterior uvea of the human eye.

Choroidal Ganglion Cell Changes in Human Glaucomatous Eyes

PURPOSE

Choroidal ganglion cells (CGC) are an important source of vasodilative innervation of the posterior ciliary arteries, which also supplies the lamina cribrosa region of the optic nerve. The purpose of this study was to investigate whether CGC undergo quantitative and morphologic changes in human glaucomatous eyes.

METHODS

Twenty-five human glaucomatous eyes (15 with primary open angle glaucoma, 10 with pseudoexfoliation glaucoma) and 38 normal eyes (31 age-matched) were investigated. Scleral and choroidal whole mounts were stained for NADPH diaphorase, the CGC quantified in the outer and inner choroid and in the different quadrants separately, and the diameter of the CGC measured. Serial semi- and ultrathin sections were studied by light and electron microscopy.

RESULTS

In glaucomatous eyes, the total number of CGC was significantly decreased. The most striking loss of CGC was found in the temporal quadrant adjacent to the optic nerve, where only single CGC persisted. The remaining CGC showed a normal ultrastructural appearance but a shift toward larger cells.

CONCLUSION

Smaller CGC and those directly adjacent to the optic nerve seem to be most susceptible to the yet unknown pathogenetic factors responsible for this CGC loss. Since the most pronounced loss of CGC occurred in the vicinity of the optic nerve it is tempting to speculate that the vasodilative regulation of the vessels supplying the lamina cribrosa region is impaired in eyes with POAG.

Comparative anatomy of nitrergic intrinsic choroidal neurons (ICN) in various avian species

Intrinsic choroidal neurons (ICN) represent a peculiar feature of eyes in higher primates and birds. They account for up to 2000 in human and duck eyes but are virtually absent or rare in all other mammalian species investigated so far. It has been suggested that ICN are involved in regulation of ocular blood supply, hence influencing intraocular pressure, and changes in choroidal thickness, thus influencing accommodation. The present study was undertaken in order to compare differences in various avian species with respect to ICN as well as to provide data on some avian species relevant for experimental ophthalmic research, i.e. chicken and quail. Choroids from 12 avian species were processed for NADPH-diaphorase histochemistry or, in some cases, neuronal nitric oxide synthase immunocytochemistry. ICN were quantified and normalized to mean choroidal area. Three choroids of each galliformes (i.e. chicken, quail, turkey) and anseriformes (i.e. Muscovy duck, Mallard duck, goose) were rastered in squares of 1 mm2 and x/y coordinates were transferred into a 3D-diagram with the amount of ICN represented in the z-axis. ICN were detected in all species investigated. They were predominantly small cells with soma diameters of 20-30 microm. In turkey, and to a lesser amount in chicken, a subpopulation of ICN with somal diameters of up to 70 microm was observed. Highest mean cell counts were found in goose (6195.4; turkey 3558.4; chicken 1681.4; Muscovy duck 785.4; Mallard duck 640.8; quail 440.2). Normalized to choroidal area, highest mean cell counts were (per mm2): 12.62 in goose, 4.42 in both chicken and turkey, 2.86 in quail, 2.66 in Mallard duck and 1.89 in Muscovy duck. In galliformes, ICN were found to be accumulated temporo-cranial, while in anseriformes they were arranged in a more belt-like fashion, passing from cranio-nasal to temporo-caudal. Our results show that besides Muscovy duck, other avian species appear as suitable models for further functional experiments on ICN. The temporo-cranial accumulation of ICN in galliformes and the belt-like arrangement in anseriformes may reflect special functional requirements in regions of high visual acuity.

Sensory but not parasympathetic nerves are required for ocular vascular remodeling following chronic sympathectomy in rat

Choroidal vascularity increases following chronic sympathetic denervation in rats. The mechanisms of this remodeling are unclear. Since both nitric oxide and substance P/CGRP have been suggested as angiogenic factors in other targets, we hypothesized that sensory or parasympathetic nerves may also participate in ocular vascular remodeling. To test this hypothesis, sympathetic denervation was accomplished by superior cervical ganglionectomy. Sensory denervation was induced by subcutaneous injections of capsaicin on postnatal days 2 and 9, and ocular parasympathetic innervation was ablated by pterygopalatine ganglion excision on postnatal day 60. Eyes were processed and sectioned for light microscopic histomorphometry. Sympathetic denervation for 6 weeks resulted in increased choroidal thickness, vascular luminal area, numbers of large venules and large arterioles, and capillaries in the outer nuclear layer. Capsaicin pretreatment prevented sympathectomy-induced increases in choroidal thickness, vascular luminal area and large venules and large arterioles, whereas pterygopalatine ganglionectomy was without effect. Both sensory and parasympathetic denervation attenuated increases in outer nuclear layer capillaries. These studies indicate that increased choroidal vascularity noted after chronic sympathectomy requires intact sensory innervation.

Immunohistochemical classification and functional morphology of human choroidal ganglion cells

PURPOSE

To characterize human choroidal ganglion cells (CGCs) further, regarding their immunohistochemical and ultrastructural appearance and their pre- and postsynaptic connections.

METHODS

. Choroidal wholemounts and serial sections of human donor eyes were stained with antibodies against neuronal nitric oxide synthase (nNOS), vasoactive intestinal peptide (VIP), tyrosine hydroxylase (TH), vesicular monoaminergic transporter (VMAT)-2, vesicular acetylcholine transporter (VAChT), neuropeptide Y (NPY), substance P (SP), calcitonin gene-related peptide (CGRP), calretinin, galanin, synaptophysin, and alpha-smooth muscle actin. Ultrathin sections of glutaraldehyde-fixed eyes were studied with an electron microscope.

RESULTS

All CGCs stained for nNOS, most for VIP, approximately 45% for calretinin, and only single neurons for NPY and galanin. Ultrastructurally, the CGCs showed an incomplete glial sheath and, in places, showed close contact to surrounding collagen fibrils. The CGCs were in close contact with numerous boutons staining for the different neuronal markers including synaptophysin, nNOS, VIP, NPY, TH, VMAT-2, VAChT, calretinin, and NPY.

CONCLUSIONS

The data indicate a complex integrative function of CGCs. The immunohistochemical and ultrastructural characteristics also indicate that the CGCs may have mechanosensory properties. The complex synaptic information points to a specific regulative CGC function in parallel with ciliary muscle contraction (accommodation). Axons originating from CGCs mainly supply the choroidal vasculature, thus implicating the CGCs as vasodilative neurons, but single CGCs may also innervate other structures such as nonvascular choroidal smooth muscle cells.

Localization of preganglionic neurons that innervate choroidal neurons of pterygopalatine ganglion

PURPOSE

The pterygopalatine ganglion (PPG) receives preganglionic input from the superior salivatory nucleus (SSN) of the facial motor complex and is the main source of parasympathetic input to the choroid in mammals. The present study was undertaken to determine in rats the location and neurotransmitters of SSN neurons innervating those PPG neurons that target the choroid and to determine the location and neurotransmitters of the PPG choroidal neurons themselves.

METHODS

Retrograde labeling from rat choroid using a fluorescent tracer, in combination with immunofluorescence labeling for nitric oxide synthase (NOS), vasoactive intestinal polypeptide (VIP), and choline acetyltransferase (ChAT), was used to characterize the location and neurotransmitters of choroidal PPG neurons. To identify SSN neurons that innervate the choroidal PPG neurons, the Bartha strain of the retrograde transneuronal tracer pseudorabies virus (PRV-Ba) was injected into rat choroid, and immunolabeling for NOS or ChAT was used to characterize their neurochemistry.

RESULTS

Fluorescent retrograde labeling showed that PPG neurons projecting to the choroid contained NOS, VIP, and ChAT and were widely distributed in PPG and its preganglionic root, the greater petrosal nerve. SSN neurons were ChAT(+), and a subset of them was found to contain NOS. PRV-Ba transneuronal retrograde labeling revealed that choroidal preganglionic neurons were localized to the rostral medioventral part of the ipsilateral SSN. The choroidal SSN neurons were ChAT(+) and appeared largely to correspond to the NOS(+) neurons of the SSN.

CONCLUSIONS

These results show that preganglionic neurons in rats that are presumed to regulate choroidal blood flow through the PPG reside within the rostral medioventral SSN, and that NOS is a marker for these SSN neurons.

Intrinsic choroidal neurons in the human eye: projections, targets, and basic electrophysiological data

PURPOSE

The chemical coding of intrinsic choroidal neurons (ICNs) has features in common with extrinsic fibers (e.g., from the pterygopalatine ganglion) making it impossible to assess whether a neuronal nitric oxide synthase (nNOS)/vasoactive intestinal polypeptide (VIP)-immunoreactive nerve fiber is of intrinsic or extrinsic origin. Neurobiotin injections into single neurons allow the visualization of projections of these cells and the determination of the origin of target innervation. Thus, this technique was used in the present study to help characterize the organization of the ICN in the human eye.

METHODS

ICNs were visualized with the fluorescent vital dye 4-Di-2-ASP. Electrophysiological properties were determined by means of intracellular recordings. The impaled neurons were iontophoretically filled with neurobiotin. After fixation, immunohistochemistry for neuronal nitric oxide synthase (nNOS), alpha-smooth muscle actin, and calcitonin gene-related peptide (CGRP) was conducted.

RESULTS

ICN processes were traced over distances of up to 2.612 micro m. They were found in the immediate vicinity of other nNOS-positive or -negative ICNs and were also found apposed to smooth muscle fibers (vascular and stromal nonvascular). CGRP-positive fibers forming boutons were observed closely associated with ICNs. Electrophysiological recording showed phasic firing without slow afterhyperpolarization, no spontaneous activity, an input resistance of 136 +/-73 MOmega, and a membrane time constant of 7 +/- 1 ms.

CONCLUSIONS

Apart from the first functional characterization of ICNs, this study provided more precise evidence of reciprocal ICN-to-ICN contacts and innervation of both choroidal nonvascular and vascular smooth muscle. The presented technique offers promising perspectives to further investigate the function of ICNs in ocular homeostasis.

Developmental cell death in vivo: rescue of neurons independently of changes at target tissues

Programmed cell death is a prominent feature of neural development that is regulated by a variety of cell-cell interactions. We used the avian ciliary ganglion to dissect the relative contributions of target tissues vs. ganglionic inputs in regulating cell death. The two populations of the ciliary ganglion innervate different targets: choroid neurons innervate vasculature, whereas ciliary neurons innervate the iris and ciliary body. By counting after labeling all neurons with Islet-1 and choroid neurons with anti-somatostatin, we determined that alpha-bungarotoxin (alpha-btx) at 12.5 microg/day rescued only ciliary neurons, whereas 75 microg/day rescued both ciliary and choroid neurons. It is unlikely that alpha-btx acted by blocking nerve transmission at both targets because the choroid vasculature lacked transcripts for alpha-btx binding molecules. In addition, no inherent trophic activity could be ascribed to alpha-btx, and survival could not be attributed to differences in total trophic activity of eyes from saline vs. alpha-btx-treated embryos. In contrast, the alpha7 antagonist alpha-methyllycaconitine (MLA) rescued ciliary neurons at 2.6 microg/day, whereas 26 microg/day rescued choroid neurons. Nerve terminals of ciliary neurons rescued with alpha-btx were significantly larger; however, differences in nerve terminal size or branching of axons were not observed in ciliary neurons rescued with MLA or choroid neurons rescued by either MLA or alpha-btx. Our results suggest that neuronal survival can be promoted independently of changes at the target tissues when orthograde signals acting by means of neuronal alpha7 nicotinic receptors are blocked.

Distribution and organization of the nerve fiber and ganglion cells of the human choroid

Antibodies to the 68, 160 and 200 kD of the neurofilament triplets were used to study the distribution and organization of neuronal structures in the human choroid. Choroidal axons were observed in the suprachoroid and vascular laminae but absent from the choriocapillary layer. Most axons were situated in the suprachoroid. In this layer, there were band-like bundles. The two thickest band-like bundles could constitute the long ciliary nerve, while the rest could constitute short ciliary nerves. These bundles ran through the suprachoroid, branching out on the suprachoroid and the vascular laminae until they reached the ciliary body. In the submacular area of the suprachoroid, the branches of the band-like bundles were so intermingled that they looked like a meshwork. In the vascular layer, the large vessels and their primary branches were accompanied by paravascular axons. Some paravascular axons penetrated the medium-caliber vessel layer and in the submacular area interwove to form a network parallel to the arteriole walls. In addition, perivascular axons were revealed by antibodies to neuropeptides. Choroidal ganglion cells were more numerous in the central choroid, specifically in a circumferential area corresponding to the entrance of the short posterior ciliary arteries and their primary branches, and in the vicinity of the submacular area. These cells presented bipolar and multipolar morphology. The high concentration of innervation in the central human choroid could be necessary to maintain strict blood flow in this zone; thus if required, these neuron structures could induce early vasodilation reflexes at the entrance of the choroidal blood vessels to increase the blood flow.

Innervation of the uvea by galanin and somatostatin immunoreactive axons in macaques and baboons

The neuropeptide galanin has not been localized previously in the primate uvea, and the neuropeptide somatostatin has not been localized in the uvea of any mammal. Here, the distribution of galanin-like and somatostatin-like immunoreactive axons in the iris, ciliary body and choroid of macaques and baboons using double and triple immunofluorescence labeling techniques and confocal microscopy was reported. In the ciliary body, galanin-like immunoreactive axons innervated blood vessels and the ciliary processes, particularly at their bases. In the iris, the majority of these axons was associated with the loose connective tissue in the stroma. Somatostatin-like immunoreactive axons were found in many of the same areas of the uvea supplied by cholinergic nerves. In the ciliary body, there were labelled axons within the ciliary processes and ciliary muscle. They were also found alongside blood vessels in the ciliary stroma. In the iris, somatostatin-like immunoreactive axons were abundant in the sphincter muscle and less so in the dilator muscle. A unilateral sympathectomy had no effect on the distribution of somatostatin-like or galanin-like immunoreactive axons, and these axons did not contain the sympathetic marker tyrosine hydroxylase. They did not contain the parasympathetic marker choline acetyltransferase, either. The galanin-like immunoreactive axons contained other neuropeptides found in sensory nerves, including calcitonin gene-related peptide, substance P and cholecystokinin. Somatostatin-like immunoreactive axons did not contain any of these sensory neuropeptides or galanin-like immunoreactivity, and they were neither labelled with an antibody to 200kDa neurofilament protein, nor did they bind isolectin-IB(4). Nevertheless, they are likely to be of sensory origin because somatostatin-like immunoreactive perikarya have previously been localized in the trigeminal ganglion of primates. Taken together, these findings indicate galanin and somatostatin are present in two different subsets of sensory axons in primate uvea.

Reflex choroidal blood flow responses of the eyeball following somatic sensory stimulation in rats

The effect of cutaneous mechanical stimulation on choroidal blood flow (ChBF) of the eyeball measured using a laser Doppler flowmeter was examined in anesthetized rats. Noxious pinching stimulation of a forepaw for 20 s produced increases in ChBF and mean arterial blood pressure (MAP), whereas brushing of a forelimb produced no changes in either parameter. After spinal transection at the fourth thoracic (T4) level, forepaw pinching stimulation did not produce any MAP changes in 9 of 11 spinalized rats. In these nine spinalized animals, pinching stimulation of a forepaw produced no significant responses in ChBF. After the cutting of cervical sympathetic trunks in five spinal rats, forepaw pinching showed no effect on MAP, but produced an increase in ChBF, which was abolished by an intravenous (i.v.) injection of 1-(2-trifluoromethylphenyl) imidazole (TRIM), a selective inhibitor of neuronal nitric oxide synthase (nNOS). In another four spinalized rats, whose cervical sympathetic trunks were intact and the superior salivary nucleus (SSN) was destroyed, forepaw pinching showed no effect on MAP, but produced a decrease in ChBF, which was abolished by an i.v. injection of phentolamine, an alpha-adrenoceptor antagonist. The present experiment shows that somatic afferent stimulation can produce reflex responses of the ChBF of the eyeball, either a vasodilative response using parasympathetic efferent fibers or a vasoconstrictive response using sympathetic efferent fibers, independent of systemic blood pressure. It was also shown that the somatically induced vasodilative response was due to a release of nitric oxide (NO) from parasympathetic nerves and the vasoconstrictive response was due to a release of noradrenaline from sympathetic nerves.

Adrenergic supersensitivity of rabbit choroidal blood vessels after sympathetic denervation

PURPOSE

To demonstrate the phenomenon of adrenergic denervation supersensitivity in rabbit choroidal blood vessels after superior cervical ganglionectomy.

METHODS

Twenty four albino rabbits of both sexes weighing 2-3 kg were randomly separated into two groups. Twelve rabbits received bilateral superior cervical sympathectomy 2 weeks prior to the study (group s). The other 12 rabbits served as controls (group n). Four different concentrations of 0.1 ml phenylephrine, 0.05%, 0.025%, 0.013%, and 0.007% were slowly injected into the vitreous body near the retinal surface in group (n) and (s) rabbits (n = 6 in each group). The choroidal blood flow (PF), blood volume (CMBC), and velocity (V) were measured simultaneously by laser Doppler flowmetry (Perimed, PF 4001).

RESULTS

The PF showed similar decreases in group (n) and (s) rabbits after injection of 0.05%, 0.025%, and 0.013% phenylephrine. With 0.007% phenylephrine, the PF remained unchanged in group (n) rabbits, but decreased significantly in group (s) rabbits (p = 0.0007). Velocity decreased similarly in both group (n) and (s) rabbits except for the 0.007% phenylephrine, concentration in which velocity decreased significantly in group s rabbits (p = 0.0001). There was no statistical difference in CMBC between group n and s rabbits at any of the test concentrations.

CONCLUSIONS

The difference in PF decrease between group (n) and (s) rabbits with 0.007% phenylephrine demonstrated the existence of choroidal blood vessel denervation supersensitivity. The decrease in PF was achieved mainly through a decrease in blood cell velocity.

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

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 neurons in the duck choroid are contacted by CGRP-immunoreactive nerve fibres: evidence for a local pre-central reflex arc in the eye

Intrinsic choroidal neurons represent peripherally displaced autonomic nerve cells supposed to work as a local integrative network similar to the enteric nervous system, to control choroidal vasculature and stromal smooth muscle. A typical feature of such intramural neuronal networks is the innervation by primary afferent collaterals expressing peptides, e.g. CGRP. The present study was aimed at determining primary afferent contacts on nitrergic intrinsic choroidal neurons (ICN) in the duck eye. In addition, a sympathetic innervation of ICN was assessed. Choroids were immunohistochemically processed for the following markers: neuronal nitric oxide synthase (nNOS), galanin (GAL), calcitonin gene-related peptide (CGRP), and tyrosine hydroxylase (TH). For evaluation, fluorescence as well as confocal laser scanning microscopy were used. For electron microscopy, immunoperoxidase staining for CGRP in combination with NADPH-diaphorase histochemistry was applied. ICN immunoreactive for nNOS or GAL spread over the entire choroid, although they were concentrated in an equatorial zone passing obliquely from naso-cranial to temporo-caudal. About 40% of ICN showed close relationships with CGRP-immunoreactive nerve fibres, originating most likely in the trigeminal ganglion, as seen in the fluorescence and confocal laserscanning microscope. These appositions could be ultrastructurally defined as both synapses and close contacts without synaptic specialization. Some ICN endowed with CGRP-positive fibres also received TH-immunoreactive boutons. CGRP-immunoreactive profiles were also detected in close relationship to choroidal non-vascular smooth muscle cells and collagen fibres connected to them. In many instances, they were intercalated between smooth muscle cells and processes of ICN forming triads. These results suggest that ICN, similar to other intramural autonomic systems integrate signals from trigeminal primary afferent collaterals. The 'sensory' terminals of these primary afferents may be located in the anterior eye segment but also within the smooth muscle stroma of the choroid itself. Thus, ocular homeostasis may be regulated via intraocular pre-central reflexes which are probably subject to sympathetic modulation.

BK-Type K(Ca) channels in two parasympathetic cell types: differences in kinetic properties and developmental expression

The intrinsic electrical properties of identified choroid and ciliary neurons of the chick ciliary ganglion were examined by patch-clamp recording methods. These neurons are derived from a common pool of mesencephalic neural crest precursor cells but innervate different target tissues and have markedly different action potential waveforms and intrinsic patterns of repetitive spike discharge. Therefore it is important to determine whether these cell types express different types of plasma membrane ionic channels, and to ascertain the developmental stages at which these cell types begin to diverge. This study has focused on large-conductance Ca(2+)-activated K(+) channels (K(Ca)), which are known to regulate spike waveform and repetitive firing in many cell types. Both ciliary ganglion cell types, identified on the basis of size and somatostatin immunoreactivity, express a robust macroscopic K(Ca) carried by a kinetically homogeneous population of large-conductance (BK-type) K(Ca) channels. However, the kinetic properties of these channels are different in the two cell types. Steady-state fluctuation analyses of macroscopic K(Ca) produced power spectra that could be fitted with a single Lorentzian curve in both cell types. However, the resulting corner frequency was significantly lower in choroid neurons than in ciliary neurons, suggesting that the underlying K(Ca) channels have a longer mean open-time in choroid neurons. Consistent with fluctuation analyses, significantly slower gating of K(Ca) channels in choroid neurons was also observed during macroscopic activation and deactivation at membrane potentials positive to -30 mV. Differences in the kinetic properties of K(Ca) channels could also be observed directly in single-channel recordings from identified embryonic day 13 choroid and ciliary neurons. The mean open-time of large-conductance K(Ca) channels was significantly greater in choroid neurons than in ciliary neurons in excised inside-out patches. The developmental expression of functional K(Ca) channels appears to be regulated differently in the two cell types. Although both cell types acquire functional K(Ca) at the same developmental stages (embryonic days 9-13), functional expression of these channels in ciliary neurons requires target-derived trophic factors. In contrast, expression of functional K(Ca) channels proceeds normally in choroid neurons developing in vitro in the absence of target-derived trophic factors. Consistent with this, extracts of ciliary neuron target tissues (striated muscle of the iris/ciliary body) contain K(Ca) stimulatory activity. However, K(Ca) stimulatory activity cannot be detected in extracts of the smooth muscle targets of choroid neurons.

Changes in choroidal innervation in Royal College of Surgeons rats with hereditary retinal degeneration

In Royal College of Surgeons (RCS) rats with hereditary retinal degeneration loss of retinal pigmented epithelium (RPE) and choriocapillaris is most pronounced in the upper-temporal quadrant. To investigate whether changes in choroidal vasodilative innervation might be involved in the RPE degeneration, we analyzed whole mount preparations of the retina and choroid stained for nitric oxide synthase and for NADPH-diaphorase (d) of 19 dystrophic RCS rats and 24 age-matched congenic controls of different age groups. Density of NADPH-d-positive nerve fibers was quantitatively evaluated in the upper-temporal and lower-nasal quadrant. Our results revealed that even in control animals there were much less positively stained nerve fibers in the upper-temporal than in the lower-nasal quadrant. Nerve fiber density in both quadrants increased for up to 3 months and remained nearly constant throughout life. In the dystrophic animals up to 3 months of age nerve fiber density was similar to that seen in the controls. In dystrophic animals older than 3 months nerve fiber density in the upper-temporal quadrant decreased significantly, whereas density in the lower-nasal quadrant revealed nearly the same values as in the age-matched controls. Decrease of NADPH-d stained nerve fibers in this quadrant occurred prior to the vascular changes in the choriocapillaris. In the retina of RCS dystrophic rats an increase of NADPH-d-positive amacrine cells was found only in 3-month-old animals. Most of these cells were located in the vicinity of irregularly arranged branches of the central retinal artery. In animals 5 months of age and older the number of cells decreased to the same values found in controls, so that we assume that increase of NADPH-d-positive amacrine cells is involved in capillary degeneration or sprouting.

Expression and channel properties of alpha-bungarotoxin-sensitive acetylcholine receptors on chick ciliary and choroid neurons

Cell-specific expression of nicotinic acetylcholine receptors (AChRs) was examined using ciliary and choroid neurons isolated from chick ciliary ganglia. At embryonic days 13 and 14 (E13,14) the neurons can be distinguished by size, with ciliary neuron soma diameters exceeding those of choroid neurons by about twofold. Both neuronal populations are known to express two major AChR types: alpha3*-AChRs recognized by mAb35, that contain alpha3, alpha5, beta4, and occasionally beta2 subunits, and alpha-bungarotoxin (alphaBgt)-AChRs recognized and blocked by alphaBgt, that contain alpha7 subunits. We found that maximal whole cell current densities (I/C(m)) mediated by alphaBgt-AChRs were threefold larger for choroid compared with ciliary neurons, while alpha3*-AChR current densities were similar in the two populations. Different densities of total cell-surface alphaBgt-AChRs could not explain the distinct alphaBgt-AChR response densities associated with ciliary and choroid neurons. Ciliary ganglion neurons display abundant [(125)I]-alphaBgt binding ( approximately 10(6) sites/neuron), but digital fluorescence measurements revealed equivalent site densities on both populations. AChR channel classes having single-channel conductances of approximately 30, 40, 60, and 80 pS were present in patches excised from both ciliary and choroid neurons. Treating the neurons with alphaBgt selectively abolished the 60- and 80-pS events, identifying them as arising from alphaBgt-AChRs. Kinetic measurements revealed brief open and long closed durations for alphaBgt-AChR channel currents, predicting a very low probability of being open (p(o)) when compared with 30- or 40-pS alpha3*-AChR channels. None of the channel parameters associated with the 60- and 80-pS alphaBgt-AChRs differed detectably, however, between choroid and ciliary neurons. Instead calculations based on the combined whole cell and single-channel results indicate that choroid neurons express approximately threefold larger numbers of functional alphaBgt-AChRs (N(F)) per unit area than do ciliary neurons. Comparison with total surface [(125)I]-alphaBgt-AChR sites (N(T)), reveals that N(F)/N(T) << 1 for both neuron populations, suggesting that "silent" alphaBgt-AChRs predominate. Choroid neurons may therefore express a higher density of functional alphaBgt-AChRs by recruiting a larger fraction of receptors from the silent pool than do ciliary neurons.

Presynaptic muscarinic facilitation of parasympathetic neurotransmission after sympathectomy in the rat choroid

The effect of sympathectomy on parasympathetic regulation of ocular perfusion was investigated. Uveal blood flow through the vortex veins was measured by laser Doppler flowmetry during electrical stimulation of the superior salivatory nucleus, which activates ocular parasympathetic nerves, in adult rats with intact innervation and 2 days or 6 weeks after excision of the ipsilateral superior cervical ganglion. In all groups, parasympathetic stimulation produced comparable increases in flux, which were abolished by the selective neuronal nitric-oxide synthetase inhibitor, 1-(2-trifluoromethylphenyl) imidazole. Atropine had no effect in control and acutely sympathectomized rats but abolished the flux increase in four of six chronically sympathectomized animals, and 1-(2-trifluoromethylphenyl) imidazole eliminated the residual response. The muscarinic receptor agonist bethanechol did not affect basal flow in control or sympathectomized rats. However, bethanechol enhanced parasympathetically mediated vasodilation, but only in rats studied at 6 weeks after sympathectomy, a finding consistent with the appearance of muscarinic prejunctional facilitation of nitrergic transmission. In chronically sympathectomized rats, the M(2) and M(4) receptor antagonists methoctramine and tropicamide did not affect choroidal flow during parasympathetic activation. However, pirenzepine increased flux, implying the presence of M(1) inhibitory autoreceptors on these nerves. Parasympathetically mediated increased flux was partially blocked by the M(3) antagonist 4-diphenylacetoxy-N-methylpiperdine, and the remaining vasodilation was blocked by atropine. We conclude that parasympathetic prejunctional facilitatory M(3) and probably M(5) receptors adopt a crucial role after chronic sympathectomy in maintaining nitrergic vasodilatory ocular neurotransmission in the face of down-regulated nitric oxide transmitter mechanisms.

Regional regulation of choroidal blood flow by autonomic innervation in the rat

Regional influences of parasympathetic and sympathetic innervation on choroidal blood flow were investigated in anesthetized rats. Parasympathetic pterygopalatine neurons were activated by electrically stimulating the superior salivatory nucleus, whereas sympathetic neurons were activated by cervical sympathetic trunk stimulation and uveal blood flow was measured by laser Doppler flowmetry. Parasympathetic stimulation increased flux in the anterior choroid and nasal vortex veins but not in the posterior choroid. Vasodilation was blocked completely by the neuronal nitric oxide synthase inhibitor 1-(2-trifluoromethylphenyl)imidazole but was unaffected by atropine. Sympathetic stimulation decreased flux in all regions, and this was blocked by prazosin. Parasympathetic stimulation did not affect vasoconstrictor responses to sympathetic stimulation in the posterior choroid but attenuated the decrease in blood flow through the anterior choroid and vortex veins via a nitrergic mechanism. We conclude that sympathetic alpha-noradrenergic vasoconstriction occurs throughout the choroid, whereas parasympathetic nitrergic vasodilation plays a selective role in modulating blood flow in anterior tissues of the eye.

Receptors with opposing functions are in postsynaptic microdomains under one presynaptic terminal

Fast excitatory synaptic transmission through vertebrate autonomic ganglia is mediated by postsynaptic nicotinic acetylcholine receptors (nAChRs). We demonstrate a unique postsynaptic receptor microheterogeneity on chick parasympathetic ciliary ganglion neurons-under one presynaptic terminal, nAChRs and glycine receptors formed separate but proximal clusters. Terminals were loaded with [3H]glycine via the glycine transporter-1 (GlyT-1), which localized to the cholinergic presynaptic terminal membrane; depolarization evoked [3H]glycine release that was calcium independent and blocked by the GlyT-1 inhibitor sarcosine. Ganglionic synaptic transmission mediated by nAChRs was attenuated by glycine. Coexistence of separate clusters of receptors with opposing functions under one terminal contradicts Dale's principle and provides a new mechanism for modulating synaptic activity in vivo.

The significance of nitric oxide for parasympathetic vasodilation in the eye and other orbital tissues in the cat

The role of nitric oxide formation in the vasodilation in the eye and other orbital tissues caused by pre-ganglionic stimulation of the facial nerve was studied in cats under alpha-chloralose anaesthesia. Regional blood flows were determined with radioactive microspheres during unilateral stimulation of the facial nerve before and after inhibition of nitric oxide synthase (NOS), alone or in combination with muscarinic blockade.N(omega)-nitro-L-arginine (L-NA), a non-selective NOS-inhibitor, caused a significant increase in mean arterial blood pressure (MABP) and a decrease in cardiac output (CO). Concomitantly, local blood flows on the non-stimulated control side were reduced in most of the investigated tissues, indicating marked vasoconstriction. An inhibitor selective for neuronal NOS, 7-nitro-indazole (7-NI), had no significant effect on MABP, CO or local blood flows. During facial nerve stimulation at 5 Hz (n =6), choroidal blood flow on the stimulated side was 108+/-41% (P</=0.05) higher than on the non-stimulated side during control conditions, an effect that was completely abolished by L-NA. During stimulation at 10 Hz (n =8), the choroidal blood flow was 171+/-38% (P</=0.01) higher on the stimulated side during control conditions. The corresponding values after L-NA and subsequent administration of atropine were 97+/-21% (P</=0.05, compared to control conditions) and 50+/-14% (P</=0.05, compared to control conditions), respectively. Atropine alone had no significant effect on the increase in choroidal blood flow caused by stimulation at 10 Hz (n =7), whereas subsequent administration of L-NA caused a statistically significant reduction. Administration of 7-NI had no significant effect on the choroidal vasodilation at 10 Hz (n =7), whereas subsequent administration of L-NA caused significant reduction, at least as compared to control conditions. These results suggest that nitric oxide is of greater significance for the choroidal vasodilation, caused by facial nerve stimulation, in the cat than it is in the rabbit. However, no definitive conclusions can be made concerning the source of the nitric oxide. Direct release of nitric oxide from the parasympathetic nerve fibres could contribute as well as nitric oxide formed in the vascular endothelium, secondary to the release of acetylcholine and/or VIP. At high frequencies, a part of the choroidal vasodilation seems to be independent of nitric oxide.

Sympathetic vasodilation in the rat anterior choroid mediated by beta(1)-adrenoceptors

Electrical stimulation of the preganglionic superior cervical nerve produced a frequency-dependent vasoconstrictor response in the anterior choroidal blood vessels of the eye of anesthetized rats. Systemic administration of phentolamine (5 mg kg(-1)) reversed the vasoconstriction to a vasodilator response. This sympathetic-evoked vasodilation was not antagonized by inhibition of nitric oxide synthase with N(G)-nitro-L-arginine methyl ester (L-NAME) (20 mg kg(-1)) or by inhibition of cyclo-oxygenase with indomethacin (20 mg kg(-1)). Intravenous administration of propranolol (1 mg kg(-1)), as well as selective beta(1)-adrenoceptor antagonists atenolol (3 mg kg(-1)), timolol (0.3 mg kg(-1)), and betaxolol (0.1 mg kg(-1)), totally abolished the sympathetic nerve evoked ocular vasodilation. In contrast, the selective beta(2)-adrenoceptor antagonist, ICI-118, 551 ((+/-)-1-[2, 3-(Dihydro-7-methyl-1H-inden-4-yl)oxy]-3-[(1-methylethyl)amino]-2- butanol) (0.3 mg kg(-1), i.v.), was without effect. These results support the conclusion that the residual sympathetic ocular vasodilation observed in the rat anterior choroid after alpha-adrenoceptor blockade is mediated exclusively by neurogenic release of norepinephrine acting on vascular beta(1)-adrenoceptors.

Immunohistochemical study of rabbit choroidal innervation

Immunocytochemical methods with antibodies to the light (68 kDa), medium (160 kDa), and heavy (200 kDa) chain subunits of the neurofilament triplet have been used to visualize neuronal structures in rabbit choroids. Choroidal nerve fibers were present in the suprachoroid and vascular laminae and absent in the choriocapillary layer. These fibers may be classified as perivascular and intervascular. Perivascular fibers surround all arterial and venous blood vessels and form a network; these fibers were labeled with the three NF antibodies, although they were more easily visualized with anti NF-160 and anti NF-200 than anti NF-68. Intervascular fibers formed two groups. The first group consisted of fibers situated between the blood vessels and parallel to the blood vessel wall surface (paravascular fibers); these fibers were better observed using anti NF-160 and NF-200 than anti NF-68. The second group consisted of fibers which travel the entire length of the choroid until they reach the nerve plexus of the ciliary body (long tract fibers). The plexus was observed with anti NF-68, anti NF-160 and anti NF-200; however, the long tract fibers were more clearly visualized with anti NF-160 and anti NF-200 than with anti NF-68. Two types of choroidal cell were also labeled: ganglion cells and melanocytes. Ganglion cells are small, scarce neurons situated in the peripheral choroid; they were labeled with anti NF-160 and anti NF-200. The melanocytes were only labeled with anti NF-200 and they were the only non neuronal structure visualized using antibodies against neurofilaments.

Rapid synaptic transmission in the avian ciliary ganglion is mediated by two distinct classes of nicotinic receptors

We analyzed the kinetics and pharmacology of EPSCs in two kinds of neurons in the embryonic avian ciliary ganglion. Whole-cell voltage-clamp recordings revealed that the singly innervated ciliary neurons had large-amplitude (1.5-8.0 nA) EPSCs that could be classified according to the kinetics of their falling phases. Most of the neurons responded with an EPSC the falling phase of which followed a double exponential time course with time constants of approximately 1 and 10 msec. The EPSCs of the remaining ciliary neurons followed a single time constant ( approximately 8 msec). Multiple innervated choroid neurons had smaller-amplitude responses (0.2-1.5 nA when all inputs were activated) that appeared to contain only a slowly decaying component (tau = 12 msec). The fast and slow components of EPSC decay seen in most ciliary neurons could be pharmacologically isolated with two toxins against nicotinic acetylcholine receptors (AChRs). The fast component was blocked by 50 nM alpha-bungarotoxin (alpha-BuTx), which binds alpha7-subunit-containing AChRs. The slow component was selectively blocked by 50 nM alpha-conotoxin MII (alpha-CTx-MII), which blocks mammalian AChRs containing an alpha3/beta2 subunit interface. A combination of both alpha-BuTx and alpha-CTx-MII abolished nearly all evoked current. Similar pharmacological results were found for ciliary neurons with monoexponentially decaying EPSCs and for choroid neurons. These results suggest that nerve-evoked transmitter acts on at least two different populations of AChRs on autonomic motor neurons in the ciliary ganglion.

Fine structure of the choroidal coat of the avian eye. Vascularization, supporting tissue and innervation

To clarify further the functional anatomy of the avian choroid, including its innervation, 12 adult White-Leghorn chickens were studied by standard electron microscopy and immunoelectron microscopy with somatostatin antibody. The endothelial cells of the blood vessels in the choriocapillaris have fenestrations only facing the retina, while the nuclei are situated toward the sclera. In addition to tight junctions and zonulae adherentes, adjoining endothelial cells form gap junctions and dense plaques with attached filaments resembling those of smooth muscle cells. The fine structure of arteries and veins is similar to that of the vasculature described in other organs. The supporting tissue is organized in trabeculae, i.e., bridges of cellular and fibrous elements that surround and sustain blood and lymphatic vessels. This tissue consists primarily of a system of fusiform or star-shaped smooth muscle cells, connected to each other and to those in the vessels' walls through macular junctions of the adherent type, less prominent than desmosomes, and perhaps also punctiform gap junctions. Occasionally, trabecular smooth muscle cells approach the lymphatic vessels, which lack a muscular tunica, and abut their endothelium with spinous appendages. This stromal muscle tissue may act as a pump for moving the lymph. The suprachoroidea consists of large lymphatic lacunae and the multilayered membrana fusca. The elongated fuscal cells form adherent junctions, tight junctions, and perhaps also gap junctions, suggesting that the membrana fusca exerts complex functions. Nerves containing myelinated axons reach the choroid and divide into smaller branches, a few of which innervate the membrana fusca. Numerous, thin nerve branches reach both the walls of arteries and veins and the trabeculae, and synaptic terminals abut the outer muscular layers of the vessel's wall and the smooth muscle cells of the supporting tissue. Immunocytochemistry reveals the presence of numerous somatostatin-positive and somatostatin-negative axons and synaptic terminals within both trabeculae and vascular tunica media. The somatostatin-positive axons are presumed to be cholinergic axons of the choroid neurons residing in the ciliary ganglion. Taken together, these observations indicate that the avian choroid is a highly vascularized muscular sheath that may be endowed with degrees of motility and elasticity higher than those of the mammalian choroid and may therefore play an important role in compensation for experimental defocus.

Activin receptor mRNA expression by neurons of the avian ciliary ganglion

Previous studies have suggested that activin may serve as a neurodifferentiation factor regulating somatostatin expression in neurons of the avian ciliary ganglion (CG). As one aspect of examining the role of activin in CG development, we inquired whether any of the known activin receptors are expressed by developing CG neurons in vivo. In addition, we examined whether activin A mRNA is expressed in the choroid layer and iris of the chicken eye. Oligonucleotide primers were designed for the chicken activin receptor type IIA (cActR-IIA), type IIB (cActR-IIB), and activin A. In reverse-transcription-polymerase chain reaction (rtPCR), an appropriately sized product was amplified from CG cDNA using primers to the cActR-IIA but not the cActR-IIB. Sequencing confirmed the identity of the PCR product as a fragment of the cActR-IIA. It thus appears that mRNA for the type IIA but not the type IIB activin receptor is expressed in the chicken CG. An antisense strand digoxigenin-labeled riboprobe complimentary to a 358-bp portion of the cActR-IIA kinase region hybridized to cells within cryostat sections of embryonic CG. From E6.5-E18, hybridization of this probe appears to be specific for cells with a neuronal morphology. Using rtPCR with activin A-specific primers we detected activin mRNA in the choroid layer of E14 and E19 eyes, and from the iris at E14. Our results are consistent with a role for activin as a neurodifferentiation factor in vivo, and imply that within the CG, the cActR-IIA is specifically expressed by neurons, and that activin A is expressed in the targets of these neurons.

Choroidal ganglion cell plexus and retinal vasculature in monkeys with laser-induced glaucoma

The choroid of primates possesses an elaborate nitrergic nerve fiber plexus containing a great number of ganglion cells. Postganglionic nerve fibers innervate mainly the choroidal vasculature. In addition, the choroid contains an elastic muscular system closely associated to the vasculature. The goal of the present investigation was to analyze how sustained IOP elevation would affect the choroidal vasculature with its specialized innervation and the adjacent retina. For this purpose the posterior eye segment of 15 rhesus monkeys which after laser coagulation of the trabecular meshwork developed elevated IOP up to 4 years were studied using immunohistochemical and histochemical methods, and scanning electron microscopy of corrosion casts. The most striking finding was a significant reduction of choroidal thickness and loss of choroidal ganglion cells and nerve fibers, especially in the central portion of the choroid. Corrosion casts of the choroidal vasculature showed a slight decrease in capillary density and a decrease in length of the arterioles in glaucomatous eyes. Whole mount preparations of the retina stained for NADPH diaphorase revealed a significant reduction in positively stained amacrine cells, reduction in diameter of arterioles and changes in the staining pattern of the retinal vasculature, particularly in the perimacular region.

Central neural circuits for the light-mediated reflexive control of choroidal blood flow in the pigeon eye: a laser Doppler study

Electrical stimulation in pigeons of the input from the medial subdivision of the nucleus of Edinger-Westphal (EWM) to the choroidal neurons of the ipsilateral ciliary ganglion, which themselves have input to the choroidal blood vessels of the ipsilateral eye, increases choroidal blood flow (ChBF). Since the EWM receives input from the contralateral suprachiasmatic nucleus (SCN), which in turn receives contralateral retinal input, the present study sought to determine if activation of the SCN by microstimulation or by retinal illumination of the contralateral eye would also yield increases in ChBF in that same eye. Using laser Doppler flowmetry (LDF) to measure ChBF, we found that electrical activation of the contralateral SCN by 100-Hz anodal pulse trains yielded increases in ChBF that were stimulus related and proportional to the stimulating current. These increases in ChBF elicited by the SCN stimulation were accompanied by increases in choroidal volume (vasodilation), but not by increases in systemic blood pressure. Furthermore, the increases could be blocked reversibly by lidocaine injection into the EWM. These results suggest that the increases in ChBF in the eye contralateral to the SCN stimulation were specifically mediated by the SCN-EWM pathway. Retinal illumination with a fiber optic light source was also found to increase ChBF in the illuminated eye, and these effects too could be blocked reversibly with lidocaine injection into the EWM or permanently by the EWM lesion. Control studies confirmed that the light-elicited increases were mediated by increases in choroidal volume (i.e. vasodilation), were not accompanied by systemic blood pressure increases, and were not artifactually generated by transocular illumination of the LDF probe. Thus, the SCN-EWM circuit may be involved in regulating ChBF in response to the level of retinal illumination and/or the visual patterns falling on the retina.

Neural nitric oxide mediates Edinger-Westphal nucleus evoked increase in choroidal blood flow in the pigeon

PURPOSE

Nitric oxide (NO) has been identified as a putative neurotransmitter in choroidal perivascular nerve fibers originating parasympathetically. Although constitutively produced NO has been implicated in the regulation of the choroidal circulation, the specific role of neurally derived NO in choroidal vasodilation has not been determined. This study examined the role of neurally derived NO in the control of the choroidal blood flow (ChBF) in vivo.

METHODS

Resting ChBF and a increase in ChBF elicited by electrical stimulation of the nucleus of Edinger-Westphal (EW) were measured transclerally by laser Doppler flowmetry in anesthetized pigeons before and after administration of a selective inhibitor of neural NO synthase, 7-Nitroindazole (7NI; 50 mg/kg given intraperitoneally); a nonselective NO synthase inhibitor, Ng-nitro-L-arginine methyl ester (L-NAME; 30 mg/kg given intravenously); L-arginine (300 mg/kg given intravenously) followed by 7NI (50 mg/kg given intraperitoneally); or vehicle.

RESULTS

The 7NI and L-NAME, but not the vehicle, attenuated the EW-evoked response (maximally by 78% and 83%, respectively), and this effect lasted for at least 1 hour. Pretreatment with L-arginine abolished this effect of 7NI. Resting ChBF was reduced and systemic blood pressure was increased after L-NAME administration, but both were unchanged after 7NI or vehicle were administered.

CONCLUSIONS

Neurally derived NO is responsible for a major component of the ChBF increase caused by EW stimulation in pigeons. This represents the first demonstration in vivo that neuronally produced NO is an important factor in the control of ChBF by the parasympathetic nervous system. In particular, neuronally produced NO appears to play a role in rapid upregulation of ChBF in the pigeon, whereas endothelially produced NO plays a major role in control of resting ChBF.

Distribution within the choroid of cholinergic nerve fibers from the ciliary ganglion in pigeons

The distribution of the ciliary ganglion (CG) innervation to the pigeon choroid was determined immunohistochemically, using antisera against choline acetyltransferase (CHAT) and a neurofilament-related protein (the 3A10 antigen). Single-labeling revealed that the nerve fibers containing these two antigens were similarly distributed in the pigeon choroid, with the superior and temporal quadrants of the eye containing the most fibers. Both types of fibers surrounded and ramified on choroidal blood vessels. Additionally, CHAT+ varicosities were evident among vessels in the choroid and choriocapillaris. Double-label immunofluorescence revealed that CHAT and the 3A10 antigen were almost completely colocalized in choroidal nerve fibers, but absent from CHAT+ varicosities. Substance P-containing and calcitonin gene-related peptide-containing choroidal nerve fibers were poor in 3A10+ labeling. Transection of the postganglionic fibers of the CG reduced CHAT+ and 3A10+ nerve fibers in the choroid to 3-5% of normal abundance, with most of the residual fibers being located in the nasal and inferior quadrants. The present results suggest that the CG in pigeon preferentially influences choroidal blood flow in the superior and temporal parts of the eye, which are involved in high acuity and binocular vision.

Sympathetic innervation of the rat choroid: an autoradiographic tracing and immunohistochemical study

The sympathetic innervation of the choroid was investigated by means of the anterograde tracer 3H-leucine, injected into the rostral part of the superior cervical ganglion. The tracer was autoradiographically visualized at the light- and electron-microscopic levels. Labelled unmyelinated fibres were found in the choroid and labelled terminals were observed in close proximity to the smooth muscle cells of arterioles. The labelled terminals contain granular vesicles of different size and clear vesicles; the mitochondria were of the electron-dense type and no cell-to-cell synaptic contacts were observed. In addition, tyrosine hydroxylase immunocytochemistry was performed. Immunostained terminals found in the choroid show ultrastructural features similar to those found in the tracing experiments: granular vesicles of different size, clear vesicles and electron-dense mitochondria. On the basis of previous studies and the present observations, it is concluded that the choroid has a dual innervation, a parasympathetic innervation from the pterygopalatine ganglion and a sympathetic innervation from the superior cervical ganglion. The dual innervation is most likely involved in maintaining the homeostasis of vasodilatation and vasoconstriction in the choroid.

Understanding the choroid

Based on previous work, this paper describes the anatomical and functional characteristics of the choroidal vasculature, namely the choriocapillaris, the arterial and arteriovenous anastomosis, the segmental distribution of the short posterior ciliary arteries, and the choroidal veins. The characteristics of the choroidal innervation with reference to the sensory nerve endings are reviewed. Some features of Bruch's membrane may explain the fundoscopic and angiographic appearance of the angioid streaks and the role of its basement membranes in the formation and transport of drusen.

Expression and in vitro function of beta 1-integrin laminin receptors in the developing avian ciliary ganglion

In chick development, ciliary ganglion (CG) neurons go through a period of axon extension from approximately embryonic day (E)4 to E8, followed by a period of synaptogenesis and neuronal cell death. By examining the immunohistochemical localization of laminin, in conjunction with Dil labeling of the ciliary nerve projection, we have determined that the pathway taken by these neurons is rich in laminin expression. Therefore, laminins are good candidate molecules for mediating outgrowth of these neurons in vivo. In vitro, the ability of CG neurons to extend neurites on laminin-1 (EHS laminin, alpha 1 beta 1 gamma 1) is maximal up to E8, then declines dramatically. CG neuron outgrowth on laminin-1 requires the activity of beta 1-class integrins. We have used subunit-specific antibodies to determine which of the five beta 1-containing heterodimers known to be laminin receptors (alpha 1 beta 1, alpha 2 beta 1, alpha 6 beta 1, alpha 7 beta 1) are expressed, and which mediate neurite outgrowth. While we could not detect expression of alpha 2 or alpha 7, we have found that alpha 1, alpha 3 beta 1, and alpha 6 beta 1 are expressed on the surface of ciliary ganglion neuron cell bodies and axons, both in vitro and in vivo. Furthermore, antibodies against alpha 3 and alpha 6, but not alpha 1, interfered with CG neurite outgrowth on laminin-1 in vitro. Taken together, these data suggest that interactions of cell surface alpha 3 beta 1 and alpha 6 beta 1 integrins with laminin-1 are likely to mediate growth of CG neurons during pathfinding in vivo.

Two types of vasodilatation in cat choroid elicited by electrical stimulation of the short ciliary nerve

Choroidal blood vessels are innervated by three types of vasoactive nerve fibers: sympathetic, parasympathetic and sensory fibers in the short ciliary nerve. We investigated whether or not stimulation of the short ciliary nerve elicits vasodilatation. In 30 cats (2-4 kg) anesthetized with pentobarbital sodium (30 mg kg-1, i.v.) and artificially ventilated (pancuronium bromide; 0.2 mg kg-1 hr-1, i.v.), choroidal blood flow was continuously measured trans-sclerally with a laser Doppler flowmeter. The lateral short ciliary nerve was stimulated electrically (0-50 V, 2 msec, 20 Hz, for 10 sec) at two sites, one close to the eyeball (site P) and the other between the main and accessory ciliary ganglia (site Q). Choroidal vasodilatation occurred with a high incidence (80%) in response to electrical stimulation of the short ciliary nerve at site P or Q, when cats had been treated with the alpha-adrenergic blocking agent phentolamine (3 mg kg-1) to eliminate sympathetic vasoconstrictor effects. A long-lasting vasodilatation was observed during 1% capsaicin application to the nerve bundle at site P, but not at site Q and capsaicin nearly abolished the vasodilatation evoked by stimulation at site P, but not that evoked from site Q. Vasodilatation elicited by electrical stimulation at site P or Q was not sensitive to the ganglion-blocking agent hexamethonium (3 mg kg-1, i.v.).(ABSTRACT TRUNCATED AT 250 WORDS)

Increased and decreased choroidal blood flow elicited by cervical sympathetic nerve stimulation in the cat

The effect of electrical stimulation of the cervical sympathetic nerve on choroidal blood flow in the cat was investigated. Flow at various sites in 30 pentobarbital-anesthetized cats was continuously measured trans-sclerally using a laser Doppler flowmeter. Changes in either direction, increases and decreases, occurred in response to electrical stimulation of the peripheral cut end of the cervical sympathetic nerve. These changes in flow appeared to depend on the site of choroidal blood flow measurement, as decreases were seen at sites with a high baseline blood flow and increases at sites with a low baseline level. Both types of response were reduced when the cats were treated with the alpha-adrenoreceptor antagonist phentolamine, but not by treatment with the beta-adrenoceptor antagonist propranolol. The decrease in choroidal blood flow elicited by cervical sympathetic nerve stimulation appears to be mediated via the vasoconstrictor fibers in that nerve. A choroidal blood flow increase may occur as a secondary effect following vasoconstriction of the arterioles elicited by cervical sympathetic nerve stimulation, producing a passive net increase in choroidal blood flow.

Association of a choroidal ganglion cell plexus with the fovea centralis

PURPOSE

After recently demonstrating an NADPH-diaphorase-, nitric oxide synthase (NOS)-positive ganglion cell plexus in the human choroid that was absent in rabbit and rat eyes, the authors extended their comparative studies to nonhuman primates and to subprimate mammals.

METHODS

The authors investigated the choroids of diurnal cynomolgus monkeys with well-developed fovea centralis and accommodative systems; diurnal tree shrews without a fovea centralis or accommodative capacity; nocturnal owl monkeys with substantial accommodative capacity but without a fovea centralis; cats with an area centralis but no fovea centralis; and pigs without an area centralis or a fovea centralis. The latter two species have moderately developed ciliary muscles. Wholemounts of the choroid of eight cynomolgus monkey, two owl monkey, four tree shrew, four cat, and four pig eyes were stained for NADPH-diaphorase. In addition, frozen sections through the cynomolgus monkey choroid were stained for NOS and vasoactive intestinal polypeptide (VIP).

RESULTS

In all species, the choroidal vessels were surrounded by NADPH-diaphorase-positive nerve fibers. A ganglion cell plexus, however, was seen only in cynomolgus monkey eyes. The ganglion cells stained for NOS and VIP.

CONCLUSIONS

The presence of intrachoroidal nitrergic nerve cells restricted to species with a fully developed fovea centralis may indicate a functional correlation of these structures.

The effects of choroidal or ciliary nerve transection on myopic eye growth induced by goggles

PURPOSE

To determine the role of the choroidal and ciliary nerves and the functions they control, choroidal blood flow (CBF) and accommodation-pupil diameter, respectively, in myopia induced by form-vision deprivation.

METHODS

Three groups of chicks were studied: chicks with choroidal nerves cut in the right eye, chicks with ciliary nerves cut in the right eye, and sham control chicks that received the same surgical preparation but no nerve cuts. A plastic, dome-shaped goggle was glued over the right eye of birds in all three groups after orbital surgery, and, 2 weeks later, CBF was measured using laser Doppler flowmetry. Refractive status was then measured using streak retinoscopy, and axial, nasotemporal, and dorsoventral lengths were measured using vernier calipers after enucleation. The eyes were also weighed.

RESULTS

In the sham control birds, considerable ocular enlargement in all dimensions and a high degree of myopia (-14.68 diopters) was observed in the goggled eye, and CBF in the goggled eye was 66% of that in the nongoggled eye. In birds with choroidal nerve cuts, the degree of enlargement of the goggled eye was less in all dimensions, and the myopia in the goggled eye (-4.74 D) was attenuated compared to that observed in the sham controls. CBF in the goggled eye was 21% of that in nongoggled eye. Finally, in the birds with ciliary nerve cuts, nasotemporal and dorsoventral enlargement of the goggled eye were similar to that in the shams, but the axial elongation and the degree of myopia (-9.57 D) were less than observed in sham control eyes. As in the shams, CBF in the goggled eye was reduced to 59% of that in the nongoggled eye.

CONCLUSIONS

These results show that although elimination of accommodation and severe reductions in CBF do affect eye growth (the latter more so), they do not prevent form-vision deprivation-induced myopia. Thus, either the mechanism of visual deprivation-induced myopia is different from that in idiopathic human myopia, or CBF levels and accommodation do not play a major role in either.

Species differences in choroidal vasodilative innervation: evidence for specific intrinsic nitrergic and VIP-positive neurons in the human eye

PURPOSE

There is evidence that vasodilation of choroidal vessels results from facial nerve stimulation. To obtain more information about the role of this innervation, the authors examined the presence and spatial organization of nitrergic and vasoactive intestinal peptide (VIP) immunoreactive nerves in the human choroid. For comparison, the choroid of rabbit and rat eyes, with different types of retinal vascularization and no fovea, were studied.

METHODS

Whole mounts of five human, nine rat, and two rabbit choroids were stained for NADPH-diaphorase. In addition, immunocytochemical staining was carried out on tangential frozen sections of two human choroids using antibodies against nitric oxide synthase (NOS), synaptophysin, and VIP.

RESULTS

In all species, a perivascular network of diaphorase-positive nerve fibers with varicose terminals accompanied the arteries and arterioles of the choroidal stroma. A striking difference to rat and rabbit choroids was the presence of numerous positively stained ganglion cells in human choroids. Positively stained axons connected the neurons with each other and with the perivascular network. Most of the ganglion cells were concentrated in the temporal-central region, adjacent to the fovea. Immunocytochemically, the choroidal ganglion cells were immunoreactive for NOS. Some ganglion cells stained for VIP. Staining for synaptophysin demonstrated varicose terminals innervating the perikarya of the ganglion cells. Many of these terminals stained for NOS and VIP.

CONCLUSIONS

The presence of an intrinsic nerve cell plexus that is specifically localized in human eyes in the temporal-central portion of the choroid indicates a functional significance of the nitrergic choroidal innervation for the fovea.