Injuries of many peripheral nerves are common during accidents and occasionally during surgical operations. As such, it is essential to investigate the changes that occur in the motor neuron somata of these nerves after such injuries. When the axon is cut (axotomy), the nerve cell body (soma) usually undergoes profound alterations in structure, metabolism, and physiological activity (Grqfstein, 1975). Axotomy usually involves removal of a significant portion of the nerve cell volume, but most of the synthetic machinery of the cell, because it is localized in the soma, is left intact, and the defect produced in the surface membrane at the site of injury is small in relation to the total cell surface that remains (Grafstein, 1975). The Nissl granules are strikingly present in the large somata of motor neurons that supply skeletal muscle. For example, they are abundant in the motor neuron somata of ventral grey horn of the spinal cord. These granules are more obvious in large, highly active cells, such as spinal motor neurons (Williams et al, 1989). They are scattered throughout the neuronal soma and they extend into the dendrites (except in very thin dendrites) but are absent in the axon and axon hillock (Junqueira et al, 1986). The typical morphological changes in the cell body first recognized by Nissl (1892) include swelling of the cell and the apparent disappearance of basophilic material («Nissl substance») from the cytoplasm. The prominence of the latter phenomenon led to the general application of the term «chromatolysis» for the response to axotomy. However, it has become increasingly clear that the morphological manifestations of this response are different in different cells, and that chromatolysis itself is not invariably seen (Romanes, 1941). Hence the term «axon reaction», «retrograde reaction» or «cell body response» have come to be considered more appropriate to designate the whole range of alterations that may occur (Grafstein, 1975). The characteristics of these alterations have been considered in great detail by Cragg (1970) and Lieberman (1971 and 1974). During chromatolysis, usually there is also a shift of the nucleus from its normal central location in the soma to the peripheral one, but away from the axon hillock. Chromatolysis sets in approximately one day after the injury of the axon and reaches its height within about two weeks (Greep, 1966). In certain cases the cell may die but in majority of cases the process is reversible and the Nissl bodies reappear, the cell resumes its normal contour and the nucleus returns to its central position. However, it has become increasingly clear that the morphological manifestations of this response are different in different cells and that the chromatolysis itself is not invariably seen. As such, the terms, «axonal reaction», «retrograde reaction» or «cell body response» have been considered more appropriate to designate the whole range of alterations that may occur (Grafstein, 1975). The features of the response to axotomy that have been described above are seen to some degree in most neurons with axons that terminate outside the central nervous system. However, in some cases the reaction had been overlooked because it did not have the features of typical chromatolysis. Romanes (1941) produced injuries (crushing, cutting and violent rupture of the nerves) to median, ulnar, radial and musculocutaneous nerves in rabbit. He found that after a postoperative survival period of 7 to 21 days, none of the cells in the cervical region of spinal cord displayed the typical reaction which has been designated chromatolysis. He also found that some of the cells on the operated side showed an arrangement of Nissl substance which was not visible on the unoperated side, consisting of a grouping of the Nissl substance asa more homogenous ring around the centrally placed nucleus with a clearer zone of cytoplasm between this and the cell membrane; the Nissl substance was absent in the dendrites. However, de Neef (1901) found in the same animal (rabbit) that anything but violent rupture of the nerves, was ineffectual in producing chromatolysis. Van Gehuchten (1900), Bucy, (1928), Geist (1933) and many others also did not find the classical reaction (chromatolysis) in the cell body of ventral grey horn neurons after peripheral nerve trauma. In spite of this chromatolysis is frequently used as an experimental method for determining localization in the spinal cord (Romanes, 1946).
Ten Sprague-Dawley rats (6 males, 4 females) were used in the study. Under general anaesthesia (30 mg per Kg Nembutal sodium, intraperitoneally) and aseptic conditions, the trunk of the right accessory nerve (before it supplies the sternocleidomastoid and trapezius muscles) was exposed in the neck and a portion removed to prevent re-union. After 21 to 28 days of post-operative survival, the animals were killed, their circulation flushed with normal saline and perfused with 10 % formal-saline at a pressure of 120 mm Hg. After perfusion, the medulla oblongata and the 1st, 2nd, 3rd, 4th, 5th and 6th cervical segments of spinal cord were removed by a dorsal approach, separated from each other, embedded in paraffin wax and their serial transverse sections cut at a thickness of 40 micrometers. The sections were mounted on slides and stained with thionine. On the operated (right) side, a varying number of neuron somata of the ventral grey horn showed certain retrograde changes (or cell body response). No retrograde changes were observed in the neuron somata on the left (control) side. The retrograde changes (cell body response) shown by these neuron somata were of the following two types:
a) Neuron somata with typical chromatolysis. These somata showed dispersion of Nissl bodies and loss of affinity for stain (thionine). The cell often appeared more round than usual apparently because of some swelling. They had peripheral (eccentric) nucleus. Their nucleoli were either central or eccentric. From 15,42 per cent to 30,21 per cent of somata with cell body response were found to show typical chromatolysis.
b) Neuron somata with retrograde changes (cell body response) but without a typical chromatolysis. In these somata, there was a grouping of the Nissl substance as a more homogenous ring around the centrally placed nucleus with a clearer zone of cytoplasm between this and the cell membrane. Nissl substance was absent in their dendrites. From 69,79 per cent to 84,58 per cent of somata with cell body response were found to be of this type.
The work is submitted to the Scientific International Conference «Modern problems of experimental and clinical medicine modern formation. Problems and solutions of a problem of agriculture economy and management theoretical and applied sociological, politological and marketing researches», (Thailand), 20-30 December, 2010, came to the editorial office оn 22.11.2010.