Descending serotonergic facilitation and the antinociceptive effects of pregabalin in a rat model of osteoarthritic pain

Background: Descending facilitation, from the brainstem, promotes spinal neuronal hyperexcitability and behavioural hypersensitivity in many chronic pain states. We have previously demonstrated enhanced descending facilitation onto dorsal horn neurones in a neuropathic pain model, and shown this to enable the analgesic effectiveness of gabapentin. Here we have tested if this hypothesis applies to other pain states by using a combination of approaches in a rat model of osteoarthritis (OA) to ascertain if 1) a role for descending 5HT mediated facilitation exists, and 2) if pregabalin (a newer analogue of gabapentin) is an effective antinociceptive agent in this model. Further, quantitative-PCR experiments were undertaken to analyse the alpha(2)delta-1 and 5-HT3A subunit mRNA levels in L3-6 DRG in order to assess whether changes in these molecular substrates have a bearing on the pharmacological effects of ondansetron and pregabalin in OA.Results: Osteoarthritis was induced via intra-articular injection of monosodium iodoacetate (MIA) into the knee joint. Control animals were injected with 0.9% saline. Two weeks later in vivo electrophysiology was performed, comparing the effects of spinal ondansetron (10-100 mu g/50 mu l) or systemic pregabalin (0.3-10 mg/kg) on evoked responses of dorsal horn neurones to electrical, mechanical and thermal stimuli in MIA or control rats. In MIA rats, ondansetron significantly inhibited the evoked responses to both innocuous and noxious natural evoked neuronal responses, whereas only inhibition of noxious evoked responses was seen in controls. Pregabalin significantly inhibited neuronal responses in the MIA rats only; this effect was blocked by a pre-administration of spinal ondansetron. Analysis of alpha(2)delta-1 and 5-HT3A subunit mRNA levels in L3-6 DRG revealed a significant increase in alpha(2)delta-1 levels in ipsilateral L3&4 DRG in MIA rats. 5-HT3A subunit mRNA levels were unchanged.Conclusion: These data suggest descending serotonergic facilitation plays a role in mediating the brush and innocuous mechanical punctate evoked neuronal responses in MIA rats, suggesting an adaptive change in the excitatory serotonergic drive modulating low threshold evoked neuronal responses in MIA-induced OA pain. This alteration in excitatory serotonergic drive, alongside an increase in alpha(2)delta-1 mRNA levels, may underlie pregabalin's state dependent effects in this model of chronic pain

Pregabalin Suppresses Spinal Neuronal Hyperexcitability and Visceral Hypersensitivity in the Absence of Peripheral Pathophysiology

ABSTRACT Background: Opioid-induced hyperalgesia is recognized in the laboratory and the clinic, generating central hyperexcitability in the absence of peripheral pathology. We investigated pregabalin, indicated for neuropathic pain, and ondansetron, a drug that disrupts descending serotonergic processing in the central nervous system, on spinal neuronal hyperexcitability and visceral hypersensitivity in a rat model of opioid-induced hyperalgesia. Methods: Male Sprague-Dawley rats (180 -200 g) were implanted with osmotic mini-pumps filled with morphine (90 g ⅐ l Ϫ1 ⅐

De Novo Mutations in SLC1A2 and CACNA1A Are Important Causes of Epileptic Encephalopathies

Epileptic encephalopathies (EEs) are the most clinically important group of severe early-onset epilepsies. Next-generation sequencing has highlighted the crucial contribution of de novo mutations to the genetic architecture of EEs as well as to their underlying genetic heterogeneity. Our previous whole-exome sequencing study of 264 parent-child trios revealed more than 290 candidate genes in which only a single individual had a de novo variant. We sought to identify additional pathogenic variants in a subset (n = 27) of these genes via targeted sequencing in an unsolved cohort of 531 individuals with a diverse range of EEs. We report 17 individuals with pathogenic variants in seven of the 27 genes, defining a genetic etiology in 3.2% of this unsolved cohort. Our results provide definitive evidence that de novo mutations in SLC1A2 and CACNA1A cause specific EEs and expand the compendium of clinically relevant genotypes for GABRB3. We also identified EEs caused by genetic variants in ALG13, DNM1, and GNAO1 and report a mutation in IQSEC2. Notably, recurrent mutations accounted for 7/17 of the pathogenic variants identified. As a result of high-depth coverage, parental mosaicism was identified in two out of 14 cases tested with mutant allelic fractions of 5%–6% in the unaffected parents, carrying significant reproductive counseling implications. These results confirm that dysregulation in diverse cellular neuronal pathways causes EEs, and they will inform the diagnosis and management of individuals with these devastating disorders

ECOLOGY AND COEXISTENCE OF SCAPHIRHYNCHUS STURGEON AT MULTIPLE SCALES

Transforming river systems and their surrounding habitats is the most widespread threat to the function of lotic ecosystems. To meet increasing demands for the limited supply of fresh water, humans have extensively altered river systems through diversions and impoundments, use for irrigation, drinking water, food fishing, generating hydro-electricity, and transporting goods and services. These modifications have resulted in an oversimplification of riverine habitats and global declines of many fluvial dependent species. Sturgeons are a group of fluvial dependent species affected by river modifications and may be the most imperiled group of species on Earth. Most sturgeons are threatened across the globe due to a combination of unregulated harvest and habitat loss. The federally endangered pallid sturgeon (Scaphirhynchus albus) and a congener, the threatened shovelnose sturgeon (S. platorynchus) are two species that depend solely on the large rivers of North America. Both species have experienced declines from habitat loss within the Mississippi River basin and overharvest due to the demand for black egg caviar, and are now protected from harvest where they overlap in range. However, pallid sturgeon populations continue to decline while shovelnose sturgeon have remained stable. Efforts to conserve pallid sturgeon have been ongoing for decades, but most studies describing pallid sturgeon life history have been conducted in altered habitats, making it difficult to determine unknown aspects of pallid sturgeon ecology and conservation needs. As a result, knowledge gaps still remain in our understanding of habitat needs during early life and adulthood for both species. Further, little information exists on how these similar sturgeons coexisted historically and why they are now on such different population trajectories. To address these issues, I investigated Scaphirhynchus sturgeon ecology and coexistence at multiple scales. I first examined the environmental life history of pallid and shovelnose sturgeon within the Mississippi River basin (Chapter 2). Using microchemistry techniques, my goal was to assess how to improve species conservation by identifying ecologically relevant management boundaries for pallid and shovelnose sturgeon. My results highlighted a mismatch between conservation boundaries and Scaphirhynchus sturgeon river use and I suggested that managers should consider expanding current protections for pallid sturgeon to include the unprotected sections of the Mississippi River. Chapters 3 and 4 of my dissertation centered on habitat use at smaller spatial scales (\u3c 1 m2) and the individual differences between pallid and shovelnose sturgeon that may occur within different microhabitats (e.g., substrate and velocity). For example, alluvial sand dunes are thought to provide energetic relief for benthic fishes in energetically costly riverine landscapes. However, use of alluvial dune habitat is not well understood, and it is unclear whether dunes provide refuge that effectively reduces energetic costs. I designed a scale-relevant experiment to examine the energetic responses (measured as oxygen consumption; MO2) associated with sand dune habitat in rivers (Chapter 3). Using respirometry, I tested whether pallid sturgeon experienced reduced energetic costs with different configurations of simulated sand dune habitat. Sturgeon displayed distinct station holding behaviors when behind a dune, in front of a dune, and with no dune present. Dune location did not affect energy expenditure, but sturgeon MO2 was on average 16−20% higher in the absence of a sand dune configuration. This was the first experiment to provide a potential mechanism for over two decades of research on why sturgeon, and other benthic fishes, exhibit selection for sand dune habitat in large rivers. In Chapter 4, I combined a separate respirometry study with morphological analysis to identify mechanisms behind differences in ecological success between pallid and shovelnose sturgeon. I proposed that identifying a complex of subtle characteristics in which these and other species differ may be more effective in elucidating both historical coexistence and divergent ecological success of similar species in contemporary habitats compared to identifying just one limiting similarity between species. Using this ‘subtle difference hypothesis’, I showed how metabolic rate associated with habitat use and internal and external morphology can lead to different predicted growth rates for pallid and shovelnose sturgeon, which correspond well to observed differences in ecological success between these species in the wild. Lastly, I reviewed multiple aspects of pallid and shovelnose sturgeon ecology within a framework for assessing surrogate species approaches to conservation in fisheries science (Chapter 5). I suggested that sufficient data regarding life history, niche overlap, genetic similarity, and population vital rates collected at multiple spatial and temporal scales need to be available for surrogates and their targets before implementing a surrogate approach. Although similar ecologically, subtle to large differences at multiple life stages between pallid and shovelnose sturgeon may hinder the use of shovelnose sturgeon as surrogates to infer conservation needs of pallid sturgeon. However, broader similarities between the species may be important for their joint conservation