Indmedica Home | About Indmedica | Medical Jobs | Advertise On Indmedica
Search Indmedica Web
Indmedica - India's premier medical portal

Journal of the Anatomical Society of India

A Golgi Study of Medial Geniculate Body In Rat

Author(s): Dada, R.; *Khanna, J.; *Prakash R.

Vol. 51, No. 1 (2002-01 - 2002-06)

Department of Anatomy, All India Institue of Medical Sciences, & *University College of Medical Sciences, Delhi.

Abstract

Medial Geniculate Body (MGB) a part of the metathalamus is an important auditory relay station. It is a gross topographical formation and its divisions, and nuclei are not well defined. Review of literature shows that not much work has been done on MGB of rat and there is no unanimity regarding the divisions and neuronal type in MGB of other animals such as tree strew, opossum and cat. Thus the present study was done to determine the neuronal architecture of MGB of rat as it is a standard laboratory animal. This will help to fill in the gap in the comparative anatomy and determine if rat could be used as a mammalian model for future research on auditory thalamus.

Key words: Auditory thalamus, Golgi cox.

Introduction:

The MGB of rat is a tripartite structure composed of three divisions – ventral (MGv), dorsal (MGd) and medial (MGm). The internal boundaries between these divisions are not clearly distinguishable and there is no unanimity regarding the divisions, neuronal morphology in different species like cat, opossum and tree strew. In the present study on rat MGB we found that each division is uniquely characterized by neurons with constituent dendritic morphology. Morest (1964) proposed a tripartite structure of cat auditory thalamus. He divided cat MGB into 3 division MGm, MGv and MGd on basis of dendritic morphology of intrinsic neuronal population. This scheme contrasts with cytoarchitectural model of Rioch (1929) which specified only 2 divisions a lateral pars principalis and a medial pars magnocellularis. Historically the cytoarchitectural observations have led to MGB parcellation into 2 divisions whereas studies using Golgi method have yielded 3 divisions in cat.

In the present study dendrtitic morphology of rat MGB was studied using Golgi method. This will determine if rat auditory thalamus can be used as a mammalian prototype for further research on auditory thalamus.

Material and Methods:

20 albino rat (Lewis strain) brains were processed for Golgi study using Fox Golgi Cox technique. Free hand (90-100 um thick) sections were cut and viewed under the light microscope and photographed.

Results:

The rat MGB was parcelled by studying the regional variation in dendritic patterning of principal neurons into 3 major divisions. Two principal types of neurons were identified based on their patterns of dendritic arborization. These were tufted or bushy and stellate neurons. Tufted/bushy neurons have oblong to round cell body from which two to three major dendritic trunks extend in one direction. Each dendrite branches profusely from the same point close to cell body like sheaves of wheat or broom which produce an impression of a bush thus the name bushy or tufted neuron. The second order branching arises in same part of dendritic field. The other principal neuronal type is the stellate neuron. Stellate neurons have several primary dendrites which extend from the cell body in all directions and thus have a star shaped dendritic field. The stellate configuration results from basic radiate branching pattern which is characterized by a tendency of second and higher order dendrites to bifurcate dichotomously into consecutive daughter branches.

In the ventral division (MGv) the principal neuronal type was the busy tufted neuron (Fig. 1) and their orientation was in register with the afferent brachial axons which divides the MGV into ovoid and ventral nuclei (Dada et al, 2001).

In the dorsal division (MGd) stellate neurons (Fig. 2) are the principal neuronal type. MGd contain very few tufted neurons but these are less tufted than the tufted / bushy neurons of MGv.

The MGm has a heterogenous population of magnocellular stellate and bushy tufted neurons. The distribution of neurons characterized by morphological features of dendrites corresponds to anatomical regions of MGB identified by cytoarchitecture and myeloarchitecture (Dada et al., 2001).

Discusion:

Cajal (1911) described neurons of dorsal division in rapid Golgi preparation of a newborn kitten. He reported that dorsal division had stellate neurons. In the present study the dorsal division had stellate neurons with radiating dendritic fields. Grossman (1973) identified 2 principal neuronal types in MGB but did not identify their location in the MGB divisions. Cytoarcthitectural studies have led to MGB parcellation into 2 divisions whereas studies using Golgi method have shown that MGB has 3 division the MGm, MGv and MGd. The present study also identified 3 divisions of rat MGB with 2 principal neuronal types. These were the stellate and bushy neurons. Similar findings have been reported by Oliver (1982) in tree strew, Morest and Winer (1986) in opossum and Clerici (1987) and Winer (1984) in man. We have previously reported that rat MGB had 3 divisions using Nissl, Peters Protein Silver and Luxol fast blue preparation (Dada et al 2001) and the present study using Golgi aided in clearer charactrization of these 3 divisions. Thus from this study we can conclude that neuronal morphology of rat MGB are typical of most mammalian forms. Thus rat which is a standard laboratory animal could provide a useful model for study of auditory thalamus.

Referenes:

  1. Clerici, W.J.; Coleman, J.R.; Manwell, B. (1987) : Cytoarchitecture of the medial geniculate body of adult and infant rats. Anatomical Records 218: 23.
  2. Dada, R; Khanna, J; Prakash, R. (2001): Morphometric analysis of rat MGB. Journal of the Anatomical Society of India 50(2): 160-162.
  3. Grossman, A; Lieberman, A.R.; Webster, K.E. (1973): A Golgi study of the rat dorsal lateral geniculate nucleus. Journal of Comparative Neurology 150: 441-466.
  4. Morest. D.K. (1964): The neuronal structure of medial geniculate body of cat. Journal of Anatomy. 98: 611-630.
  5. Morest, D.K. (1965): The laminar structure of the medial geniculate body of cat. Journal of Anatomy. 99: 143-160.
  6. Oliver, D.L. (1982): A Golgi study of medial geniculate body in tree strew (Tupaia glic). Journal of Comparative Neurology. 209: 1-16.
  7. Ramon Y, Cajal (1911): Histologic du systeme Nerveux de I’Hemme et des Vertebres. L Azoulay, Trans, Paris : Malonie (1972) reprint.
  8. Rioch (1929): Studies on the diencephalon of carnivora : I. The nuclear cofiguration of the thalamus, epithalamus and hypothelamus of the dog and cat. Journal of Comparative Neurology. 49. 1-119.
  9. Winer, J.A. (1984) : The human medial geniculate body. Hearing Research. 15: 225-247.
Missing Image

Figure 1. Microphotograph of tufted neuron of ventral division of Medial Geniculate Body.

Missing Image

Figure 2. Microphotograph of stellate neurons of dorsal division of Medial Geniculate Body.

Access free medical resources from Wiley-Blackwell now!

About Indmedica - Conditions of Usage - Advertise On Indmedica - Contact Us

Copyright © 2005 Indmedica