Distance Properties of Short LDPC Codes and their Impact on the BP, ML and Near-ML Decoding Performance

Parameters of LDPC codes, such as minimum distance, stopping distance, stopping redundancy, girth of the Tanner graph, and their influence on the frame error rate performance of the BP, ML and near-ML decoding over a BEC and an AWGN channel are studied. Both random and structured LDPC codes are considered. In particular, the BP decoding is applied to the code parity-check matrices with an increasing number of redundant rows, and the convergence of the performance to that of the ML decoding is analyzed. A comparison of the simulated BP, ML, and near-ML performance with the improved theoretical bounds on the error probability based on the exact weight spectrum coefficients and the exact stopping size spectrum coefficients is presented. It is observed that decoding performance very close to the ML decoding performance can be achieved with a relatively small number of redundant rows for some codes, for both the BEC and the AWGN channels

Interaction between environmental and genetic factors modulates schizophrenic endophenotypes in the Snap-25 mouse mutant blind-drunk

To understand the pathophysiology of neuropsychiatric disorders such as schizophrenia requires consideration of multiple genetic and non-genetic factors. However, very little is known about the consequences of combining models of synaptic dysfunction with controlled environmental manipulations. Therefore, to generate new insights into gene–environment interactions and complex behaviour, we examined the influence of variable prenatal stress (PNS) on two mouse lines with mutations in synaptosomal-associated protein of 25 kDa (Snap-25): the blind-drunk (Bdr) point mutant and heterozygous Snap-25 knockout mice. Neonatal development was analysed in addition to an assessment of adult behavioural phenotypes relevant to the psychotic, cognitive and negative aspects of schizophrenia. These data show that PNS influenced specific anxiety-related behaviour in all animals. In addition, sensorimotor gating deficits previously noted in Bdr mutants were markedly enhanced by PNS; significantly, these effects could be reversed with the application of anti-psychotic drugs. Moreover, social interaction abnormalities were observed only in Bdr animals from stressed dams but not in wild-type littermates or mutants from non-stressed mothers. These results show for the first time that combining a synaptic mouse point mutant with a controlled prenatal stressor paradigm produces both modified and previously unseen phenotypes, generating new insights into the interactions between genetics and the environment relevant to the study of psychiatric disease

Prenatal stress programs neuroendocrine stress responses and affective behaviors in second generation rats in a sex-dependent manner

AbstractAn adverse environment in early life is often associated with dysregulation of the hypothalamo-pituitary-adrenal (HPA) axis and higher rates of mood disorders in adulthood. In rats, exposure to social stress during pregnancy results in hyperactive HPA axis responses to stress in the adult offspring and heightened anxiety behavior in the males, but not the females. Here we tested whether, without further intervention, the effects of prenatal stress (PNS) in the first filial generation (F1) are transmitted to the F2 generation via the maternal line. F1 control and PNS female rats were mated with control males and housed under non-stress conditions throughout pregnancy. HPA axis responses to acute stress, anxiety- and depressive-like behavior were assessed in the adult F2 offspring.ACTH and corticosterone responses to an acute stressor were markedly enhanced in F2 PNS females compared with controls. This was associated with greater corticotropin releasing hormone (Crh) mRNA expression in the paraventricular nucleus and reduced hippocampal glucocorticoid (Gr) and mineralocorticoid receptor (Mr) mRNA expression. Conversely, in the F2 PNS males, HPA axis responses to acute stress were attenuated and hippocampal Gr mRNA expression was greater compared with controls.F2 PNS males exhibited heightened anxiety-like behavior (light-dark box and elevated plus maze) compared with F2 control males. Anxiety-like behavior did not differ between F2 control and PNS females during metestrus/diestrus, however at proestrus/estrus, F2 control females displayed a reduction in anxiety-like behavior, but this effect was not observed in the F2 PNS females. Heightened anxiety in the F2 PNS males was associated with greater Crh mRNA expression in the central nucleus of the amygdala compared with controls. Moreover, Crh receptor-1 (Crhr1) mRNA expression was significantly increased, whereas Crhr2 mRNA was significantly decreased in discrete regions of the amygdala in F2 PNS males compared with controls, with no differences in the F2 females. No differences in depressive-like behavior (sucrose preference or forced swim test) were observed in either sex. In conclusion, the effects of maternal stress during pregnancy on HPA axis regulation and anxiety-like behavior can be transmitted to future generations in a sex-dependent manner. These data have implications for human neuropsychiatric disorders with developmental origins