NEUROANATOMICAL PATHWAYS LINKING VISION AND OLFACTION IN MAMMALS

Retinal projections to several telencephalic structures have been demo nstrated in a wide range of mammalian species following intraocular in jections of tritiated amino acids and cholera toxin subunit-B conjugat ed to horseradish peroxidase. Since these regions are also innervated by olfactory fibers, we investigated the distribution of convergent pr ojections using simultaneous injections of different anterograde trace rs in the eye and olfactory bulbs. Convergent projections from the ret ina and from the olfactory bulbs were observed in the piriform cortex, olfactory tubercle, the cortical region of the medial amygdala, later al hypothalamus, and the bed nucleus of the stria terminalis. A few re tinal fibers also invade the nucleus of the lateral olfactory tract, t he bed nucleus of the accessory olfactory bulb and the diagonal band o f Broca. Injections of retrograde tracers in the medial amygdala, the bed nucleus or the lateral hypothalamus shows that the visuo-olfactory convergence mainly involves projections originating from the accessor y olfactory bulb, and to a lesser extent from the ventromedial region of the main olfactory bulb. Fewer than 20 retinotelencephalic ganglion cells were identified in the retina, mainly located contralateral to the injection site. Ganglion cells were medium sized and possessed two long slender opposing dendrites. These retinal and olfactory projecti ons could provide an anatomical substrate for the modulation of gonado tropin hormone levels and the olfactory influence on light mediated rh ythms related to reproductive physiology.