This article describes a detailed protocol for the precise delivery of solutions into brain tissue using a quartz microneedle. The method emphasizes careful control of injection speed and technique to minimize tissue damage and ensure effective solution distribution.
Take a quartz microneedle with customized holes, attached to a syringe filled with water, and connected to a micropump to control the delivery rate.
Take a secured, anesthetized rat with the exposed injection site.
Position the microneedle and place a paraffin film underneath. Put a drop of the injection solution on it.
Retract the water to create an air bubble, then lower the microneedle to draw the solution.
Allow a drop to form, ensuring clear passage.
Use a sharp needle to puncture the brain's membrane.
Insert the microneedle while set at a low delivery speed to prevent tissue fragment penetration into the needle.
Once positioned, go slightly deeper. Stop the delivery and raise it again to avoid backflow.
Start the delivery with increased speed. The holes in the needle ensure optimal distribution of the injected solution.
Allow sufficient time before withdrawing the needle to facilitate diffusion.
Cut a small piece of plastic paraffin film and place it on the skull. Using the 10-microliter pipette, make a drop of the solution to apply on the plastic paraffin film. Stop the pump. Slightly retrieve the pusher of the pump, and create a little air bubble in the capillary by gently pulling the piston of the microinjection syringe.
Lower the tip of the needle until it reaches the drop. Draw the sample by pulling the piston of the microinjection syringe very slowly, avoiding any bubble formation. Replace the pump pusher in contact with the piston, and turn on the pump at a flow rate of 0.3 microliters per minute.
Then wait until the formation of a drop before proceeding to the next step. Afterward, lower the flow to 0.1 microliters per minute. Nick the dura with a stainless steel bevel-tip needle and slowly lower the needle to enter into the brain tissue. When the desired position is reached, go down an additional 0.1 millimeters, then stop the pump.
Raise the stereostatic arm by 0.1 millimeters, and start the pump again at 0.3 microliters per minute. After that, start the timer and the injection. Monitor the bubble movement while injecting. At the end, stop the pump and wait five minutes before slowly retrieving the needle.
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