Changes in glutamate and glutamine distributions in the retinas of cystine/glutamate antiporter knockout mice

Purpose

The cystine/glutamate antiporter is involved in the export of intracellular glutamate in exchange for extracellular cystine. Glutamate is the main neurotransmitter in the retina and plays a key metabolic role as a major anaplerotic substrate in the tricarboxylic acid cycle to generate adenosine triphosphate (ATP). In addition, glutamate is also involved in the outer plexiform glutamate-glutamine cycle, which links photoreceptors and supporting Müller cells and assists in maintaining photoreceptor neurotransmitter supply. In this study, we investigated the role of xCT, the light chain subunit responsible for antiporter function, in glutamate pathways in the mouse retina using an xCT knockout mouse. As xCT is a glutamate exporter, we hypothesized that loss of xCT function may influence the presynaptic metabolism of photoreceptors and postsynaptic levels of glutamate.

Methods

Retinas of C57BL/6J wild-type (WT) and xCT knockout (KO) mice of either sex were analyzed from 6 weeks to 12 months of age. Biochemical assays were used to determine the effect of loss of xCT on glycolysis and energy metabolism by measuring lactate dehydrogenase activity and ATP levels. Next, biochemical assays were used to measure whole-tissue glutamate and glutamine levels, while silver-intensified immunogold labeling was performed on 6-week and 9-month-old retinas to visualize and quantify the distribution of glutamate, glutamine, and related neurochemical substrates gamma-aminobutyric acid (GABA) and glycine in the different layers of the retina.

Results

Biochemical analysis revealed that loss of xCT function did not alter the lactate dehydrogenase activity, ATP levels, or glutamate and glutamine contents in whole retinas in any age group. However, at 6 weeks of age, the xCT KO retinas revealed altered glutamate distribution compared with the age-matched WT retinas, with accumulation of glutamate in the photoreceptors and outer plexiform layer. In addition, at 6 weeks and 9 months of age, the xCT KO retinas also showed altered glutamine distribution compared with the WT retinas, with glutamine labeling significantly decreased in Müller cell bodies. No significant difference in GABA or glycine distribution were found between the WT and xCT KO retinas at 6 weeks or 9 months of age.

Conclusion

Loss of xCT function results in glutamate metabolic disruption through the accumulation of glutamate in photoreceptors and a reduced uptake of glutamate by Müller cells, which in turn decreases glutamine production. These findings support the idea that xCT plays a role in the presynaptic metabolism of photoreceptors and postsynaptic levels of glutamate and derived neurotransmitters in the retina.

Obstetric management following fertility-sparing radical vaginal trachelectomy for cervical cancer

Radical vaginal trachelectomy now affords a fertility-sparing procedure for the treatment of early-stage cervical cancer in young women. Subsequent obstetric management within this group of women remains a challenge to the obstetrician, with risks of premature labour a continuing probability throughout pregnancy. Here we describe four cases of successful pregnancy following radical vaginal trachelectomy within our unit. The merits of early antenatal intervention, regular lower uterine segment length monitoring and use of daily progesterone pessaries are discussed, alongside the current supportive evidence. We conclude with a discussion of proposed recommendations for obstetric management of pregnancy in women post-radical vaginal trachelectomy.

Restrained eating: an experimental disentanglement of the disinhibiting variables of perceived calories and food type

The influence of food type on the restrained eating pattern was examined. In Study 1, subjects rated the degree to which each of 149 foods were dietary permissable or dietary forbidden. The number of avoided foods correlated positively with restraint score. Study 2 compared Herman and Mack's (1975) 1- and 2-milk shake preloads to two nonforbidden preloads of equivalent calories. Food type, and not perceived calories, was found to be the element of the preload required to cause disinhibition among restrained eaters, both within the experiment and outside the experimental setting. Study 3 examined the effects of anticipated consumption (varying food type and calories) on the restrained eating pattern. Only restrained eaters anticipating a forbidden food (whether high or low in calories) were disinhibited. The restrained literature was reconsidered in light of the forbidden food hypothesis.

Restrained eating: An experimental disentanglement of the disinhibiting variables of perceived calories and food type

The influence of food type on the restrained eating pattern was examined. In Study 1, subjects rated the degree to which each of 149 foods were dietary permissable or dietary forbidden. The number of avoided foods correlated positively with restraint score. Study 2 compared Herman and Mack's (1975) 1- and 2-milk shake preloads to two nonforbidden preloads of equivalent calories. Food type, and not perceived calories, was found to be the element of the preload required to cause disinhibition among restrained eaters, both within the experiment and outside the experimental setting. Study 3 examined the effects of anticipated consumption (varying food type and calories) on the restrained eating pattern. Only restrained eaters anticipating a forbidden food (whether high or low in calories) were disinhibited. The restrained literature was reconsidered in light of the forbidden food hypothesis.