1. Thinking Big: Estradiol Regulates Memory and Bioenergetics
K. Bell1, W. Wang2, P.E Gold3, D.L Korol4
Department of Biology, Syracuse University, Syracuse, NY, USA
Introduction
Background and Rational
Methods Zero-Net Flux
Discussion
References
Lactate metabolism, an important energy pathway
involved in memory consolidation, is determined to
be mediated by estrogens in female Rats. In this
experiment we have measured the glucose and
lactate responses in the cerebrospinal fluid from the
ventral hippocampus of ovariectomized rats treated
with injections of either estradiol or oil vehicle. with
estradiol or oil vehicle.
Experimental Timeline
Estrogens shift cognitive strategies
• Rats with high estrogen levels excel on hippocampus-based tasks
and rats with low estrogen levels do poorly on hippocampus-
sensitive tasks (Korol, 2004).
Estrogens regulate bioenergetics
• Estrogens may shift energy substrates in the brain from glucose
to other sources such as lactate (Yao, 2012).
Neurons use extracellular glucose or astrocytic lactate
• Neurons can use glucose or lactate for energy, both of which
originate from circulating glucose. Glucose from the blood is
either consumed by neurons or astrocytes. Astrocytes either
store glucose as glycogen, which can then be broken down into
lactate, or convert glucose directly to lactate; lactate is then
shuttled to the neurons for further catabolism and production of
ATP.
Lactate is important for spatial working memory
• We and others have previously shown in male rats that blocking
lactate entry into hippocampal neurons impairs memory and
infusing lactate into the hippocampus enhances memory.
Inhibition of glial glycogenolysis also impairs memory
(Newman, 2011), pointing to lactate as an important contributor
to normal memory function.
Subjects
Female Sprague Dawley rats (n= 15-20, 3 months old) were
housed separately with free access to food and water, and
were kept on a 12:12 light: dark cycle.
Surgeries
• Rats were anesthized with 5.0% Isoflurane for 10 minutes
prior to beginning ovariectomy. Surgery began with
administering 3.5% inhalation dosage of Isoflurane,
0.09mL Penicillin, flunoxin (.001% of measured body
weight) and 1mL of 0.9% Saline.
• One week following ovariectomy, Cannula implantation
(CMA cannula: out diameter 0.8mm) with a biosensor
probe (CMA12 probe 20kDa cutoff) was inserted into the
hippocampus to measure estrogen, and lactate levels.
Treatments
• Oil Vehicle : 0.5 µg/kg infused bilaterally into the ventral
hippocampus
• Estradiol infusion: 4.5µg/kg and 45µg/kg of 17β-estradiol
infused bilaterally into the ventral hippocampus at 24 and
48 hours before any additional testing or training.
Testing
Microdialysis:
• Subjects received a biosensor probe perfused with
artificial cerebral spinal fluid of a known glucose
concentration in the range of 0-2.0mM, with a flow rate of
1µL/min.
Graph A: The perfusate glucose or lactate concentration at
which there is no net concentration change is the point of
zero flux.
Expected Results
Graph B: ZNF linear plot of basal level glucose concentrations in
estradiol (1.0mM) and oil vehicle (0.5mM) treated rats. Each point
represents data from one rat.
Graph C: ZNF linear plot of basal lactate concentrations in oil
vehicle (1.0mM) and estradiol (0.5mM) treated rats. Values are
reciprocals of glucose concentrations.
Graph D: Represents studied and expected extracellular
Glucose and Lactate concentrations. Glucose and Lactate
Concentrations Change Reciprocally During SA (Newman et
al., 2011).
Histology
• Brains were sectioned at 40µm through the hippocampus
on a cryostat and stained with cresyl violet.
• Vaginal smears were taken for 8 days prior to training to
ensure successful ovariectomy and estradiol injections.
Vaginal smears were stained with Toluidine Blue for
staging.
Future Directions
We will test estradiol effects on the hippocampal glucose and
lactate response to place learning, which is a task that may
selectively engage the hippocampus
• Newman et al. (2011). Lactate Produced by Glycogenolysis in
Astrocytes Regulates Memory. PLoS ONE 6(12): e28427.
• Korol, D.L. (2004). Role of estrogen in balancing contributions
from multiple memory systems. Neurobiology of Learning and
Memory, 82, 309-323.
• Jia Yao et al. (2012). Ovarian hormone loss induces bioenergetic
deficits and mitochondrial β-amyloid. Neurobiology of Aging ,
1507–1521.
• Fan Ding et al. (2013). Ovariectomy induces a shift in fuel
availability and metabolism in the hippocampus of the female
transgenic model of familial Alzheimer’s. PLoS
ONE. 2013;8(3):e59825.
• Chuquet et al. (2010). Predominant enhancement of glucose
uptake in astrocytes versus neurons during activation of the
somatosensory cortex. J Neurosci. 2010 Nov 10;30(45):15298-
303.
• We expect the measured glucose concentration to be
less in oil treated rats, as opposed to rats treated
with estradiol.
• Basal lactate levels were opposite to that of glucose
concentrations indicating that lactate could be
another possible substrate to power metabolic
processes. However, it is also possible that glucose
and lactate levels can both be decreased, which
indicates the complete impairment of estrogens in
the rats brain involved in bioenergetics.
Acknowledgments
Funding for this project was provided by NSF IOS 0843175 and IOS
1318490 and by Syracuse University.