Serotonin Enhances Central Olfactory Neuron Responses to Female Sex Pheromone in the Male Sphinx MothManduca sexta

Abstract

In the brain of the sphinx moth Manduca sexta, sex-pheromonal information is processed in a prominent male-specific area of the antennal lobe called the macroglomerular complex (MGC). Whole-cell patch-clamp recordings from identified projection (output) neurons in the MGC have shown that serotonin [5-hydroxytryptamine (5-HT)] increases both the excitability of MGC projection 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 current (I(A)) and shifts its voltage for half-maximal inactivation to more negative potentials without affecting the half-maximal voltage for activation. This reduces the "window current" between the voltage activation and inactivation curves, decreasing the tonically active I(A) near the resting potential and causing the cell to depolarize. 5-HT's effect in this case is to decrease both the transient and resting K(+) conductance by modulating the same 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 significantly over a 24 hr period. Interestingly, 5-HT levels are highest at times when the moths are most active. We suggest that by controlling the responsiveness of antennal-lobe projection neurons to olfactory stimuli, 5-HT will have significant impact on the performance of odor-dependent behaviors.

The insecticide pymetrozine selectively affects chordotonal mechanoreceptors

“…Similarly, the serotonergic effects might result from the modulation of chordotonal sensillae, or of other sensory cells, by serotonin (e.g. Ramirez and Orchard, 1990;Kloppenburg et al, 1999) in a way mimicking and potentiating pymetrozine effects.…”

The cloning of one putative octopamine receptor and two putative serotonin receptors from the tobacco hawkmoth, Manduca sexta

“…The physiological and behavioral effects of 5HT on the olfactory system of moths have been extensively studied and it has been suggested that 5HT acts as a circadian modulator of olfactory sensitivity (Kloppenburg et al, 1999;Gatellier et al, 2004). In the AL of M. sexta, 5HT increases the excitability of intrinsic neurons by reducing two potassium conductances (Kloppenburg et al, 1999) and so to begin to study the cellular mechanisms by which 5HT has this effect, we cloned the 5HT receptors from M. sexta.…”

“…In the AL of M. sexta, 5HT increases the excitability of intrinsic neurons by reducing two potassium conductances (Kloppenburg et al, 1999) and so to begin to study the cellular mechanisms by which 5HT has this effect, we cloned the 5HT receptors from M. sexta. We found that while both of the Ms5HT1 receptors contain amino acid residues characteristic of 5HT receptors, they differ significantly in their amino-terminal and 3rd cytoplasmic loop region, which indicates that they are two distinct receptors.…”

“…Within the antennal lobe, serotonin appears to play a role in the maintenance of a circadian rhythm in the sensitivity of the moth olfactory system. Serotonin titers in the antennal lobes are highest during periods of peak activity (Gatellier et al, 2004;Kloppenburg et al, 1999) and exogenous serotonin increases the behavioral sensitivity of male Bombyx mori to female sex pheromone (Gatellier et al, 2004) and the excitability of antennal lobe neurons of Manduca sexta by reducing two potassium currents (Mercer et al, 1995;Kloppenburg et al, 1999). While the physiological and behavioral effects of serotonin in the lepidopteran antennal lobe are well established, little is known about the functional properties of the receptors mediating these effects.…”

Global and local modulatory supply to the mushroom bodies of the moth Spodoptera littoralis

“…Evidence suggests that it may influence olfactory learning in honey bees (Mercer and Menzel, 1982) and modulate the sensitivity and excitability of projection neurons in the antennal lobes of the moth Manduca sexta (Mercer et al, 1995;Kloppenburg et al, 1999).…”