Neurochemical organization of the ventral striatum’s olfactory tubercle

Abstract

The ventral striatum is a collection of brain structures, including the nucleus accumbens, ventral pallidum and the olfactory tubercle (OT). While much attention has been devoted to the nucleus accumbens, a comprehensive understanding of the ventral striatum and its contributions to neurological diseases requires an appreciation for the complex neurochemical makeup of the ventral striatum's other components. This review summarizes the rich neurochemical composition of the OT, including the neurotransmitters, neuromodulators and hormones present. We also address the receptors and transporters involved in each system as well as their putative functional roles. Finally, we end with briefly reviewing select literature regarding neurochemical changes in the OT in the context of neurological disorders, specifically neurodegenerative disorders. By overviewing the vast literature on the neurochemical composition of the OT, this review will serve to aid future research into the neurobiology of the ventral striatum.

The Neurotransmitter Receptor Architecture of the Mouse Olfactory System

“…Usually, dopaminergic receptors become active following the perception of reward promising olfactory signals, explaining the role of the olfactory tubercle as a motivational and evaluating area for olfactory preferences (Ikemoto, 2007;Zhang et al, 2017;Murata et al, 2019). The neurochemical structure of the olfactory tubercle has been extensively researched (Cansler et al, 2020). Its unique position in the olfactory system is caused by the fact that the olfactory tubercle is considered to be part of the olfactory cortex as well as the ventral striatum (de Olmos and Heimer, 1999;Cansler et al, 2020).…”

“…The neurochemical structure of the olfactory tubercle has been extensively researched (Cansler et al, 2020). Its unique position in the olfactory system is caused by the fact that the olfactory tubercle is considered to be part of the olfactory cortex as well as the ventral striatum (de Olmos and Heimer, 1999;Cansler et al, 2020). Because of the high dopamine receptor density, the olfactory tubercle displays a receptor profile, which is more similar to the striatal than to the olfactory system (Knable et al, 1994;Sulzer et al, 2016).…”

The Tubular Striatum

“…For instance, do D1 and D2 medium spiny neurons in the TuS influence local activity in ways important for learning, as observed recently in the nucleus accumbens? The neurochemical composition of the TuS is rich (Cansler et al, 2020), with a wealth of intrinsic and extrinsic systems in place for investigation. Understanding the microcircuitry of the TuS will be critical for guiding functional studies in behaving animals.…”

Hypothetical Roles of the Olfactory Tubercle in Odor-Guided Eating Behavior

“…Axonal projections from the nucleus of the solitary tract to the OT suggest that visceral signals are directly transferred to the OT via this pathway ( Ruggiero et al, 1998 ). The OT expresses various receptors of neuromodulatory inputs, opioids, hormones, and neurosteroids ( Cansler et al, 2020 ). In the anteromedial OT, various orexigenic peptides (orexin and prodynorphin) and receptors (orexin receptors 1 and 2, ghrelin receptor, and opioid receptor kappa 1) were highly expressed compared to those in the lateral OT.…”

“…In contrast, D2 receptor-expressing neurons in the anteromedial domain and D1 receptor-expressing neurons in the lateral domain may suppress eating by low evaluation, demotivation, and disgusting response to food-related odors and flavors. The OT also expresses orexigenic and anorexigenic peptides and their receptors ( Cansler et al, 2020 ; Nogi et al, 2020 ), which may endow OT domains with homeostatic control over odor-guided eating behaviors ( Aime et al, 2007 ; Palouzier-Paulignan et al, 2012 ). For instance, hunger state and its orexigenic hormonal signals such as orexin and ghrelin might upregulate the responses of D1 receptor-expressing neurons in the anteromedial OT to food odors and flavors, resulting in increase of food intake.…”