title: Characteristics of dorsal root ganglia neurons sensitive to Substance P.
abstract: BACKGROUND
  Substance P modulates ion channels and the excitability of sensory neurons in pain pathways. Within the heterogeneous population of Dorsal Root Ganglia (DRG) primary sensory neurons, the properties of cells that are sensitive to Substance P are poorly characterized. To define this population better, dissociated rat DRG neurons were tested for their responsiveness to capsaicin, ATP and acid. Responses to ATP were classified according to the kinetics of current activation and desensitization. The same cells were then tested for modulation of action potential firing by Substance P.
  
  
  RESULTS
  Acid and capsaicin currents were more frequently encountered in the largest diameter neurons. P2X3-like ATP currents were concentrated in small diameter neurons. Substance P modulated the excitability in 20 of 72 cells tested (28%). Of the Substance P sensitive cells, 10 exhibited an increase in excitability and 10 exhibited a decrease in excitability. There was no significant correlation between sensitivity to capsaicin and to Substance P. Excitatory effects of Substance P were strongly associated with cells that had large diameters, fired APs with large overshoots and slowly decaying after hyperpolarizations, and expressed acid currents at pH 7. No neurons that were excited by Substance P presented P2X3-like currents. In contrast, neurons that exhibited inhibitory effects of Substance P fired action potentials with rapidly decaying after hyperpolarizations.
  
  
  CONCLUSIONS
  We conclude that excitatory effects of Substance P are restricted to a specific neuronal subpopulation with limited expression of putative nociceptive markers.
authors.forename: Eder Ricardo
authors.initials: ER
authors.lastname: Moraes
authors.forename: Christopher
authors.initials: C
authors.lastname: Kushmerick
authors.affiliation: Departamento de Fisiologia e Biofísica ICB, Universidade Federal de Minas Gerais, Belo Horizonte, MG 31270-901, Brasil. lnaves@icb.ufmg.br.
authors.forename: Ligia Araujo
authors.initials: LA
authors.lastname: Naves
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002211:Capsaicin / Q000737:chemistry; D005727:Ganglia, Spinal / Q000187:drug effects* / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008297:Male; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism*; D016011:Normal Distribution; D051381:Rats; D017208:Rats, Wistar; D058477:Receptors, Purinergic P2X3 / Q000378:metabolism; D013373:Substance P / Q000378:metabolism*; D050916:TRPV Cation Channels / Q000378:metabolism
chemical_list: D058477:Receptors, Purinergic P2X3; D050916:TRPV Cation Channels; C493922:Trpv1 protein, rat; D013373:Substance P; D000255:Adenosine Triphosphate; D002211:Capsaicin