Novel subdivisions of the rat accessory olfactory bulb revealed by the combined method with lectin histochemistry, electrophysiological and optical recordings

Wistaria floribunda agglutinin and peanut agglutinin were found to bind his tochemically to the anterior and posterior regions, respectively, of the vo meronasal nerve and glomerular layers in the rat accessory olfactory bulb. Furthermore, Ricinus communis agglutinin showed strong binding to the anter ior region of the vomeronasal nerve and glomerular layers, whereas it bound weakly and/or moderately to the rostral two-thirds of the posterior glomer ular layer but not at all to the caudal one-third. This suggests that the p osterior region is further divided into two subregions. An electrophysiolog ical mapping study in sagittal slice preparations demonstrated that stimula tion given within the anterior vomeronasal nerve layer elicited field poten tials within the anterior region of the external plexiform layer, whereas s hocks to the rostral two-thirds and the caudal one-third of the posterior v omeronasal nerve layer provoked field responses within the rostral two-thir ds and within the caudal one-third of the posterior external plexiform laye r, respectively, indicating that the posterior external plexiform layer is also divided into two subregions. Real-time optical imaging showed similar results as above, except that neural activity also spread into mitral cell layers. Furthermore, the most anterior and posterior ends of the neural act ivity evoked in the rostral two-thirds of the posterior region immediately adjoined the posterior border of that evoked in the anterior region and the anterior border of that evoked in the caudal one-third of the posterior re gion, respectively. Moreover, the granule cell layer was also found to have similar boundaries. Thus, optical imaging studies demonstrated individual precise boundaries of these subdivisions, which were positioned right benea th those defined by Ricinus communis agglutinin histochemistry. The presence of functional segregation in each layer leads us to conclude t hat there are at least three different input-output pathways in the rat vom eronasal system. (C) 1999 IBRO. Published by Elsevier Science Ltd.