Antihyperalgesic Activity of Atomoxetine on Diabetes-Induced Neuropathic Pain: Contribution of Noradrenergic and Dopaminergic Systems

Selenoprotein T, a potential treatment of attention-deficit/hyperactivity disorder and comorbid pain in neonatal 6-OHDA lesioned mice

pathological pain and Attention-deficit/hyperactivity disorder (ADHD) are two complex multifactorial syndromes. The comorbidity of ADHD and altered pain perception is well documented in children, adolescents, and adults. According to pathophysiological investigations, the dopaminergic system's dysfunction provides a common basis for ADHD and comorbid pain. Growing evidence suggests that oxidative stress may be crucial in both pathologies. Recent studies revealed that a small peptide encompassing the redox-active site of selenoprotein T (PSELT), protects dopaminergic neurons and fibers as well as lesioned nerves in animal models. The current study aims to examine the effects of PSELT treatment on ADHD-like symptoms and pain sensitivity, as well as the role of catecholaminergic systems in these effects. Our results demonstrated that intranasal administration of PSELT reduced the hyperactivity in the open field, decreased the impulsivity displayed by 6-OHDA-lesioned male mice in the 5-choice serial reaction time task test and improved attentional performance. In addition, PSELT treatment significantly increased the nociception threshold in both normal and inflammatory conditions. Furthermore, anti-hyperalgesic activity was antagonized with sulpiride pre-treatment, but not by phentolamine, or propranolol pre-treatments. The present study suggests that PSELT reduces the severity of ADHD symptoms in mice and possesses potent antinociceptive effects which could be related to the involvement of D2/D3 dopaminergic receptors.

Catecholaminergic and Cholinergic Systems Mediate Beneficial Effect of Vortioxetine on Diabetes-Induced Neuropathic Pain

The therapeutic potential of vortioxetine on mechanical hyperalgesia/allodynia was investigated in rats with streptozotocin-induced diabetes, and its possible mechanism of action was elucidated in this study. The obtained findings demonstrated that subacute vortioxetine treatment (5 and 10 mg/kg for 2 weeks) increased the reduced paw-withdrawal thresholds of diabetic rats both in the Randall-Selitto and Dynamic plantar tests. Moreover, the falling latencies of animals did not change in the Rota-rod assessments. These results suggest that vortioxetine administration significantly improved diabetes-induced hyperalgesia and allodynia responses in the rats without affecting their motor coordination. The vortioxetine (5 mg/kg)-induced antihyperalgesic and antiallodynic effects were reversed by AMPT, yohimbine, ICI 118,551, sulpiride and atropine pre-treatments, suggesting the involvement of the catecholaminergic system, α₂- and β₂-adrenoceptors, D_2/3 dopaminergic receptors and cholinergic muscarinic receptors in the exhibited pharmacological activity, respectively. Moreover, the data from the immunohistochemical studies indicated that the inhibition of c-Fos overexpression in dorsal horn neurons also mediates the beneficial effect of this drug. Vortioxetine induced no difference in plasma glucose levels in diabetic rats. If clinical studies confirm these findings, the concomitant beneficial effect of vortioxetine on mood disorders and its neutral activity profile on glycemic control may make it an alternative drug for the treatment of neuropathic pain.

Effect of atomoxetine on ADHD-pain hypersensitization comorbidity in 6-OHDA lesioned mice

BACKGROUND

Methylphenidate and atomoxetine are used for the treatment of attention-deficit/hyperactivity disorder (ADHD). Our previous studies established the validity of the 6-hydroxydopamine (6-OHDA) mouse model of ADHD and demonstrated hypersensitivity to pain, in line with clinical reports in ADHD patients. Acute methylphenidate treatment reduces hyperactivity and increases attention, but does not affect pain behaviors in this mouse model. Whereas atomoxetine has been shown to be effective against some symptoms of ADHD, nothing is known about its possible action on comorbid pain hypersensitivity. The objectives of the present research are (1) to investigate the effects of acute and chronic treatment with atomoxetine on ADHD-like symptoms and nociceptive thresholds, and (2) to explore the catecholaminergic systems underlying these effects.

METHODS

Sham and 6-OHDA cohorts of male mice were tested for hyperactivity (open field), attention and impulsivity (5-choice serial reaction time task test), and thermal (hot plate test) and mechanical (von Frey test) thresholds after acute or repeated treatment with vehicle or atomoxetine (1, 3 or 10 mg/kg).

RESULTS

Acute administration of atomoxetine (10 mg/kg) reduced the hyperactivity and impulsivity displayed by 6-OHDA mice, without affecting attention or nociception. However, atomoxetine administered at 3 mg/kg/day for 7 days alleviated the ADHD-like core symptoms and attenuated the hyperalgesic responses. Furthermore, hyperlocomotion and anti-hyperalgesic activity were antagonized with phentolamine, propranolol, and sulpiride pre-treatments.

CONCLUSION

These findings demonstrated that when administered chronically, atomoxetine has a significant effect on ADHD-associated pain hypersensitization, likely mediated by both α- and β-adrenergic and D2/D3 dopaminergic receptors, and suggest new indications for atomoxetine that will need to be confirmed by well-designed clinical trials.

Gut Microbiome Alteration after Reboxetine Administration in Type-1 Diabetic Rats

Antidepressants are drugs commonly used in clinical settings. However, there are very limited studies on the effects of these drugs on the gut microbiota. Herein, we evaluated the effect of reboxetine (RBX), a selective norepinephrine (noradrenaline) reuptake inhibitor (NRI), on gut microbiota in both diabetic and non-diabetic rats. This is the first report of relation between reboxetine use and the gut microbiota to our knowledge. In this study, type-1 diabetes induced by using streptozotocin (STZ) and RBX was administered to diabetic rats and healthy controls for 14 days. At the end of the treatment, stool samples were collected. Following DNA extraction, amplicon libraries for the V3-V4 region were prepared and sequenced with the Illumina Miseq platform. QIIME was used for preprocessing and analysis of the data. As a result, RBX had a significant effect on gut microbiota structure and composition in diabetic and healthy rats. For example, RBX exposure had a pronounced microbial signature in both groups, with a low Firmicutes/Bacteroidetes ratio and low Lactobacillus levels. While another abundance phylum after exposure to RBX was Proteabacteria, other notable taxa in the diabetic group included Flavobacterium, Desulfovibrionaceae, Helicobacteriaceae, Campylobacterales, and Pasteurellacae when compared to the untreated group.

Catecholaminergic and opioidergic system mediated effects of reboxetine on diabetic neuropathic pain

RATIONALE

Current data indicate that the noradrenergic system plays a critical role in neuropathic pain treatment. Notably, drugs that directly affect this system may have curative potential in neuropathy-associated pain.

OBJECTIVES

The aim of this study was to evaluate the potential therapeutic efficacy of reboxetine, a potent and selective noradrenaline reuptake inhibitor, on hyperalgesia and allodynia responses in rats with experimental diabetes. Furthermore, mechanistic studies were performed to elucidate the possible mode of actions.

METHODS

Experimental diabetes was induced by a single dose of streptozotocin. Mechanical hyperalgesia, mechanical allodynia, thermal hyperalgesia, and thermal allodynia responses in diabetic rats were evaluated by Randall-Selitto, dynamic plantar, Hargreaves, and warm plate tests, respectively.

RESULTS

Reboxetine treatment (8 and 16 mg/kg for 2 weeks) demonstrated an effect comparable to that of the reference drug, pregabalin, improving the hyperalgesic and allodynic responses secondary to diabetes mellitus. Pretreatment with phentolamine, metoprolol, SR 59230A, and atropine did not alter the abovementioned effects of reboxetine; however, the administration of α-methyl-para-tyrosine methyl ester, propranolol, ICI-118,551, SCH-23390, sulpiride, and naltrindole significantly inhibited these effects. Moreover, reboxetine did not induce a significant difference in the rat plasma glucose levels.

CONCLUSIONS

Our findings indicate that the antihyperalgesic and antiallodynic effects of reboxetine are mediated by the catecholaminergic system; β₂-adrenoceptors; D₁-, D₂/D₃-dopaminergic receptors; and δ-opioid receptors. The results suggest that this analgesic effect of reboxetine, besides its neutral profile on glycemic control, may be advantageous in the pharmacotherapy of diabetic neuropathy-induced pain.