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Fig. 3. Genetic techniques can be used to dissect circuits within the spinal cord.
Populations of interneurons derived from progenitor cells can be identified in
neonatal mice. Schematic shows different populations of cells that can be
identified currently. V0 cells are commissural interneurons that consist of
both glutamatergic and glycinergic/GABAergic cells. Animals lacking these
commissural cells have poor left-right coordination. V1 interneurons are
considered to be inhibitory and are a heterogeneous population. At least a
portion of them is involved in regulating the speed of the rhythm
(Gosgnach et al., 2006).
Renshaw cells form part of the V1 population and have been well characterized
(Sapir et al., 2004), but the
contribution of individual classes of V1 neurons to rhythm generation has not
been well established. V2 cells are also likely to be heterogeneous and
consist of ipsilateral propriospinal interneurons projecting across several
segments. One possibility is that these cells are involved in flexor-extensor
coordination. V3 cells are glutamatergic commissural interneurons that may
play a role in coordination of patterns. Cells expressing a transcription
factor termed Hb9 are present in lamina VIII and exhibit several intrinsic
properties thought to be important for rhythm generation
(Wilson et al., 2005). Figure
adapted from a previously published embryonic schematic
(Goulding and Pfaff,
2005).
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