Date of Award

5-1-1980

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Psychology

Abstract

The following studies were designed to determine whether zinc deficiency, either prenatal or postnatal, could influence the time course of development of long-term memory in rats. Three nutritional conditions were imposed on litters of rat pups. One group (zinc deficient-ZD) was subjected to a zinc-deficient diet and deionized water. Members of a second group (pair fed-PF) were allowed to eat as much of the zinc-deficient diet as a certain member of the ZD group consumed on the previous day, along with zinc-supplemented water. This PF group was starved, since zinc deficiency typically causes anorexia. The third group (ad libitum-AL) was allowed ad libitum access to the same diet and zinc-supplemented water. In the prenatal deficiency study, these conditions were imposed on pregnant dams from Day 13 to Day 21 of gestation. To produce postnatal deficiency, the conditions were instituted on dams the first postnatal day and continued until weaning, 21 days after delivery. At all other times, ad libitum access to standard Purina Laboratory Rat Chow and tap water was provided.

The behavioral task consisted of a classical conditioned fear training phase (pairing of a tone with footshock) followed 42 days later by a test for suppression of an independently established operant response (bar pressing for food reward) upon presentation of the conditioned stimulus (CS). Suppression of the operant, in this paradigm, reflected long-term memory of the CS. The sequence of events was identical for each S. However, fear conditioning was initiated at four different ages: Day 11 (D11), Day 14 (D14), Day 17 (D17), or Day 20 (D20) of life.

Previous investigators (Coulter, Collier, & Campbell, 1976) using only the equivalent of the present AL group found no suppression of the operant response in the two youngest groups (D11 and D14) and significant suppression in the two older groups (D17 and D20). They interpreted this as indicating a capacity for long-term memory which normally develops very close to Day 16 of life in rat pups. It was proposed, in this study, that the ZD and PF groups would show some retardation in the development of long-term memory. The AL groups would be expected to replicate the findings of Coulter, Collier, and Campbell (1976). The ZD and PF groups might not show suppression in the D17 group and possibly not in the D20 group. Differences in results between the ZD and PF groups would reflect specific (zinc deficiency) as opposed to general (undernutrition) dietary effects.

The prenatal deficiency produced no significant overall group differences in suppression. Imposition of the nutritional conditions from Day 13 to Day 21 of gestation apparently did not alter the development of long-term memory in the pups. In contrast, postnatal deficiency did produce significant overall group differences in suppression in the D17 group. ZD animals showed significantly less suppression than PF or AL animals in that group, indicating a disruption of long-term memory in the ZD animals. No sex differences were found for this effect. All postnatal D20 groups showed similar suppression, indicating that the effect of postnatal zinc deficiency on long-term memory development in the rat is a delay rather than a permanent deficit.

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