Data about behavioral dissection of two spinal intracellular antinociceptive pathways elicited by oxytocin in the formalin test
Description
SUMMARY: Oxytocin (OXT) inhibits pain transmission at the spinal cord level by activating oxytocin receptors (OTRs). Nevertheless, the main in vivo intracellular pathway triggered by OTR activation remains unknown. Hence, by using a behavioral approach with selective pharmacological drugs, we showed that OXT (by OTR activation) recruits two differential spinal intracellular pathways mediated by Gq or Gi proteins during a peripheral nociceptive stimulus. METHODS: Adult Wistar rats were used. The experimental procedures followed the NIH Guide for the Care and Use of Animals and INB-UNAM Ethics Committee recommendations. To test the above hypothesis, the formalin test was used. Subcutaneous formalin injection into the rat’s hind paw evokes a well-known early nociceptive biphasic response (phase I [PI], and phase II [PII]) behaviorally characterized as a number of flinches in the injected paw (lasting approximately one hour) and a long-lasting hypersensitivity (peaking at the third or fourth week) measured as a diminution of the paw withdrawal threshold (measured with von Frey filaments). Early nocifensive behavior was quantified as the number of flinches of the injected paw during 1-min periods every 5 min, up to 60 min after formalin injection. After acute nociceptive evaluation, animals were maintained for the next 30 days to measure long-lasting mechanical allodynia. This hypersensitivity was assessed using the “up-and-down” method. KEY RESULTS: Intrathecal (i.t.) OXT reduces early (number of flinches in the second phase of formalin) and late (secondary mechanical allodynia, the third phase) formalin-induced nociception, an effect abolished by the OTR antagonist (L-368,899). Furthermore, the antinociception observed during the early phase was also reverted by U-73122 (PLC inhibitor), but not by pertussis toxin (Gαi/o protein inhibitor) or gallein (Gβ/γ subunit inhibitor). In contrast, the late oxytocin-induced behavioral analgesia was blocked by pertussis and gallein but not by U-73122. Taken together, our data suggest that spinal OXT recruits two differential spinal intracellular pathways mediated by: (i) Gq and activation of the (PLC/NOS/GC/K+ATP pathway; and (ii) Gi(β/γ) proteins activation. DATA CONTAINED IN THE .XML FILES. The .xml files contain the data obtained from the flinches evoked by formalin and the semi-processed raw data related to the 50% paw withdrawal threshold over 4 weeks. The PDF file shows the figures constructed using the data in the .xml files.