Characterization and regulation of neurokinin1 receptors in primary cultures of rat neonatal spinal neurons.
Neurokinin1 receptors are the primary target of substance P released from neurons during neural transmission, yet little is known regarding the regulation of neurokinin1 receptors on neurons. 125I-Bolton-Hunter-substance P was used in the present studies to determine whether primary cultures of rat neonatal spinal cord express neurokinin1 receptors and, therefore, can be used as a model to explore regulation of neuronal neurokinin1 receptors. 125I-Bolton-Hunter-substance P bound to a single site in neuron-enriched cultures with an affinity of 256 nM, which is comparable to its high affinity binding on adult rat spinal cord. Treatment of neuron-enriched cultures with 10 nM substance P resulted in a 47% decrease in 125I-Bolton-Hunter-substance P binding at 24 h which was due to a decrease in affinity of the receptor. However, at 48 h after treatment with substance P, 125I-Bolton-Hunter-substance P binding increased by 44%. The increase in binding was due to a two-fold increase in receptor density. These changes occurred in the presence of 0.5 microM tetrodotoxin, decreasing the likelihood that the changes in binding were secondary to the release of transmitters by substance P. Furthermore, substance P1-7, a metabolite of substance P that has putative physiological effects, did not alter 125I-Bolton-Hunter-substance P binding. These data provide evidence that neuronal neurokinin1 receptors are under homologous regulation in primary cultures of neonatal rat spinal cord and suggest that a similar mechanism occurs in vivo. Furthermore, the data suggest that a decrease in affinity of the neurokinin1 receptor may contribute, in part, to tachyphylaxis to substance P.
Seybold
V S
VS
Department of Cell Biology and Neuroanatomy, University of Minnesota, Minneapolis 55455, USA.
Abrahams
L G
LG
D000818:Animals; D000831:Animals, Newborn; D001667:Binding, Competitive; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D007150:Immunohistochemistry; D051381:Rats; D017207:Rats, Sprague-Dawley; D018040:Receptors, Neurokinin-1 / Q000378:metabolism*; D013116:Spinal Cord / Q000378:metabolism*; D013373:Substance P / Q000494:pharmacology*
D018040:Receptors, Neurokinin-1; D013373:Substance P