Circadian Disruptions in the Myshkin Mouse Model of Mania Are Independent of Deficits in Suprachiasmatic Molecular Clock Function.

BACKGROUND: Alterations in environmental light and intrinsic circadian function have strong associations with mood disorders. The neural origins underpinning these changes remain unclear, although genetic deficits in the molecular clock regularly render mice with altered mood-associated phenotypes. METHODS: A detailed circadian and light-associated behavioral characterization of the Na+/K+-ATPase α3 Myshkin (Myk/+) mouse model of mania was performed. Na+/K+-ATPase α3 does not reside within the core circadian molecular clockwork, but Myk/+ mice exhibit concomitant disruption in circadian rhythms and mood. The neural basis of this phenotype was investigated through molecular and electrophysiological dissection of the master circadian pacemaker, the suprachiasmatic nuclei (SCN). Light input and glutamatergic signaling to the SCN were concomitantly assessed through behavioral assays and calcium imaging. RESULTS: In vivo assays revealed several circadian abnormalities including lengthened period and instability of behavioral rhythms, and elevated metabolic rate. Grossly aberrant responses to light included accentuated resetting, accelerated re-entrainment, and an absence of locomotor suppression. Bioluminescent recording of circadian clock protein (PERIOD2) output from ex vivo SCN revealed no deficits in Myk/+ molecular clock function. Optic nerve crush rescued the circadian period of Myk/+ behavior, highlighting that afferent inputs are critical upstream mediators. Electrophysiological and calcium imaging SCN recordings demonstrated changes in the response to glutamatergic stimulation as well as the electrical output indicative of altered retinal input processing. CONCLUSIONS: The Myshkin model demonstrates profound circadian and light-responsive behavioral alterations independent of molecular clock disruption. Afferent light signaling drives behavioral changes and raises new mechanistic implications for circadian disruption in affective disorders.

Frequency and Duration of Adrenal Suppression Following Glucocorticoid Therapy in Children With Rheumatic Diseases.

OBJECTIVE: Adrenal suppression (AS), a glucocorticoid (GC) side effect with potentially significant morbidity, is poorly understood. The purpose of our study was to determine frequency, duration, and predictors of AS following a gradual taper of GC in children with rheumatic conditions. METHODS: A prospective, observational cohort study was conducted. All patients ages ≤16 years ready to discontinue GC after >4 weeks of therapy were included. Morning cortisol was tested 4 weeks after GC taper to physiologic doses and then repeatedly until normalization. GCs were subsequently discontinued and a low-dose adrenocorticotropic hormone stimulation test was performed. RESULTS: The study was completed by 31 of 39 patients. The median age was 12.9 years and median duration of GC therapy was 39.6 weeks. Seventeen patients (54.8%) had AS. Of the patients with AS, 50% showed recovery by 7 months. Two patients had persistent AS at 12 months and 1 patient at 2 years. A higher maximum GC dose was a significant predictor for the development of AS. CONCLUSION: More than 50% of our patients had AS after GC discontinuation, despite a gradual taper of GC. Stress steroids should be considered in children treated with long-term GC, even after steroid discontinuation, to prevent possible adrenal crisis.