Using quantitative microdialysis in hibernating Arctic ground squirrels (AGS), striatal glutamate concentrations ([glu]dia) progressively increased to approximately 200 μM after 3 days of microdialysis in euthermic but not hibernating ground squirrels. Initially, the progressive increase in [glu]dia was thought to be related to greater tissue response in euthermic animals. Alternatively, given the vastly different body temperatures between the two groups (37 vs. 3°C), glutamate might have originated from microbes, replicating at a faster rate in the warmer animals. To test these hypotheses, microdialysis was repeated using sterile technique and tissue response surrounding the probe tract was assessed in hematoxylin and eosin stained sections. Using sterile microdialysis technique, traumatic tissue response was greater in euthermic compared to hibernating tissue. However, sterile microdialysis abolished the progressive increase in glutamate. To confirm the microbial origin of glutamate we monitored [glu]dia collected in vitro from probes immersed in glutamine-rich liquid medium incubated at 37°C. In vitro, [glu]dia increased as much as in vivo. Two bacteria isolated from in vitro dialysate and liquid medium were both identified as Ralstonia pickettii. Growth of these isolates as well as glutamate release was enhanced when glutamine rather than NH4NO3 was added to the medium suggesting the bacteria utilize glutamine preferentially over ammonium as a nitrogen source.
- Penetrating brain injury
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