Folia Psychiatrica et Neurologica Japonica, Vol. 33, No. 1, 1979
Experimental Chronic Lead Poisoning Kenichi Nagatoshi, M.D. Department of Neurology, Toxicology Institute, Kumanioto University Medical School, Kumarrioto
INTRODUCTION
Regarding chronic lead poisoning, Gordon et ~ 1 have . ~ reported clinical observations of an infant, and Moncrieff et ~ 1 have . ~ described the mental deterioration in children. Many researchers described severe changes in the CNS” in children. On the other hand, histopathological changes of the CNS in adult patients have been rarely described and histopathological changes experimentally induced by chronic lead poisoning have not yet been reported. For this reason, the changes in the nervous system of adult rats experimentally induced by lead carbonate were examined in the present study. MATERIALS AND METHODS
The wislar strain of male rats (body weight 4 0 0 g ) was used-I0 in the experimental and 10 in the control group. To each rat of the experimental group, 1 g/kg of lead carbonate mixed with rations was given orally each day for 600 days. 2-3 days after withdrawal of the drug, the experimental and control rats were perfused through the heart with 3% glutaraldehyde in a phosphate buffer for 40 min. Blocks from several parts of the brain, spinal cord and peripheral nerve were postfixed in 2% osmium tetroxide in phosphate buffer for two hours at OOC. They were dehydrated -
Received for publication Oct. 5 , 1978.
in graded alcohol and embedded in epon. Sections for light microscopy were cut on a Porter-Blum I microtome, and stained with toluidine blue. Ultra thin sections of 500 A thick were stained with uranyl acetate and lead acetate. They were examined by a Hitachi 12 A electron microscope. RESULTS
The average increase in body weight of the rats is shown in Table 1. The increase in body weight of the experimental group was slightly less than that of the control group. On the 300th day after beginning the lead carbonate administration, the increase in body weight stopped. It started to decrease after the 300th day and on the 600th day, the body weight decreased to 400 g. All of the experimental rats showed anemia and were inactive in behavior with a slight disturbance of gait. Histopathological Findings In the peripheral nerves, the anterior nerve root fibers and posterior nerve root fibers were intact (Fig. 1 ) . Changes in the proximal part of the peripheral nerve fibers were slight. However, the distal parts of the nerve fibers under the knee were severely damaged (Fig. 2 ) . This change belonged to periaxial segmental demyelination (Fig. 3). At the motor endplate, the axon terminal contained large vacuoles and degenerated mitochondria or showed atrophy with high electron density (Fig. 4). There was no
K. Nagatoshi
124
700
600
500
400
g day
1
I
1
I
I
I
100
200
300
400
500
600
-------
Poisoning group Controlled group
Table 1: The Curved Line of Body Weight
change in the spinal cord, when compared with the control group. No remarkable change was found in the central nervous system. However, some perivascular edema of the capillary in the cortex were found (Fig. 5 ) . In addition, many satellite cells and microglial cells contained brown-yellowish substances (Fig. 6 ) . Observing several parts of the nervous systcm by electron microscope, the ganglion cells in the dorsal root contained numerous lipofuscins in the cytoplasm (Fig. 7). T h e endothelial cells and satellite cells in the cerebral cortex contained many vesicles in their cytoplasms (Fig. 8 ) . The endothelial
Fig. 1 : Anterior root fibers (under half) and dorsal root ganglion with nerve fibers (upper half). There is no noticeable change either of the fibers. Toluidine blue stain. X
230
Fig. 2: Transverse section of sciatic nerve fibers at the part of knee. Myelinated nerve fibers are remarkably decreased and solid changes of many myelinated nerve fibers. Toluidine blue stain. X 90 Fig. 3. Longitudinal section of sciatic nerve fibers. This shows periaxial segmental demyelination (arrow) Toluidine blue stain. X
300
Fig. 4: Motor neuron endplate. Large vacuoles ( V ) and degenerated mitochondria are observed in the endplate. X 50000
125
Experimental Chronic Lead Poisoning
Fig. 1
Fig. 3
Fig. 2
Fig. 4
126
K. Nagatoshi
Fig. 6 Fig. 5 : Cerebral cortex. Perivascular edema of capillaries (arrow) are observed. Toluidine blue stain. X 300 Fig. 6: Cerebral cortex. Satellite cells of the blood vessel and microglial cells (arrow) contain a great deal of brown-yellowish substances. Toluidine blue stain. x 200 Fig. 7: Dorsal root ganglion cell. A great deal of lysosornes is contained in the cytoplasm of ganglion cell. ( N ) nucleus. X 5500
Fig. 7
Experimental Chronic Lead Poisoning
127
cells showed high electron density with many vesicles and ribosomes, and perivascular edema was found diffusely showing a swelling of perivascular feet of astrocytes (Figs. 9 and 10) and the myelinated nerve fibers adjacent to edema were destroyed (Fig. 10). However, the nerve cells situated near the edema did not show any change. Observed by a light microscope, the satellite cells and microglial cells contained a great deal of lysosomes in their cytoplasms (Figs. 11 and 12).
Fig. 8: Capillary in the cerebral cortex. Endothelial cell (E) and satellite cell (S) contain many pinocytotic vesicles. (L) Lumen of blood vessel. X 40000 Fig. 9: Cerebral cortex. Along the blood vessel, perivascular edema is seen. The processes of astrocytes are swollen. The blood vessel shows electron high density and irregular shape. X 7500
K. Nagatoshi
i28
Fig. 11
Experimental Chronic Lead Poisoning
DISCUSSION In 1880-8 1, Gomvult' first described chronic lead poisoning leading to nerve fiber lesion (segmental demyelination) . Villaverde2 reported that the distal parts of the nerves showed severe lesions and a minor degree of damage was seen at all levels. Schlaepher" examined lead poisoned rats and reported that significant alterations were predominantly located in the dorsal root ganglia. The ganglion cells showed an increase of lysosomal acid phosphatase activity. Focal concentrations of this enzymatic activity were also noted in the perinodal axoplasm of the peripheral nerve fibers. Lampert and Schochet" studied chronic poisoning in rats by an electron microscope and found degeneration and proliferation of Schwann cells, degeneration of related myclin segments beginning at the nodes of Ranvier or Schmitt-Lantermann clefts, and separation, disintegration and phagocytosis of myelin lamellas. New lamellas formed later from Schwann cell processes, but some degenerated again. Similar findings as described above were observed in the present experiment. However, in the peripheral nerve, only the distal part was severely damaged. Michael' experimented on lead encephalopathy in neonatal Long-Evans rats. He reported petechial hemorrhages in the cerebellum, following edema in the internal granular layer, and concluded that growing
Fig. 10: Cerebral cortex. Perivascular edema: processes of astrocytes are swollen and myelinated nerve fibers adjacent to the edema are destructive (arrow). Nerve cell is intact (under right). ( N ) nucleus. X 7500 Fig. 11: Satellite cell and nerve cell. Satellite cell contains a great deal of lysosomes. ( N ) nerve nucleus. X 4500 Fig. 12: Microglial cell contains a great deal of lysosome-like substances. X 4500
129
capillaries were the primary lesion of the central nervous system damaged by intoxication. The endothelial bud (or angioblast) appears to be a structure sensitive to lead poisoning and encephalopathy probably results from the death of many of these buds. Wells et ~ 1 . ' ~reported histopathological lesions in the brain consisting of focal vacuolation of the neuropil, neuronal necrosis and changes in the capillary walls. They stated that the encephalopathy was associated with elevated blood and tissue lead levels, but could not be correlated with pathological effects in other organs, and the nature of the lesions suggested a basic change in the transport mechanism between the blood and brain. Raimondi et d . l o emphasized capillary changes in homogenization of basement membrane in the gray matter, and glial swelling. Michael' reported hemorrhagic lesions throughout the brain and in the cerebellum. There were fluidfilled cavities in the internal granular layer and fiber tracts. Krigman et a1.6 used postnatal 30-day rats and reported that the neurons were smaller, and more important, the proliferation of neurite processes in the neuropil was retarded. There was also an apparent reduction in the number of synapses per neuron. Bouldin et ul.' experimented on acute lead encephalopathy in adult guinea pigs and found that there was no cerebral capillary alteration or demonstrable BBB dysfunction. From this, the encephalopathy in the absence of any vascular alteration suggested that lead can produce a primary toxic effect at the neuronal level. In the present study, lead carbonate was given to animals for a long time in order to find histopathological changes. As a result, a leading change was found in the blood vessels : there was perivascular edema, and endothelial cells contained many pinocytotic vesicles. The increase of pinocytotic vesicles in the endothelial cells probably show acceleration of permiability of the blood brain barrier. Moreover the myelinated nerve
K. Nagatoshi
130
fibers adjacent to the edema were destroyed. In addition to these findings, pericytes and microglial cells contained a great deal of lysosomal substances, while the nerve cells were intact. From the above findings, it is suggested that lead directly induces a primary toxic effect on the blood vessel and induces perivascular edema. Following this change, the nerve fibers adjacent to the edema may become involved. On the other hand, there is a possibility that lead produces a primary toxic effect at the neuronal level but no histopathological change in the nerve cell was found. Then, many satellite cells and microglial cells contained a great deal of lysosomal substances. This might have some relation to the lead invading the brain. Up to today, histopathological changes in CNS of adult animals experimentally induced by lead have not yet been reported. However, the histopathological changes were similar to those of the neonatal animal. Further detailed research in the future is necessary to find out whether or not lead directly effects the nerve cell or organellae. SUMMARY
In the peripheral nerve, the distal part of the nerve fibers was remarkably damaged-periaxial segmental demyelinationwhile the proximal part of nerve fibers was only slightly affected. In the CNS, perivascular edema of the small blood vessels and capillaries was observed in the cerebral cortex and cerebellar cortex. All endothelial cells of these blood vessels showed a high electron density with many pinocytotic vesicles and ribosomes. Following these changes, the nerve fibers adjacent to the edema were destroyed. The above-mentioned findings seem to indicate that lead induces a toxic effect on the blood vessel and produces perivascular edema in the CNS of adult animals. This may induce brain dysfunction.
ACKNOWLEDGEMENT
I wish to thank Prof. T. Miyakawa, Dr. I. Shikaki, Dr. A. Shimoji and Dr. R. Kuramot0 for their cooperation in the present study. REFERENCES 1 Bouldin, T. W. and Krigman, M. R.: Acute
lead encephalopathy in the guinea pig, Acta, Neuropath (Berl.), 33: 185-1 90, 1975. 2 de Villaverde, J. M.: Quoted by Meyer, A. pp. 268-269 (1926, 1927).
3 Gombault, A,: Contribution ii 1'Ctude anatomique de la nCvrite parenchymateuse subaigiie ou chronique: nivrite segmentaire pki-axile, Archives de Neurologie, 1: 11-38, 1880-1881. 4 Gordon, I. and Whitehead, T. P.: Lead
poisoning in an infant from lead nippleshields: association with rickets, Lancet, 2: 647-650, 1949. 5 Krigman, M.R., Druse, M., Traylor, T. D.,
Wilson, M. H., Newell, L. R. and Hogan, E. L.: Lead encephalopathy in the developing rat: effect on cortical ontogenesis, J Neuropath & Exper Neurol, 33: 58-73, 1974. 6 Lampert,
P. W. and Schochet, S. S.: Demyelination and remyelination in lead neuropathy, Electron microscopic studies, J Neuropath & Exper Neurol, 27: 527545, 1968 b. 7 Michael, F. P.: Lead encephalopathy in neonatal Long-Evans rats poisoned via an esophageal catheter, Amer J of Path, 86: 4 8 5 4 8 8 , 1977. 8 Moncrieff, A. A., Koumides, 0. P., Clay-
ton, B. E., Patrick, A. D. and Renwick, A.G.E.: Lead poisoning in children, Arch of Disease in Childhood, 39: 1-13, 1964. 9 Pentschew, A. and Garro, F.: Lead encephalomyelopathy of the suckling rat and its implications on the porphyrinopathic nervous disease, Acta Neuropath (Berl.), 6: 266-278,
1966.
10 Raimondi, J., Beckman, F. and Evans, P.: Fine structural changes in human lead encephalopathy, J Neuropath & Exp Neurol, 72: 154, 1968. 1 1 Schlaepfer, W. W.: Ultrastructural and histochemical studies of a primary sensory neuropathy in rats produced by chronic lead intoxication, J Neuropath & Exper
Experimental Chronic Lead Poisoning Neurol, 27: 11 1-1 12, 1968. 12 Verhaart, W.J.C.: Lead encephalopathy simulating diffuse sclerosis in a Chinese infant, Amer J of Disease of Children, 61: 1246-1250, 1941.
131
13 Wells, G.A.H., Howell, J. McC. and Gopi-
nath, C. : Experimental lead encephalopathy of calves, Histopathological observations on the nature and distribution of the lesions, Neurol & Applied Neurobiol, 2: 175-190, 1976.
Experimental Chronic Lead Poisoning Kenichi Nagatoshi, M.D. Department of Neurology, Toxicology Institute, Kumanioto University Medical School, Kumarrioto
INTRODUCTION
Regarding chronic lead poisoning, Gordon et ~ 1 have . ~ reported clinical observations of an infant, and Moncrieff et ~ 1 have . ~ described the mental deterioration in children. Many researchers described severe changes in the CNS” in children. On the other hand, histopathological changes of the CNS in adult patients have been rarely described and histopathological changes experimentally induced by chronic lead poisoning have not yet been reported. For this reason, the changes in the nervous system of adult rats experimentally induced by lead carbonate were examined in the present study. MATERIALS AND METHODS
The wislar strain of male rats (body weight 4 0 0 g ) was used-I0 in the experimental and 10 in the control group. To each rat of the experimental group, 1 g/kg of lead carbonate mixed with rations was given orally each day for 600 days. 2-3 days after withdrawal of the drug, the experimental and control rats were perfused through the heart with 3% glutaraldehyde in a phosphate buffer for 40 min. Blocks from several parts of the brain, spinal cord and peripheral nerve were postfixed in 2% osmium tetroxide in phosphate buffer for two hours at OOC. They were dehydrated -
Received for publication Oct. 5 , 1978.
in graded alcohol and embedded in epon. Sections for light microscopy were cut on a Porter-Blum I microtome, and stained with toluidine blue. Ultra thin sections of 500 A thick were stained with uranyl acetate and lead acetate. They were examined by a Hitachi 12 A electron microscope. RESULTS
The average increase in body weight of the rats is shown in Table 1. The increase in body weight of the experimental group was slightly less than that of the control group. On the 300th day after beginning the lead carbonate administration, the increase in body weight stopped. It started to decrease after the 300th day and on the 600th day, the body weight decreased to 400 g. All of the experimental rats showed anemia and were inactive in behavior with a slight disturbance of gait. Histopathological Findings In the peripheral nerves, the anterior nerve root fibers and posterior nerve root fibers were intact (Fig. 1 ) . Changes in the proximal part of the peripheral nerve fibers were slight. However, the distal parts of the nerve fibers under the knee were severely damaged (Fig. 2 ) . This change belonged to periaxial segmental demyelination (Fig. 3). At the motor endplate, the axon terminal contained large vacuoles and degenerated mitochondria or showed atrophy with high electron density (Fig. 4). There was no
K. Nagatoshi
124
700
600
500
400
g day
1
I
1
I
I
I
100
200
300
400
500
600
-------
Poisoning group Controlled group
Table 1: The Curved Line of Body Weight
change in the spinal cord, when compared with the control group. No remarkable change was found in the central nervous system. However, some perivascular edema of the capillary in the cortex were found (Fig. 5 ) . In addition, many satellite cells and microglial cells contained brown-yellowish substances (Fig. 6 ) . Observing several parts of the nervous systcm by electron microscope, the ganglion cells in the dorsal root contained numerous lipofuscins in the cytoplasm (Fig. 7). T h e endothelial cells and satellite cells in the cerebral cortex contained many vesicles in their cytoplasms (Fig. 8 ) . The endothelial
Fig. 1 : Anterior root fibers (under half) and dorsal root ganglion with nerve fibers (upper half). There is no noticeable change either of the fibers. Toluidine blue stain. X
230
Fig. 2: Transverse section of sciatic nerve fibers at the part of knee. Myelinated nerve fibers are remarkably decreased and solid changes of many myelinated nerve fibers. Toluidine blue stain. X 90 Fig. 3. Longitudinal section of sciatic nerve fibers. This shows periaxial segmental demyelination (arrow) Toluidine blue stain. X
300
Fig. 4: Motor neuron endplate. Large vacuoles ( V ) and degenerated mitochondria are observed in the endplate. X 50000
125
Experimental Chronic Lead Poisoning
Fig. 1
Fig. 3
Fig. 2
Fig. 4
126
K. Nagatoshi
Fig. 6 Fig. 5 : Cerebral cortex. Perivascular edema of capillaries (arrow) are observed. Toluidine blue stain. X 300 Fig. 6: Cerebral cortex. Satellite cells of the blood vessel and microglial cells (arrow) contain a great deal of brown-yellowish substances. Toluidine blue stain. x 200 Fig. 7: Dorsal root ganglion cell. A great deal of lysosornes is contained in the cytoplasm of ganglion cell. ( N ) nucleus. X 5500
Fig. 7
Experimental Chronic Lead Poisoning
127
cells showed high electron density with many vesicles and ribosomes, and perivascular edema was found diffusely showing a swelling of perivascular feet of astrocytes (Figs. 9 and 10) and the myelinated nerve fibers adjacent to edema were destroyed (Fig. 10). However, the nerve cells situated near the edema did not show any change. Observed by a light microscope, the satellite cells and microglial cells contained a great deal of lysosomes in their cytoplasms (Figs. 11 and 12).
Fig. 8: Capillary in the cerebral cortex. Endothelial cell (E) and satellite cell (S) contain many pinocytotic vesicles. (L) Lumen of blood vessel. X 40000 Fig. 9: Cerebral cortex. Along the blood vessel, perivascular edema is seen. The processes of astrocytes are swollen. The blood vessel shows electron high density and irregular shape. X 7500
K. Nagatoshi
i28
Fig. 11
Experimental Chronic Lead Poisoning
DISCUSSION In 1880-8 1, Gomvult' first described chronic lead poisoning leading to nerve fiber lesion (segmental demyelination) . Villaverde2 reported that the distal parts of the nerves showed severe lesions and a minor degree of damage was seen at all levels. Schlaepher" examined lead poisoned rats and reported that significant alterations were predominantly located in the dorsal root ganglia. The ganglion cells showed an increase of lysosomal acid phosphatase activity. Focal concentrations of this enzymatic activity were also noted in the perinodal axoplasm of the peripheral nerve fibers. Lampert and Schochet" studied chronic poisoning in rats by an electron microscope and found degeneration and proliferation of Schwann cells, degeneration of related myclin segments beginning at the nodes of Ranvier or Schmitt-Lantermann clefts, and separation, disintegration and phagocytosis of myelin lamellas. New lamellas formed later from Schwann cell processes, but some degenerated again. Similar findings as described above were observed in the present experiment. However, in the peripheral nerve, only the distal part was severely damaged. Michael' experimented on lead encephalopathy in neonatal Long-Evans rats. He reported petechial hemorrhages in the cerebellum, following edema in the internal granular layer, and concluded that growing
Fig. 10: Cerebral cortex. Perivascular edema: processes of astrocytes are swollen and myelinated nerve fibers adjacent to the edema are destructive (arrow). Nerve cell is intact (under right). ( N ) nucleus. X 7500 Fig. 11: Satellite cell and nerve cell. Satellite cell contains a great deal of lysosomes. ( N ) nerve nucleus. X 4500 Fig. 12: Microglial cell contains a great deal of lysosome-like substances. X 4500
129
capillaries were the primary lesion of the central nervous system damaged by intoxication. The endothelial bud (or angioblast) appears to be a structure sensitive to lead poisoning and encephalopathy probably results from the death of many of these buds. Wells et ~ 1 . ' ~reported histopathological lesions in the brain consisting of focal vacuolation of the neuropil, neuronal necrosis and changes in the capillary walls. They stated that the encephalopathy was associated with elevated blood and tissue lead levels, but could not be correlated with pathological effects in other organs, and the nature of the lesions suggested a basic change in the transport mechanism between the blood and brain. Raimondi et d . l o emphasized capillary changes in homogenization of basement membrane in the gray matter, and glial swelling. Michael' reported hemorrhagic lesions throughout the brain and in the cerebellum. There were fluidfilled cavities in the internal granular layer and fiber tracts. Krigman et a1.6 used postnatal 30-day rats and reported that the neurons were smaller, and more important, the proliferation of neurite processes in the neuropil was retarded. There was also an apparent reduction in the number of synapses per neuron. Bouldin et ul.' experimented on acute lead encephalopathy in adult guinea pigs and found that there was no cerebral capillary alteration or demonstrable BBB dysfunction. From this, the encephalopathy in the absence of any vascular alteration suggested that lead can produce a primary toxic effect at the neuronal level. In the present study, lead carbonate was given to animals for a long time in order to find histopathological changes. As a result, a leading change was found in the blood vessels : there was perivascular edema, and endothelial cells contained many pinocytotic vesicles. The increase of pinocytotic vesicles in the endothelial cells probably show acceleration of permiability of the blood brain barrier. Moreover the myelinated nerve
K. Nagatoshi
130
fibers adjacent to the edema were destroyed. In addition to these findings, pericytes and microglial cells contained a great deal of lysosomal substances, while the nerve cells were intact. From the above findings, it is suggested that lead directly induces a primary toxic effect on the blood vessel and induces perivascular edema. Following this change, the nerve fibers adjacent to the edema may become involved. On the other hand, there is a possibility that lead produces a primary toxic effect at the neuronal level but no histopathological change in the nerve cell was found. Then, many satellite cells and microglial cells contained a great deal of lysosomal substances. This might have some relation to the lead invading the brain. Up to today, histopathological changes in CNS of adult animals experimentally induced by lead have not yet been reported. However, the histopathological changes were similar to those of the neonatal animal. Further detailed research in the future is necessary to find out whether or not lead directly effects the nerve cell or organellae. SUMMARY
In the peripheral nerve, the distal part of the nerve fibers was remarkably damaged-periaxial segmental demyelinationwhile the proximal part of nerve fibers was only slightly affected. In the CNS, perivascular edema of the small blood vessels and capillaries was observed in the cerebral cortex and cerebellar cortex. All endothelial cells of these blood vessels showed a high electron density with many pinocytotic vesicles and ribosomes. Following these changes, the nerve fibers adjacent to the edema were destroyed. The above-mentioned findings seem to indicate that lead induces a toxic effect on the blood vessel and produces perivascular edema in the CNS of adult animals. This may induce brain dysfunction.
ACKNOWLEDGEMENT
I wish to thank Prof. T. Miyakawa, Dr. I. Shikaki, Dr. A. Shimoji and Dr. R. Kuramot0 for their cooperation in the present study. REFERENCES 1 Bouldin, T. W. and Krigman, M. R.: Acute
lead encephalopathy in the guinea pig, Acta, Neuropath (Berl.), 33: 185-1 90, 1975. 2 de Villaverde, J. M.: Quoted by Meyer, A. pp. 268-269 (1926, 1927).
3 Gombault, A,: Contribution ii 1'Ctude anatomique de la nCvrite parenchymateuse subaigiie ou chronique: nivrite segmentaire pki-axile, Archives de Neurologie, 1: 11-38, 1880-1881. 4 Gordon, I. and Whitehead, T. P.: Lead
poisoning in an infant from lead nippleshields: association with rickets, Lancet, 2: 647-650, 1949. 5 Krigman, M.R., Druse, M., Traylor, T. D.,
Wilson, M. H., Newell, L. R. and Hogan, E. L.: Lead encephalopathy in the developing rat: effect on cortical ontogenesis, J Neuropath & Exper Neurol, 33: 58-73, 1974. 6 Lampert,
P. W. and Schochet, S. S.: Demyelination and remyelination in lead neuropathy, Electron microscopic studies, J Neuropath & Exper Neurol, 27: 527545, 1968 b. 7 Michael, F. P.: Lead encephalopathy in neonatal Long-Evans rats poisoned via an esophageal catheter, Amer J of Path, 86: 4 8 5 4 8 8 , 1977. 8 Moncrieff, A. A., Koumides, 0. P., Clay-
ton, B. E., Patrick, A. D. and Renwick, A.G.E.: Lead poisoning in children, Arch of Disease in Childhood, 39: 1-13, 1964. 9 Pentschew, A. and Garro, F.: Lead encephalomyelopathy of the suckling rat and its implications on the porphyrinopathic nervous disease, Acta Neuropath (Berl.), 6: 266-278,
1966.
10 Raimondi, J., Beckman, F. and Evans, P.: Fine structural changes in human lead encephalopathy, J Neuropath & Exp Neurol, 72: 154, 1968. 1 1 Schlaepfer, W. W.: Ultrastructural and histochemical studies of a primary sensory neuropathy in rats produced by chronic lead intoxication, J Neuropath & Exper
Experimental Chronic Lead Poisoning Neurol, 27: 11 1-1 12, 1968. 12 Verhaart, W.J.C.: Lead encephalopathy simulating diffuse sclerosis in a Chinese infant, Amer J of Disease of Children, 61: 1246-1250, 1941.
131
13 Wells, G.A.H., Howell, J. McC. and Gopi-
nath, C. : Experimental lead encephalopathy of calves, Histopathological observations on the nature and distribution of the lesions, Neurol & Applied Neurobiol, 2: 175-190, 1976.
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