Neurotrophin-3 down-regulates trkA mRNA, NGF high-affinity binding sites, and associated phenotype in adult DRG neurons

Neurotrophin-3 (NT-3) binds to multiple trks, not only its initially identified receptor trkC. Recent studies in our laboratory show that NT-3 negatively regulates nociceptive phenotype associated with the trkA subpopulation. Due to the extensive overlap in trkA and trkC expression it is uncertain whether there is a direct influence of NT-3 on trkA in adult sensory neurons. Thus, the aim of this study was to examine whether NT-3 might alter trkA and associated neuronal phenotype outside of the trkC subpopulation. The effect of a seven-day intrathecal infusion of NT-3 on intact, uninjured adult rat dorsal root ganglion neurons was investigated. Serial sections were processed for receptor radioautography or in situ hybridization to identify and colocalize neurons expressing high-affinity nerve growth factor (NGF) binding sites, substance P (SP), trkC, or trkA mRNAs and to examine the influence of NT-3 on these populations. NT-3 does not appear to alter trkC expression, but evokes a notable reduction in trkA, high-affinity NGF binding sites, and SP levels. It is unlikely that signalling by trkC greatly influences this response because the down-regulation of SP occurs most notably in trkA neurons that lack trkC. Moreover, we have shown here that message levels of two trkA isoforms are differentially modulated by NT-3; infusion results in greater down-regulation of the noninsert containing isoform. These findings suggest a clinically relevant role for NT-3 as an antagonist to NGF, but also raise the caution that not just trkC-positive neurons are influenced following exposure to the neurotrophin.     

Attitudes towards mental health,mental health research and digital interventions by young adults with type 1 diabetes: A qualitative analysis

Background

Young people with type 1 diabetes are at increased risk of mental disorders. Whereas treatment need is high, difficulty recruiting young people with type 1 diabetes into psychosocial studies complicates development, testing and dissemination of these interventions.

Objective

Interviews with young adults with type 1 diabetes were conducted to examine attitudes towards mental health and mental health research, including barriers and motivators to participation in mental health studies and preferred sources of mental health support. The interviews were audio‐taped, transcribed and evaluated via thematic analysis.

Setting and participants

Young adults with type 1 diabetes were recruited via social media channels of 3 advocacy organizations. A total of 31 young adults (26 females and 5 males) with an average age of 22 years were interviewed between October 2015 and January 2016.

Results

Participants were largely unaware of their increased vulnerability to common mental health problems and knew little about mental health research. Major barriers to participation included perceived stigma and lifestyle issues and low levels of trust in researchers. Opportunities to connect with peers and help others were described as key motivators. Psychological distress was considered normal within the context of diabetes. A need for some level of human contact in receiving psychosocial support was expressed.

Discussion and conclusion

Findings provide valuable insights into the complex dynamics of engaging young adults with type 1 diabetes in mental health studies. Interviewees provided practical suggestions to assist investigation and delivery of psychosocial interventions for this vulnerable group.     

Ex vivo and in situ PLGA microspheres uptake by pig ileal Peyer's patch segment

We investigated the ability of pig ileal Peyer's patch segments to transport intestinal poly (D,L-lactide-co-glycolide) microspheres (PLGA MS) from intestinal lumen across the mucosae using in situ and ex vivo segments with confocal laser scanning microscopy (CLSM) and transmission electronic microscopy (TEM). From a global aspect, CLSM suggested that PLGA MS were translocated by M cells labelled with a FITC-conjugated anti-cytokeratin peptide 18, and transported through the follicle-associated epithelium (FAE) in the dome area in both types of experiments. At the ultrastructural level, TEM showed the traffic of PLGA MS throughout M cells, their transport into the basolateral invaginations of the M cells and their subsequent migration into the dome area and the follicular area in contact with macrophages and lymphatic vessels. Although in situ experiments allowed following the migration of PLGA MS until mesenteric lymph nodes, an ex vivo model could be used as a useful tool to study the targeting ability of PLGA MS formulations to the gut-associated lymphoid tissue (GALT).     

Role of the GLT-1 subtype of glutamate transporter in glutamate homeostasis: the GLT-1-preferring inhibitor WAY-855 produces marginal neurotoxicity in the rat hippocampus

Glutamate is the major excitatory neurotransmitter in the central nervous system and is tightly regulated by cell surface transporters to avoid increases in concentration and associated neurotoxicity. Selective blockers of glutamate transporter subtypes are sparse and so knock-out animals and antisense techniques have been used to study their specific roles. Here we used WAY-855, a GLT-1-preferring blocker, to assess the role of GLT-1 in rat hippocampus. GLT-1 was the most abundant transporter in the hippocampus at the mRNA level. According to [(3)H]-l-glutamate uptake data, GLT-1 was responsible for approximately 80% of the GLAST-, GLT-1-, and EAAC1-mediated uptake that occurs within dissociated hippocampal tissue, yet when this transporter was preferentially blocked for 120 h with WAY-855 (100 microm), no significant neurotoxicity was observed in hippocampal slices. This is in stark contrast to results obtained with TBOA, a broad-spectrum transport blocker, which, at concentrations that caused a similar inhibition of glutamate uptake (10 and 30 microm), caused substantial neuronal death when exposed to the slices for 24 h or longer. Likewise, WAY-855, did not significantly exacerbate neurotoxicity associated with simulated ischemia, whereas TBOA did. Finally, intrahippocampal microinjection of WAY-855 (200 and 300 nmol) in vivo resulted in marginal damage compared with TBOA (20 and 200 nmol), which killed the majority of both CA1-4 pyramidal cells and dentate gyrus granule cells. These results indicate that selective inhibition of GLT-1 is insufficient to provoke glutamate build-up, leading to NMDA receptor-mediated neurotoxic effects, and suggest a prominent role of GLAST and/or EAAC1 in extracellular glutamate maintenance.     

Developmental down-regulation of GAP-43 expression and timing of target contact in rat corticospinal neurons

During early nervous system development axons grow toward the target tissue that they will innervate. As axons invade target tissue, growth slows and ceases. Neurons express high levels of the growth-associated protein GAP-43 during developmental axon growth, declining with maturation. It has been suggested that target contact provides a signal which down-regulates GAP-43 expression. To study this issue in more detail, we used in situ hybridization to quantify relative changes in GAP-43 mRNA in corticospinal tract neurons identified by Fast Blue retrograde labeling. We also used anterograde transport of biotinylated dextran amine to study the invasion of target by corticospinal axons. We find that GAP-43 mRNA is high during the first postnatal week and then declines in two phases. Approximately half of the initial level of GAP-43 expression in corticospinal neurons is lost by P12; then expression remains at a plateau until P21. Between P21 and P28, GAP-43 expression again declines by half and then remains steady at the adult level (one fourth of initial level). Corticospinal axons initially invade spinal gray matter during the first 2 postnatal weeks, in a rostrocaudal gradient. Varicosities suggestive of terminal boutons become numerous during the third and fourth week, and the morphology of corticospinal axon terminals achieves the mature form at the end of the fourth week. These data suggest that the first phase of down-regulation of GAP-43 in corticospinal neurons is coincident with initial target contact and that the second phase is coincident with final maturation of terminal arborization.     

Transcultural adaptation of the Liver Disease Quality of Life instrument (LDQOL 1.0) for its use in the Spanish population

Instruments of health-related quality of life (HRQOL) help us to interpret the results of treatments and health interventions. In Spain there is no HRQOL instrument specifically designed for use in patients with liver disease or to measure the effect of interventions such as liver transplantation. The Liver Disease Quality of Life (LDQOL 1.0) questionnaire is an American instrument developed for use in these patients. The aim of this study was to produce an appropriate version of this questionnaire for use in Spain. Cultural adaptation was performed in 3 phases: a) modification for use in Spain of a Hispanic version of this questionnaire supplied by the original authors; b) back-translation to English of a new version of the questionnaire and comparison with the original version in English, and c) a pilot test in a small sample of patients. In the first phase consisting of revision of the Hispanic version, the changes were mainly linguistic due to cultural and idiomatic differences. The validated Spanish version of the SF-36 was directly incorporated and items that could be of interest to local investigators were added. Few changes were made in the second phase of the process: changes involved an item on the appearance of feces and another item on taking naps. In the final phase, various changes suggested by the patients were introduced. Before applying the new version of the LDQOL 1.0 in clinical studies in Spain, its psychometric properties (its reliability, validity and sensitivity to change) must be verified in a subsequent validation study.     

Effect of anti-nerve growth factor treatment on pituitary adenylate cyclase activating polypeptide expression in adult sensory neurons exposed to adjuvant induced inflammation

Expression of pituitary adenylate cyclase activating polypeptide (PACAP) is increased in sensory neurons exposed to adjuvant induced peripheral inflammation. Local elevation in expression of the neurotrophin nerve growth factor (NGF) is a main factor contributing to the neuronal response to inflammation. This study examines the role of endogenous NGF in inflammation-associated increases in PACAP expression using the adjuvant-induced peripheral inflammation model with or without systemic administration of antibodies against NGF. Quantitative in situ hybridization was used to detect changes in neuronal PACAP mRNA expression and to correlate this expression with neuronal mRNA expression of the NGF receptor tyrosine kinase (trk) A. The results from this study show that inflammation triggered increases in PACAP expression occurs in small- to medium-sized dorsal root ganglion (DRG) neurons that also express trkA, and that this elevation in PACAP expression is prevented by systemic injection of anti-NGF. This supports a role for NGF as a positive regulator of PACAP expression during inflammation.     

Nerve growth factor induces functional nicotinic acetylcholine receptors on rat sensory neurons in culture

Neonatal sensory neurons from rat nodose ganglia express nicotinic acetylcholine receptors when grown in tissue culture without other cell types. The present study investigates the role of nerve growth factor in inducing these receptors. Nerve growth factor has little effect on the growth and survival of nodose neurons in culture, although most neurons were found by quantitative radioautography to have high-affinity nerve growth factor receptors. Nerve growth factor strongly influenced the expression of nicotinic receptors on these neurons: the proportion of acetylcholine-sensitive neurons was approximately 60% in cultures with nerve growth factor compared with 15% in cultures grown without nerve growth factor. The proportion of acetylcholine-sensitive neurons increased over the first week, plateaued by day 12 and remained high for at least three weeks. In contrast, without NGF, the proportion of acetylcholine-sensitive neurons was low throughout the three-week period. The results indicate that nerve growth factor is an important factor in promoting nicotinic receptors on these neurons in culture.