F - Pup Motor Development

Objectives:

To observe pup development in terms of physical appearance and motor responses.
To screen pups for developmental milestones.

Introduction:

Many pharmaceuticals and environmental chemicals can alter brain development, altering behavior. Some of these changes can be quite subtle, merely delaying the appearance of a behavior by a couple of days, while others can be quite severe, resulting in persistent morphological and behavioral changes throughout life, such as is observed with Fetal Alcohol Syndrome. As pregnant mothers experience illnesses that must be treated, it is important to understand the effects that various treatments will have on her developing fetus. Understanding the behavioral development of the rat is an important foundation for developing screens for potentially teratogenic substances. Some very detailed screens have been developed (e.g., Altman J and Sudarshan K, 1975).

Procedure:

Preparation: Read Chapter 25: Infancy (Alberts, 2005) before the lab this week. The slab will be spread out over a number of days over a number of weeks. Sharing the workload with your group will make this less onerous. You’re TA will inform you when the pups have been born, and you should start screening them on the day after birth if possible. Prepare a chart where you can note either the presence/absence of a trait (eyes open, pinna separated from head, ear canal open, presence of fur), the latency to observe a behavior (righting reflex, orientation on an inclined place, placing reflex), and the quantification of a behavior (distance traveled in 1 minute, duration of a wire hang). You’ll need a page for each day, and a column for each pup. Do not worry about tracking individual pups; we are interested in litter effects so merely calculate means and percentages for each trait.

Testing: On each testing day, prepare a small clean cage. Place all the pups in this cage. Test each pup individually for all the traits, and then return it to the mother when the battery of tests is completed before proceeding to the next pup.

Examine the pup to determine if the eyes are open, if the pinna (fleshy part of ear) is separated from the head, if the external auditory meatus (ear canal) is open, and if fur has appeared yet. Score each of these as “Yes” or “No”. Weigh the pup.

For the next series of test, start a timer when you place the rat in position, and stop it when the behavior is complete. If the behavior fails to appear score the test as unsuccessful. Righting Reflex: Place the pup on its back and time how long it takes until it is back on all 4 feet. Orientation on an Inclined Plane: Place the pup nose-down on the inclined plane apparatus. Time how long it takes to turn around 180 degrees. If it looses its grip and falls to the bottom of the plane, place it nose-down again. If it falls a second time, score the test as unsuccessful. Placing Reflex: Gently pick up the pup by the base of the tail near the body and lift it. Time how long until it flays its forepaws outwards (the placing reflex).

For the next series of behaviors, quantify the behavior. Locomotion: Place the pup in the middle of the movement mat and start the timer. Count how many gridlines it crosses in 1 minute. Wire hang: Place a stack of paper towels under the wire to soften any fall. Gently place the pup’s forepaws on the wire and let go. Time how long it can hang. If it falls immediately, replace it once. If it can hang for 30 seconds, stop the test and score it as 30 seconds.

Variations