An Antibody to Calcitonin Gene-Related Peptide Reduces Trigeminal Fos Expression

Katie Bowler1, Matthew Worsley1, Julian Yates1, Lisa Broad2, Emanuele Sher2, Robert Benschop3, Kirk Johnson3, Peter Robinson1, Fiona Boissonade1. 1University of Sheffield, Sheffield, United Kingdom, 2Eli Lilly, Erl Wood, United Kingdom, 3Eli Lilly, Indianapolis, United States.

Objectives: Calcitonin gene-related peptide (CGRP) is a powerful pro-inflammatory mediator that is thought to play a significant role in the development of inflammation and pain. The aim of this study was to assess the ability of a monoclonal CGRP antibody to modify central neuronal activation in response to stimulation of the inflamed ferret tooth pulp.

Methods: Eight adult ferrets were prepared under anaesthesia (ketamine 25 mg/kg, xylazine 2 mg/kg, IM) to allow electrical tooth pulp stimulation, recording from the digastric muscle and intravenous injections at subsequent experiments. In all of these animals pulpal inflammation was induced by introducing human caries into a deep buccal cavity. Four days later the animals were treated intravenously with either a CGRP antibody (Sigma-Aldrich, 2 mg/ml/kg, n = 5) or vehicle (phosphate-buffered saline (PBS), 1 ml/kg, n = 3). Six days after the initial setup the animals were re-anaesthetised (alfaxalone, induction: 4 mg/kg, maintenance: 10.5 – 16 mg/kg/h, IV) and the jaw opening reflex (JOR) threshold was measured. The tooth pulps were then stimulated at 10 × JOR threshold for 90 minutes. 120 minutes from the start of the stimulation, animals were perfused with fixative and brainstems processed for Fos immunohistochemistry.

Results: Stimulation of inflamed tooth pulps induced ipsilateral Fos expression in two regions of the trigeminal nucleus, subnucleus caudalis (Vc) and subnucleus oralis (Vo). Significantly fewer (50%) (p = 0.032, unpaired t-test) Fos-positive nuclei are present within Vc of those animals treated with the CGRP antibody than in those treated with the vehicle.

Conclusions: These results suggest that the CGRP antibody significantly reduced the number of trigeminal brainstem neurones activated by stimulation of the inflamed tooth pulp. Previous studies using this model have demonstrated an ability to predict clinical analgesic activity. Thus these data indicate that this antibody may have significant efficacy to reduce inflammatory mediated transmission in the trigeminal nucleus.