Estradiol and testosterone differently affect visceral pain-related behavioural responses in male and female rats.

In the study of pain, the presence of sex differences is well known, with female subjects being more affected in a number of chronic painful conditions; however, the underlying mechanisms and the involvement of gonadal hormones, are still controversial. This study evaluated visceral pain in a validated rat model of artificial calculosis and the effects of estradiol and testosterone administration. Adult male and female rats were divided into groups and treated with one of the substances or Oil (vehicle) for 5 days, starting 2 days before surgery, with half receiving an artificial calculosis (Stone) and half only a sham (Sham) procedure.

Trigeminal pain transmission requires reactive oxygen species production.

Three experiments were conducted in order to investigate the possible involvement of the reactive oxygen species in the nociception within the subnucleus caudalis of the spinal trigeminal nucleus (Vc). In the first experiment the extracellular level of hydrogen peroxide was evaluated by microdialysis in the Vc of two groups of six rats before and after a formalin (group 1) or saline solution (group 2) injection into the upper lip. In the second experiment the formalin test was conducted in three groups of 6 rats after a microinjection of 2-methoxyestradiol (2-ME, a superoxide-dismutase inhibitor; group 1) or N-acetylcysteine (NAC, an oxygen intermediate scavenger; group 2) or saline solution (group 3) into the Vc.

Evidence that GABAergic neurons in the spinal trigeminal nucleus are involved in the transmission of inflammatory pain in the rat: a microdialysis and pharmacological study.

The aim of this experiment was to investigate the role of the gamma-aminobutyric acid (GABA)-ergic transmission in the nociception within the spinal trigeminal nucleus. The formalin test was used as an animal model of inflammatory pain. Two groups of six rats were used.