Pigs as animal model for low-birth-weight babies. Developing cognitive tests and examining neuroprotection

Abstract

In this thesis the cognitive performance of piglets with low birth weight (LBW) caused by intra-uterine growth restriction (IUGR), and the effects of a possible therapy to prevent IUGR-related brain damage and associated cognitive impairments were studied. To achieve these goals, several conditions had to be fulfilled. First, an appropriate cognitive task had to be selected and validated. Then, the effects of IUGR in this task had to be investigated using the most suitable task. In addition, basic pharmacokinetic data of the putative therapeutic drug were collected in sows and piglets. Finally, the effects of the therapeutic drug on IUGR piglets were assessed. A test for visual discrimination and a test for spatial cognition were developed and applied. Based on the behavioural performance of the pigs in both tasks, the latter was found most suitable as it allows for species-specific behaviour, and matches the capabilities and motivation of the pig the best. This spatial test, ‘the cognitive pig holeboard’ was therefore further developed and automated. To improve validity of this cognitive test, a study with biperiden (a muscarinic M1 receptor blocker, inducing temporary cognitive impairments) was performed with both conventional pigs and Göttingen minipigs. During the training phase, both groups were able to reach nearly errorless performance.Biperiden had only a minor effect on holeboard performance overall, and mainly on reference memory performance. Furthermore, LBW piglets were trained in the cognitive pig holeboard test. Both LBW and their normal birth weight littermates were able to learn the task. After presenting them a reversal (rewards hidden in different places than before), the LBW piglets showed a transiently retarded acquisition of this task supporting the hypothesis that LBW is related to (mild) subsequent cognitive impairments. These results were not replicated in the next experiment in which allopurinol was tested as a possible therapy to prevent brain damage in IUGR neonates. The differences in the set-up of training could have caused these different findings. In this experiment, piglets were, via the sow, chronically treated with allopurinol during the last trimester of pregnancy. No detrimental effects of treatment were found but a beneficial effect on holeboard performance could not be demonstrated in both LBW and normal birth weight piglets. Though, on brain level long-lasting increased mBDNF and PSD95 protein levels in the dorsal hippocampus of allopurinol treated pigs were found. This could be seen as a promising indicator for the efficacy of chronic prenatal allopurinol treatment. Both proteins are part of the BDNF mediated neuronal plasticity pathway that is involved in spatial memory performance. To conclude with, the LBW piglet model is considered to be suitable for further development and practical application. Enhanced postnatal care of the piglets could increase translatability of the model. The cognitive pig holeboard is found to be a reliable behavioural task for measuring several components of spatial learning and memory of various pig breeds from the age of weaning onwards. Therefore this test can be applied when testing the LBW piglet and possible preventive therapeutics.