[S-adenosyl-L-methionine concentration in cerebral interstitial fluid monitored by intracerebral microdialysis]

Ketamine-anesthetized gerbils were implanted with 0.5 mm diameter microdialysis tubing through the cortex, hippocampus and thalamus with a stereotaxic instrument. The cannula was perfused with artificial cerebrospinal fluid at a flow rate of 2 microliters/min. Samples of the perfusate representing the cerebral interstitial fluid were collected and subsequently analyzed for their content of S-adenosyl-L-methionine (SAM) with high performance liquid chromatography (HPLC). In vitro tests using the dialysis cannula gave SAM recovery which varied from 3.44 +/- 0.31% (n = 3) at a perfusion flow rate of 8 microliters/min to 43.8 +/- 3.81% (n = 3) at 0.5 microliters/min (mean +/- SEM). The in vivo SAM content of the perfusate was studied and the endogenous SAM level in cerebral interstitial fluid of gerbil was 3.49 +/- 1.52 nmol per ml (n = 3). Intraperitoneal injection of SAM (250 mg/kg) produced 10-fold increases in the perfusate SAM concentration. After the experiment the brains were checked by immunopathological study using anti-albumin antibody to examine the degree of damage to the blood-brain barrier permeability. These results show that intracerebral microdialysis offers several potential advantages for studies of extracellular neurochemistry.