Measuring oxytocin levels in specific brain regions can be challenging, but there are several established methods that can be used to quantify oxytocin concentrations in the ventral tegmental area (VTA), nucleus accumbens (NAC), hypothalamus (Hypo), and amygdala.

One common method for measuring oxytocin levels in specific brain regions is microdialysis. This involves implanting a microdialysis probe into the brain region of interest and perfusing the probe with a saline solution to collect extracellular fluid. Oxytocin in the collected samples can then be quantified using enzyme-linked immunosorbent assay (ELISA) or radioimmunoassay (RIA) methods. Microdialysis is a widely used technique for measuring oxytocin release in the brain, but it requires specialized equipment and expertise.

Another method for measuring oxytocin levels in specific brain regions is by using punch biopsies. In this method, a small tissue sample is taken from the brain region of interest using a fine-tipped punch biopsy needle, and the oxytocin content of the tissue sample can be quantified using ELISA or RIA methods.

There are several papers available that describe the procedures for measuring oxytocin levels in specific brain regions using these and other methods. Some examples include:

1. Bosch et al. (2013) - "Oxytocin in the nucleus accumbens shell reverses CRFR2-evoked passive stress-coping after traumatic stress"

2. Bales et al. (2007) - "Chronic intranasal oxytocin causes long-term impairments in partner preference formation in male prairie voles"

3. Cho et al. (1999) - "Measurement of oxytocin levels in brain by microdialysis"

4. Cushing et al. (2003) - "Dose-dependent effects of central oxytocin on feeding in neonatal rats"

I hope this information is helpful, and best of luck with your research!