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Extracellular ascorbate modulates glutamate dynamics: role of behavioral activation.

Sandstrom MI, Rebec GV - BMC Neurosci (2007)

Bottom Line: A physiological increase in extracellular ascorbate (AA), an antioxidant vitamin found throughout the striatum, elevates extracellular glutamate (GLU).Interestingly, when ambient light returned to the lights-off group, 1000 microM prolonged the GLU increase relative to the 250 microM group.Our results not only support evidence that elevated striatal AA increases extracellular GLU but also indicate that this effect depends on behavioral state and the corresponding level of endogenous GLU release.

View Article: PubMed Central - HTML - PubMed

Affiliation: Central Michigan University, Psychology Department, Mount Pleasant, MI, USA. sands1m@cmich.edu <sands1m@cmich.edu>

ABSTRACT

Background: A physiological increase in extracellular ascorbate (AA), an antioxidant vitamin found throughout the striatum, elevates extracellular glutamate (GLU). To determine the role of behavioral arousal in this interaction, microdialysis was used to measure striatal GLU efflux in rats tested in either a lights-off or lights-on condition while reverse dialysis either maintained the concentration of AA at 250 microM or increased it to 1000 microM to approximate endogenous changes.

Results: When lights were off, both locomotion and GLU increased regardless of AA dose. In contrast, animals in the lights-on condition were behaviorally inactive, and infusion of 1000, but not 250, microM AA significantly increased extracellular GLU. Interestingly, when ambient light returned to the lights-off group, 1000 microM prolonged the GLU increase relative to the 250 microM group.

Conclusion: Our results not only support evidence that elevated striatal AA increases extracellular GLU but also indicate that this effect depends on behavioral state and the corresponding level of endogenous GLU release.

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Related in: MedlinePlus

Locomotor responses to light manipulation among the two groups of animals tested: open bars indicate the group experiencing continuous ambient light; hatched bars indicate those experiencing 75-mins of darkness restricted to the experimental period. Mean (± SEM) quadrant crossings according to periods are collapsed across dialysis session in the main graph as AA treatment was found to have no effect on locomotor behavior. Status of lights is indicated by the upper X-axis, and the three consecutive dialysis periods by the lower from left to right. Note the increase in behavior associated with turning off lights during the experimental period, only among those animals that experienced lights off (hatched bars) that lingered when lights were turned back on (post period). * p < 0.02 for between-subject comparisons of lights-on versus darkness exposed animals (hatched versus open bars); † p < 0.05 for within-subjects comparisons with initial (lights on) baseline among darkness exposed animals (hatched bars only).
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Figure 1: Locomotor responses to light manipulation among the two groups of animals tested: open bars indicate the group experiencing continuous ambient light; hatched bars indicate those experiencing 75-mins of darkness restricted to the experimental period. Mean (± SEM) quadrant crossings according to periods are collapsed across dialysis session in the main graph as AA treatment was found to have no effect on locomotor behavior. Status of lights is indicated by the upper X-axis, and the three consecutive dialysis periods by the lower from left to right. Note the increase in behavior associated with turning off lights during the experimental period, only among those animals that experienced lights off (hatched bars) that lingered when lights were turned back on (post period). * p < 0.02 for between-subject comparisons of lights-on versus darkness exposed animals (hatched versus open bars); † p < 0.05 for within-subjects comparisons with initial (lights on) baseline among darkness exposed animals (hatched bars only).

Mentions: During the baseline period when lights were on, all rats rested quietly and tended to remain in a single corner of the open field. All six rats exposed to continuous light (lights-on) showed minimal to no ambulation throughout the session. In contrast, the six exposed to darkness (lights-off) during the experimental period showed spontaneous locomotion as well as rearing and exploratory sniffing, and this activity persisted, albeit at a lower level, even as ambient light returned in the post-experimental period. Fig. 1 depicts this darkness-induced behavior increase for quadrant crosses. These animals crossed more quadrants than those in the lights-on group during both the experimental [t(11) = -3.53, p < 0.01] and post-experimental [t(11) = -3.02, p = 0.01] periods. While it was expected that returning ambient light (post-experimental) following darkness exposure would result in more immediate behavioral cessation, their decreased locomotion was not significant [t(11) = 2.047, p = 0.065]. Quadrant crosses were unaffected by reverse dialysis of either 250 or 1000 μM AA [p > 0.05 in both cases] ruling out an effect of AA alone on locomotion.


Extracellular ascorbate modulates glutamate dynamics: role of behavioral activation.

Sandstrom MI, Rebec GV - BMC Neurosci (2007)

Locomotor responses to light manipulation among the two groups of animals tested: open bars indicate the group experiencing continuous ambient light; hatched bars indicate those experiencing 75-mins of darkness restricted to the experimental period. Mean (± SEM) quadrant crossings according to periods are collapsed across dialysis session in the main graph as AA treatment was found to have no effect on locomotor behavior. Status of lights is indicated by the upper X-axis, and the three consecutive dialysis periods by the lower from left to right. Note the increase in behavior associated with turning off lights during the experimental period, only among those animals that experienced lights off (hatched bars) that lingered when lights were turned back on (post period). * p < 0.02 for between-subject comparisons of lights-on versus darkness exposed animals (hatched versus open bars); † p < 0.05 for within-subjects comparisons with initial (lights on) baseline among darkness exposed animals (hatched bars only).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC1884166&req=5

Figure 1: Locomotor responses to light manipulation among the two groups of animals tested: open bars indicate the group experiencing continuous ambient light; hatched bars indicate those experiencing 75-mins of darkness restricted to the experimental period. Mean (± SEM) quadrant crossings according to periods are collapsed across dialysis session in the main graph as AA treatment was found to have no effect on locomotor behavior. Status of lights is indicated by the upper X-axis, and the three consecutive dialysis periods by the lower from left to right. Note the increase in behavior associated with turning off lights during the experimental period, only among those animals that experienced lights off (hatched bars) that lingered when lights were turned back on (post period). * p < 0.02 for between-subject comparisons of lights-on versus darkness exposed animals (hatched versus open bars); † p < 0.05 for within-subjects comparisons with initial (lights on) baseline among darkness exposed animals (hatched bars only).
Mentions: During the baseline period when lights were on, all rats rested quietly and tended to remain in a single corner of the open field. All six rats exposed to continuous light (lights-on) showed minimal to no ambulation throughout the session. In contrast, the six exposed to darkness (lights-off) during the experimental period showed spontaneous locomotion as well as rearing and exploratory sniffing, and this activity persisted, albeit at a lower level, even as ambient light returned in the post-experimental period. Fig. 1 depicts this darkness-induced behavior increase for quadrant crosses. These animals crossed more quadrants than those in the lights-on group during both the experimental [t(11) = -3.53, p < 0.01] and post-experimental [t(11) = -3.02, p = 0.01] periods. While it was expected that returning ambient light (post-experimental) following darkness exposure would result in more immediate behavioral cessation, their decreased locomotion was not significant [t(11) = 2.047, p = 0.065]. Quadrant crosses were unaffected by reverse dialysis of either 250 or 1000 μM AA [p > 0.05 in both cases] ruling out an effect of AA alone on locomotion.

Bottom Line: A physiological increase in extracellular ascorbate (AA), an antioxidant vitamin found throughout the striatum, elevates extracellular glutamate (GLU).Interestingly, when ambient light returned to the lights-off group, 1000 microM prolonged the GLU increase relative to the 250 microM group.Our results not only support evidence that elevated striatal AA increases extracellular GLU but also indicate that this effect depends on behavioral state and the corresponding level of endogenous GLU release.

View Article: PubMed Central - HTML - PubMed

Affiliation: Central Michigan University, Psychology Department, Mount Pleasant, MI, USA. sands1m@cmich.edu <sands1m@cmich.edu>

ABSTRACT

Background: A physiological increase in extracellular ascorbate (AA), an antioxidant vitamin found throughout the striatum, elevates extracellular glutamate (GLU). To determine the role of behavioral arousal in this interaction, microdialysis was used to measure striatal GLU efflux in rats tested in either a lights-off or lights-on condition while reverse dialysis either maintained the concentration of AA at 250 microM or increased it to 1000 microM to approximate endogenous changes.

Results: When lights were off, both locomotion and GLU increased regardless of AA dose. In contrast, animals in the lights-on condition were behaviorally inactive, and infusion of 1000, but not 250, microM AA significantly increased extracellular GLU. Interestingly, when ambient light returned to the lights-off group, 1000 microM prolonged the GLU increase relative to the 250 microM group.

Conclusion: Our results not only support evidence that elevated striatal AA increases extracellular GLU but also indicate that this effect depends on behavioral state and the corresponding level of endogenous GLU release.

Show MeSH
Related in: MedlinePlus