5-Hydroxytryptamine 7 receptor agonist LP-211 in combination with gabapentin ameliorates neuropathic pain comorbidities associated with mechanical allodynia in diabetic and nerve-ligated rats

Neuropsychiatric disorders, such as depression and anxiety, are frequently associated with neuropathic pain. Despite the availability of various analgesics, their efficacy in treating neuropathic pain comorbidities has been limited. The aim of this study was to evaluate the impact of a 5-hydroxytryptamine 7 agonist (LP-211) in combination with gabapentin on two distinct models of neuropathic pain in rats, namely streptozotocin-induced diabetic neuropathic pain and partial sciatic nerve ligation. The sensory-discriminative parameter of mechanical allodynia was assessed using Von Frey monofilaments. We evaluated the affective components of neuropathic mechanical allodynia, such as depression and anxiety, using a forced swim test, sucrose preference test, elevated plus maze, and novelty-induced hypophagia, respectively. We measured the levels of monoamines in the hippocampus using HPLC. The electrical activity of neurons was estimated through in-vivo electrophysiology. LP-211 alone did not result in a significant increase in paw withdrawal thresholds, but when combined with gabapentin, it showed a significant increase. Furthermore, the combination treatment reduced the neuronal response of wide dynamic range neurons because of mechanical stimulation, and a significant modulation of monoamines in the hippocampus was observed. Importantly, the combination treatment exhibited antidepressant-like activity, by a significant decrease in immobility time and an increase in percentage sucrose preference. It also demonstrated anxiolytic-like activity, as indicated by an increase in time spent in open arms and an increase in food intake in a novel environment. Overall, the results of this study provide evidence that multiple therapies with different mechanisms may alleviate mechanical allodynia and its comorbidities.