High levels of cortisol in blood are frequently observed in patients with major depressive disorders and increased cortisol level induces depressivelike symptoms in animal models. However, it is still unclear whether maternal cortisol level during pregnancy is a critical factor resulting in neuropsychiatric disorders in offspring. In this study, we increased cortisol level in rats by repetitively injecting corticosterone subcutaneously (Corti. Mom, 20 mg/kg/day) during pregnancy and evaluated the behavioral patterns of their pups (Corti.Pups) via forced swimming (FS), open field (OF), elevated plus maze (EPM) and Morris water maze (MWM) tests during the immediate post-weaning period (postnatal day 21 to 25). In results, corticosterone significantly increased plasma cortisol levels in both Corti.Moms and Corti.Pups. Unlike depressive animal models, Corti.Pups showed higher hyperactive behaviors in the FS and OF tests than normal pups (Nor.Pups) born from rats (Nor.Moms) treated with saline. Furthermore, Corti.Pups spent more time and traveled longer distance in the open arms of EPM test, exhibiting higher extremity. These patterns were consistent with behavioral symptoms observed in animal models of attention deficit hyperactivity disorder (ADHD), which is characterized by hyperactivity, impulsivity, and inattention. Additionally, Corti.Pups swam longer and farther to escape in MWM test, showing cognitive declines associated with attention deficit. Our findings provide evidence that maternal cortisol level during pregnancy may affect the neuroendocrine regulation and the brain development of offspring, resulting in heterogeneous developmental brain disorders such as ADHD.

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A-type K channels (I channels) contribute to learning and memory mechanisms by regulating neuronal excitabilities in the CNS, and their expression level is targeted by Ca influx via synaptic NMDA receptors (NMDARs) during long-term potentiation (LTP). However, it is not clear how local synaptic Ca changes induce I downregulation throughout the neuron, extending from the active synapse to the soma. In this study, we tested if two major receptors of endoplasmic reticulum (ER), ryanodine (RyRs), and IP (IP R) receptors, are involved in Ca -mediated I downregulation in cultured hippocampal neurons of rats. The downregulation of I channels was induced by doubling the Ca concentration in culture media (3.6 mM for 24 hrs) or treating with glycine (200 μM for 3 min) to induce chemical LTP (cLTP), and the changes in I peaks were measured electrophysiologically by a whole-cell patch. We confirmed that Ca or glycine treatment significantly reduced I peaks and that their effects were abolished by blocking NMDARs or voltage-dependent Ca channels (VDCCs). In this cellular processing, blocking RyRs (by ryanodine, 10 μM) but not IP Rs (by 2APB, 100 μM) completely abolished I downregulation, and the LTP observed in hippocampal slices was more diminished by ryanodine rather than 2APB. Furthermore, blocking RyRs also reduced Ca -mediated PKA activation, indicating that sequential signaling cascades, including the ER and PKA, are involved in regulating I downregulation. These results strongly suggest a possibility that RyR contribution and mediated I downregulation are required to regulate membrane excitability as well as synaptic plasticity in CA3-CA1 connections of the hippocampus. © 2017 Wiley Periodicals, Inc.

Excessive influx and the subsequent rapid cytosolic elevation of Ca2+ in neurons is the major cause to induce hyperexcitability and irreversible cell damage although it is an essential ion for cellular signalings. Therefore, most neurons exhibit several cellular mechanisms to homeostatically regulate cytosolic Ca2+ level in normal as well as pathological conditions. Delayed rectifier K+ channels (IDR channels) play a role to suppress membrane excitability by inducing K+ outflow in various conditions, indicating their potential role in preventing pathogenic conditions and cell damage under Ca2+-mediated excitotoxic conditions. In the present study, we electrophysiologically evaluated the response of IDR channels to hyperexcitable conditions induced by high Ca2+ pretreatment (3.6 mM, for 24 hours) in cultured hippocampal neurons. In results, high Ca2+-treatment significantly increased the amplitude of IDR without changes of gating kinetics. Nimodipine but not APV blocked Ca2+-induced IDR enhancement, confirming that the change of IDR might be targeted by Ca2+ influx through voltage-dependent Ca2+ channels (VDCCs) rather than NMDA receptors (NMDARs). The VDCC-mediated IDR enhancement was not affected by either Ca2+-induced Ca2+ release (CICR) or small conductance Ca2+-activated K+ channels (SK channels). Furthermore, PP2 but not H89 completely abolished IDR enhancement under high Ca2+ condition, indicating that the activation of Src family tyrosine kinases (SFKs) is required for Ca2+-mediated IDR enhancement. Thus, SFKs may be sensitive to excessive Ca2+ influx through VDCCs and enhance IDR to activate a neuroprotective mechanism against Ca2+-mediated hyperexcitability in neurons.