This article describes a method for drug delivery to the brain using an injectrode system. The process involves precise placement of the injectrode in the target brain region of an anesthetized rat, followed by drug injection and monitoring of neuronal activity.
Start with an injectrode, an electrode-containing injection system. This features a microneedle and a silver wire electrode inserted within a glass micropipette.
Fill the injectrode with a test drug solution containing a dye to facilitate tracking of the drug's spread within the brain.
Attach a syringe filled with mineral oil to the injectrode. Wipe away any excess liquid.
Secure this injectrode onto a stereotaxic unit and connect it to a micropump system.
Position the injectrode on the target brain region of an anesthetized rat with a surgical hole in the skull.
Gradually lower the injectrode to penetrate the target region.
Halt the insertion upon receiving specific electrical signals that confirm the optimal injectrode placement.
Cover the exposed skull with warm agar to prevent tissue drying.
Allow the brain tissue to stabilize.
Inject the desired dosage of the drug.
Record electrical signals to monitor neuronal activity in response to the administered drug.
Prepare the injectrode by first filling a 5 to 10-microliter syringe with mineral oil. Next, prepare the drug of interest with a dye in physiological saline. Here, 0.5% Chicago Sky blue is mixed with 300 micromolar GABA. Now, fill the injection pipette by first loading a 1-milliliter syringe with the prepared solution, and then using the syringe to load the pipette.
When removing the syringe, keep light pressure on the plunger so a vacuum does not remove solution from the injectrode. Check for escaping fluid at possible leak points. Swab up any excess fluid and recheck for leakage. Now attach the micro-syringe with mineral oil to the injectrode. Then, wipe away any excess solution with gauze.
Check the injection tip. It should be possible to flow small drops of solution through it. Otherwise, it is blocked or leaking. Now, securely mount the injectrode to a micropump system. Then, move the position of the injectrode to the target coordinates, and lower the electrode to the superior colliculus, which can be identified through the recording of visual evoked potentials.
While the electrode is lowered, apply a small positive pressure by applying a low rate of injection to avoid clogging. Interrupt the injection when the structure is reached. After inserting the injectrode, cover the exposed cortex with warm agar to prevent desiccation. After the final placement of the electrode, wait 30 minutes to allow the stabilization of the tissue surrounding the electrode. Then, inject 400 to 800 nanoliters of solution at a rate of 40 nanoliters per minute until inactivation of neuronal activity in the superior colliculus.
The electrode should show a reduction in spikes during the injection of the inhibitory solution.
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