The major excitatory neurotransmitter in the antennal lobe is acetylcholine, while the major inhibitory neurotransmitter is GABA. There is some evidence for the excitatory function of glutamate as well. In addition, the presence of neuromodulators such as biogenic amines (serotonin, octopamine, dopamine, histamine) and neuropeptides is also known [Berg et al., 2007]．Evidence also comes from the effect of exogenous serotonin [Kloppenburg & Mercer, 2008]．Brain serotonin levels vary in a circadian rhythm that has been shown to correlate with changes in behavioural sensitivity and exogenous serotonin increases the sensitivity of pheromone-sensitive antennal lobe projection neurons [Gatellier et al., 2004; Kloppenburg et al., 1999]．Physiological effects are similar for projection neurons of the ordinary glomeruli [Dacks et al., 2008]．This enhacing effect of serotonin was also shown at population level in response to electrical stimulation [Hill et al., 2003]．In the bee, histamine has been confirmed by immunohistochemistry and been shown to have an inhibitory effect [Sachse et al., 2006]. However, in the silkmoth, histamine could not be detected [Iwano et al., 2005]. There are thus possibly some differences between species.


　　　　　　　　


References


Berg BG, Schachtner J, Utz S, Homberg U (2007) Distribution of neuropeptides in the primary olfactory center of the heliothine moth Heliothis virescens. Cell Tissue Res 327:385-398.

Dacks AM, Christensen TA, Hildebrand JG (2008) Modulation of olfactory information processing in the antennal lobe of Manduca sexta by serotonin. J Neurophysiol 99:2077-2085.

Gatellier L, Nagao T and Kanzaki R (2004) Serotonin modifies the sensitivity of the male silkmoth to pheromone. J Exp Biol 207: 2487-2496

Hill ES, Okada K and Kanzaki R (2003) Visualization of modulatory effects of serotonin in the silkmoth antennal lobe. J Exp Biol 206: 345-352

Iwano M and Kanzaki R (2005) Immunocytochemical identification of neuroactive substances in the antennal lobe of the male silkworm moth Bombyx mori. Zool Sci 22: 199-211

Kloppenburg P, Ferns D, Mercer AR (1999) Serotonin enhances central olfactory neuron responses to female sex pheromone in the male sphinx moth Manduca sexta. J Neurosci 19:8172-8181.

Kloppenburg P, Mercer AR (2008) Serotonin modulation of moth central olfactory neurons. Annu Rev Entomol 53:179-190.
Sachse S, Peele P, Silbering AF, Guhmann M, Galizia CG (2006) Role of histamine as a putative inhibitory transmitter in the honeybee antennal lobe. Front Zool 3:22.