Do respiratory neurons control female receptive behavior: a suggested role for a medullary central pattern generator?

Nucleus retroambiguus (NRA) consists of a column of neurons in the caudal medulla with crossed descending axons that terminate in almost all spinal segments. Many of these neurons transmit the drive for expiratory movements to the spinal cord. The same neurons are also known to participate, however, in other motor acts, such as vomiting and abdominal straining, for which it appears that the medullary circuits controlling the respiratory pattern are reconfigured. Plasticity in projections from the NRA to hindlimb motor nuclei provides evidence that some of these projections are involved in yet another motor act, female receptive behavior. Here, we present the hypothesis that the medullary circuits are also reconfigured to act as a central pattern generator for this behavior. In addition, we suggest that during estrus, plasticity is shown not only in spinal cord connections, but also in a selected membrane property of hindlimb motoneurons.