Systemic and intra-rhinal-cortical 17-β estradiol administration modulate object-recognition memory in ovariectomized female rats

• Published in: Hormones and behavior Vol. 64; no. 4; pp. 642 - 652
• Main Authors: Gervais, Nicole J., Jacob, Sofia, Brake, Wayne G., Mumby, Dave G.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 01.09.2013; Elsevier
• Subjects: 17-β Estradiol; Administration, Intranasal; Animals; Behavioral psychophysiology; Biological and medical sciences; Delayed nonmatch-to-sample; Entorhinal cortex; Estradiol - administration & dosage; Estradiol - analogs & derivatives; Female; Fundamental and applied biological sciences. Psychology; Hormones and behavior; Infusions, Intraventricular; Injections, Intravenous; Novelty preference; Object-recognition memory; Ovariectomy; Perirhinal cortex; Psychology. Psychoanalysis. Psychiatry; Psychology. Psychophysiology; Rats; Rats, Long-Evans; Recognition (Psychology) - drug effects; Retention (Psychology) - drug effects; Visual Perception - drug effects; Object-recognition memory; Delayed nonmatch-to-sample; 17-β Estradiol; Novelty preference; Perirhinal cortex; Entorhinal cortex; Recognition memory; Ovariectomy; Rat; Estrogen; Rodentia; Central nervous system; Novelty stimulus; Estradiol; Ovarian hormone; Encephalon; Time lag; Vertebrata; Mammalia; Animal; Female; Stimulus preference; Sex steroid hormone
• ISSN: 0018-506X; 1095-6867
• DOI: 10.1016/j.yhbeh.2013.08.010

Previous studies using the novel-object-preference (NOP) test suggest that estrogen (E) replacement in ovariectomized rodents can lead to enhanced novelty preference. The present study aimed to determine: 1) whether the effect of E on NOP performance is the result of enhanced preference for novelty, per se, or facilitated object-recognition memory, and 2) whether E affects NOP performance through actions it has within the perirhinal cortex/entorhinal cortex region (PRh/EC). Ovariectomized rats received either systemic chronic low 17-β estradiol (E2; ~20pg/ml serum) replacement alone or in combination with systemic acute high administration of estradiol benzoate (EB; 10μg), or in combination with intracranial infusions of E2 (244.8pg/μl) or vehicle into the PRh/EC. For one of the intracranial experiments, E2 was infused either immediately before, immediately after, or 2h following the familiarization (i.e., learning) phase of the NOP test. In light of recent evidence that raises questions about the internal validity of the NOP test as a method of indexing object-recognition memory, we also tested rats on a delayed nonmatch-to-sample (DNMS) task of object recognition following systemic and intra-PRh/EC infusions of E2. Both systemic acute and intra-PRh/EC infusions of E enhanced novelty preference, but only when administered either before or immediately following familiarization. In contrast, high E (both systemic acute and intra-PRh/EC) impaired performance on the DNMS task. The findings suggest that while E2 in the PRh/EC can enhance novelty preference, this effect is probably not due to an improvement in object-recognition abilities. •Adult ovariectomized rats with chronic and phasic E2 replacement•Intra-PRh/EC E2 modulates object-recognition memory.•Enhanced novelty preference may not reflect improved recognition abilities.