BDNF-induced TrkB activation down-regulates the K+-Cl- cotransporter KCC2 and impairs neuronal Cl- extrusion.

Pathophysiological activity and various kinds of traumatic insults are known to have deleterious long-term effects on neuronal Cl- regulation, which can lead to a suppression of fast postsynaptic GABAergic responses. Brain-derived neurotrophic factor (BDNF) increases neuronal excitability through a conjunction of mechanisms that include regulation of the efficacy of GABAergic transmission. Here, we show that exposure of rat hippocampal slice cultures and acute slices to exogenous BDNF or neurotrophin-4 produces a TrkB-mediated fall in the neuron-specific K+-Cl- cotransporter KCC2 mRNA and protein, as well as a consequent impairment in neuronal Cl- extrusion capacity.

Postnatal development of rat hippocampal gamma rhythm in vivo.

Network oscillations in the gamma-frequency band (20-100 Hz) may have a central role in the timing and coordination of neural activity in the adult brain, yet their appearance in the course of development has remained unexplored. Moreover, electroencephalogram (EEG)-based classification of the vigilance states [active sleep (AS), quiet sleep (QS), or awake (W)] has been thought to be possible only after the second postnatal week. We now report the presence of spontaneous hippocampal gamma oscillations in the area CA3 of freely moving rats at postnatal days (P) 5-10.