Gabapentin reverses central pain sensitization following a collagenase-induced intrathalamic hemorrhage in rats

Purpose: The treatment of central neuropathic pain remains amongst the biggest challenges for pain specialists. The main objective of this study was to assess gabapentin (GBP), amitriptyline (AMI), and carbamazepine (CARBA) for the treatment of a rodent central neuropathic pain model. Methods: Male Sprague Dawley rats were trained on the rotarod, Hargreaves, Von Frey and acetone behavioral tests, and baseline values were obtained prior to surgery. A stereotaxic injection of either a collagenase solution or saline was made in the right ventral posterolateral thalamic nucleus. The rats were tested on days 2, 4, 8, and 11 postsurgery. They were retested at regular intervals from day 15 to day 25 postsurgery, after oral administration of either the vehicle (n=7 and n=8 rats with intracerebral injections of collagenase and saline, respectively) or the different drugs (GBP [60 mg/kg], AMI [10 mg/kg], CARBA [100 mg/kg]; n=8 rats/drug). Results: A significant decrease in the mechanical thresholds and no change in heat threshold were observed in both hind limbs in the collagenase group, as we had previously shown elsewhere. Reversal of the mechanical hypersensitivity was achieved only with GBP (P<0.05). AMI and CARBA, at the dosages used, failed to show any effect on mechanical thresholds. Transient cold allodynia was observed in some collagenase-injected rats but failed to be statistically significant. Conclusion: Intrathalamic hemorrhaging in the ventrolateral thalamic nucleus induced a bilateral mechanical allodynia, which was reversed by GBP but not AMI or CARBA.