Effect of buspirone on thermal sensory and pain thresholds in human volunteers

Abstract

Background: Buspirone is a partial 5-HT1A receptor agonist. Animal studies have shown that modulation of serotoninergic transmission at the 5-HT1A receptor can induce analgesia in acute pain models. However, no studies have been published so far on the effects of serotonin receptor agonists on pain perception in humans.

Methods: The effects of buspirone (30 mg p.o.) on thermal sensory and pain thresholds were investigated in twelve female volunteers (26 +/- 2 yrs) in a prospective, randomized, double-blind, double-dummy, placebo-controlled study with morphine (10 mg i.v.) as positive control.

Results: Morphine significantly increased the heat pain detection threshold (DeltaT: placebo 1.0 degrees C and 1.3 degrees C, p < 0.05) at 60 minutes. Buspirone caused mild sedation in six participants at 60 minutes, but was without effect on any of the measured parameters.

Conclusion: Buspirone in the maximal recommended dose was without significant effect on thermal pain. However, as it is only a partial agonist at the 5-HT1A receptor and also acts on other receptor types, the negative results of the present study do not rule out a possible analgesic effect of more specific 5-HT1A receptor agonists.

Figure 1

Hemodynamic parameters. Hemodynamic parameters 60 and 120 minutes following buspirone and morphine administration: The values are expressed as change in the blood pressure or heart rate from the pre-treatment value. a) Systolic blood pressure change, b) Heart rate change. Blood pressure and heart rate changes following the two drugs were not significantly different than with placebo (p < 0.05). BP_0', BP_60', BP_120' = systolic blood pressure at the time of drug administration (0) and 60 and 120 minutes after drug administration. HR_0', HR_60', HR_120' = heart rate at the time of drug administration (0) and 60 and 120 minutes after drug administration.

Figure 2

Sedation scores. Ramsay sedation scores for the subjects before and 60 and 120 minutes following the drug administration. The initial score always 2 (cooperative and tranquil) in all participants. * = statistical significance of the Ramsay scores compared to pretreatment score (p < 0.05). ** = statistical significance of the Ramsay scores compared to placebo at the same time point (p < 0.05).

Figure 3

Thermal sensory and pain thresholds. The effect of the two drugs (morphine and buspirone) on the tested thermal sensory qualities: a) HDT, b) HPDT, c) CDT and d) CPDT. Data are expressed as means ± SD of the difference between the baseline threshold values measured before and 60 or 120 minutes after the administration. * = statistical significance of change in threshold compared to pretreatment (p < 0.05). HDT = heat detection threshold, HPDT = heat pain detection threshold, CDT = cold detection threshold, CPDT = cold pain detection threshold.