AFFERENT AND EFFERENT CONNECTIONS OF THE NUCLEUS SPHERICUS IN THE SNAKE THAMNOPHIS-SIRTALIS - CONVERGENCE OF OLFACTORY AND VOMERONASAL INFORMATION IN THE LATERAL CORTEX AND THE AMYGDALA

This paper is an account of the afferent and efferent projections of t he nucleus sphericus (NS), which is the major secondary vomeronasal st ructure in the brain of the snake Thamnophis sirtalis. There are four major efferent pathways from the NS: 1) a bilateral projection that co urses, surrounding the accessory olfactory tract, and innervates sever al amygdaloid nuclei (nucleus of the accessory olfactory tract, dorsol ateral amygdala, external amygdala, and ventral anterior amygdala), th e rostral parts of the dorsal and lateral cortices, and the accessory olfactory bulb; 2) a bilateral projection that courses through the med ial forebrain bundle and innervates the olfactostriatum (rostral and v entral striatum); 3) a commissural projection that courses through the anterior commissure and innervates mainly the contralateral NS; and 4 ) a meager bilateral projection to the lateral hypothalamus. On the ot her hand, important afferent projections to the NS arise solely in the accessory olfactory bulb, the nucleus of the accessory olfactory trac t, and the contralateral NS. This pattern of connections has three imp ortant implications: first, the lateral cortex probably integrates olf actory and vomeronasal information. Second, because the NS projection to the hypothalamus is meager and does not reach the ventromedial hypo thalamic nucleus, vomeronasal information from the NS is not relayed d irectly to that nucleus, as previously reported. Finally, a structure located in the rostral and ventral telencephalon, the olfactostriatum, stands as the major tertiary vomeronasal center in the snake brain. T hese three conclusions change to an important extent our previous pict ure of how vomeronasal information is processed in the brain of reptil es. (C) 1997 Wiley-Liss, Inc.