Abstract
This study aimed to assess the possible topical antinociceptive activity of Vanillosmopsis arborea Baker essential oil (EOVA) and to clarify the underlying mechanism, using the acute model of chemical (eye wiping) nociception in mice. EOVA (25 to 200 mg/kg; p.o. and topical) evidenced significant antinociception against chemogenic pain in the test model of formalin-induced neuroinflammatory pain. Local application of 5 M NaCl solution on the corneal surface of the eye produced a significant nociceptive behavior, characterized by eye wiping. The number of eye wipes was counted during the first 30 s. EOVA (25, 50, 100, and 200 mg/kg; p.o. and topical) significantly decreased the number of eye wipes. Naloxone, yohimbine, L-NAME, theophylline, glibenclamide, and ruthenium red had no effect on the antinociceptive effect of EOVA. However, ondansetron, p-chlorophenylalanine methyl ester (PCPA), capsazepine, prazosin, and atropine prevented the antinociception induced by EOVA. These results indicate the topical antinociceptive effect of EOVA and showed that 5-HT, α1, TRPV1, and central muscarinic receptors might be involved in the antinociceptive effect of EOVA in the acute corneal model of pain in mice.
Highlights
The small size of the cornea and the extensive branching of the peripheral axons of corneal neurons make this structure the most densely innervated tissue of the body [1]
Vanillosmopsis arborea Baker is native to the Araripe National Forest, in the Northeast of Brazil in the state of Ceara
Administered essential oil from Vanillosmopsis arborea Baker bark (EOVA) (25, 50, 100, or 200 mg/kg) respectively (P < 0.001, P < 0.01, P < 0.01, and P < 0.0001, resp.) decreased the number of eye wipes induced by the local application of 5 M NaCl solution on the corneal surface (Table 3(a))
Summary
The small size of the cornea and the extensive branching of the peripheral axons of corneal neurons make this structure the most densely innervated tissue of the body [1]. The majority of corneal sensory fibers are polymodal nociceptors, which are activated by noxious mechanical, thermal, and chemical stimuli [2]. Long-lasting pain relief following corneal abrasions, corneal ulcers or ophthalmic surgery is difficult to achieve with current analgesics. The use of topical NSAIDs and acetominophen is constrained by their gradual onset and limited efficacy, and the adverse side effects of systemic opioids are well known [3]. There are few studies concerning the traditional use of this plant. Biological and pharmacological studies have shown that its essential oil presents antimicrobial, antiinflammatory and gastroprotective activities [4]
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