This article describes a protocol for using magnetic resonance imaging (MRI) and proton magnetic resonance spectroscopy (MRS) to study neuronal activity in the rat barrel cortex. The method involves stimulating the whiskers to activate the barrel cortex and measuring metabolite changes.
Begin with an anesthetized rat on the magnetic resonance imaging or MRI bed.
The rat’s head is angled to expose the left barrel cortex, a sensory region connected to the right whiskers, which are fastened with tape.
Secure a radiofrequency detector coil above the rat’s head.
Position the MRI bed inside the scanner and image to confirm proper brain positioning.
Perform an MRI scan and obtain a structural brain image. Compare it with a functional MRI image showing activated regions after whisker stimulation.
Then, perform localized proton magnetic resonance spectroscopy, or MRS to measure baseline metabolite activity in neurons.
Initiate airflow to move the right whiskers, activating the barrel cortex neurons.
To sustain this activation, astrocytes produce lactate, a neuronal metabolite, and supply it to neurons.
Repeat proton MRS and compare the stimulated and baseline spectra. An increased lactate peak after stimulation confirms successful barrel cortex activation.
To correctly position the surface coil for proton Magnetic Resonance Spectroscopy or MRS, rotate the head approximately 30 degrees clockwise so that the surface coil can be placed just above the left barrel cortex in a horizontal position, and located at the magnet center when inside the magnet. Plug the surface coil and fix the coil into place with tape. Check that the sail can still move correctly when the air puff system is on.
Then place the bed into the magnet and check the sail movement again. Confirm the correct position of the animal with the localization sequence as demonstrated, and drag the T2-turboRARE sequence tab into the Instruction Name window. Then click Continue to execute the scan program, and to allow the correct localization of the Voxel within the somatosensory barrel field cortex.
At the end of the scan, track the laser sequence tab into the Instruction Name window, and place the Voxel at the center of the somatosensory barrel field cortex area. Click adjustment platform to open the edited scan instruction, and click Wobble to slightly change the impedance of the receiver coil for tuning. When the tuning is finished, click Apply to close the instruction editor and to apply the changes in the edited instruction.
Record a B0 map and start the proton MRS acquisition. During a resting period. Acquire another localization sequence to compare with the first one, and confirm that the rat did not move during the laser acquisition. Then turn on the air puff system, and use the laser sequence to perform a second proton MRS.
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