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Increased motivation during learning task and VIP expression in rats exposed to mild neonatal hypoxia

Prenatal exposure to acute hypoxia can cause developmental disturbances due to hypoxic-ischemic brain injury, and some of the consequences, such as learning difficulties, may only show up later in life. The aim of this study was to detect possible changes in learning outcomes in a rat non-invasive neonatal hypoxia model and check their correspondence to the expression of VIP (vasoactive intestinal peptide) gene in hippocampus, which has been suggested to have a role in information gating during spatial navigation, memory encoding and motivated learning behavior. Experimental Wistar Han rats of both sexes were exposed to normobaric hypoxic conditions (8% O2, 92% N2), in a warm (≈ 27°C) normobaric chamber, for 2 hours on the first postnatal day (PND1) to mimic mild midgestational hypoxic brain injury in humans. At the same time control rats were kept under normoxic conditions (21% O₂, 78% N₂). From PND39 to PND43 rat memory was tested in a T-maze as the number of correct choices in a ten-trial sessions during the five consecutive days. On PND50 rats were sacrificed and hippocampal tissue was collected. Differential gene expression for VIP was determined using real- time PCR based on Taq-man chemistry, with Actb and Hprt1 as reference genes. Although both groups reached similar levels of learning at the end of the experiment, in comparison to the control group hypoxic rats displayed higher number of correct choices during the first three days of testing, with statistical significance on the second day. Real-time PCR showed significant increase in VIP gene expression in the hippocampus of hypoxic rats. We can speculate that the initially higher incidence of correct choices in the hypoxic group, corresponding to the upregulated VIP gene expression, may represent an increased motivation for the reward in a learning task, which has counteracted possible hypoxia-induced learning impairments.

T-maze ; gene expression ; hippocampus

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