Effect of capsaicin pretreatment on capsaicin-evoked release of immunoreactive somatostatin and substance P from primary sensory neurons.
Release of immunoreactive somatostatin (I-SRIF) and immunoreactive substance P (I-SP) was studied from slices prepared from upper dorsal horn (UDH) and lower dorsal plus ventral horn (LDH-VH) of rat spinal cord. Superfusion with capsaicin (10 microM) led to release of I-SRIF and I-SP from UDH slices but not from LDH-VH slices. The capsaicin-evoked release of I-SP was 6 fold higher than that of I-SRIF. A pulse of 60 mM K+ applied after the capsaicin pulse caused release of I-SRIF and I-SP from UDH as well as LDH-VH slices. Pretreatment of rats with capsaicin (125 mg/kg, s.c.) led to a nearly 40% depletion of I-SP in slices from UDH only. Capsaicin-evoked release from these slices was reduced by 81% for I-SRIF and by 79% for I-SP. Release evoked by K+ remained unchanged. These results indicate that capsaicin causes release of both I-SRIF and-I-SP and that this release is most likely restricted to primary sensory neurons. The marked reduction of the release of I-SP after systemic capsaicin pretreatment may well represent one of the, or even the reason for the insensitivity of capsaicin pretreated rats towards chemogenic pain.
D000818:Animals; D002211:Capsaicin / Q000494:pharmacology*; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology*; D066298:In Vitro Techniques; D008297:Male; D009046:Motor Neurons / Q000187:drug effects; D009474:Neurons / Q000187:drug effects*; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D013004:Somatostatin / Q000276:immunology / Q000378:metabolism*; D013116:Spinal Cord / Q000187:drug effects / Q000378:metabolism*; D013373:Substance P / Q000276:immunology / Q000378:metabolism*
D005231:Fatty Acids, Unsaturated; D013373:Substance P; D013004:Somatostatin; D011188:Potassium; D002211:Capsaicin