Olfactory and vomeronasal projections have been traditionally viewed as terminating in contiguous non-overlapping areas of the basal telencephalon. Original reports, however, described areas such as the anterior medial amygdala where both chemosensory afferents appeared to overlap. We addressed this issue by injecting dextran amines in the main or accessory olfactory bulbs of rats and the results were analyzed with light and electron microscopes. Simultaneous injections of different fluorescent dextran amines in the main and accessory olfactory bulbs were performed and the results were analyzed using confocal microscopy. Similar experiments with dextran amines in the olfactory bulbs plus FluoroGold in the bed nucleus of the stria terminalis indicate that neurons projecting through the stria terminalis could be integrating olfactory and vomeronasal inputs. Retrograde tracing experiments using FluoroGold or dextran amines confirm that areas of the rostral basal telencephalon receive inputs from both the main and accessory olfactory bulbs. While both inputs clearly converge in areas classically considered olfactory-recipient (nucleus of the lateral olfactory tract, anterior cortical amygdaloid nucleus, and cortex-amygdala transition zone) or vomeronasal-recipient (ventral anterior amygdala, bed nucleus of the accessory olfactory tract, and anteroventral medial amygdaloid nucleus), segregation is virtually complete at posterior levels such as the posteromedial and posterolateral cortical amygdalae. This provides evidence that areas so far considered receiving a single chemosensory modality are likely sites for convergent direct olfactory and vomeronasal inputs. Therefore, areas of the basal telencephalon should be reclassified as olfactory, vomeronasal, or mixed chemosensory structures, which could facilitate understanding of olfactory-vomeronasal interactions in functional studies.

The temporal pole (TP) is the rostralmost portion of the human temporal lobe. Characteristically, it is only present in human and nonhuman primates. TP has been implicated in different cognitive functions such as emotion, attention, behavior, and memory, based on functional studies performed in healthy controls and patients with neurodegenerative diseases through its anatomical connections (amygdala, pulvinar, orbitofrontal cortex). TP was originally described as a single uniform area by Brodmann area 38, and von Economo (area TG of von Economo and Koskinas), and little information on its cytoarchitectonics is known in humans. We hypothesize that 1) TP is not a homogenous area and we aim first at fixating the precise extent and limits of temporopolar cortex (TPC) with adjacent fields and 2) its structure can be correlated with structural magnetic resonance images. We describe here the macroscopic characteristics and cytoarchitecture as two subfields, a medial and a lateral area, that constitute TPC also noticeable in 2D and 3D reconstructions. Our findings suggest that the human TP is a heterogeneous region formed exclusively by TPC for about 7 mm of the temporal tip, and that becomes progressively restricted to the medial and ventral sides of the TP. This cortical area presents topographical and structural features in common with nonhuman primates, which suggests an evolutionary development in human species.

Hippocampal formation plays a prominent role in episodic memory formation and consolidation. It is likely that episodic memory representations are constructed from cortical information that is mostly funnelled through the entorhinal cortex to the hippocampus. The entorhinal cortex returns processed information to the neocortex. Retrograde tracing studies have shown that neocortical afferents to the entorhinal cortex originate almost exclusively in polymodal association cortical areas. However, the use of retrograde studies does not address the question of the laminar and topographical distribution of cortical projections within the entorhinal cortex. We examined material from 60 Macaca fascicularis monkeys in which cortical deposits of either 3 H-amino acids or biotinylated dextran-amine as anterograde tracers were made into different cortical areas (the frontal, cingulate, temporal and parietal cortices). The various cortical inputs to the entorhinal cortex present a heterogeneous topographical distribution. Some projections terminate throughout the entorhinal cortex (afferents from medial area 13 and posterior parahippocampal cortex), while others have more limited termination, with emphasis either rostrally (lateral orbitofrontal cortex, agranular insular cortex, anterior cingulate cortex, perirhinal cortex, unimodal visual association cortex), intermediate (upper bank of the superior temporal sulcus, unimodal auditory association cortex) or caudally (parietal and retrosplenial cortices). Many of these inputs overlap, particularly within the rostrolateral portion of the entorhinal cortex. Some projections were directed mainly to superficial layers (I-III) while others were heavier to deep layers (V-VI) although areas of dense projections typically spanned all layers. A primary report will provide a detailed analysis of the regional and laminar organization of these projections. Here we provide a general overview of these projections in relation to the known neuroanatomy of the entorhinal cortex.

Apically and basally located receptor neurons in the vomeronasal sensory epithelium express G(i2 alpha)- and G(o alpha)-proteins, V1R and V2R vomeronasal receptors, project to the anterior and posterior accessory olfactory bulb and respond to different stimuli, respectively. The extent to which secondary projections from the two portions of the accessory olfactory bulb are convergent in the vomeronasal amygdala is controversial. This issue is addressed by using anterograde and retrograde tract-tracing methods in rats including electron microscopy. Injections of dextran-amines, Fluoro Gold, cholera toxin-B subunit and Fast Blue were delivered to the anterior and posterior accessory olfactory bulb, bed nucleus of the stria terminalis, dorsal anterior amygdala and bed nucleus of the accessory olfactory tract/anteroventral medial amygdaloid nucleus. We have demonstrated that, apart from common vomeronasal-recipient areas, only the anterior accessory olfactory bulb projects to the bed nucleus of the stria terminalis, medial division, posteromedial part, and only the posterior accessory olfactory bulb projects to the dorsal anterior amygdala and deep cell layers of the bed nucleus of the accessory olfactory tract and the anteroventral medial amygdaloid nucleus. These results provide evidence that, excluding areas of convergence, the V1R and V2R vomeronasal pathways project to specific areas of the amygdala. These two vomeronasal subsystems are therefore anatomically and functionally separated in the telencephalon.