Carnosine synthase deficiency is compatible with normal skeletal muscle and olfactory function but causes reduced olfactory sensitivity in aging mice

Carnosine (β-alanyl-l-histidine) and anserine (β-alanyl-3-methyl-l-histidine) are abundant peptides in the nervous system and skeletal muscle of many vertebrates. Many in vitro and in vivo studies demonstrated that exogenously added carnosine can improve muscle contraction, has antioxidant activity, and can quench various reactive aldehydes. Some of these functions likely contribute to the proposed anti-aging activity of carnosine. However, the physiological role of carnosine and related histidine-containing dipeptides (HCDs) is not clear. In this study, we generated a mouse line deficient in carnosine synthase (Carns1). HCDs were undetectable in the primary olfactory system and skeletal muscle of Carns1-deficient mice. Skeletal muscle contraction in these mice, however, was unaltered, and there was no evidence for reduced pH-buffering capacity in the skeletal muscle. Olfactory tests did not reveal any deterioration in 8-month-old mice lacking carnosine. In contrast, aging (18–24-month-old) Carns1-deficient mice exhibited olfactory sensitivity impairments that correlated with an age-dependent reduction in the number of olfactory receptor neurons. Whereas we found no evidence for elevated levels of lipoxidation and glycation end products in the primary olfactory system, protein carbonylation was increased in the olfactory bulb of aged Carns1-deficient mice. Taken together, these results suggest that carnosine in the olfactory system is not essential for information processing in the olfactory signaling pathway but does have a role in the long-term protection of olfactory receptor neurons, possibly through its antioxidant activity.     

Nijmegen breakage syndrome: The clearance pathway for mutant nibrin protein is allele specific

The autosomal recessive disorder Nijmegen breakage syndrome (NBS) is caused by mutations in the NBN gene which codes for the protein nibrin (NBS1; p95). In the majority of cases, a 5 bp deletion, a founder mutation, leads to a hypomorphic 70 kD protein, p70-nibrin, after alternative initiation of translation. Protein levels are of relevance for the clinical course of the disease, particularly with regard to malignancy. Here, mechanisms and efficiency of mutant protein clearance were examined in order to establish whether these have an impact on nibrin abundance. Cell lines from NBS patients and retroviral transductants were treated with proteasome and lysosome inhibitors and examined by semi-quantitative immunoblotting for p70-nibrin and p95-nibrin levels. The results show that p70-nibrin is degraded by the proteasome with varying efficiency in cell lines from different NBS patients leading to lower or higher steady state levels of this partially active protein fragment. In contrast, a previously described NBN missense mutation, which disturbs protein folding due to the substitution of a critical arginine by tryptophan, was found to be cleared by lysosomal microautophagy leading also to lower cellular levels. The data show that truncated nibrin and misfolded nibrin have different clearance pathways.     

Electrolocation in the presence of jamming signals: electroreceptor physiology

Responses of ampullary and tuberous electroreceptor afferents were studied using moving electrolocation targets and electrical modulations of the animal's electric organ discharge as stimuli. The ability of the electroreceptors to encode these stimuli was measured with and without various forms of electrical jamming signals. The goal of this study was to measure the deterioration in electroreceptor responses due to the jamming signals, and to compare these results with the behavioral measures of electrolocation under the same conditions of jamming as described in the preceding report (Bastian 1987). 1. Three types of jamming stimuli were used to interfere with the tuberous electroreceptor afferents' ability to respond to the test stimuli mentioned above: Broad-band noise, high frequency stimuli consisting of a sinusoidal waveform having a frequency maintained at a chosen difference frequency (DF) from the EOD frequency of the fish being studied, and 5 or 50 Hz sinusoidal stimuli. 2. The tuberous receptor afferents' spontaneous frequency was sensitive to continuous presentation of all but the 5 Hz jamming signals. The 4 Hz DF signal caused the largest increase in spontaneous activity, the 50 Hz stimulus was intermediate in effectiveness, and the noise stimulus caused the smallest increase. Estimates of the variability of the ongoing receptor activity were also made, and both the 4 Hz DF and the 50 Hz stimuli reduced the coefficient of variation of the receptor activity, but noise had no significant effect on this parameter. Noise, 4 Hz DF, and 50 Hz jamming signals also reduced the tuberous receptors' responses to a 100 ms EOD amplitude modulation, and the 5 Hz stimulus was again ineffective. 3. Noise and 4 Hz DF jamming were also effective in reducing tuberous receptor afferents' responses to a moving metal electrolocation target. The 4 Hz DF stimulus was most effective in reducing the receptor's ability to encode information about the target. Receptor responses showed about a three-fold larger decrease per 10 dB increase in DF jamming amplitude as compared to similar sized increases in noise amplitude. Threshold target distances were also determined with and without noise and DF jamming, and again, the noise stimulus was less effective in reducing the distance at which electrolocation targets were just detectable. 4. Recordings from ampullary receptor afferents confirmed that the galvanic potentials produced by metal electrolocation targets stimulate these receptors while EOD distortions caused by such objects probably do not.(ABSTRACT TRUNCATED AT 400 WORDS)     

Activation of the medial preoptic area (MPOA) ameliorates loss of maternal behavior in a Shank2 mouse model for autism

Impairments in social relationships and awareness are features observed in autism spectrum disorders (ASDs). However, the underlying mechanisms remain poorly understood. Shank2 is a high‐confidence ASD candidate gene and localizes primarily to postsynaptic densities (PSDs) of excitatory synapses in the central nervous system (CNS). We show here that loss of Shank2 in mice leads to a lack of social attachment and bonding behavior towards pubs independent of hormonal, cognitive, or sensitive deficits. Shank2 ^−/− mice display functional changes in nuclei of the social attachment circuit that were most prominent in the medial preoptic area (MPOA) of the hypothalamus. Selective enhancement of MPOA activity by DREADD technology re‐established social bonding behavior in Shank2 ^−/− mice, providing evidence that the identified circuit might be crucial for explaining how social deficits in ASD can arise.     

Horseradish peroxidase labeled antisera--a diagnostic method for evaluating the percentages of B lymphocytes in peripheral blood.

Horseradish peroxidase labeled antisera supplied commercially was used to evaluate B lymphocytes in peripheral blood. This technique not only gave comparable results to the conventional fluorescein method, but also proved to be more advantageous.