Cell-to-cell communication within the rat anterior pituitary was investigated in 60-day-old male rats with immunohistochemistry, scanning electron microscopy, freeze-fracture electron microscopy, and conventional transmission electron microscopy. A dense cytoreticular network of cytoplasmic processes from the folliculostellate cells was found to contain immunoreactive S-100 protein and was observed throughout the anterior pituitary. Nonimmunoreactive cells, which were granular, were situated in the center of each network. Almost all of the granulated cells were situated in close proximity to the folliculostellate cells. Scanning electron microscopy revealed that the gland consisted of microlobules enclosed by a basal lamina. On the surface of the microlobules were blood vessels whose branches invaded its internal structures. Cytoplasmic processes from folliculostellate cells projected outside the microlobule. Freeze-fracture electron microscopy demonstrated the presence of numerous intramembranous particles on the P-face of the plasma membrane. Scattered on the cell surface were groups of particles forming gap junctions. Meshworks of ridges which were representations of tight junctions were also observed near clusters of microvillous fragments. Clusters of particles forming small gap junctions were located between the meshworks of tight junctions. Small gap junctions were clearly observed by conventional electron microscopy between junctional complexes in a manner similar to that seen by freeze-fracture electron microscopy. Slender cytoplasmic processes of folliculostellate cells came in contact near the basal lamina and were adjoined by small gap junctions. The ratio of nongranular cells which contained gap junctions to those in which the junctions were absent was about 1:1. The size of the gap junctions ranged from 50 nm to 3 microns. No gap junctions were observed along the plasma membranes of the granular cells. The significance of an intercellular communication system within the anterior pituitary gland of the rat is to establish a mechanism for rapid transmission of information in an organ which lacks direct innervation.

The transition of the dental histology course at the University of Texas Health Science Center at San Antonio Dental School was completed gradually over a five-year period. A pilot project was initially conducted to study the feasibility of integrating virtual microscopy into a traditional light microscopic lecture and laboratory course. Because of the difficulty of procuring quality calcified and decalcified sections of teeth, slides from the student loan collection in the oral histology block of the course were outsourced for conversion to digital images and placed on DVDs along with a slide viewer. The slide viewer mimicked the light microscope, allowing horizontal and vertical movement and changing of magnification, and, in addition, a feature to capture static images. In a survey, students rated the ease of use of the software, quality of the images, maneuverability of the images, and questions regarding use of the software, effective use of laboratory, and faculty time. Because of the positive support from the students, our entire student loan collection of 153 glass slides was subsequently converted to virtual images and distributed on an Apricorn pocket external hard drive. Students were asked to assess the virtual microscope over a four-year period. As a result of the surveys, light microscopes have been totally eliminated, and microscope exams have been replaced with project slide examinations. In the future, we plan to expand our virtual slides and incorporate computer testing.

Since the ability of alveolar epithelial cells to ingest inhaled fine particles has not been characterized in detail, the present study seeks to evaluate this physiological activity. We used a 0.2% suspension of intact or lecithin-coated polystyrene latex beads (240 nm in diameter). A 5-ml suspension of intact or lecithin-coated latex beads was intratracheally administered to rats using a compressor nebulizer. Thereafter, the lungs were perfused intratracheally with glutaraldehyde solution and cut into small pieces. The samples were postfixed with osmium tetroxide, embedded in epoxy resin and examined under an electron microscope. Both lecithin-coated and uncoated beads were incorporated into alveolar macrophages. Some of the ingested beads in the alveolar macrophages were sequestered within lysosomes. Types I and II alveolar epithelial cells selectively incorporated only lecithin-coated beads, which were also observed within the cytoplasm of monocytes in the capillary lumen. These findings suggest that alveolar epithelial cells can incorporate exogenous particles, which are then transferred from the alveoli to intravascular spaces by transcytosis.

Germ line DNA directs the development of the next generation and, as such, is profoundly different from somatic cell DNA. Spermatogenic cells obtained from young adult lacI transgenic mice display a lower spontaneous mutant frequency and greater in vitro base excision repair activity than somatic cells and tissues obtained from the same mice. However, spermatogenic cells from old lacI mice display a 10-fold higher mutant frequency. This increased spontaneous mutant frequency occurs coincidentally with decreased in vitro base excision repair activity for germ cell and testicular extracts that in turn corresponds to a decreased abundance of AP endonuclease. To directly test whether a genetic diminution of AP endonuclease results in increased spontaneous mutant frequencies in spermatogenic cell types, AP endonuclease heterozygous (Apex ؉/؊ ) knockout mice were crossed with lacI transgenic mice. Spontaneous mutant frequencies were significantly elevated (approximately twofold) for liver and spleen obtained from 3-month-old Apex ؉/؊ lacI ؉ mice compared to frequencies from Apex ؉/؉ lacI ؉ littermates and were additionally elevated for somatic tissues from 9-monthold mice. Spermatogenic cells from 9-month-old Apex ؉/؊ lacI ؉ mice were significantly elevated twofold compared to levels for 9-month-old Apex ؉/؉ lacI ؉ control mice. These data indicate that diminution of AP endonuclease has a significant effect on spontaneous mutagenesis in somatic and germ line cells.Maintenance of germ cell genetic integrity is fundamental to the development of healthy offspring. However, DNA is constantly exposed to endogenous sources of damage (15). If left unrepaired, DNA damage can lead to errors during replication, thus generating de novo germ line mutations. Such mutations can result in genetic diseases. It has been suggested that most spontaneous germ line mutations occur in male gametes rather than female gametes (11,18,55), and there is a paternal age effect associated with several dominant genetic disorders (8,11,14,19,36,52,55). Studies on germ line mutagenesis were facilitated greatly by the development of mice transgenic for the lacI or lacZ reporter genes. Using these models, a direct assessment of in vivo spontaneous mutant frequencies for male germ cells and somatic cells and tissues is possible. lacI transgenic mice display an approximately 10-fold lower spontaneous mutant frequency (0.6 ϫ 10 Ϫ5 ) for male germ cells than for somatic cells and tissues (4.8 ϫ 10 Ϫ5 ) obtained from young adults (26,47,60). Notably, a 10-fold higher spontaneous mutant frequency was observed for spermatogenic cells obtained from old (28-month-old) mice (2.9 ϫ 10 Ϫ5 to 4.9 ϫ 10 Ϫ5 ) than for young adult (60-day-old) mice (0.4 ϫ 10 Ϫ5 to 0.8 ϫ 10 Ϫ5 ), thereby indicating a paternal age effect in the mouse model (60). The lacI transgenic mice represent the first mouse model used to study mechanisms mediating the paternal age effect.The results demonstrating a lower spontaneous mutant frequency in the male germ line led to questions about how a...

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