We investigated the distribution of retinoid Z receptor beta (RZR beta), a putative nuclear melatonin receptor, mRNA in the rat brain and spinal cord using in situ hybridization. The RZR beta riboprobe uniquely hybridized with the neurons in several sensory pathways including the dorsal horn of the spinal cord, whereas the regions involved in the motor control were generally unlabeled. RZR beta mRNA was also highly expressed in the dorsomedial portion of the suprachiasmatic nucleus, pars tuberalis and some limbic areas. This result suggests that RZR beta plays a specific role as a transcription factor in the sensory, neuroendocrine and limbic systems.