Juxtacapsular nucleus of the stria terminalis of the adult rat: Extrinsic inputs, cell types, and neuronal modules: A combined Golgi and electron microscopic study

Abstract

This study unravels the microscopic organization of the juxtacapsular nucleus of the bed nuclei of the stria terminalis (Ju) by using silver impregnation and electron microscopic techniques. Examination of Golgi-impregnated specimens demonstrates that the Ju has precise boundaries primarily determined by a conical condensation of fibers of the stria terminalis (StT) around the nucleus. The internal capsule, ansa peduncularis, and medial forebrain bundle together with the StT provide extrinsic afferents to the neuropil of the Ju. Two main neuron types are found in the Ju: interneurons (including basket and neurogliaform cells) and projection neurons (bipolar and small pyramidal cells). The bipolar cell type accounts for about 80% of the sampled neurons. Short-axon neurons located within the dorsal part of the Ju send descending fibers that appear to terminate on the bipolar neurons, suggesting the existence of vertically oriented functional units within the nucleus. With the electron microscope, Ju neurons are seen in clusters of two or three neurons coupled by gap junctions. The neuropil contains numerous dendrites, axons, myelinated axons, and several types of synaptic interactions, including axospinous, axoshaft, and axosomatic. Within the neuropil, Ju neurons appear to be presynaptically modulated by axoaxonal interactions. The present findings suggest a model wherein bipolar neurons represent the output system of the Ju controlled by the interneurons, which would, in turn, be modulated by collaterals arising from the tributary fiber tracts. Additional neural interaction between Ju neurons utilizes gap junction-mediated electrotonic coupling.

Contrasting distribution of physiological cell types in different regions of the bed nucleus of the stria terminalis

“…For the juxtacapsular nucleus, there is consensus that the majority of neurons are small cells with spiny and often bipolar dendritic trees (McDonald 1983;Larriva-Sahd 2004), consistent with our results. For BNST-AL, there is also agreement that the dominant cell type is characterized by an ovoid soma from which emerge four to five dendrites that branch several times, are aspiny proximally, moderately to densely spiny more distally, and often exhibit dendritic varicosities (McDonald 1983;Larriva-Sahd 2006).…”

“…Three prior Golgi studies described the morphological properties of BNST-A neurons (McDonald 1983;Larriva-Sahd 2004, 2006. For the juxtacapsular nucleus, there is consensus that the majority of neurons are small cells with spiny and often bipolar dendritic trees (McDonald 1983;Larriva-Sahd 2004), consistent with our results.…”

Histological and cytological study of the bed nuclei of the stria terminalis in adult rat. II. Oval nucleus: Extrinsic inputs, cell types, neuropil, and neuronal modules

“…The core of the Ov exhibits a neuron type that strongly resembles the basket cells described by Ramón y Cajal (1904) in the mammalian neocortex and by Larriva-Sahd (2004) in the adult rat Ju of the BST. BCs have a small (15-20 m), triangular or pear-shaped soma that gives rise to two or four primary divergent dendrites that divide sequentially into secondary and terminal (i.e., tertiary) branches (Fig.…”

“…Furthermore, the author describes a peculiar small spiny neuron restricted to a small region in the ventral part of the lateral BST that he termed the juxtacapsular nucleus (Ju). More recently, a detailed account of the cytological features of the adult rat Ju was made by Larriva-Sahd (2004). Four neuron types and the interactions among them and with the adjacent tracts were described.…”

What is the bed nucleus of the stria terminalis?

“…The BST can be roughly divided into anterior and posterior subdivisions, each containing several nuclei, which can be identified based on their projection pattern and neurochemical identity (Cassell et al, 1986;Day et al, 1999;Larriva-Sahd, 2004, 2006McDonald,1983;Moga et al,1989;Veinante and Freund-Mercier, 1997 posterior group (BSTpost) may contribute more to reproduction and defense. However, the anterior and posterior BST are highly interconnected, ruling out unrelated or distinct functions for the two general areas.…”