A Golgi study on the habenular nucleus of the cat

Abstract

The habenular nucleus of kittens was studied using the rapid Golgi and the Golgi-Kopsch silver impregnation methods. The neurons of the medial habenular nucleus (MH) were classified into two types. The type I neurons, the main constituents of the MH, had piriform cell bodies with a mean diameter of 12 mum by 18 mum and two to five primary dendrites; dendrites had many spines. The type II neurons (14 X 23 mum) were fusiform in shape and one to three primary dendrites arose from each pole of the cell bodies; dendrites had few spines. The axons of both types of neurons were traced into the fasciculus retroflexus Meynerti (FR), and intranuclear axon-collaterals arose from axons of the type I neurons. The neurons of the lateral habenular nucleus (LH) were divided into four groups. Type I, II and III neurons were projection neurons of large, medium and small size, respectively. The type I neurons (27 X 43 mum) with four to seven primary dendrites were located mainly in the rostral and ventral areas of the LH. The type II neurons (15 X 33 mum) with two to four primary dendrites, the main constituents of the LH, were distributed throughout the LH. The type III neurons (15 X 25 mum) with two primary dendrites emerging from each pole of the soma were localized to the mediocaudal areas of the LH. The vast majority of axons of these projection neurons passed ventrally or ventrocaudally to enter the FR; only a few axons of these neurons were traced into the stria medullaris thalami (SM). The type IV neurons (12 X 25 mum) were small cells with short axons, suggesting the existence of a neural circuitry intrinsic to the LH. Bundle formation and glomerular arrangement of dendrites were observed in the medium-sized LH neurons. The afferent fibers terminating within the MH coursed in the most part of the SM. These afferents were classified into medium-caliber type I and fine type II fibers; both of these fibers emitted many intranuclear collaterals. There were also observed many fibers of passage which ran between the SM and FR, or between the habenular commissure (HC) and FR. The afferent fibers to the LH were divided into three groups; afferents via the HC, ascending and descending afferents. Most of the descending afferents entered the LH through the SM; some of them traversed the LH to join the FR or HC, or to extend to the pretectal region. The vast majority of the ascending afferents entered the LH via the FR; some of them extended rostrally to enter the SM. Some fibers in the HC also terminated within the LH. In addition to these afferents, many fibers of passage were seen to run through the LH and to bridge over between the SM and FR, or between the SM and HC.

A Golgi Study on the Neuronal Organization of the Habenular Ganglion in the Red Stingray, Dasyatis akajei

“…Morphological features of the MH ...., -a neurons observed in the present study were similar to those of the MH neurons noted in the lamprey (Heier 1948), frog (Kemali and Braitenberg 1969;Kemali and Lazar 1985) and mouse (RamOn y Cajal), and the type I MH neurons in the cat (Iwahori 1977). As was reported in the mouse and cat, the dendritic field of the MH neurons in the red stingray was occasionally impregnated in an overlapped manner, suggesting the existence of the glomerular structure in the MH.…”

“…The type I LH neurons in the present study resembled the multipolar neurons seen in the LH of the mustel, mouse and cat. On the other hand, general features of the type II LH neurons in the red stingray were similar to those of the interneurons seen in the cat LH (Iwahori 1977). However, the exact character of the type II LH neurons requires further study.…”

“…As was reported in the mouse and cat, the dendritic field of the MH neurons in the red stingray was occasionally impregnated in an overlapped manner, suggesting the existence of the glomerular structure in the MH. On the other hand, the LH neurons show fairly clear species differences: the LH neurons observed in the lamprey (Heier 1948) were unipolar or bipolar cells, whereas those in the selachian (Houser 1901), frog (Kemali and Lazar 1985), mouse (Ram& y Cajal 1911) and cat (Iwahori 1977) were usually multipolar neurons. In the LH of the red stingray, two types of neurons were distinguished.…”

A Golgi Study on the Afferent Fibers to the Habenular Ganglion in the Red Stingray, Dasyatis akajei

“…In the red stingray, the MH and LH received different SM fibers; this is known to be the case in many other species as well. The terminal patterns of the SM fibers in the MH observed in the present study were similar to those observed in the mouse (RamOn y Cajal 1911) and cat (Iwahori 1977). Convergence of several terminals seen in the present study was also observed in the cat.…”

“…In mammals, terminal patterns of the afferent fibers in the HG was studied in detail using the rapid Golgi method (RamOn y Cajal 1911;Iwahori 1977) as well as the experimental methods (Herkenham and Nauta 1977). The afferent fibers to the selachian HG have been studied by numerous investigators (Edinger 1892;Haller 1898;Ariens Kappers 1906;Sterzi 1909;Ariens Kappers and Carpenter 1911;Johnston 1911;Bergquist 1932;Addens 1945;Farner 1978;Smeets, Nieuwenhuys and Roberts 1983).…”