Visualization of lamina I of the dorsal horn in live adult rat spinal cordslices

The superficial dorsal horn of the spinal cord, particularly lamina I, play s a key role in the integration and relay of pain related sensory input. To study the physiology of lamina I neurons in slices, a clear delineation of this layer can be greatly advantageous. Yet, it has remained difficult to distinguish this layer in live tissue in conventional transverse spinal sli ces because of its very narrow thickness at the edge of the dorsal horn. We describe here the criteria we used to delineate lamina I in live tissue us ing gradient contrast videomicroscopy in 400 mu m-thick parasagittal spinal cord slices from adult rats (30-60-day-old). Because of the longitudinal o rientation of the neurons in this layer, the resulting distinctive reticula ted appearance of lamina I made it possible to readily distinguish it from lamina II. The usefulness of this distinguishing parameter is demonstrated by our ability to contrast synaptic properties of neurons in lamina I from those in lamina II. Complete morphological identification of lamina I neuro ns however also requires visualization of the eel in the horizontal plane. To maintain compatibility with the parasagittal slice, we used 3D reconstru ctions from confocal images of the recorded neurons. Rotation of the neuron in space allowed for its morphological characterization in all three plane s (horizontal, parasagittal, and transverse). This approach therefore prese nts optimal conditions for systematic electrophysiological recording from v isually identified lamina I neurons. (C) 2000 Elsevier Science B.V. All rig hts reserved.