Subnuclear organization of the rat habenular complexes

Abstract

The habenular complexes represent phylogenetically constant structures in the diencephalon of all vertebrates. Available evidence suggests that this area is engaged in a variety of important biological functions, such as reproductive behaviors, central pain processing, nutrition, sleep‐wake cycles, stress responses, and learning. Based on Nissl‐stained sections, one medial nucleus and two lateral nuclei (divisions) have been widely accepted in the rat. Cytochemical, hodologic, and functional studies suggest a considerably more complex subnuclear structure. To improve our knowledge of the precise structural composition of the habenular complexes, we have systematically investigated their fine ultrastructure in the rat. Based on the detailed analysis of complete series of large, semithin sections supplemented with electron photomicrographs of selected fields, clear criteria for the delineation of five distinct subnuclei of the medial and ten subnuclei of the lateral habenular complexes were elaborated for the first time. All 15 subnuclei were reconstructed, and their dimensions were determined. A medial and lateral stria medullaris were described. Different roots of the fasciculus retroflexus were differentiated within the medial and lateral habenular complexes. The topographical relationships with respect to the adjacent habenular areas as well as to the neighboring thalamic nuclei were identified and demonstrated. The new understanding of the subnuclear organization of the habenular complexes certainly will facilitate further functional investigations. Whether the newly identified subnuclei finally will be recognized as functionally distinct awaits ongoing immunocytochemical, hodologic, and functional studies. J. Comp. Neurol. 407:130–150, 1999. © 1999 Wiley‐Liss, Inc.

Bilateral Lesions of the Habenula Induce Attentional Disturbances in Rats

“…Falling between these two extremes were shortened latencies for incorrect responses and for retrieving the food pellet in lesioned animals, which appeared already in the first block of postoperative test sessions and then remained stable. Given that the habenula consists of 15 subnuclei (Andres et al, 1999;Geisler et al, 2003), it is understandable that alterations with different properties exist. Elucidating the circuits involved in these various alterations will clearly require further experiments.…”

“…Consistent with such widespread influences, it is implicated in diverse functions including anxiety (Murphy et al, 1996;Kurumaji et al, 2003), stress (Amat et al, 2001;Sica et al, 2000), analgesia (Cohen and Melzack, 1993), maternal behavior (Corodimas et al, 1993;Felton et al, 1998), sleep (Haun et al, 1992;Valjakka et al, 1998), behavioral flexibility (Thornton and Evans, 1982), reinforcement (Sutherland and Nakajima, 1981), and spatial memory (Lecourtier et al, 2004). The recent description of 15 subnuclei within the habenular complex (Andres et al, 1999;Geisler et al, 2003) should eventually be of great assistance for future research aimed at elucidating the particular circuits that mediate these specific behaviors.…”

Glutamatergic axons from the lateral habenula mainly terminate on GABAergic neurons of the ventral midbrain

“…It is divided into a medial (MHb) and a lateral (LHb) part and consists of a heterogeneous group of neurons containing a variety of neurotransmitters and neuromodulators (Geisler et al 2003;Andres et al 1999 (Fig. 2).…”

Lesions of the habenula produce stress- and dopamine-dependent alterations in prepulse inhibition and locomotion

“…The habenula complex, a paired midline structure just medial to the thalamus, provides a neural pathway that mediates forebrain control over midbrain dopaminergic and serotonergic firing (Sutherland, 1982;Andres et al, 1999). The habenula receives convergent input from most limbic brain regions including the hypothalamus, central amygdala, substantia innominata, diagonal band of Broca, nucleus accumbens, septum, and prefrontal cortical regions (Sutherland, 1982;Ellison, 2002).…”