Neuroscience
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Despite evidence that high-affinity GABA(A) receptor subunit mRNA and protein are present in dorsal root ganglia (DRG), low-affinity currents dominate those detected in acutely dissociated DRG neurons in vitro. This observation raises the possibility that high-affinity receptors are normally trafficked out of the DRG toward central and peripheral terminals. We therefore hypothesized that with time in culture, there would be an increase in high-affinity GABA(A) currents in DRG neurons. ⋯ However, the emergence of a high-affinity current blocked by THIP and insensitive to bicuculline was detected in a subpopulation of cultured neurons as well in association with an increase in ρ2- and ρ3-subunit mRNA in cultured DRG neurons. Our results suggest that high-affinity δ-subunit-containing GABA(A) receptors are normally trafficked out of the DRG where they are targeted to peripheral and central processes. They also highlight that the interpretation of data obtained from cultured DRG neurons should be made with caution.
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Spinal neuroinflammation has been shown to play an important role in the development of morphine tolerance and morphine withdrawal-induced hyperalgesia. Lipoxins are endogenous lipoxygenase-derived eicosanoids that can function as "braking signals" in inflammation. The present study investigated the effect of 5 (S), 6 (R)-lipoxin A4 methyl ester (LXA4ME), a stable synthetic analog of lipoxin A4, on the expression of antinociceptive tolerance and withdrawal-induced hyperalgesia in chronic morphine-treated rats. ⋯ However, LXA4ME treatment significantly attenuated the development of hyperalgesia and the expression of spinal antinociceptive tolerance to intrathecal morphine in both mechanical and thermal test. Moreover, the administration of LXA4ME during the induction of morphine tolerance inhibited the activation of microglia and astrocytes; reduced the expression of proinflammatory cytokines interleukin-1β (IL-1β), IL-6, and tumor necrosis factor-α (TNF-α); upregulated the expression of anti-inflammatory cytokines IL-10 and transforming growth factor-β1 (TGF-β1); and inhibited nuclear factor-kappa B (NF-κB) activation at the L5 lumbar spinal cord. These results suggest that treatment of LXA(4)ME provides a potential preventative or therapeutic approach for morphine tolerance and associated abnormal pain sensitivity.
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One of the primary lines of defense against oxidative stress is the selenoprotein family, a class of proteins that contain selenium in the form of the 21st amino acid, selenocysteine. Within this class of proteins, selenoprotein P (Sepp1) is unique, as it contains multiple selenocysteine residues and is postulated to act in selenium transport. Recent findings have demonstrated that neuronal selenoprotein synthesis is required for the development of parvalbumin (PV)-interneurons, a class of GABAergic neurons involved in the synchronization of neural activity. ⋯ Finally, as impaired PV-interneuron function has been implicated in several neuropsychiatric conditions, we performed multiple behavioral tests on Sepp1(-/-) mice. Our behavioral results indicate that Sepp1(-/-) mice have impairments in contextual fear extinction, latent inhibition, and sensorimotor gating. In sum, these findings demonstrate the important supporting role of Sepp1 on ApoER2-expressing PV-interneurons.
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Comparative Study
Ventral tegmental area neurons are either excited or inhibited by cocaine's actions in the peripheral nervous system.
Cocaine's multiple pharmacological substrates are ubiquitously present in the peripheral and central nervous system. Thus, upon its administration, cocaine acts in the periphery before directly acting in the brain. We determined whether cocaine alters ventral tegmental area (VTA) neuronal activity via its peripheral actions. ⋯ Cocaine-MI and cocaine-HCl each produced changes in VTA neuron activity under full DA receptor blockade. However, the duration of inhibition was shortened and the number of excitations increased, and they occurred with an earlier onset during DA receptor blockade. These findings indicate that cocaine acts peripherally with a short latency and alters the activity of VTA neurons before its well-known direct actions in the brain.
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Early-life stress has been shown to increase susceptibility to anxiety and substance abuse. Disrupted activity within the anterior insular cortex (AIC) has been shown to play a role in both of these disorders. Altered serotonergic processing is implicated in controlling the activity levels of the associated cognitive networks. ⋯ Our data indicate that chronic alcohol consumption leads to greater AIC activity and may indicate a compensatory upregulation of presynaptic 5-HT(1A) receptors. Our results also indicate that AIC activity may be less effectively regulated by 5-HT in ethanol-naive NR animals than in NR monkeys in response to chronic ethanol self-administration. These data suggest possible mechanisms for increased alcohol seeking and possible addiction potential among young adults who had previously experienced early-life stress that include disruptions in both AIC activity and serotonin system dynamics.