BRAIN-LESIONS AND DELAYED WATER MAZE-LEARNING DEFICITS AFTER INTRACEREBROVENTRICULAR SPERMINE

The effects of spermine on the acquisition and retention of spatial le arning in the Morris water maze were studied. Spermine 25 and 125 nmol i.c.v, did not alter the ability of rats to End a hidden platform in the water maze when administered before training over 5 days, However, the inhibitory effect of the benzodiazepine, diazepam (3 mg/kg i.p.,3 0 min prior to training), on path length to target was markedly potent iated by the higher dose of spermine, consistent with spermine acting as a functional antagonist at the NMDA receptor. This drug combination did not affect performance on visible platform trials. Administration of doses of 125 and 250 nmol (but not 62.5 nmol) of spermine i.c.v, i n the week prior to training (daily for 5 days) dose-dependently inhib ited subsequent learning of a platform position in the absence of drug . There higher doses of spermine produced neuronal loss and increased [H-3]PK11195 binding indicating microglial activation predominantly in the hippocampus and to a lesser extent in the striatum, septum, thala mus and amygdala. Spermine 125 nmol i.c.v. (daily for 7 days) also abo lished retention of a previously learned platform position when admini stered in an interval between training and retention testing. The inhi bitory effects of spermine 125 nmol i.c.v. (daily for 7 days) on subse quent spatial learning were not antagonised by concomitant administrat ion of 30 nmol dizocilpine. These results demonstrate that spermine pr oduces a delayed neurotoxic effect in particular neuronal populations in the brain that selectively impair spatial learning and recall. (C) 1995 Elsevier Science B.V. All rights reserved.