QUANTITATIVE MICRODIALYSIS OF NEUROPEPTIDE-Y

The feasibility of using the difference method of quantitative microdi alysis to measure neuropeptide Y (NPY) was evaluated in vitro and in v ivo. The accuracy of this method was tested in vitro under steady-stat e conditions for 3 test solutions containing known concentrations of N PY. The estimated concentrations of NPY were 1.2 +/- 0.6, 3.7 +/- 0.9, and 15.1 +/- 0.7 pg/mu l (mean +/- SEM) in agreement with the actual concentrations of NPY in the test solutions which were 1.1 +/- 0.8, 4. 6 +/- 0.6, and 14.6 +/- 0.5 pg/mu l (mean +/- SEM of solution samples) , respectively. The responsiveness of the estimated NPYext measure to changes in the external concentration of NPY was also evaluated in vit ro. An accurate estimate of NPY(e)xt was obtained within the first sam pling period (within 15 min) after a 2-3-fold increase in the test sol ution concentration of NPY and within 2-3 sampling periods (15-45 min) in response to a 2-3-fold decrease in the test solution concentration of NPY. In vivo, the estimated basal concentration of NPY in dialysis samples from probes in the medial basal hypothalamus of anesthetized female rats (n = 4) was 4.0 +/- 1.6 pg/mu l and increased to 9.5 +/- 0 .3 pg/mu l during K+ stimulation. Relative recovery was 22% in vivo un der steady-state conditions and ranged from 14% to 30% during dynamic conditions. These results demonstrate that the difference method of qu antitative microdialysis accurately estimates picomolar concentrations of NPY in vitro, and is sufficiently sensitive to detect basal and in creasing concentrations of NPY in vivo.