These terms and their abbreviation in English “NBST or BST” are used to refer to a practically seamless continuum of neuronal cell clusters bordering the concave edge of the caudate nucleus, from its head to its tail, the septal region of the amygdaloid body, and within which passes the stria terminalis.

Various names have been used to refer to these cell clusters such as the “support nucleus” (M Volsch 1910) or “secondary nuclei of the stria” (CWA Kappers 1921) or even the “enveloping nucleus” (EW Lauer 1945) and “interstitial nuclei” (R Diepen 1962).

In this bed, in addition to the stria terminalis (see Chap. 6), the large thalamo-striate vein and its tributaries are routed before it drains into the internal cerebral vein. Cell clusters of the BNST are in contact with the two aforementioned elements and are usually interposed there between.

The BST, which we seem to have more or less rediscovered in recent years, is already well known from the work mentioned above and especially since the memorable anatomy works performed by JB Johnston, in 1923. In a long article devoted to the evolution of the forebrain, the author described this structure from the early stages of embryonic life and showed its central position and its role: establishing communication between the amygdaloid complex and the olfactory area. Subsequently, many contributors have clarified the anatomy of the BST, including OJ Andy and H Stephan, in 1968, who studied its paraseptal portion; F Sanides, in 1957, who studied its caudal portion; and, above all, H Strenge et al., in 1977, who carried out an exhaustive and accurate histological study of the entire cell mass using serial sections perpendicular to the arch that forms the BST. We should also recall the work of JS De Olmos (2004) who studied the connections between the BST and the amygdala in particular.

Three portions are usually identified for the BST: the rostro-medial portion, the intermediate portion and the caudal portion.

At the level of pre-septal area, the BST is in the centre of the striatum and positioned medially with respect to the anterior branch of the internal capsule. It insinuates itself between the caudate nucleus, element of the dorsal striatum and the nucleus accumbens (Fig. 10.1a, a’), element of the ventral striatum which has just received one or more branches of the stria terminalis. It is medially covered by subependymal epithelium, which forms, at this level, the inferior recess of the front horn (or anterior cornu) of the lateral ventricle.

At the commissural level, the BST always underlies the caudate nucleus and is positioned against the lateral ventricular wall, inside the crus anterior of the internal capsule. It remains in a dorsal position with respect to the anterior commissure, which forms its median trajectory, slightly arched, with a dorsal convexity (Fig. 10.1b, b’ and c, c’ and Fig.10.2).

At the rear of the anterior commissure, the BST remains connected to the head of the caudate nucleus, which it follows up to the posterior third (Fig. 10.1d, d’).

For R Walter et al. (1991), who have studied the differential distribution of histochemical markers in the BST of the human brain, this rostro-medial portion is the part which specifically corresponds to the BST due to the fact that beyond this point, the presence of the dorsal part of the magno-prothalamic and parvocellular nuclei, initially described by H Brockaus, makes it difficult to interpret the results. Thus, the marks of A Walter et al. only concern the rostro-medial part of the NBST.

This section begins beyond the head of the nucleus where the thalamus contacts the body of the caudate nucleus. A thalamo-caudate sinus forms immediately and extends along a groove in a circular arch to the tail of the caudate nucleus. The cells, which form the BST and especially those adjacent to the thalamus, play an important role such as demonstrated by numerous recent studies. This is not surprising if we refer to embryology as it is clear that the thalamo-caudate sinus is a strategic area where the striatum and thalamus become closer to each other so as to allow the diencephalo-telencephalic junction and the incorporation of the diencephalon in the median brain (see Chap. 3). At the level of the dorsal surface of the thalamus, the furrow occupied by the BST is also bordered, on the ventricular side, by a thin white substance lamina, the lamina affixa or lamina cornea, an embryonic residue of the telencephalic white substance separating the striated body from the thalamus. The role played by this lamina affixa is to attach the thalamo-striate vein to the bottom of the furrow. It also transforms this furrow into a triangle, which corresponds to the location of the BST. This triangle will also expand into a square or rectangle according to the areas being observed (Fig. 10.3
).

Beyond this point and especially at the level of the posterior surface of the thalamus, the lamina affixa disappears and the ventricular wall of the BST consists only of the ependymal layer.

The NBST cells (Figs. 10.3 and 10.4) have been described by H Strenge et al. (1977):

H Strenge et al. also included in their work good anatomical diagrams of the sections that he had performed for the BST study. These sections are still used as references for locating the BST. The observations made by H Strenge et al. (1977) were purely histological, even if they could seem, at that time, of little interest. They actually played a major role in the BST study because they showed, for the first time, that the BST had a complex constitution and that we could observe a real zoning with several different cell areas.

Thus, other contributors (JS De Olmos et al. 1985; MM Moga et al. 1989) showed, in mammals, by means of histological and histochemical methods, that there is a cyto-architecture and a chemo-architectony specific to their NBST.

According to these authors, five main sectors were identified in animals, a lateral sector, a medial sector, a central sector, a latero-ventral sector and a postero-medial sector.

The outcome of this research in animals generated a particular enthusiasm, and parallel studies on the human NBST were rapidly conducted. In 1985, P Gaspar et al. carried out immuno-cytochemical studies on the septal region of the human brain and demonstrated its catecholaminergic innervation. The following year, E. Fliers et al. (1986) discovered the presence of vasopressin cells in the BST. Due to the fact that immunohistochemical methods could now be used to locate cell islands with a specific function, this technique was rapidly used to prepare a chemical map of the NBST. The anatomical subdivisions of this formation in humans were thus observed by using these methods, successively by a French team, A Lesur et al. (1989), and then by a German-Hungarian team, A Walter et al. (1991).

Walter et al. used a very wide range of histochemical markers (13 in total). In addition to the Lesur markers, they used VIP, substance P, NPH (neurophysins), MBP (myelin basic protein), Cab (calbindin), Syn (synaptophysin), CHR-A (chromogranin), NT (neurotensin), NPY (neuropeptide Y) and the glial fibrillary acid protein. They were able to conclude that there are, in fact, in humans, only three identifiable sectors: the lateral sector, the central sector and the medial sector. The lateral sector, located against the internal capsule, is heterogeneous and includes small neurons and other medium-sized neurons. Most of these neurons are NPY or Syn positive. The central sector consists of a homogeneous set of neurons of similar shape and diameter. This sector has the distinction of being divided into two areas, on coronal sections: a supra-commissural area and a peri-ventral and sub-commissural area. The authors rightly consider that these two areas correspond to the same formation as they all have the same immunohistochemical characteristics: VIP innervation density and presence of somatostatin fibres and neurons (DF Swaab 2003). The medial area is located below the tapered end of the lower edge of the lateral ventricle. It is a heterogeneous sector (such as the lateral sector). It is in this sector that the BST neurons with the smallest diameters are observed. This sector has a VIP innervation (JN Zhou et al. 1995) as well as a less dense peptidergic and aminergic innervation.