Abstract:The present study investigated the antinociceptive effects of Ocimum basilicum L. (Lamiaceae) leaf essential oil (LEO) and (-)-linalool (LIN) in formalin (2%)-, glutamate (25 μM)-and capsaicin (2.5 µg)-induced orofacial nociception models in mice. The involvement of these substances was further evaluated on the neuronal excitability of the hippocampal dentate gyrus. Male mice (n=8/group) were pretreated separately with LEO and by LIN (50, 100, and 200 mg/kg, i.p.), morphine (5 mg/kg, i.p.) and vehicle (saline + Tween 80 0.2%), before injection of nociceptive agent into the right upper lip (perinasal area). The LEO and LIN reduced the nociceptive face-rubbing behaviour in both phases on formalin test. LEO and LIN, at high doses, produced significantly antinociceptive effect in the capsaicin and glutamate tests. In hippocampal slices, LEO inhibited the population spike generated by stimulation of the hylus (antidromic stimulation), with an IC50 of 0.1±0.05 mg/mL. This response was reversibly blocked by lidocaine (0.5 mg/mL), a known voltage-dependent sodium channel antagonist and by LIN (0.5 mg/mL). Our results suggest that LEO and LIN modulate neurogenic and inflammatory pain in the tests of orofacial nociception induced by formalin, capsaicin and glutamate. Part of these effects may be associated with decreased peripheral and central neuronal excitability.
Ocimum basilicum L. is an aromatic herb used in Brazil to treat illnesses such as respiratory and rheumatic problems, vomiting, and pain. In the present study, the chemical composition, acute toxicity, and antinociceptive effects of the essential oil (EO) of the cultivar "Maria Bonita" obtained from O. basilicum L. PI 197442 genotype were evaluated in Swiss mice (20-35 g each). Lethal dose to cause 50 % death (LD50) was calculated from a dose-response curve (100-5000 mg/kg body wt.; n = 6) as 532 mg/kg body wt. In the acetic acid-induced writhing test (0.6 % i. p.), EO (50, 100, and 200 mg/kg body wt., n = 8, s. c.) was effective in reducing the abdominal contractions at all doses (48-78 %). In the hot-plate test, EO significantly increased the latency at 50 mg/kg body wt. at all times (37-52 %, n = 8, s. c.). However, the effects of morphine and EO at 50 mg/kg were reverted in the presence of naloxone, an opioid antagonist. In the formalin test, EO significantly reduced paw licking time in the first and second phases of pain at 200 mg/kg body wt. (38 and 75 %, respectively, n = 8, s. c.). The results suggested that the peripheral and central antinociceptive effects of EO are related to the inhibition of the biosynthesis of pain mediators, such as prostaglandins and prostacyclins, and its ability to interact with opioid receptors.
The racemate linalool and its levogyrus enantiomer [(−)-LIN] are present in many essential oils and possess several pharmacological activities, such as antinociceptive and anti-inflammatory. In this work, the effects of essential oil obtained from the cultivation of the Ocimum basilicum L. (EOOb) derived from Germplasm Bank rich in (−)-LIN content in the excitability of peripheral nervous system were studied. We used rat sciatic nerve to investigate the EOOb and (−)-LIN effects on neuron excitability and the extracellular recording technique was used to register the compound action potential (CAP). EOOb and (−)-LIN blocked the CAP in a concentration-dependent way and these effects were reversible after washout. EOOb blocked positive amplitude of 1st and 2nd CAP components with IC50 of 0.38 ± 0.2 and 0.17 ± 0.0 mg/mL, respectively. For (−)-LIN, these values were 0.23 ± 0.0 and 0.13 ± 0.0 mg/mL. Both components reduced the conduction velocity of CAP and the 2nd component seems to be more affected than the 1st component. In conclusion EOOb and (−)-LIN inhibited the excitability of peripheral nervous system in a similar way and potency, revealing that the effects of EOOb on excitability are due to the presence of (−)-LIN in the essential oil.
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