Determination of extracellular release of neurotensin in discrete rat brain regions utilizing in vivo microdialysis/electrospray mass spectrometry

In vivo microdialysis was used together with structure-specific high sensit ivity nano-flow capillary liquid chromatography/micro-electrospray mass spe ctrometry to quantify and compare extracellular neurotensin from discrete r egions of the rat brain. Microdialysis probes were implanted in the hypotha lamus or globus pallidus/ventral pallidum in unanesthetized freely moving a nimals. Utilizing this specific methodology, recovered basal levels of neur otensin were detectable in hypothalamus and globus pallidus/ventral pallidu m. The basal level of neurotensin in these regions were slightly higher in hypothalamus (101 +/- 11 amol/10 mu l, n = 6) compared to those in the glob us pallidus/ventral pallidum region (74 +/- 12 amol/10 mu l, n = 8) in samp les collected for 30 min at a flow-rate of 0.4 mu l/min 150-180 min after t he microdialysis probe implantation. After a pulse of 1.0 mu l of 100 mM KC l-containing artificial cerebrospinal fluid during the next 30-min sampling period (180-210 min), the recovered neurotensin increased in hypothalamus and globus pallidus/ventral pallidum by 544% (548 +/- 90 amol/10 mu l) and 674% (499 +/- 99 amol/10 mu l), respectively. The basal levels of endogenou sly released neurotensin in the hypothalamus and globus pallidus/ventral pa llidum were lower in the present study compared to those previously reporte d in the rat brain using in vivo microdialysis and radioimmunoassays. Our d ata demonstrate the effectiveness of combining in vivo microdialysis and st ructure-specific micro-electrospray mass spectrometry for the quantitation of basal and stimulated in vivo levels of endogenous neurotensin (NT) in di fferent brain areas. (C) 1999 Elsevier Science B.V. All rights reserved.