EFFECTS OF CHANGES IN RAT-BRAIN GLUCOSE ON SEROTONERGIC AND NORADRENERGIC NEURONS

Microdialysis was used in the freely moving rat to measure the effects of graded changes in brain glucose on the serotonergic and noradrener gic projections to the hippocampus. The concentration of glucose in th e dialysate was monitored using an enzyme-based assay. A systemic inje ction of insulin caused a steep decline in glucose level which was res tored to the control level by oral administration of glucose solution, The changes in 5-hydroxytryptamine (5-HT) and noradrenaline were a mi rror image of the glucose changes: they rose after insulin injection a nd returned to control during glucose administration. A delayed increa se was shown by 5-hydroxyindoleacetic acid (5-HIAA) which did not retu rn to baseline on glucose administration. The metabolite dihydroxyphen ylacetic acid (DOPAC) decreased after insulin administration and incre ased above control during glucose administration. While the responses of 5-HT, noradrenaline and 5-HIAA to hypoglycaemia resemble those to m ild stress, the changes in DOPAC are the reverse of those produced by stress.