Early-postnatal iron deficiency impacts plasticity in the dorsal and ventral hippocampus in piglets.

In this study, we investigated whether alterations in plasticity markers such as brain-derived neurotrophic factor (BDNF), p75 neurotrophin receptor (p75NTR) and tyrosine receptor kinase B (TrkB) are underlying iron deficiency (ID)-induced cognitive impairments in iron depleted piglets. Newborn piglets were either fed an iron-depleted diet (21mg Fe/kg) or an iron-sufficient diet (88mg Fe/kg) for four weeks. Subsequently, eight weeks after iron repletion (190-240mg Fe/kg) we found a significant decrease in mature BDNF (14kDa) and proBDNF (18kDa and 24kDa) protein levels in the ventral hippocampus, whereas we found increases in the dorsal hippocampus. The phosphorylation of cAMP response element binding protein (CREB) follows the mature BDNF protein level pattern. No effects were found on BDNF and CREB protein levels in the prefrontal cortex. The protein levels of the high affinity BDNF receptor, TrkB, was significantly decreased in both dorsal and ventral hippocampus of ID piglets, whereas it was increased in the prefrontal cortex. Together, our data suggest a disrupted hippocampal plasticity upon postnatal ID.

Non-anemic Iron Deficiency from Birth to Weaning Does Not Impair Growth or Memory in Piglets.

Early iron deficiency is associated with impaired (cognitive) development, the severity of which depends on the timing and duration of the under-supply of iron. To design effective treatment and prevention strategies for iron deficiency in humans, suited animal models are needed. In an earlier study (Antonides et al., 2015b) we separated 10 pairs of piglets from their mothers within a few days after birth and reared one sibling with artificial iron-deficient (ID) and the other with balanced control milk until weaning. ID piglets grew slower and showed poorer reference memory (RM) performance than their controls in a spatial holeboard task, even weeks after iron repletion. One putative intervening factor in that study was pre-weaning maternal deprivation. In an attempt to refine the piglet iron-deficiency model, we assessed whether piglets reared by sows, but withheld iron supplementation, can serve as animal model of iron deficiency. As sow milk is inherently ID, piglets normally receive a prophylactic iron injection. Ten pairs of piglets were housed with foster sows until weaning (4 weeks). One sibling per pair was randomly assigned to the control group (receiving iron dextran injections: 40 mg iron per kilogram body mass on days 3 and 10), the other to the ID group. From weaning, all pigs were fed a balanced commercial diet. Blood samples were taken in week 1, 3.5, 6, and 12. Pre-weaning blood iron values of ID piglets were lower than those of controls, but recovered to normal values after weaning. Hemoglobin of ID piglets did not reach anemic values. Hematocrit and hemoglobin of ID animals did not decrease, and serum iron even increased pre-weaning, suggesting that the piglets had access to an external source of iron, e.g., spilled feed or feces of the foster sows. Growth, and spatial memory assessed in the holeboard from 10 to 16 weeks of age, was unaffected in ID pigs. We conclude that sow-raised piglets are not a suitable model for iron-deficiency induced cognitive deficits in humans. Based on our previous and the present study, we conclude that growth and memory are only impaired in piglets that suffered from pre-weaning anemia.

Pre-weaning dietary iron deficiency impairs spatial learning and memory in the cognitive holeboard task in piglets.

Iron deficiency is the most common nutritional deficiency in humans, affecting more than two billion people worldwide. Early-life iron deficiency can lead to irreversible deficits in learning and memory. The pig represents a promising model animal for studying such deficits, because of its similarities to humans during early development. We investigated the effects of pre-weaning dietary iron deficiency in piglets on growth, blood parameters, cognitive performance, and brain histology later in life. Four to six days after birth, 10 male sibling pairs of piglets were taken from 10 different sows. One piglet of each pair was given a 200 mg iron dextran injection and fed a control milk diet for 28 days (88 mg Fe/kg), whereas the other sibling was given a saline injection and fed an iron deficient (ID) milk diet (21 mg Fe/kg). Due to severely retarded growth of two of the ID piglets, only eight ID piglets were tested behaviorally. After dietary treatment, all piglets were fed a balanced commercial pig diet (190-240 mg Fe/kg). Starting at 7.5 weeks of age, piglets were tested in a spatial cognitive holeboard task. In this task, 4 of 16 holes contain a hidden food reward, allowing measurement of working (short-term) memory and reference (long-term) memory (RM) simultaneously. All piglets received 40-60 acquisition trials, followed by a 16-trial reversal phase. ID piglets showed permanently retarded growth and a strong decrease in blood iron parameters during dietary treatment. After treatment, ID piglets' blood iron values restored to normal levels. In the holeboard task, ID piglets showed impaired RM learning during acquisition and reversal. Iron staining at necropsy at 12 weeks of age showed that ID piglets had fewer iron-containing cells in hippocampal regions CA1 and dentate gyrus (DG). The number of iron-containing cells in CA3 correlated positively with the average RM score during acquisition across all animals. Our results support the hypothesis that early-life iron deficiency leads to lasting cognitive deficits. The piglet as a model animal, tested in the holeboard, can be useful in future research for assessing long-term cognitive effects of early-life diets or diet-induced deficiencies.

Very low birth weight piglets show improved cognitive performance in the spatial cognitive holeboard task.

Low birth weight (LBW) is common in humans and has been found to cause lasting cognitive and developmental deficits later in life. It is thought that the primary cause is intra-uterine growth restriction (IUGR) due to a shortage of oxygen and supply of nutrients to the fetus. Pigs appear to be a good model animal to investigate long-term cognitive effects of LBW, as LBW is common in commercially farmed breeds of pigs. Moreover, pigs are developmentally similar to humans and can be trained to perform complex tasks. In this study, we trained ten very low birth weight (vLBW) piglets and their ten normal birth weight (NBW) siblings in a spatial cognitive holeboard task in order to investigate long-term cognitive effects of LBW. In this task, four out of sixteen holes contain a hidden food reward, which allows measuring working memory (WM) (short-term memory) and reference memory (RM) (long-term memory) in parallel. Piglets were trained for 46-54 trials during the acquisition phase, followed by a 20-trial reversal phase in which a different set of four holes was baited. Both groups acquired the task and improved their performance over time. A mixed model repeated measures ANOVA revealed that vLBW piglets showed better RM performance than NBW piglets in both the acquisition and reversal phase. Additionally, WM scores in the vLBW were less disrupted than in the NBW animals when switched to the reversal phase. These findings are contrary to findings in humans. Moreover, vLBW pigs had lower hair cortisol concentrations (HCCs) than NBW pigs in flank hair at 12 weeks of age. These results could indicate that restricted intra-uterine growth causes compensatory mechanisms to arise in early development that result in beneficial effects for vLBW piglets, increasing their low survival chances in early-life competition.

Chronic allopurinol treatment during the last trimester of pregnancy in sows: effects on low and normal birth weight offspring.

Low-birth-weight (LBW) children are born with several risk factors for disease, morbidity and neonatal mortality, even if carried to term. Placental insufficiency leading to hypoxemia and reduced nutritional supply is the main cause for LBW. Brain damage and poor neurological outcome can be the consequence. LBW after being carried to term gives better chances for survival, but these children are still at risk for poor health and the development of cognitive impairments. Preventive therapies are not yet available. We studied the risk/efficacy of chronic prenatal treatment with the anti-oxidative drug allopurinol, as putative preventive treatment in piglets. LBW piglets served as a natural model for LBW. A cognitive holeboard test was applied to study the learning and memory abilities of these allopurinol treated piglets after weaning. Preliminary analysis of the plasma concentrations in sows and their piglets suggested that a daily dose of 15 mg.kg(-1) resulted in effective plasma concentration of allopurinol in piglets. No adverse effects of chronic allopurinol treatment were found on farrowing, birth weight, open field behavior, learning abilities, relative brain, hippocampus and spleen weights. LBW piglets showed increased anxiety levels in an open field test, but cognitive performance was not affected by allopurinol treatment. LBW animals treated with allopurinol showed the largest postnatal compensatory body weight gain. In contrast to a previous study, no differences in learning abilities were found between LBW and normal-birth-weight piglets. This discrepancy might be attributable to experimental differences. Our results indicate that chronic prenatal allopurinol treatment during the third trimester of pregnancy is safe, as no adverse side effects were observed. Compensatory weight gain of treated piglets is a positive indication for the chronic prenatal use of allopurinol in these animals. Further studies are needed to assess the possible preventive effects of allopurinol on brain functions in LBW piglets.

A behavioral view on chimpanzee personality: exploration tendency, persistence, boldness, and tool-orientation measured with group experiments.

Human and nonhuman animals show personality: temporal and contextual consistency in behavior patterns that vary among individuals. In contrast to most other species, personality of chimpanzees, Pan troglodytes, has mainly been studied with non-behavioral methods. We examined boldness, exploration tendency, persistence and tool-orientation in 29 captive chimpanzees using repeated experiments conducted in an ecologically valid social setting. High temporal repeatability and contextual consistency in all these traits indicated they reflected personality. In addition, Principal Component Analysis revealed two independent syndromes, labeled exploration-persistence and boldness. We found no sex or rank differences in the trait scores, but the scores declined with age. Nonetheless, there was considerable inter-individual variation within age-classes, suggesting that behavior was not merely determined by age but also by dispositional effects. In conclusion, our study complements earlier rating studies and adds new traits to the chimpanzee personality, thereby supporting the existence of multiple personality traits among chimpanzees. We stress the importance of ecologically valid behavioral research to assess multiple personality traits and their association, as it allows inclusion of ape studies in the comparison of personality structures across species studied behaviorally, and furthers our attempts to unravel the causes and consequences of animal personality.