title: Chronic administration of amitriptyline differentially alters neuropathic pain-related behaviour in the presence and absence of a depressive-like phenotype.
abstract: Chronic pain and depression share a complex, reciprocal relationship. Furthermore, in addition to treating depression, antidepressants such as amitriptyline are a first-line treatment for chronic pain conditions, indicating possible common neural substrates underlying both depression and pain. However, there is a paucity of studies examining the effect of antidepressant treatment on nociceptive and neuropathic pain responding in the presence of a depressive phenotype. The current study aimed to examine the effect of chronic amitriptyline administration on neuropathic pain-related behaviour and associated neuroinflammatory processes in the olfactory bulbectomised (OB) rat model of depression. Nociceptive responding to mechanical, innocuous cold or noxious heat stimuli in sham or OB rats was not altered by chronic amitriptyline administration. The induction of neuropathic pain following L5-L6 spinal nerve ligation (SNL) resulted in robust mechanical and cold allodynia and heat hyperalgesia in both sham and OB vehicle-treated animals. Chronic amitriptyline administration attenuated SNL-induced mechanical allodynia in both sham and OB rats at day 7 post-SNL, an effect which was enhanced and prolonged in OB rats. In comparison, chronic amitriptyline administration attenuated SNL-induced cold allodynia and heat hyperalgesia in sham, but not OB, rats. Evaluating the affective/motivational aspect of pain using the place escape avoidance paradigm revealed that OB-SNL rats exhibit reduced noxious avoidance behaviour when compared with sham counterparts, an effect not altered by chronic amitriptyline administration. Chronic amitriptyline administration prevented the increased expression of GFAP, IL-10 and CCL5, and enhanced the expression of TNFα, in the prefrontal cortex of OB-SNL rats. In conclusion, these data demonstrate that chronic amitriptyline differentially alters somatic nociceptive responding following peripheral nerve-injury, depending on stimulus modality and the presence or absence of a depressive-like phenotype, an effect which may involve modulation of neuroinflammatory processes.
authors.affiliation: Physiology, School of Medicine, National University of Ireland Galway, University Road, Galway, Ireland; Pharmacology and Therapeutics, School of Medicine, National University of Ireland Galway, University Road, Galway, Ireland; NCBES Galway Neuroscience Centre and Centre for Pain Research, National University of Ireland Galway, University Road, Galway, Ireland.
authors.forename: Nikita N
authors.initials: NN
authors.lastname: Burke
authors.affiliation: Pharmacology and Therapeutics, School of Medicine, National University of Ireland Galway, University Road, Galway, Ireland; NCBES Galway Neuroscience Centre and Centre for Pain Research, National University of Ireland Galway, University Road, Galway, Ireland.
authors.forename: David P
authors.initials: DP
authors.lastname: Finn
authors.affiliation: Physiology, School of Medicine, National University of Ireland Galway, University Road, Galway, Ireland; NCBES Galway Neuroscience Centre and Centre for Pain Research, National University of Ireland Galway, University Road, Galway, Ireland. Electronic address: michelle.roche@nuigalway.ie.
authors.forename: Michelle
authors.initials: M
authors.lastname: Roche
mesh_terms: D000639:Amitriptyline / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D000929:Antidepressive Agents, Tricyclic / Q000008:administration & dosage / Q000494:pharmacology*; D003863:Depression / Q000503:physiopathology / Q000523:psychology*; D004195:Disease Models, Animal; D005904:Glial Fibrillary Acidic Protein / Q000378:metabolism; D006930:Hyperalgesia / Q000188:drug therapy / Q000276:immunology / Q000523:psychology; D016753:Interleukin-10 / Q000378:metabolism; D008297:Male; D009437:Neuralgia / Q000188:drug therapy* / Q000276:immunology / Q000523:psychology; D010147:Pain Measurement / Q000379:methods; D059348:Peripheral Nerve Injuries / Q000150:complications; D010641:Phenotype; D017397:Prefrontal Cortex / Q000276:immunology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013127:Spinal Nerves / Q000601:surgery; D013997:Time Factors; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
chemical_list: D000929:Antidepressive Agents, Tricyclic; D005904:Glial Fibrillary Acidic Protein; D014409:Tumor Necrosis Factor-alpha; D016753:Interleukin-10; D000639:Amitriptyline
keywords: Antidepressant; Cytokines; Hargreaves test; Mechanical allodynia; Neuroinflammation; Olfactory bulbectomy; PEAP; Prefrontal cortex; Spinal nerve ligation; Thermal hyperalgesia; von Frey test