Giorgio P. Martinelli

Presenilin-1 forms complexes with the cadherin/catenin cell-cell adhesion system and is recruited to intercellular and synaptic contacts.

In MDCK cells, presenilin-1 (PS1) accumulates at intercellular contacts where it colocalizes with components of the cadherin-based adherens junctions. PS1 fragments form complexes with E-cadherin, beta-catenin, and alpha-catenin, all components of adherens junctions. In confluent MDCK cells, PS1 forms complexes with cell surface E-cadherin; disruption of Ca(2+)-dependent cell-cell contacts reduces surface PS1 and the levels of PS1-E-cadherin complexes. PS1 overexpression in human kidney cells enhances cell-cell adhesion. Together, these data show that PS1 incorporates into the cadherin/catenin adhesion system and regulates cell-cell adhesion. PS1 concentrates at intercellular contacts in epithelial tissue; in brain, it forms complexes with both E- and N-cadherin and concentrates at synaptic adhesions. That PS1 is a constituent of the cadherin/catenin complex makes that complex a potential target for PS1 FAD mutations.

Cold ischemic injury accelerates the progression to chronic rejection in a rat cardiac allograft model

BACKGROUND The pathogenesis of chronic rejection likely involves an interplay between immunogenic and nonimmunogenic factors. The objective of this study was to determine the influence of cold ischemic preservation injury on the rate of progression to chronic rejection in the Lewis to F344 cardiac allograft model. METHODS To induce an ischemic injury, donor hearts were stored for 3 hr at 4 degrees C in University of Wisconsin solution before transplantation. Allografts were excised at 1, 7, and 90 days after transplantation or at rejection. Vasculopathy was graded for degree of intimal thickening based on the involvement of vascular perimeter and luminal compromise. RESULTS The degree of vessel injury in ischemic injured allografts at 90 days was significantly greater than in nonischemic injured allografts (2.8+/-0.4 vs. 1.6+/-0.5, P<0.05). Ischemic injury in syngeneic grafts did not induce a vasculopathy. Immunoperoxidase staining with R73 (anti-T cell) and ED1 (anti-macrophage) monoclonal antibodies revealed that, in ischemic injured allografts at 90 days after transplantation, the infiltrate was composed predominantly of T cells and macrophages. Additionally, ischemic injured allografts excised at 7 days after transplantation showed cellular infiltrates composed of R73-positive T cells and rare interleukin-2 receptor-positive cells, which was not observed in nonischemic allografts or ischemic syngeneic grafts. CONCLUSIONS The progression to chronic vasculopathy in this model is principally an immunologic process, which is accelerated by an ischemic insult to the allograft. The vascular injury is mediated in part by T cells and macrophages.

Presence of glutamate, glycine, and γ‐aminobutyric acid in the retina of the larval sea lamprey: Comparative immunohistochemical study of classical neurotransmitters in larval and postmetamorphic retinas

The neurochemistry of the retina of the larval and postmetamorphic sea lamprey was studied via immunocytochemistry using antibodies directed against the major candidate neurotransmitters [glutamate, glycine, γ‐aminobutyric acid (GABA), aspartate, dopamine, serotonin] and the neurotransmitter‐synthesizing enzyme tyrosine hydroxylase. Immunoreactivity to rod opsin and calretinin was also used to distinguish some retinal cells. Two retinal regions are present in larvae: the central retina, with opsin‐immunoreactive photoreceptors, and the lateral retina, which lacks photoreceptors and is mainly neuroblastic. We observed calretinin‐immunostained ganglion cells in both retinal regions; immunolabeled bipolar cells were detected in the central retina only. Glutamate immunoreactivity was present in photoreceptors, ganglion cells, and bipolar cells. Faint to moderate glycine immunostaining was observed in photoreceptors and some cells of the ganglion cell/inner plexiform layer. No GABA‐immunolabeled perikarya were observed. GABA‐immunoreactive centrifugal fibers were present in the central and lateral retina. These centrifugal fibers contacted glutamate‐immunostained ganglion cells. No aspartate, serotonin, dopamine, or TH immunoreactivity was observed in larvae, whereas these molecules, as well as GABA, glycine, and glutamate, were detected in neurons of the retina of recently transformed lamprey. Immunoreactivity to GABA was observed in outer horizontal cells, some bipolar cells, and numerous amacrine cells, whereas immunoreactivity to glycine was found in amacrine cells and interplexiform cells. Dopamine and serotonin immunoreactivity was found in scattered amacrine cells. Amacrine and horizontal cells did not express classical neurotransmitters (with the possible exception of glycine) during larval life, so transmitter‐expressing cells of the larval retina appear to participate only in the vertical processing pathway. J. Comp. Neurol. 499:810–827, 2006.

L-baclofen-sensitive GABAB binding sites in the medial vestibular nucleus localized by immunocytochemistry

L-Baclofen-sensitive GABAB binding sites in the medial vestibular nucleus (MVN) were identified immunocytochemically and visualized ultrastructurally in L-baclofen-preinjected rats and monkeys, using a mouse monoclonal antibody with specificity for the p-chlorophenyl moiety of baclofen. Saline-preinjected animals showed no immunostain. In drug-injected animals, there was evidence for both pre- and postsynaptic GABAergic inhibition in MVN mediated by GABAB receptors. These neural elements could be utilized in control of velocity storage in the vestibulo-ocular reflex.

Direct projections from the caudal vestibular nuclei to the ventrolateral medulla in the rat.

While the basic pathways mediating vestibulo-ocular, -spinal, and -collic reflexes have been described in detail, little is known about vestibular projections to central autonomic sites. Previous studies have primarily focused on projections from the caudal vestibular region to solitary, vagal and parabrachial nuclei, but have noted a sparse innervation of the ventrolateral medulla. Since a direct pathway from the vestibular nuclei to the rostral ventrolateral medulla would provide a morphological substrate for rapid modifications in blood pressure, heart rate and respiration with changes in posture and locomotion, the present study examined anatomical evidence for this pathway using anterograde and retrograde tract tracing and immunofluorescence detection in brainstem sections of the rat medulla. The results provide anatomical evidence for direct pathways from the caudal vestibular nuclear complex to the rostral and caudal ventrolateral medullary regions. The projections are conveyed by fine and highly varicose axons that ramify bilaterally, with greater terminal densities present ipsilateral to the injection site and more rostrally in the ventrolateral medulla. In the rostral ventrolateral medulla, these processes are highly branched and extremely varicose, primarily directed toward the somata and proximal dendrites of non-catecholaminergic neurons, with minor projections to the distal dendrites of catecholaminergic cells. In the caudal ventrolateral medulla, the axons of vestibular nucleus neurons are more modestly branched with fewer varicosities, and their endings are contiguous with both the perikarya and dendrites of catecholamine-containing neurons. These data suggest that vestibular neurons preferentially target the rostral ventrolateral medulla, and can thereby provide a morphological basis for a short latency vestibulo-sympathetic pathway.

The ultrastructure of GABA-immunoreactive vestibular commissural neurons related to velocity storage in the monkey

The purpose of the present study was to visualize the synaptic interactions of GABAergic neurons involved in the mediation of velocity storage. In the previous report, ultrastructural studies of degenerating neurons were conducted following midline section of rostral medullary commissural fibers with subsequent behavioral testing. The midline lesion caused functionally discrete damage to the velocity storage component, but not to the direct pathway, of the angular vestibulo-ocular reflex, and the degenerating neurons were interpreted as potential participants in the velocity storage network. We concluded that at least some of the commissural axons mediating velocity storage originate from clusters of neurons in the lateral crescents of the rostral medial vestibular nucleus. In the present report, immunocytochemical evidence is presented that many vestibular commissural neurons, putatively involved in mediating velocity storage, are GABAergic. These cells have large nuclei, small round or narrow tubular mitochondria, occasional cisterns and vacuoles, but few other organelles. Their axons are thinly-myelinated, and terminate in boutons containing mitochondria of similar ultrastructural appearance and a moderate density of round/pleomorphic synaptic vesicles. Such terminals often form axoaxonic synapses, and less frequently axodendritic contacts, with non-GABAergic elements. On the basis of the present results, we conclude that a portion of the commissural neurons of the velocity storage pathway is GABAergic. The observation of GABAergic axoaxonic synapses in this pathway is interpreted as a structural basis for presynaptic inhibition of medial vestibular nucleus circuits by velocity storage-related commissural neurons. Conversely, substantial ultrastructural evidence for postsynaptic inhibition of non-GABAergic commissural cells argues for a dual role for GABAergic terminals mediating velocity storage: presynaptic inhibition of non-GABAergic vestibular cells by GABAergic velocity storage commissural axons, and postsynaptic inhibition of non-GABAergic velocity storage cells by GABAergic axons. Both pre- and postsynaptic inhibitory arrangements could provide the morphologic basis for disinhibitory activation of the velocity storage network within local neuronal circuits.

L-citrulline immunostaining identifies nitric oxide production sites within neurons.

The cellular and subcellular localization of L-citrulline was analyzed in the adult rat brain and compared with that of traditional markers for the presence of nitric oxide synthase. Light, transmission electron, and confocal laser scanning microscopy were used to study tissue sections processed for immunocytochemistry employing a monoclonal antibody against L-citrulline or polyclonal anti-neuronal nitric oxide synthase sera, and double immunofluorescence to detect neuronal nitric oxide synthase and L-citrulline co-localization. The results demonstrate that the same CNS regions and cell types are labeled by neuronal nitric oxide synthase polyclonal antisera and L-citrulline monoclonal antibodies, using both immunocytochemistry and immunofluorescence. Short-term pretreatment with a nitric oxide synthase inhibitor reduces L-citrulline immunostaining, but does not affect neuronal nitric oxide synthase immunoreactivity. In the vestibular brainstem, double immunofluorescence studies show that many, but not all, neuronal nitric oxide synthase-positive cells co-express L-citrulline, and that local intracellular patches of intense L-citrulline accumulation are present in some neurons. Conversely, all L-citrulline-labeled neurons co-express neuronal nitric oxide synthase. Cells expressing neuronal nitric oxide synthase alone are interpreted as neurons with the potential to produce nitric oxide under other stimulus conditions, and the subcellular foci of enhanced L-citrulline staining are viewed as intracellular sites of nitric oxide production. This interpretation is supported by ultrastructural observations of subcellular foci with enhanced L-citrulline and/or neuronal nitric oxide synthase staining that are located primarily at postsynaptic densities and portions of the endoplasmic reticulum. We conclude that nitric oxide is produced and released at focal sites within neurons that are identifiable using L-citrulline as a marker.

γ-Aminobutyric Acid Is Present in a Spatially Discrete Subpopulation of Hair Cells in the Crista Ampullaris of the Toadfish Opsanus tau

Although γ‐aminobutyric acid (GABA) and glutamate are known to be present in the vestibular sensory epithelia of a variety of species, the functional relationship between these two transmitters is not clear. The present study addresses the three‐dimensional spatial distribution of GABA and glutamate immunoreactivity in the vestibular labyrinth of the oyster toadfish by using whole end organs labeled by immunofluorescence with monoclonal anti‐GABA and/or antiglutamate antibodies and visualized as whole mounts by multiphoton confocal microscopy. We find glutamate‐immunoreactive hair cells present throughout the sensory epithelium. In contrast, prominent GABA immunoreactivity is restricted to a small population of hair cells located in the central region of the crista. Double immunofluorescence reveals two distinct staining patterns in GABA‐labeled hair cells. Most (∼80%) GABA‐labeled cells show trace levels of glutamate, appropriate for the metabolic/synthetic role of cytoplasmic glutamate. The remainder of the GABA‐stained cells contain substantial levels of both GABA and glutamate, suggesting transmitter colocalization. In the toadfish utricle, glutamatergic hair cells are present throughout the macula. GABA‐immunoreactive hair cells follow the arc of the striola, and most GABA‐labeled receptor cells coexpress glutamate. The localization of GABA was explored in other species as well. In the pigeon, GABAergic hair cells are present throughout the crista ampullaris. Our findings demonstrate that multiple, neurochemically distinct types of hair cells are present in vestibular sensory epithelia. These observations, together with the excitatory activity generally associated with 8th nerve afferent fibers, strongly suggest that GABA serves an important, specific, and complex role in determining primary afferent response dynamics. J. Comp. Neurol. 471:1–10, 2004.

Monoclonal antibodies for ultrastructural visualization of l-baclofen-sensitive GABAB receptor sites

Monoclonal antibodies were raised against the L-enantiomer of baclofen conjugated by glutaraldehyde to keyhole limpet hemocyanin. Hybridoma clones were selected for their stability and their production of high titers of antibodies directed against the p-chlorophenyl moiety of the L-baclofen molecule. The chosen antibody showed no cross-reactivity with conjugates of GABA and other neurotransmitters to human or bovine serum albumin. Specificity was further confirmed by the ability of L-baclofen-HCl to inhibit the binding of the antibody to L-baclofen-bovine serum albumin conjugate. Immunocytochemical studies were conducted on brain tissue from rats and monkeys injected with baclofen to localize baclofen-sensitive GABAB receptor sites. In these animals, the molecular layer of cerebellar cortex was clearly immunostained and the granular layer showed only some pale immunoreactivity. Ultrastructural observations were conducted in cerebellar cortex, as well as in the substantia nigra and the vestibular nuclei. Discrete labeling of neuronal profiles was observed in these structures, and both immunoperoxidase and colloidal gold methods were employed successfully. Material from saline-injected control animals showed no immunoreactivity at both light and electron microscopic levels. We conclude that the anti-L-baclofen antibody preferentially recognizes the p-chlorophenyl moiety of the baclofen molecule. Antibodies of such specificity are useful tools for the ultrastructural localization of baclofen-sensitive GABAB receptor sites. In general, antibodies directed against accessible moieties of specific neuroactive substances may serve as valuable markers for their sites of action.

Ultrastructural observations of efferent terminals in the crista ampullaris of the toadfish, Opsanus tau.

The present study was conducted to visualize the ultrastructural features of vestibular efferent boutons in the oyster toadfish, Opsanus tau. The crista ampullaris of the horizontal semicircular canal was processed for and examined by routine transmission electron microscopy. The results demonstrate that such boutons vary in size and shape, and contain a heterogeneous population of lucent vesicles with scattered dense core vesicles. Efferent contacts with hair cells are characterized by local vesicle accumulations in the presynaptic terminal and a subsynaptic cistern in the postsynaptic region of the hair cell. Serial efferent to hair cell to afferent synaptic arrangements are common, particularly in the central portion of the crista. However, direct contacts between efferent terminals and afferent neurites were not observed in our specimens. The existence of serial synaptic contacts, often with a row of vesicles in the efferent boutons lining the efferent-afferent membrane apposition, suggests that the efferent influence on the crista may involve both synaptic and nonsynaptic, secretory mechanisms. Further, it is suggested that differences in more subtle aspects of synaptic architecture and/or transmitter and receptor localization and interaction may render the efferent innervation of the peripheral crista less effective in influencing sensory processing.