Analytical Chemistry
Article
Prefrontal ACh and Glu Interaction. We also measured
prefrontocortical signaling to test the method under the
challenging condition of a high sampling rate. The mPFC is a
known center of emotional and cognitive function and is often
studied in psychiatric and attentional disorders.38,39 To uncover
physiologically and behaviorally relevant neurotransmitter
interactions in the mPFC, common microdialysis sampling
rates (i.e., 10- 30 min/sample) remain inadequate. Here, we
have made such measurements every 60 s to better capture
concentration dynamics on a more physiologically relevant time
scale.39 Measurement at short intervals requires high sensitivity
(1 μL samples are collected containing femtomoles of analyte)
and good throughput because of the large number of samples
generated (e.g., 80 samples per session in Figure 5).
The ACh esterase inhibitor neostigmine (5 min perfusion)
elevated ACh concentrations in the mPFC as expected but also
correlated with a transient increase in mPFC Glu concen-
tration. This result suggests that muscarinic or nicotinic ACh
receptors in the mPFC are responsible for stimulating Glu
release. Past studies have shown that exogenous ACh receptor
agonists such as nicotine enhance cognition and stimulate Glu
activity in the mPFC.40 Our data show that stimulated
endogenous ACh is capable of enhancing Glu release in this
brain area. This ACh−Glu interaction may play a role in
cognition and the beneficial effects of drugs which stimulate
ACh receptors.40 Interestingly, other neurotransmitter systems,
including the monoamines, were left unaffected by neostigmine
perfusion. These results show how a comprehensive view of
neuropharmacological effects can be assayed by the method.
They also show the value of the temporal resolution as the
transient rise of Glu would likely be undetected at longer
sampling intervals.
ACKNOWLEDGMENTS
■
We thank the Center for Statistical Consultation and Research
(CSCAR) at the University of Michigan for assistance with
statistical analyses. This work was supported by NIH grant R37
EB003320 (R.T.K.) and National Institute on Drug Abuse T32
training grant DA07268 (O.S.M.).
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CONCLUSION
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The results show that benzoylation with HPLC-MS is a robust
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AUTHOR INFORMATION
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Corresponding Author
*Address: Department of Chemistry, University of Michigan,
930 N. University Ave., Ann Arbor, MI 48109-1055. Phone:
418
dx.doi.org/10.1021/ac202794q | Anal. Chem. 2012, 84, 412−419