Behavioral Effects of Postnatal Zinc Deficiency and Kryptopyrrole in the Rat

Zinc deficiency has been shown to have a wide range of behavioral effects in the rat. The experiments presented below were conducted to determine the effects of postnatal zinc deficiency (birth-21 days) on avoidance learning and on measures of emotionality. Kryptopyrrole, a substance which has been shown to produce catatonic freezing behavior and atypical electrical activity in rat brains, was administered to half of the Ss to study possible zinc deficiency-kryptopyrrole interactions. Dams were made zinc deficient from the day of delivery until day 21 on a diet contaning less than 1 ppm zinc. Two dietary control groups were used: a pair fed group which were fed an amount equivalent to that consumed by their zinc deficient counterparts and an ad libitum group allowed free access to food. 12 S_s were assigned to each dietary condition. Within each dietary condition 6 Ss were injected with 1 microliter of kryptopyrrole per lOQg body weight; 6 Ss within each dietary condition served as saline injected controls. Behavioral testing was begun when the animals were 54-55 days of age. Experiment I was an open field test of emotionality in which the £\u3es were not differentiated as to injection group. Data recorded were the number of defecation responses and number of squares entered per trial. Experiment I showed generally that the zinc deficient were not significantly more fearful of the open field. In fact, the ad libitum group ranked first in the number of defecation responses. Experiment II was a two-way avoidance conditioning experiment consisting of 3 days of CS habituation, 5 days avoidance acquisition, 3 days extinction, and 5 days of reacquisition. The number of conditioned responses (CRs), number of intertrial responses (ITRs), and response latency were recorded. There were no significant differences with respect to CRs in all conditioning phases except in extinction in which the zinc deficient S_s exhibited slower extinction. The most clear difference was the extremely high rate of ITR responding shown by the zinc deficient group in avoidance acquisition, extinction, and reacquisition. Also observed were highly significant trials x nutrition x injection interactions in extinction and reacquisition in the number of ITRs. There were no significant differences with respect to response latencies except during extinction in which the zinc deficient group exhibited shorter latencies. The injection variable had no significant effect at the injection levels used. Experiment III was a second open field experiment in which the Ss were differentiated with respect to injection condition, although they received no injections during the experiment. The zinc deficient Ss exhibited hyperactivity with repeated exposures to the open field