Medial forebrain bundle of the rat: IV. Cytoarchitecture of the caudal (lateral hypothalamic) part of the medial forebrain bundle bed nucleus

Abstract

In the preceding study (Geeraedts et al.: J. Comp. Neurol. 294:507-536, '90), the rostral or telencephalic portion of the rat's bed nucleus of the medial forebrain bundle (MFB) has been parcellated into several cytoarchitectonically distinct cellular groups and subgroups. The purpose of the present investigation is to subject the caudal or lateral hypothalamic (LH) portion of the MFB bed nucleus to a detailed cytoarchitectonic analysis. This analysis is based on the same materials, methods, and cytoarchitectonic criteria that were also employed in the preceding study. In contrast to descriptions in the literature, it was found that the LH-region constitutes a very heterogeneous population of neurons with an evident arrangement into groups, several of which have not been identified previously. Many of these cellular groups are partly or entirely located within the boundary of the LH-trajectory of the MFB as previously established by Nieuwenhuys et al. (J. Comp. Neurol. 206:49-81, '82). These groups are designated here as the MFB-related cellular groups. They appear to be arranged into two longitudinal zones. Both zones are caudally replaced by the ventral tegmental area (VTA) and a part of the mesencephalic tegmentum (TEGM1). The lateral zone lies in close proximity to the internal capsule/cerebral peduncle and comprises the following cellular groups: the ventrolateral subarea of the lateral hypothalamic area (LHVL), the anterolateral subarea of the lateral hypothalamic area (LHAL), the lateral tuberal nucleus (TUL), the pre-subthalamic nucleus (PSUT), the retro-subthalamic nucleus (RSUT), the anterodorsal subarea of the lateral hypothalamic area (LHAD), and the lateral hypothalamic nucleus (LHN). The medial zone consists of the following cellular groups: the intermediate hypothalamic area (IHA), the medial tuberal nucleus (TUM), the perifornical nucleus (PFX), the lateral supramammillary nucleus (SUL), the submammillothalamic nucleus (SMT), and the nucleus geminus posterior (GEP). The cellular groups of the medial zone together with the tuberomammillary nucleus groups of the medial zone together with the tuberomammillary nucleus (TUMM) are positioned at the interface between the lateral and the medial hypothalamus, and form an array of cellular groups indicated in our study as the intermediate division of the hypothalamus. The MFB-related cellular groups are dorsally, medially, ventrally, and laterally surrounded by rather well-known brain structures. Both the MFB-related cellular groups and the surrounding structures have been identified and delimited. This resulted in a new, elaborate cytoarchitectonic atlas of the rat's lateral hypothalamic region.(ABSTRACT TRUNCATED AT 400 WORDS)

Coaxiality of Foxb1- and parvalbumin-expressing neurons in the lateral hypothalamic PV1-nucleus

“…Within the adult ventrolateral hypothalamus, the location of the Foxb1-expressing population of neurons [11] coincides with that occupied by the PV1-nucleus [1,2]. This locus partially perpetrates the LHVL2-region, as defined in a seminal publication by Nieuwenhuys and his co-workers [3]. On the basis of our observation that a compact and well-defined mantle of Foxb1-expressing cells surround the parvalbumin-expressing neurons of the eponymous nucleus [1,2], we propose that this be henceforth referred to as the PV1-Foxb1-nucleus.…”

“…Celio). [3,4], disposed in the horizontal plane, and sandwiched between the optic tract laterally and the fornix medially [1,2]. Around embryonic day 14.5, Foxb1-expressing neurons stemming from the periventricular zone migrate towards the ventrolateral hypothalamus.…”

Expression of Foxb1 Reveals Two Strategies for the Formation of Nuclei in the Developing Ventral Diencephalon

“…The rostral limit of this group reaches the level of the optic tract (not shown). From the anatomical point of view, these cells find themselves in the proximity of the lateral tuberal nucleus; the region of the hypothalamus underlying the Foxb1-expressing cells has been termed 'ventrolateral nucleus of the lateral hypothalamic area' [Geeraedts et al, 1990]), on a Nissl-cytoarchitectonic basis. Because our material undergoes treatment with RNAse as part of the in situ hybridization protocol, it was not possible to classify the labeled cells on cytoarchitectonic grounds as belonging to the lateral tuberal nucleus or to both this and the lateroventral nucleus.…”

“…Two nuclei, however, have been described in the general area where Foxb1 is expressed: the lateral tuberal nucleus and the ventrolateral nucleus of the lateral hypothalamic area [Geeraedts et al, 1990]. Both are found in the caudal portion of the so-called 'bed nucleus of the medial forebrain bundle' [Geeraedts et al, 1990].…”

Discharge properties of neurons recorded in the parvalbumin-positive (PV1) nucleus of the rat lateral hypothalamus

“…Three cell types, namely small and large PV-positive neurons as well as PV-negative ones, were reported in PV1-nucleus [6,4]. Despite the small numbers of our samples the few cells (n = 4) characterized by activity in the ı-frequency range were all recorded in the posterior part of the nucleus.…”