Imaging and quantification of neuropeptides in mouse pituitary tissue by atmospheric pressure matrix‐assisted laser desorption/ionization mass spectrometry

Rationale Atmospheric pressure matrix‐assisted laser desorption/ionization (AP‐MALDI) mass spectrometry has enabled the untargeted analysis and imaging of neuropeptides and proteins in biological tissues under ambient conditions. Sensitivity in AP‐MALDI can be improved by using sample‐specific preparation methods. Methods A comprehensive and detailed optimization strategy including instrument parameters, matrix spraying and sample tissue washing pretreatment was implemented to enhance the sensitivity and coverage of neuropeptides in mouse pituitary tissues by commercial AP‐MALDI mass spectrometry imaging (MSI). Results The sensitivity of a commercial AP‐MALDI system for endogenous neuropeptides in mouse pituitary was enhanced by up to 15.2‐fold by shortening the transmission gap from the sample plate to the inlet, attaching copper adhesive tape to an indium tin oxide‐coated glass slide, optimizing the matrix spray solvent and using sample tissue washing pretreatment. Following careful optimization, the distributions of nine endogenous neuropeptides were successfully visualized in the pituitary. Furthermore, the quantitative capability of AP‐MALDI for neuropeptides was evaluated and the concentrations of neuropeptides oxytocin and vasopressin in the pituitary posterior lobe were increased approximately twofold under hypertonic saline stress. Conclusion Mouse pituitary neuropeptides have emerged as important signaling molecules due to their role in stress response. This work indicates the potential of modified AP‐MALDI as a promising AP MSI method for in situ visualization and quantification of neuropeptides in complex biological tissues.