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Abstract
Interactions of glucose and cognitive function have been reported both in the presence
of elevated arterial blood glucose levels and with decreased cerebral glucose metabolism.
In order to test the peripheral vs. central effects of this phenomenon, we induced
irreversible hyperglycemia and depression of cerebral glucose metabolism in separate
designs by means of either intraperitoneal (i.p.) or intracerebroventricular (i.c.v.)
administration of streptozotocin (STZ), which is known to damage insulin-producing
cells. Behavioral functions, such as locomotor activity, learning, and memory, were
investigated under these different conditions. IP treatment with STZ decreased locomotor
activity and increased initial step-through latencies on the passive avoidance test.
No effects of elevated arterial blood glucose levels on retention of passive avoidance
learning checked at 24 h and 144 h after training were observed. I.c.v. treatment
of STZ increased the rate of locomotor activity and impaired retention in the passive
avoidance test at 24 h, without further forgetfulness at 144 h. This finding may indicate
disturbed acquisition and/or consolidation of memory, which may remain impaired but
at a constant level, without further deterioration. Enhanced motor activity and impaired
acquisition of passive avoidance learning without further impairment have also been
reported as a characteristical behavioral pattern after disruption of the cholinergic
system. It is therefore postulated that the observed behavioral abnormalities consequent
on an impairment of cerebral glucose metabolism may be suggestive of cholinergic dysfunction.