This study of the tree shrew, Tupaia belangeri, provides evidence for an intracollicular pathway that arises in the superficial gray layer and terminates in the optic layer. As a first step, Nissl, myelin, and cytochrome oxidase stains were used to identify the layers of the superior colliculus in the tree shrew. Second, anterograde and retrograde axonal transport methods were used to determine relationships between laminar borders and patterns of connections. Intraocular injections of wheat germ agglutinin conjugated to horseradish peroxidase showed that the border between the superficial gray and optic layers in the tree shrew is marked by a sharp decrease in the density of retinotectal projections. The optic layer also could be distinguished from the subjacent intermediate gray layer by differences in connections. Of the two layers, only the intermediate gray layer received projections following injections of wheat germ agglutinin conjugated to horseradish peroxidase within substantia nigra pars reticulata. Similarly, following injections of horseradish peroxidase or biocytin in the paramedian pons, the intermediate gray but not the optic layer contained labeled cells of origin for the main premotor pathway from the tectum, the predorsal bundle. Next, cells in the superficial gray layer were intracellularly injected with biocytin in living brain slices. Axons were traced from narrow and wide field vertical cells in the deep part of the superficial gray layer to the gray matter surrounding the fiber fascicles of the optic layer. Small extracellular injections of biocytin in brain slices showed that the optic layer gray matter contains a population of stellate cells that are in position to receive the input from the superficial layer. Finally, small extracellular injections of biocytin in the intermediate gray layer filled cells that sent prominent apical dendrites into the optic layer, where they may be directly contacted by the superficial gray layer cells. Taken together, the results support the hypothesis that the optic layer is functionally distinct from its adjacent layers, and may provide a link in the transfer of information from the superficial, retinal recipient, to the intermediate, premotor, layer of the superior colliculus.

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Interlaminar connections of the superior colliculus in the tree shrew. III: The optic layer.

These experiments were designed to test the idea that the optic layer in the tree shrew, Tupaia belangeri, is functionally distinct and provides a link between the visuosensory superficial and the premotor intermediate layers of the superior colliculus. First, cells in the optic layer were intracellularly labeled with biocytin in living brain slices. Compared to cells in the adjacent lower part of the superficial gray layer, which have apical dendrites that ascend toward the tectal surface, optic layer cells have dendritic fields that are restricted for the most part to the optic layer itself. The differences in dendritic-field location imply that superficial gray and optic layer cells have different patterns of input. The axons of optic layer cells terminate densely within the optic layer and, in addition, project in a horizontally restricted fashion to the overlying superficial gray and subjacent intermediate gray layers. This pattern also is different from the predominantly descending interlaminar projections of lower superficial gray layer cells. Next, cells in the intermediate gray layer were labeled in order to examine the relationships between optic layer cells and these subjacent neurons that project from the superior colliculus to oculomotor centers of the brain stem. Neurons in the upper part of the intermediate gray layer send apical dendrites into the optic layer and therefore can receive signals from the superficial gray layer either directly, from descending axons of lower superficial gray layer cells, or indirectly, through intervening optic layer cells. In contrast, lower intermediate gray layer cells have more radiate dendritic fields that are restricted to the intermediate gray layer. Thus, these lower cells must depend on descending projections from optic or upper intermediate gray layer cells for signals from the superficial gray layer. Together, these results support the idea that the optic layer is a distinct lamina that provides a link between the superficial and intermediate gray layers. They also are consistent with the traditional view that descending intracollicular projections play a role in the selection of visual targets for saccades.

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A commentary on the pathogenesis and biochemical profile of alcohol-induced depression.

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Adrenocorticotropic Hormone↗

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The use of immunohistochemistry for evaluating the liver.

Immunohistochemistry has been utilized in recent years primarily for diagnosis of infectious diseases of the liver, especially in humans. The utility of immunohistochemistry has extended to experimental and toxicologic pathology in a variety of areas: identification of cell phenotype, cell receptors, cytokine and chemikine production, and functional cell changes such as enzyme induction. In addition, markers for experimental carcinogenesis studies are detectable by immunohistochemical changes as well as novel antigen induction such as placental glutathione-S-transferase, oncofetal proteins, oncogene products, and typing of neoplasms. Immunohistochemistry is also used to detect the origin and function of various cell types in developmental and toxicity studies. Careful use of immunohistochemical procedures in conjunction with routine pathology and molecular techniques enhance the ability of the toxicologic pathologist to diagnose unique conditions and to understand mechanisms of lesion development.

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Infectious tenosynovitis (viral arthritis): influence of maternal antibodies on the development of tenosynovitis lesions after experimental infection by day-old chickens with tenosynovitis virus.

When chicks with maternal antibodies against infectious tenosynovitis (viral arthritis) virus were inoculated orally at 1 day old with tenosynovitis virus, they were protected against developing active tenosynovitis lesions 3 weeks later. They were not protected against subcutaneous inoculation, however. Breeder vaccination against tenosynovitis resulted in immunity of the progeny against oral infection at 1 day old, whereas progeny from unvaccinated breeders were susceptible to such a challenge.

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