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Abstract
We compared 5-hydroxytryptamine (5-HT), norepinephrine and dopamine for their efficacy
at increasing excitatory postsynaptic current frequency in layer V pyramidal cells
from rat medial prefrontal cortical slices. 5-HT, norepinephrine and dopamine increased
the excitatory postsynaptic current frequency by 15.9-, 4.5- and 1.7-fold, respectively.
Similar to previous results with 5-HT-induced excitatory postsynaptic currents, blockade
of mu-opioid receptors, of alpha-amino-3-hydroxy-5-methylisoxazole-4-proprionic acid
(AMPA) receptors and fast Na+ channels suppressed the norepinephrine-induced excitatory
postsynaptic currents. The norepinephrine-induced, and in most cases, the dopamine-induced
increase in excitatory postsynaptic current frequency was blocked by the alpha1-adrenoceptor
antagonist prazosin while the alpha2-adrenoceptor antagonist yohimbine did not block
either the norepinephrine- or the 5-HT-induced increase in excitatory postsynaptic
currents frequency. The potency of three 5-HT2 receptor antagonists with varying selectivity
for 5-HT2A/2B/2C receptors tested against the 5-HT-induced increase in excitatory
postsynaptic current frequency are in agreement with the affinity of these drugs for
the 5-HT2A receptor. These findings suggest that 5-HT2A receptor or alpha1-adrenoceptor
activation enhance neurotransmitter release from a similar subset of glutamate terminals
that innervate apical dendrites of layer V pyramidal cells.