University of Illinois (U of I) research is showing that the baby pig can help provide answers to the study of infant brain development in predicting behavioral problems such as cognitive deficits, anxiety disorders, depression and autism.
Researchers are finding that baby pigs can be trained in traditional learning and memory tests that can directly benefit human health.
“Studies suggest that inadequate nutrition, stress and infection leave fingerprints in early brain development that can make a person more vulnerable to behavior disorders later in life,” says Rodney Johnson, DVM, U of I professor of animal sciences and director of the Division of Nutritional Sciences. “We are interested in learning how the brain develops during this time and how cognitive ability is affected. Our goal is to understand how to promote brain and cognitive development, and minimize potential experiential influences that might hinder the process.”
The use of the pig in neuroscience research is gaining in popularity because pigs anatomically resemble humans and many of their organs grow and develop similarly.
Pigs are also precocial, meaning they are born with well-developed sensory and motor systems, allowing them to be very mobile and weaned at an early age.
“Most important, the pig brain’s growth spurt occurs perinatally – a little before and a little after birth,” Johnson says. “In contrast, the rodent’s brain growth spurt occurs after birth and the non-human primate’s occurs before birth, making them less ideal to study and compare to humans.”
The brain’s rapid growth spurt involves a critical period of time, Johnson says.
“We know that if something goes wrong during this developmental period, the brain can be permanently altered,” he says. “We believe that events occurring during this developmental period may underlie some of the behavioral problems that emerge later in life.”
For the study, piglets were weaned at 2 days of age and provided a milk system that delivered 14 small meals a day to mimic the number of meals they’d receive from their mothers.
At 2 weeks of age, piglets were trained to find a milk reward in an eight-arm radial maze, a large version of models typically used to study rodent behavior. The eight arms of the maze came equipped with cups the exact size piglets fed from during the day. Seven bowls contained inaccessible milk and one bowl contained milk that was accessible. The goal was to teach the piglets how to find the accessible bowl of milk.
To create cues for the piglets, researchers covered the opening of each maze arm with a blue or white curtain. The piglets learned color cues to remember where to find milk. In the first test, accessible milk was behind the blue curtain.
“The piglets learned quickly after day one where to find their reward,” Johnson says. “This simple associative learning task was not hard for them to complete.
“But then, we did a reversal learning test where the white curtain became the entrance to the cup of accessible milk. This was more complicated because the piglets had to learn to stop going to the blue and then associate white with milk. It required a greater cognitive load, but it was one that they learned over time.”
Researchers also studied how peripheral immune activation affects cognitive processing. One group of piglets received an immunostimulant to mimic a common viral infection, which took pigs more time to complete the reversal learning test.
“When the immune system encounters an infectious agent, it responds and conveys information to the brain,” he explains. “We were able to show that when the peripheral immune system conveyed information to the brain in the neonate, their cognitive abilities were hindered. That reveals another advantage of the neonatal piglet model.”
The Johnson lab is using MRI imaging to study brain development in piglets from 2 weeks of age until sexual maturity or an adolescent stage.