Spinal dopamine receptor mechanisms regulating the micturition reflex after spinal cord injury - Project Summary We previously discovered a subpopulation of dopaminergic neurons that reside in the rat spinal cord. Following spinal cord injuries (SCI), these neurons undergo plasticity and release a low level of dopamine (DA) to modulate lower urinary tract (LUT) activity. However, we found the effects of DA on the recovered micturition reflex cannot simply be interpreted by activation of either the D1 or D2 receptor alone nor by simultaneous stimulation of the two. Instead, stimulating D1 receptors appears to synergize the effect induced by D2 activation on voiding in SCI rats. Recently, a D1-D2 receptor heterooligomer (heteromer) was uncovered in the brain which is linked to several neurological behaviors or disorders. In the preliminary data, we detected D1-D2 heteromer levels in the rat lower spinal cord, and the expression of this receptor complex is upregulated following SCI. Accordingly, we hypothesize that spinal D1-D2 heteromers regulate the micturition reflex in rats with SCI and stimulation of this receptor complex improves involuntary micturition function. Using multiple experimental approaches, including co-immunoprecipitation, ELISA, in situ proximity ligation assay, RNAscope, quantitative PCR, western blot, micturition reflex and functional recordings, we will 1) determine whether spinal D1-D2 receptor heteromers tonically regulate micturition reflexes in rats with SCI, 2) test whether co- stimulating spinal D1 and D2 receptors increases heteromer formation and improves involuntary micturition function in rats with SCI as a potential strategy for translation, and 3) elucidate whether the D1-D2 complex acts on micturition function via an intracellular Gq/11-PLC-Ca++ signaling pathway. This project will challenge traditional concepts concerning DA receptors in the spinal cord, aid in further appreciation of DA-ergic machinery regulating the micturition reflex, and establish plausible pharmacotherapeutic targets for SCI- induced urinary disorders.
