Afferents to the rostral olfactory bulb in sheep with special emphasis on the cholinergic, noradrenergic and serotonergic connections

The olfactory bulb (OB) is involved in the processing of olfactory informat ion particularly through the activation of its afferents. To localize their cell origin in sheep, a specific retrograde fluorescent tracer, Fluoro-Gol d, was injected into the olfactory bulb of seven ewes. By using immunocytoc hemical techniques, retrogradely labeled neurons were colocalized with chol ine acetyltransferase, tyrosine hydroxylase, dopamine-beta-hydroxylase and serotonin to characterize cholinergic, noradrenergic and serotonergic Fluor o-Gold-labeled neurons. Most afferents originated from the ipsilateral side of the injection site. The OB received major inputs from the anterior olfa ctory nucleus (AON), the piriform cortex (PC), the olfactory tubercle, the diagonal band of Broca (DBB) and the amygdala. Other retrogradely labeled n eurons were observed in the taenia tecta, the septum, the nucleus of the la teral olfactory tract, the preoptic area, the lateral hypothalamic area, th e mediobasal hypothalamus, the lateral part of the premammillary nucleus, t he paraventricular nucleus of the hypothalamus, the paraventricular thalami c nucleus, the central grey, the substantia nigra (SN), the ventral tegment al area (VTA), the lateral nucleus to the interpeduncular nucleus (IIP), th e raphe and the locus coeruleus (LC). Contralateral labeling was also found in the AON, the PC, the SN compacta, the VTA, the IIP and the LC. Choliner gic Fluoro-Gold-labeled neurons belonged to the horizontal and vertical bra nch of the DBB. Noradrenergic afferents came from the LC and serotoninergic afferents came from the medial raphe nuclei and the IIP. These data are di scussed in relation with olfactory learning in the context of maternal beha vior in sheep. (C) 1999 Elsevier Science B.V. All rights reserved.