Modulation of memory with septal injections of morphine and glucose: effects on extracellular glucose levels in the hippocampus.
The concentration of glucose in the extracellular fluid (ECF) of the hippocampus decreases substantially during memory testing on a hippocampus-dependent memory task. Administration of exogenous glucose, which enhances task performance, prevents this decrease, suggesting a relationship between hippocampal glucose availability and memory performance. In the present experiment, spontaneous alternation performance and task-related changes in hippocampal ECF glucose were assessed in rats after intraseptal administration of morphine, which impairs memory on a spontaneous alternation task, and after co-administration of intraseptal glucose, which attenuates that impairment. Consistent with previous findings, spontaneous alternation testing resulted in a decrease in hippocampal ECF glucose levels in control rats. However, rats that received intraseptal morphine prior to testing showed memory impairments and an absence of the task-related decrease in hippocampal ECF glucose levels. Intraseptal co-administration of glucose with morphine attenuated the memory impairment, and ECF glucose levels in the hippocampus decreased in a manner comparable to that seen in control rats. These data suggest that fluctuations in hippocampal ECF glucose levels may be a marker of mnemonic processing and support the view that decreases in extracellular glucose during memory testing reflect increased glucose demand during memory processing.
McNay
Ewan C
EC
Section of Endocrinology, Yale University School of Medicine, USA.
Canal
Clinton E
CE
Sherwin
Robert S
RS
Gold
Paul E
PE
D000701:Analgesics, Opioid / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D005110:Extracellular Space / Q000187:drug effects / Q000378:metabolism*; D005947:Glucose / Q000008:administration & dosage / Q000378:metabolism* / Q000494:pharmacology*; D006624:Hippocampus / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D018782:Maze Learning / Q000187:drug effects; D008568:Memory / Q000187:drug effects*; D017551:Microdialysis; D008845:Microinjections; D009020:Morphine / Q000008:administration & dosage / Q000494:pharmacology*; D009043:Motor Activity / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D020665:Septum of Brain / Q000502:physiology*
D000701:Analgesics, Opioid; D009020:Morphine; D005947:Glucose