Calcium responses to pheromones and plant odours in the antennal lobe of the male and female moth Heliothis virescens

In male moths, the primary olfactory integration centre, the antennal lobe, consists of two systems. The macroglomerular complex processes pheromone i nformation, while the ordinary glomeruli process plant odour information. F emales lack a macroglomerular complex. We measured the spatial representati on of odours using in-vivo optical recording. We found that: (1) pheromone substances elicited activity exclusively in the MGC. No response was found in female antennal lobes. (2) Plant odours elicited combinatorial activity patterns in the ordinary glomeruli in both males and females. No response w as found in the MGC of male moths. (3) A clean air puff often led to activi ty, in both males and females, suggesting that mechano-sensory information is also processed in the antennal lobe. (4) With an interstimulus interval of 5 or 10 s, strongly activated glomeruli were able to follow the temporal structure of the stimulus, while others lost their phase-locking. Some glo meruli showed "off" responses. These properties were odour dependent. This confirms and extends previous studies, showing the functional significance of the two subsystems for processing olfactory information. Pheromones are coded in a combinatorial manner within the macroglomerular complex, with ea ch glomerulus corresponding to one information channel. Plant odours are co ded in an across-glomeruli code in the ordinary glomeruli.