P. Kloppenburg et al., Serotonin enhances central olfactory neuron responses to female sex pheromone in the male sphinx moth Manduca sexta, J NEUROSC, 19(19), 1999, pp. 8172-8181
In the brain of the sphinx moth Manduca sexta, sex-pheromonal information i
s processed in a prominent male-specific area of the antennal lobe called t
he macroglomerular complex (MGC). Whole-cell patch-clamp recordings from id
entified projection (output) neurons in the MGC have shown that serotonin [
5-hydroxytryptamine (5-HT)] increases both the excitability of MGC projecti
on neurons and their responses to stimulation with pheromone. At least two
types of voltage-activated potassium currents in these cells are modulated
by 5-HT. 5-HT decreases the maximal conductance of a transient potassium cu
rrent (I-A) and shifts its voltage for half-maximal inactivation to more ne
gative potentials without affecting the half-maximal voltage for activation
. This reduces the "window current" between the voltage activation and inac
tivation curves, decreasing the tonically active I-A near the resting poten
tial and causing the cell to depolarize. 5-HT's effect in this case is to d
ecrease both the transient and resting K+ conductance by modulating the sam
e channel (I-A). 5-HT also decreases the maximal conductance of a sustained
potassium current [I-K(V)] without affecting its voltage dependence. Using
HPLC, we show also that levels of 5-HT in the antennal lobes fluctuate sig
nificantly over a 24 hr period. Interestingly, 5-HT levels are highest at t
imes when the moths are most active. We suggest that by controlling the res
ponsiveness of antennal-lobe projection neurons to olfactory stimuli, 5-HT
will have significant impact on the performance of odor-dependent behaviors
.