INTERBULBAR RECIPROCAL INHIBITION IN FROG OLFACTION

Frogs were submitted in acute experiments to electrical stimulation of both ipsi- and contralateral homologous olfactory nerve bundles subse rving the dorsal olfactory mucosae. Mitral layer responses on one side were recorded. When both stimulations were given at different onset t imes and equal intensity, the ipsilateral mitral layer response fell t o a sharp minimum of 42 % when the contralateral stimulation was given 25 ms before the ipsilateral one. When both stimuli were adjusted for maximal temporal inhibition and the intensity of the contralateral st imulation was varied, the amplitude of the ipsilateral response decrea sed as the intensity of the contralateral stimulation increased until intensity equalization was obtained. This interbulbar inhibition was s uppressed either by sagittal transection through the interbulbar adhes ion or local infusion of bicuculline in the ipsilateral olfactory bulb . It was unaffected by transection of habenular commissure. These find ings suggest first, that the neuroreceptors located in the dorsal olfa ctory mucosae project to both olfactory bulbs, and second, that it exi sts at mitral layer level of the frog, a reciprocal inhibition which c an subserve frog orientation towards proximal odour source.