Illustrated Review of the Ventral Striatum's Olfactory Tubercle

Abstract

Modern neuroscience often relies upon artistic renderings to illustrate key aspects of anatomy. These renderings can be in 2 or even 3 dimensions. Three-dimensional renderings are especially helpful in conceptualizing highly complex aspects of neuroanatomy which otherwise are not visually apparent in 2 dimensions or even intact biological samples themselves. Here, we provide 3 dimensional renderings of the gross- and cellular-anatomy of the rodent olfactory tubercle. Based upon standing literature and detailed investigations into rat brain specimens, we created biologically inspired illustrations of the olfactory tubercle in 3 dimensions as well as its connectivity with olfactory bulb projection neurons, the piriform cortex association fiber system, and ventral pallidum medium spiny neurons. Together, we intend for these illustrations to serve as a resource to the neuroscience community in conceptualizing and discussing this highly complex and interconnected brain system with established roles in sensory processing and motivated behaviors.

Keywords: 3-dimensional; anatomy; olfaction; olfactory bulb; olfactory cortex; piriform cortex.

Figure 1.

Illustrated gross anatomy of the OT and its spatial organization throughout one rat. (A) Illustration of the inferior aspect of a rat brain indicating the location of the OT (purple shaded) relative to the OB (olfactory bulb), PCX (piriform cortex, yellow shaded), lateral olfactory tract (LOT), and optic chiasm (OC). (B) Brightfield microscope image of a single coronal rat brain section stained with cresyl violet (top) and (lower) a 2D drawing of this section indicating the location of OT cell layers and the islands of Calleja (IC) relative to neighboring brain structures including the PCX, ventral pallidum (VP), nucleus accumbens (NAc), and anterior commissure (AC). Layer 1, light blue; layer 2, dark blue; layer 3, purple. (C) 2D drawings of the OT throughout successive alternate coronal brain sections from the same rat as in (B). IC are indicated in pink. The PCX and LOT are also drawn to help provide a reference for the OT location. Green arrowhead indicates region with narrow layer 1. Black horizontal arrow indicates section illustrated in (B).

Figure 2.

3D illustrations highlight the morphology and the laminar organization of the OT. (A) Illustration of the OT from an anterolateral perspective. (B) Illustration of the OT from an anteromedial perspective. (C) “Pulled-apart” view the OT from the anterolateral perspective (same as in (A)) to depict laminar morphology as it progresses anterior to posterior as well as the localization of the islands of Calleja.

Figure 3.

Cellular composition of the OT. Same OT coronal 3D image as in (Figure 2C), yet including drawings of an assortment of cells to illustrate the cellular diversity in the OT. IC, islands of Calleja; MFL, multiform layer; DCL, dense cell layer; ML, molecular layer. Cell types include d, dwarf cells; c, crescent cells; ss, spindle-shaped cells; lms, large; moderately spined cells; ms, medium sized, moderately spiny cells; r, radiate cells; lsp, large, spine-poor cells; sm, symmetrical, medium sized densely-spined cells; msds, medium sized, densely-spined cells; p, pial cells. Cellular morphologies illustrated based upon Fallon et al. (1978), Millhouse and Heimer (1984), and Millhouse, (1987).

Figure 4.

Olfactory sensory input into the OT. (A) 3D illustration of the innervation of the OT by 2 sources of main olfactory system information. (B) A focused image of (A) highlighting the input of the anterolateral OT by olfactory bulb tufted cells (black). (C) A focused image of (A) highlighting the input of the anterolateral OT by piriform cortex association fibers (black) which convey bisynaptic odor information into the OT by means of mitral cells (purple).

Figure 5.

OT connectivity with the ventral pallidum. 3D representation of the OT with the ventral pallidum and nucleus accumbens illustrated dorsally. The illustration depicts MSNs of the OT innervating the lateral aspect of the ventral pallidum as well as cells within the striatal bridges (indicated by sparse presence of the ventral pallidum) forming a source for possible connectivity directly between the OT and nucleus accumbens.

Figure 6.

A summary of the OT and its connectivity. This illustration incorporates the previous illustrations to provide an overview of the OT’s anatomy as well as its major connectivity.