Effect of salinity on osmoregulatory patch epithelia in gills of the blue crab Callinectes sapidus.

In euryhaline crabs, ion-transporting cells are clustered into osmoregulatory patches on the lamellae of the posterior gills. To examine changes in the branchial osmoregulatory patch in the blue crab Callinectes sapidus in response to change in salinity and to correlate these changes with other osmoregulatory responses, crabs were acclimated to a range of salinities between 10 and 35 ppt. When crabs that had been acclimated to 35 ppt were subsequently transferred to 10 ppt, both the size of the osmoregulatory patch on individual gill lamellae and the specific activity of Na+, K+-ATPase in whole-gill homogenates increased only after the first 24 h of exposure to dilute seawater. Enzyme activity and size of patch area increased gradually and reached their maxima (increasing by 200% and 60%, respectively) 6 days following transfer to 10 ppt seawater and then remained at these levels. Patch size at acclimation varied inversely with the salinity for seawater dilutions below 26 ppt (the isosmotic point of the crab), although it did not vary in salinities at or above 26 ppt. Thus, the size of the patch clearly is modulated with acclimation salinity, but it increases only in those salinities in which the crab hyperosmoregulates. An increase in the total RNA/DNA ratio in gill homogenates, the lack of mitotic figures in the lamellae, and the lack of incorporation of bromodeoxyuridine into nuclei of lamellar epithelial cells during acclimation to dilute seawater were interpreted as evidence that no cell proliferation had occurred and that increases in the size of the osmoregulatory patch occurred through differentiation of existing gas exchange cells or of undifferentiated epithelial cells into ion-transporting cells.

Hemolymph levels of methyl farnesoate increase in response to osmotic stress in the green crab, Carcinus maenas.

The salinity of estuarine environments can vary widely, exposing resident organisms to considerable osmotic stress. The green crab Carcinus maenas is well known for its ability to osmoregulate in response to such stress. Therefore, we tested the relationship between osmoregulation and hemolymph levels of methyl farnesoate (MF), a compound previously shown to rise in response to various types of environmental stresses. When crabs were transferred from 100% seawater to dilute (hypo-osmotic) seawater, hemolymph osmolality dropped rapidly, reaching an acclimation level 48 h after transfer. Hemolymph levels of MF also rose in these animals after a delay of 6 h, and reached a maximum level at 48 h. MF levels remained elevated as long as the crabs were maintained in dilute seawater, and quickly returned to basal levels when the animals were returned to full strength seawater. In most (but not all) animals, MF levels were elevated when hemolymph osmolality fell below the isosmotic point (approx. 800 mOsm/kg). These data suggest that MF may have a role in osmoregulation by this species. In addition, the elevation of MF by hypo-osmotic seawater suggests an experimental strategy for manipulating MF levels in crustaceans.

A follow-up study of recent special education graduates of learning disabilities programs.

This study investigated the postschool vocational and community adjustment of recent special education graduates from a southwestern metropolitan school district. Sixty-four students with learning disabilities (LD) who had attended self-contained classes at 12 high schools were randomly selected. A questionnaire, administered either via the telephone or in person, was the source of data. Thirty-eight of the LD sample were in competitive employment. In general, the LD students received very few community services. For the most part, they received no agency support after graduation. Most of the LD subjects lived with parents or other relatives and most had a driver's license and car. Implications for postsecondary services and future research are discussed.

Ontogenetic Change in Digestive Enzyme Activity of Larval and Postlarval White Shrimp Penaeus setiferus (Crustacea, Decapoda, Penaeidae).

Whole specimens of developmental stages of Penaeus setiferus (Linnaeus, 1767) were homogenized and assayed for activities of digestive enzymes. In all developmental stages, activities were present for trypsin, carboxypeptidase A and B, amylase, and non-specific esterase; none for pepsin or lipase were detected. Activities assayed with substrates for chymotrypsin and aminopeptidase are not apparently due to the presence of these enzymes in the gut. Peak activities for all enzymes occurred during late zoeal or early mysis larval stages; low activities occurred at metamorphosis. During postlarval development, amylase activity increased steadily (by a tenfold increase over five weeks), whereas most other enzyme activities were relatively constant until the fifth week of postlarval development. Although it alters enzyme activity, diet does not appear to be the primary effector of ontogenetic change in digestive enzyme activity. Instead, ontogenetic change in digestive enzyme activity may reflect either a developmentally cued change in enzyme synthesis, or a secondary effect of change in the function and relative size of the midgut during its differentiation.

Ontogenetic Changes in Enzyme Distribution and Midgut Function in Developmental Stages of Penaeus setiferus (Crustacea, Decapoda, Penaeidae).

Ultrastructure and histochemical distribution of enzymes were examined in the midgut of larval and postlarval stages of Penaeus setiferus. Acid phosphatase and esterase activities were present in all gut tissues at all stages. Protease activity was present in the anterior and lateral midgut caeca, as well as in the anterior portion of the midgut trunk (MGT) of larvae and early postlarvae (PL1-PL4). Amylase activity could not be detected histochemically in larvae or early postlarvae, even though it was detected in assays of whole-animal homogenates. In later postlarvae, both protease and amylase activities were present in the hepatopancreas and anterior MGT, but were absent from the anterior midgut diverticulum. In larvae, alkaline phosphatase activity is present throughout the midgut, suggesting that absorption is widespread. In juveniles, activity is restricted to the hepatopancreas and regions of the MGT within the cephalothorax. The abdominal MGT (or "intestine") is no longer absorptive by the time the hepatopancreas has attained its adult form. Although epithelial cells of the MGT synthesize protein and produce electron-dense secretory vesicles, they are substantially different in ultrastructure from those cells in the hepatopancreas responsible for digestive enzyme synthesis and secretion. Epithelial cells of the larval anterior and lateral midgut caeca are structurally and functionally similar to cells of the postlarval hepatopancreas. However, the lateral midgut caeca retain these features as they transform into the hepatopancreas, while the anterior midgut caeca lose these functions as they degenerate into the anterior diverticulum and change in ultrastructure during early postlarval development. The anterior and posterior midgut diverticula of postlarvae are similar ultrastructurally even though they differ in ontogenetic history.