Anterior cingulate cortex connectivity is associated with suppression of behaviour in a rat model of chronic pain

Centralizing the Knowledge and Interpretation of Pain in Chemotherapy-Induced Peripheral Neuropathy: A Paradigm Shift towards Brain-Centric Approaches

Chemotherapy-induced peripheral neuropathy (CIPN) is a side effect of cancer treatment, often linked with pain complaints. Patients report mechanical and thermal hypersensitivity that may emerge during chemotherapy treatment and may persist after cancer remission. Whereas the latter situation disturbs the quality of life, life itself may be endangered by the appearance of CIPN during cancer treatment. The causes of CIPN have almost entirely been ascribed to the neurotoxicity of chemotherapeutic drugs in the peripheral nervous system. However, the central consequences of peripheral neuropathy are starting to be unraveled, namely in the supraspinal pain modulatory system. Based on our interests and experience in the field, we undertook a review of the brain-centered alterations that may underpin pain in CIPN. The changes in the descending pain modulation in CIPN models along with the functional and connectivity abnormalities in the brain of CIPN patients are analyzed. A translational analysis of preclinical findings about descending pain regulation during CIPN is reviewed considering the main neurochemical systems (serotoninergic and noradrenergic) targeted in CIPN management in patients, namely by antidepressants. In conclusion, this review highlights the importance of studying supraspinal areas involved in descending pain modulation to understand the pathophysiology of CIPN, which will probably allow a more personalized and effective CIPN treatment in the future.

Neuroimaging uncovers neuronal and metabolic changes in pain modulatory brain areas in a rat model of chemotherapy-induced neuropathy - MEMRI and ex vivo spectroscopy studies

Chemotherapy-induced neuropathy (CIN) is one of the most common complications of cancer treatment with sensory dysfunctions which frequently include pain. The mechanisms underlying pain during CIN are starting to be uncovered. Neuroimaging allows the identification of brain circuitry involved in pain processing and modulation and has recently been used to unravel the disruptions of that circuitry by neuropathic pain. The present study evaluates the effects of paclitaxel, a cytostatic drug frequently used in cancer treatment, at the neuronal function in the anterior cingulate cortex (ACC), hypothalamus and periaqueductal gray (PAG) using manganese-enhanced magnetic resonance imaging (MEMRI). We also studied the metabolic profile at the prefrontal cortex (PFC) and hypothalamus using ex vivo spectroscopy. Wistar male rats were intraperitoneal injected with paclitaxel or vehicle solution (DMSO). The evaluation of mechanical sensitivity using von Frey test at baseline (BL), 21 (T21), 28 (T28), 49 (T49) and 56 days (T56) after CIN induction showed that paclitaxel-injected rats presented mechanical hypersensitivity from T21 until T56 after CIN induction. The evaluation of the locomotor activity and exploratory behaviors using open-field test at T28 and T56 after the first injection of paclitaxel revealed that paclitaxel-injected rats walked higher distance with higher velocity at late point of CIN accompanied with a sustained exhibition of anxiety-like behaviors. Imaging studies performed using MEMRI at T28 and T56 showed that paclitaxel treatment increased the neuronal activation in the hypothalamus and PAG at T56 in comparison with the control group. The analysis of data from ex vivo spectroscopy demonstrated that at T28 paclitaxel-injected rats presented an increase of N-acetyl aspartate (NAA) levels in the PFC and an increase of NAA and decrease of lactate (Lac) concentration in the hypothalamus compared to the control group. Furthermore, at T56 the paclitaxel-injected rats presented lower NAA and higher taurine (Tau) levels in the PFC. Together, MEMRI and metabolomic data indicate that CIN is associated with neuroplastic changes in brain areas involved in pain modulation and suggests that other events involving glial cells may be happening.

The neurobiology of pain and facial movements in rodents: Clinical applications and current research

One of the most controversial aspects of the use of animals in science is the production of pain. Pain is a central ethical concern. The activation of neural pathways involved in the pain response has physiological, endocrine, and behavioral consequences, that can affect both the health and welfare of the animals, as well as the validity of research. The strategy to prevent these consequences requires understanding of the nociception process, pain itself, and how assessment can be performed using validated, non-invasive methods. The study of facial expressions related to pain has undergone considerable study with the finding that certain movements of the facial muscles (called facial action units) are associated with the presence and intensity of pain. This review, focused on rodents, discusses the neurobiology of facial expressions, clinical applications, and current research designed to better understand pain and the nociceptive pathway as a strategy for implementing refinement in biomedical research.

Neuroimaging Systematic Review in Persistent Postural-Perceptual Dizziness: The Elaborate Alterations in the Delicate Network to Remain Balanced

OBJECTIVES

Persistent postural-perceptual dizziness (PPPD) is a chronic functional vestibular disorder that may have normal physical examination, clinical laboratory testing and vestibular evaluation. However, advances in neuroimaging have provided new insights in brain functional connectivity and structure in patients with PPPD. This systematic review was aimed at identifying significant structural or alterations in functional connectivity in patients with PPPD.

DATABASES REVIEWED

Science Direct, Pubmed, Embase via Ovid databases, and Cochrane library.

METHODS

This review following the guidelines of PRISMA, systematically and independently examined papers published up to March 2021 which fulfilled the predetermined criteria. PROSPERO Registration (CRD42020222334).

RESULTS

A total of 15 studies were included (MRI = 4, SPECT = 1, resting state fMRI = 4, task-based fMRI = 5, task-based fMRI + MRI = 1). Significant changes in the gray matter volume, cortical folding, blood flow, and connectivity were seen at different brain regions involved in vestibular, visual, emotion, and motor processing.

CONCLUSION

There is a multisensory dimension to the impairment resulting in chronic compensatory changes in PPPD that is evident by the significant alterations in multiple networks involved in maintaining balance. These changes observed offer some explanation for the symptoms that a PPPD patient may experience.Systematic Review Registration: This study is registered with PROSPERO (CRD42020222334).

Role of the Anterior Cingulate Cortex in Translational Pain Research

As the most common symptomatic reason to seek medical consultation, pain is a complex experience that has been classified into different categories and stages. In pain processing, noxious stimuli may activate the anterior cingulate cortex (ACC). But the function of ACC in the different pain conditions is not well discussed. In this review, we elaborate the commonalities and differences from accumulated evidence by a variety of pain assays for physiological pain and pathological pain including inflammatory pain, neuropathic pain, and cancer pain in the ACC, and discuss the cellular receptors and signaling molecules from animal studies. We further summarize the ACC as a new central neuromodulation target for invasive and non-invasive stimulation techniques in clinical pain management. The comprehensive understanding of pain processing in the ACC may lead to bridging the gap in translational research between basic and clinical studies and to develop new therapies.

The search for translational pain outcomes to refine analgesic development: Where did we come from and where are we going?

Pain measures traditionally used in rodents record mere reflexes evoked by sensory stimuli; the results thus may not fully reflect the human pain phenotype. Alterations in physical and emotional functioning, pain-depressed behaviors and facial pain expressions were recently proposed as additional pain outcomes to provide a more accurate measure of clinical pain in rodents, and hence to potentially enhance analgesic drug development. We aimed to review how preclinical pain assessment has evolved since the development of the tail flick test in 1941, with a particular focus on a critical analysis of some nonstandard pain outcomes, and a consideration of how sex differences may affect the performance of these pain surrogates. We tracked original research articles in Medline for the following periods: 1973-1977, 1983-1987, 1993-1997, 2003-2007, and 2014-2018. We identified 606 research articles about alternative surrogate pain measures, 473 of which were published between 2014 and 2018. This indicates that preclinical pain assessment is moving toward the use of these measures, which may soon become standard procedures in preclinical pain laboratories.

Neuroimaging of pain in animal models: a review of recent literature

Neuroimaging of pain in animals allows us to better understand mechanisms of pain processing and modulation. In this review, we discuss recently published brain imaging studies in rats, mice, and monkeys, including functional magnetic resonance imaging (MRI), manganese-enhanced MRI, positron emission tomography, and electroencephalography. We provide an overview of innovations and limitations in neuroimaging techniques, as well as results of functional brain imaging studies of pain from January 1, 2016, to October 10, 2018. We then discuss how future investigations can address some bias and gaps in the field. Despite the limitations of neuroimaging techniques, the 28 studies reinforced that transition from acute to chronic pain entails considerable changes in brain function. Brain activations in acute pain were in areas more related to the sensory aspect of noxious stimulation, including primary somatosensory cortex, insula, cingulate cortex, thalamus, retrosplenial cortex, and periaqueductal gray. Pharmacological and nonpharmacological treatments modulated these brain regions in several pain models. On the other hand, in chronic pain models, brain activity was observed in regions commonly associated with emotion and motivation, including prefrontal cortex, anterior cingulate cortex, hippocampus, amygdala, basal ganglia, and nucleus accumbens. Neuroimaging of pain in animals holds great promise for advancing our knowledge of brain function and allowing us to expand human subject research. Additional research is needed to address effects of anesthesia, analysis approaches, sex bias and omission, and potential effects of development and aging.