Antennal lobe responses

The results discusssed above suggest that information about pheromones and about host- and food volatiles is generally detected and transmitted via different primary neurons to the CNS, emd in principle by the use of two different mechanisms. In most insect species, it appears that pheromone receptor cells, each containing one type of membrane receptor, transfer information about a particular compound to CNS via a labeled line system (Boeckh, 1980). This 

In the case of host and food volatiles another mechanism (across-fiber pattern) is suggested (Boeckh, 1980). Here, the key information about the quality of a single host volatile is apparently transmitted to the CNS via over-lapping lines. However, it is also possible that information about certain host volatiles (as about pheromones) may be mediated via specialized cells and the labeled line mechanism. In addition to these two mechanisms, temporal response pattern may also modify the coding process (Boeckh, 1980). 

Recordings from antennal lobe neurons of Antherea sp. demonstrated that neurons responding to pheromones were located in the medial cluster, while no neurons studied in the lateral cluster responded to these compounds (Boeckh and Boeckh, 1979). Responses to pheromones were exclusively excitatory with a phasic-tonic pattern imposed upon a low resting activity (ca 1 imps ). Responses were elicited exclusively by stimulation with sex pheromones on the ipsilateral antennae. All central neurons responding to pheromones were activated by both components of their respective pheromone blends in the two Antherea species. Only a quantitative difference in the effect on the neurons 

---

Galizia, C. G., Sachse, S. and Mustaparta, H. (2000). Calcium responses to pheromones and plant odours in the antennal lobe of the male and female moth Heliothis virescens. Journal of Comparative Physiology A 186 1049-1063. 

Axons originating in sensilla that are responsive to food odorants and those that originate in sex pheromone-responsive neurons terminate in different glomeruli, the first synaptic relay station within the antennal lobe (Boeckh and Ernst,... 

Matsumoto S. and Hildebrand J. (1981) Olfactory mechanisms in the moth Manduca sexta response characteristics and morphology of central neurons in the antennal lobes. Proc. R. Soc. London Ser. B 213, 249-277. 

Sun X. J., Tolbert L. P. and Hildebrand J. G. (1997) Synaptic organization of the uniglomerular projection neurons of the antennal lobe of the moth Manduca sexta a laser scanning confocal and electron microscopic study. J. Comp. Neurol. 379, 2-20. Takken W., van Loon J. J. A. and Adam W. (2001) Inhibition of host-seeking response and olfactory responsiveness in Anopheles gambiae following blood feeding. J. Insect. Physiol. 47, 303-310. 

Age and hormone-level dependent plasticity in antennal lobe neural responses... 

Figure 24.3 Temporal analysis of responses measured simultaneously in five different antennal lobe neurons in the moth Manduca sexta. The matrices show patterns of neural synchrony evoked by either of two pheromone components or a binary mixture at two concentrations. The number of synchronous events was averaged over 20 trials and calculated for 500 ms from stimulus onset. The gray scale ranges from 0 to 3.8 coincident spikes per stimulus. The horizontal displays below the matrices show the averaged spiking rate in each single neuron (gray scale ranges from 0 to 5.5 spikes per stimulus period). Neural synchrony was influenced not only by the odor quality but also by both stimulus intensity and blend interactions (redrawn from Christensen eta ., 2000).

Figure 24.4 Gray-scaled signals of optical recordings of calcium activity from the antennal lobe of the moth Helicoverpa zea. A, B and C show thresholded (>50 percent of maximum) responses to the pheromone components Z11-16 Ald and Z9-16 Ald and a behavioral antagonist Z11-16 Ac, respectively. D A schematic figure of the organization of the macroglomerular complex in H. zea (from Vickers et al., 1998). The position of the glomeruli coincides with the foci of calcium responses, i.e. response to Z11-16 Ald takes place in the cumulus, Z9-16 Ald in the DM-P glomerulus and Z11-16 Ac in the DM-A glomerulus. These activity patterns corroborate the innervation patterns of functionally identified projection neurons (redrawn from Vickers et al., 1998).

Carlsson M. A. and Hansson B. S. (2003) Dose-response characteristics of glomerular activity in the moth antennal lobe. Chem. Senses, (in press). 

Martini S, Silvotti L, Shirazi A, Ryba NJP, Hrindelli R (2001) Co-expression of putative pheromone receptors in the sensory neurons of the vomeronasal organ. J Neurosci 21 843-848 Meijerink J, Carlsson MA, Hansson BS (2003) Spatial representation of odorant structure in the moth antennal lobe a study of structure-response relationships at low doses. J Comp Neurol 467 11-21... 

The presence of different receptor neuron types forms the basis for detection of and discrimination among odorants in the environment. In addition, important processing of the information takes place in the brain, resulting in the behavioral responses. The three olfactory areas of the insect brain are the antennal lobe, the mushroom bodies (important in learning and memory), and the lateral... 

Linster, C., Masson, C., Kerszberg, M., Personnaz, L., Dreyfus, G. Computational diversity in a formal model of the insect olfactory macroglomerulus. Neural Comput. 5, 228-241 (1993) Linster, C., Smith, B.H. A computational model of the response of honey bee antennal lobe circuitry to odor mixtures Overshadowing, blocking and unblocking can arise from lateral inhibition. Behav. Brain Res. 87, 1-14 (1997)... 

The extreme sensitivity of the receptor neurons is combined with a most efficient processing of their responses by the central nervous system. Via the axons of the receptor neurons the nerve impulses are conducted to the antennal lobe, the first synaptic station of the central olfactory pathway in insects. The axons of the pheromone receptor neurons terminate on local interneurons and projection neurons (PN) of the macroglomerular complex (MGC) (Hildebrand 1996). The silk moth has... 

---