Electrical impedance myography detects dystrophin-related muscle changes in mdx mice.

BACKGROUND: The lack of functional dystrophin protein in Duchenne muscular dystrophy (DMD) causes chronic skeletal muscle inflammation and degeneration. Therefore, the restoration of functional dystrophin levels is a fundamental approach for DMD therapy. Electrical impedance myography (EIM) is an emerging tool that provides noninvasive monitoring of muscle conditions and has been suggested as a treatment response biomarker in diverse indications. Although magnetic resonance imaging (MRI) of skeletal muscles has become a standard measurement in clinical trials for DMD, EIM offers distinct advantages, such as portability, user-friendliness, and reduced cost, allowing for remote monitoring of disease progression or response to therapy. To investigate the potential of EIM as a biomarker for DMD, we compared longitudinal EIM data with MRI/histopathological data from an X-linked muscular dystrophy (mdx) mouse model of DMD. In addition, we investigated whether EIM could detect dystrophin-related changes in muscles using antisense-mediated exon skipping in mdx mice. METHODS: The MRI data for muscle T2, the magnetic resonance spectroscopy (MRS) data for fat fraction, and three EIM parameters with histopathology were longitudinally obtained from the hindlimb muscles of wild-type (WT) and mdx mice. In the EIM study, a cell-penetrating peptide (Pip9b2) conjugated antisense phosphorodiamidate morpholino oligomer (PPMO), designed to induce exon-skipping and restore functional dystrophin production, was administered intravenously to mdx mice. RESULTS: MRI imaging in mdx mice showed higher T2 intensity at 6 weeks of age in hindlimb muscles compared to WT mice, which decreased at ≥ 9 weeks of age. In contrast, EIM reactance began to decline at 12 weeks of age, with peak reduction at 18 weeks of age in mdx mice. This decline was associated with myofiber atrophy and connective tissue infiltration in the skeletal muscles. Repeated dosing of PPMO (10 mg/kg, 4 times every 2 weeks) in mdx mice led to an increase in muscular dystrophin protein and reversed the decrease in EIM reactance. CONCLUSIONS: These findings suggest that muscle T2 MRI is sensitive to the early inflammatory response associated with dystrophin deficiency, whereas EIM provides a valuable biomarker for the noninvasive monitoring of subsequent changes in skeletal muscle composition. Furthermore, EIM reactance has the potential to monitor dystrophin-deficient muscle abnormalities and their recovery in response to antisense-mediated exon skipping.

Abnormal habenula functional connectivity characterizes treatment-resistant depression.

BACKGROUND: A significant proportion of patients with major depressive disorder are resistant to antidepressant medication and psychological treatments. A core symptom of treatment-resistant depression (TRD) is anhedonia, or the inability to feel pleasure, which has been attributed to disrupted habenula function - a component of the reward network. This study aimed to map detailed neural circuitry architecture related to the habenula to identify neural mechanisms of TRD. METHODS: 35 TRD patients, 35 patients with treatment-sensitive depression (TSD), and 38 healthy controls (HC) underwent resting-state functional magnetic resonance imaging. Functional connectivity analyses were performed using the left and right habenula as seed regions of interest, and the three groups were compared using whole-brain voxel-wise comparisons. RESULTS: The TRD group demonstrated hyperconnectivity of the left habenula to the left precuneus cortex and the right precentral gyrus, compared to the TSD group, and to the right precuneus cortex, compared to the TSD and HC groups. In contrast, TSD demonstrated hypoconnectivity than HC for both connectivity measures. These connectivity values were significantly higher in patients with a history of suicidal ideation. CONCLUSIONS: This study provides evidence that, unlike TSD, TRD is characterized by hyperconnectivity of the left habenula particularly with regions of the default mode network. An increased interplay between reward and default mode networks is linked to suicidality and could be a possible mechanism for anhedonia in hard to treat depression.

Characterization of CRF1 receptor antagonists with differential peripheral vs central actions in CRF challenge in rats.

The aim of this study was to investigate peripheral and central roles of corticotropin-releasing factor (CRF) in endocrinological and behavioral changes. Plasma adrenocorticotropin (ACTH) concentration was measured as an activity of hypothalamic-pituitary-adrenal (HPA) axis. As behavioral changes, locomotion and anxiety behavior were measured after CRF challenge intravenously (i.v.) for the peripheral administration or intracerebroventricularly (i.c.v.) for the central administration. Plasma ACTH concentration was significantly increased by both administration routes of CRF; however, hyperlocomotion and anxiety behavior were induced only by the i.c.v. administration. In the drug discovery of CRF1 receptor antagonists, we identified two types of compounds, Compound A and Compound B, which antagonized peripheral CRF-induced HPA axis activation to the same extent, but showed different effects on the central CRF signal. These had similar in vitro CRF1 receptor binding affinities (15 and 10nM) and functional activities in reporter gene assay (15 and 9.5nM). In the ex vivo binding assays using tissues of the pituitary, oral treatment with Compound A and Compound B at 10mg/kg inhibited [125I]-CRF binding, whereas in the assay using tissues of the frontal cortex, treatment of Compound A but not Compound B inhibited [125I]-CRF binding, indicating that only Compound A inhibited central [125I]-CRF binding. In the peripheral CRF challenge, increase in plasma ACTH concentration was significantly suppressed by both Compound A and Compound B. In contrast, Compound A inhibited the increase in locomotion induced by the central CRF challenge while Compound B did not. Compound A also reduced central CRF challenge-induced anxiety behavior and c-fos immunoreactivity in the cortex and the hypothalamic paraventricular nucleus. These results indicate that the central CRF signal, rather than the peripheral CRF signal would be related to anxiety and other behavioral changes, and CRF1 receptor antagonism in the central nervous system may be critical for identifying drug candidates for anxiety and mood disorders.

TAK-063, a phosphodiesterase 10A inhibitor, modulates neuronal activity in various brain regions in phMRI and EEG studies with and without ketamine challenge.

TAK-063 is a selective phosphodiesterase 10A (PDE10A) inhibitor that produces potent antipsychotic-like and pro-cognitive effects at 0.3mg/kg (26% PDE10A occupancy in rats) or higher in rodents through the balanced activation of the direct and indirect pathways of striatal medium spiny neurons (MSNs). In this study, we evaluated the specific binding of TAK-063 using in vitro autoradiography (ARG) and the modulation of brain activity using pharmacological magnetic resonance imaging (phMRI) and electroencephalography (EEG). [3H]TAK-063 significantly accumulated in the caudate-putamen (CPu), ventral pallidum (VP), substantia nigra (SN), hippocampus (Hipp), and amygdala (Amy), but not in the frontal cortex (Fcx), brainstem (Bs), or cerebellum (Cb) in an ARG study using rat brain sections. [3H]TAK-063 accumulation in the CPu was more than eighteen-fold higher than that in the Hipp and Amy. TAK-063 at 0.3mg/kg increased the blood oxygenation level-dependent (BOLD) signal in the striatum and Amy, and decreased it in the Fcx in a phMRI study with anesthetized rats. TAK-063 at 0.3mg/kg significantly reduced the ketamine-induced increase in EEG gamma power both in awake and anesthetized rats. TAK-063 at 0.2mg/kg (35% PDE10A occupancy in monkeys) also reduced the ketamine-induced increase in EEG gamma power in awake monkeys. In line with the EEG data, TAK-063 at 0.3mg/kg reversed the ketamine-induced BOLD signal changes in the cortex, Bs, and Cb in a phMRI study with anesthetized rats. These data suggest that TAK-063 at about 30% PDE10A occupancy modulates activities of multiple brain regions through activation of neuronal circuits in rats and monkeys.

Brown Norway rats, a putative schizophrenia model, show increased electroencephalographic activity at rest and decreased event-related potential amplitude, power, and coherence in the auditory sensory gating paradigm.

In recent schizophrenia clinical research, electroencephalographic (EEG) oscillatory activities induced by a sensory stimulus or behavioral tasks have gained considerable interest as functional and pathophysiological biomarkers. The Brown Norway (BN) rat is a putative schizophrenia model that shows naturally low sensorimotor gating and deficits in cognitive performance, although other phenotypes have not been studied. The present study aimed to investigate the neurophysiological features of BN rats, particularly EEG/event-related potential (ERP). EEG activity was recorded at rest and during the auditory sensory gating paradigm under an awake, freely moving condition. Frequency and ERP analysis were performed along with time-frequency analysis of evoked power and intertrial coherence. Compared with Wistar-Kyoto rats, a well-documented control line, BN rats showed increased EEG power at rest, particularly in the theta and gamma ranges. In ERP analysis, BN rats showed reduced N40-P20 amplitude but normal sensory gating. The rats also showed reduced evoked power and intertrial coherence against auditory stimuli. These results suggest that BN rats show features of EEG/ERP measures clinically relevant to schizophrenia and may provide additional opportunities for translational research.

Different P50 sensory gating measures reflect different cognitive dysfunctions in schizophrenia.

The P50 is an early component of auditory evoked potentials and a measure of sensory gating deficits. This evoked potential component is thought to be an important endophenotype candidate for schizophrenia. Recent research suggests that instead of the P50 ratio, S1 and S2 amplitudes should be evaluated for sensory gating. However, no studies have focused on the relationship between cognitive dysfunction and P50 sensory gating deficits using S1 and S2 amplitudes. The purpose of the present study was to investigate the association between the P50 ratio (S2/S1), S1 and S2 amplitudes, and neuropsychological cognitive domains using stepwise multiple linear regression analyses. Results demonstrated a significant relationship between executive functioning and the P50 ratio and between sustained attention and S2 amplitude, respectively. Our findings suggest that the P50 ratio and S2 amplitude reflect distinct neurophysiological substrates associated with different cognitive functions.

Potentiation of NMDA receptor-mediated synaptic responses by microglia.

To study the influence of microglia on glutamatergic synaptic transmission in the acute phase of neuronal injury, we first examined the effects of primary cultured microglia transferred onto the organotypic cortical slice cultures. In these microglia-transferred cortical slice cultures, stimulation of the subcortical white matter induced fast excitatory postsynaptic potentials followed by N-methyl-D-aspartate (NMDA) receptor-mediated plateau-like potentials that were never observed in control slice cultures. A similar potentiation of NMDA receptor-mediated postsynaptic responses was also observed by an application of a microglial-conditioned medium (MCM, 10% v/v) in acute cortical slices. These effects of MCM disappeared after boiling or incubation with proteinase K. After fractionation of MCM by anion-exchange chromatography, the enhancing activity of each fraction was quantitated electrophysiologically. When each fraction was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the fraction 24 which showed the most potent enhancing activity on NMDA receptor-mediated responses contained a relatively strong protein band with a molecular mass of approximately 70 kDa. MCM also enhanced both glutamate- and NMDA-induced inward currents recorded from acutely isolated cortical neurons. It was also noted that glutamate and NMDA induced transient large inward currents during an application of MCM, which were never observed in the control condition. These observations strongly suggest that NMDA receptor-mediated responses can be potentiated by both heat- and protease-labile (presumably 70-kDa proteins) molecules released from microglia.

Proteases involved in long-term potentiation.

Much attention has been paid to proteases involved in long-term potentiation (LTP). Calpains, Ca-dependent cysteine proteases, have first been demonstrated to be the mediator of LTP by the proteolytic cleavage of fodrin, which allows glutamate receptors located deep in the postsynaptic membrane to move to the surface. It is now generally considered that calpain activation is necessary for LTP formation in the cleavage of substrates such as protein kinase Czeta, NMDA receptors, and the glutamate receptor-interacting protein. Recent studies have shown that serine proteases such as tissue-type plasminogen activator (tPA), thrombin, and neuropsin are involved in LTP. tPA contributes to LTP by both receptor-mediated activation of cAMP-dependent protein kinase and the cleavage of NMDA receptors. Thrombin induces a proteolytic activation of PAR-1, resulting in activation of protein kinase C, which reduces the voltage-dependent Mg2+ blockade of NMDA receptor-channels. On the other hand, neuropsin may act as a regulatory molecule in LTP via its proteolytic degradation of extracellular matrix protein such as fibronectin. In addition to such neuronal proteases, proteases secreted from microglia such as tPA may also contribute to LTP. The enzymatic activity of each protease is strictly regulated by endogenous inhibitors and other factors in the brain. Once activated, proteases can irreversibly cleave peptide bonds. After cleavage, some substrates are inactivated and others are activated to gain new functions. Therefore, the issue to identify substrates for each protease is very important to understand the molecular basis of LTP.