Neurotransmitter organization of the nucleus of Edinger-Westphal and its projection to the avian ciliary ganglion

Urocortin-positive nerve fibres and cells are present in the human choroid

BACKGROUND

Choroidal vascular regulation is mediated by the autonomic nervous system in order to gain proper blood flow control. While the mechanisms behind this control are unknown, neuroregulatory peptides are involved in this process. To better understand choroidal function, we investigate the presence of urocortin-1 (UCN), a neuroregulatory peptide with vascular effects, in the human choroid and its possible intrinsic and extrinsic origin.

METHODS

Human choroid and eye-related cranial ganglia (superior cervical ganglion- SCG, ciliary ganglion-CIL, pterygopalatine ganglion-PPG, trigeminal ganglion-TRI) were prepared for immunohistochemistry against UCN, protein-gene product 9.5 (PGP9.5), substance P (SP), tyrosine hydroxylase (TH) and vesicular acetylcholine transporter (VAChT). For documentation, confocal laser scanning microscopy was used.

RESULTS

In choroidal stroma, UCN-immunoreactivity was present in nerve fibres, small cells and intrinsic choroidal neurons (ICN). Some UCN+ nerve fibres colocalised for VAChT, while others were VAChT. A similar situation was found with SP: some UCN+ nerve fibres showed colocalisation for SP, while others lacked SP. Colocalisation for UCN and TH was not observed. In eye-related cranial ganglia, only few cells in the SCG, PPG and TRI were UCN+, while many cells of the CIL displayed weak UCN immunoreactivity.

CONCLUSION

UCN is part of the choroidal innervation. UCN+/VAChT+ fibres could derive from the few cells of the PPG or cells of the CIL, if these indeed supply the choroid. UCN+/SP+ fibres might originate from ICN, or the few UCN+ cells detected in the TRI. Further studies are necessary to establish UCN function in the choroid and its implication for choroidal autonomic control.

The relative sizes of nuclei in the oculomotor complex vary by order and behaviour in birds

Eye movements are a critical component of visually guided behaviours, allowing organisms to scan the environment and bring stimuli of interest to regions of acuity in the retina. Although the control and modulation of eye movements by cranial nerve nuclei are highly conserved across vertebrates, species variation in visually guided behaviour and eye morphology could lead to variation in the size of oculomotor nuclei. Here, we test for differences in the size and neuron numbers of the oculomotor nuclei among birds that vary in behaviour and eye morphology. Using unbiased stereology, we measured the volumes and numbers of neurons of the oculomotor (nIII), trochlear (nIV), abducens (nVI), and Edinger-Westphal (EW) nuclei across 71 bird species and analysed these with phylogeny-informed statistics. Owls had relatively smaller nIII, nIV, nVI and EW nuclei than other birds, which reflects their limited degrees of eye movements. In contrast, nVI was relatively larger in falcons and hawks, likely reflecting how these predatory species must shift focus between the central and temporal foveae during foraging and prey capture. Unexpectedly, songbirds had an enlarged EW and relatively more nVI neurons, which might reflect accommodation and horizontal eye movements. Finally, the one merganser we measured also has an enlarged EW, which is associated with the high accommodative power needed for pursuit diving. Overall, these differences reflect species and clade level variation in behaviour, but more data are needed on eye movements in birds across species to better understand the relationships among behaviour, retinal anatomy, and brain anatomy.

Ocular Autonomic Nervous System: An Update from Anatomy to Physiological Functions

The autonomic nervous system (ANS) confers neural control of the entire body, mainly through the sympathetic and parasympathetic nerves. Several studies have observed that the physiological functions of the eye (pupil size, lens accommodation, ocular circulation, and intraocular pressure regulation) are precisely regulated by the ANS. Almost all parts of the eye have autonomic innervation for the regulation of local homeostasis through synergy and antagonism. With the advent of new research methods, novel anatomical characteristics and numerous physiological processes have been elucidated. Herein, we summarize the anatomical and physiological functions of the ANS in the eye within the context of its intrinsic connections. This review provides novel insights into ocular studies.

Neural control of choroidal blood flow

The choroid is richly innervated by parasympathetic, sympathetic and trigeminal sensory nerve fibers that regulate choroidal blood flow in birds and mammals, and presumably other vertebrate classes as well. The parasympathetic innervation has been shown to vasodilate and increase choroidal blood flow, the sympathetic input has been shown to vasoconstrict and decrease choroidal blood flow, and the sensory input has been shown to both convey pain and thermal information centrally and act locally to vasodilate and increase choroidal blood flow. As the choroid lies behind the retina and cannot respond readily to retinal metabolic signals, its innervation is important for adjustments in flow required by either retinal activity, by fluctuations in the systemic blood pressure driving choroidal perfusion, and possibly by retinal temperature. The former two appear to be mediated by the sympathetic and parasympathetic nervous systems, via central circuits responsive to retinal activity and systemic blood pressure, but adjustments for ocular perfusion pressure also appear to be influenced by local autoregulatory myogenic mechanisms. Adaptive choroidal responses to temperature may be mediated by trigeminal sensory fibers. Impairments in the neural control of choroidal blood flow occur with aging, and various ocular or systemic diseases such as glaucoma, age-related macular degeneration (AMD), hypertension, and diabetes, and may contribute to retinal pathology and dysfunction in these conditions, or in the case of AMD be a precondition. The present manuscript reviews findings in birds and mammals that contribute to the above-summarized understanding of the roles of the autonomic and sensory innervation of the choroid in controlling choroidal blood flow, and in the importance of such regulation for maintaining retinal health.

GABAergic innervation of the ciliary ganglion in macaque monkeys - A light and electron microscopic study

The vertebrate ciliary ganglion (CG) is a relay station in the parasympathetic pathway activating the iris sphincter and ciliary muscle to mediate pupillary constriction and lens accommodation, respectively. While the postganglionic motoneurons in the CG are cholinergic, as are their inputs, there is evidence from avian studies that GABA may also be involved. Here, we used light and electron microscopic methods to examine the GABAergic innervation of the CG in Macaca fascicularis monkeys. Immunohistochemistry for the gamma aminobutyric acid synthesizing enzyme glutamic acid decarboxylase (GAD) and choline acetyltransferase (ChAT) revealed that all CG neurons are contacted by ChAT-positive terminals. A subpopulation of 17.5% of CG neurons was associated with terminal boutons expressing GAD-immunoreactivity in addition. Double-labeling for GAD and synaptophysin confirmed that these were synaptic terminals. Electron microscopic analysis in conjunction with GABA-immunogold staining showed that (1) GAD-positive terminals mainly target dendrites and spines in the perisomatic neuropil of CG neurons; (2) GABA is restricted to a specific terminal type, which displays intermediate features lying between classically excitatory and inhibitory endings; and (3) if a CG neuron is contacted by GABA-positive terminals, virtually all perisomatic terminals supplying it show GABA immunoreactivity. The source of this GABAergic input and whether GABA contributes to a specific CG function remains to be investigated. Nevertheless, our data indicate that the innervation of the ciliary ganglion is more complex than previously thought, and that GABA may play a neuromodulatory role in the control of lens or pupil function. J. Comp. Neurol. 525:1517-1531, 2017. © 2016 Wiley Periodicals, Inc.

Type-specific photoreceptor loss in pigeons after disruption of parasympathetic control of choroidal blood flow by the medial subdivision of the nucleus of Edinger-Westphal

The medial part of the nucleus of Edinger–Westphal (EWM) in birds mediates light-regulated adaptive increases in choroidal blood flow (ChBF). We sought to characterize the effect of loss of EWM-mediated ChBF regulation on photoreceptor health in pigeons housed in either moderate intensity diurnal or constant light (CL). Photoreceptor abundance following complete EWM destruction was compared to that following a lesion in the pupil control circuit (as a control for spread of EWM lesions to the nearby pupil-controlling lateral EW) or following no EW damage. Birds were housed post-lesion in a 12 h 400 lux light/12 h dark light cycle for up to 16.5 months, or in constant 400 lux light for up to 3 weeks. Paraformaldehyde–glutaraldehyde fixed eyes were embedded in plastic, sectioned, slide-mounted, and stained with toluidine blue/azure II. Blinded analysis of photoreceptor outer segment abundance was performed, with outer segment types distinguished by oil droplet tint and laminar position. Brains were examined histologically to assess lesion accuracy. Disruption of pupil control had no adverse effect on photoreceptor outer segment abundance in either diurnal light or CL, but EWM destruction led to 50–60% loss of blue/violet cone outer segments in both light conditions, and a 42% loss of principal cone outer segments in CL. The findings indicate that adaptive regulation of ChBF by the EWM circuit plays a role in maintaining photoreceptor health and mitigates the harmful effect of light on photoreceptors, especially short wavelength-sensitive cone photoreceptors.

The identification and neurochemical characterization of central neurons that target parasympathetic preganglionic neurons involved in the regulation of choroidal blood flow in the rat eye using pseudorabies virus, immunolabeling and conventional pathway tracing methods

The choroidal blood vessels of the eye provide the main vascular support to the outer retina. These blood vessels are under parasympathetic vasodilatory control via input from the pterygopalatine ganglion (PPG), which in turn receives its preganglionic input from the superior salivatory nucleus (SSN) of the hindbrain. The present study characterized the central neurons projecting to the SSN neurons innervating choroidal PPG neurons, using pathway tracing and immunolabeling. In the initial set of studies, minute injections of the Bartha strain of the retrograde transneuronal tracer pseudorabies virus (PRV) were made into choroid in rats in which the superior cervical ganglia had been excised (to prevent labeling of sympathetic circuitry). Diverse neuronal populations beyond the choroidal part of ipsilateral SSN showed transneuronal labeling, which notably included the parvocellular part of the paraventricular nucleus of the hypothalamus (PVN), the periaqueductal gray, the raphe magnus (RaM), the B3 region of the pons, A5, the nucleus of the solitary tract (NTS), the rostral ventrolateral medulla (RVLM), and the intermediate reticular nucleus of the medulla. The PRV+ neurons were located in the parts of these cell groups that are responsive to systemic blood pressure signals and involved in systemic blood pressure regulation by the sympathetic nervous system. In a second set of studies using PRV labeling, conventional pathway tracing, and immunolabeling, we found that PVN neurons projecting to SSN tended to be oxytocinergic and glutamatergic, RaM neurons projecting to SSN were serotonergic, and NTS neurons projecting to SSN were glutamatergic. Our results suggest that blood pressure and volume signals that drive sympathetic constriction of the systemic vasculature may also drive parasympathetic vasodilation of the choroidal vasculature, and may thereby contribute to choroidal baroregulation during low blood pressure.

Central pupillary light reflex circuits in the cat: II. Morphology, ultrastructure, and inputs of preganglionic motoneurons

Preganglionic motoneurons supplying the ciliary ganglion control lens accommodation and pupil diameter. In cats, these motoneurons make up the preganglionic Edinger-Westphal population, which lies rostral, dorsal, and ventral to the oculomotor nucleus. A recent cat study suggested that caudal motoneurons control the lens and rostral motoneurons control the pupil. This led us to examine the morphology, ultrastructure, and pretectal inputs of these populations. Preganglionic motoneurons retrogradely labeled by introducing tracer into the cat ciliary ganglion generally fell into two morphologic categories. Fusiform neurons were located rostrally, in the anteromedian nucleus and between the oculomotor nuclei. Multipolar neurons were found caudally, dorsal and ventral to the oculomotor nucleus. The dendrites of preganglionic motoneurons within the anteromedian nucleus crossed the midline, providing a possible basis for consensual responses. Ultrastructurally, several different classes of synaptic profiles contact preganglionic motoneurons, suggesting that their activity may be modified by a variety of inputs. Furthermore, there were differences in the synaptic populations contacting the rostral vs. caudal populations, supporting the contention that these populations display functional differences. Anterogradely labeled pretectal terminals were observed in close association with labeled preganglionic motoneurons, particularly in the rostral population. Ultrastructural analysis revealed that these terminals, packed with clear, spherical vesicles, made asymmetric synaptic contacts onto motoneurons in the rostral population, indicating that these cells serve the pupillary light reflex. Thus, the preganglionic motoneurons found in the cat display morphologic, ultrastructural, and connectional differences suggesting that this rostral preganglionic population is specialized for pupil control, whereas more caudal elements control the lens.

The Edinger-Westphal nucleus: a historical, structural, and functional perspective on a dichotomous terminology

The eponymous term nucleus of Edinger-Westphal (EW) has come to be used to describe two juxtaposed and somewhat intermingled cell groups of the midbrain that differ dramatically in their connectivity and neurochemistry. On one hand, the classically defined EW is the part of the oculomotor complex that is the source of the parasympathetic preganglionic motoneuron input to the ciliary ganglion (CG), through which it controls pupil constriction and lens accommodation. On the other hand, EW is applied to a population of centrally projecting neurons involved in sympathetic, consumptive, and stress-related functions. This terminology problem arose because the name EW has historically been applied to the most prominent cell collection above or between the somatic oculomotor nuclei (III), an assumption based on the known location of the preganglionic motoneurons in monkeys. However, in many mammals, the nucleus designated as EW is not made up of cholinergic, preganglionic motoneurons supplying the CG and instead contains neurons using peptides, such as urocortin 1, with diverse central projections. As a result, the literature has become increasingly confusing. To resolve this problem, we suggest that the term EW be supplemented with terminology based on connectivity. Specifically, we recommend that 1) the cholinergic, preganglionic neurons supplying the CG be termed the Edinger-Westphal preganglionic (EWpg) population and 2) the centrally projecting, peptidergic neurons be termed the Edinger-Westphal centrally projecting (EWcp) population. The history of this nomenclature problem and the rationale for our solutions are discussed in this review.

Immunohistochemical localization of AMPA-type glutamate receptor subunits in the nucleus of the Edinger-Westphal in embryonic chick

The Edinger-Westphal nucleus (EW) in birds is responsible for the control of pupil constriction, accommodation, and choroidal blood flow. The activation of EW neurons is mediated by the neurotransmitter glutamate, in large part through AMPA-type glutamate receptors (GluRs), whose behavior varies according to the subunit composition. We investigated the developmental expression of the GluR subunits in EW of the chick (Gallus gallus) using immunohistochemistry on tissue from embryonic days 10 through 20 (E10-E20). Of the three antibodies used, one recognized the GluR1 subunit, another the GluR4 subunit, and the third recognized a sequence common to GluR2 and GluR3 subunits. No immunolabeling of EW neurons for any GluR subunits was observed prior to E12, although immunolabeling was seen in somatic oculomotor prior to E12. At E12, immunoreactivity for each of the three antibodies was in only approximately 2% of EW neurons. By E14, the abundance of GluR1+ perikarya in EW had increased to 13%, and for GluR2/3 had increased to 48%. The perikaryal abundance of the immunoreactivity for GluR1 and GluR2/3 declined to 3% and 23%, respectively, by E16. At E14, 33% of EW neurons immunolabeled for GluR4, and their frequency increased to 43% by E16, and remained at that approximate percentage through hatching. The increased expression of GluR1 and GluR4 in EW at E14 coincides with the reported onset of the expression of the calcium-binding protein parvalbumin, and the calcium currents associated with AMPA receptors formed by these two subunits may play a role in the occurrence of parvalbumin expression.

Projections from the hypothalamic paraventricular nucleus and the nucleus of the solitary tract to prechoroidal neurons in the superior salivatory nucleus: Pathways controlling rodent choroidal blood flow

Using intrachoroidal injection of the transneuronal retrograde tracer pseudorabies virus (PRV) in rats, we previously localized preganglionic neurons in the superior salivatory nucleus (SSN) that regulate choroidal blood flow (ChBF) via projections to the pterygopalatine ganglion (PPG). In the present study, we used higher-order transneuronal retrograde labeling following intrachoroidal PRV injection to identify central neuronal cell groups involved in parasympathetic regulation of ChBF via input to the SSN. These prominently included the hypothalamic paraventricular nucleus (PVN) and the nucleus of the solitary tract (NTS), both of which are responsive to systemic BP and are involved in systemic sympathetic vasoconstriction. Conventional pathway tracing methods were then used to determine if the PVN and/or NTS project directly to the choroidal subdivision of the SSN. Following retrograde tracer injection into SSN (biotinylated dextran amine 3K or Fluorogold), labeled perikarya were found in PVN and NTS. Injection of the anterograde tracer, biotinylated dextran amine 10K (BDA10K), into PVN or NTS resulted in densely packed BDA10K+terminals in prechoroidal SSN (as defined by its enrichment in nitric oxide synthase-containing perikarya). Double-label studies showed these inputs ended directly on prechoroidal nitric oxide synthase-containing neurons of SSN. Our study thus establishes that PVN and NTS project directly to the part of SSN involved in parasympathetic vasodilatory control of the choroid via the PPG. These results suggest that control of ChBF may be linked to systemic blood pressure and central control of the systemic vasculature.

Multiple Manifestations of Microstimulation in the Optic Tectum: Eye Movements, Pupil Dilations, and Sensory Priming

It is well established that the optic tectum (or its mammalian homologue, the superior colliculus) is involved in directing gaze toward salient stimuli. However, salient stimuli typically induce orienting responses beyond gaze shifts. The role of the optic tectum in generating responses such as pupil dilation, galvanic responses, or covert shifts is not clear. In the present work, we studied the effects of microstimulation in the optic tectum of the barn owl ( Tyto alba) on pupil diameter and on eye shifts. Experiments were conducted in lightly anesthetized head-restrained barn owls. We report that low-level microstimulation in the deep layers of the optic tectum readily induced pupil dilation responses (PDRs), as well as small eye movements. Electrically evoked PDRs, similar to acoustically evoked PDRs, were long-lasting and habituated to repeated stimuli. We further show that microstimulation in the external nucleus of the inferior colliculus also induced PDRs. Finally, in experiments in which tectal microstimulations were coupled with acoustic stimuli, we show a tendency of the microstimulation to enhance pupil responses and eye shifts to previously habituated acoustic stimuli. The enhancement was dependent on the site of stimulation in the tectal spatial map; responses to sounds with spatial cues that matched the site of stimulation were more enhanced compared with sounds with spatial cues that did not match. These results suggest that the optic tectum is directly involved in autonomic orienting reflexes as well as in gaze shifts, highlighting the central role of the optic tectum in mediating the body responses to salient stimuli.

PHOX2A regulation of oculomotor complex nucleogenesis

Brain nuclei are spatially organized collections of neurons that share functional properties. Despite being central to vertebrate brain circuitry, little is known about how nuclei are generated during development. We have chosen the chick midbrain oculomotor complex (OMC) as a model with which to study the developmental mechanisms of nucleogenesis. The chick OMC comprises two distinct cell groups: a dorsal Edinger-Westphal nucleus of visceral oculomotor neurons and a ventral nucleus of somatic oculomotor neurons. Genetic studies in mice and humans have established that the homeobox transcription factor gene PHOX2A is required for midbrain motoneuron development. We probed, in forced expression experiments, the capacity of PHOX2A to generate a spatially organized midbrain OMC. We found that exogenous Phox2a delivery to embryonic chick midbrain can drive a complete OMC molecular program, including the production of visceral and somatic motoneurons. Phox2a overexpression was also able to generate ectopic motor nerves. The exit points of such auxiliary nerves were invested with ectopic boundary cap cells and, in four examples, the ectopic nerves were seen to innervate extraocular muscle directly. Finally, Phox2a delivery was able to direct ectopic visceral and somatic motoneurons to their correct native spatial positions, with visceral motoneurons settling close to the ventricular surface and somatic motoneurons migrating deeper into the midbrain. These findings establish that in midbrain, a single transcription factor can both specify motoneuron cell fates and orchestrate the construction of a spatially organized motoneuron nuclear complex.

The multifunctional choroid

The choroid of the eye is primarily a vascular structure supplying the outer retina. It has several unusual features: It contains large membrane-lined lacunae, which, at least in birds, function as part of the lymphatic drainage of the eye and which can change their volume dramatically, thereby changing the thickness of the choroid as much as four-fold over a few days (much less in primates). It contains non-vascular smooth muscle cells, especially behind the fovea, the contraction of which may thin the choroid, thereby opposing the thickening caused by expansion of the lacunae. It has intrinsic choroidal neurons, also mostly behind the central retina, which may control these muscles and may modulate choroidal blood flow as well. These neurons receive sympathetic, parasympathetic and nitrergic innervation. The choroid has several functions: Its vasculature is the major supply for the outer retina; impairment of the flow of oxygen from choroid to retina may cause Age-Related Macular Degeneration. The choroidal blood flow, which is as great as in any other organ, may also cool and warm the retina. In addition to its vascular functions, the choroid contains secretory cells, probably involved in modulation of vascularization and in growth of the sclera. Finally, the dramatic changes in choroidal thickness move the retina forward and back, bringing the photoreceptors into the plane of focus, a function demonstrated by the thinning of the choroid that occurs when the focal plane is moved back by the wearing of negative lenses, and, conversely, by the thickening that occurs when positive lenses are worn. In addition to focusing the eye, more slowly than accommodation and more quickly than emmetropization, we argue that the choroidal thickness changes also are correlated with changes in the growth of the sclera, and hence of the eye. Because transient increases in choroidal thickness are followed by a prolonged decrease in synthesis of extracellular matrix molecules and a slowing of ocular elongation, and attempts to decouple the choroidal and scleral changes have largely failed, it seems that the thickening of the choroid may be mechanistically linked to the scleral synthesis of macromolecules, and thus may play an important role in the homeostatic control of eye growth, and, consequently, in the etiology of myopia and hyperopia.

Comparison of the distributions of urocortin-containing and cholinergic neurons in the perioculomotor midbrain of the cat and macaque

Urocortin is a novel neurotransmitter that appears to play a role in eating and drinking behavior. Most urocortin-positive (urocortin(+)) neurons in rodents are found in the cytoarchitecturally defined Edinger-Westphal nucleus (EW). However, the EW is traditionally described as the source of the preganglionic parasympathetic outflow to the ciliary ganglion. We examined the distribution of urocortin(+) cells and motoneurons by use of immunohistochemical staining for this peptide and for choline acetyltransferase (ChAT) in macaque monkeys, in which most preganglionic motoneurons inhabit the EW, and in cats, in which most do not. In both species, lack of overt double labeling indicated that the ChAT(+) and urocortin(+) cells are separate populations. In the monkey, most nonoculomotor ChAT(+) neurons were found within the EW. In contrast, urocortin(+) cells were distributed mainly between the oculomotor nuclei and in the supraoculomotor area. In the cat, most nonoculomotor ChAT(+) cells were located in the supraoculomotor area and anteromedian nucleus. Few were present in the cat EW. Instead, this nucleus was filled with urocortin(+) cells. These results highlight the fact the term EW has come to indicate different nuclei in different species. Consequently, we have adopted the identifiers preganglionic (EW(PG)) and urocortin-containing (EW(U)) to designate the cytoarchitecturally defined EW nuclei in monkeys and cats, respectively. Furthermore, we propose a new open-ended nomenclature for the perioculomotor (pIII) cells groups that have distinctive projections and neurochemical signatures. This will allow more effective scientific discourse on the connections and function of groups such as the periculomotor urocortin (pIII(U)) and preganglionic (pIII(PG)) populations.

In situ hybridization histochemical and immunohistochemical evidence that striatal projection neurons co-containing substance P and enkephalin are overrepresented in the striosomal compartment of striatum in rats

In a prior study, we showed that the few striatal projection neurons that contain both substance P (SP) and enkephalin (ENK) in rats may preferentially project to the substantia nigra pars compacta. Since striatal neurons that project to the pars compacta are thought to preferentially reside in the striosomal compartment, we investigated if striatal neurons that contain both SP and ENK are preferentially localized to the patch compartment. We used in situ hybridization histochemistry to double-label sections for SP and ENK to identify SP/ENK co-containing neurons, and immunolabeling of adjacent sections for the mu opiate receptor (MOR) to define the striosomal compartment. We found that 32.3% of neurons containing both SP and ENK were localized to the striosomal compartment, which itself only made up 12.8% of the striatum. Our results further showed that the density of neurons co-containing SP and ENK was three-fold higher in striosomes than in the matrix compartment. These results are consistent with the notion that SP/ENK colocalizing neurons preferentially project to pars compacta, and these and our prior results additionally raise the possibility that neurons of this type in the striatal matrix may also project to the pars compacta.

Involvement of urocortinergic neurons below the midbrain central gray in the physiological response to restraint stress in pigeons

The present study was carried out to identify the diencephalic and midbrain neurons in pigeons that respond to stress (using restraint as the stressor) and determine if the urocortinergic neurons (expressing urocortin 1, Ucn1) below the midbrain central gray are among those activated. Immunolabeling for the immediate early gene Egr-1 was used to identity stress-responsive neurons, following 1-3 h of restraint. A large increase in nuclear Egr-1 immunolabeling was observed in several dorsomedial thalamic nuclei, and in a stream of neurons extending from below the mesencephalic central gray (overlapping the nucleus of Darkschewitsch at these levels) to just anterior to the nucleus of Edinger-Westphal. A more modest increase in neuronal nuclear Egr-1 was observed in the medial posterior hypothalamic area, the mesencephalic periventricular area, the ventral tegmental area, the inferior colliculus, the nucleus paramedianus of the midbrain, and the intercollicular nucleus. The distribution and abundance of urocortin-immunolabeled neurons coincided with that of the stress-responsive neurons below the mesencephalic periaqueductal gray, and about 50% of these urocortin neurons were activated by stress. These results suggest that, as in some mammals, the urocortinergic neurons of the paramedian subgriseal mesencephalon respond to stress. In those mammals, in which the boundaries of the nucleus of Edinger-Westphal are indistinct, the caudal part of the homologous field of urocortinergic neurons has been referred to as the nucleus of Edinger-Westphal. In pigeons, in which the nucleus of Edinger-Westphal is cytoarchitectonically well-defined, the caudal part of this urocortinergic field clearly does not include the nucleus of Edinger-Westphal.

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.

The extraocular motor nuclei: organization and functional neuroanatomy

The organization of the motoneuron subgroups in the brainstem controlling each extraocular eye muscle is highly stable through the vertebrate species. The subgroups are topographically organized in the oculomotor nucleus (III) and are usually considered to form the final common pathway for eye muscle control. Eye muscles contain a unique type of slow non-twitch, fatigue-resistant muscle fiber, the multiply innervated muscle fibers (MIFs). The recent identification the MIF motoneurons shows that they too have topographic organization, but very different from the classical singly innervated muscle fiber (SIF) motoneurons. The MIF motoneurons lie around the periphery of the oculomotor nucleus (III), trochlear nucleus (IV), and abducens nucleus (VI), slightly separated from the SIF subgroups. The location of four different types of neurons in VI are described and illustrated: (1) SIF motoneurons, (2) MIF motoneurons, (3) internuclear neurons, and (4) the paramedian tract neurons which project to the flocculus. Afferents to the motoneurons arise from the vestibular nuclei, the oculomotor and abducens internuclear neurons, the mesencephalic and pontine burst neurons, the interstitial nucleus of Cajal, nucleus prepositus hypoglossi, the supraoculomotor area and the central mesencephalic reticular formation and the pretectum. The MIF and SIF motoneurons have different histochemical properties and different afferent inputs. The hypothesis that SIFs participate in moving the eye and MIFs determine the alignment seems possible but is not compatible with the concept of a final common pathway.

Cellular Localization of AMPA Type Glutamate Receptor Subunits in the Basal Ganglia of Pigeons (Columba livia)

Corticostriatal and thalamostriatal projections utilize glutamate as a neurotransmitter in mammals and birds. The influence on striatum is mediated, in part, by ionotropic AMPA-type glutamate receptors, which are heteromers composed of GluR1-4 subunits. Although the cellular localization of AMPA-type subunits has been well characterized in mammalian basal ganglia, their localization in avian basal ganglia has not. We thus carried out light microscopic single- and double-label and electron microscopic single-label immunohistochemical studies of GluR1-4 distribution and cellular localization in pigeon basal ganglia. Single-label studies showed that the striatal neuropil is rich in GluR1, GluR2, and GluR2/3 immunolabeling, suggesting the localization of GluR1, GluR2 and/or GluR3 to the dendrites and spines of striatal projection neurons. Double-label studies and perikaryal size distribution determined from single-label material indicated that about 25% of enkephalinergic and 25% of substance P-containing striatal projection neuron perikarya contained GluR1, whereas GluR2 was present in about 75% of enkephalinergic neurons and all substance-P -containing neurons. The perikaryal size distribution for GluR2 compared to GluR2/3 suggested that enkephalinergic neurons might more commonly contain GluR3 than do substance P neurons. Parvalbuminergic and calretininergic striatal interneurons were rich in GluR1 and GluR4, a few cholinergic striatal interneurons possessed GluR2, but somatostatinergic striatal interneurons were devoid of all subunits. The projection neurons of globus pallidus all possessed GluR1, GluR2, GluR2/3 and GluR4 immunolabeling. Ultrastructural analysis of striatum revealed that GluR1 was preferentially localized to dendritic spines, whereas GluR2/3 was found in spines, dendrites, and perikarya. GluR2/3-rich spines were generally larger than GluR1 spines and more frequently possessed perforated post-synaptic densities. These results show that the diverse basal ganglia neuron types each display different combinations of AMPA subunit localization that shape their responses to excitatory input. For striatal projection neurons and parvalbuminergic interneurons, the combinations resemble those for the corresponding cell types in mammals, and thus their AMPA responses to glutamate are likely to be similar.

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.

Urocortin 1-containing neurons in the human Edinger-Westphal nucleus

The topographical location of neurons containing urocortin 1, a peptide related to corticotropin-releasing factor was investigated in human postmortem brain by immunohistochemistry, and compared with the location of neurons containing choline acetyltransferase, a marker for cholinergic cells. A three-dimensional computer reconstruction of the urocortin 1 and choline acetyltransferase-positive population of neurons within the oculomotor area was made. It was shown that the urocortin 1-positive neurons are located within the area identified as the Edinger-Westphal nucleus according to the human brain stem atlas, and that the neurons identified as Edinger-Westphal nucleus in the atlas are not choline acetyltransferase-positive. This finding agrees with recent animal studies showing that urocortin 1-positive neurons are not identical with the parasympathetic cholinergic neurons projecting to the ciliary ganglion. They indicate that the neurons identified as Edinger-Westphal nucleus in the human brain stem atlas belong to the non-preganglionic Edinger-Westphal nucleus, whereas the location of preganglionic Edinger-Westphal nucleus remains unidentified.

Differential loss of striatal projection systems in Huntington's disease: a quantitative immunohistochemical study

Prior studies suggest differences exist among striatal projection neuron types in their vulnerability to Huntington's disease (HD). In the present study, we immunolabeled the fibers and terminals of the four main types of striatal projection neuron in their target areas for substance P, enkephalin, or glutamic acid decarboxylase (GAD), and used computer-assisted image analysis to quantify the abundance of immunolabeled terminals in a large sample of HD cases ranging from grade 0 to grade 4 [J. Neuropathol. Exp. Neurol. 44 (1985) 559], normalized to labeling in control human brains. Our goal was to characterize the relative rates of loss of the two striatopallidal projection systems (to the internal versus the external pallidal segments) and the two striatonigral projections systems (to pars compacta versus pars reticulata). The findings for GAD and the two neuropeptides were similar--the striatal projection to the external pallidal segment was the most vulnerable, showing substantial loss by grade 1. Loss of fibers in both subdivisions of the substantia nigra was also already great by grade 1. By contrast, the loss in the striatal projection system to the internal segment of globus pallidus proceeded more gradually. By grade 4 of HD, however, profound loss in all projection systems was apparent. These findings support the notion that the striatal neurons preferentially projecting to the internal pallidal segment are, in fact, less vulnerable in HD than are the other striatal projection neuron types.

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.

Evidence that urocortin is absent from neurons of the Edinger-Westphal nucleus in pigeons

The Edinger-Westphal nucleus (EWN) is a central preganglionic parasympathetic cell group that gives rise to cholinergic input to the ciliary ganglion, thereby regulating several neurovegetative ocular functions. Recently, the supposed presence of the neuropeptide urocortin (UCN) has been reported in EWN neurons in rodent brain. The purpose of the present study was to examine the distribution of UCN in avian brain and to investigate by immunohistochemical analysis the possible use of this substance as an EWN marker in a non-mammalian class of vertebrates. Brain tissue of pigeons was incubated with a specific antibody against UCN and the results showed labeling of many small neurons, forming a double wing in the dorsal mesodiencephalic transition area. Their size and shape, however, differed from those of EWN neurons, and they were preferentially located rostral to the EWN. Double-label experiments employing an antibody against the enzyme choline acetyltransferase (ChAT) showed that UCN is not localized to the cholinergic cells of the EWN and confirmed the rostral distributionof UCN never overlapping the ChAT+ EWN cells. Taken together, these results suggest that, at least in pigeons, the UCN+ population does not belong to the traditionally defined EWN.

Interspecific differences in the expression of the AMPA-type glutamate receptors and parvalbumin in the nucleus of Edinger-Westphal of chicks and pigeons

The distribution of AMPA-type glutamate receptor (GluR) subunits was studied in the Edinger-Westphal nucleus (EW) of chicks and pigeons. GluR1, GluR2, GluR3 and GluR4 subunits appeared to be present in EW neurons of both species, but interspecific differences were observed in the abundance of the different types of subunits found in EW neurons. Of particular note, GluR2 immunoreactivity was present in the vast majority (ca. 80%) of neurons of pigeon EW but was found in only a small fraction (ca. 15%) of chick EW neurons. Scarcity of the GluR2 subunit in chick EW was confirmed by in situ hybridization. Because of the tendency for parvalbumin to be localized to neurons that are selectively deficient in GluR2, we also studied the localization of parvalbumin, as well as other calcium-binding proteins, in EW of chick and pigeon. Parvalbumin was found in more than 50% of chick EW neurons but was not detected in pigeon EW neurons. Our results suggest that there are major glutamatergic inputs to EW neurons in both pigeons and chicks. Furthermore, there are likely to be more AMPA-type calcium-permeable glutamate receptors in EW neurons of chick than in pigeon, since it is known that the subtype containing the edited GluR2 subunit is not calcium permeable.

The distribution of dopamine, substance P, vasoactive intestinal polypeptide and neuropeptide Y immunoreactivity in the brain of the collared dove, Streptopelia decaocto

This study is part of a program intended to provide the neuroanatomical framework for investigations of the role of brain areas in specific aspects of behavior in the collared dove. In the present study, the distribution of dopamine-, substance P-, vasoactive intestinal polypeptide (VIP)- and neuropeptide Y (NPY)-immunoreactivity are mapped throughout the brain of this bird. For each substance, our observations are compared with data from studies in other species of birds. Over all, our data confirm the results of previous reports, but a few differences with data from some of these studies are found. The immunohistochemical data are used in an attempt to define more precisely cell areas and their subdivisions in the avian forebrain and brainstem, and to compare these areas to nuclei in the brain of mammals.

Synaptic interactions regulate gephyrin expression in avian cholinergic neurons in vivo

Our recent studies of chick parasympathetic ciliary ganglion (CG) neurons demonstrate a unique postsynaptic receptor microheterogeneity - under one presynaptic terminal, excitatory nicotinic acetylcholine receptor (nAChR) clusters and separate inhibitory glycine receptor (GlyR) clusters coexist in distinct membrane microregions. Gephyrin, a peripheral membrane protein that is required for GlyR clustering at synapses in the rodent central nervous system, is also expressed in chick CG neurons where it codistributes with GlyRs, but not nAChRs. We now extend these findings by characterizing the regulation of gephyrin expression in chick CG neurons in vivo. We show that developmental increases in gephyrin transcript levels occur during pre- and postganglionic synapse formation. The increases are induced by both innervation and target tissue interactions, with the target tissues having the greater regulatory influence. The time course of the developmental rise in gephyrin mRNA levels most closely resembles that reported for functional GlyR expression, but not that of functional nAChRs nor GABA(A) receptors. We also demonstrate that gephyrin is concentrated in the postsynaptic density of a subset of synapses on both the ciliary and choroid neurons in the CG and is stably expressed from embryonic to adult stages. Altogether, our results suggest that gephyrin is a synapse organizing molecule that functions to localize GlyRs, but not nAChRs, to discrete postsynaptic membrane microregions in chick CG neurons in vivo.

Morphological analogy of the rostral midline area in the chicken midbrain to the anteromedian nucleus in the mammalian midbrain

Substance P-immunoreactive neurons projecting from the midbrain to the spinal cord of the chicken were examined by the use of the retrograde tract-tracing method combined with immunohistochemical techniques. Many small neurons were densely clustered in the rostral midline area of the midbrain (RMA), and showed substance P-immunoreactivity. These substance P-immunoreactive neurons sent axons to the intermediomedial cell column (avian autonomic preganglion) and its vicinity in the lumbar spinal segments. On the basis of the strong neuroanatomical analogy in the cytoarchitectural features, immunoreactivity, and fiber connections, the RMA was assumed to be the avian homologue of the anteromedian nucleus in the mammalian midbrain.

Receptor targeting and heterogeneity at interneuronal nicotinic cholinergic synapses in vivo

Within a single neuron the correct targeting of the diverse neurotransmitter receptor types to discrete synaptic regions is crucial for proper function. However, the molecular mechanisms that underlie neuronal receptor clustering and targeting are still largely undefined. Here we report advances in defining the mechanisms that mediate nicotinic acetylcholine receptor (nAChR) targeting to interneuronal synapses. Recent in vivo studies have demonstrated that one subunit plays a critical role in the differentiation of nicotinic cholinergic synapses on vertebrate autonomic neurons. The major cytoplasmic loop of the alpha3 subunit targets specific nAChR subtypes to the synapse. In contrast, nAChR complexes that lack the alpha3 targeting domain are excluded and are perisynaptic. Additional studies have demonstrated a greater complexity to alpha3-nAChR targeting due to a unique postsynaptic receptor microheterogeneity - under one presynaptic terminal, alpha3-nAChR clusters are separate, but proximal to, glycine receptor (GlyR) clusters in discrete postsynaptic membrane microregions. The surprising coexistence under one nerve ending of separate clusters of receptors that respond to different fast-acting transmitters with opposing functions may represent a novel mechanism for modulating synaptic activity. Overall, the receptor targeting and clustering studies reviewed in this issue suggest that a common mechanism underlies the formation of the diverse types of interneuronal synapses but differs from that responsible for neuromuscular junction assembly in vertebrates.

Substance P-immunoreactive neurons in the rostromedian area of the midbrain send axons to the lower spinal cord in the chicken

Substance P-immunoreactivity in neurons projecting to the spinal cord was examined using retrograde tract-tracing method combined with immunohistochemical techniques in chickens. Many small substance P-immunoreactive neurons were densely clustered in the midline area in the rostral midbrain, the rostromedian area (80% of the neurons in the rostromedian area). Some of these substance P-immunoreactive neurons in the rostromedian area (about 20% of substance P-immunoreactive neurons) were retrogradely labeled by small injections of wheat germ agglutinin conjugated horseradish peroxidase into the central part of the lumber segments including the intermediomedial nucleus, suggesting the projections from the rostromedian area to the lower spinal preganglionic regions. From the present data and mammalian previous studies, it was suggested that the midline area in the midbrain has fiber connections with the regions related autonomic functions, and all of which exhibit substance P-immunoreactivity.

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.

A simple and sensitive antigen retrieval method for free-floating and slide-mounted tissue sections

The masking of antigens by aldehyde-containing fixatives or by paraffin embedding procedures is a problem for immunohistochemical studies. Enzymatic digestion, formic acid treatment, microwave heating and autoclave heating have been used to deal with this problem, with microwave heating-based antigen retrieval having become widely used as the method of choice. Microwave heating, however, has the shortcoming that it is difficult to precisely control the heating temperature and it is difficult to apply this method of heating to free-floating sections without damaging the sections. We describe here a simple, reliable and sensitive antigen retrieval method that uses water-bath heating. By this method, the temperature can be precisely controlled to yield effective antigen retrieval with minimal tissue damage in free-floating or paraffin-embedded slide-mounted sections. We found that the best results were obtained with a 30 min incubation in a 10-50 mM sodium citrate solution (pH 8.5-9.0) preheated to and maintained at 80 degrees C in a water-bath, followed by 30 min incubation in 0.3-3% nonfat dry milk to reduce nonspecfic staining. This method is highly effective for both 40 microm free floating sections, slide-mounted cryostat sections and paraffin-embedded slide-mounted sections, and it works well for tissue from diverse species (human, rat, mouse, pigeon, and zebra finch) and for diverse antigens (e.g. enkephalin, substance P, huntingtin, GluR1, GFAP, and ubiquitin). This method was also found to enhance immunolabeling in glutaraldehyde-fixed tissue that had been prepared for ultrastructural examination, without having a deleterious effect on the ultrastructure.

Influence of ophthalmic nerve fibers on choroidal blood flow and myopic eye growth in chicks

Ophthalmic sensory nerve fibers containing substance P and calcitonin gene-related peptide' innervate the choroid in mammals and are known to vasodilate choroidal blood vessels. The avian choroid is also innervated by ophthalmic nerve fibers containing substance P and calcitonin gene-related peptide. The present studies were carried out to determine the influence of these sensory fibers on choroidal blood flow in birds and characterize their interaction with manipulations affecting eye growth. In these studies, ChBF was measured using laser Doppler flowmetry in both eyes in the following groups of birds: (1) normal chicks; (2) chicks with right optic nerve transected for 2 weeks; (3) chicks with right optic nerve transected and a goggle over the right eye for 2 weeks; and (4) chicks with right optic and ophthalmic nerves transected and a goggle over the right eye for 2 weeks. The eyes were refracted and various ocular dimensions measured after the blood-flow measurements. It was found that optic nerve transection reduced ChBF to 30% of normal. Placing a goggle (which increases ocular temperature by 4 degrees C) over an optic nerve transected eye nearly doubled choroidal blood flow over that in an optic nerve transected eye without a goggle. Additional transection of the ophthalmic nerve in a goggled optic nerve-transected eye, yielded choroidal blood flow that was indistinguishable from that in a nongoggled optic nerve-transected eye. Optic nerve transection had a slight stunting effect on axial growth of the eye. While myopic axial elongation was observed in goggled eyes with the optic nerve cut, the extent of myopia was less than in normal goggled eyes. Ophthalmic nerve transection further reduced the myopia induced by goggling in an optic nerve cut eye. These results suggest that ophthalmic nerve input to the choroid exerts a vasodilatory influence, which is activated in a goggled eye. This increased choroidal blood flow may be in response to elevated ocular temperatures caused by the goggling and this increase appears to be masked in goggled eyes with an intact optic nerve by the reduction in choroidal blood flow normally accompanying myopic eye growth. Our results thus show that the induction of myopic eye growth (as in our optic nerve cut eyes with a goggle) need not be accompanied by a decrease in choroidal blood flow from the baseline no-goggle condition (in this case, with the optic nerve cut).

A true neuronal consensual pupillary reflex in chicks

The existence of a true neuronal consensual pupillary reflex (CPR) in birds has long been debated. In this century Noll (Noll, A. (1915). Archiv für Physiologie (Leipzig), 350-372.) claimed to observe a neuronal CPR in a pigeon, but this was contradicted by Levine (Levine, J. (1955). Science, 122, 699.), who observed a direct transillumination effect (Durchleuchtungs-effekt) due to the retinas of the two eyes of the pigeon being in close apposition. To determine if a neuronal CPR exists, we transected the optic nerves of 28 chicks and observed and videotaped the direct and indirect pupillary responses. Twenty-one of the chicks exhibited no direct response in the operated eye but did exhibit an indirect pupillary response. The non-operated eye showed a direct but no indirect response. These results conclusively demonstrate for the first time that a true neuronal CPR does exist in chickens.

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.

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.

Agrin mRNA expression in the developing chick Edinger-Westphal nucleus

Agrin is a large extracellular matrix protein that directs the accumulation of acetylcholine receptors at the neuromuscular junction. Recent evidence suggests that agrin may be involved in organizing synapses in the visual system as well. Focussing on the pathway that controls accommodation and pupilloconstriction, this study examined the temporal pattern of agrin expression with reference to the organization of cholinergic synapses between embryonic chick Edinger-Westphal and ciliary ganglion neurons. In situ hybridization with an S35-labeled agrin cRNA probe was used to characterize agrin expression in the Edinger-Westphal nucleus during development. Agrin mRNA was detected in the Edinger-Westphal nucleus at all time points studied, from embryonic day 7 (E7, Hamburger and Hamilton stage 31) through newly hatched chicks. Throughout this period, agrin mRNA expression in Edinger-Westphal neurons was lower than in nearby oculomotor and trochlear neurons, suggesting that cells projecting to neuronal targets may require less agrin than those projecting to muscle. Agrin mRNA expression in the Edinger-Westphal nucleus at E7, E8, E9, and E10 was significantly higher than at E12. The early appearance of agrin mRNA coincides with the period during which acetylcholine receptors are being organized on ciliary ganglion neurons, consistent with the possibility that agrin contributes to neuron-neuron synapse formation in this pathway.

Development of parvalbumin immunoreactivity in the chick Edinger Westphal nucleus

To determine when the calcium-binding protein parvalbumin appears during development, neurons in the chick Edinger Westphal nucleus were examined for parvalbumin immunoreactivity at a variety of embryonic stages. Parvalbumin immunoreactivity appeared on embryonic day 14 (E14, Hamburger and Hamilton stage 40) in predominantly lateral Edinger Westphal neurons. Cytochrome oxidase activity within the nucleus was examined throughout development, as an indicator of physiological activity, and expression of cytochrome oxidase was compared with that of parvalbumin. Cytochrome oxidase activity was found to be uniformly high in all parts of the Edinger Westphal nucleus throughout development. Either the Edinger Westphal nucleus in physiologically active quite early in its development or other energy demands mask the correlation of cytochrome oxidase with electrical activity. Cytochrome oxidase was expressed well before parvalbumin immunoreactivity appeared. Voltage-activated calcium currents were characterized in E12 Edinger Westphal neurons. In both amplitude and composition, E12 calcium currents resemble those of E16 neurons, excluding the possibility that calcium currents appear de novo during or just prior to the appearance of parvalbumin. Both cytochrome oxidase activity and calcium currents are observed in Edinger Westphal neurons well before the appearance of parvalbumin during development. These findings do not exclude the possibility that physiological activity affects the expression of parvalbumin since other factors such as changing patterns of synaptic activity or the appearance of calcium conducting NMDA receptors have yet to be examined. However, they raise the possibility that additional factors such as an intrinsic developmental program or a change in the neuron's basal intracellular calcium requirements may also be involved.

The ratio of pre- to postganglionic neurons and related issues in the autonomic nervous system

The motor outflow of the autonomic nervous system (ANS) is differentiated into two major divisions, parasympathetic (PSNS) and sympathetic (SNS). Both are organized hierarchically into pre- and postganglionic levels, but classically the two divisions have been assumed to differ in their ratios of pre- to postganglionic neurons. The PSNS been characterized as having lower ('one-to-few') ratios, whereas the SNS has been described as possessing higher ('one-to-many') ratios. These patterns have been assumed to measure differing divergences of the outflows. In this review, a ratio of pre- to postganglionic neurons is called a ratio index, and the idea that the PSNS and SNS have characteristically different ratio indexes and divergences is called the ratio rule. The putative differences in the ratio indexes of the two divisions - as well as Fulton's influential proposal that they form one of the bases of contrasting functional capacities of the PSNS and SNS - have been widely accepted for nearly for nearly three quarters of a century. A survey of the original observations yielding the concept of the ratio rule as well as the more recent estimates of pre- and postganglionic numbers, however, challenges both the generality and the adequacy of the ratio rule and indexes. The originally formulated differences between the PSNS and SNS represent an overgeneralization since they were based on observations of only two ganglia, the ciliary ganglion in the PSNS and the superior cervical ganglion in the SNS. Furthermore, these original estimates were based on limited samples and were subject to a number of counting artifacts. A survey of the literature suggests that ratio indexes vary much more within each ANS division than they do between the two divisions. When ganglia other than the ciliary and superior cervical are examined, the two divisions of the ANS have broad, largely overlapping ranges of ratio indexes. Additionally, other PSNS-SNS pairs can be found in which the relative sizes of their respective indexes are completely contrary to the ratio rule. For a given ganglion, there are substantial differences in the ratio index between species, between individuals of the same species, and between stages of development in the same species. Furthermore, both divisions of the ANS have wide and largely overlapping ranges of physiological effects varying from specific to diffuse, from local to widespread. Finally, the ratio index measure ignores the degree of convergence found in different ganglia, and it is insensitive to the fact that many ganglia have multiple functionally distinct motor neuron pools, each with separate inputs varying in their degrees of divergence and/or convergence. Thus ratio indexes do not differentiate the PSNS from the SNS, and conclusions based on such putative distinctions are questionable.

The relationship of choroidal blood flow and accommodation to the control of ocular growth

We have carried out a number of different studies in chicks to examine the relationship between choroidal blood flow and myopic eye growth, and between accommodation and myopic eye growth. Our studies on choroidal blood flow show that myopic eye growth produced by form vision degradation leads to dramatic reductions in choroidal blood flow. These reductions appear directly attributable to the eye enlargement and the reduction in choroidal blood flow does not appear to be permissive for eye growth, since experimentally reduced choroidal blood flow hinders eye growth. Choroidal blood flow that is slightly above normal, however, may slightly enhance eye growth. Our studies on accommodation do not reveal any major necessary role of accommodation in regulating normal growth or in form vision degradation induced myopic eye growth. We found preliminary evidence, however, that chronically stimulating accommodation over a 2 week period, thereby producing excessive time in accommodation, may be sufficient for yielding a small but significant degree of myopic refractive error. Our studies suggest that neither fluctuations in choroidal blood flow nor an intact accommodative apparatus are essential for normal eye growth or myopic eye growth produced by form deprivation. Further studies are needed to confirm that excessive time in accommodation might be sufficient for producing myopia. Finally, our finding that choroidal blood flow is substantially reduced in myopic eyes may have implications for the etiology of the retinal problems suffered by humans with moderate to severe myopia.

Multiple subtypes of voltage-gated calcium currents in the Edinger-Westphal nucleus

Avian Edinger-Westphal (EW) neurons provide a unique opportunity to compare electrophysiologically the membranes of cell bodies and terminals in the same population of neurons. Axons that originate from neurons in the lateral region of the EW nucleus form a morphologically distinct presynaptic terminal, known as a calyx, on ciliary ganglion neurons. Several studies have shown that calyciform terminals in the ciliary ganglion exhibit predominantly N-type, high-voltage-activated (HVA) calcium channels. The goal of this study was to characterize and compare the calcium currents expressed in EW cell somas with those reported in the terminals. Whole-cell patch-clamp techniques were used to record from cell bodies in the lateral EW nucleus in slice preparations. Slices were obtained from embryonic day 16 chicks, matching the age of the embryos in which calyces were studied. Recordings were localized to the lateral region of the EW nucleus using Lucifer yellow fills. Voltage-step commands from -70 to 0 mV produced calcium currents with both a sustained and an inactivating component. Depolarization steps to 0 mV from a holding potential of -40 mV eliminated the inactivating component. These recordings suggested the presence of both LVA and HVA calcium currents. Application of 0.1 mM NiCl2 produced a reversible decrease in the amplitude of the whole-cell calcium current, preferentially affecting the inactivating component. The Ni2+(-)sensitive current activated and inactivated rapidly in a voltage-dependent manner. Treatment with 0.1 mM cadmium chloride caused a reversible reduction in the amplitude of the calcium current.(ABSTRACT TRUNCATED AT 250 WORDS)

NADPH-diaphorase reactivity in ciliary ganglion neurons: a comparison of distributions in the pigeon, cat, and monkey

Ciliary ganglia from the pigeon, cat, and monkey were investigated for the presence of NADPH-diaphorase reactivity by use of a standard histochemical method. In the pigeon, where the ganglion is known to control lens and pupil function, and the choroidal vasculature, about one-third of the ganglion cells were densely stained and most other somata were lightly stained. In some cases, preganglionic terminals with a cap-like morphology were also darkly stained. The pattern of NADPH-diaphorase staining in mammals was very different from that seen in pigeons. In both mammalian species, where the ganglion is known to control lens and pupil function, a small number (less than 2%) of the ganglion cells were shown to be densely NADPH-diaphorase positive, revealing their neuronal processes. The presence of NADPH-diaphorase positive cells in pigeon, cat, and monkey ciliary ganglia suggests that nitric oxide may be used for intercellular communication in this ganglion, or in light of the known importance of nitric oxide in vascular control, some of these positive neurons may participate in the control of choroidal vasodilation.

Distribution of choline acetyltransferase immunoreactivity in the pigeon brain

We have investigated the distribution of cholinergic perikarya and fibers in the brain of the pigeon (Columba livia). With this aim, pigeon brain sections were processed immunohistochemically by using an antiserum specific for chicken choline acetyltransferase. Our results show cholinergic neurons in the pigeon basal telencephalon, the hypothalamus, the habenula, the pretectum, the midbrain tectum, the dorsal isthmus,the isthmic tegmentum, and the cranial nerve motor nuclei. Cholinergic fibers were prominent in the dorsal telencephalon, the striatum, the thalamus, the tectum, and the interpeduncular nucleus. Comparison of our results with previous studies in birds suggests some major cholinergic pathways in the avian brain and clarifies the possible origin of the cholinergic innervation of some parts of the avian brain. In addition, comparison of our results in birds with those in other vertebrate species shows that the organization of the cholinergic systems in many regions of the avian brain (such as the basal forebrain, the epithalamus, the isthmus, and the hindbrain) is much like that in reptiles and mammals. In contrast, however, birds appear largely to lack intrinsic cholinergic neurons in the dorsal ("neocortex-like") parts of the telencephalon.

Localisation of substance P-like immunoreactivity in the ciliary ganglia of monkey (Macaca fascicularis) and cat: a light- and electron-microscopic study

The present study describes substance P-like immunoreactivity in the ciliary ganglia of monkey (Macaca fascicularis) and cat. About 60% of neurons in the monkey ciliary ganglion and 40% in the cat ciliary ganglion were substance P-like immunoreactive, ranging from faint to moderate staining. Substance P-like immunoreactivity was located in cell bodies, dendritic profiles and axons. In the monkey, substance P-like immunoreactive pericellular arborisations were associated with about 0.5%-3% of the ganglion cells, which were either negatively, faintly or moderately stained. An electron-microscopic study demonstrated the presence of either substance P-like immunoreactive positive or negative axon terminals synapsing or closely associated with positive dendritic profiles in both the monkey and cat ciliary ganglia. The results suggest that substance P plays an important role in the ciliary ganglion, perhaps as a modulator or transmitter.

The peripheral and central projections of the Edinger-Westphal nucleus in the rat. A light and electron microscopic tracing study

The peripheral and central efferent projections of the rostral part of the Edinger-Westphal nucleus in the rat were investigated at the light and electron microscopic level by means of iontophoretic injections of the anterograde tracer Phaseolus vulgaris-leucoagglutinin and retrograde tracer injections of Fast blue and Nuclear yellow into the facial nucleus and into the principal olive. Two pathways leaving the rostral part of the Edinger-Westphal nucleus were studied, a peripheral and a central descending pathway. Fluorescent experiments demonstrated that the central pathway fibers originated from distinct individual Edinger-Westphal neurons. These neurons were mainly distributed throughout the rostral part of the Edinger-Westphal nucleus and had fusiform cell bodies. The neurons rarely form collateral projections. The central descending pathway left the Edinger-Westphal nucleus medially and terminated bilaterally in the principal olive, in the subnuclei A, B and C of the inferior olive and ipsilaterally in the medial accessory olive. The central pathway also terminated contralaterally in the lateral parabrachial nucleus, the facial nucleus, the trigeminal brainstem nuclear complex, the lateral reticular nucleus and the rostroventral reticular nucleus. The projection to the facial nucleus provides evidence for the existence of a polysynaptic loop forming the central part of the corneal blink reflex. Projections from the Edinger-Westphal nucleus to the cerebellar cortex or the deep nuclei, as described in cat and primate, could not be confirmed. The peripheral pathway left the Edinger-Westphal nucleus ventrally and terminated on dendrites of ciliary ganglion cells, along smooth muscle cells of ciliary ganglion associated arterioles and in the proximity of ciliary ganglion associated venules. The central and peripheral terminals that originate in the Edinger-Westphal nucleus all had similar ultrastructural features: clear, round vesicles and electron dense mitochondria. The terminals originating from the central descending pathway were often found to be arranged in glomerular-like structures. The central and peripheral terminals made asymmetric synaptic membrane specializations (Gray type one), except terminals innervating the ciliary ganglion associated vessels, which showed no synaptic contacts.

Ultrastructure of the macaque ciliary ganglion

The primate ciliary ganglion is an obligatory relay in the pathways that control the lens and pupil for the near response and the light reflex, two functions which have been the target of increasing inquiry in behavioural physiology paradigms. This investigation provides a comprehensive description of the ultrastructure of the ciliary ganglion in the rhesus monkey (Macaca mulatta). The results indicate that the ciliary ganglion contains a heterogeneous population of neurons in terms of somatic size, cytoplasmic contents and somatodendritic distribution of terminals. Variations in the clear and dense-cored vesicle content of the synaptic profiles present in the ganglion suggest that the synaptic inputs are also heterogeneous and may mediate separate functions. Several characteristic ultrastructural features of the macaque ciliary ganglion are noteworthy. Despite the large size of the neuronal somata, most cells do not exhibit contacts directly onto the somatic membrane. However, the few somata that do receive direct input often display several axosomatic contacts. The vast majority of synaptic interactions occur in the perisomatic neuropil, where the postsynaptic elements consist of simple and complex somatic appendages, as well as dendrites with their appendages. There is little neuropil independent of these immediately perisomatic regions. In some cases, axonal terminals form the central element of complex glomeruli, in which they are presynaptic to numerous spine-like profiles. In other cases, axon terminals and their postsynaptic targets are found within shallow depressions in the somatic membrane or, occasionally, deeply embedded within the borders of the postganglionic neuron. The somata and all the non-myelinated neuronal elements are surrounded by interdigitating, electron-dense processes of satellite cells. These glial cells are sometimes found in shallow recesses, or deeply embedded within the borders of the neuronal somata. The complexity of the ultrastructure of the ciliary ganglion in the macaque suggests that this ganglion may not be a simple relay in the parasympathetic outflow to the eye, but may instead be the site of neuronal processing of the preganglionic input.