Sensory-motor circuits in the spinal cord integrate sensory feedback from muscles and modulate locomotor behavior. Although we know how the sensory-motor system generally works, the main issue lies in identifying all neurons involved and understanding their interrelationships. Many interneurons contribute to sensory-motor circuits and have been well studied. For example, Renshaw cells (RC) are inhibitory interneurons that prevent motor neurons from over-activity. A distinguishing feature of RCs is that they are the only interneurons within the ventral-most region of the spinal cord expressing the calcium binding protein calbindin (CB). Recent studies have found other subpopulations of ventral horn interneurons outside of the RC area that express CB, but knowledge regarding the function and connectivity of these neurons is limited. We hypothesize CB expression serves a functional purpose for ventral horn interneurons and as well as identifying RCs. Here we compare known characteristics of RCs with other ventral horn interneurons that express CB. We analyze anatomical location; cellular density; expression of neurotransmitters; motor neuron and sensory afferent contacts; expression of calcium binding proteins CB, calretinin and parvalbumin; and premotor neuron identification.