Transport across the rabbit foetal yolk-sac of fractions of IgG from several mammalian species

Electrophoretically migrating fast and slow IgG fractions of rabbit, mouse, human, guinea-pig, dog, horse and cow sera were prepared by DEAE-cellulose chromatography, labelled with either 131I or 125I, and tested in passage across yolk-sac splanchnopleur of rabbits. In foetal sera, slow IgG generally reached higher concentrations than fast IgG, but even with mouse Ig, which has a high ratio between the two fractions, the difference was only four-fold. This differential between fast and slow IgG was not sufficient to explain the absorptive selectivity between IgG of different species. The capacity of isotopically labelled rabbit and equine IgG to be transported across the rabbit foetal yolk sac was also studied using fractions prepared by isoelectric focusing. Marked differences in concentration quotient (CQ) values (CQ equals (concentration in foetal serum)/(concentration in injected material)) between individual pI peaks for these species were found.

Isoelectric focusing analysis of transmission of fractions of bovine IgG across the gut of the suckling rat

Twelve-day-old rats were fed a mixture of fast and slow chromatographically prepared fractions of bovine IgG, labelled with ¹²⁵I and ¹³¹I. The pooled young rat sera were submitted to analysis by electrofocusing. The results show a wide variation of concentration quotients between the different pI peaks of IgG, with the more basic fractions being transmitted more readily in both fractions. One slow IgG peak (pI 7.8) in particular is transmitted very readily. These findings reinforce the concept of selectivity in transmission.

The possible use of the young rat gut as a test for protein integrity is discussed.

Effector system mechanisms of coordination

Current interest in motor learning has prompted researchers to develop models that explain the events or mechanisms underlying skill acquisition. For the most part these models have focused on sensory and perceptual mechanisms. This commentary presents a theoretical explanation of effector system mechanisms of coordination. Options are available in the central control centers and their peripheral components, tonic and phasic motor units. Implications for the methodology of motor learning are discussed as they relate to a paramount factor responsible for prompting individuals to select the most efficacious effector system mechanism option.

Effects of cytosine arabinoside on differential gene expression in embryonic neural retina. I. Accumulation of glutamine synthetase with suppression of macromolecular synthesis

The analogue of cytidine, cytosine arabinoside (Ara-C), elicited a significant increase in the level of glutamine synthetase (GS) in embryonic chick neural retina in the absence of the steroid inducer of the enzyme. The increase was due to de novo synthesis of GS and was mediated by RNA which accumulated in the presence of the effective concentration of Ara-C. Accumulation of GS did not result from the inhibition of DNA synthesis for which Ara-C is best known. This new effect of Ara-C involves differential suppression of macromolecular synthesis in this system: the concentration of Ara-C which caused maximum GS accumulation suppressed overall protein and RNA syntheses 65-75% without inhibiting the transcription and translation of templates essential for GS synthesis. Withdrawal of Ara-C resulted in restoration of RNA synthesis and cessation of GS accumulation, even though preformed templates for the enzyme were present; however, if all RNA synthesis was arrested with actinomycin D at the time of Ara-C withdrawal, GS continued to accumulate. The results are consistent with the hypothesis that Ara-C differentially affects the activity of structural and regulatory genes involved in the regulation of GS levels in the retina: Ara-C allows transcription of the enzyme-specific templates, but reversibly inhibits the expression of regulatory genes which limit the accumulation of GS.

The effects of size-selective predation and environmental variation on the distribution and abundance of a Chironomid, Paraborniella tonnoiri Freeman

Larvae of the Australian chironomid P. tonnoiri live in temporary rainpools and aestivate in the dry mud during the summer drought. Over most of their range, they are restricted to large, deep, vegetated pools. A number of factors influence population numbers, but the most critical in determining the species' distribution is the presence of another chironomid, Allotrissocladius sp. Fourth-instar Allotrissocladius larvae kill P. tonnoiri when the latter are in first and possibly second instar. The deep, vegetated pools have ample food available when P. tonnoiri breeds, so young larvae grow rapidly through their early instars and soon cease to be vulnerable. In shallower, non-vegetated pools, with much less food, the larvae grow more slowly, are vulnerable for longer, and are consequently eliminated. P. tonnoiri is also absent from areas where low temperatures during early life may slow its growth, and it seems likely that the same mechanism is responsible. The study thus suggests that it may seldom be enough to know about the gross structure and physical characteristics of an ecosystem in order to predict whether or not a species will persist in it-it is also necessary to know some of the details of when and how it interacts with others.

Studies in vivo and in vitro of the transfer of rat IgG and rat albumen across the intestinal walls of young rats

Preparations of radioactively labelled rat albumen and IgG have been fed together in equal concentrations to 3-, 14- and 24-day-old rats. Quantitative experiments showed that both proteins were absorbed at 3 days of age, but by the 14th day, the transmission of rat albumen had ceased. No proteins were absorbed by 24-day-old rats. Gel filtration studies of the intra-lumenal contents collected 30 min after feeding have demonstrated clear differences in the relative gastric digestion of the administered proteins. In marked contrast to the <i>in vivo</i> studies, it has been shown that everted intestinal sacs prepared from 14- and 24-day-old rats are able to transport both rat albumen and IgG <i>in vitro</i>, significantly more of the former than of the latter protein being transferred under the given experimental conditions.

Transmission of IgA to the rabbit foetus and the suckling rat

The transmission of purified preparations of rabbit and human colostral IgA globulin were studied in the rabbit across the yolk-sac splanchnopleur and in the young rat across the gut. Little or no IgA was transferred in either species.

Salient differences between internal and external standards for hospitalizing opiate addicts

Drug addicts evaluated by the treatment staff prior to treatment were compared on several self-concept scales with those screened elsewhere by contract agencies. Persons committed directly to treatment demonstrated a greater degree of psychopathology and less middle-class identification than those found suitable after local pretreatment evaluation. Those evaluated elsewhere showed a significantly higher rate of failure to complete successfully the inpatient phase. The study has implications for any program where prescreening is done prior to coming to the institution and suggests the need for a final pretreatment evaluation a: the institution if successful completion of the program is to be maximized.