Systems neuroscienceExposure to novelty and forced swimming evoke stressor-dependent changes in extracellular GABA in the rat hippocampus
Section snippets
Animals
Male Wistar rats (breeding stock University of Bristol) were housed three per cage under standard housing conditions (lights on from 05:00–19:00 h; temperature 21–22 °C; relative humidity 40–60%; free access to food pellets and drinking water). At the time of surgery, the body weight of the rats was about 220 g. Rats were handled once per day (5 min per rat) starting 1 week before surgery to allow them to familiarise to the experimenter and the i.c.v. injection procedure and was continued after
Pharmacological characterization of hippocampal extracellular levels of GABA as measured by in vivo microdialysis
Fig. 1 shows an example of a chromatogram of GABA in a standard and of GABA in a dialysate sample. Mean basal levels of extracellular GABA were 373.0±16.2 fmol/10 min sample (n=61), not corrected for the recovery of the dialysis membrane. There was no significant correlation between hippocampal extracellular levels of GABA and behavioural activity under baseline (i.e. non-stress conditions; r=0.062, P>0.05). Perfusion of the probe with Ringer solution containing a high concentration of
Discussion
The data presented here are the first to demonstrate that extracellular GABA in the hippocampus responds to stress in a stressor-dependent manner. Novel cage exposure, a mild psychological stressor, increased hippocampal GABA levels. In contrast, forced swimming in 25 °C water, a stressor with combined physical and psychological aspects, resulted in a profound decrease in extracellular GABA in this brain structure. When the physical impact of forced swimming was limited by using 35 °C water,
Conclusion
In summary, these data demonstrate for the first time rapid and stressor-specific changes in extracellular GABA in the hippocampus of the rat, that seem to be independent of CRF. These data are of particular significance for the study of tonic inhibition by GABA in the hippocampus as they show that changes in the extracellular concentrations of this neurotransmitter, probably a key determinant for the degree of tonic inhibition, occur under physiologically relevant circumstances like stress. As
Acknowledgments
Supported by the Neuroendocrinology Charitable Trust grant PMS/MMS-02/03/884.
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