THE OXYTOCIN ANTAGONIST 1-DEAMINO-2-D-TYR-(OET)-4-THR-8-ORN-OXYTOCIN REVERSES THE INCREASE IN THE WITHDRAWAL RESPONSE LATENCY TO THERMAL, BUT NOT MECHANICAL NOCICEPTIVE STIMULI FOLLOWING OXYTOCIN ADMINISTRATION OR MASSAGE-LIKE STROKING IN RATS

In this study the effect of exogenous oxytocin and of massage-like str oking on the withdrawal latency responses to heat and mechanical nocic eptive stimulation were investigated in rats. A hot-plate test and the Randall-Selitto test were used to assess the withdrawal responses. Ex ogenous oxytocin (0.1-1 mg/kg) and stroking (a low frequency mechanica l stimulation) significantly increased the withdrawal latencies in res ponse to mechanical and to thermal nociceptive stimuli. The effect of oxytocin and of stroking in the hot-plate test was reversed by the oxy tocin antagonist (1-deamino-2-D-Tyr-(Oet)-4-Thr-8-Orn-oxytocin) direct ed against the uterine receptor. In contrast, the antagonist did not a ffect the prolonged response latency in the mechanical nociceptive sti mulation test following either exogenous oxytocin or stroking. These r esults support the view that (1) oxytocin administration affects direc tly or indirectly nociceptive related behaviour in response to heat st imulation and (2) massage-like stroking may have an anti-nociceptive e ffect via activation of oxytocinergic mechanisms. Since the response t o mechanical stimulation was not blocked by the antagonist the mechani sms mediating the withdrawal latency to heat and mechanical stimulatio n could be different.