100 



DIETRICH SCHNEIDER 



transmitter substance which, in the post-fibre, ehcits membrane effects. 

 In the synapse, the transmitter (e.g. acetylchoHne) has to bridge over a 

 synaptic cleft of 500A at a maximum ; in Bombyx the " transmitter " 

 (Bombykol) has to bridge over a very much larger distance. It is not 

 clear how far reaching such a comparison is, because the properties of the 



pre -fiber 



Acetylcholine 



post- fiber 



EMITTER 



TRANSMITTER 



RECEPTOR 



Bombyx female 

 lure gland 

 cell 



Bombykol 



Bombyx male 

 olfactory 

 receptor cell 



Fig. 10. Chemical information transfer in two highly specialized systems : 

 (1) pre- and postsynaptic cholinergic nerve fibres ; (2) Bombyx female and male. 



post-synaptic membrane and the olfactory receptor membrane have not 

 been sufficiently worked out. Our knowledge of metabolic processes 

 involved in the production and breakdown of synaptic transmitters is 

 much more extensive than our knowledge of sexual attraction in Bombyx 

 and Port/ietria, where only the transmitter is known with certainty. 



CONCLUSION 



With electrophysiological methods it was possible to work out some 

 details of olfactory receptor function in a few coleoptera and lepidoptera. 

 Single unit olfactory receptors studied so far are of the sensillum basi- 

 conicum type. The first detectable electrical reaction of the receptor is a 

 slow, graded receptor potential. Depolarization of the receptor membrane 

 and nerve impulses are observed. In beetles at least, the receptor potential 

 due to certain odours may be hyper-polarization which consequently 

 blocks impulse generation. 



Summated receptor potentials of a number of simultaneously active 

 olfactory units are probably the main cause of a slow potential called the 

 " electroantennogram ". Using this response as a test, the effects of sexual 

 attractants on antennae of male Porthetria dispar and Bombyx mori have 

 been checked over a wide concentration range. The response as the 

 logarithm of the stimulating concentration rises over a certain range. In 

 Bombyx, however, there is only a slight increase of response between 

 10" 10 and lO'Vg of lure substance. In this range the animal may not be 



