RESUMEN
Introduction: Camphor is a popular compound for therapeutic and cosmetic use with a distinctive odour, and somatosensory warming and cooling properties. The mechanisms for its action remain unclear. Objective: The current study examined the effects of two enantiomers of camphor and related monoterpenoid compounds on mechanoreceptors. Methods: Extracellular recordings were made in an in vitro bath preparation. Camphor, borneol, eugenol, carveol, and thymol were tested on the neural activity of St I and St II slowly adapting mechanoreceptors in the rat vibrissal hair follicle preparation. Results: All compounds tested (0.5 - 2 mM bath concentrations) resulted in dose-dependent depression of spontaneous and mechanically evoked firing (dynamic and static phases). The mean latency of responses also increased. Both St I and St II were similarly affected, although (-)-camphor had a greater depressant effect on St II than on St I units. Differences were found across the different compounds for their effect on the dynamic and static phases. Thymol was found to have the greatest depressant effect on these phases. The broad spectrum TRP blocker ruthenium red did not reverse the depressant effects of camphor. The depressant effects of the compounds appeared similar to those obtained using the local anaesthetic lignocaine. The depressant effects of camphor and of lignocaine were partially reversed by the K+ channel blocker tetraethylammonium. Conclusions: The results question whether the depressant effects of camphor and related compounds act through TRP channels. Perhaps the use of more selective blockers may reveal the molecular mechanisms through which these compounds act.
RESUMEN
AIM: Early life adverse effects have been associated with an increased risk of suffering pain syndromes in adulthood. Although animal models are of great importance to study modifications of pain sensitivity, up to date the results obtained are contradicting due to the varied methodologies used. Therefore, the aim of the present study was to characterise, as a whole, possible modifications in visceral and somatic nociceptive responses in male and female ICR mice, submitted to two different protocols of maternal separation (MS), and possible modifications in the electrophysiological properties of peripheral nociceptive Aδ-primary afferents. MAIN METHODS: Male and female mice were submitted to 3 or 4-8 hr of daily MS from postnatal day (PND) 2-17 and early weaned. On PND 67 von Frey, hot plate and writhing tests were performed. Afterwards electrophysiological recordings were carried out, using the in vitro skin-saphenous nerve preparation in males. KEY FINDINGS: The short separation protocol of MS did not modify nociceptive sensitivity; but when mice were separated from their dams for the long separation, mechanical pain thresholds were modified in male and female mice and visceral nociception was increased in female mice. Electrophysiological recordings showed that cutaneous Aδ-fibres were sensitised and their mechanotransduction properties were altered in both MS protocols. SIGNIFICANCE: Although MS increases the activity and the mechanosensitivity of cutaneous Aδ-afferent fibres at both short and long periods of separation, only the longer interval of time induces nociceptive sensitivity alterations during adulthood. These results highlight the possible influence of a stress free environment during childhood to reduce nociceptive alterations in adulthood.