RESUMEN
γ-aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the adult brain. However, electrophysiological findings indicate that GABA exerts excitation in dendrites of mature eorlieal neurons. Little is known about morphological basis of GABA-medi-ated excitation in dendrites of mature cortical neurons. The effect of activated GABAA receptors is mainly determined by intraceUular chloride ion, whose active influx is mainly mediated by Na+-K +-Cl- cotransporter isoform 1 (NKCC1) and exclusion is mainly executed by K+-Cl- cotransporter isoform 2 ( KCC2 ). In the present study, by using immunofluorescent double staining and fluorescent density analysis, the expression and distribution of NKCCI- and KCC2-immunoreactivities in the dendrite and soma of adult rat neocortical neurons were detected in vivo and in vitro. The present results showed that both cytoplasm and membrane of neuronal soma and dendrite expressed NKCC1, while KCC2 only expressed in membrane of soma and dendrite. The results also indicated that the dendrites rather than the somata of neurons expressed more NKCC1 in adult rat neocortex, while the level of KCC2 expression in the dendrite membrane was similar to that in the membrane of somata. The similar expression pattern of NKCC1 and KCC2 in the dendrites and the somata was also observed in neocortical neurons cultured for 20 days in vitro. The present results suggest that the more NKCC1 expreasion in dendrites may contribute to GABA-mediated excitation in neuronal dendrites of adult neocortex neurons.