Expression of PPD by GABA-immunoreactive and non-immunoreactive neurons. a-c: Confocal images of a transverse section of the L4 segment from a rat that had been fixed with glutaraldehyde/formaldehyde and reacted with antibodies against PPD (magenta) and GABA (green). This field shows a single PPD-immunoreactive neuron in lamina IIo (arrow), which is GABA-immunoreactive and is surrounded by other GABA-immunoreactive neurons, as well as by neurons that lack GABA, three of which are indicated with asterisks. Note that the PPD occupies the perikaryal cytoplasm but is excluded from the nucleus, whereas GABA staining is seen throughout the nucleus and cytoplasm. Also, note that there is a high density of punctate GABA immunoreactivity throughout the neuropil, which consists of the dendrites and axons of GABAergic neurons. The GABA-negative neuronal cell bodies stand out as dark "holes" within this neuropil staining. d-f: a PPD-immunoreactive neuron (arrowhead) near the lamina II/III border that is not GABA-immunoreactive. Both sets of images are from a single optical section. Scale bar = 10 μm.