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Virtually all organisms manifest regular periods of behavioral quiescence and activity. In mammals and birds, these periods have evolved into regular episodes of wakefulness and sleep. The sleep period itself has further differentiated into two distinct states, slow wave sleep (SWS) and rapid eye movement (REM) sleep. In humans, SWS has further differentiated into four distinct stages, each identified by a specific pattern on the electroencephalogram (EEG). REM sleep is very similar to wakefulness in many ways; the main difference is that there is behavioral quiescence during REM sleep. For this reason, REM sleep is often referred to as .

Lectins are carbohydrate-binding proteins that recognize distinct oligosaccharide moieties of glycoproteins and glycolipids. In vertebrates, endogenous lectins serve a variety of functions, including cell adhesion, cell recognition, signal transduction, and endocytosis, in both neuronal and nonneuronal cells (–). A role for cell surface carbohydrate recognition has been described in processes, such as fertilization, development, leukocyte homing, and the innate immune response (,). Among the known classes of vertebrate carbohydrate-binding proteins are some cytokines (e.g., interleukin 1β [IL-1β]) and growth factors, which possess a receptor-binding domain and a carbohydrate recognition domain (,).

Saporin conjugates have proven extremely versatile and valuable in the selective destruction of a variety of cell types. In the nervous system, the use of saporin-conjugated toxins has generally been directed toward neurons. We were interested in whether saporin conjugates could be used to target other nervous tissue cell types, particularly the myelin-forming cells. Taking advantage of the fact that myelin is rich in G ganglioside and that the B fragment of cholera toxin has a high affinity for G, we used a conjugate of the B fragment of cholera toxin and saporin (CTB-sap) to target myelin-producing cells (oligodendrocytes) in the central nervous system (CNS) (Fig. 1). We found that CTB-sap is effective in removing oligodendrocytes in addition to other glial cells and largely leaves neurons intact. We successfully used CTB-sap to study demyelination and remyelination in the spinal cord (), and our preliminary results suggest that CTB-sap will be useful for inducing demyelinating lesions in other parts of the CNS.