title: Evidence for the existence of different receptor sites for algesic agents at the endings of muscular group IV afferent units.
abstract: The hypothesis that different receptor sites for algesic agents exist at free nerve endings in skeletal muscle has been tested by administering bradykinin and 5-hydroxytryptamine (5-HT) repeatedly in anaesthetized cats and evaluating the response behaviour of single group IV afferent units from the gastrocnemius-soleus muscle. Repeated intraarterial administration of bradykinin at intervals of 1 and 2 min usually elicited fibre responses without tachyphylaxis. Injections of equieffective doses of 5-HT, however, given in the same manner evoked fibre reactions that were strongly tachyphylactic. In units responding to both bradykinin and 5-HT a refractoriness to 5-HT could be induced by repeated injections of this agent without impairing the stimulating potency of bradykinin on the same nerve ending. Such a lack of cross-tachyphylaxis seems to apply also to the effects of histamine on one side and bradykinin or 5-HT on the other. These findings suggest that bradykinin, 5-HT and probably histamine exert their excitatory action on muscular group IV afferent units via different receptor sites.
mesh_terms: D000818:Animals; D001920:Bradykinin / Q000494:pharmacology; D002415:Cats; D004594:Electrophysiology; D006632:Histamine / Q000494:pharmacology; D007269:Injections, Intra-Arterial; D007273:Injections, Intramuscular; D009132:Muscles / Q000294:innervation*; D009411:Nerve Endings / Q000648:ultrastructure*; D009475:Neurons, Afferent / Q000502:physiology; D010146:Pain; D011955:Receptors, Drug; D011984:Sensory Receptor Cells / Q000648:ultrastructure*; D012701:Serotonin / Q000494:pharmacology; D013618:Tachyphylaxis
chemical_list: D011955:Receptors, Drug; D012701:Serotonin; D006632:Histamine; D001920:Bradykinin