Monosodium glutamate and sweet taste: generalization of conditioned taste aversion between glutamate and sweet stimuli in rats.

Even though monosodium glutamate (MSG) is a prototypical umami substance, previous studies reported that a conditioned taste aversion (CTA) to MSG, mixed with amiloride to block the taste of sodium, generalizes to sucrose. These findings suggest that the taste of glutamate mimics the taste of sucrose and raise the question of whether glutamate has a broadly tuned sweet taste component. To test this hypothesis, CTA experiments were conducted to test for generalization between MSG and several sweet stimuli: sucrose, glucose, maltose, saccharin and SC-45647. Strong bidirectional generalization was seen between MSG mixed with amiloride and sucrose, glucose, saccharin and SC-45647. Weak generalization was seen between MSG and maltose, and sucrose and maltose. None of the CTAs generalized to NMDA. These findings support the hypothesis that the taste of MSG has broadly tuned, sweet-like characteristics, possibly due to the convergence of afferent signals for MSG, natural sugars and artificial sweeteners.

Regional specificity of tubulin heterogeneity in adult mouse brain.

Eight alpha and twelve beta isoforms of tubulin were isolated from discrete regions of the mouse brain using high-resolution isoelectric focusing and identified by two-dimensional gel electrophoresis and immunoreactivity. In the different regions, the number of isoforms was identical, but their relative proportion varied except for alpha 2, 3, 4, 5, 6 and beta 1 bands. The patterns of the inferior and superior colliculi were nearly similar. The cerebellum, compared with the inferior and superior colliculi is characterized by a decrease of alpha band 7 and beta bands 3 and 7 and an increase of alpha band 8 and beta bands 2, 4, 10, 11, 12. The forebrain displays an intermediate pattern between the cerebellum and the colliculi. These results suggest that in functionally different regions of the brain the number of isotypes of tubulin is identical but their relative proportion differs with an apparent correlation between the function of the neuronal subpopulations and the pattern of isotubulins.

Increase of junctional and background 16S (tailed, asymmetric) acetylcholinesterase during postnatal maturation of rat and mouse sternocleidomastoid muscle.

Acetylcholinesterase (AChE) is found both in motor end-plate (MEP)-free and MEP-rich regions of rat or mouse muscle. We studied the developmental aspects of the localization of asymmetric 16S AChE in both regions of the sternocleidomastoid muscle, which has a well-defined zone of motor innervation. In the rat, the proportion of 16S AChE to total AChE increases in the MEP-rich region, and becomes significantly higher than in the MEP-free regions between the first and the second weeks after birth. In the mouse, at birth, the MEP-rich region already has a higher relative content in 16S AChE than the MEP-free regions. Total 16S AChE amounts increase during postnatal development, not only in the MEP-rich region but also in the MEP-free regions. Thus, 16S AChE is not eliminated from MEP-free regions during muscle maturation and growth. Two distinct pools of 16S AChE are distinguished in the muscles, both of which increase during postnatal development: junctional and background 16S AChE.

Polymorphism of acetylcholinesterase and identification of new molecular forms after sedimentation analysis.

Acetylcholinesterase (AChE) is composed of several distinct molecular forms, which are identified and partly resolved by velocity sedimentation analysis on sucrose gradients. We made the assumption that each AChE form sediments as a peak of activity with a gaussian shape in the continuous sucrose gradient. We experimentally demonstrate that the complex AChE profiles can be decomposed in gaussian distributions of separate molecular entities. We performed a high salt-detergent extraction of AChE from mouse skeletal muscle and isolated fractions enriched in each particular from. These fractions were then submitted to a second sedimentation, to assess the stability and to further characterize each AChE form. Then, we calculated the statistical significance level of each AChE form and identified up to 9 separate molecular specifies in mouse adult muscle. These forms are the major "4 S", "6.5 S", "10 S", "12 S" and "16 S" and minor molecular active components of AChE. These results suggest complex structural interactions between catalytic and non catalytic subunits of AChE and do not simply fit the tailed asymmetric globular model of AChE with six molecular species.