Background & Objective: It's been considered that midbrain region namely rostral ventromedial medulla (RVM) is the coring point of modulation of pain. The periaqueductal gray (PAG) matter has been documented to act as antinociceptive along with RVM. However, there are evidences demonstrating that RVM get a few connections from the cuneiformsnucleus (CnF) which might indicate CnF does have the same mechanism as PAG. Thus in this study, we tried to explore the antinociception effects of CnF and GABA_A circuits.

 Methods: Rats were anesthetized with Thiopental drug. Using the stereotaxic apparatus and Paxinos atlas, the point representing for CnF location over the scalp has been designated. One week after the surgery, rats were fully prepared for tests. Animals were put in three groups. First for control group, 0.5 µl of normal saline was injected into the CnF. Later, a few nanograms of bicucculline (as a GABA_A antagonist) were administered into the CnF, dose dependently.

 Results: From the results, it has been shown that CnF has a role in antinociception effect since the injection of bicucculline increased tail flick latency (TFL) and even further increased TFL when administered dose dependently (with high doses).

 Conclusion: According to results of current study, CnF has a significant role in pain modulation and circuits of GABAergic system also plays a key role on its antinociception effect.