The effect of scopolamine on local glucose metabolism in rat brain

Abstract

The effects of the muscarinic acetylcholine inhibitor scopolamine on local cerebral glucose metabolism (LCMRG) was examined. Scopolamine, 0.4 mg/kg, was injected intravenously into male Wistar rats 25 min prior to metabolic studies. The autoradiographic [ 14C]2-deoxyglucose technique was used to measure LCMRG in 5 experimental and 5 control animals. An analysis of variance was performed to test for significant regional differences. The following decreases in LCMRG expressed as a percentage change from control values were observed. The greatest decrease occurred in the globus pallidus (57.5%, P < 0.005) while the caudate nucleus only decreased to 82.6% ( P < 0.05). This may correlate with proposed cholinergic extrapyramidal pathways. Ammons Horn of hippocampus decreased to 61.1% ( P < 0.005) and the dentate gyrus to 71.8% ( P < 0.005). These are proposed cholinergic limbic pathways from the septal nuclei. The marked effect on Ammons Horn may also relate to the specific impairment of recent memory induced by scopolamine. The auditory (67.3%), frontal (70.7%) and parietal cortex (70.1%) and the lateral thalamus (73.1%) were all significantly depressed ( P < 0.005), which may be related to the proposed role of cholinergic pathways in the reticular activating system. Changes in the limbic structures including the hypothalamus (75.0%, P < 0.01), mamillary body (75.1%, P < 0.01), septal nuclei (80.5%, P < 0.05) and nucleus accumbens (89.0%, P > 0.05) were not as marked. Brain stem and cerebellar structures were not significantly affected.