B cell memory and idiotype network regulation

This investigation examined the clonal dynamics of B-cell expression and evaluated the role of idiotype network interactions in shaping the expressed secondary B-cell repertoire. Three interrelated experimental approaches were applied. The first approach was designed to distinguish between regulatory influences controlled by the major histocompatibility complex (MHC) and regulatory influences controlled by non-MHC factors including the idiotype network. This approach consisted of studies on the clonal dynamics and heterogeneity of the expressed IgG antibody repertoire of BALB/c mice. The second approach involved the analysis of the clonal dynamics of antibody responses of outbred rabbits. This analysis was coupled with studies to detect the occurrence and activity of constituents of the idiotype network. In the third approach the transfer of rabbit lymphocytes from immunized donors to MHC matched naive recipients was used to examine the effects of recipient non-MHC immunoregulatory influences on the expression of donor memory B-cells. Although many memory B cells were unaffected by non-MHC influences, these data show that non-MHC immunoregulatory influences can affect the expression of B-cells in the secondary response of inbred mice and outbred rabbits. The results also indicate that most IgG antibody responses are heterogeneous and are characterized by a stable group of dominant clonotypes. Clonal dominance and B-cell memory were found to be established early in an immune response. The expression of B memory clones appeared to be favored over the expression of virgin B cells. The injection of anti-tetanus antibody induced the antigen independent production of anti-tetanus antibody, probably through idiotypic mechanisms. These results demonstrate that both antibody and antigen can affect the expressed B-ceIl repertoire. Thus, idiotypic interactions are capable of influencing the expression of B-cells and these findings support the existence and function of an idiotype network with strong immunoregulatory potential. ^

The association of allergies and attention deficit hyperactivity disorder in children

To investigate the association between allergies and attention deficit hyperactivity disorder (ADHD), a case-control study was conducted using the National Longitudinal Survey of Youth population. Cases were between the ages of 4 and 11 years and were classified either by a maternal-reported diagnosis or by the Behavior Problems Index Hyperactivity Scale. Controls were chosen from the same age group but had a score of less than 14 on the overall Behavior Problems Index. A history of allergies was considered positive if any of the following conditions were reported as requiring treatment by a doctor or other health professional: asthma, allergic conditions, or food allergies. A strong association was observed between allergies and a maternal-reported diagnosis while controlling for demographic, socioeconomic, perinatal, and environmental factors (adjusted odds ratio = 2.85 (95% CI = 1.49-5.42)). Other risk factors found to be important risk factors for a diagnosis of ADHD were gender (male), gestational age ($<$36 weeks), and maternal education ($\leq$high school). No association between allergies and cases classified as ADHD based on the hyperactivity symptom scale was observed. This study confirms other studies that reported an allergy/ADHD association in diagnoses populations. Further investigation confirming the association and explanation of the reasons and underlying mechanisms of the observed association is warranted. These studies should use validated diagnostic criteria for the diagnosis of ADHD symptoms and allergies, adequate sample sizes, and control for confounding. ^

The contributions of the hippocampal formation, perirhinal cortex and areas TH/TF to object, spatial and contextual recognition memory in primates

Adult monkeys (Macaca mulatta) with lesions of the hippocampal formation, perirhinal cortex, areas TH/TF, as well as controls were tested on tasks of object, spatial and contextual recognition memory. ^ Using a visual paired-comparison (VPC) task, all experimental groups showed a lack of object recognition relative to controls, although this impairment emerged at 10 sec with perirhinal lesions, 30 sec with areas TH/TF lesions and 60 sec with hippocampal lesions. In contrast, only perirhinal lesions impaired performance on delayed nonmatching-to-sample (DNMS), another task of object recognition memory. All groups were tested on DNMS with distraction (dDNMS) to examine whether the use of active cognitive strategies during the delay period could enable good performance on DNMS in spite of impaired recognition memory (revealed by the VPC task). Distractors affected performance of animals with perirhinal lesions at the 10-sec delay (the only delay in which their DNMS performance was above chance). They did not affect performance of animals with areas TH/TF lesions. Hippocampectomized animals were impaired at the 600-sec delay (the only delay at which prevention of active strategies would likely affect their behavior). ^ While lesions of areas TH/TF impaired spatial location memory and object-in-place memory, hippocampal lesions impaired only object-in-place memory. The pattern of results for perirhinal cortex lesions on the different task conditions indicated that this cortical area is not critical for spatial memory. ^ Finally, all three lesions impaired contextual recognition memory processes. The pattern of impairment appeared to result from the formation of only a global representation of the object and background, and suggests that all three areas are recruited for associating information across sources. ^ These results support the view that (1) the perirhinal cortex maintains storage of information about object and the context in which it is learned for a brief period of time, (2) areas TH/TF maintain information about spatial location and form associations between objects and their spatial relationship (a process that likely requires additional time) and (3) the hippocampal formation mediates associations between objects, their spatial relationship and the general context in which these associations are formed (an integrative function that requires additional time). ^

STUDIES ON CHOLINERGIC FUNCTION AND MEMORY IN MICE (CHOLINOTOXINS, WORKING, REFERENCE MEMORY, RADIAL ARM MAZE)

Considerable evidence suggests that central cholinergic neurons participate in either acquisition, storage or retrieval of information. Experiments were designed to evaluate information processing in mice following either reversible or irreversible impairment in central cholinergic activity. The cholinergic receptor antagonists, atropine and methylatropine were used to reversibly inhibit cholinergic transmission. Irreversible impairment in central cholinergic function was achieved by central administration of the cholinergic-specific neurotoxins, N-ethyl-choline aziridinium (ECA) and N-ethyl-acetylcholine aziridinium (EACA).^ ECA and EACA appear to act by irreversible inhibition of high affinity choline uptake (proposed rate-limiting step in acetylcholine synthesis). Intraventricular administration of ECA or EACA produced persistent reduction in hippocampal choline acetyltransferase activity. Other neuronal systems and brain regions showed no evidence of toxicity.^ Mice treated with either ECA or EACA showed behavioral deficits associated with cholinergic dysfunction. Passive avoidance behavior was significantly impaired by cholinotoxin treatment. Radial arm maze performance was also significantly impaired in cholinotoxin-treated animals. Deficits in radial arm maze performance were transient, however, such that rapid and apparent complete behavioral recovery was seen during retention testing. The centrally active cholinergic receptor antagonist atropine also caused significant impairment in radial arm maze behavior, while equivalent doses of methylatropine were without effect.^ The relative effects of cholinotoxin and receptor antagonist treatment on short-term (working) memory and long-term (reference) memory in radial arm maze behavior were examined. Maze rotation studies indicated that there were at least two different response strategies which could result in accurate maze performance. One strategy involved the use of response algorithms and was considered to be a function of reference memory. Another strategy appeared to be primarily dependent on spatial working memory. However, all behavioral paradigms with multiple trails have reference memory requirements (i.e. information useful over all trials). Performance was similarly affected following either cholinotoxin or anticholinergic treatment, regardless of the response strategy utilized. In addition, rates of behavioral recovery following cholinotoxin treatment were similar between response groups. It was concluded that both cholinotoxin and anticholinergic treatment primarily resulted in impaired reference memory processes. ^

AROUSAL, FATIGUE AND MENTAL PERFORMANCE: THE EFFECTS OF FASTING ON COGNITION

This study examined the effects of skipping breakfast on selected aspects of children's cognition, specifically their memory (both immediate and one week following presentation of stimuli), mental tempo, and problem solving accuracy. Test instruments used included the Hagen Central/Incidental Recall Test, Matching Familiar Figures Test, McCarthy Digit Span and Tapping Tests. The study population consisted of 39 nine-to eleven year old healthy children who were admitted for overnight stays at a clinical research setting for two nights approximately one week apart. The study was designed to be able to adequately monitor and control subjects' food consumption. The design chosen was the cross-over design where randomly on either the first or second visit, the child skipped breakfast. In this way, subjects acted as their own controls. Subjects were tested at noon of both visits, this representing an 18-hour fast.^ Analysis focused on whether or not fasting for this period of time affected an individual's performance. Results indicated that for most of the tests, subjects were not significantly affected by skipping breakfast for one morning. However, on tests of short-term central and incidental recall, subjects who had skipped breakfast recalled significantly more of the incidental cues although they did so at no apparent expense to their storing of central information. In the area of problem-solving accuracy, subjects skipping breakfast at time two made significantly more errors on hard sections of the MFF Test. It should be noted that although a large number of tests were conducted, these two tests showed the only significant differences.^ These significant results in the areas of short-term incidental memory and in problem solving accuracy were interpreted as being an effect of subject fatigue. That is, when subjects missed breakfast, they were more likely to become fatigued and in the novel environment presented in the study setting, it is probable that these subjects responded by entering Class II fatigue which is characterized by behavioral excitability, diffused attention and altered performance patterns. ^