We did this routinely in my lab. I generally agree with the advice given by @ksmith5 and @MGradwell. Specific instructions can be found is some of my papers:
Marvizon, J C, V Martinez, E F Grady, N W Bunnett, E A Mayer. Neurokinin 1 receptor internalization in spinal cord slices induced by dorsal root stimulation is mediated by NMDA receptors. J Neurosci 17: 8129-8136 (1997).
Marvizon, J C, E F Grady, E Stefani, N W Bunnett, E A Mayer. Substance P release in the dorsal horn assessed by receptor internalization: NMDA receptors counteract a tonic inhibition by GABAB receptors. Eur J Neurosci 11: 417-426 (1999).
Adelson, D W, L Lao, G Zhang, W Kim, J C Marvizón. Substance P release and neurokinin 1 receptor activation in the rat spinal cord increases with the firing frequency of C-fibers. Neuroscience 161: 538-553 (2009). PMC2692762
Chen, W, J A McRoberts, J C G Marvizón. μ-Opioid receptor inhibition of substance P release from primary afferents disappears in neuropathic pain but not inflammatory pain. Neuroscience 267: 67-82 (2014). PMC3998911
Here are some tips:
-The vibratome that you use to cut the spinal cord is critical. We use a Integraslice 7550PSDS with a microscope attached. Previously we used the standard TPI Vibratome, but we had to modify it to decrease the forward movement and increase the vibration amplitude.
-Tilt the microscope so you can examine the dorsal surface of the spinal cord. You can also mount the spinal cord so it is not completely vertical. You will also need a good light source.
-We glue the spinal cord to an agar block using Loctite. The consistency of the agar is critical - it should be hard enough not to move with the spinal cord. Both the spinal cord and the agar have to be dry before applying the Loctite to the agar. The we glue to it the ventral surface of the spinal cord.
-Select the dorsal roots that you are going to cut while cleaning the dura. Cut away all the others. Completely eliminate the ventral roots.
-aCSF bubbled with O2 / CO2 should be added to the spinal cord immediately after gluing it to the agar. We keep the aCSF ice-cold and bubbled throughout the cutting process.
-The cyanoacrylate glue Loctite should work almost instantly. We apply it in a thin layer using the wooden part of a cotton-tipped applicator cut at a slanting angle.
-After you glue the spinal cord to the agar block, separate the roots from the spinal cord by gently pulling. Then grab the end of the first root with fine forceps and sink it in the agar below the cutting plane, so that the root is pulled down away from the blade.
-Carefully aim the blade just above the point of entry of the root by looking through the microscope.
-Cut with minimum forward speed and high transverse speed (vibration).
-Before making the second cut, grab the tip of the root (which was sunk into the agar) and place the whole root on top of the agar block. The root should be stretched a little. Otherwise, you would cut it with the second cut.
-Move the blade down 400 - 450 micrometers.
-Made the second cut. It the root is wide (L4 or L5), you will cut through part of the root, but the remaining should be undamaged. If this is a problem, select L3, L2 or L1.
-Carefully inspect the entry zone of the root through the microscope for damage. Reject the slice if this is not good.
-Detach the slice from the agar by grabbing the strip of Loctite attached to the ventral surface.
-Keep the slice on a nylon net inside a beaker with aCSF bubbled with O2 / CO2. The bubbles will attach to the root and pull the slice to the surface. To avoid this, place a ring with a net over the slice or carefully thread the end of the root through the net.
-Do not use the end of the root (which you have been handling) for stimulation. In my experience, hook electrodes or electrodes on a side chamber work much better than suction electrodes.