Picture naming in early sequential bilinguals: a 1-year follow-up.

In a previous study, a cross-sectional approach was used to investigate developmental changes in basic-level lexical production and cognitive processing in early sequential bilinguals, exploring the effects of age and years of experience during single-language (Spanish or English) and mixed-language (alternating between Spanish and English) picture naming (K. Kohnert, E. Bates, & A. E. Hernandez, 1999). The current study reports on the performance, 1 year later, of a subgroup of these original study participants (n = 28; mean age = 10.2 years) on the same experimental task. Overall, from Time 1 to Time 2 testing, gains were greater in English than in Spanish and in the high-competition mixed-language processing condition than in the single-language processing condition. These results reinforce previous findings of a shift toward greater strength in L2 with increasing age (and years of language experience), as well as the primary role of cognitive development in control of the dual-language system. In addition, examination of individual performance revealed a complex non-monotonic pattern of L1-L2 change across time within an overall pattern of increasing speed, accuracy, and control of the dual-lexical system.     

Balancing bilinguals II: lexical comprehension and cognitive processing in children learning Spanish and English.

The present study investigated developmental changes in lexical comprehension skills in early sequential bilinguals, in both Spanish (L1) and English (L2), exploring the effects of age, years of experience, and basic-level cognitive processing (specifically the ability to maintain performance during mixed vs. single-language processing) within a timed picture-word verification task. Participants were 100 individuals, 20 at each of five different age levels (ages in years, 5-7, 8-10, 11-13, 14-16, and adults). All had learned Spanish as a first language in the home, with formal English experience beginning at 5 years. Gains (as indexed by increased response speed) were made in both languages across age, although these gains were greater in English than in Spanish. The youngest participants were relatively "balanced" in their crosslinguistic performance. By middle childhood, performance was better in English. There were no response decrements at any age between the mixed and single-language processing conditions. These results are compared to those from a previous study that investigated basic-level lexical production in developing Spanish-English bilinguals. Both studies show a move toward English dominance in middle childhood, but the transition occurs earlier in comprehension. The production study showed differences between mixed and single-language processing (reflecting potential interlanguage interference) that are not evident in comprehension.     

Islet graft-induced changes of beta-hydroxybutyrate dehydrogenase and glucose-6-phosphatase activity in liver cells of diabetic recipient rats.

It is known that the liver is a favourable site for implantation of pancreatic islets since the grafted islets remain metabolically intact and provide long-term normoglycemia in diabetic animals. However, the long-term effects exerted by the grafted tissue on the host organ are not well defined. We therefore investigated by light and electron microscopy the effects of syngeneic islets on the host organ after intraportal transplantation into the liver of streptozotocin (STZ)-induced diabetic LEW.1W rats. In addition, tissue sections of graft-bearing liver were stained by enzyme histochemical methods for beta-hydroxybutyrate dehydrogenase (HBDH) and glucose-6-phosphatase (G6Pase). At 12 weeks after transplantation, the changes seen in the hepatocytes surrounding the grafted islets were hyperproliferation and accumulation of glycogen. Hepatocytes adjacent to the implanted islets displayed increased HBDH activity, whereas G6Pase activity was variable, either decreased or increased. Increased HBDH activity was also observed in the periportal region and in liver cells extending to the central veins. The results demonstrate that intraportal islet grafts, in addition to normalizing glucose homeostasis, exert remarkable effects on the liver parenchyma of experimentally diabetic recipient rats.     

Development of cytotoxic islet cell antibodies in rats following damage of the pancreas by complete Freund's adjuvant combined with a nondiabetogenic dose of streptozotocin

The possible relationship between destruction of pancreatic beta cells and islet cell surface antibodies (ICSA) was examined in a rat model using complete Freund's adjuvant (CFA), a lymphocyte activator, in combination with the beta cell toxin, streptozotocin (STZ). In addition to this treatment, the rat insulinoma cell line, RIN5AH, as a readily accessible source of insulin-producing cells, was utilized to potentiate the production of ICSA. Intraperitoneal injections of CFA to male Lewis rats, followed 24 h later by a single nondiabetogenic dose of STZ, produced a 47% (p less than 0.01) reduction in pancreatic insulin content associated with degranulation and necrosis of insulin-immunoreactive cells. Eight weeks after treatment, ICSA were detectable that mediated the complement-dependent lysis of neonatal rat islet cells. Injections of RIN5AH cells, following treatment with CFA/STZ, did neither increase the severity of histopathological changes in the exocrine pancreas nor the extent of beta cell necrosis, but gave rise to higher levels of cytotoxic ICSA. Immunization with RIN cells alone, although increasing ICSA levels above those of the other experimental groups, produced no major histopathological changes. These results indicate that ICSA are the consequence of beta cell damage, and they are not capable of promoting or initiating beta cell necrosis in this model.     

Young L2 learners' performance on a novel morpheme task

The teaching of an invented language rule has been proposed as a possible non-biased, language-independent assessment technique useful in differentiating young L2 learners with specific language impairment from their typically developing peers. The current study explores these notions by testing typically developing sequential bilingual children's ability to learn an invented language rule in either L1 (Spanish) or L2 (English). Participants were 20 children, age 3:6-5:8, who attended a Head Start programme. For all children, Spanish was the primary language spoken in the home and English was the primary language of instruction. Children were randomly assigned two groups. Group L1 was taught the novel language rule in Spanish; Group L2 was taught the novel language rule in English. Performance was better for the L1 group than for the L2 group. Moreover, not all of these typical language learners were able to learn the new rule, even in their strongest language. These findings suggest that even for typically developing children, specific language proficiency as well as individual differences are closely linked to performance on this novel morpheme learning task.     

Chronic hyperglycemia but not glucose variability determines HbA1c levels in well-controlled patients with type 2 diabetes

To determine the relationships between HbA1c, characteristics of hyperglycemia and glycemic variability in well-controlled type 2 diabetes (HbA1c<7.0%), we studied 63 primary-care patients (36 men and 27 women), aged 34-75 years, with type 2 diabetes for 2-32 years using a continuous glucose monitoring system (CGMS) and standardized meal test (MMT). Duration of hyperglycemia (>8.0 mmol/l), standard deviation score (S.D.-score) and mean amplitude of glycemic excursions (MAGE) were analyzed from CGMS data and postprandial glucose during MMT (PPG(MMT)). Patients were hyperglycemic for 5.7h/day (median), experienced 4.1 hyperglycemic episodes/day, and 78% exceeded PPG levels of 8.0 mmol/l. HbA1c, though associated with the extent of hyperglycemia (r=0.40, p<0.001), failed to correlate with S.D.-score and MAGE. Multiple regression analysis demonstrated that HbA1c was predicted only by fasting glucose (R(2)=0.24, p<0.001) but neither by PPG(MMT), duration of hyperglycemia, S.D.-score nor MAGE. CGMS and meal test provide the tools for complete characterization of glycemia in type 2 diabetes. In well-controlled type 2 diabetes, HbA1c correlates with chronic hyperglycemia but not with glucose variability. Our data suggest that chronic sustained hyperglycemia and glucose fluctuations are two independent components of dysglycemia in diabetes.     

Effects of islet cell surface antibodies on isolated neonatal rat islets of Langerhans in vitro

Islet cell surface antibodies (ICSA) were raised by immunization of rabbits with viable neonatal rat pancreatic islet cell suspensions. By absorption with liver powder and spleen cells unspecific cytotoxic components were removable from the sera. Cytotoxic effect of islet cell antiserum against islet cells was indicated by 51Cr-release. In dependence on serum concentration beta-cell damage induced by ICSA-positive serum was detectable by insulin leakage from neonatal rat islets of Langerhans. The immune cytolytic effect of rabbit anti-rat islet cell surface serum was accompanied by morphological alterations of the islet surface structure as revealed by scanning electron microscopy. Pretreatment of pancreatic islets with cytotoxic islet cell antiserum results in an increased insulin leakage even after the removal of the cytotoxic conditions suggesting the persistence of cell membrane lesions. Insulin secretion of islets of Langerhans first exposed to cytotoxic ICSA-positive serum is still stimulated by 15 mmol/1 glucose plus 0.1 mmol/1 3-isobutyl-1-methylxanthine (IBMX) but taking into account the increased insulin leakage the secretory capacity of these islets is significantly diminished.     

Purification of mouse monoclonal antibodies by chromatography on sepharose 6 B

By using Sepharose 6 B, a simple procedure for purification of mouse monoclonal antibodies (mcAbs) of the IgM and IgG class from ascites has been developed. The procedure which was applied to purify mcAbs against insulin and pancreatic islet cells permits either direct chromatographic separation from ascites protein components or after precipitating the immunoglobulins with ammonium sulphate. Recovery of the immunoglobulins was found to be approximately 80%, and the immunological reactivity, as tested by indirect immunofluorescence and ligand binding assay, was almost completely retained. For purification of IgG from ascites, precipitation with ammonium sulphate is recommended prior to chromatography on Sepharose 6 B, whereas IgM can directly be subjected without any pretreatment.