Abstract
Head trauma leading to concussion and electroconvulsive shock (ECS) in humans causes amnesia for events that occurred shortly before the injury (retrograde amnesia). The present experiment investigated the amnesic effect of lidocaine and ECS in 25 rats trained on a working memory version of the Morris water task. Each day, the escape platform was moved to a new location; learning was evidenced by a decrease in the latency to find the platform from the first to the second trial. "Consolidation" of this newly encoded spatial engram was disrupted by bilateral inactivation of the dorsal hippocampus with 1 microliter of 4% lidocaine applied as soon as possible after the first trial. When trial 2 was given after recovery from the lidocaine (30 min after the injection), a normal decrease in latency indicated that the new engram was not disrupted. When trial 2 was given under the influence of lidocaine (5 min after injection), absence of latency decrease demonstrated both the success of the inactivation and the importance of hippocampus for the task. To examine the role of events immediately after learning, ECS (30 or 100 mA, 50 Hz, 1.2 sec) was applied 0 sec to 45 sec after a single escape to the new platform location. A 2-h delay between ECS and trial 2 allowed the effects of ECS to dissipate. ECS applied 45 sec or 30 sec after trial 1 caused no retrograde amnesia: escape latencies on trial 2 were the same as in control rats. However, ECS applied 0 sec or 15 sec after trial 1 induced clear retrograde amnesia: escape latencies on trial 2 were no shorter than on trial 1. It is concluded that the consolidation of a newly formed memory for spatial location can only be disrupted by ECS within 30 sec after learning.
Full text
PDF
Images in this article
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Barnes C. A. Spatial learning and memory processes: the search for their neurobiological mechanisms in the rat. Trends Neurosci. 1988 Apr;11(4):163–169. doi: 10.1016/0166-2236(88)90143-9. [DOI] [PubMed] [Google Scholar]
- Fenton A. A., Bures J. Interhippocampal transfer of place navigation monocularly acquired by rats during unilateral functional ablation of the dorsal hippocampus and visual cortex with lidocaine. Neuroscience. 1994 Feb;58(3):481–491. doi: 10.1016/0306-4522(94)90074-4. [DOI] [PubMed] [Google Scholar]
- Holzhäuer M. S., Bures J. Influence of electroconvulsive shock and naloxone on acquisition and retention of a spatial navigation task in rats. Physiol Behav. 1986 Oct;38(4):551–556. doi: 10.1016/0031-9384(86)90424-5. [DOI] [PubMed] [Google Scholar]
- Lynch S., Yarnell P. R. Retrograde amnesia: delayed forgetting after concussion. Am J Psychol. 1973 Sep;86(3):643–645. [PubMed] [Google Scholar]
- McGaugh J. L. Time-dependent processes in memory storage. Science. 1966 Sep 16;153(3742):1351–1358. doi: 10.1126/science.153.3742.1351. [DOI] [PubMed] [Google Scholar]
- Panakhova E., Buresová O., Bures J. Persistence of spatial memory in the Morris water tank task. Int J Psychophysiol. 1984 Aug;2(1):5–10. doi: 10.1016/0167-8760(84)90066-7. [DOI] [PubMed] [Google Scholar]