Transient, high levels of SNAP-25 expression in cholinergic amacrine cells during postnatal development of the mammalian retina.

In the present study, we have examined the development of cholinergic amacrine cells in the retina of the Brazilian opossum, Monodelphis domestica. An antibody directed against choline acetyltransferase (ChAT) revealed that ChAT-like immunoreactivity (ChAT-IR) was first observed at 15 days postnatal (15PN). By 25PN, ChAT-IR identified two matching populations of amacrine cells in the inner nuclear and ganglion cell layer. Bromodeoxyuridine birth-dating analysis coupled with immunolabeling with the anti-ChAT antibody revealed that the cholinergic amacrine cells are born postnatally, between 2PN and 15PN. In addition, we have examined the differentiation of the cholinergic amacrine cells by using an antibody directed against a presynaptic terminal-associated protein, synaptosomal-associated protein of 25 kDa (SNAP-25). Double-labeling analysis revealed that relatively high levels of SNAP-25-IR were selectively present in cholinergic amacrine cells prior to eye opening. However, in the mature retina, high levels of SNAP-25-IR were no longer observed in the ChAT-IR amacrine cells. These results reveal a distinct period in development, prior to eye opening, when high levels of SNAP-25-IR are selectively expressed in cholinergic amacrine cells. The specificity and time course of the high levels of SNAP-25 in cholinergic amacrine cells may be critical in mediating the transient properties of these cells during visual system development.

Immunoreactivity for intracellular androgen receptors in identified subpopulations of neurons, astrocytes and oligodendrocytes in primate prefrontal cortex.

Sex differences in and hormone malleability of a variety of cognitive and mnemonic functions suggest that the association cortices in human and nonhuman primates are targets of gonadal hormone stimulation. One mechanism involved in this stimulation may be genomic actions mediated by intracellular androgen receptors. To identify potential cellular targets of this influence, single- and double-labeling immunohistochemical methods were used to precisely localize androgen receptor proteins in the prefrontal association cortex of adult rhesus monkeys. In both the dorsolateral and orbitofrontal regions, receptor antibodies labeled substantial populations of small intensely immunoreactive nuclei, as well as much larger and less strongly immunoreactive nuclei in all major cellular layers and/or in underlying white matter. Double-labeling studies revealed that large and small immunolabeled nuclei were further distinguished by colocalization with different classes of cell-specific markers. Whereas the large, pale receptor-immunoreactive nuclei colocalized with immunomarkers for neurons, the small, strongly immunoreactive nuclei colocalized exclusively with glial markers. Among androgen receptor-immunoreactive glia, a majority were immunoreactive for astrocyte markers, with smaller numbers of nuclei colocalized with oligodendrocyte markers; immunolabels for microglia failed to colocalize with androgen receptor immunoreactivity. This discovery of an unexpectedly large population of androgen receptor bearing glia suggests that direct functional interactions between endocrine signaling pathways and glial cells such as those coming into view in studies in subcortical and allocortical structures may also take place in the cerebral cortex and contribute to gonadal hormone stimulation of cortical processing of cognitive information.

Ectomycorrhizal specificity patterns in a mixed Pinus contorta and Picea engelmannii forest in Yellowstone National Park.

We used molecular genetic methods to test two hypotheses, (i) that host plant specificity among ectomycorrhizal fungi would be common in a closed-canopy, mixed Pinus contorta-Picea engelmannii forest in Yellowstone National Park and (ii) that specificity would be more common in the early successional tree species, P. contorta, than in the invader, P. engelmannii. We identified 28 ectomycorrhizal fungal species collected from 27 soil cores. The proportion of P. engelmannii to P. contorta ectomycorrhizae was nearly equal (52 and 48%, respectively). Of the 28 fungal species, 18 composed greater than 95% of the fungal community. No species was associated exclusively with P. contorta, but four species, each found in only one core, and one species found in two cores were associated exclusively with P. engelmannii. These fungi composed less than 5% of the total ectomycorrhizae. Thus, neither hypothesis was supported, and hypothesized benefits of ectomycorrhizal specificity to both trees and fungi probably do not exist in this system.