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Projections From the Posterolateral Olfactory Amygdala to the Ventral Striatum: Neural Basis for Reinforcing Properties of Chemical Stimuli

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Projections From the Posterolateral Olfactory Amygdala to the Ventral Striatum: Neural Basis for Reinforcing Properties of Chemical Stimuli

Isabel Ubeda-Bañon et al. BMC Neurosci.

Abstract

Background: Vertebrates sense chemical stimuli through the olfactory receptor neurons whose axons project to the main olfactory bulb. The main projections of the olfactory bulb are directed to the olfactory cortex and olfactory amygdala (the anterior and posterolateral cortical amygdalae). The posterolateral cortical amygdaloid nucleus mainly projects to other amygdaloid nuclei; other seemingly minor outputs are directed to the ventral striatum, in particular to the olfactory tubercle and the islands of Calleja.

Results: Although the olfactory projections have been previously described in the literature, injection of dextran-amines into the rat main olfactory bulb was performed with the aim of delimiting the olfactory tubercle and posterolateral cortical amygdaloid nucleus in our own material. Injection of dextran-amines into the posterolateral cortical amygdaloid nucleus of rats resulted in anterograde labeling in the ventral striatum, in particular in the core of the nucleus accumbens, and in the medial olfactory tubercle including some islands of Calleja and the cell bridges across the ventral pallidum. Injections of Fluoro-Gold into the ventral striatum were performed to allow retrograde confirmation of these projections.

Conclusion: The present results extend previous descriptions of the posterolateral cortical amygdaloid nucleus efferent projections, which are mainly directed to the core of the nucleus accumbens and the medial olfactory tubercle. Our data indicate that the projection to the core of the nucleus accumbens arises from layer III; the projection to the olfactory tubercle arises from layer II and is much more robust than previously thought. This latter projection is directed to the medial olfactory tubercle including the corresponding islands of Calleja, an area recently described as critical node for the neural circuit of addiction to some stimulant drugs of abuse.

Figures

Figure 1
Figure 1
Projections from the main olfactory bulb. Parasaggital (A) and coronal (B-F) Nissl-counterstained sections of the rat brain showing anterograde labeling (B-F) after a biotinylated dextran-amine injection into the main olfactory bulb (A). For abbreviations, see list. Calibration bar: A 1250 μm; B, C, E 400 μm; D, F 100 μm.
Figure 2
Figure 2
Projections from the posterolateral cortical amygdaloid nucleus. Coronal Nissl-counterstained sections of the rat brain showing anterograde labeling (B-F) after a biotinylated dextran-amine injection into the posterolateral cortical amygdaloid nucleus (A). For abbreviations, see list. Calibration bar: A, B, E 400 μm; C, F 100 μm; D 50 μm.
Figure 3
Figure 3
Projections from layers of the posterolateral cortical amygdaloid nucleus. Coronal sections of rat brain showing anterograde labeling (B, D) after injection of fluorescein dextran-amine into layers II (A) and III (C) of the posterolateral cortical amygdaloid nucleus, respectively. For abbreviations, see list. Calibration bar: A, C 400 μm; B, D 200 μm.
Figure 4
Figure 4
Projections to the ventral striatum. Coronal sections of rat brain showing retrograde labeling (B, D) after Fluoro-Gold injections into the olfactory tubercle (A) and core of the nucleus accumbens (C), respectively. For abbreviations, see list. Calibration bar: A, C 400 μm; B, D 100 μm.

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