URB937 prevents the development of mechanical allodynia in rats with trigeminal neuralgia

This dataset comprises the findings obtained in the study aimed at investigating the effects of URB937, a peripherally restricted fatty acid amide hydrolase inhibitor, in preventing and abolishing the trigeminal mechanical allodynia developed by rats subjected to chronic constriction injury of the infraorbital nerve (IoN-CCI).

In vivo assessments performed in male Sprague-Dawley rats within the preventive and abrogative paradigm:

- IoN-CCI model: following anaesthesia, the rat’s head was fixed in a stereotaxic frame and a mid-line scalp incision was made, exposing the skull and nasal bone. The edge of the orbit was dissected free, and the orbital contents were deflected with a cotton-tipped wooden rod to give access to the left IoN, which was loosely ligated with two chromic catgut ligatures (5-0) (2 mm apart). The scalp incision was closed us-ing silk sutures (5-0). In sham operated rats, the IoN was exposed using the same procedure, but the nerve was not ligated.

- Prevention of mechanical allodynia: IoN-CCI animals were treated with URB937 (1mg/kg, i.p.) or vehicle (10% polyethylene glycol 200, 10% Tween 80 and saline) from day +1 after surgery and then every other day until day +25. The animals were tested with mechanical stimulation test (MST) the day before surgery (for baseline measurement) and on days +5, +12, +18 and +26 after surgery. Sham animals were treated with vehicle and subjected to the same procedure.

- Abrogation of mechanical allodynia: IoN-CCI animals were subjected to chronic treatment with URB937 (1mg/kg, i.p.) or vehicle (10% polyethylene glycol 200, 10% Tween 80 and saline) after the complete development of allodynia. The animals underwent the MST the day before surgery (for baseline measurement) and on days +5, +12, +18 and +25 after surgery. On day +25, after MST, rats were treated with URB937 or vehicle and then daily until day +29 (5 total injections). On day +29, animals underwent MST 1 hour after URB937 or vehicle treatment. Sham animals were treated with vehicle and subjected to the same procedure.

- Mechanical stimulation test (MST): a graded series of five Von Frey hairs (0.015 g, 0.127 g, 0.217 g, 0.745 g, and 2.150 g) were applied within the IoN territory, near the center of the vibrissal pad. Von Frey hairs were applied in an ascending order of intensity either ipsi- or contralaterally. For each rat, and at every designated time, a mean score for the five von Frey filaments was determined. The final MST responses of each rat are expressed as percentages to their baseline values.

Ex vivo assessments performed on samples collected at the end of the last MST:

- Gene expression analysis: mRNA expression levels of calcitonin gene-related peptide (CGRP), tumor necrosis factor alpha (TNF-alpha), interleukin (IL)-1beta and IL-10 in the medulla, cervical spinal cord and trigeminal ganglion ipsilateral to IoN-CCI. mRNA levels were measured by rt-PCR. All samples were assayed in triplicate and gene expression levels were calculated according to the ΔΔCt method and expressed as relative quantification.

RESULTS:

URB937 significantly prevented the development of mechanical allodynia and the IoN-CCI-induced changes in mRNA expression levels of CGRP and cytokines in the evaluated areas. Similarly, treatment with URB937 after allodynia development significantly counteracted the IoN-CCI-induced changes in CGRP and cytokines gene expression; this was not associated with a significant abrogation of the mechanical allodynia.