No abstract

A fascinating yet perhaps overlooked trait of the p75 neurotrophin receptor (p75NTR) is its ability to bind ligands with no obvious neurotrophic function. Using cultured basal forebrain (BF) neurons, this study demonstrates selective internalization of amyloid β (Aβ) 1–42 in conjunction with p75NTR (labelled with IgG192-Cy3) by cholinergic cells. Active under resting conditions, this process was enhanced by high K+ stimulation and was insensitive to inhibitors of regulated synaptic activity—tetrodotoxin or botulinum neurotoxins (BoNT type/A and/B). Blockade of sarco-endoplasmic reticulum (SERCA) Ca2+ ATPase with thapsigargin and CPA or chelation of Ca2+ with EGTA-AM strongly suppressed the endocytosis of p75NTR, implicating the role of ER released Ca2+. The uptake of IgG192-Cy3 was also reduced by T-type Ca2+ channel blocker mibefradil but not Cd2+, an indiscriminate blocker of high voltage-activated Ca2+ currents. A strong co-localization of IgG192-Cy3 with late endosome (Rab7) or lysosome (Lamp1) qualifier proteins suggest these compartments as the primary destination for internalized IgG192 and Aβ. Selective uptake and labeling of BF cholinergic cells with IgG192-Cy3 injected into the prefrontal cortex was verified also in vivo. The significance of these findings in relation to Aβ clearance in the cerebral cortex and pathophysiology of Alzheimer’s disease is discussed.

Nerve growth factor (NGF) is known to intensify pain in various ways, so perturbing pertinent effects without negating its essential influences on neuronal functions could help the search for much-needed analgesics. Towards this goal, cultured neurons from neonatal rat trigeminal ganglia—a locus for craniofacial sensory nerves—were used to examine how NGF affects the Ca2+-dependent release of a pain mediator, calcitonin gene-related peptide (CGRP), that is triggered by activating a key signal transducer, transient receptor potential vanilloid 1 (TRPV1) with capsaicin (CAP). Measurements utilised neurons fed with or deprived of NGF for 2 days. Acute re-introduction of NGF induced Ca2+-dependent CGRP exocytosis that was inhibited by botulinum neurotoxin type A (BoNT/A) or a chimera of/E and/A (/EA), which truncated SNAP-25 (synaptosomal-associated protein with Mr = 25 k) at distinct sites. NGF additionally caused a Ca2+-independent enhancement of the neuropeptide release evoked by low concentrations (<100 nM) of CAP, but only marginally increased the peak response to ≥100 nM. Notably, BoNT/A inhibited CGRP exocytosis evoked by low but not high CAP concentrations, whereas/EA effectively reduced responses up to 1 µM CAP and inhibited to a greater extent its enhancement by NGF. In addition to establishing that sensitisation of sensory neurons to CAP by NGF is dependent on SNARE-mediated membrane fusion, insights were gleaned into the differential ability of two regions in the C-terminus of SNAP-25 (181–197 and 198–206) to support CAP-evoked Ca2+-dependent exocytosis at different intensities of stimulation.

No abstract

Acute and chronic trigeminal (TG) neuropathies are the cause of considerable distress, with limited treatments available at present. Nociceptive neurons enriched with the vanilloid type 1 receptor (VR1) partake in pain sensation and sensitization in the TG system. While VR1 blockers with anti-nociceptive potential are of substantial medical interest, their use remains limited due to poor selectivity and lack of cell-targeting capabilities. This study describes a methodology for the alleviation of nociception via targeted depletion of VR1 in TG sensory neurons in rats. In cultured TG ganglion neurons, VR1 expression was virtually abolished by lentiviral short hairpin RNA (LV-VR1). By decorating GFP encoding LV (LV-GFP) and LV-VR1 with IgG192 for targeting TG sensory neurons enriched with the p75 neurotrophin receptor (p75NTR), transduction of a reporter GFP and VR1 depletion was achieved after injection of targeted vectors into the whisker pad. In IgG192/LV-VR1-injected rats, the behavioral response to capsaicin exposure as well as Erk 1/2 phosphorylation and VR1 current activation by capsaicin were significantly reduced. This pioneering investigation, thus, provides a proof of principle for a means of attenuating TG nociception, revealing therapeutic potential.