Steroid hormone signaling activates thermal nociception during Drosophila peripheral nervous system development

Sensory neurons enable animals to detect environmental changes and avoid harm. An intriguing open question concerns how the various attributes of sensory neurons arise in development. Drosophila melanogaster larvae undergo a behavioral transition by robustly activating a thermal nociceptive escape behavior during the second half of larval development (3rd instar). The Class 4 dendritic arborization (C4da) neurons are multimodal sensors which tile the body wall of Drosophila larvae and detect nociceptive temperature, light, and mechanical force. In contrast to the increase in nociceptive behavior in the 3rd instar, we find that ultraviolet light-induced Ca2+ activity in C4da neurons decreases during same period of larval development. Loss of ecdysone receptor has previously been shown to reduce nociception in 3rd instar larvae. We find that ligand dependent activation of ecdysone signaling is sufficient to promote nociceptive responses in 2nd instar larvae and suppress expression of subdued (encoding a TMEM16 channel). Reduction of subdued expression in 2nd instar C4da neurons not only increases thermal nociception but also decreases the response to ultraviolet light. Thus, steroid hormone signaling suppresses subdued expression to facilitate the sensory switch of C4da neurons. This regulation of a developmental sensory switch through steroid hormone regulation of channel expression raises the possibility that ion channel homeostasis is a key target for tuning the development of sensory modalities.

Blocking Neuropilin-1 in Drosophila melanogaster as a Possible Treatment for Pain and SARS-CoV-2

This study aims to validate a method of neuropilin-1 blocking in Drosophila melanogaster to aid the development of chronic pain treatment as well as increase scientific understanding of SARS-CoV-2 cell entry. If Drosophila melanogaster are exposed to monoclonal antibodies (mAbs) used for targeted chemotherapy against neuropilin-1, then this targeted protein blocking method may allow for the development of new pain treatment and possible SARS-CoV-2 treatment. mAbs were microinjected into mutant flies to block NRP-1 activity. Then, a thermal nociception and von frey assay were done to test drosophila nociception. Finally, an IHC assay was performed to quantify protein activity. Overall, the hypothesis was supported as both nociception assays showed significant data proving mutant flies had delayed or no reactions to stimuli. The Von Frey assay did show some varying results, but the data is still significant. However, the IHC did show that there was still some NRP-1 activity in the mutant flies. NRP-1 was able to be partially blocked by mAbs. The collected data may apply to the expansion of research in pain treatment as well as COVID-19 research. Chronic pain is a prevalent area of research that is still not completely solved today. The fight against the SARS-CoV-2 is an ongoing fight and further research is mandatory in finding treatments for this deadly virus.

The long-term effects of repeated heroin vapor inhalation during adolescence on measures of nociception and anxiety-like behavior in adult Wistar rats

ABSTRACTThe United States continues to experience a public health crisis related to the nonmedical use of opioid drugs. Adolescents represent a vulnerable group due to increased experimentation with illicit substances that is often associated with the adolescent period, and because adolescent drug use can result in long-term effects that differ from those caused by drug use initiated during adulthood. The present study examined the effects of repeated heroin inhalation, a common route of administering opioids, during adolescence, on measures of nociception and anxiety-like behavior in adulthood. Rats were exposed twice daily to 30-minutes of heroin vapor from post-natal day (PND) 36 to PND 45. At 12 weeks of age, baseline thermal nociception was assessed across a range of temperatures with a warm-water tail-withdrawal assay. Anxiety-like behavior was assessed in an elevated plus-maze (EPM) and activity was measured in an open field arena. Starting at 23 weeks of age, baseline thermal nociception was re-assessed, nociception was determined after acute heroin or naloxone injection, and anxiety-like behavior was redetermined in the EPM. Adolescent heroin inhalation altered baseline thermal nociception in female rats at 12 weeks of age and in both female and male rats at ∼23 weeks. Heroin-treated animals exhibited an increase in anxiety-like behavior when tested in the elevated plus-maze, showed blunted heroin-induced analgesia, but exhibited no effect on naloxone-induced hyperalgesia. The present study demonstrates for the first time that heroin vapor inhalation during adolescence produces behavioral and physiological consequences in rats that persist well into adulthood.

Chronic THC vapor rescues inflammation-related thermal hyperalgesia and causes cell type-specific modifications in vlPAG neurons

To reduce reliance on opioids for the treatment of pain in the clinic, ongoing work is testing the utility of cannabinoid drugs as a potential alternative for treatment of chronic pain and/or as a strategy for reducing opioid drug dosage and duration of treatment (i.e., so-called opioid-sparing effects). Previous preclinical work has shown robust anti-hyperalgesic effects of systemic THC and acute anti-hyperalgesic effects of vaporized THC. Here, we used a vapor inhalation model in rats to test chronic THC vapor inhalation effects on thermal nociception and mechanical sensitivity, as well as midbrain (i.e., periaqueductal gray [PAG]) neuronal function, in adult male rats with chronic inflammatory pain. We report that chronic THC vapor inhalation produces a robust anti-hyperalgesic effect in rats with chronic inflammatory pain, and that this effect persists 24 hours after cessation of THC exposure. We demonstrate that chronic THC vapor inhalation also modulates intrinsic and synaptic properties of ventrolateral PAG (vlPAG) neurons, including reductions in action potential firing rate and reductions in spontaneous inhibitory synaptic transmission, and that these effects occur specifically in neurons that respond to current input with a delayed firing phenotype. Finally, we show that the suppressive effect of the bath-applied mu-opioid receptor (MOR) agonist DAMGO on synaptic inhibition in the vlPAG is enhanced in slices taken from rats with a history of chronic THC vapor inhalation. Collectively, these data show that chronic THC vapor inhalation produces lasting attenuation of thermal hyperalgesia and reduces synaptic inhibition in the vlPAG of rats with chronic inflammatory pain.

Preserved Thermal Pain in 3xTg-AD Mice With Increased Sensory-Discriminative Pain Sensitivity in Females but Affective-Emotional Dimension in Males as Early Sex-Specific AD-Phenotype Biomarkers

The increase of the aging population, where quite chronic comorbid conditions are associated with pain, draws growing interest across its investigation and the underlying nociceptive mechanisms. Burn injuries associated problems might be of relevance in the older adult’s daily life, but in people with dementia, exposure to high temperatures and heat sources poses a significantly increased risk of burns. In this brief report, the hind paws and tail pain withdrawal reflexes and the emotional responses to thermal nociception in 3xTg-AD mice were characterized for the first time in the plantar test and compared to their non-transgenic (NTg) counterparts. We studied a cohort of male and female 3xTg-AD mice at asymptomatic (2 months), early (6 months), middle (9 months), and advanced (12 and 15 months) stages of the disease and as compared to sex- and age-matched NTg control mice with normal aging. At 20 and 40W intensities, the sensorial-discriminative thresholds eliciting the withdrawal responses were preserved from asymptomatic to advanced stages of the disease compared to NTg counterparts. Moreover, 3xTg-AD females consistently showed a greater sensory-discriminative sensitivity already at premorbid ages, whereas increased emotionality was shown in males. False-negative results were found in “blind to sex and age” analysis, warning about the need to study sexes independently. The current results and previous report in cold thermal stimulation provide two paradigms unveiling sex-specific early AD-phenotype nociceptive biomarkers to study the mechanistic underpinnings of sex-, age- and AD-disease-dependent thermal pain sensitivity.

Pramipexole and tolcapone alleviate thermal and mechanical nociception in naive rats.

Introduction: Parkinson&rsquo;s disease (PD) is &#1072; neurodegenerative disorder characterized mainly by its motor symptoms. The non-motor symptoms including pain are increasingly recognized in the last few decades. Existing evidence suggests that the dopaminergic neurotransmission has an essential role in pain control. Aim: The aim of the present study was to investigate the antinociceptive effect of dopaminergic drugs pramipexole and tolcapone against chemical and thermal stimuli in naive rats. Materials and methods: Male Wistar rats divided into 8 groups (n=8): saline; diclofenac 25 mg/kg body weight (bw) (positive control); pramipexole 0.5; 1 and 3 mg/kg bw; tolacapone 5; 15 and 30 mg/kg bw. Paw pressure and plantar tests were performed. Paw withdrawal pressure and latent time were measured. Statistical analysis was done by SPSS 19. Results: In the paw pressure test, pramipexole, in a dose of 1 and 3 mg/kg bw and tolcapone in a dose of 30 mg/kg bw, increased significantly the latency at 1, 2, and 3 hours compared to saline (p<0.05). In the plantar test, only the highest dose of pramipexole reached significance at 3 hours compared to the control rats (p<0.05). In contrast to pramipexole the three experimental groups with tolcapone markedly increased the latent time at 1 and 3 hours compared to saline (p<0.05). Conclusions: Pramipexole and tolcapone reduce mechanical and thermal nociception in na&iuml;ve rats by enhancing dopaminergic neurotransmission at both spinal and supraspinal levels. In addition, tolcapone stimulates noradrenergic mediation which may contribute to its antinociceptive effect.

Functional Profile of Systemic and Intrathecal Cebranopadol in Nonhuman Primates

Background Cebranopadol, a mixed nociceptin/opioid receptor full agonist, can effectively relieve pain in rodents and humans. However, it is unclear to what degree different opioid receptor subtypes contribute to its antinociception and whether cebranopadol lacks acute opioid-associated side effects in primates. The authors hypothesized that coactivation of nociceptin receptors and μ receptors produces analgesia with reduced side effects in nonhuman primates. Methods The antinociceptive, reinforcing, respiratory-depressant, and pruritic effects of cebranopadol in adult rhesus monkeys (n = 22) were compared with μ receptor agonists fentanyl and morphine using assays, including acute thermal nociception, IV drug self-administration, telemetric measurement of respiratory function, and itch-scratching responses. Results Subcutaneous cebranopadol (ED50, 2.9 [95% CI, 1.8 to 4.6] μg/kg) potently produced antinociception compared to fentanyl (15.8 [14.6 to 17.1] μg/kg). Pretreatment with antagonists selective for nociceptin and μ receptors, but not δ and κ receptor antagonists, caused rightward shifts of the antinociceptive dose–response curve of cebranopadol with dose ratios of 2 and 9, respectively. Cebranopadol produced reinforcing effects comparable to fentanyl, but with decreased reinforcing strength, i.e., cebranopadol (mean ± SD, 7 ± 3 injections) versus fentanyl (12 ± 3 injections) determined by a progressive-ratio schedule of reinforcement. Unlike fentanyl (8 ± 2 breaths/min), systemic cebranopadol at higher doses did not decrease the respiratory rate (17 ± 2 breaths/min). Intrathecal cebranopadol (1 μg) exerted full antinociception with minimal scratching responses (231 ± 137 scratches) in contrast to intrathecal morphine (30 μg; 3,009 ± 1,474 scratches). Conclusions In nonhuman primates, the μ receptor mainly contributed to cebranopadol-induced antinociception. Similar to nociceptin/μ receptor partial agonists, cebranopadol displayed reduced side effects, such as a lack of respiratory depression and pruritus. Although cebranopadol showed reduced reinforcing strength, its detectable reinforcing effects and strength warrant caution, which is critical for the development and clinical use of cebranopadol. Editor’s Perspective What We Already Know about This Topic What This Article Tells Us That Is New

Effects of vapor exposure to Δ9-tetrahydrocannabinol (THC) in the Maine Lobster (Homarus americanus)

Rationale: Despite a long history of use in synaptic physiology, the lobster has been a neglected model for behavioral pharmacology. A restauranteur proposed that exposing lobster to cannabis smoke reduces anxiety and pain during the cooking process. It is unknown if lobster gill respiration in air would result in significant Δ9-tetrahydrocannabinol (THC) uptake and whether this would have any detectable behavioral effects. Objective: The primary goal was to determine tissue THC levels in the lobster after exposure to THC vapor. Secondary goals were to determine if THC vapor altered locomotor behavior or nociception. Methods: Tissue samples were collected from muscle, brain and hemolymph of Homarus americanus (N=3 per group) following 30 or 60 minutes of exposure to vapor generated by an e-cigarette device using THC (100 mg/mL in a propylene glycol vehicle). Separate experiments assessed locomotor behavior and hot water nociceptive responses following THC vapor exposure. Results: THC vapor produced duration-related THC levels in all tissues examined. Locomotor activity was decreased (distance, speed, time-mobile) by 30 min inhalation of THC. Lobsters exhibit a temperature-dependent withdrawal response to immersion of tail, antennae or claws in warm water; this is novel evidence of thermal nociception for this species. THC exposure for 60 minutes had only marginal effect on nociception under the conditions assessed. Conclusions: Vapor exposure of lobsters, using an e-cigarette based model, produces dose-dependent THC levels in all tissues and reduces locomotor activity. Hot water nociception is temperature dependent in the lobster, but no clear effects of THC inhalation were confirmed.

The Drosophila gene smoke alarm regulates nociceptor-epidermis interactions and thermal nociception behavior

The detection and processing of noxious sensory input depends on the proper growth and function of nociceptor sensory neurons in the peripheral nervous system. In Drosophila melanogaster, the class IV (cIV) multidendritic dendritic arborization (md-da) neurons detect noxious stimuli through their highly branched dendrites that innervate the epidermis of the larval body wall. Here, we describe requirements of a previously uncharacterized gene named smoke alarm (smal), a discoidin domain receptor, in cIV md-da dendrite morphogenesis and nociception behavior. We find that smal mutant larvae exhibit thermal hyperalgesia that is fully rescued with a BAC transgene containing smal. Consistent with this phenotype, a smal reporter gene was expressed in nociceptors and other peripheral sensory neurons. Smal::GFP protein localized to punctate structures throughout the cIV md-da neurons. We further show that smal loss-of-function results in reduced nociceptor dendrite branching. Interestingly, mammalian homologues of smal act as collagen receptors, and we find that smal mutant dendrites showed an increase in epidermal cell ensheathment relative to animals that are wild type for smal. Based on this phenotype we propose that Smal protein function is required for attachment of dendrites to the extracellular matrix (ECM) and the loss of activity results in thermal hyperalgesia.