Friday, December 31st
Modeling Emotional Pain in an Animal Model of Neuropathic Pain
Often, the focus in animal models of chronic pain is on the experience of pain. However, in humans, co-morbidity with depressive symptoms is highly common. We modelled this in rats using the sciatic nerve ligation (SNL) model of chronic neuropathic pain. The level of neuropathic pain was assessment by von Frey hairs and demonstrated clear mechanical allodynia. We tested a battery of behavioral tests to examine comorbid emotional symptoms, which identified large individual variability, with some animals presenting only symptoms of mechanical allodynia (emotionally-unaffected), but others exhibiting also comorbid emotional symptoms (emotionally-affected). Both groups displayed similar levels of mechanical allodynia. Preventing the degradation of endogenous cannabinoids by inhibiting fatty acid amide hydrolase (FAAH) did not reduce mechanical allodynia, but significantly reduced emotional symptoms exclusively in emotionally-affected individuals. In aggregate, this shows that the mechanisms involved in the emotional symptoms differ from underlying neuropathic pain per se. Enhancing endocannabinoid modulation may be beneficial for the emotional symptoms co-morbidity, even if not reducing the chronic pain per se. This could already contribute significantly to the well-being of patients suffering from chronic pain.