The Journal of Neuroscience, April 15, 2003, 23(8):3373
Serotonin Induces Tonic Firing in Layer V Pyramidal Neurons of
Rat Prefrontal Cortex during Postnatal Development
Zhong-wei
Zhang
Centre de Recherche Université Laval Robert-Giffard,
Département de Psychiatrie, Faculté de Médicine,
Université Laval, Québec City, G1J 2G3, Canada
The effects of serotonin (5-HT) on neuronal activity were examined
during postnatal development in layer V pyramidal neurons of the rat
prefrontal cortex (PFC) in vitro. Whole-cell patch-clamp recordings were made in slices obtained from rats aged between postnatal day (P) 6 and P31. In P14 or younger neurons, bath
application of 5-HT (10 µM) induced a large
depolarization followed by tonic firing at 2-5 Hz. The excitatory
effects of 5-HT decreased rapidly after P14, so that by P21, 5-HT
produced a small depolarization or hyperpolarization without cell
firing. The excitatory effects of 5-HT at younger ages were attributed
to 5-HT2A receptors because the effects were mimicked by
the 5-HT2 agonist
-methyl-5-HT but not by the
5-HT3 agonist 1-(m-chlorophenyl)-biguanide, nor by the 5-HT2B/2C agonist 1-(3-chlorophenyl)piperazine, and
were blocked by the 5-HT2A antagonists ketanserin and
-phenyl-1-(2-phenylethyl)-4-piperidinemethanol. The excitatory
responses persisted in 0 [Ca2+]o and
high [Mg2+]o in the presence of TTX or
blockers of ionotropic glutamate receptors, suggesting that the effects
were mediated essentially by postsynaptic mechanisms. The responses to
5-HT involve a reduction of K+ conductance and an
enhancement of the hyperpolarization-activated Na+/K+ current. The developmental
decline of 5-HT-induced excitatory effects was associated with a
downregulation of 5-HT2A receptor function and a decrease
in the input resistance during early life. These results suggest that
5-HT is an important regulator of neuronal activity in the neonatal PFC
and may play a role in activity-dependent developmental processes.
Key words:
neocortex; slice; patch clamp; serotonin; excitation; development; postnatal
Copyright © 2003 Society for Neuroscience 0270-6474/03/2383373-12$05.00/0