Pharmacological Characterization of Orofacial Nociception in Female Rats Following Nitroglycerin Administration

Abstract

Rodent models of human disease can be valuable for understanding the mechanisms of a disease and for identifying novel therapies. However, it is critical that these models be vetted prior to committing resources to developing novel therapeutics. Failure to confirm the model can lead to significant losses in time and resources. One model used for migraine headache is to administer nitroglycerin to rodents. Nitroglycerin is known to produce migraine-like pain in humans and is presumed to do the same in rodents. It is not known, however, if the mechanism for nitroglycerin headaches involves the same pathological processes as migraine. In the absence of known mechanisms, it becomes imperative that the model not only translates into successful clinical trials but also successfully reverse translates by demonstrating efficacy of current therapeutics. In this study female rats were given nitroglycerin and nociception was evaluated in OPADs. Estrous was not monitored. Based on the ED50 of nitroglycerin a dose of 10 mg/kg was used for experiments. Sumatriptan, caffeine, buprenorphine and morphine were administered to evaluate the reverse translatability of the model. We found that nitroglycerin did not produce mechanical allodynia in the face of the rats, which is reported to be a consequence of migraine in humans. Nitroglycerin reduced the animals’ participation in the assay. The reduced activity was verified using an assay to measure exploratory behavior. Furthermore, the effects of nitroglycerin were not reversed or prevented by agents that are effective acute therapies for migraine. Two interesting findings from this study, however, were that morphine and nitroglycerin interact to increase the rats’ tolerance of mechanical stimuli on their faces, and they work in concert to slow down the central motor pattern generator for licking on the reward bottle. These interactions suggest that nitroglycerin generated nitric oxide and mu opioid receptors interact with the same neuronal circuits in an additive manner. The interaction of nitroglycerin and morphine on sensory and motor circuits deserves additional examination. In conclusion, based on the results of this study the use of nitroglycerin at these doses in naïve female rats is not recommended as a model for migraine headaches.

Nitroglycerin as a model of migraine: Clinical and preclinical review

“…While some studies report limited periorbital mechanical hypersensitivity to an acute dose of NTG (10 mg/kg) in rats ( Sufka et al, 2016 ), others observe increased tail-flick ( Greco et al, 2008 ) and orofacial responses to formalin ( Demartini et al, 2017 ) with the same dosing. Other behavioural models measuring thermal sensitivity have also reported increased sensitivity post-NTG (10 mg/kg) in mice ( Sureda-Gibert et al, 2018 ) but not in rats ( Caudle et al, 2020 ). It also remains unclear whether these differences can be attributed to the type of NTG formulation (Farkas et al, 2015) and/or underlying biological parameters, such as sex ( Boes and Levy, 2012 , Greco et al, 2013 ), stress ( Raoof et al, 2022 ), or the microbiome composition ( Lanza et al, 2021 , Kang et al, 2022 ), all of which can contribute to NTG-induced hyperalgesia in rodents in a different manner.…”

Systemic administration of monosodium glutamate induces sexually dimorphic headache- and nausea-like behaviours in rats

“…This dose has been shown to reproducibly produce headache-like behaviors and mechanical allodynia in rats. 5,11 The final dose of ethanol in any injection ranged from 0.54 to 0.60 g/kg, which is below the dose needed to produce acute intoxication in rats (2.5 g/kg). 52 For experiments investigating the effects of the combination of MSG and GTN, MSG (350 mg/kg, estimated ED 50 value) was combined with GTN (10 mg/kg) and administered i.p.…”

Does fructose have a protective role on migraine?—experimental evidence in a rat model of metabolic syndrome under omega-3 supplementation

“…Concerning the NTG model, it has been described that it can reproduce the main components of migraine in rodents and humans (119,120). However, it is relevant to mention that the model has some restrictions, such as a different pattern of responses depending on the rodent species and sex, or the previous history of migraine in humans (12,119). As for the inflammatory mediators' analysis, whereas isoflurane does not seem to alter the CGRP levels (121), it can affect the brain contents of proinflammatory cytokines, as described beforehand (122).…”

“…The age of animals was selected based on a previous literature study (11). Males were used instead of females, considering the great hormonal influence in the migraine NTG model (12). From a total of 96 rats, three died due to NTG injections and one was euthanized after oral gavage of n-3, by recommendation of the responsible Veterinarian.…”