The distinctive significance of analgesic drugs and olfactory stimulants on learned pain in mice

Abstract

Chronic pain is often intractable to analgesics, and in animals it involves a conditioned nociceptive response (CR) - learned pain. The neural pathways of nociception and olfactory function in the brain overlap. The influence of olfactory stimuli on acute pain has been studied in some depth in animal and human models, but the influence of olfactory stimuli on learned pain has not been understood. We examined the effects of analgesic drugs and olfactory stimulants (preferred or repellent odor) on acute pain, the unconditioned nociceptive response (UCR) and the CR in mice. The CR was provoked by repeated injection of formalin into the hind-paw in animals in the same context, which elicited the typical pain behaviors of paw licking (including biting). The analgesic drugs acetaminophen, fentanyl, gabapentin and fluvoxamine diminished the UCR but did not affect the CR. In contrast, the preferred odor reduced both the UCR and the CR. Our findings suggest that, like chronic pain, the CR is resistant to analgesic drugs and that preferred odor suppress the neural pathways that mediate the CR of pain perception.

Pain, Smell, and Taste in Adults: A Narrative Review of Multisensory Perception and Interaction

“…Olfaction has been linked to depression [72] and odor sensitivity has been associated with personality traits [73], indicating a strong connection to the affective domain. Olfactory substances are known to exert beneficial effects on physiological and psychological processes in animals and humans alike [74][75][76].…”

A Computing System for Measuring the Relationship of Smell and Pain

“…The participant dipping his hand inside the ice water with temperature kept at 7°C, and constantly monitored with digital thermometer performance as well as physiological arousal in humans [14], [6], [3]. Furthermore, certain smells increased the pain tolerance in rats and mice [13], [15]. Similarly, [8], [16], [17] reported how smells of essential oils can be used to influence pain and possibly lead to relief of pain.…”