Making sense of electrical sense in crayfish.

The five sensory modalities of humans are also found in a wide range of invertebrates. Other vertebrates have evolved additional special senses, such as the magnetic sense, which are also found in some invertebrates. However, there remain a few sensory abilities that curiously appear to be found in either vertebrates or invertebrates, but not both. For example, electrosensitivity - the ability to detect electric fields in water - which should benefit vertebrates and invertebrates alike, is apparently only used by vertebrates. However, recent reports suggest that some invertebrates could have an electric sense. Here we examine that possibility further and demonstrate a behavioural threshold to low-level electrical fields in two freshwater invertebrates. The responses are not low enough for them to detect the Earth's magnetic field as some other electroreceptive species can do, but sufficiently low for them to use in navigation or prey and predator detection. This finding challenges the current view of the sensory world of aquatic invertebrates and has implications for the evolution of this ability.

Modulation of azaserine-induced pancreatic foci by phenolic antioxidants in rats.

Effects of the dietary phenolic antioxidants butylated hydroxyanisole [(BHA) CAS: 25013-16-5; (1,1-dimethylethyl)-4-methoxyphenol] and butylated hydroxytoluene [(BHT) CAS: 128-37-0; 2,6-di-tert-butyl-p-cresol] on pancreatic tumorigenesis were examined. Male LEW inbred rats were given injections of 30 mg azaserine [CAS: 115-02-6; diazoacetate (ester) serine] per kg body weight once a week for 3 weeks and maintained on either a control diet or 0.45% BHA- or 0.45% BHT-supplemented control diet throughout the initiation and post-initiation phases of the experiment. At 4 months post initiation, pancreatic tissue sections were quantitatively examined for the number and size of preneoplastic foci. BHT and BHA treatments reduced the number of acidophilic foci per pancreas by 32 and 48%, respectively, but were without effect on focal size. By contrast, basophilic foci were not subject to modulation by these antioxidants. A constellation of enzyme activities involved in carcinogen inactivation and known to be perturbed by antioxidant treatment was examined in liver and pancreas. The hepatic activities of glucose-6-phosphate dehydrogenase, glutathione reductase, and glutathione-S-transferases were markedly elevated while catalase and superoxide dismutase activities were unchanged. Glutathione peroxidase activity was diminished. In the pancreas, only glutathione peroxidase activity was affected, and it was reduced in both the BHA and BHT treatment groups. Although the pancreas is refractory to the enzyme inductive effects of these antioxidants, morphometric analysis of foci demonstrated chemoprevention by BHA and BHT of azaserine-induced foci. Whether this reduction reflected inhibition of an initiation, postinitiation , or a combination of effects was not known.

Caloric restriction and intervention in pancreatic carcinogenesis in the rat.

In two experiments, the effects of caloric restriction during the postinitiation phase of pancreatic carcinogenesis were evaluated. Male Lewis rats were given injections of azaserine at 14 days of age and weaned to the postinitiation test protocols at 21 days of age. In the first experiment, the caloric content of the diets was restricted by 10, 15, 20, and 30% of the intakes of the ad libitum-fed rats. A sixth group was fed diet ad libitum for only 5-6 h/day; i.e., they were "meal-fed". The development of putative preneoplastic lesions (henceforth termed foci) was evaluated by quantitative stereological (morphometric) analysis of the pancreas. Caloric restriction during the 4-month postinitiation phase resulted in a significant reduction in focal development beginning at 10% caloric restriction and increasing with more severe restriction. The caloric intake of the meal-fed group closely matched the caloric intake of the 10 or 15% caloric restriction groups and the focal response of the meal-fed rats was similar to the groups restricted in calories by 15 to 20%. In the second experiment, rats were initiated with azaserine and weaned to one of four groups: ad libitum; meal-fed; meal-fed for 2 months and ad libitum thereafter; or ad libitum for 2 months and meal-fed thereafter. Foci were evaluated at 2 and 4 months; neoplasm incidence and multiplicity were determined at 14 months postinitiation. Compared to the ad libitum group, the meal-fed group had significantly fewer foci at all times of evaluation and significantly fewer neoplasms. When rats were meal fed for 2 months and then switched to ad libitum feeding for the remainder of the experiment, the focal outcome at 4 months was similar to the group meal fed for all 4 months; and at 14 months the neoplastic outcome was intermediate between the ad libitum and the meal-fed group. Intervention in the ad libitum feeding regimen at 2 months by meal feeding for the remainder of the experiment resulted in a significant decrease in the focal and neoplastic development, as compared to the group fed ad libitum continuously. These two intervention groups were intermediate in response between the meal-fed and ad libitum-fed groups. These results indicate that the postinitiation phase of pancreatic carcinogenesis can be modulated by relatively simple dietary interventions such as moderate caloric restriction.

Morphology, physiology, and homology of the N-cell and muscle receptor organs in the thorax of the crayfish Cherax destructor.

The serial homology of arthropods, together with our ability to identify individual neurons from segment to segment, and from animal to animal, provides opportunities for studying the changes wrought by natural selection on specific neural elements when functional requirements change in different parts of the trunk. Using this concept as a guide, we studied the morphology and physiology of the thoracic N-cells and muscle receptor organs (MROs) of the crayfish Cherax destructor for evidence of serial homology and functional plasticity. Methylene blue staining, together with anterograde and retrograde filling with cobalt through cut axons, revealed the morphology of the receptors, disposition of their endings, and the pathways of their axons from receptor to ganglion. The seventh thoracic segment has tonic and phasic MROs with receptor muscles in parallel with different heads of the deep thoraco-abdominal extensor muscle. The sixth segment has a tonic MRO with a receptor muscle in parallel with one head of the abdominal abductor. These three receptors are typical MROs complete with accessory nerves. Thoracic segments 1-5 each give rise to one mechanosensory N-cell with a small cell body and long processes ramifying in a target muscle. N-cell 5 is associated with the abdominal-thoracic abductor muscle, and the other four are associated with parts of the epimeral attractor. The responses of N-cells 1-4 range from tonic to phasico-tonic and show a range of thresholds to passive muscle stretch and active contraction. Cobalt introduced into bundles of nerve fibers known to include N-cell axons reveals projections with branching patterns and morphology similar to abdominal MROs. The present findings, together with information on thoracic MROs and N-cells from other species, were tabulated according to neurotome. The clear pattern revealed leads us to propose that N-cells are derivatives of segmentally repeating MROs modified to monitor postural and locomotory movements in the less mobile thorax.

Early Intervention Project: can its claims be substantiated and its effects replicated?

A comprehensive report to the National Institute of Health on the diagnosis, etiology, epidemiology, and treatment of autism indicated that early intervention has the potential of being an effective intervention (Bristol et al., 1996). In spite of this positive outlook, several research and methodological questions remain regarding time of treatment initiation, intensity of treatment and duration of treatment, random assignment, comparative treatment designs, and treatment integrity. Against this backdrop we consider the claims made by the Early Intervention Project (EIP; Lovaas, 1987, 1993; McEachin, Smith, & Lovaas, 1993). The EIP claims to produce recovery from autism in 47% of the cases and to greatly reduce its severity in an additional 42% of cases. This article evaluates the EIP against threats to internal and external validity and is found to suffer from a number of methodological problems. Based on rebuttals to criticisms of their program, the EIP authors seem unwilling to admit any methodological flaws in the sampling, design, and analysis of data of the EIP. It is recommended that parents and fair hearing officers adopt an attitude of healthy skepticism before proceeding to an unqualified endorsement of the EIP as a treatment for autism.

Evaluation of promotion of pancreatic carcinogenesis in rats by benzyl acetate.

Benzyl acetate was found to induce liver tumours and gastric squamous neoplasms in mice in a chronic bioassay conducted through the National Toxicology Program. An increased incidence of acinar cell adenomas of the pancreas of F344 rats was noted in the bioassay, but the significance of these lesions was confounded because the benzyl acetate was given by gavage in corn oil. The use of corn oil as a vehicle has been shown to enhance the growth of such lesions in the rat pancreas. The current studies were undertaken to evaluate benzyl acetate alone as an initiator and promoter of carcinogenesis in the pancreas. Alkaline elution analysis of acinar cell DNA showed no evidence of damage 1 hr after administration of benzyl acetate. Significant stimulation of growth of azaserine-induced foci was observed in a 6-month study, and a low but significant incidence of carcinoma in situ was observed in rats fed benzyl acetate in the diet for 2 yr. These experiments suggest that benzyl acetate is a weak promoter of the growth of carcinogen-induced and spontaneous pre-neoplastic foci in the pancreas.

Comorbidity of hyperactivity-impulsivity-inattention and conduct problems: risk factors in social, affective, and academic domains.

Children showing a comorbid behavior pattern of hyperactivity-impulsivity-inattention and conduct problems (HIA + CP) were contrasted to children having only an internalizing and externalizing behavior pattern (I + E) and matched controls. Children displaying the HIA + CP behavior pattern were at greater risk on a number of outcome measures in social and academic domains beginning in Grade 3 and continuing into Grade 4. The most marked differences among the three groups were found on peer measures of rejection and friendship and teacher ratings of social skills. On average, almost two-thirds of the HIA + CP group were rejected by their peers compared to one-third of the I + E group and only 12.5% controls. Over 70% of the HIA + CP group had no reciprocated friendships from Grade 3 to Grade 4 compared to less than half of the I + E group and approximately one-fourth of controls. Contrary to much theorizing in the literature, the HIA + CP and I + E groups showed average levels of academic self-concept and did not differ from controls in on measures of social self-concept and academic self-concept and general self-esteem. These findings were interpreted in light of positive illusory biases and the established link between aggressive behavior and egotism. The current article offers partial support for Lynam's (1996) notion of the "fledgling psychopath."

Insights for robotic design from studies of the control of abdominal position in crayfish.

Studies of the control of position and movement of the abdomen of crayfish illustrate a number of features of invertebrate sensory-motor systems that have implications for their use to inform robotic design. We use the abdominal slow extensor motor system to illustrate three of them here: first, the way in which a behaviorally flexible length-servo device can be achieved with very few elements; second, the importance of knowledge of the biological and behavioral context in which the elements operate; third, that design solutions resulting from natural selection have been constrained by the previous evolutionary history of the animal, which can affect the outcomes in ways that may not be immediately apparent in a design context.

Tailflick escape behavior in larval and juvenile lobsters (Homarus americanus) and crayfish (Cherax destructor).

We examined the escape behavior of larvae and postlarvae of the American lobster (Homarus americanus) and of adult immature (stage ADI) crayfish (Cherax destructor). Responses to standardized water jet stimuli delivered through a pipette were observed and analyzed. Lobster larvae did not respond to stimuli within 60 ms, indicating that they do not have functional giant fibers. The first movement by lobster larvae in response to water jet stimuli was a hyperextension of the abdomen. Larval escape responses also showed very little habituation. Postlarval lobsters and ADI crayfish showed the same range of responses as adult animals. Displacement efficiency of tailflicks exhibited by the different animals and stages was examined and related to the morphology of the animals. A separate behavior from tailflicking by larval lobsters in response to water jet stimuli was also observed. Here, the abdomen was hyperextended and the thoracic appendages were promoted. We termed this behavior a "starburst" response. The features of the tailflicking behavior suggest that it evolved to make the larvae difficult prey to handle for small, slower moving predators, and possibly to allow them to ride the bow waves of faster moving predators.

Conceptual and psychometric concerns about the 1992 AAMR definition of mental retardation.

The new American Association on Mental Retardation (AAMR) definition of mental retardation (Luckasson et al., 1992) represents a radical departure from previous definitions. In the present paper we examined the extent to which the new definition provides decision rules to guide clinicians and researchers in classification efforts. We concluded that the IQ criterion of 75 will increase the proportion of the general population eligible near the cut-off score. Moreover, the 10 adaptive skill areas adopted fail to consider developmental factors and cannot be assessed reliably with current scales. Proposed differentiation by levels of needed supports is also challenged as being imprecise and not amenable to reliable measurement. Implications of this new definition for diagnostic practices and research endeavors were explored.

Heightened concerns over the 1992 AAMR definition: advocacy versus precision.

We reiterated our earlier concerns (MacMillan et al., 1993) regarding the 1992 AAMR definition of mental retardation and replied to a defense of the definition (Reiss, 1994). Our major point here is that definitional precision should not be sacrificed to advance a particular ideological position. The result of such a compromise is a definition lacking precision and necessitating identification dependent upon assessment of behavioral dimensions for which there is currently no reliable measurement. We explored the varied purposes served by classification systems and criticized the new AAMR definition for lack of precision needed to serve research. In addition, we attempted to reduce confusion over the concepts of reliability, assessment, test bias, and use of factor analysis to establish the independence of adaptive skill domains. Some factual errors and incorrect representations in Reiss's article were pointed out.

The labyrinth of IDEA: school decisions on referred students with subaverage general intelligence.

A sample of 150 children referred to Student Study Teams was assessed with a psychometric battery. Behavioral and academic ratings were obtained from teachers. Forty-three children scored at or below 75 on the WISC-III. We examined schools' subsequent classification decisions to ascertain how schools dealt with low-IQ students with academic and behavioral problems. Schools reached decisions regarding 35 of the children: Only 6 were classified as having mental retardation, and 18, as having learning disabilities. Findings were discussed in terms of (a) decline in identification rates of mild mental retardation and (b) the extent to which school decisions adhere to the research criteria.

Differences in adolescents' self-concept as a function of academic level, ethnicity, and gender.

The relations of dimensions of self-concept of adolescents with their academic level, ethnicity, and gender were investigated. A self-concept inventory assessing 11 aspects of self-concept was administered to a sample of 1,140 eight-grade students stratified with regard to academic level (regular class, educationally marginal, learning handicapped), ethnicity (white, black, and Hispanic), and gender. Results showed that regular class students had higher levels of self-concept on most scales than did students who were educationally marginal or learning handicapped; the latter two groups showed few differences. Black students had higher self-concept ratings than did white and Hispanic students on most scales. An interaction on two academically related dimensions of self-concept revealed that white students who were educationally marginal had the lowest level of academic and verbal self-concept. Implications of the results for theories of self-concept formation were discussed.

Laboratory and field studies on the effect of molinate, clomazone, and thiobencarb on nontarget aquatic invertebrates.

The midge Chironomus tepperi was used in laboratory experiments to assess the relative toxicity of formulated molinate, clomazone, and thiobencarb, three herbicides used in Australian rice crops. Static bioassays were initiated with first-instar larvae at herbicide concentrations between 0.0625 and 2 times the anticipated field concentrations (AFCs) expected from the registered application rates. Adult emergence success, development time, and wing length were used as indices of the effect of each herbicide. Clomazone had no effect on any parameters at concentrations up to 0.288 mg/L (p > 0.05). Molinate significantly increased development time at concentrations equivalent to the AFC (3.6 mg/L) and above (p < 0.05). Thiobencarb reduced emergence success of adult C. tepperi at 0.0625 times the AFC (0.1875 mg/L) as well as decreasing male adult size and increasing development time for males and females at 0.125 times the AFC (p < 0.05). Nontarget effects of the herbicides on aquatic invertebrate communities were assessed in shallow experimental ponds using commercial application rates. One week after treatment, only thiobencarb had a significant effect, suppressing populations of chironomids, calanoids, and cyclopoids (p < 0.05). Four weeks later, all populations had recovered, equaling or exceeding control densities.

Discrepancy between definitions of learning disabilities and school practices: an empirical investigation.

Students referred by general education teachers to school study teams (SSTs) were evaluated for learning disabilities (LD) eligibility. We classified children as LD on the basis of a WISC-III Full Scale IQ of 82 or higher and a 22-point discrepancy between IQ and any WRAT-R achievement score. Research decisions were then contrasted with actual school-based decisions regarding the child as LD. Over half of the students referred to SSTs were certified by the schools as LD, yet less than half of these school-certified students with LD evidenced the aptitude-achievement discrepancy required by the state. Examination of the cases called LD by the schools revealed that children were classified as LD on the basis of low absolute achievement, regardless of whether or not a discrepancy existed. Moreover, in cases where a discrepancy was found but the school did not classify the child as LD, that child evidenced significantly higher achievement, despite exhibiting the requisite 22-point discrepancy. The school-identified students with LD constituted an extremely heterogeneous group, including students with mental retardation along with a substantial number who failed to qualify for any special education services. Findings are discussed in terms of the discrepancy between criteria specified in state regulations and what the committee members at the school site seemed to use in classifying children with LD.

Learning disabilities, low achievement, and mild mental retardation: more alike than different?

Children identified with learning disabilities (LD), low achievement (LA), or mild mental retardation (MMR) were contrasted on 41 measures of ability, academic achievement, social skills, problem behavior, academic engaged time, perceptual-motor skills, and school history. Both multivariate, univariate, and meta-analytic comparisons among the three groups showed relatively large differences on measures of aptitude and achievement, with the LD group scoring higher on measures of cognitive ability than the LA and MMR groups and the LA group showing higher tested academic achievement than the LD and MMR groups. Teacher ratings of academic competence showed similar levels of functioning for the LD and LA groups. No differences among the groups were found on measures of social skills, problem behaviors, or academic engaged time, or on most indices reflecting school history. Results were interpreted in light of studies contrasting LD and LA groups. Comparisons with earlier studies were difficult in light of demographic differences in samples and the lower cognitive and academic functioning of children in the present study. The current study showed that 61% of the LD group could be differentiated from the LA group, with LD-MMR and LA-MMR differentiation levels being 68.5% and 67.5%, respectively.