The Effect of Zinc and Zinc Plus Copper on Memory

1. The Effect of Zinc and Zinc Plus Copper on Memory Tizoc Perez-Casillas Department of Psychology, George Mason University, Fairfax, Virginia BACKGROUND • Zinc is a fundamental trace metal needed in the body and brain in order to maintain healthy bodily functions and neurological activity • The National Institute of Health recommends daily consumption of 11mg of zinc for males nineteen and older and 8mg for females that are neither lactating nor pregnant • Zinc is acquired from a normal diet (high in fish and meat products), through vitamins, and may be subscribed in some cases • The Age-Related Eye Disease Study Research Group (AREDS) supplemented the elderly with zinc tablets in order to aid in the treatment of advanced macular degeneration (AREDS, 2001), the leading cause of blindness in America • Although zinc is essential, an excessive consumption could cause copper deficiency (hypocupremia) (Prasad, Brewer, Schoomaker, & Rabbani, 1978). Also, it may lead to a more anxious behavior and cause cognitive impairments when given pre-natally (Flinn et al., 2005) • HYPOTHESIS • An increase in zinc dosage in older animals will lead to an increased anxious behavior and will cause learning and retention impairments, which will be at least partly remediated by copper • METHODS • Forty-five, ten-month-old, Long Evans female rats were caged and maintained for four months on either lab (control) water (n=15), zinc carbonate (10ppm ZnCO3) (n=15), or zinc carbonate plus copper carbonate (10ppm ZnCO3 + 0.2ppm CuCO3) (n=15) • Rats were housed by groups of three in a polycarbonate cage and maintained on a 12 hr light/dark cycle with ad libitum to food and water • Training and subsequent fear conditioning (FC) sessions occurred in 2 identical Plexiglas chambers (Coulbourn Instruments). The “freezing” behavior exhibited by the rats, which implies fear, was recorded by a video camera • Day 1 – Training: FreezeScan 1.0 software (Clever Sys, Inc.) delivered a 20 second tone (85dB) (CS) that co-terminated with a 2-second foot shock (0.8mA) (US) at the end of minutes 3, 4, and 5. • Day 2 – Contextual Conditioning: rats were placed in the same unaltered box as Day 1. No tone nor shock • Day 3-8 – Cued Conditioning and Extinction: rats were placed in an altered FC chamber (metal walls were covered with black stripes and shapes, and Plexiglas and bedding covered the iron grids). The rats were given 160 seconds to acclimate before the CS was presented without the shock. • Day 12 – Cued Extinction: after 8 consecutive days of fear conditioning/extinction, rats were not tested until 4 days later RESULTS Cued Fear Conditioning: Trial 1 Cued Fear Conditioning: Trial 6 Cued Fear Conditioning: Trial 7 Mean Percent Freezing Mean Percent Freezing Mean Percent Freezing Minutes Minutes Minutes Figure 1: Day 3- Cued Conditioning, percent freezing across 6 minutes Figure 2: Day 8- Cued Extinction, percent freezing across 6 minutes Figure 3: Day 12- Cued Extinction, percent freezing across 6 minutes Fear Conditioning Cued Retention (pre-acquisition) Fear Conditioning Cued Extinction (tone/shock phase) Mean Percent Freezing Mean Percent Freezing 12 12 Days Since Training Days Since Training Figure 4: Cued Extinction percent freezing means across 1st 3 minutes Figure 5: Cued Extinction tone/shock phase, percent freezing across last 3 minutes • The rats maintained on zinc carbonate seemed more anxious when placed in the FC chamber, as shown by their increased freezing rate • Over a period of days, the rats maintained on lab water extinguished fear faster than the other rat groups. The rats maintained on zinc carbonate extinguished fear at a slower rate in comparison to the other two rat groups • CONCLUSION • An excess ingestion of zinc may cause an increase in anxiousness • Zinc may cause cognitive deficits, specifically to learning and retention of memory • The deficits of learning and memory retention promoted by zinc are partly remediated by copper • Due to stress, individuals with Posttraumatic Stress Disorder may be at a greater risk for developing the cognitive deficits that zinc may induce • REFERENCES AND ACKNOWLEDGEMENTS • Age-Related Eye Disease Study Research Group (2002). AREDS report No. 7. Journal of Nutrition, 132(4): 697-702. • Flinn, J.M., Hunter, D., Linkous, D.H., Lanzirotti, A., Smith, L.N., Brightwell, J., & Jones, B.F. (2005). Enhanced dietary zinc consumption in rats causes spatial memory deficits and increased zinc levels within the brain. Physiology and Behavior, 83(5): 793–803. • Prasad, A.S., Brewer, G.J., Schoomaker, E.B., & Rabbani, P. (2007). Hypocupremia induced by zinc therapy in adults. Journal of the American Medical Association, 240, 2166-2168 • Dr. Jane Flinn • Dr. Jim Sanford • Dr, Linda ChrosniakGretchen Knaack • The 2009 Psychology Honors Class! *Contextual Results Are Not Presented* FURTHER INFORMATION: Tizoc Perez-Casillas tperezca@gmu.edu