This study was designed to investigate the potential existence of the response of neurons in the parafascicular nucleus of the thalamus to acute myocardial ischaemia induced by selective coronary artery occlusion and the effects of midazolam on the response in rats.

The left anterior descending branch of the coronary artery was instrumented with a snare occluder in anaesthetized Sprague-Dawley rats. A single-barrel glass microelectrode was used for recording the unit discharges of the neuron in the parafascicular nucleus. The neuron responding only to noxious somatic stimulation was further examined for the response to coronary artery occlusion. Once the effect of coronary artery occlusion on the discharges was detected, the pharmacological effects of midazolam and flumazenil were examined.

It was observed that the discharge rate of the neuron was markedly increased following coronary artery occlusion. Midazolam attenuated the increase in the discharges of the neuron induced by coronary artery occlusion (P < 0.05). The effect of midazolam was reversed by flumazenil.

The parafascicular nucleus is involved in the modulation of cardiac nociception and midazolam possesses antinociceptive property in modulating cardiac pain.

Visceral pain is one of the most common forms of pain and for which new drugs would be welcome. The aim of this study was to investigate whether gabapentin inhibits induced abdominal contractions in mice and to examine the effect of its co-administration with morphine.

A total of 96 mice received acetic acid intraperitoneally after administration of saline or gabapentin (1, 5, 10, 50 and 100 mg kg−1) or morphine (0.25, 0.5, 1, 3 and 5 mg kg−1) or a combination of morphine and gabapentin. Other groups also received naloxone. The number of writhes were counted.

Both gabapentin and morphine reduced writhing in a dose-dependent manner. The number of writhes was decreased significantly by gabapentin (50 and 100 mg kg−1) and morphine (0.5, 1, 3 and 5 mg kg−1) (P < 0.001). Also, the lowest dose of morphine 0.25 mg kg−1 when combined with low doses of gabapentin significantly decreased the number of writhes (P < 0.005). The combination of a low effective dose of gabapentin (50 mg kg−1) with a low dose of morphine decreased the writhing by 94% as compared to the controls. The antinociceptive effect of combined administration was not reversed by naloxone.

These data demonstrated the comparable efficacy of gabapentin with morphine in visceral pain. Also, the results showed that the combination of doses of gabapentin and morphine, which were ineffective alone, produced a significant analgesic effect in the writhing model of pain. This may be clinically important in the management of visceral pain.