Environmental Modulations of the Number of Midbrain Dopamine Neurons in Adult Mice

The overall goal of the following experiment is to provide controlled environmental situations that stimulate brain plasticity and behavioral changes in mice. This is achieved by housing mice in male female pairs versus male, male and female female control pairs to study the effects of prolonged gender pairing on the brain as an alternative, mice may be housed together in cages filled with different objects for exploring and playing versus standard house cages to study the effects of environment enrichment on the brain. Other treatments such as drug administration can be added to these environmental stimulations to help identify the mechanisms behind the observed brain and behavioral changes.

The results show that these environmental enrichments and treatments induce changes in the number of midbrain dopaminergic neurons that are dependent on midbrain, GABAergic synaptic transmission. Environmental enrichment is a paradigm that increases somatosensory motor and cognitive stimulation for mice. Using this approach, studies have shown increased neuroplasticity and also improvements in learning and memory in many models of disease.

The implications of this technique extend towards understanding mechanisms of adult brain plasticity brought about by environmental influences. And this is relevant for treating many these diseases of the the brain and mind. We first had an idea for this method when we first noticed that the number of midbrain dopamine neurons is changing in response to perturbing midbrain neuronal activity driven by synaptic inputs.

Visual demonstration of the osmotic pump and brain infusion cannula can be critical as the procedures can be quite difficult to learn from. Written descriptions For gender pairing. Group house sexually mature age matched male and female mice by gender, avoiding litter made pairing randomly place each mouse in a male, male pair, a female female pair, or a male female pair in a clean cage in isolation with ad lido access to food and water here and throughout the gender pairing.

Keep all extraneous environmental stimuli constant or equally distributed to all of the mice and house the animals continuously for seven days. For environmental enrichment, randomly assign sexually mature age matched male or female mice to one of three groups, standard housed running wheel or environment enriched for at least three days. Keep them this way.

With ad lido access to food and water for 14 days. During the environmental enrichment, the standard housed cage should contain only litter. The running wheel should contain litter plus two running wheels, and the environmental enriched should have litter two running wheels and toys.

Subject the environmental enriched mice to additional super enrichment by placing them together in a larger cage containing novel toys for one hour per day. At the same time each day for five days a week, return the mice to their environmental enriched cage. After each session, maintain the novelty by presenting a different set of toys for each session.

Cleaning any toys that are to be represented to the mice with soapy water and 80%ethanol. To remove any scent, displace the standard housed and running wheel groups in the same way for a similar period of time each day as well, but without the addition of the super enrichment materials the day before the implantation. Using aseptic technique, fill each sterile osmotic pump, connecting tube and cannula with sterile drug or vehicle solution according to the manufacturer's instructions.

Then connect the pieces together and incubate them overnight in sterile saline at 37 degrees Celsius on the day of the surgery. After confirming sedation by tow pinch, apply eye ointment to the animal and place it supine on a heat pad. Next, using aseptic technique, make a midline incision through the skin, starting from two centimeters posterior to the back edge of the skull, and finishing between the eyes blunt, dissect the skin away from the underlying fascia down the back of the mouse, creating a subcutaneous pocket large enough to comfortably fit the pump and connecting tube.

Then scrape the fascia clean from over the dorsal aspect of the skull and use an approximately 1.5 millimeter diameter dental burr to drill down into the skull at the appropriate stereotaxic coordinates until a thin flexible layer of bone remains, peel this layer away with fine forceps. Once the skull is cleaned of any blood and bone fragments and there is no further bleeding, use a cannula holder to place the pump and connecting tube into the just created pocket. Now position the tip of the cannula at the appropriate stereotaxic coordinates on the surface of the brain and then carefully lower the tubing into the brain, one millimeter short of the required depth.

Ensure the surface of the skull is clean and dry once more, and then use a toothpick to smooth freshly prepared dental acrylic over the entire exposed area of skull, including into the burr hole around the cannula before the acrylic hardens. Lower the cannula tip the remaining depth into the target. Then when the cannula is in place, carefully layer a second coat of freshly prepared dental acrylic onto the skull, as well as over the white plastic support for the cannula fixing the cannula in place.

Once the acrylic has hardened carefully remove the cannula holder and use a heated scalpel blade to melt through the plastic cannula tab. Then suture the skin closed over the entire implant. Apply antiseptic ointment to the skin margins and administer an anti-inflammatory to the animal.

Finally, remove the mouse from the frame. Place it under a heat lamp and monitor the animal until it is fully recovered. Adult male mice paired with female adult mice for seven days have approximately 12%more midbrain th positive SNC area neurons than males paired with males.

By contrast, females paired with males have approximately 12%fewer TH positive SNC neurons than females paired with females. The number of TH positive SNC and ventral teal area neurons is also increased in adult male mice subjected to an environmentally enriched pairing plus super enrichment for 14 days. With environmental enriched plus super enrichment with vehicle infusion animals exhibiting approximately 14%more th positive SNC neurons.

Then standard housed animals infused with vehicle animals subjected to environmental enriched plus super enrichment housing with gabaa receptor antagonist infusion, however, do not exhibit this increase. While attempting environmental manipulations, it is important to remember to minimize any disturbances to animals to a minimum, such as keeping noise to a minimum and avoiding case changes. Too often When setting up an enriched environment, it's critical to include varied nest material and to keep the nest site constant to minimize stress for your animals.

After watching this video, you should have a good understanding of how to manipulate the environment of adult mice in order to bring about changes in brain and behavior. Don't forget when working with the drugs, they can be extremely hazardous, so always wear protective clothing when preparing the osmotic pumps.