The behavioral data is presented as daily averages for each variable. (Digler, et al., 2010).
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Pigs play a vital role in TBI research due to their physiological similarities to humans, and the 8-arm radial maze is extensively utilized for studying learning and memory. Initially described by Dilger et al. (2010) for piglets as young as 2 weeks old, this maze involves training subjects for a milk reward placed in 8 PVC bowls equipped with covered lids (included with your order). Intramaze cues, such as surrounding curtains, are employed, demonstrating piglets’ capability to learn simple associative acquisition tasks effectively.
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The pig radial arm maze is distinct from its rodent counterpart as it is tailored for both spatial and non-spatial tasks (Digler et al., 2010).
Due to the similarities in neuroanatomy between pigs and humans, pigs are highly favored in neuroscience research. Compared to rodents, pigs exhibit cognitive abilities more akin to humans (Gieling et al., 2011). Notably, similarities in neural growth patterns between neonatal piglets and human infants are observed. Additionally, piglets are easy to wean, do not experience separation anxiety from their mothers, and can be trained using a reward-based system. These factors collectively make piglets ideal for conducting learning and memory tasks, which heavily rely on the proper functioning of the hippocampus. However, the hippocampus is particularly vulnerable to the effects of excessive production of central pro-inflammatory cytokines due to the presence of cytokine receptors, potentially impairing learning and memory capabilities. This vulnerability is especially critical during incomplete brain growth, potentially leading to significant deficiencies in information processing and retention (Digler et al., 2010).
An effective apparatus for conducting behavioral tasks that measure learning and memory is the pig 8-arm radial maze. Its design allows for various configurations where milk rewards are alternately placed in different arms, each marked by differently colored curtains. Piglets learn to associate specific colors with accessible milk, applying this knowledge in subsequent tasks.
The subjects’ activity is monitored by a ceiling-mounted video camera positioned directly above the central octagonal area. Before testing, the subjects receive a nutritionally complete, medicated commercial piglet milk administered automatically via a digital timer to replicate natural feeding intervals. Milk is provided every hour for 14 hours, followed by a 10-hour period without milk to stimulate hunger as a motivational factor during behavioral assessments. Each arm includes a bowl of milk concealed behind curtains to prevent olfactory cues. Only the bowl behind the correct arm remains accessible to motivate subjects and facilitate learning (Digler et al., 2010).
Arm 2 acts as the initial starting point for subjects during the behavioral assay. The assessment spans 8 days, divided into two tasks: acquisition and reversal, each conducted over 4 consecutive days with 8 trials per day. In the acquisition phase, the correct arm is obscured by a blue curtain, while the other 7 arms are covered by white curtains. Following the acquisition phase, the reversal task begins, reversing the curtain colors: incorrect arms are covered in blue, and the correct arm is covered in white.
Subjects failing to complete a task within the allotted time are gently guided to locate the milk reward in the correct arm as part of a shaping procedure, limited to the acquisition phase. The maximum trial time (60s) is recorded for these subjects.
Each testing day assigns each of the 8 arms as the correct arm once. The order of arms is randomized across testing days but remains consistent within each testing day. Despite Arm 2 being the designated starting arm, it also rotates as the correct arm on different days (Digler et al., 2010).
Several subjects were designated as controls, selected from different litters and raised following the identical protocol described earlier. However, these subjects did not receive any experimental interventions, allowing for an assessment of their response during the behavioral evaluation (Digler et al., 2010).
After completing the acquisition phase, the subjects were stratified into two experimental groups based on weight, gender, and their litter of origin. Subsequently, they received intraperitoneal injections of either sterile saline or poly I
. Three hours after the injection, the subjects participated in the reversal testing phase.
Following the 8-day behavioral assessment, control subjects were randomly assigned to two treatment groups and received intraperitoneal injections of either sterile saline or poly I
. Four hours post-injection, the subjects were anesthetized and then euthanized. Blood and tissue samples were collected immediately after euthanasia (Digler et al., 2010).
The tissue samples are processed to isolate total RNA, which is quantified using spectrophotometry to determine its concentration. Purified samples undergo a DNAse I digestion procedure before being reverse transcribed into cDNA.
Quantitative RT-PCR is performed in which the sample cDNA and reference cDNA is amplified via PCR. (Digler, et al., 2010)
Determination of plasma concentrations of cytokine is done using porcine-specific antibodies in enzyme immunoassays. This allows the evaluation of which cytokines become elevated and can cause possible disruption to the learning tasks. (Digler, et al., 2010).
Several variables and parameters are recorded to carry out the data analyses:
The behavioral data is presented as daily averages for each variable. (Digler, et al., 2010).
A non-spatial version of the radial arm maze was chosen because neonatal piglets have limited visual acuity and incomplete development of certain brain regions necessary for spatial learning tasks. (Digler et al., 2010)
Moreover, the experiment did not detect any sexually dimorphic effects of the cytokines. (Digler et al., 2010)
Digler, R. N. & Johnson, R. W. (2010). Behavioral assessment of cognitive function using a translational neonatal piglet model. Brain, Behavior, and Immunity, 24(7), 1156-1165.
Gieling, E.T., Nordquist, R. E., & Staay, F. J. (2011). Assessing learning and memory in pigs. Animal Cognition, 14(2), 151-173
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