Interbulbar reciprocal inhibition in frog olfaction

Frogs were submitted in acute experiments to electrical stimulation of both ipsi- and contralateral homologous olfactory nerve bundles subserving the dorsal olfactory mucosae. Mitral layer responses on one side were recorded. When both stimulations were given at different onset times and equal intensity, the ipsilateral mitral layer response fell to 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 stimulation was varied, the amplitude of the ipsilateral response decreased as the intensity of the contralateral stimulation increased until intensity equalization was obtained. This interbulbar inhibition was suppressed either by sagittal transection through the interbulbar adhesion or local infusion of bicuculline in the ipsilateral olfactory bulb. It was unaffected by transection of habenular commissure. These findings suggest first, that the neuroreceptors located in the dorsal olfactory mucosae project to both olfactory bulbs, and second, that it exists at mitral layer level of the frog, a reciprocal inhibition which can subserve frog orientation towards proximal odour source.