CHEMORECEPTION: LOCOMOTION AND ORIENTATION 



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Figure 10 Glomerular connections in (a) fishes and (b) mammals. From Allison (1953). 



important inhibitory system, which makes possible suppression of peripheral 

 information carried by the fila olfactoria when it arrives at the bulb. The 

 reciprocal, or two-way, synapses can either mediate the inhibition directly 

 on arrival of the impulses or they can be activated by granule cells when 

 these are stimulated via recurrent collaterals of mitral cells (Nicoll 1971; 

 Price 1968; Westecker 1970; Yamamoto 1961; Yamamoto and Yamamoto 

 1962). Synaptic membrane complexes on dendritic terminals of the granule 

 cells, mentioned by Andres, are probably related with those inhibitory 

 functions. 



The fact that the olfactory cell axons contain varying numbers of micro- 

 tubules (2 to 18) again suggests functional differences between olfactory 

 receptors; this may be related to different odor discriminatory properties of 

 these cells. 



The great similarity in cytoarchitecture of the olfactory bulb in all verte- 

 brates is paralleled in its electrophysiological characteristics. Orthodromic 

 stimulation produces in the bulb an electrical response that has three parts 

 (Bruckmoser 1973): the impulse from the olfactory fila, the response of the 

 mitral cells, and inhibitory activity by the granule cells. 



There is general agreement that much of the processing of olfactory in- 

 formation occurs in the bulbs. In the rabbit, for example, the glomeruli seem 

 to behave as individual discriminators; specific odors may stimulate only 

 some glomeruli (Leveteau and MacLeod 1969). Much less is known about 

 such functional detail in fish, but the evidence indicates that the more caudal 

 telencephalon receives from the bulb highly processed information, mainly 

 through the axons of the mitral cells, bundled into the lateral olfactory tract. 

 The telencephalic region in Scyliorhinus which receives this information is 



