RESUMEN
Transient or lasting increases in glucocorticoids accompany deficits in hippocampus-dependent memory formation. Recent data indicate that the formation and consolidation of declarative and spatial memory are mechanistically related to different patterns of hippocampal network oscillations. These include gamma oscillations during memory acquisition and the faster ripple oscillations (approximately 200 Hz) during subsequent memory consolidation. We therefore analysed the effects of acutely applied glucocorticoids on network activity in mouse hippocampal slices. Evoked field population spikes and paired-pulse responses were largely unaltered by corticosterone or cortisol, respectively, despite a slight increase in maximal population spike amplitude by 10 microm corticosterone. Several characteristics of sharp waves and superimposed ripple oscillations were affected by glucocorticoids, most prominently the frequency of spontaneously occurring sharp waves. At 0.1 microm, corticosterone increased this frequency, whereas maximal (10 microm) concentrations led to a reduction. In addition, gamma oscillations became slightly faster and less regular in the presence of high doses of corticosteroids. The present study describes acute effects of glucocorticoids on sharp wave-ripple complexes and gamma oscillations in mouse hippocampal slices, revealing a potential background for memory deficits in the presence of elevated levels of these hormones.
Asunto(s)
Glucocorticoides/farmacología , Hipocampo/efectos de los fármacos , Memoria/efectos de los fármacos , Red Nerviosa/efectos de los fármacos , Potenciales de Acción/efectos de los fármacos , Animales , Relojes Biológicos/efectos de los fármacos , Corticosterona/farmacología , Relación Dosis-Respuesta a Droga , Hipocampo/fisiología , Masculino , Trastornos de la Memoria/inducido químicamente , Ratones , Ratones Endogámicos C57BL , Red Nerviosa/fisiología , Plasticidad Neuronal/efectos de los fármacosRESUMEN
The substitution of thyrectomized patients with carcinoma of the thyroid with L-thyroxin has advantages compared to a substitution with triiodothyronine, 200 mug T4/d are sufficient to obtain a negative TRH test in most patients. For security it is suggested to performe a general substitution of these patients with 300 mug T4/d. This dose is very well tolerated. To high doses of substitution cause a "damage" of the thyreotrop in a part of the patients. This is demonstrated by a transient thyreotropic insufficiency after withdrawal of the substitution. The results demonstrated here suggest that the central suppression of TSH secretion is better correlated with plasma T4 than plasma T3 levels.
