[Changes in monoamine metabolites measured by in vivo microdialysis of the brainstem following experimental subarachnoid hemorrhage in rats].

We investigated the function of monoaminergic neuron in the brainstem by measuring its metabolites using in vivo microdialysis following experimental subarachnoid hemorrhage in rats. Dialysis probe was implanted into the nucleus tractus solitarius (NTS) and continuous perfusion was then started. The perfusates were collected every 10-20 minutes and assayed by high-performance liquid chromatography (HPLC) with electrochemical detection (ECD). The main monoamine metabolites in extracellular space measured in NTS were 3,4-dihydroxy-phenylacetic acid (DOPAC), homovanillic acid (HVA), and 5-hydroxyindoleacetic acid (5-HIAA). The extracellular content of DOPAC was abruptly increased after cisternal autologous blood (0.3ml) injection, reached a peak at 20-40 minutes, and then decreased over 120 minutes. The content of HVA and 5-HIAA changed as well as DOPAC. These results showed non-specific response for ischemia of the brainstem, because the similar changes were seen after cisternal saline injection. The disappearance rate of monoamine metabolites after pargyline administration (75 mg/kg, i.p.) at various time periods after cisternal blood injection was most rapid at 2 days after SAH and recovered gradually. In particular the decline curve of DOPAC consisted of two compartments and early compartment was disturbed more severely than late compartment. These results indicate that the functional disturbance of nerve terminals is more severe than nerve cell body in adrenergic neurons.