beta-Adrenergic, but not benzodiazepine, binding sites are reduced in dystrophic mouse brain

Specific alterations in the levels of N-acetyl-aspartyl-glutamate in the nervous system of the dystrophic mouse

Determinations of N-acetyl-aspartate (NAA) and N-acetyl-aspartyl-glutamate (NAAG) levels were obtained by ion-exchange HPLC from 10 regions of the male dystrophic mouse brain as well as from those of non-dystrophic littermate controls. Similar to previous studies in the rat, NAA levels in control mice were distributed rather uniformly while NAAG levels exhibited a pronounced rostrocaudal gradient, with highest levels found in the lumbar spinal cord. Contrary to a recent report, we found no significant alterations in gross brain or spinal cord levels of NAA. In contrast, levels of NAAG were substantially and differentially reduced in several regions of the dystrophic mouse nervous system. These results demonstrate a pathological dissociation between NAA and NAAG, whose levels are known to display differential regional, ontogenetic and phylogenetic patterns. In addition, they may represent an ability of neural tissue to differentially regulate their steady-state levels, if indeed they can be shown to be biosynthetically related. The pronounced and non-uniform NAAG reductions observed in the dystrophic CNS underscores recent suggestions of a role for the neuropeptide in central systems involved in the control of motor function.

Decrease in N-acetyl-L-aspartic acid in brain of myodystrophic mice

Brain tissue from myodystrophic mice (male 129/ReJ-dy and female 129 B6F1/J-dy) was examined to determine whether CNS abnormalities accompany the known muscular defects. Brain N-acetyl-L-aspartate, aspartate, and glutamate were significantly lower than in brain from control mice. These amino acids are only slightly reduced in brains of female dystrophic mice.

Strain differences in brain alpha2- and beta-adrenergic receptor binding in dystrophic mice

We have examined alpha 2-adrenergic [( 3H]-clonidine) and beta-adrenergic [( 3H]-dihydroalprenolol; DHA) binding in brain membranes from four different dystrophic mouse mutants: 129/ReJ-dy; 129 B6F1/J-dy; C57BL/6J-dy and C57BL/6J-dy2J. As shown previously, male 129/ReJ-dy mice have significantly fewer brain [3H]-DHA binding sites than their littermate controls. In marked contrast, the remaining three mutants showed no differences in [3H]-DHA binding when compared to their respective controls although there were inter-strain differences, e.g., C57BL/6J-dy2J mice have significantly fewer binding sites than the 129B6F1/J-dy mice. On the other hand, we saw no strain differences in alpha 2-binding. In one mutant, however, (129 B6F1/J-dy) we observed a 50% increase in alpha 2-binding sites compared to littermate controls. We conclude that weight loss or undernutrition may be an important factor in determining brain levels of adrenergic binding sites in dystrophic mouse brain.

Benzodiazepine receptors in fish brain: [3H]-flunitrazepam binding and modulatory effects of GABA in rainbow trout

We have identified and partially characterised benzodiazepine binding sites in whole brain membranes of male rainbow trout. In terms of Bmax and KD values trout brain receptors are remarkably similar to those in rat and human brain. The Hill coefficient was 0.98, indicating a single binding site. GABA (10(-4) M) was able to significantly elevate binding of [3H]-FNZ through a change in KD rather than Bmax. This effect was prevented by the GABA receptor antagonist bicuculline methiodide.