Cyclic AMP regulates the expression of neurokinin, receptors by neonatal rat spinal neurons in culture

Neurokinin, (NK1) receptors are up-regulated in the spinal cord during peri pheral inflammation, but the biochemical mediators regulating this change h ave not been resolved. The promoter region of the gene encoding the NK1 rec eptor contains a cyclic AMP (cAMP)-responsive element. Therefore, we used p rimary cultures of neonatal rat spinal cord to test whether increasing intr acellular cAMP can increase expression of NK1 receptors. Treatment with dib utyryl-cAMP (dbcAMP) resulted in a time-dependent increase in I-125-Bolton- Hunter-substance P (BHSP) binding in the cultures; treatment with dibutyryl -cyclic GMP did not. Treatment with forskolin plus 9-isobutyl-1-methylxanth ine mimicked the increase in binding, providing further evidence for the in volvement of cAMP in this effect. Scatchard analyses indicated that the inc rease in BHSP binding was due to an increase in binding capacity. The cAMP- induced increase in BHSP binding was preceded by an increase in levels of m RNA for NK1 receptor and was attenuated by pretreatment with cycloheximide. These data indicate that the cAMP-induced increase in binding was due to i ncreased synthesis of NK1 receptors, Comparison of substance P (SP)-induced production of inositol phosphates between cultures pretreated with dbcAMP and controls suggested that increased expression of NK1 receptors did not r esult in increased generation of second messenger by NK1 receptor activatio n. Together, these data indicate that a persistent increase in intracellula r cAMP increases expression of NK1 receptors. Because NK1 receptor activati on contributes to increased excitability of spinal neurons, the increased e xpression of NK1 receptors may be important in maintaining responsiveness o f spinal neurons to SP in central mechanisms underlying hyperalgesia.