Brain research bulletin
-
Brain research bulletin · Oct 2006
Comparative StudyIndependent component model of the default-mode brain function: Assessing the impact of active thinking.
The "default-mode" network is an ensemble of cortical regions, which are typically deactivated during demanding cognitive tasks in functional magnetic resonance imaging (fMRI) studies. Using functional connectivity, this network can be conceptualized and studied as a "stand-alone" function or system. Regardless of the task, independent component analysis (ICA) produces a picture of the "default-mode" function even when the subject is performing a simple sensori-motor task or just resting in the scanner. ⋯ Nonetheless, a variable recruitment of the cingulate regions was evident, with greater extension of the anterior and lesser extension of the posterior clusters when switching from lower to higher working memory loads. A co-activation of the hippocampus was only found under no working memory load. As a generalization of our results, the variability of the default-mode pattern may link the default-mode system as a whole to cognition and may more directly support use of the ICA model for evaluating cognitive decline in brain disorders.
-
Brain research bulletin · Oct 2006
Comparative StudyChanges of K+ -Cl- cotransporter 2 (KCC2) and circuit activity in propofol-induced impairment of long-term potentiation in rat hippocampal slices.
Enhancing inhibition via gamma-aminobutyric acid type A (GABA(A)) receptors contributes to anesthetic-induced impairment of long-term potentiation (LTP) of excitatory synaptic transmission, which may account for general anesthesia-associated memory impairment (amnesia). The neuron-specific K+ -Cl- cotransporter 2 (KCC2) is necessary for fast synaptic inhibition via maintaining the low intracellular chloride concentration required for the hyperpolarizing actions of GABA via GABA(A) receptors. To explore a possible role of KCC2-dependent inhibition in anesthetic-induced impairment of LTP, we used field excitatory postsynaptic potentials (fEPSP) recording and immunoblotting to study the effect of propofol on LTP maintenance and KCC2 expression in CA1 region of rat hippocampal slices. ⋯ These propofol-induced effects were completely abolished by picrotoxin, a specific GABA(A) receptor-chloride channel blocker. Thus, enhancement of GABAergic inhibition and suppression of neuronal excitability may account for the sustained expression of KCC2 and the impairment of LTP by propofol. Together, this study supports a novel role for KCC2 in LTP expression and gives hints to a molecular mechanism, by which anesthetics might cause impairment of LTP.
-
Brain research bulletin · Oct 2006
Comparative StudyAntidepressant treatment reduces Fos-like immunoreactivity induced by swim stress in different columns of the periaqueductal gray matter.
Antidepressant treatment attenuates behavioral changes induced by uncontrollable stress. The periaqueductal gray matter (PAG) is proposed to be a brain site involved in the behavioral responses to uncontrollable stress and antidepressant effects. The main goal of the present study was to investigate the effect of antidepressant treatment on the pattern of neural activation of the PAG along its mediolateral and rostrocaudal subregions after a forced swim stress episode. ⋯ FLI in the PAG correlated positively with to the immobility time and negatively with to climbing behavior scored during the test. These results indicate that neurons in the PAG are activated by uncontrollable stress. Moreover, inhibitory action of antidepressants on this activity may be associated with the anti-immobility effects of these drugs in the FST.