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 information, while the ordinary glomeruli process plant odour information. Females lack a macroglomerular complex. We measured the spatial representation 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 was found in the MGC of male moths. (3) A clean air puff often led to activity, 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 glomeruli 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 each glomerulus corresponding to one information channel. Plant odours are coded in an across-glomeruli code in the ordinary glomeruli.