Pain modulation is complex, but noradrenergic signalling promotes anti-nociception, with a 2 -adrenergic agonists used clinically. To better understand the noradrenergic/ peptidergic modulation of nociception, we examined the octopaminergic inhibition of aversive behaviour initiated by the Caenorhabditis elegans nociceptive ASH sensory neurons. Octopamine (OA), the invertebrate counterpart of norepinephrine, modulates sensory-mediated reversal through three a-adrenergic-like OA receptors. OCTR-1 and SER-3 antagonistically modulate ASH signalling directly, with OCTR-1 signalling mediated by Ga o . In contrast, SER-6 inhibits aversive responses by stimulating the release of an array of 'inhibitory' neuropeptides that activate receptors on sensory neurons mediating attraction or repulsion, suggesting that peptidergic signalling may integrate multiple sensory inputs to modulate locomotory transitions. These studies highlight the complexity of octopaminergic/peptidergic interactions, the role of OA in activating global peptidergic signalling cascades and the similarities of this modulatory network to the noradrenergic inhibition of nociception in mammals, where norepinephrine suppresses chronic pain through inhibitory a 2 -adrenoreceptors on afferent nociceptors and stimulatory a 1 -receptors on inhibitory peptidergic interneurons.

The apolipoprotein E (APOE) ε4 allele is the major genetic risk factor for Alzheimer's disease (AD). Multiple regulatory elements, spanning the extended TOMM40-APOE-APOC2 region, regulate gene expression at this locus. Regulatory element DNA methylation changes occur under different environmental conditions, such as disease. Our group and others have described an APOE CpG island as hypomethylated in AD, compared to cognitively normal controls. However, little is known about methylation of the larger TOMM40-APOE-APOC2 region. The hypothesis of this investigation was that regulatory element methylation levels of the larger TOMM40-APOE-APOC2 region are associated with AD. The aim was to determine whether DNA methylation of the TOMM40-APOE-APOC2 region differs in AD compared to cognitively normal controls in post-mortem brain and peripheral blood. DNA was extracted from human brain (n = 12) and peripheral blood (n = 67). A methylation array was used for this analysis. Percent methylation within the TOMM40-APOE-APOC2 region was evaluated for differences according to tissue type, disease state, AD-related biomarkers, and gene expression. Results from this exploratory analysis suggest that regulatory element methylation levels within the larger TOMM40-APOE-APOC2 gene region correlate with AD-related biomarkers and TOMM40 or APOE gene expression in AD.

Monoamines and neuropeptides modulate neuronal excitability and synaptic strengths, shaping circuit activity to optimize behavioral output. In C. elegans, a pair of bipolar polymodal nociceptors, the ASHs, sense 1-octanol to initiate escape responses. In the present study, 1-octanol stimulated large increases in ASH Ca(2+), mediated by L-type voltage-gated Ca(2+) channels (VGCCs) in the cell soma and L-plus P/Q-type VGCCs in the axon, which were further amplified by Ca(2+) released from intracellular stores. Importantly, 1-octanol-dependent aversive responses were not inhibited by reducing ASH L-VGCC activity genetically or pharmacologically. Serotonin, an enhancer of 1-octanol avoidance, potentiated 1-octanol-dependent ASH depolarization measured electrophysiologically, but surprisingly, decreased the ASH somal Ca(2+) transients. These results suggest that ASH somal Ca(2+) transient amplitudes may not always be predictive of neuronal depolarization and synaptic output. Therefore, although increases in steady-state Ca(2+) can reliably indicate when neurons become active, quantitative relationships between Ca(2+) transient amplitudes and neuronal activity may not be as straightforward as previously anticipated.

Neuromodulators, such as serotonin (5-HT), alter neuronal excitability and synaptic strengths, and define different behavioral states. Neuromodulator-dependent changes in neuronal activity patterns are frequently measured using calcium reporters because calcium imaging can easily be performed on intact functioning nervous systems. With only 302 neurons, the nematode provides a relatively simple, yet powerful, system to understand neuromodulation at the level of individual neurons. hermaphrodites are repelled by 1-octanol, and the initiation of these aversive responses is potentiated by 5-HT. 5-HT acts on the ASH polymodal nociceptors that sense the 1-octanol stimulus. Surprisingly, 5-HT suppresses ASH Ca transients while simultaneously potentiating 1-octanol-dependent ASH depolarization. Here we further explore this seemingly inverse relationship. Our results show the following (1) 5-HT acts downstream of depolarization, through Gα-mediated signaling and calcineurin, to inhibit L-type voltage-gated Ca channels; (2) the 1-octanol-evoked Ca transients in ASHs inhibit depolarization; and (3) the Ca-activated K channel, SLO-1, acts downstream of 5-HT and is a critical regulator of ASH response dynamics. These findings define a Ca-dependent inhibitory feedback loop that can be modulated by 5-HT to increase neuronal excitability and regulate behavior, and highlight the possibility that neuromodulator-induced changes in the amplitudes of Ca transients do not necessarily predict corresponding changes in depolarization. Neuromodulators, such as 5-HT, modify behavior by regulating excitability and synaptic efficiency in neurons. Neuromodulation is often studied using Ca imaging, whereby neuromodulator-dependent changes in neuronal activity levels can be detected in intact, functioning circuits. Here we show that 5-HT reduces the amplitude of depolarization-dependent Ca transients in a nociceptive neuron, through Gα signaling and calcineurin but that Ca itself inhibits depolarization, likely through Ca-activated K channels. The net effect of 5-HT, therefore, is to increase neuronal excitability through disinhibition. These results establish a novel 5-HT signal transduction pathway, and demonstrate that neuromodulators can change Ca signals and depolarization amplitudes in opposite directions, simultaneously, within a single neuron.

Neurofibrillary tangles (NFTs), composed of hyperphosphorylated tau, are a key pathologic feature of Alzheimer’s disease (AD). Tau phosphorylation is under the control of multiple kinases and phosphatases, including Fyn. Previously, our group found an association between two regulatory single nucleotide polymorphisms (SNPs) in the FYN gene with increased tau levels in the CSF. In this study, we hypothesized that Fyn expression in the brain is influenced by AD status and genetic content. We found that Fyn protein, but not mRNA, levels were increased in AD patients compared to cognitively normal controls and are associated with regulatory region SNPs. Additionally, expression of the FYN 3’ UTR can decrease expression in multiple cell lines, suggesting this regulatory region plays an important role in FYN expression. Taken together, these data suggest that FYN expression is regulated according to AD status and regulatory region haplotype, and genetic variants may be instrumental in the development of NFTs in AD and other tauopathies.