Abstract

The cortical (CoA) and the medial (MeA) nuclei of the amygdala are involved in the processing of olfactory information relevant to social recognition in the ewe. To better understand the neural pathways responsible for these effects, the connections of both CoA and MeA with the telencephalic and diencephalic regions were studied by injecting an anterograde (Biotin-Dextran-Amine, BDA) or a retrograde (Fluorogold, FG) neuronal tracer into either the CoA or the MeA. Concerning the primary olfactory structures, the CoA receives inputs from both the main olfactory bulb and the accessory olfactory bulb (AOB), while the MeA is innervated by cells only from the AOB. Among the other olfactory structures, only the entorhinal cortex and the tenia tecta are connected with both the CoA and the MeA. With respect to the other secondary olfactory structures, the connections with the CoA and the MeA show segregating neuronal routes. The CoA is connected with the accessory olfactory nucleus, the piriform, the endopiriform and the orbitofrontal cortices while the MeA exhibited connections with the nucleus of the lateral olfactory tract, the perirhinal and the insular cortices. Concerning the diencephalic structures, only the MeA receives projections from the PVN and the MBH. On the other hand, we showed that the BNST is the major site of connection with both the CoA and the MeA. Reciprocal projections were observed between the CoA and the MeA and between both nuclei and the basal or the lateral nuclei of the amygdala with the exception of the CoA which does not send inputs to the lateral nucleus. These data are discussed in relation with olfactory learning in the context of sexual and maternal behavior in sheep.

Keywords: Fluorogold; Dextran amine; Neural tract-tracing; Olfaction; Social behavior

Abbreviations: 3V, third ventricle; AOB, accessory olfactory bulb; AON, anterior olfactory nucleus; AC, anterior commissure; B, basal amygdaloid nucleus; BNST, bed nucleus of the stria terminalis; C, caudate nucleus; CeA, central amygdaloid nucleus; CoA, cortical amygdaloid nucleus; E, endopiriform nucleus; EC, entorhinal cortex; Fx, fornix; Gl, glomerular layer of the olfactory bulb; Gr, granular cell layer of the olfactory bulb; HDB, horizontal limb of the diagonal band of Broca; IC, insular cortex; L, lateral amygdaloid nucleus; LHA, lateral hypothalamic area; LOT, lateral olfactory tract; LOTn, nucleus of the lateral olfactory tract; LV, lateral ventricle; MBH, mediobasal hypothalamus; MeA, medial amygdaloid nucleus; Mi, mitral cell layer of the olfactory bulb; MOB, main olfactory bulb; MS, medial septum; MT, mamillothalamic tract; OC, optic chiasma; OFC, orbitofrontal cortex; OT, optic tract; OV, olfactory ventricle; PC, piriform cortex; PM, premamillary nucleus; POA, preoptic area; POAdl, dorsolateral part of the POA; POAm, medial part of the POA; PRh, perirhinal cortex; Pu, putamen; PVN, paraventricular nucleus; RT, reticular nucleus of the thalamus; S, subiculum; SON, supraoptic nucleus; TT, tenia tecta; VA, ventral anterior nucleus of the thalamus; VDB, vertical limb of the diagonal band of Broca; VH, ventral hippocampus

Article Outline

1. Material and methods

1.1. Animals

1.2. Injection procedures

1.3. Histological procedures

1.4. Immunohistochemistry

1.4.1. FG staining

1.4.2. BDA staining

1.5. Analysis of sections

2. Results

2.1. Connections with the medial amygdala

2.1.1. Telencephalic structures

2.1.2. Diencephalic structures

2.1.3. Intra-amygdaloid connections

2.2. Connections with cortical amygdala

2.2.1. Telencephalic structures

2.2.2. Diencephalic structures

2.2.3. Intra-amygdaloid connections

3. Discussion

Acknowledgements

References