Neuronal subthreshold excitability and firing behaviour are markedly influenced by the activation and deactivation of the somato-dendritic hyperpolarization-activated cation current (Ih). Here, we evaluated possible contributions of Ih to hyperexcitability in an animal model of absence seizures (WAG/Rij rats). We investigated pyramidal neurons of the somatosensory neocortex, the site of generation of spike-wave discharges. Ih-mediated functions in neurons from WAG/Rij rats, Wistar rats (sharing the same genetic background with WAG/Rij, but less epilepsy-prone) and ACI rats (an inbred strain, virtually free of seizures) were compared. We complemented whole-cell recordings from layer 2-3 pyramidal neurons with immunohistochemistry, Western blot and RT-PCR analysis of the h-channel subunits HCN1-4. The fast component of Ih activation in WAG/Rij neurons was significantly reduced (50% reduction in the h-current density) and four times slower than in neurons from nonepileptic Wistar or ACI rats. The results showing decreases in currents corresponded to a 34% reduction in HCN1 protein in the WAG/Rij compared to the Wistar neocortex, but HCN1 mRNA showed stable expression. The other three Ih subunit mRNAs and proteins (HCN2-4) were not affected. The alterations in Ih magnitude and kinetics of gating in WAG/Rij neurons may contribute to augmented excitatory postsynaptic potentials, the increase in their temporal summation and the facilitation of burst firing of these neurons because each of these effects could be mimicked by the selective Ih antagonist ZD 7288. We suggest that the deficit in Ih-mediated functions may contribute to the development and onset of spontaneously occurring hyperexcitability in a rat model of absence seizures.
SUMMARYPilocarpine-induced status epilepticus (SE) results in chronic spontaneous recurrent seizures resembling human temporal lobe epilepsy. In this and other experimental models, behaviorally monitored seizure frequency was suggested to vary in a circadian fashion, and to increase with time. We re-addressed those hypotheses using continuous video-electroencephalography (EEG) telemetry in rats with SE at 30 days of age. In 11 chronically epileptic animals monitored up to 300 days after SE in a fixed 12 h light/dark cycle, we found that seizure frequency did not correlate with circadian rhythm.
Aim: Depolarization-induced contraction of smooth muscle is thought to be mediated by Ca 2+ influx through voltage-gated L-type Ca 2+ channels. We describe a novel contraction mechanism that is independent of Ca 2+ entry. Methods: Pharmacological experiments were carried out on isolated rat gut longitudinal smooth muscle preparations, measuring isometric contraction strength upon high K + -induced depolarization. Results: Treatment with verapamil, which presumably leads to a conformational change in the channel, completely abolished K + -induced contraction, while residual contraction still occurred when Ca 2+ entry was blocked with Cd 2+ . These results were further confirmed by measuring intracellular Ca 2+ transients using Fura-2. Co-application of Cd 2+ and the ryanodine receptor blocker DHBP further reduced contraction, albeit incompletely. Additional blockage of either phospholipase C (U 73122) or inositol 1,4,5-trisphophate (IP 3 ) receptors (2-APB) abolished most contractions, while sole application of these blockers and Cd 2+ (without parallel ryanodine receptor manipulation) also resulted in incomplete contraction block. Conclusion: We conclude that there are parallel mechanisms of depolarization-induced smooth muscle contraction via (a) Ca 2+ entry and (b) Ca 2+ entry-independent, depolarization-induced Ca 2+ -release through ryanodine receptors and IP 3 , with the latter being dependent on phospholipase C activation.
Obesity is one of the most challenging diseases of the 21st century and is accompanied by behavioural disorders. Exercise, dietary adjustments, or time-restricted feeding are the only successful long-term treatments to date. Fibroblast growth factor 21 (FGF21) plays a key role in dietary regulation, but FGF21 resistance is prevalent in obesity. The aim of this study was to investigate in obese mice whether weight reduction leads to improved behaviour and whether these behavioural changes are associated with decreased plasma FGF21 levels. After establishing a model for diet-induced obesity, mice were subjected to three different interventions for weight reduction, namely dietary change, treadmill exercise, or time-restricted feeding. In this study, we demonstrated that only the combination of dietary change and treadmill exercise affected all parameters leading to a reduction in weight, fat, and FGF21, as well as less anxious behaviour, higher overall activity, and improved olfactory detection abilities. To investigate the interrelationship between FGF21 and behavioural parameters, feature selection algorithms were applied designating FGF21 and body weight as one of five highly weighted features. In conclusion, we concluded from the complementary methods that FGF21 can be considered as a potential biomarker for improved behaviour in obese mice after weight reduction.
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