Behavioral, Cellular and Molecular Responses to Cold and Mechanical Stimuli in Rats with Bilateral Dopamine Depletion in the Mesencephalic Dopaminergic Neurons

Pathological pain: Non-motor manifestations in Parkinson disease and its treatment

In addition to motor symptoms, non-motor manifestations of Parkinson's disease (PD), i.e. pain, depression, sleep disturbance, and autonomic disorders, have received increasing attention. As one of the non-motor symptoms, pain has a high prevalence and is considered an early pre-motor symptom in the development of PD. In relation to pathological pain and its management in PD, particularly in the early stages, it is hypothesized that the loss of dopaminergic neurons causes a functional deficit in supraspinal structures, leading to an imbalance in endogenous descending modulation. Deficits in dopaminergic-dependent pathways also affect non-dopaminergic neurotransmitter systems that contribute to the pathological processing of nociceptive input, the integration, and modulation of pain in PD. This review examines the onset and progression of pain in PD, with a particular focus on alterations in the central modulation of nociception. The discussion highlights the importance of abnormal endogenous descending facilitation and inhibition in PD pain, which may provide potential clues to a better understanding of the nature of pathological pain and its effective clinical management.

Reinforcing effect of tramadol in the rat

Tramadol is one of the most commonly prescribed analgesic opioids in various pharmacopeias. Tramadol has been linked to abuse in recent clinical investigations. However, the behavioral effects and neural substrates of the drug have not been well characterized in preclinical studies. As a result, the present study investigated the effects of tramadol on behavioral sensitizations in rats. Its impacts on cellular and molecular alterations in the brain were also investigated. In conditioned place preference (CPP) paradigm, tramadol induced behavioral as well as motor sensitizations. These effects were dramatically reduced by intraperitoneal administration of naltrexone, an opioid receptor antagonist. Tramadol caused changes in several molecular markers (pERK1/2, Δ-FosB, PKCγ, PKMζ GAD67) in the anterior cingulate cortex, which could indicate an increase in excitation within this structure. Tramadol is demonstrated in the present study to be a reinforcing drug in rats, as it increased both behavioral and motor sensitizations. Tramadol's effects are most likely due to the high levels of excitation it causes in the brain, which is mostly caused by the activation of opioid receptors.

Modulation of KIF17/NR2B crosstalk by tozasertib attenuates inflammatory pain in rats

Chronic pain is among the most burdensome and devastating disorders affecting millions of people worldwide. Recent studies suggest the role of kinesin nanomotors in development and maintenance of chronic pain. KIF17 is a member of kinesin superfamily that binds to NR2B cargo system via mLin10 scaffolding protein and makes the NMDARs functional at cell surface. NMDA receptor activation is known to induce the central sensitization and excitotoxicity which can be recognized by the glial cells followed by the release of cytokine storm at spinal and supraspinal level leading to chronic pain. In this study, we have investigated the role of aurora kinase in the regulation of KIF17 and NR2B trafficking in the animal model of chronic inflammatory pain. Tozasertib (10, 20, and 40 mg/kg i.p.), a pan aurora kinase inhibitor, significantly attenuates acute inflammatory pain and suppresses enhanced pain hypersensitivity to heat, cold, and mechanical stimuli in CFA-injected rats. Molecular investigations suggest enhanced expression of KIF17/mLin10/NR2B in L4-L5 dorsal root ganglion (DRG) and spinal cord of CFA-injected rats which was significantly attenuated on treatment with tozasertib. Moreover, tozasertib treatment significantly attenuated CFA-induced oxido-nitrosative stress and macrophage activation in DRG and microglia activation in spinal cord of rats. Findings from the current study suggest that tozasertib mediates anti-nociceptive activity by inhibiting aurora kinase-mediated KIF17/mLin10/NR2B signaling.