Messenger RNA localization and further characterisation of the putative tachykinin receptor NK4 (NK3B)

We have previously shown that a cloned receptor, highly homologous to the NK3 tachykinin peptide receptor, encodes a novel functional tachykinin receptor NK4. Examining sites of receptor mRNA expression by Northern blot we show that NK4 mRNA is expressed in numerous rat tissues, in contrast to the NK3 receptor which has been shown to have a distribution principally in nervous tissues. We have localised the NK4 receptor mRNA in rat brain and spinal cord using in situ hybridisation. NK4 receptor mRNA is widely expressed in neurons in the rat central nervous system, including cerebral cortex, hippocampus, hypothalamus and dorsal horn of the spinal cord. During peripheral inflammation of the hindpaw, NK4 mRNA shows complex patterns of regulation. We have also investigated some pharmacological properties of this receptor expressed ectopically in Xenopus oocytes. We show that the functional antagonism of dynorphin at the NK4 receptor is reversed by the non-specific opioid antagonist naloxone and that tachykinin-evoked responses at the NK4 receptor are inhibited by the non-peptide NK3 receptor antagonist SR142801 in a concentration dependent manner.