CHANGES IN THE CENTRAL NERVOUS SYSTEM IN THE CAT AS THE RESULT OF TRI-O-CRESYL PHOSPHATE POISONING
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165
CHANGES IN THE CENTRAL NERVOUS SYSTEM
IN THE CAT AS THE RESULT OF TRI-O-CRESYL
PHOSPHATE POISONING
BY
J. B. CAVANAGH AND G. N. PATANGIA1
1
{From the Department of Pathology, Guy's Hospital Medical School, S~E.l,
and the Department of Anatomy, Royal Free Hospital Medical School, W.C.I)
INTRODUCTION
IN another report the changes produced by tri-o-cresyl phosphate
(T.O.C.P.) in the peripheral nerves in the cat were set out in some detail
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(Cavanagh, 1964). The pattern of damage encountered in this species
showed quite clearly that fibres of largest diameter and greatest length
were more prone to be affected than any other type of fibre. The distal
neuropathy so produced affected both motor and sensory nerve fibres
and occurred in the presence of apparently normal nerve cells, and the
centripetal progress of the damage was closely analogous to the "dying
back" process that has long been recognized as a common one amongst
human neurological diseases (Gowers, 1902; Spatz, 1952; Greenfield,
1954).
At one time, following the outbreak of poisoning by o-cresyl phosphates
in the early months of 1930, the paralysis in man was considered by exam-
ining neurologists to be predominantly motor in type and essentially a
peripheral neuropathy. The follow-up studies of Zeligs (1938) and the
post-mortem descriptions of the changes in late cases by Aring (1942)
clearly demonstrated, however, the participation of the long spinal
pathways in the process. One of us, furthermore, showed (Cavanagh,
1954) that a similar distal lesion also occurred in the long spinal tracts in
the chicken thus confirming the general systemic nature of the intoxication
suggested by Hunter et al. (1944).
One of the conclusions drawn from the observations upon the peripheral
nerves of cats was that, since the degeneration was frequently confined to
the terminal and subterminal portions of the nerves, the same might also
occur in the central nervous system. It was possible, therefore, that a
'Present address: Institute of Neurology, Queen Square, W.C.I.
^Present address: Department of Anatomy, Medical College, Gauhati, Assam, India.166 J. B. CAVANAGH AND G. N. PATANGIA
much more widespread degree of damage might in fact be occurring in the
CNS than could be demonstrated by standard neuropathological tech-
niques. These are relatively insensitive techniques and in general only
show major amounts of structural change, or changes in a late stage of
development. It was felt that if this experimental system was to have
maximum usefulness in throwing light on human disease processes any
study that enhanced precision on this point would be of value.
Only two previous reports on the anatomical changes produced in cats
by this group of substances have been published (Smith and Lillie, 1931;
Henschler, 1958) neither of which enables us to gain a clear picture of the
detailed lesions in the central nervous system. Particular attention has
been paid in the present study to rapid fixation of tissues, for autolysis
occurs in the nerve cells of animals very quickly after death, and it must
be confessed that most of the previously described changes in these cells
were probably derived from this cause. The perfusion methods used here
have given us some confidence in stating what structures are normal
morphologically and what are not.
MATERIALS AND METHODS
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The source, maintenance and treatment of the cats were detailed in
the previous publication (Cavanagh, 1964). The tri-o-cresyl phosphate
was obtained through the courtesy of Dr. H. F. Bondy from Coalite and
Chemical Products Ltd. It was administered by subcutaneous injection
in the flank in doses from 0-75 ml./kg. to 0-05 ml./kg. With the larger
doses only one injection was necessary to produce the neuro-intoxication,
but because the oil would sometimes lead to the formation of abscesses
which discharged, the injection had then to be repeated. With smaller
doses repeated injections had to be given to produce the requisite amount
of paresis (see Table I), the effects being cumulative.
Weakness and ataxia particularly in the bind limbs came on about
thirteen days after injection and progressed during the succeeding three
weeks. At the chosen time the animal was killed by injection of Nembutal
and the body was perfused through the aorta first with a small quantity of
saline and then with formal-acetic (formalin 10 per cent-acetic acid 1 per
cent) fixative. In a few animals later in the series formal-saline was
substituted for this, but although this gave equally good fixation the
hardening of the tissues was less rapid, and a further twenty-four hours'
fixation was necessary before blocks were cut out.
Standard blocks of cerebrum, including the motor cortex, mid-brain,
pons and cerebellum, upper and lower medulla, and of spinal cord at C3,
C7, Th5, Thl2, L2 and L5 levels were taken in every instance. The tissues
were slowly dehydrated, embedded in paraffin and sections were cut at 15 P.
These were routinely stained with hsmatoxylin and eosin, cresyl fast violet,
and the Glees and Marsland method for nerve fibres. Other standardTABLE I.—DISTRIBUTION OF CHANGES IN SPINAL CORD AND MEDULLARY TRACTS AT VARIOUS TIMES FROM DOSING
Day at Hyaline
death Subcorticospinal neurones
Dose No. of from Fasciculus Gracilis Spinocerebellar tracts Corticospinal tracts tracts (jgracile
Cat No. (.m./kg.) injections injection Cerv. Thor. Lumb. Brain Cerv. Thor. Lumb. Medulla Cerv. Thor. Lumb. Cerv. Thor. Lumb. nucleus)
Cr. 3 0-25 2 14
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T.P. 5 0-5 2 14
T.P. 26 0-25 2 15
T.P. 11 0-25 3 21
Cr. 4 0-25 2 21
T.P. 8 0-75 1 22
T.P. 6 0-5 1 29
T.P. 24 0-25 3 38
T.P. 19 0-25 4 39
T.P. 13 0-1 5 41
T.P. 12 0-25 5 42
T.P. 15 0-5 3 42
T.P. 14 0-1 5 45
T.P. 10 0-5 2 45
T.P. 17 005 9 59
T.P. 29 01 4 60
T.P. 20 0-25 4 64
T.P. 2 0-5 1 117168 J. B. CAVANAGH AND G. N. PATANGIA
stains were sometimes employed and the Swank-Davenport modification
of the Marcbi method for degenerated myelin was also occasionally used,
but with little additional information emerging. Frozen sections were
in several instances used to confirm the presence of myelin breakdown
products.
Pretermincd Degeneration Methods
Frozen sections were cut from several levels of brain-stem and spinal
cord at 20 n and stained by the methods of Nauta and Gygax (1954) and of
Nauta (1957). These methods require some experience both in their
execution and in their interpretation. When artefacts due to inadequate
fixation or due to handling of the tissues are avoided, the best results
occur in the presence of a few staining normal fibres. The method
demonstrates granular fragmentation of both stem axons and also pre-
terminal fibres. The former, in the tracts, are readily shown after one
week of fixation; the latter need from three to twelve months fixation for
optimal staining. The results with material fixed with formal-acetic acid
were if anything superior to those with tissue fixed in formalin alone.
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Nuclear Population Estimates
Counts of nuclei of all cells in tracts at various levels of the spinal cord
were made with an Ehrlich square ocular at a magnification of 645
diameters. Five control animals were used and in both the control and
experimental animals between 25 and 40 fields were covered, approxi-
mately half of these from each side. Previous trials showed that there was
no statistical difference between the two sides, either in the experimental or
the control animals.
RESULTS
Qualitative Results with Standard Techniques
The general changes in the white matter of the spinal cord and medulla
are set out in the table (Table I), the degrees of change being expressed as
either negative (—), one plus (+) or two plus ( 4 + ) . It will be seen that
with the doses employed very few changes were discernible in the long
tracts during the first month after injection. Such slight changes as were
demonstrable consisted in vacuolation and fragmentation of occasional
individual axons and myelin sheaths, with a reactionary infiltration of these
by microglial cells. These changes were visible only in the upper cervical
levels in the ascending tracts and in the lumbosacral regions in the descend-
ing pathways. By the end of the first month (fig. 1, Plate XXXII), however,
all these long pathways showed varying degrees of damage at their distal
ends and often for a considerable distance along their lengths. Cellular
changes were much as earlier but greater in degree, and there was an
increasing proportion of astroglial infiltration in the affected areas withC.N.S. CHANGES DUE TO T.O.C.P. 169
time (fig. 2). Axonal degeneration, characterized by swelling, increase in
argyrophilia, eosinophilic change and fragmentation, was marked indica-
ting the progressive nature of the damage, and the myelin sheath changes
accompanying these were not remarkable. Foam cells containing
sudanophilic lipid were found when they were looked for in frozen sections.
No change was found in the nerve cells of spinal ganglia or any part of
the central grey areas for the first five weeks in any animal. Everywhere
neuronal nuclear and cytoplasmic appearances were normal. After this
time, however, a new change began to make its appearance that has not
been observed before. Nerve cells of the gracile nuclei began to show
eosinophilic hyaline change so that all nuclear and cytoplasmic details
became lost. The earliest appearance of this change was in animal Cr4.
three weeks after injection, but in this cat only a very few cells were so
affected. In cats kept for longer periods this change became progressively
more severe and extensive until it was difficult to find a normal nerve cell in
the gracile nuclei (fig. 3). In long surviving animals with severe disability
a few affected cells also occurred in the cuneate nuclei and rarely in other
regions such as in the anterior horn cells and in Clarke's column. Micro-
glia and a few fibrillary astrocytes occurred in association with this change.
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Histochemical Tests
Tests on the hyaline material in nerve cells showed no metachromasia
with basic dyes, a negative reaction with the periodic acid-Schiff procedure
and with lipid stains and weakly positive reaction with tests for protein
groups. Accumulation of lipids and of polysaccharides could, therefore,
be excluded and it was probable that most of the hyaline material con-
sisted of basic proteins. Occasionally in silver preparations a suggestion
of neurofibrillary thickening was found, but this was morphologically
unlike that found in neurofibrillary degeneration of nerve cells in human
brain disease.
Changes in Nuclear Populations in Posterior Columns
and in Corticospinal Tracts
In the posterior columns variation in the mean number of cells per
standard field from one level to another in the normal animal was small.
In poisoned animals counts of nuclei in the gracile tracts showed an in-
crease in number of nuclei per field which varied according to the duration
of survival after dosing and to the spinal level (fig. 4). There was also
some variation that correlated approximately with the functional state of
the animal, but since it was not possible to assess change in any one func-
tion that could specifically be ascribed to these tracts one cannot be precise
on this point.
From the figure (fig. 4) it will be seen that in the cervical level the number
of cells per unit area has more than doubled between thirty and forty days170 J. B. CAVANAGH AND G. N. PATANGIA
»oo\
•00%
Medulla
loon
IOO%
. * • eoo%
C3
K>OV
* C7 " ^
100%
nod .»...#. >oo\
Th5
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lOO* 100%
100%
Thl2
too*
L2
20 20 4O
OATS AFTER INJECTION A DAY S AFTER INJECTS B
FIG. 4.—Changes in nuclear populations of fasciculus gracilis (A) and corticospinal
tracts (B) in cats at various days after injection of T.O.C.P. Dots are counts of
nuclear numbers per unit area expressed as percentage of normal (100 per cent).
after injection. Increase above normal was slight at fourteen days but
appreciable at about twenty-one days. In the thoracic levels the same
pattern is evident, but the numbers of nuclei do not reach the figure found
in the cervical levels. The change in the lumbar regions is even less
marked.
Changes in the nuclear populations in the corticospinal tracts are analo-
gous to those in the posterior columns, both in the order of increase and
the distribution of the change along the tracts, but in this case the lower
thoracic and lumbar levels showed the highest cell densities. The cell
counts at medullary and cervical levels were less markedly changed.C.N.S. CHANGES DUE TO T.O.C.P. 171
Since there was no appreciable difference found in the length of nuclei
of the tracts in longitudinal and transverse sections the correction used by
Abercrombie (1946) for peripheral nerve was not employed in obtaining
the figures for these tables. This is in accord with the observations of
Joseph (1954) in his nuclear population study of degeneration following
section of the posterior columns in the rabbit.
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HMuUa
C.2
c.e
T.7
LS
Fio. 5.—T.P. 32. 19 days from injection. Diagram of lesions (dots) in anterior
vermis, nucleus gracilis, inferior olive and lumbosacral grey matter. Based on Nauta
preparations.TABLB n.—DISTRIBUTION OF PRETERMINAL DEGENERATION (NAUTA) IN GREY SUBSTANCE OF SPINAL CORD AND BRAIN-STEM AT
VARIOUS TIMES AFTER DOSING
Dorsal
Survival Funicular Projections Lateral Lateral
Cat Dose No. of (days from Spinal Grey Matter Gradle Cuneate cervical reticular
No. (ml./kg) Injections 1st injection) C. Th. L. S. nucleus nucleus nucleus nucleus Vermis Other sites
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T.P. 30 0-25 1 7 - - — — — u
T.P. 31 0-25 1 15 + - -
T.P. 26 0-25 2 18 - + - + Inf. olive +
T.P. 32 0-25 1 19 + + + - + — + + Inf. olive + <
T.P. 11 0-25 3 21 + + - - -
T.P. 6 0-25 1 2 9 - + + + + - + + + Nuc. dentatus + O
Nuc. fastigii + X
T.P. 24 0-25 3 38 + + Inf. olive +
Inf. olive + Q
T.P. 33 0-25 1 3 9 + 4 + + + + Inf. olive + O
T.P. 12 0-25 5 42 + - + — Inf. olive+ + +
TJP. 14 01 5 4 5 + 4 — — Dorsal \ lemniscal
Ventral J nuc. +
T.P. 17 0-05 9 59 + - — — Medial vestibular nuc. +
T.P. 29 0-1 4 6 0 + 4 ++ + N u c dentatus and
fastigii +
GIA
Nuc. interpositus +
Medial vestibular nuc +
Dorsal lemniscal nuc. +
Inf. olive + +
T.P. 2 0-5 1 117 + + +++ + + — Inf. olive +
T.P. 35 01 3 329 +C.N.S. CHANGES DUE TO T.O.C.P. 173
Preterminal Degeneration Studies (Table II; figs. 5 to 8)
The most striking outcome of this important aspect of the investigation
was that relatively few additional areas of damage over and above those
predictable from the tract changes were found. Almost all the changes
were explicable on the basis of terminal degeneration of long ascending
and descending spinal cord pathways. The number of these pathways was,
however, greater than has been formerly considered, probably in part
because we kept the animals alive considerably longer than other authors
and thus the full pattern of degeneration was allowed to develop.
(a) Dorsal fimiculi.—From the eighteenth day after inoculation increas-
ing amounts of preterminal degeneration were found symmetrically
throughout both gracile nuclei. They were confined to these nuclei and
none were present in the cuneate nuclei with sole exception of one animal
(T.P. 29) in which a small amount was visible in the ventral part of the
latter. This accords with the absence of any changes, axonal or glial, in
the cuneate tracts in any animal.
(b) Spinocerebellar tracts.—Degeneration was found in both dorsal and
ventral spinocerebellar tracts above C.7 spinal level, and most marked
at their rostral ends, from the end of the third week. Preterminal changes
were correspondingly abundant in the anterior vermis and on either side
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of the fissura secunda. The earliest change was encountered in these
tracts in T.P. 26, killed on the eighteenth day, in which degenerated
preterminals could only be seen in the most anterior region of the vennis
(lingula). Outside the cerebellar cortex changes were also found consis-
tently in the lateral reticular nucleus of the medulla, in the nuclei fastigii,
interpositus and dentatus of the cerebellum, and in a group of cells at the
junction of mid-brain and pons. These probably represent terminals of
collaterals from the spinocerebellar system (Jensen and Brodal, 1954), but
in addition may well contain terminals from other ascending systems
whose projection centres are not well defined. On the cervical spinal
cord degenerating collaterals could be traced from the ventral spino-
cerebellar tracts to the intermediate areas and anterior horns of the grey
matter.
(c) Spino-olivary tracts.—Degenerating preterminals occurred early and
were abundant in the ventrolateral portions of both the medial accessory
and the dorsal accessory nuclei of the interior olives. Serial sections
showed that these changes were limited to these regions which, according
to Brodal et al. (1950), are projection centres for the spino-olivary tracts.
In addition degenerating fibres could be traced from the dorsolateral white
matter into the lateral cervical nucleus. This centre has been shown by
Brodal and Rexed (1953) in the cat to receive fibres from that region of the
spinal cord that lies caudal to the origins of the dorsal spinocerebellar
tracts. Grundfest and Carter (1954) from electro-physiological evidence
considered that the spino-olivary fibres relayed in this centre.174 J. B. CAVANAGH AND G. N. PATANGIA
{d) Lateral corticospinal tracts.—The highest level in which degenerating
fibres have been found in these tracts is in the cervical regions (C.7).
From the eighteenth day onwards, below this level, there was in all cats a
steadily increasing amount of damage. Fragmenting fibres from these
tracts could be traced in most cases into the intermediate grey matter of
'(canton)
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FIG. 6.—T.P. 33. 39 days from injection. Diagram of lesions (dots) in cerebellar
vermis, medulla and spinal cord. Based on Nauta preparations.C.N.S. CHANGES DUE TO T.O.C.P. 175
C.6.
T.I.
T.7.
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L.2.
L.7.
S.I.
S.2.
Fio. 7.—T.P. 14. 45 days from injection. Diagram of lesions (dots) in spinal cord.
Based on Nauta preparations.
the lumbosacral spinal cord. These were seen in only very small numbers,
however, in the nucleus proprius of the posterior horn, a centre which,
according to Chambers and Liu (1957) and Nyberg-Hansen and Brodal
(1963) receives terminals from the posterior group of fibres which enter
the spinal grey matter. Most of the degenerating fibres seemed to come
from the anterior group of entering corticospinalfibreswhich terminate in176 J. B. CAVANAGH AND G. N. PATANGIA
the intermediate grey matter. No degenerating preterminals were found
upon anterior horn cells, on any motor cranial nerve nuclei, or on cells
of the reticular formation.
(e) Subcortical-spinalfibres.—(i)In lateral funiculi. Apart from the
well-defined corticospinal tracts, other degenerating fibres were present in
the lateral white matter that might arise from the red nuclei, or from the
reticular formation (Kuru, Kurati and Koyama, 1959; Staal, 1961).
Degenerating fibres in these pathways were confined to the lumbosacral
regions.
(ii) In ventral funiculi. Degenerating fibres were constantly present
lying on either side of the anteriorfissureand beneath the pia on the ventral
surface of the cord below the mid-thoracic level. Even from the 18th day
degenerating preterminals from fibres entering the anterior horns from
these pathways could be discerned in the caudal levels, their numbers
increasing with time.
The exact origins and terminations of the fibres in these ventral path-
ways are still the subject of discussion. The large diameter fibres in the
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Ffeni
Medulla
Fio. 8A.
For caption see p. 177C.N.S. CHANGES DUE TO T.O.C.P. 177
Medulla or decimation
of Pyramidi
C.2.
C4.
C.7.
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T.4.
T.IO.
L.4.
S.2.
Fia 8B.
FIG. 8.—T.P. 29. 60 days after injection. Diagram to show lesion (dots) (A) in
cerebellum and medulla, (B) in spinal cord. Based on Nauta preparations.
immediate neighbourhood of the ventromedian fissure have been tenta-
tively considered to be extensions of the medial longitudinal fasciculus of
the brain-stem (Massopust, 1957; Staal, 1961). Fibres lying lateral and
ventrolateral to these, in the caudal half of the spinal cord may arise from
12 BRAIN—VOL. LXXXVUI178 J. B. CAVANAGH AND G. N. PATANGIA
the tectum of the mid-brain from the interstitial nucleus of Cajal, from
Deiter's (vestibular) nuclei and from the pontine reticular formation (Staal,
1961; Staal and Verhaart, 1963). Because of the ill-defined limits of these
pathways, it is not possible to decide from this material the origins of the
fibres undergoing degeneration. No cell changes were detected in these
or any other mid-brain region.
(f) Spinal grey columns.—There is considerable uncertainty as to the
origin of the preterminal fibres found to be undergoing massive degenera-
tion in the grey columns of the lumbosacral region. The absence of
degenerating fibres in the juxta-griseal white matter and their presence
only in long pathways suggest that internuncial fibres are not attacked.
Fibres from the corticospinal tracts are considered in the cat to end almost
exclusively on neurones in the intermediate zone (Chambers and Liu,
1957; Nyberg-Hansen and Brodal, 1963). Moreover in confirmation of
this Lloyd (1941) found, from electrophysiological data, that all cortico-
spinal fibres ended upon internuncial neurones in this species. Besides
their likely origin from several brain-stem centres noted above, the
additional possibility remains that some of these degenerating preterminals
may be the proximal (monosynaptic) fibres of dorsal root ganglion cells,
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but in fact degenerating preterminals were not found in the immediate
neighbourhood of spinal motoneurones in the lumbosacral levels. In the
cervical region, however, many degenerating preterminals were present
near motoneurones, and these, we believe, may be collaterals from spino-
cerebellar fibres (Liu, 1953).
DISCUSSION
The purposes of this communication are twofold. First, to demonstrate
that the changes in the central nervous system following neurointoxication
by tri-or/Ao-cresyl phosphate are the same in their general nature as those
disclosed in the peripheral nervous system. This has in fact been done
with regard to fibre length, for the change whether in ascending or descend-
ing pathways is more marked in longer than in shorter tracts and shows a
diminishing effect as the perikarya of the affected fibres is approached.
This pattern is reflected, as the cell-population measurements show, in the
glial response along the course of these tracts. It has not been possible to
establish the other correlation, namely with fibre diameter, for the central
nervous system, because the methods for enumerating fibre size in central
fibres are less satisfactory than for peripheral nerve. It has been attempted
by Haggqvist (1937) and by Lassek and Rasmussen (1939) and then-
results show that most of the pyramidal fibres are in the small diameter
group. Only about 2 per cent are in fact over about 12p. This has been
recently confirmed by van Beusekom (1955) in the cat. The appearances
of the fibres in the dorsal funiculi lead us to believe that these also are of
small diameter, and certainly their conduction, according to Holmgren
(1954), is very slow (4-4-1-5 m./sec). Only the spinocerebellar tractC.N.S. CHANGES DUE TO T.O.C.P. 179
seems on inspection under the microscope to have consistently large dia-
meter fibres. Measurements have shown that they range from 10n to 18n
in the cat and have correspondingly high conduction velocities (86-160
m./sec.) (Grundfest and Campbell, 1942). The actual numbers of large
fibres is, however, small compared with the numbers of small diameter
fibres in this tract (van Beusekom, 1955). Since in the cat there appears to
be no great difference in the amount of degeneration in these three major
pathways, fibre diameter, at least in the central nervous system, does not
appear to be an important factor in predisposing to damage.
The second purpose was to determine by using the Nauta method,
whether any fibre systems, other than those revealed by standard methods,
were degenerating terminally. We had been much impressed by the
widespread terminal changes in the peripheral nerves, the extent of which
was not at all revealed by examining peripheral nerve trunks. While
these distal changes are ultimately reversible in peripheral nerves, there is
less evidence that the same regenerative capacity obtains in the CNS, or
that, when it does occur, it is as effective (Liu and Chambers, 1955, 1958).
Any discontinuity, therefore, however short, would disrupt function.
Additional long pathways, such as the spino-olivary tracts and subcortico-
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spinal tracts were also extensively damaged, but again only in their distal
regions. No evidence was found for degeneration in short intersegmental
fibres and no additional pathways in the brain-stem were found to be
affected. The lesion is not, therefore, a graded effect in many different
fibre systems, although it could be behaving as such in those systems that
are affected. This does not exclude the possibility, however, that the
metabolic disturbance ultimately leading to distal atrophy is shared by
many neurones of diverse type and that only those with the longest fibres
progress to a state of irrecoverable damage.
An additional feature of interest in this connexion is the occurrence
of hyaline degeneration of nerve cells, particularly in the gracile nuclei, but
occasionally elsewhere, as a late phenomenon. This is not an effect
peculiar to ortho-ciesyl phosphates for similar changes have been seen
by the authors in a few long survivors from paralysis due to 'Mipafox'
(N, N^diamidic-dimethyl-phosphoronuoridate). So long delayed is the
change, however, that it would seem likely that it might be a transneuronal
type of atrophy due to extensive denervation of this nucleus rather than to
a late toxic effect.
SUMMARY
The changes found in the CNS of cats after tri-o/V/io-cresyl phosphate
are consistent with this being a "dying back" process of nerve fibres in the
long pathways. Preterminal studies (Nauta) have shown degeneration in
the projection areas of most of the long ascending and descending spinal
tracts. No additional areas of degeneration have been found elsewhere in
the brain. Whereas fibre length would seem important in the mechanism180 J. B. CAVANAGH AND G. N. PATANGIA
of degeneration, fibre diameter has less influence in the CNS than it
appears to have in determining the peripheral nerve lesions.
ACKNOWLEDGMENTS
We would like to acknowledge the interest and helpful advice of Pro-
fessor R. E. M. Bowden particularly in respect of the interpretation of
the pretenninal degeneration studies. The help of Miss F. H. Ellis and
Mr. J. Burnard, of the Royal Free Hospital School of Medicine, in
photography is gratefully acknowledged. One of us (J. B. C.) was in
receipt of a research fellowship from the Endowment Fund of Guy's
Hospital during the course of this work. The other of us (G. N. P.)
gratefully acknowledges the receipt of an overseas Scholarship from the
Government of Assam (India).
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Ficl.—T.P. 14. 45 days from injection. Dorsal columns in cervical region showing
scattered axonal swelling and fragmentation in fasciculus gracilis. Glees & Marsland.
X130.
FIG. 2.—T.P. 15. 42 days from injection. Dorsal columns in cervical region showing
increased nuclear numbers in fasciculus gracilis. Cresyl fast violet. X55.
To illustrate article by J. B. Cavanagh and G. N. Patangia.PLATE XXXIII
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FIG. 3.—T.P. 2. 117 days From injection. Hyaline neurones in gracile nucleus.
Haematoxylin and eosin. x 940.
To illustrate article by J. B. Cavanagh and G. N. Patangia.You can also read
