It is common experience that pain subsides by touching the skin near the painful site although the mechanism has not been fully elucidated yet. We previously reported that touch (gentle mechanical cutaneous stimulation) inhibited the somatocardiac sympathetic C-reflex evoked by excitation of unmyelinated C-afferent fibers in anesthetized rats (1-2). Such an inhibitory effect was greater when touch was applied to ipsilateral and closer spinal segment to C-afferent input, and was significantly reduced by i.v. injection of non-specific opioid receptor antagonist, naloxone (1). Thus, the present study examined whether the effect of touch is mediated via spinal opioid receptors. Also, we attempted to clarify the subtype of opioid receptors contributing to this effect. For these purposes, we employed tonic noxious heat stimulation in deeply-anesthetized rats. Experiments were performed on male Wistar rats (5-6 months), that were under urethane anesthesia (1.4 g/kg s.c.). The trachea was cannulated for artificial ventilation. A common carotid artery and jugular vein were catheterized for recording blood pressure and heart rate (HR) and supplying anesthetics and other substances, respectively. A catheter was implanted in the spinal subarachnoid space at the lumbar enlargement level (3) for intrathecal injection of saline or opioid receptor antagonists (5 rats in each group). Heat stimulation (at 46-48°C for 45-43 seconds, respectively) was applied to the lower back using a Peltier thermode at fixed intervals. The same temperature and duration of heat stimulation was used throughout the experiment. Touch was applied to the right inner thigh for 10 minutes using a soft elastomer brush (1-2). Statistical analyses were performed using the one-way factorial or repeated measures ANOVA followed by Bonferroni’s multiple comparisons test and statistical significant level was set at p < 0.05. Data were expressed as mean ± SEM. Heat stimulation altered HR by 11.2 ± 0.62 beat per minutes. Evoked HR responses were significantly inhibited by touch in the saline group. The inhibition occurred during touch (by 27.9 ± 7.1 % of pre-touch response) and continued at 10-15 minutes after touch (by 31.8 ± 7.2 %). In the naloxone and CTOP (μ-opioid receptor antagonist) groups, the inhibitory effect of touch was not observed. In the naltrindole (δ-opioid receptor antagonist) group, heat-induced HR responses were inhibited during touch (by 36.7 ± 6.8 %). Prior to touch, the magnitude of heat-induced HR responses and basal HR did not differ between groups. Basal HR over the experimental period was stable in all groups. The present study results suggest that touch inhibits nociceptive transmission into autonomic reflex pathways predominantly via μ-opioid receptors in the spinal cord.