Intraspinal circuits supporting synergy between the bladder and urethral sphincter in mice

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Project summary Detrusor-sphincter-dyssynergia (DSD) is a major urological problem inducing inefficient voiding, increased amount of post-void residual urine and high intravesical pressure after spinal cord injury (SCI). Until recently the majority of studies on spinal mechanisms of coordination between external urethral sphincter (EUS) and the bladder (BL) were conducted in female rats, although in clinical practice DSD develops more often in males. Furthermore, sexual dimorphism in anatomy and function of the lower urinary tract (LUT) suggests differences in the spinal neural circuits of male and female. With development of genetic modifications and optogenetic techniques the mouse model of LUT dysfunction is becoming more useful than the rat. Therefore, in the proposed project “Intraspinal circuits supporting synergy between the bladder and urethral sphincter in mice” we will use transgenic mice of both sexes for electrophysiological, optogenetic, immunohistochemical, pharmacological and anatomical studies of spinal cord circuits involved in interaction between the bladder (BL) and the external urethral sphincter (EUS) in spinal intact animals and after spinal cord injury. We will test several hypotheses in in vivo and in vitro experiments. In urethane anesthetized animals of both sexes, we will determine functional differences in spinal regulation of micturition and in control and SCI mice. Male and female animals will be also used to determine hypothesized sexual dimorphism in LUT-related spinal circuits and their plasticity after chronic SCI. Using electrical stimulation of the Lumbar Spinal Coordinating Center (LSCC) which we have recently discovered in L3/L4 spinal segments, we will test whether an external command can initiate voiding. Using trans-synaptic viral labeling, we will trace neuronal populations involved in coordination between EUS and BL to determine structural and functional differences in LUT spinal networks between males and females. In spinal cord slice preparations, we will use transgenic mice expressing channel rhodopsin (ChR2) in inhibitory or excitatory neurons to study reactions of EUS motoneurons to light-evoked activity of LUT-related spinal interneurons embedded in specific spinal pathways, and will identify and characterize the inhibitory circuit which is responsible for EUS relaxation. We will define the role of the L3/L4 LSCC in activity of EUS motoneurons and EUS relaxation and its mode of interaction with L6/S1 motor neuronal pool. We will evaluate the contribution of a hypothesized recurrent inhibitory circuit in L6/S1 to the generation of EUS bursting and relaxation as well as to bladder-sphincter coordination. The long-term objectives of the research project are to increase our understanding of the pathophysiological mechanisms inducing DSD and voiding problems after SCI and to develop new and effective therapeutic interventions for the treatment of DSD in spinal cord disorders. Considering gender related differences in neural control of the LUT different approaches to DSD treatment in males and females may be recommended.