The Prenatal Development of the Human Orbit

During the 1970s, as part of his work for a doctor's thesis in which he described the development of the human orbit in great detail, the first author established the largest anatomical collection of embryonic and fetal orbits ever. Unfortunately, he died before the thesis could be finished. The thousands of sections have now been scanned at high resolution and made publicly available on the Internet at www.visible-orbit.org; 3-D reconstruction software is being developed. The Discussion and part of the 'Methods' section of this thesis are published in translation in this article. The conclusions of the first author at the time read as follows: (1) initially, the developing orbit is vaguely indicated by condensations in the mesenchymal connective tissue area; (2) in this connective tissue area, chondral, osseous and muscular structures develop and grow until, in the fully developed stage, the orbital content is surrounded by bony surfaces with a thin layer of connective tissue as periosteum, and by a muscle fragment; (3) the embryonic and early fetal phase, during which one can only speak of a 'regio orbitalis,' is followed by a period in which we can speak of a primordial orbit; (4) the phase of the primordial orbit extends until after birth; (5) the surface area of all orbital walls increases more or less linearly; (6) the 'musculus orbitalis Mülleri' occupies a special place in the orbital wall; (7) the so-called 'regio craniolateralis' is the primordium, which, in the fully developed stage, is occupied by the thick intersection of the frontolateral and the horizontal part of the frontal bone; (8) in the frontal plane, the shape of the primordial orbit, as well as that of the fully developed orbit, is more or less round; (9) the prenatal development of an eye socket is a complex event, characterized by changes in composition, shape and size of the orbital wall; and (10) the orbit can only be denoted by the term "eye socket" when it is fully developed. At the end of the thesis, he also presented the following postulates: (1) in the prenatal orbit, the development of the so-called 'periorbita' is at the forefront; (2) the mutual rotation of the orbital axes and the frontalization of the eyes from approx. 180 degrees in the early prenatal stages to approx. 50 degrees in adulthood do not seem to be caused by mechanical influences of the surrounding tissue; (3) the pterygopalatine fossa and the 'cavum cerebri' are not part of the orbit at any developmental stage; (4) in the prenatal skull, the inferior nasal concha, which forms part of the maxilla in the fully developed skull, is part of the 'capsula nasalis'; and (5) in order to achieve normal development of the eye socket in microphthalmus and anophthalmus, the normal orbital content should be restored.

The involvement of glutamate-gated channels in negative feedback from horizontal cells to cones

Photoreceptors are the light sensitive cells in the retina. They project to horizontal cells and bipolar cells via a glutamatergic feed forward pathway. Horizontal cells are strongly electrically coupled and integrate in that way the input from the photoreceptors. Horizontal cells feedback to cones negatively. The combined signal from the photoreceptors and the horizontal cells is sent to the bipolar cells. The feedback pathway from horizontal cells to cones is thought to form the basis for the center/surround organization of bipolar cells. The nature of the feedback pathway is an issue of intense debate. It was thought for a long time that this feedback pathway was GABAergic, because cones have GABA-receptors and horizontal cells release GABA via a GABA-transporter working in the reversed direction. However, recently we showed in goldfish that horizontal cells feed back to cones via an alternative mechanism. In goldfish, negative feedback from horizontal cells to cones shifts the calcium current of the cone to more negative potentials. This feedback pathway is independent of GABA, since feedback cannot be blocked by either saturating concentrations of PTX, the GABA-transporter blocker SKF89976A, or application of GABA. The mechanism of negative feedback from horizontal cells to cones involves hemichannels located at the tips of the invaginating horizontal cells, just opposite to the calcium channels of the cones. Current flowing through these hemichannels changes the extracellular potential deep in the synaptic cleft and in that way modulates the calcium current of the cones. Such a modulation of the extracellular potential is called ephaptic. If negative feedback from horizontal cells to cones is indeed ephaptic, other channels present in the synapse should also be able to act as a current source, i.e., should also be able to change the output of the cone. We showed that glutamate-gated channels present at the tips of the horizontal cell dendrites can also mediate feedback responses. Surprisingly, although the glutamate-gated conductance of the horizontal cells is eight times the hemichannel conductance, glutamate-gated channels are not the major current source in negative feedback from horizontal cells to cones. In this chapter we present evidence that this is due to the more focal localization of the hemichannels, compared to a diffuse and extrasynaptic localization of the glutamate-gated channels.

Localization of the AMPA subunit GluR2 in the outer plexiform layer of goldfish retina

L-glutamate, the photoreceptor neurotransmitter, depolarizes horizontal cells and OFF bipolar cells by ionotropic AMPA-glutamate receptors. The AMPA-receptor subunit (GluR4) is localized to dendrites of OFF bipolar cells in goldfish retina. Here, we used immunohistochemical techniques to identify AMPA-receptor subunits on horizontal cell dendrites. A monoclonal antibody against rat GluR2, with high sequence homology to the recently cloned goldfish GluR2a receptor, was used for light- and electron-microscopical immunocytochemistry. Light- and dark-adapted retinas were analyzed, with no major difference in results. GluR2-immunoreactivity (IR) was restricted to a narrow band in the outer plexiform layer, in which it appeared as bright dome-shaped structures amidst numerous puncta. At the ultrastructural level, GluR2-IR was found in horizontal cell dendrites that invaginated cones and rods. Dendrites of OFF bipolar cells were not labeled. GluR2-IR was present mostly in horizontal cell dendrites that were the lateral elements of the triad, rather than in dendrites that were the central elements. In light-adapted retinas, GluR2-IR was found in many horizontal cell spinules. GluR2-IR was observed, on occasion, in a mixed rod/cone (Mb) ON bipolar cell process that innervated rod spherules. Verification of the Mb ON bipolar cell was made by protein kinase C and metabotropic mGluR1alpha immunolabeling. The presence of GluR2-IR in lateral elements suggests that lateral horizontal cell dendrites are postsynaptic to cones rather than only sites of feedback inhibition. All horizontal cell types express the GluR2 subunit, uniquely differentiating themselves from OFF bipolar cells that express the GluR4 subunit. This differentiation most likely has a major influence on the glutamate pharmacology and response kinetics of these cell types to glutamate.

Analysis of the cellular infiltrate in the iris during experimental autoimmune encephalomyelitis

PURPOSE

Previous studies have shown that experimental autoimmune encephalomyelitis (EAE) and anterior uveitis (AU) develop in Lewis rats immunized with myelin basic protein (MBP). The purpose of this study was to characterize the dynamics, distribution, and phenotype of infiltrating cells in the iris during EAE-associated AU.

METHODS

Lewis rats were immunized with MBP emulsified in complete Freund's adjuvant (CFA) or with CFA alone. Cellular infiltration of the iris was analyzed at various time points by immunohistochemistry of wholemounts, flow cytometry, and immunoelectron microscopy, by using monoclonal antibodies specific for monocytes/macrophages (ED1), T lymphocytes (R73, W3.25, OX8), T-cell activation markers (OX39, OX40), granulocytes (HIS48), major histocompatibility complex (MHC) class II (OX6), and neurofilament (2H3).

RESULTS

MBP-immunized rats showed development of characteristic monophasic EAE, followed, after resolution of paralysis, by mild self-limited AU. Initially, focal infiltrates of round MHC class II(+) and ED1(+) cells were found in the iris. During the course of AU, the midiris became massively infiltrated with ED1(+) monocytes-macrophages, R73(+) T cells, granulocytes (HIS48(+)), and MHC class II(+) cells. The influx of T cells consisted of CD4(+) and CD8(+) cells, of which only a small fraction (<14 and 11%, respectively) expressed activation markers. The infiltrating cells accumulated in proximity to myelinated and nonmyelinated nerve bundles and in the vicinity of blood vessels in the iris. No evidence was found for demyelination or nerve degradation. Neither EAE nor AU developed in CFA-treated control rats.

CONCLUSIONS

These data show that EAE-associated AU is characterized by a transient mixed cellular infiltrate consisting of monocytes-macrophages, granulocytes, and CD4 and CD8 T cells. The preferential accumulation of inflammatory cells in the vicinity of nerve fibers suggests that AU in this model may result from autoreactivity to nerve antigens.

Immunohistochemical localization of substance P and substance P receptor (NK1) in the olivary pretectal nucleus of the rat

The olivary pretectal nucleus (OPN) is the first central nucleus in the pupillary light reflex arc (PLR). Substance P (SP) is a neuropeptide present in the OPN. The present immunohistochemical study, performed at the ultrastructural level, aimed to determine the synaptic localization of SP and SP receptor in the OPN. Three types of SP-positive terminals were found. The most abundant type was of retinal origin, characterized by electron-lucent mitochondria and round vesicles, organized in glomerular structures, making asymmetric synaptic contacts with dendrites, and profiles containing pleomorphic vesicles, also making synaptic contacts with dendrites. The second type of SP-immunoreactive terminal contained electron-dense mitochondria and pleomorphic vesicles. This type made symmetric synaptic contacts and may originate from the ventral part of the lateral geniculate nucleus. The third type of SP-immunoreactive terminals contained electron-dense mitochondria, clear round vesicles, and made an asymmetric synaptic contact. This type originates from the contralateral OPN. SP receptors of the NK1 subtype were revealed to be on dendrites and were part of the glomerular-like arrangement. On account of the present observations, it can be concluded that retinal projections to the OPN use SP as a neuromodulator and synapse on NK1 receptor-containing dendrites of large neurons projecting to the Edinger-Westphal nucleus. Since SP also modulates the parasympathetic component of the PLR, we postulate that SP plays a modulating role in all components of the PLR.

New indirect pathways subserving the pupillary light reflex: projections of the accessory oculomotor nuclei and the periaqueductal gray to the Edinger-Westphal nucleus and the thoracic spinal cord in rats

The pupillary light reflex (PLR) is under the control of retinal ganglion cells projecting to the olivary pretectal nucleus (OPN). The OPN has a major projection to the Edinger-Westphal (EW) nucleus, which exerts its parasympathetic action on the iris musculature via the ciliary ganglion. The accessory oculomotor nuclei (AON) and the periaqueductal gray (PAG) receive input from the OPN and influence the PLR. The present study in rats aimed to elucidate the possible projections from the AON and PAG to the EW nucleus. The anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L) was iontophoretically injected into the interstitial nucleus of Cajal (INC), the nucleus of the posterior commissure (NPC), the nucleus of Darkschewitsch (ND) and the rostral part of the PAG. The projections were studied at the light and electron microscopic level. The INC, NPC and ND have small projections to the EW nucleus, whereas the rostral part of the PAG densely projects to the EW nucleus. Without exception INC, NPC, ND and PAG varicosities are presynaptic to dendritic profiles in the EW nucleus and contain electron dense mitochondria, round vesicles and make asymmetric synaptic contacts. In addition the ND and PAG project to the thoracic level of the spinal cord. The fibres are presynaptic to dendritic profiles and contain electron dense mitochondria, round vesicles and make asymmetric synaptic contacts. The present observations allow the conclusion that the parasympathetic preganglionic neurons in the EW nucleus are not only controlled by the OPN-EW pathway but also by indirect pathways running via the AON and PAG. Moreover light-sensitive information is also transferred via an OPN-PAG-spinal cord pathway to the sympathetic superior cervical ganglion (SCG) that innervates the iris, suggesting that the PAG may have an integrative function in the sympathetic and parasympathetic control of the PLR.

Ciliary muscle capillaries have blood-tissue barrier characteristics

It was determined whether the capillaries in the ciliary muscle are of the blood-tissue barrier or of the permeable non-barrier type. Ciliary body and iris of normal human and animal eyes were examined by electron microscopy and by immunohistochemical staining with a panel of antibodies recognizing endothelial blood-brain barrier markers. In addition, horseradish peroxidase (HRP) tracer studies of the anterior segment were carried out in rabbits. Our results demonstrated that the capillary endothelium in human and rabbit ciliary muscle has few luminal pinocytotic vesicles and a morphological aspect suggesting the presence of tight junctions. Ciliary muscle and iris capillaries stained positive for the blood-brain barrier markers Glucose-Transporter-1 and P-Glycoprotein, while staining for the PAL-E antigen and the transferrin receptor was absent. In the rabbit ciliary muscle, vascular leakage of exogenous HRP tracer was absent. It was concluded that this functional barrier and the observed phenotype of ciliary muscle capillaries are consistent with a blood-tissue barrier function similar to that of the iris microvasculature.

Tract-tracing in the nervous system of vertebrates using horseradish peroxidase and its conjugates: tracers, chromogens and stabilization for light and electron microscopy

Surprisingly the first generation of tract-tracing techniques based on intra-axonal transport, that is the methods utilizing the uptake and transport of horseradish peroxidase (HRP), still rank among the most widely used neuroanatomical tracing techniques. The success of these methods can be ascribed to several characteristics. They are fast and easy to implement. Complicated injection apparatus is unnecessary. The reaction products are visualized through simple histochemical reactions, and they are permanent or can be stabilized into permanency. Most usefully, the reaction products are visible in the light and electron microscopes. HRP (mol. wt. 44 kDa) is extracted from the roots of the horseradish plant (Cochlearia armoracia L.). Uptake of HRP into cells occurs via a passive process of endocytosis. Since lectins like wheat germ agglutinin (WGA) and bacterial toxin fragments (subunit B of cholera toxin (CTB)) strongly induce active, receptor-mediated uptake mechanisms, conjugates of these substances with HRP have been successfully applied in sensitive tract-tracing HRP and its conjugates are transported both in anterograde and retrograde direction. Retrograde transport occurs in small vesicles that are incorporated in lysosome-like vacuoles and in the Golgi apparatus. These vesicles differ in membrane properties from the anterogradely transported HRP vesicles. The retrogradely transported vesicles tend to fuse and thus accumulate HRP at high densities, facilitating the visibility of the final reaction product. The anterogradely transported HRP does not accumulate directly in lysosome-like bodies and is distributed diffusely and therefore often requires specific visualization methods. HRP and WGA-HRP may therefore be used in anterograde and retrograde transneuronal (multineuron) transport studies. Even in fixed material, labeling through diffusion of HRP can provide details on neural connections. Visualization of transported HRP is achieved by means of using the oxidative enzymatic activity of HRP to precipitate a chromogen according to the following reaction: [symbol: see text] The final reaction product may be soluble in buffer or ethanol and may require stabilization to prevent fading. In this protocol we discuss the widely used chromogens 3,3'-diaminobenzidine tetrahydrochloride (DAB), 3,3',5,5'-tetramethylbenzidine (TMB), benzidine dihydrochloride (BDHC) and p-phenylenediamine dihydrochloride with pyrocatechol (PPD-PC). Other possible chromogens, not discussed here, are 4-chloro-1-naphthol (4C1N), 3-amino-9-ethylcarbazole (AEC) and o-phenylenediamine (OPD). The visualization of the reaction product can be further improved by intensification with metal salts. At the light microscopic level (LM) this intensification enables color differentiation between distinct markers. In the present protocol we provide an up-to-date guideline for the application of HRP and its conjugates in tracing with special emphasis on electron microscopic (EM) visualization. Some modifications for stabilization and of metal intensification to enhance visibility are incorporated in conjunction with specific methods for multiple labeling in combined tract-tracing experiments.

The ultrastructure of the olivary pretectal nucleus in rats. A tracing and GABA immunohistochemical study

The olivary pretectal nucleus is a primary visual centre, involved in the pupillary light reflex. In the present study an ultrastructural analysis was made of the olivary pretectal nucleus by means of separate, anterograde and retrograde tracing techniques and immunohistochemistry of gamma-aminobutyric acid. Large-projection neurons and two types of gamma-aminobutyric acid-immunoreactive (GABA-ir) neurons are observed in the olivary pretectal nucleus. The primary dendrites of the projection neurons have a dichotomous appearance, the secondary dendrites a multipolar appearance. At the ultrastructural level the projection neurons have well-developed Golgi fields, abundant rough endoplasmic reticulum and the nucleus is always heavily indented. Numerous small GABA-ir neurons and a few medium-sized GABA-ir neurons are found. The small GABA-ir neurons contain a few stacks of rough endoplasmic reticulum and the nucleus is oval-shaped. The medium-sized GABA-ir neurons have well-developed Golgi fields, a moderate number of rough endoplasmic reticulum stacks and an indented nucleus. GABA-positive dendritic profiles containing vesicles also are observed. In the neuropil of the olivary pretectal nucleus, retinal terminals are found that contain round clear vesicles and electron-lucent mitochondria. They make asymmetric synaptic contacts (Gray type I) with dendritic profiles and with profiles containing vesicles. Terminals originating from the contralateral olivary pretectal nucleus exhibit small, round clear vesicles, electron-dense mitochondria and make asymmetric synaptic contacts (Gray type I) mainly with dendritic profiles. Two types of GABA-ir terminals were found. One type is incorporated in glomerulus-like arrangements, whereas the other type is not. GABA-ir terminals contain pleomorphic vesicles, electron-dense mitochondria and make symmetric synaptic contacts (Gray type II). Retinal terminals, terminals originating from the contralateral olivary pretectal nucleus and GABA-ir terminals are organized in glomerulus-like structures, in which dendrites of the large projection neurons form the central elements. Triadic arrangements are observed in these structures; a retinal terminal contacts a dendrite and a GABA-ir terminal and the GABA-ir terminal also contacts the dendrite. The complexity of the synaptic organization and the abundancy of inhibitory elements in the olivary pretectal nucleus suggest that the olivary pretectal nucleus is strongly involved in processing visual information in the pupillary light reflex arc.

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.

Efferent synaptic organization of the olivary pretectal nucleus in the albino rat. An ultrastructural tracing study

In this study an ultrastructural analysis was made of the efferent projections of the olivary pretectal nucleus in the rat. The anterograde tracer Phaseolus vulgaris leucoagglutinin was injected iontophoretically into the olivary pretectal nucleus. Ascending and descending pathways were studied. In the descending pathway special attention was paid to the fine structural features of the olivary pretectal nucleus efferents projecting to the Edinger-Westphal nucleus, the interstitial nucleus of Cajal, the nucleus of Darkschewitsch and the periaqueductal gray. The projection to the superior colliculus and the pontine nucleus was also studied at the ultrastructural level. All the labeled terminals in the descending pathway showed ultrastructurally similar features: clear, round vesicles and electron dense mitochondria. The terminals made asymmetric synaptic membrane specializations (Gray type I), the postsynaptic profiles were dendritic. In the interstitial nucleus of Cajal and the superior colliculus the terminals are organized in glomerulus-like structures. The terminals in the descending pathway were enwrapped by astrocytic processes, also in the glomerulus-like structures. In the ascending pathway the projection to the ventral part of the lateral geniculate nucleus was studied. Almost all terminals in the ascending pathway showed similar ultrastructural features as in the descending pathway: electron dense mitochondria, clear, round vesicles and asymmetric synaptic membrane specializations (Gray type I). The terminals are organized in glomerulus-like structures. To identify the projecting neurons in the interstitial nucleus of Cajal and the Edinger-Westphal nucleus, retrograde tracing experiments were performed. Therefore the beta subunit of cholera toxin conjugated with horseradish peroxidase was injected into the facial nucleus.(ABSTRACT TRUNCATED AT 250 WORDS)

Efferent projections of the olivary pretectal nucleus in the albino rat subserving the pupillary light reflex and related reflexes. A light microscopic tracing study

The olivary pretectal nucleus is a primary visual centre sensitive to luminance changes. It is involved in the pupillary light reflex, the consensual pupillary light reflex and related reflexes, such as the lid closure reflex whereby pupillary constriction takes place. Since the olivary pretectal nucleus is a small nucleus, previous studies using degeneration, horseradish peroxidase and radioactive amino acid tracing were limited regarding to the exclusiveness of the projections from the olivary pretectal nucleus. In the present study the position of the olivary pretectal nucleus in the rat was first localized by physiological recording of the neurons upon luminance stimulation. Subsequently, an anterograde tracer Phaseolus vulgaris leucoagglutinin was injected iontophoretically. This allows a much more precise localization of the olivary pretectal nucleus projections. Ascending and descending pathways originating from the olivary pretectal nucleus were observed. Ascending fibres project bilaterally to the intergeniculate leaflet, the ventral part of the lateral geniculate nucleus and ipsilaterally to the anterior pretectal nucleus. In addition, contralateral projections were observed to the zona incerta and the fields of Forel. Descending fibres project bilaterally to the periaqueductal gray, the nucleus of Darkschewitsch, the interstitial nucleus of Cajal, the Edinger-Westphal nucleus and the intermediate gray layer of the superior colliculus. Also a contralateral projection to the oculomotor nucleus and an ipsilateral projection to the pontine nucleus and the nucleus of the optic tract were found. Furthermore, the contralateral olivary pretectal nucleus received a small projection. Retrograde tracing experiments using two fluorescent dyes revealed that the fibres projecting to the contralateral olivary pretectal nucleus and to the contralateral interstitial nucleus of Cajal are collaterals. The projection from the olivary pretectal nucleus to the facial nucleus which has been described to receive an input in cats could not be confirmed for the rat. The fact that the Edinger-Westphal nucleus, the interstitial nucleus of Cajal and the superior colliculus receive an input from the olivary pretectal nucleus suggests that this primary visual centre is not only involved in the pupillary light reflex, but also in controlling eye and head position and saccadic eye movements. Although visual acuity largely depends on receptive field sizes of retinal ganglion cells and their central connections, the stronger sympathetic influence during the pupillary light reflex in animals with frontally placed eyes compared to animals with laterally placed eyes may also contribute to the higher visual acuity in animals with frontally placed eyes.

Peripheral neural circuits regulating IOP? A review of its anatomical backbone

The peripheral nervous system is classically separated into a somatic division containing both afferent and efferent pathways and an autonomic division composed of efferents only. The somatic afferent division is divided in A- and B-neurons. The B-neurons are supposed to be autonomic afferents as part of a reflex system involved in homeostasis. Recent data obtained by neuronal tracing and immunohistochemical experiments concerning the eye related peripheral nervous system endorse the existence of these peripheral reflex systems. Somatic afferents of trigeminal origin synaptically innervate parasympathetic neurons in the pterygopalatine ganglion. This probably represents a pathway mediating autonomically regulated ocular activity in response to sensory stimulation. In addition, it has been hypothesized that trigeminal sensory nerve fibres have an efferent function in response to noxious stimuli e.g. the ocular injury response. Sympathetic nerve fibres originating in the superior cervical ganglion course through the trigeminal and pterygopalatine ganglion without forming direct synaptic contacts. These fibres, however, contain clusters of vesicles suggesting some kind of interneural communication. Parasympathetic nerve fibres of pterygopalatine origin course through the ciliary ganglion. These nerve fibre terminals also contain clusters of vesicles without direct synaptic contacts. Experimental data concerning the distribution of neuropeptides revealed a more detailed knowledge of the anterior eye segment innervation. These experimental data are subject to some debate. The pros and cons of different techniques are discussed. Neural circuits regulating IOP have long been postulated. The possible role of peripheral reflex systems in the regulation of IOP is discussed.

Sympathetic innervation of the rat's eye and peripheral ganglia: an electron microscopic autoradiographic tracing study

The sympathetic innervation of the rat anterior eye segment and related peripheral ganglia was studied using light and electron microscopic autoradiography after anterograde tracing with 3H-leucine from the superior cervical ganglion. In the trigeminal and pterygopalatine ganglia, unmyelinated nerve fibers were labeled. Some fibers contained accumulations of small vesicles. Close apposition of these labeled sympathetic fibers with other unmyelinated fibers was common, and was also observed at sites where accumulations of vesicles were found. In the iris, ciliary body and trabeculum, numerous fibers and vesicle-containing varicosities were labeled, which all had a similar morphology. No labeling was found in the cornea. Sympathetic fibers traversing the trigeminal and pterygopalatine ganglion closely appose other unmyelinated fibers and contain clusters of vesicles without forming classical synaptic contacts. However, non-synaptic information transfer needs further investigation. The anterior eye segment, except for the cornea, is densely innervated by sympathetic nerve terminals.

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.

Annual review of selected dental literature: report of the Committee on Scientific Investigation of the American Academy of Restorative Dentistry

The annual review of selected dental literature this year cites 384 published papers and reports. This year's review contains more editorial comment than reviews of years passed. New data on the biological responses to materials is emphasized in several sections. Observations on new compounds able to prevent plaque formation are presented. Clinically relevant advances in knowledge concerning the etching of different tooth structures are reported along with the effect of etching procedures on the dental pulp. Evaluation of periodontal diseases in all age groups is a topic. Limitations of current diagnostic techniques in periodontal disease, temporomandibular disorders, and implant therapy are included. There are new views on the use of dental amalgam. The future use of dental mercury is predicted. Interest in new ceramic systems is indicated as the demand for esthetics continues. Clinical information is emphasized over scientific information throughout this year's review.

Facial parasympathetic innervation of the rat choroid, lacrimal glands and ciliary ganglion. An ultrastructural pterygopalatine tracing and immunohistochemical study

The pterygopalatine parasympathetic innervation of the rat choroid, lacrimal glands and ciliary ganglion was ultrastructurally studied by anterograde 3H-leucine tracing. Numerous unmyelinated fibers and vesicle-containing terminals were labeled in these structures. No direct synaptic contacts were found. In the choroid, similar terminals were immunoreactive to vasoactive intestinal polypeptide (VIP). A regulatory feedback loop within the eye-related peripheral nervous system is endorsed by the present results. The finding of fibers and terminals of pterygopalatine origin in the lacrimal glands agrees with earlier studies in cats and monkeys. In the ciliary ganglion, pterygopalatine terminals most likely influence the ganglion cells by nonsynaptic release of neurotransmitters or neuromodulators including VIP.

Substance P in rat corneal and iridal nerves: an ultrastructural immunohistochemical study

The distribution of substance P (SP) within the nerve fibers of the rat cornea and iris was studied using electron microscopic immunohistochemistry. Numerous SP-immunoreactive fibers were found throughout the corneal and iridal stroma. The most intense staining was found within varicosities containing numerous vesicles. Similar SP-immunoreactive varicosities were found in fibers in close proximity to the iris sphincter and dilator muscles. On account of previous ultrastructural work the SP-containing fibers and varicosities must be assumed to be of trigeminal origin. Additionally, the distribution of SP and calcitonin gene-related peptide (CGRP) in corneal and iridal fibers of rats is similar, suggesting that CGRP and SP are colocalized and may be coreleased from the same varicosities.

Report of the Committee on Scientific Investigation of the American Academy of Restorative Dentistry

The committee screened several hundred articles, citing 518 published papers. Some are present quality in research, others provide clinical interest, and some are identified as misleading. New techniques in pulp physiology and pathology are reported. Laser use and techniques in prevention, restorative dentistry, and materials use are reported. Epidemiology of selected diseases and the results of various formulations for treatment are cited. Diagnosis of craniomandibular dysfunction is well represented as well as references to literature reviews and other sophisticated scientific investigation. Research on adhesives is presented in respect to bonding agents for dentin and enamel. Several clinical studies are included, along with customary laboratory reports on several materials.

Ultrastructural identification of trigeminal nerve endings in the rat cornea and iris

Trigeminal nerve terminals in the rat cornea and iris were ultrastructurally identified using anterograde tracing with Phaseolus vulgaris-leukoagglutinin (PHA-L). Electron microscopic immunohistochemistry was used to demonstrate the presence and localization of calcitonin gene-related peptide (CGRP) in cornea and iris. In the cornea and iris, nerve fibers were labelled with PHA-L throughout the stroma. Labelling was most obvious within varicosities, densely packed with mainly clear and a few granular vesicles and containing dark mitochondria. Numerous fibers in the stroma of cornea and iris were CGRP-positive. CGRP-positive staining was most intense within varicosities, containing mainly clear and incidentally granular vesicles and dark mitochondria, similar to the structures labelled with PHA-L. CGRP-positive varicosities packed with mainly clear and few granular vesicles also were demonstrated in fibers adjacent to the sphincter and dilator muscles of the iris. In the corneal epithelium, small terminals containing vesicles were CGRP-positive. Trigeminal nerve fibers innervating the rat cornea and iris contained numerous varicosities packed with vesicles. These areas are CGRP-positive, so it can be implied that CGRP is released from these varicosities as a response to triggering impulses. This agrees with the hypothesis that in addition to their afferent function, sensory fibers also exert an efferent modulating function.

Elimination of immune precipitates from the rat corneal stroma: a histological study

The pathogenesis of peripheral corneal lesions of immune aetiology, like Mooren's ulcer and catarrhal infiltrates, has been related to the formation or deposition of immune compkexes. The present investigation was undertaken to study the mechanisms involved in the elimination of immune precipitates from the cornea. Immune precipitates were induced by injecting human serum albumin (HSA) and rabbit anti-HSA serum into opposite sites of the rat corneal stroma. This resulted in a line-shaped opacity in the stroma, which remained visible by slit-lamp for 7 days, and disappeared without clinical signs of keratitis and uveitis. At the ultrastructural level, the immune precipitates were clearly visible. Keratocytes in the vicinity of the immune precipitates appeared activated, as suggested by their less flattened appearance and well-developed rough endoplasmic reticulum. The arrangement of the collagen fibrils was not affected. Cells with a macrophage-like morphology were also present and contained electron-dense material, closely resembling the precipitate, suggesting phagocytosis. Separate corneas were injected with latex beads, which is known to induce migration of Langerhans cells into the cornea. Immunohistochemical analysis revealed that both latex beads and immune precipitates induced migration of macrophages (ED1+) into the rat corneal stroma. However, differences were observed with regard to the expression of MHC class II antigens by these ED1+ cells and the presence of complement deposits in the corneal stroma. ED1+ cells in corneas injected with latex beads were all MHC class II positive (OX4+), whereas most of the ED1+ cells at the site of the immune precipitates were negative (OX4-).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of strain rate on the behavior of elastomeric impression

The effects of strain rate on the ultimate tensile strength, ultimate elongation at fracture, and elastic recovery of five commonly used elastomeric dental impression materials were studied. Each specimen was prepared by standard mixing techniques, placed for setting in a standard ASTM mold, removed, trimmed, and mounted in an Instron testing unit. Tensile load was applied and plotted on a load versus displacement curve as the specimen was stretched axially until rupture. Five specimens of each material were tested, respectively, at strain rates of 100, 200, and 500 mm/min crosshead speed. Specimens were then removed, reassembled, and measured with an electronic caliper to assess the elastic recovery; measurements were repeated after 1 minute, 30 minutes, 1 hour, and 24 hours. Findings of this study indicated that (1) polysulfide materials exhibited the greatest amount of deformation, and the lowest tensile strengths of the materials studied; (2) higher tensile strengths were observed with higher strain rates; and (3) polysulfide materials showed the greatest amount of elongation at rupture, with the highest values occurring at the higher strain rates.

Ultrastructural identification of trigeminal nerve terminals in the pterygopalatine ganglion of rats: an anterograde tracing and immunohistochemical study

Trigeminal nerve terminals in the rat pterygopalatine ganglion (PPG) were ultrastructurally identified using anterograde tracing with Phaseolus vulgaris-leucoagglutinin (PHA-L). Electron microscopic immunohistochemistry was used to demonstrate the presence of substance P (SP) and calcitonin gene-related peptide (CGRP) in nerve terminals of the PPG. Adjacent to the rostral part of the PPG an additional minor area was described. Perikarya in this minor rostral part were more spherical and had irregular outlines. Ultrastructurally, the glial enwrapment of the nerve terminals seemed to be more loosely arranged in comparison to that in the major rostral part of the PPG. With PHA-L, numerous labelled nerve fibres and terminals were found in all parts of the PPG. The ultrastructure of these terminals was uniform, many of them showing synaptic contacts. Numerous terminals in the PPG were SP-positive, whereas only a few were CGRP-positive. Fibres stained positive for both neuropeptides. The PPG is shown to be synaptically innervated by sensory fibres arising in the trigeminal ganglion, with the strong suggestion of SP and CGRP acting as neurotransmitters. A modulatory interaction between the autonomic and sensory system, resembling an axon reflex mechanism in the peripheral nervous system is endorsed.

Report of the Committee on Scientific Investigation of the American Academy of Restorative Dentistry

Subjects of the past decade in the dental literature are reflected in this year's Committee report. We note the decrease in the prevalence of caries, the influence of dental implants, the advancements in dental materials, and the continued efforts to control adhesive events in the oral cavity. This year we included comments from and about many significant review articles published this past year. The Committee continues to be concerned about the quality of some of the work reported and the quality of the reporting. We have attempted to select the distinguished work, that which provides new information to our profession. The subjects covered include pulp biology, caries prevention, periodontics, implants, craniomandibular function and dysfunction, occlusion, and dental materials.

Report of the Committee on Scientific Investigation of the American Academy of Restorative Dentistry

The growth in the dental literature continues to escalate, as evidenced by the publication of at least 326 new books in 1988 and 1989 and more than 20 new journals in 1989. There still appears to be undue emphasis on quantity instead of quality of research. This proliferation in the literature poses ever increasing difficulties to this Committee in filtering out the articles that are of particular interest to the members of the Academy and identifying those that are most likely to have a major impact on dental practice and service. The subjects covered include periodontics, caries and preventive dentistry, craniomandibular disorders, occlusion, pulp biology, ceramics, and restorative dental materials.

Pre- and post-ganglionic nerve fibres of the pterygopalatine ganglion and their allocation to the eyeball of rats

The origin, course and distribution of pre- and postganglionic neurons of the pterygopalatine ganglion (PPG) in the rat were studied using acetylcholinesterase staining, wheat germ agglutinin coupled to horseradish peroxidase (WGA-HRP) histochemistry and autoradiography. These methods were used in a selected and planned fashion to reveal details concerning the innervation of the lacrimal gland and portions of the eye. The PPG in rats consists of a rostral triangular portion and additional perikarya surrounding the distal part of the major petrosal nerve. Fibres from the superior cervical ganglion (SCG) reach the PPG via the inferior petrosal sinus. Application of WGA-HRP was made after transections: (1) rostral to the PPG; and (2) caudal to the PPG. The first of these applications labelled mainly fibres in the PPG; the second application labelled preganglionic parasympathetic brainstem neurons dorsolateral to the facial nucleus (i.e. the lacrimal nucleus), rostral cells in the SCG and trigeminal sensory fibres. WGA-HRP injections of the lacrimal gland, the conjunctiva and the anterior chamber of the eye all labelled cells in different parts of the PPG. This means that the PPG contains sensory and sympathetic nerve fibres and that the PPG has a topographical organisation along the rostrocaudal axis. Isotope injections of the PPG anterogradely labelled fibres passing through the ciliary ganglion that innervated the conjunctiva, the limbus and parts of the choroid.

The allocation of nerve fibres to the anterior eye segment and peripheral ganglia of rats. I. The sensory innervation

The distribution of sensory trigeminal nerve fibres in the anterior eye segment and the autonomic eye related ganglia, i.e. the parasympathetic ciliary and pterygopalatine ganglia and the sympathetic superior cervical ganglion, was studied in rats. For this the trigeminal ganglion was injected with tritiated leucine and wheat germ agglutinin coupled to horseradish peroxidase (WGA-HRP). After injection of WGA-HRP into the trigeminal ganglion, ganglion cell somata in the superior cervical and the pterygopalatine ganglion were labelled. As labelling of these cell bodies with WGA-HRP is the result of retrograde transport it must be assumed that cell bodies in these ganglia project to the trigeminal ganglion. [3H]Leucine injection into the trigeminal ganglion revealed the presence of labelled nerve fibres in the pterygopalatine ganglion and the nodose ganglion i.e. the sensory ganglion of the vagus nerve. Labelled nerve fibres were absent in the ciliary and superior cervical ganglion. As [3H]leucine labelling of nerve fibres is the result of anterograde transport exclusively, it can be concluded that trigeminal nerve fibres project to the nodose ganglion and the pterygopalatine ganglion, but not to the ciliary and superior cervical ganglion. In the retrobulbar structures, sensory nerve fibres occurred between the inferior oblique and the lateral rectus muscle and were present medial to the medial rectus muscle. Within the anterior eye segment, sensory nerve fibres were found in the cornea epithelium, stroma and adjacent to the endothelium. In addition, labelled fibres were found in the anterior stroma of the ciliary body, throughout the iris up to the pupillary border and in the conjunctiva. Most sensory nerve fibres which innervate the cornea, the iris and the ciliary body traverse the ciliary cleft.

The allocation of nerve fibres to the anterior eye segment and peripheral ganglia of rats. II. The sympathetic innervation

The sympathetic innervation of the peripheral ganglia related to the eye, i.e. the trigeminal ganglion, the ciliary ganglion and the pterygopalatine ganglion, and of the anterior eye segment was studied in rats. Selective labelling of sympathetic nerves was obtained by means of injection of [3H]leucine into the superior cervical ganglion. Bundles of sympathetic nerve fibres were found in the trigeminal ganglion and the pterygopalatine ganglion but were absent in the ciliary ganglion. In addition individual sympathetic nerve fibres, which may have contacts with trigeminal ganglion cells, were found between the ganglion cell bodies all over the trigeminal ganglion indicating a sympathetic innervation of this ganglion. In the anterior eye segment, there appeared to be a sympathetic innervation of the ciliary cleft, the ciliary body and the iris. Within the ciliary body sympathetic nerve fibres innervate the central stroma and the stroma of the ciliary processes. Labelled sympathetic nerve fibres were also observed in the stroma of the iris and were most abundant in its periphery. Most sympathetic fibres reach the iris and ciliary body by way of the base of the ciliary body. Only few sympathetic fibres are present in the ciliary cleft. No sympathetic innervation of the cornea was found.

Report of the Committee on Scientific Investigation of the American Academy of Restorative Dentistry

Dental research continued to grow during 1988. Unfortunately the quality does not always parallel the quantity of publications. This report obviously does not encompass all of the literature but focuses on studies that are related to trends and to matters that are considered controversial. Likewise the particular interests of the members of the American Academy of Restorative Dentistry were taken into consideration. The subjects covered include periodontics, preventive dentistry, bulp biology, craniomandibular disorders, ceramics, color in restorative dentistry, and dental materials.

Satellite cells as blood-ganglion cell barrier in autonomic ganglia

In a preliminary study a difference in the uptake and transport of wheat germ agglutinin-horseradish peroxidase (WGA-HRP) between the trigeminal ganglion and the superior cervical ganglion was observed. After injection of WGA-HRP and HRP into the trigeminal ganglion, peroxidase was found in the space between the satellite cell processes and the ganglion cells. The ganglion cells showed pinocytosis and uptake of WGA-HRP and HRP. In the superior cervical ganglion WGA-HRP and HRP were found alongside the satellite cells but were absent in the space between satellite cells and ganglion cells. Intravenous injection revealed the presence of HRP in the space between sensory ganglion cells and their satellite cells of the trigeminal and nodose ganglion whereas HRP was absent in the space between autonomic ganglion cells and their satellite cells of the superior cervical, medial cervical and pterygopalatine ganglion although HRP lined the satellite cell membranes. By means of electron microscopy, satellite cell processes in the superior cervical ganglion were found to enwrap ganglion cells very tightly with a marginal space between both cell types. Satellite cells and their processes were mutually anchored by numerous tight junctions. In the trigeminal ganglion the extracellular space between ganglion cells and satellite cells was larger and satellite cells were found to be more loosely arranged around the ganglion cells. Satellite cell processes were only occasionally linked by tight junctions. It is concluded that satellite cells in autonomic ganglia comprise an effective barrier for WGA-HRP and HRP and probably large molecules in general. This barrier is absent in sensory ganglia.

The innervation of the rabbit's anterior eye segment: a retrograde tracing study

The differential innervation of the distinct elements of the anterior segment of the rabbit eye, i.e. cornea, conjunctiva, ciliary body, iris, and trabecular meshwork, was studied using horseradish peroxidase-wheatgerm agglutinin (HRP-WGA) as a tracer. HRP-WGA was injected into the anterior chamber, the conjunctiva, or the cornea, and the animals were killed after 6 to 96 hr. The HRP-WGA localization was studied at the light and electron microscopic level. Injection into the anterior chamber led to an ubiquitous spread of the tracer in all elements of the anterior segment, resulting in a consistent retrograde labelling of neurons in the trigeminal (sensory), superior cervical (sympathetic) and ciliary (parasympathetic) ganglion. Neurons in the proximal part of the pterygopalatine ganglion (parasympathetic) were labelled only when the injected tracer was present in the conjunctiva. Varying survival times after corneal injection were used to establish restricted corneal uptake. Up to 16 hr after corneal injection, HRP-WGA was limited to the cornea and led to the exclusive labelling of neurons in the trigeminal ganglion, indicating that the central cornea has an almost exclusive sensory innervation. The trigeminal sensory neurons projecting to the cornea were restricted to a small antero-medial part of the trigeminal ganglion. Electron microscopy revealed four different cell types in the trigeminal ganglion. However, distinct elements of the anterior segment did not project to specific cell types.

Potassium ferricyanide: a stabilizer for horseradish peroxidase

Sodium nitroprusside has been used as a stabilizing agent for HRP histochemistry since 1919. However, it is known to have toxic effects orally, intravenously, and subcutaneously. In order to avoid the use of sodium nitroprusside as a stabilizer in HRP histochemistry, we have tested other chemically related compounds to stabilize the reaction product equally well. We will show that potassium ferricyanide is an excellent stabilizer of the chromogen reaction product. In addition, the reaction product remains stable without noticeable changes over a period of several months. As it is far less toxic than sodium nitroprusside, it should be the stabilizer of choice, especially in those laboratories where the histochemical HRP reaction is used frequently.

Retinopretectal projections in albino and pigmented rabbits: an autoradiographic study

The ipsilateral and contralateral retinal projection was studied in pigmented rabbits and in 3 strains of albino rabbits by anterograde transport of [3H]proline and [3H]fucose combined with autoradiographic techniques. Special attention was paid to the terminals in the pretectal area of both the pigmented and albino strains. On the contralateral side terminal labeling was found in both pigmented and albino rabbits in the nucleus of the optic tract (NOT), the anterior pretectal nucleus (PA), the posterior pretectal nucleus (PP) and the pretectal olivary nucleus (PO). Ipsilaterally labeling was found only in the pigmented strain in small patches in the PP. Ipsilateral projection was not found in the albinos in the pretectal area. The results are in agreement with the findings of Scalia in pigmented rabbits. The absence of ipsilateral labeling in the pretectal region in albinos is in contrast with earlier findings of Giolli and Takahashi et al., in pigmented rabbits but is in agreement with the observations of Takahashi and Oyster. Since no radioactively labeled fibers were found to project to the NOT in either pigmented or albino rabbits, these results do not support the hypothesis of Collewijn that the inverted optokinetic nystagmus in albinos is due to misrouting of the ipsilateral retinal fibers to the NOT.

Faculty practice: advantages and disadvantages

In considering the advantages and disadvantages of full-time dental faculty members involved in private practice, some suggestions for coping with problems represented by the disadvantages have been cited. Faculty members may find a more satisfactory climate for the patient service aspect of their professional activity in a system where several options are made available from which a teacher may select his preferred office environment and practice style.