6 research outputs found
Loss of Mecp2 causes atypical synaptic and molecular plasticity of parvalbumin-expressing interneurons reflecting rett syndrome–like sensorimotor defects
Rett syndrome (RTT) is caused in most cases by loss-of-function mutations in the X-linked gene encoding methyl CpG-binding protein 2 (MECP2). Understanding the pathological processes impacting sensory-motor control represents a major challenge for clinical management of individuals affected by RTT, but the underlying molecular and neuronal modifications remain unclear. We find that symptomatic male Mecp2 knockout (KO) mice show atypically elevated parvalbumin (PV) expression in both somatosensory (S1) and motor (M1) cortices together with excessive excitatory inputs converging onto PV-expressing interneurons (INs). In accordance, high-speed voltage-sensitive dye imaging shows reduced amplitude and spatial spread of synaptically induced neuronal depolarizations in S1 of Mecp2 KO mice. Moreover, motor learning-dependent changes of PV expression and structural synaptic plasticity typically occurring on PV+ INs in M1 are impaired in symptomatic Mecp2 KO mice. Finally, we find similar abnormalities of PV networks plasticity in symptomatic female Mecp2 heterozygous mice. These results indicate that in Mecp2 mutant mice the configuration of PV+ INs network is shifted toward an atypical plasticity state in relevant cortical areas compatible with the sensory-motor dysfunctions characteristics of RTT.Rett syndrome (RTT) is caused in most cases by loss-of-function mutations in the X-linked gene encoding methyl CpG-binding protein 2 (MECP2). Understanding the pathological processes impacting sensory-motor control represents a major challenge for clinical management of individuals affected by RTT, but the underlying molecular and neuronal modifications remain unclear. We find that symptomatic male Mecp2 knockout (KO) mice show atypically elevated parvalbumin (PV) expression in both somatosensory (S1) and motor (M1) cortices together with excessive excitatory inputs converging onto PV-expressing interneurons (INs). In accordance, high-speed voltage-sensitive dye imaging shows reduced amplitude and spatial spread of synaptically induced neuronal depolarizations in S1 of Mecp2 KO mice. Moreover, motor learning-dependent changes of PV expression and structural synaptic plasticity typically occurring on PV + INs in M1 are impaired in symptomatic Mecp2 KO mice. Finally, we find similar abnormalities of PV networks plasticity in symptomatic female Mecp2 heterozygous mice. These results indicate that in Mecp2 mutant mice the configuration of PV + INs network is shifted toward an atypical plasticity state in relevant cortical areas compatible with the sensory-motor dysfunctions characteristics of RTT
Effects of forced swimming stress on ERK and histone H3 phosphorylation in limbic areas of Roman high-and low-avoidance rats
Stressful events evoke molecular adaptations of neural circuits through chromatin remodeling and regulation of gene expression. However, the identity of the molecular pathways activated by stress in experimental models of depression is not fully understood. We investigated the effect of acute forced swimming (FS) on the phosphorylation of the extracellular signal-regulated kinase (ERK)1/2 (pERK) and histone H3 (pH3) in limbic brain areas of genetic models of vulnerability (RLA, Roman low-avoidance rats) and resistance (RHA, Roman high-avoidance rats) to stress-induced depression-like behavior. We demonstrate that FS markedly increased the density of pERK-positive neurons in the infralimbic (ILCx) and the prelimbic area (PrLCx) of the prefrontal cortex (PFCx), the nucleus accumbens, and the dorsal blade of the hippocampal dentate gyrus to the same extent in RLA and RHA rats. In addition, FS induced a significant increase in the intensity of pERK immunoreactivity (IR) in neurons of the PFCx in both rat lines. However, RHA rats showed stronger pERK-IR than RLA rats in the ILCx both under basal and stressed conditions. Moreover, the density of pH3-positive neurons was equally increased by FS in the PFCx of both rat lines. Interestingly, pH3-IR was higher in RHA than RLA rats in PrLCx and ILCx, either under basal conditions or upon FS. Finally, colocalization analysis showed that in the PFCx of both rat lines, almost all pERK-positive cells express pH3, whereas only 50% of the pH3-positive neurons is also pERK-positive. Moreover, FS increased the percentage of neurons that express exclusively pH3, but reduced the percentage of cells expressing exclusively pERK. These results suggest that (i) the distinctive patterns of FS-induced ERK and H3 phosphorylation in the PFCx of RHA and RLA rats may represent molecular signatures of the behavioural traits that distinguish the two lines and (ii) FS-induced H3 phosphorylation is, at least in part, ERK-independent
Differential effects of FS on the intensity of pH3 immunostaining in the PrLCx and the ILCx.
<p>(<b>A</b>) Representative high magnification images showing pH3 immunostaining in ILCx of RLA animals under basal conditions and after FS. Arrowheads indicate pH3-expressing neurons with different immunolabeling intensity (black arrowhead: higher intensity; white arrowhead: lower intensity). (<b>B</b>, <b>C</b>) Quantitative analysis of pH3-labeling intensity in PrLCx (<b>B</b>) and ILCx (<b>C</b>). PrLCx: RHA Bs = 0.06 ± 0.004; RLA Bs = 0.06 ± 0.004; RHA FS = 0.12 ± 0.005; RLA FS = 0.10 ± 0.009; two-way ANOVA: (line) F<sub>(1,18)</sub> = 4.93, p = 0.03<sup> $</sup>; (FS): F<sub>(1,18)</sub> = 154.81, p < 0.0001***; (line x FS interaction) F<sub>(1,18)</sub> = 1.26, n.s. Bonferroni <i>post-hoc</i> test FS p < 0.05<sup>§</sup>. Student’s t-test for independent samples: p < 0.05<sup>◊</sup>). (<b>D-G</b>) Quantitative analysis of pH3-labeling intensity distributions in the PrLCx (<b>D</b>, <b>E</b>) and the ILCx (<b>F</b>, <b>G</b>) of each experimental group. PrLCx χ<sup>2</sup> test: RHA Bs > RLA Bs, p < 0.05<sup>#</sup>; RHA FS > RLA FS, p < 0.001<sup>###</sup>; ILCx χ<sup>2</sup> test: RHA Bs > RLA Bs, p < 0.001<sup>###</sup>; RHA FS > RLA FS, p < 0.01<sup>##</sup>). Number of animals in each experimental group: RHA Bs, n = 6; RLA Bs, n = 6; RHA FS, n = 5; RLA FS, n = 5. Scale bar = 20 μm.</p
Effect of FS on pERK-immunostaining in the DG.
<p>(<b>A</b>) The red box indicates the brain region where the analysis was performed. The DG was further divided into dorsal (Db) and ventral (Vb) blades. (<b>B</b>) Representative micrographs of Db and Vb of the DG oriented as in (<b>A</b>). (<b>C</b>, <b>D</b>) Quantitative analysis of pERK immunostained cell density in the Db (<b>C</b>) and Vb (<b>D</b>) of the DG. Db: RHA Bs = 3.75 ± 1.09; RLA Bs = 3.02 ± 0.39; RHA FS = 9.69 ± 1.23; RLA FS = 9.37 ± 1.01; two-way ANOVA: (line) F<sub>(1,19)</sub> = 0.28, n.s.; (FS) F<sub>(1,19)</sub> = 37.16, p < 0.0001***; (line x FS interaction) F<sub>(1,19)</sub> = 0.04, n.s.; Vb: RHA Bs = 3.08 ± 0.68; RLA Bs = 2.83 ± 0.57; RHA FS = 4.72 ± 0.62; RLA FS = 3.50 ± 0.38; two-way ANOVA (line) F<sub>(1,19)</sub> = 1.54, n.s.; (FS): F<sub>(1,19)</sub> = 3.77, p = 0.06; (line x FS interaction) F<sub>(1,19)</sub> = 0.66, n.s.). Number of animals in each experimental group: RHA Bs, n = 6; RLA Bs, n = 6; RHA FS, n = 5; RLA FS, n = 5. Scale bar = 50 μm.</p
FS increases the phosphorylation of histone H3 in the PrLCx and ILCx of RLA and RHA rat lines.
<p>(<b>A</b> and <b>B</b>) Representative micrographs showing pH3 immunohistochemical labeling in the PrLCx (<b>A</b>) and the ILCx (<b>B</b>) of each experimental group. (<b>C</b>, <b>D</b>) Quantitative analysis of pH3 labeled cell density in PrLCx (<b>C</b>) and ILCx (<b>D</b>). PrLCx: RHA Bs = 109.8 ± 28.1; RLA Bs = 127.5 ± 13.4; RHA FS = 288.8 ± 44.6; RLA FS = 338.6 ± 30.7; two-way ANOVA: (line) F<sub>(1,18)</sub> = 1.17, n.s.; (FS) F<sub>(1,18)</sub> = 39.01, p < 0.0001***; (line x FS interaction) F<sub>(1,18)</sub> = 0.26, n.s.; ILCx: RHA Bs = 97.4 ± 23.7; RLA Bs = 100.8 ± 16.6; RHA FS = 202.1 ± 18.9; RLA FS = 214.0 ± 9.9; two-way ANOVA: (line) F<sub>(1,18)</sub> = 0.16, n.s.; (FS) F<sub>(1,18)</sub> = 32.76, p < 0.0001***; (line x FS interaction) F<sub>(1,18)</sub> = 0.05, n.s. Number of animals in each experimental group: RHA Bs, n = 6; RLA Bs, n = 6; RHA FS, n = 6; RLA FS, n = 5. Scale bar = 50 μm.</p
Effect of FS on the intensity of pERK expression in PFCx: peroxidase immunolabelling.
<p>(<b>A</b>) Representative micrographs showing pERK immunostaining in pyramidal neurons of the upper layers of the ILCx of RLA animals under basal condition and after FS. Arrowheads indicate pERK-expressing neurons with different level of intensity: black arrowhead at higher intensity and white arrowhead at lower intensity. (<b>B</b>, <b>C</b>) Quantitative analysis of pERK-labeling intensity in the PrLCx (<b>B</b>) and the ILCx (<b>C</b>). PrLCx: RHA Bs = 0.11 ± 0.02; RLA Bs = 0.10 ± 0.02; RHA FS = 0.16 ± 0.01; RLA FS = 0.12 ± 0.01; two-way ANOVA: (line) F<sub>(1,18)</sub> = 1.50, n.s.; (FS): F<sub>(1,18)</sub> = 3.74, p = 0.06; (line x FS interaction) F<sub>(1,18)</sub> = 1.45, n.s.); ILCx: RHA Bs = 0.13 ± 0.02; RLA Bs = 0.13 ± 0.02; RHA FS = 0.19 ± 0.02; RLA FS = 0,16 ± 0,02; two-way ANOVA: (line) F<sub>(1,18)</sub> = 0.51, n.s.; (FS): F<sub>(1,18)</sub> = 5.65, p = 0.03*; (line x FS interaction) F<sub>(1,18)</sub> = 0.32, n.s. Number of animals in each experimental group: RHA Bs, n = 6; RLA Bs, n = 6; RHA FS, n = 5; RLA FS, n = 5. Scale bar = 20 μm.</p