Default-Mode-Like Network Activation in Awake Rodents

During wakefulness and in absence of performing tasks or sensory processing, the default-mode network (DMN), an intrinsic central nervous system (CNS) network, is in an active state. Non-human primate and human CNS imaging studies have identified the DMN in these two species. Clinical imaging studies have shown that the pattern of activity within the DMN is often modulated in various disease states (e.g., Alzheimer's, schizophrenia or chronic pain). However, whether the DMN exists in awake rodents has not been characterized. The current data provides evidence that awake rodents also possess ‘DMN-like’ functional connectivity, but only subsequent to habituation to what is initially a novel magnetic resonance imaging (MRI) environment as well as physical restraint. Specifically, the habituation process spanned across four separate scanning sessions (Day 2, 4, 6 and 8). At Day 8, significant (p<0.05) functional connectivity was observed amongst structures such as the anterior cingulate (seed region), retrosplenial, parietal, and hippocampal cortices. Prior to habituation (Day 2), functional connectivity was only detected (p<0.05) amongst CNS structures known to mediate anxiety (i.e., anterior cingulate (seed region), posterior hypothalamic area, amygdala and parabracial nucleus). In relating functional connectivity between cingulate-default-mode and cingulate-anxiety structures across Days 2-8, a significant inverse relationship (r = −0.65, p = 0.0004) was observed between these two functional interactions such that increased cingulate-DMN connectivity corresponded to decreased cingulate anxiety network connectivity. This investigation demonstrates that the cingulate is an important component of both the rodent DMN-like and anxiety networks

Respiratory Rates and Head Displacement During Awake Resting-State fMRI for Days 2-8.

<p><b>A.</b> Respiratory rates significantly decreased between Day 2 and every other scanning session (Days 4-8) where the lowest respiratory rate was measured at Day 8. Respiratory rates between Day 2 and each of the other scanning days (Days 4, 6 and 8) were statistically compared using a 2-tailed unpaired, t-tests. (<b>Day 4</b>: t₁₀ = 2.42, p = 0.036; <b>Day 6</b>: t₁₂ = 2.52, p = 0.027; <b>Day 8</b>: t₁₂ = 3.64, p = 0.027) The ANOVA test revealed significant between day differences for respiratory rate (F_3,22 = 3.99, p = 0.021), but not for head displacement (F_3,22 = 0.88, p = 0.47). <b>B.</b> Head displacement was less than the size of the imaging voxel for all scanning sessions, but did not significantly differ between Days 2-8. The displacement is relative to a reference volume (Volume 60 of 120). Respiratory rates and head displacement between Day 2 and each of the other scanning days (Days 4, 6 and 8) were statistically compared using a 2-tailed unpaired, t-tests (<b>Day 4</b>: t₁₀ = 0.58, p = 0.57; <b>Day 6</b>: t₁₂ = 0.39, p = 0.70; <b>Day 8</b>: t₁₂ = 1.55, p = 0.15). Error bars represent s.e.m. Day 2 (N = 7); Day 4 (N = 5); Day 6 (N = 7); Day 8 (N = 7). # p<0.05 and ## p<0.005.</p

A-740003 [N-(1-{[(cyanoimino)(5quinolinylamino)methyl]amino}-2,2-dimethylpropyl)-2-(3,4-dimethoxyphenyl)acetamide], a novel and selective P2X7 receptor antagonist, dose-dependently reduces neuropathic pain in the rat

ABSTRACT ATP-sensitive P2X 7 receptors are localized on cells of immunological origin including glial cells in the central nervous system. Activation of P2X 7 receptors leads to rapid changes in intracellular calcium concentrations, release of the proinflammatory cytokine interleukin-1␤ (IL-1␤), and following prolonged agonist exposure, cytolytic plasma membrane pore formation. P2X 7 knockout mice show reduced inflammation as well as decreased nociceptive sensitivity following peripheral nerve injury. A-740003 (N-(1-{[(cyanoimino)(5-quinolinylamino) methyl] amino}-2,2-dimethylpropyl)-2-(3,4-dimethoxyphenyl)acetamide) is a novel competitive antagonist of P2X 7 receptors (IC 50 values ϭ 40 nM for human and 18 nM for rat) as measured by agonist-stimulated changes in intracellular calcium concentrations. A-740003 showed weak or no activity (IC 50 Ͼ 10 M) at other P2 receptors and an array of other neurotransmitter and peptide receptors, ion channels, reuptake sites, and enzymes. A-740003 potently blocked agonist-evoked IL-1␤ release (IC 50 ϭ 156 nM) and pore formation (IC 50 ϭ 92 nM) in differentiated human THP-1 cells. Systemic administration of A-740003 produced dose-dependent antinociception in a spinal nerve ligation model (ED 50 ϭ 19 mg/kg i.p.) in the rat. A-740003 also attenuated tactile allodynia in two other models of neuropathic pain, chronic constriction injury of the sciatic nerve and vincristine-induced neuropathy. In addition, A-740003 effectively reduced thermal hyperalgesia observed following intraplantar administration of carrageenan or complete Freund&apos;s adjuvant (ED 50 ϭ 38 -54 mg/kg i.p.). A-740003 was ineffective in attenuating acute thermal nociception in normal rats and did not alter motor performance at analgesic doses. These data demonstrate that selective blockade of P2X 7 receptors in vivo produces significant antinociception in animal models of neuropathic and inflammatory pain

Functional Connectivity in the Anxiety Network in Non-habituated, Awake Rats.

<p><b>A-B.</b> Functional connectivity amongst the anterior cingulate cortex and brain regions implicated in anxiety was significantly greater during the initial scanning session at Day 2. All statistical maps are superimposed upon an in-house, high-resolution rat anatomical template. <b>B.</b> Functional connectivity at Day 2 and Day 8 is quantified between the cingulate and anteroventral thalamus, and also with the posterior hypothalamic area. The ANOVA test yielded insignificant results for the cingulate-anteroventral thalamus (F_3,22 = 2.49, p = 0.087) and cingulate-posterior hypothalamic area (F_3,22 = 1.37, p = 0.27) functional interactions. Two-tailed, t-test did reveal significant differences particularly between Day 2 and Day 8 (cingulate-anteroventral thalamus- <b>Day 4</b>: t₁₀ = 1.91, p = 0.09; <b>Day 6</b>: t₁₂ = 1.31, p = 0.22; <b>Day 8</b>: t₁₂ = 2.26, p = 0.043). (cingulate-posterior hypothalamic area- <b>Day 4</b>: t₁₀ = 1.07, p = 0.30; <b>Day 6</b>: t₁₂ = 0.52, p = 0.61; <b>Day 8</b>: t₁₂ = 2.74, p = 0.018). All error bars represent s.e.m. Day 2 (N = 7); Day 4 (N = 5); Day 6 (N = 7); Day 8 (N = 7). # p<0.05 <b>C.</b> A significant inverse correlation was detected between the cingulate-default mode and cingulate-anxiety network structures. One statistical outlier (Z = 3.76) was detected using Grubb's test for outlier detection, and not included in correlation analysis. For N = 26, Z-critical  =  2.84 (p<0.05).</p