Preabsorption of blocking peptide. Photomicrographs of paraventricular nucleus (Pa; column 1) and supraoptic nucleus (SO; column 2) of the Long-Evans rat, grass rat, and Syrian hamster after preabsorption with orexin A blocking peptide. Note that preabsorption with blocking peptide eliminates cell bodies seen in Figures 2 and 3. 3V: third ventricle; OC: optic chiasm. Scale bar = 200 μm.