Changes of different monoamine transmitters in cerebrospinal fluid of rats with scopolamine induced delirium

Objective To investigate the effect of different monoamine sedatives on reversing the delirium behavior of rats with scopolamine-induced delirium and on the nomoamine levels in cerebrospinal fluid(CSF),so as to explore the underlying mechanisms of postoperative delirium.Methods Thirty Sprague-Dawley rats were randomly divided into 5 groups(n=6),including peritoneal injection of 1 mL normal saline(NS group),1.8 mg/kg of scopolamine(S Group),scopolamine(1.8 mg/kg) /dexmedetomidine(30 μg/kg)(S+D group),scopolamine(1.8 mg/kg)/tramadol(10 mg/kg)(S+T group),and scopolamine(1.8 mg/kg)/clozapine(5 mg/kg)(S+C group).The mood and behavior of rats were examined by open field test and levels of monoamine transmitters in CSF were assessed by high performance liquid chromatography(HPLC).Results Compared to NS group,horizontal locomotion number,and frequency of rearing and leaning were increased significantly in S group(P0.05);meanwhile,the time spent and the horizontal locomotion in the central part of the open field were also significantly increased compared to those of NS group(P0.05);the concentration of monoamine transmitters in CSF was increased slowly after scopolamine administration.Rats in S+T group and NS group showed similar behavior features,but the concentration of 5-hydroxyindold-3-acetic acid(5-HIAA) was decreased,and those of 3,4-dihydroxyphenylacetic acid(DOPAC) and homovanillic acid(HVA) were increased significantly in S+T group(P0.05).Moreover,the mood and behavior features in the open field test were significantly different in S+C and S+D groups compared to those in NS group,and the differences became statistically significant at 5-20 min after the injection(P0.05).Monoamine neurotransmitter concentration in S+C and S+D groups were similar to those before intraperitoneal injection and in NS group(P0.05).Conclusion Tramadol can reverse the delirium behavior induced by scopolamine in rats.Delirium induced by scopolamine may correlate with an increased cerebral concentration of 5-hydroxytryptamine(5-HT) and higher sensibility or quantity of 5-HT receptor,and may have less correlation with dopaminum(DA) or α2 adrenergic system.(Shanghai Med J,2010,33: 541-545)