Changes in monoaminergic neuronal function in the lower brain stem following subarachnoid hemorrhage induced in rats

1. We investigated the function of monoaminergic neurons in the lower brain stem following subarachnoid hemorrhage (SAH) induced in rats, by measuring monoamine metabolites, using in vivo microdialysis techniques. 2. A dialysis probe was implanted in the nucleus tractus solitarius (NTS) and the perfusates were assayed by high-performance liquid chromatography (HPLC) with electrochemical detection (ECD). 3. The main monoamine metabolites measured in the NTS extracellular space were 3,4-dihydroxyphenyl acetic acid (DOPAC), homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA). 4. Monoamine metabolites in the rat NTS were nonspecifically increased, at least in the acute phase after cisternal injection of blood or saline. 5. The disappearance rates of the 5-HIAA decline and the early phase of DOPAC decline after pargyline administration (75 mg/kg, i.p.) were most rapid at 2 days after the induction of SAH, then recovered gradually. 6. These results suggest that functions of noradrenergic and serotonergic neurons in the NTS may be disturbed predominantly in the case of induced vasospasm in rats.