Constructing an Olfactometer for Rodent Olfactory Behavior Studies

We are investigating the involvement of olfaction in learning and memory. This research explores how the sense of smell influences cognitive processes, including information acquisition, retention, and recall. We are examining the neural pathways connecting the olfactory system to the brain regions responsible for memory formation, such as the hippocampus.

In Alzheimer's research, pathogens, including viruses and bacteria, may enter the brain through the nose and travel to regions involved in learning and memory, such as the hippocampus. This pathway involves the olfactory system, which provides a direct route from the nasal cavity to the brain. In our studies, we found that, as the animal learns to discriminate odorants in a go/no-go task, the capping of high gamma frequency neuron oxidations through the face of theta gap oxidations changes in a matter that results in divergence between that rewarded and unrewarded odorant.

This can be used to determine the identity of the odor. Manufactured olfactometers have limitations, such as high costs, repair delays, and maintenance needs. We provide a guide to build a cost-effective, computer-controlled olfactometer using readily available components, empowering researchers in olfaction and animal behavior.

Companies manufacturing and selling automated olfactometers often go out of business or experience supply chain issues. Learning how to build an olfactometer allows a user to customize the olfactometer based upon research needs. Our protocol is not dependent on specific parts, and many components can be upgraded or changed, depending on in-stock supplies available.

To begin, set up the single-pole, single-throw, or SPST, momentary push-button switches. Using a soldering iron, solder two wires to each SPST momentary push-button switch. Attach the SPST momentary push-button switch to the control box.

Then, secure the wires by twisting them or applying tape to keep them organized. Place the odor valves into the designated slots of the odor valve rack, located in the center of the whiteboard. Next, peel the insulation from the wires connected to each valve.

Using a soldering iron, solder one wire from each valve to a thicker wire. Place one wire into the ground terminal on the screw terminal strip block, located on the back of the whiteboard, and insert the second wire into the corresponding pin on the SSR-48RACK Connect pins one through eight on the SSR-48RACK to two pinch valves each. For each valve, connect one wire from a push button to the 24-volt power supply and the other wire to the pin on the SSR-48RACK that connects to the valve.

Now, place the water valve and final valve into the appropriate slots on the valve plate. Connect the water valve and the final valve to the ground terminal and pins 17 and 18, respectively, on the SSR-48RACK. Attach push buttons to the 24-volt power supply and pins 17 and 18.

Next, purchase a suitable power supply and an extension cord. Using wire cutters, remove the plug from the power cord of the power supply. Cut one end of the wire that powers the SSR-48RACK.

Then, connect one of the wires to the G screw on the power supply and the other wire to the V1 terminal on the power supply. Next, connect one wire from the G2 terminal to the ground on the screw terminal strip block. Then, connect one wire from the V1 terminal to the five-volt screw terminal strip block.

Finally, connect one wire from the V3 terminal to the 24-volt screw terminal strip block. Place two flow meters into the flow meter holders. Obtain an aquarium pump that provides two liter per minute air flow.

Connect a short piece of tubing from each of the aquarium pump's two outputs to the two inputs of a T-connector. Attach a piece of tubing from the output of the T-connector to the input of an active carbon filter. Connect tubing from the output of the carbon filter to a T-connector.

Then connect the two outputs of this T-connector to a ball valve, which will control the air flow rate. Next, connect the output of each ball valve to the input of the flow meters. Connect the 50 cubic centimeters per minute flow meter output to the top manifold to supply air to the 40-milliliter odor equilibration vials with odorants in mineral oil.

Connect the output from each odor vial to its corresponding input on the lower manifold, and close the loop on the air flow system. Afterward, place each piece of tubing into the pinch valves. Connect the output of the two liter per minute flow meter to the side input of the lower manifold and the output of the lower manifold to the input of the final diverting valve.

Connect the default on output of the final valve to the odor delivery tube in the go or no-go chamber. Then connect the default off output of the final valve to an exhaust tube. Now, attach an 18-gauge needle to the tip of a five-milliliter syringe designated for water reward delivery.

Connect one tube to the needle tip. Then, connect the other end of the tube to the input of the water valve and the tubing from the output of the water valve to the limit. To begin, weigh each mouse individually on a calibrated scale and record the weight of each mouse in a laboratory log.

After weighing, gently place each mouse into the designated mouse chamber. Activate the sensors and stimuli delivery systems to prepare for the olfactory discrimination task. Start the MATLAB program to control experimental parameters, such as delivering odor stimuli for 2.5 seconds, dispensing water, and recording responses.

Analyze data in real time to provide immediate feedback on the animal's performance. Then, reverse the odor pair, setting the previously rewarded scent as unrewarded and vice versa. After that, test the animal's cognitive flexibility by observing its ability to unlearn and relearn scent associations, gaining insights into olfactory learning plasticity in mice.

On the first day of the go or no-go task in the forward direction, the mouse gradually improved to 80%correct responses, learning to lick only for ethyl acetate. On the last day of the forward task, the mouse reached a consistent proficiency, maintaining performance at or above 80%correct. After reversing the odorants, the mouse's correct response rate dropped to around 10%on the first day in the reverse direction.

By the last day in the reverse task, the mouse regained proficiency, achieving consistent performance at or above 80%correct.