ADJACENT LAMINAR TERMINATIONS OF 2 CENTRIFUGAL AFFERENT PATHWAYS TO THE ACCESSORY OLFACTORY-BULB IN THE MOUSE

Antreograde and retrograde axonal tracing methods were combined with transection of the stria terminalis to investigate the centrifugal afferent connections of the accessory olfactory bulb in the mouse. Injection of 3H-proline into the postero-medial cortical amygdaloid nucleus (C3) gives rise to anterograde autoradiographic labeling of a pathway terminating in the internal granular layer of the accessory olfactory bulb (AOB). Transection of the ipsilateral stria terminalis completely abolishes labeling of this pathway. Injections further rostral, in the bed nucleus of the accessory olfactory tract (BNAOT) and medial amygdaloid nucleus (M), give rise to labeling of a 2nd ipsilateral afferent pathway to the AOB which terminates in the internal plexiform layer (IPL) and is unaffected by strial transection. Injections of wheat germ lectin-HRP [horseradish peroxidase] conjugate into the AOB confirm that it receives afferents from the ipsilateral BR AOT, M and C3 and from a few cells in the contralateral C3. Transection of the ipsilateral stria terminals prevents retrograde labeling of any cells in the ipsilateral C3, but does not affect labeling of cells in M or BNAOT (or contralateral C3). The conjugate is transported anterogradely in this system, labeling the efferent projections of the AOB to BNAOT, M and C3. The AOB receives at least 2 sets of ipsilateral afferents: one set from C3, via the stria terminalis, terminating in the internal granular layer, and a 2nd set from M and/or BNAOT terminating in the IPL and probably running in the accessory olfactory tract.