RESUMO
In humans and experimental animals, structural and functional changes in neural circuits can accompany the development of epilepsy. In the dentate gyrus, seizures enhance adult neurogenesis, but it is unclear to what extent newborn granule cells participate in seizure-induced synaptic reorganization. During the first weeks of their existence, mouse newborn granule cells labeled with enhanced green fluorescent protein have only short dendrites that lack excitatory input. We report that pilocarpine-induced seizures accelerated the morphological development of labeled granule cells, causing their dendrites to extend through the molecular layer. In whole-cell recordings 5-16 d after seizure induction, perforant-path stimulation now evoked glutamatergic input to newborn granule cells. These synaptic responses were mediated by monosynaptic as well as recurrent polysynaptic input. Thus, seizures facilitated functional integration of adult-generated granule cells. One month later, subsequent generations of newborn cells also showed alterations in dendrite morphology, suggesting persistent effects of seizures on granule cell maturation. The sensitivity of newborn granule cells to seizures could contribute to hyperexcitability during the latent period.
Assuntos
Dendritos/ultraestrutura , Convulsões/patologia , Animais , Animais Recém-Nascidos , Divisão Celular , Cruzamentos Genéticos , Dendritos/efeitos dos fármacos , Feminino , Proteínas de Fluorescência Verde/genética , Humanos , Masculino , Camundongos , Camundongos Transgênicos , Pilocarpina , Convulsões/induzido quimicamenteRESUMO
Neurogenesis in the dentate gyrus begins before birth but then continues into adulthood. Consequently, many newborn granule cells must integrate into a preexisting hippocampal network. Little is known about the timing of this process or the characteristics of the first established synapses. We used mice that transiently express enhanced green fluorescent protein in newborn granule cells to examine their synaptic input. Although newborn granule cells had functional glutamate receptors, evoked and spontaneous synaptic currents were exclusively GABAergic with immature characteristics including slow rise and decay phases and depolarized reversal potentials. Synaptic currents in newborn granule cells were relatively insensitive to the GABA(A) receptor modulator zolpidem compared with neighboring mature granule cells. Consistent with the kinetics and pharmacology, newborn granule cells isolated by fluorescent cell sorting lacked the alpha1 GABA(A) receptor subunit. Our results indicate that newborn granule cells initially receive only GABAergic synapses even in the adult.
