Modulation of nociception allows animals to prioritise their survival by adapting their behaviour in different contexts. In mammals, this is executed by neurons from the brain, and is referred to as the descending control of nociception. Whether insects have this control, or have the neural circuits underpinning it, has not been clarified. Here, we review evidence supporting descending control of nociception control in insects, and consider which neuronal sub-types and brain areas may be involved.

Keywords: Pain; Nociception; Disorders of Consciousness; Consciousness

Chronic pain has increasingly become a significant health challenge, not just as a symptomatic manifestation but also as a pathological condition with profound socioeconomic implications. Despite the expansion of medical interventions, the prevalence of chronic pain remains remarkably persistent, prompting a turn towards non-pharmacological treatments, such as therapeutic education, exercise and cognitive-behavioral therapy. With the advent of cognitive neuroscience, pain is often presented as a primary output derived from the brain, aligning with Engel's Biopsychosocial Model which views disease not solely from a biological perspective but also considering psychological and social factors. This paradigm shift, brings forward potential misconceptions and over-simplifications. The current review delves into the intricacies of nociception and pain perception. It questions long-standing beliefs like the cerebral-centric view of pain, the forgotten role of the peripheral nervous system in pain chronification, misconceptions around central sensitization syndromes, the controversy about the existence of a dedicated pain neuromatrix, the consciousness of the pain experience and the possible oversight of factors beyond the nervous system. In re-evaluating these aspects, the review emphasizes the critical need for understanding the complexity of pain, urging the scientific and clinical community to move beyond reductionist perspectives and consider the multifaceted nature of this phenomenon.

Windup, a progressive increase in spinal response to repetitive stimulations of nociceptive peripheral fibres, is a useful model to study central sensitization to pain. Windup is expressed by neurons in of both dorsal and ventral horn of the spinal cord. In juvenile rats, it has been demonstrated both in vivo and in vitro that windup depends on calcium-dependent intrinsic properties and their modulation by synaptic components. However, the involvement of these two components in the adult remain controversial. In the present study, by means of electromyographic and extracellular recordings, we show that windup in adult, in vivo, depends on a synaptic balance between excitatory NMDA receptors and inhibitory glycinergic receptors. We also demonstrate the involvement of L-type calcium channels in both the dorsal and ventral horn of the spinal cord. These results indicate that windup in adults is similar to juveniles rats and that windup properties are the same regardless spinal network, i.e. sensory or motor.

This review article discusses the involvement of the Brain-Derived Neurotrophic Factor (BDNF) in the control of pain. BDNF, a neurotrophin known for its essential role in neuronal survival and plasticity, has garnered significant attention for its potential implications as a modulator of nociception and pain. This comprehensive review aims to provide insights into the multifaceted interactions between BDNF and pain pathways, encompassing both physiological and pathological pain conditions. I delve into the molecular mechanisms underlying BDNF's involvement in pain processing and discuss potential therapeutic applications of BDNF and its mimetics in managing pain. Furthermore, I highlight recent advancements and challenges in translating BDNF-related research into clinical practice.

Analgesic products for piglet castration are critically needed. This requires extensive animal experimentation such as to meet regulatory-required proof of efficacy. At present, there are no validated methods of assessing pain in neonatal piglets. This poses challenges for investigators to optimize trial design and to meet ethical obligations to minimize the number of animals needed. Pain in neonatal piglets may be subtle, transient and / or variably expressed and, in the absence of validated methods, investigators must rely on using a range of biochemical, physiological and behavioural variables, many of which appear to have very low (or unknown) sensitivity or specificity for documenting pain, or pain-relieving effects. A previous systematic review of this subject was hampered by the high degree of variability in the literature base both in terms of methods used to assess pain and pain mitigation, as well as in outcomes reported. In this setting we provide a narrative review, to assist in determining the optimal methods currently available to detect piglet pain during castration and methods to mitigate castration-induced pain. In overview, the optimal outcome variables identified are nociceptive motor and vocal response scores during castration, and quantitative sensory-threshold response testing and pain-associated behaviour scores following castration.

Although the majority of mobile phone (MP) users do not attribute adverse effects on health or well-being to MP-emitted radiofrequency (RF) electromagnetic fields (EMFs), the exponential increase in the number of RF devices necessitates continuing research aimed at the objective investigation of such concerns. In this work, we investigate the effects of acute exposure from Long Term Evolution (LTE) MP EMFs on thermal pain threshold in healthy young adults. We use a protocol that was validated in a previous study in a capsaicin-induced hyperalgesia model, and was also successfully used to show that exposure from an RF source mimicking a Universal Mobile Telecommunications System (UMTS) MP led to mildly stronger desensitization to repeated noxious thermal stimulation relative to the sham condition. Using the same experimental design, we did not find any effects of LTE exposure on thermal pain threshold. The present results are in accordance with previous evidence suggesting that effects are likely to be placebo/nocebo effects and are unrelated to the brief acute LTE EMF exposure itself. The fact that this is dissimilar to our previous results on UMTS exposure implies that RF modulations might differentially affect pain perception, and points to the necessity of further research in the topic.

Chronic inflammatory diseases are considered the most significant cause of death worldwide. Current treatments for inflammatory diseases are limited due to the lack of understanding of the biological factors involved in early-stage disease progression. Nerve growth factor (NGF) is a neurotrophic factor directly associated with inflammatory and autoimmune diseases like osteoarthritis, multiple sclerosis, and rheumatoid arthritis. It has been shown that NGF levels are significantly upregulated at the site of inflammation and play a crucial role in developing a robust inflammatory response. However, little is known about NGF's temporal expression profile during the initial progressive phase of inflammation. This study aimed to determine the temporal expression pattern of NGF in rat skin during Adjuvant-Induced Arthritis (AIA). Sprague Dawley rats were randomly divided into control and Complete Freund's Adjuvant (CFA) treated groups. Levels of NGF were evaluated following unilateral AIA at different time points and it was found that peripheral inflammation due to AIA significantly upregulated the expression of NGF mRNA and Protein in a biphasic pattern. These results suggest that NGF signaling is crucial for initiating and maintaining peripheral neurogenic inflammation in rats during AIA.

The leaves and stems of Bauhinia guianensis Aubl. are used in traditional Amazonian phytotherapy for the treatment of pain and inflammation. This study investigates the anti-inflammatory and antinociceptive effects of hydroethanolic extracts from B. guianensis Aubl. leaves and stems (HELBg and HESBg, respectively) in in vivo models of inflammation and hyperalgesia. Danio rerio experimental animals were submitted to the acute inflammation test, induced by intraperitoneal (ip.) administration of carrageenan 20 μg / animal (abdominal edema), the groups were previously treated orally with saline solution 2 μl / animal (SS), Dimethyl sulfoxide 2 μl / animal (DMSO), Indomethacin 10 mg/kg, HELBg 100 mg/kg and HESBg 100 mg/kg, n = 12 per experimental group, to evaluate inhibition of edema and alterations histopathology of the liver, intestine and kidney of these animals. The antinociceptive effect was observed from the body curvature index and the behavioral responses of Danio rerio, after an experimental protocol for the induction of hyperalgesia, by ip. administration of 10 μl / animal of 2.5% acetic acid, the animals were previously orally treated with saline solution 2 μl/animal (SS), dimethyl sulfoxide 2 μl/animal (DMSO), morphine 2.5 mg/kg, HELBg 100 mg/kg and HESBg 100 mg/kg, n = 5 per experimental group. In carrageenan-induced edema, the group treated with HESBg inhibited edema formation over the 3 hours of the experiment. Maximum edema was inhibited by 54% (p < 0.05) when compared to the control group. Both HELBg and HESBg prevented body curvature index changes (t (df = 3 8) =, 6.96 and t (df = 3, 8) = 6.61, respectively, both p < 0.0001). In the behavioral parameters sensitive to antinociceptive pharmacological modulation, due to the abdominal constriction induced by acetic acid, the administration of HELBg and HESBg resulted in an improvement in swimming activity, by increasing the distance covered (F (df = 3, 16) = 6.50 and F (df = 3, 16)  = 7.72, respectively, both p < 0.0001), decrease in freezing time (F (df = 3, 16)  = 2.04 and F (df = 3, 16)  = 1.28, respectively, both p < 0.0059), increase in the number of ascents to the upper area of the tank (F (df = 3, 16)  = 33.02 and F (df = 3, 16)  = 35.62, respectively, both p < 0.0009 ) and decreased time spent in that area (F (df = 3, 16)  = 101.19 and F (df = 3, 16)  = 103.59, respectively, both p < 0.0038). It is reasonable to suppose that both extracts modulated the variations induced by carrageenan and acetic acid through the inhibition of prostaglandin biosynthesis, decreasing the release of inflammatory mediators and the sensitization of peripheral nociceptors and, consequently, the perception of pain. These results suggest that HELBg and HESBg have anti-inflammatory and antinociceptive activities, probably of peripheral origin and linked to the inhibition of prostaglandin biosynthesis.

The leaves and stems of Bauhinia guianensis Aubl. are used in traditional Amazonian phytotherapy for the treatment of pain and inflammation. This study investigates the anti-inflammatory and antinociceptive effects of hydroethanolic extracts from B. guianensis Aubl. leaves and stems (HELBg and HESBg, respectively) in in vivo models of inflammation and hyperalgesia. Danio rerio experimental animals were submitted to the acute inflammation test, induced by intraperitoneal (ip.) administration of carrageenan 20 μg / animal (abdominal edema), the groups were previously treated orally with saline solution 2 μl / animal (SS), Dimethyl sulfoxide 2 μl / animal (DMSO), Indomethacin 10 mg/Kg, HELBg 100 mg/Kg and HESBg 100 mg/Kg, n = 12 per experimental group, to evaluate inhibition of edema and alterations histopathology of the liver, intestine and kidney of these animals. The antinociceptive effect was observed from the body curvature index and the behavioral responses of Danio rerio, after an experimental protocol for the induction of hyperalgesia, by ip administration. of 10 μl / animal of 2.5% acetic acid, the animals were previously orally treated with saline solution 2 μl/animal (SS), dimethyl sulfoxide 2 μl/animal (DMSO), morphine 2.5 mg/Kg, HELBg 100 mg/Kg and HESBg 100 mg/Kg, n = 5 per experimental group. In carrageenan-induced edema, the group treated with HESBg inhibited edema formation over the 3 hours of the experiment. Maximum edema was inhibited by 54% (p < 0.05) when compared to the control group. Both HELBg and HESBg prevented body curvature index changes (t (df = 3 8) =, 6.96 and t (df = 3, 8) = 6.61, respectively, both p < 0.0001). In the behavioral parameters sensitive to antinociceptive pharmacological modulation, due to the abdominal constriction induced by acetic acid, the administration of HELBg and HESBg resulted in an improvement in swimming activity, by increasing the distance covered (F (df = 3, 16) = 6.50 and F (df = 3, 16)  = 7.72, respectively, both p < 0.0001), decrease in freezing time (F (df = 3, 16)  = 2.04 and F (df = 3, 16)  = 1.28, respectively, both p < 0.0059), increase in the number of ascents to the upper area of the tank (F (df = 3, 16)  = 33.02 and F (df = 3, 16)  = 35.62, respectively, both p < 0.0009 ) and decreased time spent in that area (F (df = 3, 16)  = 101.19 and F (df = 3, 16)  = 103.59, respectively, both p < 0.0038). It is reasonable to suppose that both extracts modulated the variations induced by carrageenan and acetic acid through the inhibition of prostaglandin biosynthesis, decreasing the release of inflammatory mediators and the sensitization of peripheral nociceptors and, consequently, the perception of pain. These results suggest that HELBg and HESBg have anti-inflammatory and antinociceptive activities, probably of peripheral origin and linked to the inhibition of prosta-glandin biosynthesis